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Sample records for two-reaction oxidation mechanism

  1. Oxidation Mechanism of Copper Selenide

    Science.gov (United States)

    Taskinen, Pekka; Patana, Sonja; Kobylin, Petri; Latostenmaa, Petri

    2014-09-01

    The oxidation mechanism of copper selenide was investigated at deselenization temperatures of copper refining anode slimes. The isothermal roasting of synthetic, massive copper selenide in flowing oxygen and oxygen - 20% sulfur dioxide mixtures at 450-550 °C indicate that in both atmospheres the mass of Cu2Se increases as a function of time, due to formation of copper selenite as an intermediate product. Copper selenide oxidises to copper oxides without formation of thick copper selenite scales, and a significant fraction of selenium is vaporized as SeO2(g). The oxidation product scales on Cu2Se are porous which allows transport of atmospheric oxygen to the reaction zone and selenium dioxide vapor to the surrounding gas. Predominance area diagrams of the copper-selenium system, constructed for selenium roasting conditions, indicate that the stable phase of copper in a selenium roaster gas with SO2 is the sulfate CuSO4. The cuprous oxide formed in decomposition of Cu2Se is further sulfated to CuSO4.

  2. Mechanisms of oxidative stress and vascular dysfunction

    Science.gov (United States)

    Nedeljkovic, Z; Gokce, N; Loscalzo, J

    2003-01-01

    The endothelium regulates vascular homoeostasis through local elaboration of mediators that modulate vascular tone, platelet adhesion, inflammation, fibrinolysis, and vascular growth. Impaired vascular function contributes to the pathogenesis of atherosclerosis and acute coronary syndromes. There is growing pathophysiological evidence that increased generation of reactive oxygen species and oxidative stress participates in proatherogenic mechanisms of vascular dysfunction and atherothrombosis. In this review, the role of oxidative stress in mechanisms of vascular dysfunction is discussed, and potential antioxidant strategies are reviewed. PMID:12743334

  3. Oxidation mechanisms for alloys in single-oxidant gases

    Energy Technology Data Exchange (ETDEWEB)

    Whittle, D.P.

    1981-03-01

    Scales formed on alloys invariably contain the alloy constituents in a ratio different from that in the alloy, owing to the differing thermodynamic tendencies of the alloy components to react with the oxidant and to differences in diffusion rates in scale and alloy phases. This complex interrelationship between transport rates and the thermodynamics of the alloy-oxidant system can be analyzed using multicomponent diffusion theory when transport-controlled growth of single or multi-layered scales occurs. In particular, the superimposition of the diffusion data on an isothermal section of the appropriate phase diagram indicates the likely morphologies of the reaction products, including the sequence of phases found in the scale, the occurrence of internal oxidation and the development of an irregular metal/scale interface. The scale morphologies on alloys are also time-dependent: there is an initial transient stage, a steady state period, and a final breakdown, the latter often related to mechanical influences such as scale adherence, spallation, thermal or mechanical stresses and void formation. Mechanical influences have a more devastating effect in alloy oxidation due to the changes in alloy surface composition during the steady state period.

  4. High quality factor indium oxide mechanical microresonators

    Energy Technology Data Exchange (ETDEWEB)

    Bartolomé, Javier, E-mail: j.bartolome@fis.ucm.es; Cremades, Ana; Piqueras, Javier [Department of Materials Physics, Faculty of Physics, Universidad Complutense de Madrid, 28040 Madrid (Spain)

    2015-11-09

    The mechanical resonance behavior of as-grown In{sub 2}O{sub 3} microrods has been studied in this work by in-situ scanning electron microscopy (SEM) electrically induced mechanical oscillations. Indium oxide microrods grown by a vapor–solid method are naturally clamped to an aluminum oxide ceramic substrate, showing a high quality factor due to reduced energy losses during mechanical vibrations. Quality factors of more than 10{sup 5} and minimum detectable forces of the order of 10{sup −16} N/Hz{sup 1/2} demonstrate their potential as mechanical microresonators for real applications. Measurements at low-vacuum using the SEM environmental operation mode were performed to study the effect of extrinsic damping on the resonators behavior. The damping coefficient has been determined as a function of pressure.

  5. Reassessing the atmospheric oxidation mechanism of toluene

    Science.gov (United States)

    Ji, Yuemeng; Zhao, Jun; Terazono, Hajime; Misawa, Kentaro; Levitt, Nicholas P.; Li, Yixin; Lin, Yun; Peng, Jianfei; Wang, Yuan; Duan, Lian; Pan, Bowen; Zhang, Fang; Feng, Xidan; An, Taicheng; Marrero-Ortiz, Wilmarie; Secrest, Jeremiah; Zhang, Annie L.; Shibuya, Kazuhiko; Molina, Mario J.; Zhang, Renyi

    2017-08-01

    Photochemical oxidation of aromatic hydrocarbons leads to tropospheric ozone and secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. Toluene is the most abundant aromatic compound under urban environments, but its detailed chemical oxidation mechanism remains uncertain. From combined laboratory experiments and quantum chemical calculations, we show a toluene oxidation mechanism that is different from the one adopted in current atmospheric models. Our experimental work indicates a larger-than-expected branching ratio for cresols, but a negligible formation of ring-opening products (e.g., methylglyoxal). Quantum chemical calculations also demonstrate that cresols are much more stable than their corresponding peroxy radicals, and, for the most favorable OH (ortho) addition, the pathway of H extraction by O2 to form the cresol proceeds with a smaller barrier than O2 addition to form the peroxy radical. Our results reveal that phenolic (rather than peroxy radical) formation represents the dominant pathway for toluene oxidation, highlighting the necessity to reassess its role in ozone and SOA formation in the atmosphere.

  6. Current viewpoints on oxide adherence mechanisms

    Science.gov (United States)

    Smialek, J. L.; Browning, R.

    1985-01-01

    Additional hot stage Auger experiments have provided surface segregation data for NiCrAl + or - Y or Zr alloys in agreement with other investigations. This data, combined with experimental and theoretical evidence of the Al2O3-metal bond strength, is presented in support of a chemical mechanism of Al2O3 scale adhesion. Both the detrimental effects of sulfur segregation and the beneficial effects of dopant segregation may be important. Chemical features of the dopants are compared in light of these proposed mechanisms, namely delta H sub f (sulfide), delta H sub f (oxide), electron orbital configuration, and insolubility in Ni.

  7. Mechanical characterization of microwave sintered zinc oxide

    Indian Academy of Sciences (India)

    A K Mukhopadhyay; M Ray Chaudhuri; A Seal; S K Dalui; M Banerjee; K K Phani

    2001-04-01

    The mechanical characterization of microwave sintered zinc oxide disks is reported. The microwave sintering was done with a specially designed applicator placed in a domestic microwave oven operating at a frequency of 2.45 GHz to a maximum power output of 800 Watt. These samples with a wide variation of density and hence, of open pore volume percentage, were characterized in terms of its elastic modulus determination by ultrasonic time of flight measurement using a 15 MHz transducer. In addition, the load dependence of the microhardness was examined for the range of loads 0.1–20 N. Finally, the fracture toughness data (IC) was obtained using the indentation technique.

  8. Control mechanisms in mitochondrial oxidative phosphorylation

    Institute of Scientific and Technical Information of China (English)

    Jana Hroudová; Zdeněk Fi(s)ar

    2013-01-01

    Distribution and activity of mitochondria are key factors in neuronal development, synaptic plasticity and axogenesis. The majority of energy sources, necessary for cellular functions, originate from oxidative phosphorylation located in the inner mitochondrial membrane. The adenosine-5'- triphosphate production is regulated by many control mechanism–firstly by oxygen, substrate level, adenosine-5'-diphosphate level, mitochondrial membrane potential, and rate of coupling and proton leak. Recently, these mechanisms have been implemented by "second control mechanisms," such as reversible phosphorylation of the tricarboxylic acid cycle enzymes and electron transport chain complexes, allosteric inhibition of cytochrome c oxidase, thyroid hormones, effects of fatty acids and uncoupling proteins. Impaired function of mitochondria is implicated in many diseases ranging from mitochondrial myopathies to bipolar disorder and schizophrenia. Mitochondrial dysfunctions are usually related to the ability of mitochondria to generate adenosine-5'-triphosphate in response to energy demands. Large amounts of reactive oxygen species are released by defective mitochondria, similarly, decline of antioxidative enzyme activities (e.g. in the elderly) enhances reactive oxygen species production. We reviewed data concerning neuroplasticity, physiology, and control of mitochondrial oxidative phosphorylation and reactive oxygen species production.

  9. Oxidant Stress in Renal Inflammation: Mechanisms and Remedies

    NARCIS (Netherlands)

    Ishola, D.A.

    2006-01-01

    Our overall hypothesis was that oxidant stress is a central player in renal inflammation; pharmacological reduction of oxidant stress should therefore relieve renal inflammation. We explored pro- and anti-oxidant mechanisms in three experimental renal injury models. OXIDANT-DEPENDENT RENAL

  10. Electrical properties of mechanically activated zinc oxide

    Directory of Open Access Journals (Sweden)

    Vojisavljević K.

    2006-01-01

    Full Text Available Microstructural properties of a commercial zinc oxide powder were modified by mechanical activation in a high-energy vibro-mill. The obtained powders were dry pressed and sintered at 1100°C for 2 h. The electrical properties of grain boundaries of obtained ZnO ceramics were studied using an ac impedance analyzer. For that purpose, the ac electrical response was measured in the temperature range from 23 to 240°C in order to determine the resistance and capacitance of grain boundaries. The activation energies of conduction were obtained using an Arrhenius equation. Donor densities were calculated from Mott-Schottky measurements. The influence of microstructure, types and concentrations of defects on electrical properties was discussed.

  11. Oxidative Damage and Its Possible Mechanism

    Directory of Open Access Journals (Sweden)

    Tingting Wang

    2016-06-01

    Full Text Available Purpose: The paper tries to assess the protective effect of fisetin against •OH-induced DNAdamage, then to investigate the possible mechanism.Methods: The protective effect was evaluated based on the content of malondialdehyde(MDA. The possible mechanism was analyzed using various antioxidant methods in vitro,including •OH scavenging (deoxyribose degradation, •O2- scavenging (pyrogallolautoxidation, DPPH• scavenging, ABTS•+ scavenging, and Cu2+-reducing power assays.Results: Fisetin increased dose-dependently its protective percentages against •OH-inducedDNA damage (IC50 value =1535.00±29.60 μM. It also increased its radical-scavengingpercentages in a dose-dependent manner in various antioxidants assays. Its IC50 values in•OH scavenging, •O2- scavenging, DPPH• scavenging, ABTS•+ scavenging, and Cu2+-reducing power assays, were 47.41±4.50 μM, 34.05±0.87 μM, 9.69±0.53 μM, 2.43±0.14μM, and 1.49±0.16 μM, respectively.Conclusion: Fisetin can effectively protect DNA against •OH-induced oxidative damagepossibly via reactive oxygen species (ROS scavenging approach, which is assumed to behydrogen atom (H• and/or single electron (e donation (HAT/SET pathways. In the HATpathway, the 3’,4’-dihydroxyl moiety in B ring of fisetin is thought to play an importantrole, because it can be ultimately oxidized to a stable ortho-benzoquinone form.

  12. A Novel Method of Mechanical Oxidation of CNT for Polymer Nanocomposite Application: Evaluation of Mechanical, Dynamic Mechanical, and Rheological Properties

    Directory of Open Access Journals (Sweden)

    Priyanka Pandey

    2014-01-01

    Full Text Available A new approach of oxidation of carbon nanotubes has been used to oxidize the CNTs. A comparative aspect of the mechanical oxidation and acid oxidation process has been established. FTIR analysis and titration method have shown the higher feasibility of the mechanical oxidation method to oxidize the CNTs. Comparatively less damage to the CNTs has been observed in case of mechanically oxidized as compared to acid oxidized CNTs. The mechanical properties of the nanocomposites reinforced with the acid oxidized CNT (ACNT and mechanically oxidized CNTs (McCNT were analyzed and relatively higher properties in the nanocomposites reinforced with McCNT were noticed. The less degree of entanglement in the McCNTs was noticed as compared to ACNTs. The dynamic mechanical analysis of the nanocomposites revealed much improved load transfer capability in the McCNT reinforced composites. Further, the rheological properties of the nanocomposites revealed the higher performance of McCNT reinforced composites.

  13. Pathway and mechanism of oxidative stress in Alzheimer's disease

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Current hypotheses of pathogenesis of neuronal degeneration in Alzheimer's disease (AD) have been proposed, including formation of free radicals, oxidative stress, mitochondrial dysfunction, inflammatory processes, genetic factors, environmental impact factors, apoptosis, and so on. Especially, oxidative stress plays an essential role in AD pathogenesis by the function of linking agent. Oxidative stress in AD mainly includes lipid peroxidation, protein oxidation and DNA oxidation. Lipid peroxidation plays a key role in the development and progression of AD. Protein oxidation is an important mechanism in AD. Oxidative damage to DNA may plays an important role in aging and AD.

  14. Primary atmospheric oxidation mechanism for toluene.

    Science.gov (United States)

    Baltaretu, Cristian O; Lichtman, Eben I; Hadler, Amelia B; Elrod, Matthew J

    2009-01-08

    The products of the primary OH-initiated oxidation of toluene were investigated using the turbulent flow chemical ionization mass spectrometry technique at temperatures ranging from 228 to 298 K. A major dienedial-producing pathway was detected for the first time for toluene oxidation, and glyoxal and methylglyoxal were found to be minor primary oxidation products. The results suggest that secondary oxidation processes involving dienedial and epoxide primary products are likely responsible for previous observations of glyoxal and methylglyoxal products from toluene oxidation. Because the dienedial-producing pathway is a null cycle for tropospheric ozone production and glyoxal and methylglyoxal are important secondary organic aerosol precursors, these new findings have important implications for the modeling of toluene oxidation in the atmosphere.

  15. OXIDATIVE DNA DAMAGE IN DIESEL BUS MECHANICS

    Science.gov (United States)

    Rationale: Diesel exposure has been associated with adverse health effects, including susceptibility to asthma, allergy and cancer. Previous epidemiological studies demonstrated increased cancer incidence among workers exposed to diesel. This is likely due to oxid...

  16. Exploring Electric Polarization Mechanisms in Multiferroic Oxides

    Energy Technology Data Exchange (ETDEWEB)

    Tyson, Trevor A. [New Jersey Institute of Technology (NJIT), Newark, NJ (United States)

    2017-01-24

    Multiferroic oxides are a class of systems which exhibit coupling between the electrical polarization and the magnetization. These materials show promise to lead to devices in which ferromagnetic memory can be written with magnetic fields or magnetic bits can be written by an electric field. The work conducted in our research focuses on single phase materials. We studied the detailed coupling of the spin and lattice correlations in these systems. In the first phase of the proposal, we explored the complex spin spiral systems and low temperature behavior of hexagonal layered REMnO3 (RE= rare earth, Y and Sc) system following the detailed structural changes which occurred on crossing into the magnetic states. The techniques were applied to other layered materials such as superconductors and thermoelectric where the same layered motif exists. The second phase of the proposal focused on understanding the mechanisms involved in the onset high temperature ferroelectricity ion hexagonal REMnO3 and at low temperature in E-Type magnetic ordered perovskite REMnO3. We wsynthesized preovskite small A site multiferroics by high pressure and high temperature methods. Detailed measurement of the structural properties and dynamics were conducted over a range of length scales from atomic to mesoscopic scale using, x-ray absorption spectroscopy, x-ray diffuse scattering, x-ray and neutron pair distribution analysis and high resolution x-ray diffraction. Changes in vibration modes which occur with the onset of polarization were probed with temperature and pressure dependent infrared absorption spectroscopy. In addition the orthorhombic system (small radius RE ions) which is believed to exhibit electronically driven ferroelectricity and is also not understood was examined. The multiple length scale synchrotron based measurements may assist in developing more detailed models of these materials and possibly lead to device applications. The experimental

  17. The mechanism of the partial oxidation of methane

    Science.gov (United States)

    Sinev, Mikhail Yu; Korshak, V. N.; Krylov, Oleg V.

    1989-01-01

    The principal characteristics of the homogeneous and heterogeneous-catalytic conversion of methane into condensation products (C2 and C3 hydrocarbons) and partial oxidation products (methanol and formaldehyde) are considered. Data are presented concerning the most effective catalysts and data relating to the mechanism of the activation of methane on oxide and oxide halide catalysts, the nature of the active centres, and the kinetics of the partial oxidation of methane are analysed. It is shown that the oxidative condensation of methane in the presence of the catalysts considered is a heterogeneous-homogeneous process, which imposes special requirements in its practical realisation. The bibliography includes 118 references.

  18. Interaction mechanisms between slurry coatings and solid oxide fuel cell interconnect alloys during high temperature oxidation

    DEFF Research Database (Denmark)

    Persson, Åsa Helen; Mikkelsen, L.; Hendriksen, P.V.;

    2012-01-01

    Six different coatings consisting of fluorite-, corundum-, spinel- or perovskite-type oxides were deposited on a Fe22Cr alloy (Crofer 22APU) and oxidized at 900°C in moisturized air.Five of the coatings prevented break-away oxidation otherwise observed for the uncoated alloy, and the parabolic...... oxidation rate constant was reduced with 50–90% of that for uncoated alloy. One coating consisting of MnCo2O4 did not significantly affect the oxidation rate of the alloy, and just as for uncoated samples break-away oxidation occurred for MnCo2O4 coated samples. The interaction mechanisms between...

  19. Mechanism of Oxidative Stress in Neurodegeneration

    Directory of Open Access Journals (Sweden)

    Sonia Gandhi

    2012-01-01

    Full Text Available Biological tissues require oxygen to meet their energetic demands. However, the consumption of oxygen also results in the generation of free radicals that may have damaging effects on cells. The brain is particularly vulnerable to the effects of reactive oxygen species due to its high demand for oxygen, and its abundance of highly peroxidisable substrates. Oxidative stress is caused by an imbalance in the redox state of the cell, either by overproduction of reactive oxygen species, or by dysfunction of the antioxidant systems. Oxidative stress has been detected in a range of neurodegenerative disease, and emerging evidence from in vitro and in vivo disease models suggests that oxidative stress may play a role in disease pathogenesis. However, the promise of antioxidants as novel therapies for neurodegenerative diseases has not been borne out in clinical studies. In this review, we critically assess the hypothesis that oxidative stress is a crucial player in common neurodegenerative disease and discuss the source of free radicals in such diseases. Furthermore, we examine the issues surrounding the failure to translate this hypothesis into an effective clinical treatment.

  20. The oxidation mechanism of the antioxidant quercetin in nonaqueous media

    Energy Technology Data Exchange (ETDEWEB)

    Sokolova, Romana, E-mail: romana.sokolova@jh-inst.cas.cz [J. Heyrovsky Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejskova 3, 18223 Prague (Czech Republic); Degano, Ilaria [Department of Chemistry and Industrial Chemistry, University of Pisa, Via Risorgimento 35, 56100 Pisa (Italy); Ramesova, Sarka; Bulickova, Jana; Hromadova, Magdalena; Gal, Miroslav; Fiedler, Jan [J. Heyrovsky Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejskova 3, 18223 Prague (Czech Republic); Valasek, Michal [Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, 16610 Prague 6 (Czech Republic)

    2011-08-30

    The knowledge of the degradation pathways of natural dyes used in medieval textiles is necessary for the restoration of their original color. Quercetin, one of such colorants, reportedly yields the wide spectrum of oxidation products in different types of media. This study deals with electrochemical oxidation mechanism of quercetin in nonaqueous solution, which has not been yet attempted. The final oxidation product at the first oxidation wave was identified by HPLC-DAD and GC-MS techniques as 2-(3',4'-dihydroxybenzoyl)-2,4,6-trihydroxybenzofuran-3(2H)-one. The apparent two-electron process at the potential of the first oxidation wave yields current-voltage shapes with one-electron characteristics. The in situ spectroelectrochemistry measurements proved the oxidation mechanism leading through a short-lived anion radical. Two possibilities of the oxidation mechanism are discussed: two one-electron transfers, which do not have identical but similar redox potentials, or the presence of a disproportionation chemical reaction following the first one electron transfer. The quinone formed in either case is stable only on the time scale of a fast spectroelectrochemistry and undergoes fast hydroxylation reaction, where 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxybenzofuran-3-one is formed. This compound is oxidized at the potential of the second oxidation wave of quercetin.

  1. Kinetics and mechanism of synthetic CoS oxidation process

    Directory of Open Access Journals (Sweden)

    Štrbac N.

    2006-01-01

    Full Text Available The results of investigation of kinetics and mechanism for synthetic a-CoS oxidation process are presented in this paper. Based on experimental data obtained using DTA and XRD analysis and constructed PSD diagrams for Co-S-O system, mechanism of synthetic a-CoS oxidation process is suggested. Characteristic kinetic parameters were obtained for experimental isothermal investigations of desulfurization degree using Sharp method.

  2. Reaction mechanisms of ruthenium tetroxide mediated oxidations of organic compounds

    Energy Technology Data Exchange (ETDEWEB)

    Froehaug, Astrid Elisabeth

    1995-12-31

    This thesis reports a study of the mechanism of ruthenium tetroxide mediated oxidations of saturated hydrocarbons, ethers, alkenes and alcohols. Several methods were used. The RuO{sub 4}-mediated oxidations of adamantane and cis-decalin were studied in CCl{sub 4}-CH{sub 3}CN-H{sub 2}O and in acetone-water. The rate of reaction was found to be moderately influenced by the polarity of the solvent. Solvent properties other than the polarity were also found to influence the reaction rates. From the oxidations of adamantane and adamantane-1,3,5,7-d{sub 4} two primary kinetic deuterium isotope effects were found. These were comparable with the deuterium isotope effects found for the analogous oxidations of cis-decalin and cis-decalin-d{sub 18}. The results seem to exclude both a one step hydride abstraction reaction mechanism and a one step concerted mechanism, as well as a scheme where two such mechanisms compete. The observations may be explained by a two step reaction mechanism consisting of a pre-equilibrium with formation of a substrate-RuO{sub 4} complex followed by a concerted rate determining reaction. The RuO{sub 4}-mediated oxidation of ethers was of kinetic second order with a small enthalpy of activation and a large negative entropy of activation. Oxidation of cyclopropylmethyl methyl ether gave methyl cyclopropanecarboxylate, no rearranged products were observed. On RuO{sub 4} oxidations in CCl{sub 4} with NaIO{sub 4} as stoichiometric oxidant, no chlorinated products were observed. Several observations not in agreement with a hydride or a hydrogen abstraction mechanism may be explained by assuming that the reaction proceeds by either a concerted reaction or by a reversible oxidative addition of the ether to RuO{sub 4} followed by a slow concerted step. 228 refs., 9 figs., 27 tabs.

  3. Defect centers in chemical-mechanical polished MOS oxides

    Energy Technology Data Exchange (ETDEWEB)

    Shaneyfelt, M.R.; Warren, W.L.; Hetherington, D.L.; Timon, R.P.; Resnick, P.J.; Winokur, P.S.

    1994-12-31

    Defect centers generated in vacuum-ultraviolet irradiated chemical-mechanical polished oxides have been characterized using electron paramagnetic resonance and C-V analysis. Both oxide trap E{sub {gamma}} and interface trap P{sub b0} centers were detected in unpolished and polished oxides. In addition, another interface defect center known as the P{sub b1} center was only identified in the polished oxides, suggesting that the polishing process altered the SiO{sub 2}/Si interface.

  4. Enhanced disinfection efficiency of mechanically mixed oxidants with free chlorine.

    Science.gov (United States)

    Son, Hyunju; Cho, Min; Kim, Jaeeun; Oh, Byungtaek; Chung, Hyenmi; Yoon, Jeyong

    2005-02-01

    To the best of our knowledge, this study is the first investigation to be performed into the potential benefits of mechanically mixed disinfectants in controlling bacterial inactivation. The purpose of this study was to evaluate the disinfection efficiency of mechanically mixed oxidants with identical oxidant concentrations, which were made by adding small amounts of subsidiary oxidants, namely ozone (O3), chlorine dioxide (ClO2), hydrogen peroxide (H2O2) and chlorite (ClO2(-)), to free available chlorine (Cl2), using Bacillus subtilis spores as the indicator microorganisms. The mechanically mixed oxidants containing Cl2/O3, Cl2/ClO2 and Cl2/ClO2(-) showed enhanced efficiencies (of up to 52%) in comparison with Cl2 alone, whereas no significant difference was observed between the mixed oxidant, Cl2/H2O2, and Cl2 alone. This enhanced disinfection efficiency can be explained by the synergistic effect of the mixed oxidant itself and the effect of intermediates such as ClO2(-)/ClO2, which are generated from the reaction between an excess of Cl2 and a small amount of O3/ClO2(-). Overall, this study suggests that mechanically mixed oxidants incorporating excess chlorine can constitute a new and moderately efficient method of disinfection.

  5. Gate oxide punching thru mechanism in plasma dry etching

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The punching thru mechanism of gate oxide (thickness about 15A) was investi- gated. Because of the thin thickness of gate oxide, gate oxide punching thru may easily happen during the plasma process. It was found that what caused the punching thru was not only the selectivity of poly-silicon/oxide but also the pattern topography. We used the basic SRAM pattern to check this topography effect, and found that gate oxide located at the narrow spacing of two parallel serpentine lines was the most easily punched thru. What caused the topography effect was the starvation of oxygen in these places which were induced by the residue of poly-silicon and enhanced by electron shading effect. So, to solve the issue of gate oxide punching thru, firstly the selectivity should be enough, secondly we should pay attention to the etching pattern topography.

  6. Molecular mechanisms of ROS production and oxidative stress in diabetes.

    Science.gov (United States)

    Newsholme, Philip; Cruzat, Vinicius Fernandes; Keane, Kevin Noel; Carlessi, Rodrigo; de Bittencourt, Paulo Ivo Homem

    2016-12-15

    Oxidative stress and chronic inflammation are known to be associated with the development of metabolic diseases, including diabetes. Oxidative stress, an imbalance between oxidative and antioxidative systems of cells and tissues, is a result of over production of oxidative-free radicals and associated reactive oxygen species (ROS). One outcome of excessive levels of ROS is the modification of the structure and function of cellular proteins and lipids, leading to cellular dysfunction including impaired energy metabolism, altered cell signalling and cell cycle control, impaired cell transport mechanisms and overall dysfunctional biological activity, immune activation and inflammation. Nutritional stress, such as that caused by excess high-fat and/or carbohydrate diets, promotes oxidative stress as evident by increased lipid peroxidation products, protein carbonylation and decreased antioxidant status. In obesity, chronic oxidative stress and associated inflammation are the underlying factors that lead to the development of pathologies such as insulin resistance, dysregulated pathways of metabolism, diabetes and cardiovascular disease through impaired signalling and metabolism resulting in dysfunction to insulin secretion, insulin action and immune responses. However, exercise may counter excessive levels of oxidative stress and thus improve metabolic and inflammatory outcomes. In the present article, we review the cellular and molecular origins and significance of ROS production, the molecular targets and responses describing how oxidative stress affects cell function including mechanisms of insulin secretion and action, from the point of view of possible application of novel diabetic therapies based on redox regulation.

  7. Oxidative Stress-Mediated Atherosclerosis: Mechanisms and Therapies

    Directory of Open Access Journals (Sweden)

    Xinyu Yang

    2017-08-01

    Full Text Available Atherogenesis, the formation of atherosclerotic plaques, is a complex process that involves several mechanisms, including endothelial dysfunction, neovascularization, vascular proliferation, apoptosis, matrix degradation, inflammation, and thrombosis. The pathogenesis and progression of atherosclerosis are explained differently by different scholars. One of the most common theories is the destruction of well-balanced homeostatic mechanisms, which incurs the oxidative stress. And oxidative stress is widely regarded as the redox status realized when an imbalance exists between antioxidant capability and activity species including reactive oxygen (ROS, nitrogen (RNS and halogen species, non-radical as well as free radical species. This occurrence results in cell injury due to direct oxidation of cellular protein, lipid, and DNA or via cell death signaling pathways responsible for accelerating atherogenesis. This paper discusses inflammation, mitochondria, autophagy, apoptosis, and epigenetics as they induce oxidative stress in atherosclerosis, as well as various treatments for antioxidative stress that may prevent atherosclerosis.

  8. Comparison and Parametric Study of Flameless Oxidation in a Gas Turbine Using Two Kinetics Mechanisms

    Directory of Open Access Journals (Sweden)

    Mohamed Hamdi

    2008-01-01

    Full Text Available The so-called “Flameless Oxidation” is a novel combustion mode, in which combustion products are re-circulated and mixed into the fresh incoming fuel and air streams. This reduces the concentration of the reactants and thereby reducing the reaction rate through avoiding the formation of sharp high temperature zones in the combustion chamber. Flameless combustion has been acknowledged as one of the most interesting combustion technologies to meet both the targets of high energy efficiency and low pollutant emissions. This technology has already been successfully applied and exploited in industrial burners. The present investigation is concerned with the application of the flameless combustion mode to an adiabatic combustor, typically used in gas turbine engines. Detailed chemical kinetics calculations, by means of a specific zero-dimensional loop reactor model, have been performed to analyze its chemical aspects. The model simulates the combustor by a number of reactors that represent different zones in the combustion chamber. The main objective of this study is to increase the understanding of NOx formation from flameless mode, where currently very few experimental data are available. The investigation is focused on a comparison of the influence of pressure, residence time and temperature on the NOx and CO emissions, using two reaction mechanisms of the C/H/O/N system: the Miller-Bowman mechanism and the GRI_MECH3.0 mechanism. Simulation results clearly illustrate that even at high operating temperatures and pressures, NOx emissions could be reduced by flameless combustion to very low levels. A comparison between the predictions obtained by using the two chemical kinetics mechanisms is presented and discussed. It is shown that the predictions of the Miller-Bowman mechanism deviate from the predictions of the GRI3.0 mechanism in many aspects, especially as related to NOx emission results.

  9. Mechanism of glucose electrochemical oxidation on gold surface

    KAUST Repository

    Pasta, Mauro

    2010-08-01

    The complex oxidation of glucose at the surface of gold electrodes was studied in detail in different conditions of pH, buffer and halide concentration. As observed in previous studies, an oxidative current peak occurs during the cathodic sweep showing a highly linear dependence on glucose concentration, when other electrolyte conditions are unchanged. The effect of the different conditions on the intensity of this peak has stressed the limitations of the previously proposed mechanisms. A mechanism able to explain the presence of this oxidative peak was proposed. The mechanism takes into account ion-sorption and electrochemical adsorption of OH-, buffer species (K2HPO4/KH2PO4) and halides. © 2010 Elsevier Ltd. All rights reserved.

  10. Metal-oxide-metal point contact junction detectors. [detection mechanism and mechanical stability

    Science.gov (United States)

    Baird, J.; Havemann, R. H.; Fults, R. D.

    1973-01-01

    The detection mechanism(s) and design of a mechanically stable metal-oxide-metal point contact junction detector are considered. A prototype for a mechanically stable device has been constructed and tested. A technique has been developed which accurately predicts microwave video detector and heterodyne mixer SIM (semiconductor-insulator-metal) diode performance from low dc frequency volt-ampere curves. The difference in contact potential between the two metals and geometrically induced rectification constitute the detection mechanisms.

  11. Kinetics and mechanism of the oxidation of amaranth with hypochlorite.

    Science.gov (United States)

    Nadupalli, S; Koorbanally, N; Jonnalagadda, S B

    2011-07-14

    The reaction mechanism of the oxidation of Amaranth dye (2-hydroxy-1-(4-sulfonato-1-naphthylazo) naphthalene-3,6-disulfonate) with hypochlorite under varied pH conditions was elucidated by a kinetic approach. Under excess concentration of oxidant, the reaction followed pseudo-first-order kinetics with respect to Amaranth, and the oxidation was found to occur through two competitive reactions, initiated by hypochlorite and hypochlorous acid. The reaction order with respect to both OCl(-) ion and HOCl was unity. While the latter reaction was fast, the significance of the oxidation paths depended on the relative concentration of the two oxidizing species, which was dictated by the reaction pH. The role of the H(+) ion in the reaction was established. For the hypochlorite ion and hypochlorous acid facilitated reactions, the second-order rate coefficients were 1.9 and 23.2 M(-1) s(-1), respectively. The energy parameters were E(a) = 33.7 kJ mol(-1), ΔH(‡) = 31.2 kJ mol(-1) and ΔS(‡) = -190.6 J K(-1) mol(-1) for the OCl(-) ion-driven oxidation, and E(a) = 26.9 kJ mol(-1), ΔH(‡) = 24.3 kJ mol(-1) and ΔS(‡) = -222.8 J K(-1) mol(-1) for the reaction with HOCl-initiated oxidation. The major oxidation products for both the pathways were 3,4-dihydroxy naphthalene-2,7-disulfonic sodium salt (P(1)), dichloro-1,4-naphthoquione (P(2)) and naphtha(2,3)oxirene-2, 3-dione (P(3)). On the basis of the primary salt effect and other kinetic data, the rate law for the overall reaction and probable reaction mechanism was elucidated. The proposed mechanism was validated by simulations using Simkine-2.

  12. MECHANISM OF THE OXIDATION OF HEMOGLOBIN BY COPPER (II COMPLXES

    Directory of Open Access Journals (Sweden)

    M. BAYATI

    1994-07-01

    Full Text Available An outer sphere electron transfer mechanism by which human hemoglobin reduces the complexes of copper(II and, in turn, is oxidized to methemoglobin has been characterized. We have found that the rate of oxidation of hemoglobin is a function of pH, temperature, concentration of copper(II, and the environment of the hemoglobin. Prior to oxidation, copper(II complex binds to specific sites on the surface of the protein by losing one or more of its ligands, forming a ternary complex. This process is followed by electron transfer between the Cu(II and Fe(H with the Cu(II-deoxyhemoglobin being the active intermediate. The dominant factors which govern the rate of oxidation of hemoglobin by coppcr(I I complexes seem to be the stability constant of the Cu(II complexes and the overall redox potential of the ternary complex.

  13. Microstructure and Mechanical Properties of Graphene Oxide/Copper Composites

    Directory of Open Access Journals (Sweden)

    HONG Qi-hu

    2016-09-01

    Full Text Available Graphene oxide/copper (GO/Cu composites were successfully synthesized through the ball milling and vacuum hot press sintering process. The morphologies of the mixture powders, and the microstructure and mechanical properties of GO/Cu composites were investigated by OM, SEM, XRD, hardness tester and electronic universal testing machine, respectively. The results show that the GO/Cu composites are compact. Graphene oxide with flake morphology is uniformly dispersed and well consolidated with copper matrix. When the mass fraction of graphene oxide is 0.5%, the microhardness and compress strength at RT reach up to 63HV and 276MPa, increased by 8.6% and 28%, respectively. The strengthening mechanism is load transfer effect, dislocation strengthening and fine crystal reinforcing.

  14. Quantum chemical investigation of mechanisms of silane oxidation

    DEFF Research Database (Denmark)

    Mader, Mary M.; Norrby, Per-Ola

    2001-01-01

    Several mechanisms for the peroxide oxidation of organosilanes to alcohols are compared by quantum chemical calculations, including solvation with the PCM method. Without doubt, the reaction proceeds via anionic, pentacoordinate silicate species, but a profound difference is found between in vacuo...

  15. Oxidative stress and diabetic neuropathy : pathophysiotogical mechanisms and treatment perspectives

    NARCIS (Netherlands)

    2002-01-01

    Increased oxidative stress is a mechanism that probably plays a major role in the development of diabetic complications, including peripheral neuropathy. This review summarises recent data from in vitro and in vivo studies that have been performed both to understand this aspect of the pathophysiolog

  16. Effect of atmospheric oxidative plasma treatments on polypropylenic fibers surface: Characterization and reaction mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Nisticò, Roberto, E-mail: roberto.nistico@unito.it [University of Torino, Department of Chemistry and NIS Centre of Excellence, Via P. Giuria 7, 10125 Torino (Italy); Magnacca, Giuliana [University of Torino, Department of Chemistry and NIS Centre of Excellence, Via P. Giuria 7, 10125 Torino (Italy); Faga, Maria Giulia; Gautier, Giovanna [CNR-IMAMOTER, Strada delle Cacce 73, 10135 Torino (Italy); D’Angelo, Domenico; Ciancio, Emanuele [Clean-NT Lab, Environment Park S.p.A., Via Livorno 60, 10144 Torino (Italy); Lamberti, Roberta; Martorana, Selanna [Herniamesh S.r.l., Via F.lli Meliga 1/C, 10034 Chivasso (Italy)

    2013-08-15

    Atmospheric pressure plasma-dielectric barrier discharge (APP-DBD, open chamber configuration) was used to functionalize polypropylene (PP) fibers surface in order to generate oxidized-reactive groups such as hydroperoxides, alcohols and carbonyl species (i.e. ketones and others). Such a species increased the surface polarity, without causing material degradation. Three different types of plasma mixture (He, He/O{sub 2}, He/O{sub 2}/H{sub 2}O) under three different values of applied power (750, 1050, 1400 W) were investigated. The formed plasma species (O{sub 2}{sup +}, O single atom and OH radical) and their distribution were monitored via optical emission spectrometry (OES) measurements, and the plasma effects on PP surface species formation were followed by X-ray photoemission spectroscopy (XPS). Results allowed to better understand the reaction pathways between plasma phase and PP fibers. In fact, two reaction mechanisms were proposed, the first one concerning the plasma phase reactions and the second one involving material surface modifications.

  17. Elucidation of the electrochromic mechanism of nanostructured iron oxides films

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Lobato, M.A.; Martinez, Arturo I.; Castro-Roman, M. [Center for Research and Advanced Studies of the National Polytechnic Institute, Cinvestav Campus Saltillo, Carr. Saltillo-Monterrey Km. 13, Ramos Arizpe, Coah. 25900 (Mexico); Perry, Dale L. [Mail Stop 70A1150, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 (United States); Zarate, R.A. [Departamento de Fisica, Facultad de Ciencias, Universidad Catolica del Norte, Casilla 1280, Antofagasta (Chile); Escobar-Alarcon, L. (Departamento de Fisica, Instituto Nacional de Investigaciones Nucleares, A.P. 18-1027, 11801 Mexico)

    2011-02-15

    Nanostructured hematite thin films were electrochemically cycled in an aqueous solution of LiOH. Through optical, structural, morphological, and magnetic measurements, the coloration mechanism of electrochromic iron oxide thin films was elucidated. The conditions for double or single electrochromic behavior are given in this work. During the electrochemical cycling, it was found that topotactic transformations of hexagonal crystal structures are favored; i.e. {alpha}-Fe{sub 2}O{sub 3} to Fe(OH){sub 2} and subsequently to {delta}-FeOOH. These topotactic redox reactions are responsible for color changes of iron oxide films. (author)

  18. Elucidation of mechanisms in manganese and iron based oxidation catalysis : Mechanistic insights and development of novel approaches applied to transition metal catalyzed oxidations catalysis

    NARCIS (Netherlands)

    Angelone, Davide

    2016-01-01

    Oxidation chemistry is central to life and to the modern chemical industry and hence understanding chemical oxidation is essential to developing new processes and elucidating biological oxidation mechanisms. Elucidating mechanisms in inorganic oxidation catalysis and simultaneously developing new to

  19. Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

    Energy Technology Data Exchange (ETDEWEB)

    Herbinet, O; Pitz, W J; Westbrook, C K

    2007-09-20

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran et al. for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO{sub 2} production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.

  20. Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

    Energy Technology Data Exchange (ETDEWEB)

    Herbinet, O; Pitz, W J; Westbrook, C K

    2007-09-17

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran et al. for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO2 production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.

  1. Histidine oxidation photosensitized by pterin: pH dependent mechanism.

    Science.gov (United States)

    Castaño, Carolina; Oliveros, Esther; Thomas, Andrés H; Lorente, Carolina

    2015-12-01

    Aromatic pterins accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder, due to the oxidation of tetrahydrobiopterin, the biologically active form of pterins. In this work, we have investigated the ability of pterin, the parent compound of aromatic pterins, to photosensitize the oxidation of histidine in aqueous solutions under UV-A irradiation. Histidine is an α-amino acid with an imidazole functional group, and is frequently present at the active sites of enzymes. The results highlight the role of the pH in controlling the competition between energy and electron transfer mechanisms. It has been previously demonstrated that pterins participate as sensitizers in photosensitized oxidations, both by type I (electron-transfer) and type II mechanisms (singlet oxygen ((1)O2)). By combining different analytical techniques, we could establish that a type I photooxidation was the prevailing mechanism at acidic pH, although a type II mechanism is also present, but it is more important in alkaline solutions.

  2. Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

    Energy Technology Data Exchange (ETDEWEB)

    Herbinet, O; Pitz, W J; Westbrook, C K

    2007-09-20

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran et al. for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO{sub 2} production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.

  3. Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

    Energy Technology Data Exchange (ETDEWEB)

    Herbinet, O; Pitz, W J; Westbrook, C K

    2007-09-17

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran et al. for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO2 production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.

  4. Mechanical modeling of porous oxide fuel pellet A Test Problem

    Energy Technology Data Exchange (ETDEWEB)

    Nukala, Phani K [ORNL; Barai, Pallab [ORNL; Simunovic, Srdjan [ORNL; Ott, Larry J [ORNL

    2009-10-01

    A poro-elasto-plastic material model has been developed to capture the response of oxide fuels inside the nuclear reactors under operating conditions. Behavior of the oxide fuel and variation in void volume fraction under mechanical loading as predicted by the developed model has been reported in this article. The significant effect of void volume fraction on the overall stress distribution of the fuel pellet has also been described. An important oxide fuel issue that can have significant impact on the fuel performance is the mechanical response of oxide fuel pellet and clad system. Specifically, modeling the thermo-mechanical response of the fuel pellet in terms of its thermal expansion, mechanical deformation, swelling due to void formation and evolution, and the eventual contact of the fuel with the clad is of significant interest in understanding the fuel-clad mechanical interaction (FCMI). These phenomena are nonlinear and coupled since reduction in the fuel-clad gap affects thermal conductivity of the gap, which in turn affects temperature distribution within the fuel and the material properties of the fuel. Consequently, in order to accurately capture fuel-clad gap closure, we need to account for fuel swelling due to generation, retention, and evolution of fission gas in addition to the usual thermal expansion and mechanical deformation. Both fuel chemistry and microstructure also have a significant effect on the nucleation and growth of fission gas bubbles. Fuel-clad gap closure leading to eventual contact of the fuel with the clad introduces significant stresses in the clad, which makes thermo-mechanical response of the clad even more relevant. The overall aim of this test problem is to incorporate the above features in order to accurately capture fuel-clad mechanical interaction. Because of the complex nature of the problem, a series of test problems with increasing multi-physics coupling features, modeling accuracy, and complexity are defined with the

  5. Catalytic routes and oxidation mechanisms in photoreforming of polyols

    Energy Technology Data Exchange (ETDEWEB)

    Sanwald, Kai E.; Berto, Tobias F.; Eisenreich, Wolfgang; Gutiérrez, Oliver Y.; Lercher, Johannes A.

    2016-12-01

    Photocatalytic reforming of biomass-derived oxygenates leads to H2 generation and evolution of CO2 via parallel formation of organic intermediates through anodic oxidations on a Rh/TiO2 photocatalyst. The reaction pathways and kinetics in the photoreforming of C3–C6 polyols were explored. Polyols are converted via direct and indirect hole transfer pathways resulting in (i) oxidative rupture of C–C bonds, (ii) oxidation to a-oxygen functionalized aldoses and ketoses (carbonyl group formation) and (iii) light-driven dehydration. Direct hole transfer to chemisorbed oxygenates on terminal Ti(IV)-OH groups, generating alkoxy-radicals that undergo ß-C–C-cleavage, is proposed for the oxidative C–C rupture. Carbonyl group formation and dehydration are attributed to indirect hole transfer at surface lattice oxygen sites [Ti_ _ _O_ _ _Ti] followed by the generation of carbon-centered radicals. Polyol chain length impacts the contribution of the oxidation mechanisms favoring the C–C bond cleavage (internal preferred over terminal) as the dominant pathway with higher polyol carbon number.

  6. Oxidative Stress in Intracerebral Hemorrhage: Sources, Mechanisms, and Therapeutic Targets

    Directory of Open Access Journals (Sweden)

    Xin Hu

    2016-01-01

    Full Text Available Intracerebral hemorrhage (ICH is associated with the highest mortality and morbidity despite only constituting approximately 10–15% of all strokes. Complex underlying mechanisms consisting of cytotoxic, excitotoxic, and inflammatory effects of intraparenchymal blood are responsible for its highly damaging effects. Oxidative stress (OS also plays an important role in brain injury after ICH but attracts less attention than other factors. Increasing evidence has demonstrated that the metabolite axis of hemoglobin-heme-iron is the key contributor to oxidative brain damage after ICH, although other factors, such as neuroinflammation and prooxidases, are involved. This review will discuss the sources, possible molecular mechanisms, and potential therapeutic targets of OS in ICH.

  7. Mechanism-Based Design of Green Oxidation Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Rybak-Akimova, Elena [Tufts Univ., Medford, MA (United States)

    2015-03-16

    situation. Growing families of synthetic iron complexes that resemble active sites of metalloenzymes produce metal-based intermediates (rather than hydroxyl radicals) in reactions with oxygen donors. These complexes are very promising for selective oxygen and peroxide activation. In order to understand the mechanisms of metal-based small molecule activation, kinetically competent metal-oxygen intermediates must be identified. One of the grand challenges identified by the Department of Energy workshop "Catalysis for Energy" is understanding mechanisms and dynamics of catalyzed reactions. The research summarized herein focuses on detailed characterization of the formation and reactivity of various iron-peroxo- and iron-oxo intermediates that are involved in catalysis. Rates of rapid reactions were studied at low temperatures by a specialized technique termed cryogenic stopped-flow spectrophotometry. These measurements identified reaction conditions which favor the formation of catalytically competent oxidants. Chemical structures of reactive complexes was determined, and new, efficient catalysts for hydrocarbon oxidation were synthesized. Importantly, these catalysts are selective, they promote oxidation of hydrocarbons at a specific site. The catalysts are also efficient and robust, hundreds of cycles of substrate oxidation occur within minutes at room temperature. Furthermore, they enable utilization of environmentally friendly oxidants, such as hydrogen peroxide, which produces water as the only byproduct. Mechanistic insights uncovered the role of various acid-containing additives in catalytic oxidations. Proton delivery to the active catalytic sites facilitated oxidations, similarly to the catalytic pathways in metal-containing enzymes. Under certain conditions, two metals in one complex can act in concert, modeling the reactivity of a bacterial enzyme which converts methane into methanol. In related studies, a family of nickel complexes that react with carbon dioxide at

  8. Mechanism-Based Design of Green Oxidation Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Rybak-Akimova, Elena [Tufts Univ., Medford, MA (United States)

    2015-03-16

    situation. Growing families of synthetic iron complexes that resemble active sites of metalloenzymes produce metal-based intermediates (rather than hydroxyl radicals) in reactions with oxygen donors. These complexes are very promising for selective oxygen and peroxide activation. In order to understand the mechanisms of metal-based small molecule activation, kinetically competent metal-oxygen intermediates must be identified. One of the grand challenges identified by the Department of Energy workshop "Catalysis for Energy" is understanding mechanisms and dynamics of catalyzed reactions. The research summarized herein focuses on detailed characterization of the formation and reactivity of various iron-peroxo- and iron-oxo intermediates that are involved in catalysis. Rates of rapid reactions were studied at low temperatures by a specialized technique termed cryogenic stopped-flow spectrophotometry. These measurements identified reaction conditions which favor the formation of catalytically competent oxidants. Chemical structures of reactive complexes was determined, and new, efficient catalysts for hydrocarbon oxidation were synthesized. Importantly, these catalysts are selective, they promote oxidation of hydrocarbons at a specific site. The catalysts are also efficient and robust, hundreds of cycles of substrate oxidation occur within minutes at room temperature. Furthermore, they enable utilization of environmentally friendly oxidants, such as hydrogen peroxide, which produces water as the only byproduct. Mechanistic insights uncovered the role of various acid-containing additives in catalytic oxidations. Proton delivery to the active catalytic sites facilitated oxidations, similarly to the catalytic pathways in metal-containing enzymes. Under certain conditions, two metals in one complex can act in concert, modeling the reactivity of a bacterial enzyme which converts methane into methanol. In related studies, a family of nickel complexes that react with carbon dioxide at

  9. Resistive switching characteristics and mechanisms in silicon oxide memory devices

    Science.gov (United States)

    Chang, Yao-Feng; Fowler, Burt; Chen, Ying-Chen; Zhou, Fei; Wu, Xiaohan; Chen, Yen-Ting; Wang, Yanzhen; Xue, Fei; Lee, Jack C.

    2016-05-01

    Intrinsic unipolar SiOx-based resistance random access memories (ReRAM) characterization, switching mechanisms, and applications have been investigated. Device structures, material compositions, and electrical characteristics are identified that enable ReRAM cells with high ON/OFF ratio, low static power consumption, low switching power, and high readout-margin using complementary metal-oxide semiconductor transistor (CMOS)-compatible SiOx-based materials. These ideas are combined with the use of horizontal and vertical device structure designs, composition optimization, electrical control, and external factors to help understand resistive switching (RS) mechanisms. Measured temperature effects, pulse response, and carrier transport behaviors lead to compact models of RS mechanisms and energy band diagrams in order to aid the development of computer-aided design for ultralarge-v scale integration. This chapter presents a comprehensive investigation of SiOx-based RS characteristics and mechanisms for the post-CMOS device era.

  10. Mechanism for the oxidation of phenol by sulfatoferrate(VI): Comparison with various oxidants.

    Science.gov (United States)

    Peings, Vanessa; Frayret, Jérôme; Pigot, Thierry

    2015-07-01

    The oxidative action of a solid and stable potassium sulfatoferrate(VI) material on phenol was studied in aqueous solution under different stoichiometries. The performance towards phenol and the total organic carbon is compared to that of potassium permanganate and calcium hypochlorite. The total mineralization of phenol is not completely achieved by the studied chemical oxidants, and some oxidation products have been identified by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector analysis. A radical reaction pathway, involving the formation of oxidation intermediates or by-products such as benzoquinone, phenoxyphenol and ring opening products, is proposed for the decomposition of phenol by ferrate(VI). Phenoxyphenol is also involved in the oxidation mechanism for permanganate whereas chlorinated phenols are produced by hypochlorite. The role of the chloride anion impurity of the potassium sulfatoferrate(VI) material has been highlighted in this study; no negative impact on the removal of phenol and its mineralization is observed compared to the use of a pure commercial ferrate(VI). The efficiency of sulfatoferrate(VI) for the oxidative removal of phenol from industrial wastewater is also confirmed.

  11. Mechanism of chlorinating lanthanum oxide and cerium oxide with ammonium chloride

    Institute of Scientific and Technical Information of China (English)

    朱国才; 李赋屏; 肖明贵

    2003-01-01

    Using ammonium chloride(NH4Cl)as a chlorinating agent,the effects of chlorinating temperature,at 300℃ for 90 min,and have no advantage to chlorination of lanthanum and cerium oxides at higher temperature.The thermal decomposition of LaCl3 and CeCl3 is carried out to explore the mechanism of chlorinating lanthanum and cerium oxides.At the same time,the chlorination of lanthanum and cerium oxides is not devoted to the HCl decomposed from NH4Cl,but to NH4Cl directly taking part in the chlorination of La2O3 and CeO2.The lanthanum and cerium oxides in chlorination firstly form intermediate LaOCl and CeOCl,and then transfer to LaCl3 and CeCl3,fither prove the existence of the intermediates LaOCl and CeOCl.Therefore the chlorinating temperature and time should strictly be controlled when the lanthanum oxide and cerium oxide are chlorinated with NH4 Cl.And over-dosage of NH4 Cl should be also applied in the process of chlorination.

  12. Complete reaction mechanisms of mercury oxidation on halogenated activated carbon.

    Science.gov (United States)

    Rungnim, Chompoonut; Promarak, Vinich; Hannongbua, Supa; Kungwan, Nawee; Namuangruk, Supawadee

    2016-06-05

    The reaction mechanisms of mercury (Hg) adsorption and oxidation on halogenated activated carbon (AC) have been completely studied for the first time using density functional theory (DFT) method. Two different halogenated AC models, namely X-AC and X-AC-X (X=Cl, Br, I), were adopted. The results revealed that HgX is found to be stable-state on the AC edge since its further desorption from the AC as HgX, or further oxidation to HgX2, are energetically unfavorable. Remarkably, the halide type does not significantly affect the Hg adsorption energy but it strongly affects the activation energy barrier of HgX formation, which obviously increases in the order HgIBr-AC>Cl-AC. Thus, the study of the complete reaction mechanism is essential because the adsorption energy can not be used as a guideline for the rational material design in the halide impregnated AC systems. The activation energy is an important descriptor for the predictions of sorbent reactivity to the Hg oxidation process.

  13. Mechanism of inducible nitric oxide synthase exclusion from mycobacterial phagosomes.

    Directory of Open Access Journals (Sweden)

    Alexander S Davis

    2007-12-01

    Full Text Available Mycobacterium tuberculosis is sensitive to nitric oxide generated by inducible nitric oxide synthase (iNOS. Consequently, to ensure its survival in macrophages, M. tuberculosis inhibits iNOS recruitment to its phagosome by an unknown mechanism. Here we report the mechanism underlying this process, whereby mycobacteria affect the scaffolding protein EBP50, which normally binds to iNOS and links it to the actin cytoskeleton. Phagosomes harboring live mycobacteria showed reduced capacity to retain EBP50, consistent with lower iNOS recruitment. EBP50 was found on purified phagosomes, and its expression increased upon macrophage activation, paralleling expression changes seen with iNOS. Overexpression of EBP50 increased while EBP50 knockdown decreased iNOS recruitment to phagosomes. Knockdown of EBP50 enhanced mycobacterial survival in activated macrophages. We tested another actin organizer, coronin-1, implicated in mycobacterium-macrophage interaction for contribution to iNOS exclusion. A knockdown of coronin-1 resulted in increased iNOS recruitment to model latex bead phagosomes but did not increase iNOS recruitment to phagosomes with live mycobacteria and did not affect mycobacterial survival. Our findings are consistent with a model for the block in iNOS association with mycobacterial phagosomes as a mechanism dependent primarily on reduced EBP50 recruitment.

  14. Mechanism of nitrite oxidation by eosinophil peroxidase: implications for oxidant production and nitration by eosinophils.

    Science.gov (United States)

    van Dalen, Christine J; Winterbourn, Christine C; Kettle, Anthony J

    2006-03-15

    Eosinophil peroxidase is a haem enzyme of eosinophils that is implicated in oxidative tissue injury in asthma. It uses hydrogen peroxide to oxidize thiocyanate and bromide to their respective hypohalous acids. Nitrite is also a substrate for eosinophil peroxidase. We have investigated the mechanisms by which the enzyme oxidizes nitrite. Nitrite was very effective at inhibiting hypothiocyanous acid ('cyanosulphenic acid') and hypobromous acid production. Spectral studies showed that nitrite reduced the enzyme to its compound II form, which is a redox intermediate containing Fe(IV) in the haem active site. Compound II does not oxidize thiocyanate or bromide. These results demonstrate that nitrite is readily oxidized by compound I, which contains Fe(V) at the active site. However, it reacts more slowly with compound II. The observed rate constant for reduction of compound II by nitrite was determined to be 5.6x10(3) M(-1) x s(-1). Eosinophils were at least 4-fold more effective at promoting nitration of a heptapeptide than neutrophils. This result is explained by our finding that nitrite reacts 10-fold faster with compound II of eosinophil peroxidase than with the analogous redox intermediate of myeloperoxidase. Nitration by eosinophils was increased 3-fold by superoxide dismutase, which indicates that superoxide interferes with nitration. We propose that at sites of eosinophilic inflammation, low concentrations of nitrite will retard oxidant production by eosinophil peroxidase, whereas at higher concentrations nitrogen dioxide will be a major oxidant formed by these cells. The efficiency of protein nitration will be decreased by the diffusion-controlled reaction of superoxide with nitrogen dioxide.

  15. Oxidant mechanisms in childhood obesity: the link between inflammation and oxidative stress.

    Science.gov (United States)

    Codoñer-Franch, Pilar; Valls-Bellés, Victoria; Arilla-Codoñer, Angela; Alonso-Iglesias, Eulalia

    2011-12-01

    Evidence of obesity-induced oxidative stress in adults has emerged in the past several years, and similar evidence has been demonstrated in children more recently. The reactive species of oxygen or nitrogen can chemically alter all major classes of biomolecules by modifying their structure and function. Organisms have developed mechanisms to protect biomolecules from the deleterious effects of free radicals. These include the enzymes superoxide dismutase, catalase, and glutathione peroxidase, as well as water and lipid-soluble antioxidants, such as glutathione, ascorbate (vitamin C), α-tocopherol (vitamin E), and β-carotene. Obesity creates oxidant conditions that favor the development of comorbid diseases. Energy imbalances lead to the storage of excess energy in adipocytes, resulting in both hypertrophy and hyperplasia. These processes are associated with abnormalities of adipocyte function, particularly mitochondrial stress and disrupted endoplasmic reticulum function. In this sense, oxidative stress can also be induced by adipocyte associated inflammatory macrophages. There is a close link among obesity, a state of chronic low-level inflammation, and oxidative stress. In addition, the dysregulation of adipocytokines, which are secreted by adipose tissue and promoted by oxidative stress, act synergistically in obesity-related metabolic abnormalities. Adipocytokines link the local and systemic inflammation responses in the context of obesity. It is thought that the evaluation of oxidative status may allow for the identification of patients at an increased risk of complications. Decreasing the levels of chronic inflammation and oxidative stress in childhood may decrease cardiovascular morbidity and mortality in adulthood. Copyright © 2011 Mosby, Inc. All rights reserved.

  16. Oxide cathode mechanisms: Electronic and structural features of oxide cathode surfaces

    Science.gov (United States)

    Cunningham, J.; Nunan, J.

    1985-01-01

    This report describes studies made upon systems selected for their ability to model various important features of oxide cathodes and the mechanisms which enable them to function as efficient thermionic emitters at moderate temperatures. An account is given of experiments which aimed to simulate conditions upon the surfaces of polycrystalline samples of alkaline earth oxides (e.g., SrO and BaO/SrO or MgO and BaO/MgO) at various stages of their preparation in similiar fashion to that used in the thermal activation of oxide cathodes. Accounts are given of experiments which examined the interaction between the gases O2, N2O, H2 or Ch4 and appropriately preactivated surface of pure and mixed alkaline earth oxide samples. Accounts are given of experiments involving the controlled deposition in UHV conditions of zero-valent Ba ad-atoms-in amounts ranging from submonolayer to multilayer coverage - upon layers of SrO or BaO previously prepared in UHV conditions by evaporation of the corresponding metal and its subsequent oxidation. UPS spectra have been undertaken in order to examine surfaces of samples prepared by evaporation of barium metal or strontium metal and to study effects upon the UPS spectra by exposures to the gases N20, O2 and CH4.

  17. Stepwise mechanism of oxidative ammonolysis of propane to acrylonitrile over gallium-antimony oxide catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Osipova, Z.G.; Sokolovskii, V.D.

    1979-03-01

    The stepwise mechanism of oxidative ammonolysis of propane to acrylonitrile over gallium-antimony oxide catalysts GaSb/sub 19/O/sub x/, GaSb/sub 3/Ni/sub 1.5/0/sub x/, and GaSb/sub 2.5/Ni/sub 1.5/PW/sub 0//sub 0.25/O/sub x/ was studied at 450/sup 0/ and 550/sup 0/C by introducing alternating pulses of 0.5Vertical Bar3< propane/0.6Vertical Bar3< ammonia/helium (to reduce the steady-state catalytic surface) and 0.5Vertical Bar3< propane/0.6Vertical Bar3< ammonia/1.86Vertical Bar3< oxygen/helium mixtures into a fluidized-bed catalytic reactor. Over all the catalysts studied, the rates of acrylonitrile formation during the two types of pulses were very similar, but carbon dioxide was formed much faster during the reducing pulses, particularly at 450/sup 0/C. These findings suggested that acrylonitrile is formed by a stepwise redox mechanism involving consecutive interaction of propane and ammonia with the surface oxygen of the catalysts and oxidation of the reduced catalyst surface by gas-phase oxygen. The formation of carbon dioxide proceeds by both stepwise and associative mechanisms, the latter being more important at higher temperatures. The results are similar to published results for ammoxidation of propylene and olefins.

  18. Optical and mechanical anisotropy of oxide glass fibers

    DEFF Research Database (Denmark)

    Deubener, J.; Yue, Yuanzheng

    2012-01-01

    Upon fiber drawing, glass forming oxide melts are thermally quenched and mechanically stretched. High cooling rates (up to 106 K/min) of quenched glass fibres lead to higher enthalpy state of liquids, thereby, to higher fictive temperature than regular quenching (e.g. 20 K/min) of bulk glass...... products [1], whereas stretching (frozen-in strain) results in optical and mechanical anisotropy of glass fibers, which is quantified inter alia by the specific birefringence [2]. The paper will stress the later effects by combining previous results on the structural origins of birefringence...... and anisotropic shrinkage in silica and phosphate fibers with recent studies on relaxation of optical anisotropy in E-glass fibers [3,4]....

  19. Evaluation of structural deformations of a mechanical connecting unit oxidizer supplies by thermo-mechanical simulation

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sang Woo [Dept. of Mechanical Engineering, Institute of Machine Convergence Technology, Hankyong National University, Anseong (Korea, Republic of)

    2016-10-15

    A Mechanical connecting unit (MCU) used in ground facilities for a Liquid propellant rocket (LPR) acts as a bridge between the onboard system and the ground oxidizer filling system. It should be resistant to structural deformations in order to guarantee successful supply of a cryogenic oxidizer and high pressure gases without reduction of sealing capability. The MCU consists of many components and linkages and operates under harsh conditions induced by a cryogenic oxidizer, high pressure gases and other mechanical forces. Thus, the evaluation of structural deformation of the MCU considering complex conditions is expensive and time consuming. The present study efficiently evaluates the structural deformations of the key components of the MCU by Thermo-mechanical simulation (TMS) based on the superposition principle. Deformations due to the mechanical loadings including weights, pressures, and spring forces are firstly evaluated by using a non-linear flexible body simulation module (FFlex) of Multi-body dynamics (MBD) software, RecurDyn. Then, thermal deformations for the deformed geometries obtained by RecurDyn were subsequently calculated. It was conducted by using a Finite element (FE) analysis software, ANSYS. The total deformations for the onboard plate and multi-channel plate in the connecting section due to the mechanical and thermal loadings were successfully evaluated. Moreover, the outer gaps at six points between two plates were calculated and verified by comparison to the measured data. Their values and tendencies showed a good agreement. The author concluded that the TMS using MBD software considering flexible bodies and an FE simulator can efficiently evaluate structural deformations of the MCU operating under the complex load and boundary conditions.

  20. Synthesis, Growth Mechanism, and Applications of Zinc Oxide Nanomaterials

    Institute of Scientific and Technical Information of China (English)

    Shulin JI; Changhui YE

    2008-01-01

    This article reviews recent progresses in growth mechanism, synthesis, and applications of zinc oxide nanomaterials (mainly focusing on one-dimensional (1D) nanomaterials). In the first part of this article, we briefly introduce the importance, the synthesis methods and growth mechanisms, the properties and applications of ZnO 1D nanomaterials. In the second part of this article, the growth mechanisms of ZnO 1D nanomaterials will be discussed in detail in the framework of vapor-liquid-solid (VLS), vapor-solid (VS), and aqueous solution growth (ASG) approaches. Both qualitative and quantitative information will be provided to show how a controlled synthesis of ZnO 1D nanomaterials can be achieved. In the third part of this article, we present recent progresses in our group for the synthesis of ZnO 1D nanomaterials, and the results from other groups will only be mentioned briefly. Especially, experiment designing according to theories will be elaborated to demonstrate the concept of controlled synthesis. In the fourth part of this article, the properties and potential applications of ZnO 1D nanomaterials will be treated. Finally, a summary part will be presented in the fifth section. The future trend of research for ZnO 1D nanomaterials will be pointed out and key issues to be solved will be proposed.

  1. Kinetics and Mechanisms of Ciprofloxacin Oxidation on Hematite Surfaces.

    Science.gov (United States)

    Martin, Sébastien; Shchukarev, Andrey; Hanna, Khalil; Boily, Jean-François

    2015-10-20

    Adsorption of antibiotics at mineral surfaces has been extensively studied over the past 20 years, yet much remains to be learned on their interfacial properties and transformation mechanisms. In this study, interactions of Ciprofloxacin (CIP), a fluoroquinolone antibiotic with two sets of synthetic nanosized hematite particles, with relatively smooth (H10, 10-20 nm in diameter) and roughened (H80, 80-90 nm in diameter) surfaces, were studied by means of liquid chromatography (LC), mass spectrometry (MS), and spectroscopy (vibration and X-ray photoelectron). Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy provides evidence for inner-sphere bidentate complex formation of CIP at hematite surfaces in 0.01 M NaCl, irrespective of pH and particle size. ATR-FTIR spectroscopy also revealed that the sorbed mother CIP molecule decayed to other surface species over a period of at least 65 h. This was supported by the detection of three daughter products in the aqueous phase by LC/MS. The appearance of NH3(+) groups during the course of these experiments, revealed by cryogenic XPS, provides further evidence that CIP oxidation proceeds through an opening of piperazine ring via N-dealkylation. Additional in vacuo FTIR experiments under temperature-programmed desorption also showed that oxidation of sorbed byproducts were effectively degraded beyond 450 °C, a result denoting considerably strong (inter)molecular bonds of both mother and daughter products. This work also showed that rougher, possibly multidomainic particles (H80) generated slower rates of CIP decomposition but occurring through more complex schemes than at smoother particle surfaces (H10). This work thus uncovered key aspects of the binding of an important antibiotic at iron oxide surfaces, and therefore provided additional constraints to our growing understanding of the fate of emerging contaminants in the environment.

  2. Mechanism of heterogeneous reaction of carbonyl sulfide on magnesium oxide.

    Science.gov (United States)

    Liu, Yongchun; He, Hong; Xu, Wenqing; Yu, Yunbo

    2007-05-24

    Heterogeneous reaction of carbonyl sulfide (OCS) on magnesium oxide (MgO) under ambient conditions was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), quadrupole mass spectrometer (QMS), and density functional theory (DFT) calculations. It reveals that OCS can be catalytically hydrolyzed by surface hydroxyl on MgO to produce carbon dioxide (CO2) and hydrogen sulfide (H2S), and then H2S can be further catalytically oxidized by surface oxygen or gaseous oxygen on MgO to form sulfite (SO3(2-)) and sulfate (SO4(2-)). Hydrogen thiocarbonate (HSCO2-) was found to be the crucial intermediate. Surface hydrogen sulfide (HS), sulfur dioxide (SO2), and surface sulfite (SO3(2-)) were also found to be intermediates for the formation of sulfate. Furthermore, the surface hydroxyl contributes not only to the formation of HSCO2- but also to HSCO2- decomposition. On the basis of experimental results, the heterogeneous reaction mechanism of OCS on MgO was discussed.

  3. Wet oxidation of activated sludge: transformations and mechanisms.

    Science.gov (United States)

    Urrea, José Luis; Collado, Sergio; Laca, Amanda; Díaz, Mario

    2014-12-15

    Wet oxidation (WO) is an interesting alternative for the solubilization and mineralization of activated sludge. The effects of different temperatures (160-200 °C) and pressures (4-8 MPa), on the evolution of chemical composition and rheological characteristics of a thickened activated sludge during WO are analyzed in this work. Soluble COD increases initially to a maximum and then diminishes, while the apparent viscosity of the mixture falls continuously throughout the experiment. Based on the experimental evolution of the compositions and rheological characteristics of the sludge, a mechanism consisting of two stages in series is proposed. Initially, the solid organic compounds are solubilized following a pseudo-second order kinetic model with respect to solid COD. After that, the solubilized COD was oxidized, showing a pseudofirst kinetic order, by two parallel pathways: the complete mineralization of the organic matter and the formation of highly refractory COD. Kinetic parameters of the model, including the activation energies are mentioned, with good global fitting to the experiments described.

  4. Cyclic nitroxides inhibit the toxicity of nitric oxide-derived oxidants: mechanisms and implications

    Directory of Open Access Journals (Sweden)

    Ohara Augusto

    2008-03-01

    Full Text Available The substantial therapeutic potential of tempol (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy and related cyclic nitroxides as antioxidants has stimulated innumerous studies of their reactions with reactive oxygen species. In comparison, reactions of nitroxides with nitric oxide-derived oxidants have been less frequently investigated. Nevertheless, this is relevant because tempol has also been shown to protect animals from injuries associated with inflammatory conditions, which are characterized by the increased production of nitric oxide and its derived oxidants. Here, we review recent studies addressing the mechanisms by which cyclic nitroxides attenuate the toxicity of nitric oxidederived oxidants. As an example, we present data showing that tempol protects mice from acetaminophen-induced hepatotoxicity and discuss the possible protection mechanism. In view of the summarized studies, it is proposed that nitroxides attenuate tissue injury under inflammatory conditions mainly because of their ability to react rapidly with nitrogen dioxide and carbonate radical. In the process the nitroxides are oxidized to the corresponding oxammonium cation, which, in turn, can be recycled back to the nitroxides by reacting with upstream species, such as peroxynitrite and hydrogen peroxide, or with cellular reductants. An auxiliary protection mechanism may be down-regulation of inducible nitric oxide synthase expression. The possible therapeutic implications of these mechanisms are addressed.O considerável potencial terapêutico de tempol (4-hidroxi-2,2, 6,6-tetrametil-1piperiniloxila e nitróxidos cíclicos relacionados como antioxidantes tem estimulado inúmeros estudos de suas reações com espécies reativas derivadas de oxigênio. Em comparação, as reações de nitróxidos com oxidantes derivados do óxido nítrico têm sido investigadas menos frequentemente. Todavia, essas reações são relevantes porque o tempol é também capaz de proteger

  5. Oxidative stress mechanisms and potential therapeutics in Alzheimer disease.

    Science.gov (United States)

    Moreira, P I; Siedlak, S L; Aliev, G; Zhu, X; Cash, A D; Smith, M A; Perry, G

    2005-07-01

    Oxidative damage of biological macromolecules is a hallmark of most neurodegenerative disorders such as Alzheimer, Parkinson and diffuse Lewy body diseases. Another important phenomenon involved in these disorders is the alteration of iron and copper homeostasis. Data from the literature support the involvement of metal homeostasis in mitochondrial dysfunction, protein alterations and nucleic acid damage which are relevant in brain function and consequently, in the development of neurodegenerative disorders. Although alterations in transition metal homeostasis, redox activity, and localization are well documented, it must be determined how alterations of specific copper- and iron-containing metalloenzymes are also involved in Alzheimer disease. The clarification of these phenomena can open a new window for understanding the mechanisms underlying neurodegeneration and, consequently, for the development of new therapeutic strategies such as gene therapy and new pharmaceutical formulations with antioxidant and chelating properties.

  6. Mechanism Study of Reversible Resistivity Change in Oxide Thin Film

    Energy Technology Data Exchange (ETDEWEB)

    Hong, S.; Chang, S. H.; Phatak, C.; Magyari-Kope, Blanka; Nishi, Y; Chattopadhyay, Soma; Kim, Jung Ho

    2015-01-01

    Here we present our findings related to the mechanism of reversible resistivity in Pt/TiO2/Pt cells and in Ta2O5 thin films. Our findings for Pt/TiO2/Pt cells indicate that there exists a photovoltaic-like effect, which modulates the resistance reversibly by a few orders of magnitude, depending on the intensity of impinging x-rays. We found that this effect, combined with the x-ray irradiation induced phase transition confirmed by transmission electron microscopy, triggers a non-volatile reversible resistance change. For Ta2O5 thin films, we found that there are strong correlations among oxygen vacancy number and positions and energy gaps. Ab initio band structure calculations explain the evolution of the electronic excitation spectrum as a function of oxygen vacancy number and positions and importantly provide a predictive description of the oxygen deficient Ta oxide that may improve the desired performance based on atomic level design.

