WorldWideScience

Sample records for coordinated catalytic activity

  1. Catalytic dioxygen activation by Co(II) complexes employing a coordinatively versatile ligand scaffold.

    Science.gov (United States)

    Sharma, Savita K; May, Philip S; Jones, Matthew B; Lense, Sheri; Hardcastle, Kenneth I; MacBeth, Cora E

    2011-02-14

    The ligand bis(2-isobutyrylamidophenyl)amine has been prepared and used to stabilize both mononuclear and dinuclear cobalt(II) complexes. The nuclearity of the cobalt product is regulated by the deprotonation state of the ligand. Both complexes catalytically oxidize triphenylphosphine to triphenylphosphine oxide in the presence of O(2).

  2. Coordination chemistry and catalytic activity of N-heterocyclic carbene iridium(I) complexes.

    Science.gov (United States)

    Fu, Ching-Feng; Chang, Yung-Hung; Liu, Yi-Hong; Peng, Shei-Ming; Elsevier, Cornelis J; Chen, Jwu-Ting; Liu, Shiuh-Tzung

    2009-09-21

    Iridium complexes [(CO)2Ir(NHC-R)Cl] (R = Et-, 3a; PhCH2-, 3b; CH3OCH2CH2-, 3c; o-CH3OC6H4CH2-, 3d; NHC: N-heterocyclic carbene) are prepared via the carbene transfer from [(NHC-R)W(CO)5] to [Ir(COD)Cl]2. By using substitution with 13CO, we are able to estimate the activation energy (G) of the CO-exchange in 3a-d, which are in the range of 12-13 kcal mol-1, significantly higher than those for the phosphine analog [(CO)2Ir(PCy3)Cl]. Reactions of 3b and 3d with an equimolar amount of PPh3 result in the formation of the corresponding [(NHC-R)Ir(CO)(PPh3)Cl] with the phosphine and NHC in trans arrangement. In contrast, the analogous reaction of 3a or 3c with phosphine undergoes substitution followed by the anion metathesis to yield the corresponding di-substituted [(NHC-R)Ir(CO)(PPh3)2]BF4 (5) directly. Treatment of 3b or 3d with excess of PPh3 leads to the similar product of disubstitution 5b and 5d. The analysis for the IR data of carbonyliridium complexes provides the estimation of electron-donating power of NHCs versus phosphines. The NHC moiety on the iridium center cannot be replaced by phosphines, even 1,2-bis(diphenylphohino)ethane (dppe). All the carbene moieties on the iridium complexes are inert toward sulfur treatment, indicating a strong interaction between NHC and the iridium centers. Complexes 3a-c are active on the catalysis of the oxidative cyclization of 2-(o-aminophenyl)ethanol to yield the indole compound. The phosphine substituted complexes or analogs are less active.

  3. Catalytic activity of Au nanoparticles

    DEFF Research Database (Denmark)

    Larsen, Britt Hvolbæk; Janssens, Ton V.W.; Clausen, Bjerne

    2007-01-01

    Au is usually viewed as an inert metal, but surprisingly it has been found that Au nanoparticles less than 3–5 nm in diameter are catalytically active for several chemical reactions. We discuss the origin of this effect, focusing on the way in which the chemical activity of Au may change with par......Au is usually viewed as an inert metal, but surprisingly it has been found that Au nanoparticles less than 3–5 nm in diameter are catalytically active for several chemical reactions. We discuss the origin of this effect, focusing on the way in which the chemical activity of Au may change...... with particle size. We find that the fraction of low-coordinated Au atoms scales approximately with the catalytic activity, suggesting that atoms on the corners and edges of Au nanoparticles are the active sites. This effect is explained using density functional calculations....

  4. Computational evaluation of sub-nanometer cluster activity of singly exposed copper atom with various coordinative environment in catalytic CO{sub 2} transformation

    Energy Technology Data Exchange (ETDEWEB)

    Shanmugam, Ramasamy [Department of Chemistry, Thiagarajar College, Madurai, Tamilnadu 625 009 (India); National Center for Catalysis Research, Indian Institute of Technology Madras, Chennai, Tamilnadu 600 036 (India); Thamaraichelvan, Arunachalam [Faculty of Allied Health Sciences, Chettinad Hospital & Research Institute, Kelambakkam, Tamilnadu 603 103 (India); Ganesan, Tharumeya Kuppusamy [Department of Chemistry, The American College, Madurai, Tamilnadu 625 002 (India); Viswanathan, Balasubramanian, E-mail: bvnathan@iitm.ac.in [National Center for Catalysis Research, Indian Institute of Technology Madras, Chennai, Tamilnadu 600 036 (India)

    2017-02-28

    Highlights: • On interaction with adsorbate CO{sub 2,} the adsorbent changes its configuration around the metal. • Electron transfer is faster in low coordinative environment of Cu. • CO formation is more favorable on Cu sites with even coordination number. • Cu at coordination number two has a over potential of −0.35 V. - Abstract: Metal cluster, at sub-nanometer level has a unique property in the activation of small molecules, in contrast to that of bulk surface. In the present work, singly exposed active site of copper metal cluster at sub-nanometer level was designed to arrive at the energy minimised configurations, binding energy, electrostatic potential map, frontier molecular orbitals and partial density of states. The ab initio molecular dynamics was carried out to probe the catalytic nature of the cluster. Further, the stability of the metal cluster and its catalytic activity in the electrochemical reduction of CO{sub 2} to CO were evaluated by means of computational hydrogen electrode via calculation of the free energy profile using DFT/B3LYP level of theory in vacuum. The activity of the cluster is ascertained from the fact that the copper atom, present in a two coordinative environment, performs a more selective conversion of CO{sub 2} to CO at an applied potential of −0.35 V which is comparatively lower than that of higher coordinative sites. The present study helps to design any sub-nano level metal catalyst for electrochemical reduction of CO{sub 2} to various value added chemicals.

  5. Computational evaluation of sub-nanometer cluster activity of singly exposed copper atom with various coordinative environment in catalytic CO2 transformation

    Science.gov (United States)

    Shanmugam, Ramasamy; Thamaraichelvan, Arunachalam; Ganesan, Tharumeya Kuppusamy; Viswanathan, Balasubramanian

    2017-02-01

    Metal cluster, at sub-nanometer level has a unique property in the activation of small molecules, in contrast to that of bulk surface. In the present work, singly exposed active site of copper metal cluster at sub-nanometer level was designed to arrive at the energy minimised configurations, binding energy, electrostatic potential map, frontier molecular orbitals and partial density of states. The ab initio molecular dynamics was carried out to probe the catalytic nature of the cluster. Further, the stability of the metal cluster and its catalytic activity in the electrochemical reduction of CO2 to CO were evaluated by means of computational hydrogen electrode via calculation of the free energy profile using DFT/B3LYP level of theory in vacuum. The activity of the cluster is ascertained from the fact that the copper atom, present in a two coordinative environment, performs a more selective conversion of CO2 to CO at an applied potential of -0.35 V which is comparatively lower than that of higher coordinative sites. The present study helps to design any sub-nano level metal catalyst for electrochemical reduction of CO2 to various value added chemicals.

  6. Coordinating Shared Activities

    Science.gov (United States)

    Clement, Bradley

    2004-01-01

    Shared Activity Coordination (ShAC) is a computer program for planning and scheduling the activities of an autonomous team of interacting spacecraft and exploratory robots. ShAC could also be adapted to such terrestrial uses as helping multiple factory managers work toward competing goals while sharing such common resources as floor space, raw materials, and transports. ShAC iteratively invokes the Continuous Activity Scheduling Planning Execution and Replanning (CASPER) program to replan and propagate changes to other planning programs in an effort to resolve conflicts. A domain-expert specifies which activities and parameters thereof are shared and reports the expected conditions and effects of these activities on the environment. By specifying these conditions and effects differently for each planning program, the domain-expert subprogram defines roles that each spacecraft plays in a coordinated activity. The domain-expert subprogram also specifies which planning program has scheduling control over each shared activity. ShAC enables sharing of information, consensus over the scheduling of collaborative activities, and distributed conflict resolution. As the other planning programs incorporate new goals and alter their schedules in the changing environment, ShAC continually coordinates to respond to unexpected events.

  7. Trends in the Catalytic CO Oxidation Activity of Nanoparticles

    DEFF Research Database (Denmark)

    Nørskov, Jens Kehlet; Falsig, Hanne; Larsen, Britt Hvolbæk

    2008-01-01

    Going for gold: Density functional calculations show how gold nanoparticles are more active catalysts for CO oxidation than other metal nanoparticles. The high catalytic activity of nanosized gold clusters at low temperature is found to be related to the ability of low-coordinate metal atoms...

  8. Computational Introduction of Catalytic Activity into Proteins.

    Science.gov (United States)

    Bertolani, Steve J; Carlin, Dylan Alexander; Siegel, Justin B

    2016-01-01

    Recently, there have been several successful cases of introducing catalytic activity into proteins. One method that has been used successfully to achieve this is the theozyme placement and enzyme design algorithms implemented in Rosetta Molecular Modeling Suite. Here, we illustrate how to use this software to recapitulate the placement of catalytic residues and ligand into a protein using a theozyme, protein scaffold, and catalytic constraints as input.

  9. Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

    OpenAIRE

    Satoshi Kamiguchi; Sayoko Nagashima; Teiji Chihara

    2014-01-01

    Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the clu...

  10. Argumentation for coordinating shared activities

    Science.gov (United States)

    Clement, Bradley J.; Barrett, Anthony C.; Schaffer, Steven R.

    2004-01-01

    an increasing need for space missions to be able to collaboratively (and competitively) develop plans both within and across missions. In addition, interacting spacecraft that interleave onboard planning and execution must reach consensus on their commitments to each other prior to execution. In domains where missions have varying degrees of interaction and different constraints on communication and computation, the missions will require different coordination protocols in order to efficiently reach consensus with in their imposed deadlines. We describe a Shared Activity Coordination (SHAC) framework that provides a decentralized algorithm for negotiating the scheduling of shared activities over the lifetimes of multiple agents and a foundation for customizing protocols for negotiating planner interactions. We investigate variations of a few simple protocols based on argumentation and distributed constraints satisfaction techniques and evaluate their abilities to reach consistent solutions according to computation, time, and communication costs in an abstract domain where spacecraft propose joint measurements.

  11. CO2 Activation over Catalytic Surfaces.

    Science.gov (United States)

    Álvarez, Andrea; Borges, Marta; Corral-Pérez, Juan José; Olcina, Joan Giner; Hu, Lingjun; Cornu, Damien; Huang, Rui; Stoian, Dragos; Urakawa, Atsushi

    2017-11-17

    This article describes the main strategies to activate and convert carbon dioxide (CO2 ) into valuable chemicals over catalytic surfaces. Coherent elements such as common intermediates are identified in the different strategies and concisely discussed based on the reactivity of CO2 with the aim to understand the decisive factors for selective and efficient CO2 conversion. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Method to produce catalytically active nanocomposite coatings

    Science.gov (United States)

    Erdemir, Ali; Eryilmaz, Osman Levent; Urgen, Mustafa; Kazmanli, Kursat

    2016-02-09

    A nanocomposite coating and method of making and using the coating. The nanocomposite coating is disposed on a base material, such as a metal or ceramic; and the nanocomposite consists essentially of a matrix of an alloy selected from the group of Cu, Ni, Pd, Pt and Re which are catalytically active for cracking of carbon bonds in oils and greases and a grain structure selected from the group of borides, carbides and nitrides.

  13. Method to produce catalytically active nanocomposite coatings

    Energy Technology Data Exchange (ETDEWEB)

    Erdemir, Ali; Eryilmaz, Osman Levent; Urgen, Mustafa; Kazmanli, Kursat

    2017-12-19

    A nanocomposite coating and method of making and using the coating. The nanocomposite coating is disposed on a base material, such as a metal or ceramic; and the nanocomposite consists essentially of a matrix of an alloy selected from the group of Cu, Ni, Pd, Pt and Re which are catalytically active for cracking of carbon bonds in oils and greases and a grain structure selected from the group of borides, carbides and nitrides.

  14. Catalytic oxidation of zinc/sulfur coordination sites in proteins by selenium compounds.

    Science.gov (United States)

    Chen, Y; Maret, W

    2001-08-01

    Zinc/thiolate (cysteine) coordination occurs in a very large number of proteins. These coordination sites are thermodynamically quite stable. Yet the redox chemistry of thiolate ligands confers extraordinary reactivities on these sites. The significance of such ligand-centered reactions is that they affect the binding and release of zinc, thus helping to distribute zinc, and perhaps controlling zinc-dependent cellular events. One new aspect focuses on the thiolate ligands of zinc as targets for the redox action of selenium compounds. A distinctive feature of this chemistry is the capacity of selenols to catalyze the oxidation of zinc/thiolate sites. We here use a chromophoric compound, 2-nitrophenylselenocyanate, to investigate its reaction mechanism with the zinc/thiolate clusters of metallothionein, a protein that is a cellular reservoir for zinc and together with its apoprotein, thionein, is involved in zinc distribution as a zinc donor/acceptor pair. The reaction is particularly revealing as it occurs in two steps. A selenenylsulfide intermediate is formed in the fast oxidative step, followed by the generation of 2-nitrophenylselenol that initiates the second, catalytic step. The findings demonstrate the high reactivity of selenium compounds with zinc/thiolate coordination sites and the potent catalytic roles that selenoproteins and selenium redox drugs may have in affecting gene expression via modulation of the zinc content of zinc finger proteins.

  15. Catalytic

    Directory of Open Access Journals (Sweden)

    S.A. Hanafi

    2014-03-01

    Full Text Available A series of dealuminated Y-zeolites impregnated by 0.5 wt% Pt catalysts promoted by different amounts of Ni, Pd or Cr (0.3 and 0.6 wt% were prepared and characterized as hydrocracking catalysts. The physicochemical and structural characterization of the solid catalysts were investigated and reported through N2 physisorption, XRD, TGA-DSC, FT-IR and TEM techniques. Solid catalysts surface acidities were investigated through FT-IR spectroscopy aided by pyridine adsorption. The solid catalytic activities were evaluated through hydroconversion of n-hexane and n-heptane employing micro-catalytic pulse technique directly connected to a gas chromatograph analyzer. The thermal stability of the solids was also investigated up to 800 °C. Crystallinity studies using the XRD technique of all modified samples proved analogous to the parent Y-zeolite, exhibiting nearly an amorphous and microcrystalline character of the second metal oxides. Disclosure of bimetallic catalysts crystalline characterization, through XRD, was not viable. The nitrogen adsorption–desorption isotherms for all samples concluded type I adsorption isotherms, without any hysteresis loop, indicating that the entire pore system is composed of micropores. TEM micrographs of the solid catalysts demonstrate well-dispersed Pt, Ni and Cr nanoparticles having sizes of 2–4 nm and 7–8 nm, respectively. The catalytic activity results indicate that the bimetallic (0.5Pt–0.3Cr/D18H–Y catalyst is the most active towards n-hexane and n-heptane isomerization while (0.5Pt–0.6Ni/D18H–Y catalyst can be designed as most suitable as a cracking catalyst.

  16. Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

    Directory of Open Access Journals (Sweden)

    Satoshi Kamiguchi

    2014-04-01

    Full Text Available Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the cluster framework is retained up to 350–450 °C. One of the active sites is a Brønsted acid resulting from a hydroxo ligand that is produced by the elimination of hydrogen halide from the halogen and aqua ligands. The other active site is a coordinatively unsaturated metal, which can be isoelectronic with the platinum group metals by taking two or more electrons from the halogen ligands. In the case of the rhenium chloride cluster Re3Cl9, the cluster framework is stable at least up to 300 °C under inert atmosphere; however, it is reduced to metallic rhenium at 250–300 °C under hydrogen. The activated clusters are characterized by X-ray diffraction analyses, Raman spectrometry, extended X-ray absorption fine structure analysis, thermogravimetry–differential thermal analysis, infrared spectrometry, acid titration with Hammett indicators, and elemental analyses.

  17. Coordination kinetics of different metal ions with the amidoximated polyacrylonitrile nanofibrous membranes and catalytic behaviors of their complexes

    Energy Technology Data Exchange (ETDEWEB)

    Li, Fu; Dong, Yong Chun; Kang, Wei Min; Cheng, Bowen; Qu, Xiang; Cui, Guixin [School of Textiles, Tianjin Polytechnic University, Tianjin (China)

    2016-12-15

    Two transition metal ions (Fe{sup 3+} and Cu{sup 2+}) and a rare earth metal ion (Ce{sup 3+}) were selected to coordinate with amidoximated polyacrylonitrile (PAN) nanofibrous membrane for preparing three metal modified PAN nanofibrous membrane complexes (M-AO-n-PANs, M = Fe, Cu, or Ce) as the heterogeneous Fenton catalysts for the dye degradation in water under visible irradiation. The coordination kinetics of three metal ions with modified PAN nanofibrous membranes was studied and the catalytic properties of the resulting complexes were also compared. The results indicated that increasing metal ion concentrations in solution or higher coordination temperature led to a significant increase in metal content, particularly in Fe and Cu contents of the complexes. Their coordination process could be described using Langmuir isotherm and pseudo-second-order kinetic equations. Moreover, Fe-AO-n-PAN had the best photocatalytic efficiency for the dye degradation in acidic medium, but a lower photocatalytic activity than Cu-AO-n-PAN in alkali medium.

  18. 20 CFR 631.37 - Coordination activities.

    Science.gov (United States)

    2010-04-01

    ... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false Coordination activities. 631.37 Section 631.37 Employees' Benefits EMPLOYMENT AND TRAINING ADMINISTRATION, DEPARTMENT OF LABOR PROGRAMS UNDER TITLE III OF THE JOB TRAINING PARTNERSHIP ACT State Administration § 631.37 Coordination activities. (a...

  19. Coordinated Neuronal Activity Enhances Corticocortical Communication.

    Science.gov (United States)

    Zandvakili, Amin; Kohn, Adam

    2015-08-19

    Relaying neural signals between cortical areas is central to cognition and sensory processing. The temporal coordination of activity in a source population has been suggested to determine corticocortical signaling efficacy, but others have argued that coordination is functionally irrelevant. We reasoned that if coordination significantly influenced signaling, spiking in downstream networks should be preceded by transiently elevated coordination in a source population. We developed a metric to quantify network coordination in brief epochs, and applied it to simultaneous recordings of neuronal populations in cortical areas V1 and V2 of the macaque monkey. Spiking in the input layers of V2 was preceded by brief epochs of elevated V1 coordination, but this was not the case in other layers of V2. Our results indicate that V1 coordination influences its signaling to direct downstream targets, but that coordinated V1 epochs do not propagate through multiple downstream networks as in some corticocortical signaling schemes. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Synthesis, characterization and study of catalytic activity of Silver ...

    Indian Academy of Sciences (India)

    Catalytic activity was tested using liquid-phase selective oxidation of benzylic alcohols to aldehydes. The influence of some parameters such as optimum weight of Ag, catalyst dosage, oxidant and various solvents were studied. The superior catalytic performance of the Ag/ZnO nanocomposite was observed in microwave ...

  1. Synthesis, Characterization, and Catalytic Activity of Pd(II Salen-Functionalized Mesoporous Silica

    Directory of Open Access Journals (Sweden)

    Rotcharin Sawisai

    2017-01-01

    Full Text Available Salen ligand synthesized from 2-hydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde was used as a palladium chelating ligand for the immobilization of the catalytic site. Mesoporous silica supported palladium catalysts were prepared by immobilizing Pd(OAc2 onto a mesoporous silica gel through the coordination of the imine-functionalized mesoporous silica gel. The prepared catalysts were characterized by X-ray diffraction (XRD, scanning electron microscopy (SEM, energy dispersive X-ray (EDX, inductivity couple plasma (ICP, nitrogen adsorption-desorption, and Fourier transform infrared (FT-IR spectroscopy. The solid catalysts showed higher activity for the hydroamination of C-(tetra-O-acetyl-β-D-galactopyranosylallene with aromatic amines compared with the corresponding homogenous catalyst. The heterogeneous catalytic system can be easily recovered by simple filtration and reused for up to five cycles with no significant loss of catalytic activity.

  2. Understanding the catalytic activity of nanoporous gold: Role of twinning in fcc lattice

    Science.gov (United States)

    Krajčí, Marian; Kameoka, Satoshi; Tsai, An-Pang

    2017-07-01

    Nanoporous gold (NPG) prepared by de-alloying Al2Au exhibits correlation between the high catalytic reactivity towards CO oxidation and the density of twinning defects in the fcc lattice of NPG. It was also discovered that on the internal surface of NPG, quite common twinning defects can create close-packed rows of six-coordinated catalytically active Au atoms denoted as W-chains. In this work, using density functional theory methods, we investigate energy conditions for formation, thermal stability, and chemical reactivity of these active sites. The possibility of dioxygen chemisorption on various surface sites is studied in detail. A contribution from the dispersion interactions is also considered. The calculated surface density of the active six-coordinated atoms in NPG comparable with that of supported gold nanoparticle catalysts, exothermic chemisorption of dioxygen, and the energy profiles of reaction pathways for CO oxidation indicate that the six-coordinated sites created by twinning can significantly contribute to the catalytic activity of NPG.