  7. Fisetin Protects DNA Against Oxidative Damage and Its Possible Mechanism

    Science.gov (United States)

    Wang, Tingting; Lin, Huajuan; Tu, Qian; Liu, Jingjing; Li, Xican

    2016-01-01

    Purpose: The paper tries to assess the protective effect of fisetin against •OH-induced DNA damage, then to investigate the possible mechanism. Methods: The protective effect was evaluated based on the content of malondialdehyde (MDA). The possible mechanism was analyzed using various antioxidant methods in vitro, including •OH scavenging (deoxyribose degradation), •O2- scavenging (pyrogallol autoxidation), DPPH• scavenging, ABTS•+ scavenging, and Cu2+-reducing power assays. Results: Fisetin increased dose-dependently its protective percentages against •OH-induced DNA damage (IC50 value =1535.00±29.60 µM). It also increased its radical-scavenging percentages in a dose-dependent manner in various antioxidants assays. Its IC50 values in •OH scavenging, •O2- scavenging, DPPH• scavenging, ABTS•+ scavenging, and Cu2+-reducing power assays, were 47.41±4.50 µM, 34.05±0.87 µM, 9.69±0.53 µM, 2.43±0.14 µM, and 1.49±0.16 µM, respectively. Conclusion: Fisetin can effectively protect DNA against •OH-induced oxidative damage possibly via reactive oxygen species (ROS) scavenging approach, which is assumed to be hydrogen atom (H•) and/or single electron (e) donation (HAT/SET) pathways. In the HAT pathway, the 3’,4’-dihydroxyl moiety in B ring of fisetin is thought to play an important role, because it can be ultimately oxidized to a stable ortho-benzoquinone form. PMID:27478791

  8. Pro-oxidant and anti-oxidant mechanism(s) of BHT and beta-carotene in photocarcinogenesis.

    Science.gov (United States)

    Black, Homer S

    2002-04-01

    An hypothesis for the role of free radicals in cancer was elaborated by D. Harman in 1962 who suggested that it might be possible to reduce the extent of damage caused by free radicals through three dietary changes: (i) caloric reduction, i.e., lowering the level of free radical reactions arising in the course of normal metabolism; (ii) minimize dietary components that tend to increase the level of free radical reactions (e.g., polyunsaturated fats); and (iii) supplement the diet with one or more free radical reaction inhibitors (anti-oxidants). With respect to (ii) and (iii), lipid peroxidation exemplifies the type of chain reaction initiated by free radicals, with unsaturated fatty acids being the primary center of free radical attack. Anti-oxidants act as free radical scavengers and are able to terminate these reactions. Indeed, the phenolic anti-oxidant butylated hydroxytoluene (BHT), and the carotenoid beta-carotene, have both been shown to influence photocarcinogenesis, although the lack of correlation between physicochemical parameters and pathophysiological responses is apparent in both instances. The bimolecular rate constant for reaction of BHT with model peroxyl radicals is low while beta-carotene is highly reactive. However, both are able to efficiently inhibit lipid peroxidation reactions in biological membranes. Indeed, the influence of photocarcinogenesis by both BHT and beta-carotene is diminished as the level of dietary fat decreases, pointing to the involvement of lipid peroxidative reactions. Nevertheless, the mode of action of BHT in inhibiting photocarcinogenesis appears to be related to dose-diminution resulting from an increased spectral absorbance of the stratum corneum. On the other hand, beta-carotene has no such effect and may actually exacerbate photocarcinogenesis under certain dietary conditions. This paradox points to the complex relationship between chemical mechanisms and biological mode of action of anti-oxidants in

  9. Preparation and mechanical properties of graphene oxide: cement nanocomposites.

    Science.gov (United States)

    Babak, Fakhim; Abolfazl, Hassani; Alimorad, Rashidi; Parviz, Ghodousi

    2014-01-01

    We investigate the performance of graphene oxide (GO) in improving mechanical properties of cement composites. A polycarboxylate superplasticizer was used to improve the dispersion of GO flakes in the cement. The mechanical strength of graphene-cement nanocomposites containing 0.1-2 wt% GO and 0.5 wt% superplasticizer was measured and compared with that of cement prepared without GO. We found that the tensile strength of the cement mortar increased with GO content, reaching 1.5%, a 48% increase in tensile strength. Ultra high-resolution field emission scanning electron microscopy (FE-SEM) used to observe the fracture surface of samples containing 1.5 wt% GO indicated that the nano-GO flakes were well dispersed in the matrix, and no aggregates were observed. FE-SEM observation also revealed good bonding between the GO surfaces and the surrounding cement matrix. In addition, XRD diffraction data showed growth of the calcium silicate hydrates (C-S-H) gels in GO cement mortar compared with the normal cement mortar.

  10. Study of antibacterial mechanism of graphene oxide using Raman spectroscopy

    Science.gov (United States)

    Nanda, Sitansu Sekhar; Yi, Dong Kee; Kim, Kwangmeyung

    2016-01-01

    Graphene oxide (GO) is extensively proposed as an effective antibacterial agent in commercial product packaging and for various biomedical applications. However, the antibacterial mode of action of GO is yet hypothetical and unclear. Here we developed a new and sensitive fingerprint approach to study the antibacterial activity of GO and underlying mechanism, using Raman spectroscopy. Spectroscopic signatures obtained from biomolecules such as Adenine and proteins from bacterial cultures with different concentrations of GO, allowed us to probe the antibacterial activity of GO with its mechanism at the molecular level. Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) were used as model micro-organisms for all the experiments performed. The observation of higher intensity Raman peaks from Adenine and proteins in GO treated E. coli and E. faecalis; correlated with induced death, confirmed by Scanning electron Microscopy (SEM) and Biological Atomic Force Microscopy (Bio-AFM). Our findings open the way for future investigations of the antibacterial properties of different nanomaterial/GO composites using Raman spectroscopy. PMID:27324288

  11. Study of antibacterial mechanism of graphene oxide using Raman spectroscopy

    Science.gov (United States)

    Nanda, Sitansu Sekhar; Yi, Dong Kee; Kim, Kwangmeyung

    2016-06-01

    Graphene oxide (GO) is extensively proposed as an effective antibacterial agent in commercial product packaging and for various biomedical applications. However, the antibacterial mode of action of GO is yet hypothetical and unclear. Here we developed a new and sensitive fingerprint approach to study the antibacterial activity of GO and underlying mechanism, using Raman spectroscopy. Spectroscopic signatures obtained from biomolecules such as Adenine and proteins from bacterial cultures with different concentrations of GO, allowed us to probe the antibacterial activity of GO with its mechanism at the molecular level. Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) were used as model micro-organisms for all the experiments performed. The observation of higher intensity Raman peaks from Adenine and proteins in GO treated E. coli and E. faecalis; correlated with induced death, confirmed by Scanning electron Microscopy (SEM) and Biological Atomic Force Microscopy (Bio-AFM). Our findings open the way for future investigations of the antibacterial properties of different nanomaterial/GO composites using Raman spectroscopy.

  12. Failure Mechanisms in High Chrome Oxide Gasifier Refractories

    Science.gov (United States)

    Bennett, James P.; Kwong, Kyei-Sing

    2011-04-01

    Gasification is a high-temperature, high-pressure chemical process used to convert a carbon feedstock into CO and H2 (syngas) for use in power generation and the production of chemicals. It is also a leading candidate as a source of hydrogen in a hydrogen economy and is one of several technologies expected to see increased use in advanced fossil fuel power systems in the future. Gasification is being evaluated because of its high efficiency, its ability to capture CO2 for sequestration or reuse in other applications, and its potential for carbon feedstock fuel flexibility. At the heart of the gasification process is a gasifier, a high pressure chemical reaction vessel used to contain the interactions between carbon and water in a shortage of oxygen, producing syngas. The gasifier is lined with high chrome oxide materials to protect the containment vessel. Gasifiers are complex systems, and failure of the refractories used to line them was identified by industry as a limitation to their reliability and availability and to their increased use. NETL researchers have examined spent high-Cr2O3 (over 90 pct Cr2O3) refractories from numerous gasifiers to determine in-service failure mechanisms. This analysis revealed that premature failure of the high chrome oxide refractories was related to ash in the carbon feedstock, which liquefies during gasification and interacts with the refractories, leading to wear by chemical dissolution or spalling (structural and chemical). A discussion of this postmortem wear of spent refractory materials and of thermodynamic modeling used to explain microstructural changes leading to wear are explained in this article. This information will serve the basis to develop improved performance refractory materials.

  13. Mechanisms of lithium transport in amorphous polyethylene oxide

    Science.gov (United States)

    Duan, Yuhua; Halley, J. W.; Curtiss, Larry; Redfern, Paul

    2005-02-01

    We report calculations using a previously reported model of lithium perchlorate in polyethylene oxide in order to understand the mechanism of lithium transport in these systems. Using an algorithm suggested by Voter, we find results for the diffusion rate which are quite close to experimental values. By analysis of the individual events in which large lithium motions occur during short times, we find that no single type of rearrangement of the lithium environment characterizes these events. We estimate the free energies of the lithium ion as a function of position during these events by calculation of potentials of mean force and thus derive an approximate map of the free energy as a function of lithium position during these events. The results are consistent with a Marcus-like picture in which the system slowly climbs a free energy barrier dominated by rearrangement of the polymer around the lithium ions, after which the lithium moves very quickly to a new position. Reducing the torsion forces in the model causes the diffusion rates to increase.

  14. Oxidative Stress in Neurodegenerative Diseases: Mechanisms and Therapeutic Perspectives

    Directory of Open Access Journals (Sweden)

    Ailton Melo

    2011-01-01

    Full Text Available The incidence and prevalence of neurodegenerative diseases (ND increase with life expectancy. This paper reviews the role of oxidative stress (OS in ND and pharmacological attempts to fight against reactive oxygen species (ROS-induced neurodegeneration. Several mechanisms involved in ROS generation in neurodegeneration have been proposed. Recent articles about molecular pathways involved in ROS generation were reviewed. The progress in the development of neuroprotective therapies has been hampered because it is difficult to define targets for treatment and determine what should be considered as neuroprotective. Therefore, the attention was focused on researches about pharmacological targets that could protect neurons against OS. Since it is necessary to look for genes as the ultimate controllers of all biological processes, this paper also tried to identify gerontogenes involved in OS and neurodegeneration. Since neurons depend on glial cells to survive, recent articles about the functioning of these cells in aging and ND were also reviewed. Finally, clinical trials testing potential neuroprotective agents were critically reviewed. Although several potential drugs have been screened in in vitro and in vivo models of ND, these results were not translated in benefit of patients, and disappointing results were obtained in the majority of clinical trials.

  15. Identifying Potential Mechanisms Enabling Acidophily in the Ammonia-Oxidizing Archaeon “

    NARCIS (Netherlands)

    Lehtovirta-Morley, L.E.; Sayavedra-Soto, L.A.; Gallois, N.; Schouten, S.; Stein, L.Y.; Prosser, J.I.; Nicol, G.W.

    2016-01-01

    Ammonia oxidation is the first and rate-limiting step in nitrification and is dominated by two distinct groups of microorganismsin soil: ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). AOA are often more abundant than AOBand dominate activity in acid soils. The mechanism of amm

  16. Electro-oxidation process and mechanism of molybdenite decomposition under ultrasonic effect

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    According to the characteristics and shortcomings of the traditional roasting process and the electro-oxidation process in the molybdenum metallurgical industry,the ultrasound electro-oxidation process was proposed to strengthen the oxidative decomposition or leaching of molybdenum.Laboratory work was carried out in an electrochemical cell with 15 nun electrode spacing at 25℃ under ultrasonic effect.The optimum conditions were found through experiments.The electro-oxidation mechanism of molybdenite decomposition under ultrasonic was investigated.A model of electro-oxidation mechanism of molybdenum under ultrasonic was given.

  17. Mechanisms of Mn(II) catalytic oxidation on ferrihydrite surfaces and the formation of manganese (oxyhydr)oxides

    Science.gov (United States)

    Lan, Shuai; Wang, Xiaoming; Xiang, Quanjun; Yin, Hui; Tan, Wenfeng; Qiu, Guohong; Liu, Fan; Zhang, Jing; Feng, Xionghan

    2017-08-01

    Oxidation of Mn(II) is an important process that controls the mobility and bioavailability of Mn, as well as the formation of Mn (oxyhydr)oxides in natural systems. It was found that the surfaces of minerals, such as iron (oxyhydr)oxides, can accelerate Mn(II) oxidation to a certain degree, but the underlying mechanism has not been clearly understood. This study explores the reaction pathways and mechanisms of Mn(II) oxidation on ferrihydrite surfaces at neutral pH, commonly found in natural environments, by comparisons with montmorillonite, amorphous Al(OH)3, goethite, and magnetite using macroscopic experiments and spectroscopic analyses. Results show that when Mn(II) concentrations are below 4 mM, macroscopic Mn(II) adsorption on the three iron (oxyhydr)oxide surfaces conforms well to the Langmuir equation, with ferrihydrite showing the highest adsorption capacity. With Mn(II) concentrations ranging within 6-24 mM, the adsorbed Mn(II) is mainly oxidized into manganite (γ-MnOOH) and/or feitknechtite (β-MnOOH) by dissolved O2, and Mn(II) removal on a unit mass basis in the presence of magnetite is the highest compared with ferrihydrite and goethite. Ferrihydrite, a semiconductor material, shows stronger catalytic ability for Mn(II) oxidation on the same surface area than insulator minerals (i.e., montmorillonite and amorphous Al(OH)3). Additionally, the products of Mn(II) oxidation in the presence of semiconductor iron (oxyhydr)oxides (i.e., ferrihydrite, goethite, or magnetite) at the same Fe/Mn molar ratio include both manganite and a small amount of Mn(IV) minerals, and the Mn average oxidation states (Mn AOSs) of these products follow the order: magnetite > goethite > ferrihydrite. Magnetite and goethite, with relatively smaller SSAs and lower band gap energies, exhibit greater catalysis for Mn(II) oxidation than ferrihydrite at the same Fe/Mn ratio, which goes against the conventional interfacial effect and is related to the electrochemical properties. Thus

  18. Mainz Isoprene Mechanism 2 (MIM2: an isoprene oxidation mechanism for regional and global atmospheric modelling

    Directory of Open Access Journals (Sweden)

    D. Taraborrelli

    2008-07-01

    Full Text Available We present an oxidation mechanism of intermediate size for isoprene (2-methyl-1,3-butadiene suitable for simulations in regional and global atmospheric chemistry models, which we call MIM2. It is a reduction of the corresponding detailed mechanism in the Master Chemical Mechanism (MCM v3.1 and intended as the second version of the well-established Mainz Isoprene Mechanism (MIM. Our aim is to improve the representation of tropospheric chemistry in regional and global models under all NOx regimes. We evaluate MIM2 and re-evaluate MIM through comparisons with MCM v3.1. We find that MIM and MIM2 compute similar O3, OH and isoprene mixing ratios. Unlike MIM, MIM2 produces small relative biases for NOx and organic nitrogen-containing species due to a good representation of the alkyl and peroxy acyl nitrates (RONO2 and RC(OOONO2. Moreover, MIM2 computes only small relative biases with respect to hydrogen peroxide (H2O2, methyl peroxide (CH3OOH, methanol (CH3OH, formaldehyde (HCHO, peroxy acetyl nitrate (PAN, and formic and acetic acids (HCOOH and CH3C(OOH, being always below ≈6% in all NOx scenarios studied. Most of the isoprene oxidation products are represented explicitly, including methyl vinyl ketone (MVK, methacrolein (MACR, hydroxyacetone and methyl glyoxal. MIM2 is mass-conserving with respect to carbon, including CO2 as well. Therefore, it is suitable for studies assessing carbon monoxide (CO from biogenic sources, as well as for studies focused on the carbon cycle. Compared to MIM, MIM2 considers new species like acetaldehyde (CH3CHO, propene (CH2=CHCH3 and glyoxal (CHOCHO with global chemical production rates for the year 2005 of 7.3, 9.5 and 33.8 Tg/yr, respectively. Our new mechanism is expected to substantially improve the results of atmospheric chemistry models by more

  19. Mainz Isoprene Mechanism 2 (MIM2: an isoprene oxidation mechanism for regional and global atmospheric modelling

    Directory of Open Access Journals (Sweden)

    D. Taraborrelli

    2009-04-01

    Full Text Available We present an oxidation mechanism of intermediate size for isoprene (2-methyl-1,3-butadiene suitable for simulations in regional and global atmospheric chemistry models, which we call MIM2. It is a reduction of the corresponding detailed mechanism in the Master Chemical Mechanism (MCM v3.1 and intended as the second version of the well-established Mainz Isoprene Mechanism (MIM. Our aim is to improve the representation of tropospheric chemistry in regional and global models under all NOx regimes. We evaluate MIM2 and re-evaluate MIM through comparisons with MCM v3.1. We find that MIM and MIM2 compute similar O3, OH and isoprene mixing ratios. Unlike MIM, MIM2 produces small relative biases for NOx and organic nitrogen-containing species due to a good representation of the alkyl and peroxy acyl nitrates (RONO2 and RC(OOONO2. Moreover, MIM2 computes only small relative biases with respect to hydrogen peroxide (H2O2, methyl peroxide (CH3OOH, methanol (CH3OH, formaldehyde (HCHO, peroxy acetyl nitrate (PAN, and formic and acetic acids (HCOOH and CH3C(OOH, being always below ≈6% in all NOx scenarios studied. Most of the isoprene oxidation products are represented explicitly, including methyl vinyl ketone (MVK, methacrolein (MACR, hydroxyacetone and methyl glyoxal. MIM2 is mass-conserving with respect to carbon, including CO2 as well. Therefore, it is suitable for studies assessing carbon monoxide (CO from biogenic sources, as well as for studies focused on the carbon cycle. Compared to MIM, MIM2 considers new species like acetaldehyde (CH3CHO, propene (CH2=CHCH3 and glyoxal (CHOCHO with global chemical production rates for the year 2005 of 7.3, 9.5 and 33.8 Tg/yr, respectively. Our new mechanism is expected to substantially improve the results of atmospheric chemistry models by

  20. Atmospheric oxidation mechanism of phenol initiated by OH radical.

    Science.gov (United States)

    Xu, Cui; Wang, Liming

    2013-03-21

    The gas-phase oxidation mechanism of phenol initiated by OH radical was investigated using DFT and ab initio calculations. The initiation of the reaction is dominated by OH addition to ortho-position, forming P2, which subsequently combines with O2 at the ipso-position to form P2-1-OO adduct. A concerted HO2 elimination process from P2-1-OO was found to be much faster than the common ring closure to bicyclic intermediates. The HO2 elimination process from P2-1-OO forms 2-hydroxy-3,5-cyclohexadienone (HCH) as the main product and is also responsible for the experimental fact that the rate constants for reaction between P2 and O2 are about 2 orders of magnitude higher than those between other aromatic-OH adducts and O2. It was speculated that HCH would isomerize to catechol, which is thermodynamically more stable than HCH and was the experimentally observed main product, possibly through heterogeneous processes. Reaction of P2 with NO2 proceeded by addition to form P2-n-NO2 (n = 1, 3, 5), followed by HONO elimination from P2-1/3-NO2 to form catechol. The barriers for HONO elimination and catechol formation are below the separate reactants P2 and NO2, being consistent with the experimental observation of catechol in the absence of O2, while H2O elimination from P2-1/3-NO2 to form 2-nitrophenol (2NP) is hindered by high barriers. The most likely pathway for 2NP is the reaction of phenoxy radical and NO2.

  1. Oxidation of Proteins in Plants-Mechanisms and Consequences

    DEFF Research Database (Denmark)

    Sweetlove, Lee J; Møller, Ian M

    2009-01-01

    The production of reactive oxygen and reactive nitrogen species in plant cells can lead to a variety of modifications of proteins through oxidation of amino acid side groups. The widespread occurrence of such modifications is becoming appreciated as new proteomic approaches allow their systematic...... or postponing oxidation of residues more important for the function of the protein.......The production of reactive oxygen and reactive nitrogen species in plant cells can lead to a variety of modifications of proteins through oxidation of amino acid side groups. The widespread occurrence of such modifications is becoming appreciated as new proteomic approaches allow their systematic...... of modified proteins by affinity purification. Although there are several technical caveats with such approaches, they have been useful in documenting the extent of oxidative modification of proteins and have highlighted a number of proteins where oxidative modification is critical for protein function...

  2. Study on mechanism of wet air oxidation of emulsification wastewater.

    Science.gov (United States)

    Tang, Wen W; Zeng, Xin P; Xiao, Yao M; Gu, Guo W

    2009-04-01

    Wet air oxidation (WAO) can effectively be used to treat high-concentration, non-biodegradable emulsification wastewater that contains nonionic matters. Gas chromatograph analysis of emulsification wastewater after oxidation indicated that a catalyst increased production of fatty acids but could not promote its oxidation between 160 and 180 degrees C. When the temperature was greater than or equal to 220 degrees C, the catalyst not only increased production of fatty acids initially but effectively promoted its oxidation in later stages and significantly reduced the concentration of residual surfactants. Experiments proved that fatty acids (especially acetic acid) were the primary intermediate products and that oxidation of these acids was the rate-limiting step. During the process of catalytic WAO of emulsification wastewater, active oxygen molecules attacked organic matters resulting in production of fatty acids, ketone, alcohol, hydrocarbon, and oligo-polyether through radical chain reactions.

  3. [Molecular mechanism of accelerating ageing by oxidative stress].

    Science.gov (United States)

    Yoshikawa, Toshikazu; Naito, Yuji

    2009-07-01

    Reactive oxygen species are important for many life sustaining processes of cells and tissues, but they can also induce cell damage and death. If their production and levels within cells are not effectively controlled, then the detrimental effects of oxidative stress can accumulate. Oxidative stress is widely thought to underpin many ageing processes, and the oxidative stress theory of ageing is one of the most widely acknowledged theories of ageing. As well as being the major source of reactive oxygen species, mitochondria are also a major site of oxidative damage. The purpose of this review is a concise and current review of the role of oxidative stress in ageing process. Emphasis is placed upon the roles of mitochondrial proton leak, the uncoupling proteins, and the anti-ageing effects of caloric restriction.

  4. [Mechanism study of fluoride adsorption by hydrous metal oxides].

    Science.gov (United States)

    Guo, Hui-Chao; Li, Wen-Jun; Chang, Zhi-Dong; Wang, Huan-Ying; Zhou, Yue

    2011-08-01

    Hydrous oxides of cerium, aluminum, nickel and copper were prepared by alkaline precipitation method. Langmuir adsorption isotherm was studied and specific surface area was measured by BET method through N2 adsorption-desorption process. IR characterization of hydrous metal oxides before and after fluoride adsorption was also studied. Results show that different hydrous metal oxides have different specific surface areas and their pore size distributions also are not all the same. Adsorption capacity is not directly dependent on the specific surface area. Isotherm study indicates that the adsorption follows Langmuir model and shows the feature of monolayer adsorption. IR study before and after fluoride adsorption shows that different hydrous metal oxides have similar adsorption sites in the same IR region as well as adsorption sites in the different IR region. The comprehensive interaction of these adsorption sites with fluoride ions results in the different adsorption capacity of different hydrous metal oxides.

  5. The mechanism of electroforming of metal oxide memristive switches

    Science.gov (United States)

    Joshua Yang, J.; Miao, Feng; Pickett, Matthew D.; Ohlberg, Douglas A. A.; Stewart, Duncan R.; Lau, Chun Ning; Williams, R. Stanley

    2009-05-01

    Metal and semiconductor oxides are ubiquitous electronic materials. Normally insulating, oxides can change behavior under high electric fields—through 'electroforming' or 'breakdown'—critically affecting CMOS (complementary metal-oxide-semiconductor) logic, DRAM (dynamic random access memory) and flash memory, and tunnel barrier oxides. An initial irreversible electroforming process has been invariably required for obtaining metal oxide resistance switches, which may open urgently needed new avenues for advanced computer memory and logic circuits including ultra-dense non-volatile random access memory (NVRAM) and adaptive neuromorphic logic circuits. This electrical switching arises from the coupled motion of electrons and ions within the oxide material, as one of the first recognized examples of a memristor (memory-resistor) device, the fourth fundamental passive circuit element originally predicted in 1971 by Chua. A lack of device repeatability has limited technological implementation of oxide switches, however. Here we explain the nature of the oxide electroforming as an electro-reduction and vacancy creation process caused by high electric fields and enhanced by electrical Joule heating with direct experimental evidence. Oxygen vacancies are created and drift towards the cathode, forming localized conducting channels in the oxide. Simultaneously, O2- ions drift towards the anode where they evolve O2 gas, causing physical deformation of the junction. The problematic gas eruption and physical deformation are mitigated by shrinking to the nanoscale and controlling the electroforming voltage polarity. Better yet, electroforming problems can be largely eliminated by engineering the device structure to remove 'bulk' oxide effects in favor of interface-controlled electronic switching.

  6. The mechanism of electroforming of metal oxide memristive switches.

    Science.gov (United States)

    Joshua Yang, J; Miao, Feng; Pickett, Matthew D; Ohlberg, Douglas A A; Stewart, Duncan R; Lau, Chun Ning; Williams, R Stanley

    2009-05-27

    Metal and semiconductor oxides are ubiquitous electronic materials. Normally insulating, oxides can change behavior under high electric fields--through 'electroforming' or 'breakdown'--critically affecting CMOS (complementary metal-oxide-semiconductor) logic, DRAM (dynamic random access memory) and flash memory, and tunnel barrier oxides. An initial irreversible electroforming process has been invariably required for obtaining metal oxide resistance switches, which may open urgently needed new avenues for advanced computer memory and logic circuits including ultra-dense non-volatile random access memory (NVRAM) and adaptive neuromorphic logic circuits. This electrical switching arises from the coupled motion of electrons and ions within the oxide material, as one of the first recognized examples of a memristor (memory-resistor) device, the fourth fundamental passive circuit element originally predicted in 1971 by Chua. A lack of device repeatability has limited technological implementation of oxide switches, however. Here we explain the nature of the oxide electroforming as an electro-reduction and vacancy creation process caused by high electric fields and enhanced by electrical Joule heating with direct experimental evidence. Oxygen vacancies are created and drift towards the cathode, forming localized conducting channels in the oxide. Simultaneously, O(2-) ions drift towards the anode where they evolve O(2) gas, causing physical deformation of the junction. The problematic gas eruption and physical deformation are mitigated by shrinking to the nanoscale and controlling the electroforming voltage polarity. Better yet, electroforming problems can be largely eliminated by engineering the device structure to remove 'bulk' oxide effects in favor of interface-controlled electronic switching.

  7. The mechanism of the catalytic oxidation of hydrogen sulfide: II. Kinetics and mechanism of hydrogen sulfide oxidation catalyzed by sulfur

    NARCIS (Netherlands)

    Steijns, M.; Derks, F.; Verloop, A.; Mars, P.

    1976-01-01

    The kinetics of the catalytic oxidation of hydrogen sulfide by molecular oxygen have been studied in the temperature range 20–250 °C. The primary reaction product is sulfur which may undergo further oxidation to SO2 at temperatures above 200 °C. From the kinetics of this autocatalytic reaction we

  8. Influence of Magnetic Pulseprocessing on Oxide Materials Physics and Mechanical Properties

    Directory of Open Access Journals (Sweden)

    M.N. Shipko

    2014-07-01

    Full Text Available Internal stresses, specific single-crystal blocks, stoichiometric impurity of oxides composition and other factors lead to low strength properties of ferromagnetic iron oxides. Weakening of such defects and increasing iron oxides microhardness, their fracture and mechanic strength are possible by using magnetic pulse processing. The results of experimental studies of the magnetic pulse field effecting on the iron oxides strength properties are shown. Mössbauer spectroscopy, porosimetry, X-ray structure analysis are used to find the mechanisms of this effect. The strength properties change is the result of set of microscopic and quantum effects superposition. It provides easy defects restructuring of solids: vacancies, dislocations, voids.

  9. The mechanisms of pyrite oxidation and leaching: A fundamental perspective

    Science.gov (United States)

    Chandra, A. P.; Gerson, A. R.

    2010-09-01

    Pyrite is the earth's most abundant sulfide mineral. Its frequent undesirable association with minerals of economic value such as sphalerite, chalcopyrite and galena, and precious metals such as gold necessitates costly separation processes such as leaching and flotation. Additionally pyrite oxidation is a major contributor to the environmental problem of acid rock drainage. The surface oxidation reactions of pyrite are therefore important both economically and environmentally. Significant variations in electrical properties resulting from lattice substitution of minor and trace elements into the lattice structure exist between pyrite from different geographical locations. Furthermore the presence of low coordination surface sites as a result of conchoidal fracture causes a reduction in the band gap at the surface compared to the bulk thus adding further electrochemical variability. Given the now general acceptance after decades of research that electrochemistry dominates the oxidation process, the geographical location, elemental composition and semi-conductor type (n or p) of pyrite are important considerations. Aqueous pyrite oxidation results in the production of sulfate and ferrous iron. However other products such as elemental sulfur, polysulfides, hydrogen sulfide, ferric hydroxide, iron oxide and iron(III) oxyhydroxide may also form. Intermediate species such as thiosulfate, sulfite and polythionates are also proposed to occur. Oxidation and leach rates are generally influenced by solution Eh, pH, oxidant type and concentration, hydrodynamics, grain size and surface area in relation to solution volume, temperature and pressure. Of these, solution Eh is most critical as expected for an electrochemically controlled process, and directly correlates with surface area normalised rates. Studies using mixed mineral systems further indicate the importance of electrochemical processes during the oxidation process. Spatially resolved surface characterisation of fresh

  10. Electrochemical oxidation of fluoroquinolone antibiotics: Mechanism, residual antibacterial activity and toxicity change.

    Science.gov (United States)

    Zhu, Linyan; Santiago-Schübel, Beatrix; Xiao, Hongxia; Hollert, Henner; Kueppers, Stephan

    2016-10-01

    In this paper, we studied the electrochemical oxidation mechanisms of three typical fluoroquinolone antibiotics (FQs), and investigated residual antibacterial activity and toxicity changes after oxidation processes. Electrochemistry coupled to mass spectrometry (EC-MS) was used to study the oxidation processes of ciprofloxacin (CIP), norfloxacin (NOR) and ofloxacin (OFL). Eight oxidation products for each parent compound were identified and their chemical structures were elucidated. The transformation trend of each product, with the continuous increase of voltage from 0 to 3000 mV, was recorded by online EC-MS. The oxidation pathways were proposed based on the structural information and transformation trends of oxidation products. We found the oxidation mechanisms of FQs consisted of the hydroxylation and cleavage of piperazinyl ring via reactions with hydroxyl radicals, while the fluoroquinolone core remained intact. The antibacterial activity of the parent compounds and their oxidation mixtures was estimated using zone inhibition tests for gram-negative bacteria Salmonella typhimurium. It was found that the oxidation mixtures of CIP and NOR retained the antibacterial properties with lower activity compared to their parent compounds, while the antibacterial activity of OFL was almost eliminated after oxidation. Furthermore, the toxicity of the three FQs and their oxidation mixtures were evaluated using algal growth inhibition test (Desmodesmus subspicatus). The median effective concentration (EC50) values for the algal inhibition tests were calculated for the end point of growth rate. The toxicity of CIP and NOR to green algae after electrochemical oxidation, remained unchanged, while that of OFL significantly increased. The results presented in this paper contribute to an understanding of the electrochemical oxidation mechanisms of FQs, and highlight the potential environmental risks of FQs after electrochemical oxidation processes. Copyright © 2016 Elsevier

  11. Oxidation mechanism of Fe–16Cr alloy as SOFC interconnect in dry/wet air

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Zhi-Yuan [School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Wang, Li-Jun, E-mail: lijunwang@ustb.edu.cn [School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Li, Fu-Shen [School of Material Science Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Chou, Kuo-Chih [School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

    2013-10-15

    Highlights: •A special thermodynamic description corresponding to the kinetics was applied. •We reported the relationships of degradation time with temperature and moisture. •”Turning time” in the Fe–16Cr alloy oxidation kinetic model was given. •The oxidation mechanism of Fe–16Cr alloy in the wet air was discussed. -- Abstract: Experimental study on the oxidation corrosions of Fe–16Cr alloy was carried out at 800–1100 °C under dry/wet air conditions. Faster oxidation rate was observed at higher temperature and water vapor content. The degradation time t{sub d} between two stages in oxidation process showed an exponential relationship with elevating corrosion temperature in dry air, and a linear relationship with the water content in the case of water vapor introduced to the system. The mechanism of oxidation corrosions of Fe–16Cr alloy was suggested by the Real Physical Picture (RPP) model. It was found that the break-away oxidation in stage II was controlled by diffusion at initial both in dry and wet air, then became linear with the exposure time, which implied that the oxidation rate was then controlled by chemical reaction of the interface between the metal and the oxidized scale. Moreover, the effect of water in the oxidation process is not only to supply more oxygen into system, but also to modify the structures of oxide scale due to the existence of hydrogen atom, which results in the accelerated corrosions.

  12. Mechanical and tribological properties of oxide layers obtained on titanium in the thermal oxidation process

    Science.gov (United States)

    Aniołek, K.; Kupka, M.; Barylski, A.; Dercz, G.

    2015-12-01

    The paper presents the results of tests concerning a modification to the surface of titanium Grade 2 in the thermal oxidation process. It describes the oxidation kinetics of the tested material in the temperature range of 600-800 °C, with a duration from 20 min to 72 h. The greatest increase in mass was found in specimens oxidised at a temperature of 800 °C. The morphology of the obtained oxide layers was determined. The particles of oxides formed were noticeably larger after oxidation at a temperature of 600 °C. Raising temperature resulted in the formation of fine compact particles in the oxide layer. A phase analysis of oxidation products showed that TiO2 in the crystallographic form of rutile and Ti3O are the prevalent types of oxide at a temperature of 600 and 700 °C. On the other hand, only rutile formed at a temperature of 800 °C. Tribological tests showed that the presence of an oxide layer on the surface of titanium significantly improved resistance to abrasive wear. It was found that volumetric wear had decreased by 48% for a specimen oxidised at a temperature of 600 °C and by more than 60% for a specimen subjected to isothermal soaking at a temperature of 700 °C.

  13. Evaluation of the Mechanisms of Mayonnaise Phospholipid Oxidation.

    Science.gov (United States)

    Kato, Shunji; Iseki, Tatsuya; Hanzawa, Yasuhiko; Otoki, Yurika; Ito, Junya; Kimura, Fumiko; Miyazawa, Teruo; Nakagawa, Kiyotaka

    2017-04-03

    Mayonnaise, which is widely used in foods, is rich in lipids and therefore susceptible to oxidation during the manufacturing process, which can result in loss of quality. Herein, we detected and analyzed phosphatidylcholine hydroperoxide (PCOOH) isomers present in fresh mayonnaise using LC-MS/MS. The PCOOH isomer composition suggests that mayonnaise phospholipid peroxidation is predominantly initiated by radical-oxidation (i.e. upon autoxidation), rather than singlet oxygen-oxidation (e.g. upon light exposure), during manufacturing, packaging and/or storage. This LC-MS/MS method will be useful for elucidating the cause of lipid peroxidation in mayonnaise and related foods. Such information will be valuable to ensure maintenance of product quality.

  14. Mechanical Properties of Glass Surfaces Coated with Tin Oxide

    DEFF Research Database (Denmark)

    Swindlehurst, W. E.; Cantor, B.

    1978-01-01

    of tin tetrachloride on industrial soda glass at ~800K to thicknesses of ~3×10-8 and 3×10 -7 m, commercially by the `titanising' process on industrial soda glass at ~800K to a thickness of ~3.10-9 m, and in the laboratory by radio frequency sputtering from tin oxide powder over a range of glass......The effect of tin oxide coatings on the coefficient of friction and fracture strength of glass surfaces is studied. Experiments were performed partly on commercially treated glass bottles and partly on laboratory prepared microscope slides. Coatings were applied in the laboratory by decomposition...

  15. Mechanism of catalytic oxidation of water-lipid substrate

    Science.gov (United States)

    Kraynik, V. V.; Ushkalova, V. N.

    2010-05-01

    The processes of ethyl oleate water-emulsion oxidation in the presence of copper (II) complexes with α-alanine as a catalyst were investigated spectroscopically. UV spectra of the samples revealed the competitive nature of the formation and decomposition of hydroperoxides in the course of oxidation. Vis spectra of the aqueous phase revealed the constant presence of copper (II) complex with α-alanine and the formation of a similar complex with copper (I) in organic phase. The involvement of these complexes in the reactions of chain nucleation and decay of hydroperoxides is suggested.

  16. Thermo-mechanical behavior of graphene oxide hydrogel

    Science.gov (United States)

    Ghosh, Rituparna; Deka Boruah, Buddha; Misra, Abha

    2017-02-01

    Graphene oxide hydrogel with encapsulated water presents a unique structural characteristic similar to open cell foam. It is demonstrated that the encapsulated water plays a vital role in tailoring compressive behavior of graphene oxide hydrogel under varying thermal conditions. The present study is focused on systematically evaluating both the temperature and frequency dependence on compressive behavior of hydrogel to elucidate the evolution of stiffness in a wider temperature range. The stiffness of the hydrogel is further tailored through encapsulation of nanoparticles to achieve an extraordinary enhancement in storage modulus. It is concluded that the change in phase of water provides a large gradient in the stiffness of the hydrogel.

  17. Efficient synthesis of graphene oxide and the mechanisms of oxidation and exfoliation

    Science.gov (United States)

    Yuan, Rui; Yuan, Jing; Wu, Yanping; Chen, Lei; Zhou, Huidi; Chen, Jianmin

    2017-09-01

    An efficient method for the preparation of graphene oxide (GO) was descried through inducing the ultrasonic in the rate-determining step of oxidation processes. Both the transformation procedures and the detailed molecular behavior of parent graphene (PG), partially oxidized graphene (PGO) and GO in H2SO4 and aqueous solution were investigated by molecular dynamic simulation (MD) combining with experiments. The results obtained from MD simulation show that the addition of KMnO4 truly marked the beginning of the reaction which carried out from the border of PG flakes to the centre. This oxidation procedure was the rate-determining step and mainly contained three steps: the boundary carbon atoms oxidized, the distance of the corresponding interlayer enlarged and the oxidizing agent diffused into the unoxidized region, the processes was repeated until oxidized completely. So, the introducing ultrasonic in this section can accelerate not only the exfoliation of layers but also the diffusion of oxidizer and finally raises the oxidation efficiency dramatically. To further clarify these simulation results, the GO was prepared by the method mentioned above. The analyses results for the X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS) of the resulting GO show that the ultrasonic method could perfectly shortens the oxidation time from 12 h to 3 h and forms the higher degree of oxidation products with more carboxylic acid groups on its edges. Thus, this study provides a better understanding of the transformation procedures of graphite and proposes an efficient way to produce GOs suitable for various chemical modifications.

  18. Characterization of nano-scale protective oxide films: application on metal chemical mechanical planarization

    OpenAIRE

    Karagöz, Ayşe; Craciun, V.; Başım, Gül Bahar

    2015-01-01

    This study focuses on the characterization of nano-scale metal oxide films for chemical mechanical planarization (CMP) applications. The protective nature of the self-grown metal oxide layers in the CMP slurry environment enable topographic selectivity required for metallization of interconnects. Tungsten was selected as the model metal film to study the formation and characteristics of the metal oxide nano-layers since tungsten CMP is very well-established in conventional semiconductor manuf...

  19. Mechanisms of Nanoparticle-Induced Oxidative Stress and Toxicity

    Directory of Open Access Journals (Sweden)

    Amruta Manke

    2013-01-01

    Full Text Available The rapidly emerging field of nanotechnology has offered innovative discoveries in the medical, industrial, and consumer sectors. The unique physicochemical and electrical properties of engineered nanoparticles (NP make them highly desirable in a variety of applications. However, these novel properties of NP are fraught with concerns for environmental and occupational exposure. Changes in structural and physicochemical properties of NP can lead to changes in biological activities including ROS generation, one of the most frequently reported NP-associated toxicities. Oxidative stress induced by engineered NP is due to acellular factors such as particle surface, size, composition, and presence of metals, while cellular responses such as mitochondrial respiration, NP-cell interaction, and immune cell activation are responsible for ROS-mediated damage. NP-induced oxidative stress responses are torch bearers for further pathophysiological effects including genotoxicity, inflammation, and fibrosis as demonstrated by activation of associated cell signaling pathways. Since oxidative stress is a key determinant of NP-induced injury, it is necessary to characterize the ROS response resulting from NP. Through physicochemical characterization and understanding of the multiple signaling cascades activated by NP-induced ROS, a systemic toxicity screen with oxidative stress as a predictive model for NP-induced injury can be developed.

  20. Mechanical Properties of Glass Surfaces Coated with Tin Oxide

    DEFF Research Database (Denmark)

    Swindlehurst, W. E.; Cantor, B.

    1978-01-01

    of tin tetrachloride on industrial soda glass at ~800K to thicknesses of ~3×10-8 and 3×10 -7 m, commercially by the `titanising' process on industrial soda glass at ~800K to a thickness of ~3.10-9 m, and in the laboratory by radio frequency sputtering from tin oxide powder over a range of glass...

  1. Water Oxidation Mechanisms of Metal Oxide Catalysts by Vibrational Spectroscopy of Transient Intermediates

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Miao [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division; Univ. of California, Berkeley, CA (United States); Frei, Heinz [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division; Univ. of California, Berkeley, CA (United States)

    2017-02-22

    Water oxidation is an essential reaction of an artificial photosystem for solar fuel generation because it provides electrons needed to reduce carbon dioxide or protons to a fuel. Earth-abundant metal oxides are among the most attractive catalytic materials for this reaction because of their robustness and scalability, but their efficiency poses a challenge. Knowledge of catalytic surface intermediates gained by vibrational spectroscopy under reaction conditions plays a key role in uncovering kinetic bottlenecks and provides a basis for catalyst design improvements. Recent dynamic infrared and Raman studies reveal the molecular identity of transient surface intermediates of water oxidation on metal oxides. In conclusion, combined with ultrafast infrared observations of how charges are delivered to active sites of the metal oxide catalyst and drive the multielectron reaction, spectroscopic advances are poised to play a key role in accelerating progress toward improved catalysts for artificial photosynthesis.

  2. Ab initio atomistic thermodynamics study on the oxidation mechanism of binary and ternary alloy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Shi-Yu, E-mail: buaasyliu@gmail.com [College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300387 (China); Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong (China); Liu, Shiyang [Institute of Information Optics, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Li, De-Jun [College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300387 (China); Wang, Sanwu, E-mail: sanwu-wang@utulsa.edu [Department of Physics and Engineering Physics, The University of Tulsa, Tulsa, Oklahoma 74104 (United States); Guo, Jing; Shen, Yaogen, E-mail: meshen@cityu.edu.hk [Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong (China)

    2015-02-14

    Utilizing a combination of ab initio density-functional theory and thermodynamics formalism, we have established the microscopic mechanisms for oxidation of the binary and ternary alloy surfaces and provided a clear explanation for the experimental results of the oxidation. We construct three-dimensional surface phase diagrams (SPDs) for oxygen adsorption on three different Nb-X(110) (X = Ti, Al or Si) binary alloy surfaces. On the basis of the obtained SPDs, we conclude a general microscopic mechanism for the thermodynamic oxidation, that is, under O-rich conditions, a uniform single-phase SPD (type I) and a nonuniform double-phase SPD (type II) correspond to the sustained complete selective oxidation and the non-sustained partial selective oxidation by adding the X element, respectively. Furthermore, by revealing the framework of thermodynamics for the oxidation mechanism of ternary alloys through the comparison of the surface energies of two separated binary alloys, we provide an understanding for the selective oxidation behavior of the Nb ternary alloy surfaces. Using these general microscopic mechanisms, one could predict the oxidation behavior of any binary and multi-component alloy surfaces based on thermodynamics considerations.

  3. The influence of initial defects on mechanical stress and deformation distribution in oxidized silicon

    Directory of Open Access Journals (Sweden)

    Kulinich O. A.

    2008-10-01

    Full Text Available The near-surface silicon layers in silicon – dioxide silicon systems with modern methods of research are investigated. It is shown that these layers have compound structure and their parameters depend on oxidation and initial silicon parameters. It is shown the influence of initial defects on mechanical stress and deformation distribution in oxidized silicon.

  4. Effects of mechanical milling on the carbothermal reduction of oxide of WC/Co hardmetal scrap

    Science.gov (United States)

    Lee, Gil-Geun; Ha, Gook-Hyun

    2016-03-01

    The effects of mechanical milling on the carbothermal reduction of oxidized WC/Co hardmetal scrap with solid carbon were examined. Mixed powders were manufactured by milling the WC/Co hard metal scrap oxide and carbon powder in either a tumbler-ball mill or a planetary-ball mill. The milling type affected the carbothermal reduction of the oxide owing to the differing collision energies (mechanical milling energies) in the mills. The hardmetal scrap oxide powder (WO3, CoWO4) milled at high energy was more greatly reduced and at a lower temperature than that milled at lower mechanical energy. The formation of WC by the carburization reaction with solid carbon reached completion at a lower temperature after higher-energy milling than after lower-energy milling. The WC/Co composite particles synthesized by the combined oxidationmechanical milling-carbothermal reduction process were smaller when the initial powder was milled at higher mechanical energy.

  5. Structure and the catalysis mechanism of oxidative chlorination in nanostructural layers of a surface of alumina.

    Science.gov (United States)

    Kurta, Sergiy A; Mykytyn, Igor M; Tatarchuk, Tetiana R

    2014-01-01

    On the basis of X-ray diffraction and mass spectrometric analysis of carrier γ-Al2O3 and catalysts CuCl2/CuCl on its surface, the chemical structure of the active centers of two types oxidative chlorination catalysts applied and permeated type of industrial brands "Harshow" and "MEDС-B" was investigated. On the basis of quantum-mechanical theory of the crystal, field complexes were detected by the presence of CuCl2 cation stoichiometry and structure of the proposed model crystal quasichemical industrial catalyst permeated type MEDС-B for oxidative chlorination of ethylene. On the basis of quantum-mechanical calculations, we propose a new mechanism of catalysis crystal quasichemical oxidative chlorination of ethylene reaction for the catalysts of this type (MEDС-B) and confirmed the possibility of such a mechanism after the analysis of mass spectrometric studies of the active phase (H2 [CuCl4]) catalyst oxidative chlorination of ethylene. The possibility of the formation of atomic and molecular chlorine on the oxidative chlorination of ethylene catalyst surface during Deacon reaction was displaying, which may react with ethylene to produce 1,2-dichloroethane. For the active phase (H [CuCl2]), catalyst offered another model of the metal complex catalyst oxidative chlorination of ethylene deposited type (firm 'Harshow,' USA) and the mechanism of catalysis of oxidative chlorination of ethylene with this catalyst.

  6. Atmospheric Oxidation Mechanisms for Diethyl Ether and its Oxidation Products, Ethyl Formate and Ethyl Acetate.

    Science.gov (United States)

    Orlando, J. J.; Tyndall, G. S.

    2006-12-01

    Carbon-containing compounds are present in the earth's atmosphere as the result of emissions from natural and anthropogenic sources. Their oxidation in the atmosphere, initiated by such oxidants as OH, ozone, and nitrate radicals, leads to potentially harmful secondary pollutants such as ozone, carbonyl species, organic acids and aerosols. Ethers and esters are two classes of compounds that contribute to the complex array of organic compounds found in anthropogenically-influenced air. Additional ester is present as a result of the oxidation of the ethers. In this paper, the oxidation of diethyl ether and its two main oxidation products, ethyl formate and ethyl acetate, are studied over ranges of temperature, oxygen partial pressure, and NOx concentration, using an environmental chamber / FTIR absorption technique. Major end-products (the esters from diethyl ether; organic acids and anhydrides from the esters) are quantified, and these data are interpreted in terms of the chemistry of the various alkoxy and peroxy radicals generated. Emphasis is placed on the effects of chemical activation on the behavior of the alkoxy radicals, as well as on a novel peroxy radical rearrangement that may contribute to the observed products of ether oxidation under some conditions. Finally, the data are used, in conjunction with data on similar species, to provide a general representation of ether and ester oxidation in the atmosphere.

  7. Development of 3D Oxide Fuel Mechanics Models

    Energy Technology Data Exchange (ETDEWEB)

    Spencer, B. W. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Casagranda, A. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Pitts, S. A. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Jiang, W. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2017-07-27

    This report documents recent work to improve the accuracy and robustness of the mechanical constitutive models used in the BISON fuel performance code. These developments include migration of the fuel mechanics models to be based on the MOOSE Tensor Mechanics module, improving the robustness of the smeared cracking model, implementing a capability to limit the time step size based on material model response, and improving the robustness of the return mapping iterations used in creep and plasticity models.

  8. Oxidation mechanism of Penicillium digitatum spores through neutral oxygen radicals

    Science.gov (United States)

    Hashizume, Hiroshi; Ohta, Takayuki; Takeda, Keigo; Ishikawa, Kenji; Hori, Masaru; Ito, Masafumi

    2014-01-01

    To investigate the inactivation process of Penicillium digitatum spores through neutral oxygen species, the spores were treated with an atmospheric-pressure oxygen radical source and observed in-situ using a fluorescent confocal-laser microscope. The treated spores were stained with two fluorescent dyes, 1,1‧-dioctadecyl-3,3,Y,3‧-tetramethylindocarbocyanine perchlorate (DiI) and diphenyl-1-pyrenylphosphine (DPPP). The intracellular organelles as well as the cell membranes in the spores treated with the oxygen radical source were stained with DiI without a major morphological change of the membranes. DPPP staining revealed that the organelles were oxidized by the oxygen radical treatment. These results suggest that neutral oxygen species, especially atomic oxygen, induce a minor structural change or functional inhibition of cell membranes, which leads to the oxidation of the intracellular organelles through the penetration of reactive oxygen species into the cell.

  9. Radiation induced defects and thermoluminescence mechanism in aluminum oxide

    Energy Technology Data Exchange (ETDEWEB)

    Atobe, K.; Kobayashi, T.; Awata, T. [Naruto Univ. of Education, Tokushima (Japan); Okada, M. [Kyoto Univ., Kumatori, Osaka (Japan). Research Reactor Inst; Nakagawa, M. [Kagawa Univ., Faculty of Education, Takamatsu, Kagawa (Japan)

    2001-01-01

    The thermoluminescence of the irradiated aluminum oxides were measured to study the radiation induced defects and their behaviors. Neutron and {gamma}-ray irradiation were performed for a shingle crystal of the high purity aluminum oxide. The thermoluminescence glow curve and its activation energy were measured. The spectroscopy measurement on the thermoluminescence and the absorption are also carried out. The observed 430 and 340 nm peaks are discussed relating to the F{sup +} and F centers, respectively. Activation state of the F center transits to 3P state through 1P state by emitting phonons. Trapped electron on 3P state emits phonon of 2.9 eV (430 nm) during transition to the ground state. The above reaction can be written by the equation. F{sup +} + e {yields} (F){sup *} {yields} F + h{nu}(2.9 eV, 470 nm). (Katsuta, H.)

  10. Oxidative Stress in Glaucomatous Neurodegeneration: Mechanisms and Consequences

    OpenAIRE

    2006-01-01

    Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. Although ROS are essential participants in cell signaling and regulation, when their cellular production overwhelms the intrinsic antioxidant capacity, damage to cellular macromolecules such as DNA, proteins, and lipids ensues. Such a state of “oxidative stress” is thought to contribute to the pathogenesis of a number of neurodegenerative diseases. Growing evidence supports the in...

  11. Elucidation of mechanisms in manganese and iron based oxidation catalysis: Mechanistic insights and development of novel approaches applied to transition metal catalyzed oxidations catalysis

    OpenAIRE

    Angelone, Davide

    2016-01-01

    Oxidation chemistry is central to life and to the modern chemical industry and hence understanding chemical oxidation is essential to developing new processes and elucidating biological oxidation mechanisms. Elucidating mechanisms in inorganic oxidation catalysis and simultaneously developing new tools to do so is the theme of this thesis. Spectroscopic techniques, especially Raman and UV-vis absorption, are used, together with Density Functional theory (DFT), to observe and characterise the ...

  12. Isothermal oxidation behavior and mechanism of a nickel-based superalloy at 1000°C

    Science.gov (United States)

    Zhu, Zhi-yuan; Cai, Yuan-fei; Gong, You-jun; Shen, Guo-ping; Tu, Yu-guo; Zhang, Guo-fu

    2017-07-01

    The oxidation behavior of a nickel-based superalloy at 1000°C in air was investigated through X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analysis. A series of oxides, including external oxide scales (Cr2O3, (TiO2 + MnCr2O4)) and internal oxides (Al2O3,TiN), were formed on the surface or sub-surface of the substrate at 1000°C in experimental still air. The oxidation resistance of the alloy was dependent on the stability of the surface oxide layer. The continuity and density of the protective Cr2O3 scale were affected by minor alloying elements such as Ti and Mn. The outermost oxide scale was composed of TiO2 rutile and MnCr2O4 spinel, and the growth of TiO2 particles was controlled by the outer diffusion of Ti ions through the pre-existing oxide layer. Severe internal oxidation occurred beneath the external oxide scale, consuming Al and Ti of the strength phase γ' (Ni3(Al,Ti)) and thereby severely deteriorating the surface mechanical properties. The depth of the internal oxidation region was approximately 35 μm after exposure to experimental air at 1000°C for 80 h.

  13. Oxidation Control and Non-equilibrium Phase Formation in Cu-Cr Alloys during Mechanical Alloying

    Institute of Scientific and Technical Information of China (English)

    Xiaolong CUI; Lai WANG; Min QI

    2001-01-01

    Using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and optical microscopy, phase transformation of Cu-Cr alloys with various compositions during mechanical alloying process has been investigated. Besides the formation of supersaturated solid solution, the results show that a kind of amorphous oxide formed in the process,and the addition of carbon has obviously effect on the suppression of oxidation and the deoxidization of oxide. The reactive milling has a remarkable effect on the behavior of oxidation.

  14. Insights into the Mechanism and Kinetics of Thermo-Oxidative Degradation of HFPE High Performance Polymer.

    Science.gov (United States)

    Kunnikuruvan, Sooraj; Parandekar, Priya V; Prakash, Om; Tsotsis, Thomas K; Nair, Nisanth N

    2016-06-02

    The growing requisite for materials having high thermo-oxidative stability makes the design and development of high performance materials an active area of research. Fluorination of the polymer backbone is a widely applied strategy to improve various properties of the polymer, most importantly the thermo-oxidative stability. Many of these fluorinated polymers are known to have thermo-oxidative stability up to 700 K. However, for space and aerospace applications, it is important to improve its thermo-oxidative stability beyond 700 K. Molecular-level details of the thermo-oxidative degradation of such polymers can provide vital information to improve the polymer. In this spirit, we have applied quantum mechanical and microkinetic analysis to scrutinize the mechanism and kinetics of the thermo-oxidative degradation of a fluorinated polymer with phenylethenyl end-cap, HFPE. This study gives an insight into the thermo-oxidative degradation of HFPE and explains most of the experimental observations on the thermo-oxidative degradation of this polymer. Thermolysis of C-CF3 bond in the dianhydride component (6FDA) of HFPE is found to be the rate-determining step of the degradation. Reaction pathways that are responsible for the experimentally observed weight loss of the polymer is also scrutinized. On the basis of these results, we propose a modification of HFPE polymer to improve its thermo-oxidative stability.

  15. Bismuth oxide based ceramics with improved electrical and mechanical properties: Part II. Structural and mechanical properties

    NARCIS (Netherlands)

    Kruidhof, H.; Seshan, K.; Velde, van de G.M.H.; Vries, de K.J.; Burggraaf, A.J.

    1988-01-01

    Coprecipitation as a method of preparation for bismuth oxides based ceramics yields relatively strong and machineable materials in comparison with the solid state reaction. Compositions within the system (1−x)Bi2O3|xEr2O3 containing up to twenty five mole percent of erbium oxide show a slow transiti

  16. Vulnerability of the retinal microvasculature to oxidative stress: ion channel-dependent mechanisms.

    Science.gov (United States)

    Fukumoto, Masanori; Nakaizumi, Atsuko; Zhang, Ting; Lentz, Stephen I; Shibata, Maho; Puro, Donald G

    2012-05-01

    Although oxidative stress is a hallmark of important vascular disorders such as diabetic retinopathy, it remains unclear why the retinal microvasculature is particularly vulnerable to this pathophysiological condition. We postulated that redox-sensitive ion channels may play a role. Using H(2)O(2) to cause oxidative stress in microvascular complexes freshly isolated from the adult rat retina, we assessed ionic currents, cell viability, intracellular oxidants, and cell calcium by using perforated-patch recordings, trypan blue dye exclusion, and fura-2 fluorescence, respectively. Supporting a role for the oxidant-sensitive ATP-sensitive K (K(ATP)) channels, we found that these channels are activated during exposure of retinal microvessels to H(2)O(2). Furthermore, their inhibition by glibenclamide significantly lessened H(2)O(2)-induced microvascular cell death. Additional experiments established that by increasing the influx of calcium into microvascular cells, the K(ATP) channel-mediated hyperpolarization boosted the vulnerability of these cells to oxidative stress. In addition to the K(ATP) channel-dependent mechanism for increasing the lethality of oxidative stress, we also found that the vulnerability of cells in the capillaries, but not in the arterioles, was further boosted by a K(ATP) channel-independent mechanism, which our experiments indicated involves the oxidant-induced activation of calcium-permeable nonspecific cation channels. Taken together, our findings support a working model in which both K(ATP) channel-independent and K(ATP) channel-dependent mechanisms render the capillaries of the retina particularly vulnerable to oxidative stress. Identification of these previously unappreciated mechanisms for boosting the lethality of oxidants may provide new targets for pharmacologically limiting damage to the retinal microvasculature during periods of oxidative stress.

  17. Kinetics and mechanism of the oxidation of some diols by benzyltrimethylammonium tribromide

    Indian Academy of Sciences (India)

    Garima Goswami; Seema Kothari; Kalyan K Banerji

    2001-02-01

    The kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers by benzyltrimethylammonium tribromide (BTMAB) have been studied in 3:7 (/) acetic acid-water mixture. The vicinal diols yield the carbonyl compounds arising out of the glycol bond fission while the other diols give the hydroxycarbonyl compounds. The reaction is first-order with respect to BTMAB. Michaelis-Menten type kinetics is observed with respect to diol. Addition of benzyltrimethylammonium chloride does not affect the rate. Tribromide ion is postulated to be the reactive oxidizing species. Oxidation of [1,1,2,2-2H4] ethanediol shows the absence of a kinetic isotope effect. The reaction exhibits substantial solvent isotope effect. A mechanism involving a glycol-bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidized by a hydride ion transfer to the oxidant, as are the monohydric alcohols.

  18. Metal Oxide Nanomaterial QNAR Models: Available Structural Descriptors and Understanding of Toxicity Mechanisms

    Directory of Open Access Journals (Sweden)

    Jiali Ying

    2015-10-01

    Full Text Available Metal oxide nanomaterials are widely used in various areas; however, the divergent published toxicology data makes it difficult to determine whether there is a risk associated with exposure to metal oxide nanomaterials. The application of quantitative structure activity relationship (QSAR modeling in metal oxide nanomaterials toxicity studies can reduce the need for time-consuming and resource-intensive nanotoxicity tests. The nanostructure and inorganic composition of metal oxide nanomaterials makes this approach different from classical QSAR study; this review lists and classifies some structural descriptors, such as size, cation charge, and band gap energy, in recent metal oxide nanomaterials quantitative nanostructure activity relationship (QNAR studies and discusses the mechanism of metal oxide nanomaterials toxicity based on these descriptors and traditional nanotoxicity tests.

  19. Kinetics and mechanism of the oxidation of some -hydroxy acids by hexamethylenetetramine-bromine

    Indian Academy of Sciences (India)

    Dimple Garg; Seema Kothari

    2004-11-01

    The oxidation of lactic acid, mandelic acid and ten monosubstituted mandelic acids by hexamethylenetetramine-bromine (HABR) in glacial acetic acid, leads to the formation of the corresponding oxoacid. The reaction is first order with respect to each of the hydroxy acids and HABR. It is proposed that HABR itself is the reactive oxidizing species. The oxidation of -deuteriomandelic acid exhibits the presence of a substantial kinetic isotope effect (/ = 5.91 at 298 K). The rates of oxidation of the substituted mandelic acids show excellent correlation with Brown’s + values. The reaction constants are negative. The oxidation exhibits an extensive cross conjugation between the electron-donating substituent and the reaction centre in the transition state. A mechanism involving transfer of a hydride ion from the acid to the oxidant is postulated.

  20. On the mechanism of hydrogen-promoted gold-catalyzed CO oxidation

    KAUST Repository

    Quinet, Elodie

    2009-12-10

    The kinetics of CO oxidation, H2 oxidation and preferential CO oxidation (PrOx) over Au/Al2O3 catalysts have been investigated. The catalysts with the smallest particles (∼2 nm) are the most active for all three reactions. As previously observed, the presence of H2 greatly promotes CO oxidation, which becomes faster than CO-free H2 oxidation at low temperature. From these results and on the basis of previous works, we propose a complete PrOx mechanism. The reaction involves Au-OOH, Au-OH and Au-H intermediates, also involved in H2 oxidation, and benefits from the presence of low-coordination sites. © 2009 Elsevier Inc. All rights reserved.

  1. Outer-Sphere Mechanism in the Oxidation of Pyrrole-2- Carboxaldehyde by Hexacyanoferrate (III Complex.

    Directory of Open Access Journals (Sweden)

    Abd-Alhakeem H. Abu-Nawwas

    2014-01-01

    Full Text Available The kinetics and mechanism of base-catalyzed oxidation of pyrrole-2-carboxaldehyde with hexacyanoferrate (III is reported. The reaction showed first order with respect to aldahyde , alkali and hexaeyanoferrate(III. The kinetic data suggest that the oxidation involves the formation of an anion of the substrate undergoes oxidation with hexaeyanoferrate(III via outer sphere mechanism process. The free radical thus produced is further oxidized to form the final products. A suitable mechanism was proposed and rate law was derived as − d[Fe CN 6 ] 3− = 2k1k2 RC(OH2 [Fe CN 6 ] 3−[OH−] k−1 H2O

  2. Determination of mechanism for soot oxidation with NO on potassium supported Mg-Al hydrotalcite mixed oxides

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y.; Su, Q.; Gao, X. [Institute of Internal Combustion Engine, Dalian University of Technology, Dalian (China); Li, Q.; Wang, Z.; Zhang, Z. [School of Chemistry and Chemical Engineering, University of Jinan, Jinan (China)

    2011-11-15

    Soot oxidation with NO (in the absence of gas phase O{sub 2}) on potassium-supported Mg-Al hydrotalcite mixed oxides (K/MgAlO) was studied using a temperature-programmed reaction and in situ FTIR techniques. Nitrite and the ketene group were identified as the reaction intermediates and thus a nitrite-ketene mechanism was proposed in which surface active oxygen on K sites of K/MgAlO is transferred to soot by NO through nitrites. In the absence of gas phase O{sub 2}, soot oxidation with NO at lower temperatures (below 450 C) is limited by the amount of active oxygen on the K sites. This kind of active oxygen is not reusable but can be replenished in the presence of gas phase O{sub 2}. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Kinetics and mechanism of 5-hydroxymethylfurfural oxidation and their implications for catalyst development

    NARCIS (Netherlands)

    Davis, S.E.; Benavidez, A.; Gosselink, R.W.; Bitter, J.H.; Jong, de K.P.; Datye, A.K.; Davis, R.J.

    2014-01-01

    The reaction mechanism of 5-hydroxymethylfurfural (HMF) oxidation in neutral aqueous solution with O2 to 5-hydroxymethyl-2-furancarboxylic acid (HFCA) and 2,5-furandicarboxylic acid (FDCA) was evaluated over a 3 wt% Pt/activated carbon catalyst in a semibatch reactor and confirmed that the mechanism

  4. Theoretical investigations on oxidative stability of solvents and oxidative decomposition mechanism of ethylene carbonate for lithium ion battery use.

    Science.gov (United States)

    Xing, Lidan; Li, Weishan; Wang, Chaoyang; Gu, Fenglong; Xu, Mengqing; Tan, Chunlin; Yi, Jin

    2009-12-31

    The electrochemical oxidative stability of solvent molecules used for lithium ion battery, ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate in the forms of simple molecule and coordination with anion PF(6)(-), is compared by using density functional theory at the level of B3LYP/6-311++G (d, p) in gas phase. EC is found to be the most stable against oxidation in its simple molecule. However, due to its highest dielectric constant among all the solvent molecules, EC coordinates with PF(6)(-) most strongly and reaches cathode most easily, resulting in its preferential oxidation on cathode. Detailed oxidative decomposition mechanism of EC is investigated using the same level. Radical cation EC(*+) is generated after one electron oxidation reaction of EC and there are five possible pathways for the decomposition of EC(*+) forming CO(2), CO, and various radical cations. The formation of CO is more difficult than CO(2) during the initial decomposition of EC(*+) due to the high activation energy. The radical cations are reduced and terminated by gaining one electron from anode or solvent molecules, forming aldehyde and oligomers of alkyl carbonates including 2-methyl-1,3-dioxolane, 1,3,6-trioxocan-2-one, 1,4,6,9-tetraoxaspiro[4.4]nonane, and 1,4,6,8,11-pentaoxaspiro[4.6]undecan-7-one. The calculation in this paper gives a detailed explanation on the experimental findings that have been reported in literatures and clarifies the mechanism on the oxidative decomposition of EC.

  5. Mechanisms of Nitrogen Oxide Formation During Ensiling of Dairy Feeds

    Science.gov (United States)

    This product is the abstract of a proposed paper. The emission of NOx has been observed during the ensiling process (Peterson et al. 1958, Maw et al. 2002). Substantial NOx is not inherently present in corn. It is generated by an unknown mechanism during the early days of the ens...

  6. Effects of Graphene Oxide and Chemically-Reduced Graphene Oxide on the Dynamic Mechanical Properties of Epoxy Amine Composites

    Directory of Open Access Journals (Sweden)

    Cristina Monteserín

    2017-09-01

    Full Text Available Composites based on epoxy/graphene oxide (GO and epoxy/reduced graphene oxide (rGO were investigated for thermal-mechanical performance focusing on the effects of the chemical groups present on nanoadditive-enhanced surfaces. GO and rGO obtained in the present study have been characterized by Fourier transform infrared spectroscopy (FTIR, X-ray photoelectron spectroscopy (XPS, and X-ray powder diffraction (XRD demonstrating that materials with different oxidation degrees have been obtained. Thereafter, GO/epoxy and rGO/epoxy nanocomposites were successfully prepared and thoroughly characterized by dynamic mechanical thermal analysis (DMTA and transmission electron microscopy (TEM. A significant increase in the glass transition temperature was found in comparison with the neat epoxy. The presence of functional groups on the graphene surface leads to chemical interactions between these functional groups on GO and rGO surfaces with the epoxy, contributing to the possible formation of covalent bonds between GO and rGO with the matrix. The presence of oxidation groups on GO also contributes to an improved exfoliation, intercalation, and distribution of the GO sheets in the composites with respect to the rGO based composites.

  7. Influence of Oxides on Microstructures and Mechanical Properties of High-Strength Steel Weld Joint

    Science.gov (United States)

    Cai, Yangchuan; Luo, Zhen; Huang, Zunyue; Zeng, Yida

    2016-11-01

    A comprehensive investigation was conducted into the effect of oxides on penetrations, microstructures and mechanical properties of BS700MC super steel weld bead. Boron oxide changed the penetration of weld bead by changing the Marangoni convection in the weld pool and contracting the welding arc. Chromium oxide only changed the Marangoni convection in the weld pool to increase the penetration of super steel. Thus, the super steel weld bead has higher penetration coated with flux boron oxide than that coated with chromium oxide. In other words, the activating flux TIG (A-TIG) welding with flux boron oxide has less welding heat input than the A-TIG welding with flux chromium oxide. As a result, on the one hand, there existed more fine and homogeneous acicular ferrites in the microstructure of welding heat-affected zone when the super steel was welded by A-TIG with flux boron oxide. Thus, the weld beads have higher value of low-temperature impact toughness. On the other hand, the softening degree of welding heat-affected zone, welded by A-TIG with flux boron oxide, will be decreased for the minimum value of welding heat input.

  8. Cellular and Molecular Mechanisms of Arrhythmia by Oxidative Stress

    Directory of Open Access Journals (Sweden)

    Ali A. Sovari

    2016-01-01

    Full Text Available Current therapies for arrhythmia using ion channel blockade, catheter ablation, or an implantable cardioverter defibrillator have limitations, and it is important to search for new antiarrhythmic therapeutic targets. Both atrial fibrillation and heart failure, a condition with increased arrhythmic risk, are associated with excess amount of reactive oxygen species (ROS. There are several possible ways for ROS to induce arrhythmia. ROS can cause focal activity and reentry. ROS alter multiple cardiac ionic currents. ROS promote cardiac fibrosis and impair gap junction function, resulting in reduced myocyte coupling and facilitation of reentry. In order to design effective antioxidant drugs for treatment of arrhythmia, it is essential to explore the molecular mechanisms by which ROS exert these arrhythmic effects. Activation of Ca2+/CaM-dependent kinase II, c-Src tyrosine kinase, protein kinase C, and abnormal splicing of cardiac sodium channels are among the recently discovered molecular mechanisms of ROS-induced arrhythmia.

  9. Anomalous mechanical behavior and crack growth of oxide glasses

    Science.gov (United States)

    Seaman, Jared Hilliard

    This thesis is concerned with analytically describing anomalous mechanical behaviors of glass. A new slow crack growth model is presented that considers a semi-elliptical crack in a cylindrical glass rod subjected to 4-point bending that is both loaded statically and under a time-dependent load. This model is used to explain a suppression of the loading-rate dependency of ion-exchanged strengthened glass. The stress relaxation behavior of an ion-exchanged strengthened glass is then analyzed in view of a newly observed water-assisted surface stress relaxation mechanism. By making refinements to a time-dependent Maxwell material model for stress buildup and relaxation, the anomalous subsurface compressive stress peak in ion-exchanged strengthened glass is explained. The notion of water-assisted stress relaxation is extended to the crack tip, where high tensile stresses exist. A toughening effect has historically been observed for cracks aged at subcritical stress intensity factors, where crack tip stress relaxation is hypothesized. A simple fracture mechanics model is developed that estimates a shielding stress intensity factor that is then superimposed with the far-field stress intensity factor. The model is used to estimate anomalous "restart" times for aged cracks. The same model predicts a non-linear crack growth rate for cracks loaded near the static fatigue limit. Double cantilever beam slow crack growth experiments were performed and new slow crack growth data for soda-lime silicate glass was collected. Interpretation of this new experimental slow crack growth data suggests that the origin of the static fatigue limit in glass is due to water-assisted stress relaxation. This thesis combines a number of studies that offer a new unified understanding of historical anomalous mechanical behaviors of glass. These anomalies are interpreted as simply the consequence of slow crack growth and water-assisted surface stress relaxation.

  10. Mechanical behavior of intragranular, nano-porous electrodeposited zinc oxide

    Energy Technology Data Exchange (ETDEWEB)

    Raghavan, Rejin, E-mail: r.raghavan@mpie.de [Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkstrasse 39, 3602 Thun (Switzerland); Elias, Jamil [Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkstrasse 39, 3602 Thun (Switzerland); Erni, Rolf; Parlinska, Magdalena [Empa, Swiss Federal Laboratories for Materials Science and Technology, Electron Microscopy Center, Ueberlandstrasse 129, 8600 Duebendorf (Switzerland); Philippe, Laetitia; Michler, Johann [Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkstrasse 39, 3602 Thun (Switzerland)

    2015-03-02

    The mechanical properties and deformation mechanisms of nano-porous ZnO thin films electrodeposited on glass substrates were determined by nanoindentation and in situ scanning electron microscope (SEM) micropillar compression. The intragranular nature of the nanoscale porosity within the individual mono-crystals of the films was probed at nano- and micro-scales for determining their mechanical response. The hardness (3.5 GPa) and reduced elastic modulus (65 GPa) of the compact thin film were found to decrease by increasing the intragranular porosity controlled by the electrochemical deposition potential of ZnO. Focused ion beam (FIB) cross-sections of residual imprints reveal that the decrease in hardness and elastic modulus observed is primarily due to compaction of the nano-porous structure. In situ SEM compression of FIB machined micropillars reveals brittle fracture and near theoretical strengths in the compact film (~ 2 GPa), and a higher flaw tolerant response despite lower failure stress in the most porous film. - Highlights: • Micromechanical behavior of intragranular, nanoporous electrodeposited ZnO thin films • Densification by closure of porosity during indentation • Resistance to fracture by crack deflection and blunting in porous films during microcompression.

  11. Mechanical anomaly impact on metal-oxide-semiconductor capacitors on flexible silicon fabric

    KAUST Repository

    Ghoneim, Mohamed T.

    2014-06-09

    We report the impact of mechanical anomaly on high-κ/metal-oxide-semiconductor capacitors built on flexible silicon (100) fabric. The mechanical tests include studying the effect of bending radius up to 5 mm minimum bending radius with respect to breakdown voltage and leakage current of the devices. We also report the effect of continuous mechanical stress on the breakdown voltage over extended periods of times.

  12. Role of dissolved Mn(III) in transformation of organic contaminants: Non-oxidative versus oxidative mechanisms.

    Science.gov (United States)

    Hu, Erdan; Zhang, Ya; Wu, Shuyan; Wu, Jun; Liang, Liyuan; He, Feng

    2017-03-15

    Mn(III) is a strong oxidant for one electron transfer, which may be important in the transformation of organic contaminants during water/wastewater treatment and biogeochemical redox processes. This study explored the reaction mechanisms of dissolved Mn(III) with organics. The role of dissolved Mn(III) either as a catalyst or an oxidant in reactions with organics was recognized. Aquo and/or hydroxo (or free) Mn(III), generated from the bisulfite activated permanganate process, facilitated efficient N-dealkylation of atrazine via a β-elimination mechanism, resulting no net redox reaction. In contrast, free Mn(III) degraded 4-chlorophenol via intramolecular redox processes, the same as hydroxyl radical (OH), resulting in dechlorination,OH substitution, ring-opening and mineralization. Mn(III)-pyrophosphate compounds did not react with atrazine because complexation by pyrophosphate rendered Mn(III) unable to bond with atrazine, thus the electron and proton transfers between the reactants couldn't occur. However, it degraded 4-chlorophenol at a slower rate compared to free Mn(III), due to its reduced oxidation potential. These results showed two distinct mechanisms on the degradation of organic contaminants and the insights may be applied in natural manganese-rich environments and water treatment processes with manganese compounds. Copyright © 2017 Elsevier Ltd. All rights reserved.

  13. Synthesis, structural and mechanical characterization of sputtered tungsten oxide coatings

    Energy Technology Data Exchange (ETDEWEB)

    Parreira, N.M.G. [ICEMS-Grupo de Materiais e Engenharia de Superficies, Faculdade de Ciencias e Tecnologia da Universidade de Coimbra-Polo II, 3030-201 Coimbra (Portugal)]. E-mail: nuno.parreira@dem.uc.pt; Carvalho, N.J.M. [ICEMS-Grupo de Materiais e Engenharia de Superficies, Faculdade de Ciencias e Tecnologia da Universidade de Coimbra-Polo II, 3030-201 Coimbra (Portugal)]. E-mail: nuno.carvalho@dem.uc.pt; Cavaleiro, A. [ICEMS-Grupo de Materiais e Engenharia de Superficies, Faculdade de Ciencias e Tecnologia da Universidade de Coimbra-Polo II, 3030-201 Coimbra (Portugal)]. E-mail: albano.cavaleiro@dem.uc.pt

    2006-07-03

    Tungsten oxide coatings were deposited without substrate bias by DC reactive magnetron sputtering of a tungsten target using oxygen as reactive gas. By tuning the partial pressure of oxygen (p {sub O{sub 2}}/p {sub Ar}) between 0 and 4, the oxygen content of the films was changed from 0 to 75 at.%. The structure of the films (investigated by X-ray diffraction) depends on their oxygen content. For low oxygen contents, the {alpha}-W and {beta}-W{sub 3}O phases were observed (< 30 at.%), and with the increase of oxygen content (30 at.% < O < 67 at.%) the structure became amorphous. A transition region was obtained for oxygen content between 67 at.% and 75 at.%, and when O > 75 at.%, a nanocrystalline (WO{sub 3}) structure was reached. The hardness and Young's modulus were evaluated by depth sensing indentation. The decrease in hardness followed the four different ranges of chemical compositions accordingly, from {approx} 23 GPa for pure W down to {approx} 7 GPa for WO{sub 3} films. A similar behaviour was observed for the Young's modulus, which ranged from 450 GPa to 150 GPa. The cohesion/adhesion of the films were investigated using a scratch-test apparatus. These coatings displayed a low adhesion (critical load, L {sub c} < 15 N) to the steel substrate because the depositions were carried out intentionally without an adhesion interfacial layer.

  14. Disentangling specific versus generic doping mechanisms in oxide heterointerfaces

    Science.gov (United States)

    Gabel, J.; Zapf, M.; Scheiderer, P.; Schütz, P.; Dudy, L.; Stübinger, M.; Schlueter, C.; Lee, T.-L.; Sing, M.; Claessen, R.

    2017-05-01

    More than a decade after the discovery of the two-dimensional electron system (2DES) at the interface between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) its microscopic origin is still under debate. Several explanations have been proposed, the main contenders being electron doping by oxygen vacancies and electronic reconstruction, i.e., the redistribution of electrons to the interface to minimize the electrostatic energy in the polar LAO film. However, no experiment thus far could provide unambiguous information on the microscopic origin of the interfacial charge carriers. Here we utilize a novel experimental approach combining photoelectron spectroscopy (PES) with highly brilliant synchrotron radiation and apply it to a set of samples with varying key parameters that are thought to be crucial for the emergence of interfacial conductivity. Based on microscopic insight into the electronic structure, we obtain results tipping the scales in favor of polar discontinuity as a generic, robust driving force for the 2DES formation. Likewise, other functionalities such as magnetism or superconductivity might be switched in all-oxide devices by polarity-driven charge transfer.

  15. Mechanism of oxidation of inorganic sulfur compounds by thiosulfate-grown Thiobacillus thiooxidans.

    Science.gov (United States)

    Masau, R J; Oh, J K; Suzuki, I

    2001-04-01

    Thiobacillus thiooxidans was grown at pH 5 on thiosulfate as an energy source, and the mechanism of oxidation of inorganic sulfur compounds was studied by the effect of inhibitors, stoichiometries of oxygen consumption and sulfur, sulfite, or tetrathionate accumulation, and cytochrome reduction by substrates. Both intact cells and cell-free extracts were used in the study. The results are consistent with the pathway with sulfur and sulfite as the key intermediates. Thiosulfate was oxidized after cleavage to sulfur and sulfite as intermediates at pH 5, the optimal growth pH on thiosulfate, but after initial condensation to tetrathionate at pH 2.3 where the organism failed to grow. N-Ethylmaleimide (NEM) inhibited sulfur oxidation directly and the oxidation of thiosulfate or tetrathionate indirectly. It did not inhibit the sulfite oxidation by cells, but inhibited any reduction of cell cytochromes by sulfur, thiosulfate, tetrathionate, and sulfite. NEM probably binds sulfhydryl groups, which are possibly essential in supplying electrons to initiate sulfur oxidation. 2-Heptyl-4-hydroxy-quinoline N-oxide (HQNO) inhibited the oxidation of sulfite directly and that of sulfur, thiosulfate, and tetrathionate indirectly. Uncouplers, carbonyl cyanide-m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP), inhibited sulfite oxidation by cells, but not the oxidation by extracts, while HQNO inhibited both. It is proposed that HQNO inhibits the oxidation of sulfite at the cytochrome b site both in cells and extracts, but uncouplers inhibit the oxidation in cells only by collapsing the energized state of cells, delta muH+, required either for electron transfer from cytochrome c to b or for sulfite binding.

  16. Reaction mechanism for methanol oxidation on Au(1 1 1): A density functional theory study

    Science.gov (United States)

    Liu, Shuping; Jin, Peng; Zhang, Donghui; Hao, Ce; Yang, Xueming

    2013-01-01

    The microscopic reaction mechanism for methanol oxidation on Au(1 1 1) surface has been thoroughly investigated by means of density functional theory (DFT) computations. The adsorption geometries and energies were obtained for all the adsorbates, including the reactants, the products, and various possible intermediates on the metal. According to different oxygen conditions, we propose two possible reaction pathways for methanol oxidation on Au(1 1 1): (1) HCHO esterification: the intermediate formaldehyde and methoxy couple to yield methyl formate at low oxygen coverage or without the presence of oxygen atoms; (2) HCHO oxidation: the formaldehyde is oxidized to form formate at high oxygen coverage, which further dissociates to give CO2. Our study emphasizes the critical role of oxygen coverage during the methanol oxidation reaction, and can perfectly explain the difference in product distributions observed in previous experiments.

  17. Kinetics and mechanism of the oxidation of substituted benzylamines by cetyltrimethylammonium permanganate

    Indian Academy of Sciences (India)

    Raghvendra Shukla; Pradeep K Sharma; László Kótai; Kalyan K Banerji

    2003-04-01

    Oxidation of meta- and para-substituted benzylamines by cetyltrimethylammonium permanganate (CTAP) to the corresponding aldimines is first order with respect to both the amine and CTAP. Oxidation of deuteriated benzylamine (PhCD2NH2) exhibited the presence of a substantial kinetic isotope effect (/ = 5.60 at 293 K). This confirmed the cleavage of an -C-H bond in the ratedetermining step. Correlation analyses of the rates of oxidation of 19 monosubstituted benzylamines were performed with various single and multiparametric equations. The rates of the oxidation showed excellent correlations in terms of Yukawa-Tsuno and Brown’s equations. The polar reaction constants are negative. The oxidation exhibited an extensive cross-conjugation, in the transition state, between the electron-donating substituents and the reaction centre. A mechanism involving a hydride-ion transfer from the amine to CTAP in the rate-determining step has been proposed.

  18. Influence of thermo-oxidation on dielectric and mechanical properties of epoxy/amine resins

    Science.gov (United States)

    Ernault, Estève; Richaud, Emmanuel; Fayolle, Bruno

    2016-05-01

    This objective of this work is to compare the changes of electrical and mechanical properties during thermo-oxidation of epoxy, in order to improve the choice of end life criterion. The thermal oxidation of DGEBA totally cured with linear aliphatic hardener is investigated under several temperature and oxygen pressure. Chemical changes are followed thanks to infra-red spectroscopy, macromolecular changes thanks to differential scanning calorimetry (changes of Tg). During thermo-oxidation at 110°C in air, volume resistivity and tensile properties in terms of modulus and deformation at break changes are assessed. The results show a formation of polar groups corresponding to oxidation products and a decrease of molecular mobility associated to a crosslinking process. Furthermore, it appears that the oxidation process leads to an embrittlement process whereas electrical properties are not significantly modified.

  19. The Neurotoxicity of Nitrous Oxide: The Facts and “Putative” Mechanisms

    Directory of Open Access Journals (Sweden)

    Sinead Savage

    2014-01-01

    Full Text Available Nitrous oxide is a widely used analgesic agent, used also in combination with anaesthetics during surgery. Recent research has raised concerns about possible neurotoxicity of nitrous oxide, particularly in the developing brain. Nitrous oxide is an N-methyl-d-aspartate (NMDA-antagonist drug, similar in nature to ketamine, another anaesthetic agent. It has been linked to post-operative cardiovascular problems in clinical studies. It is also widely known that exposure to nitrous oxide during surgery results in elevated homocysteine levels in many patients, but very little work has investigated the long term effect of these increased homocysteine levels. Now research in rodent models has found that homocysteine can be linked to neuronal death and possibly even cognitive deficits. This review aims to examine the current knowledge of mechanisms of action of nitrous oxide, and to describe some pathways by which it may have neurotoxic effects.

  20. Selective laser melting additive manufactured Inconel 718 superalloy parts: High-temperature oxidation property and its mechanisms

    Science.gov (United States)

    Jia, Qingbo; Gu, Dongdong

    2014-10-01

    This work presented a comprehensive study of high-temperature oxidation behaviors and mechanisms of Selective laser melting (SLM) processed Inconel 718 superalloy parts using different methods including isothermal oxidation testing, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The experimental results revealed that the oxidation process of the tested parts processed at a lower volumetric laser energy density experienced the severe spallation. On reasonably increasing the applied volumetric laser energy density, the oxidation kinetics of the as-produced parts obeyed a parabolic law, exhibiting the significantly improved oxidation resistance performance. The constitutional phases within the oxidation film were identified and the corresponding formation mechanisms were elucidated in detail according to the thermodynamic principles. The cross-sectional morphologies of oxidized Inconel 718 parts indicated that the oxidation microstructure mainly consisted of an external oxidation layer and an internal oxidation zone. The oxidation process was controlled by the outward diffusion of oxide forming elements and inward penetration of oxygen, by which the interaction mechanisms between the microstructures and internal oxidation zones were clarified. On the basis of the experimental results and theoretical analyses, the physical oxidation mechanisms were accordingly established to illustrate the oxidation behaviors of SLM-processed Inconel 718 parts at elevated operative temperatures.

  1. LDL oxidation by platelets propagates platelet activation via an oxidative stress-mediated mechanism.

    Science.gov (United States)

    Carnevale, Roberto; Bartimoccia, Simona; Nocella, Cristina; Di Santo, Serena; Loffredo, Lorenzo; Illuminati, Giulio; Lombardi, Elisabetta; Boz, Valentina; Del Ben, Maria; De Marco, Luigi; Pignatelli, Pasquale; Violi, Francesco

    2014-11-01

    Platelets generate oxidized LDL (ox-LDL) via NOX2-derived oxidative stress. We investigated if once generated by activated platelets ox-LDL can propagate platelet activation. Experiments were performed in platelets from healthy subjects (HS), hyper-cholesterolemic patients and patients with NOX2 hereditary deficiency. Agonist-stimulated platelets from HS added with LDL were associated with a dose-dependent increase of reactive oxidant species and ox-LDL. Agonist-stimulated platelets from HS added with a fixed dose of LDL (57.14 μmol/L) or added with homogenized human atherosclerotic plaque showed enhanced ox-LDL formation (approximately +50% and +30% respectively), which was lowered by a NOX2 inhibitor (approximately -35% and -25% respectively). Compared to HS, ox-LDL production was more pronounced in agonist-stimulated platelet rich plasma (PRP) from hyper-cholesterolemic patients but was almost absent in PRP from NOX2-deficient patients. Platelet aggregation and 8-iso-PGF2α-ΙΙΙ formation increased in LDL-treated washed platelets (+42% and +53% respectively) and PRP (+31% and +53% respectively). Also, LDL enhanced platelet-dependent thrombosis at arterial shear rate (+33%) but did not affect platelet activation in NOX2-deficient patients. Platelet activation by LDL was significantly inhibited by CD36 or LOX1 blocking peptides, two ox-LDL receptor antagonists, or by a NOX2 inhibitor. LDL-added platelets showed increased p38MAPK (+59%) and PKC (+51%) phosphorylation, p47(phox) translocation to platelet membrane (+34%) and NOX2 activation (+30%), which were inhibited by ox-LDL receptor antagonists. Platelets oxidize LDL, which in turn amplify platelet activation via specific ox-LDL receptors; both effects are mediated by NOX2 activation. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  2. Kinetics and mechanism of the oxidation process of two-component Fe-Al alloys

    Science.gov (United States)

    Przewlocka, H.; Siedlecka, J.

    1982-01-01

    The oxidation process of two-component Fe-Al alloys containing up to 7.2% Al and from 18 to 30% Al was studied. Kinetic measurements were conducted using the isothermal gravimetric method in the range of 1073-1223 K and 1073-1373 K for 50 hours. The methods used in studies of the mechanism of oxidation included: X-ray microanalysis, X-ray structural analysis, metallographic analysis and marker tests.

  3. The liquid phase oxidation of n-butane: a search for plausible mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Hobbs, C.C. [Celanese Ltd., TX (United States). Corpus Christi Technical Center

    1998-12-31

    This articles deals with an approach that has given some key information about the mechanisms of the liquid phase oxidation of butane to acetic acid. This procedure has been developed over the last 34 years; however, much of what will be discussed represents a synthesis of previous insights. Many of the observations are relatively recent and have not been previously published. In principle, this approach should be applicable to many oxidation processes. (orig.)

  4. The oxidation mechanism of szomolnokite in intermittently fired domestic boilers

    Energy Technology Data Exchange (ETDEWEB)

    Koebel, M.; Elsener, M.; Zimmermann, U.

    1989-06-01

    Using thermogravimetry and exposure experiments on initially formed iron (II)-sulfate hydrates the consecutive reactions of the primary corrosion product szomolnokite under the typical operating conditions of domestic boilers were investigated. The reaction mechanism thus deduced is in accordance with thermodynamic equilibrium considerations in the system Fe/sub 2/O/sub 3/-H/sub 2/SO/sub 4/-H/sub 2/O/crystalline phase. The reaction mechanism consists of the following steps: (1) H/sub 2/SO/sub 4/ (vapour) -> H/sub 2/SO/sub 4/ (liquid). (2) H/sub 2/SO/sub 4/ + Fe + H/sub 2/O -> FeSO/sub 4/xH/sub 2/O + H/sub 2/. (3) 2FeSO/sub 4/xH/sub 2/O + 0,5 O/sub 2/ -> 2Fe(OH)SO/sub 4/ + H/sub 2/O. (4a) Fe(OH)SO/sub 4/ + H/sub 2/SO/sub 4/ + 3H/sub 2/O -> FeH(SO/sub 4/)/sub 2/x4H/sub 2/O. (4b) Fe(OH)SO/sub 4/ + H/sub 2/SO/sub 4/ -> Fe(H/sub 3/O)(SO/sub 4/)/sub 2/. (5a) 2FeH(SO/sub 4/)/sub 2/x4H/sub 2/O -> Fe/sub 2/(SO/sub 4/)/sub 3/ + H/sub 2/SO/sub 4/ + 8H/sub 2/O. (5b) 2Fe(H/sub 3/O)(SO/sub 4/)/sub 2/ -> Fe/sub 2/ (SO/sub 4/)/sub 3/ + H/sub 2/SO/sub 4/ + 2 H/sub 2/O. With this reaction mechanism the most frequently occurring crystalline phases in corrosion samples from oil fired domestic boilers can be explained. (orig.).

  5. Waste incineration corrosion processes: Oxidation mechanisms by electrochemical impedance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Perez, F.J.; Hierro, M.P.; Nieto, J. [Departamento de Ciencia de los Materiales. Facultad de Ciencias Quimicas, Grupo de Investigacion de Ingenieria de Superficies, Universidad Complutense de Madrid, 28040 Madrid (Spain)

    2008-07-15

    Molten chloride mixtures are formed in waste incineration plants during waste firing and energy production. These mixtures are responsible for degradation processes like hot corrosion. In order to evaluate the damage of molten salt mixtures in waste incineration environments, the alloys 625 and 617 were exposed beneath a molten KCl-ZnCl{sub 2} mixture at 650 C in air. The corrosion process was monitored by electrochemical impedance spectroscopy (EIS). An extensive microscopy analysis has been done in order to correlate the electrochemical results, and to establish an electrochemical mechanism for such high temperature corrosion processes. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

  6. Passivation Mechanism of 316L Stainless Steel in Oxidizing Acid Solution

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The compositions and the chemical valence states of elements of 316L stainless steel passive film formed in the oxidizing acid solution were studied by X-ray Photoelectron Spectroscopic (XPS) analysis. The electrochemical polarization curve was measured. The passivation process in the oxidizing acid solution was studied by AC impedance technology. The results indicated that the stable compounds layer was formed on the surface of the sample and the adsorption was the main step in the nitrite solution during passivation process. The catalysis passivation mechanism was put forward according to the experimental results. During passivation process, the water molecule was adsorbed on the surface of the sample at first in the oxidizing acid solution. The oxidizer in the solution played a role as catalyst. The oxide and hydroxide, which could be changed each other and finally formed stable passive film, were generated from adsorbing intermediate under the catalytic action. The mathematical models for predicting the steady polarization curve and the AC impedance spectra at certain conditions have been obtained. The passivation mechanism of 316L stainless steel in the oxidizing acid solution can be interpreted by the catalysis passivation mechanism.

  7. Mechanisms of MDMA (ecstasy)-induced oxidative stress, mitochondrial dysfunction, and organ damage.

    Science.gov (United States)

    Song, Byoung-Joon; Moon, Kwan-Hoon; Upreti, Vijay V; Eddington, Natalie D; Lee, Insong J

    2010-08-01

    Despite numerous reports about the acute and sub-chronic toxicities caused by MDMA (3,4-methylenedioxymethamphetamine, ecstasy), the underlying mechanism of organ damage is poorly understood. The aim of this review is to present an update of the mechanistic studies on MDMA-mediated organ damage partly caused by increased oxidative/nitrosative stress. Because of the extensive reviews on MDMA-mediated oxidative stress and tissue damage, we specifically focus on the mechanisms and consequences of oxidative-modifications of mitochondrial proteins, leading to mitochondrial dysfunction. We briefly describe a method to systematically identify oxidatively-modified mitochondrial proteins in control and MDMA-exposed rats by using biotin-N-maleimide (biotin-NM) as a sensitive probe for oxidized proteins. We also describe various applications and advantages of this Cys-targeted proteomics method and alternative approaches to overcome potential limitations of this method in studying oxidized proteins from MDMA-exposed tissues. Finally we discuss the mechanism of synergistic drug-interaction between MDMA and other abused substances including alcohol (ethanol) as well as application of this redox-based proteomics method in translational studies for developing effective preventive and therapeutic agents against MDMA-induced organ damage.

  8. Crystallographic shear mechanisms in Rh one-dimensional oxides

    Science.gov (United States)

    Hernando, María; Boulahya, Khalid; Parras, Marina; González-Calbet, José M.

    2005-02-01

    Electron diffraction and high resolution electron microscopy have been used to characterize two new one-dimensional superstructures in the A sbnd Rh sbnd O system (A = Ca, Sr) related to the 2H-ABO 3-type. They are formed by the intergrowth of n A 3A'BO 6 blocks, showing the Sr 4RhO 6-type, with A 12A' 2B 8O 30 blocks, constituted by two A 3O 9 and two A 3A'O 6 layers alternating in the stacking sequence 1:1, leading to the A 27A' 7B 13O 60 ( n=5) and A 30A' 8B 14O 66 ( n=6) compositions. A crystallographic shear mechanism is proposed to describe the structural relationship between Sr 4RhO 6 (A 3A'BO 6-type) and the new superstructures.

  9. Toxic mechanisms of copper oxide nanoparticles in epithelial kidney cells

    DEFF Research Database (Denmark)

    Thit, Amalie; Selck, Henriette; Bjerregaard, Henning F.

    2015-01-01

    CuO NPs have previously been reported as toxic to a range of cell cultures including kidney epithelial cells from the frog, Xenopus laevis (A6). Here we examine the molecular mechanisms affecting toxicity of Cu in different forms and particle sizes. A6 cells were exposed to ionic Cu (Cu2+) or Cu......O particles of three different sizes: CuO NPs of 6 nm (NP6), larger Poly-dispersed CuO NPs of toxic than NP6, Micro and Cu2+ to A6 cells, causing DNA damage, decreased cell viability...... and levels of reduced glutathione (GSH) and eventually cell death. We show that ROS (Reactive Oxygen Species) generation plays a key role and occurs early in Poly toxicity as Poly-induced DNA damage and cell death could be mitigated by the antioxidant NAC (N-acetyl-cysteine). Here we propose a model...

  10. Study of the Stereochemistry and Oxidation Mechanism of Plant Polyphenols, Assisted by Computational Chemistry.

    Science.gov (United States)

    Matsuo, Yosuke

    2017-01-01

     In recent years, plant polyphenols have attracted great attention due to their wide range of biological activities. Certain kinds of polyphenols have complex structures; therefore, it is difficult to elucidate their total structure, including stereochemistry. In this study, we reinvestigated the stereostructures of two major C-glycosidic ellagitannins contained in Quercus plants, vescalagin and castalagin, and revised their stereostructures based on theoretical calculations of spectroscopic data. We also determined the structures of quercusnins A and B, isolated from the sapwood of Quercus crispula, based on theoretical calculations of NMR data. The oxidation mechanism of polyphenols has not been entirely elucidated. Therefore, we have also studied the oxidation mechanism of tea catechins during black tea production. Our investigation of the oxidation mechanism of black tea pigment theaflavins revealed that the difference in the position of the galloyl ester affords different oxidation products of theaflavins. In addition, oxidation products of pyrogallol-type catechins could be classified into three types-dehydrotheasinensins, theacitrins, and proepitheaflagallins; their detailed production and degradation mechanisms were also examined.

  11. Decomposition mechanism of melamine borate in pyrolytic and thermo-oxidative conditions

    Energy Technology Data Exchange (ETDEWEB)

    Hoffendahl, Carmen; Duquesne, Sophie; Fontaine, Gaëlle; Bourbigot, Serge, E-mail: serge.bourbigot@ensc-lille.fr

    2014-08-20

    Highlights: • Decomposition of melamine borate in pyrolytic and thermo-oxidative conditions was investigated. • With increasing temperature, orthoboric acid forms boron oxide releasing water. • Melamine decomposes evolving melamine, ammonia and other fragments. • Boron oxide is transformed into boron nitride and boron nitride-oxide structures through presence of ammonia. - Abstract: Decomposition mechanism of melamine borate (MB) in pyrolytic and thermo-oxidative conditions is investigated in the condensed and gas phases using solid state NMR ({sup 13}C and {sup 11}B), X-ray photoelectron spectroscopy (XPS), pyrolysis-gas chromatography–mass spectrometry (py-GCMS) and thermogravimetric analysis coupled with a Fourier transform infrared spectrometer (TGA–FTIR). It is evidenced that orthoboric acid dehydrates to metaboric and then to boron oxide. The melamine is partially sublimated. At the same time, melamine condensates, i.e., melem and melon are formed. Melon is only formed in thermo-oxidative conditions. At higher temperature, melem and melon decompose releasing ammonia which reacts with the boron oxide to form boron nitride (BN) and BNO structures.

  12. Photocatalytic and photoelectrochemical oxidation mechanisms of methanol on TiO2 in aqueous solution

    Science.gov (United States)

    Ahmed, Amira Y.; Kandiel, Tarek A.; Ivanova, Irina; Bahnemann, Detlef

    2014-11-01

    Methanol is an available, small, and colorless molecule, which can be used for the photocatalytic activity evaluation without the sensitization problem associated with most dye molecules. Thus, TiO2 suspended in aqueous methanol solutions is commonly employed as a model test for the photocatalytic degradation of organic pollutants in aerobic system or for photocatalytic hydrogen production in absence of molecular oxygen. It is, hence, important to explore the mechanism of its photocatalytic and photoelectrochemical oxidation on TiO2 in aqueous solution. In this mini-review, the possible mechanisms for water and methanol oxidation on TiO2 will therefore be presented and discussed.

  13. Mechanism of oxidative stress involved in the toxicity of ZnO nanoparticles against eukaryotic cells

    Directory of Open Access Journals (Sweden)

    M. Saliani

    2016-01-01

    Full Text Available ZnO NPs (zinc oxide nanoparticles has generated significant scientific interest as a novel antibacterial and anticancer agent. Since oxidative stress is a critical determinant of ZnO NPs-induced damage, it is necessary to characterize their underlying mode of action. Different structural and physicochemical properties of ZnO NPs such as particle surface, size, shape, crystal structure, chemical position, and presence of metals can lead to changes in biological activities including ROS (reactive oxygen species production. However, there are some inconsistencies in the literature on the relation between the physicochemical features of ZnO NPs and their plausible oxidative stress mechanism. Herein, the possible oxidative stress mechanism of ZnO NPs was reviewed. This is worthy of further detailed evaluations in order to improve our understanding of vital NPs characteristics governing their toxicity. Therefore, this study focuses on the different reported oxidative stress paradigms induced by ZnO NPs including ROS generated by NPs, oxidative stress due to the NPs-cell interaction, and role of the particle dissolution in the oxidative damage. Also, this study tries to characterize and understand the multiple pathways involved in oxidative stress induced by ZnO NPs. Knowledge about different cellular signaling cascades stimulated by ZnO NPs lead to the better interpretation of the toxic influences induced by the cellular and acellular parameters. Regarding the potential benefits of toxic effects of ZnO NPs, in-depth evaluation of their toxicity mechanism and various effects of these nanoparticles would facilitate their implementation for biomedical applications.

  14. Physical and chemical mechanisms in oxide-based resistance random access memory.

    Science.gov (United States)

    Chang, Kuan-Chang; Chang, Ting-Chang; Tsai, Tsung-Ming; Zhang, Rui; Hung, Ya-Chi; Syu, Yong-En; Chang, Yao-Feng; Chen, Min-Chen; Chu, Tian-Jian; Chen, Hsin-Lu; Pan, Chih-Hung; Shih, Chih-Cheng; Zheng, Jin-Cheng; Sze, Simon M

    2015-01-01

    In this review, we provide an overview of our work in resistive switching mechanisms on oxide-based resistance random access memory (RRAM) devices. Based on the investigation of physical and chemical mechanisms, we focus on its materials, device structures, and treatment methods so as to provide an in-depth perspective of state-of-the-art oxide-based RRAM. The critical voltage and constant reaction energy properties were found, which can be used to prospectively modulate voltage and operation time to control RRAM device working performance and forecast material composition. The quantized switching phenomena in RRAM devices were demonstrated at ultra-cryogenic temperature (4K), which is attributed to the atomic-level reaction in metallic filament. In the aspect of chemical mechanisms, we use the Coulomb Faraday theorem to investigate the chemical reaction equations of RRAM for the first time. We can clearly observe that the first-order reaction series is the basis for chemical reaction during reset process in the study. Furthermore, the activation energy of chemical reactions can be extracted by changing temperature during the reset process, from which the oxygen ion reaction process can be found in the RRAM device. As for its materials, silicon oxide is compatible to semiconductor fabrication lines. It is especially promising for the silicon oxide-doped metal technology to be introduced into the industry. Based on that, double-ended graphene oxide-doped silicon oxide based via-structure RRAM with filament self-aligning formation, and self-current limiting operation ability is demonstrated. The outstanding device characteristics are attributed to the oxidation and reduction of graphene oxide flakes formed during the sputter process. Besides, we have also adopted a new concept of supercritical CO2 fluid treatment to efficiently reduce the operation current of RRAM devices for portable electronic applications.

  15. Chemical kinetic mechanism for the oxidation of paraffinic hydrocarbons needed for primary reference fuels

    Energy Technology Data Exchange (ETDEWEB)

    Westbrook, C.K.; Pitz, W.J.

    1993-03-01

    A detailed chemical kinetic reaction mechanism is described which simulates the oxidation of the primary reference fuels n-heptane and iso-octane. The high temperature subset of these mechanisms is identified, and the extensions to deal with low temperature conditions are also explained. The algorithms used to assign reaction rates to elementary steps in the reaction mechanism are described, and the means of identifying the different chemical species and the relevant reactions are outlined. Finally, we show how interested kinetic modeling researchers can obtain copies of this reaction mechanism.

  16. Mechanical properties of bioplastics cassava starch film with Zinc Oxide nanofiller as reinforcement

    Science.gov (United States)

    Harunsyah; Yunus, M.; Fauzan, Reza

    2017-06-01

    This study focuses on investigating the influence of zinc oxide nanofiller on the mechanical properties of bioplastic cassava starch films. Bioplastic cassava starch film-based zinc oxide reinforced composite biopolymeric films were prepared by casting technique. The content of zinc oxide in the bioplastic films was varied from 0.2%, 0.4%, 0.6%, 0.8% and 1.0% (w/w) by weight of starch. Surface morphologies of the composites bioplastic films were examined by scanning electron microscope (SEM).The result showed that the Tensile strength (TS) was improved significantly with the additional of zinc oxide but the elongation at break (EB %) of the composites was decreased. The maximum tensile strength obtained was 22.30 kgf / mm on the additional of zinc oxide by 0.6% and plastilizer by 25%. Based on data of FTIR, the produced film plastic did not change the group function and it can be concluded that theinteraction in film plastic produced was only a physical interaction. Biodegradable plastic film based on cassava starch-zinc oxide and plasticizer glycerol showed that interesting mechanical properties being transparent, clear, homogeneous, flexible, and easily handled.

  17. Oxidative stress-driven parvalbumin interneuron impairment as a common mechanism in models of schizophrenia

    Science.gov (United States)

    Steullet, P; Cabungcal, J-H; Coyle, J; Didriksen, M; Gill, K; Grace, A A; Hensch, T K; LaMantia, A-S; Lindemann, L; Maynard, T M; Meyer, U; Morishita, H; O'Donnell, P; Puhl, M; Cuenod, M; Do, K Q

    2017-01-01

    Parvalbumin inhibitory interneurons (PVIs) are crucial for maintaining proper excitatory/inhibitory balance and high-frequency neuronal synchronization. Their activity supports critical developmental trajectories, sensory and cognitive processing, and social behavior. Despite heterogeneity in the etiology across schizophrenia and autism spectrum disorder, PVI circuits are altered in these psychiatric disorders. Identifying mechanism(s) underlying PVI deficits is essential to establish treatments targeting in particular cognition. On the basis of published and new data, we propose oxidative stress as a common pathological mechanism leading to PVI impairment in schizophrenia and some forms of autism. A series of animal models carrying genetic and/or environmental risks relevant to diverse etiological aspects of these disorders show PVI deficits to be all accompanied by oxidative stress in the anterior cingulate cortex. Specifically, oxidative stress is negatively correlated with the integrity of PVIs and the extracellular perineuronal net enwrapping these interneurons. Oxidative stress may result from dysregulation of systems typically affected in schizophrenia, including glutamatergic, dopaminergic, immune and antioxidant signaling. As convergent end point, redox dysregulation has successfully been targeted to protect PVIs with antioxidants/redox regulators across several animal models. This opens up new perspectives for the use of antioxidant treatments to be applied to at-risk individuals, in close temporal proximity to environmental impacts known to induce oxidative stress. PMID:28322275

  18. Kinetics and Mechanism of the Oxidation of Menthol by Potassium Bromate in Acidic Solution

    Directory of Open Access Journals (Sweden)

    Ravikant na

    2014-06-01

    Full Text Available No suitable method is available for the estimation of menthol, hence in all kinetic results reported in this chapter, menthol was in excess over potassium bromate and the stoichiometry was also determined under the experimental conditions where menthol (substrate was in excess over potassium bromate (oxidant. Present study was focused on the analysis of kinetics and mechanism of oxidation of neomenthol by potassium bromate in acidic medium. For oxidizing neomenthol, potassium bromate stock solution (5.0×10─2 mol. dm─3 was prepared by dissolving exactly weighed quantity of potassium bromate in doubly distilled water. The suitable reaction mixtures were prepared and left at 313 K for over 24 hours to ensure complete oxidation of neomenthol. The unreacted potassium bromate was determined iodometrically and the results indicate that one mole of potassium bromate is consumed for every three moles of neomenthol and leads to the formation of menthone (ketone.

  19. Effect of oxidation on the Mechanical Properties of Liquid Gallium and Eutectic Gallium-Indium

    CERN Document Server

    Xu, Qin; Guo, Qiti; Jaeger, Heinrich; Brown, Eric

    2012-01-01

    Liquid metals exhibit remarkable mechanical properties, in particular large surface tension and low viscosity. However, these properties are greatly affected by oxidation when exposed to air. We measure the viscosity, surface tension, and contact angle of gallium (Ga) and a eutectic gallium-indium alloy (eGaIn) while controlling such oxidation by surrounding the metal with an acid bath of variable concentration. Rheometry measurements reveal a yield stress directly attributable to an oxide skin that obscures the intrinsic behavior of the liquid metals. We demonstrate how the intrinsic viscosity can be obtained with precision through a scaling technique that collapses low- and high-Reynolds number data. Measuring surface tension with a pendant drop method, we show that the oxide skin generates a surface stress that mimics surface tension and develop a simple model to relate this to the yield stress obtained from rheometry. We find that yield stress, surface tension, and contact angle all transition from solid-...

  20. Kinetics and mechanism of the oxidation of organic sulphides by 2,2'-bipyridinium chlorochromate

    Indian Academy of Sciences (India)

    Shashi Vyas; Pradeep K Sharma

    2002-04-01

    The oxidation of 34 organic sulphides by 2,2'-bipyridinium chlorochromate (BPCC) resulted in the formation of the corresponding sulphoxides. The reaction is first order with respect to both BPCC and the sulphide, and is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: obs = a+b [H+]. The oxidation was studied in 19 different organic solvents. An analysis of the solvent effect by Swain’s equation showed that the both cation- and anion-solvating powers of the solvents play important roles. The rates of oxidation meta- and -substituted phenyl methyl sulphides were correlated with Charton’s LDR equation. The rates of the -compounds showed excellent correlation with the LDRS equation. Oxidation of the -compounds is more susceptible to the delocalization effect. Oxidation of the -compounds exhibited a greater dependence on the field effect. In the oxidation of the -compounds, the contribution of delocalized effect is slightly more than that of the field effect. The oxidation of alkyl phenyl sulphides is subject to both polar and steric effects of the alkyl groups. Polar reaction constants are negative, indicating an electron-deficient sulphur centre in the rate-determining step. A mechanism involving formation of a sulphurane intermediate in the slow step has been proposed.

  1. Effect of native oxide mechanical deformation on InP nanoindentation

    Science.gov (United States)

    Almeida, C. M.; Prioli, R.; Ponce, F. A.

    2008-12-01

    Native oxide has been found to have a noticeable effect on the mechanical deformation of InP during nanoindentation. The indentations were performed using spherical diamond tips and the residual impressions were studied by atomic force microscopy. It has been observed that in the early stages of mechanical deformation, plastic flow occurs in the oxide layer while the indium phosphide is still in the elastic regime. The deformed native oxide layer results in a pile-up formation that causes an increase in the contact area between the tip and the surface during the nanoindentation process. This increase in the projected contact area is shown to contribute to the apparent high pressure sustained by the crystal before the onset of plastic deformation. It is also shown that the stress necessary to generate the first dislocations from the crystal surface is ˜3 GPa higher than the stress needed for slip to occur when dislocations are already present in the crystalline structure.

  2. Effect of internal oxidation on the microstructure and mechanical properties of C-103 alloy

    Energy Technology Data Exchange (ETDEWEB)

    Sankar, M., E-mail: msankar_iitk@yahoo.co.in [Defence Metallurgical Research Laboratory, Hyderabad-500058, Andhra Pradesh (India); Baligidad, R.G.; Satyanarayana, D.V.V.; Gokhale, A.A. [Defence Metallurgical Research Laboratory, Hyderabad-500058, Andhra Pradesh (India)

    2013-07-01

    The effect of internal oxidation on the microstructure and mechanical properties of niobium alloy, C-103 has been investigated. Tensile specimens and test coupons of alloy containing different levels of oxygen (100–2500 ppm) were characterized with respect to microstructure and mechanical properties. It has been observed that for oxygen contents in the range ∼400–1000 ppm, hafnium oxide precipitated exclusively along the grain boundaries, while for oxygen content of ∼2500 ppm, precipitates formed both at the grain boundaries and within the grains near surface region of the alloy. The internal oxidation has resulted in embrittlement of the alloy resulting in considerable lowering of strength as well as ductility. Further, the strength and ductility are found to decrease progressively with the increase in average oxygen content of the alloy.

  3. Fourier transform infrared difference spectroscopy for studying the molecular mechanism of photosynthetic water oxidation

    Directory of Open Access Journals (Sweden)

    Hsiu-An eChu

    2013-05-01

    Full Text Available The photosystem II reaction center mediates the light-induced transfer of electrons from water to plastoquinone, with concomitant production of O2. Water oxidation chemistry occurs in the oxygen-evolving complex (OEC, which consists of an inorganic Mn4CaO5 cluster and its surrounding protein matrix. Light-induced Fourier transform infrared (FTIR difference spectroscopy has been successfully used to study the molecular mechanism of photosynthetic water oxidation. This powerful technique has enabled the characterization of the dynamic structural changes in active water molecules, the Mn4CaO5 cluster, and its surrounding protein matrix during the catalytic cycle. This mini-review presents an overview of recent important progress in FTIR studies of the OEC and implications for revealing the molecular mechanism of photosynthetic water oxidation.

  4. Theoretical elucidation of the competitive electro-oxidation mechanisms of formic acid on Pt(111).

    Science.gov (United States)

    Gao, Wang; Keith, John A; Anton, Josef; Jacob, Timo

    2010-12-29

    The mechanisms of formic acid (HCOOH) oxidation on Pt(111) under electrochemical conditions have been studied using density functional theory and then compared with the analogous gas-phase reaction. Results show that HCOOH oxidation under a water-covered surface behaves substantially differently than in the gas phase or using a solvation model involving only a few water molecules. Using these models, we evaluated the detailed reaction process, including energies and geometric structures of intermediates and transition states under the influence of different solvation models and electrode potentials. Our calculations indicate that this potential-dependent electrochemical oxidation proceeds via a multipath mechanism (involving both the adsorbed HCOOH and HCOO intermediates), a result succinctly rationalizing conflicting experimental observations. Moreover, this study highlights how subtle changes in electrochemical reaction environments can influence (electro)catalysis.

  5. Oxidative Stress-Mediated Skeletal Muscle Degeneration: Molecules, Mechanisms, and Therapies

    Directory of Open Access Journals (Sweden)

    Min Hee Choi

    2016-01-01

    Full Text Available Oxidative stress is a loss of balance between the production of reactive oxygen species during cellular metabolism and the mechanisms that clear these species to maintain cellular redox homeostasis. Increased oxidative stress has been associated with muscular dystrophy, and many studies have proposed mechanisms that bridge these two pathological conditions at the molecular level. In this review, the evidence indicating a causal role of oxidative stress in the pathogenesis of various muscular dystrophies is revisited. In particular, the mediation of cellular redox status in dystrophic muscle by NF-κB pathway, autophagy, telomere shortening, and epigenetic regulation are discussed. Lastly, the current stance of targeting these pathways using antioxidant therapies in preclinical and clinical trials is examined.

  6. Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

    Indian Academy of Sciences (India)

    Madhu Khurana; Pradeep K Sharma; Kalyan K Banerji

    2000-04-01

    Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: obs = + [H+]. The oxidation of -deuterioformic acid exhibits a substantial primary kinetic isotope effect (H/D = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed

  7. Synthesis, crystal growth and mechanical properties of Bismuth Silicon Oxide (BSO) single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Riscob, B. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujarat (India); Shkir, Mohd. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Ganesh, V. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Vijayan, N.; Maurya, K.K. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Kishan Rao, K. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Bhagavannarayana, G., E-mail: bhagavan@mail.nplindia.ernet.in [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India)

    2014-03-05

    Highlights: • Synthesis of Bismuth Silicon Oxide (BSO). • Single crystal growth of BSO by Czochralski (Cz) method. • Complete mechanical analysis by device fabrication point of view. • Theoretical and experimental calculations of mechanical properties. -- Abstract: Bismuth Silicon Oxide (BSO) is an efficient material for piezo-electric and electro-optic applications. In this article, growth of BSO single crystal by high temperature Czochralski melt growth technique and its detailed mechanical characterization by Vickers microhardness, fracture toughness, crack propagation, brittleness index and yield strength have been reported. The raw material was synthesized by solid state reaction using the stoichiometric ratio of high purity bismuth tri-oxide and silicon di-oxide. The synthesized material was charged in the platinum crucible and then melted. The required rotation and pulling rate was optimized for BSO single crystal growth and good quality single crystal has been harvested after a time span of 5 days. Powder X-ray diffraction analysis confirms the parent crystallization phase of BSO. The experimentally studied mechanical behavior of the crystal is explained using various theoretical models. The anisotropic nature of the crystals is studied using Knoop indentation technique.

  8. Coloration and bleaching mechanism of niobium oxide electrochromic thin films; Sanka niobu electromic usumaku no chakushoshoku mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Yoshimura, K.; Miki, T.; Tazawa, M.; Jin, P.; Igarashi, K.; Tanemura, S. [National Industrial Research Institute of Nagoya, Nagoya (Japan)

    1997-11-25

    In order to search for the coloration and bleaching mechanism of niobium oxide, considerations were given on optical properties and electron conditions in niobium oxide thin films (glass plates as substrates coated with ITO) prepared by using the reactive DC magnetron sputtering process. The films were so grown that their thickness will all be 100 nm to facilitate data comparison. Coloration and bleaching of the grown test films were conducted by cyclic voltammetry. Electron spectra were measured by using XPS, and electron energy was analyzed. Coloration of niobium oxide occurs as a result of change in valency electron state from an Nb {sup 5+} state to an Nb {sup 4+} state, while change in the XPS spectra also corresponds with the above change. However, the XPS spectra differ greatly between crystalline samples and amorphous samples. The coloration and bleaching mechanism of the crystallized Nb2O5 film can be explained by a reaction formula similar to that for WO3. However, with regard to the amorphous Nb2O5 film, an independent reaction involving water in the film seems to occur together with the same reaction as in the crystallized film. 9 refs., 5 figs.

  9. Co(salophen)-Catalyzed Aerobic Oxidation of p-Hydroquinone: Mechanism and Implications for Aerobic Oxidation Catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Anson, Colin W.; Ghosh, Soumya; Hammes-Schiffer, Sharon; Stahl, Shannon S.

    2016-03-30

    Macrocyclic metal complexes and p-benzoquinones are commonly used as co-catalytic redox mediators in aerobic oxidation reactions. In an effort to gain insight into the mechanism and energetic efficiency of these reactions, we investigated Co(salophen)-catalyzed aerobic oxidation of p-hydroquinone. Kinetic and spectroscopic data suggest that the catalyst resting-state consists of an equilibrium between a CoII(salophen) complex, a CoIII-superoxide adduct, and a hydrogen-bonded adduct between the hydroquinone and the CoIII–O2 species. The kinetic data, together with density functional theory data, suggest that the turnover-limiting step features proton-coupled electron transfer from a semi-hydroquinone species and a CoIII-hydroperoxide intermediate. Additional experimental and computational data suggest that a coordinated H2O2 intermediate oxidizes a second equivalent of hydroquinone. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The NSF provided partial support for the EPR instrumentation (NSF CHE-0741901).

  10. Oxidative Stress-Related Mechanisms and Antioxidant Therapy in Diabetic Retinopathy

    Directory of Open Access Journals (Sweden)

    Cheng Li

    2017-01-01

    Full Text Available Diabetic retinopathy (DR is one of the most common microvascular complications of diabetes and is the leading cause of blindness in young adults. Oxidative stress has been implicated as a critical cause of DR. Metabolic abnormalities induced by high-glucose levels are involved in the development of DR and appear to be influenced by oxidative stress. The imbalance between reactive oxygen species (ROS production and the antioxidant defense system activates several oxidative stress-related mechanisms that promote the pathogenesis of DR. The damage caused by oxidative stress persists for a considerable time, even after the blood glucose concentration has returned to a normal level. Animal experiments have proved that the use of antioxidants is a beneficial therapeutic strategy for the treatment of DR, but more data are required from clinical trials. The aims of this review are to highlight the improvements to our understanding of the oxidative stress-related mechanisms underlying the development of DR and provide a summary of the main antioxidant therapy strategies used to treat the disease.

  11. Oxidative Stress-Related Mechanisms and Antioxidant Therapy in Diabetic Retinopathy

    Science.gov (United States)

    Miao, Xiao

    2017-01-01

    Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes and is the leading cause of blindness in young adults. Oxidative stress has been implicated as a critical cause of DR. Metabolic abnormalities induced by high-glucose levels are involved in the development of DR and appear to be influenced by oxidative stress. The imbalance between reactive oxygen species (ROS) production and the antioxidant defense system activates several oxidative stress-related mechanisms that promote the pathogenesis of DR. The damage caused by oxidative stress persists for a considerable time, even after the blood glucose concentration has returned to a normal level. Animal experiments have proved that the use of antioxidants is a beneficial therapeutic strategy for the treatment of DR, but more data are required from clinical trials. The aims of this review are to highlight the improvements to our understanding of the oxidative stress-related mechanisms underlying the development of DR and provide a summary of the main antioxidant therapy strategies used to treat the disease.

  12. Study on Mechanism of Soy Protein Oxidation Induced by Lipid Peroxidation Products

    Directory of Open Access Journals (Sweden)

    Wei Wu

    2013-01-01

    Full Text Available Oxidative modification of soy protein by lipid peroxidation products, which was potentially present in a lipoxygenase-catalyzed polyunsaturated fatty acid peroxidation system, was investigated in this study. 13S-Hydroperoxy-9Z, 11E-Octadecadienoic acid (HPODE, malondialdehyde and acrolein were selected as representative primary product and secondary byproducts of lipid peroxidation and 2, 2’-azobis-(2-amidinopropane dihydrochloride (AAPH -derived peroxyl radical peroxyl radicals were chosen to simulate lipid peroxidation-derived free radical. Incubation of soy protein with increasing concentration of AAPH, HPODE, malondialdehyde and acrolein resulted in gradual generation of protein carbonyl derivatives, loss of free sulphydryl groups, total sulphydryl groups, free amine, available lysine, surface hydrophobicity and formation of oxidation aggregates. The average distribution model of protein accessible groups could explain majority mechanism of lipid peroxidation products-mediated soy protein oxidation. Primary oxidation aggregates further developed into insoluble aggregates by covalent cross-linking also may provide a partial mechanism of lipid peroxidation products-mediated soy protein oxidation.

  13. Physiology and Mechanism of Phototrophic Fe(II) Oxidation by Rhodopseudomonas palustris TIE-1

    Science.gov (United States)

    Jiao, Y.; Newman, D.

    2007-12-01

    Phototrophic Fe(II)-oxidizing bacteria use electrons from ferrous iron [Fe(II)] and energy from light to drive reductive CO2 fixation. This metabolism is thought to be ancient in origin, and plays an important role in environmental iron cycling. It has been implicated in the deposition of Banded Iron Formations, a class of ancient sedimentary iron deposits. Consistent with this hypothesis, we discovered that hydrogen gas, a thermodynamically favorable electron donor to Fe(II), in an Archean atmosphere would not have inhibited phototrophic Fe(II) oxidation. To understand this physiology and the connection to BIF formation at the molecular level, the mechanisms of phototrophic Fe(II) oxidation were examined in a model organism Rhodopseudomonas palustris TIE-1. Increased expression of a putative decaheme c-type cytochrome, encoded by pioA, was observed when cells were grown under Fe(II)-oxidizing conditions. Two genes located immediately downstream of pioA in the same operon, pioB and pioC, encode a putative outer membrane beta-barrel protein and a putative high potential iron-sulfur protein, respectively. Deletion studies demonstrated that all three genes are involved in phototrophic Fe(II) oxidation. This study provides our first insight into the molecular mechanisms of this metabolism, which will be further characterized by in vitro biochemical studies.

  14. Optical, structural, and mechanical properties of different valence-cation-doped bismuth vanadate oxides

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, G.; Pandey, O.P.; Singh, K. [School of Physics and Materials Science, Thapar University, Patiala-147004, Punjab (India)

    2012-07-15

    The optical, structural, and mechanical properties of Bi{sub 4}V{sub 2-x}M{sub x}O{sub 11-{delta}} (0{<=}x{<=}0.4 in the steps of 0.1, M = Mn, Ga, As) oxides have been investigated. The parameters like band gap (E{sub g}), Urbach energy (E{sub u}), grain size, hardness (H), and fracture strength (K) have been calculated as a function of dopant concentration, i.e., 0{<=}x{<=}0.4. In addition to this, the infrared spectra have been obtained for all the dopant oxides with different dopant concentrations. The results are discussed in light of correlation of these optical and mechanical parameters to their electrical properties. The fractured surface is analyzed by X-ray dot mapping to check the segregation of elements and their effect on mechanical properties. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Engineering the Mechanical Properties of Monolayer Graphene Oxide at the Atomic Level.

    Science.gov (United States)

    Soler-Crespo, Rafael A; Gao, Wei; Xiao, Penghao; Wei, Xiaoding; Paci, Jeffrey T; Henkelman, Graeme; Espinosa, Horacio D

    2016-07-21

    The mechanical properties of graphene oxide (GO) are of great importance for applications in materials engineering. Previous mechanochemical studies of GO typically focused on the influence of the degree of oxidation on the mechanical behavior. In this study, using density functional-based tight binding simulations, validated using density functional theory simulations, we reveal that the deformation and failure of GO are strongly dependent on the relative concentrations of epoxide (-O-) and hydroxyl (-OH) functional groups. Hydroxyl groups cause GO to behave as a brittle material; by contrast, epoxide groups enhance material ductility through a mechanically driven epoxide-to-ether functional group transformation. Moreover, with increasing epoxide group concentration, the strain to failure and toughness of GO significantly increases without sacrificing material strength and stiffness. These findings demonstrate that GO should be treated as a versatile, tunable material that may be engineered by controlling chemical composition, rather than as a single, archetypical material.

  16. Theoretical study of the dark-oxidation reaction mechanisms for organic polymers

    Science.gov (United States)

    Wang, Guixiu; Zhu, Rongxiu; Zhang, Dongju; Liu, Chengbu

    2006-08-01

    To model the dark-oxidation mechanism of organic polymers, the reactions of the corresponding model compounds, including cumene, methyl 2-methylbutyrate, methyl methacrylate and methylacrylic acid, with triplet O 2 molecule, have been studied by performing density functional theory calculations at the UB3LYP/6-31G(d) level. The calculated results show that these model compounds can be oxygenated by O 2 via an H-abstract mechanism. The structures of initial contact charge transfer complexes, transition states, intermediates of cage-like pairs of radicals, and final hydro-peroxides involved in the reactions have been shown in details. The present results are expected to provide a general guidance for understanding the dark-oxidation mechanism of organic polymers.

  17. Identification of New Oxidation Products of Bezafibrate for Better Understanding of Its Toxicity Evolution and Oxidation Mechanisms during Ozonation.

    Science.gov (United States)

    Sui, Qian; Gebhardt, Wilhelm; Schröder, Horst Friedrich; Zhao, Wentao; Lu, Shuguang; Yu, Gang

    2017-02-21

    Bezafibrate (BF), a frequently detected pharmaceutical in the aquatic environment, could be effectively removed by ozonation. However, the toxicity of treated water increased, suggesting the generation of toxic oxidation products (OPs). In this study, eight OPs of BF ozonation were identified using a LTQ Orbitrap hybrid mass spectrometer coupled with HPLC, and six of them have not been previously reported during BF ozonation. Based on the abundant fragments and high assurance of accurate molar mass, structure elucidation was comprehensively performed and discussed. Hydroxylation, loss of methyl propionic acid group, and Crigée mechanism were observed as the oxidation mechanisms of BF ozonation. The toxicity of identified OPs calculated by quantitative structure activity relationship indicated that three OPs were probably more toxic than the precursor compound BF. This result together with the evolution of identified OPs in the treated solutions, indicated that two OPs, namely N-(3,4-dihydroxyphenethyl)-4-chlorobenzamide and N-(2,4-dihydroxyphenethyl)-4-chlorobenzamide, were the potential toxicity-causing OPs during BF ozonation. To the best of our knowledge, this is the first attempt to identify toxicity-causing OPs during the BF ozonation.

  18. The role of Mn oxide doping in phosphate removal by Al-based bimetal oxides: adsorption behaviors and mechanisms.

    Science.gov (United States)

    Wu, Kun; Liu, Ting; Ma, Chao; Chang, Bing; Chen, Rong; Wang, Xiaochang

    2014-01-01

    This study investigated the behaviors and mechanisms of phosphate adsorbed onto manganese (Mn) oxide-doped aluminum (Al) oxide (MODAO). The isotherm results demonstrated that the maximum amount of phosphorus (P) adsorbed onto MODAO was 59.8 mg/g at T = 298 K (pH 6.0). This value was nearly twice the amount of singular AlOOH and could increase with rising temperatures. The kinetic results illustrated that most of the P was adsorbed onto MODAO within 5 h, which was shorter than the equilibrium time of phosphate adsorption onto AlOOH. The Elovich model effectively described the adsorption kinetic data of MODAO because of its heterogeneous surface. The optimal solution pH for phosphate removal was approximately 5.0 because of electrostatic interaction effects. Meanwhile, the decrease in P uptake with increasing ion strength suggested that phosphate adsorption occurred through an outer-sphere complex. Phosphates would compete for adsorption sites on the surface of MODAO in the presence of fluoride ion or sulfate. In addition, the spectroscopic analysis results of Fourier transform infrared spectroscopy and X-ray photoemission spectroscopy indicated that removal mechanisms of phosphate primarily include adhesion to surface hydroxyl groups and ligand exchange.

  19. Modeling of thermo-mechanical and irradiation behavior of mixed oxide fuel for sodium fast reactors

    Science.gov (United States)

    Karahan, Aydın; Buongiorno, Jacopo

    2010-01-01

    An engineering code to model the irradiation behavior of UO2-PuO2 mixed oxide fuel pins in sodium-cooled fast reactors was developed. The code was named fuel engineering and structural analysis tool (FEAST-OXIDE). FEAST-OXIDE has several modules working in coupled form with an explicit numerical algorithm. These modules describe: (1) fission gas release and swelling, (2) fuel chemistry and restructuring, (3) temperature distribution, (4) fuel-clad chemical interaction and (5) fuel-clad mechanical analysis. Given the fuel pin geometry, composition and irradiation history, FEAST-OXIDE can analyze fuel and cladding thermo-mechanical behavior at both steady-state and design-basis transient scenarios. The code was written in FORTRAN-90 program language. The mechanical analysis module implements the LIFE algorithm. Fission gas release and swelling behavior is described by the OGRES and NEFIG models. However, the original OGRES model has been extended to include the effects of joint oxide gain (JOG) formation on fission gas release and swelling. A detailed fuel chemistry model has been included to describe the cesium radial migration and JOG formation, oxygen and plutonium radial distribution and the axial migration of cesium. The fuel restructuring model includes the effects of as-fabricated porosity migration, irradiation-induced fuel densification, grain growth, hot pressing and fuel cracking and relocation. Finally, a kinetics model is included to predict the clad wastage formation. FEAST-OXIDE predictions have been compared to the available FFTF, EBR-II and JOYO databases, as well as the LIFE-4 code predictions. The agreement was found to be satisfactory for steady-state and slow-ramp over-power accidents.

  20. Mechanism of the cathodic process coupled to the oxidation of iron monosulfide by dissolved oxygen.

    Science.gov (United States)

    Duinea, Mădălina I; Costas, Andreea; Baibarac, Mihaela; Chiriță, Paul

    2016-04-01

    This study investigated the mechanism of iron monosulfide (FeS) oxidation by dissolved oxygen (O2(aq)). Synthetic FeS was reacted with O2(aq) for 6days and at 25°C. We have characterized the initial and reacted FeS surface using Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) analysis, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). It was found that during the aqueous oxidation of FeS new solid phases (disulfide, polysulfide, elemental sulfur, ferric oxyhydroxides and Fe3O4) develop on the mineral surface. The results of potentiodynamic polarization experiments show that after 2days of FeS electrode immersion in oxygen bearing solution (OBS) at initial pH 5.1 and 25°C the modulus of cathodic Tafel slopes dramatically decreases, from 393mV/dec to 86mV/dec. This decrease is ascribed to the change of the mechanism of electron transfer from cathodic sites to O2 (mechanism of cathodic process). The oxidation current densities (jox) indicate that mineral oxidative dissolution is not inhibited by pH increase up to 6.7. Another conclusion, which emerges from the analysis of jox, is that the dissolved Fe(3+) does not intermediate the aqueous oxidation of FeS. The results of electrochemical impedance spectroscopy (EIS) show that after 2days of contact between electrode and OBS the properties of FeS/water interface change. From the analysis of the EIS, FTIR spectroscopy, Raman spectroscopy and SEM/EDX data we can conclude that the change of FeS/water interface properties accompanies the formation of new solid phases on the mineral surface. The new characteristics of the surface layer and FeS/water interface do not cause the inhibition of mineral oxidation.

  1. MNDO and DFT Computational Study on the Mechanism of the Oxidation of 1,2-Diphenylhydrazine by Iodine

    OpenAIRE

    Gideon A. Shallangwa; Uzairu, Adamu; Victor O. Ajibola; Abba, Hamza

    2014-01-01

    The reaction mechanisms of the oxidation of 1,2-diphenylhydrazine by iodine have been examined using semiempirical and density functional theory methods, the oxidation proceeded via two independent pathways that can be separately monitored. One pathway involved the chain multistep mechanism. The other pathway occurred via a one-step mechanism in which a “cyclic” activated complex was formed which on disproportionation gave the products. The one-step “cyclic” activated complex mechanism procee...

  2. On the mechanism of the direct pathway for formic acid oxidation at a Pt(111) electrode.

    Science.gov (United States)

    Xu, Jie; Yuan, Daofu; Yang, Fan; Mei, Dong; Zhang, Zunbiao; Chen, Yan-Xia

    2013-03-28

    In order determine whether formate is a reaction intermediate of the direct pathway for formic acid oxidation at a Pt electrode, formic acid (HCOOH) oxidation at a Pt(111) electrode has been studied by normal and fast scan voltammetry in 0.1 M HClO4 solutions with different HCOOH concentrations. The relationship between the HCOOH oxidation current density (j(ox)) and formate coverage (θ(formate)) is quantitatively analyzed. The kinetic simulation reveals that the previously proposed formate pathway, with decomposition of the bridge-bonded formate (HCOO(B)) as a rate determining step (rds), cannot be the main pathway responsible for the majority of the current for HCOOH oxidation. Instead, a kinetic model based on a mechanism with formic acid adsorption [structure: see text], along with simultaneous C-H bond activation as the rds for the direct pathway, explains the measured data well. It was found for the relatively slow rate of formic acid oxidation, that adsorption-desorption of the formate is faster, which competes for the surface sites for formic acid oxidation.

  3. A computational chemistry investigation of the mechanism of the water-assisted decomposition of trichloroethylene oxide.

    Science.gov (United States)

    Huang, Jinqing; Yeung, Chi Shun; Ma, Jiani; Gayner, Emma R; Phillips, David Lee

    2014-03-06

    Trichloroethylene oxide is a downstream product in the oxidative metabolism of trichloroethylene (TCE) and it may be involved in cytochrome P450 inactivation, protein function destruction, and nucleic acid base alkalization. To explore the hydrolysis mechanism of the decomposition of TCE oxide, an investigation using Second-order Møller-Plesset perturbation theory in conjunction with density functional theory has been conducted to analyze the effect of the water solvation shell on probable reaction steps. The decomposition of TCE oxide is accelerated by coordinated water molecules (up to seven), which reveals that water molecules can help to solvate the TCE oxide molecule and activate the release of the Cl(-) leaving group. After the opening of the epoxide ring, several pathways are proposed to account for the dehalogenation step along with the formation of CO as well as three carboxylic acids (formic acid, glyoxylic acid, and dichloroacetic acid). The predominant pathways were examined by comparing the computed activation energies for the formation of the products to each other for the possible reaction steps examined in this work. After rationally analyzing the computational results, the ring-opening reaction has been identified as the rate-determining step. The rate constant estimated for the TCE oxide decomposition from the calculations performed here was found to be reasonably consistent with previous experimental observations reported in the literature.

  4. Assessment of nickel oxide substituted bioactive glass-ceramic on in vitro bioactivity and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Kumar Vyas, V.; Sampath Kumar, A.; Ali, A.; Prasad, S.; Srivastava, P.; Prasanna Mallick, S.; Ershad, Md.; Prasad Singh, S.; Pyare, R.

    2016-07-01

    Many type of oxide substituted glass-ceramics like strontium, cobalt, barium and titanium have shown bioactivity with improved mechanical properties. The present work reports the in vitro bioactivity and mechanical properties of nickel oxide substituted in bioactive glass-ceramic and results were compared with 45S5 bioactive glass-ceramic. Bioactive glass ceramics were processed through controlled crystallization of their respective bioactive glasses. The formed crystalline phases in bioactive glass-ceramics were identified using X-ray diffraction (XRD) analysis. The formation of HA layer was assessed by immersing them in the simulated body fluid (SBF) for different soaking periods. The formation of hydroxyapatite was confirmed by FTIR spectrometry, SEM and pH measurement. Densities and mechanical properties of the samples were found to increase considerably with an increasing the concentration of nickel oxide. A decrease in glass transition temperature (Tg) with NiO addition showed that the nickel oxide had acted as an intermediate in smaller quantities in the bioactive glass. The cell culture studies demonstrated that the samples containing low concentration of NiO from 0 to 1.65mol% were non-cytotoxic against osteoblast cells. Finally, this investigation clearly concluded that NiO doped bioactive glass would be potential biomaterials for biomedical applications. (Author)

  5. Mechanism study of organic antioxidant and inorganic salt on suppressing coal oxidation

    Institute of Scientific and Technical Information of China (English)

    YU Shui-jun; YU Ming-gao; JIA Hai-lin; ZUO Qiu-ling

    2007-01-01

    The advantages and disadvantages of Organic antioxidant and inorganic salt on suppressing coal oxidation were analyzed on the basis of the theory that coal oxidation mechanisms can be attributed to the free radical chain-type reaction mechanism.The inhibition curves on suppressing coal oxidation of the different type and different concentration of Organic antioxidant and inorganic salt were given through experimental study and data processing.Then some conclusions can be gained from the experimental study combining with theoretical analysis.First the inhibition mechanism of the organic antioxidant and inorganic salt is different.The former is that the chemical action is the dominant position.It can be called as the chain termination theory because the free radical is captured during coal oxidation.And the later is that the physical effect is the dominant position.It can be called as the decreasing-temperature theory because the liquid membrane which was formed by the inorganic salt can make coal body be the state of wetness and prevent oxygen from coal surface.Second the inhibition effect of the organic antioxidant is higher than the inorganic salt in the later period.But it is lower in the early period.

  6. Substrate Oxidation by Indoleamine 2,3-Dioxygenase: EVIDENCE FOR A COMMON REACTION MECHANISM.

    Science.gov (United States)

    Booth, Elizabeth S; Basran, Jaswir; Lee, Michael; Handa, Sandeep; Raven, Emma L

    2015-12-25

    The kynurenine pathway is the major route of L-tryptophan (L-Trp) catabolism in biology, leading ultimately to the formation of NAD(+). The initial and rate-limiting step of the kynurenine pathway involves oxidation of L-Trp to N-formylkynurenine. This is an O2-dependent process and catalyzed by indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase. More than 60 years after these dioxygenase enzymes were first isolated (Kotake, Y., and Masayama, I. (1936) Z. Physiol. Chem. 243, 237-244), the mechanism of the reaction is not established. We examined the mechanism of substrate oxidation for a series of substituted tryptophan analogues by indoleamine 2,3-dioxygenase. We observed formation of a transient intermediate, assigned as a Compound II (ferryl) species, during oxidation of L-Trp, 1-methyl-L-Trp, and a number of other substrate analogues. The data are consistent with a common reaction mechanism for indoleamine 2,3-dioxygenase-catalyzed oxidation of tryptophan and other tryptophan analogues.

  7. Reaction Mechanism and Control of Selectivity in Catalysis by Oxides: Some Challenges and Open Questions

    Directory of Open Access Journals (Sweden)

    Siglinda Perathoner

    2001-11-01

    Full Text Available Some aspects of the reaction mechanisms in multistep selective (ammoxidation reactions over oxide surfaces are discussed evidencing some of the challenges for surface science and theory in describing these reactions, and for applied catalysis in order to have a more in deep identification of the key factors governing surface reactivity and which may be used to improve catalytic performances. In particular, the role of chemisorbed species in the modification of the surface reactivity and the presence of multiple pathways of reaction are evidenced by comparing the behavior of V-based catalysts in C3-C4 alkanes and alkene oxidation.

  8. A study on synthesis and oxidation mechanism of mono-alkyl phosphate

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Oxidation of white phosphorus by peroxides to produce mono-alkyl phosphate in the alcoholic solution has been studied under non-and catalytic conditions. In this paper,the mechanism of the oxidation process was analyzed. The content of mono-alkyl phosphate in the product is affected by different types of alcoholic solution and peroxide solvent. The result shows the availability of the following order for the activity of the peroxide solvent and alcoholic solutions-tert-butyl hydroperoxide>(di) benzoyl perox...

  9. Kinetics and Mechanism of Oxidation of L-Cystine by Hexacyanoferrate(III in Alkaline Medium

    Directory of Open Access Journals (Sweden)

    Annapurna Nowduri

    2009-01-01

    Full Text Available Kinetics of oxidation of L-cystine by hexacyanoferrate(III was studied in alkaline medium at 30 °C. The reaction was followed spectrophotometrically at λmax = 420 nm. The reaction was found to be first order dependence each on [HCF(III] and [cystine]. It was found that the rate of the reaction increases with increase in [OH-]. The oxidation product of the reaction was found to be cysteic acid. A plausible mechanism has been proposed to account for the experimental results.

  10. Nitric oxide formation mechanisms, and their computation in pulverized coal combustion

    Energy Technology Data Exchange (ETDEWEB)

    Flour, I.; Dal Secco, S.

    1995-10-01

    This report consists of a review of several articles on nitric oxide emissions from coal-fired furnace. Three mechanisms have been identified, depending on the initial nitrogen sources and the composition of specific flame regions: - thermal-NO, formed from molecular nitrogen in the combustion products region at high temperature, - prompt-NO, formed from molecular nitrogen in the oxidation zone, - fuel-NO, formed from the fuel-bound nitrogen, partly during the coal pyrolysis (homogeneous reactions) and partly through reactions on the surface of the particle. In the combustion of pulverized coal, the fuel-NO mechanism accounts for the main source of nitric oxide formed. Detailed schemes of those reactions - when available - are too much complex to be used in tri-dimensional computation of pollutant emissions in furnaces of practical interest. According to the literature, reduced schemes seem to have been applied most frequently. The reaction schemes for the fuel-NO and the prompt-NO are based on the results of De Soete. For the homogeneous reactions, the intermediate species formed is assumed to be mainly HCN, leading to both formation and reduction reactions for NO, depending on the flame region. The formation of nitric oxide from the char-bound nitrogen, through heterogeneous reactions on the surface on the particle, is modelled by assuming the char-bound nitrogen to be released as HCN, with a rate proportional to char combustion. The released char nitrogen then reacts through the same path as the HCN released during pyrolysis. In the thermal-NO mechanism, nitric oxide is formed from molecular nitrogen, through the extended Zeldovich mechanism. This scheme contains radical species (O, N), which concentrations are assumed to be determined from the stationary condition or the equilibrium assumption. However, in spite of the use of reduced schemes for NO formation, the modelling of the important effect of the turbulent fluctuations has to be taken into account.

  11. Kinetics and Mechanism of Ruthenium(III) Catalyzed Oxidation of Butanone and Uncatalyzed Oxidation of Cychlohexanone by Cerium(IV) in Acid Sulphate Medium

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Priyamvada; Hemkar, Shalini; Khandelwal, C. L.; Sharma, P. D. [Univ. of Rajasthan, Jaipur (India)

    2012-02-15

    The kinetics of ruthenium(III) chloride catalyzed oxidation of butanone and uncatalyzed oxidation of cyclohexanone by cerium(IV) in sulphuric acid medium have been studied. The kinetic rate law(I) in case of butanone conforms to the proposed mechanism. Kinetics and activation parameters have been evaluated conventionally. Kinetically preferred mode of reaction is via ketonic and not the enolic forms.

  12. CLEPS 1.0: A new protocol for cloud aqueous phase oxidation of VOC mechanisms

    Science.gov (United States)

    Mouchel-Vallon, Camille; Deguillaume, Laurent; Monod, Anne; Perroux, Hélène; Rose, Clémence; Ghigo, Giovanni; Long, Yoann; Leriche, Maud; Aumont, Bernard; Patryl, Luc; Armand, Patrick; Chaumerliac, Nadine

    2017-03-01

    A new detailed aqueous phase mechanism named the Cloud Explicit Physico-chemical Scheme (CLEPS 1.0) is proposed to describe the oxidation of water soluble organic compounds resulting from isoprene oxidation. It is based on structure activity relationships (SARs) which provide global rate constants together with branching ratios for HOṡ abstraction and addition on atmospheric organic compounds. The GROMHE SAR allows the evaluation of Henry's law constants for undocumented organic compounds. This new aqueous phase mechanism is coupled with the MCM v3.3.1 gas phase mechanism through a mass transfer scheme between gas phase and aqueous phase. The resulting multiphase mechanism has then been implemented in a model based on the Dynamically Simple Model for Atmospheric Chemical Complexity (DSMACC) using the Kinetic PreProcessor (KPP) that can serve to analyze data from cloud chamber experiments and field campaigns. The simulation of permanent cloud under low-NOx conditions describes the formation of oxidized monoacids and diacids in the aqueous phase as well as a significant influence on the gas phase chemistry and composition and shows that the aqueous phase reactivity leads to an efficient fragmentation and functionalization of organic compounds.

  13. The effect of interlayer adhesion on the mechanical behaviors of macroscopic graphene oxide papers.

    Science.gov (United States)

    Gao, Yun; Liu, Lu-Qi; Zu, Sheng-Zhen; Peng, Ke; Zhou, Ding; Han, Bao-Hang; Zhang, Zhong

    2011-03-22

    High mechanical performances of macroscopic graphene oxide (GO) papers are attracting great interest owing to their merits of lightweight and multiple functionalities. However, the loading role of individual nanosheets and its effect on the mechanical properties of the macroscopic GO papers are not yet well understood. Herein, we effectively tailored the interlayer adhesions of the GO papers by introducing small molecules, that is, glutaraldehyde (GA) and water molecules, into the gallery regions. With the help of in situ Raman spectroscopy, we compared the varied load-reinforcing roles of nanosheets, and further predicted the Young's moduli of the GO papers. Systematic mechanical tests have proven that the enhancement of the tensile modulus and strength of the GA-treated GO paper arose from the improved load-bearing capability of the nanosheets. On the basis of Raman and macroscopic mechanical tests, the influences of interlayer adhesions on the fracture mechanisms of the strained GO papers were inferred.

  14. Amine oxidation mediated by lysine-specific demethylase 1: quantum mechanics/molecular mechanics insights into mechanism and role of lysine 661.

    Science.gov (United States)

    Karasulu, Bora; Patil, Mahendra; Thiel, Walter

    2013-09-11

    We report classical molecular dynamics (MD) simulations and combined quantum mechanics/molecular mechanics (QM/MM) calculations to elucidate the catalytic mechanism of the rate-determining amine oxidation step in the lysine-specific demethylase 1 (LSD1)-catalyzed demethylation of the histone tail lysine (H3K4), with flavin adenine dinucleotide (FAD) acting as cofactor. The oxidation of substrate lysine (sLys) involves the cleavage of an α-CH bond accompanied by the transfer of a hydride ion equivalent to FAD, leading to an imine intermediate. This hydride transfer pathway is shown to be clearly favored for sLys oxidation over other proposed mechanisms, including the radical (or single-electron transfer) route as well as carbanion and polar-nucleophilic mechanisms. MD simulations on six NVT ensembles (covering different protonation states of sLys and K661 as well as the K661M mutant) identify two possible orientations of the reacting sLys and FAD subunits (called "downward" and "upward"). Calculations at the QM(B3LYP-D/6-31G*)/CHARMM22 level provide molecular-level insights into the mechanism, helping to understand how LSD1 achieves the activation of the rather inert methyl-CH bond in a metal-free environment. Factors such as proper alignment of sLys (downward orientation), transition-state stabilization (due to the protein environment and favorable orbital interactions), and product stabilization via adduct formation are found to be crucial for facilitating the oxidative α-CH bond cleavage. The current study also sheds light on the role of important active-site residues (Y761, K661, and W695) and of the conserved water-bridge motif. The steric influence of Y761 helps to position the reaction partners properly, K661 is predicted to get deprotonated prior to substrate binding and to act as an active-site base that accepts a proton from sLys to enable the subsequent amine oxidation, and the water bridge that is stabilized by K661 and W695 mediates this proton

  15. Kinetics and mechanism of oxidation of aliphatic alcohols by tetrabutylammonium tribromide

    Indian Academy of Sciences (India)

    Manju Baghmar; Pradeep K Sharma

    2001-04-01

    Oxidation of nine primary aliphatic alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the polymerization of acrylonitrile. Tetrabutylammonium chloride has no effect on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The oxidation of [1,1-2H2]ethanol exhibits a substantial kinetic isotope effect. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The reaction is susceptible to both polar and steric effects of substituents. A mechanism involving transfer of a hydride ion in the ratedetermining step has been proposed.

  16. Kinetics and mechanism of the oxidation of some neutral and acidic -amino acids by tetrabutylammonium tribromide

    Indian Academy of Sciences (India)

    Raghvendra Shukla; Pradeep K Sharma; Kalyan K Banerji

    2004-03-01

    The oxidation of eleven amino acids by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid results in the formation of the corresponding carbonyl compounds and ammonia. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with some of the amino acids while others exhibit second-order dependence. It failed to induce polymerization of acrylonitrile. The effect of solvent composition indicate that the rate of reaction increases with increase in the polarity of the medium. Addition of tetrabutylammonium chloride has no effect on the rate of oxidation. Addition of bromide ion causes decrease in the oxidation rate but only to a limiting value. The reaction is susceptible to both polar and steric effects of the substituents. A suitable mechanism has been proposed.

  17. H2 O2-induced higher order chromatin degradation: A novel mechanism of oxidative genotoxicity

    Indian Academy of Sciences (India)

    Gregory W Konat

    2003-02-01

    The genotoxicity of reactive oxygen species (ROS) is well established. The underlying mechanism involves oxidation of DNA by ROS. However, we have recently shown that hydrogen peroxide (H2O2), the major mediator of oxidative stress, can also cause genomic damage indirectly. Thus, H2O2 at pathologically relevant concentrations rapidly induces higher order chromatin degradation (HOCD), i.e. enzymatic excision of chromatin loops and their oligomers at matrix-attachment regions. The activation of endonuclease that catalyzes HOCD is a signalling event triggered specifically by H2O2. The activation is not mediated by an influx of calcium ions, but resting concentrations of intracellular calcium ions are required for the maintenance of the endonuclease in an active form. Although H2O2-induced HOCD can efficiently dismantle the genome leading to cell death, under sublethal oxidative stress conditions H2O2-induced HOCD may be the major source of somatic mutations.