  3. Catalytic activities of zeolite compounds for decomposing aqueous ozone.

    Science.gov (United States)

    Kusuda, Ai; Kitayama, Mikito; Ohta, Yoshio

    2013-12-01

    The advanced oxidation process (AOP), chemical oxidation using aqueous ozone in the presence of appropriate catalysts to generate highly reactive oxygen species, offers an attractive option for removing poorly biodegradable pollutants. Using the commercial zeolite powders with various Si/Al ratios and crystal structures, their catalytic activities for decomposing aqueous ozone were evaluated by continuously flowing ozone to water containing the zeolite powders. The hydrophilic zeolites (low Si/Al ratio) with alkali cations in the crystal structures were found to possess high catalytic activity for decomposing aqueous ozone. The hydrophobic zeolite compounds (high Si/Al ratio) were found to absorb ozone very well, but to have no catalytic activity for decomposing aqueous ozone. Their catalytic activities were also evaluated by using the fixed bed column method. When alkali cations were removed by acid rinsing or substituted by alkali-earth cations, the catalytic activities was significantly deteriorated. These results suggest that the metal cations on the crystal surface of the hydrophilic zeolite would play a key role for catalytic activity for decomposing aqueous ozone. Copyright © 2013 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

  4. Coordinated Voltage Control of Active Distribution Network

    Directory of Open Access Journals (Sweden)

    Xie Jiang

    2016-01-01

    Full Text Available This paper presents a centralized coordinated voltage control method for active distribution network to solve off-limit problem of voltage after incorporation of distributed generation (DG. The proposed method consists of two parts, it coordinated primal-dual interior point method-based voltage regulation schemes of DG reactive powers and capacitors with centralized on-load tap changer (OLTC controlling method which utilizes system’s maximum and minimum voltages, to improve the qualified rate of voltage and reduce the operation numbers of OLTC. The proposed coordination has considered the cost of capacitors. The method is tested using a radial edited IEEE-33 nodes distribution network which is modelled using MATLAB.

  5. Resolving the Structure of Active Sites on Platinum Catalytic Nanoparticles

    DEFF Research Database (Denmark)

    Chang, Lan Yun; Barnard, Amanda S.; Gontard, Lionel Cervera

    2010-01-01

    Accurate understanding of the structure of active sites is fundamentally important in predicting catalytic properties of heterogeneous nanocatalysts. We present an accurate determination of both experimental and theoretical atomic structures of surface monatomic steps on industrial platinum...... nanoparticles. This comparison reveals that the edges of nanoparticles can significantly alter the atomic positions of monatomic steps in their proximity, which can lead to substantial deviations in the catalytic properties compared with the extended surfaces....

  6. Coordination and standardization of federal sedimentation activities

    Science.gov (United States)

    Glysson, G. Douglas; Gray, John R.

    1997-01-01

    In August 1964, the Bureau of the Budget issued Circular A-67 to set forth guidelines for the coordination of water-data acquisition activities throughout the Federal government. The U.S. Department of the Interior was assigned the task of implementing Circular A-67, which in turn redelegated this responsibility to the U.S. Geological Survey (USGS). Delegation of the lead responsibility for water-data coordination to the USGS occurred because of its historical role as the primary agency for water-data acquisition in the United States. To provide overall leadership for implementing the provisions of Circular A-67, the USGS established the Office of Water Data Coordination in the Water Resources Division (WRD). In addition, regional and district offices of the WRD were delegated responsibility for coordinating water data within their geographic areas of responsibility. On December 10, 1991, the Office of Management and Budget issued OMB Number Memorandum M-92-01, which expands the USGS's coordination role to encompass all water information. This includes data critical to water resources in the following categories: - surface- and ground-water quality and quantity,

  7. Structural assessment and catalytic consequences of the oxygen coordination environment in grafted Ti-calixarenes.

    Science.gov (United States)

    Notestein, Justin M; Andrini, Leandro R; Kalchenko, Vitaly I; Requejo, Felix G; Katz, Alexander; Iglesia, Enrique

    2007-02-07

    Calixarene-Ti complexes were grafted onto SiO2 (0.18-0.24 Ti nm-2) to form isolated and accessible Ti centers persistently coordinated to multidentate calixarene ligands. Grafted Ti-tert-butylcalix[4]arenes gave Ti K-edge absorption spectra with pre-edge features at 4968.6-4968.9 eV, independently of Ti surface density and of their use in epoxidation catalysis. The structure and reactivity of grafted Ti-calix[4]arenes were weakly dependent on thermal treatment below 573 K, and the relative epoxidation rates of trans- and cis-alkenes showed that calixarene ligands did not restrict access to Ti centers more than corresponding calcined Ti-SiO2 materials. For all materials, 13C NMR and UV-visible spectroscopies confirmed the presence of Ti-O-Si connectivity and identical ligand-to-metal transitions. Grafted Ti-homooxacalix[3]arene complexes, however, gave weaker pre-edge features at higher energies ( approximately 4969.5 eV), consistent with greater Ti 3d occupancy and coordination numbers greater than four, and 20-fold lower cyclohexene epoxidation rate constants (per Ti) than on calix[4]arene-based materials. These different rates and near-edge spectra result from aldehyde formation caused by unimolecular cleavage of ether linkages in homooxacalix[3]arene ligands during grafting, leading to higher coordination and electron density at Ti centers. Materials based on tert-butylcalix[4]arene and homooxacalix[3]arenes led to similar epoxidation rates and near-edge spectra after calcination, consistent with the conversion of both materials to isolated Ti centers with identical structure. These materials provide a systematic approach for relating oxidation reactivity to Ti 3d occupancy, a descriptor of Lewis acid strength, and Ti coordination, because they provide Ti centers with varying electron density and coordination, but maintain accessible active centers with uniform structure and unrestricted access to reactants.

  8. Effect of support on the catalytic activity of manganese oxide catalyts for toluene combustion.

    Science.gov (United States)

    Pozan, Gulin Selda

    2012-06-30

    The aim of this work was to study combustion of toluene (1000ppm) over MnO(2) modified with different supports. α-Al(2)O(3) and γ-Al(2)O(3) obtained from Boehmite, γ-Al(2)O(3) (commercial), SiO(2), TiO(2) and ZrO(2) were used as commercial support materials. In view of potential interest of this process, the influence of support material on the catalytic performance was discussed. The deposition of 9.5MnO(2) was performed by impregnation over support. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction and oxidation (TPR/TPO) and thermogravimetric analysis (TGA). The catalytic tests were carried out at atmospheric pressure in a fixed-bed flow reactor. 9.5MnO(2)/α-Al(2)O(3)(B) (synthesized from Boehmite) catalyst exhibits the highest catalytic activity, over which the toluene conversion was up to 90% at a temperature of 289°C. Considering all the characterization and reaction data reported in this study, it was concluded that the manganese state and oxygen species played an important role in the catalytic activity. Copyright © 2012 Elsevier B.V. All rights reserved.

  9. Update of technical coordinating committee activities

    Energy Technology Data Exchange (ETDEWEB)

    Alvarado, R.A.

    1995-12-31

    The Technical Coordinating Committee has its origins in the earliest days of implementing the Low-Level Radioactive Waste Policy Act. Between 1982 and 1985, individuals in several of the states felt that coordination among the states would be beneficial to all by affording states a cost-effective method for sharing ideas, discussing alternatives, and presenting solutions to common problems. At the current time, the committee comprises members from each of the sited states. Various compacts, federal agencies, and industry groups participate in committee activities. The Low-Level Management Program provides support for the committee through the provision of logistical support and limited manpower allocation. Activities of the committee have recently focused on waste treatment and minimization technologies. The committee also has worked diligently to see the review of the 3RSTAT computer code completed. The committee has taken a position on various regulatory proposals the past year. The committee expects to continue its work until new sites are brought online.

  10. Melting Phase Transitions and Catalytic Activity of Bilayer Gold Nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Yanting Wang; Sergey N. Rashkeev

    2009-06-01

    Recent experiments in oxidation catalysis indicate that bilayer gold nanostructures exhibit exceptional catalytic activity at ambient temperatures. Here we use molecular dynamics simulations to show that an unsupported bilayer gold nanocluster has a broad and mild second-order melting phase transition. The transition is characterized by an interplay between the intralayer and interlayer diffusion processes, and the transition temperature region ranges from about 300 K to 1200 K. We suggest that surface thermal instabilities of partially melted bilayer gold nanoclusters result in their exceptional catalytic activity at ambient temperatures. For gold nanoclusters with more than two layers, the melting transition temperature range narrows, and the activity of the cluster decreases due to the suppression of surface fluctuations. These results systematically explain experimental observations showing that catalytic ability of gold nanoclusters decreases with size.

  11. Natural clinoptilolite exchanged with iron: characterization and catalytic activity in nitrogen monoxide reduction

    Directory of Open Access Journals (Sweden)

    Daria Tito-Ferro

    2016-12-01

    Full Text Available The aim of this work was to characterize the natural clinoptilolite from Tasajeras deposit, Cuba, modified by hydrothermal ion-exchange with solutions of iron (II sulfate and iron (III nitrate in acid medium. Besides this, its catalytic activity to reduce nitrogen monoxide with carbon monoxide/propene in the presence of oxygen was evaluated. The characterization was performed by Mössbauer and UV-Vis diffuse reflectance spectroscopies and adsorption measurements. The obtained results lead to conclude that in exchanged samples, incorporated divalent and trivalent irons are found in octahedral coordination. Both irons should be mainly in cationic extra-framework positions inside clinoptilolite channels as charge compensating cations, and also as iron oxy-hydroxides resulting from limited hydrolysis of these cations. The iron (III exchanged samples has a larger amount of iron oxy-hydroxides agglomerates. The iron (II exchanged samples have additionally iron (II sulfate adsorbed. The catalytic activity in the nitrogen monoxide reduction is higher in the exchanged zeolites than starting. Among all samples, those exchanged of iron (II has the higher catalytic activity. This lead to outline that, main catalytically active centers are associated with divalent iron.

  12. Synthesis, characterization and study of catalytic activity of Silver ...

    Indian Academy of Sciences (India)

    The highly dispersed Ag metal particles on ZnO surface was considered to be responsible for the catalytic activity. Keywords. Ag/ZnO nanocomposite; selective oxidation; benzyl alcohol; heterogeneous catalysis. 1. Introduction. The heterogeneous catalysis is recently extended to synthetic organic chemistry for production of ...

  13. Peroxidase-like catalytic activities of ionic metalloporphyrins ...

    Indian Academy of Sciences (India)

    The efficiency order for the various PS-MTPPS was seen to be Co>Mn>Fe, with CoTPPS showing efficiency comparable to that of horseradish peroxidase. The catalytic efficiency was found to be increasing with temperature for all the catalysts. The re-usability of these PS-MTPPS systems for peroxidase-like activity was also ...

  14. Catalytic Activity Control via Crossover between Two Different Microstructures

    KAUST Repository

    Zhou, Yuheng

    2017-09-08

    Metal nanocatalysts hold great promise for a wide range of heterogeneous catalytic reactions, while the optimization strategy of catalytic activity is largely restricted by particle size or shape control. Here, we demonstrate that a reversible microstructural control through the crossover between multiply-twinned nanoparticle (MTP) and single crystal (SC) can be readily achieved by solvent post-treatment on gold nanoparticles (AuNPs). Polar solvents (e.g. water, methanol) direct the transformation from MTP to SC accompanied by the disappearance of twinning and stacking faults. A reverse transformation from SC to MTP is achieved in non-polar solvent (e.g. toluene) mixed with thiol ligands. The transformation between two different microstructures is directly observed by in-situ TEM and leads to a drastic modulation of catalytic activity towards the gas-phase selective oxidation of alcohols. There is a quasi-linear relationship between TOFs and MTP concentrations. Based on the combined experimental and theoretical investigations of alcohol chemisorption on these nanocatalysts, we propose that the exposure of {211}-like microfacets associated with twin boundaries and stack faults accounts for the strong chemisorption of alcohol molecules on MTP AuNPs and thus the exceptionally high catalytic activity.

  15. Catalytic Ethanol Dehydration over Different Acid-activated Montmorillonite Clays.

    Science.gov (United States)

    Krutpijit, Chadaporn; Jongsomjit, Bunjerd

    2016-01-01

    In the present study, the catalytic dehydration of ethanol to obtain ethylene over montmorillonite clays (MMT) with mineral acid activation including H2SO4 (SA-MMT), HCl (HA-MMT) and HNO3 (NA-MMT) was investigated at temperature range of 200 to 400°C. It revealed that HA-MMT exhibited the highest catalytic activity. Ethanol conversion and ethylene selectivity were found to increase with increased reaction temperature. At 400°C, the HA-MMT yielded 82% of ethanol conversion having 78% of ethylene yield. At lower temperature (i.e. 200 to 300°C), diethyl ether (DEE) was a major product. The highest activity obtained from HA-MMT can be attributed to an increase of weak acid sites and acid density by the activation of MMT with HCl. It can be also proven by various characterization techniques that in most case, the main structure of MMT did not alter by acid activation (excepted for NA-MMT). Upon the stability test for 72 h during the reaction, the MMT and HA-MMT showed only slight deactivation due to carbon deposition. Hence, the acid activation of MMT by HCl is promising to enhance the catalytic dehydration of ethanol.

  16. Thrombomodulin binding selects the catalytically active form of thrombin

    Science.gov (United States)

    Handley, Lindsey D.; Treuheit, Nicholas A.; Venkatesh, Varun J.; Komives, Elizabeth A.

    2015-01-01

    Human α-thrombin is a serine protease with dual functions. Thrombin acts as a procoagulant, cleaving fibrinogen to make the fibrin clot, but when bound to thrombomodulin (TM), it acts as an anticoagulant, cleaving protein C. A minimal TM fragment consisting of the 4th, 5th, and most of the 6th EGF-like domain (TM456m) has been prepared that has much improved solubility, thrombin-binding capacity, and anticoagulant activity over previous TM456 constructs. In the present work we compare backbone amide exchange of human α-thrombin in three states: apo, PPACK-bound, and TM456m-bound. Beyond causing decreased amide exchange at their binding sites, TM and PPACK both cause decreased amide exchange in regions more distant from the active site, within the γ-loop and the adjacent N-terminus of the heavy chain. The decreased amide exchange in the N-terminus of the heavy chain is consistent with the historic model of activation of serine proteases, which involves insertion of this region into the β-barrel promoting the correct conformation of the catalytic residues. Contrary to crystal structures of thrombin, HDXMS results suggest that the conformation of apo-thrombin does not yet have the N-terminus of the heavy chain properly inserted for optimal catalytic activity, and that binding of TM allosterically promotes the catalytically active conformation. PMID:26468766

  17. Thrombomodulin Binding Selects the Catalytically Active Form of Thrombin.

    Science.gov (United States)

    Handley, Lindsey D; Treuheit, Nicholas A; Venkatesh, Varun J; Komives, Elizabeth A

    2015-11-03

    Human α-thrombin is a serine protease with dual functions. Thrombin acts as a procoagulant, cleaving fibrinogen to make the fibrin clot, but when bound to thrombomodulin (TM), it acts as an anticoagulant, cleaving protein C. A minimal TM fragment consisting of the fourth, fifth, and most of the sixth EGF-like domain (TM456m) that has been prepared has much improved solubility, thrombin binding capacity, and anticoagulant activity versus those of previous TM456 constructs. In this work, we compare backbone amide exchange of human α-thrombin in three states: apo, D-Phe-Pro-Arg-chloromethylketone (PPACK)-bound, and TM456m-bound. Beyond causing a decreased level of amide exchange at their binding sites, TM and PPACK both cause a decreased level of amide exchange in other regions including the γ-loop and the adjacent N-terminus of the heavy chain. The decreased level of amide exchange in the N-terminus of the heavy chain is consistent with the historic model of activation of serine proteases, which involves insertion of this region into the β-barrel promoting the correct conformation of the catalytic residues. Contrary to crystal structures of thrombin, hydrogen-deuterium exchange mass spectrometry results suggest that the conformation of apo-thrombin does not yet have the N-terminus of the heavy chain properly inserted for optimal catalytic activity, and that binding of TM allosterically promotes the catalytically active conformation.

  18. Finely tunable fabrication and catalytic activity of gold multipod nanoparticles.

    Science.gov (United States)

    Choi, Soon; Moon, Youngseo; Yoo, Hyojong

    2016-05-01

    Gold multipod nanoparticles (Au Multipod NPs) containing multi-branches with sharp edges and tips were synthesized in high yield through a facile seed-mediated method using cetyltrimethylammonium bromide (CTAB), Brij35, Au seed nanoparticles, Ag(+) ions, ascorbic acid, and sodium salicylate. The branch lengths of Au Multipod NPs were finely controlled by adjusting the molar ratio of mixed surfactants, and in particular by changing the amount of sodium salicylate. A formation mechanism for the star-shaped topologies was proposed and experimentally proved. The catalytic activity of the synthesized Au Multipod NPs was evaluated in ethanol electrooxidation reaction. The dependence of the catalytic performances on the nanostructural morphology was investigated. Copyright © 2016 Elsevier Inc. All rights reserved.

  19. Structured catalysts and reactors for three phase catalytic reactions: manipulating activity and selectivity in nitrite hydrogenation

    NARCIS (Netherlands)

    Brunet Espinosa, Roger

    2016-01-01

    This work aimed at fabricating structured catalytic reactors for fast multiphase reactions, namely, nitrite hydrogenation and H2O2 decomposition. These reactors allowed a better understanding of these reactions and an improvement in terms of catalytic activity and selectivity.

  20. Reconstituted IMPDH polymers accommodate both catalytically active and inactive conformations.

    Science.gov (United States)

    Anthony, Sajitha A; Burrell, Anika L; Johnson, Matthew C; Duong-Ly, Krisna C; Kuo, Yin-Ming; Simonet, Jacqueline C; Michener, Peter; Andrews, Andrew; Kollman, Justin M; Peterson, Jeffrey R

    2017-08-09

    Several metabolic enzymes undergo reversible polymerization into macromolecular assemblies. The function of these assemblies is often unclear but in some cases they regulate enzyme activity and metabolic homeostasis. The guanine nucleotide biosynthetic enzyme inosine monophosphate dehydrogenase (IMPDH) forms octamers that polymerize into helical chains. In mammalian cells, IMPDH filaments can associate into micron-length assemblies. Polymerization and enzyme activity are regulated in part by binding of purine nucleotides to an allosteric regulatory domain. ATP promotes octamer polymerization, whereas GTP promotes a compact, inactive conformation whose ability to polymerize is unknown. Also unclear is whether polymerization directly alters IMPDH catalytic activity. To address this, we identified point mutants of human IMPDH2 that either prevent or promote polymerization. Unexpectedly, we found that polymerized and non-assembled forms of recombinant IMPDH have comparable catalytic activity, substrate affinity, and GTP sensitivity and validated this finding in cells. Electron microscopy revealed that substrates and allosteric nucleotides shift the equilibrium between active and inactive conformations in both the octamer and the filament. Unlike other metabolic filaments, which selectively stabilize active or inactive conformations, recombinant IMPDH filaments accommodate multiple states. These conformational states are finely tuned by substrate availability and purine balance, while polymerization may allow cooperative transitions between states. © 2017 by The American Society for Cell Biology.

  1. Heterogeneous Catalysis "On Demand": Mechanically Controlled Catalytic Activity of a Metal Surface.

    Science.gov (United States)

    Mazur, Tomasz; Lach, Slawomir; Grzybowski, Bartosz A

    2017-12-27

    A metal surface passivated with a tightly packed self-assembled monolayer (SAM) can be made catalytically active upon the metal's mechanical deformation. This deformation renders the SAM sparser and exposes additional catalytic sites on the metal's surface. If the deformation is elastic, return of the metal to the original shape "heals" the SAM and nearly extinguishes the catalytic activity. Kelvin probe force microscopy and theoretical considerations both indicate that the catalytic domains "opening up" in the deformed SAM are of nanoscopic dimensions.