  18. Structural, mechanical and magneto-electronic properties of the ternary sodium palladium and platinum oxides

    Energy Technology Data Exchange (ETDEWEB)

    Sadiq, Saima [Malakand Univ., Chakdara Dir (Pakistan). Center for Computational Materials Science; Malakand Univ., Chakdara Dir (Pakistan). Dept. of Chemistry; Ali, Zahid; Ahmad, Iftikhar; Khan, Imad; Rehman, Gul [Malakand Univ., Chakdara Dir (Pakistan). Center for Computational Materials Science; Malakand Univ., Chakdara Dir (Pakistan). Dept. of Physics; Sadiq, Muhammad; Rehman, Najeeb Ur [Malakand Univ., Chakdara Dir (Pakistan). Dept. of Chemistry

    2015-07-01

    Ternary palladium and platinum oxides NaPd{sub 3}O{sub 4} and NaPt{sub 3}O{sub 4} are studied theoretically using DFT. The calculated structural parameters and geometry are found consistent with the experiments. The mechanical properties analysis show that both compounds are elastically stable; anisotropic and reveal the ductile nature. Electronic cloud explain that the chemical bond between Na and Pd/Pt is ionic, whereas between O and Pd/Pt is covalent. The electronic band structures and densities of states demonstrate that these compounds are metals. The d-state splitting explains the origin of the electronic behaviour of these oxides. The optimised magnetic phase energies and magnetic susceptibility confirm that these oxides are paramagnetic metals.

  19. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    Science.gov (United States)

    Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.

    2014-05-01

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  20. Kinetics and mechanism of oxidation of aliphatic primary alcohols by quinolinium bromochromate

    Indian Academy of Sciences (India)

    Sonu Saraswat; Vinita Sharma; K K Banerji

    2003-02-01

    Oxidation of nine aliphatic primary alcohols by quinolinium bromochromate (QBC) in dimethylsulphoxide leads to the formation of the corresponding aldehydes. The reaction is first order with respect to both QBC and the alcohol. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: obs = + [H+]. The oxidation of [1,1-2H2]ethanol (MeCD2OH) exhibits a substantial primary kinetic isotope effect. The reaction has been studied in nineteen different organic solvents. The solvent effect was analysed using Taft’s and Swain's multiparametric equations. The rate of oxidation is susceptible to both polar and steric effects of the substituents. A suitable mechanism has been proposed.

  1. Mechanical grooving of oxidized porous silicon to reduce the reflectivity of monocrystalline silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Zarroug, A.; Dimassi, W.; Ouertani, R.; Ezzaouia, H. [Laboratoire de Photovoltaique, Centre des Recherches et des Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)

    2012-10-15

    In this work, we are interested to use oxidized porous silicon (ox-PS) as a mask. So, we display the creating of a rough surface which enhances the absorption of incident light by solar cells and reduces the reflectivity of monocrystalline silicon (c-Si). It clearly can be seen that the mechanical grooving enables us to elaborate the texturing of monocrystalline silicon wafer. Results demonstrated that the application of a PS layer followed by a thermal treatment under O2 ambient easily gives us an oxide layer of uniform size which can vary from a nanometer to about ten microns. In addition, the Fourier transform infrared (FTIR) spectroscopy investigations of the PS layer illustrates the possibility to realize oxide layer as a mask for porous silicon. We found also that this simple and low cost method decreases the total reflectivity (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Investigation of agglomerated Cu seed on Cu oxidation after chemical mechanical planarization

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Jeng-Yu, E-mail: jylin@ttu.edu.tw [Department of Chemical Engineering, Tatung University, Taipei 104, Taiwan (China); Chou, Shu-Wei [Department of Chemical Engineering, Tatung University, Taipei 104, Taiwan (China); Cheng, Min-Yuan [TSMC, No. 8, Li-Hsin Rd. 6, Science-Based Industrial Park, Hsinchu 300-77, Taiwan (China)

    2010-11-01

    After chemical mechanical planarization (CMP), the reason which caused the formation of Cu-oxide defects at the interface between Cu deposit and TaN barrier layer has been studied. The experimental results of atomic force microscopy, secondary ion mass spectroscopy, X-ray diffraction demonstrated that the agglomeration phenomenon was found on Cu seed in the thickness of only 10 nm, thus resulting in the electrodeposited Cu film with more abundant C impurities at Cu/TaN interface and lower (1 1 1)/(2 0 0) ratio compared to the thick one (30 nm). Therefore it caused the Cu deposit with poor corrosion resistance and then the Cu-oxide defects were easily formed after CMP. As a result, the correlation between Cu-oxide defects at the Cu/TaN interface and the agglomeration on Cu seed layer was proposed herein.

  3. An evolutionary comparative scan for longevity-related oxidative stress resistance mechanisms in homeotherms.

    Science.gov (United States)

    Pamplona, Reinald; Barja, Gustavo

    2011-10-01

    Key mechanisms relating oxidative stress to longevity from an interespecies comparative approach are reviewed. Long-lived animal species show low rates of reactive oxygen species (ROS) generation and oxidative damage at their mitochondria. Comparative physiology also shows that the specific compositional pattern of tissue macromolecules (proteins, lipids and nucleic acids) in long-lived animal species gives them an intrinsically high resistance to modification that likely contributes to their superior longevity. This is obtained in the case of lipids by decreasing the degree of fatty acid unsaturation, and in the case of proteins by lowering their methionine content. These findings are also substantiated from a phylogenomic approach. Nutritional or/and pharmacological interventions focused to modify some of these molecular traits were translated with modifications in animal longevity. It is proposed that natural selection tends to decrease the mitochondrial ROS generation and to increase the molecular resistance to the oxidative damage in long-lived species.

  4. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Gupta, Sanjay D. [V. B. Institute of Science, Department of Physics, C. U. Shah University, Wadhwan City - 363030, Surendranagar (India); Jha, Prafulla K., E-mail: prafullaj@yahoo.com [Department of Physics, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara-390002 (India)

    2014-05-28

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  5. Progesterone modulates the LPS-induced nitric oxide production by a progesterone-receptor independent mechanism.

    Science.gov (United States)

    Wolfson, Manuel Luis; Schander, Julieta Aylen; Bariani, María Victoria; Correa, Fernando; Franchi, Ana María

    2015-12-15

    Genital tract infections caused by Gram-negative bacteria induce miscarriage and are one of the most common complications of human pregnancy. LPS administration to 7-day pregnant mice induces embryo resorption after 24h, with nitric oxide playing a fundamental role in this process. We have previously shown that progesterone exerts protective effects on the embryo by modulating the inflammatory reaction triggered by LPS. Here we sought to investigate whether the in vivo administration of progesterone modulated the LPS-induced nitric oxide production from peripheral blood mononuclear cells from pregnant and non-pregnant mice. We found that progesterone downregulated LPS-induced nitric oxide production by a progesterone receptor-independent mechanism. Moreover, our results suggest a possible participation of glucocorticoid receptors in at least some of the anti-inflammatory effects of progesterone.

  6. Light induced oxidative water splitting in photosynthesis: energetics, kinetics and mechanism.

    Science.gov (United States)

    Renger, Gernot

    2011-01-01

    The essential steps of photosynthetic water splitting take place in Photosystem II (PSII) and comprise three different reaction sequences: (i) light induced formation of the radical pair P680(+)Q(A)(-), (ii) P680(+) driven oxidative water splitting into O(2) and four protons, and (iii) two step plastoquinone reduction to plastoquinol by Q(A)(-). This mini-review briefly summarizes our state of knowledge on energetics, kinetics and mechanism of oxidative water splitting. Essential features of the two types of reactions involved are described: (a) P680(+) reduction by the redox active tyrosine Y(z) and (b) sequence of oxidation steps induced by Y(z)(ox) in the water-oxidizing complex (WOC). The rate of the former reaction is limited by the non-adiabatic electron transfer (NET) step and the multi-phase kinetics shown to originate from a sequence of relaxation processes. In marked contrast, the rate of the stepwise oxidation by Y(z)(ox) of the WOC up to the redox level S(3) is not limited by NET but by trigger reactions which probably comprise proton shifts and/or conformational changes. The overall rate of the final reaction sequence leading to formation and release of O(2) is assumed to be limited by the electron transfer step from the S(3) state of WOC to Y(z)(ox) due to involvement of an endergonic redox equilibrium. Currently discussed controversial ideas on possible pathways are briefly outlined. Several crucial points of the mechanism of oxidative water splitting, like O-O bond formation, role of local proton shift(s), details of hydrogen bonding, are still not clarified and remain a challenging topic of future research.

  7. Mechanisms of Action Involved in Ozone Therapy: Is healing induced via a mild oxidative stress?

    Science.gov (United States)

    Sagai, Masaru; Bocci, Velio

    2011-12-20

    The potential mechanisms of action of ozone therapy are reviewed in this paper. The therapeutic efficacy of ozone therapy may be partly due the controlled and moderate oxidative stress produced by the reactions of ozone with several biological components. The line between effectiveness and toxicity of ozone may be dependent on the strength of the oxidative stress. As with exercise, it is well known that moderate exercise is good for health, whereas excessive exercise is not.Severe oxidative stress activates nuclear transcriptional factor kappa B (NFκB), resulting in an inflammatory response and tissue injury via the production of COX2, PGE2, and cytokines. However, moderate oxidative stress activates another nuclear transcriptional factor, nuclear factor-erythroid 2-related factor 2 (Nrf2). Nrf2 then induces the transcription of antioxidant response elements (ARE). Transcription of ARE results in the production of numerous antioxidant enzymes, such as SOD, GPx, glutathione-s-transferase(GSTr), catalase (CAT), heme-oxygenase-1 (HO-1), NADPH-quinone-oxidoreductase (NQO-1), phase II enzymes of drug metabolism and heat shock proteins (HSP). Both free antioxidants and anti-oxidative enzymes not only protect cells from oxidation and inflammation but they may be able to reverse the chronic oxidative stress. Based on these observations, ozone therapy may also activate Nrf2 via moderate oxidative stress, and suppress NFκB and inflammatory responses. Furthermore, activation of Nrf2 results in protection against neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. Mild immune responses are induced via other nuclear transcriptional factors, such as nuclear factor of activated T-cells (NFAT) and activated protein-1 (AP-1).Additionally, the effectiveness of ozone therapy in vascular diseases may also be explained by the activation of another nuclear transcriptional factor, hypoxia inducible factor-1α (HIF-1a), which is also induced via moderate oxidative

  8. Mechanisms of Action Involved in Ozone Therapy: Is healing induced via a mild oxidative stress?

    Directory of Open Access Journals (Sweden)

    Sagai Masaru

    2011-12-01

    Full Text Available Abstract The potential mechanisms of action of ozone therapy are reviewed in this paper. The therapeutic efficacy of ozone therapy may be partly due the controlled and moderate oxidative stress produced by the reactions of ozone with several biological components. The line between effectiveness and toxicity of ozone may be dependent on the strength of the oxidative stress. As with exercise, it is well known that moderate exercise is good for health, whereas excessive exercise is not. Severe oxidative stress activates nuclear transcriptional factor kappa B (NFκB, resulting in an inflammatory response and tissue injury via the production of COX2, PGE2, and cytokines. However, moderate oxidative stress activates another nuclear transcriptional factor, nuclear factor-erythroid 2-related factor 2 (Nrf2. Nrf2 then induces the transcription of antioxidant response elements (ARE. Transcription of ARE results in the production of numerous antioxidant enzymes, such as SOD, GPx, glutathione-s-transferase(GSTr, catalase (CAT, heme-oxygenase-1 (HO-1, NADPH-quinone-oxidoreductase (NQO-1, phase II enzymes of drug metabolism and heat shock proteins (HSP. Both free antioxidants and anti-oxidative enzymes not only protect cells from oxidation and inflammation but they may be able to reverse the chronic oxidative stress. Based on these observations, ozone therapy may also activate Nrf2 via moderate oxidative stress, and suppress NFκB and inflammatory responses. Furthermore, activation of Nrf2 results in protection against neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. Mild immune responses are induced via other nuclear transcriptional factors, such as nuclear factor of activated T-cells (NFAT and activated protein-1 (AP-1. Additionally, the effectiveness of ozone therapy in vascular diseases may also be explained by the activation of another nuclear transcriptional factor, hypoxia inducible factor-1α (HIF-1a, which is also induced via

  9. Kinetics and mechanism of heterogeneous oxidation of sulfur dioxide by ozone on surface of calcium carbonate

    Directory of Open Access Journals (Sweden)

    L. Li

    2006-01-01

    Full Text Available Sulfate particles play a key role in the air quality and the global climate, but the heterogeneous formation mechanism of sulfates on surfaces of atmospheric particles is not well established. Carbonates, which act as a reactive component in mineral dust due to their special chemical properties, may contribute significantly to the sulfate formation by heterogeneous processes. This paper presents a study on the oxidation of SO2 by O3 on CaCO3 particles. Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS, the formation of sulfite and sulfate on the surface was identified, and the roles of O3 and water in oxidation processes were determined. The results showed that in the presence of O3, SO2can be oxidized to sulfate on the surface of CaCO3 particles. The reaction is first order in SO2 and zero order in O3. The reactive uptake coefficient for SO2 [(0.6–9.8×1014 molecule cm-3] oxidation by O3 [(1.2–12×1014 molecule cm-3] was determined to be (1.4±0.3×10-7 using the BET area as the reactive area and (7.7±1.6×10-4 using the geometric area. A two-stage mechanism that involves adsorption of SO2 followed by O3 oxidation is proposed and the adsorption of SO2 on the CaCO3 surface is the rate-determining step. The proposed mechanism can well explain the experiment results. The atmospheric implications were explored based on a box model calculation. It was found that the heterogeneous reaction might be an important pathway for sulfate formation in the atmosphere.

  10. Mechanisms of realization of THz-waves of nitrogen oxide occurrence physiological effects

    Directory of Open Access Journals (Sweden)

    Vyacheslav F. Kirichuk

    2013-11-01

    Full Text Available In this review, there is generalized material of many experimental researches in interaction of THz-waves molecular emission and absorption spectrum (MEAS of nitrogen oxide occurrence with bioobjects. Thrombocytes and experimental animals were used as bioobjects. The experiments let indicate changes caused by THz-waves: at the cellular, tissular, system, organismic levels. There are all data of changes in physiological mechanisms of reglations at all levels: autocrine, paracrine, endocrine and nervous. There is a complex overview of experimental material firstly performed in the article. There had been shown that the effect of THz-waves of the given occurrence is realized by the changed activity of nitroxidergic system. It had been proved that THz-waves of nitrogen oxide occurrence can stimulate nitrogen oxide producing in organs and tissues in condition of its low concentration. Possible mechanisms of antiaggregative effect of the given waves had been described. There had been shown the possibility of regulating of vascular tone and system hemodynamics with the help of the studying these frequencies. The represented data of lipid peroxidation and enzymatic and nonenzymatic components of organism system under the influence of THz-waves of nitrogen oxide occurrence in stress conditions. Besides, there were shown changes of stress-regulating system activity and in concentration of important mediators - catecholamines and glucocorticosteroids. These data let characterize mechanism of realization of THz-waves basic effects. The research had shown the possibility of THz-waves of nitrogen oxide occurrence usage as a method of natural physiological noninvasive regulation of significant organism functions.

  11. Kinetics and Mechanism of Oxidation of t-Butylbenzylamine by Diperiodatoargentate(III in Aqueous Alkali

    Directory of Open Access Journals (Sweden)

    Mahantesh A. Angadi

    2012-01-01

    Full Text Available t-Butylbenzylamine (t-BA is used as a free base in the synthesis of salbutamol drug. Its mechanism of oxidation was proposed from kinetic studies. The kinetics of oxidation of t-butylbenzylamine by diperiodatoargentate(III (DPA was studied spectrophotometrically by monitoring decrease in absorbance of DPA. The reaction was found to be first order each in [DPA] and [t-BA]. The effect of alkali concentration in a wide range on rate of reaction was studied. The rate of reaction was found to be increased with increase in [OH–] in the lower range of [OH–], decreasing effect in the middle range and at higher range again increasing effect on rate of reaction was observed. The added periodate retarded the rate of reaction. The polymerization test revealed that oxidation was occurred with the intervention free radical. A suitable mechanism was proposed for a middle range of [OH–]. The active species of silver(III periodate for all the three different stages of [OH–] are assayed. Rate law was derived and verified. The oxidative product of t-BA was characterized by LC-ESI-MS spectra.

  12. Mechanism and kinetics of the oxidation of synthetic alpha-NiS

    Directory of Open Access Journals (Sweden)

    BOYAN BOYANOV

    2008-02-01

    Full Text Available The results of an investigation of the mechanism and kinetics of the oxidation process of synthetic a-NiS are presented in this paper. The mechanism of a-NiS oxidation was investigated based on the comparative analysis of DTA–TG–DTG and XRD results, as well as the constructed phase stability diagrams (PSD for the Ni–S–O system. The kinetic investigations of the oxidation process were performed under isothermal conditions (temperature range 823–1073 K. The obtained degrees of desulfurization were used in the calculation process according to the Sharp model and the kinetic parameters, including the activation energies and the rate constants of the characteristic reactions, for the oxidation of a-NiS were determined. These results enabled the formulation of a kinetic equation for the desulfurization process: ‑ln(1−a = k1t = 27.89 exp(–9860/Tt, with an activation energy of 82±4 kJ mol-1, for the first stage of the process and –ln (1 − a = k2t = 1.177 exp(–4810/Tt, with an activation energy of 40±2 kJ mol-1, for the second stage.

  13. Effects of cryomilling on the microstructures and high temperature mechanical properties of oxide dispersion strengthened steel

    Science.gov (United States)

    Gwon, Jin-Han; Kim, Jeoung-Han; Lee, Kee-Ahn

    2015-04-01

    The effects of cryomilling on the microstructures and high temperature mechanical properties of oxide dispersion-strengthened (ODS) steel were examined. Cryomilling was newly tried on this ODS steel to control oxides, grains, and dislocation microstructures. Fe-14Cr-3W-0.4Ti (wt.%) alloy powder and 0.3 wt.%Y2O3 powder were mixed and were mechanically alloyed (MA) through ball milling at each of room temperature (RT) and -150 °C and then hot isostatic pressing (HIP), hot rolling, and annealing processes were implemented to manufacture two types of ODS ferritic steel, K1 (RT) and K4 (-150 °C). Oxide particles were shown to be finer and more uniformly distributed in K4 (5-10 nm size distribution) than in K1 (average size 30 nm). The two alloys were subjected to high temperature compression (RT ∼ 900 °C) tests. K4 represented higher yield strength under all temperature conditions. However, K4 showed rapid strength decreases at high temperatures exceeding 700 °C and showed similar levels of strengths to K1 at 900 °C. This is considered attributable to the fact that although cryomilling increased the number density of oxide particles, it simultaneously reduced grain sizes too much, so that grain boundary weakening at high temperatures could not be sufficiently prevented.

  14. Mechanisms and evolution of oxidative sulfur metabolism in green sulfur bacteria

    Directory of Open Access Journals (Sweden)

    Lea Haarup Gregersen

    2011-05-01

    Full Text Available Green sulfur bacteria (GSB constitute a closely related group of photoautotrophic and thiotrophic bacteria with limited phenotypic variation. They typically oxidize sulfide and thiosulfate to sulfate with sulfur globules as an intermediate. Based on genome sequence information from 15 strains, the distribution and phylogeny of enzymes involved in their oxidative sulfur metabolism was investigated. At least one homolog of sulfide:quinone oxidoreductase (SQR is present in all strains. In all sulfur-oxidizing GSB strains except the earliest diverging Chloroherpeton thalassium, the sulfide oxidation product is further oxidized to sulfite by the dissimilatory sulfite reductase (DSR system. This system consists of components horizontally acquired partly from sulfide-oxidizing and partly from sulfate-reducing bacteria. Depending on the strain, the sulfite is probably oxidized to sulfate by one of two different mechanisms that have different evolutionary origins: adenosine-5’-phosphosulfate reductase (APR or polysulfide reductase-like complex 3 (PSRLC3. Thiosulfate utilization by the SOX system in GSB has apparently been acquired horizontally from proteobacteria. SoxCD does not occur in GSB, and its function in sulfate formation in other bacteria has been replaced by the DSR system in GSB. Sequence analyses suggested that the conserved soxJXYZAKBW gene cluster was horizontally acquired by Chlorobium phaeovibrioides DSM 265 from the Chlorobaculum lineage and that this acquisition was mediated by a mobile genetic element. Thus, the last common ancestor of currently known GSB was probably photoautotrophic, hydrogenotrophic, and contained SQR but not DSR or SOX. In addition, the predominance of the Chlorobium-Chlorobaculum-Prosthecochloris lineage among cultured GSB could be due to the horizontally acquired DSR and SOX systems. Finally, based upon structural, biochemical, and phylogenetic analyses, a uniform nomenclature is suggested for sqr genes in

  15. Quantum chemical study of the mechanisms of oxidation of ethylene by Molybdyl and Tungstyl Chloride

    Indian Academy of Sciences (India)

    RICHARD TIA; EVANS ADEI; JOSEPH BAIDOO; JULIANA EDOR

    2016-05-01

    The mechanisms of oxidation of olefins with $MoO_{2}Cl_{2}$ and $WO_{2}Cl_{2}$ are studied with DFT. Theformation of epoxide from these reactions is not very feasible by any of the postulated paths. If the epoxideprecursor will form at all, it will arise via initial $[3+2]_{O},_{Cl}$ addition of ethene to $MoO_{2}Cl_{2}$ and $WO_{2}Cl_{2}$ to form an intermediate, followed by re-arrangement to form the precursor, from which the epoxide can begenerated by hydrolysis. The chlorohydrin precursor was also found to originate from $[3+2]_{O},_{Cl}$ addition ofethene to $MoO_{2}Cl_{2}$ . The results also indicate that a dichloride is not a likely product in the oxidation of ethyleneby molybdyl chloride. However, in the case of WO2Cl2, the formation of a dichloride may not be precluded.The formation of acetaldehyde and vinyl alcohol from the oxidation of ethylene does not appear energeticallyfeasible with $MoO_{2}Cl_{2}$ , but appears thermodynamically plausible with WO2Cl2. Thus, the oxidation ofethylene with $MoO_{2}Cl_{2}$ will most likely lead to the formation of chlorohydrins predominantly via $[3+2]_{O},_{Cl}$ addition; oxidation with WO2Cl2 may also form chlorohydrins, but only extremely slowly. The oxyhalidesMO2Cl2 become weaker oxidants in the order CrO2Cl2 >>$MoO_{2}Cl_{2}$ >$WO_{2}Cl_{2}$ . Corresponding to this, reactionsinvolving reduction of the metal [3 + 2] and [2+1] show a sharp increase in barrier going from Cr to W;reactions without a change in metal oxidation state ([2 + 2]) show much smaller variations, which are possiblymainly determined by sterics.

  16. Mechanism of Copper/Azodicarboxylate-Catalyzed Aerobic Alcohol Oxidation: Evidence for Uncooperative Catalysis.

    Science.gov (United States)

    McCann, Scott D; Stahl, Shannon S

    2016-01-13

    Cooperative catalysis between Cu(II) and redox-active organic cocatalysts is a key feature of important chemical and enzymatic aerobic oxidation reactions, such as alcohol oxidation mediated by Cu/TEMPO and galactose oxidase. Nearly 20 years ago, Markó and co-workers reported that azodicarboxylates, such as di-tert-butyl azodicarboxylate (DBAD), are effective redox-active cocatalysts in Cu-catalyzed aerobic alcohol oxidation reactions [Markó, I. E., et al. Science 1996, 274, 2044], but the nature of the cooperativity between Cu and azodicarboxylates is not well understood. Here, we report a mechanistic study of Cu/DBAD-catalyzed aerobic alcohol oxidation. In situ infrared spectroscopic studies reveal a burst of product formation prior to steady-state catalysis, and gas-uptake measurements show that no O2 is consumed during the burst. Kinetic studies reveal that the anaerobic burst and steady-state turnover have different rate laws. The steady-state rate does not depend on [O2] or [DBAD]. These results, together with other EPR and in situ IR spectroscopic and kinetic isotope effect studies, reveal that the steady-state mechanism consists of two interdependent catalytic cycles that operate in sequence: a fast Cu(II)/DBAD pathway, in which DBAD serves as the oxidant, and a slow Cu(II)-only pathway, in which Cu(II) is the oxidant. This study provides significant insight into the redox cooperativity, or lack thereof, between Cu and redox-active organic cocatalysts in aerobic oxidation reactions.

  17. Reaction Mechanism for m-Xylene Oxidation in the Claus Process by Sulfur Dioxide.

    Science.gov (United States)

    Sinha, Sourab; Raj, Abhijeet; Al Shoaibi, Ahmed S; Chung, Suk Ho

    2015-09-24

    In the Claus process, the presence of aromatic contaminants such benzene, toluene, and xylenes (BTX), in the H2S feed stream has a detrimental effect on catalytic reactors, where BTX form soot particles and clog and deactivate the catalysts. Among BTX, xylenes are proven to be most damaging contaminant for catalysts. BTX oxidation in the Claus furnace, before they enter catalyst beds, provides a solution to this problem. A reaction kinetics study on m-xylene oxidation by SO2, an oxidant present in Claus furnace, is presented. The density functional theory is used to study the formation of m-xylene radicals (3-methylbenzyl, 2,6-dimethylphenyl, 2,4-dimethylphenyl, and 3,5-dimethylphenyl) through H-abstraction and their oxidation by SO2. The mechanism begins with SO2 addition on the radicals through an O-atom rather than the S-atom with the release of 180.0-183.1 kJ/mol of reaction energies. This exothermic reaction involves energy barriers in the range 3.9-5.2 kJ/mol for several m-xylene radicals. Thereafter, O-S bond scission takes place to release SO, and the O-atom remaining on aromatics leads to CO formation. Among four m-xylene radicals, the resonantly stabilized 3-methylbenzyl exhibited the lowest SO2 addition and SO elimination rates. The reaction rate constants are provided to facilitate Claus process simulations to find conditions suitable for BTX oxidation.

  18. Propene metathesis over silica-supported tungsten oxide catalyst-catalyst induction mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Basrur, A.G.; Patwardhan, S.R.; Vyas, S.N. (Indian Inst. of Tech., Bombay (India))

    1991-01-01

    The propene metathesis reaction was studied from the point of view of elucidating the mechanism of catalyst induction and establishing conditions for maximum activity. Instrumental techniques such as ESR, IR, and TPD were used to study the various aspects. During catalyst induction, trace quantities of acetone and acetaldehyde were detected in the product stream, indicating that lattice oxygen from tungsten oxide might be responsible for these products. Induction appeared to proceed via two steps since pretreatment of the catalyst with nitrogen and hydrogen yielded a decreased amount of acetone in the latter case whereas acetaldehyde remained unaffected. ESR studies indicated some interaction between tungsten oxide and silica at the catalyst preparatory stage as well as stabilization of reduced tungsten species on the catalyst after its use and regeneration. Catalyst activity appeared to depend on conditions of pretreatment. Change in nitrogen pretreatment temperature from 500 to 600{sup o}C resulted in transition from strong to negligible external mass transfer behavior of the catalyst. TPD studies in this context showed possible loss of lattice oxygen from tungsten oxide under the above-mentioned conditions of catalyst pretreatment. ESR studies indicated the reduction of WO{sub 3} to a nonstoichiometric oxidation state. Hence catalytic activity appears to be related to the nonstoichiometric state of tungsten oxide, which may be WO{sub 2.9} (as deduced from the blue-violet color of the used catalyst).

  19. Mechanisms of carbon nanotube-induced toxicity: Focus on oxidative stress

    Energy Technology Data Exchange (ETDEWEB)

    Shvedova, Anna A., E-mail: ats1@cdc.gov [Pathology and Physiology Research Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, University of Rome “Tor Vergata”, Rome (Italy); Department of Physiology and Pharmacology, West Virginia University, Morgantown, WV, University of Rome “Tor Vergata”, Rome (Italy); Pietroiusti, Antonio [Department of Biopathology, University of Rome “Tor Vergata”, Rome (Italy); Fadeel, Bengt [Division of Molecular Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm (Sweden); Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA (United States); Kagan, Valerian E. [Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA (United States)

    2012-06-01

    Nanotechnologies are emerging as highly promising technologies in many sectors in the society. However, the increasing use of engineered nanomaterials also raises concerns about inadvertent exposure to these materials and the potential for adverse effects on human health and the environment. Despite several years of intensive investigations, a common paradigm for the understanding of nanoparticle-induced toxicity remains to be firmly established. Here, the so-called oxidative stress paradigm is scrutinized. Does oxidative stress represent a secondary event resulting inevitably from disruption of biochemical processes and the demise of the cell, or a specific, non-random event that plays a role in the induction of cellular damage e.g. apoptosis? The answer to this question will have important ramifications for the development of strategies for mitigation of adverse effects of nanoparticles. Recent examples of global lipidomics studies of nanoparticle-induced tissue damage are discussed along with proteomics and transcriptomics approaches to achieve a comprehensive understanding of the complex and interrelated molecular changes in cells and tissues exposed to nanoparticles. We also discuss instances of non-oxidative stress-mediated cellular damage resulting from direct physical interference of nanomaterials with cellular structures. -- Highlights: ► CNT induced non-random oxidative stress associated with apoptosis. ► Non-oxidative mechanisms for cellular toxicity of carbon nanotubes. ► Biodegradation of CNT by cells of innate immune system. ► “Omics”-based biomarkers of CNT exposures.

  20. Thermally evaporated mechanically hard tin oxide thin films for opto-electronic apllications

    Science.gov (United States)

    Tripathy, Sumanta K.; Rajeswari, V. P.

    2014-01-01

    Tungsten doped tin oxide (WTO) and Molybdenum doped tin oxide (MoTO) thin film were deposited on corn glass by thermal evaporation method. The films were annealed at 350°C for one hour. Structural analysis using Xray diffraction data shows both the films are polycrystalline in nature with monoclinic structure of tin oxide, Sn3O4, corresponding to JCPDS card number 01-078-6064. SEM photograph showed that both the films have spherical grains with size in the range of 20-30 nm. Compositional analysis was carried out using EDS which reveals the presence of Sn, O and the dopant Mo/W only thereby indicating the absence of any secondary phase in the films. The films are found to contain nearly 6 wt% of Mo, 8 wt% of W as dopants respectively. The transmission pattern for both the films in the spectral range 200 - 2000 nm shows that W doping gives a transparency of nearly 80% from 380 nm onwards while Mo doping has less transparency of 39% at 380nm. Film hardness measurement using Triboscope shows a film hardness of about 9-10 GPa for both the films. It indicates that W or M doping in tin oxide provides the films the added advantage of withstanding the mechanical wear and tear due to environmental fluctuations By optimizing the optical and electrical properties, W/Mo doped tin oxide films may be explored as window layers in opto-electronic applications such as solar cells.

  1. Reaction mechanism for the free-edge oxidation of soot by O 2

    KAUST Repository

    Raj, Abhijeet

    2012-11-01

    The reaction pathways for the oxidation by O 2 of polycyclic aromatic hydrocarbons present in soot particles are investigated using density functional theory at B3LYP/6-311++G(d,p) level of theory. For this, pyrene radical (4-pyrenyl) is chosen as the model molecule, as most soot models present in the literature employ the reactions involving the conversion of 4-pyrenyl to 4-phenanthryl by O 2 and OH to account for soot oxidation. Several routes for the formation of CO and CO 2 are proposed. The addition of O 2 on a radical site to form a peroxyl radical is found to be barrierless and exothermic with reaction energy of 188kJ/mol. For the oxidation reaction to proceed further, three pathways are suggested, each of which involve the activation energies of 104, 167 and 115kJ/mol relative to the peroxyl radical. The effect of the presence of H atom on a carbon atom neighboring the radical site on the energetics of carbon oxidation is assessed. Those intermediate species formed during oxidation with seven-membered rings or with a phenolic group are found to be highly stable. The rate constants evaluated using transition state theory in the temperature range of 300-3000K for the reactions involved in the mechanism are provided. © 2012 The Combustion Institute.

  2. Epiphytes modulate Posidonia oceanica photosynthetic production, energetic balance, antioxidant mechanisms and oxidative damage

    Directory of Open Access Journals (Sweden)

    Monya Mendes Costa

    2015-12-01

    Full Text Available Epiphytes impose physical barriers to light penetration into seagrass leaves causing shading, which may decrease the production of oxygen reactive species (ROS, but also constitute a physical aggression that may trigger the production of ROS, leading to oxidative damage. Here we investigate the effects of epiphytes on Posidonia oceanica under both interactive perspectives, light attenuation and oxidative stress. Specifically the role of epiphytes in net photosynthesis, chlorophyll a and b, photoprotection (Violaxanthin+Anteraxanthin+Zeaxanthin cycle, soluble sugar and starch contents, enzymatic (ascorbate peroxidase (APX and dehydroascorbate reductase (DHAR and global (trolox equivalent antioxidant capacity (TEAC and oxygen radical antioxidant capacity (ORAC antioxidant responses, phenolics and oxidative damage (malondialdehyde are tested. Leaves with epiphytes showed higher chlorophyll b and lower content in VAZ cycle carotenoids. Epiphyte shading was the probable reason for the lower VAZ de-epoxidation-ratio of leaves with epiphytes. In spite of being shaded, leaves with epiphytes showed higher antioxidant levels, indicating that epiphytes trigger the production of ROS. Both ORAC and TEAC and also APX and DHAR activities were higher in leaves with epiphytes, indicating that this response was related with its presence. Malondialdehyde concentrations also suggest oxidative damage caused by epiphytes. We conclude that the epiphyte load causes oxidative stress in P. oceanica and the mechanisms to scavenge ROS were not completely effective to avoid cell damage.

  3. Detailed chemical kinetic mechanism for the oxidation of biodiesel fuels blend surrogate.

    Energy Technology Data Exchange (ETDEWEB)

    Herbinet, O; Pitz, W J; Westbrook, C K

    2009-07-21

    Detailed chemical kinetic mechanisms were developed and used to study the oxidation of two large unsaturated esters: methyl-5-decenoate and methyl-9-decenoate. These models were built from a previous methyl decanoate mechanism and were compared with rapeseed oil methyl esters oxidation experiments in a jet stirred reactor. A comparative study of the reactivity of these three oxygenated compounds was performed and the differences in the distribution of the products of the reaction were highlighted showing the influence of the presence and the position of a double bond in the chain. Blend surrogates, containing methyl decanoate, methyl-5-decenoate, methyl-9-decenoate and n-alkanes, were tested against rapeseed oil methyl esters and methyl palmitate/n-decane experiments. These surrogate models are realistic kinetic tools allowing the study of the combustion of biodiesel fuels in diesel and homogeneous charge compression ignition engines.

  4. [Oxidative stress in mechanism of psychosomatic disorders realization in duodenal ulcer in students].

    Science.gov (United States)

    Oparin, A G; Oparin, A A

    2005-01-01

    To study the role of oxidative stress in mechanism of psychosomatic disorders involvement in pathogenesis of ulcerogenesis. Psychosomatic disorders (PSD) and oxidative stress (OS) were assessed in 120 students with duodenal ulcer (DU) who had no concomitant pathology. Examination for PSD included interviewing by questionnaires. OS was judged by the level of lipid peroxidation products (malonic dialdehyde and dienic conjugates) and antioxidant activity--by glutathion peroxidase and superoxidedismutase. Melatonin was measured by enzyme immunoassay. A close correlation was discovered between the severity and features of PSD, lowering of melatonin, severity of OS and clinical features of the disease. DU students develop PSD which become leading factors of ulcerogenesis. One of the mechanisms of their participation in ulcerogenesis may be related with lowering of melatonin which is a potent stress regulator and corrector of lipid peroxidation and antioxidant activity.

  5. Acetone gas sensing mechanism on zinc oxide surfaces: A first principles calculation

    Science.gov (United States)

    Sadeghian Lemraski, M.; Nadimi, E.

    2017-03-01

    Semiconducting metal oxide gas sensors have attracted growing interest as a result of their outstanding performance in the bio and industrial applications. Nevertheless, the sensing mechanism is yet not totally understood. In this study, we extensively investigate the adsorption mechanism of acetone molecule on ZnO-based thin film sensors by performing ab initio density functional theory calculations and employing quantum molecular dynamic simulations. Since the sensitivity of a metal oxide sensor is exceedingly depends on molecular oxygen exposure and operating temperature, we explore the competitive adsorption of acetone and oxygen molecule on the most stable orientation of ZnO surface (10 1 ̅ 0) at different temperatures. Results indicate that at elevated temperatures acetone gains required thermal energy to remove preadsorbed oxygen molecule from the surface in a competitive process. We will show that this competition is responsible for the resistive switching behavior in the ZnO-based gas sensors.

  6. Thermal cycling, oxidation behaviour and mechanical properties of graded and duplex PSZ TBC coatings

    Energy Technology Data Exchange (ETDEWEB)

    Musil, J. [SKODA, Plzen (Czech Republic); Alaya, M.; Oberacker, R. [Univ. of Karlsruhe (Germany)

    1995-07-01

    Plasma sprayed duplex and graded ZrO{sub 2} thermal barrier coatings (TBCs) on an Inconel 617 substrate with a NiCrAlY bond coat were investigated and compared with regard to their thermal cycling, oxidation behaviour and mechanical properties. On the basis of FE - calculations the stress distribution within thermally cycled coating systems was analyzed. The calculations show that the graded coating structure relaxes considerably the stresses resulting from the internal constraint due to thermal expansion difference between both metallic and ceramic materials and hence must lead to a better thermal cycling behaviour of the graded TBC systems. Mechanical tests confirm it. However, taking into account their poor oxidation behaviour, the lifetime of duplex TBC systems which are under steady-state thermal load conditions is much higher than that of graded ones.

  7. Kinetics and mechanism of the oxidative bromination of o-xylene in solution

    Energy Technology Data Exchange (ETDEWEB)

    Dorfman, Ya.A.; Emel' yanova, V.S.; Efremenko, I.G.; Doroshkevich, D.M.; Korolev, A.V.

    1988-07-01

    The kinetics of oxidative bromination of aromatic compounds have been studied in HNO/sub 3/-HBr-H/sub 2/SO/sub 4/-H/sub 2/O-O/sub 2/ solution. A kinetic equation which describes the results was derived for P/sub O/sub 2// > 5 /times/ 10/sup 4/ Pa. The equation parameters were determined at a temperature of 323 K. Quantum mechanical CNDO calculations were carried out in order to study the nature of the reactive intermediates involved: NO/sub 2/ NO(OH)/sup +/, N(OH)/sub 2//sup 2 +/, NO(OH)Br, and N(OH)/sub 2/Br/sup +/. A mechanism has been proposed to account for the oxidative bromination of aromatic compounds in HNO/sub 3/-H/sub 2/SO/sub 4/-HBr-O/sub 2/-H/sub 2/ solution.

  8. In situ thermally reduced graphene oxide/epoxy composites: thermal and mechanical properties

    Science.gov (United States)

    Olowojoba, Ganiu B.; Eslava, Salvador; Gutierrez, Eduardo S.; Kinloch, Anthony J.; Mattevi, Cecilia; Rocha, Victoria G.; Taylor, Ambrose C.

    2016-10-01

    Graphene has excellent mechanical, thermal, optical and electrical properties and this has made it a prime target for use as a filler material in the development of multifunctional polymeric composites. However, several challenges need to be overcome to take full advantage of the aforementioned properties of graphene. These include achieving good dispersion and interfacial properties between the graphene filler and the polymeric matrix. In the present work, we report the thermal and mechanical properties of reduced graphene oxide/epoxy composites prepared via a facile, scalable and commercially viable method. Electron micrographs of the composites demonstrate that the reduced graphene oxide (rGO) is well dispersed throughout the composite. Although no improvements in glass transition temperature, tensile strength and thermal stability in air of the composites were observed, good improvements in thermal conductivity (about 36 %), tensile and storage moduli (more than 13 %) were recorded with the addition of 2 wt% of rGO.

  9. Section i: Thermodynamic Properties of Hydrocarbon Radicals, Peroxy Hydrocarbon and Peroxy Chlorohydrocarbon Molecules and Radicals. Section II. Kinetics and Reaction Mechanisms For: (1) Chloroform Pyrolysis and Oxidation; (2) Benzene and Toluene Oxidation Under Atmospheric Conditions.

    Science.gov (United States)

    Lay, Tsan-Horng

    1995-01-01

    photooxidation of benzene and other aromatic species in the atmosphere. OH addition to the benzene ring, the subsequent reaction of O_2 with the hydroxyl-2,4-cyclohexadienyl to form hydroxyl -2-peroxy-4-cyclohexenyl (benzene-OH-O_2 adduct), are chemical activation reactions and are a function of both pressure and temperature. The kinetics of these two reaction systems at various pressure & temperatures using a quantum version of Rice-Ramsperger-Kassel theory (QRRK) and a modified strong collision approach are analyzed and calculated. The analogue reaction system of toluene photooxidation is also analyzed. Reaction mechanisms are developed for initial steps of atmospheric oxidation of benzene and toluene, which include reverse reaction rates determined from thermodynamic parameters and microscopic reversibility. The model results show good agreement with the limited available experimental data.

  10. Synthesis mechanism of low-voltage praseodymium oxide doped zinc oxide varistor ceramics prepared through modified citrate gel coating.

    Science.gov (United States)

    Abdullah, Wan Rafizah Wan; Zakaria, Azmi; Ghazali, Mohd Sabri Mohd

    2012-01-01

    High demands on low-voltage electronics have increased the need for zinc oxide (ZnO) varistors with fast response, highly non-linear current-voltage characteristics and energy absorption capabilities at low breakdown voltage. However, trade-off between breakdown voltage and grain size poses a critical bottle-neck in the production of low-voltage varistors. The present study highlights the synthesis mechanism for obtaining praseodymium oxide (Pr(6)O(11)) based ZnO varistor ceramics having breakdown voltages of 2.8 to 13.3 V/mm through employment of direct modified citrate gel coating technique. Precursor powder and its ceramics were examined by means of TG/DTG, FTIR, XRD and FESEM analyses. The electrical properties as a function of Pr(6)O(11) addition were analyzed on the basis of I-V characteristic measurement. The breakdown voltage could be adjusted from 0.01 to 0.06 V per grain boundary by controlling the amount of Pr(6)O(11) from 0.2 to 0.8 mol%, without alteration of the grain size. The non-linearity coefficient, α, varied from 3.0 to 3.5 and the barrier height ranged from 0.56 to 0.64 eV. Breakdown voltage and α lowering with increasing Pr(6)O(11) content were associated to reduction in the barrier height caused by variation in O vacancies at grain boundary.

  11. Reaction pathway and oxidation mechanisms of dibutyl phthalate by persulfate activated with zero-valent iron

    Energy Technology Data Exchange (ETDEWEB)

    Li, Huanxuan [School of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, China, Guangzhou 510640 (China); Wan, Jinquan, E-mail: ppjqwan@scut.edu.cn [School of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, China, Guangzhou 510640 (China); State Key Lab Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640 (China); Ma, Yongwen [School of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, China, Guangzhou 510640 (China); State Key Lab Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640 (China); Wang, Yan [School of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, China, Guangzhou 510640 (China)

    2016-08-15

    This study investigated reaction pathway and oxidation mechanisms of dibutyl phthalate (DBP) by persulfate (PS) activated with zero-valent iron (ZVI). The DBP degradation was studied at three pH values (acidic, neutral and basic) in the presence of different organic scavengers. Using a chemical probe method, both sulfate radical (SO{sub 4}·{sup −}) and hydroxyl radical (·OH) were found to be primary oxidants at pH 3.0 and pH 7.0, respectively while ·OH was the major specie to oxidize DBP at pH 11.0. A similar result was found in an experiment of Electron Spin Resonance spin-trapping where in addition to ·OH, superoxide radical (O{sub 2}·{sup −}) was detected at pH 11.0. The transformation of degradation products including dimethyl phthalate (DMP), diethyl phthalate (DEP), phthalic anhydride, and acetophenone exhibited diverse variation during the reaction processes. The phthalic anhydride concentration appeared to be maximum at all pHs. Another eleven intermediate products were also found at pH 3.0 by GC–MS and HPLC analysis, and their degradation mechanisms and pathways were proposed. It was suggested that dealkylation, hydroxylation, decarboxylation and hydrogen extraction were the dominant degradation mechanisms of DBP at pH 3.0. - Highlights: • Both SO{sub 4}{sup −}· and ·OH were found to be the major active species at pH 3.0 and pH 7.0. • ·OH and ·O2– were the primary oxidants pH 11.0. • The intermediate products were investigated as well as the degradation pathway. • Dealkylation, hydroxylation, decarboxylation, H-extraction were the major mechanisms.

  12. Oxygen reduction and transportation mechanisms in solid oxide fuel cell cathodes

    Science.gov (United States)

    Li, Yihong; Gemmen, Randall; Liu, Xingbo

    In recent years, various models have been developed for describing the reaction mechanisms in solid oxide fuel cell (SOFC) especially for the cathode electrode. However, many fundamental issues regarding the transport of oxygen and electrode kinetics have not been fully understood. This review tried to summarize the present status of the SOFC cathode modeling efforts, and associated experimental approaches on this topic. In addition, unsolved problems and possible future research directions for SOFC cathode kinetics had been discussed.

  13. Fracton pairing mechanism for unconventional superconductors: Self-assembling organic polymers and copper-oxide compounds

    DEFF Research Database (Denmark)

    Milovanov, A.V.; Juul Rasmussen, J.

    2002-01-01

    or holes) exchange fracton excitations, quantum oscillations of fractal lattices that mimic the complex microscopic organization of the unconventional superconductors. For the copper oxides, the superconducting transition temperature T-c as predicted by the fracton mechanism is of the order of similar to...... description of the complex fractal sets underlying the fracton spectrum. A generalized kinetic equation containing integer time and fractional real-space derivatives is found for the fracton excitations in the harmonic approximation. The fracton superconductivity mechanism is further discussed in connection...

  14. Oxidation mechanism of formic acid on the bismuth adatom-modified Pt(111) surface.

    Science.gov (United States)

    Perales-Rondón, Juan Victor; Ferre-Vilaplana, Adolfo; Feliu, Juan M; Herrero, Enrique

    2014-09-24

    In order to improve catalytic processes, elucidation of reaction mechanisms is essential. Here, supported by a combination of experimental and computational results, the oxidation mechanism of formic acid on Pt(111) electrodes modified by the incorporation of bismuth adatoms is revealed. In the proposed model, formic acid is first physisorbed on bismuth and then deprotonated and chemisorbed in formate form, also on bismuth, from which configuration the C-H bond is cleaved, on a neighbor Pt site, yielding CO2. It was found computationally that the activation energy for the C-H bond cleavage step is negligible, which was also verified experimentally.

  15. A transition in mechanisms of size dependent electrical transport at nanoscale metal-oxide interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Jiechang; Nonnenmann, Stephen S.; Qin, Wei; Bonnell, Dawn A., E-mail: bonnell@lrsm.seas.upenn.edu [Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)

    2013-12-16

    As device miniaturization approaches nanoscale dimensions, interfaces begin to dominate electrical properties. Here the system archetype Au/SrTiO{sub 3} is used to examine the origin of size dependent transport properties along metal-oxide interfaces. We demonstrate that a transition between two classes of size dependent electronic transport mechanisms exists, defined by a critical size ε. At sizes larger than ε an edge-related tunneling effect proportional to 1/D (the height of the supported Au nanoparticle) is observed; interfaces with sizes smaller than ε exhibit random fluctuations in current. The ability to distinguish between these mechanisms is important to future developments in nanoscale device design.

  16. Effect of nickel oxide substitution on bioactivity and mechanical properties of bioactive glass

    Indian Academy of Sciences (India)

    VIKASH KUMAR VYAS; A SAMPATH KUMAR; S P SINGH; RAM PYARE

    2016-09-01

    A small amount of nickel oxide is doped in bioglass$^{\\circledR}$ system and it is replaced by silica. The use of 45S5 glass composition is one such material able to bond strongly to bone within 42 days. The 45S5 bioglass$^{\\circledR}$ system develops a hydroxyl carbonate apatite (HCA) layer, which is chemically and crystallographically similar to mineral phase of bone. But it has low fracture toughness and mechanical weakness due to an amorphous glass network andit is not compatible for load-bearing applications. In the present work, the effect of addition of nickel oxide that annualizes the improvement in its mechanical strength and bioactivity is studied. Bioactivity of base glass and doped glass samples were tested through their HCA abilities by immersing them in simulated body fluid (SBF) for different days. The formation of HCA was confirmed by FTIR spectroscopy and pH measurement. Densities and mechanical properties of samples were also increased considerably by increasing the concentration of nickel oxide.

  17. Embryonic oxidative stress as a mechanism of teratogenesis with special emphasis on diabetic embryopathy.

    Science.gov (United States)

    Ornoy, Asher

    2007-07-01

    Reactive oxygen species (ROS) are involved in the etiology of numerous diseases including cardio-vascular diseases and diabetes mellitus. There is evidence that several teratogens affect the developing embryo by increasing its oxidative stress and, because of its relatively weak antioxidant defense, especially at the early stages of organogenesis, result in severe embryonic damage. This mechanism seems to operate in diabetes-induced embryonic damage as well as in the mechanism of teratogenicity caused by ionizing radiation, hypoxia, alcohol and cocaine use and cigarette smoking. We studied the role of oxidative stress in diabetic induced embryopathy, both in vivo and in vitro. Under diabetic condition there was a significant decrease in the activity of endogenous antioxidant enzymes and of vitamins C and E in the embryos and their yolk sacs. The lowest activity was observed in the malformed experimental embryos when compared to experimental embryos without anomalies. Similar results were obtained in the Cohen diabetic rats, where the diabetic prone (CDs) rats were unable to increase their antioxidant enzyme activity in spite of the diabetes. Studies performed by other investigators show similar results. Human and animal studies show that the main mechanism of fetal damage induced by high levels of ionizing irradiation, cocaine and alcohol abuse, hypoxia and cigarette smoking is also by increased embryonic oxidative stress. Similarly, several drugs exert their teratogenic activity via embryonic oxidative stress. Abnormal placentation may also cause enhanced placental oxidative stress, resulting in embryonic death, preeclampsia or congenital anomalies. Inability of the developing embryo to cope with that stress may result in embryonic death and/or congenital anomalies. Animal studies also show that a variety of antioxidants are effective in decreasing the damaging effects of heightened oxidative stress induced by teratogens. Effective antioxidants, which might also

  18. Comparison of automatically generated reaction mechanism for oxidation of simple hydrocarbons in IC engine

    Directory of Open Access Journals (Sweden)

    Muhammad Mansha

    2011-10-01

    Full Text Available In this work, a detailed kinetic reaction mechanism, consisting of 208 reactions and 79 species, has been developed todescribe the oxidation of simple hydrocarbon fuel (natural gas in IC engine. The performance of the proposed mechanismis tested using simulation, tool CHEMKIN 4.1.1, and experimental measurements. The simulation results of the proposedreaction scheme were compared with those of reference mechanisms (GRI v3.0 and Konnov 0.5 version as well as experimentaldata. Based upon simulation results, it can be concluded that the proposed mechanism shows good concordanceswith GR I3.0 mechanism especially in the prediction of temperature, pressure, and major product species (H2O, CO2 profilesat stoichiometric conditions (= 1.0. Although, there are some discrepancies among each predicted profile, the proposeddetailed mechanism is good to describe the oxidation of natural gas in IC engine. The experimental data also showed favorableresults for prediction of major product species (CO2, H2O & CO at various engine operating speeds in idle mode.

  19. Validation and updating of detailed kinetic mechanisms: The case of ethane oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Rota, R.; Bonini, F.; Servida, A.; Morbidelli, M.; Carra, S. (Politecnico di Milano (Italy). Dipt. di Chimica Fisica Applicata)

    1994-11-01

    The authors have investigated experimentally the oxidation of ethane in a perfectly stirred reactor in the temperature range 870--1,080 K and for fuel-air stoichiometric ratio ranging from 0.25 to 1.27. The concentrations of the main molecular species have been measured by probe sampling and GC analysis. These experimental results have been compared with predictions of three popular detailed kinetic mechanisms previously presented in the literature. A reasonable agreement between the experimental results and the model predictions has been found for almost all the species and the mechanisms. The only relevant exception is acetylene, which is greatly overpredicted by one of the mechanisms for all the investigated conditions. Parametric sensitivity analysis has been used for updating such a mechanism in order to improve the agreement with the experimental observations.

  20. Selective oxidation of alcohols with alkali metal bromides as bromide catalysts: experimental study of the reaction mechanism.

    Science.gov (United States)

    Moriyama, Katsuhiko; Takemura, Misato; Togo, Hideo

    2014-07-03

    A bromide-catalyzed oxidation of alcohols was developed which proceeded in the presence of an alkali metal bromide and an oxidant under mild conditions. The reaction involved an organic-molecule-free oxidation using KBr and Oxone and a Brønsted acid assisted oxidation using KBr and aqueous H2O2 solution to provide a broad range of carbonyl compounds in high yields. Moreover, the bromide-catalyzed oxidation of primary alcohols enabled the divergent synthesis of carboxylic acids and aldehydes under both reaction conditions in the presence of TEMPO. A possible catalytic mechanism was suggested on the basis of various mechanistic studies.

  1. Spectroscopic and electrical sensing mechanism in oxidant-mediated polypyrrole nanofibers/nanoparticles for ammonia gas

    Science.gov (United States)

    Ishpal; Kaur, Amarjeet

    2013-05-01

    Ammonia gas sensing mechanism in oxidant-mediated polypyrrole (PPy) nanofibers/nanoparticles has been studied through spectroscopic and electrical investigations. PPy nanofibers/nanoparticles have been synthesized by chemical oxidation method in the presence of various oxidizing agents such as ammonium persulfate (APS), potassium persulfate (PPS), vanadium pentoxide (V2O5), and iron chloride (FeCl3). Scanning electron microscopy study revealed that PPy nanofibers of about 63, 71 and 79 nm diameters were formed in the presence of APS, PPS, V2O5, respectively, while PPy nanoparticles of about 100-110 nm size were obtained in the presence of FeCl3 as an oxidant. The structural investigations and confirmation of synthesis of PPy were established through Fourier transform infrared and Raman spectroscopy. The gas sensing behavior of the prepared PPy samples is investigated by measuring the electrical resistance in ammonia environment. The observed gas sensing response ( δR R × 100 ) at 100 ppm level of ammonia is 4.5 and 18 % for the samples prepared with oxidizing agents FeCl3 and APS, respectively, and by changing the ammonia level from 50 to 300 ppm, the sensing response varies from 4.5 to 11 % and 10 to 39 %, respectively. Out of all four samples, the PPy nanofibers prepared in the presence of APS have shown the best sensing response. The mechanism of gas sensing response of the PPy samples has been investigated through Raman spectroscopy study. The decrease of charge carrier concentration through reduction of polymeric chains has been recognized through Raman spectroscopic measurements recorded in ammonia environment.

  2. Spectroscopic and electrical sensing mechanism in oxidant-mediated polypyrrole nanofibers/nanoparticles for ammonia gas

    Energy Technology Data Exchange (ETDEWEB)

    Ishpal; Kaur, Amarjeet, E-mail: amarkaur@physics.du.ac.in [University of Delhi, Department of Physics and Astrophysics (India)

    2013-05-15

    Ammonia gas sensing mechanism in oxidant-mediated polypyrrole (PPy) nanofibers/nanoparticles has been studied through spectroscopic and electrical investigations. PPy nanofibers/nanoparticles have been synthesized by chemical oxidation method in the presence of various oxidizing agents such as ammonium persulfate (APS), potassium persulfate (PPS), vanadium pentoxide (V{sub 2}O{sub 5}), and iron chloride (FeCl{sub 3}). Scanning electron microscopy study revealed that PPy nanofibers of about 63, 71 and 79 nm diameters were formed in the presence of APS, PPS, V{sub 2}O{sub 5}, respectively, while PPy nanoparticles of about 100-110 nm size were obtained in the presence of FeCl{sub 3} as an oxidant. The structural investigations and confirmation of synthesis of PPy were established through Fourier transform infrared and Raman spectroscopy. The gas sensing behavior of the prepared PPy samples is investigated by measuring the electrical resistance in ammonia environment. The observed gas sensing response ({Delta}R/Rx100) at 100 ppm level of ammonia is {approx}4.5 and 18 % for the samples prepared with oxidizing agents FeCl{sub 3} and APS, respectively, and by changing the ammonia level from 50 to 300 ppm, the sensing response varies from {approx}4.5 to 11 % and {approx}10 to 39 %, respectively. Out of all four samples, the PPy nanofibers prepared in the presence of APS have shown the best sensing response. The mechanism of gas sensing response of the PPy samples has been investigated through Raman spectroscopy study. The decrease of charge carrier concentration through reduction of polymeric chains has been recognized through Raman spectroscopic measurements recorded in ammonia environment.

  3. Mechanism of Rh-Catalyzed Oxidative Cyclizations: Closed versus Open Shell Pathways.

    Science.gov (United States)

    Park, Yoonsu; Ahn, Seihwan; Kang, Dahye; Baik, Mu-Hyun

    2016-06-21

    A conceptual theory for analyzing and understanding oxidative addition reactions that form the cornerstone of many transition metal mediated catalytic cycles that activate C-C and C-H bonds, for example, was developed. The cleavage of the σ- or π-bond in the organic substrate can be envisioned to follow a closed or an open shell formalism, which is matched by a corresponding electronic structure at the metal center of the catalyst. Whereas the assignment of one or the other mechanistic scenario appears formal and equivalent at first sight, they should be recognized as different classes of reactions, because they lead to different reaction optimization and control strategies. The closed-shell mechanism involves heterolytic bond cleavages, which give rise to highly localized charges to form at the transition state. In the open-shell pathway, bonds are broken homolytically avoiding localized charges to accumulate on molecular fragments at the transition states. As a result, functional groups with inductive effects may exert a substantial influence on the energies of the intermediate and transition states, whereas no such effect is expected if the mechanism proceeds through the open-shell mechanism. If these functional groups are placed in a way that opens an electronic communication pathway to the molecular sites where charges accumulate, for example, using hyperconjugation, electron donating groups may stabilize a positive charge at that site. An instructive example is discussed, where this stereoelectronic effect allowed for rendering the oxidative addition diastereoselective. No such control is possible, however, when the open-shell reaction pathway is followed, because the inductive effects of functional groups have little to no effect on the stabilities of radical-like substrate states that are encountered when the bonds are broken in a homolytic fashion. Whether the closed-shell or open-shell mechanism for oxidative addition is followed is determined by the

  4. Oxidation behavior and mechanism of powder metallurgy Rene95 nickel based superalloy between 800 and 1000 deg. C

    Energy Technology Data Exchange (ETDEWEB)

    Zheng Lei, E-mail: zhenglei_ustb@sina.com [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 10083 (China); Zhang Maicang; Dong Jianxin [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 10083 (China)

    2010-10-01

    The oxidation behaviors of powder metallurgy (PM) Rene95 Ni-based superalloy in the temperature range of 800-1000 deg. C are investigated in air by virtue of isothermal oxidation testing, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the oxidation kinetics follows a square power law as the time extends at each temperature. The oxidation layers are detected to be composed of Cr{sub 2}O{sub 3}, TiO{sub 2} and a small amount of NiCr{sub 2}O{sub 4}. The cross-sectional morphologies indicate that the oxidation layer consists of three parts: Cr-rich oxide layer, Cr and Ti duplex oxide layer, and oxidation affected zone. Theoretical analyses of oxidation kinetics and thicknesses of oxidation layers confirm that the activation energy of oxidation of PM Rene95 superalloy is 165.32 kJ mol{sup -1} and the oxidation process is controlled by diffusions of oxygen, Cr, and Ti. Accordingly, a diffusion-controlled mechanism is suggested to understand the oxidation behaviors of PM Rene95 superalloy at elevated temperatures.

  5. Structure and Mechanism of ORF36, an Amino Sugar Oxidizing Enzyme in Everninomicin Biosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Vey, Jessica L.; Al-Mestarihi, Ahmad; Hu, Yunfeng; Funk, Michael A.; Bachmann, Brian O.; Iverson, T.M. (Vanderbilt)

    2010-12-07

    Everninomicin is a highly modified octasaccharide that belongs to the orthosomycin family of antibiotics and possesses potent Gram-positive antibiotic activity, including broad-spectrum efficacy against multidrug resistant enterococci and Staphylococcus aureus. Among its distinctive structural features is a nitro sugar, L-evernitrose, analogues of which decorate a variety of natural products. Recently, we identified a nitrososynthase enzyme encoded by orf36 from Micromonospora carbonacea var. africana that mediates the flavin-dependent double oxidation of synthetically generated thymidine diphosphate (TDP)-L-epi-vancosamine to the corresponding nitroso sugar. Herein, we utilize a five-enzyme in vitro pathway both to verify that ORF36 catalyzes oxidation of biogenic TDP-L-epi-vancosamine and to determine whether ORF36 exhibits catalytic competence for any of its biosynthetic progenitors, which are candidate substrates for nitrososynthases in vivo. Progenitors solely undergo single-oxidation reactions and terminate in the hydroxylamine oxidation state. Performing the in vitro reactions in the presence of {sup 18}O{sub 2} establishes that molecular oxygen, rather than oxygen from water, is incorporated into ORF36-generated intermediates and products and identifies an off-pathway product that correlates with the oxidation product of a progenitor substrate. The 3.15 {angstrom} resolution X-ray crystal structure of ORF36 reveals a tetrameric enzyme that shares a fold with acyl-CoA dehydrogenases and class D flavin-containing monooxygenases, including the nitrososynthase KijD3. However, ORF36 and KijD3 have unusually open active sites in comparison to these related enzymes. Taken together, these studies map substrate determinants and allow the proposal of a minimal monooxygenase mechanism for amino sugar oxidation by ORF36.

  6. Reaction pattern and mechanism of light induced oxidative water splitting in photosynthesis.

    Science.gov (United States)

    Renger, Gernot; Kühn, Philipp

    2007-06-01

    This mini review is an attempt to briefly summarize our current knowledge on light driven oxidative water splitting in photosynthesis. The reaction leading to molecular oxygen and four protons via photosynthesis comprises thermodynamic and kinetic constraints that require a balanced fine tuning of the reaction coordinates. The mode of coupling between electron (ET) and proton transfer (PT) reactions is shown to be of key mechanistic relevance for the redox turnover of Y(Z) and the reactions within the WOC. The WOC is characterized by peculiar energetics of its oxidation steps in the WOC. In all oxygen evolving photosynthetic organisms the redox state S(1) is thermodynamically most stable and therefore this general feature is assumed to be of physiological relevance. Available information on the Gibbs energy differences between the individual redox states S(i+1) and S(i) and on the activation energies of their oxidative transitions are used to construct a general reaction coordinate of oxidative water splitting in photosystem II (PS II). Finally, an attempt is presented to cast our current state of knowledge into a mechanism of oxidative water splitting with special emphasis on the formation of the essential O-O bond and the active role of the protein environment in tuning the local proton activity that depends on time and redox state S(i). The O-O linkage is assumed to take place within a multistate equilibrium at the redox level of S(3), comprising both redox isomerism and proton tautomerism. It is proposed that one state, S(3)(P), attains an electronic configuration and nuclear geometry that corresponds with a hydrogen bonded peroxide which acts as the entatic state for the generation of complexed molecular oxygen through S(3)(P) oxidation by Y(Z)(ox).

  7. Thermal catalytic oxidation of octachloronaphthalene over anatase TiO2 nanomaterial and its hypothesized mechanism

    Science.gov (United States)

    Su, Guijin; Li, Qianqian; Lu, Huijie; Zhang, Lixia; Huang, Linyan; Yan, Li; Zheng, Minghui

    2015-12-01

    As an environmentally-green technology, thermal catalytic oxidation of octachloronaphthalene (CN-75) over anatase TiO2 nanomaterials was investigated at 300 °C. A wide range of oxidation intermediates, which were investigated using various techniques, could be of three types: naphthalene-ring, single-benzene-ring, and completely ring-opened products. Reactive oxygen species on anatase TiO2 surface, such as O2-• and O2-, contributed to oxidative degradation. Based on these findings, a novel oxidation degradation mechanism was proposed. The reaction at (101) surface of anatase TiO2 was used as a model. The naphthalene-ring oxidative products with chloronaphthols and hydroxyl-pentachloronaphthalene-dione, could be formed via attacking the carbon of naphthalene ring at one or more positions by nucleophilic O2-. Lateral cleavage of the naphthalene ring at different C1-C10 and C4-C9, C1-C2 and C4-C9, C1-C2 or and C3-C4 bond positions by electrophilic O2-• could occur. This will lead to the formation of tetrachlorophenol, tetrachloro-benzoic acid, tetrachloro-phthalaldehyde, and tetrachloro-acrolein-benzoic acid, partially with further transformation into tetrachlorobenzene-dihydrodiol and tetrachloro-salicylic acid. Unexpectedly, the symmetric half section of CN-75 could be completely remained with generating the intricate oxidative intermediates characteristically containing tetrachlorobenzene structure. Complete cleavage of naphthalene ring could produce the ring-opened products, such as formic and acetic acids.

  8. Microstructure, mechanical and oxidation behavior of RE-containing lead-free solders

    Science.gov (United States)

    Dudek, Martha A.

    Pb-free solders pose new challenges associated with their incorporation and reliability during service of electronic components. Recently, a new class of alloys containing rare-earth (RE) elements has been discovered. In this study, solder alloys containing lanthanum (La), cerium (Ce) and yttrium (Y) were developed and characterized. It was found that small additions of La and Ce to Sn-Ag-Cu alloys significantly improved their ductility. This has direct implications for mechanical shock and drop reliability. Microstructure characterization of solder and solder/Cu joints containing Sn-3.9Ag-0.7Cu-XRE (X = 0, 0.1, 0.5 and 2 weight percent) was conducted using optical microscopy, scanning electron microscopy and transmission electron microscopy. It was found that RE elements refined the solder microstructure. A serial-sectioning 3D reconstruction process was used to visualize the RE-containing intermetallics. Solidification of these alloys was studied using differential scanning calorimetry. The melting point of Sn-3.9Ag-0.7Cu did not change with the incorporation of RE elements. Additionally, the effect of RE content on shear and creep of lap-shear joints was studied. It was found that additions of La and Ce up to 0.5 weight percent improved the elongation of Sn-3.9Ag-0.7Cu. Y-containing alloys did not show an improvement. Creep tests were conducted at 60, 95 and 120 degrees Celsius. RE content did not markedly alter the creep behavior. Due to RE's high affinity for oxygen, oxidation of RE-containing alloys may affect their mechanical performance. Thus, the effect of 2 weight percent Ce, La or Y on the oxidation behavior was studied at 60, 95 and 130 degrees Celsius. All alloys exhibited parabolic oxidation kinetics. La and Y-containing alloys oxidized significantly faster than the Ce-containing alloy. Sn whiskering was observed to take place during oxidation, likely due to the compressive stresses developed during oxidation. Serial-sectioning with a focused ion beam

  9. Surface reaction mechanisms during ozone and oxygen plasma assisted atomic layer deposition of aluminum oxide.

    Science.gov (United States)

    Rai, Vikrant R; Vandalon, Vincent; Agarwal, Sumit

    2010-09-07

    We have elucidated the reaction mechanism and the role of the reactive intermediates in the atomic layer deposition (ALD) of aluminum oxide from trimethyl aluminum in conjunction with O(3) and an O(2) plasma. In situ attenuated total reflection Fourier transform infrared spectroscopy data show that both -OH groups and carbonates are formed on the surface during the oxidation cycle. These carbonates, once formed on the surface, are stable to prolonged O(3) exposure in the same cycle. However, in the case of plasma-assisted ALD, the carbonates decompose upon prolonged O(2) plasma exposure via a series reaction kinetics of the type, A (CH(3)) --> B (carbonates) --> C (Al(2)O(3)). The ratio of -OH groups to carbonates on the surface strongly depends on the oxidizing agent, and also the duration of the oxidation cycle in plasma-assisted ALD. However, in both O(3) and O(2) plasma cycles, carbonates are a small fraction of the total number of reactive sites compared to the hydroxyl groups.

  10. Microstructure Refinement and Strengthening Mechanisms of a 9Cr Oxide Dispersion Strengthened Steel by Zirconium Addition

    Directory of Open Access Journals (Sweden)

    Haijian Xu

    2017-02-01

    Full Text Available To study the effects of zirconium (Zr addition on the microstructure, hardness and the tensile properties of oxide dispersion strengthened (ODS ferritic–martensitic steels, two kinds of 9Cr-ODS ferritic–martensitic steels with nominal compositions (wt.% of Fe-9Cr-2W-0.3Y2O3 and Fe-9Cr-2W-0.3Zr-0.3Y2O3 were fabricated by the mechanical alloying (MA of premixed powders and then consolidated by hot isostatic pressing (HIP techniques. The experimental results showed that the average grain size decreases with Zr addition. The trigonal δ-phase Y4Zr3O12 oxides and body-centered cubic Y2O3 oxides are formed in the 9Cr-Zr-ODS steel and 9Cr non-Zr ODS steel, respectively, and the average size of Y4Zr3O12 particles is much smaller than that of Y2O3. The dispersion morphology of the oxide particles in 9Cr-Zr-ODS steel is significantly improved and the number density is 1.1×1023/m3 with Zr addition. The 9Cr-Zr-ODS steel shows much higher tensile ductility, ultimate tensile strength and Vickers hardness at the same time.

  11. Morphology, thermal, mechanical, and barrier properties of graphene oxide/poly(lactic acid) nanocomposite films

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seong Woo; Choi, Hyun Muk [Kyonggi University, Suwon (Korea, Republic of)

    2016-01-15

    To improve the physical and gas barrier properties of biodegradable poly(lactic acid) (PLA) film, two graphene nanosheets of highly functionalized graphene oxide (0.3 wt% to 0.7 wt%) and low-functionalized graphene oxide (0.5 wt%) were incorporated into PLA resin via solution blending method. Subsequently, we investigated the effects of material parameters such as loading level and degree of functionalization for the graphene nanosheets on the morphology and properties of the resultant nanocomposites. The highly functionalized graphene oxide (GO) caused more exfoliation and homogeneous dispersion in PLA matrix as well as more sustainable suspensions in THF, compared to low-functionalized graphene oxide (LFGO). When loaded with GO from 0.3 wt% to 0.7 wt%, the glass transition temperature, degree of crystallinity, tensile strength and modulus increased steadily. The GO gave rise to more pronounced effect in the thermal and mechanical reinforcement, relative to LFGO. In addition, the preparation of fairly transparent PLA-based nanocomposite film with noticeably improved barrier performance achieved only when incorporated with GO up to 0.7wt%. As a result, GO may be more compatible with hydrophilic PLA resin, compared to LFGO, resulting in more prominent enhancement of nanocomposites properties.

  12. Skin aging and oxidative stress: Equol's anti-aging effects via biochemical and molecular mechanisms.

    Science.gov (United States)

    Lephart, Edwin D

    2016-11-01

    Oxygen in biology is essential for life. It comes at a cost during normal cellular function, where reactive oxygen species (ROS) are generated by oxidative metabolism. Human skin exposed to solar ultra-violet radiation (UVR) dramatically increases ROS production/oxidative stress. It is important to understand the characteristics of human skin and how chronological (intrinsic) aging and photo-aging (extrinsic aging) occur via the impact of ROS production by cascade signaling pathways. The goal is to oppose or neutralize ROS insults to maintain good dermal health. Botanicals, as active ingredients, represent one of the largest categories used in dermatology and cosmeceuticals to combat skin aging. An emerging botanical is equol, a polyphenolic/isoflavonoid molecule found in plants and food products and via gastrointestinal metabolism from precursor compounds. Introductory sections cover oxygen, free radicals (ROS), oxidative stress, antioxidants, human skin aging, cellular/molecular ROS events in skin, steroid enzymes/receptors/hormonal actions and genetic factors in aging skin. The main focus of this review covers the characteristics of equol (phytoestrogenic, antioxidant and enhancement of extracellular matrix properties) to reduce skin aging along with its anti-aging skin influences via reducing oxidative stress cascade events by a variety of biochemical/molecular actions and mechanisms to enhance human dermal health. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. Adsorption treatment of oxide chemical mechanical polishing wastewater from a semiconductor manufacturing plant by electrocoagulation

    Energy Technology Data Exchange (ETDEWEB)

    Chou, Wei-Lung, E-mail: wlchou@sunrise.hk.edu.tw [Department of Safety, Health and Environmental Engineering, Hungkuang University, No. 34, Chung-Chie Road, Sha-Lu, Taichung 433, Taiwan (China); Wang, Chih-Ta [Department of Safety Health and Environmental Engineering, Chung Hwa University of Medical Technology, Tainan Hsien 717, Taiwan (China); Chang, Wen-Chun; Chang, Shih-Yu [Department of Safety, Health and Environmental Engineering, Hungkuang University, No. 34, Chung-Chie Road, Sha-Lu, Taichung 433, Taiwan (China)

    2010-08-15

    In this study, metal hydroxides generated during electrocoagulation (EC) were used to remove the chemical oxygen demand (COD) of oxide chemical mechanical polishing (oxide-CMP) wastewater from a semiconductor manufacturing plant by EC. Adsorption studies were conducted in a batch system for various current densities and temperatures. The COD concentration in the oxide-CMP wastewater was effectively removed and decreased by more than 90%, resulting in a final wastewater COD concentration that was below the Taiwan discharge standard (100 mg L{sup -1}). Since the processed wastewater quality exceeded the direct discharge standard, the effluent could be considered for reuse. The adsorption kinetic studies showed that the EC process was best described using the pseudo-second-order kinetic model at the various current densities and temperatures. The experimental data were also tested against different adsorption isotherm models to describe the EC process. The Freundlich adsorption isotherm model predictions matched satisfactorily with the experimental observations. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the COD adsorption of oxide-CMP wastewater on metal hydroxides was feasible, spontaneous and endothermic in the temperature range of 288-318 K.