  2. Modeling Students' Units Coordinating Activity

    Science.gov (United States)

    Boyce, Steven James

    2014-01-01

    Primarily via constructivist teaching experiment methodology, "units coordination" (Steffe, 1992) has emerged as a useful construct for modeling students' psychological constructions pertaining to several mathematical domains, including counting sequences, whole number multiplicative conceptions, and fractions schemes. I describe how…

  3. Flexible macrocycles as versatile supports for catalytically active metal clusters

    Energy Technology Data Exchange (ETDEWEB)

    Ryan, JD; Gagnon, KJ; Teat, SJ; McIntosh, RD

    2016-02-12

    Here we present three structurally diverse clusters stabilised by the same macrocyclic polyphenol; t-butylcalix[8]arene. This work demonstrates the range of conformations the flexible ligand is capable of adopting, highlighting its versatility in metal coordination. In addition, a Ti complex displays activity for the ring-opening polymerisation of lactide

  4. High-energy coordination polymers (CPs) exhibiting good catalytic effect on the thermal decomposition of ammonium dinitramide

    Science.gov (United States)

    Li, Xin; Han, Jing; Zhang, Sheng; Zhai, Lianjie; Wang, Bozhou; Yang, Qi; Wei, Qing; Xie, Gang; Chen, Sanping; Gao, Shengli

    2017-09-01

    High-energy coordination polymers (CPs) not only exhibit good energetic performances but also have a good catalytic effect on the thermal decomposition of energetic materials. In this contribution, two high-energy CPs Cu2(DNBT)2(CH3OH)(H2O)3·3H2O (1) and [Cu3(DDT)2(H2O)2]n (2) (H2DNBT = 3,3‧-dinitro-5,5‧-bis(1H-1,2,4-triazole and H3DDT = 4,5-bis(1H-tetrazol-5-yl)-2H-1,2,3-triazole) were synthesized and structurally characterized. Furthermore, 1 was thermos-dehydrated to produce Cu2(DNBT)2(CH3OH)(H2O)3 (1a). The thermal decomposition kinetics of 1, 1a and 2 were studied by Kissinger's method and Ozawa's method. Thermal analyses and sensitivity tests show that all compounds exhibit high thermal stability and low sensitivity for external stimuli. Meanwhile, all compounds have large positive enthalpy of formation, which are calculated as being (1067.67 ± 2.62) kJ mol-1 (1), (1464.12 ± 3.12) kJ mol-1 (1a) and (3877.82 ± 2.75) kJ mol-1 (2), respectively. The catalytic effects of 1a and 2 on the thermal decomposition of ammonium dinitramide (ADN) were also investigated.

  5. Intramolecular Crosstalk between Catalytic Activities of Receptor Kinases

    KAUST Repository

    Kwezi, Lusisizwe

    2018-01-22

    Signal modulation is important for the growth and development of plants and this process is mediated by a number of factors including physiological growth regulators and their associated signal transduction pathways. Protein kinases play a central role in signaling, including those involving pathogen response mechanisms. We previously demonstrated an active guanylate cyclase (GC) catalytic center in the brassinosteroid insensitive receptor (AtBRI1) within an active intracellular kinase domain resulting in dual enzymatic activity. Here we propose a novel type of receptor architecture that is characterized by a functional GC catalytic center nested in the cytosolic kinase domain enabling intramolecular crosstalk. This may be through a cGMP-AtBRI1 complex forming that may induce a negative feedback mechanism leading to desensitisation of the receptor, regulated through the cGMP production pathway. We further argue that the comparatively low but highly localized cGMP generated by the GC in response to a ligand is sufficient to modulate the kinase activity. This type of receptor therefore provides a molecular switch that directly and/or indirectly affects ligand dependent phosphorylation of downstream signaling cascades and suggests that subsequent signal transduction and modulation works in conjunction with the kinase in downstream signaling.

  6. Activity of catalytic silver nanoparticles modulated by capping agent hydrophobicity.

    Science.gov (United States)

    Janani, Seralathan; Stevenson, Priscilla; Veerappan, Anbazhagan

    2014-05-01

    In this paper, a facile in situ method is reported for the preparation of catalytic silver nanoparticles (AgNPs) using N-acyl tyramine (NATA) with variable hydrophobic acyl length. Scanning electron microscopic analysis shows that NATA exists initially as larger aggregates in alkaline aqueous solution. The addition of AgNO3 dissociates these larger aggregate and subsequently promotes the formation of self-assembled NATA and AgNPs. Characterization of AgNPs using UV-vis spectroscopy, scanning electron microscope and transmission electron microscope revealed that the hydrophobic acyl chain length of NATA does not influence the particle size, shape and morphology. All NATA-AgNPs yielded relatively identical values in full width at half-maximum (FWHM) analysis, indicating that the AgNPs prepared with NATA are relatively polydispersed at all tested acyl chain lengths. These nanoparticles are able to efficiently catalyze the reduction of 4-nitro phenol to 4-amino phenol, 2-nitro aniline to 1,2-diamino benzene, 2,4,6-trinitro phenol to 2,4,6-triamino phenol by NaBH4 in an aqueous environment. The reduction reaction rate is determined to be pseudo-first order and the apparent rate constant is linearly dependent on the hydrophobic acyl chain length of the NATA. All reaction kinetics presented an induction period, which is dependent on the N-acyl chain length, indicating that the hydrophobic effects play a critical role in bringing the substrate to the metal nanoparticle surface to induce the catalytic reaction. In this study, however, the five catalytic systems have similar size and polydispersity, differing only in terms of capping agent hydrophobicity, and shows different catalytic activity with respect to the alkyl chain length of the capping agent. As discussed, the ability to modulate the metal nanoparticles catalytic property, by modifying the capping agent hydrophobicity represents a promising future for developing an efficient nanocatalyst without altering the size

  7. Protein composition of catalytically active human telomerase from immortal cells

    DEFF Research Database (Denmark)

    Cohen, Scott B; Graham, Mark E; Lovrecz, George O

    2007-01-01

    Telomerase is a ribonucleoprotein enzyme complex that adds 5'-TTAGGG-3' repeats onto the ends of human chromosomes, providing a telomere maintenance mechanism for approximately 90% of human cancers. We have purified human telomerase approximately 10(8)-fold, with the final elution dependent...... on the enzyme's ability to catalyze nucleotide addition onto a DNA oligonucleotide of telomeric sequence, thereby providing specificity for catalytically active telomerase. Mass spectrometric sequencing of the protein components and molecular size determination indicated an enzyme composition of two molecules...... each of telomerase reverse transcriptase, telomerase RNA, and dyskerin....

  8. [Penicillin acylase from Escherichia coli: catalytically active subunits].

    Science.gov (United States)

    Kabakov, V E; Kliachko, N L; Levashov, A V

    1995-05-01

    Gel filtration under denaturing conditions was used to isolate the alpha- and beta-subunits of penicillin acylase (PA). Refolded subunits were obtained through removing urea by dialysis. Both renatured subunits were catalytically active during hydrolysis of phenylacetic acid p-nitroanilide; this activity decreased after addition of a serine-specific inhibitor--phenylmethanesulfonyl fluoride. The subunits were also active in reversed micelles of Aerosol OT (AOT) in octane, the optimum hydration degree being 11.9 and 17.5 for the light (alpha) and heavy (beta) subunits, respectively. The positions of the maxima were consistent with both theoretically calculated optimum hydration degrees and the earlier reported profile of enzymatic activity for native PA in reversed micelles.

  9. Cycloaddition of CO 2 to challenging N -tosyl aziridines using a halogen-free niobium complex: Catalytic activity and mechanistic insights

    KAUST Repository

    Arayachukiat, Sunatda

    2017-11-06

    An efficient and facile approach to the regioselective synthesis of N-tosyloxazolidinones from the corresponding N-tosylaziridines and CO2 was developed using dual catalytic systems involving an early transition metal coordination compound as a Lewis acid and a nucleophilic cocatalyst. Among the screened Lewis acids, halogen-free niobium pentaethoxide (Nb(OEt)5) displayed the best catalytic activity when used in the presence of tetrabutylammonium iodide (TBAI). Systematic DFT calculations, supported by catalytic experiments, demonstrate that CO2 insertion is the rate determining step for this process and it is highly dependent on the steric hindrance at the niobium center.

  10. Triggering activity of catalytic rod-like supramolecular polymers.

    Science.gov (United States)

    Huerta, Elisa; van Genabeek, Bas; Lamers, Brigitte A G; Koenigs, Marcel M E; Meijer, E W; Palmans, Anja R A

    2015-02-23

    Supramolecular polymers based on benzene-1,3,5-tricarboxamides (BTAs) functionalized with an L- or D-proline moiety display high catalytic activity towards aldol reactions in water. High turnover frequencies (TOF) of up to 27×10(-4) s(-1) and excellent stereoselectivities (up to 96% de, up to 99% ee) were observed. In addition, the catalyst could be reused and remained active at catalyst loadings and substrate concentrations as low as 0.1 mol % and 50 mM, respectively. A temperature-induced conformational change in the supramolecular polymer triggers the high activity of the catalyst. The supramolecular polymer's helical sense in combination with the configuration of the proline (L- or D-) is responsible for the observed selectivity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Reactive oxygen species inhibit catalytic activity of peptidylarginine deiminase

    DEFF Research Database (Denmark)

    Damgaard, Dres; Bjørn, Mads Emil; Jensen, Peter Østrup

    2017-01-01

    on calcium and reducing conditions. However, reactive oxygen species (ROS) have been shown to induce citrullination of histones in granulocytes. Here we examine the ability of H2O2 and leukocyte-derived ROS to regulate PAD activity using citrullination of fibrinogen as read-out. H2O2 at concentrations above...... 40 µM inhibited the catalytic activity of PAD2 and PAD4 in a dose-dependent manner. PMA-stimulated leukocytes citrullinated fibrinogen and this citrullination was markedly enhanced when ROS formation was inhibited by the NADPH oxidase inhibitor diphenyleneiodonium (DPI). In contrast, PAD released...... from stimulated leukocytes was unaffected by exogenously added H2O2 at concentrations up to 1000 µM. The role of ROS in regulating PAD activity may play an important part in preventing hypercitrullination of proteins....

  12. Non-cell autonomous and non-catalytic activities of ATX in the developing brain

    Directory of Open Access Journals (Sweden)

    Raanan eGreenman

    2015-03-01

    Full Text Available The intricate formation of the cerebral cortex requires a well-coordinated series of events, which are regulated at the level of cell-autonomous and non-cell autonomous mechanisms. Whereas cell-autonomous mechanisms that regulate cortical development are well-studied, the non cell-autonomous mechanisms remain poorly understood. A non-biased screen allowed us to identify Autotaxin (ATX as a non cell-autonomous regulator of neural stem cell proliferation. ATX (also known as ENPP2 is best known to catalyze lysophosphatidic acid (LPA production. Our results demonstrate that ATX affects the localization and adhesion of neuronal progenitors in a cell autonomous and non-cell autonomous manner, and strikingly, this activity is independent from its catalytic activity in producing LPA.

  13. Non-cell autonomous and non-catalytic activities of ATX in the developing brain.

    Science.gov (United States)

    Greenman, Raanan; Gorelik, Anna; Sapir, Tamar; Baumgart, Jan; Zamor, Vanessa; Segal-Salto, Michal; Levin-Zaidman, Smadar; Aidinis, Vassilis; Aoki, Junken; Nitsch, Robert; Vogt, Johannes; Reiner, Orly

    2015-01-01

    The intricate formation of the cerebral cortex requires a well-coordinated series of events, which are regulated at the level of cell-autonomous and non-cell autonomous mechanisms. Whereas cell-autonomous mechanisms that regulate cortical development are well-studied, the non-cell autonomous mechanisms remain poorly understood. A non-biased screen allowed us to identify Autotaxin (ATX) as a non-cell autonomous regulator of neural stem cells. ATX (also known as ENPP2) is best known to catalyze lysophosphatidic acid (LPA) production. Our results demonstrate that ATX affects the localization and adhesion of neuronal progenitors in a cell autonomous and non-cell autonomous manner, and strikingly, this activity is independent from its catalytic activity in producing LPA.

  14. Coordination modes of bridge carboxylates in dinuclear manganese compounds determine their catalase-like activities.

    Science.gov (United States)

    Jiang, Xiaojun; Liu, Hui; Zheng, Bing; Zhang, Jingyan

    2009-10-28

    To explore the role of bridge carboxylate coordination modes on the catalase-like activities of dinuclear manganese compounds, [Mn(II)2(bpmapa)2(H2O)2](ClO4)2 (1), [Mn(II)2(pbpmapa)2(H2O)2](ClO4)2 (2), and [Mn(II)2(bpmaa)2(H2O)3](ClO4)2 (3) (bpmapa = [bis(2-pyridylmethyl)amino]propionic acid, pbpmapa = alpha-phenyl-beta-[bis(2-pyridylmethyl)amino]propionic acid, and bpmaa = [bis(2-pyridylmethyl)amino]acetic acid), in which Mn(II)-Mn(II) centers have a similar coordination sphere but different carboxylate-Mn bridging modes have been synthesized and structurally characterized by single X-ray diffraction, UV-visible, IR, and EPR spectroscopies, and their catalase-like activities were investigated. Studies of their catalytic activities and the influence of the nitrogenous bases on their catalytic activities indicated that the carboxylate-Mn coordination mode was crucial in H2O2 deprotonation, and eventually in H2O2 disproportionation. Compound 1 with a bidentate carboxylate bridge showed higher catalase-like activity than 2 and 3, in which the carboxylate groups have a monodentate bridging mode. The deprotonation ability of the carboxylate anion was determined by the O-C-O angle and the distance between the weakly bound oxygen of the bridging carboxylate to the manganese ion. The smaller the angle, and the shorter the distance, the stronger the basicity that the carboxylate anion exhibits. The bidentate mu-1,1 bridging coordination mode functionally mimicked the glutamate residues at the manganese catalase active site. Our results suggested that increasing the basicity of the bridging carboxylate ligand of the catalase model compounds will increase their deprotonation ability and lead to more active catalase mimics.

  15. Steric, electronic, and secondary effects on the coordination chemistry of ionic phosphine ligands and the catalytic behavior of their metal complexes

    NARCIS (Netherlands)

    Snelders, D.J.M.|info:eu-repo/dai/nl/304836257; van Koten, G.|info:eu-repo/dai/nl/073839191; Klein Gebbink, R.J.M.|info:eu-repo/dai/nl/166032646

    2011-01-01

    The effects of introducing ionic functionalities in phosphine ligands on the coordination chemistry of these ligands and the catalytic behavior of the corresponding metal complexes are reviewed. The steric and electronic consequences of such functionalizations are discussed. Apart from these steric

  16. Direct instrumental identification of catalytically active surface sites

    Science.gov (United States)

    Pfisterer, Jonas H. K.; Liang, Yunchang; Schneider, Oliver; Bandarenka, Aliaksandr S.

    2017-09-01

    The activity of heterogeneous catalysts—which are involved in some 80 per cent of processes in the chemical and energy industries—is determined by the electronic structure of specific surface sites that offer optimal binding of reaction intermediates. Directly identifying and monitoring these sites during a reaction should therefore provide insight that might aid the targeted development of heterogeneous catalysts and electrocatalysts (those that participate in electrochemical reactions) for practical applications. The invention of the scanning tunnelling microscope (STM) and the electrochemical STM promised to deliver such imaging capabilities, and both have indeed contributed greatly to our atomistic understanding of heterogeneous catalysis. But although the STM has been used to probe and initiate surface reactions, and has even enabled local measurements of reactivity in some systems, it is not generally thought to be suited to the direct identification of catalytically active surface sites under reaction conditions. Here we demonstrate, however, that common STMs can readily map the catalytic activity of surfaces with high spatial resolution: we show that by monitoring relative changes in the tunnelling current noise, active sites can be distinguished in an almost quantitative fashion according to their ability to catalyse the hydrogen-evolution reaction or the oxygen-reduction reaction. These data allow us to evaluate directly the importance and relative contribution to overall catalyst activity of different defects and sites at the boundaries between two materials. With its ability to deliver such information and its ready applicability to different systems, we anticipate that our method will aid the rational design of heterogeneous catalysts.

  17. Catalytic activity of gold on nanocrystalline diamond support

    Energy Technology Data Exchange (ETDEWEB)

    Veres, Miklos; Toth, Sara; Koos, Margit [Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, PO Box 49, 1525 Budapest (Hungary); Perevedentseva, Elena [Department of Physics, National Dong Hwa University, Hualien (Taiwan); Karmenyan, Artashes V. [Institute of Biophotonics, National Yang-Ming University, Taipei (China)

    2010-04-15

    A simple and easily realizable method was found for the preparation of supported Au catalyst by sputtering island type gold film onto nanocrystalline diamond particles, that can catalyse CO oxidation to CO{sub 2}. The oxidation of CO molecules from ambient air was observed and investigated by spectroscopic methods. Characteristic CO peaks of molecules adsorbed on gold surface and an increased intensity of the CO{sub 2} bands were detected, indicating the catalyst effect of the Au film. The catalytic efficiency was found to be dependent on the morphology of the deposited gold layer. Our measurements indicate also that CO molecules could adsorb permanently on active Au sites, leading to lowered activity of the catalyst. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Guiding catalytically active particles with chemically patterned surfaces

    Science.gov (United States)

    Uspal, William; Popescu, Mihail; Dietrich, Siegfried; Tasinkevych, Mykola

    Catalytically active Janus particles in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former leads to self-phoresis, while the latter gives rise to chemi-osmosis, providing an additional contribution to self-motility. Chemi-osmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate ``point-particle'' approach, that by chemically patterning a planar substrate (e.g., by adsorbing two different materials) one can direct the motion of Janus particles: the induced chemi-osmotic flows can cause particles to either ``dock'' at a chemical step between the two materials, or to follow a chemical stripe. These theoretical predictions are confirmed by full numerical calculations. Generically, docking occurs for particles which tend to move away from their catalytic caps, while stripe-following occurs in the opposite case. Our analysis reveals the physical mechanisms governing this behavior.

  19. Enhanced Catalysis Activity in a Coordinatively Unsaturated Cobalt-MOF Generated via Single-Crystal-to-Single-Crystal Dehydration.

    Science.gov (United States)

    Ren, Hai-Yun; Yao, Ru-Xin; Zhang, Xian-Ming

    2015-07-06

    Hydrothermal reaction of Co(NO3)2 and terphenyl-3,2",5",3'-tetracarboxyate (H4tpta) generated Co3(OH)2 chains based 3D coordination framework Co3(OH)2(tpta)(H2O)4 (1) that suffered from single-crystal-to-single-crystal dehydration by heating at 160 °C and was transformed into dehydrated Co3(OH)2(tpta) (1a). During the dehydration course, the local coordination environment of part of the Co atoms was transformed from saturated octahedron to coordinatively unsaturated tetrahedron. Heterogenous catalytic experiments on allylic oxidation of cyclohexene show that dehydrated 1a has 6 times enhanced catalytic activity than as-synthesized 1 by using tert-butyl hydroperoxide (t-BuOOH) as oxidant. The activation energy for the oxidation of cylcohexene with 1a catalyst was 67.3 kJ/mol, far below the value with 1 catalysts, which clearly suggested that coordinatively unsaturated Co(II) sites in 1a have played a significant role in decreasing the activation energy. It is interestingly found that heterogeneous catalytic oxidation of cyclohexene in 1a not only gives the higher conversion of 73.6% but also shows very high selectivity toward 2-cyclohexene-1-one (ca. 64.9%), as evidenced in high turnover numbers (ca. 161) based on the open Co(II) sites of 1a catalyst. Further experiments with a radical trap indicate a radical chain mechanism. This work demonstrates that creativity of coordinatively unsaturated metal sites in MOFs could significantly enhance heterogeneous catalytic activity and selectivity.

  20. Identification of coevolving residues and coevolution potentials emphasizing structure, bond formation and catalytic coordination in protein evolution.

    Directory of Open Access Journals (Sweden)

    Daniel Y Little

    Full Text Available The structure and function of a protein is dependent on coordinated interactions between its residues. The selective pressures associated with a mutation at one site should therefore depend on the amino acid identity of interacting sites. Mutual information has previously been applied to multiple sequence alignments as a means of detecting coevolutionary interactions. Here, we introduce a refinement of the mutual information method that: 1 removes a significant, non-coevolutionary bias and 2 accounts for heteroscedasticity. Using a large, non-overlapping database of protein alignments, we demonstrate that predicted coevolving residue-pairs tend to lie in close physical proximity. We introduce coevolution potentials as a novel measure of the propensity for the 20 amino acids to pair amongst predicted coevolutionary interactions. Ionic, hydrogen, and disulfide bond-forming pairs exhibited the highest potentials. Finally, we demonstrate that pairs of catalytic residues have a significantly increased likelihood to be identified as coevolving. These correlations to distinct protein features verify the accuracy of our algorithm and are consistent with a model of coevolution in which selective pressures towards preserving residue interactions act to shape the mutational landscape of a protein by restricting the set of admissible neutral mutations.

  1. Synthesis, crystal structures, luminescence and catalytic properties of two d¹⁰ metal coordination polymers constructed from mixed ligands.

    Science.gov (United States)

    Wang, Xiao-xiao; Zhang, Ming-xi; Yu, Baoyi; Van Hecke, Kristof; Cui, Guang-hua

    2015-03-15

    Two new coordination polymers [Cd(bmb)(hmph)]n (1), {[Ag(bmb)]·H2btc}n (2) (bmb=1,4-bis(2-methylbenzimidazol-1-ylmethyl)benzene, H2hmph=homophthalic acid, H3btc=1,3,5-benzenetetracarboxylic acid) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction methods, IR spectroscopy, TGA, XRPD and elemental analysis. Complex 1 features a 3D threefold interpenetrating dia array with a 4-connected 6(6) topology. Complex 2 shows a 1D helix chain structure connected by L1 ligands, which is finally extended into a rarely 2D 4L2 supramolecular network via C-H⋯O hydrogen bond interactions. In addition, the luminescence and catalytic properties of the two complexes for the degradation of the methyl orange azo dye in a Fenton-like process were presented. The degradation efficiency of the methyl orange azo dye for 1 and 2 are 56% and 96%, respectively. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Structural Basis for Catalytic Activation of a Serine Recombinase

    Energy Technology Data Exchange (ETDEWEB)

    Keenholtz, Ross A.; Rowland, Sally-J.; Boocock, Martin R.; Stark, W. Marshall; Rice, Phoebe A. (Glasgow); (UC)

    2014-10-02

    Sin resolvase is a site-specific serine recombinase that is normally controlled by a complex regulatory mechanism. A single mutation, Q115R, allows the enzyme to bypass the entire regulatory apparatus, such that no accessory proteins or DNA sites are required. Here, we present a 1.86 {angstrom} crystal structure of the Sin Q115R catalytic domain, in a tetrameric arrangement stabilized by an interaction between Arg115 residues on neighboring subunits. The subunits have undergone significant conformational changes from the inactive dimeric state previously reported. The structure provides a new high-resolution view of a serine recombinase active site that is apparently fully assembled, suggesting roles for the conserved active site residues. The structure also suggests how the dimer-tetramer transition is coupled to assembly of the active site. The tetramer is captured in a different rotational substate than that seen in previous hyperactive serine recombinase structures, and unbroken crossover site DNA can be readily modeled into its active sites.

  3. Mutations in the catalytic loop HRD motif alter the activity and function of Drosophila Src64.

    Directory of Open Access Journals (Sweden)

    Taylor C Strong

    Full Text Available The catalytic loop HRD motif is found in most protein kinases and these amino acids are predicted to perform functions in catalysis, transition to, and stabilization of the active conformation of the kinase domain. We have identified mutations in a Drosophila src gene, src64, that alter the three HRD amino acids. We have analyzed the mutants for both biochemical activity and biological function during development. Mutation of the aspartate to asparagine eliminates biological function in cytoskeletal processes and severely reduces fertility, supporting the amino acid's critical role in enzymatic activity. The arginine to cysteine mutation has little to no effect on kinase activity or cytoskeletal reorganization, suggesting that the HRD arginine may not be critical for coordinating phosphotyrosine in the active conformation. The histidine to leucine mutant retains some kinase activity and biological function, suggesting that this amino acid may have a biochemical function in the active kinase that is independent of its side chain hydrogen bonding interactions in the active site. We also describe the phenotypic effects of other mutations in the SH2 and tyrosine kinase domains of src64, and we compare them to the phenotypic effects of the src64 null allele.

  4. A computational modelling study of the catalytically active perovskite LaCoO3.

    OpenAIRE

    Khan, S.

    2007-01-01

    Atomistic and quantum mechanical computational modelling of the bulk and surface structures of the catalytically active perovskite LaCoC>3 have been undertaken to develop a better understanding of the processes involved during catalytic oxidation. Two catalytically important effects have been studied firstly the creation of oxygen vacancies resulting from Sr2* doping at the La3+ site or reduction of Co3+ and secondly substitution by Ce4+at the La3+ site. Bulk atomistic calculations were carri...

  5. Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

    Energy Technology Data Exchange (ETDEWEB)

    Sherly, K. B.; Rakesh, K. [Mahatma Gandhi University Regional Research Center in Chemistry, Department of Chemistry, Mar Athanasius College, Kothamangalam-686666, Kerala (India)

    2014-01-28

    Nanoscaled materials are of great interest due to their unique enhanced optical, electrical and magnetic properties. Sulfate-promoted zirconia has been shown to exhibit super acidic behavior and high activity for acid catalyzed reactions. Nanocrystalline zirconia was prepared in the presence of polysaccharide template by interaction between ZrOCl{sub 2}⋅8H{sub 2}O and chitosan template. The interaction was carried out in aqueous phase, followed by the removal of templates by calcination at optimum temperature and sulfation. The structural and textural features were characterized by powder XRD, TG, SEM and TEM. XRD patterns showed the peaks of the diffractogram were in agreement with the theoretical data of zirconia with the catalytically active tetragonal phase and average crystalline size of the particles was found to be 9 nm, which was confirmed by TEM. TPD using ammonia as probe, FTIR and BET surface area analysis were used for analyzing surface features like acidity and porosity. The BET surface area analysis showed the sample had moderately high surface area. FTIR was used to find the type species attached to the surface of zirconia. UV-DRS found the band gap of the zirconia was found to be 2.8 eV. The benzylation of o-xylene was carried out batchwise in atmospheric pressure and 433K temperature using sulfated zirconia as catalyst.

  6. Iron Coordination and Halogen-Bonding Assisted Iodosylbenzene Activation

    DEFF Research Database (Denmark)

    Wegeberg, Christina; Poulsen de Sousa, David; McKenzie, Christine

    The iron complex of the hexadentate ligand N,N,N'-tris(2-pyridylmethyl)ethylendiamine-N'-acetate (tpena) efficiently catalyzes selective oxidations of electron-rich olefins and sulfides by insoluble iodosylbenzene (PhIO). Surprisingly, these reactions are faster and more selective than homogenous...... catalytic mixtures using soluble terminal oxygen transfer agents. Isolation of a reactive iron-terminal oxidant adduct, an unique Fe(III)-OIPh complex, is facilitated by strong stabilizing supramolecular halogen-bonding. L3-edge XANES suggests +1.6 for the average oxidation state for the iodine atom3...... in the iron(III)-coordinated PhIO. This represents a reduction of iodine relative to the original “hypervalent” (+3) PhIO. The equivalent of electron density must be removed from the {(tpena)Fe(III)O} moiety, however Mössbauer spectroscopy shows that the iron atom is not high valent....

  7. Surface modification of nanoclays by catalytically active transition metal ions.

    Science.gov (United States)

    Nawani, Pranav; Gelfer, Mikhail Y; Hsiao, Benjamin S; Frenkel, Anatoly; Gilman, Jeffrey W; Khalid, Syed

    2007-09-11

    A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.

  8. Surface Modification of Nanoclays by Catalytically Active Transition Metal Ions

    Energy Technology Data Exchange (ETDEWEB)

    Nawani,P.; Gelfer, M.; Hsiao, B.; Frenkel, A.; Gilman, J.; Khalid, S.

    2007-01-01

    A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.

  9. Synthesis, characterization and catalytic activity of nanosized Ni complexed aminoclay

    Science.gov (United States)

    Ranchani, A. Amala Jeya; Parthasarathy, V.; Devi, A. Anitha; Meenarathi, B.; Anbarasan, R.

    2017-11-01

    A novel Ni complexed aminoclay (AC) catalyst was prepared by complexation method followed by reduction reaction. Various analytical techniques such as FTIR spectroscopy, UV-visible spectroscopy, DSC, TGA, SEM, HRTEM, EDX, XPS and WCA measurement are used to characterize the synthesized material. The AC-Ni catalyst system exhibited improved thermal stability and fiber-like morphology. The XPS results declared the formation of Ni nanoparticles. Thus, synthesized catalyst was tested towards the Schiff base formation reaction between various bio-medical polymers and aniline under air atmosphere at 85 °C for 24 h. The catalytic activity of the catalyst was studied by varying the % weight loading of the AC-Ni system towards the Schiff base formation. The Schiff base formation was quantitatively calculated by the 1H-NMR spectroscopy. While increasing the % weight loading of the AC-Ni catalyst, the % yield of Schiff base was also increased. The k app and Ti values were determined for the reduction of indole and α-terpineol in the presence of AC-Ni catalyst system. The experimental results were compared with the literature report.

  10. Phosphorus modification increases catalytic activity and stability of ZSM-5 zeolite on supercritical catalytic cracking of n-dodecane

    Science.gov (United States)

    Ji, Yajun; Yang, Honghui; Zhang, Qiang; Yan, Wei

    2017-07-01

    Supercritical catalytic cracking of hydrocarbon fuel for active thermal protection of aircraft is a promising technique. The catalytic reaction with stable activity is crucial for practical application. Phosphorus-modified ZSM-5 zeolites (ZSM-5-P) were prepared by impregnation and applied in supercritical cracking of n-dodecane to enhance the stability of thermal protection. ZSM-5-P were characterized by XRD, N2 adsorption-desorption, SEM mapping, NH3-TPD and pyridine-absorbed FTIR. The acid amount of ZSM-5-P decreased with the increase of phosphorus content. The catalytic performance achieved maximum at phosphorus content of 0.5 wt% (ZSM-5-0.5P). Its gas generation rate (GGR) achieved 64.2%, and heat sink reached 3094 kJ/kg, which was 20.2% higher than that of unmodified catalyst (2576 kJ/kg). The carbon deposition decreased with the increase of phosphorus content. Besides, ZSM-5-0.5P and ZSM-5-1P maintained stable activity (over 50% for GGR) and high heat sinks (3000 kJ/kg) even after reaction for 60 min.

  11. Impaired coordination of nucleophile and increased hydrophobicity in the +1 subsite shift levansucrase activity towards transfructosylation.

    Science.gov (United States)

    Elena Ortiz-Soto, Maria; Possiel, Christian; Görl, Julian; Vogel, Andreas; Schmiedel, Ramona; Seibel, Jürgen

    2017-05-30

    Bacterial levansucrases produce β(2,6)-linked levan-type polysaccharides using sucrose or sucrose analogues as donor/acceptor substrates. However, the dominant reaction of Bacillus megaterium levansucrase (Bm-LS) is hydrolysis. Single domain levansucrases from Gram-positive bacteria display a wide substrate-binding pocket with open access to water, challenging engineering for transfructosylation-efficient enzymes. We pursued a shift in reaction specificity by either modifying the water distribution in the active site or the coordination of the catalytic acid/base (E352) and the nucleophile (D95), thus affecting the fructosyl-transfer rate and allowing acceptors other than water to occupy the active site. Two serine (173/422) and two water-binding tyrosine (421/439) residues located in the first shell of the catalytic pocket were modified. Library variants for positions 173, 421 and 422, which coordinate the position of D95 and E352, show increased transfructosylation (30-200%) and modified product spectra. Substitutions at position 422 have a higher impact on sucrose affinity, while changes at position 173 and 421 have a strong effect on the overall catalytic rate. As most retaining glycoside hydrolases (GHs) Bm-LS catalyzes hydrolysis and transglycosylation via a double displacement reaction involving two-transition states (TS1 and TS2). Hydrogen bonds of D95 with the side chains of S173 and S422 contribute a total of 2.4 kcal mol-1 to TS1 stabilization, while hydrogen bonds between invariant Y421, E352 and the glucosyl C-2 hydroxyl-group of sucrose contribute 2.15 kcal mol-1 stabilization. Changes at Y439 render predominantly hydrolytic variants synthesizing shorter oligosaccharides. © The Author 2016. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  12. Modeling the active site of [FeFe]-hydrogenase: Electro-catalytic ...

    Indian Academy of Sciences (India)

    Electro-catalytic hydrogen evaluation studies (from acetic acid) have been performed using com- pounds 1–6 as electro-catalysts. The mechanistic aspects of relevant electro–catalytic proton reductions have been discussed in detail. Keywords. Modeling the active site; [FeFe]-hydrogenase; spectroscopy; electrocatalytic ...

  13. Facile synthesis of Al2O3-Pt nanocomposite and its catalytic activity

    Science.gov (United States)

    Das, Subhasis; Bordoloi, Ankur; Ghosalya, Manoj Kumar; Gopinath, Chinnakonda S.; Bala, Tanushree

    2017-11-01

    Pt nanoparticles were synthesized on γ-alumina support in presence of oleic acid which was found to prevent clustering of Pt nanoparticles on the support. Various percentage of Pt loading on the alumina changed the catalytic activity for preferential oxidation of CO at relatively low temperature in H2 rich stream. Pt nanoparticles when synthesized in absence of oleic acid, were all clustered and did not have any catalytic activity. The presence of oleic acid promoted stability preventing agglomeration of Pt nanoparticles. The catalyst thus prepared was characterized thoroughly and their catalytic activity was studied in details.

  14. Non-coordinating-Anion-Directed Reversal of Activation Site: Selective C-H Bond Activation of N-Aryl Rings.

    Science.gov (United States)

    Wang, Dawei; Yu, Xiaoli; Xu, Xiang; Ge, Bingyang; Wang, Xiaoli; Zhang, Yaxuan

    2016-06-13

    An Rh-catalyzed selective C-H bond activation of diaryl-substituted anilides is described. In an attempt to achieve C-H activation of C-aryl rings, we unexpectedly obtained an N-aryl ring product under non-coordinating anion conditions, whereas the C-aryl ring product was obtained in the absence of a non-coordinating anion. This methodology has proved to be an excellent means of tuning and adjusting selective C-H bond activation of C-aryl and N-aryl rings. The approach has been rationalized by mechanistic studies and theoretical calculations. In addition, it has been found and verified that the catalytic activity of the rhodium catalyst is obviously improved by non-coordinating anions, which provides an efficient strategy for obtaining a highly chemoselective catalyst. Mechanistic experiments also unequivocally ruled out the possibility of a so-called "silver effect" in this transformation involving silver. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. DEVELOPMENT OF HIGH ACTIVITY, CATALYTIC SYSTEMS FOR NOx REDUCTION

    Energy Technology Data Exchange (ETDEWEB)

    Unknown

    2001-12-01

    This project was directed at an investigation of catalytic NO{sub x} reduction on carbonaceous supports at low temperatures. The experimental work was conducted primarily in a packed bed reactor/gas flow system that was constructed for this work. The analytical techniques employed were mass spectrometry, NO{sub x} chemiluminescence, and gas chromatography. The experimental plan was focused on steady-state reactivity experiments, followed by temperature programmed desorption (TPD) of surface intermediates, and also selected temperature-programmed reaction (TPR) experiments. Both uncatalyzed and catalyzed (potassium-promoted) phenolic resin char, were investigated as well as the catalytic effect of additional CO in the gas phase.

  16. Euro-VO-Coordination of virtual observatory activities in Europe

    Science.gov (United States)

    Genova, Françoise; Allen, Mark G.; Arviset, Christophe; Lawrence, Andy; Pasian, Fabio; Solano, Enrique; Wambsganss, Joachim

    2015-06-01

    The European Virtual Observatory Euro-VO has been coordinating European VO activities through a series of projects co-funded by the European Commission over the last 15 years. The bulk of VO work in Europe is ensured by the national VO initiatives and those of intergovernmental agencies. VO activities at the European level coordinate the work in support of the three "pillars" of the Virtual Observatory: support to the scientific community, take-up by the data providers, and technological activities. Several Euro-VO projects have also provided direct support to selected developments and prototyping. This paper explains the methodology used by Euro-VO over the years. It summarises the activities which were performed and their evolutions at different stages of the development of the VO, explains the Euro-VO role with respect to the international and national levels of VO activities, details the lessons learnt for best practices for the coordination of the VO building blocks, and the liaison with other European initiatives, documenting the added-value of European coordination. Finally, the current status and next steps of Euro-VO are briefly addressed.

  17. Degradation of paracetamol by catalytic wet air oxidation and sequential adsorption - Catalytic wet air oxidation on activated carbons

    Energy Technology Data Exchange (ETDEWEB)

    Quesada-Penate, I. [Universite de Toulouse, INPT, UPS, Laboratoire de Genie Chimique, 4, Allee Emile Monso, F-31432 Toulouse (France); CNRS, Laboratoire de Genie Chimique, F-31432 Toulouse (France); Julcour-Lebigue, C., E-mail: carine.julcour@ensiacet.fr [Universite de Toulouse, INPT, UPS, Laboratoire de Genie Chimique, 4, Allee Emile Monso, F-31432 Toulouse (France); CNRS, Laboratoire de Genie Chimique, F-31432 Toulouse (France); Jauregui-Haza, U.J. [Instituto Superior de Tecnologias y Ciencias Aplicadas, Ave. Salvador Allende y Luaces, Habana (Cuba); Wilhelm, A.M.; Delmas, H. [Universite de Toulouse, INPT, UPS, Laboratoire de Genie Chimique, 4, Allee Emile Monso, F-31432 Toulouse (France); CNRS, Laboratoire de Genie Chimique, F-31432 Toulouse (France)

    2012-06-30

    Highlights: Black-Right-Pointing-Pointer Three activated carbons (AC) compared as adsorbents and oxidation catalysts. Black-Right-Pointing-Pointer Similar evolution for catalytic and adsorptive properties of AC over reuses. Black-Right-Pointing-Pointer Acidic and mesoporous AC to be preferred, despite lower initial efficiency. Black-Right-Pointing-Pointer Oxidative degradation of paracetamol improves biodegradability. Black-Right-Pointing-Pointer Convenient hybrid adsorption-regenerative oxidation process for continuous treatment. - Abstract: The concern about the fate of pharmaceutical products has raised owing to the increasing contamination of rivers, lakes and groundwater. The aim of this paper is to evaluate two different processes for paracetamol removal. The catalytic wet air oxidation (CWAO) of paracetamol on activated carbon was investigated both as a water treatment technique using an autoclave reactor and as a regenerative treatment of the carbon after adsorption in a sequential fixed bed process. Three activated carbons (ACs) from different source materials were used as catalysts: two microporous basic ACs (S23 and C1) and a meso- and micro-porous acidic one (L27). During the first CWAO experiment the adsorption capacity and catalytic performance of fresh S23 and C1 were higher than those of fresh L27 despite its higher surface area. This situation changed after AC reuse, as finally L27 gave the best results after five CWAO cycles. Respirometry tests with activated sludge revealed that in the studied conditions the use of CWAO enhanced the aerobic biodegradability of the effluent. In the ADOX process L27 also showed better oxidation performances and regeneration efficiency. This different ageing was examined through AC physico-chemical properties.

  18. 23 CFR 450.208 - Coordination of planning process activities.

    Science.gov (United States)

    2010-04-01

    ... 23 Highways 1 2010-04-01 2010-04-01 false Coordination of planning process activities. 450.208 Section 450.208 Highways FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION PLANNING AND RESEARCH PLANNING ASSISTANCE AND STANDARDS Statewide Transportation Planning and Programming § 450.208...

  19. Coordinating technology introduction and entrepreneurial activities in rural areas

    NARCIS (Netherlands)

    Fokkema, J.E.; Pennink, B.J.W.; Simatupang, T.M.

    2017-01-01

    © Copyright 2017 Inderscience Enterprises Ltd. The main purpose of this research is to investigate how technology introduction projects in rural areas should be coordinated in order to achieve local economic development and the role of social capital and entrepreneurial activities. Characteristics

  20. Effects of FGFR2 kinase activation loop dynamics on catalytic activity.

    Science.gov (United States)

    Karp, Jerome M; Sparks, Samuel; Cowburn, David

    2017-02-01

    The structural mechanisms by which receptor tyrosine kinases (RTKs) regulate catalytic activity are diverse and often based on subtle changes in conformational dynamics. The regulatory mechanism of one such RTK, fibroblast growth factor receptor 2 (FGFR2) kinase, is still unknown, as the numerous crystal structures of the unphosphorylated and phosphorylated forms of the kinase domains show no apparent structural change that could explain how phosphorylation could enable catalytic activity. In this study, we use several enhanced sampling molecular dynamics (MD) methods to elucidate the structural changes to the kinase's activation loop that occur upon phosphorylation. We show that phosphorylation favors inward motion of Arg664, while simultaneously favoring outward motion of Leu665 and Pro666. The latter structural change enables the substrate to bind leading to its resultant phosphorylation. Inward motion of Arg664 allows it to interact with the γ-phosphate of ATP as well as the substrate tyrosine. We show that this stabilizes the tyrosine and primes it for the catalytic phosphotransfer, and it may lower the activation barrier of the phosphotransfer reaction. Our work demonstrates the value of including dynamic information gleaned from computer simulation in deciphering RTK regulatory function.

  1. Effects of FGFR2 kinase activation loop dynamics on catalytic activity.

    Directory of Open Access Journals (Sweden)

    Jerome M Karp

    2017-02-01

    Full Text Available The structural mechanisms by which receptor tyrosine kinases (RTKs regulate catalytic activity are diverse and often based on subtle changes in conformational dynamics. The regulatory mechanism of one such RTK, fibroblast growth factor receptor 2 (FGFR2 kinase, is still unknown, as the numerous crystal structures of the unphosphorylated and phosphorylated forms of the kinase domains show no apparent structural change that could explain how phosphorylation could enable catalytic activity. In this study, we use several enhanced sampling molecular dynamics (MD methods to elucidate the structural changes to the kinase's activation loop that occur upon phosphorylation. We show that phosphorylation favors inward motion of Arg664, while simultaneously favoring outward motion of Leu665 and Pro666. The latter structural change enables the substrate to bind leading to its resultant phosphorylation. Inward motion of Arg664 allows it to interact with the γ-phosphate of ATP as well as the substrate tyrosine. We show that this stabilizes the tyrosine and primes it for the catalytic phosphotransfer, and it may lower the activation barrier of the phosphotransfer reaction. Our work demonstrates the value of including dynamic information gleaned from computer simulation in deciphering RTK regulatory function.