  14. Mechanical and Abrasive Wear Properties of Anodic Oxide Layers Formed on Aluminium

    Institute of Scientific and Technical Information of China (English)

    W.Bensalah; K.Elleuch; M.Feki; M.Wery; H.F.Ayedi

    2009-01-01

    Aluminium oxide coatings were formed on aluminium substrates in oxalic acid-sulphuric acid bath. Abrasion tests of the obtained anodic layers were carried out on a pin-on-disc machine in accordance with the ISO/DP 825 specifications. The Vickers microhardness, D (HV0.2). and the abrasion weight loss, Wa (mg) were measured. Influence of oxalic acid concentration (Cox), bath temperature (T) and anodic current density (J) on D and Wa has been examined, and the sulphuric acid concentration (Caul) was maintained at 160 g.L-1. It was found that high microhardness and abrasive wear resistance of oxide layers were produced under low temperatures and high current densities with the addition of oxalic acid. The morphology and the composition of the anodic oxide layer were examined by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy and glow-discharge optical emission spectroscopy (GDOES). It was found that the chemistry of the anodizing electrolyte, temperature, and current density are the controlling factors of the mechanical properties of the anodic oxide layer.

  15. The Origin of Hierarchical Structure in Self-Assembled Graphene Oxide Papers and the Effect on Mechanical Properties

    Science.gov (United States)

    Nandy, Krishanu

    The quest for new materials with ever improving properties has motivated interest in bulk nanostructured materials. Graphene, a two-dimensional sheet of hexagonally arranged carbon atoms, has been of particular interest given its exceptional mechanical, thermal, optical and electrical properties. Graphene oxide is a chemically modified form of graphene in which the honeycomb lattice of carbon atoms is decorated with oxygen bearing functional groups. Graphene oxide represents a facile route for the production of large quantities of graphene based materials, is stable in aqueous and polar organic solvents and has the potential for further chemical modification. In this dissertation, the origin and influence of hierarchical structure on the mechanical properties of graphene oxide paper and graphene oxide paper based materials has been investigated. Free-standing papers derived from graphene oxide are of interest as structural materials due to their impressive mechanical properties. While studies have investigated the mechanical properties of graphene oxide papers, little is known about the formation mechanism. Using a series of flash-freezing experiments on graphene oxide papers undergoing formation, a stop-motion animation of the fabrication process was obtained. The results explain the origin of the hierarchical nature of graphene oxide papers and provide a method for the tailoring of graphene oxide based materials. An in depth study of fusion of graphene oxide papers demonstrates a simple single-step route for the fabrication of practical materials derived from graphene oxide papers. Fused papers retain the properties of constituent papers allowing for the fabrication of mechanical heterostructures that replicate the hierarchical nature of natural materials. The contribution of the hierarchical nature of graphene oxide papers to the mechanical properties was examined by comparing papers formed by two different mechanisms. The intermediate length scale structures

  16. New insights into atrazine degradation by cobalt catalyzed peroxymonosulfate oxidation: kinetics, reaction products and transformation mechanisms.

    Science.gov (United States)

    Ji, Yuefei; Dong, Changxun; Kong, Deyang; Lu, Junhe

    2015-03-21

    The widespread occurrence of atrazine in waters poses potential risk to ecosystem and human health. In this study, we investigated the underlying mechanisms and transformation pathways of atrazine degradation by cobalt catalyzed peroxymonosulfate (Co(II)/PMS). Co(II)/PMS was found to be more efficient for ATZ elimination in aqueous solution than Fe(II)/PMS process. ATZ oxidation by Co(II)/PMS followed pseudo-first-order kinetics, and the reaction rate constant (k(obs)) increased appreciably with increasing Co(II) concentration. Increasing initial PMS concentration favored the decomposition of ATZ, however, no linear relationship between k(obs) and PMS concentration was observed. Higher efficiency of ATZ oxidation was observed around neutral pH, implying the possibility of applying Co(II)/PMS process under environmental realistic conditions. Natural organic matter (NOM), chloride (Cl(-)) and bicarbonate (HCO3(-)) showed detrimental effects on ATZ degradation, particularly at higher concentrations. Eleven products were identified by applying solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC/MS) techniques. Major transformation pathways of ATZ included dealkylation, dechlorination-hydroxylation, and alkyl chain oxidation. Detailed mechanisms responsible for these transformation pathways were discussed. Our results reveal that Co(II)/PMS process might be an efficient technique for remediation of groundwater contaminated by ATZ and structurally related s-triazine herbicides.

  17. Mechanism of the development of a weakly alkaline barrier slurry without BTA and oxidizer

    Science.gov (United States)

    Xiaodong, Luan; Yuling, Liu; Xinhuan, Niu; Juan, Wang

    2015-07-01

    Controllable removal rate selectivity with various films (Cu, Ta, SiO2) is a challenging job in barrier CMP. H2O2 as an oxidizer and benzotriazole (BTA) as an inhibitor is considered to be an effective method in barrier CMP. Slurries that contain hydrogen peroxide have a very short shelf life because H2O2 is unstable and easily decomposed. BTA can cause post-CMP challenges, such as organic residue, toxicity and particle adhesion. We have been engaged in studying a weakly alkaline barrier slurry without oxidizer and benzotriazole. Based on these works, the objective of this paper is to discuss the mechanism of the development of the barrier slurry without oxidizer and benzotriazole by studying the effects of the different components (containing colloidal silica, FA/O complexing agent, pH of polishing solution and guanidine nitrate) on removal rate selectivity. The possible related polishing mechanism has also been proposed. Project supported by the Major National Science and Technology Special Projects (No. 2009ZX02308), the National Natural Science Foundation of Hebei Province, China (No. E2013202247), and the Department of Education-Funded Research Projects of Hebei Province, China (No. QN2014208).

  18. Mechanisms for chelator stimulation of microbial Fe(III) -oxide reduction

    Science.gov (United States)

    Lovley, D.R.; Woodward, J.C.

    1996-01-01

    The mechanisms by which nitrilotriacetic acid (NTA) stimulated Fe(III) reduction in sediments from a petroleum-contaminated aquifer were investigated in order to gain insight into how added Fe(III) chelators stimulate the activity of hydrocarbon-degrading, Fe(III)-reducing microorganisms in these sediments, and how naturally occurring Fe(III) chelators might promote Fe(III) reduction in aquatic sediments. NTA solubilized Fe(III) from the aquifer sediments. NTA stimulation of microbial Fe(III) reduction did not appear to be the result of making calcium, magnesium, potassium, or trace metals more available to the microorganisms. Stimulation of Fe(III) reduction could not be attributed to NTA serving as a source of carbon or fixed nitrogen for Fe(III)-reducing bacteria as NTA was not degraded in the sediments. Studies with the Fe(III)-reducing microorganism, Geobacter metallireducens, and pure Fe(III)-oxide forms, demonstrated that NTA stimulated the reduction of a variety of Fe(III) forms, including highly crystalline Fe(III)-oxides such as goethite and hematite. The results suggest that NTA solubilization of insoluble Fe(III)-oxide is an important mechanism for the stimulation of Fe(III) reduction by NTA in aquifer sediments.

  19. Mechanical response and deformation mechanisms of ferritic oxide dispersion strengthened steel structures produced by selective laser melting

    Energy Technology Data Exchange (ETDEWEB)

    Dryepondt, Sebastien N [ORNL; Boegelein, T [University of Liverpool, UK; Pandey, Amit [LGFCS; Dawson, K [University of Liverpool, UK; Tatlock, G.J. [University of Liverpool, UK

    2015-01-28

    Oxide dispersion strengthened (ODS) ferritic steels typically contain a fine dispersion of nanoscopic Y(Al, Ti) oxides, leading to an improvement in mechanical and physical properties. For a rapid prototyping technique, selective laser melting (SLM), was successfully applied to consolidate as-mechanically alloyed ODS-PM2000 (Fe 19Cr 5.5Al 0.5Ti 0.5Y2O3; all wt.%) powder to fabricate solid and thin-walled builds of different thickness. Our work is intended to act as a first study to investigate the tensile response of such configurations at room temperature, using miniaturized test specimens along and perpendicular to the growth direction. The 0.2% offset yield strength of as-grown wall builds was inferior to conventional PM2000 alloy (recrystallized), but could be significantly increased by conducting post-build heat treatments. Young s modulus and yield strength showed anisotropy and were enhanced when testing perpendicular to the build growth direction. Electron backscatter diffraction revealed a strong [001] fibre texture along the growth direction, which explains the anisotropic behaviour. In addition, studies on the morphology of the individual fracture surfaces, the grain structure of the cross-section near this region and the size distribution of ODS particles in such builds were conducted. A fine dispersion of precipitates was retained in all SLM builds, and findings suggest that a certain amount of Y is probably still in atomic solution in the as-grown condition and forms new small nanoscopic dispersoids during annealing, which lead to enhanced strengthening.

  20. Insights of ibuprofen electro-oxidation on metal-oxide-coated Ti anodes: Kinetics, energy consumption and reaction mechanisms.

    Science.gov (United States)

    Wang, Chong; Yu, Yanxin; Yin, Lifeng; Niu, Junfeng; Hou, Li-An

    2016-11-01

    Electrochemical degradation of ibuprofen (IBP) was performed on three types of Ti-based metal oxide electrodes. The degradation of IBP followed pseudo-first-order kinetics and the electrochemical degradation rate constant (k) over Ti/SnO2-Sb/Ce-PbO2 (9.4 × 10(-2) min(-1)) was 2.0 and 1.7 times of the values over Ti/Ce-PbO2 (4.7 × 10(-2) min(-1)) and Ti/SnO2-Sb (5.6 × 10(-2) min(-1)), respectively. The removal of total organic carbon and the energy consumption per order for IBP degradation were 93.2% and 13.1 Wh L(-1), respectively, under the optimal conditions using Ti/SnO2-Sb/Ce-PbO2 anode. Six aromatic intermediate products of IBP were identified by ultra-high-performance liquid chromatography coupled with a quadrupole time-of-flight mass spectrometer. The electrochemical mineralization mechanism of IBP was proposed. It was supposed that OH radicals produced on the surface of anode attacked IBP to form hydroxylated IBP derivatives that were then followed by a series of hydroxylation, loss of isopropanol and isopropyl, decarboxylation and benzene ring cleavage processes to form simple linear carboxylic acids. By successive hydroxylation, these carboxylic acids were then oxidized to CO2 and H2O, achieving the complete mineralization of IBP.

  1. Synthesis Mechanism of Low-Voltage Praseodymium Oxide Doped Zinc Oxide Varistor Ceramics Prepared Through Modified Citrate Gel Coating

    Directory of Open Access Journals (Sweden)

    Wan Rafizah Wan Abdullah

    2012-04-01

    Full Text Available High demands on low-voltage electronics have increased the need for zinc oxide (ZnO varistors with fast response, highly non-linear current-voltage characteristics and energy absorption capabilities at low breakdown voltage. However, trade-off between breakdown voltage and grain size poses a critical bottle-neck in the production of low-voltage varistors. The present study highlights the synthesis mechanism for obtaining praseodymium oxide (Pr6O11 based ZnO varistor ceramics having breakdown voltages of 2.8 to 13.3 V/mm through employment of direct modified citrate gel coating technique. Precursor powder and its ceramics were examined by means of TG/DTG, FTIR, XRD and FESEM analyses. The electrical properties as a function of Pr6O11 addition were analyzed on the basis of I-V characteristic measurement. The breakdown voltage could be adjusted from 0.01 to 0.06 V per grain boundary by controlling the amount of Pr6O11 from 0.2 to 0.8 mol%, without alteration of the grain size. The non-linearity coefficient, α, varied from 3.0 to 3.5 and the barrier height ranged from 0.56 to 0.64 eV. Breakdown voltage and α lowering with increasing Pr6O11 content were associated to reduction in the barrier height caused by variation in O vacancies at grain boundary.

  2. Mechanical characterisation of tungsten–1 wt.% yttrium oxide as a function of temperature and atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Palacios, T.; Jiménez, A. [Materials Science Department, Technical University of Madrid, E.T.S. de Ingenieros de Caminos, Canales y Puertos, C/Profesor Aranguren s/n, 28040 Madrid (Spain); Muñóz, A.; Monge, M.A.; Ballesteros, C. [Departamento de Física, Universidad Carlos III de Madrid, Leganés (Spain); Pastor, J.Y. [Materials Science Department, Technical University of Madrid, E.T.S. de Ingenieros de Caminos, Canales y Puertos, C/Profesor Aranguren s/n, 28040 Madrid (Spain)

    2014-11-15

    This study evaluates the mechanical behaviour of an Y{sub 2}O{sub 3}-dispersed tungsten (W) alloy and compares it to a pure W reference material. Both materials were processed via mechanical alloying (MA) and subsequent hot isostatic pressing (HIP). We performed non-standard three-point bending (TPB) tests in both an oxidising atmosphere and vacuum across a temperature range from 77 K, obtained via immersion in liquid nitrogen, to 1473 K to determine the mechanical strength, yield strength and fracture toughness. This research aims to evaluate how the mechanical behaviour of the alloy is affected by oxides formed within the material at high temperatures, primarily from 873 K, when the materials undergo a massive thermal degradation. The results indicate that the alloy is brittle to a high temperature (1473 K) under both atmospheres and that the mechanical properties degrade significantly above 873 K. We also used Vickers microhardness tests and the dynamic modulus by impulse excitation technique (IET) to determine the elastic modulus at room temperature. Moreover, we performed nanoindentation tests to determine the effect of size on the hardness and elastic modulus; however, no significant differences were found. Additionally, we calculated the relative density of the samples to assess the porosity of the alloy. Finally, we analysed the microstructure and fracture surfaces of the tested materials via field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In this way, the relationship between the macroscopic mechanical properties and micromechanisms of failure could be determined based on the temperature and oxides formed.

  3. Mechanical characterisation of tungsten-1 wt.% yttrium oxide as a function of temperature and atmosphere

    Science.gov (United States)

    Palacios, T.; Jiménez, A.; Muñóz, A.; Monge, M. A.; Ballesteros, C.; Pastor, J. Y.

    2014-11-01

    This study evaluates the mechanical behaviour of an Y2O3-dispersed tungsten (W) alloy and compares it to a pure W reference material. Both materials were processed via mechanical alloying (MA) and subsequent hot isostatic pressing (HIP). We performed non-standard three-point bending (TPB) tests in both an oxidising atmosphere and vacuum across a temperature range from 77 K, obtained via immersion in liquid nitrogen, to 1473 K to determine the mechanical strength, yield strength and fracture toughness. This research aims to evaluate how the mechanical behaviour of the alloy is affected by oxides formed within the material at high temperatures, primarily from 873 K, when the materials undergo a massive thermal degradation. The results indicate that the alloy is brittle to a high temperature (1473 K) under both atmospheres and that the mechanical properties degrade significantly above 873 K. We also used Vickers microhardness tests and the dynamic modulus by impulse excitation technique (IET) to determine the elastic modulus at room temperature. Moreover, we performed nanoindentation tests to determine the effect of size on the hardness and elastic modulus; however, no significant differences were found. Additionally, we calculated the relative density of the samples to assess the porosity of the alloy. Finally, we analysed the microstructure and fracture surfaces of the tested materials via field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In this way, the relationship between the macroscopic mechanical properties and micromechanisms of failure could be determined based on the temperature and oxides formed.

  4. Effect of Y2O3 and Total Oxide Addition on Mechanical Properties of Pressureless Sintered β-SiC

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The effect of Y2O3 and the total oxide volume fraction (Y2O3+Al2O3) on density and mechanical properties of lowtemperature (1770~1940℃) pressureless sintered β-SiC ceramics were presented. The optimum temperature forpressureless sintering of β-SiC was found to be ~1850℃ and the optimum content of Y2O3 in the oxides was foundto be between 40 and 57 wt pct. The highest sintered density was achieved by adding oxides at 14 vol. pct. Both ofthe highest strength and fracture toughness were achieved at ~14 vol. pct oxide addition and yttria concentrationsbetween 40 and 57 wt pct in the oxides. Hardness, on the other hand, was found to be the highest for samples with14 vol. pct oxide addition and ~64 wt pct Y2O3 in oxides.

  5. Oxidized low-density lipoprotein (Ox-LDL) impacts on erythrocyte viscoelasticity and its molecular mechanism.

    Science.gov (United States)

    Wang, Xiang; Yang, Li; Liu, Yao; Gao, Wei; Peng, Weiyan; Sung, K-L Paul; Sung, Lanping Amy

    2009-10-16

    The oxidized low-density lipoprotein (Ox-LDL) plays an important role in atherosclerosis, yet it remains unclear if it damages circulating erythrocytes. In this study, erythrocyte deformability and its membrane proteins after Ox-LDL incubations are investigated by micropipette aspiration, thiol radical measurement, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Results show that Ox-LDL incubation reduces the erythrocyte deformability, decreases free thiol radical contents in erythrocytes, and induces the cross-linking among membrane proteins. SDS-PAGE analysis reveals a high molecular weight (HMW) complex as well as new bands between spectrins and band 3 and reduced ratios between band 3 and other major membrane skeletal proteins. Analyses indicate that Ox-LDL makes erythrocytes harder to deform through a molecular mechanism by which the oxidation of free thiol radicals forms disulfide bonds among membrane skeletal proteins.

  6. [Oxidative stress in patients with mechanical jaundice of different origin and severity].

    Science.gov (United States)

    Silina, E V; Stupin, V A; Gakhramanov, T V; Khokonov, M A; Bolevich, S B; Men'shova, N I; Sinel'nikova, T G

    2011-01-01

    This randomized clinical study included 118 patients with mechanical jaundice (MJ) of different origin and severity. It highlighted the role of free radical-generation processes (FRP) in the development of the disease within 1 day after its onset. Disbalance of FRP affects oxygen and lipid components of oxidative stress and is especially well pronounced in severe cases and in patients with tumours. It becomes increasingly apparent with time from the onset of jaundice and endotoxicosis. FRP disbalance precedes clinical manifestation of jaundice and persists for a long time even after alleviation of its clinical symptoms. Certain signs have a prognostic values. Therapy with reamberin at a daily dose of 400 ml is shown to effectively correct oxidative stress associated with MJ of tumorous and non-tumorous origin regardless of the severity of the disease. Positive effect of antioxidative therapy is accompanied by the improvement of laboratory characteristics, clinical picture, and outcome of the disease.

  7. Mechanism of scaling on oxidation reactor wall in TiO2 synthesis by chloride process

    Institute of Scientific and Technical Information of China (English)

    ZHOU E; YUAN Zhang-fu; WANG Zhi; FANG Xian-Guo; GONG Jia-Zhu

    2006-01-01

    The mechanism of scaling on the oxidation reactor wall in TiO2 synthesis process was investigated. The formation of wall scale is mostly due to being deposited and sintered of TiO2 particle formed in the gas phase reaction of TiCl4 with O2. The gas-phase oxidation of TiCl4 was in a high temperature tubular flow reactor with quartz and ceramic rods put in center respectively. Scale layers are formed on reactor wall and two rods. Morphology and phase composition of them were characterized by transmission electron microscope(TEM), scan electron micrographs(SEM) and X-ray diffraction(XRD). The state of reactor wall has a little effect on scaling formation. With uneven temperature distribution along axial of reactor, the higher the reaction temperature is, the thicker the scale layer and the more compact the scale structure is.

  8. Abiotic and biological mechanisms of nitric oxide removal from waste air in biotrickling filters.

    Science.gov (United States)

    Chen, Jian-Meng; Ma, Jian-Feng

    2006-01-01

    Nitric oxide (NO) may participate in the ozone layer depletion and forming of nitric acid. Abiotic and biological mechanisms of NO removal from waste gases were studied in a biotrickling filter. The abiotic NO removal rate in the biotrickling filter was estimated by a review of the literature. The abiotic and biological removals were also verified in the biotrickling filter. The result has shown that chemical oxidation and bionitrification were both involved in the NO removal. It was found that the NO removal in high concentration (approximately 1000 ppm or higher) was in large measure the result of abiotic removal in both gas-phase and liquid-phase reactions. When NO concentration is low (less than approximately 100 ppm), bionitrification was the main process in the NO removal process in the biotrickling filter.

  9. Effect of coatings on oxidation resistance and mechanical performance of Ti60 alloy

    Energy Technology Data Exchange (ETDEWEB)

    Tang Zhaolin; Wang Fuhui; Wu Weitao [Academia Sinica, Shenyang, LN (China). Inst. of Corrosion and Protection of Metals; Wang Qingjiang; Li Dong [Institute of Metals Research, The Chinese Academy of Sciences, Shenyang 110015 (China)

    1998-10-31

    The effect of several sputtered coatings on oxidation resistance and mechanical performance of Ti60 alloy was investigated. Sputtered pure Al, Ti-36Al, Ni-16Cr-2.5Al(wt%) coatings and reactively-sputtered Al{sub 2}O{sub 3} film were effective in inhibiting the oxidation and oxygen-embrittlement of Ti60 alloy at 600-700 C, while Al{sub 2}O{sub 3} and TiAl coatings exhibited a better effect than Al and NiCrAl coatings from the point of view of coating-substrate compatibility. The tensile test after 100h exposure at 600 C in air also showed that Ti60 alloy with Al{sub 2}O{sub 3} and TiAl coatings exhibited a higher ductility than that with Al and NiCrAl coatings, which exhibited a good correlation with coating-substrate compatibility. (orig.) 17 refs.

  10. Reaction Mechanism of Thiophene on Vanadium Oxides under FCC Operating Conditions

    Institute of Scientific and Technical Information of China (English)

    Wang Peng; Zheng Aiguo; Tian Huiping; Long Jun

    2004-01-01

    The reaction mechanism of thiophene on vanadium oxides under FCC operating conditions had been preliminary studied using in-situ FT-IR analysis of thiophene and atmospheric pressure continuous fixed-bed reaction, followed by characterization via pyridine adsorption-temperature programmed desorption method, and FT-IR and XPS spectra. The research had discovered that, under 500C thiophene could undergo the redox reaction with V2O5, while being converted into CO, CO2 as well as SO2 with its conversion rate reaching 41.2%. At the same time the oxidation number of vanadium decreased. The existence of a few Bronsted acid centers on V2O5 could lead to an increase of H2S yield among the products derived from the reaction with thiophene.

  11. Mechanical behaviors of alumina ceramics doped with rare-earth oxides

    Institute of Scientific and Technical Information of China (English)

    YAO Yijun; LI Chuncheng; WANG Ling; JIANG Xiaolong; QIU Tai

    2010-01-01

    The effects of three types of additives Y2O3, La2O3, and Sm2O3 on the sintering and mechanical behaviors of alumina ceramics were investigated. The bending strengths of alumina ceramics with Sm2O3 and Y2O3 additions were 455 and 439 MPa, respectively, higher than that with La2O3 addition. The fracture toughness of the ceramics with Sm2O3 and Y2O3 were also higher than that with La2O3 addition. The fracture mode of rare earth oxides doped alumina ceramics exhibited obvious transgranular fractures as well as intergranular fracture. The results of research show that the improvement of bending strength and fracture toughness of alumina ceramics with rare earth oxides was achieved by refining the grain size and strengthening the grain boundary.

  12. FORMATION MECHANISM OF NANOSIZED TIN OXIDE (SnO2 POWDER DURING HYDROTHERMAL SYNTHESIS

    Directory of Open Access Journals (Sweden)

    M. Ozan ÖZER

    2011-06-01

    Full Text Available Preparation of nanosized SnO₂ electroceramic powders via hydrothermal synthesis was investigated as a function of initial concentration and treatment time in order to understand the formation and growth mechanisms. SnO₂ powder was successfully synthesized from the hydrous tin oxide by hydro- thermal synthesis at 200°C. Crystalline SnO₂ particles with a specific surface area as high as 170 m₂/g were produced in a single step without requiring any calcination process. As initial concentration of metal cation increases from 0.0125 to 0.05 M, an Ostwald ripening type growth process was observed in the crystallite size from 3.1 to 4.6 nm. Evolution of tin oxide particles was also investigated by al- tering the treatment time from 1 to 24 h and a diffusion controlled growth behavior was observed as a function of synthesis time.

  13. Antimicrobial properties and mechanism of magnesium oxide nanoparticles on Campylobacter, E. coli O157:H7, and Salmonella

    Science.gov (United States)

    Background: Metal oxide nanoparticles have considerable potential as antimicrobial agents in food safety applications due to their structure, surface properties, and stability. In this study, the antibacterial effects and mechanisms of Magnesium Oxide Nanoparticles (MgO NPs, with an average size o...

  14. Treatment of statin compounds by advanced oxidation processes: Kinetic considerations and destruction mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Razavi, Behnaz, E-mail: brazavi@uci.ed [Urban Water Research Center, Department of Civil and Environmental Engineering, University of California, Irvine, Irvine, CA 92697-2175 (United States); Song Weihua, E-mail: wsong@uci.ed [Urban Water Research Center, Department of Civil and Environmental Engineering, University of California, Irvine, Irvine, CA 92697-2175 (United States); Santoke, Hanoz, E-mail: hsantoke@uci.ed [Urban Water Research Center, Department of Civil and Environmental Engineering, University of California, Irvine, Irvine, CA 92697-2175 (United States); Cooper, William J., E-mail: wcooper@uci.ed [Urban Water Research Center, Department of Civil and Environmental Engineering, University of California, Irvine, Irvine, CA 92697-2175 (United States)

    2011-03-15

    This study examined the use of advanced oxidation/reduction processes (AO/RPs) for the destruction of cholesterol lowering statin pharmaceuticals. AO/RPs which utilize the oxidizing hydroxyl radical ({sup {center_dot}O}H) and reducing aqueous electron (e{sup -}{sub aq}), to degrade chemical contaminants are alternatives to traditional water treatment methods, and are alternatives as water reuse becomes more generally implemented. Four major statin pharmaceuticals, fluvastatin, lovastatin, pravastatin and simvastatin, were studied, and the absolute bimolecular reaction rate constants with {sup {center_dot}O}H determined, (6.96{+-}0.16)x10{sup 9}, (2.92{+-}0.06)x10{sup 9}, (4.16{+-}0.13)x10{sup 9}, and (3.13{+-}0.15)x10{sup 9} M{sup -1} s{sup -1}, and for e{sup -}{sub aq} (2.31{+-}0.06)x10{sup 9}, (0.45{+-}0.01)x10{sup 9}, (1.26{+-}0.01)x10{sup 9}, and (0.69{+-}0.02)x10{sup 9} M{sup -1} s{sup -1}, respectively. To provide additional information on the radicals formed upon oxidation, transient spectra were measured and the overall reaction efficiency determined. Radical-based destruction mechanisms for destruction of the statins are proposed based on the LC-MS determination of the stable reaction by-products formed using {sup 137}Cs {gamma}-irradiation of statin solutions. Knowing the reaction rates, reaction efficiencies and destruction mechanisms of these compounds is essential for the consideration of the use of advanced oxidation/reduction processes for the destruction of statins in aqueous systems.

  15. Treatment of statin compounds by advanced oxidation processes: Kinetic considerations and destruction mechanisms

    Science.gov (United States)

    Razavi, Behnaz; Song, Weihua; Santoke, Hanoz; Cooper, William J.

    2011-03-01

    This study examined the use of advanced oxidation/reduction processes (AO/RPs) for the destruction of cholesterol lowering statin pharmaceuticals. AO/RPs which utilize the oxidizing hydroxyl radical ( rad OH) and reducing aqueous electron (e -aq), to degrade chemical contaminants are alternatives to traditional water treatment methods, and are alternatives as water reuse becomes more generally implemented. Four major statin pharmaceuticals, fluvastatin, lovastatin, pravastatin and simvastatin, were studied, and the absolute bimolecular reaction rate constants with rad OH determined, (6.96±0.16)×10 9, (2.92±0.06)×10 9, (4.16±0.13)×10 9, and (3.13±0.15)×10 9 M -1 s -1, and for e -aq (2.31±0.06)×10 9, (0.45±0.01)×10 9, (1.26±0.01)×10 9, and (0.69±0.02)×10 9 M -1 s -1, respectively. To provide additional information on the radicals formed upon oxidation, transient spectra were measured and the overall reaction efficiency determined. Radical-based destruction mechanisms for destruction of the statins are proposed based on the LC-MS determination of the stable reaction by-products formed using 137Cs γ-irradiation of statin solutions. Knowing the reaction rates, reaction efficiencies and destruction mechanisms of these compounds is essential for the consideration of the use of advanced oxidation/reduction processes for the destruction of statins in aqueous systems.

  16. Boldine protects endothelial function in hyperglycemia-induced oxidative stress through an antioxidant mechanism.

    Science.gov (United States)

    Lau, Yeh Siang; Tian, Xiao Yu; Huang, Yu; Murugan, Dharmani; Achike, Francis I; Mustafa, Mohd Rais

    2013-02-01

    Increased oxidative stress is involved in the pathogenesis and progression of diabetes. Antioxidants are therapeutically beneficial for oxidative stress-associated diseases. Boldine ([s]-2,9-dihydroxy-1,10-dimethoxyaporphine) is a major alkaloid present in the leaves and bark of the boldo tree (Peumus boldus Molina), with known an antioxidant activity. This study examined the protective effects of boldine against high glucose-induced oxidative stress in rat aortic endothelial cells (RAEC) and its mechanisms of vasoprotection related to diabetic endothelial dysfunction. In RAEC exposed to high glucose (30 mM) for 48 h, pre-treatment with boldine reduced the elevated ROS and nitrotyrosine formation, and preserved nitric oxide (NO) production. Pre-incubation with β-NAPDH reduced the acetylcholine-induced endothelium-dependent relaxation; this attenuation was reversed by boldine. Compared with control, endothelium-dependent relaxation in the aortas of streptozotocin (STZ)-treated diabetic rats was significantly improved by both acute (1 μM, 30 min) and chronic (20mg/kg/daily, i.p., 7 days) treatment with boldine. Intracellular superoxide and peroxynitrite formation measured by DHE fluorescence or chemiluminescence assay were higher in sections of aortic rings from diabetic rats compared with control. Chronic boldine treatment normalized ROS over-production in the diabetic group and this correlated with reduction of NAD(P)H oxidase subunits, NOX2 and p47(phox). The present study shows that boldine reversed the increased ROS formation in high glucose-treated endothelial cells and restored endothelial function in STZ-induced diabetes by inhibiting oxidative stress and thus increasing NO bioavailability. Copyright © 2012 Elsevier Inc. All rights reserved.

  17. Thermally evaporated mechanically hard tin oxide thin films for opto-electronic apllications

    Energy Technology Data Exchange (ETDEWEB)

    Tripathy, Sumanta K.; Rajeswari, V. P. [Centre for Nano Science and Technology, GVP College of Engineering (Autonomous), Visakhapatnam- 530048 (India)

    2014-01-28

    Tungsten doped tin oxide (WTO) and Molybdenum doped tin oxide (MoTO) thin film were deposited on corn glass by thermal evaporation method. The films were annealed at 350°C for one hour. Structural analysis using Xray diffraction data shows both the films are polycrystalline in nature with monoclinic structure of tin oxide, Sn{sub 3}O{sub 4}, corresponding to JCPDS card number 01-078-6064. SEM photograph showed that both the films have spherical grains with size in the range of 20–30 nm. Compositional analysis was carried out using EDS which reveals the presence of Sn, O and the dopant Mo/W only thereby indicating the absence of any secondary phase in the films. The films are found to contain nearly 6 wt% of Mo, 8 wt% of W as dopants respectively. The transmission pattern for both the films in the spectral range 200 – 2000 nm shows that W doping gives a transparency of nearly 80% from 380 nm onwards while Mo doping has less transparency of 39% at 380nm. Film hardness measurement using Triboscope shows a film hardness of about 9–10 GPa for both the films. It indicates that W or M doping in tin oxide provides the films the added advantage of withstanding the mechanical wear and tear due to environmental fluctuations By optimizing the optical and electrical properties, W/Mo doped tin oxide films may be explored as window layers in opto-electronic applications such as solar cells.

  18. Reaction Mechanism for m- Xylene Oxidation in the Claus Process by Sulfur Dioxide

    KAUST Repository

    Sinha, Sourab

    2015-09-24

    In the Claus process, the presence of aromatic contaminants such benzene, toluene, and xylenes (BTX), in the H2S feed stream has a detrimental effect on catalytic reactors, where BTX form soot particles and clog and deactivate the catalysts. Among BTX, xylenes are proven to be most damaging contaminant for catalysts. BTX oxidation in the Claus furnace, before they enter catalyst beds, provides a solution to this problem. A reaction kinetics study on m-xylene oxidation by SO2, an oxidant present in Claus furnace, is presented. The density functional theory is used to study the formation of m-xylene radicals (3-methylbenzyl, 2,6-dimethylphenyl, 2,4-dimethylphenyl, and 3,5-dimethylphenyl) through H-abstraction and their oxidation by SO2. The mechanism begins with SO2 addition on the radicals through an O-atom rather than the S-atom with the release of 180.0-183.1 kJ/mol of reaction energies. This exothermic reaction involves energy barriers in the range 3.9-5.2 kJ/mol for several m-xylene radicals. Thereafter, O-S bond scission takes place to release SO, and the O-atom remaining on aromatics leads to CO formation. Among four m-xylene radicals, the resonantly stabilized 3-methylbenzyl exhibited the lowest SO2 addition and SO elimination rates. The reaction rate constants are provided to facilitate Claus process simulations to find conditions suitable for BTX oxidation. © 2015 American Chemical Society.

  19. Mechanism of H2S-mediated protection against oxidative stress in Escherichia coli.

    Science.gov (United States)

    Mironov, Alexander; Seregina, Tatyana; Nagornykh, Maxim; Luhachack, Lyly G; Korolkova, Natalya; Lopes, Liubov Errais; Kotova, Vera; Zavilgelsky, Gennady; Shakulov, Rustem; Shatalin, Konstantin; Nudler, Evgeny

    2017-06-06

    Endogenous hydrogen sulfide (H2S) renders bacteria highly resistant to oxidative stress, but its mechanism remains poorly understood. Here, we report that 3-mercaptopyruvate sulfurtransferase (3MST) is the major source of endogenous H2S in Escherichia coli Cellular resistance to H2O2 strongly depends on the activity of mstA, a gene that encodes 3MST. Deletion of the ferric uptake regulator (Fur) renders ∆mstA cells hypersensitive to H2O2 Conversely, induction of chromosomal mstA from a strong pLtetO-1 promoter (P tet -mstA) renders ∆fur cells fully resistant to H2O2 Furthermore, the endogenous level of H2S is reduced in ∆fur or ∆sodA ∆sodB cells but restored after the addition of an iron chelator dipyridyl. Using a highly sensitive reporter of the global response to DNA damage (SOS) and the TUNEL assay, we show that 3MST-derived H2S protects chromosomal DNA from oxidative damage. We also show that the induction of the CysB regulon in response to oxidative stress depends on 3MST, whereas the CysB-regulated l-cystine transporter, TcyP, plays the principle role in the 3MST-mediated generation of H2S. These findings led us to propose a model to explain the interplay between l-cysteine metabolism, H2S production, and oxidative stress, in which 3MST protects E. coli against oxidative stress via l-cysteine utilization and H2S-mediated sequestration of free iron necessary for the genotoxic Fenton reaction.

  20. Mechanisms of oxidation of guanine in DNA by carbonate radical anion, a decomposition product of nitrosoperoxycarbonate.

    Science.gov (United States)

    Lee, Young Ae; Yun, Byeong Hwa; Kim, Seog K; Margolin, Yelena; Dedon, Peter C; Geacintov, Nicholas E; Shafirovich, Vladimir

    2007-01-01

    Peroxynitrite is produced during inflammation and combines rapidly with carbon dioxide to yield the unstable nitrosoperoxycarbonate, which decomposes (in part) to CO(3) (.-) and (.)NO(2) radicals. The CO(3) (.-) radicals oxidize guanine bases in DNA through a one-electron transfer reaction process that ultimately results in the formation of stable guanine oxidation products. Here we have explored these mechanisms, starting with a spectroscopic study of the kinetics of electron transfer from 20-22mer double-stranded oligonucleotides to CO(3) (.-) radicals, together with the effects of base sequence on the formation of the end-products in runs of one, two, or three contiguous guanines. The distributions of these alkali-labile lesions were determined by gel electrophoresis methods. The cascade of events was initiated through the use of 308 nm XeCl excimer laser pulses to generate CO(3) (.-) radicals by an established method based on the photodissociation of persulfate to sulfate radicals and the oxidation of bicarbonate. Although the Saito model (Saito et al., J. Am. Chem. Soc. 1995, 117, 6406-6407) predicts relative ease of one-electron oxidations in DNA, following the trend 5'-GGG > 5'-GG > 5'-G, we found that the rate constants for CO(3) (.-)-mediated oxidation of guanines in these sequence contexts (k(5)) showed only small variation within a narrow range [(1.5-3.0)x10(7) M(-1) s(-1)]. In contrast, the distributions of the end-products are dependent on the base sequence context and are higher at the 5'-G in 5'-GG sequences and at the first two 5'-guanines in the 5'-GGG sequences. These effects are attributed to a combination of initial hole distributions among the contiguous guanines and the subsequent differences in chemical reaction yields at each guanine. The lack of dependence of k(5) on sequence context indicates that the one-electron oxidation of guanine in DNA by CO(3) (.-) radicals occurs by an inner-sphere mechanism.

  1. Silicon oxide nanowire growth mechanisms revealed by real-time electron microscopy

    Science.gov (United States)

    Kolíbal, Miroslav; Novák, Libor; Shanley, Toby; Toth, Milos; Šikola, Tomáš

    2015-12-01

    Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains contradictory results reported in prior studies. We also show that under wet atmospheres the Ga droplets can be mobile and promote nanowire growth as they traverse the silicon substrate.Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains

  2. Datasets used in the manuscript titled "Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms and organic aerosol"

    Data.gov (United States)

    U.S. Environmental Protection Agency — This dataset documents that all of the data used in the manuscript "Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic...

  3. Mechanical Characterization of Hybrid Vesicles Based on Linear Poly(Dimethylsiloxane-b-Ethylene Oxide) and Poly(Butadiene-b-Ethylene Oxide) Block Copolymers

    OpenAIRE

    2016-01-01

    Poly(dimethylsiloxane-ethylene oxide) (PDMS-PEO) and poly(butadiene-b-ethylene oxide) (PBd-PEO) are two block copolymers which separately form vesicles with disparate membrane permeabilities and fluidities. Thus, hybrid vesicles formed from both PDMS-PEO and PBd-PEO may ultimately allow for systematic, application-specific tuning of vesicle membrane fluidity and permeability. However, given the relatively low strength previously noted for comb-type PDMS-PEO vesicles, the mechanical robustness...

  4. Mechanisms for Electron Transfer Through Pili to Fe(III) Oxide in Geobacter

    Energy Technology Data Exchange (ETDEWEB)

    Lovley, Derek R. [Univ. of Massachusetts, Amherst, MA (United States)

    2015-03-09

    The purpose of these studies was to aid the Department of Energy in its goal of understanding how microorganisms involved in the bioremediation of metals and radionuclides sustain their activity in the subsurface. This information is required in order to incorporate biological processes into decision making for environmental remediation and long-term stewardship of contaminated sites. The proposed research was designed to elucidate the mechanisms for electron transfer to Fe(III) oxides in Geobacter species because Geobacter species are abundant dissimilatory metal-reducing microorganisms in a diversity of sites in which uranium is undergoing natural attenuation via the reduction of soluble U(VI) to insoluble U(IV) or when this process is artificially stimulated with the addition of organic electron donors. This study investigated the novel, but highly controversial, concept that the final conduit for electron transfer to Fe(III) oxides are electrically conductive pili. The specific objectives were to: 1) further evaluate the conductivity along the pili of Geobacter sulfurreducens and related organisms; 2) determine the mechanisms for pili conductivity; and 3) investigate the role of pili in Fe(III) oxide reduction. The studies demonstrated that the pili of G. sulfurreducens are conductive along their length. Surprisingly, the pili possess a metallic-like conductivity similar to that observed in synthetic organic conducting polymers such as polyaniline. Detailed physical analysis of the pili, as well as studies in which the structure of the pili was genetically modified, demonstrated that the metallic-like conductivity of the pili could be attributed to overlapping pi-pi orbitals of aromatic amino acids. Other potential mechanisms for conductivity, such as electron hopping between cytochromes associated with the pili were definitively ruled out. Pili were also found to be essential for Fe(III) oxide reduction in G. metallireducens. Ecological studies demonstrated

  5. Cyclobutyl methyl ketone as a model compound for pinonic acid to elucidate oxidation mechanisms

    Directory of Open Access Journals (Sweden)

    A. P. Praplan

    2012-04-01

    Full Text Available 3-Methyl-1,2,3-tricarboxylic acid (MBTCA, terpenylic acid and diaterpenylic acid acetate were identified in secondary organic aerosol (SOA from α-pinene photooxidation or ozonolysis. These compounds display interesting structural features: MBTCA has a high oxygen to carbon ratio, terpenylic acid contains a lactone ring in its structure and diaterpenylic acid acetate possesses an ester functional group. The reaction mechanisms leading to these products are still unknown, but it was demonstrated experimentally in earlier studies that MBTCA is formed from pinonic acid, a primary ozonolysis product of α-pinene. Because the direct observation of pinonic acid oxidation in a smog chamber would be difficult due to its relatively low volatility, a model compound possessing the substructure of interest was used instead: cyclobutyl methyl ketone (CMK. From its oxidation, several organic acids could be measured with ion chromatography (IC coupled to a mass spectrometer (MS. Succinic acid, the analogous product of MBTCA is formed at molar yields of 2 to 5%. Butyrolactone is detected as butanoic acid, due to hydrolysis in the sampling device. A monocarboxylic acid with nominal mass 146 was detected in the absence of nitrogen oxides (NOx and could be the analogous product of diaterpenylic acid acetate. However, due to a lack of available standards, the exact structure of this compound remains unelucidated. Finally, 4-oxobutanoic acid could also be measured and two structures of its expected analogous compound from pinonic acid oxidation are proposed. Because these compounds are primary products of the CMK oxidation, reaction mechanisms capable of adding one or two carboxylic functional groups without formation of stable intermediate products needs to be formulated. Such a formation mechanism of MBTCA from pinonic acid was found in the literature; however, it includes a hydrogen atom migration to an acyloxy radical, which is expected to loose

  6. Hydrogen sulfide increases nitric oxide production from endothelial cells by an Akt-dependent mechanism

    Directory of Open Access Journals (Sweden)

    Arturo J Cardounel

    2011-12-01

    Full Text Available Hydrogen sulfide (H2S and nitric oxide (NO are both gasotransmitters that can elicit synergistic vasodilatory responses in the in the cardiovascular system, but the mechanisms behind this synergy are unclear. In the current study we investigated the molecular mechanisms through which H2S regulates endothelial NO production. Initial studies were performed to establish the temporal and dose-dependent effects of H2S on NO generation using EPR spin trapping techniques. H2S stimulated a two-fold increase in NO production from endothelial nitric oxide synthase (eNOS, which was maximal 30 min after exposure to 25-150 µM H2S. Following 30 min H2S exposure, eNOS phosphorylation at Ser 1177 was significantly increased compared to control, consistent with eNOS activation. Pharmacological inhibition of Akt, the kinase responsible for Ser 1177 phosphorylation, attenuated the stimulatory effect of H2S on NO production. Taken together, these data demonstrate that H2S up-regulates NO production from eNOS through an Akt-dependent mechanism. These results implicate H2S in the regulation of NO in endothelial cells, and suggest that deficiencies in H2S signaling can directly impact processes regulated by NO.

  7. Bioactivity and mechanical behaviour of cobalt oxide-doped bioactive glass

    Indian Academy of Sciences (India)

    Vikash Kumar Vyas; Arepalli Sampath Kumar; Sunil Prasad; S P Singh; Ram Pyare

    2015-08-01

    Bioactive glasses are materials capable of bonding implants to tissues. 45S5 Bio-glass® is one such material capable of bonding strongly to bone within 6 weeks. It develops a hydroxy-carbonate apatite layer on the implant that is chemically and crystallographically equivalent to the mineral phase of bone. However, it suffers from a mechanical weakness and low fracture toughness due to an amorphous glass network and is not suitable for load-bearing applications. In order to improve its mechanical strength and bioactivity, the present work explores the effects of cobalt oxide additions. Bioactivity of the glass samples was assessed through their hydroxyapatite formation ability by immersing them in the simulated body fluid for different soaking periods. The formation of hydroxyapatite was confirmed by Fourier transform infrared spectrometry, pH measurement and microstructure evaluation through scanning electron microscopy. Densities and mechanical properties of the samples were found to increase considerably with an increase in the concentration of cobalt oxide.

  8. Influence of graphene oxide on mechanical, morphological, barrier, and electrical properties of polymer membranes

    Directory of Open Access Journals (Sweden)

    Ali Ammar

    2016-03-01

    Full Text Available This paper expresses a short review of research on the effects of graphene oxide (GO as a nanocomposite element on polymer morphology and resulting property modifications including mechanical, barrier, and electrical conductivity. The effects on mechanical enhancement related to stress measurements in particular are a focus of this review. To first order, varying levels of aggregation of GO in different polymer matrices as a result of their weak inter-particle attractive interactions mainly affect the nanocomposite mechanical properties. The near surface dispersion of GO in polymer/GO nanocomposites can be investigated by studying the surface morphology of these nanocomposites using scanning probe microscopy such as atomic force microscope (AFM and scanning electron microscope (SEM. In the bulk, GO dispersion can be studied by wide-angle X-ray scattering (WAXD by analyzing the diffraction peaks corresponding to the undispersed GO fraction in the polymer matrix. In terms of an application, we review how the hydrophilicity of graphene oxide and its hydrogen bonding potential can enhance water flux of these nanocomposite materials in membrane applications. Likewise, the electrical conductivity of polymer films and bulk polymers can be advantageously enhanced via the percolative dispersion of GO nanoparticles, but this typically requires some additional chemical treatment of the GO nanoparticles to transform it to reduced GO.

  9. Mechanisms and chemistry of dye adsorption on manganese oxides-modified diatomite.

    Science.gov (United States)

    Al-Ghouti, Mohammad A; Al-Degs, Yehya S; Khraisheh, Majeda A M; Ahmad, Mohammad N; Allen, Stephen J

    2009-08-01

    The investigations into structural changes which occur during adsorbent modification and the adsorption mechanisms are essential for an effective design of adsorption systems. Manganese oxides were impregnated onto diatomite to form the type known as delta-birnessite. Initial investigations established the effectiveness of manganese oxides-modified diatomite (MOMD) to remove basic and reactive dyes from aqueous solution. The adsorption capacity of MOMD for methylene blue (MB), hydrolysed reactive black (RB) and hydrolysed reactive yellow (RY) was 320, 419, and 204mg/g, respectively. Various analytical techniques were used to characterise the structure and the mechanisms of the dye adsorption process onto MOMD such as Fourier transform infrared (FTIR), X-ray diffraction (XRD) and atomic absorption spectrometry (A.A.). A small shift to higher values of the d-spacing of dye/MOMD was observed indicating that a small amount of the dye molecules were intercalated in the MOMD structure and other molecules were adsorbed on the external surface of MOMD. Two mechanisms of dye adsorption onto MOMD were proposed; intercalation of the dye in the octahedral layers and adsorption of the dye on the MOMD external surface. Moreover, the results demonstrated that the MOMD structure was changed upon insertion of MB and RY with an obvious decrease in the intensity of the second main peak of the MOMD X-ray pattern.

  10. Reduced silanized graphene oxide/epoxy-polyurethane composites with enhanced thermal and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Jing, E-mail: linjin00112043@126.com [School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006 (China); Zhang, Peipei [Worcester Polytechnic Institute, Worcester, MA 01605 (United States); Zheng, Cheng; Wu, Xu; Mao, Taoyan; Zhu, Mingning; Wang, Huaquan; Feng, Danyan; Qian, Shuxuan; Cai, Xianfang [School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006 (China)

    2014-10-15

    Graphical abstract: The synthesis route for EPUAs/R-Si-GEO composites. - Highlights: • Reduced silanized graphene oxide as fillers. • The graphene layers were well distributed in the epoxy-polyurethane composites. • The thermal stabilities of composites were greatly improved by incorporation of the graphene. • Mechanical properties of composites were greatly enhanced by the incorporation of the graphene. - Abstract: This paper describes the synthesis of reduced silanized graphene oxide/epoxy-polyurethane (EPUAs/R-Si-GEO) composites with enhanced thermal and mechanical properties. Graphene oxide (GEO), prepared from natural graphite flakes, was modified with methacryloxypropyltrimethoxysilane to prepare silanized GEO (Si-GEO), and was then reduced by NaHSO{sub 3} to prepare R-Si-GEO (partially reduced Si-GEO). EPAc/R-Si-GEO (R-Si-GEO/epoxy acrylate copolymers) was synthesized via an in situ polymerization of R-Si-GEO and epoxy acrylic monomers. EPUAs/R-Si-GEO was obtained by curing reaction between EPAc/R-Si-GEO and an isocyanate curing agent. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used to characterize the surface and crystal structure of the modified graphene and EPUAs/R-Si-GEO. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize their morphology. Thermal gravimetric analysis (TGA), tensile strength, elongation at break, and cross-linking density measurements showed that the thermal stability and mechanical properties of EPUAs/R-Si-GEO were greatly enhanced by the addition of R-Si-GEO.

  11. Understanding flocculation mechanism of graphene oxide for organic dyes from water: Experimental and molecular dynamics simulation

    Science.gov (United States)

    Liu, Jun; Li, Peng; Xiao, Hang; Zhang, Yayun; Shi, Xiaoyang; Lü, Xiaomeng; Chen, Xi

    2015-11-01

    Flocculation treatment processes play an important role in water and wastewater pretreatment. Here we investigate experimentally and theoretically the possibility of using graphene oxide (GO) as a flocculant to remove methylene blue (MB) from water. Experimental results show that GO can remove almost all MB from aqueous solutions at its optimal dosages and molecular dynamics simulations indicate that MB cations quickly congregate around GO in water. Furthermore, PIXEL energy contribution analysis reveals that most of the strong interactions between GO and MB are of a van der Waals (London dispersion) character. These results offer new insights for shedding light on the molecular mechanism of interaction between GO and organic pollutants.

  12. A novel mechanism involved in the coupling of mitochondrial biogenesis to oxidative phosphorylation

    Directory of Open Access Journals (Sweden)

    Jelena Ostojić

    2014-01-01

    Full Text Available Mitochondria are essential organelles that are central to a multitude of cellular processes, including oxidative phosphorylation (OXPHOS, which produces most of the ATP in animal cells. Thus it is important to understand not only the mechanisms and biogenesis of this energy production machinery but also how it is regulated in both physiological and pathological contexts. A recent study by Ostojić et al. [Cell Metabolism (2013 18, 567-577] has uncovered a regulatory loop by which the biogenesis of a major enzyme of the OXPHOS pathway, the respiratory complex III, is coupled to the energy producing activity of the mitochondria.

  13. Understanding flocculation mechanism of graphene oxide for organic dyes from water: Experimental and molecular dynamics simulation

    Directory of Open Access Journals (Sweden)

    Jun Liu

    2015-11-01

    Full Text Available Flocculation treatment processes play an important role in water and wastewater pretreatment. Here we investigate experimentally and theoretically the possibility of using graphene oxide (GO as a flocculant to remove methylene blue (MB from water. Experimental results show that GO can remove almost all MB from aqueous solutions at its optimal dosages and molecular dynamics simulations indicate that MB cations quickly congregate around GO in water. Furthermore, PIXEL energy contribution analysis reveals that most of the strong interactions between GO and MB are of a van der Waals (London dispersion character. These results offer new insights for shedding light on the molecular mechanism of interaction between GO and organic pollutants.

  14. Deciphering the mechanisms against oxidative stress in developing and mature akinetes of the cyanobacterium Aphanizomenon ovalisporum.

    Science.gov (United States)

    Kaplan-Levy, Ruth N; Hadas, Ora; Sukenik, Assaf

    2015-07-01

    Cells of filamentous cyanobacteria of the orders Nostocales and Stigonematales can differentiate into dormant forms called akinetes. Akinetes play a key role in the survival, abundance and distribution of the species, contributing an inoculum for their perennial blooms. In the cyanobacterium Aphanizomenon ovalisporum, potassium deficiency triggers the formation of akinetes. Here we present experimental evidence for the production of reactive oxygen species (ROS) during akinete development in response to potassium deficiency. The function of ROS as a primer signal for akinete differentiation was negated. Nevertheless, akinetes acquired protective mechanisms against oxidative damage during their differentiation and maintained them as they matured, giving akinetes advantages enabling survival in harsh conditions.

  15. Quantum/molecular mechanics study of firefly bioluminescence on luciferase oxidative conformation

    Science.gov (United States)

    Pinto da Silva, Luís; Esteves da Silva, Joaquim C. G.

    2014-07-01

    This is the first report of a computational study of the color tuning mechanism of firefly bioluminescence, using the oxidative conformation of luciferase. The results of these calculations demonstrated that the electrostatic field generated by luciferase is fundamental both for the emission shift and efficiency. Further calculations indicated that a shift in emission is achieved by modulating the energy, at different degrees, of the emissive and ground states. These differences in energy modulation will then lead to changes in the energy gap between the states.

  16. Structure and the catalysis mechanism of oxidative chlorination in nanostructural layers of a surface of alumina

    OpenAIRE

    Kurta, Sergiy A; Mykytyn, Igor M; Tatarchuk, Tetiana R

    2014-01-01

    On the basis of X-ray diffraction and mass spectrometric analysis of carrier γ-Al2O3 and catalysts CuCl2/CuCl on its surface, the chemical structure of the active centers of two types oxidative chlorination catalysts applied and permeated type of industrial brands “Harshow” and “MEDС-B” was investigated. On the basis of quantum-mechanical theory of the crystal, field complexes were detected by the presence of CuCl2 cation stoichiometry and structure of the proposed model crystal quasichemical...

  17. Kinetics and Mechanism of Oxidation of Some Diols by Dihydroxydiperiodatoargentate(Ⅲ) in Alkaline Medium

    Institute of Scientific and Technical Information of China (English)

    SHAN, Jin-Huan; LI, Sheng-Min; HUO, Shu-Ying; SHEN, Shi-Gang; SUN, Han-Wen

    2006-01-01

    The kinetics of oxidation of ethylene glycol and 1,3-butylene glycol by dihydroxydiperiodatoargentate(Ⅲ) in alkaline medium have been studied by spectrophotometry in the range of 298.2-318.2 K. It is shown that the reaction was first order with respect to each reductant and Ag(Ⅲ), and kobs increased with an increase of [OH-]. A plausible mechanism of reaction involving a pre-equilibrium of adduct formation between complex and reductants was proposed, which could be applied to explain all experimental phenomena, and the activation parameters of the ratedetermining step have been also calculated.

  18. Green Route Fabrication of Graphene Oxide Reinforced Polymer Composites with Enhanced Mechanical Properties

    OpenAIRE

    Mahendran, R.; Sridharan, D.; Santhakumar, K.; G. Gnanasekaran

    2016-01-01

    A facile and “Green” route has been applied to fabricate graphene oxide (GO) reinforced polymer composites utilizing “deionized water” as solvent. The GO was reinforced into water soluble poly(vinyl alcohol) (PVA) and poly-2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) matrix by ultrasonication followed by mechanical stirring. The incorporation and dispersion of the GO in the polymer matrix were analyzed by XRD, FE-SEM, AFM, FT-IR, and TGA. Further, the FE-SEM and AFM images revealed th...

  19. Formation Mechanism of Nanosized Tin Oxide (SnO2) Powder During Hydrothermal Synthesis

    OpenAIRE

    M. Ozan ÖZER; Suvaci, Ender; DOĞAN, Aydın

    2011-01-01

    Preparation of nanosized SnO2 electroceramic powders via hydrothermal synthesis was investigated as a function of initial concentration and treatment time in order to understand the formation and growth mechanisms.  SnO2 powder was successfully synthesized from the hydrous tin oxide by hydrothermal synthesis at 200°C.  Crystalline SnO2 particles with a specific surface area as high as 170 m2/g were produced in a single step without requiring any calcination process.  As ini...

  20. A Proposed Mechanism of Photocatalytic Oxidation of Trichloroethylene in Gas Phase

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    GC/MS has been used to identify gas phase products and intermediates formed during the gas phase photocatalytic oxidation of trichloroethylene (TCE) on TiO2 with low BET surface area.A new byproduct, oxalyl choloride (ClCOCOCl) was detected together with other byproducts such as COCl2, CHCl3, DCAC and C2HCl5.Firstly the method of perturbation on the reaction system was conducted.Very little amount of water was carried into the feed gas and subsequent changes were observed.The discussion based on the product distribution changes led to a postulated mechanism consisting of two stages.

  1. Effect of Oxide Nanoparticles on Thermal and Mechanical Properties of Electrospun Separators for Lithium-Ion Batteries

    Directory of Open Access Journals (Sweden)

    Marco Zaccaria

    2012-01-01

    Full Text Available This study reports the fabrication and characterization of poly(ethylene oxide (PEO and poly(vinylidenefluoride-co-chlorotrifluoroethylene (PVDF-CTFE nanofibrous separators for lithium-ion batteries loaded with different amounts of fumed-silica and tin oxide nanoparticles. Membrane morphological characterization (SEM, TEM showed the presence of good-quality nanofibres containing nanoparticles. Thermal degradation and membrane mechanical properties were also investigated, and a remarkable effect of nanoparticle addition on membrane mechanical properties was found. In particular, PEO membranes were strengthened by the addition of metal oxide, whereas PVDF-CTFE membranes acquired ductility.

  2. Kinetics and mechanisms of reactions between H2O2 and copper and copper oxides.

    Science.gov (United States)

    Björkbacka, Åsa; Yang, Miao; Gasparrini, Claudia; Leygraf, Christofer; Jonsson, Mats

    2015-09-28

    One of the main challenges for the nuclear power industry today is the disposal of spent nuclear fuel. One of the most developed methods for its long term storage is the Swedish KBS-3 concept where the spent fuel is sealed inside copper canisters and placed 500 meters down in the bedrock. Gamma radiation will penetrate the canisters and be absorbed by groundwater thereby creating oxidative radiolysis products such as hydrogen peroxide (H2O2) and hydroxyl radicals (HO˙). Both H2O2 and HO˙ are able to initiate corrosion of the copper canisters. In this work the kinetics and mechanism of reactions between the stable radiolysis product, H2O2, and copper and copper oxides were studied. Also the dissolution of copper into solution after reaction with H2O2 was monitored by ICP-OES. The experiments show that both H2O2 and HO˙ are present in the systems with copper and copper oxides. Nevertheless, these species do not appear to influence the dissolution of copper to the same extent as observed in recent studies in irradiated systems. This strongly suggests that aqueous radiolysis can only account for a very minor part of the observed radiation induced corrosion of copper.

  3. Ozone-induced injury and oxidative stress in bronchiolar epithelium are associated with altered pulmonary mechanics.

    Science.gov (United States)

    Sunil, Vasanthi R; Vayas, Kinal N; Massa, Christopher B; Gow, Andrew J; Laskin, Jeffrey D; Laskin, Debra L

    2013-06-01

    In these studies, we analyzed the effects of ozone on bronchiolar epithelium. Exposure of rats to ozone (2 ppm, 3 h) resulted in rapid (within 3 h) and persistent (up to 72 h) histological changes in the bronchiolar epithelium, including hypercellularity, loss of cilia, and necrotizing bronchiolitis. Perivascular edema and vascular congestion were also evident, along with a decrease in Clara cell secretory protein in bronchoalveolar lavage, which was maximal 24 h post-exposure. Ozone also induced the appearance of 8-hydroxy-2'-deoxyguanosine, Ym1, and heme oxygenase-1 in the bronchiolar epithelium. This was associated with increased expression of cleaved caspase-9 and beclin-1, indicating initiation of apoptosis and autophagy. A rapid and persistent increase in galectin-3, a regulator of epithelial cell apoptosis, was also observed. Following ozone exposure (3-24 h), increased expression of cyclooxygenase-2, inducible nitric oxide synthase, and arginase-1 was noted in bronchiolar epithelium. Ozone-induced injury and oxidative stress in bronchiolar epithelium were linked to methacholine-induced alterations in pulmonary mechanics. Thus, significant increases in lung resistance and elastance, along with decreases in lung compliance and end tidal volume, were observed at higher doses of methacholine. This indicates that ozone causes an increase in effective stiffness of the lung as a consequence of changes in the conducting airways. Collectively, these studies demonstrate that bronchiolar epithelium is highly susceptible to injury and oxidative stress induced by acute exposure to ozone; moreover, this is accompanied by altered lung functioning.

  4. Polyphenol Stilbenes: Molecular Mechanisms of Defence against Oxidative Stress and Aging-Related Diseases

    Directory of Open Access Journals (Sweden)

    Mika Reinisalo

    2015-01-01

    Full Text Available Numerous studies have highlighted the key roles of oxidative stress and inflammation in aging-related diseases such as obesity, type 2 diabetes, age-related macular degeneration (AMD, and Alzheimer’s disease (AD. In aging cells, the natural antioxidant capacity decreases and the overall efficiency of reparative systems against cell damage becomes impaired. There is convincing data that stilbene compounds, a diverse group of natural defence phenolics, abundant in grapes, berries, and conifer bark waste, may confer a protective effect against aging-related diseases. This review highlights recent data helping to clarify the molecular mechanisms involved in the stilbene-mediated protection against oxidative stress. The impact of stilbenes on the nuclear factor-erythroid-2-related factor-2 (Nrf2 mediated cellular defence against oxidative stress as well as the potential roles of SQSTM1/p62 protein in Nrf2/Keap1 signaling and autophagy will be summarized. The therapeutic potential of stilbene compounds against the most common aging-related diseases is discussed.

  5. Update on the Mechanisms of Pulmonary Inflammation and Oxidative Imbalance Induced by Exercise

    Directory of Open Access Journals (Sweden)

    O. F. Araneda

    2016-01-01

    Full Text Available The mechanisms involved in the generation of oxidative damage and lung inflammation induced by physical exercise are described. Changes in lung function induced by exercise involve cooling of the airways, fluid evaporation of the epithelial surface, increased contact with polluting substances, and activation of the local and systemic inflammatory response. The present work includes evidence obtained from the different types of exercise in terms of duration and intensity, the effect of both acute performance and chronic performance, and the influence of special conditions such as cold weather, high altitude, and polluted environments. Levels of prooxidants, antioxidants, oxidative damage to biomolecules, and cellularity, as well as levels of soluble mediators of the inflammatory response and its effects on tissues, are described in samples of lung origin. These samples include tissue homogenates, induced sputum, bronchoalveolar lavage fluid, biopsies, and exhaled breath condensate obtained in experimental protocols conducted on animal and human models. Finally, the need to simultaneously explore the oxidative/inflammatory parameters to establish the interrelation between them is highlighted.

  6. Catalytic oxidation ofS(IV) on activated carbon in aqueous suspension: kinetics and mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Brodzinsky, R.

    1981-02-01

    Activated carbon and combustion produced soot particles have been studied for their catalytic effect on the oxidation of aqueous sulfur(IV) species. Detailed kinetic studies of the reaction were performed on three different activated carbons and on a soot collected in a highway tunnel. Combustion produced soots were tested for their catalytic behavior and found to be similar to the activated carbons. The reaction rate was found to be linearly dependent on the concentration of carbon particles in the solution. The rate was found to follow a Langmuir adsorption isotherm for its dependence on oxygen and the product of two adsorption isotherms for S(IV). The reaction is independent of the pH of the solution when the pH is below 7.6. The reaction does not occur when the pH is above 7.6. The three aqueous S(IV) species are catalyzed in their oxidation by the carbon particles in a similar manner. Activation energies for the reactions on the different carbons are all about 8.5 kcal/mole. A possible four-step reaction mechanism is proposed. It consists of the adsorption of a dissolved oxygen molecule onto the carbon surface, followed by the adsorption of two S(IV) molecules or ions. These are oxidized on the surface to sulfate, which desorbs from the surface, regenerating the catalytically active site.

  7. Dependence of the structure and mechanics of metaphase chromosomes on oxidized cysteines.

    Science.gov (United States)

    Eastland, Adrienne; Hornick, Jessica; Kawamura, Ryo; Nanavati, Dhaval; Marko, John F

    2016-09-01

    We have found that reagents that reduce oxidized cysteines lead to destabilization of metaphase chromosome folding, suggesting that chemically linked cysteine residues may play a structural role in mitotic chromosome organization, in accord with classical studies by Dounce et al. (J Theor Biol 42:275-285, 1973) and Sumner (J Cell Sci 70:177-188, 1984a). Human chromosomes isolated into buffer unfold when exposed to dithiothreitol (DTT) or tris(2-carboxyethyl)phosphine (TCEP). In micromanipulation experiments which allow us to examine the mechanics of individual metaphase chromosomes, we have found that the gel-like elastic stiffness of native metaphase chromosomes is dramatically suppressed by DTT and TCEP, even before the chromosomes become appreciably unfolded. We also report protein labeling experiments on human metaphase chromosomes which allow us to tag oxidized and reduction-sensitive cysteine residues. PAGE analysis using fluorescent labels shows a small number of labeled bands. Mass spectrometry analysis of similarly labeled proteins provides a list of candidates for proteins with oxidized cysteines involved in chromosome organization, notably including components of condensin I, cohesin, the nucleosome-interacting proteins RCC1 and RCC2, as well as the RNA/DNA-binding protein NONO/p54NRB.

  8. Signaling in a polluted world: oxidative stress as an overlooked mechanism linking contaminants to animal communication

    Directory of Open Access Journals (Sweden)

    Valeria Marasco

    2016-08-01

    Full Text Available The capacity to communicate effectively with other individuals plays a critical role in the daily life of an individual and can have important fitness consequences. Animals rely on a number of visual and non-visual signals, whose production brings costs to the individual. The theory of honest signaling states that these costs are higher for low than for high-quality individuals, which prevents cheating and makes signals, such as skin and plumage colouration, indicators of individual’s quality or condition. The condition-dependent nature of signals makes them ideally suited as indicators of environmental quality, implying that signal production might be affected by contaminants. In this mini-review article, we have made the point that oxidative stress (OS is one overlooked mechanism linking exposure to contaminants to signaling because (i many contaminants can influence the individual’s oxidative balance, and (ii generation of both visual and non-visual signals is sensitive to oxidative stress. To this end, we have provided the first comprehensive review on the way both non-organic (heavy metals, especially mercury and organic (persistent organic pollutants contaminants may influence either OS or sexual signaling. We have also paid special attention to emerging classes of pollutants like brominated flame-retardants and perfluoroalkoxy alkanes in order to stimulate research in this area. We have finally provided suggestions and warnings for future work on the links among OS, sexual signaling and contaminant exposure.

  9. HCV Core Protein Uses Multiple Mechanisms to Induce Oxidative Stress in Human Hepatoma Huh7 Cells

    Science.gov (United States)

    Ivanov, Alexander V.; Smirnova, Olga A.; Petrushanko, Irina Y.; Ivanova, Olga N.; Karpenko, Inna L.; Alekseeva, Ekaterina; Sominskaya, Irina; Makarov, Alexander A.; Bartosch, Birke; Kochetkov, Sergey N.; Isaguliants, Maria G.

    2015-01-01

    Hepatitis C virus (HCV) infection is accompanied by the induction of oxidative stress, mediated by several virus proteins, the most prominent being the nucleocapsid protein (HCV core). Here, using the truncated forms of HCV core, we have delineated several mechanisms by which it induces the oxidative stress. The N-terminal 36 amino acids of HCV core induced TGFβ1-dependent expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases 1 and 4, both of which independently contributed to the production of reactive oxygen species (ROS). The same fragment also induced the expression of cyclo-oxygenase 2, which, however, made no input into ROS production. Amino acids 37–191 of HCV core up-regulated the transcription of a ROS generating enzyme cytochrome P450 2E1. Furthermore, the same fragment induced the expression of endoplasmic reticulum oxidoreductin 1α. The latter triggered efflux of Ca2+ from ER to mitochondria via mitochondrial Ca2+ uniporter, leading to generation of superoxide anions, and possibly also H2O2. Suppression of any of these pathways in cells expressing the full-length core protein led to a partial inhibition of ROS production. Thus, HCV core causes oxidative stress via several independent pathways, each mediated by a distinct region of the protein. PMID:26035647

  10. Anti-oxidation mechanism of SiC-B4C-C composites

    Institute of Scientific and Technical Information of China (English)

    LIU Qi-cheng; XU Xie-wen; HUANG Qi-zhong; HUANG Bai-yun

    2005-01-01

    Mixture of green petroleum coke, B4C and SiC together with short carbon fiber were employed as starting materials, the mixture was press-formed without any binder after grinding, dense and homogeneous binderless SiC-B4C-C(carbon/ceramic) composites were then obtained after sintering. Composites thus prepared possess excellent anti-oxidation property, that is, mass loss less than 1% within the temperature range from 900 to 1100℃ for 10h. Anti-oxidation mechanism was also discussed from the viewpoint of thermodynamics, excellent anti-oxidation property of materials thus prepared can be discribed to 1) solid SiO2 formed from SiC, which restrains the filtering of oxygen and simultaneously, its volume expansion brought about by the reaction takes roles both walling up the original pores and making the material more compact; 2) liquid B2O3 from the reaction of B4C not only makes the combination with C, B4C and SiC tighter through forming solid solution, but also effect of reaction SiC(s)+2CO(g)=SiO2(s)+3C(s) is an expansive process, which improves the microstructure of the material.

  11. Evidence of interfacial charge trapping mechanism in polyaniline/reduced graphene oxide nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Islam, Rakibul; Brun, Jean-François; Roussel, Frederick, E-mail: frederick.roussel@univ-lille1.fr [University of Lille, Sciences & Technologies, Unité Matériaux et Transformations (UMET), UMR CNRS 8207, U.F.R. de Physique, P5, 59655 Villeneuve d' Ascq Cedex (France); COMUE Lille Nord de France, BP 50458-59658 Villeneuve d' Ascq Cedex (France); Papathanassiou, Anthony N. [Physics Department, Solid State Physics Section, University of Athens, Panepistimiopolis, GR15784 Zografos, Athens (Greece); Chan Yu King, Roch [Science Division, University of Science and Arts of Oklahoma, Chickasha, Oklahoma 73018 (United States)

    2015-08-03

    Relaxation mechanisms in polyaniline (PANI)/Reduced Graphene Oxide (RGO) nanocomposites are investigated using broad band dielectric spectroscopy. The multilayered nanostructural features of the composites and the intimate interactions between PANI and RGO are evidenced by field emission scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Increasing the RGO fraction in the composites results in a relaxation process observed at a frequency of ca. 5 kHz. This mechanism is associated with an electrical charge trapping phenomenon occurring at the PANI/RGO interfaces. The dielectric relaxation processes are interpreted according to the Sillars approach and the results are consistent with the presence of conducting prolate spheroids (RGO) embedded into a polymeric matrix (PANI). Dielectric permittivity data are analyzed within the framework of the Kohlrausch-William-Watts model, evidencing a Debye-like relaxation process.

  12. Kinetics and Mechanism of Oxidation of Lactic Acid by Dihydroxyditelluratoargentate(Ⅲ) in Alkaline Medium

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The kinetics of the oxidation of lactic acid(Lac) by dihydroxyditelluratoargentate(Ⅲ)[abbreviated as DDA of Ag(Ⅲ)] anions was studied in an aqueous alkaline medium by conventional spectrophotometry in a temperature range of 25—40 ℃. The order of the redox reaction of lactic acid and DDA was found to be first-order. The rates increased with the increase in [OH-] and decreased with the increase in [tellurate]. No free radical was detected. In the view of this the dihydroxymonotelluratoargentate(Ⅲ) species(DMA) is assumed to be the active species. A plausible mechanism involving a two-electron transfer is proposed, and the rate equation derived from the mechanism can be used to explain all the experimental results. The activation parameters(25 ℃) and the rate constants of the rate-determining step along with the preequilibrium constants at different temperatures were evaluated.

  13. Kinetics and Mechanism of Oxidation of Lactic Acid by Dihydroxyditelluratoargentate(Ⅲ)in Alkaline Medium

    Institute of Scientific and Technical Information of China (English)

    SHANJin-huan; WANGLi; LIUBao-sheng; SHENShi-gang

    2003-01-01

    The kinetics of the oxidation of lactic acid(Lac) by dihydroxyditelluratoargentate(Ⅲ)[abbreviated as DDA of Ag(Ⅲ)]anions was studied in an aqueous alkaline medium by conventional spectrophotometry in a temperature range of 25-40℃.The order of the redox reaction of lactic acid and DDA was found to be first-order.The rates increased with the increase in [OH-]and decreased with the increase in [tellurate].No free radical was detected.In the view of this the dihydroxymonotelluratoargentate(Ⅲ)species(DMA) is assumed to be the active species.A plausible mechanism involving a two-electron transfer is proposed,and the rate equation derived from the mechanism can be used to explain all the experimenttal results.The activation parameters(25℃)and the rate constants of the rate-determining step along with the preequilibrium constants at different temperatures were evaluated.