  2. Integrating nanotubes into microsystems with electron beam lithography and in situ catalytically activated growth

    DEFF Research Database (Denmark)

    Gjerde, Kjetil; Fornés-Mora, Marc; Kjelstrup-Hansen, Jakob

    2006-01-01

    Integration of freestanding wire-like structures such as multi walled carbon nanotubes (MWCNT) into microsystems has many potential applications. Devices such as AFM tips or improved electrodes for conductivity measurements are obvious candidates. Catalytically activated growth opens up...

  3. Effect of Precursor Synthesis on Catalytic Activity of Co3O4 in N2O Decomposition

    OpenAIRE

    Chromčáková, Ž.

    2014-01-01

    The correlation between methods of preparation, phase composition of precursors, catalytic properties of the related oxide catalysts, and the role of the cobalt ions as catalytic active sites is discussed.

  4. A novel microbial synthesis of catalytically active Ag-alginate biohydrogel and its antimicrobial activity.

    Science.gov (United States)

    Otari, S V; Patil, R M; Waghmare, S R; Ghosh, S J; Pawar, S H

    2013-07-21

    The green synthesis of supported noble metal nanoparticles is now the most exciting field for various catalytic applications as well as biomedical applications. In this paper we report a novel synthesis method of a polymer consisting of silver nanoparticles (AgNPs) using immobilized microorganisms in alginate beads. Microorganisms present in the polymer reduce aqueous AgNO3 to AgNPs which get trapped in the polymer to form Ag-Alginate (Ag-Alg) biohydrogel. The formed biohydrogel was characterized by UV-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) analysis. TEM analysis showed that less than 15 nm AgNPs formed in the polymer. The Ag-Alg biohydrogel exhibited efficient heterogeneous catalytic activity in the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 in aqueous solution with durable reusability. Also this biohydrogel showed excellent antimicrobial activity against pathogenic bacteria (antibiotic resistant) and fungi. The described synthesis method of Ag-Alg biohydrogel can be considered robust, cost effective and eco-friendly. The formed highly catalytic active biohydrogel can be used as catalyst in industries and drinking water purification.

  5. A unique nickel system having versatile catalytic activity of biological significance.

    Science.gov (United States)

    Chattopadhyay, Tanmay; Mukherjee, Madhuparna; Mondal, Arindam; Maiti, Pali; Banerjee, Arpita; Banu, Kazi Sabnam; Bhattacharya, Santanu; Roy, Bappaditya; Chattopadhyay, D J; Mondal, Tapan Kumar; Nethaji, Munirathinam; Zangrando, Ennio; Das, Debasis

    2010-04-05

    A new dinuclear nickel(II) complex, [Ni(2)(LH(2))(H(2)O)(2)(OH)(NO(3))](NO(3))(3) (1), of an "end-off" compartmental ligand 2,6-bis(N-ethylpiperazine-iminomethyl)-4-methyl-phenolato, has been synthesized and structurally characterized. The X-ray single crystal structure analysis shows that the piperazine moieties assume the expected chair conformation and are protonated. The complex 1 exhibits versatile catalytic activities of biological significance, viz. catecholase, phosphatase, and DNA cleavage activities, etc. The catecholase activity of the complex observed is very dependent on the nature of the solvent. In acetonitrile medium, the complex is inactive to exhibit catecholase activity. On the other hand, in methanol, it catalyzes not only the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very difficult to oxidize, under aerobic conditions. UV-vis spectroscopic investigation shows that TCC oxidation proceeds through the formation of an intermediate. The intermediate has been characterized by an electron spray ionizaton-mass spectrometry study, which suggests a bidentate rather than a monodentate mode of TCC coordination in that intermediate, and this proposition have been verified by density functional theory calculation. The complex also exhibits phosphatase (with substrate p-nitrophenylphosphate) and DNA cleavage activities. The DNA cleavage activity exhibited by complex 1 most probably proceeds through a hydroxyl radical pathway. The bioactivity study suggests the possible applications of complex 1 as a site specific recognition of DNA and/or as an anticancer agent.

  6. Syntheses, structures, electrochemistry and catalytic oxidation degradation of organic dyes of two new coordination polymers derived from Cu(II) and Mn(II) and 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene

    Energy Technology Data Exchange (ETDEWEB)

    Song, Ming; Mu, Bao; Huang, Ru-Dan, E-mail: huangrd@bit.edu.cn

    2017-02-15

    Two new coordination polymers (CPs), namely, [Cu{sub 2}(ttbz)(H{sub 2}btc){sub 2}(OH)]{sub n} (1) and [Mn(ttbz){sub 2}(H{sub 2}O){sub 2}]{sub n} (2) (Httbz =1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene, H{sub 3}btc =1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized and structurally characterized. Complex 1 exhibits a (3,5,5,5)-connected 2D layer with a Schläfli symbol of (3·4{sup 2})(3·4{sup 4}0.5{sup 2}0.6{sup 3})(3{sup 2}0.4{sup 4}0.5{sup 2}0.6{sup 2})(3{sup 2}0.4{sup 4}0.5{sup 3}0.6), in which the ttbz{sup -} ligand can be described as μ{sub 5}-bridge, linking Cu(II) ions into a 2D layer and H{sub 2}btc{sup -} ions play a supporting role in complex 1. The ttbz{sup -} ligand in complex 2 represents the bridging coordination mode, connecting two Mn(II) ions to form the infinite 1D zigzag chains, respectively, which are further connected by two different types of hydrogen bonds to form a 3D supramolecular. Furthermore, catalytic oxidation activities toward organic dyes and electrochemical behaviors of the title complexes have been investigated at room temperature in aqueous solutions, indicating these complexes may be applicable to color removal in a textile wastewater stream and practical applications in areas of electrocatalytic reduction toward nitrite, respectively. - Graphical abstract: Two new coordination polymers based on different structural characteristics have been hydrothermally synthesized by the mixed ligands. The catalytic oxidation activities toward organic dyes and electrochemical behaviors of the title complexes have been investigated. - Highlights: • The organic ligand containing the tetrazolyl group and triazolyl group with some advantages has been used. • Two new coordination polymers with different structural characteristics has been discussed in detail. • Catalytic oxidation activities toward organic dyes and electrochemical behaviors of the title complexes have been investigated.

  7. From Spontaneous Motor Activity to Coordinated Behaviour: A Developmental Model

    Science.gov (United States)

    Marques, Hugo Gravato; Bharadwaj, Arjun; Iida, Fumiya

    2014-01-01

    In mammals, the developmental path that links the primary behaviours observed during foetal stages to the full fledged behaviours observed in adults is still beyond our understanding. Often theories of motor control try to deal with the process of incremental learning in an abstract and modular way without establishing any correspondence with the mammalian developmental stages. In this paper, we propose a computational model that links three distinct behaviours which appear at three different stages of development. In order of appearance, these behaviours are: spontaneous motor activity (SMA), reflexes, and coordinated behaviours, such as locomotion. The goal of our model is to address in silico four hypotheses that are currently hard to verify in vivo: First, the hypothesis that spinal reflex circuits can be self-organized from the sensor and motor activity induced by SMA. Second, the hypothesis that supraspinal systems can modulate reflex circuits to achieve coordinated behaviour. Third, the hypothesis that, since SMA is observed in an organism throughout its entire lifetime, it provides a mechanism suitable to maintain the reflex circuits aligned with the musculoskeletal system, and thus adapt to changes in body morphology. And fourth, the hypothesis that by changing the modulation of the reflex circuits over time, one can switch between different coordinated behaviours. Our model is tested in a simulated musculoskeletal leg actuated by six muscles arranged in a number of different ways. Hopping is used as a case study of coordinated behaviour. Our results show that reflex circuits can be self-organized from SMA, and that, once these circuits are in place, they can be modulated to achieve coordinated behaviour. In addition, our results show that our model can naturally adapt to different morphological changes and perform behavioural transitions. PMID:25057775

  8. Solubility of cerium in LaCoO3-influence on catalytic activity.

    Science.gov (United States)

    French, S A; Catlow, C R A; Oldman, R J; Rogers, S C; Axon, S A

    2002-11-21

    The recent interest in the catalytic properties of lanthanum perovskites for methane combustion and three way catalysis has led to considerable debate as to their structure and defect chemistry. We have investigated the doping of LaCoO3 with the tetravalent cerium cation using atomistic simulation techniques. We have compared three routes for cerium insertion and identified the favoured doping mechanism, which explain experimental observations relating to the effect of cerium on catalytic activity.

  9. Catalytic Performance of a New 1D Cu(II Coordination Polymer {Cu(NO3(H2O}(HTae(4,4′-Bpy for Knoevenagel Condensation

    Directory of Open Access Journals (Sweden)

    Edurne S. Larrea

    2016-12-01

    Full Text Available The {Cu(NO3(H2O}(HTae(4,4′-Bpy (H2Tae = 1,1,2,2-tetraacetylethane, 4,4′-Bpy = 4,4′-Dipyridyl 1D coordination polymer has been obtained by slow evaporation. The crystal structure consists of parallel and oblique {Cu(HTae(4,4′-Bpy} zig-zag metal–organic chains stacked along the [100] crystallographic direction. Copper(II ions are in octahedral coordination environment linked to two nitrogen atoms of two bridging 4,4′-Bpy and to two oxygen atoms of one HTae molecule in the equatorial plane. The occupation of the axial positions varies from one copper atom to another, with different combinations of water molecules and nitrate anions, giving rise to a commensurate super-structure. By means of the thermal removal of water molecules, copper coordinatively unsaturated centres are obtained. These open metal sites could act as Lewis acid active sites in several heterogeneous catalytic reactions. The dehydrated compound, CuHTaeBpy_HT, has been tested as a heterogeneous recoverable catalyst for Knoevenagel condensation reactions. The catalyst is active and heterogeneous for the condensation of aldehydes with malononitrile at 60 °C using a molar ratio catalyst:substrate of 3 % and toluene as solvent. The catalyst suffers a partial loss of activity when reusing it, but can be reused at least four times.

  10. Reactivity and Catalytic Activity of Hydrogen Atom Chemisorbed Silver Clusters.

    Science.gov (United States)

    Manzoor, Dar; Pal, Sourav

    2015-06-18

    Metal clusters of silver have attracted recent interest of researchers as a result of their potential in different catalytic applications and low cost. However, due to the completely filled d orbital and very high first ionization potential of the silver atom, the silver-based catalysts interact very weakly with the reacting molecules. In the current work, density functional theory calculations were carried out to investigate the effect of hydrogen atom chemisorption on the reactivity and catalytic properties of inert silver clusters. Our results affirm that the hydrogen atom chemisorption leads to enhancement in the binding energy of the adsorbed O2 molecule on the inert silver clusters. The increase in the binding energy is also characterized by the decrease in the Ag-O and increase in the O-O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O-O bond length, a significant red shift in the O-O stretching frequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbed silver clusters show low reaction barriers and high heat of formation of the final products for the environmentally important CO oxidation reaction as compared to the parent catalytically inactive clusters. The obtained results were compared with those of the corresponding gold and hydrogen atom chemisorbed gold clusters obtained at the same level of theory. It is expected the current computational study will provide key insights for future advances in the design of efficient nanosilver-based catalysts through the adsorption of a small atom or a ligand.

  11. Cold catalytic recovery of loaded activated carbon using iron oxide-based nanoparticles.

    Science.gov (United States)

    Bach, Altai; Zelmanov, Grigory; Semiat, Raphael

    2008-01-01

    A novel approach for the recovery of spent activated carbon by an advanced oxidation process using iron oxide-based nanocatalysts was proposed and investigated. Model organic contaminants, such as ethylene glycol and phenol, were chosen for this study as water pollutants. It was shown that there are several advantages in using catalytic oxidation recovery of activated carbon with iron oxide-based nanocatalysts: low temperature reactivity of catalytic recovery without heating; and a relatively large number of adsorption-recovery cycles, without a reduction in the adsorptive properties of the virgin activated carbon or without a performance decrease from the first adsorption-recovery cycle of the new modified adsorptive properties of the activated carbon. The catalytic recovery takes place without ultraviolet light or any visible radiation sources. Results show a high efficiency of catalytic recovery of spent activated carbon using iron oxide-based nanocatalysts. A 97-99% efficiency of spent activated carbon catalytic regeneration was achieved under chosen conditions after 15-20 min of reaction. The process may be also considered as cold in situ recovery of active carbon.

  12. Bimetallic alloy Pt/Ag nanoparticles with enhanced catalytic activity for formic acid oxidation

    Science.gov (United States)

    Guo, Chunmei; Hu, Jingbo

    2014-05-01

    Here, we report the synthesis of Pt/Ag bimetallic alloy catalyst through combining the ion implantation and electrodeposition method. Ag nanoparticles are employed as the seeds for the growth of Pt nanoparticles. Pt/Ag alloy catalyst demonstrates much higher catalytic activity than pure Pt catalyst, which is about three times more active on the basis of equivalent Pt electrochemically active surface area than that of the pure Pt catalyst. The ion implantation of Ag efficiently enhances the catalytic activity of Pt catalyst for formic acid oxidation.

  13. Effects of copper-precursors on the catalytic activity of Cu/graphene catalysts for the selective catalytic oxidation of ammonia

    Science.gov (United States)

    Li, Jingying; Tang, Xiaolong; Yi, Honghong; Yu, Qingjun; Gao, Fengyu; Zhang, Runcao; Li, Chenlu; Chu, Chao

    2017-08-01

    Different copper-precursors were used to prepare Cu/graphene catalysts by an impregnation method. XRD, Raman spectra, TEM, BET, XPS, H2-TPR, NH3-TPD, DRIFTS and catalytic activity test were used to characterize and study the effect of precursors on the catalytic activity of Cu/graphene catalysts for NH3-SCO reaction. The large specific surface area of Cu/graphene catalysts and high dispersion of the metal particles on the graphene caused the well catalytic activity of NH3-SCO reaction. Compared to Cu/GE(AC), Cu/GE(N) showed better catalytic performance, and the complete NH3 removal efficiency was obtained at 250 °C with N2 selectivity of 85%. The copper-precursors had influence on the distribution of surface Cu species and further affected the catalytic activity of Cu/GE catalysts. The more amount of surface Cu species and highly dispersed CuO particles on the graphene surface formed by using copper nitrate as precursor could significantly improve the reducibility of catalysts and enhance NH3 adsorption, thereby improving the catalytic activity of Cu/graphene catalyst.

  14. Multi-shelled ceria hollow spheres with a tunable shell number and thickness and their superior catalytic activity.

    Science.gov (United States)

    Liao, Yuanyuan; Li, Yuan; Wang, Lei; Zhao, Yongxia; Ma, Danyang; Wang, Biqing; Wan, Yongxia; Zhong, Shengliang

    2017-01-31

    In this work, ceria multi-shelled nanospheres with a tunable shell number and thickness were prepared by a facile coordination polymer (CP) precursor method without the use of any template and surfactant. Interestingly, the number, thickness and structure of the shell can be tuned by varying the reaction time, reaction temperature, ratio of reagent and calcination temperature. The formation process of the multi-shelled hollow spheres was also investigated, which experienced a core contraction and shell separation process. Moreover, the multi-shelled CeO2 hollow nanospheres displayed excellent photocatalytic activity in the degradation of RhB. Au and AuPd nanoparticle loaded multi-shelled CeO2 nanocomposites were also prepared. Results show that Au/CeO2 multi-shelled hollow nanospheres showed eximious catalytic activity for the reduction of p-nitrophenol with a reaction rate constant k of 0.416 min. In addition, AuPd/CeO2 exhibited a remarkable catalytic activity for the conversion of CO. Employing this method, heavy rare earth oxide multi-shelled structures and light rare earth oxide solid spheres were obtained. This method may be employed for the preparation of other materials with complex structures.

  15. Role of the Support Effects on the Catalytic Activity of Gold Clusters: A Density Functional Theory Study

    Directory of Open Access Journals (Sweden)

    Tetsuya Taketsugu

    2011-11-01

    Full Text Available It is demonstrated that the support effects play a crucial role in the gold nanocatalysis. Two types of support are considered—the “inert” support of hexagonal boron nitride (h-BN with the N and B vacancy defects and the “active” support of rutile TiO2(110. It is demonstrated that Au and Au2 can be trapped effectively by the vacancy defects in h-BN. In that case, the strong adsorption on the surface defects is accompanied by the charge transfer to/from the adsorbate. The excess of the positive or negative charge on the supported gold clusters can considerably promote their catalytic activity. Therefore gold clusters supported on the defected h-BN surface can not be considered as pseudo-free clusters. We also demonstrate that the rutile TiO2(110 support energetically promotes H2 dissociation on gold clusters. We show that the formation of the OH group near the supported gold cluster is an important condition for H2 dissociation. We demonstrate that the active sites towards H2 dissociation on the supported Aun are located at corners and edges of the gold cluster in the vicinity of the low coordinated oxygen atoms on TiO2(110. Thus catalytic activity of a gold nanoparticle supported on the rutile TiO2(110 surface is proportional to the length of the perimeter interface between the nanoparticle and the support.

  16. Removal performance and mechanism of ibuprofen from water by catalytic ozonation using sludge-corncob activated carbon as catalyst.

    Science.gov (United States)

    Wang, Hongjuan; Zhang, Liqiu; Qi, Fei; Wang, Xue; Li, Lu; Feng, Li

    2014-09-01

    To discover the catalytic activity of sludge-corncob activated carbon in catalytic ozonation of Ibuprofen, the performance of sludge-corncob activated carbon and three selected commercial activated carbons as catalysts in catalytic ozonation was investigated. The observation indicates the degradation rate of Ibuprofen increases significantly in the presence of sludge-corncob activated carbon and the catalytic activity of sludge-corncob activated carbon is much higher than that of the other three commercial activated carbons. Ibuprofen's removal rate follows pseudo-first order kinetics model well. It is also found that the adsorption removal of Ibuprofen by sludge-corncob activated carbon is less than 30% after 40 min. And the removal efficiency of Ibuprofen in the hybrid ozone/sludge-corncob activated carbon system is higher than the sum of sludge-corncob activated carbon adsorption and ozonation alone, which is a supportive evidence for catalytic reaction. In addition, the results of radical scavenger experiments demonstrate that catalytic ozonation of Ibuprofen by sludge-corncob activated carbon follows a hydroxyl radical reaction pathway. During ozonation of Ibuprofen in the presence of activated carbon, ozone could be catalytically decomposed to form hydrogen peroxide, which can promote the formation of hydroxyl radical. The maximum amount of hydrogen peroxide occurs in the presence of sludge-corncob activated carbon, which can explain why sludge-corncob activated carbon has the best catalytic activity among four different activated carbons.

  17. Catalytic activity of titania zirconia mixed oxide catalyst for dimerization eugenol

    Science.gov (United States)

    Tursiloadi, S.; Kristiani, A.; Jenie, S. N. Aisyiyah; Laksmono, J. A.

    2017-01-01

    Clove oil has been found to possess antibacterial, antifungal, antiviral, antitumor, antioxidant and insecticidal properties. The major compound of clove oil is eugenol about 49-87%. Eugenol as phenolic compounds exhibits antioxidant and antimicrobial activities. The derivative compound of eugenol, dieugenol, show antioxidant potency better than parent eugenol. A series of TiO2-ZrO2 mixed oxides (TZ) with various titanium contents from 0 to 100wt%, prepared by using sol gel method were tested their catalytic activity for dimerization eugenol, Their catalytic activity show that these catalysts resulted a low yield of dimer eugenol, dieugenol, about 2-9 % and the purity is more than 50%.

  18. The Role of Organic Capping Layers of Platinum Nanoparticles in Catalytic Activity of CO Oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jeong Y.; Aliaga, Cesar; Renzas, J. Russell; Lee, Hyunjoo; Somorjai, Gabor A.

    2008-12-17

    We report the catalytic activity of colloid platinum nanoparticles synthesized with different organic capping layers. On the molecular scale, the porous organic layers have open spaces that permit the reactant and product molecules to reach the metal surface. We carried out CO oxidation on several platinum nanoparticle systems capped with various organic molecules to investigate the role of the capping agent on catalytic activity. Platinum colloid nanoparticles with four types of capping layer have been used: TTAB (Tetradecyltrimethylammonium Bromide), HDA (hexadecylamine), HDT (hexadecylthiol), and PVP (poly(vinylpyrrolidone)). The reactivity of the Pt nanoparticles varied by 30%, with higher activity on TTAB coated nanoparticles and lower activity on HDT, while the activation energy remained between 27-28 kcal/mol. In separate experiments, the organic capping layers were partially removed using ultraviolet light-ozone generation techniques, which resulted in increased catalytic activity due to the removal of some of the organic layers. These results indicate that the nature of chemical bonding between organic capping layers and nanoparticle surfaces plays a role in determining the catalytic activity of platinum colloid nanoparticles for carbon monoxide oxidation.

  19. Control of a catalytic activity of gold nanoparticles embedded in DNA hydrogel by swelling/shrinking the hydrogel's matrix.

    Science.gov (United States)

    Che, Yuxin; Zinchenko, Anatoly; Murata, Shizuaki

    2015-05-01

    By incorporating catalytically active nanoparticles into polymeric hydrogel one can tune the catalytic activity of such a hybrid material by affecting the state of polymer matrix. Herein, hybrid hydrogel was prepared by metallization of DNA cross-liked hydrogel via absorption of gold precursor and reduction by NaBH4, and its catalytic activity under various swelling ratio was studied spectroscopically. Catalytic activity of Au nanoparticles in hydrogel was shown to depend drastically on a swelling degree of hydrogel easily controlled by a change in an ionic strength of solution. Increase of the catalytic reaction rate was proportional to the volume of hybrid hydrogel indicating that diffusion of reactants toward catalytic centers inside hydrogel is crucial for the efficient catalysis by soft-matter-based hybrid material. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. PREPARATION, CHARACTERIZATION, AND CATALYTIC ACTIVITY TEST OF Ni-Mo/NATURAL ZEOLITE ON PYRIDINE HYDRODENITROGENATION

    Directory of Open Access Journals (Sweden)

    Sri Kadarwati

    2010-12-01

    Full Text Available Preparation, characterization, and catalytic activity test of Ni-Mo/natural zeolite on pyridine hydrodenitrogenation were carried out. Preparation of catalyst was conducted by impregnation method using nickel nitrate hexahydrate and ammonium heptamolibdate precursor as Ni and Mo source respectively. Characterization of catalyst was conducted by using gravimetry, atomic absorption spectrophotometry, and X-ray diffraction method. Catalytic activity test on pyridine hydrodenitrogenation was carried out by using flow system reactor with hydrogen flow rate variable. The research results showed that the catalyst's total acidity and crystallinity are increased with level of impregnation success of 96.71% and 90.08% respectively. Ni-Mo/natural zeolites able to increase the catalytic conversion up to 71.78% at 350 °C and hydrogen flow rate of 10 mL/min with more highly varied product distribution. Assuming that the pyridine hydrodenitrogenation follows the pseudo first order kinetics.

  1. The Impact of Enzyme Orientation and Electrode Topology on the Catalytic Activity of Adsorbed Redox Enzymes

    Science.gov (United States)

    McMillan, Duncan G. G.; Marritt, Sophie J.; Kemp, Gemma L.; Gordon-Brown, Piers; Butt, Julea N.; Jeuken, Lars J. C.

    2014-01-01

    It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200 nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes. PMID:24634538

  2. Anticancer Activities of Mononuclear Ruthenium(II Coordination Complexes

    Directory of Open Access Journals (Sweden)

    William M. Motswainyana

    2015-01-01

    Full Text Available Ruthenium compounds are highly regarded as potential drug candidates. The compounds offer the potential of reduced toxicity and can be tolerated in vivo. The various oxidation states, different mechanism of action, and the ligand substitution kinetics of ruthenium compounds give them advantages over platinum-based complexes, thereby making them suitable for use in biological applications. Several studies have focused attention on the interaction between active ruthenium complexes and their possible biological targets. In this paper, we review several ruthenium compounds which reportedly possess promising cytotoxic profiles: from the discovery of highly active compounds imidazolium [trans-tetrachloro(dmso(imidazoleruthenate(III] (NAMI-A, indazolium [trans-tetrachlorobis(1H-indazoleruthenate(III](KP1019, and sodium trans-[tetrachloridobis(1H-indazoleruthenate(III] (NKP-1339 to the recent work based on both inorganic and organometallic ruthenium(II compounds. Half-sandwich organometallic ruthenium complexes offer the opportunity of derivatization at the arene moiety, while the three remaining coordination sites on the metal centre can be functionalised with various coordination groups of various monoligands. It is clear from the review that these mononuclear ruthenium(II compounds represent a strongly emerging field of research that will soon culminate into several ruthenium based antitumor agents.

  3. One-step preparation of Fe3O4/Pd@polypyrrole composites with enhanced catalytic activity and stability.

    Science.gov (United States)

    Zhang, Hui; Liu, Yang; Wu, Jie; Xin, Baifu

    2016-08-15

    Core/shell Fe3O4/Pd@polypyrrole (PPy) composites with a Fe3O4 core and a PPy shell embedding Pd nanoparticles were prepared in one-step. The diameter of highly dispersed Pd nanoparticles was as small as 2.9nm owing to coordination interaction generated between Pd(2+) ions and amino groups on PPy chains. The outer PPy shell was only 6.8nm: on one hand, the coverage was beneficial to improving the stability of resulting composites; on the other hand, the shell was thin enough to permit free contact between embedding Pd nanoparticles and reactants. Additionally, the as-prepared Fe3O4/Pd@PPy composites displayed good magnetic separation property due to incorporation of Fe3O4 nanospheres. Based on above merits, they served as suitable catalyst candidates. Their catalytic performance and reusability were evaluated by reduction of 4-nitrophenol with sodium borohydride as reducing agent. Compared with traditional Fe3O4/Pd composites, Fe3O4/Pd@PPy composites not only showed superior catalytic activity; but also exhibited much better stability in successive cycling tests. Copyright © 2016 Elsevier Inc. All rights reserved.

  4. Effect of ceria structural properties on the catalytic activity of Au-CeO2 catalysts for WGS reaction.

    Science.gov (United States)

    Vindigni, F; Manzoli, M; Tabakova, T; Idakiev, V; Boccuzzi, F; Chiorino, A

    2013-08-28

    Two gold based catalysts supported on ceria prepared by different methods (urea gelation coprecipitation, UGC, and coprecipitation, CP) have been synthesized and tested in the WGS reaction, showing quite different catalytic behaviors. Interestingly, the two catalysts have the same gold loading (3 wt% Au was inserted by deposition-precipitation) and the FTIR spectroscopy of the adsorbed CO revealed the same amount of gold exposed sites. With the aim to elucidate how the preparation method affects the properties of the support, a morphological, structural and textural characterization has been performed by HRTEM, XRD, BET and Raman analyses, as well as FTIR spectroscopy to probe both the Au and the support exposed sites. It was found that the UGC method gave rise to an enhancement of the defectivity of ceria and to an increase of the reactivity under reductive treatment. Further FTIR measurements of adsorbed acetone demonstrated the presence of two kinds of Ce(4+) sites with different coordination, (CUS) Ce(4+) A and (CUS) Ce(4+) B, on the UGC sample. Such sites can influence the catalytic activity, possibly favoring the water dissociation, making ceria prepared by UGC a better support for Au catalysts than the CP-prepared one.

  5. Tailoring nanoscopic confines to maximize catalytic activity of hydronium ions

    Science.gov (United States)

    Shi, Hui; Eckstein, Sebastian; Vjunov, Aleksei; Camaioni, Donald M.; Lercher, Johannes A.

    2017-05-01

    Acid catalysis by hydronium ions is ubiquitous in aqueous-phase organic reactions. Here we show that hydronium ion catalysis, exemplified by intramolecular dehydration of cyclohexanol, is markedly influenced by steric constraints, yielding turnover rates that increase by up to two orders of magnitude in tight confines relative to an aqueous solution of a Brønsted acid. The higher activities in zeolites BEA and FAU than in water are caused by more positive activation entropies that more than offset higher activation enthalpies. The higher activity in zeolite MFI with pores smaller than BEA and FAU is caused by a lower activation enthalpy in the tighter confines that more than offsets a less positive activation entropy. Molecularly sized pores significantly enhance the association between hydronium ions and alcohols in a steric environment resembling the constraints in pockets of enzymes stabilizing active sites.

  6. Handling Conflicts in Autonomous Coordination of Distributed Collaborative Activities

    OpenAIRE

    Franke, Jörn; Charoy, François; Ulmer, Cédric

    2011-01-01

    International audience; Coordination between different organizations in dynamic situations, such as a disaster response, is challenging. Organizations are autonomous and coordinate the situation from their point of view. There is no central authority to coordinate all operations. To coordinate their actions, organi- zations need to exchange information on what they are doing. However, they cannot share everything with everybody due to privacy, regulatory or strategic reasons. Currently, only ...

  7. Catalytic Intermolecular Cross-Couplings of Azides and LUMO-Activated Unsaturated Acyl Azoliums

    KAUST Repository

    Li, Wenjun

    2017-02-15

    An example for the catalytic synthesis of densely functionalized 1,2,3-triazoles through a LUMO activation mode has been developed. The protocol is enabled by intermolecular cross coupling reactions of azides with in situ-generated alpha,beta-unsaturated acyl azoliums. High yields and broad scope as well as the investigation of reaction mechanism are reported.

  8. Influence of Al content on textural properties and catalytic activity of ...

    Indian Academy of Sciences (India)

    A series of hierarchical porous aluminosilicate materials were prepared using hydrothermal treatment of the composite formed by polystyrene colloidal spheres and aluminosilicate gel. Influence of Al content on the textural properties, acidic properties and catalytic activity of the hierarchical porous aluminosilicate materials ...

  9. Catalytic activity of polymer-bound Ru (III)–EDTA complex

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 24; Issue 2. Catalytic activity of polymer-bound Ru(III)–EDTA complex. Mahesh K Dalal R N Ram. Catalysts ... the reaction was investigated. A rate expression is proposed based on the observed initial rate data. Recycling efficiency of the catalyst has also been studied.

  10. A reconstruction strategy to synthesize mesoporous SAPO molecular sieve single crystals with high MTO catalytic activity.

    Science.gov (United States)

    Wang, Chan; Yang, Miao; Li, Mingrun; Xu, Shutao; Yang, Yue; Tian, Peng; Liu, Zhongmin

    2016-05-11

    Mesoporous SAPO-34 single crystals with tunable porosity and Si content have been fast synthesized within 4 hours by a reconstruction strategy, which show excellent hydrothermal stability and MTO catalytic activity. This new strategy is further proven to be applicable to prepare other mesoporous SAPO molecular sieve single crystals.

  11. Improved acylation of phytosterols catalyzed by Candida antarctica lipase A with superior catalytic activity

    DEFF Research Database (Denmark)

    Panpipat, Worawan; Xu, Xuebing; Guo, Zheng

    2013-01-01

    This work reported a novel approach to synthesize phytosterol (ˇ-sitosterol as a model) fatty acid esters by employing Candida antarctica lipase A (CAL A) which shows a superior catalytic activity to other lipases. A series of ˇ-sitosteryl fatty acid esters (C2–C18) have been successfully prepared...

  12. Synthesis and catalytic activity of histidine-based NHC ruthenium complexes.

    Science.gov (United States)

    Monney, Angèle; Venkatachalam, Galmari; Albrecht, Martin

    2011-03-28

    Main-chain C,N-protected histidine has been successfully alkylated at both side-chain nitrogens. The corresponding histidinium salt was metallated with ruthenium(II) by a transmetalation procedure, thus providing histidine-derived NHC ruthenium complexes. These bio-inspired complexes show appreciable activity in the catalytic transfer hydrogenation of ketones.

  13. High catalytic activity of palladium nanoparticle clusters supported on a spherical polymer network.

    Science.gov (United States)

    Sultanova, Elza D; Salnikov, Vadim V; Mukhitova, Rezeda K; Zuev, Yuriy F; Osin, Yuriy N; Zakharova, Lucia Ya; Ziganshina, Albina Y; Konovalov, Alexander I

    2015-09-04

    In this communication we report the synthesis of Pd nanoparticle clusters achieved via the assembly of Pd nanoparticles on the surface of a spherical polymer network. The network exhibits flexibility and adapts to the cluster formation. The nanoclusters display high catalytic activity toward p-nitrophenol reduction and the Suzuki-Miyaura coupling reaction.

  14. Aligned carbon nanotube with electro-catalytic activity for oxygen reduction reaction

    Science.gov (United States)

    Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

    2010-08-03

    A catalyst for an electro-chemical oxygen reduction reaction (ORR) of a bundle of longitudinally aligned carbon nanotubes having a catalytically active transition metal incorporated longitudinally in said nanotubes. A method of making an electro-chemical catalyst for an oxygen reduction reaction (ORR) having a bundle of longitudinally aligned carbon nanotubes with a catalytically active transition metal incorporated throughout the nanotubes, where a substrate is in a first reaction zone, and a combination selected from one or more of a hydrocarbon and an organometallic compound containing an catalytically active transition metal and a nitrogen containing compound and an inert gas and a reducing gas is introduced into the first reaction zone which is maintained at a first reaction temperature for a time sufficient to vaporize material therein. The vaporized material is then introduced to a second reaction zone maintained at a second reaction temperature for a time sufficient to grow longitudinally aligned carbon nanotubes over the substrate with a catalytically active transition metal incorporated throughout the nanotubes.

  15. Catalytic promiscuity of a proline-based tautomerase : Aldolase activities and enzyme redesign

    NARCIS (Netherlands)

    Rahimi, Mehran

    2016-01-01

    Numerous enzymes have been found to catalyze additional and completely different types of reactions relative to the natural activity they evolved for. This interesting phenomenon, called catalytic promiscuity, has proven to be a fruitful guide for the development of novel biocatalysts for organic

  16. Methylene bridge regulated geometrical preferences of ligands in cobalt(III) coordination chemistry and phenoxazinone synthase mimicking activity.

    Science.gov (United States)

    Panja, Anangamohan; Shyamal, Milan; Saha, Amrita; Mandal, Tarun Kanti

    2014-04-14

    Two new azide bound cobalt(III) complexes, [Co(L(1))(N3)3] (fac-1) and [Co(L(2))(N3)3] (mer-2), where L(1) is bis(2-pyridylmethyl)amine and L(2) is (2-pyridylmethyl)(2-pyridylethyl)amine, derived from tridentate reduced Schiff-base ligands have been reported. Interestingly, a methylene bridge regulated preferential coordination mode of ligands is noticed in their crystal structures: it is found in a facial arrangement in fac-1 and has a meridional disposition in mer-2. Both complexes show phenoxazinone synthase-like activity and the role of the structural factor on the catalytic activity is also explored. Moreover, the easily reducible cobalt(III) center in mer-2 favors the oxidation of o-aminophenol. The ESI-MS positive spectra together with UV-vis spectroscopy clearly suggest the formation of a catalyst-substrate adduct by substitution of the coordinated azide ions in the catalytic cycle.

  17. Direct Hysteresis Heating of Catalytically Active Ni–Co Nanoparticles as Steam Reforming Catalyst

    DEFF Research Database (Denmark)

    Mortensen, Peter Mølgaard; Engbæk, Jakob Soland; Vendelbo, Søren Bastholm

    2017-01-01

    We demonstrated a proof-of-concept catalytic steam reforming flow reactor system heated only by supported magnetic nickel–cobalt nanoparticles in an oscillating magnetic field. The heat transfer was facilitated by the hysteresis heating in the nickel–cobalt nanoparticles alone. This produced...... a sufficient power input to equilibrate the reaction at above 780 °C with more than 98% conversion of methane. The high conversion of methane indicated that Co-rich nanoparticles with a high Curie temperature provide sufficient heat to enable the endothermic reaction, with the catalytic activity facilitated...... by the Ni content in the nanoparticles. The magnetic hysteresis losses obtained from temperature-dependent hysteresis measurements were found to correlate well with the heat generation in the system. The direct heating of the catalytic system provides a fast heat transfer and thereby overcomes the heat...

  18. Biobased Chitosan Nanocomposite Films Containing Gold Nanoparticles: Obtainment, Characterization, and Catalytic Activity Assessment.

    Science.gov (United States)

    Ramirez, Oscar; Bonardd, Sebastián; Saldías, Cesar; Radic, Deodato; Leiva, Ángel

    2017-05-17

    A "green" two-step methodology to prepare biobased gold-chitosan nanocomposite films using chitosan and AuCl 4 - as a stabilizer and precursor, respectively, is reported. The biobased nanocomposites were prepared in situ by a wet chemical reduction method. Effects of hydrazine and l-ascorbic acid as different strength reducing agents on the characteristics of gold nanoparticles were observed. In addition, the performance of these nanocomposite films as catalytic materials was assessed. The relevance of this work underlies that the catalytic activity, conversion degree and order of the reaction of the 4-nitrophenol-sodium borohydride (4NP-NaBH 4 ) reduction system depend on the size distribution, content and mainly to the location of gold nanoparticles in the nanocomposite films. Finally, the potential recyclability of these nanocomposite films as catalytic materials was studied.

  19. Modulation of catalytic activity in multi-domain protein tyrosine phosphatases.

    Directory of Open Access Journals (Sweden)

    Lalima L Madan

    Full Text Available Signaling mechanisms involving protein tyrosine phosphatases govern several cellular and developmental processes. These enzymes are regulated by several mechanisms which include variation in the catalytic turnover rate based on redox stimuli, subcellular localization or protein-protein interactions. In the case of Receptor Protein Tyrosine Phosphatases (RPTPs containing two PTP domains, phosphatase activity is localized in their membrane-proximal (D1 domains, while the membrane-distal (D2 domain is believed to play a modulatory role. Here we report our analysis of the influence of the D2 domain on the catalytic activity and substrate specificity of the D1 domain using two Drosophila melanogaster RPTPs as a model system. Biochemical studies reveal contrasting roles for the D2 domain of Drosophila Leukocyte antigen Related (DLAR and Protein Tyrosine Phosphatase on Drosophila chromosome band 99A (PTP99A. While D2 lowers the catalytic activity of the D1 domain in DLAR, the D2 domain of PTP99A leads to an increase in the catalytic activity of its D1 domain. Substrate specificity, on the other hand, is cumulative, whereby the individual specificities of the D1 and D2 domains contribute to the substrate specificity of these two-domain enzymes. Molecular dynamics simulations on structural models of DLAR and PTP99A reveal a conformational rationale for the experimental observations. These studies reveal that concerted structural changes mediate inter-domain communication resulting in either inhibitory or activating effects of the membrane distal PTP domain on the catalytic activity of the membrane proximal PTP domain.

  20. Antibacterial & Catalytic Activities of 2,2\\'-Dithio (2-Hydroxyphenyl ...

    African Journals Online (AJOL)

    This paper describes the in vitro evaluation of antibacterial activity of DNBH and its ruthenium complexes. All the synthesized compounds exhibited antibacterial activity against the Gram-positive bacteria namely Staphylococcus aureus at a conc of 100-25 mg/ml and Gram-negative bacteria such as Escherichia coli, ...

  1. Designer Ligands. Part 13. Synthesis and Catalytic Activity of ...

    African Journals Online (AJOL)

    Copper(I), copper(II), cobalt(II) and zinc(II) complexes of a macrocyclic, multidentate Schiff-base ligand have been prepared and, with the exception of the zinc(II) complex, have been shown to exhibit biomimetic catecholase activity. Keywords: Copper(II);Cobalt(II); Zinc(II); Biomimetic complexes; Catecholase activity

  2. Stereospecific synthesis and catalytic activity of L-histidylidene metal complexes.

    Science.gov (United States)

    Monney, Angèle; Alberico, Elisabetta; Ortin, Yannick; Müller-Bunz, Helge; Gladiali, Serafino; Albrecht, Martin

    2012-08-07

    We report on the synthesis, metal coordination, and catalytic impact of histidylidene, a histidine-derived N-heterocyclic carbene (NHC) ligand. The histidinium salt 3, comprising methyl substituents at both heterocyclic nitrogens and protected at the C- and N-terminus of the amino acid, was rhodated and iridated by a transmetallation protocol using Ag(2)O. Ambient temperature and short reaction times were pivotal for full retention of configuration at the α-carbon. The stereospecificity of the reaction was conveniently probed by (31)P NMR spectroscopy after transmetallation with rhodium(I) and coordination of enantiopure (S)-Ph-binepine. The histidylidene rhodium complexes are highly efficient catalysts for the mild hydrosilylation of ketones. For the cationic complexes [Rh(cod)(histidylidene)(phosphine)](+), lowering the temperature shifted the rate-limiting step of the catalytic reaction to an earlier stage that is not enantioselective. Hence the asymmetric induction-which is governed by the chiral phosphine-did not improve at low temperature.