  14. Effects of mechanical force on grain structures of friction stir welded oxide dispersion strengthened ferritic steel

    Energy Technology Data Exchange (ETDEWEB)

    Han, Wentuo, E-mail: hanwentuo@hotmail.com [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Kimura, Akihiko [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Tsuda, Naoto [Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Serizawa, Hisashi [Joining and Welding Research Institute, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Chen, Dongsheng [Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Je, Hwanil [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Fujii, Hidetoshi [Joining and Welding Research Institute, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Ha, Yoosung [Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Morisada, Yoshiaki [Joining and Welding Research Institute, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Noto, Hiroyuki [Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)

    2014-12-15

    The weldability of oxide dispersion strengthened (ODS) ferritic steels is a critical obstructive in the development and use of these steels. Friction stir welding has been considered to be a promising way to solve this problem. The main purpose of this work was to reveal the effects of mechanical force on grain structures of friction stir welded ODS ferritic steel. The grain appearances and the misorientation angles of grain boundaries in different welded zones were investigated by the electron backscatter diffraction (EBSD). Results showed that the mechanical force imposed by the stir tool can activate and promote the recrystallization characterized by the transformation of boundaries from LABs to HABs, and contribute to the grain refinement. The type of recrystallization in the stir zone can be classified as the continuous dynamic recrystallization (CDRX)

  15. Kinetics and Mechanism of the Oxidation of Glycol by Dihydroxyditelluratoargentate(Ⅲ) with Spectrophotometry

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The kinetics of the oxidation of glycol by dihydroxyditelluratoargentate (Ⅲ) complex(DDA) was studied in alkaline medium with spectrophotometry(in a temperature range of 16.6-40 ℃).The first-order rates with respect to glycol and Ag(Ⅲ) were all found.The rates increased with the increase in [OH-] and decreased with the increase in [TeO2-4].No effect was found with the addition of KNO3 and no free radical was detected.In view of this,the dihydroxymonotelluratoargentate(Ⅲ) species(DMA) is assumed to be the active species.A plausible mechanism involving a two-electron transfer is proposed,and the rate equation derived from the mechanism can explain all experimental observations.Activation parameters of the rate-determining step and constants are evaluated.

  16. A novel chiral stationary phase LC-MS/MS method to evaluate oxidation mechanisms of edible oils.

    Science.gov (United States)

    Ito, Junya; Shimizu, Naoki; Kobayashi, Eri; Hanzawa, Yasuhiko; Otoki, Yurika; Kato, Shunji; Hirokawa, Takafumi; Kuwahara, Shigefumi; Miyazawa, Teruo; Nakagawa, Kiyotaka

    2017-08-30

    The elucidation of lipid oxidation mechanisms of food is vital. In certain lipids, characteristic lipid hydroperoxide isomers are formed by different oxidation mechanisms (i.e., photo-oxidation or auto-oxidation). For example, linoleic acid is photo-oxidized to 13-9Z, 11E-hydroperoxyoctadecadienoic acid (HPODE), 12-9Z,13E-HPODE, 10-8E,12Z-HPODE and 9-10E,12Z-HPODE, whereas 13-9Z, 11E-HPODE, 13-9E,11E-HPODE, 9-10E,12Z-HPODE and 9-10E,12E-HPODE are formed by auto-oxidation. Therefore, we considered that oxidation mechanisms could be evaluated by analyzing these characteristic positional and cis/trans lipid hydroperoxide isomers. In this study, we developed a novel chiral stationary phase LC-MS/MS (CSP-LC-MS/MS) method to analyze the positional and cis/trans isomers of HPODE, with the use of a chiral column and sodium ion. Also, as an application of the method, either light-exposed or heated edible oils were treated with lipase to hydrolyze triacylglycerols. The resultant fatty acids including HPODE isomers were analyzed with the developed method. As a result, HPODE isomers characteristic to photo-oxidation were certainly detected in light-exposed edible oils. On the other hand, in heated edible oils, the HPODE isomers characteristic to auto-oxidation were largely increased. Thus, the combination of the developed CSP-LC-MS/MS method with lipase proves to be a powerful tool to evaluate the involvement and mechanisms of lipid oxidation in the process of food deterioration.

  17. Activation of Proinflammatory Responses in Cells of the Airway Mucosa by Particulate Matter: Oxidant- and Non-Oxidant-Mediated Triggering Mechanisms

    Directory of Open Access Journals (Sweden)

    Johan Øvrevik

    2015-07-01

    Full Text Available Inflammation is considered to play a central role in a diverse range of disease outcomes associated with exposure to various types of inhalable particulates. The initial mechanisms through which particles trigger cellular responses leading to activation of inflammatory responses are crucial to clarify in order to understand what physico-chemical characteristics govern the inflammogenic activity of particulate matter and why some particles are more harmful than others. Recent research suggests that molecular triggering mechanisms involved in activation of proinflammatory genes and onset of inflammatory reactions by particles or soluble particle components can be categorized into direct formation of reactive oxygen species (ROS with subsequent oxidative stress, interaction with the lipid layer of cellular membranes, activation of cell surface receptors, and direct interactions with intracellular molecular targets. The present review focuses on the immediate effects and responses in cells exposed to particles and central down-stream signaling mechanisms involved in regulation of proinflammatory genes, with special emphasis on the role of oxidant and non-oxidant triggering mechanisms. Importantly, ROS act as a central second-messenger in a variety of signaling pathways. Even non-oxidant mediated triggering mechanisms are therefore also likely to activate downstream redox-regulated events.

  18. The mechanical and thermal responses of colliding oxide-coated aluminum nanoparticles

    Science.gov (United States)

    Ma, Bo; Zhao, Feng; Cheng, Xinlu; Miao, Feng; Zhang, Jidong

    2017-04-01

    The aggregation and fracture of oxide-coated metal nanoparticles have a significant influence on their physical and chemical behaviors in synthesis, combustion, or detonation. How does the dynamic loading caused by the impact between nanoparticles affect them? Motivated by this issue, we carried out molecular dynamic simulations of two colliding aluminum nanoparticles to investigate their mechanical and thermal properties and response at impact velocities of 200 m/s, 600 m/s, 1000 m/s, and 2000 m/s. At the relatively low impact velocities (equal to or less than 1000 m/s), it was observed that the particles are mildly deformed and adhere to each other, but the shells do not undergo fracture under the dynamic loading. The metal core and oxide shell behave elastically at 200 m/s and elasto-plastically at 600 m/s. A concentration of dynamic volumetric stress appears but no concentration of shear stress and no formation of a hot spot. Due to the low intensity of the loading and the efficient propagation of the stress wave, the shells fail to fracture. At an impact velocity of 2000 m/s, the impact region of the shell undergoes ductile fracture, and the two particles undergo sintering and form a new particle re-coated with oxide, resulting from the concentration of dynamic shear stress and the formation of a hot spot. At all impact velocities in our simulations, the impact between the nanoparticles improves the aggregation but has a little effect on the fracture of the oxide shell.

  19. Mechanism of H2S Oxidation by the Dissimilatory Perchlorate-Reducing Microorganism Azospira suillum PS

    Science.gov (United States)

    Mehta-Kolte, Misha G.; Loutey, Dana; Wang, Ouwei; Youngblut, Matthew D.; Hubbard, Christopher G.; Wetmore, Kelly M.; Conrad, Mark E.

    2017-01-01

    ABSTRACT The genetic and biochemical basis of perchlorate-dependent H2S oxidation (PSOX) was investigated in the dissimilatory perchlorate-reducing microorganism (DPRM) Azospira suillum PS (PS). Previously, it was shown that all known DPRMs innately oxidize H2S, producing elemental sulfur (So). Although the process involving PSOX is thermodynamically favorable (ΔG°′ = −206 kJ ⋅ mol−1 H2S), the underlying biochemical and genetic mechanisms are currently unknown. Interestingly, H2S is preferentially utilized over physiological electron donors such as lactate or acetate although no growth benefit is obtained from the metabolism. Here, we determined that PSOX is due to a combination of enzymatic and abiotic interactions involving reactive intermediates of perchlorate respiration. Using various approaches, including barcode analysis by sequencing (Bar-seq), transcriptome sequencing (RNA-seq), and proteomics, along with targeted mutagenesis and biochemical characterization, we identified all facets of PSOX in PS. In support of our proposed model, deletion of identified upregulated PS genes traditionally known to be involved in sulfur redox cycling (e.g., Sox, sulfide:quinone reductase [SQR]) showed no defect in PSOX activity. Proteomic analysis revealed differential abundances of a variety of stress response metal efflux pumps and divalent heavy-metal transporter proteins, suggesting a general toxicity response. Furthermore, in vitro biochemical studies demonstrated direct PSOX mediated by purified perchlorate reductase (PcrAB) in the absence of other electron transfer proteins. The results of these studies support a model in which H2S oxidation is mediated by electron transport chain short-circuiting in the periplasmic space where the PcrAB directly oxidizes H2S to So. The biogenically formed reactive intermediates (ClO2− and O2) subsequently react with additional H2S, producing polysulfide and So as end products. PMID:28223460

  20. Nanosecond multi-pulse laser-induced damage mechanisms in pure and mixed oxide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Frank R., E-mail: frank.wagner@fresnel.fr; Gouldieff, Céline, E-mail: celine.gouldieff@univ-rennes1.fr; Natoli, Jean-Yves, E-mail: jean-yves.natoli@fresnel.fr; Commandré, Mireille, E-mail: mireille.commandre@fresnel.fr

    2015-10-01

    We report on nanosecond laser-induced damage of pure and mixed oxide thin films deposited by ion beam sputtering. Silica, hafnia and alumina as well as their binary mixtures have been tested in S-on-1 mode at 355 nm and 266 nm using a multiscale approach. The results were analyzed qualitatively to discuss the different fatigue behaviors observed. The absence of a multi-photon absorption step in the 1-on-1 damage thresholds as a function of the band gap indicates defect-mediated damage mechanisms. During the multi-pulse experiments we observed laser-induced defects that cause fatigue effects and preexisting low-density defects, which are insensitive to multiple pulse irradiation. Depending on material and beam size both types of defects (preexisting and light-induced) may contribute equally to the observed damage probability. Comparing the fatigue behavior of the mixtures to their constituting pure oxides, we found that, in general, the fatigue behavior of binary mixtures cannot be interpolated from the behaviors of the pure oxides. - Highlights: • Multi-pulse laser damage can be analyzed plotting damaging shot number vs. fluence. • A fatigue effect was only observed for small laser beams, avoiding worse precursors. • The fatigue behavior of a mixture cannot be interpolated from the pure oxides. • SiO{sub 2} and Al{sub 2}O{sub 3} damage at 266 nm is due to deterministic material modifications. • Hafnia multi-pulse laser damage with small beams is stochastic even at 266 nm.

  1. Kinetics and Mechanism of Oxidation of Diethyl Ether by Chloramine-T in Acidic Medium

    Directory of Open Access Journals (Sweden)

    Y. I. Hassan

    2012-01-01

    Full Text Available The kinetics of oxidation of diethyl ether (DE with sodium N-chloro-p-toluenesulphonamide (CAT in hydrochloric acid solution has been studied at (313°K.The reaction rate show a first order dependence on [CAT] and fractional order dependence on each [DE] and [H+] .The variation of ionic strength of the medium has no significant effect on the reaction rate , addition of p-toluenesulphonamide (p-TSA affects the reaction rate marginally the rate increased with decreasing dielectric constant of the medium , the stochiometry of the reaction was found to be 1:2 and oxidation products were identified , A Michaelis – Menten type mechanism has been suggested to explain the results.The equilibrium and the decomposition constants of CAT – diethyl ether complex have been evaluated. Thermodynamic parameters were computed by studying reaction at temperatures range ( 308 – 323°K for the rate limiting step and for the observed first order constants by the linear Arrhenius plot. The mechanism proposed and the derived rate law are consistent with observed kinetics.

  2. Theoretical study of the oxidation mechanisms of thiophene initiated by hydroxyl radicals.

    Science.gov (United States)

    Shiroudi, Abolfazl; Deleuze, Michael S

    2015-11-01

    The mechanisms for the oxidation of thiophene by OH radicals under inert conditions (Ar) have been studied using density functional theory in conjunction with various exchange-correlation functionals. These results were compared with benchmark CBS-QB3 theoretical results. Kinetic rate constants were estimated by means of variational transition state theory (VTST) and the statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Effective rate constants were calculated via a steady-state analysis based upon a two-step model reaction mechanism. In line with experimental results, the computed branching ratios indicate that the most kinetically efficient process involves OH addition to a carbon atom adjacent to the sulfur atom. Due to the presence of negative activation energies, pressures larger than 10(4) bar are required to reach the high-pressure limit. Nucleus-independent chemical shift indices and natural bond orbital analysis show that the computed activation energies are dictated by changes in aromaticity and charge-transfer effects due to the delocalization of lone pairs from sulfur to empty π(*) orbitals. Graphical Abstract CBS-QB3 energy profiles for the reaction pathways 1-3 characterizing the oxidation of thiophene by hydroxyl radicals into the related products.

  3. Microstructure and Mechanical Properties of Ultrafine-Grained Austenitic Oxide Dispersion Strengthened Steel

    Science.gov (United States)

    Mao, Xiaodong; Kang, Suk Hoon; Kim, Tae Kyu; Kim, Seul Cham; Oh, Kyu Hwan; Jang, Jinsung

    2016-11-01

    316L stainless steel based austenitic oxide dispersion strengthened (AODS) steel was fabricated by mechanical alloying (MA) and hot isostatic pressing (HIP). The AODS sample exhibited an ultrafine-grained (UFG) structure with a bimodal grain size distribution (large grains of about 1200 nm and fine grains of about 260 nm). Two groups of oxide particles were observed; fine Y2Ti2O7 of about 7.7 nm and coarse Cr2O3 particles of about 200 nm in diameter. Tensile tests of the hot-rolled AODS steel samples showed yield strength of up to 890 MPa at room temperature, which is nearly four times higher than that of conventional 316L stainless steel. Micro-indentation and hardness tests indicated even higher yield strength of up to 1200 MPa, which shows a good agreement with the calculated value by combining of the grain refinement strengthening by the Hall-Petch relation and the dispersion strengthening by the Orowan mechanism. The lower strength from tensile tests should be attributed to the formation of micro-cracks at the interfaces between coarse Cr2O3 particles and the matrix. Coarse Cr2O3 particles were also frequently observed inside the fracture surface dimples of the creep ruptured sample at 923 K (650 °C) and 140 MPa. It is thus suggested that the yield strength and elongation could be further improved by controlling the coarse Cr2O3 particles.

  4. Reduced silanized graphene oxide/epoxy-polyurethane composites with enhanced thermal and mechanical properties

    Science.gov (United States)

    Lin, Jing; Zhang, Peipei; Zheng, Cheng; Wu, Xu; Mao, Taoyan; Zhu, Mingning; Wang, Huaquan; Feng, Danyan; Qian, Shuxuan; Cai, Xianfang

    2014-10-01

    This paper describes the synthesis of reduced silanized graphene oxide/epoxy-polyurethane (EPUAs/R-Si-GEO) composites with enhanced thermal and mechanical properties. Graphene oxide (GEO), prepared from natural graphite flakes, was modified with methacryloxypropyltrimethoxysilane to prepare silanized GEO (Si-GEO), and was then reduced by NaHSO3 to prepare R-Si-GEO (partially reduced Si-GEO). EPAc/R-Si-GEO (R-Si-GEO/epoxy acrylate copolymers) was synthesized via an in situ polymerization of R-Si-GEO and epoxy acrylic monomers. EPUAs/R-Si-GEO was obtained by curing reaction between EPAc/R-Si-GEO and an isocyanate curing agent. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used to characterize the surface and crystal structure of the modified graphene and EPUAs/R-Si-GEO. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize their morphology. Thermal gravimetric analysis (TGA), tensile strength, elongation at break, and cross-linking density measurements showed that the thermal stability and mechanical properties of EPUAs/R-Si-GEO were greatly enhanced by the addition of R-Si-GEO.

  5. Effects of simulated microgravity on nitric oxide level in cardiac myocytes and its mechanism

    Institute of Scientific and Technical Information of China (English)

    熊江辉; 李莹辉; 聂捷琳

    2003-01-01

    The depression of cardiac contractility induced by space microgravity is an important issue of aerospace medicine research, while its precise mechanism is still unknown. In the present study, we explored effects of simulated microgravity on nitric oxide (NO) level, inducible nitric oxide synthase (iNOS) expression and related regulative mechanism using electron spin resonance (ESR) spectroscopy, immunocytochemistry and in situ hybridization. We found a remarkable increase of NO level and up-regulation of iNOS and iNOS mRNA expression in rat cardiac myocytes under simulated microgravity. Staurosporine (a nonselective protein kinase inhibitor), calphostin C (a selective protein kinase C inhibitor), partially inhibited the effect of simulated microgravity. Thus regulative effect of simulated microgravity on iNOS expression is mediated at least partially via activation of protein kinase C. These results indicate that NO system in cardiac myocytes is sensitive to simulated microgravity and may play an important role in the depression of cardiac contractility induced by simulated microgravity.

  6. Bio-geochemical mechanisms influencing the stability of As-bearing iron oxides

    Science.gov (United States)

    Garrido, F.; Dictor, M. C.; Morin, G.; Bodénan, F.; Baranger, P.

    2003-04-01

    Hydrous Ferric Oxydes (HFO) often occurring in the organo-mineral matrix of soils and sediments act as a preferential substrate for the fixation of toxic metals and metalloids as arsenic. The chemical stability of these complexes strongly depends on the physico-chemical and biological conditions of the medium. In this context, the aim of this work was to study mobility factors of arsenic by analogy with bio-geochemical reactions involved in soils and sediments. We studied the conditions of arsenic release in solution upon the reaction of synthetic As-doped iron-oxide minerals with specific micro-organisms (Fe(III)-reducing bacteria or As(V)-reducing bacteria) under controlled laboratory conditions. Our results showed that As release in solution proceeds in two step. First, a rapid As release in solution is caused by competitive sorption processes with other oxy-anions present in the culture medium. In a second step, the microbial reduction of Fe(III) and/or As(V) become the main factor affecting the stability of the As-iron oxide complexes. These two mechanisms were regulated by the physico-chemical conditions of the medium (pH, Eh and phosphate concentration). These results should help in a better understanding of the arsenic mobility in polluted environment. They confirm the major influence of the biological factor on the stability of the As trapping by HFO. This latter chemical trapping mechanism being involved in numerous As water-treatment processes.

  7. Radiation induced oxidative degradation of polymers—III. Effect of radiation on mechanical properties

    Science.gov (United States)

    Seguchi, Tadao; Arakawa, Kazuo; Ito, Masayuki; Hayakawa, Naohiro; Machi, Sueo

    The changes of mechanical properties of various kinds of polyethylene (PE) and ethylene-propylene copolymer (EPR) with the irradiation in air, in oxygen of 10 atm, and under vacuum were investigated. The decrease in the elongation ( E b) and the tensile strength ( T b) of PE by the irradiation in oxygen is larger than under vacuum. The changes of E b well reflect the degradation of PE. In case of EPR, the T b decreases sharply with dose in any environments, and the E b decreases under vacuum to a larger extent than in oxygen. The modulus at 200% elongation of EPR increases with dose under vacuum, but decreases in oxygen. When the samples were irradiated in air, the changes of the mechanical properties were the intermediate between oxygen and vacuum and dependent on the ratio of oxidation and non-oxidation layers in the film. The antioxidant (Irganox 1010 or DPPD) mixed in polymers was found to retard effectively the polymer degradation by the irradiation in oxygen.

  8. Radiation induced oxidative degradation of polymers. 3. Effect of radiation on mechanical properties. [Gamma radiation

    Energy Technology Data Exchange (ETDEWEB)

    Seguchi, T.; Arakawa, K.; Ito, M.; Hayakawa, N.; Machi, S. (Japan Atomic Energy Research Inst., Takasaki, Gunma. Takasaki Radiation Chemistry Research Establishment)

    1983-01-01

    The changes of mechanical properties of various kinds of polyethylene (PE) and ethylene-propylene copolymer (EPR) with the irradiation in air, in oxygen of 10 atm, and under vacuum were investigated. The decrease in the elongation (Esub(b)) and the tensile strength (Tsub(b)) of PE by the irradiation in oxygen is larger than under vacuum. The changes of Esub(b) well reflect the degradation of PE. In case of EPR, the Tsub(b) decreases sharply with dose in any environments, and the Esub(b) decreases under vacuum to a larger extent than in oxygen. The modulus at 200% elongation of EPR increases with dose under vacuum, but decreases in oxygen. When the samples were irradiated in air, the changes of the mechanical properties were the intermediate between oxygen and vacuum and dependent on the ratio of oxidation and non-oxidation layers in the film. The antioxidant (Irganox 1010 or DPPD) mixed in polymers was found to retard effectively the polymer degradation by the irradiation in oxygen.

  9. Chromium vaporization from mechanically deformed pre-coated interconnects in Solid Oxide Fuel Cells

    Science.gov (United States)

    Falk-Windisch, Hannes; Sattari, Mohammad; Svensson, Jan-Erik; Froitzheim, Jan

    2015-11-01

    Cathode poisoning, associated with Cr evaporation from interconnect material, is one of the most important degradation mechanisms in Solid Oxide Fuel Cells when Cr2O3-forming steels are used as the interconnect material. Coating these steels with a thin Co layer has proven to decrease Cr vaporization. To reduce production costs, it is suggested that thin metallic PVD coatings be applied to each steel strip before pressing the material into interconnect shape. This process would enable high volume production without the need for an extra post-coating step. However, when the pre-coated material is mechanically deformed, cracks may form and lower the quality of the coating. In the present study, Chromium volatilization is measured in an air-3% H2O environment at 850 °C for 336 h. Three materials coated with 600 nm Co are investigated and compared to an uncoated material. The effect of deformation is investigated on real interconnects. Microscopy observations reveal the presence of cracks in the order of several μm on the deformed pre-coated steel. However, upon exposure, the cracks can heal and form a continuous surface oxide rich in Co and Mn. As an effect of the rapid healing, no increase in Cr vaporization is measured for the pre-coated material.

  10. Mechanism and Kinetics Study for Photocatalytic Oxidation Degradation: A Case Study for Phenoxyacetic Acid Organic Pollutant

    Directory of Open Access Journals (Sweden)

    Kian Mun Lee

    2015-01-01

    Full Text Available Photocatalysis is a rapidly expanding technology for wastewater treatment, including a wide range of organic pollutants. Thus, understanding the kinetics and mechanism of the photocatalytic oxidation (PCO for degradation of phenoxyacetic acid (PAA is an indispensable component of risk assessment. In this study, we demonstrated that the central composite design (CCD coupled with response surface methodology (RSM was successfully employed to probe the kinetics and mechanism of PCO degradation for PAA using an efficient zinc oxide (ZnO photocatalyst. In our current case study, four independent factors such as ZnO dosage, initial concentration of PAA, solution pH, and reaction time on the PCO degradation for PAA were examined in detail. Based on our results obtained from RSM analyses, an efficient pathway leading to the high degradation rate (>90% was applying 0.4 g/L of ZnO dosage with 16 mg/L of concentration of PAA at pH 6.73 for 40 minutes. The experimental results were fitted well with the derived response model with R2 = 0.9922. This study offers a cost-effective way for probing our global environmental water pollution issue.

  11. Review on Zinc Oxide Nanoparticles:Antibacterial Activity and Toxicity Mechanism

    Institute of Scientific and Technical Information of China (English)

    Amna Sirelkhatim; Shahrom Mahmud; Azman Seeni; Noor Haida Mohamad Kaus; Ling Chuo Ann; Siti Khadijah Mohd Bakhori; Habsah Hasan; Dasmawati Mohamad

    2015-01-01

    Antibacterial activity of zinc oxide nanoparticles (ZnO-NPs) has received significant interest worldwide par-ticularly by the implementation of nanotechnology to synthesize particles in the nanometer region. Many microorganisms exist in the range from hundreds of nanometers to tens of micrometers. ZnO-NPs exhibit attractive antibacterial properties due to increased specific surface area as the reduced particle size leading to enhanced particle surface reactivity. ZnO is a bio-safe material that possesses photo-oxidizing and photocatalysis impacts on chemical and biological species. This review covered ZnO-NPs antibacterial activity including testing methods, impact of UV illumination, ZnO particle properties (size, concentration, morphology, and defects), particle surface modification, and minimum inhibitory con-centration. Particular emphasize was given to bactericidal and bacteriostatic mechanisms with focus on generation of reactive oxygen species (ROS) including hydrogen peroxide (H2O2), OH-(hydroxyl radicals), and O2-2 (peroxide). ROS has been a major factor for several mechanisms including cell wall damage due to ZnO-localized interaction, enhanced membrane permeability, internalization of NPs due to loss of proton motive force and uptake of toxic dissolved zinc ions. These have led to mitochondria weakness, intracellular outflow, and release in gene expression of oxidative stress which caused eventual cell growth inhibition and cell death. In some cases, enhanced antibacterial activity can be attributed to surface defects on ZnO abrasive surface texture. One functional application of the ZnO antibacterial bioactivity was discussed in food packaging industry where ZnO-NPs are used as an antibacterial agent toward foodborne diseases. Proper incorporation of ZnO-NPs into packaging materials can cause interaction with foodborne pathogens, thereby releasing NPs onto food surface where they come in contact with bad bacteria and cause the bacterial death and

  12. Oxidative stress protection and stomatal patterning as components of salinity tolerance mechanism in quinoa (Chenopodium quinoa).

    Science.gov (United States)

    Shabala, Lana; Mackay, Alex; Tian, Yu; Jacobsen, Sven-Erik; Zhou, Daowei; Shabala, Sergey

    2012-09-01

    Two components of salinity stress are a reduction in water availability to plants and the formation of reactive oxygen species. In this work, we have used quinoa (Chenopodium quinoa), a dicotyledonous C3 halophyte species displaying optimal growth at approximately 150 mM NaCl, to study mechanisms by which halophytes cope with the afore-mentioned components of salt stress. The relative contribution of organic and inorganic osmolytes in leaves of different physiological ages (e.g. positions on the stem) was quantified and linked with the osmoprotective function of organic osmolytes. We show that the extent of the oxidative stress (UV-B irradiation) damage to photosynthetic machinery in young leaves is much less when compared with old leaves, and attribute this difference to the difference in the size of the organic osmolyte pool (1.5-fold difference under control conditions; sixfold difference in plants grown at 400 mM NaCl). Consistent with this, salt-grown plants showed higher Fv/Fm values compared with control plants after UV-B exposure. Exogenous application of physiologically relevant concentrations of glycine betaine substantially mitigated oxidative stress damage to PSII, in a dose-dependent manner. We also show that salt-grown plants showed a significant (approximately 30%) reduction in stomatal density observed in all leaves. It is concluded that accumulation of organic osmolytes plays a dual role providing, in addition to osmotic adjustment, protection of photosynthetic machinery against oxidative stress in developing leaves. It is also suggested that salinity-induced reduction in stomatal density represents a fundamental mechanism by which plants optimize water use efficiency under saline conditions.

  13. Catalytic conversion of methane: Carbon dioxide reforming and oxidative coupling

    KAUST Repository

    Takanabe, Kazuhiro

    2012-01-01

    Natural gas conversion remains one of the essential technologies for current energy needs. This review focuses on the mechanistic aspects of the development of efficient and durable catalysts for two reactions, carbon dioxide reforming and the oxidative coupling of methane. These two reactions have tremendous technological significance for practical application in industry. An understanding of the fundamental aspects and reaction mechanisms of the catalytic reactions reviewed in this study would support the design of industrial catalysts. CO 2 reforming of methane utilizes CO 2, which is often stored in large quantities, to convert as a reactant. Strategies to eliminate carbon deposition, which is the major problem associated with this reaction, are discussed. The oxidative coupling of methane directly produces ethylene in one reactor through a slightly exothermic reaction, potentially minimizing the capital cost of the natural gas conversion process. The focus of discussion in this review will be on the attainable yield of C 2 products by rigorous kinetic analyses.

  14. Quantum mechanics/molecular mechanics simulation of the ligand vibrations of the water-oxidizing Mn4CaO5 cluster in photosystem II.

    Science.gov (United States)

    Nakamura, Shin; Noguchi, Takumi

    2016-10-11

    During photosynthesis, the light-driven oxidation of water performed by photosystem II (PSII) provides electrons necessary to fix CO2, in turn supporting life on Earth by liberating molecular oxygen. Recent high-resolution X-ray images of PSII show that the water-oxidizing center (WOC) is composed of an Mn4CaO5 cluster with six carboxylate, one imidazole, and four water ligands. FTIR difference spectroscopy has shown significant structural changes of the WOC during the S-state cycle of water oxidation, especially within carboxylate groups. However, the roles that these carboxylate groups play in water oxidation as well as how they should be properly assigned in spectra are unresolved. In this study, we performed a normal mode analysis of the WOC using the quantum mechanics/molecular mechanics (QM/MM) method to simulate FTIR difference spectra on the S1 to S2 transition in the carboxylate stretching region. By evaluating WOC models with different oxidation and protonation states, we determined that models of high-oxidation states, Mn(III)2Mn(IV)2, satisfactorily reproduced experimental spectra from intact and Ca-depleted PSII compared with low-oxidation models. It is further suggested that the carboxylate groups bridging Ca and Mn ions within this center tune the reactivity of water ligands bound to Ca by shifting charge via their π conjugation.

  15. Effects of Mn on the mechanical properties and high temperature oxidation of 9Cr2WVTa steel

    Science.gov (United States)

    Jin, Xiaojie; Chen, Shenghu; Rong, Lijian

    2017-10-01

    The mechanical properties and high temperature oxidation behaviors of 9Cr2WVTa steels with Mn contents in the range of 0.04-0.93 wt% were investigated. There are no obvious differences in the tensile properties at room temperature and high temperature, only a slight reduction in the impact toughness when Mn content reaches 0.93 wt%. Remarkably, the high temperature oxidation resistance is significantly improved with an increase of Mn content. After 500 h of oxidation, a (Fe0.6Cr0.4)2O3 oxide scale is developed on the steel with 0.04 wt% Mn, Mn1.5Cr1.5O4 oxides are occasionally detected when Mn content reaches 0.47 wt%, while a thin compact scale with a mixture of Mn1.5Cr1.5O4 and Cr1.3Fe0.7O3 oxides is formed on the steel containing 0.93 wt% Mn. Addition of Mn promotes the formation of Mn-oxides, which lowers oxygen partial pressure and accelerates external oxidation of Cr. At last, the presence of Mn-Cr spinels and Cr-rich oxides improves the oxidation resistance.

  16. Fatigue mechanism of yttrium-doped hafnium oxide ferroelectric thin films fabricated by pulsed laser deposition.

    Science.gov (United States)

    Huang, Fei; Chen, Xing; Liang, Xiao; Qin, Jun; Zhang, Yan; Huang, Taixing; Wang, Zhuo; Peng, Bo; Zhou, Peiheng; Lu, Haipeng; Zhang, Li; Deng, Longjiang; Liu, Ming; Liu, Qi; Tian, He; Bi, Lei

    2017-02-01

    Owing to their prominent stability and CMOS compatibility, HfO2-based ferroelectric films have attracted great attention as promising candidates for ferroelectric random-access memory applications. A major reliability issue for HfO2 based ferroelectric devices is fatigue. So far, there have been a few studies on the fatigue mechanism of this material. Here, we report a systematic study of the fatigue mechanism of yttrium-doped hafnium oxide (HYO) ferroelectric thin films deposited by pulsed laser deposition. The influence of pulse width, pulse amplitude and temperature on the fatigue behavior of HYO during field cycling is studied. The temperature dependent conduction mechanism is characterized after different fatigue cycles. Domain wall pinning caused by carrier injection at shallow defect centers is found to be the major fatigue mechanism of this material. The fatigued device can fully recover to the fatigue-free state after being heated at 90 °C for 30 min, confirming the shallow trap characteristic of the domain wall pinning defects.

  17. Thermo-mechanical fatigue properties of a ferritic stainless steel for solid oxide fuel cell interconnect

    Science.gov (United States)

    Chiu, Yung-Tang; Lin, Chih-Kuang

    2012-12-01

    Thermo-mechanical fatigue (TMF) behavior of a newly developed ferritic stainless steel (Crofer 22 H) for planar solid oxide fuel cell (pSOFC) interconnect is investigated. TMF tests under various combinations of cyclic mechanical and thermal loadings are conducted in air at a temperature range of 25oC-800 °C. Experimental results show the number of cycles to failure for non-hold-time TMF loading is decreased with an increase in the minimum stress applied at 800 °C. There is very little effect of maximum stress applied at 25 °C on the number of cycles to failure. The non-hold-time TMF life is dominated by a fatigue mechanism involving cyclic high-temperature softening plastic deformation. A hold-time of 100 h for the minimum stress applied at 800 °C causes a significant drop of number of cycles to failure due to a synergistic action of fatigue and creep. Creep and creep-fatigue interaction mechanisms are the two primary contributors to the hold-time TMF damage. The creep damage ratio in the hold-time TMF damage is increased with a decrease in applied stress at 800 °C and an increase in number of cycles to failure.

  18. External mechanical work versus oxidative energy consumption ratio during a basketball field test.

    Science.gov (United States)

    Crisafulli, A; Melis, F; Tocco, F; Laconi, P; Lai, C; Concu, A

    2002-12-01

    A field test consisting of 5 continuous runs at the maximum speed possible, playing the ball, starting from the centre line to the basket with a final shot, was studied in order to obtain an index of mechanical work efficiency in basketball players (micro-index=Jmec/Joxy) and evaluate the correlation between micro-index and velocity, acceleration, mechanical power and lactacid anaerobic capacity, respectively. Eight male basketball players were studied; Jmec was the external mechanical work output obtained by means of a video image analysis software which gave the potential and the kinetic translational energies of athletes running and jumping and their velocity, acceleration and mechanical power. By means of a telemetric device (Kosmed K4), for measuring O2 consumption ( VO2), we obtained oxidative work (Joxy). By using this device we also assessed the excess of CO2, which was considered an index of lactacid anaerobic capacity. Non-parametric Spearman statistics revealed a significant correlation between mu index and mean velocity (ppower (ppower and endurance velocity.

  19. First half-reaction mechanism of nitric oxide synthase: the role of proton and oxygen coupled electron transfer in the reaction by quantum mechanics/molecular mechanics.

    Science.gov (United States)

    Cho, Kyung-Bin; Carvajal, Maria Angels; Shaik, Sason

    2009-01-08

    The first half-reaction of nitric oxide synthase (NOS) is investigated by means of quantum mechanical/molecular mechanical (QM/MM) calculations. An energetically feasible arginine hydroxylation path was found only when the iron-oxy complex accepted one proton from an external source. The so formed species has not been considered in heme chemistry; it is described as Por(+*)Fe(III)-OOH and is characterized by the same molecular constituency as the more known ferric-hydroperoxide species, compound 0, but has a cation-radical porphyrin moiety. The reaction itself is found to involve proton coupled electron transfer (PCET) and oxygen coupled electron transfer (OCET) steps en route to the formation of compound I and the ultimate monooxygenation of arginine. The cofactor H(4)B turns out to be a key player in the mechanism acting alternatively as an electron donor (when neutral) and an electron sink (when in its radical-cation state) and, thereby, providing the electron transfer component in the various coupled proton and oxygen transfer steps (see Scheme 4 ). The various pieces of this mechanism account for many of the experimental observations, such as the following: (a) the origins of the second proton supplied to the heme, (b) the elusiveness of compound I, (c) the inactivity of peroxide-shunt pathways in NOS first half-reaction, (d) the inhibition of the H(4)B analogue 4-amino-H(4)B due to protonation at the N3 position, (e) the roles of Trp188 (iNOS numbering) and the crystal water at the active site (W115), and so on. Alternative mechanistic hypotheses are tested and excluded, and a new mechanism for the NOS second half-reaction is proposed.

  20. Kinetics and mechanisms of oxidation of 2D woven C/SiC composites; 1: Experimental approach

    Energy Technology Data Exchange (ETDEWEB)

    Lamouroux, F.; Camus, G. (UMR 47, Pessac (France). Lab. des Composites Thermostructuraux); Thebault, J. (Societe Europeenne de Propulsion, Saint Medard-en-Jalles (France))

    1994-08-01

    The oxidation behavior of a 2D woven C/SiC composite partly protected with a SiC seal coating and heat-treated (stabilized) at 1,600 C in inert gas has been investigated through an experimental approach based on thermogravimetric analyses and optical/electron microscopy. Results of the tests, performed under flowing oxygen, have shown that the oxidation behavior of the composite material in terms of oxidation kinetics and morphological evolutions is related to the presence of thermal microcracks in the seal coating as well as in the matrix. Three different temperature domains exist. At low temperatures (< 800 C), the mechanisms of reaction between carbon and oxygen control the oxidation kinetics and are associated with a uniform degradation of the carbon reinforcement. At intermediate temperatures, (between 800 and 1,100 C), the oxidation kinetics are controlled by the gas-phase diffusion through a network of microcracks in the SiC coatings, resulting in a nonuniform degradation of the carbon phases. At high temperatures (> 1,100 C), such diffusion mechanisms are limited by sealing of the microcracks by silica; therefore, the degradation of the composite remains superficial. The study of the oxidation behavior of (i) the heat-treated composite in a lower oxygen content environment (dry air) and (ii) the as-processed (unstabilized) composite in dry oxygen confirms the different mechanisms proposed to explain the oxidation behavior of the composite material.

  1. GC-Mass Spectrokinetics Study of Probable Mechanism of the Oxidation of Diethylthiourea with Toluidine Blue

    Directory of Open Access Journals (Sweden)

    M. Qadri

    2014-03-01

    Full Text Available Thecurrent study describes the interactive role of diethylthiourea on the bleaching of toluidine blue (tolonium chloride (TB+ in acidic and basic media using the GC Mass Chromatography and Spectrophotometric technique. GC-Mass Spectrophotometric analysis was carried out to verify the decoloration of dye whether the bleaching of dye owed to leuco dye formation or degradation may also occur in the reaction mixture. The dye redox reaction process followed first order kinetics with respect to TB, DETU showed first order mechanism, first order kinetics with respect to H+. Enhanced decoloration in the presence of DETU proved that reductant‘s role is pivotal in the redox reaction. Slow decoloration in basic medium with ions was seen compared to acidic media, suggesting that pH of the medium is significant in the oxidation of DETU. The bleaching reaction of dye was investigated at different temperatures. At pH of 1.0 and 250C, the order of reaction is found to be second having rate constant value of 15.81 mol-1.L s-1,and rate law is suggested to be -d/dt [TBH ] = k2 [TB+ H+][DETU].Different reaction energy parameters were evaluated for a TB+-DETU reaction, including the energy of activation (Ea = 60.786 kJmol-1 (basic medium, 1.669kJmol-1 (acidic medium, enthalpy of activation (∆H≠ = -58.267 kJ mol-1(basic medium, -12.6kJ mol-1(acidic medium, entropy of activation (∆S≠ = -131.525Jmol-1K-1(basic medium,-243 Jmol-1K-1(acidic medium,and free energy of activation (∆G≠ = -98.119kJmol-1 (basic medium and -86.55kJmol-1 (acidic medium. A mechanism of interaction of involved ions in dye bleaching and a mechanism of oxidation based on the above findings is proposed.

  2. Physical, mechanical and electrochemical characterization of all-perovskite intermediate temperature solid oxide fuel cells

    Science.gov (United States)

    Mohammadi, Alidad

    Strontium- and magnesium-doped lanthanum gallate (LSGM) has been considered as a promising electrolyte for solid oxide fuel cell (SOFC) systems in recent years due to its high ionic conductivity and chemical stability over a wide range of oxygen partial pressures and temperatures. This research describes synthesis, physical and mechanical behavior, electrochemical properties, phase evolution, and microstructure of components of an all-perovskite anode-supported intermediate temperature solid oxide fuel cell (ITSOFC), based on porous La 0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) anode, La0.8Sr0.2Ga0.8Mg0.2O 2.8 (LSGM) electrolyte, and porous La0.6Sr0.4Fe 0.8Co0.2O3 (LSCF) cathode. The phase evolution of synthesized LSGM and LSCM powders has been investigated, and it has been confirmed that there is no reaction between LSGM and LSCM at sintering temperature. Using different amounts of poreformers and binders as well as controlling firing temperature, porosity of the anode was optimized while still retaining good mechanical integrity. The effect of cell operation conditions under dry hydrogen fuel on the SOFC open circuit voltage (OCV) and cell performance were also investigated. Characterization study of the synthesized LSGM indicates that sintering at 1500°C obtains higher electrical conductivity compared to the currently published results, while conductivity of pellets sintered at 1400°C and 1450°C would be slightly lower. The effect of sintering temperature on bulk and grain boundary resistivities was also discussed. The mechanical properties, such as hardness, Young's modulus, fracture toughness and modulus of rupture of the electrolyte were determined and correlated with scanning electron microscopy (SEM) morphological characterization. Linear thermal expansion and thermal expansion coefficient of LSGM were also measured.

  3. Fetal oxidative stress mechanisms of neurodevelopmental deficits and exacerbation by ethanol and methamphetamine.

    Science.gov (United States)

    Wells, Peter G; Bhatia, Shama; Drake, Danielle M; Miller-Pinsler, Lutfiya

    2016-06-01

    In utero exposure of mouse progeny to alcohol (ethanol, EtOH) and methamphetamine (METH) causes substantial postnatal neurodevelopmental deficits. One emerging pathogenic mechanism underlying these deficits involves fetal brain production of reactive oxygen species (ROS) that alter signal transduction, and/or oxidatively damage cellular macromolecules like lipids, proteins, and DNA, the latter leading to altered gene expression, likely via non-mutagenic mechanisms. Even physiological levels of fetal ROS production can be pathogenic in biochemically predisposed progeny, and ROS formation can be enhanced by drugs like EtOH and METH, via activation/induction of ROS-producing NADPH oxidases (NOX), drug bioactivation to free radical intermediates by prostaglandin H synthases (PHS), and other mechanisms. Antioxidative enzymes, like catalase in the fetal brain, while low, provide critical protection. Oxidatively damaged DNA is normally rapidly repaired, and fetal deficiencies in several DNA repair proteins, including oxoguanine glycosylase 1 (OGG1) and breast cancer protein 1 (BRCA1), enhance the risk of drug-initiated postnatal neurodevelopmental deficits, and in some cases deficits in untreated progeny, the latter of which may be relevant to conditions like autism spectrum disorders (ASD). Risk is further regulated by fetal nuclear factor erythroid 2-related factor 2 (Nrf2), a ROS-sensing protein that upregulates an array of proteins, including antioxidative enzymes and DNA repair proteins. Imbalances between conceptal pathways for ROS formation, versus those for ROS detoxification and DNA repair, are important determinants of risk. Birth Defects Research (Part C) 108:108-130, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  4. Severity of oxidative stress generates different mechanisms of endothelial cell death.

    Science.gov (United States)

    Burlacu, A; Jinga, V; Gafencu, A V; Simionescu, M

    2001-12-01

    The role of reactive oxygen species (ROS) in the pathogenesis of vascular diseases is well established, but few data exist on the mechanisms by which ROS induce endothelial cell (EC) death. We examined the conditions and the mechanisms by which oxidative stress induces EC death, using cultured confluent bovine aortic ECs exposed for 30 min to different concentrations of hydroxyl radicals (HO*) generated by hydrogen peroxide (H(2)O(2)) in the presence of 100 microM ferrous sulfate (FeSO(4)). Cell viability assays, Hoechst DNA staining, TUNEL (TDT-mediated dUTP-biotin nick end-labeling) analysis, agarose gel electrophoresis and annexin V assay were used to determine the effect of HO* on the viability of ECs, and to distinguish between apoptosis and necrosis. The results showed that at concentrations of up to 0.1 mM H(2)O(2)/FeSO(4), the large majority of cells are viable, except for approximately 12.5% death, which occurs by apoptosis. At a concentration of 0.2 mM H(2)O(2), the cell viability is reduced to 66%, while EC apoptosis remained at comparable values (14%). At high oxidative stress (0.5 mM H(2)O(2)), the cell viability was drastically reduced (approximately 39%), and the prevalent form of death was necrosis; apoptosis accounted for only approximately 17%. Together, these data indicate that: (1) HO* induce EC death either by apoptosis or necrosis and (2) the mechanisms of EC death differ as a function of the concentration of HO. Thus, the same insult can cause apoptosis and/or necrosis, as a function of the intensity rather than the nature of the insult.

  5. Investigations of oxidative stress effects and their mechanisms in rat brain after systemic administration of ceria engineered nanomaterials

    Science.gov (United States)

    Hardas, Sarita S.

    Advancing applications of engineered nanomaterials (ENM) in various fields create the opportunity for intended (e.g. drug and gene delivery) or unintended (e.g. occupational and environmental) exposure to ENM. However, the knowledge of ENM-toxicity is lagging behind their application development. Understanding the ENM hazard can help us to avoid potential human health problems associated with ENM applications as well as to increase their public acceptance. Ceria (cerium [Ce] oxide) ENM have many current and potential commercial applications. Beyond the traditional use of ceria as an abrasive, the scope of ceria ENM applications now extends into fuel cell manufacturing, diesel fuel additives and for therapeutic intervention as a putative antioxidant. However, the biological effects of ceria ENM exposure have yet to be fully defined. Both pro-and anti-oxidative effects of ceria ENM exposure are repeatedly reported in literature. EPA, NIEHS and OECD organizations have nominated ceria for its toxicological evaluation. All these together gave us the impetus to examine the oxidative stress effects of ceria ENM after systemic administration. Induction of oxidative stress is one of the primary mechanisms of ENM toxicity. Oxidative stress plays an important role in maintaining the redox homeostasis in the biological system. Increased oxidative stress, due to depletion of antioxidant enzymes or molecules and / or due to increased production of reactive oxygen (ROS) or nitrogen (RNS) species may lead to protein oxidation, lipid peroxidation and/or DNA damage. Increased protein oxidation or lipid peroxidation together with antioxidant protein levels and activity can serve as markers of oxidative stress. To investigate the oxidative stress effects and the mechanisms of ceria-ENM toxicity, fully characterized ceria ENM of different sizes (˜ 5nm, 15nm, 30nm, 55nm and nanorods) were systematically injected into rats intravenously in separate experiments. Three brain regions

  6. Ceruloplasmin enhances smooth muscle cell- and endothelial cell-mediated low density lipoprotein oxidation by a superoxide-dependent mechanism

    Science.gov (United States)

    Mukhopadhyay, C. K.; Ehrenwald, E.; Fox, P. L.

    1996-01-01

    Cultured vascular smooth muscle cells (SMC) and endothelial cells (EC) stimulate low density lipoprotein (LDL) oxidation by free radical-mediated, transition metal-dependent mechanisms. The physiological source(s) of metal ions is not known; however, purified ceruloplasmin, a plasma protein containing 7 coppers, oxidizes LDL in vitro. We now show that ceruloplasmin also increases LDL oxidation by vascular cells. In metal ion-free medium, human ceruloplasmin increased bovine aortic SMC- and EC-mediated LDL oxidation by up to 30- and 15-fold, respectively. The maximal response was at 100-300 microg ceruloplasmin/ml, a level at or below the unevoked physiological plasma concentration. Oxidant activity was dependent on protein structure as a specific proteolytic cleavage or removal of one of the seven ceruloplasmin copper atoms inhibited activity. Three lines of evidence indicated a critical role for cellular superoxide (O2.) in ceruloplasmin-stimulated oxidation. First, the rate of production of O2. by cells correlated with their rates of LDL oxidation. Second, superoxide dismutase effectively blocked ceruloplasmin-stimulated oxidation by both cell types. Finally, O2. production by SMC quantitatively accounted for the observed rate of LDL oxidation. To show this, the course of O2. production by SMC was simulated by repeated addition of xanthine and xanthine oxidase to culture medium under cell-free conditions. Neither ceruloplasmin nor O2. alone increased LDL oxidation, but together they completely reconstituted the oxidation rate of ceruloplasmin-stimulated SMC. These results are the first to show that ceruloplasmin stimulates EC- and SMC-mediated oxidation of LDL and that cell-derived O2. accounts quantitatively for metal-dependent, free radical-initiated oxidation of LDL by these cells.

  7. Mechanisms of pH-dependent activity for water oxidation to molecular oxygen by MnO2 electrocatalysts.

    Science.gov (United States)

    Takashima, Toshihiro; Hashimoto, Kazuhito; Nakamura, Ryuhei

    2012-01-25

    Manganese oxides function as efficient electrocatalysts for water oxidation to molecular oxygen in strongly alkaline conditions, but are inefficient at neutral pH. To provide new insight into the mechanism underlying the pH-dependent activity of the electrooxidation reaction, we performed UV-vis spectroelectrochemical detection of the intermediate species for water oxidation by a manganese oxide electrode. Layered manganese oxide nanoparticles, δ-MnO(2) (K(0.17)[Mn(4+)(0.90)Mn(3+)(0.07)□(0.03)]O(2)·0.53H(2)O) deposited on fluorine-doped tin oxide electrodes were shown to catalyze water oxidation at pH from 4 to 13. At this pH range, a sharp rise in absorption at 510 nm was observed with a concomitant increase of anodic current for O(2) evolution. Using pyrophosphate as a probe molecule, the 510 nm absorption was attributable to Mn(3+) on the surface of δ-MnO(2). The onset potential of the water oxidation current was constant at approximately 1.5 V vs SHE from pH 4 to pH 8, but sharply shifted to negative at pH > 8. Strikingly, this behavior was well reproduced by the pH dependence of the onset of 510 nm absorption, indicating that Mn(3+) acts as the precursor of water oxidation. Mn(3+) is unstable at pH oxides for water oxidation under neutral conditions is most likely due to the inherent instability of Mn(3+), whose accumulation at the surface of catalysts requires the electrochemical oxidation of Mn(2+) at a potential of approximately 1.4 V. This new model suggests that the control of the disproportionation and comproportionation efficiencies of Mn(3+) is essential for the development of Mn catalysts that afford water oxidation with a small overpotential at neutral pH.

  8. Mechanism of oxidation of 3-hydroxy-2,7-naphthalenedisulfonic acid disodium salt with oxygen in subcritical water.

    Science.gov (United States)

    Imbierowicz, Mirosław

    2017-06-01

    The article presents the results of studies on the oxidation mechanism of 3-hydroxy-2,7-naphthalenedisulfonic acid disodium salt (R-salt) with oxygen in subcritical water. To this aim, a series of experiments were carried out which showed that at a temperature of 413 K and pH > 9 the oxidation reaction of a substrate with oxygen was relatively quick and after approximately 40 min the R-salt oxidation yield exceeded 95%. In an acidic medium (pH oxidation is small. In order to identify the mechanism of R-salt oxidation, experiments were carried out at 413-569 K in solutions with pH = 10.0 and at partial oxygen pressure pO2 = 1.73 MPa. As a result of these experiments, a stable oxidation product was isolated from the reaction mixture and subjected to spectroscopic analysis. The analysis of (H)NMR of this product proved that a stable intermediate product of R-salt oxidation was 4-sulfophthalic acid sodium salt. The results of the experiments have shown that destructive oxidation of R-salt can easily be obtained at a temperature of 413 K, but satisfactory reduction of TOC in wastewater containing this substrate requires the use of very high temperature: at 569 K only 60% reduction of TOC was achieved. Copyright © 2017 Elsevier Ltd. All rights reserved.

  9. Effects of simulated oxidation on the in vitro wear and mechanical properties of irradiated and melted highly crosslinked UHMWPE.

    Science.gov (United States)

    Oral, Ebru; Neils, Andrew L; Doshi, Brinda N; Fu, Jun; Muratoglu, Orhun K

    2016-02-01

    Radiation crosslinked ultrahigh molecular weight polyethylene (UHMWPE) have reduced the wear rate of the bearing surface in total joint arthroplasty and the incidence of peri-prosthetic bone loss due to wear particles. The oxidation potential afforded to the material by the trapped residual free radicals after irradiation was addressed in first generation crosslinked UHMWPEs by using thermal treatments such as annealing or melting after irradiation. Postirradiation melted crosslinked UHMWPE did not contain detectable free radicals at the time of implantation and was expected to be resistant against oxidation for the lifetime of the implants. Recent analyses of long-term retrievals showed it was possible for irradiated and melted UHMWPEs to oxidize in vivo but studies on the effects of oxidation on these materials have been limited. In this study, we determined the effects of in vitro aging on the wear and mechanical properties of irradiated and melted UHMWPE as a function of radiation dose and found that even small amount of oxidation (oxidation index of 0.1) can have detrimental effects on its mechanical properties. There was a gradual increase in the wear rate below an oxidation index of 1 and a drastic increase thereafter. Therefore, it was shown in a simulated environment that oxidation can have detrimental effects to the clinically relevant properties of irradiated and melted UHMWPEs.

  10. Examining mechanism of toxicity of copper oxide nanoparticles to Saccharomyces cerevisiae and Caenorhabditis elegans

    Science.gov (United States)

    Mashock, Michael J.

    Copper oxide nanoparticles (CuO NPs) are an up and coming technology increasingly being used in industrial and consumer applications and thus may pose risk to humans and the environment. In the present study, the toxic effects of CuO NPs were studied with two model organisms Saccharomyces cerevisiae and Caenorhabditis elegans. The role of released Cu ions during dissolution of CuO NPs in growth media were studied with freshly suspended, aged NPs, and the released Cu 2+ fraction. Exposures to the different Cu treatments showed significant inhibition of S. cerevisiae cellular metabolic activity. Inhibition from the NPs was inversely proportional to size and was not fully explained by the released Cu ions. S. cerevisiae cultures grown under respiring conditions demonstrated greater metabolic sensitivity when exposed to CuO NPs compared to cultures undergoing fermentation. The cellular response to both CuO NPs and released Cu ions on gene expression was analyzed via microarray analysis after an acute exposure. It was observed that both copper exposures resulted in an increase in carbohydrate storage, a decrease in protein production, protein misfolding, increased membrane permeability, and cell cycle arrest. Cells exposed to NPs up-regulated genes related to oxidative phosphorylation but also may be inducing cell cycle arrest by a different mechanism than that observed with released Cu ions. The effect of CuO NPs on C. elegans was examined by using several toxicological endpoints. The CuO NPs displayed a more inhibitory effect, compared to copper sulfate, on nematode reproduction, feeding, and development. We investigated the effects of copper oxide nanoparticles and copper sulfate on neuronal health, a known tissue vulnerable to heavy metal toxicity. In transgenic C. eleganswith neurons expressing a green fluorescent protein reporter, neuronal degeneration was observed in up to 10% of the population after copper oxide nanoparticle exposure. Additionally, nematode

  11. Effect of iron oxide coatings on zinc sorption mechanisms at the clay-mineral/water interface.

    Science.gov (United States)

    Nachtegaal, Maarten; Sparks, Donald L

    2004-08-01

    Oxide surface coatings are ubiquitous in the environment, but their effect on the intrinsic metal uptake mechanism by the underlying mineral surface is poorly understood. In this study, the zinc (Zn) sorption complexes formed at the kaolinite, goethite, and goethite-coated kaolinite surfaces, were systematically studied as a function of pH, aging time, surface loading, and the extent of goethite coating, using extended X-ray absorption fine structure (EXAFS) spectroscopy. At pH 5.0, Zn partitioned to all sorbents by specific chemical binding to hydroxyl surface sites. At pH 7.0, the dominant sorption mechanism changed with reaction time. At the kaolinite surface, Zn was incorporated into a mixed metal Zn-Al layered double hydroxide (LDH). At the goethite surface, Zn initially formed a monodentate inner-sphere adsorption complex, with typical Zn-Fe distances of 3.18 A. However, with increasing reaction time, the major Zn sorption mechanism shifted to the formation of a zinc hydroxide surface precipitate, with characteristic Zn-Zn bond distances of 3.07 A. At the goethite-coated kaolinite surface, Zn initially bonded to FeOH groups of the goethite coating. With increasing aging time however, the inclusion of Zn into a mixed Zn-Al LDH took over as the dominant sorption mechanism. These results suggest that the formation of a precipitate phase at the kaolinite surface is thermodynamically favored over adsorption to the goethite coating. These findings show that the formation of Zn precipitates, similar in structure to brucite, at the pristine kaolinite, goethite, and goethite-coated kaolinite surfaces at near neutral pH and over extended reaction times is an important attenuation mechanism of metal contaminants in the environment.

  12. Dynamic Mechanical Properties of Oxide Films Formed on Metallic Surfaces as Measured Using a Tribological Approach at High Temperature

    Directory of Open Access Journals (Sweden)

    Yoshinori Isomoto Oka

    2011-01-01

    Full Text Available The surface degradation of metals in boiler tubes and turbines in high-temperature corrosive environments causes severe problems in fuel combustion power plant systems. High-temperature resistant materials have been recently developed using a thermal barrier coating (TBC and high-chromium alloys. Oxide films or coatings formed on metal surfaces at high temperatures can sometimes decrease the corrosion rate. However, the damage to the material is often accelerated by the mechanical removal of corrosion products from the material surface. It is therefore very important to investigate the mechanical and adhesive properties of the oxide films or coatings on metal surfaces used in high-temperature environments. This paper introduces a tribological method that uses a single spherical projectile impact at high temperature to measure the mechanical and adhesive properties of oxide films formed on various metal surfaces. Impact tests were performed on the surfaces of oxide films after their growth in a high-temperature furnace, and the deformed or fractured surfaces were observed in order to measure the mechanical and adhesive properties. The mechanical and adhesive properties of an elastic modulus, fracture, and exfoliation stresses were measured using the impact method, and the results depended on the type of metal oxide films and on the high-temperature environment.

  13. Evaluation of a Detailed Reaction Mechanism for Partial and Total Oxidation of C1 - C4 Alkanes

    OpenAIRE

    Quiceno González, Raúl

    2007-01-01

    In the present work a chemical kinetic mechanism was developed, suitable for modeling combustion and partial oxidation processes of C1 – C4 alkanes. The gas-phase kinetic mechanism describes intermediate and high temperature chemistry. Accordingly, the formation and evolution of important intermediate gas-phase species: Olefins and oxygenates were described in terms of different pathways typical at those temperature regimes. A previously developed mechanism suitable for high temperature condi...

  14. A mir-231-Regulated Protection Mechanism against the Toxicity of Graphene Oxide in Nematode Caenorhabditis elegans

    Science.gov (United States)

    Yang, Ruilong; Ren, Mingxia; Rui, Qi; Wang, Dayong

    2016-08-01

    Recently, several dysregulated microRNAs (miRNAs) have been identified in organisms exposed to graphene oxide (GO). However, their biological functions and mechanisms of the action are still largely unknown. Here, we investigated the molecular mechanism of mir-231 in the regulation of GO toxicity using in vivo assay system of Caenorhabditis elegans. We found that GO exposure inhibited the expression of mir-231::GFP in multiple tissues, in particular in the intestine. mir-231 acted in intestine to regulate the GO toxicity, and overexpression of mir-231 in intestine caused a susceptible property of nematodes to GO toxicity. smk-1 encoding a homologue to mammalian SMEK functioned as a targeted gene for mir-231, and was also involved in the intestinal regulation of GO toxicity. Mutation of smk-1 gene induced a susceptible property to GO toxicity, whereas the intestinal overexpression of smk-1 resulted in a resistant property to GO toxicity. Moreover, mutation of smk-1 gene suppressed the resistant property of mir-231 mutant to GO toxicity. In nematodes, SMK-1 further acted upstream of the transcriptional factor DAF-16/FOXO in insulin signaling pathway to regulate GO toxicity. Therefore, mir-231 may encode a GO-responsive protection mechanism against the GO toxicity by suppressing the function of the SMK-1 - DAF-16 signaling cascade in nematodes.

  15. Surface stress relaxation of oxide glasses: The effects on mechanical strength

    Science.gov (United States)

    Lezzi, Peter Joseph

    A new glass strengthening mechanism based upon surface compressive stress formation by surface stress relaxation of glasses that were held under a tensile stress, at a temperature lower than the glass transition temperature, in low water vapor pressure, has been demonstrated. Although glass fibers are traditionally known to become mechanically weaker when heat-treated at a temperature lower than the glass transition temperature in the presence of water vapor, the strength was found to become greater than the as-received fiber strength when fibers were subjected to a sub-critical tensile stress during heat-treatment. The observed strengthening was attributed to surface compressive residual stress formation through surface stress relaxation during the sub-critical tensile stress application in the atmosphere containing water vapor. Surface stress relaxation of the same glass fibers was shown to take place under conditions identical to those experienced by the strengthened mechanical test specimens by observing permanent bending of the fiber. Furthermore, the magnitude and presence of the residual stresses formed during bending or tensile heat-treatments were confirmed by FTIR, fiber etching, and fiber slicing methods. The method can in principle be used to strengthen any oxide glass and is not subjected to the constraints of traditional strengthening methods such as a minimum thickness for tempering, or a glass containing alkali ions for ion-exchange. Thus far, the method has been successful in strengthening silica glass, E-glass, and soda-lime silicate glass by approximately 20-30%.

  16. Nanoscale Mechanics of Graphene and Graphene Oxide in Composites: A Scientific and Technological Perspective.

    Science.gov (United States)

    Palermo, Vincenzo; Kinloch, Ian A; Ligi, Simone; Pugno, Nicola M

    2016-08-01

    Graphene shows considerable promise in structural composite applications thanks to its unique combination of high tensile strength, Young's modulus and structural flexibility which arise due to its maximal chemical bond strength and minimal atomic thickness. However, the ultimate performance of graphene composites will depend, in addition to the properties of the matrix and interface, on the morphology of the graphene used, including the size and shape of the sheets and the number of chemical defects present. For example, whilst oxidized sp(3) carbon atoms and vacancies in a graphene sheet can degrade its mechanical strength, they can also increase its interaction with other materials such as the polymer matrix of a composite, thus maximizing stress transfer and leading to more efficient mechanical reinforcement. Herein, we present an overview of some recently published work on graphene mechanical properties and discuss a list of challenges that need to be overcome (notwithstanding the strong hype existing on this material) for the development of graphene-based materials into a successful technology.

  17. Mechanical properties and scratch resistance of filtered-arc-deposited titanium oxide thin films on glass

    Energy Technology Data Exchange (ETDEWEB)

    Borrero-Lopez, Oscar, E-mail: oborlop@unex.es [Departamento de Ingenieria Mecanica, Energetica y de los Materiales, Universidad de Extremadura, 06071, Badajoz (Spain); School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Hoffman, Mark [School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Bendavid, Avi; Martin, Phil J. [CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield NSW 2070 (Australia)

    2011-09-01

    The mechanical properties and the scratch resistance of titanium oxide (TiO{sub 2}) thin films on a glass substrate have been investigated. Three films, with crystalline (rutile and anatase) and amorphous structures, were deposited by the filtered cathodic vacuum arc deposition technique on glass, and characterized by means of nanoindentation and scratch tests. The different damage modes (arc-like, longitudinal and channel cracks in the crystalline films; Hertzian cracks in the amorphous film) were assessed by means of optical and focused ion beam microscopy. In all cases, the deposition of the TiO{sub 2} film improved the contact-mechanical properties of uncoated glass. Crystalline films were found to possess a better combination of mechanical properties (i.e. elastic modulus up to 221 GPa, hardness up to 21 GPa, and fracture strength up to 3.6 GPa) than the amorphous film. However, under cyclic sliding contact above the critical fracture load, the amorphous film was found to withstand a higher number of cycles. The results are expected to provide useful insight for the design of optical coatings with improved contact-damage resistance.

  18. Exploring the Nitric Oxide Detoxification Mechanism of Mycobacterium tuberculosis Truncated Haemoglobin N

    Science.gov (United States)

    Bidon-Chanal, A.; Martí, M. A.; Estrín, D. A.; Luque, F. J.

    Mycobacterium tuberculosis, the causative agent of human tuberculosis, encodes a haemoprotein named Truncated Haemoglobin N (trHbN), which in its active site transforms nitric oxide (NO) to nitrate anion.left( {{text{NO}}_3^ - } right). The NO-dioxygenase activity of trHbN seems to be crucial for the bacillus, which can survive under the nitrosative stress conditions that occur upon infection of the host. As a defense mechanism against the copious amounts of NO produced by macrophages upon infection, the protein must achieve a high level of NO-dioxygenase activity to eliminate NO, but this is modulated by its efficiency in capturing O2 and NO. Migration of small diatomic ligands through the protein matrix is related to the presence of a doubly branched tunnel system connecting the surface and the haem cavity site. In this work, we have studied the mechanism that controls ligand diffusion and product egression with state-of-the-art molecular dynamics simulations. The results support a dual path mechanism for migration of O2 and NO through distinct branches of the tunnel, where migration of NO is facilitated upon binding of O2 to the haem group. Finally, egression of left( {{text{NO}}_3^ - } right) is preceded by the entrance of water to the haem cavity and occurs through a different pathway. Overall, the results highlight the intimate relationship between structure, dynamical behavior and biological function of trHbN.

  19. Fabrication and mechanical evaluation of hydroxyapatite/oxide nano-composite materials.

    Science.gov (United States)

    Mohamed, Khaled R; Beherei, Hanan H; El Bassyouni, Gehan T; El Mahallawy, Nahed

    2013-10-01

    In the current study, the semiconducting metal oxides such as nano-ZnO and SiO2 powders were prepared via sol-gel technique and conducted on nano-hydroxyapatite (nHA) which was synthesized by chemical precipitation. The properties of fabricated nano-structured composites containing different ratios of HA, ZnO and SiO2 were examined using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The effect of the variation of ratios between the three components on mechanical, microstructure and in-vitro properties was assessed to explore the possibility of enhancing these properties. The results proved that the mechanical properties exhibited an increment with increasing the ZnO content at the extent of HA. In-vitro study proved the formation and nucleation of apatite onto the surface of the fabricated composites after one week of immersion. It is concluded that HA composites containing SiO2 or SiO2/ZnO content had a suitable mechanical properties and ability to form apatite particles onto the composite surface. Based on bioactivity behavior, Si-HA is more bioactive than pure hydroxyapatite and nano-arrangements will provide an interface for better bone formation. Therefore, these nano-composites will be promising as bone substitutes especially in load bearing sites.

  20. Molecular mechanisms for uremic toxin-induced oxidative tissue damage via a cardiovascular-renal connection.

    Science.gov (United States)

    Watanabe, Hiroshi

    2013-01-01

    Chronic kidney disease (CKD), marked by a progressive loss in renal function, is a leading cause of hemodialysis initiation and cardiovascular disease (CVD). There are currently 13.3 million patients with CKD and 300 thousand patients are currently undergoing hemodialysis in Japan. Therefore, preventing the initiation of dialysis and reducing the risk of cardiovascular death are high-priority issues from the viewpoint of public health and economic implications. Understanding the molecular mechanism responsible for the progression of CKD and cardiovascular damage regarding crosstalk between the kidney and cardiovascular system is an important issue in controlling the pathogenesis of CKD-CVD. However, the mechanisms involved in CKD-CVD are not well understood. This hinders the development of new treatment strategies. We have been investigating the role of protein bound uremic toxins, that are difficult to remove by hemodialysis, on the onset and progression of CKD and CVD. The relationship between their redox properties and the pathogenesis of CKD-CVD was examined. In this review, we focus on two sulfate conjugated uremic toxins, namely, indoxyl sulfate (IS) and p-cresyl sulfate (PCS), and summarize recent studies that provide new insights on the molecular mechanisms responsible for uremic toxin-induced oxidative tissue damage via a cardiovascular-renal connection.

  1. Myocardial Oxidative Metabolism and Protein Synthesis during Mechanical Circulatory Support by Extracorporeal Membrane Oxygenation

    Energy Technology Data Exchange (ETDEWEB)

    Priddy, MD, Colleen M.; Kajimoto, Masaki; Ledee, Dolena; Bouchard, Bertrand; Isern, Nancy G.; Olson, Aaron; Des Rosiers, Christine; Portman, Michael A.

    2013-02-01

    Extracorporeal membrane oxygenation (ECMO) provides mechanical circulatory support essential for survival in infants and children with acute cardiac decompensation. However, ECMO also causes metabolic disturbances, which contribute to total body wasting and protein loss. Cardiac stunning can also occur which prevents ECMO weaning, and contributes to high mortality. The heart may specifically undergo metabolic impairments, which influence functional recovery. We tested the hypothesis that ECMO alters oxidative. We focused on the amino acid leucine, and integration with myocardial protein synthesis. We used a translational immature swine model in which we assessed in heart (i) the fractional contribution of leucine (FcLeucine) and pyruvate (FCpyruvate) to mitochondrial acetyl-CoA formation by nuclear magnetic resonance and (ii) global protein fractional synthesis (FSR) by gas chromatography-mass spectrometry. Immature mixed breed Yorkshire male piglets (n = 22) were divided into four groups based on loading status (8 hours of normal circulation or ECMO) and intracoronary infusion [13C6,15N]-L-leucine (3.7 mM) alone or with [2-13C]-pyruvate (7.4 mM). ECMO decreased pulse pressure and correspondingly lowered myocardial oxygen consumption (~ 40%, n = 5), indicating decreased overall mitochondrial oxidative metabolism. However, FcLeucine was maintained and myocardial protein FSR was marginally increased. Pyruvate addition decreased tissue leucine enrichment, FcLeucine, and Fc for endogenous substrates as well as protein FSR. Conclusion: The heart under ECMO shows reduced oxidative metabolism of substrates, including amino acids, while maintaining (i) metabolic flexibility indicated by ability to respond to pyruvate, and (ii) a normal or increased capacity for global protein synthesis, suggesting an improved protein balance.

  2. Oxidative stress enhances Axl-mediated cell migration through an Akt1/Rac1-dependent mechanism.

    Science.gov (United States)

    Huang, Jhy-Shrian; Cho, Chun-Yu; Hong, Chih-Chen; Yan, Ming-De; Hsieh, Mao-Chih; Lay, Jong-Ding; Lai, Gi-Ming; Cheng, Ann-Lii; Chuang, Shuang-En

    2013-12-01

    Persistent oxidative stress is common in cancer cells because of abnormal generation of reactive oxygen species (ROS) and has been associated with malignant phenotypes, such as chemotherapy resistance and metastasis. Both overexpression of Axl and abnormal ROS elevation have been linked to cell transformation and increased cell migration. However, the relationship between Axl and ROS in malignant cell migration has not been previously evaluated. Using an in vitro human lung cancer model, we examined the redox state of lung adenocarcinoma cell lines of low metastatic (CL1-0) and high metastatic (CL1-5) potentials. Here we report that Axl activation elicits ROS accumulation through the oxidase-coupled small GTPase Rac1. We also observed that oxidative stress could activate Axl phosphorylation to synergistically enhance cell migration. Further, Axl signaling activated by H2O2 treatment results in enhancement of cell migration via a PI3K/Akt-dependent pathway. The kinase activity of Axl is required for the Axl-mediated cell migration and prolongs the half-life of phospho-Akt under oxidative stress. Finally, downregulation of Akt1, but not Akt2, by RNAi in Axl-overexpressing cells inhibits the amount of activated Rac1 and the ability to migrate induced by H2O2 treatment. Together, these results show that a novel Axl-signaling cascade induced by H2O2 treatment triggers cell migration through the PI3K/Akt1/Rac1 pathway. Elucidation of redox regulation in Axl-related malignant migration may provide new molecular insights into the mechanisms underlying tumor progression.

  3. Hyperthermia induces injury to the intestinal mucosa in the mouse: evidence for an oxidative stress mechanism.

    Science.gov (United States)

    Oliver, S R; Phillips, N A; Novosad, V L; Bakos, M P; Talbert, E E; Clanton, T L

    2012-04-01

    Loss of the intestinal barrier is critical to the clinical course of heat illness, but the underlying mechanisms are still poorly understood. We tested the hypothesis that conditions characteristic of mild heatstroke in mice are associated with injury to the epithelial lining of the intestinal tract and comprise a critical component of barrier dysfunction. Anesthetized mice were gavaged with 4 kDa FITC-dextran (FD-4) and exposed to increasing core temperatures, briefly reaching 42.4°C, followed by 30 min recovery. Arterial samples were collected to measure FD-4 concentration in plasma (in vivo gastrointestinal permeability). The small intestines were then removed to measure histological evidence of injury. Hyperthermia resulted in a ≈2.5-fold elevation in plasma FD-4 and was always associated with significant histological evidence of injury to the epithelial lining compared with matched controls, particularly in the duodenum. When isolated intestinal segments from control animals were exposed to ≥41.5°C, marked increases in permeability were observed within 60 min. These changes were associated with release of lactate dehydrogenase, evidence of protein oxidation via carbonyl formation and histological damage. Coincubation with N-acetylcysteine protected in vitro permeability during hyperthermia and reduced histological damage and protein oxidation. Chelation of intracellular Ca(2+) to block tight junction opening during 41.5°C exposure failed to reduce the permeability of in vitro segments. The results demonstrate that hyperthermia exposure in mouse intestine, at temperatures at or below those necessary to induce mild heatstroke, cause rapid and substantial injury to the intestinal lining that may be attributed, in part, to oxidative stress.

  4. Investigation of the degradation mechanism of catalytic wires during oxidation of ammonia process

    Science.gov (United States)

    Pura, Jarosław; Wieciński, Piotr; Kwaśniak, Piotr; Zwolińska, Marta; Garbacz, Halina; Zdunek, Joanna; Laskowski, Zbigniew; Gierej, Maciej

    2016-12-01

    The most common catalysts for the ammonia oxidation process are 80 μm diameter platinum-rhodium wires knitted or woven into the form of a gauze. In an aggressive environment and under extreme conditions (temperature 800-900 °C, intensive gas flow, high pressure) precious elements are drained from the surface of the wires. Part of this separated material quickly decomposes on the surface in the form of characteristic "cauliflower-shape protrusions". The rest of the platinum is captured by palladium-nickel catalytic-capture gauzes located beneath. In our investigation we focused on the effects of the degradation of gauzes from one industrial catalytic system. The aim of the study was to compare the degree and the mechanism of degradation of gauzes from a different part of the reactor. The study covered PtRh7 catalytic and PdNi5 catalytic-capture gauzes. X-ray computer microtomography investigation revealed that despite strong differences in morphology, each Pt-Rh wire has a similar specific surface area. This indicates that the oxidation process and morphological changes of the wires occur in a self-regulating balance, resulting in the value of the specific surface area of the catalyst. Microtomography analysis of Pd-Ni wires revealed strong redevelopment of the wires' surface, which is related to the platinum capture phenomenon. Scanning electron microscope observations also revealed the nanostructure in the cauliflower-shape protrusions and large grains in the wires' preserved cores. The high temperature in the reactor and the long-term nature of the process do not favor the occurrence of the nanostructure in this type of material. Further and detailed analysis of this phenomena will provide a better understanding of the precious metals etching and deposition processes during oxidation.

  5. Sulfate radical-based oxidation of fluoroquinolone antibiotics: Kinetics, mechanisms and effects of natural water matrices.