  3. Effects of surface adsorption on catalytic activity of heavy meromyosin studied using a fluorescent ATP analogue.

    Science.gov (United States)

    Balaz, Martina; Sundberg, Mark; Persson, Malin; Kvassman, Jan; Månsson, Alf

    2007-06-19

    Biochemical studies in solution and with myosin motor fragments adsorbed to surfaces (in vitro motility assays) are invaluable for elucidation of actomyosin function. However, there is limited understanding of how surface adsorption affects motor properties, e.g., catalytic activity. Here we address this issue by comparing the catalytic activity of heavy meromyosin (HMM) in solution and adsorbed to standard motility assay surfaces [derivatized with trimethylchlorosilane (TMCS)]. For these studies we first characterized the interaction of HMM and actomyosin with the fluorescent ATP analogue adenosine 5'-triphosphate Alexa Fluor 647 2'- (or 3'-) O-(N-(2-aminoethyl)urethane) hexa(triethylammonium) salt (Alexa-ATP). The data suggest that Alexa-ATP is hydrolyzed by HMM in solution at a slightly higher rate than ATP but with a generally similar mechanism. Furthermore, Alexa-ATP is effective as a fuel for HMM-propelled actin filament sliding. The catalytic activity of HMM on TMCS surfaces was studied using (1) Alexa-ATP in total internal reflection fluorescence (TIRF) spectroscopy experiments and (2) Alexa-ATP and ATP in HPLC-aided ATPase measurements. The results support the hypothesis of different HMM configurations on the surface. However, a dominant proportion of the myosin heads were catalytically active, and their average steady-state hydrolysis rate was slightly higher (with Alexa-ATP) or markedly higher (with ATP) on the surface than in solution. The results are discussed in relation to the use of TMCS surfaces and Alexa-ATP for in vitro motility assays and single molecule studies. Furthermore, we propose a novel TIRF microscopy method to accurately determine the surface density of catalytically active myosin motors.

  4. Catalytic Activities of Ribozymes and DNAzymes in Water and Mixed Aqueous Media

    Directory of Open Access Journals (Sweden)

    Shu-ichi Nakano

    2017-11-01

    Full Text Available Catalytic nucleic acids are regarded as potential therapeutic agents and biosensors. The catalytic activities of nucleic acid enzymes are usually investigated in dilute aqueous solutions, although the physical properties of the reaction environment inside living cells and that in the area proximal to the surface of biosensors in which they operate are quite different from those of pure water. The effect of the molecular environment is also an important focus of research aimed at improving and expanding nucleic acid function by addition of organic solvents to aqueous solutions. In this study, the catalytic activities of RNA and DNA enzymes (hammerhead ribozyme, 17E DNAzyme, R3C ribozyme, and 9DB1 DNAzyme were investigated using 21 different mixed aqueous solutions comprising organic compounds. Kinetic measurements indicated that these enzymes can display enhanced catalytic activity in mixed solutions with respect to the solution containing no organic additives. Correlation analyses revealed that the turnover rate of the reaction catalyzed by hammerhead ribozyme increased in a medium with a lower dielectric constant than water, and the turnover rate of the reaction catalyzed by 17E DNAzyme increased in conditions that increased the strength of DNA interactions. On the other hand, R3C ribozyme and 9DB1 DNAzyme displayed no significant turnover activity, but their single-turnover rates increased in many mixed solutions. Our data provide insight into the activity of catalytic nucleic acids under various conditions that are applicable to the medical and technology fields, such as in living cells and in biosensors.

  5. Lipase immobilized catalytically active membrane for synthesis of lauryl stearate in a pervaporation membrane reactor.

    Science.gov (United States)

    Zhang, Weidong; Qing, Weihua; Ren, Zhongqi; Li, Wei; Chen, Jiangrong

    2014-11-01

    A composite catalytically active membrane immobilized with Candida rugosa lipase has been prepared by immersion phase inversion technique for enzymatic synthesis of lauryl stearate in a pervaporation membrane reactor. SEM images showed that a "sandwich-like" membrane structure with a porous lipase-PVA catalytic layer uniformly coated on a polyvinyl alcohol (PVA)/polyethersulfone (PES) bilayer was obtained. Optimum conditions for lipase immobilization in the catalytic layer were determined. The membrane was proved to exhibit superior thermal stability, pH stability and reusability than free lipase under similar conditions. In the case of pervaporation coupled synthesis of lauryl stearate, benefited from in-situ water removal by the membrane, a conversion enhancement of approximately 40% was achieved in comparison to the equilibrium conversion obtained in batch reactors. In addition to conversion enhancement, it was also found that excess water removal by the catalytically active membrane appears to improve activity of the lipase immobilized. Copyright © 2014 Elsevier Ltd. All rights reserved.

  6. A Polyphenylene Support for Pd Catalysts with Exceptional Catalytic Activity

    DEFF Research Database (Denmark)

    Wang, Feng; Mielby, Jerrik Jørgen; Richter, Felix Herrmann

    2014-01-01

    We describe a solid polyphenylene support that serves as an excellent platform for metal-catalyzed reactions that are normally carried out under homogeneous conditions. The catalyst is synthesized by palladium-catalyzed Suzuki coupling which directly results in formation of palladium nanoparticles...... confined to a porous polyphenylene network. The composite solid is in turn highly active for further Suzuki coupling reactions, including non-activated substrates that are challenging even for molecular catalysts....

  7. Catalytic Synthesis and Antifungal Activity of New Polychlorinated Natural Terpenes

    Directory of Open Access Journals (Sweden)

    Hana Ighachane

    2017-01-01

    Full Text Available Various unsaturated natural terpenes were selectively converted to the corresponding polychlorinated products in good yields using iron acetylacetonate in combination with nucleophilic cocatalyst. The synthesized compounds were evaluated for their in vitro antifungal activity. The antifungal bioassays showed that 2c and 2d possessed significant antifungal activity against Fusarium oxysporum f. sp. albedinis (Foa, Fusarium oxysporum f. sp. canariensis (Foc, and Verticillium dahliae (Vd.

  8. Investigation of the Origin of Catalytic Activity in Oxide-Supported Nanoparticle Gold

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, Ian [Univ. of Virginia, Charlottesville, VA (United States)

    2017-05-26

    Since Haruta’s discovery in 1987 of the surprising catalytic activity of supported Au nanoparticles, we have seen a very large number of experimental and theoretical efforts to explain this activity and to fully understand the nature of the behavior of the responsible active sites. In 2011, we discovered that a dual catalytic site at the perimeter of ~3nm diameter Au particles supported on TiO2 is responsible for oxidative catalytic activity. O2 molecules bind with Au atoms and Ti4+ ions in the TiO2 support and the weakened O-O bond dissociates at low temperatures, proceeding to produce O atoms which act as oxidizing agents for the test molecule, CO. The papers supported by DOE have built on this finding and have been concerned with two aspects of the behavior of Au/TiO2 catalysts: (1). Mechanistic behavior of dual catalytic sites in the oxidation of organic molecules such as ethylene and acetic acid; (2). Studies of the electronic properties of the TiO2 (110) single crystal in relation to its participation in charge transfer at the occupied dual catalytic site. A total of 20 papers have been produced through DOE support of this work. The papers combine IR spectroscopic investigations of Au/TiO2 catalysts with surface science on the TiO2(110) and TiO2 nanoparticle surfaces with modern density functional modeling. The primary goals of the work were to investigate the behavior of the dual Au/Ti4+ site for the partial oxidation of alcohols to acids, the hydrogenation of aldehydes and ketones to alcohols, and the condensation of oxygenate intermediates- all processes related to the utilization of biomass in the production of useful chemical energy sources.

  9. Synthesis, Characterization and Catalytic Activity of Cu/Cu2O Nanoparticles Prepared in Aqueous Medium

    Directory of Open Access Journals (Sweden)

    Sayed M. Badawy

    2015-07-01

    Full Text Available Copper/Copper oxide (Cu/Cu2O nanoparticles were synthesized by modified chemical reduction method in an aqueous medium using hydrazine as reducing agent and copper sulfate pentahydrate as precursor. The Cu/Cu2O nanoparticles were characterized by X-ray Diffraction (XRD, Energy Dispersive X-ray Fluorescence (EDXRF, Scanning Electron Microscope (SEM, and Transmission Electron Microscope (TEM. The analysis revealed the pattern of face-centered cubic (fcc crystal structure of copper Cu metal and cubic cuprites structure for Cu2O. The SEM result showed monodispersed and agglomerated particles with two micron sizes of about 180 nm and 800 nm, respectively. The TEM result showed few single crystal particles of face-centered cubic structures with average particle size about 11-14 nm. The catalytic activity of Cu/Cu2O nanoparticles for the decomposition of hydrogen peroxide was investigated and compared with manganese oxide MnO2. The results showed that the second-order equation provides the best correlation for the catalytic decomposition of H2O2 on Cu/Cu2O. The catalytic activity of hydrogen peroxide by Cu/Cu2O is less than the catalytic activity of MnO2 due to the presence of copper metal Cu with cuprous oxide Cu2O. © 2015 BCREC UNDIP. All rights reservedReceived: 6th January 2015; Revised: 14th March 2015; Accepted: 15th March 2015How to Cite: Badawy, S.M., El-Khashab, R.A., Nayl, A.A. (2015. Synthesis, Characterization and Catalytic Activity of Cu/Cu2O Nanoparticles Prepared in Aqueous Medium. Bulletin of Chemical Reaction Engineering & Catalysis, 10 (2: 169-174. (doi:10.9767/bcrec.10.2.7984.169-174 Permalink/DOI: http://dx.doi.org/10.9767/bcrec.10.2.7984.169-174  

  10. Reactive oxygen species inhibit catalytic activity of peptidylarginine deiminase

    DEFF Research Database (Denmark)

    Damgaard, Dres; Bjørn, Mads Emil; Jensen, Peter Østrup

    2017-01-01

    on calcium and reducing conditions. However, reactive oxygen species (ROS) have been shown to induce citrullination of histones in granulocytes. Here we examine the ability of H2O2 and leukocyte-derived ROS to regulate PAD activity using citrullination of fibrinogen as read-out. H2O2 at concentrations above...... from stimulated leukocytes was unaffected by exogenously added H2O2 at concentrations up to 1000 µM. The role of ROS in regulating PAD activity may play an important part in preventing hypercitrullination of proteins....

  11. Nitroreductase from Salmonella typhimurium: characterization and catalytic activity.

    Science.gov (United States)

    Yanto, Yanto; Hall, Mélanie; Bommarius, Andreas S

    2010-04-21

    The biocatalytic activity of nitroreductase from Salmonella typhimurium (NRSal) was investigated for the reduction of alpha,beta-unsaturated carbonyl compounds, nitroalkenes, and nitroaromatics. The synthesized gene was subcloned into a pET28 overexpression system in E.coli BL21 strain, and the corresponding expressed protein was purified to homogeneity with 15% protein mass yield and 41% of total activity recovery. NRSal showed broad substrate acceptance for various nitro compounds such as 1-nitrocyclohexene and aliphatic nitroalkenes (alkene reductase activity), as well as nitrobenzene (nitroreductase activity), with substrate conversion efficiency of > 95%. However, the reduction of enones was generally low, proceeding albeit with high stereoselectivity. The efficient biocatalytic reduction of substituted nitroalkenes provides a route for the preparation of the corresponding nitroalkanes. NRSal also demonstrated the first single isolated enzyme-catalyzed reduction of nitrobenzene to aniline through the formation of nitrosobenzene and phenylhydroxylamine as intermediates. However, chemical condensation of the two intermediates to produce azoxybenzene currently limits the yield of aniline.

  12. Trends in Catalytic Activity for SOFC Anode materials

    DEFF Research Database (Denmark)

    Rossmeisl, Jan; Bessler, W. G.

    2008-01-01

    for nine different metal/stabilized zirconia anodes. The experimentally-observed variation of electrode activity with anode material is well-correlated with the calculated stability of surface-adsorbed atomic oxygen, but uncorrelated with the stability of surface-adsorbed hydrogen. This finding indicates...

  13. Aged nano-structured platinum based catalyst: effect of chemical treatment on adsorption and catalytic activity.

    Science.gov (United States)

    Shim, Wang Geun; Nahm, Seung Won; Park, Hyuk Ryeol; Yun, Hyung Sun; Seo, Seong Gyu; Kim, Sang Chai

    2011-02-01

    To examine the effect of chemical treatment on the adsorption and catalytic activity of nanostructured platinum based catalyst, the aged commercial Pt/AC catalyst was pretreated with sulfuric acid (H2SO4) and a cleaning agent (Hexane). Several reliable methods such as nitrogen adsorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) were employed to characterize the aged Pt/AC catalyst and its chemically pretreated Pt/AC catalysts. The catalytic and adsorption activities of nano-structured heterogeneous Pt/AC catalyst were investigated on the basis of toluene oxidation and adsorption isotherm data. In addition, the adsorption isotherms of toluene were used to calculate the adsorption energy distribution functions for the parent catalyst and its pre-treated nano-structured Pt/AC catalysts. It was found that sulfuric acid aqueous treatment can enhance the catalytic performance of aged Pt/AC catalyst toward catalytic oxidation of toluene. It was also shown that a comparative analysis of the energy distribution functions for nano-structured Pt/AC catalysts as well as the pore size distribution provides valuable information about their structural and energetic heterogeneity.

  14. Magnetically recyclable reduced graphene oxide nanosheets/magnetite-palladium aerogel with superior catalytic activity and reusability.

    Science.gov (United States)

    Feng, Yan; Zhang, Hui; Xin, Baifu; Wu, Jie

    2017-11-15

    A two-step method was employed to synthesize reduced graphene oxide nanosheets/magnetite-palladium (rGSs/Fe3O4-Pd) aerogel, with excellent catalytic activity and recyclability. Firstly, graphene oxide nanosheet (GS) hydrogels were formed by the self-assembly of GSs during the hydrothermal process. Meanwhile, hematite (α-Fe2O3) and Pd nanoparticles (NPs) were synthesized and anchored onto the surface of the hydrogel. During heat-treatment, GSs were reduced to rGSs, while nonmagnetic α-Fe2O3NPs were converted to magnetic Fe3O4 NPs. The as-obtained rGSs/Fe3O4-Pd aerogel displayed a three-dimensional interconnected hierarchical porous architecture, which was rich in mesopores and macropores. Such a structure was suitable for catalysis, since it not only improved the mass diffusion and transport, but also readily exposed the catalytic Pd NPs to the reactants. The typical reduction of 4-nitrophenol was chosen as a model reaction to evaluate the catalytic performance of the aerogel. As anticipated, both the reaction rate constant and turn over frequency of the aerogel were much higher than those of the commercial Pd/C catalyst. Moreover, due to incorporation of Fe3O4 NPs, the rGSs/Fe3O4-Pd aerogel could be magnetically separated from the reaction solution and reused, without obvious loss of catalytic activity. Copyright © 2017 Elsevier Inc. All rights reserved.

  15. Nobel metal-TiO2 nanocomposites : synthesis, characterization and catalytic activity

    OpenAIRE

    Nascimento, Ana Cláudia Lobão do

    2016-01-01

    The work presented in this thesis is focused on the synthesis, characterization and catalytic activity of gold-TiO2 composites. We wanted to take advantage of the experience of the Colloid Chemistry Group, whose activity is strongly focused on the synthesis, characterization and evaluation of the formation mechanism of metal nanocrystals (mainly gold and silver) with size and shape control, which allows a fine-tuning of the optical response of these colloids in the UV-vis-NIR spectral range. ...

  16. Heating activated red mud catalytic ozonation for degradation nitrobenzene from aqueous solution: performance and influence of preparation factors.

    Science.gov (United States)

    Qi, Fei; Li, Huanan; Xu, Bingbing; Sun, Dezhi

    2014-09-01

    Red mud (RM), a waste residue of alumina refinery, has been used to develop an effective catalyst to enhance nitrobenzene (NB) removal from aqueous solution by ozonation. The result showed that the development of catalytic activity of RM was obtained by heating activation. The effects of different factors (heating temperature and time) have been examined in batch experiments. Sample prepared by heating RM at 400 degrees C for 4 h showed the highest activity in catalytic ozonation of NB. The temperature exhibited a significant effect on the performance of both NB removal and ozone decomposition. However, the effect of the heating time was insignificant. Experiments of both catalytic ozone decomposition and hydroxyl radical (*OH) inhibiting confirmed the existence of *OH in heated RM catalytic ozonation. According to the XRD pattern, the change of mineral content was the key reason for the development of catalytic activity, especially for hematite and magnetite.

  17. New electrochemiluminescence catalyst: Cu2O semiconductor crystal and the enhanced activity of octahedra synthesized by iodide ions coordination

    Science.gov (United States)

    Zhang, Ling; Qi, Liming; Gao, Wenyue; Niu, Wenxin; Luque, Rafael; Xu, Guobao

    2017-11-01

    Cuprous oxide (Cu2O) crystals are usually used as the photocatalysts of water splittings and carbon monoxide oxidations. Herein, we report the new catalytic properties of Cu2O to the electrochemilumenescence (ECL) reactions of luminol and oxygen. Adjusting the shape of Cu2O microcrystals from cube to octahedra also facilities the improved electrocatalytic acticity, where octahedral Cu2O microcrystals possess higher ECL signal by 25% at  ‑0.6 V (versus Ag/AgCl) at pH 7.4. The octahedral Cu2O microcrystals are synthesized by the coordination of iodide ions to the surface, which alters the crystals shapes from cubes to octahedra. Size-distribution of octahedra is improved with this mehod compared to the previous studies with only hydroxide ions as the coordinates. The catalytic activity of octahedral Cu2O crystals is expected to be compared with the noble metal nanomaterials and constructed the high-efficiency and low-cost ECL biosensors.

  18. Application of a silver-olefin coordination polymer as a catalytic curing agent for self-healing epoxy polymers

    Science.gov (United States)

    Everitt, D. T.; Coope, T. S.; Trask, R. S.; Wass, D. F.; Bond, I. P.

    2015-05-01

    A silver-olefin based coordination polymer was prepared in a simple, one step process to act as an initiator to facilitate the ring-opening polymerization of epoxides. Thermal analysis found the complex to be capable of curing a range of commercially available epoxy resins used in the manufacture of conventional composite materials. Curing of the oligomeric diglycidyl ether bisphenol A resin, Epon 828, in combination with a non-toxic solvent, ethyl phenylacetate, was studied by differential scanning calorimetry. The mechanical characterization of the resultant cured polymers was conducted by single lap shear tests. Tapered double cantilever beam (TDCB) test specimens containing 2.5 pph of silver-olefin initiator, both with and without embedded microcapsules, were analyzed for their healing performance. Healing efficiency values were found to be strongly dependent on the applied healing temperature. A mean recovery of 74% fracture load was found in TDCB samples after being healed at 70 °C for 48 h.

  19. The energetics of supported metal nanoparticles: relationships to sintering rates and catalytic activity.

    Science.gov (United States)

    Campbell, Charles T

    2013-08-20

    Transition metal nanoparticles on the surfaces of oxide and carbon support materials form the basis for most solid catalysts and electrocatalysts, and have important industrial applications such as fuel production, fuels, and pollution prevention. In this Account, I review my laboratory group's research toward the basic understanding of the effects of particle size and support material on catalytic properties. I focus on studies of well-defined model metal nanoparticle catalysts supported on single-crystalline oxide surfaces. My group structurally characterized such catalysts using a variety of ultrahigh vacuum surface science techniques. We then measured the energies of metal atoms in these supported nanoparticles, using adsorption calorimetry tools that we developed. These metal adsorption energies increase with increasing size of the nanoparticles, until their diameter exceeds about 6 nm. Below 6 nm, the nature of the oxide support surface reaches also greatly affects the metal adsorption energies. Using both adsorption calorimetry and temperature programmed desorption (TPD), we measured the energy of adsorbed catalytic intermediates on metal nanoparticles supported on single crystal oxide surfaces, as a function of particle size. The studies reveal correlations between a number of characteristics. These include the size- and support-dependent energies of metal surface atoms in supported metal nanoparticles, their rates of sintering, how strongly they bind small adsorbates, and their catalytic activity. The data are consistent with the following model: the more weakly the surface metal atom is attached to the nanomaterial, the more strongly it binds small adsorbates. Its strength of attachment to the nanomaterial is dominated by the number of metal-metal bonds which bind it there, but also by the strength of metal/oxide interfacial bonding. This same combination of bond strengths controls sintering rates as well: the less stable a surface metal atom is in the

  20. Comparative catalytic activity of PET track-etched membranes with embedded silver and gold nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Mashentseva, Anastassiya, E-mail: mashentseva.a@gmail.com [Institute of Nuclear Physics, Ibragimov St. 1, 050032 Almaty (Kazakhstan); The L.N. Gumilyov Eurasian National University, Satpayev Str., 2, 010008 Astana (Kazakhstan); Borgekov, Daryn [Institute of Nuclear Physics, Ibragimov St. 1, 050032 Almaty (Kazakhstan); The L.N. Gumilyov Eurasian National University, Satpayev Str., 2, 010008 Astana (Kazakhstan); Kislitsin, Sergey [Institute of Nuclear Physics, Ibragimov St. 1, 050032 Almaty (Kazakhstan); Zdorovets, Maxim [Institute of Nuclear Physics, Ibragimov St. 1, 050032 Almaty (Kazakhstan); The L.N. Gumilyov Eurasian National University, Satpayev Str., 2, 010008 Astana (Kazakhstan); Migunova, Anastassiya [Institute of Nuclear Physics, Ibragimov St. 1, 050032 Almaty (Kazakhstan)

    2015-12-15

    Irradiated by heavy ions nanoporous polyethylene terephthalate track-etched membranes (PET TeMs) after {sup +15}Kr{sup 84} ions bombardment (1.75 MeV/nucl with the ion fluency of 1 × 10{sup 9} cm{sup −2}) and sequential etching was applied in this research as a template for development of composites with catalytically enriched properties. A highly ordered silver and gold nanotubes arrays were embedded in 100 nm pores of PET TeMs via electroless deposition technique at 4 °C during 1 h. All “as-prepared” composites were examined for catalytic activity using reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride as a common reaction to test metallic nanostructures catalysts. The effect of temperature on the catalytic activity was investigated in range of 292–313 K and activation energy were calculated. K{sub app} of Ag/PET composites linearly increase with an increase of the temperature thus normal Arrhenius behavior have been seen and the activation energy was calculated to be 42.13 kJ/mol. Au/PET composites exhibit not only more powerful catalytic activity but also non-linear dependence of rate constant from temperature. K{sub app} increased with increasing temperature throughout the 292–308 K temperature range; the reaction had an activation energy 65.32 kJ/mol. In range 311–313 K rate constant dramatically decreased and the apparent activation energy at this temperature rang was −91.44 kJ/mol due some structural changes, i.e. agglomeration of Au nanoparticles on the surface of composite.