    Science.gov (United States)

    Jiang, Canlan; Ji, Yuefei; Shi, Yuanyuan; Chen, Jifei; Cai, Tianming

    2016-12-01

    Widespread occurrence of fluoroquinolone antibiotics (FQs) in surface water, groundwater, soil and sediment has been reported and their remediation is essentially needed. Sulfate radical (SO4(-)) based advanced oxidation processes (SR-AOPs) are promising technologies for soil and groundwater remediation. In this study, the degradation kinetics, mechanisms, and effects of natural water matrices on heat-activated persulfate (PS) oxidation of FQs were systematically investigated. Experimental results clearly demonstrated that 92% of CIP was removed within 180 min (pH = 7, 60 °C). Higher temperature and lower pH facilitated the degradation of ciprofloxacin (CIP). The piperazine moiety of CIP was identified as the reactive site for SO4(-) attack by comparison with substructural analogs, flumequine (FLU) and 1-(2-fluorophenyl) piperazine (FPP). A comparison of the degradation of CIP, norfloxacin (NOR), enrofloxacin (ENR) and ofloxacin (OFL) confirmed that the presence of cyclopropane ring also influence the degradation of FQs. Water matrix significantly influenced the degradation of CIP and ENR, and the degradation rate followed the order of Milli-Q water (pH = 7) > groundwater > artificial seawater > artificial surface water > lake water. Degradation products of CIP in different water matrix were enriched by solid phase extraction (SPE) and then analyzed by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS). Detailed transformation pathways of CIP were proposed and were compared with respect to different water matrices. Four transformation pathways including stepwise piperazine ring oxidation, OH/F substitution, hydroxylation, and cyclopropane ring cleavage were proposed for CIP degradation. Results clearly show that the water matrix influenced the degradation of FQs appreciably, a phenomenon that should be taken into consideration when applying SR-AOPs for remediation of soil and groundwater contaminated by

  6. Cannabidiol protects liver from binge alcohol-induced steatosis by mechanisms including inhibition of oxidative stress and increase in autophagy.

    Science.gov (United States)

    Yang, Lili; Rozenfeld, Raphael; Wu, Defeng; Devi, Lakshmi A; Zhang, Zhenfeng; Cederbaum, Arthur

    2014-03-01

    Acute alcohol drinking induces steatosis, and effective prevention of steatosis can protect liver from progressive damage caused by alcohol. Increased oxidative stress has been reported as one mechanism underlying alcohol-induced steatosis. We evaluated whether cannabidiol, which has been reported to function as an antioxidant, can protect the liver from alcohol-generated oxidative stress-induced steatosis. Cannabidiol can prevent acute alcohol-induced liver steatosis in mice, possibly by preventing the increase in oxidative stress and the activation of the JNK MAPK pathway. Cannabidiol per se can increase autophagy both in CYP2E1-expressing HepG2 cells and in mouse liver. Importantly, cannabidiol can prevent the decrease in autophagy induced by alcohol. In conclusion, these results show that cannabidiol protects mouse liver from acute alcohol-induced steatosis through multiple mechanisms including attenuation of alcohol-mediated oxidative stress, prevention of JNK MAPK activation, and increasing autophagy.

  7. Arsenic in hydrothermal apatite: Oxidation state, mechanism of uptake, and comparison between experiments and nature

    Science.gov (United States)

    Liu, Weihua; Mei, Yuan; Etschmann, Barbara; Brugger, Joël; Pearce, Mark; Ryan, Chris G.; Borg, Stacey; Wykes, Jeremey; Kappen, Peter; Paterson, David; Boesenberg, Ulrike; Garrevoet, Jan; Moorhead, Gareth; Falkenberg, Gerald

    2017-01-01

    expected to be the dominant As form in hydrothermal fluids. These results show that incorporation of As in apatite is a complicated process, and sensitive to the local fluid composition during crystallization, and that some of the complexity in As zoning in partially reacted apatite may be due to local fluctuations of As(V)/As(III) ratios in the fluid and to kinetic effects during the mineral replacement reaction. Our study shows for the first time that As(III) can be incorporated into the apatite structure, although not as efficiently as As(V). Uptake of As(III) is probably highly dependent on the reaction mechanism. As(III)O33- moieties replace phosphate groups, but cause a high strain on the lattice; as a result, As(III) is easily exchanged (or oxidized) for As(V) during hydrothermal recrystallization, and the fully reacted grains only record the preferred oxidation state (i.e., As(V)) from mixed-oxidation state solutions. Overall this study shows that the observed oxidation state of As in apatite may not reflect the original As(III)/As(V) ratio of the parent fluid, due to the complex nature of As(III) uptake and possible in situ oxidation during recrystallization.

  8. Mechanism of thiosulfate oxidation in the SoxA family of cysteine-ligated cytochromes.

    Science.gov (United States)

    Grabarczyk, Daniel B; Chappell, Paul E; Eisel, Bianca; Johnson, Steven; Lea, Susan M; Berks, Ben C

    2015-04-03

    Thiosulfate dehydrogenase (TsdA) catalyzes the oxidation of two thiosulfate molecules to form tetrathionate and is predicted to use an unusual cysteine-ligated heme as the catalytic cofactor. We have determined the structure of Allochromatium vinosum TsdA to a resolution of 1.3 Å. This structure confirms the active site heme ligation, identifies a thiosulfate binding site within the active site cavity, and reveals an electron transfer route from the catalytic heme, through a second heme group to the external electron acceptor. We provide multiple lines of evidence that the catalytic reaction proceeds through the intermediate formation of a S-thiosulfonate derivative of the heme cysteine ligand: the cysteine is reactive and is accessible to electrophilic attack; cysteine S-thiosulfonate is formed by the addition of thiosulfate or following the reverse reaction with tetrathionate; the S-thiosulfonate modification is removed through catalysis; and alkylating the cysteine blocks activity. Active site amino acid residues required for catalysis were identified by mutagenesis and are inferred to also play a role in stabilizing the S-thiosulfonate intermediate. The enzyme SoxAX, which catalyzes the first step in the bacterial Sox thiosulfate oxidation pathway, is homologous to TsdA and can be inferred to use a related catalytic mechanism. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  9. Microstructure, mechanical properties, and oxidation resistance of nanocomposite Ti Si N coatings

    Science.gov (United States)

    Zhang, C. H.; Lu, X. C.; Wang, H.; Luo, J. B.; Shen, Y. G.; Li, K. Y.

    2006-07-01

    Ti-Si-N coatings with different silicon contents (0-12 at.%) were deposited onto Si(1 0 0) wafer, AISI M42 high speed steel, and stainless steel plate, respectively. These coatings were characterized and analyzed by using a variety of analytical techniques, such as XRD, AES, SEM, XPS, nanoindentation measurements, Rockwell C-type indentation tester, and scratch tester. The results revealed that the hardness was strongly correlated to the amount of silicon addition into a growing TiN film. The maximum hardness of 47.1 GPa was achieved as the Si content was 8.6 at.%. In the mechanical and oxidation resistance measurements, the Ti-Si-N coatings showed three distinct behaviors. (i) The coatings with Si contents of no more than 8.6 at.% performed good adhesion strength quality onto the HSS substrates. (ii) The fracture toughness of the coatings decreased with the increase in Si content. (iii) The Ti-Si-N coating with 8.6 at.% Si showed the excellent oxidation resistance behavior. The cutting performance under using coolant conditions was also evaluated by a conventional drilling machine. The drills with Ti-Si-N coatings performed much better than the drills with TiN coating and the uncoated drills.

  10. Block of the Mevalonate Pathway Triggers Oxidative and Inflammatory Molecular Mechanisms Modulated by Exogenous Isoprenoid Compounds

    Directory of Open Access Journals (Sweden)

    Paola Maura Tricarico

    2014-04-01

    Full Text Available Deregulation of the mevalonate pathway is known to be involved in a number of diseases that exhibit a systemic inflammatory phenotype and often neurological involvements, as seen in patients suffering from a rare disease called mevalonate kinase deficiency (MKD. One of the molecular mechanisms underlying this pathology could depend on the shortage of isoprenoid compounds and the subsequent mitochondrial damage, leading to oxidative stress and pro-inflammatory cytokines’ release. Moreover, it has been demonstrated that cellular death results from the balance between apoptosis and pyroptosis, both driven by mitochondrial damage and the molecular platform inflammasome. In order to rescue the deregulated pathway and decrease inflammatory markers, exogenous isoprenoid compounds were administered to a biochemical model of MKD obtained treating a murine monocytic cell line with a compound able to block the mevalonate pathway, plus an inflammatory stimulus. Our results show that isoprenoids acted in different ways, mainly increasing the expression of the evaluated markers [apoptosis, mitochondrial dysfunction, nucleotide-binding oligomerization-domain protein-like receptors 3 (NALP3, cytokines and nitric oxide (NO]. Our findings confirm the hypothesis that inflammation is triggered, at least partially, by the shortage of isoprenoids. Moreover, although further studies are necessary, the achieved results suggest a possible role for exogenous isoprenoids in the treatment of MKD.

  11. Block of the mevalonate pathway triggers oxidative and inflammatory molecular mechanisms modulated by exogenous isoprenoid compounds.

    Science.gov (United States)

    Tricarico, Paola Maura; Kleiner, Giulio; Valencic, Erica; Campisciano, Giuseppina; Girardelli, Martina; Crovella, Sergio; Knowles, Alessandra; Marcuzzi, Annalisa

    2014-04-22

    Deregulation of the mevalonate pathway is known to be involved in a number of diseases that exhibit a systemic inflammatory phenotype and often neurological involvements, as seen in patients suffering from a rare disease called mevalonate kinase deficiency (MKD). One of the molecular mechanisms underlying this pathology could depend on the shortage of isoprenoid compounds and the subsequent mitochondrial damage, leading to oxidative stress and pro-inflammatory cytokines' release. Moreover, it has been demonstrated that cellular death results from the balance between apoptosis and pyroptosis, both driven by mitochondrial damage and the molecular platform inflammasome. In order to rescue the deregulated pathway and decrease inflammatory markers, exogenous isoprenoid compounds were administered to a biochemical model of MKD obtained treating a murine monocytic cell line with a compound able to block the mevalonate pathway, plus an inflammatory stimulus. Our results show that isoprenoids acted in different ways, mainly increasing the expression of the evaluated markers [apoptosis, mitochondrial dysfunction, nucleotide-binding oligomerization-domain protein-like receptors 3 (NALP3), cytokines and nitric oxide (NO)]. Our findings confirm the hypothesis that inflammation is triggered, at least partially, by the shortage of isoprenoids. Moreover, although further studies are necessary, the achieved results suggest a possible role for exogenous isoprenoids in the treatment of MKD.

  12. Microstructural evolution and some mechanical properties of nanosized yttrium oxide dispersion strengthened 13Cr steel

    Science.gov (United States)

    Tich Nguyen, Van; Phuong Doan, Dinh; BaoTrung Tran, Tran; Duong Luong, Van; Nguyen, Van An; Phan, Anh Tu

    2010-09-01

    Oxide dispersion strengthened (ODS) steels, manufactured by a mechanical alloying method, during the past few years, appear to be promising candidates for structural applications in nuclear power plants. The purpose of this work is to elaborate the manufacturing processes of ODS 13Cr steel with the addition of 1.0 wt% yttrium oxide through the powder metallurgy route using the high energy ball mill. Microstructural analysis by scanning electron microscopy (SEM), x-ray diffraction (XRD) and hardness testing have been used to optimize the technological parameters of milling, hot isostatic pressing and heat-treatment processes. The steel hardness increases with decreasing particle size of 13Cr ODS steel. The best hardness was obtained from more than 70 h of milling in the two tanks planetary ball mill or 30 h of milling in the one tank planetary ball mill and hot isostatic pressing at 1150 °C . The particle size of the steel is less than 100 nm, and the density and hardness are about 7.3 g cm-3 and 490 HB, respectively. Report submitted to the 5th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN, Hanoi, 9-12 November 2010.

  13. Characterization of microstructural and mechanical properties of a reduced activation ferritic oxide dispersion strengthened steel

    Science.gov (United States)

    Eiselt, Ch. Ch.; Klimenkov, M.; Lindau, R.; Möslang, A.

    2011-09-01

    For specific blanket and divertor applications in future fusion power reactors a replacement of presently considered Reduced Activation Ferritic Martensitic (RAFM) steels as structural material by suitable oxide dispersion strengthened (ODS) ferritic martensitic steels would allow a substantial increase of the operating temperature from ˜823 K to about 923 K. Temperatures above 973 K in the He cooled modular divertor concept necessitate the use of Reduced Activation Ferritic (RAF)-ODS-steels, which are not limited by a phase transition. The development concentrates on the ferritic ODS-steel Fe-13Cr-1W-0.3Ti-0.3Y 2O 3. The microstructures of a mechanically alloyed powder particle are observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ageing experiments for 1000 h and 3000 h at 1123.5 K and 1223.5 K of compacted Fe-13Cr-1W-0.3Ti-0.3Y 2O 3 were executed. The impact especially on the oxide particles in terms of segregation and decomposition effects were monitored by electron energy loss spectroscopy (EELS). Long term vacuum creep experiments have been performed with rolled Fe-13Cr-1W-0.3Ti-0.3Y 2O 3 at 923.5 K and 1023.5 K, which will be compared to reference alloys.

  14. Antioxidants from black and green tea: from dietary modulation of oxidative stress to pharmacological mechanisms.

    Science.gov (United States)

    Peluso, Ilaria; Serafini, Mauro

    2016-10-16

    The consumption of tea (Camellia sinensis) has been correlated with a low incidence of chronic pathologies, such as cardiovascular disease and cancer, in which oxidative stress plays a critical role. Tea catechins and theaflavins are, respectively, the bioactive phytochemicals responsible for the antioxidant activity of green tea (GT) and black tea (BT). In addition to their redox properties, tea catechins and theaflavins could have also pharmacological activities, such as the ability to lower glucose, lipid and uric acid (UA) levels. These activities are mediated by pharmacological mechanisms such as enzymatic inhibition and interaction with transporters. Epigallocatechin gallate is the most active compound at inhibiting the enzymes involved in cholesterol and UA metabolism (hydroxy-3-methyl-glutaryl-CoA reductase and xanthine oxidase respectively) and affecting glucose transporters. The structural features of catechins that significantly contribute to their pharmacological effect are the presence/absence of the galloyl moiety and the number and positions of the hydroxyl groups on the rings. Although the inhibitory effects on α-glucosidase, maltase, amylase and lipase, multidrug resistance 1, organic anion transporters and proton-coupled folate transport occur at higher concentrations than those apparent in the circulation, these effects could be relevant in the gut. In conclusion, despite the urgent need for further research in humans, the regular consumption of moderate quantities of GT and BT can effectively modulate their antioxidant capacity, mainly in people subjected to oxidative stress, and could improve the metabolism of glucose, lipid and UA.

  15. Degradation of p-nitrotoluene by 03/H2 02 process and oxidation mechanism

    Institute of Scientific and Technical Information of China (English)

    YU Ying-hui; MA Jun; HOU Yan-jun; GAO Jin-sheng

    2009-01-01

    The degradation of p-nitrotoluene by O2/H2O2 process in a bubble contact column was investigated.Effects of the molar ratio of hydrogen peroxide to ozone, pH value and t-butanol on the oxidation process were discussed. It was found that the proper H2 O2/O3 molar ratio for the degradation of p-nitrotoluene was around O. 6, different pH values and the presence of t-butanol highly influenced the removal efficiency of p-nitrotoluene. 5-metbyl-2-nitrophenol, 2-methy1-5-nitrophenol, (4-nitrophenyl) methanol, 5-(hydroxymethyl) -2-nitro phenol, acetic acid, 2-methylpropanc diacid and 2-(hydroxylmethyl) propane diacid were identified as degradation intermediates and products through GC-MS. Radical reaction mechanism and degradation pathway were proposed based on the results of experiments. It is deduced that the benzene ring of p-nitrotoluene can be only destroyed by hydroxyl radicals through a polyhydrexy intermediate pathway. Then unstable polybydroxy intermediates can be oxidized to different acids with low molecular weight rapidly.

  16. Mechanical Property and Oxidation Behavior of ATF cladding developed in KAERI

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyun-Gil; Kim, Il-Hyun; Jung, Yang-Il; Park, Dong-Jun; Park, Jung-Hwan; Park, Jeong-Yong; Koo, Yang-Hyun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    To realize the coating cladding, coating material (Cr-based alloy) as well as coating technology (3D laser coating and arc ion plating combined with vacuum annealing) can be developed to meet the fuel cladding criteria. The coated Zr cladding can be produced after the optimization of coating technologies. The coated cladding sample showed the good oxidation/corrosion and adhesion properties without the spalling and/or severe interaction with the Zr alloy cladding from the various tests. Thus, it is known that the mechanical property and oxidation behavior of coated cladding concept developed in KAERI is reasonable for applying the ATF cladding in LWRs. At the present time various ATF concepts have been proposed and developing in many countries. The ATF concepts with potentially improved accident performance can be summarized to the coating cladding, Mo-Zr cladding, FeCrAl cladding, and SiCf/SiC cladding. Regarding the cladding performance, ATF cladding concepts will be evaluated with respect to the accident scenarios and normal operations of LWRs as well as to the fuel cladding fabrication.

  17. Mechanisms of Oxidative Damage in Multiple Sclerosis and a Cell Therapy Approach to Treatment

    Directory of Open Access Journals (Sweden)

    Jonathan Witherick

    2011-01-01

    Full Text Available Although significant advances have recently been made in the understanding and treatment of multiple sclerosis, reduction of long-term disability remains a key goal. Evidence suggests that inflammation and oxidative stress within the central nervous system are major causes of ongoing tissue damage in the disease. Invading inflammatory cells, as well as resident central nervous system cells, release a number of reactive oxygen and nitrogen species which cause demyelination and axonal destruction, the pathological hallmarks of multiple sclerosis. Reduction in oxidative damage is an important therapeutic strategy to slow or halt disease processes. Many drugs in clinical practice or currently in trial target this mechanism. Cell-based therapies offer an alternative source of antioxidant capability. Classically thought of as being important for myelin or cell replacement in multiple sclerosis, stem cells may, however, have a more important role as providers of supporting factors or direct attenuators of the disease. In this paper we focus on the antioxidant properties of mesenchymal stem cells and discuss their potential importance as a cell-based therapy for multiple sclerosis.

  18. Oxidation mechanism and overall removal rates of endocrine disrupting chemicals by aquatic plants.

    Science.gov (United States)

    Reis, A R; Tabei, K; Sakakibara, Y

    2014-01-30

    The purpose of this study was to evaluate experimentally and theoretically the oxidation mechanisms and overall removal rates of phenolic endocrine disrupting chemicals (EDCs) by aquatic plants. EDCs used in this study were bisphenol-A (BPA), 2,4-dichlorophenol (2,4-DCP), 4-tert-octylphenol (4-t-OP), and pentachlorophenol (PCP). Referring to reported detection levels in aquatic environments and contaminated sites, the feed concentration of each EDC was set from 1 to 100μg/L. Experimental results showed that, except for PCP, phenolic EDCs were stably and concurrently removed by different types of aquatic plants over 70 days in long-term continuous treatments. Primal enzymes responsible for oxidation of BPA, 2,4-DCP, and 4-t-OP were peroxidases (POs). Moreover, enzymatic removal rates of BPA, 2,4-DCP, and 4-t-OP by POs were more than 2 orders of magnitude larger than those by aquatic plants. Assuming that overall removal rates of EDCs are controlled by mass transfer rates onto liquid films on the surface of aquatic plants, an electrochemical method based on the limiting current theory was developed to measure the mass transfer rates of EDCs. Because of extremely large removal rates of EDCs by POs, observed removal rates by aquatic plants were in reasonably good agreement with calculated results by a mathematical model developed based on an assumption that mass transfer limitation is a rate-limiting step.

  19. Evidence for Negative Effects of Elevated Intra-Abdominal Pressure on Pulmonary Mechanics and Oxidative Stress

    Directory of Open Access Journals (Sweden)

    I. Davarcı

    2015-01-01

    Full Text Available Objective. To compare the effects of pneumoperitoneum on lung mechanics, end-tidal CO2 (ETCO2, arterial blood gases (ABG, and oxidative stress markers in blood and bronchoalveolar lavage fluid (BALF during laparoscopic cholecystectomy (LC by using lung-protective ventilation strategy. Materials and Methods. Forty-six patients undergoing LC and abdominal wall hernia (AWH surgery were assigned into 2 groups. Measurements and blood samples were obtained before, during pneumoperitoneum, and at the end of surgery. BALF samples were obtained after anesthesia induction and at the end of surgery. Results. Peak inspiratory pressure, ETCO2, and pCO2 values at the 30th minute were significantly increased, while there was a significant decrease in dynamic lung compliance, pH, and pO2 values in LC group. In BALF samples, total oxidant status (TOS, arylesterase, paraoxonase, and malondialdehyde levels were significantly increased; the glutathione peroxidase levels were significantly decreased in LC group. The serum levels of TOS and paraoxonase were significantly higher at the end of surgery in LC group. In addition, arylesterase level in the 30th minute was increased compared to baseline. Serum paraoxonase level at the end of surgery was significantly increased when compared to AWH group. Conclusions. Our study showed negative effects of pneumoperitoneum in both lung and systemic levels despite lung-protective ventilation strategy.

  20. Designing interlayers to improve the mechanical reliability of transparent conductive oxide coatings on flexible substrates

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Eun-Hye; Yang, Chan-Woo; Park, Jin-Woo [Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of)

    2012-05-01

    In this study, we investigate the effect of interlayers on the mechanical properties of transparent conductive oxide (TCO) on flexible polymer substrates. Indium tin oxide (ITO), which is the most widely used TCO film, and Ti, which is the most widely used adhesive interlayer, are selected as the coating and the interlayer, respectively. These films are deposited on the polymer substrates using dc-magnetron sputtering to achieve varying thicknesses. The changes in the following critical factors for film cracking and delamination are analyzed: the internal stress ({sigma}{sup i}) induced in the coatings during deposition using a white light interferometer, the crystallinity using a transmission electron microscope, and the surface roughness of ITO caused by the interlayer using an atomic force microscope. The resistances to the cracking and delamination of ITO are evaluated using a fragmentation test. Our tests and analyses reveal the important role of the interlayers, which significantly reduce the compressive {sigma}{sup i} that is induced in the ITO and increase the resistance to the buckling delamination of the ITO. However, the relaxation of {sigma}{sup i} is not beneficial to cracking because there is less compensation for the external tension as {sigma}{sup i} further decreases. Based on these results, the microstructural control is revealed as a more influential factor than {sigma}{sup i} for improving crack resistance.

  1. Designing interlayers to improve the mechanical reliability of transparent conductive oxide coatings on flexible substrates

    Science.gov (United States)

    Kim, Eun-Hye; Yang, Chan-Woo; Park, Jin-Woo

    2012-05-01

    In this study, we investigate the effect of interlayers on the mechanical properties of transparent conductive oxide (TCO) on flexible polymer substrates. Indium tin oxide (ITO), which is the most widely used TCO film, and Ti, which is the most widely used adhesive interlayer, are selected as the coating and the interlayer, respectively. These films are deposited on the polymer substrates using dc-magnetron sputtering to achieve varying thicknesses. The changes in the following critical factors for film cracking and delamination are analyzed: the internal stress (σi) induced in the coatings during deposition using a white light interferometer, the crystallinity using a transmission electron microscope, and the surface roughness of ITO caused by the interlayer using an atomic force microscope. The resistances to the cracking and delamination of ITO are evaluated using a fragmentation test. Our tests and analyses reveal the important role of the interlayers, which significantly reduce the compressive σi that is induced in the ITO and increase the resistance to the buckling delamination of the ITO. However, the relaxation of σi is not beneficial to cracking because there is less compensation for the external tension as σi further decreases. Based on these results, the microstructural control is revealed as a more influential factor than σi for improving crack resistance.

  2. Protective mechanism of agmatine pretreatment on RGC-5 cells injured by oxidative stress

    Directory of Open Access Journals (Sweden)

    Y. Iizuka

    2010-04-01

    Full Text Available Agmatine has neuroprotective effects on retinal ganglion cells (RGCs as well as cortical and spinal neurons. It protects RGCs from oxidative stress even when it is not present at the time of injury. As agmatine has high affinity for various cellular receptors, we assessed protective mechanisms of agmatine using transformed RGCs (RGC-5 cell line. Differentiated RGC-5 cells were pretreated with 100 μM agmatine and consecutively exposed to 1.0 mM hydrogen peroxide (H2O2. Cell viability was determined by measuring lactate dehydrogenase (LDH, and the effects of selective alpha 2-adrenergic receptor antagonist yohimbine (0-500 nM and N-methyl-D-aspartic acid (NMDA receptor agonist NMDA (0-100 µM were evaluated. Agmatine’s protective effect was compared to a selective NMDA receptor antagonist MK-801. After a 16-h exposure to H2O2, the LDH assay showed cell loss greater than 50%, which was reduced to about 30% when agmatine was pretreated before injury. Yohimbine almost completely inhibited agmatine’s protective effect, but NMDA did not. In addition, MK-801 (0-100 µM did not significantly attenuate the H2O2-induced cytotoxicity. Our results suggest that neuroprotective effects of agmatine on RGCs under oxidative stress may be mainly attributed to the alpha 2-adrenergic receptor signaling pathway.

  3. Hypoxia and Reoxygenation: a Possible Mechanism for Placental Oxidative Stress in Preeclampsia

    Directory of Open Access Journals (Sweden)

    Tai-Ho Hung

    2006-09-01

    Full Text Available Preeclampsia is a human pregnancy-specific disorder that is diagnosed by the new appearance of hypertension and proteinuria after 20 weeks' gestation. It is a leading cause of perinatal morbidity and mortality, and the only intervention that effectively reverses the syndrome is delivery. Oxidative stress of the placenta is considered to be a key intermediary step in the pathogenesis of preeclampsia, but the cause for the stress remains unknown. Hypoxia-reoxygenation (H/R injury, as a result of intermittent placental perfusion secondary to deficient trophoblast invasion of the endometrial arteries, is a possible mechanism. In this review, we present evidence to show that there is a plausible basis from which to assume that blood flow in the intervillous space will be intermittent in all normal pregnancies. The intermittency will be exacerbated by impaired conversion of the spiral arteries, or by the presence of atherotic changes that reduce their caliber as seen in preeclampsia. Placental oxidative stress can be the consequences of fluctuations in oxygen concentrations after H/R through the actions of reactive oxygen species. On this basis, there will be a complete spectrum of placental changes among the normal, the late onset and the early onset preeclamptic states. Viewing the syndrome as a continuum of H/R insults provides new insight into the pathophysiology of pregnancy that will hopefully lead to improved clinical interventions.

  4. Lipid peroxidation and cell death mechanisms in pulmonary epithelial cells induced by peroxynitrite and nitric oxide

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Yuan-Soon [School of Medical Technology, Taipei Medical University, Taipei (Taiwan); Liou, Hung-Bin; Lin, Yu-Ping; Guo, How-Ran; Ho, Sheng-Yow; Lee, Ching-Chang; Wang, Ying-Jan [Department of Environmental and Occupational Health, National Cheng Kung University Medical College, 138 Sheng-Li Road, Tainan (Taiwan); Lin, Jen-Kun; Pan, Min-Hsiung [Institute of Biochemistry, National Taiwan University, Medical College, Taipei (Taiwan); Jeng, Jiiang-Huei [School of Dentistry, National Taiwan University and Hospital, Medical College, Taipei (Taiwan)

    2002-08-01

    Nitric oxide (NO) is an environmental pollutant found in smog and cigarette smoke. Recently, NO has been discovered to act as a molecular messenger, mediating various physiological functions. However, when an excess of NO is present, cytotoxic and mutagenic effects can also be induced. The reaction of NO with superoxide results in the formation of peroxynitrite (ONOO{sup -}), which decomposes into the hydroxyl radical and nitrogen dioxide. Both of them are potent oxidant species that may initiate and propagate lipid peroxidation. In the present study, we examined the effects of NO and ONOO{sup -} on the induction of lipid peroxidation and cell death mechanisms in rats and in A549 pulmonary epithelial cells. The results showed that ONOO{sup -} is able to induce lipid peroxidation in pulmonary epithelial cells in a dose-dependent manner. 8-Epi-prostaglandin F{sub 2{alpha}} can serve as a good biomarker of lipid peroxidation both in vitro and in vivo. Postmitotic apoptosis was found in A549 cells exposed to NO, whereas ONOO{sup -} induced cell death more characteristic of necrosis than apoptosis. Apoptosis that occurred in cells may be related to the dysfunction of mitochondria, the release of cytochrome c into cytosol, and the activation of caspase-9. The relationship between caspase activation and the cleavage of other death substrates during postmitotic apoptosis in A549 cells needs further investigation. (orig.)

  5. Final Report: Molecular mechanisms and kinetics of microbial anaerobic nitrate-dependent U(IV) and Fe(II) oxidation

    Energy Technology Data Exchange (ETDEWEB)

    O' Day, Peggy A. [Univ. of California, Merced, CA (United States); Asta, Maria P. [Univ. of California, Merced, CA (United States); Kanematsu, Masakazu [Univ. of California, Merced, CA (United States); Beller, Harry [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Zhou, Peng [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Steefel, Carl [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2015-02-27

    In this project, we combined molecular genetic, spectroscopic, and microscopic techniques with kinetic and reactive transport studies to describe and quantify biotic and abiotic mechanisms underlying anaerobic, nitrate-dependent U(IV) and Fe(II) oxidation, which influences the long-term efficacy of in situ reductive immobilization of uranium at DOE sites. In these studies, Thiobacillus denitrificans, an autotrophic bacterium that catalyzes anaerobic U(IV) and Fe(II) oxidation, was used to examine coupled oxidation-reduction processes under either biotic (enzymatic) or abiotic conditions in batch and column experiments with biogenically produced UIVO2(s). Synthesis and quantitative analysis of coupled chemical and transport processes were done with the reactive transport modeling code Crunchflow. Research focused on identifying the primary redox proteins that catalyze metal oxidation, environmental factors that influence protein expression, and molecular-scale geochemical factors that control the rates of biotic and abiotic oxidation.

  6. The Response to Oxidative DNA Damage in Neurons: Mechanisms and Disease

    Directory of Open Access Journals (Sweden)

    Laura Narciso

    2016-01-01

    Full Text Available There is a growing body of evidence indicating that the mechanisms that control genome stability are of key importance in the development and function of the nervous system. The major threat for neurons is oxidative DNA damage, which is repaired by the base excision repair (BER pathway. Functional mutations of enzymes that are involved in the processing of single-strand breaks (SSB that are generated during BER have been causally associated with syndromes that present important neurological alterations and cognitive decline. In this review, the plasticity of BER during neurogenesis and the importance of an efficient BER for correct brain function will be specifically addressed paying particular attention to the brain region and neuron-selectivity in SSB repair-associated neurological syndromes and age-related neurodegenerative diseases.

  7. Broad compositional tunability of indium tin oxide nanowires grown by the vapor-liquid-solid mechanism

    Directory of Open Access Journals (Sweden)

    M. Zervos

    2014-05-01

    Full Text Available Indium tin oxide nanowires were grown by the reaction of In and Sn with O2 at 800 °C via the vapor-liquid-solid mechanism on 1 nm Au/Si(001. We obtain Sn doped In2O3 nanowires having a cubic bixbyite crystal structure by using In:Sn source weight ratios > 1:9 while below this we observe the emergence of tetragonal rutile SnO2 and suppression of In2O3 permitting compositional and structural tuning from SnO2 to In2O3 which is accompanied by a blue shift of the photoluminescence spectrum and increase in carrier lifetime attributed to a higher crystal quality and Fermi level position.

  8. Molecular Mechanisms Involved in the Antitumor Activity of Cannabinoids on Gliomas: Role for Oxidative Stress

    Energy Technology Data Exchange (ETDEWEB)

    Massi, Paola [Department of Pharmacology, Chemotherapy and Toxicology, University of Milan, Via Vanvitelli 32, 20129 Milan (Italy); Valenti, Marta; Solinas, Marta; Parolaro, Daniela, E-mail: daniela.parolaro@uninsubria.it [Department of Structural and Functional Biology, Section of Pharmacology, Center of Neuroscience, University of Insubria, Via A. da Giussano 10, 20152 Busto Arsizio, Varese (Italy)

    2010-05-26

    Cannabinoids, the active components of Cannabis sativa, have been shown to exert antiproliferative and proapoptotic effects on a wide spectrum of tumor cells and tissues. Of interest, cannabinoids have displayed great potency in reducing the growth of glioma tumors, one of the most aggressive CNS tumors, either in vitro or in animal experimental models curbing the growth of xenografts generated by subcutaneous or intrathecal injection of glioma cells in immune-deficient mice. Cannabinoids appear to be selective antitumoral agents as they kill glioma cells without affecting the viability of non-transformed cells. This review will summarize the anti-cancer properties that cannabinoids exert on gliomas and discuss their potential action mechanisms that appear complex, involving modulation of multiple key cell signaling pathways and induction of oxidative stress in glioma cells.

  9. Molecular Mechanisms Involved in the Antitumor Activity of Cannabinoids on Gliomas: Role for Oxidative Stress

    Directory of Open Access Journals (Sweden)

    Paola Massi

    2010-05-01

    Full Text Available Cannabinoids, the active components of Cannabis sativa, have been shown to exert antiproliferative and proapoptotic effects on a wide spectrum of tumor cells and tissues. Of interest, cannabinoids have displayed great potency in reducing the growth of glioma tumors, one of the most aggressive CNS tumors, either in vitro or in animal experimental models curbing the growth of xenografts generated by subcutaneous or intrathecal injection of glioma cells in immune-deficient mice. Cannabinoids appear to be selective antitumoral agents as they kill glioma cells without affecting the viability of non-transformed cells. This review will summarize the anti-cancer properties that cannabinoids exert on gliomas and discuss their potential action mechanisms that appear complex, involving modulation of multiple key cell signaling pathways and induction of oxidative stress in glioma cells.

  10. Oxide Nanoparticle EUV (ONE) Photoresists: Current Understanding of the Unusual Patterning Mechanism

    KAUST Repository

    Jiang, Jing

    2015-01-01

    © 2015 SPST. In the past few years, industry has made significant progress to deliver a stable high power EUV scanner and a 100 W light source is now being tested on the manufacuring scale. The success of a high power EUV source demands a fast and high resolution EUV resist. However, chemcially amplied resists encounter unprecedented challenges beyond the 22 nm node due to resolution, roughness and sensitivity tradeoffs. Unless novel solutions for EUV resists are proposed and further optimzed, breakthroughs can hardly be achieved. Oxide nanoparticle EUV (ONE) resists stablized by organic ligands were originally proposed by Ober et al. Recently this work attracts more and more attention due to its extraordinanry EUV sensitivity. This new class of photoresist utilizes ligand cleavage with a ligand exchange mechanism to switch its solubilty for dual-tone patterning. Therefore, ligand selection of the nanoparticles is extremely important to its EUV performance.

  11. Oxidation of glycylglycine by ferricyanide in acid medium: Kinetics and mechanism

    Directory of Open Access Journals (Sweden)

    Krishna K. Yerneni

    2015-12-01

    Full Text Available The oxidative degradation of glycylglycine (GlyGly to formic acid, ammonium ion, and carbon dioxide occurs when it reacts with ferricyanide in acid medium, which has been studied spectrophotometrically at 303 nm at constant temperature. Kinetic runs have been performed under a pseudo-first-order condition of [GlyGly]0 >> [ferricyanide]0. The experimental rate law obtained for the redox reaction is: rate = kı [$ \\text{Fe(CN}^{3 - }_{6} $] [GlyGly]x [H+]y[Pd(II]0, where x and y are fractional orders. Effects of ionic strength and dielectric constant are also investigated. Activation parameters have been evaluated using Arrhenius and Eyring plots. A probable mechanism has been proposed and the derived rate law is consistent with the kinetic data.

  12. Poly(ethylene oxide)/clay nanaocomposites: Thermal and mechanical properties

    Science.gov (United States)

    Ejder-Korucu, Mehtap; Gürses, Ahmet; Karaca, Semra

    2016-08-01

    Poly(ethylene oxide) (PEO)/clay nanocomposites were prepared by a solution intercalation method using chloroform as a solvent. The nanocomposites were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and also investigation of some mechanical properties of the composites. Formation of nanocomposite was confirmed by XRD analysis. The increasing tendency of exfoliation degree with an increase in clay content may be attributed to easier diffusion of PEO chains to interlayer regions. An increase in PEO crystallinity in case of nanocomposite, was confirmed by an increase in the heat of melting as indicated by DSC. Improvement in tensile properties in all respect was observed for nanocomposites with clay content.

  13. Enhancement in Mechanical and Shape Memory Properties for Liquid Crystalline Polyurethane Strengthened by Graphene Oxide

    Directory of Open Access Journals (Sweden)

    Yueting Li

    2016-07-01

    Full Text Available Conventional shape memory polymers suffer the drawbacks of low thermal stability, low strength, and low shape recovery speed. In this study, main-chain liquid crystalline polyurethane (LCPU that contains polar groups was synthesized. Graphene oxide (GO/LCPU composite was fabricated using the solution casting method. The tensile strength of GO/LCPU was 1.78 times that of neat LCPU. In addition, shape recovery speed was extensively improved. The average recovery rate of sample with 20 wt % GO loading was 9.2°/s, much faster than that of LCPU of 2.6°/s. The enhancement in mechanical property and shape memory behavior could be attributed to the structure of LCPU and GO, which enhanced the interfacial interactions between GO and LCPU.

  14. Mechanical properties of solid oxide fuel cell glass-ceramic seal at high temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Milhans, Jacqueline; Li, Dongsheng; Khaleel, Mohammad A.; Sun, Xin; Al-Haik, Marwan; Harris, Adrian; Garmestani, Hamid

    2011-04-20

    Mechanical properties of solid oxide fuel cell glass-ceramic seal material, G18, are studied at high temperatures. Samples of G18 are aged for either 4h or 100h, resulting in samples with different crystallinity. Reduced modulus, hardness, and time-dependent behavior are measured by nanoindentation. The nanoindentation is performed at room temperature, 550, 650, and 750°C, using loading rates of 5 mN/s and 25 mN/s. Results show a decrease in reduced modulus with increasing temperature, with significant decrease above the glass transition temperature (Tg). Hardness generally decreases with increasing temperature, with a slight increase before Tg for the 4h aged sample. Dwell tests show that creep increases with increasing temperature, but decrease with further aging.

  15. The study of electron scattering mechanisms in single crystal oxide nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Berengue, Olivia M; Chiquito, Adenilson J [NanO LaB - Departamento de Fisica, Universidade Federal de Sao Carlos, CEP 13565-905, CP 676, Sao Carlos, Sao Paulo (Brazil); Simon, Ricardo A [UTFPR - Campus Apucarana, Rua MarcIlio Dias, 635, CEP 86812-460, Apucarana, Parana (Brazil); Leite, Edson R, E-mail: oliberengue@yahoo.com.br [Laboratorio Interdisciplinar de EletroquImica e Ceramicas, Departamento de Quimica, Universidade Federal de Sao Carlos, CEP 13565-905, CP 676, Sao Carlos, Sao Paulo (Brazil)

    2011-06-01

    We report on transport measurements of individual Sn doped In{sub 2}O{sub 3} nanowires. From these measurements we point out that spin-orbit and boundary scattering mechanisms seem to give a negligible contribution to the transport of electrons in these nanowires. In fact, these results can be extended to other oxide systems: the presence of a weak disorder arising from the random potential at the boundaries screen electrons away from the surface into the nanowire. Electrons travelling through the nanowire in inner conducting channels are not directly influenced by the surfaces and the boundary scattering is decreased. These findings were also supported by calculations of the electron distribution in the cross-section of the nanowires when some disorder is taken into account.

  16. [Interrupted alcohol treatment and liver: free radical homeostasis, nitric oxide, adaptive mechanisms].

    Science.gov (United States)

    Miskevich, D A; Borodinskiĭ, A N; Petushok, N E; Konovalenko, O V; Lelevich, V V

    2006-01-01

    Alcohol administration can result in liver damage. Reactive oxygen species (ROS), nitric oxide (NO) and their interaction are crucial factors in this process. The aim of work was to investigate, free radical state and mechanisms of adaptation of the antioxidant system (AOS) to stress, caused by interrupted alcohol intake. Repeated cycles of alcoholization caused an imbalance between production and utilization of various ROS. This imbalance was due to impairments in the system superoxide dismutase/catalase. Nevertheless, in most experimental groups there was clear reduction of lipid peroxidation (LPO) products evaluated by thiobarbituric acid reactive substances. This might be attributed to the antioxidant effect of NO. However, there was an increased level of transaminases in blood plasma. After 28 days of this experimental scheme all the parameters studied normalized.

  17. Growth mechanisms of zinc oxide and zinc sulfide films by mist chemical vapor deposition

    Science.gov (United States)

    Uno, Kazuyuki; Yamasaki, Yuichiro; Tanaka, Ichiro

    2017-01-01

    The growth mechanisms of zinc oxide and zinc sulfide films by mist chemical vapor deposition (mist-CVD) were experimentally investigated from the viewpoint of mist behaviors and chemical reactions. The proper growth model, either vaporization or the Leidenfrost model, was studied by supplying two kinds of mists with different kinds of sources, such as H2 16O and H2 18O for ZnO growth and ZnCl2 and thiourea for ZnS growth. Moreover, the origin of the oxygen atoms of ZnO was investigated using a quantitative analysis. The role of chloro complex of zinc in the growth of ZnS from aqueous solutions was also examined by systematic studies.

  18. SOLID OXIDE FUEL CELL CATHODES: Polarization Mechanisms and Modeling of the Electrochemical Performance

    Science.gov (United States)

    Fleig, Jurgen

    2003-08-01

    Several recent experimental and numerical investigations have contributed to the improved understanding of the electrochemical mechanisms taking place at solid oxide fuel cell (SOFC) cathodes and yielded valuable information on the relationships between alterable parameters (geometry/material) and the cathodic polarization resistance. Efforts to reduce the polarization resistance in SOFCs can benefit from these results, and some important aspects of the corresponding studies are reviewed. Experimental results, particularly measurements using geometrically well-defined Sr-doped LaMnO3 (LSM) cathodes, are discussed. In regard to simulations, the different levels of sophistication used in SOFC electrode modeling studies are summarized and compared. Exemplary simulations of mixed conducting cathodes that show the capabilities and limits of different modeling levels are described.

  19. Signaling Pathways and Molecular Mechanisms of Oxidative Stress in Skeletal Muscle

    Institute of Scientific and Technical Information of China (English)

    Haibing HU; Wenjing LI; Zhi FANG; Bo XUE; Longzhou LIU; Ye YANG

    2015-01-01

    Oxidative stress is a major factor affecting animal health and production performance. This paper briefly introduced the signaling pathways(i.e. NF-κB signal-ing pathway, MAPK, AP-1 and PGC-1α) of oxidative stress and the main genes regulating the signals of oxidative stress in skeletal muscle, providing a theoretical basis for reducing oxidative stress damage.

  20. Extracellular electron transfer mechanism in Shewanella loihica PV- 4 biofilms formed at indium tin oxide and graphite electrodes

    OpenAIRE

    2013-01-01

    Electroactive biofilms are capable of extracellular electron transfer to insoluble metal oxides and electrodes; such biofilms are relevant to biogeochemistry, bioremediation, and bioelectricity production. We investigated the extracellular electron transfer mechanisms in Shewanella loihica PV-4 viable biofilms grown at indium tin oxide (ITO) and graphite electrodes in potentiostat-controlled electrochemical cells poised at 0.2 V vs. Ag/AgCl. Chronoamperometry and confocal microscopy showed hi...

  1. Production of biologically safe and mechanically improved reduced graphene oxide/hydroxyapatite composites

    Science.gov (United States)

    Elif, Öztürk; Belma, Özbek; İlkay, Şenel

    2017-01-01

    As research trends included the improvement of the mechanical properties of hydroxyapatite (HA) for biological applications, HA was reinforced with different concentrations of reduced graphene oxide (RGO) in HA. In this context, graphene oxide was synthesized using the chemical exfoliation method and reduced using an environmentally safe and green method. As a green method, RGO was obtained using Melissa officinalis (melisa) extract and used as a second phase combination to the HA structure. RGO-HA composites with different concentrations of RGO in HA (0.25, 0.5, 1.0, 2.0% wt.) were prepared using the liquid precipitation method. Then they were pelleted and sintered. Characterization studies were carried out using UV-vis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), zetasizer (ZS), x-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images. The mechanical properties of the composites were analyzed using a universal testing machine. Compared to pure HA, the compressive strength values of composites were increased significantly with the increase in RGO content. The optimum increase was observed for the RGO-HA (1%) composite, which was 3.2 times higher than the pure HA sample. Therefore, the RGO-HA (1%) composite was chosen as the best composition, and its cytotoxic and proliferative effects were examined using a minimum essential media elution test and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The results showed that RGO-HA (1%) composites are biocompatible and even though they are proliferative at concentrations lower than 25%.

  2. Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol

    Science.gov (United States)

    Ng, Nga Lee; Brown, Steven S.; Archibald, Alexander T.; Atlas, Elliot; Cohen, Ronald C.; Crowley, John N.; Day, Douglas A.; Donahue, Neil M.; Fry, Juliane L.; Fuchs, Hendrik; Griffin, Robert J.; Guzman, Marcelo I.; Herrmann, Hartmut; Hodzic, Alma; Iinuma, Yoshiteru; Jimenez, José L.; Kiendler-Scharr, Astrid; Lee, Ben H.; Luecken, Deborah J.; Mao, Jingqiu; McLaren, Robert; Mutzel, Anke; Osthoff, Hans D.; Ouyang, Bin; Picquet-Varrault, Benedicte; Platt, Ulrich; Pye, Havala O. T.; Rudich, Yinon; Schwantes, Rebecca H.; Shiraiwa, Manabu; Stutz, Jochen; Thornton, Joel A.; Tilgner, Andreas; Williams, Brent J.; Zaveri, Rahul A.

    2017-02-01

    Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO3-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry-climate models. This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO3-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO3-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.

  3. Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol

    Energy Technology Data Exchange (ETDEWEB)

    Ng, Nga Lee; Brown, Steven S.; Archibald, Alexander T.; Atlas, Elliot; Cohen, Ronald C.; Crowley, John N.; Day, Douglas A.; Donahue, Neil M.; Fry, Juliane L.; Fuchs, Hendrik; Griffin, Robert J.; Guzman, Marcelo I.; Herrmann, Hartmut; Hodzic, Alma; Iinuma, Yoshiteru; Jimenez, José L.; Kiendler-Scharr, Astrid; Lee, Ben H.; Luecken, Deborah J.; Mao, Jingqiu; McLaren, Robert; Mutzel, Anke; Osthoff, Hans D.; Ouyang, Bin; Picquet-Varrault, Benedicte; Platt, Ulrich; Pye, Havala O. T.; Rudich, Yinon; Schwantes, Rebecca H.; Shiraiwa, Manabu; Stutz, Jochen; Thornton, Joel A.; Tilgner, Andreas; Williams, Brent J.; Zaveri, Rahul A.

    2017-01-01

    Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO3-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry–climate models.

    This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO3-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO3-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.

  4. Mitochondrial cytochrome c oxidase: mechanism of action and role in regulating oxidative phosphorylation.

    Science.gov (United States)

    Wilson, David F; Vinogradov, Sergei A

    2014-12-15

    Mitochondrial oxidative phosphorylation has a central role in eukaryotic metabolism, providing the energy (ATP) required for survival. Regulation of this important pathway is, however, still not understood, largely due to limitations in the ability to measure the essential metabolites, including oxygen (pO2, oxygen pressure), ADP, and AMP. In addition, neither the mechanism of oxygen reduction by mitochondrial cytochrome c oxidase nor how its rate is controlled is understood, although this enzyme determines the rate of oxygen consumption and thereby the rate of ATP synthesis. Cytochrome c oxidase is responsible for reduction of molecular oxygen to water using reducing equivalents donated by cytochrome c and for site 3 energy coupling in oxidative phosphorylation. A mechanism-based model of the cytochrome c oxidase reaction is presented in which transfer of reducing equivalents from the lower- to the higher-potential region of the coupling site occurs against an opposing energy barrier, Q. The steady-state rate equation is fitted to data for the dependence of mitochondrial respiratory rate on cytochrome c reduction, oxygen pressure (pO2), and [ATP]/[ADP][Pi] at pH 6.5 to 8.35 (where Pi is inorganic phosphate). The fit of the rate expression to the experimental data is very good for all experimental conditions. Levels of the intermediates in oxygen reduction in the oxidase reaction site have been calculated. An intermediate in the reaction, tentatively identified as peroxide, bridged between the iron and copper atoms of the reaction site has a central role in coupling mitochondrial respiration to the [ATP]/[ADP][Pi].

  5. Mechanical Properties of Water-Assembled Graphene Oxide Langmuir Monolayers: Guiding Controlled Transfer.

    Science.gov (United States)

    Harrison, Katharine L; Biedermann, Laura B; Zavadil, Kevin R

    2015-09-15

    Liquid-phase transfer of graphene oxide (GO) and reduced graphene oxide (RGO) monolayers is investigated from the perspective of the mechanical properties of these films. Monolayers are assembled in a Langmuir-Blodgett trough, and oscillatory barrier measurements are used to characterize the resulting compressive and shear moduli as a function of surface pressure. GO monolayers are shown to develop a significant shear modulus (10-25 mN/m) at relevant surface pressures while RGO monolayers do not. The existence of a shear modulus indicates that GO is acting as a two-dimensional solid driven by strong interaction between the individual GO sheets. The absence of such behavior in RGO is attributed to the decrease in oxygen moieties on the sheet basal plane, permitting RGO sheets to slide across one another with minimum energy dissipation. Knowledge of this two-dimensional solid behavior is exploited to successfully transfer large-area, continuous GO films to hydrophobic Au substrates. The key to successful transfer is the use of shallow-angle dipping designed to minimize tensile stress present during the insertion or extraction of the substrate. A shallow dip angle on hydrophobic Au does not impart a beneficial effect for RGO monolayers, as these monolayers do not behave as two-dimensional solids and do not remain coherent during the transfer process. We hypothesize that this observed correlation between monolayer mechanical properties and continuous film transfer success is more universally applicable across substrate hydrophobicities and could be exploited to control the transfer of films composed of two-dimensional materials.

  6. Mechanism associated with the Space Shuttle main engine oxidizer valve/duct system anomalous high amplitude discrete acoustical excitation

    Science.gov (United States)

    Schutzenhofer, L. A.; Jones, J. H.; Jewell, R. E.; Ryan, R. S.

    1980-01-01

    Anomalous high frequency pressure fluctuations in the Space Shuttle main engine have been experienced during hot firings. Through diagnostic analysis of hot firing engine data, it was determined that this excitation originated at the main oxidizer valve. The intensity of these fluctuations was such that the main oxidizer valve was partially consumed in fire, experienced fretting, and had seal damage. Delineated in this paper are the associated dynamical phenomena and the methodologies leading toward understanding the excitation mechanism. The results presented demonstrate that the source of the anomalous frequencies was suppressed by a simple fix and all main oxidizer valve damage was terminated.

  7. Polyamine modification by acrolein exclusively produces 1,5-diazacyclooctanes: a previously unrecognized mechanism for acrolein-mediated oxidative stress.

    Science.gov (United States)

    Tsutsui, Ayumi; Imamaki, Rie; Kitazume, Shinobu; Hanashima, Shinya; Yamaguchi, Yoshiki; Kaneda, Masato; Oishi, Shinya; Fujii, Nobutaka; Kurbangalieva, Almira; Taniguchi, Naoyuki; Tanaka, Katsunori

    2014-07-28

    Acrolein, a toxic unsaturated aldehyde generated as a result of oxidative stress, readily reacts with a variety of nucleophilic biomolecules. Polyamines, which produced acrolein in the presence of amine oxidase, were then found to react with acrolein to produce 1,5-diazacyclooctane, a previously unrecognized but significant downstream product of oxidative stress. Although diazacyclooctane formation effectively neutralized acrolein toxicity, the diazacyclooctane hydrogel produced through a sequential diazacyclooctane polymerization reaction was highly cytotoxic. This study suggests that diazacyclooctane formation is involved in the mechanism underlying acrolein-mediated oxidative stress.

  8. Catalytic Mechanism and Efficiency of Methane Oxidation by Hg(II) in Sulfuric Acid and Comparison to Radical Initiated Conditions

    OpenAIRE

    Fuller, Jack T.; Butler, Steven; Devarajan, Deepa; Jacobs, Austin; Hashiguchi, Brian G.; Konnick, Michael M.; Goddard, William A.; Gonzales, Jason M.; Periana, Roy A.; Ess, Daniel H.

    2016-01-01

    Methane conversion to methyl bisulfate by Hg^(II)(SO_4) in sulfuric acid is an example of fast and selective alkane oxidation catalysis. Dichotomous mechanisms involving C–H activation and electron transfer have been proposed based on experiments. Radical oxidation pathways have also been proposed for some reaction conditions. Hg^(II) is also of significant interest because as a d^(10) transition metal it is similar to d^(10) main-group metals that also oxidize alkanes. Density-functional cal...

  9. Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism.

    Science.gov (United States)

    Soldatova, Alexandra V; Tao, Lizhi; Romano, Christine A; Stich, Troy A; Casey, William H; Britt, R David; Tebo, Bradley M; Spiro, Thomas G

    2017-08-23

    The bacterial protein complex Mnx contains a multicopper oxidase (MCO) MnxG that, unusually, catalyzes the two-electron oxidation of Mn(II) to MnO2 biomineral, via a Mn(III) intermediate. Although Mn(III)/Mn(II) and Mn(IV)/Mn(III) reduction potentials are expected to be high, we find a low reduction potential, 0.38 V (vs Normal Hydrogen Electrode, pH 7.8), for the MnxG type 1 Cu(2+), the electron acceptor. Indeed the type 1 Cu(2+) is not reduced by Mn(II) in the absence of molecular oxygen, indicating that substrate oxidation requires an activation step. We have investigated the enzyme mechanism via electronic absorption spectroscopy, using chemometric analysis to separate enzyme-catalyzed MnO2 formation from MnO2 nanoparticle aging. The nanoparticle aging time course is characteristic of nucleation and particle growth; rates for these processes followed expected dependencies on Mn(II) concentration and temperature, but exhibited different pH optima. The enzymatic time course is sigmoidal, signaling an activation step, prior to turnover. The Mn(II) concentration and pH dependence of a preceding lag phase indicates weak Mn(II) binding. The activation step is enabled by a pKa > 8.6 deprotonation, which is assigned to Mn(II)-bound H2O; it induces a conformation change (consistent with a high activation energy, 106 kJ/mol) that increases Mn(II) affinity. Mnx activation is proposed to decrease the Mn(III/II) reduction potential below that of type 1 Cu(II/I) by formation of a hydroxide-bridged binuclear complex, Mn(II)(μ-OH)Mn(II), at the substrate site. Turnover is found to depend cooperatively on two Mn(II) and is enabled by a pKa 7.6 double deprotonation. It is proposed that turnover produces a Mn(III)(μ-OH)2Mn(III) intermediate that proceeds to the enzyme product, likely Mn(IV)(μ-O)2Mn(IV) or an oligomer, which subsequently nucleates MnO2 nanoparticles. We conclude that Mnx exploits manganese polynuclear chemistry in order to facilitate an otherwise difficult

  10. Simulation of Mechanical Behaviors of Ceramic Composites Under Stress-Oxidation Environment While Considering the Effect of Matrix Cracks

    Science.gov (United States)

    Sun, Zhigang; Shao, Hongyan; Niu, Xuming; Song, Yingdong

    2016-06-01

    This article proposes a model which takes the effect of matrix cracking into consideration and analyzes the mechanical behaviors of unidirectional ceramic matrix composites under stress-oxidation environment. The change in the rules of mass loss ratio, residual modulus and residual strength of unidirectional C/SiC composite under different stress, oxidation time, temperature and fiber volume fraction with the temperature varying from 400 to 900 °C have been discussed in this paper. The comparison between the predicted residual mechanics properties and the experiment results demonstrates that the predicted results have a good agreement with the experiment results, which means that the model is feasible to simulate mechanical behaviors of unidirectional C/SiC composite under stress oxidation environment.

  11. A novel mechanism for the oxidation reaction of VO2+ on a graphite electrode in acidic solutions

    Science.gov (United States)

    Wang, Wenjun; Fan, Xinzhuang; Liu, Jianguo; Yan, Chuanwei; Zeng, Chaoliu

    2014-09-01

    With the consideration of optimizing the performance of the all-vanadium redox flow battery (VRB), the oxidation reaction mechanism of VO2+ on a rotating graphite disk electrode has been investigated by potentiodynamic polarization in sulfuric acid solutions with various pH and vanadium concentrations. Furthermore, the reaction orders of VO2+ and H+ for the oxidation reaction of VO2+ have been calculated from the polarization results and compared with the theoretical results according to the possible reaction mechanisms available in the literature. However, a new oxidation reaction mechanism has been proposed to describe the oxidation of VO2+ at last, and the theoretic reaction orders of VO2+ and H+ based on the new mechanism are consistent with the experimental results when the electrochemical reaction is the rate-limited process. Moreover, a corresponding kinetic equation has been established for the oxidation reaction of VO2+ on a spectroscopically pure graphite electrode, and can be well used to predict the polarization behavior in V (IV) acidic solutions.

  12. Mechanism of H2S Oxidation by the Dissimilatory Perchlorate-Reducing Microorganism Azospira suillum PS.

    Science.gov (United States)

    Mehta-Kolte, Misha G; Loutey, Dana; Wang, Ouwei; Youngblut, Matthew D; Hubbard, Christopher G; Wetmore, Kelly M; Conrad, Mark E; Coates, John D

    2017-02-21

    The genetic and biochemical basis of perchlorate-dependent H2S oxidation (PSOX) was investigated in the dissimilatory perchlorate-reducing microorganism (DPRM) Azospira suillum PS (PS). Previously, it was shown that all known DPRMs innately oxidize H2S, producing elemental sulfur (S(o)). Although the process involving PSOX is thermodynamically favorable (ΔG°' = -206 kJ ⋅ mol(-1) H2S), the underlying biochemical and genetic mechanisms are currently unknown. Interestingly, H2S is preferentially utilized over physiological electron donors such as lactate or acetate although no growth benefit is obtained from the metabolism. Here, we determined that PSOX is due to a combination of enzymatic and abiotic interactions involving reactive intermediates of perchlorate respiration. Using various approaches, including barcode analysis by sequencing (Bar-seq), transcriptome sequencing (RNA-seq), and proteomics, along with targeted mutagenesis and biochemical characterization, we identified all facets of PSOX in PS. In support of our proposed model, deletion of identified upregulated PS genes traditionally known to be involved in sulfur redox cycling (e.g., Sox, sulfide:quinone reductase [SQR]) showed no defect in PSOX activity. Proteomic analysis revealed differential abundances of a variety of stress response metal efflux pumps and divalent heavy-metal transporter proteins, suggesting a general toxicity response. Furthermore, in vitro biochemical studies demonstrated direct PSOX mediated by purified perchlorate reductase (PcrAB) in the absence of other electron transfer proteins. The results of these studies support a model in which H2S oxidation is mediated by electron transport chain short-circuiting in the periplasmic space where the PcrAB directly oxidizes H2S to S(o) The biogenically formed reactive intermediates (ClO2(-) and O2) subsequently react with additional H2S, producing polysulfide and S(o) as end products.IMPORTANCE Inorganic sulfur compounds are

  13. Investigation of the oxidation mechanisms of limonene photosensitized by imidazole-2-carboxaldehyde

    Science.gov (United States)

    Rossignol, Stéphanie; Tinel, Liselotte; Aregahegn, Kifle; George, Christian

    2013-04-01

    Recent studies have revealed the significant formation of light absorbing materials, including imidazole and imidazole derivatives, in aqueous aerosol mimics in the presence of both ammonium sulphate and glyoxal (Galloway et al. 2009; Yu et al. 2011; Kampf et al. 2012). Besides the potential impact on radiative properties of secondary organic aerosols, our team has shown that imidazole-2-carboxaldehyde (IC) acts as a photosensitizer, initiating aerosols growth in the presence of gaseous limonene and UV/visible light (Aregahegn et al., abstract submitted). This work focuses on the characterisation of the chemical mechanisms leading to this aerosols growth, and on the major products identification. The molecular composition of organic/aqueous solutions exposed to UV/visible light and containing IC and limonene is followed in time by HR-ESI-MS/MS in positive and negative modes. Limonene consumption is followed by HPLC-UV. HR-ESI-MS/MS analyses are performed in parallel on IC/ammonium sulphate aerosols exposed to gaseous limonene and UV/visible light, in particular to assess the relevance of in solution experiments. Besides, the lifetime of the triplet state of IC in aqueous/organic solutions in the presence of different terpenes is monitored by laser photolysis experiments and compared in order to explain the first steps of the photosensitized reaction. First HR-ESI-MS/MS results show the formation of the major "traditional" limonene oxidation products (e.g., coming from gas phase limonene ozonolysis) during the irradiation of organic solutions containing IC and limonene: limononaldehyde, keto-limononaldehyde, limonic acid, limononic acid ... Hundreds of other oxygenated species are however detected, typically with a number of carbon atoms ranging from 4 to 20 and with O/C ratios ranging from 0.2 to 0.7. Monomers and dimers of limonene oxidation products are observed but species with lower carbon numbers than monomeric compounds are predominant. Moreover, and

  14. Complexation facilitated reduction of aromatic N-oxides by aqueous Fe(II)-tiron complex: reaction kinetics and mechanisms.

    Science.gov (United States)

    Chen, Yiling; Zhang, Huichun

    2013-10-01

    Rapid reduction of carbadox (CDX), olaquindox and several other aromatic N-oxides were investigated in aqueous solution containing Fe(II) and tiron. Consistent with previous work, the 1:2 Fe(II)-tiron complex, FeL2(6-), is the dominant reactive species as its concentration linearly correlates with the observed rate constant kobs under various conditions. The N-oxides without any side chains were much less reactive, suggesting direct reduction of the N-oxides is slow. UV-vis spectra suggest FeL2(6-) likely forms 5- or 7-membered rings with CDX and olaquindox through the N and O atoms on the side chain. The formed inner-sphere complexes significantly facilitated electron transfer from FeL2(6-) to the N-oxides. Reduction products of the N-oxides were identified by HPLC/QToF-MS to be the deoxygenated analogs. QSAR analysis indicated neither the first electron transfer nor N-O bond cleavage is the rate-limiting step. Calculations of the atomic spin densities of the anionic N-oxides confirmed the extensive delocalization between the aromatic ring and the side chain, suggesting complex formation can significantly affect the reduction kinetics. Our results suggest the complexation facilitated N-oxide reduction by Fe(II)-tiron involves a free radical mechanism, and the subsequent deoxygenation might also benefit from the weak complexation of Fe(II) with the N-oxide O atom.

  15. Kinetics and mechanism of oxidation of glycine by iron(III)-1,10-phenanthroline complex in perchloric acid medium

    Indian Academy of Sciences (India)

    T V N Partha Sarathi; A Kalyan Kumar; K Krishna Kishore; P Vani

    2005-07-01

    Kinetics and mechanism of oxidation of glycine by iron(III)-1,10-phenanthroline complex has been studied in perchloric acid medium. The reaction is first order with respect to iron(III) and glycine. An increase in (phenanthroline) increases the rate, while increase in [H+] decreases the rate. Hence it can be inferred that the reactive species of the substrate is the zwitterionic form and that of the oxidant is [Fe(phen)2(H2O)2]3+. The proposed mechanism leads to the rate law as elucidated.

  16. Gallium-doped indium oxide nanoleaves: Structural characterization, growth mechanism and optical properties

    Science.gov (United States)

    Liu, Lizhu; Chen, Yiqing; Guo, Linliang; Guo, Taibo; Zhu, Yunqing; Su, Yong; Jia, Chong; Wei, Meiqin; Cheng, Yinfen

    2011-11-01

    The novel two-dimensional (2-D) Ga-doped In2O3 nanoleaves are synthesized by a simple one-step carbonthermal evaporation method using Cu-Sn alloy as the substrates. Two basic parts construct this leaf-like nanostructure: a long central trunk and two tapered nanoribbons in symmetric distribution in relation to the trunk. The Ga-In-O alloy particles are located at or close to the tips of the central trunks and serve as catalysts for the central trunk growth by the self-catalytic vapor-liquid-solid (VLS) mechanism. And the homoepitaxial growth of tapered nanoribbon on the surface of the central trunk can be explained by vapor-solid (VS) mechanism. The room-temperature photoluminescence (PL) measurement of this nanoscaled Ga-doped In2O3 transparent conducting oxide (TCO) detected two blue peaks located at 432 nm and 481 nm, respectively, which can be used by Ru-based dye and indicates potential application in dye-sensitized solar cells (DSSCs). The successful preparation of this novel 2-D Ga-doped In2O3 nanoleaves not only enriches the synthesis of TCO materials, but also provides new blocks in future architecture of functional nano-devices.

  17. Discovery of causal mechanisms: Oxidative phosphorylation and the Calvin-Benson cycle.

    Science.gov (United States)

    Scholl, Raphael; Nickelsen, Kärin

    2015-06-01

    We investigate the context of discovery of two significant achievements of twentieth century biochemistry: the chemiosmotic mechanism of oxidative phosphorylation (proposed in 1961 by Peter Mitchell) and the dark reaction of photosynthesis (elucidated from 1946 to 1954 by Melvin Calvin and Andrew A. Benson). The pursuit of these problems involved discovery strategies such as the transfer, recombination and reversal of previous causal and mechanistic knowledge in biochemistry. We study the operation and scope of these strategies by careful historical analysis, reaching a number of systematic conclusions: (1) even basic strategies can illuminate "hard cases" of scientific discovery that go far beyond simple extrapolation or analogy; (2) the causal-mechanistic approach to discovery permits a middle course between the extremes of a completely substrate-neutral and a completely domain-specific view of scientific discovery; (3) the existing literature on mechanism discovery underemphasizes the role of combinatorial approaches in defining and exploring search spaces of possible problem solutions; (4) there is a subtle interplay between a fine-grained mechanistic and a more coarse-grained causal level of analysis, and both are needed to make discovery processes intelligible.

  18. Studies on affecting factors and mechanism of oily wastewater by wet hydrogen peroxide oxidation

    Directory of Open Access Journals (Sweden)

    Zhang Wenhu

    2017-05-01

    Full Text Available Wet hydrogen peroxide oxidation of oily wastewater is performed in a batch reactor at reaction temperature between 280 °C and 320 °C, the reaction time between 30 and 90 min. Effect of reaction parameters such as reaction time, reaction temperature, H2O2 excess (HE and initial concentration of oily wastewater is investigated. The results of orthogonal test indicate that reaction temperature is the main factor and the reaction time is the secondary factor. When the reaction temperature is 300 °C, initial concentration of oily wastewater is 1160 mg/L, the reaction time is 30 min, HE is 0.75 and the COD removal of oily wastewater could reach 70%. It will not produce pollutants and it complies with the cleaner production. The preliminary study of mechanism on oily wastewater by WPO is carried out. The result indicates that oily wastewater by WPO can be explained by free radical mechanism.

  19. Thermal, Mechanical, and Electrical Properties of Graphene Nanoplatelet/Graphene Oxide/ Polyurethane Hybrid Nanocomposite.

    Science.gov (United States)

    Pokharel, Pashupati; Lee, Sang Hyub; Lee, Dai Soo

    2015-01-01

    Hybrid nanocomposites of polyurethane (PU) were prepared by in-situ polymerization of 4,4'- diphenyl methane diisocyanate (MDI) with mixture of graphene oxide (GO) and graphene nanoplatelet (GNP) dispersed in a poly(tetramethylene ether glycol) (PTMEG). Effects of the fillers, GO and GNP, on the thermal, mechanical, and electrical properties of the nanocomposites of PU were investigated. Sonication of the hybrid of GNP and GO with PTMEG enabled effective dispersion of the fillers in the solution than the sonication of GNP alone. The addition of PTMEG in the solution prevented the GNPs from the restacking during the drying process. It was observed that the electrical conductivity and mechanical property of the nanocomposites based on the hybrid of GO and GNP were superior to the nanocomposite based on GNP alone at the same loading of the filler. At the loading of the 3 wt% hybrid filler in PU, we observed the improvement of Young's modulus -200% and the surface resistivity of 10(9.5) ohm/sq without sacrificing the elongation at break.

  20. A polarity-induced defect mechanism for conductivity and magnetism at polar-nonpolar oxide interfaces.

    Science.gov (United States)

    Yu, Liping; Zunger, Alex

    2014-10-13

    The discovery of conductivity and magnetism at the polar-nonpolar interfaces of insulating nonmagnetic oxides such as LaAlO3 and SrTiO3 has raised prospects for attaining interfacial functionalities absent in the component materials. Yet, the microscopic origin of such emergent phenomena remains unclear, posing obstacles to design of improved functionalities. Here we present first principles calculations of electronic and defect properties of LaAlO3/SrTiO3 interfaces and reveal a unifying mechanism for the origins of both conductivity and magnetism. We demonstrate that the polar discontinuity across the interface triggers thermodynamically the spontaneous formation of certain defects that in turn cancel the polar field induced by the polar discontinuity. The ionization of the spontaneously formed surface oxygen vacancy defects leads to interface conductivity, whereas the unionized Ti-on-Al antisite defects lead to interface magnetism. The proposed mechanism suggests practical design principles for inducing and controlling both conductivity and magnetism at general polar-nonpolar interfaces.

  1. Mechanical strength of cortical allografts with gamma radiation versus ethylene oxide sterilization.

    Science.gov (United States)

    Zhou, Zongke; Qin, Tingwu; Yang, Jing; Shen, Bin; Kang, Pengde; Peil, Fuxing

    2011-10-01

    We investigated the effects of gamma irradiation versus ethylene oxide (ETO) sterilization on the mechanical strength of cortical bone grafts. Tibias were collected from cadavers of mature goats. Sixty test specimens were randomized into four groups: fresh (no processing), frozen (freezing at -70 degrees C), gamma-irradiated, and ETO-sterilized specimens. Torsion, three-point bending, and compression testing were separately performed with a material testing machine. Parameters studied included maximum stress, strain, deflection, extension, load, shear modulus, and E-modulus. Compared with findings for the fresh specimens, findings were as follows for gamma-irradiated specimens: maximal shear modulus, reduced by 48%; shear stress, by 55%; deflection, by 71%; bending stress, by 51%; bending strain, by 74%; extension, by 60%; and compression strain, by 50%. However, there were no reductions in those parameters for the frozen specimens or the ETO-sterilized specimens. These findings confirm that shear, bending, and compression strength of cortical allografts are weakened by gamma irradiation at room temperature. To maintain optimum mechanical properties, ETO sterilization of allografts is better than gamma sterilization, especially for cortical bone, because it is usually used in load-bearing settings.

  2. Degradation mechanism of a low band gap polymer PTB7 by oxidation

    Science.gov (United States)

    Park, Soohyung; Jeong, Junkyeong; Lee, Hyunbok; Yi, Yeonjin

    Recently, the PCE of OPVs is at the 10% mark by using donor materials having a low band gap, such as poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl) (PTB7) and its analogues. In spite of the significant PCE improvement, the lifetime issue still remains open problem. To solve these technical limitations fundamentally, the degradation mechanism should be understood. It can be revealed by investigating the electronic structures of polymers with controlled exposure of oxygen, moisture and light. In this study, ultraviolet, X-ray and inverse photoelectron spectroscopy measurements were performed with step-by-step exposure of controlled oxygen, moisture and light to investigate the degradation mechanism of each polymer film. Theoretical calculations using density functional theory (DFT) were also performed to understand detailed degradation process. From the experimental results, we demonstrate that push-pull polymers are more sensitive to environmental conditions, compared with non-push-pull (conventional) polymers such as poly (3-hexylthiophene-2,5-diyl) (P3HT). In addition, we show high photo-oxidation of PTB7 is originated from the structural reason.

  3. Spark Plasma Sintering and Densification Mechanisms of Antimony-Doped Tin Oxide Nanoceramics

    Directory of Open Access Journals (Sweden)

    Junyan Wu

    2013-01-01

    Full Text Available Densification of antimony-doped tin oxide (ATO ceramics without sintering aids is very difficult, due to the volatilization of SnO2, formation of deleterious phases above 1000°C, and poor sintering ability of ATO particles. In this paper, monodispersed ATO nanoparticles were synthesized via sol-gel method, and then ATO nanoceramics with high density were prepared by spark plasma sintering (SPS technology using the as-synthesized ATO nanoparticles without the addition of sintering aids. The effect of Sb doping content on the densification was investigated, and the densification mechanisms were explored. The results suggest that ATO nanoparticles derived from sol-gel method show good crystallinity with a crystal size of 5–20 nm and Sb is incorporated into the SnO2 crystal structure. When the SPS sintering temperature is 1000°C and the Sb doping content is 5 at.%, the density of ATO nanoceramics reaches a maximum value of 99.2%. Densification mechanisms are explored in detail.

  4. Aluminum work function: Effect of oxidation, mechanical scraping and ion bombardment

    Science.gov (United States)

    Vinet, P.; Lemogne, T.; Montes, H.

    1985-01-01

    Surface studies have been performed on aluminum polycrystalline surfaces which have been mechanically scraped. Such studies were initiated in order to understand surface effects occurring in tribological processes which involve rubbing surfaces and the effects of adsorption of oxygen. To characterize the surfaces, the following three different experimental approaches have been used: (1) X.P.S. (X-ray photoelectron spectroscopy), in order to check the cleanliness of the surfaces and follow the adsorption and oxidation kinetics; (2) Analysis of the work function changes by following the energy spectra of secondary electrons emitted under low energy electron bombardment; and (3) Analysis of photoemission intensities under U.V. excitation. The reference state being chosen to be the surface cleaned by ion bombardment and exposures to oxygen atmospheres have been shown to lower the work function of clean polycrystalline aluminum by 1.2 eV. The oxygen pressure is found to affect only the kinetics of these experiments. Mechanical scraping has been shown to induce a decrease ( 0.3 eV) in the work function, which could sharply modify the kinetics of adsorption on the surface.

  5. Mechanically stable thermally crosslinked poly(acrylic acid)/reduced graphene oxide aerogels.

    Science.gov (United States)

    Ha, Heonjoo; Shanmuganathan, Kadhiravan; Ellison, Christopher J

    2015-03-25

    Graphene oxide (GO) aerogels, high porosity (>99%) low density (∼3-10 mg cm(-3)) porous materials with GO pore walls, are particularly attractive due to their lightweight, high surface area, and potential use in environmental remediation, superhydrophobic and superoleophilic materials, energy storage, etc. However, pure GO aerogels are generally weak and delicate which complicates their handling and potentially limits their commercial implementation. The focus of this work was to synthesize highly elastic, mechanically stable aerogels that are robust and easy to handle without substantially sacrificing their high porosity or low density. To overcome this challenge, a small amount of readily available and thermally cross-linkable poly(acrylic acid) (PAA) was intermixed with GO to enhance the mechanical integrity of the aerogel without disrupting other desirable characteristic properties. This method is a simple straightforward procedure that does not include multistep or complicated chemical reactions, and it produces aerogels with mass densities of about 4-6 mg cm(-3) and >99.6% porosity that can reversibly support up to 10,000 times their weight with full recovery of their original volume. Finally, pressure sensing capabilities were demonstrated and their oil absorption capacities were measured to be around 120 g oil per g aerogel(-1) which highlights their potential use in practical applications.

  6. Oxidative stress-induced telomeric erosion as a mechanism underlying airborne particulate matter-related cardiovascular disease

    Directory of Open Access Journals (Sweden)

    Grahame Thomas J

    2012-06-01

    Full Text Available Abstract Particulate matter (PM pollution is responsible for hundreds of thousands of deaths worldwide, the majority due to cardiovascular disease (CVD. While many potential pathophysiological mechanisms have been proposed, there is not yet a consensus as to which are most important in causing pollution-related morbidity/mortality. Nor is there consensus regarding which specific types of PM are most likely to affect public health in this regard. One toxicological mechanism linking exposure to airborne PM with CVD outcomes is oxidative stress, a contributor to the development of CVD risk factors including atherosclerosis. Recent work suggests that accelerated shortening of telomeres and, thus, early senescence of cells may be an important pathway by which oxidative stress may accelerate biological aging and the resultant development of age-related morbidity. This pathway may explain a significant proportion of PM-related adverse health outcomes, since shortened telomeres accelerate the progression of many diseases. There is limited but consistent evidence that vehicular emissions produce oxidative stress in humans. Given that oxidative stress is associated with accelerated erosion of telomeres, and that shortened telomeres are linked with acceleration of biological ageing and greater incidence of various age-related pathology, including CVD, it is hypothesized that associations noted between certain pollution types and sources and oxidative stress may reflect a mechanism by which these pollutants result in CVD-related morbidity and mortality, namely accelerated aging via enhanced erosion of telomeres. This paper reviews the literature providing links among oxidative stress, accelerated erosion of telomeres, CVD, and specific sources and types of air pollutants. If certain PM species/sources might be responsible for adverse health outcomes via the proposed mechanism, perhaps the pathway to reducing mortality/morbidity from PM would become clearer

  7. Development of a detailed chemical mechanism (MCMv3.1 for the atmospheric oxidation of aromatic hydrocarbons

    Directory of Open Access Journals (Sweden)

    C. Bloss

    2005-01-01

    Full Text Available The Master Chemical Mechanism has been updated from MCMv3 to MCMv3.1 in order to take into account recent improvements in the understanding of aromatic photo-oxidation. Newly available kinetic and product data from the literature have been incorporated into the mechanism. In particular, the degradation mechanisms for hydroxyarenes have been revised following the observation of high yields of ring-retained products, and product studies of aromatic oxidation under relatively low NOx conditions have provided new information on the branching ratios to first generation products. Experiments have been carried out at the European Photoreactor (EUPHORE to investigate key subsets of the toluene system. These results have been used to test our understanding of toluene oxidation, and, where possible, refine the degradation mechanisms. The evaluation of MCMv3 and MCMv3.1 using data on benzene, toluene, p-xylene and 1,3,5-trimethylbenzene photosmog systems is described in a companion paper, and significant model shortcomings are identified. Ideas for additional modifications to the mechanisms, and for future experiments to further our knowledge of the details of aromatic photo-oxidation are discussed.

  8. Development of a detailed chemical mechanism (MCMv3.1 for the atmospheric oxidation of aromatic hydrocarbons

    Directory of Open Access Journals (Sweden)

    C. Bloss

    2004-09-01

    Full Text Available The Master Chemical Mechanism has been updated from MCMv3 to MCMv3.1 in order to take into account recent improvements in the understanding of aromatic photo-oxidation. Newly available kinetic and product data from the literature has been incorporated into the mechanism. In particular, the degradation mechanisms for hydroxyarenes have been revised following the observation of high yields of ring-retained products, and product studies of aromatic oxidation under relatively low NOx conditions have provided new information on the branching ratios to first generation products. Experiments have been carried out at the European Photoreactor (EUPHORE to investigate key subsets of the toluene system. These results have been used to test our understanding of toluene oxidation, and where possible, refine the degradation mechanisms. The evaluation of MCMv3 and MCMv3.1 using data on benzene, toluene, p-xylene and 1,3,5-trimethylbenzene photosmog systems is described in a companion paper, and significant model shortcomings are identified. Ideas for additional modifications to the mechanisms, and for future experiments to further our knowledge of the details of aromatic photo-oxidation are discussed.

  9. Mechanisms of oxidative stress in brain ischemia injury%氧化应激在脑缺血损伤中的作用机制

    Institute of Scientific and Technical Information of China (English)

    赵丹洋; 吴伟康

    2004-01-01

    Oxidative stress has been implicated in brain injury after ischemia, which is a complex cascade. These oxidants produced by oxidative stress are directly involved in oxidative damage with cellular macromolecules such as lipids, proteins and nucleic acids, which lead to cell death. Oxidants are also mediators in signaling involving mitochondria pathway, DNA repair enzymes, and transcription factor that may lead to apoptosis after cerebral ischemia. Antioxidangt enzymes (such as superoxide dismutase,etc) provide useful tools in dissecting the events involving oxidative stress in signaling and damage in ischemic brain injury. This review focuses on the mechanisms of oxidative stress during brain ischemia.

  10. Activation of chemical biological defense mechanisms and remission of vital oxidative injury by low dose radiation

    Energy Technology Data Exchange (ETDEWEB)

    Yamaoka, K. [Okayama University Medical School, Okayama (Japan); Nomura, T. [Central Research Institute of Electric Power Industry, Tokyo (Japan); Kojima, S. [Science University of Tokyo, Chiba (Japan)

    2000-05-01

    Excessive active oxygen produced in vivo by various causes is toxic. Accumulation of oxidation injuries due to excessive active causes cell and tissue injuries, inducing various pathologic conditions such as aging and carcinogenesis. On the other hand, there are chemical defense mechanisms in the body that eliminate active oxygen or repair damaged molecules, defending against resultant injury. It is interesting reports that appropriate oxidation stress activate the chemical biological defense mechanisms. In this study, to elucidate these phenomena and its mechanism by low dose radiation, we studied on the below subjects. Activation of chemical biological defense mechanisms by low dose radiation: (1) The effects radiation on lipid peroxide (LPO) levels in the organs, membrane fluidity and the superoxide dismutase (SOD) activity were examined in rats and rabbits. Rats were irradiated with low dose X-ray over their entire bodies, and rabbits inhaled vaporized radon spring water, which primarily emitted {alpha}-ray. The following results were obtained. Unlike high dose X-ray, low dose X-ray and radon inhalation both reduced LPO levels and made the state of the SH-group on membrane-bound proteins closer to that of juvenile animals, although the sensitivity to radioactivity varied depending on the age of the animals and among different organs and tissues. The SOD activity was elevated, suggesting that low dose X-ray and radon both activate the host defensive function. Those changes were particularly marked in the organs related to immune functions of the animals which received low dose X-ray, while they were particularly marked in the brain after radon inhalation. It was also found that those changes continued for longer periods after low dose X-irradiation. (2) Since SOD is an enzyme that mediates the dismutation of O{sub 2}- to H{sub 2}O{sub 2}, the question as to whether the resultant H{sub 2}O{sub 2} is further detoxicated into H{sub 2}O and O{sub 2} or not must

  11. Radical and Non-Radical Mechanisms for Alkane Oxidations by Hydrogen Peroxide-Trifluoroacetic Acid

    Energy Technology Data Exchange (ETDEWEB)

    Camaioni, Donald M.; Bays, J. Timothy; Shaw, Wendy J.; Linehan, John C.; Birnbaum, Jerome C.

    2001-02-01

    The oxidation of cyclohexane by the H2O2-trifluoroacetic acid system is revisited. Consistent with a previous report (Deno, N.; Messer, L. A. Chem. Comm. 1976, 1051), cyclohexanol forms initially but then esterifies to cyclohexyl trifluoroacetate. Small amounts of trans-1,2-cyclohexadiyl bis(trifluoroacetate) also form. Although these products form irrespective of the presence or absence of O2, dual mechanisms are shown to operate. In the absence of O2, the dominant mechanism is a radical chain reaction that is propagated by CF3• abstracting H from C6H12 and SH2 displacement of C6H11• on CF3CO2OH. The intermediacy of C6H11• and CF3• is inferred from production of CHF3 and CO2 along with cyclohexyl trifluoroacetate, or CDF3 when cyclohexane-d12 is used. In the presence of O2, fluoroform and CO2 are suppressed, the reaction rate slows, and the rate law approaches second order (first order in peracid and in C6H12). Trapping of cyclohexyl radicals by quinoxaline is inefficient except at elevated (75 °C) temperatures. Fluoroform and CO2, telltale evidence for the chain pathway, were not produced when quinoxaline was present in room temperature reactions. These observations suggest that a parallel, nonfree radical, oxenoid insertion mechanism dominates when O2 is present. A pathway is discussed in which a biradicaloid-zwiterionic transition state is attained by hydrogen transfer from alkane to peroxide oxygen with synchronous O-O bond scission.

  12. Fabrication and mechanical characterization of graphene oxide-reinforced poly (acrylic acid)/gelatin composite hydrogels

    Science.gov (United States)

    Faghihi, Shahab; Gheysour, Mahsa; Karimi, Alireza; Salarian, Reza

    2014-02-01

    Hydrogels have found many practical uses in drug release, wound dressing, and tissue engineering. However, their applications are restricted due to their weak mechanical properties. The role of graphene oxide nanosheets (GONS) as reinforcement agent in poly (acrylic acid) (PAA)/Gelatin (Gel) composite hydrogels is investigated. Composite hydrogels are synthesized by thermal initiated redox polymerization method. Samples are then prepared with 20 and 40 wt. % of PAA, an increasing amount of GONS (0.1, 0.2, and 0.3 wt. %), and a constant amount of Gel. Subsequently, cylindrical hydrogel samples are subjected to a series of compression tests in order to measure their elastic modulus, maximum stress and strain. The results exhibit that the addition of GONS increases the Young's modulus and maximum stress of hydrogels significantly as compared with control (0.0 wt. % GONS). The highest Young's modulus is observed for hydrogel with GO (0.2 wt. %)/PAA (20 wt. %), whereas the highest maximum stress is detected for GO (0.2 wt. %)/PAA (40 wt. %) specimen. The addition of higher amounts of GONS leads to a decrease in the maximum stress of the hydrogel GO (0.3 wt. %)/PAA (40 wt. %). No significant differences are detected for the maximum strain among the hydrogel samples, as the amount of GONS increased. These results suggest that the application of GONS could be used to improve mechanical properties of hydrogel materials. This study may provide an alternative for the fabrication of low-cost graphene/polymer composites with enhanced mechanical properties beneficial for tissue engineering applications.

  13. Chemisorption of CO and Mechanism of CO Oxidation on Supported Platinum Nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Allian, Ayman D.; Takanabe, Kazuhiro; Fujdala, Kyle L.; Hao, Xianghong; Truex, Timothy J.; Cai, Juan; Buda, Corneliu; Neurock, Matthew; Iglesia, Enrique

    2011-03-30

    Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O2 pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O2 activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C16O-18O2-16O2 reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevantO2 activation steps involve directO2* (or O2) reactions with CO* to form reactive O*-O-C*dO intermediates that decompose to form CO2 and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O2. These CO-assisted O2 dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassistedO2 dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O2 reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with 12CO-13CO mixtures showed that the binding, dynamics, and thermodynamics of CO chemisorbed at

  14. Chemisorption of CO and mechanism of CO oxidation on supported platinum nanoclusters

    KAUST Repository

    Allian, Ayman Daoud

    2011-03-30

    Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O2 pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O2 activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C16O-18O2-16O 2 reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevant O2 activation steps involve direct O2* (or O2) reactions with CO* to form reactive O*-O-C*=O intermediates that decompose to form CO 2 and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O2. These CO-assisted O2 dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassisted O2 dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O2 reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with 12CO- 13CO mixtures showed that the binding, dynamics, and thermodynamics of CO

  15. Thermal-Mechanical Stability of Single Crystal Oxide Refractive Concentrators for High-Temperature Solar Thermal Propulsion

    Science.gov (United States)

    Zhu, Dongming; Jacobson, Nathan S.; Miller, Robert A.

    1999-01-01

    Single crystal oxides such as yttria-stabilized zirconia (Y2O3-ZrO2), yttrium aluminum garnet (Y3Al5O12, or YAG), magnesium oxide (MgO) and sapphire (Al2O3) are candidate refractive secondary concentrator materials for high temperature solar propulsion applications. However, thermo-mechanical reliability of these components in severe thermal environments during the space mission sun/shade transition is of great concern. Simulated mission tests are important for evaluating these candidate oxide materials under a variety of transient and steady-state heat flux conditions, and thus provide vital information for the component design. In this paper, a controlled heat flux thermal shock test approach is established for the single crystal oxide materials using a 3.0 kW continuous wave CO2 laser, with a wavelength 10.6 micron. Thermal fracture behavior and failure mechanisms of these oxide materials are investigated and critical temperature gradients are determined under various temperature and heating conditions. The test results show that single crystal sapphire is able to sustain the highest temperature gradient and heating-cooling rate, and thus exhibit the best thermal shock resistance, as compared to the yttria-stabilized zirconia, yttrium aluminum garnet and magnesium oxide.

  16. Hierarchical multiscale mechanism development for methane partial oxidation and reforming and for thermal decomposition of oxygenates on Rh.

    Science.gov (United States)

    Mhadeshwar, A B; Vlachos, D G

    2005-09-08

    A thermodynamically consistent C1 microkinetic model is developed for methane partial oxidation and reforming and for oxygenate (methanol and formaldehyde) decomposition on Rh via a hierarchical multiscale methodology. Sensitivity analysis is employed to identify the important parameters of the semiempirical unity bond index quadratic exponential potential (UBI-QEP) method and these parameters are refined using quantum mechanical density functional theory. With adjustment of only two pre-exponentials in the CH4 oxidation subset, the C1 mechanism captures a multitude of catalytic partial oxidation (CPOX) and reforming experimental data as well as thermal decomposition of methanol and formaldehyde. We validate the microkinetic model against high-pressure, spatially resolved CPOX experimental data. Distinct oxidation and reforming zones are predicted to exist, in agreement with experiments, suggesting that hydrogen is produced from reforming of methane by H2O formed in the oxidation zone. CO is produced catalytically by partial oxidation up to moderately high pressures, with water-gas shift taking place in the gas-phase at sufficiently high pressures resulting in reduction of CO selectivity.

  17. Plasma HDL reduces nonesterified fatty acid hydroperoxides originating from oxidized LDL: a mechanism for its antioxidant ability.

    Science.gov (United States)

    Kotosai, Mari; Shimada, Sachiko; Kanda, Mai; Matsuda, Namiko; Sekido, Keiko; Shimizu, Yoshibumi; Tokumura, Akira; Nakamura, Toshiyuki; Murota, Kaeko; Kawai, Yoshichika; Terao, Junji

    2013-06-01

    The antioxidant property of plasma high-density lipoprotein (HDL) is thought to be involved in potential anti-atherogenic effects but the exact mechanism is not known. We aimed to reveal the contribution of HDL on the elimination of lipid hydroperoxides (LOOH) derived from oxidized low-density lipoprotein (LDL). Oxidized LDL prepared by copper ion-induced oxidation contained nonesterified fatty acid hydroperoxides (FFA-OOH) and lysophosphatidylcholine (lysoPtdCho), in addition to cholesteryl ester hydroperoxides (CE-OOH) and phosphatidylcholine hydroperoxides (PtdCho-OOH). A platelet-activating factor-acetylhydrolase (PAF-AH) inhibitor suppressed formation of FFA-OOH and lysoPtdCho in oxidized LDL. Among LOOH species, FFA-OOH was preferentially reduced by incubating oxidized LDL with HDL. HDL exhibited selective FFA-OOH reducing ability if it was mixed with a liposomal solution containing FFA-OOH, CE-OOH and PtdCho-OOH. Two-electron reduction of the hydroperoxy group to the hydroxy group was confirmed by the formation of 13-hydroxyoctadecadienoic acid from 13-hydroperoxyoctadecadienoic acid in HPLC analyses. This reducing effect was also found in apolipoprotein A-1 (apoA-1). FFA-OOH released from PtdCho-OOH due to PAF-AH activity in oxidized LDL undergo two-electron reduction by the reducing ability of apoA1 in HDL. This preferential reduction of FFA-OOH may participate in the mechanism of the antioxidant property of HDL.

  18. Dopaminergic cell death induced by MPP(+), oxidant and specific neurotoxicants shares the common molecular mechanism.

    Science.gov (United States)

    Chun, H S; Gibson, G E; DeGiorgio, L A; Zhang, H; Kidd, V J; Son, J H

    2001-02-01

    Recent etiological study in twins (Tanner et al. 1999) strongly suggests that environmental factors play an important role in typical, non-familial Parkinson's disease (PD), beginning after age 50. Epidemiological risk factor analyses of typical PD cases have identified several neurotoxicants, including MPP(+) (the active metabolite of MPTP), paraquat, dieldrin, manganese and salsolinol. Here, we tested the hypothesis that these neurotoxic agents might induce cell death in our nigral dopaminergic cell line, SN4741 (Son et al. 1999) through a common molecular mechanism. Our initial experiments revealed that treatment with both MPP(+) and the other PD-related neurotoxicants induced apoptotic cell death in SN4741 cells, following initial increases of H(2)O(2)-related ROS activity and subsequent activation of JNK1/2 MAP kinases. Moreover, we have demonstrated that during dopaminergic cell death cascades, MPP(+), the neurotoxicants and an oxidant, H(2)O(2) equally induce the ROS-dependent events. Remarkably, the oxidant treatment alone induced similar sequential molecular events: ROS increase, activation of JNK MAP kinases, activation of the PITSLRE kinase, p110, by both Caspase-1 and Caspase-3-like activities and apoptotic cell death. Pharmacological intervention using the combination of the antioxidant Trolox and a pan-caspase inhibitor Boc-(Asp)-fmk (BAF) exerted significant neuroprotection against ROS-induced dopaminergic cell death. Finally, the high throughput cDNA microarray screening using the current model identified downstream response genes, such as heme oxygenase-1, a constituent of Lewy bodies, that can be the useful biomarkers to monitor the pathological conditions of dopaminergic neurons under neurotoxic insult.

  19. Mechanism considerations for photocatalytic oxidation, ozonation and photocatalytic ozonation of some pharmaceutical compounds in water.

    Science.gov (United States)

    Rodríguez, Eva M; Márquez, Gracia; León, Elena A; Álvarez, Pedro M; Amat, Ana M; Beltrán, Fernando J

    2013-09-30

    Aqueous solutions of four pharmaceutical compounds, belonging to the group of emergent contaminants of water: atenolol (ATL), hydrochlorothiazide (HCT), ofloxacin (OFX) and trimethoprim (TMP), have been treated with different oxidation systems, mainly, photocatalytic oxidation, ozonation and photocatalytic ozonation. TiO2 has been used as semiconductor for photocatalytic reactions both in the presence of air, oxygen or ozone-oxygen gas mixtures. Black light lamps mainly emitting at 365 nm were the source of radiation. In all cases, the influence of some variables (concentrations of semiconductor, ozone gas and pharmaceuticals and pH) on the removal of pharmaceuticals, total polyphenol content (TPC) and total organic carbon (TOC) was investigated. A discussion on the possible routes of pharmaceutical and intermediates (as TPC and TOC) elimination has been developed. Thus, OFX TiO2/UVA degradation mechanism seems to develop through the participation of non-hydroxyl free radical species. Furthermore, the presence of OFX inhibits the formation of hydroxyl radicals in the photocatalytic process. The most effective processes were those involving ozone that lead to complete disappearance of parent compounds in less than 30 min for initial pharmaceutical concentrations lower than 2.5 mg L(-1). In the ozonation systems, regardless of the pH and the presence of TiO2, pharmaceuticals are degraded through their direct reaction with ozone. Photocatalytic ozonation was the most efficient process for TPC and TOC removals (≥ 80% and ≥60% elimination after 2 h of treatment, respectively) as well as in terms of the ozone consumption efficiency (1, 5.5 and 4 mol of ozone consumed per mol of TOC mineralized, at pH 4, 7 and 9, respectively). Weakly acid conditions (pH 4) resulted to be the most convenient ones for TPC and TOC removal by photocatalytic ozonation. This was likely due to formation of hydroxyl radicals through the ozonide generated at these conditions.

  20. A photo-oxidation mechanism for patterning and hologram formation in conjugated polymer/glass composites

    Science.gov (United States)

    Levi, Ofer; Perepelitsa, Galina; Davidov, Dan; Shalom, Shoshy; Benjamin, Iris; Neumann, Ronny; Agranat, Aharon J.; Avny, Yair

    2000-08-01

    Improved diffraction efficiency was observed in holograms stored in disordered conjugated polymer/glass composites. The conjugated polymers used were alkoxy substituted poly(phenylenevinylne) analogs and the glass matrices were zirconia-organosilica xerogels. Investigation of the mechanism of hologram formation revealed evidence of a photochromic process consisting of light induced photo-oxidation (bleaching) of the embedded conjugated polymer resulting in the formation of an absorption grating and a phase grating. Investigation of the hologram formation revealed that the process was oxygen dependent. Oxygen removal increases hologram formation time by more than an order of magnitude and halves the total hologram efficiency. The oxygen dependence was also highly correlated with photobleaching of the samples and beam interaction of the writing beams. The chemical transformations upon photobleaching were shown by infrared and Raman spectroscopy to involve chain scission and oxidation of the polymer at the vinylic position of the conjugated polymer. Film preparation of the composites was optimized showing a tenfold improvement in the holographic properties compared to our previous results. The optimized treatment method allows for a high, >20%, diffraction efficiency, η, to be obtained for the 2.5-μm-thick polymer/glass films. Light sensitivity was compared for several polymer/glass composites and was correlated to the absorption curves and holographic diffraction efficiency showing that the new composites and film preparation techniques are promising for holographic materials sensitive in the blue and ultraviolet spectral regions. A method of information fixing by preventing oxygen entry to the composite film resulted in a fourfold increase of the erasure time. These findings suggest that holograms can be fixed for a long term by nonoxygen permeable coating, applied after hologram formation.

  1. Constituent phases and mechanical properties of iron oxide-additioned phosphoaluminate cement

    Directory of Open Access Journals (Sweden)

    Yang, Shuai

    2015-06-01

    Full Text Available Iron oxide was added to phosphoaluminate clinker and its effects on cement constituents were determined using XRD, DSC, SEM-EDS and conduction calorimetry analysis. The variations in compressive strength were also studied. The results showed that in moderate amounts, iron oxide acts as a mineraliser during clinker sintering, furthering the conversion of CA1-Y(PY to LHss at a lower temperature than normally required for that reaction. The main constituents of iron oxide-rich phosphoaluminate clinker included LHss, CA1-Y(PY, CP1-Z(AZ and ferrite. The EDS findings showed that the composition of the ferrite phase was nonuniform. The conclusion drawn was that by modifying the dose of Fe2O3 , the composition of phosphoaluminate cement can be controlled to produce clinker and cement compliant with different mechanical strength requirements. The conduction calorimetry findings were consistent with those results.Este trabajo estudia, mediante DRX DSC, SEM-EDS y calorimetría de conducción, el efecto de la adición de óxido de hierro a un clinker de fosfoaluminato, así como las variaciones sufridas en su resistencia a compresión. Los resultados mostraron que en cantidades moderadas, el óxido de hierro actúa como mineralizador durante la sinterización del clinker, promoviendo la conversión de CA1-Y(PY a LHss a una temperatura más baja de la normalmente requerida. Los componentes principales del clínker de fosfoaluminato con óxido de hierrop son LHss, CA1-Y(PY, CP1-Z(AZ y fase ferritica. Los resultados de EDS mostraron que la composición de esta fase ferrítica no era uniforme. DE este estudio se ha podido concluir que variando la dosificación del Fe2O3 , se puede controlar la composición del fosfoaluminato para producir clinker y cemento compatibles con diferentes requisitos de resistencia mecánica. Los resultados de calorimetría de conducción fueron consistentes con los resultados.

  2. Mechanical properties of polyethersulfone modified epoxy/3,3′-bis (maleimidophenyl)phenylphosphine oxide (BMI) intercrosslinked matrices

    Indian Academy of Sciences (India)

    R Rajasekaran; M Alagar

    2008-11-01

    Novel intercrosslinked networks of polyethersulfone modified epoxy-3,3′-bis(maleimidophenyl) phenylphosphine oxide matrix systems are developed. The polyethersulfone modification of epoxy resin is carried out by using tetramethyl ammonium hydroxide (TMAH) as a catalyst. The polyethersulfone modified epoxy systems are further modified with 4–12% 3,3′-bis(maleimidophenyl) phenylphosphine oxide and cured by using diaminodiphenylmethane. Tensile, flexural, impact properties and dynamic mechanical analysis (DMA) are carried out to assess the mechanical behaviour of the prepared neat resin castings. Mechanical studies indicate that the introduction of polyethersulfone into these epoxy resins improves the toughness without any reduction in the stress–strain values. But, the incorporation of bismaleimide (BMI) into the epoxy resin improves the stress–strain properties with a lowering of the toughness. The introduction of both polyethersulfone and bismaleimide into the epoxy resin influences the mechanical properties according to their content percentages.

  3. Poole-Frenkel-effect as dominating current mechanism in thin oxide films—An illusion?!

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, Herbert [Electronic Materials, PGI-7, Research Center Jülich, 52425 Jülich (Germany)

    2015-06-07

    In many of the publications, over 50 per year for the last five years, the Poole-Frenkel-effect (PFE) is identified or suggested as dominating current mechanism to explain measured current–electric field dependencies in metal-insulator-metal (MIM) thin film stacks. Very often, the insulating thin film is a metal oxide as this class of materials has many important applications, especially in information technology. In the overwhelming majority of the papers, the identification of the PFE as dominating current mechanism is made by the slope of the current–electric field curve in the so-called Poole-Frenkel plot, i.e., logarithm of current density, j, divided by the applied electric field, F, versus the square root of that field. This plot is suggested by the simplest current equation for the PFE, which comprises this proportionality (ln(j/F) vs. F{sup 1/2}) leading to a straight line in this plot. Only one other parameter (except natural constants) may influence this slope: the optical dielectric constant of the insulating film. In order to identify the importance of the PFE simulation studies of the current through MIM stacks with thin insulating films were performed and the current–electric field curves without and with implementation of the PFE were compared. For the simulation, an advanced current model has been used combining electronic carrier injection/ejection currents at the interfaces, described by thermionic emission, with the carrier transport in the dielectric, described by drift and diffusion of electrons and holes in a wide band gap semiconductor. Besides the applied electric field (or voltage), many other important parameters have been varied: the density of the traps (with donor- and acceptor-like behavior); the zero-field energy level of the traps within the energy gap, this energy level is changed by the PFE (also called internal Schottky effect); the thickness of the dielectric film; the permittivity of the dielectric film simulating

  4. Poole-Frenkel-effect as dominating current mechanism in thin oxide films—An illusion?!

    Science.gov (United States)

    Schroeder, Herbert

    2015-06-01

    In many of the publications, over 50 per year for the last five years, the Poole-Frenkel-effect (PFE) is identified or suggested as dominating current mechanism to explain measured current-electric field dependencies in metal-insulator-metal (MIM) thin film stacks. Very often, the insulating thin film is a metal oxide as this class of materials has many important applications, especially in information technology. In the overwhelming majority of the papers, the identification of the PFE as dominating current mechanism is made by the slope of the current-electric field curve in the so-called Poole-Frenkel plot, i.e., logarithm of current density, j, divided by the applied electric field, F, versus the square root of that field. This plot is suggested by the simplest current equation for the PFE, which comprises this proportionality (ln(j/F) vs. F1/2) leading to a straight line in this plot. Only one other parameter (except natural constants) may influence this slope: the optical dielectric constant of the insulating film. In order to identify the importance of the PFE simulation studies of the current through MIM stacks with thin insulating films were performed and the current-electric field curves without and with implementation of the PFE were compared. For the simulation, an advanced current model has been used combining electronic carrier injection/ejection currents at the interfaces, described by thermionic emission, with the carrier transport in the dielectric, described by drift and diffusion of electrons and holes in a wide band gap semiconductor. Besides the applied electric field (or voltage), many other important parameters have been varied: the density of the traps (with donor- and acceptor-like behavior); the zero-field energy level of the traps within the energy gap, this energy level is changed by the PFE (also called internal Schottky effect); the thickness of the dielectric film; the permittivity of the dielectric film simulating different oxide

  5. Mechanism study on mitochondrial fragmentation under oxidative stress caused by high-fluence low-power laser irradiation

    Science.gov (United States)

    Wu, Shengnan; Zhou, Feifan; Xing, Da

    2012-03-01

    Mitochondria are dynamic organelles that undergo continual fusion and fission to maintain their morphology and functions, but the mechanism involved is still not clear. Here, we investigated the effect of mitochondrial oxidative stress triggered by high-fluence low-power laser irradiation (HF-LPLI) on mitochondrial dynamics in human lung adenocarcinoma cells (ASTC-a-1). Upon HF-LPLI-triggered oxidative stress, mitochondria displayed a fragmented structure, which was abolished by exposure to dehydroascorbic acid (DHA), a reactive oxygen species scavenger, indicating that oxidative stress can induce mitochondrial fragmentation. Mitochondrial translocation of the profission protein dynamin-related protein 1 (Drp1) was observed following HF-LPLI, demonstrating apoptosis-related activation of Drp1. Notably, DHA pre-treatment prevented HF-LPLI-induced Drp1 activation. We conclude that mitochondrial oxidative stress through activation of Drp1 causes mitochondrial fragmentation.

  6. The conduction mechanism of stress induced leakage current through ultra-thin gate oxide under constant voltage stresses

    Institute of Scientific and Technical Information of China (English)

    Wang Yan-Gang; Xu Ming-Zhen; Tan Chang-Hua; Zhang Zhang J.F; Duan Xiao-Rong

    2005-01-01

    The conduction mechanism of stress induced leakage current (SILC) through 2nm gate oxide is studied over a gate voltage range between 1.7V and stress voltage under constant voltage stress (CVS). The simulation results show that the SILC is formed by trap-assisted tunnelling (TAT) process which is dominated by oxide traps induced by high field stresses. Their energy levels obtained by this work are approximately 1.9eV from the oxide conduction band, and the traps are believed to be the oxygen-related donor-like defects induced by high field stresses. The dependence of the trap density on stress time and oxide electric field is also investigated.

  7. The fate of iron on Mars: Mechanism of oxidation of basaltic minerals to ferric-bearing assemblages

    Science.gov (United States)

    Burns, Roger G.

    1992-01-01

    Perhaps the most conspicuous indication that chemical weathering has occurred on the surface of Mars is the overall color of the red planet and the spectroscopic features that identify ferric-bearing assemblages in the martian regolith. Apparently, Fe(2+) ions in primary minerals in parent igneous rocks on the martian surface have been oxidized to ferric iron, which occurs in degradation products that now constitute the regolith. The mineralogy of the unweathered igneous rocks prior to weathering on the martian surface is reasonably well constrained, mainly as a result of petrographic studies of the SNC meteorites. However, the alteration products resulting from oxidative weathering of these rocks are less well-constrained. The topics covered include the following: primary rocks subjected to chemical weathering; dissolution processes; oxidation of dissolved Fe(2+); mechanism of polymerization of hydrous ferric oxides; terrestrial occurrences of ferromagnesian smectites; and dehydroxylated Mg-Fe smectites on Mars.

  8. Microstructural, mechanical and oxidation features of NiCoCrAlY coating produced by plasma activated EB-PVD

    Energy Technology Data Exchange (ETDEWEB)

    He, Jian; Guo, Hongbo, E-mail: guo.hongbo@buaa.edu.cn; Peng, Hui; Gong, Shengkai

    2013-06-01

    NiCoCrAlY coatings produced by electron beam-physical vapor deposition (EB-PVD) have been extensively used as the oxidation resistance coatings or suitable bond coats in thermal barrier coating (TBC) system. However, the inherent imperfections caused by EB-PVD process degrade the oxidation resistance of the coatings. In the present work, NiCoCrAlY coatings were creatively produced by plasma activated electron beam-physical vapor deposition (PA EB-PVD). The novel coatings showed a terraced substructure on the surface of each grain due to the increased energy of metal ions and enhanced mobility of adatoms. Also a strong (1 1 1) crystallographic texture of γ/γ′ grains was observed. The toughness of the coatings got remarkably improved compared with the coatings deposited by conventional EB-PVD and the oxidation behavior at 1373 K showed that the novel coatings had excellent oxidation resistance. The possible mechanism was finally discussed.

  9. Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid and methylglyoxal

    Directory of Open Access Journals (Sweden)

    Y. Tan

    2012-01-01

    Full Text Available Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including pyruvate, oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA. Acetic acid plays a central role in the aqueous oxidation of methylglyoxal and it is a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid (20 μM–10 mM was oxidized by OH radicals, and pyruvic acid and methylglyoxal experimental samples were analyzed using new analytical methods, in order to better understand the formation of SOA from acetic acid and methylglyoxal. Glyoxylic, glycolic, and oxalic acids formed from acetic acid and OH radicals. In contrast to the aqueous OH radical oxidation of methylglyoxal, the aqueous OH radical oxidation of acetic acid did not produce succinic acid and oligomers. This suggests that the methylgloxal-derived oligomers do not form through the acid catalyzed esterification pathway proposed previously. Using results from these experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.

  10. Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid

    Directory of Open Access Journals (Sweden)

    Y. Tan

    2011-06-01

    Full Text Available Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA. Acetic acid is an important intermediate in aqueous methylglyoxal oxidation and a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. Altieri et al. (2008 proposed that acetic acid was the precursor of oligoesters observed in methylglyoxal oxidation. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid at concentrations relevant to atmospheric waters (20 μM–10 mM was oxidized by OH radical. Products were analyzed by ion chromatography (IC, electrospray ionization mass spectrometry (ESI-MS, and IC-ESI-MS. The formation of glyoxylic, glycolic, and oxalic acids were observed. In contrast to methylglyoxal oxidation, succinic acid and oligomers were not detected. Using results from these and methylglyoxal + OH radical experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.

  11. The charge percolation mechanism and simulation of Ziegler–Natta polymerizations Part III. Oxidation states of transition metals

    Directory of Open Access Journals (Sweden)

    BRANKA PILIC

    2006-04-01

    Full Text Available The oxidation state of the transition metal (Mt active centre is the most disputable question in the polymerization of olefins by Ziegler–Natta (ZN and metallocene complexes. In this paper the importance and the changes of the Mt active centres are presented and discussed on the basis of a charge percolation mechanism (CPM of olefin polymerization. Mt atoms can exist in different oxidation states and can be easily transformed from one to another state during activation. In all cases, the Mt atoms are present in several oxidation states, i.e., Mt+(n-1, Mt+(n to Mt+(n+1, producing an irregular charge distribution over the support surface. There is a tendency to equalize the oxidation states by a charge transfer from Mt+(n–1 (donor toMt+(n+1 (acceptor. This cannot occur since the different oxidation states are highly separated on the support. However, monomer molecules are adsorbed on the support producing clusters with stacked p-bonds, making a p-bond bridge between a donor and an acceptor. Once a bridge is formed (percolation moment, charge transfer occurs. The donor and acceptor equalize their oxidation states simultaneously with the polymerization of the monomer. The polymer chain is desorbed from the support, freeing the surface for subsequent monomer adsorption. The whole process is repeated with the oxidation-reduction of other donor-acceptor ensembles.

  12. A review of adaptive mechanisms in cell responses towards oxidative stress caused by dental resin monomers.

    Science.gov (United States)

    Krifka, Stephanie; Spagnuolo, Gianrico; Schmalz, Gottfried; Schweikl, Helmut

    2013-06-01

    Dental composite resins are biomaterials commonly used to aesthetically restore the structure and function of teeth impaired by caries, erosion, or fracture. Residual monomers released from resin restorations as a result of incomplete polymerization processes interact with living oral tissues. Monomers like triethylene glycol dimethacrylate (TEGDMA) or 2-hydroxylethyl methacrylate (HEMA) are cytotoxic via apoptosis, induce genotoxic effects, and delay the cell cycle. Monomers also influence the response of cells of the innate immune system, inhibit specific odontoblast cell functions, or delay the odontogenic differentiation and mineralization processes in pulp-derived cells including stem cells. These observations indicate that resin monomers act as environmental stressors which inevitably disturb regulatory cellular networks through interference with signal transduction pathways. We hypothesize that an understanding of the cellular mechanisms underlying these phenomena will provide a better estimation of the consequences associated with dental therapy using composite materials, and lead to innovative therapeutic strategies and improved materials being used at tissue interfaces within the oral cavity. Current findings strongly suggest that monomers enhance the formation of reactive oxygen species (ROS), which is most likely the cause of biological reactions activated by dental composites and resin monomers. The aim of the present review manuscript is to discuss adaptive cell responses to oxidative stress caused by monomers. The particular significance of a tightly controlled network of non-enzymatic as well as enzymatic antioxidants for the regulation of cellular redox homeostasis and antioxidant defense in monomer-exposed cells will be addressed. The expression of ROS-metabolizing antioxidant enzymes like superoxide dismutase (SOD1), glutathione peroxidase (GPx1/2), and catalase in cells exposed to monomers will be discussed with particular emphasis on the role

  13. Radioprotective cerium oxide nanoparticles: Molecular imaging investigations of conps' pharmacokinetics, efficacy, and mechanisms of action

    Science.gov (United States)

    McDonagh, Philip Reed Wills, III

    Cerium oxide nanoparticles (CONPs) are being investigated for several anti-oxidant applications in medicine. One of their most promising applications is as a radioprotective drug, an area of research in need due to the severe side effects from radiation therapy. In this work, the potential of CONPs as a radioprotective drug is examined using four criteria: favorable biodistribution/pharmacokinetics, low toxicity, ability to protect normal tissue from radiation damage, and lack of protection of tumor. The mechanisms of action of CONPs are also studied. Biodistribution was determined in radiolabeled CONPs with surface coatings including citrate, dextran T10-amine (DT10-NH2), dextran T10-polyethylene glycol (DT10-PEG), dextran T10-sulfobetaine (DT10-SB) and poly(acrylic acid) (PAA), and compared to uncoated. 89Zr was incorporated into CONPs for positron emission tomography (PET) imaging and ex vivo tissue analysis in tumor bearing mice. Compared to uncoated [ 89Zr]CONPs, coated [89Zr]CONPs showed improved biodistribution, including significantly enhanced renal clearance of PAA- [89Zr]CONPs. The toxicity of CONPs was evaluated in vitro and in vivo, with low toxicity at therapeutic doses. After clinically mimetic radiation therapy, pre-treatment of mice with coated and uncoated CONPs showed greater than 50% reduction of cell death in normal colon tissue, comparable to the clinically available radioprotective drug amifostine. Tumor control after irradiation of spontaneous colon tumors was unchanged with PAA-CONP pre-treatment, while citrate, DT10-PEG, and uncoated CONP pre-treatment had slightly less tumor control. Xenograft tumors were irradiated after pH normalizing treatment with sodium bicarbonate and PAA-CONP pre-treatment. Treatment of these tumors showed slightly less tumor control than irradiation alone or PAA-CONP plus irradiation, demonstrating that the acidic pH of the tumor microenvironment may be the basis of preventing CONPs' radioprotective properties in

  14. Kinetics and Mechanism of Oxidation of Phenyl Acetic Acid and Dl-Mandelic Acid by Permanganate in Acid Medium

    Directory of Open Access Journals (Sweden)

    B.Syama Sundar

    2014-06-01

    Full Text Available Kinetics of oxidation of phenyl acetic acid and DL- Mandelic acid by potassium permanganate in aqueous acetic acid and perchloric acid mixture reveals that the kinetic orders are first order in oxidant, first order in H+ and zero order in substrate for phenyl acetic acid. DL-Mandelic acid exhibits first order in oxidant and zero order in substrate. The results are rationalised by a mechanism involving intermediate formation of mandelic acid in case of Phenyl acetic acid and ester formation with Mn (VII in case of DL-Mandelic acid. The following order of reactivity is observed: DL-Mandelic acid > Phenyl acetic acid. The high reactivity of DL-Mandelic acid over phenyl acetic acid may be due to different mechanisms operating with the two substrates and benzaldehyde is the final product in both the cases.

  15. Electro-catalytic oxidation of phenacetin with a three-dimensional reactor: Degradation pathway and removal mechanism.

    Science.gov (United States)

    Xiao, Mengshi; Zhang, Yonggang

    2016-06-01

    Phenacetin is a common analgesic, anti-arthritic and anti-rheumatic drug. This study dealt with the degradation of phenacetin in alkaline media using a three-dimensional reactor with particle electrodes. Particular attention was paid to the degradation pathway and the reaction mechanism in the system. Liquid chromatography coupled with time-of-flight mass spectrometry was used to identify the intermediates. The phenacetin was observed to be firstly cut off the branch chains main by direct oxidation, and then the intermediates further degraded to ring opening products by hydroxyl radical resulting from indirect oxidation and finally mineralized to CO2, H2O. A possible removal mechanism was proposed that direct and indirect oxidation together did effect on the pollutants with oxygen.

  16. Interplay of Experiment and Theory in Elucidating Mechanisms of Oxidation Reactions by a Nonheme Ru(IV)O Complex.

    Science.gov (United States)

    Dhuri, Sunder N; Cho, Kyung-Bin; Lee, Yong-Min; Shin, Sun Young; Kim, Jin Hwa; Mandal, Debasish; Shaik, Sason; Nam, Wonwoo

    2015-07-08

    A comprehensive experimental and theoretical study of the reactivity patterns and reaction mechanisms in alkane hydroxylation, olefin epoxidation, cyclohexene oxidation, and sulfoxidation reactions by a mononuclear nonheme ruthenium(IV)-oxo complex, [Ru(IV)(O)(terpy)(bpm)](2+) (1), has been conducted. In alkane hydroxylation (i.e., oxygen rebound vs oxygen non-rebound mechanisms), both the experimental and theoretical results show that the substrate radical formed via a rate-determining H atom abstraction of alkanes by 1 prefers dissociation over oxygen rebound and desaturation processes. In the oxidation of olefins by 1, the observations of a kinetic isotope effect (KIE) value of 1 and styrene oxide formation lead us to conclude that an epoxidation reaction via oxygen atom transfer (OAT) from the Ru(IV)O complex to the C═C double bond is the dominant pathway. Density functional theory (DFT) calculations show that the epoxidation reaction is a two-step, two-spin-state process. In contrast, the oxidation of cyclohexene by 1 affords products derived from allylic C-H bond oxidation, with a high KIE value of 38(3). The preference for H atom abstraction over C═C double bond epoxidation in the oxidation of cyclohexene by 1 is elucidated by DFT calculations, which show that the energy barrier for C-H activation is 4.5 kcal mol(-1) lower than the energy barrier for epoxidation. In the oxidation of sulfides, sulfoxidation by the electrophilic Ru-oxo group of 1 occurs via a direct OAT mechanism, and DFT calculations show that this is a two-spin-state reaction in which the transition state is the lowest in the S = 0 state.

  17. A new leptin-mediated mechanism for stimulating fatty acid oxidation: a pivotal role for sarcolemmal FAT/CD36.

    Science.gov (United States)

    Momken, Iman; Chabowski, Adrian; Dirkx, Ellen; Nabben, Miranda; Jain, Swati S; McFarlan, Jay T; Glatz, Jan F C; Luiken, Joost J F P; Bonen, Arend

    2017-01-01

    Leptin stimulates fatty acid oxidation in muscle and heart; but, the mechanism by which these tissues provide additional intracellular fatty acids for their oxidation remains unknown. We examined, in isolated muscle and cardiac myocytes, whether leptin, via AMP-activated protein kinase (AMPK) activation, stimulated fatty acid translocase (FAT/CD36)-mediated fatty acid uptake to enhance fatty acid oxidation. In both mouse skeletal muscle and rat cardiomyocytes, leptin increased fatty acid oxidation, an effect that was blocked when AMPK phosphorylation was inhibited by adenine 9-β-d-arabinofuranoside or Compound C. In wild-type mice, leptin induced the translocation of FAT/CD36 to the plasma membrane and increased fatty acid uptake into giant sarcolemmal vesicles and into cardiomyocytes. In muscles of FAT/CD36-KO mice, and in cardiomyocytes in which cell surface FAT/CD36 action was blocked by sulfo-N-succinimidyl oleate, the leptin-stimulated influx of fatty acids was inhibited; concomitantly, the normal leptin-stimulated increase in fatty acid oxidation was also prevented, despite the normal leptin-induced increase in AMPK phosphorylation. Conversely, in muscle of AMPK kinase-dead mice, leptin failed to induce the translocation of FAT/CD36, along with a failure to stimulate fatty acid uptake and oxidation. Similarly, when siRNA was used to reduce AMPK in HL-1 cardiomyocytes, leptin failed to induce the translocation of FAT/CD36. Our studies have revealed a novel mechanism of leptin-induced fatty acid oxidation in muscle tissue; namely, this process is dependent on the activation of AMPK to induce the translocation of FAT/CD36 to the plasma membrane, thereby stimulating fatty acid uptake. Without increasing this leptin-stimulated, FAT/CD36-dependent fatty acid uptake process, leptin-stimulated AMPK phosphorylation does not enhance fatty acid oxidation. © 2017 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

  18. Induction of oxidative DNA damage by mesalamine in the presence of copper: a potential mechanism for mesalamine anticancer activity.

    Science.gov (United States)

    Zimmerman, Ryan P; Jia, Zhenquan; Zhu, Hong; Vandjelovic, Nathan; Misra, Hara P; Wang, Jianmin; Li, Yunbo

    2011-02-27

    Mesalamine is the first line pharmacologic intervention for patients with ulcerative colitis, and recent epidemiologic studies have demonstrated a protective association between therapeutic use of the drug and colorectal carcinoma. However, the mechanism by which this protection is afforded has yet to be elucidated. Because copper is found at higher than normal concentrations in neoplastic cell nuclei and is known to interact with phenolic compounds to generate reactive oxygen species, we investigated whether the reaction of mesalamine/copper was able to induce oxidative DNA strand breaks in φX-174 RF I plasmid DNA, and the various components of the mechanism by which the reaction occurred. Plasmid DNA strand breaks were induced by pharmacologically relevant concentrations of mesalamine in the presence of a micromolar concentration of Cu(II), and damage was inhibited by bathocuproinedisulfonic acid (BCS) and catalase. Further, we showed that the reaction of copper with mesalamine consumed molecular oxygen, which was inhibited by BCS. Electron paramagnetic resonance spectral analysis of the reaction of copper/mesalamine indicated the presence of the hydroxyl radical, which was inhibited by both BCS and catalase. This study demonstrates for the first time that through a copper-redox cycling mechanism, the copper-mediated oxidation of mesalamine is a pro-oxidant interaction that generates hydroxyl radicals which may participate in oxidative DNA damage. These results demonstrate a potential mechanism of the anticancer effects of mesalamine in patients with ulcerative colitis.

  19. Transformation of hydroxycarbonate green rust into crystalline iron (hydr)oxides: Influences of reaction conditions and underlying mechanisms

    NARCIS (Netherlands)

    Wang, Xiaoming; Liu, Fan; Tan, W.; Feng, Xionghan; Koopal, L.K.

    2013-01-01

    Green rusts (GRs) are found as intermediate products between FeII hydroxides and FeIII oxyhydroxides in various anoxic environments. The transformation of hydroxycarbonate green rust GR1(CO32-) by air oxidation at different conditions and the underlying mechanisms were investigated using X-ray diffr

  20. Mechanism of mechanochemical synthesis of complex oxides and the peculiarities of their nano-structurization determining sintering

    Directory of Open Access Journals (Sweden)

    Zyryanov V.V.

    2005-01-01

    Full Text Available A mechanism of superfast mechanosynthesis reaction for oxide systems is proposed on the base of a dynamics study. The threshold effect and linear dependence of the chemical response on the effective temperature of the reaction zone are established. Major factors are determined: molecular mass of reagents, enthalpy and difference of reagents in Mohs’s hardness, which also influence the composition of the primary product. Primary acts are characterized by a superfast roller mechanism of mass transfer with the formation of a transient dynamic state (D*. Secondary acts slowly approximate the composition of the product to the composition of the starting mixture by diffusion mass transfer in a deformation mixing regime with a contribution of a rotation (roller mechanism. The list of structure types for complex oxides derived by mechanosynthesis includes perovskites, fluorites, pyrochlors, sheelites, and some other ones. Powders of crystal products display multilevel structurization. In all studied complex oxides strong disordering of the “anti-glass” type was observed. The mechanism of sintering was studied in BaTiO3 powders of different origin and in metastable complex oxides derived by mechanosynthesis. The major contribution in shrinkage belongs to rearrangements of crystalline particles as a whole. Structure transformations accompany, as a rule, sintering of inhomogeneous powders derived by mechanosynthesis.

  1. A novel mechanism for poisoning of metal oxide SCR catalysts: base-acid explanation correlated with redox properties.

    Science.gov (United States)

    Chang, Huazhen; Li, Junhua; Su, Wenkang; Shao, Yuankai; Hao, Jiming

    2014-09-11

    A novel mechanism is proposed for the poisoning effect of acid gases and N2O formation on SCR catalysts involving base-acid properties correlated with redox ability of M-O or M-OH (M = Ce or V) of metal oxides and the strength of their basicity responsible for resistance to HCl and SO2 at medium and low temperatures.

  2. The atmospheric oxidation mechanism of 1,2,4-trimethylbenzene initiated by OH radicals.

    Science.gov (United States)

    Li, Yun; Wang, Liming

    2014-09-07

    The atmospheric oxidation mechanism of 1,2,4-trimethylbenzene (1,2,4-TMB) initiated by OH radicals is investigated using quantum chemistry calculations at M06-2X and ROCBS-QB3 levels. The calculations show that the initiation of the reaction is dominated by OH addition to C1, C3 and C5 to form 1,2,4-TMB-OH adducts R1, R3, and R5 with branching ratios of 0.22, 0.19, and 0.38, respectively, using ROCBS-QB3 energies. In the troposphere, the adducts react with O2 by irreversible H-abstraction to form phenolic compounds and by reversible addition to TMB-OH-O2 peroxy radicals, which will cyclize to bicyclic radicals, similar to those in benzene, toluene, and xylenes. The bicyclic radicals can further recombine with O2 to generate bicyclic peroxy and alkoxyl radicals. The bicyclic alkoxyl radicals would break the ring directly to form 1,2-dicarbonyl products and unsaturated 1,4-dicarbonyl co-products, or undergo another cyclization to form an epoxy group, followed by the ring-breakage to form 1,2-dicarbonyl products and epoxy-1,4-dicarbonyl co-products. The predicted yields of products agree reasonably with the previous experimental measurements, while considerable discrepancies also exist for the yields of nitrates, biacetyl, 4-oxo-2-pentenal, and butenedial, etc. Our mechanism also predicts a new type of epoxy-1,4-dicarbonyl compounds with a total yield of ∼0.32. The epoxy-1,4-dicarbonyl compounds have not been suggested or reported in previous studies.

  3. Integrins mediate mechanical compression-induced endothelium-dependent vasodilation through endothelial nitric oxide pathway.

    Science.gov (United States)

    Lu, Xiao; Kassab, Ghassan S

    2015-09-01

    Cardiac and skeletal muscle contraction lead to compression of intramuscular arterioles, which, in turn, leads to their vasodilation (a process that may enhance blood flow during muscle activity). Although endothelium-derived nitric oxide (NO) has been implicated in compression-induced vasodilation, the mechanism whereby arterial compression elicits NO production is unclear. We cannulated isolated swine (n = 39) myocardial (n = 69) and skeletal muscle (n = 60) arteriole segments and exposed them to cyclic transmural pressure generated by either intraluminal or extraluminal pressure pulses to simulate compression in contracting muscle. We found that the vasodilation elicited by internal or external pressure pulses was equivalent; moreover, vasodilation in response to pressure depended on changes in arteriole diameter. Agonist-induced endothelium-dependent and -independent vasodilation was used to verify endothelial and vascular smooth muscle cell viability. Vasodilation in response to cyclic changes in transmural pressure was smaller than that elicited by pharmacological activation of the NO signaling pathway. It was attenuated by inhibition of NO synthase and by mechanical removal of the endothelium. Stemming from previous observations that endothelial integrin is implicated in vasodilation in response to shear stress, we found that function-blocking integrin α5β1 or αvβ3 antibodies attenuated cyclic compression-induced vasodilation and NOx (NO(-)2 and NO(-)3) production, as did an RGD peptide that competitively inhibits ligand binding to some integrins. We therefore conclude that integrin plays a role in cyclic compression-induced endothelial NO production and thereby in the vasodilation of small arteries during cyclic transmural pressure loading.

  4. Chlorine dioxide oxidation of Escherichia coli in water - A study of the disinfection kinetics and mechanism.

    Science.gov (United States)

    Ofori, Isaac; Maddila, Suresh; Lin, Johnson; Jonnalagadda, Sreekantha B

    2017-06-07

    This study investigated the kinetics and mechanism of chlorine dioxide (ClO2) inactivation of a Gram-negative bacteria Escherichia coli (ATCC 35218) in oxidant demand free (ODF) water in detail as a function of disinfectant concentration (0.5-5.0 mg/L), water pH (6.5-8.5), temperature variations (4-37°C) and bacterial density (10(5)-10(7) cfu/mL). The effects of ClO2 on bacterial cell morphology, outer membrane permeability, cytoplasmic membrane disruption and intracellular enzymatic activity were also studied to elucidate the mechanism of action on the cells. Increasing temperature and disinfectant concentration were proportional to the rate of cell killing, but efficacy was found to be significantly subdued at 0.5 mg/L and less dependent on the bacterial density. The bactericidal efficiency was higher at alkaline pH of 8 or above as compared to neutral and slightly acidic pH of 7 and 6.5 respectively. The disinfection kinetic curves followed a biphasic pattern of rapid inactivation within the initial 2 min which were followed by a tailing even in the presence of residual biocide. The curves were adequately described by the Cavg Hom model. Transmission Electron Microscopy images of the bacteria cells exposed to lethal concentrations of ClO2 indicated very little observable morphological damage to the outer membranes of the cells. ClO2 however was found to increase the permeability of the outer and cytoplasmic membranes leading to the leakage of membrane components such as 260 nm absorbing materials and inhibiting the activity of the intracellular enzyme β-D-galactosidase. It is suggested that the disruption of the cytoplasmic membrane and subsequent efflux of intracellular components result in the inactivation of the Gram-negative bacteria.

  5. The effect of adding magnesium oxide on the mechanical properties of the tricalcium phosphate-zirconia composites

    Energy Technology Data Exchange (ETDEWEB)

    Sallemi, Imen, E-mail: imen.sallemi@hotmail.com; Bouaziz, Jamel; Ben Ayed, Foued

    2015-02-01

    The effect of magnesium oxide on the mechanical properties of the tricalcium phosphate – 50 wt.% zirconia composites was investigated during a sintering process between 1300 °C and 1400 °C. The characteristics of the samples before and after the sintering process were realized by using the differential thermal analysis, dilatometry, X-ray diffraction, the {sup 31}P magic angle scanning nuclear magnetic resonance, the scanning electron microscope and by considering such mechanical properties as the rupture strength and Vickers hardness. The mechanical performances of the tricalcium phosphate-50 wt.% zirconia composites increased with both the percentage of magnesium oxide and the sintering temperature. At 1400 °C, the mechanical properties of the composites sintered with 10 wt.% magnesium oxide reached their maximum value. Thus, Vickers hardness increased from 554 to 6350 MPa and the rupture strength of the corresponding composites varied from 5.2 to 25 MPa. The increase of the mechanical properties of the samples is due to the formation of both the tetragonal zirconia phase and the liquid phase which helps to fill the pores. The microstructure of needle form is most probably phosphate precipitates which are formed from this liquid phase. Furthermore, the presence of magnesium oxide in the composites prevented the inverse allotropic transformation of zirconia. - Highlights: • We measure the rupture strength and Vickers hardness of bioceramics. • We characterize the effect of MgO on the mechanical properties of the tricalcium phosphate – 50 wt% zirconia composites. • MgO increase the mechanical properties of the composites.

  6. Low-Frequency Mechanical Spectroscopy of Lanthanum Cobaltite Based Mixed Conducting Oxides

    Directory of Open Access Journals (Sweden)

    Wu Xiu Sheng

    2016-09-01

    Full Text Available The low-frequency mechanical spectra of lanthanum cobaltite based mixed conducting oxides have been measured using a computer-controlled inverted torsion pendulum. The results indicate that the internal friction spectra and shear modulus depend on the Sr doping contents (x. For undoped samples, no internal friction peak is observed. However, for La0.8Sr0.2CoO3‒δ, three internal friction peaks (P2, P3 and P4 are observed. In addition to these peaks, two more peaks (P0 and P1 are observed in La0.6Sr0.4CoO3‒δ. The P0 and P1 peaks show characteristics of a phase transition, while the P2, P3 and P4 peaks are of relaxation-type. Our analysis suggests that the P0 peak is due to a phase separation and the P1 peak is related to the ferromagnetic–paramagnetic phase transition. The P2, P3 and P4 peaks are associated with the motion of domain walls. The formation of this kind of domain structure is a consequence of a transformation from the paraelastic cubic phase to the ferroelastic rhombohedral phase. With partial substitution of Fe for Co, only one peak is observed, which is discussed as a result of different microstructure.

  7. Wnt Ligands Differentially Regulate Toxicity and Translocation of Graphene Oxide through Different Mechanisms in Caenorhabditis elegans

    Science.gov (United States)

    Zhi, Lingtong; Ren, Mingxia; Qu, Man; Zhang, Hanyu; Wang, Dayong

    2016-12-01

    In this study, we investigated the possible involvement of Wnt signals in the control of graphene oxide (GO) toxicity using the in vivo assay system of Caenorhabditis elegans. In nematodes, the Wnt ligands, CWN-1, CWN-2, and LIN-44, were found to be involved in the control of GO toxicity. Mutation of cwn-1 or lin-44 gene induced a resistant property to GO toxicity and resulted in the decreased accumulation of GO in the body of nematodes, whereas mutation of cwn-2 gene induces a susceptible property to GO toxicity and an enhanced accumulation of GO in the body of nematodes. Genetic interaction assays demonstrated that mutation of cwn-1 or lin-44 was able to suppress the susceptibility to GO toxicity shown in the cwn-2 mutants. Loss-of-function mutations in all three of these Wnt ligand genes resulted in the resistance of nematodes to GO toxicity. Moreover, the Wnt ligands might differentially regulate the toxicity and translocation of GO through different mechanisms. These findings could be important in understanding the function of Wnt signals in the regulation of toxicity from environmental nanomaterials.

  8. Soil nitrate reducing processes – drivers, mechanisms for spatial variation, and significance for nitrous oxide production

    Science.gov (United States)

    Giles, Madeline; Morley, Nicholas; Baggs, Elizabeth M.; Daniell, Tim J.

    2012-01-01

    The microbial processes of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are two important nitrate reducing mechanisms in soil, which are responsible for the loss of nitrate (NO3−) and production of the potent greenhouse gas, nitrous oxide (N2O). A number of factors are known to control these processes, including O2 concentrations and moisture content, N, C, pH, and the size and community structure of nitrate reducing organisms responsible for the processes. There is an increasing understanding associated with many of these controls on flux through the nitrogen cycle in soil systems. However, there remains uncertainty about how the nitrate reducing communities are linked to environmental variables and the flux of products from these processes. The high spatial variability of environmental controls and microbial communities across small sub centimeter areas of soil may prove to be critical in determining why an understanding of the links between biotic and abiotic controls has proved elusive. This spatial effect is often overlooked as a driver of nitrate reducing processes. An increased knowledge of the effects of spatial heterogeneity in soil on nitrate reduction processes will be fundamental in understanding the drivers, location, and potential for N2O production from soils. PMID:23264770

  9. Mechanism of neem limonoids-induced cell death in cancer: Role of oxidative phosphorylation.

    Science.gov (United States)

    Yadav, Neelu; Kumar, Sandeep; Kumar, Rahul; Srivastava, Pragya; Sun, Leimin; Rapali, Peter; Marlowe, Timothy; Schneider, Andrea; Inigo, Joseph R; O'Malley, Jordan; Londonkar, Ramesh; Gogada, Raghu; Chaudhary, Ajay K; Yadava, Nagendra; Chandra, Dhyan

    2016-01-01

    We have previously reported that neem limonoids (neem) induce multiple cancer cell death pathways. Here we dissect the underlying mechanisms of neem-induced apoptotic cell death in cancer. We observed that neem-induced caspase activation does not require Bax/Bak channel-mediated mitochondrial outer membrane permeabilization, permeability transition pore, and mitochondrial fragmentation. Neem enhanced mitochondrial DNA and mitochondrial biomass. While oxidative phosphorylation (OXPHOS) Complex-I activity was decreased, the activities of other OXPHOS complexes including Complex-II and -IV were unaltered. Increased reactive oxygen species (ROS) levels were associated with an increase in mitochondrial biomass and apoptosis upon neem exposure. Complex-I deficiency due to the loss of Ndufa1-encoded MWFE protein inhibited neem-induced caspase activation and apoptosis, but cell death induction was enhanced. Complex II-deficiency due to the loss of succinate dehydrogenase complex subunit C (SDHC) robustly decreased caspase activation, apoptosis, and cell death. Additionally, the ablation of Complexes-I, -III, -IV, and -V together did not inhibit caspase activation. Together, we demonstrate that neem limonoids target OXPHOS system to induce cancer cell death, which does not require upregulation or activation of proapoptotic Bcl-2 family proteins. Copyright © 2015 Elsevier Inc. All rights reserved.

  10. Theoretical study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals: the H abstraction pathway.

    Science.gov (United States)

    Shiroudi, Abolfazl; Deleuze, Michael S

    2014-05-22

    Reaction mechanisms for the initial stages of naphthalene oxidation at high temperatures (T ≥ 600 K) have been studied theoretically using density functional theory along with various exchange-correlation functionals, as well as the benchmark CBS-QB3 quantum chemical approach. These stages correspond to the removal of hydrogen atoms by hydroxyl radical and the formation thereby of 1- and 2-naphthyl radicals. Bimolecular kinetic rate constants were estimated by means of transition state theory. The excellent agreement with the available experimental kinetic rate constants demonstrates that a two-step reaction scheme prevails. Comparison with results obtained with density functional theory in conjunction with various exchange-correlation functionals also shows that DFT remains unsuited for quantitative insights into kinetic rate constants. Analysis of the computed structures, bond orders, and free energy profiles demonstrates that the reaction steps involved in the removal of hydrogen atoms by OH radicals satisfy Hammond's principle. Computations of branching ratios also show that these reactions do not exhibit a particularly pronounced site-selectivity.

  11. Quinoxaline 1, 4-di-N-oxides: Biological activities and mechanisms of actions

    Directory of Open Access Journals (Sweden)

    Guyue eCheng

    2016-03-01

    Full Text Available Quinoxaline 1, 4-di-N-oxides (QdNOs have manifold biological properties, including antimicrobial, antitumoral, antitrypanosomal and antiinflammatory/antioxidant activities. These diverse activities endow them broad applications and prospects in human and veterinary medicines. As QdNOs arouse widespread interest, the evaluation of their medicinal chemistry is still in progress. In the meantime, adverse effects have been reported in some of the QdNO derivatives. For example, genotoxicity and bacterial resistance have been found in QdNO antibacterial growth promoters, conferring urgent need for discovery of new QdNO drugs. However, the modes of actions of QdNOs are not fully understood, hindering the development and innovation of these promising compounds. Here, QdNOs are categorized based on the activities and usages, among which the antimicrobial activities are consist of antibacterial, antimycobacterial and anticandida activities, and the antiprotozoal activities include antitrypanosomal, antimalarial, antitrichomonas and antiamoebic activities. The structure-activity relationship and the mode of actions of each type of activity of QdNOs are summarized, and the toxicity and the underlying mechanisms are also discussed, providing insight for the future research and development of these fascinating compounds.

  12. Freestanding bacterial cellulose-graphene oxide composite membranes with high mechanical strength for selective ion permeation

    Science.gov (United States)

    Fang, Qile; Zhou, Xufeng; Deng, Wei; Zheng, Zhi; Liu, Zhaoping

    2016-09-01

    Graphene oxide (GO) based membranes have been widely applied in molecular separation based on the size exclusion effect of the nanochannels formed by stacked GO sheets. However, it’s still a challenge to prepare a freestanding GO-based membrane with high mechanical strength and structural stability which is prerequisite for separation application in aqueous solution. Here, a freestanding composite membrane based on bacterial cellulose (BC) and GO is designed and prepared. BC network provides a porous skeleton to spread GO sheets and uniformly incorporates into the GO layers, which endows the BC + GO composite membrane with well water-stability, excellent tensile strength, as well as improved toughness, guaranteeing its separation applicability in water environment. The resulting BC + GO membrane exhibits obviously discrepant permeation properties for different inorganic/organic ions with different size, and in particular, it can quickly separate ions in nano-scale from angstrom-scale. Therefore, this novel composite membrane is considered to be a promising candidate in the applications of water purification, food industry, biomedicine, and pharmaceutical and fuel separation.

  13. Degradation of oxcarbazepine by UV-activated persulfate oxidation: kinetics, mechanisms, and pathways.

    Science.gov (United States)

    Bu, Lingjun; Zhou, Shiqing; Shi, Zhou; Deng, Lin; Li, Guangchao; Yi, Qihang; Gao, Naiyun

    2016-02-01

    The degradation kinetics and mechanism of the antiepileptic drug oxcarbazepine (OXC) by UV-activated persulfate oxidation were investigated in this study. Results showed that UV/persulfate (UV/PS) process appeared to be more effective in degrading OXC than UV or PS alone. The OXC degradation exhibited a pseudo-first order kinetics pattern and the degradation rate constants (k obs) were affected by initial OXC concentration, PS dosage, initial pH, and humic acid concentration to different degrees. It was found that low initial OXC concentration, high persulfate dosage, and initial pH enhanced the OXC degradation. Additionally, the presence of humic acid in the solution could greatly inhibit the degradation of OXC. Moreover, hydroxyl radical (OH•) and sulfate radical (SO4 (-)••) were identified to be responsible for OXC degradation and SO4 (-)• made the predominant contribution in this study. Finally, major intermediate products were identified and a preliminary degradation pathway was proposed. Results demonstrated that UV/PS system is a potential technology to control the water pollution caused by emerging contaminants such as OXC.

  14. Soil nitrate reducing processes – drivers, mechanisms for spatial variation and significance for nitrous oxide production

    Directory of Open Access Journals (Sweden)

    Madeline Eleanore Giles

    2012-12-01

    Full Text Available The microbial processes of denitrification and dissimilatory nitrate reduction to ammonium (DNRA are two important nitrate reducing mechanisms in soil, which are responsible for the loss of nitrate (NO3-¬ and production of the potent greenhouse gas, nitrous oxide (N2O. A number of factors are known to control these processes, including O2 concentrations and moisture content, N, C, pH and the size and community structure of nitrate reducing organisms responsible for the processes. There is an increasing understanding associated with many of these controls on flux through the nitrogen cycle in soil systems. However, there remains uncertainty about how the nitrate reducing communities are linked to environmental variables and the flux of products from these processes. The high spatial variability of environmental controls and microbial communities across small sub cm areas of soil may prove to be critical in determining why an understanding of the links between biotic and abiotic controls has proved elusive. This spatial effect is often overlooked as a driver of nitrate reducing processes. An increased knowledge of the effects of spatial heterogeneity in soil on nitrate reduction processes will be fundamental in understanding the drivers, location and potential for N2O production from soils.

  15. Bovine serum albumin adsorption to iron-oxide coated sands can change microsphere deposition mechanisms.

    Science.gov (United States)

    Flynn, Raymond M; Yang, Xinyao; Hofmann, Thilo; von der Kammer, Frank

    2012-03-06

    Particulate colloids often occur together with proteins in sewage-impacted water. Using Bovine Serum Albumin (BSA) as a surrogate for protein in sewage, column experiments investigating the capacity of iron-oxide coated sands to remove latex microspheres from water revealed that microsphere attenuation mechanisms depended on antecedent BSA coverage. Dual pulse experiment (DPE) results suggested that where all BSA was adsorbed, subsequent multiple pore volume microsphere breakthrough curves reflected progressively reduced colloid deposition rates with increasing adsorbed BSA content. Modeling colloid responses suggested adsorption of 1 μg BSA generated the same response as blockage by between 7.1 × 10(8) and 2.3 × 10(9) deposited microspheres. By contrast, microsphere responses in DPEs where BSA coverage of the deposition sites approached/reached saturation revealed the coated sand maintained a finite capacity to attenuate microspheres, even when incapable of further BSA adsorption. Subsequent microsphere breakthrough curves demonstrated the matrix's colloid attenuation capacity progressively increased with continued microsphere deposition. Experimental findings suggested BSA adsorption on the sand surface approaching/reaching saturation generated attractive deposition sites for colloids, which became progressively more attractive with further colloid deposition (filter ripening). Results demonstrate that adsorption of a single type of protein may either enhance or inhibit colloid mobility in saturated porous media.

  16. Synergistic effect of graphene-oxide-doping and microwave-curing on mechanical strength of cement

    Science.gov (United States)

    Qin, Hao; Wei, Wei; Hang Hu, Yun

    2017-04-01

    In this communication, efficient reinforcement of cement matrix was obtained by graphene-oxide (GO) doping and curing treatments. The compressive strength of plain cement is 14.3±0.2 MPa. When the cement contained 0.5 wt% GO, its strength reached 19.4±0.9 MPa. The strength can be further enhanced by curing, which follows the sequence: Microwave-cured GO-cement > Microwave and water-cured GO-cement > Water-cured GO-cement > GO-cement without curing. The highest compressive strength (32.4±0.7 MPa), which was achieved by combining GO-doping and microwave curing, is 126.6±8.1% higher than that without GO-doping and microwave curing. This demonstrates a synergistic effect of GO doping and microwave-curing on the strength of cement composite materials. Furthermore, X-ray diffraction (XRD), Fourier transform Infrared Spectroscopy (FTIR), and field emission scanning electron microscope (FESEM) characterizations revealed that the combination of GO doping and microwave-curing remarkably accelerated cement hydration, leading to the regular and compact structure and thus a high compressive strength. This work provides a new way to improve the mechanical properties of cement composites.

  17. Quinoxaline 1,4-di-N-Oxides: Biological Activities and Mechanisms of Actions.

    Science.gov (United States)

    Cheng, Guyue; Sa, Wei; Cao, Chen; Guo, Liangliang; Hao, Haihong; Liu, Zhenli; Wang, Xu; Yuan, Zonghui

    2016-01-01

    Quinoxaline 1,4-di-N-oxides (QdNOs) have manifold biological properties, including antimicrobial, antitumoral, antitrypanosomal and antiinflammatory/antioxidant activities. These diverse activities endow them broad applications and prospects in human and veterinary medicines. As QdNOs arouse widespread interest, the evaluation of their medicinal chemistry is still in progress. In the meantime, adverse effects have been reported in some of the QdNO derivatives. For example, genotoxicity and bacterial resistance have been found in QdNO antibacterial growth promoters, conferring urgent need for discovery of new QdNO drugs. However, the modes of actions of QdNOs are not fully understood, hindering the development and innovation of these promising compounds. Here, QdNOs are categorized based on the activities and usages, among which the antimicrobial activities are consist of antibacterial, antimycobacterial and anticandida activities, and the antiprotozoal activities include antitrypanosomal, antimalarial, antitrichomonas, and antiamoebic activities. The structure-activity relationship and the mode of actions of each type of activity of QdNOs are summarized, and the toxicity and the underlying mechanisms are also discussed, providing insight for the future research and development of these fascinating compounds.

  18. Electro-oxidation of diclofenac at boron doped diamond: Kinetics and mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Zhao Xu; Hou Yining; Liu Huijuan; Qiang Zhimin [State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085 (China); Qu Jiuhui [State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085 (China)], E-Mail: jhqu@mail.rcees.ac.cn

    2009-07-01

    Diclofenac is a common anti-inflammatory drug. Its electrochemical degradation at boron doped diamond electrode was investigated in aqueous solution. The degradation kinetics and the intermediate products were studied. Results showed that electro-oxidation was effective in inducing the degradation of diclofenac with 30 mg/L initial concentration, ensuring a mineralization degree of 72% after a 4 h treatment with the applied bias potential of 4.0 V. The effects of applied bias potential and addition of NaCl on diclofenac degradation were investigated. Different degradation mechanisms of diclofenac were involved at various applied bias potentials. With the addition of NaCl, some chlorination intermediates including dichlorodiclofenac were identified, which lead to the total organic carbon increase compared with the electrolysis process without NaCl addition at the reaction initial period. The main intermediates including 2,6-dichlorobenzenamine, 2,5-dihydroxybenzyl alcohol, and benzoic acid are identified at the time of 2 h. 1-(2,6-Dichlorocyclohexa-2,4-dienyl)indolin-2-one were also identified. These intermediates disappeared gradually with the extension of reaction time. Small molecular acids were identified finally. Based on these results, a degradation pathway of diclofenac was proposed.

  19. Poly(ethylene oxide)/clay nanaocomposites: Thermal and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)