  1. Pyrrolidone Modifying Gold Nanocatalysts for Enhanced Catalytic Activities in Aerobic Oxidation of Alcohols and Carbon Monoxide

    Directory of Open Access Journals (Sweden)

    Yingji Song

    2017-01-01

    Full Text Available Enhancing the catalytic activity of supported metal nanoparticle is a great demand but extremely challenging to make. We reported a simple strategy for enhancing the activities by employing the polyvinylpyrrolidone (PVP additive, where a series of supported Au nanoparticle catalysts including Au/C, Au/BN, Au/TiO2, and Au/SBA-15 exhibited significantly higher activities in the oxidation of various alcohols and carbon monoxide by molecular oxygen after adding PVP to the reaction system. The XPS study indicates that PVP could electronically interact with Au to form high active Au sites for molecular oxygen, thus causing improved activities for the various oxidation reactions.

  2. Iron-substituted cubic silsesquioxane pillared clays: Synthesis, characterization and acid catalytic activity.

    Science.gov (United States)

    Potsi, Georgia; Ladavos, Athanasios K; Petrakis, Dimitrios; Douvalis, Alexios P; Sanakis, Yiannis; Katsiotis, Marios S; Papavassiliou, Georgios; Alhassan, Saeed; Gournis, Dimitrios; Rudolf, Petra

    2018-01-15

    Novel pillared structures were developed from the intercalation of iron-substituted cubic silsesquioxanes in a sodium and an acid-activated montmorillonite nanoclay and evaluated as acid catalysts. Octameric cubic oligosiloxanes were formed upon controlled hydrolytic polycondensation of the corresponding monomer (a diamino-alkoxysilane) and reacted with iron cations to form complexes that were intercalated within the layered nanoclay matrices. Upon calcination iron oxide nanoparticles are formed which are located on the silica cubes (pillars) and on the surfaces of the clay platelets. Acid activation of the nanoclay was performed in order to increase the number of acid active sites in the pristine clay and thus increase its catalytic activity. A plethora of analytical techniques including X-ray diffraction, thermal analyses, Fourier transform infrared, electron paramagnetic resonance, Raman, Mössbauer and X-ray photoelectron spectroscopies and porosimetry measurements were used in order to follow the synthesis steps and to fully characterize the final catalysts. The resulting pillared clays exhibit a high specific area and show significant acid catalytic activity that was verified using the catalytic dehydration of isopropanol asa probe reaction. Copyright © 2017 Elsevier Inc. All rights reserved.

  3. Comprehensive Characterization of AMP-activated Protein Kinase Catalytic Domain by Top-down Mass Spectrometry

    Science.gov (United States)

    Yu, Deyang; Peng, Ying; Ayaz-Guner, Serife; Gregorich, Zachery R.; Ge, Ying

    2015-01-01

    AMP-activated protein kinase (AMPK) is a serine/threonine protein kinase that is essential in regulating energy metabolism in all eukaryotic cells. It is a heterotrimeric protein complex composed of a catalytic subunit (α) and two regulatory subunits (β and γ. C-terminal truncation of AMPKα at residue 312 yielded a protein that is active upon phosphorylation of Thr172 in the absence of β and γ subunits, which is refered to as the AMPK catalytic domain and commonly used to substitute for the AMPK heterotrimeric complex in in vitro kinase assays. However, a comprehensive characterization of the AMPK catalytic domain is lacking. Herein, we expressed a His-tagged human AMPK catalytic domin (denoted as AMPKΔ) in E. coli, comprehensively characterized AMPKΔ in its basal state and after in vitro phosphorylation using top-down mass spectrometry (MS), and assessed how phosphorylation of AMPKΔ affects its activity. Unexpectedly, we found that bacterially-expressed AMPKΔ was basally phosphorylated and localized the phosphorylation site to the His-tag. We found that AMPKΔ has noticeable basal activity and was capable of phosphorylating itself and its substrates without activating phosphorylation at Thr172. Moreover, our data suggested that Thr172 is the only site phosphorylated by its upstream kinase, liver kinase B1, and that this phosphorylation dramatically increases the kinase activity of AMPKΔ. Importantly, we demonstrated that top-down MS in conjunction with in vitro phosphorylation assay is a powerful approach for monitoring phosphorylation reaction and determining sequential order of phosphorylation events in kinase-substrate systems. PMID:26489410

  4. Structural properties of cyanase. Denaturation, renaturation, and role of sulfhydryls and oligomeric structure in catalytic activity.

    Science.gov (United States)

    Little, R M; Anderson, P M

    1987-07-25

    Cyanase is an inducible enzyme in Escherichia coli that catalyzes bicarbonate-dependent decomposition of cyanate to give ammonia and bicarbonate. The enzyme is composed of 8-10 identical subunits (Mr = 17,008). The objective of this study was to clarify some of the structural properties of cyanase for the purpose of understanding the relationship between oligomeric structure and catalytic activity. Circular dichroism studies showed that cyanase has a significant amount of alpha-helix and beta-sheet structure. The one sulfhydryl group per subunit does not react with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) unless cyanase is denatured. Denaturation is apparently complete in 10 M urea or 6 M guanidine hydrochloride, but is significantly reduced in 10 M urea by the presence of azide (analog of cyanate) and is incomplete in 8 M urea. Denatured cyanase could be renatured and reactivated (greater than 85%) by removal of denaturants. Reactivation was greatly facilitated by the presence of certain anions, particularly bicarbonate, and by high ionic strength and protein concentration. The catalytic activity of renatured cyanase was associated only with oligomer. Cyanase that had been denatured in the presence of DTNB to give a cyanase-DTNB derivative could also be renatured at 26 degrees C to give active cyanase-DTNB oligomer. The active oligomeric form of the cyanase-DTNB derivative could be converted reversibly to inactive dimer by lowering the temperature to 4 degrees C or by reduction of the ionic strength and removal of monoanions. These results provide evidence that free sulfhydryl groups are not required for catalytic activity and that catalytic activity may be dependent upon oligomeric structure.

  5. 34 CFR 412.30 - What additional activities must be carried out by Curriculum Coordination Centers?

    Science.gov (United States)

    2010-07-01

    ... Curriculum Coordination Centers? 412.30 Section 412.30 Education Regulations of the Offices of the Department... NETWORK FOR CURRICULUM COORDINATION IN VOCATIONAL AND TECHNICAL EDUCATION What Conditions Must Be Met After An Award? § 412.30 What additional activities must be carried out by Curriculum Coordination...

  6. Rational design of ornithine decarboxylase with high catalytic activity for the production of putrescine.

    Science.gov (United States)

    Choi, Hyang; Kyeong, Hyun-Ho; Choi, Jung Min; Kim, Hak-Sung

    2014-09-01

    Putrescine finds wide industrial applications in the synthesis of polymers, pharmaceuticals, agrochemicals, and surfactants. Owing to economic and environmental concerns, the microbial production of putrescine has attracted a great deal of attention, and ornithine decarboxylase (ODC) is known to be a key enzyme in the biosynthetic pathway. Herein, we present the design of ODC from Escherichia coli with high catalytic efficiency using a structure-based rational approach. Through a substrate docking into the model structure of the enzyme, we first selected residues that might lead to an increase in catalytic activity. Of the selected residues that are located in the α-helix and the loops constituting the substrate entry site, a mutational analysis of the single mutants identified two key residues, I163 and E165. A combination of two single mutations resulted in a 62.5-fold increase in the catalytic efficiency when compared with the wild-type enzyme. Molecular dynamics simulations of the best mutant revealed that the substrate entry site becomes more flexible through mutations, while stabilizing the formation of the dimeric interface of the enzyme. Our approach can be applied to the design of other decarboxylases with high catalytic efficiency for the production of various chemicals through bio-based processes.

  7. Bicarbonate Modulates Photoreceptor Guanylate Cyclase (ROS-GC) Catalytic Activity*

    Science.gov (United States)

    Duda, Teresa; Wen, Xiao-Hong; Isayama, Tomoki; Sharma, Rameshwar K.; Makino, Clint L.

    2015-01-01

    By generating the second messenger cGMP in retinal rods and cones, ROS-GC plays a central role in visual transduction. Guanylate cyclase-activating proteins (GCAPs) link cGMP synthesis to the light-induced fall in [Ca2+]i to help set absolute sensitivity and assure prompt recovery of the response to light. The present report discloses a surprising feature of this system: ROS-GC is a sensor of bicarbonate. Recombinant ROS-GCs synthesized cGMP from GTP at faster rates in the presence of bicarbonate with an ED50 of 27 mm for ROS-GC1 and 39 mm for ROS-GC2. The effect required neither Ca2+ nor use of the GCAPs domains; however, stimulation of ROS-GC1 was more powerful in the presence of GCAP1 or GCAP2 at low [Ca2+]. When applied to retinal photoreceptors, bicarbonate enhanced the circulating current, decreased sensitivity to flashes, and accelerated flash response kinetics. Bicarbonate was effective when applied either to the outer or inner segment of red-sensitive cones. In contrast, bicarbonate exerted an effect when applied to the inner segment of rods but had little efficacy when applied to the outer segment. The findings define a new regulatory mechanism of the ROS-GC system that affects visual transduction and is likely to affect the course of retinal diseases caused by cGMP toxicity. PMID:25767116

  8. Molecular diversity and catalytic activity of Thermus DNA polymerases.

    Science.gov (United States)

    Gibbs, Moreland D; Reeves, Rosalind A; Mandelman, David; Mi, Qingli; Lee, Jun; Bergquist, Peter L

    2009-09-01

    Thermus aquaticus DNA polymerase (Taq polymerase) made the polymerase chain reaction feasible and led to a paradigm shift in genomic analysis. Other Thermus polymerases were reported to have comparable performance in PCR and there was an analysis of their properties in the 1990s. We re-evaluated our earlier phylogeny of Thermus species on the basis of 16S rDNA sequences and concluded that the genus could be divided into eight clades. We examined 22 representative isolates and isolated their DNA polymerase I genes. The eight most diverse polymerase genes were selected to represent the eight clades and cloned into an expression vector coding for a His-tag. Six of the eight polymerases were expressed so that there was sufficient protein for purification. The proteins were purified to homogeneity and examination of the biochemical characteristics showed that although they were competent to perform PCR, none was as thermostable as commercially available Taq polymerase; all had similar error-frequencies to Taq polymerase and all showed the expected 5'-3' exonuclease activity. We conclude that the initial selection of T. aquaticus for DNA polymerase purification was a far-reaching and fortuitous choice but simple mutagenesis procedures on other Thermus-derived polymerases should provide comparable thermostability for the PCR reaction.

  9. Active Hydrogenation Catalyst with a Structured, Peptide-Based Outer-Coordination Sphere

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Avijita; Buchko, Garry W.; Reback, Matthew L.; O' Hagan, Molly J.; Ginovska-Pangovska, Bojana; Linehan, John C.; Shaw, Wendy J.

    2012-10-05

    The synthesis, catalytic activity, and structural features of a rhodium-based hydrogenation catalyst containing a phosphine ligand coupled to a 14-residue peptide are reported. Both CD and NMR spectroscopy show that the peptide adopts a helical structure in 1:1:1 TFE/MeCN/H2O that is maintained when the peptide is attached to the ligand and when the ligand is attached to the metal complex. The metal complex hydrogenates aqueous solutions of 3-butenol to 1-butanol at 360 ± 50 turnovers/Rh/h at 294 K. This peptide- based catalyst represents a starting point for developing and characterizing a peptide-based outer-coordination sphere that can be used to introduce enzyme-like features into molecular catalysts. This work was funded by the US DOE Basic Energy Sciences, Chemical Sciences, Geoscience and Biosciences Division (AJ, JCL and WJS), the Office of Science Early Career Research Program through the Office of Basic Energy Sciences (GWB, MLR and WJS). Part of the research was conducted at the W.R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by U.S. Department of Energy’s Office of Biolog-ical and Environmental Research (BER) program located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the U.S. Department of Energy.

  10. Tuning Porphyrin Assembly and Electrochemical Catalytic Activity with Halogen Substituents.

    Science.gov (United States)

    Kawamoto, Teppei; Yoshimoto, Soichiro

    2015-10-27

    The adlayers of three metalloporphyrins, 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin cobalt(II) (CoTMePP), 5,10,15,20-tetrakis(4-bromophenyl)porphyrin cobalt(II) (CoTBrPP), and 5,10,15,20-tetrakis(4-iodophenyl)porphyrin cobalt(II) (CoTIPP), on Au(111) were investigated at the solid-liquid interface under electrochemical conditions. In situ scanning tunneling microscopy (STM) was employed to investigate the adlayer structures of CoTMePP, CoTBrPP, and CoTIPP in HClO4 solution. Highly ordered adlayers of the three metalloporphyrins were formed on the Au(111) electrode surface by simple immersion into benzene solutions containing each compound. The adlayer structure of the three cobalt porphyrin derivatives was influenced by the functional group on the phenyl moieties. In particular, a characteristic molecular assembly of CoTIPP molecules was found on Au(111) as a result of the I···I interactions between CoTIPP molecules. The adlattice constants increased in the order -OCH3 HClO4, whereas these adlayers were stable in the potential range from 0.90 to 0 V versus the reversible hydrogen electrode. A dependence upon the functional groups among the three CoTPP derivatives was clearly found in the adlattice constants and O2 reduction potentials, revealing that the two-dimensional (2D) molecular assembly and electrochemical activity for dioxygen reduction of the tetraphenylporphyrin derivatives can be tuned by introducing functional groups at the 4 positions of the phenyl moieties, especially iodine substituents.

  11. Bicarbonate Modulates Photoreceptor Guanylate Cyclase (ROS-GC) Catalytic Activity.

    Science.gov (United States)

    Duda, Teresa; Wen, Xiao-Hong; Isayama, Tomoki; Sharma, Rameshwar K; Makino, Clint L

    2015-04-24

    By generating the second messenger cGMP in retinal rods and cones, ROS-GC plays a central role in visual transduction. Guanylate cyclase-activating proteins (GCAPs) link cGMP synthesis to the light-induced fall in [Ca(2+)]i to help set absolute sensitivity and assure prompt recovery of the response to light. The present report discloses a surprising feature of this system: ROS-GC is a sensor of bicarbonate. Recombinant ROS-GCs synthesized cGMP from GTP at faster rates in the presence of bicarbonate with an ED50 of 27 mM for ROS-GC1 and 39 mM for ROS-GC2. The effect required neither Ca(2+) nor use of the GCAPs domains; however, stimulation of ROS-GC1 was more powerful in the presence of GCAP1 or GCAP2 at low [Ca(2+)]. When applied to retinal photoreceptors, bicarbonate enhanced the circulating current, decreased sensitivity to flashes, and accelerated flash response kinetics. Bicarbonate was effective when applied either to the outer or inner segment of red-sensitive cones. In contrast, bicarbonate exerted an effect when applied to the inner segment of rods but had little efficacy when applied to the outer segment. The findings define a new regulatory mechanism of the ROS-GC system that affects visual transduction and is likely to affect the course of retinal diseases caused by cGMP toxicity. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  12. Enhanced catalytic activity of solid and hollow platinum-cobalt nanoparticles towards reduction of 4-nitrophenol

    Science.gov (United States)

    Krajczewski, Jan; Kołątaj, Karol; Kudelski, Andrzej

    2016-12-01

    Previous investigations of hollow platinum nanoparticles have shown that such nanostructures are more active catalysts than their solid counterparts towards the following electrochemical reactions: reduction of oxygen, evolution of hydrogen, and oxidation of borohydride, methanol and formic acid. In this work we show that synthesised using standard galvanic replacement reaction (with Co templates) hollow platinum nanoparticles exhibit enhanced catalytic activity also towards reduction of 4-nitrophenol by sodium borohydride in water. Unlike in the case of procedures involving hollow platinum catalysts employed so far to carry out this reaction it is not necessary to couple analysed platinum nanoparticles to the surface of an electrode. Simplification of the analyzed reaction may eliminate same experimental errors. We found that the enhanced catalytic activity of hollow Pt nanoparticles is not only connected with generally observed larger surface area of hollow nanostructures, but is also due to the contamination of formed hollow nanostructures with cobalt, from which sacrificial templates used in the synthesis of hollow Pt nanostrustures have been formed. Because using sacrificial templates is a typical method of synthesis of hollow metal nanostructures, formed hollow nanoparticles are probably often contaminated, which may significantly influence their catalytic activity.

  13. Catalytic activity of pyrite for coal liquefaction reaction; Tennen pyrite no shokubai seino ni kansuru kento

    Energy Technology Data Exchange (ETDEWEB)

    Hirano, K.; Kozu, M.; Okada, T.; Kobayashi, M. [Nippon Coal Oil Co. Ltd., Tokyo (Japan)

    1996-10-28

    Since natural pyrite is easy to obtain and cheap as coal liquefaction catalyst, it is to be used for the 150 t/d scale NEDOL process bituminous coal liquefaction pilot plant. NEDO and NCOL have investigated the improvement of catalytic activity of pulverized natural pyrite for enhancing performance and economy of the NEDOL process. In this study, coal liquefaction tests were conducted using natural pyrite catalyst pulverized by dry-type bowl mill under nitrogen atmosphere. Mechanism of catalytic reaction of the natural pyrite was discussed from relations between properties of the catalyst and liquefaction product. The natural pyrite provided an activity to transfer gaseous hydrogen into the liquefaction product. It was considered that pulverized pyrite promotes the hydrogenation reaction of asphaltene because pulverization increases its contact rate with reactant and the amount of active points on its surface. It was inferred that catalytic activity of pyrite is affected greatly by the chemical state of Fe and S on its surface. 3 refs., 4 figs., 1 tab.

  14. Nickel-induced morphology change of mesostructured alumina with enhanced catalytic activity for selective CO methanation

    Science.gov (United States)

    Cao, Shubo; Chen, Aihua; Zhao, Yongbin; Lu, Yanluo

    2015-03-01

    Nickel-induced morphology change of mesostructured alumina with amorphous walls to bayerite tetrahedra when treated in water, and then to γ-alumina with worm-like mesopores topologically after it was calcined at 400 °C is reported. The catalytic activity for selective CO methanation increased significantly after this treatment.Nickel-induced morphology change of mesostructured alumina with amorphous walls to bayerite tetrahedra when treated in water, and then to γ-alumina with worm-like mesopores topologically after it was calcined at 400 °C is reported. The catalytic activity for selective CO methanation increased significantly after this treatment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07577c

  15. Gold Incorporated Mesoporous Silica Thin Film Model Surface as a Robust SERS and Catalytically Active Substrate

    Directory of Open Access Journals (Sweden)

    Anandakumari Chandrasekharan Sunil Sekhar

    2016-05-01

    Full Text Available Ultra-small gold nanoparticles incorporated in mesoporous silica thin films with accessible pore channels perpendicular to the substrate are prepared by a modified sol-gel method. The simple and easy spin coating technique is applied here to make homogeneous thin films. The surface characterization using FESEM shows crack-free films with a perpendicular pore arrangement. The applicability of these thin films as catalysts as well as a robust SERS active substrate for model catalysis study is tested. Compared to bare silica film our gold incorporated silica, GSM-23F gave an enhancement factor of 103 for RhB with a laser source 633 nm. The reduction reaction of p-nitrophenol with sodium borohydride from our thin films shows a decrease in peak intensity corresponding to –NO2 group as time proceeds, confirming the catalytic activity. Such model surfaces can potentially bridge the material gap between a real catalytic system and surface science studies.

  16. Effect of surface catalytic activity on stagnation heat-transfer rates.

    Science.gov (United States)

    Anderson, L. A.

    1973-01-01

    An experiment was made to determine the effect heterogeneous catalytic surface reactions have on heat-transfer rates in highly frozen low-density stagnation-point boundary layers. Data were obtained in arc-heated facilities that were capable of producing large percentages of chemical energy frozen in a supersonic freestream. The heat-transfer rate to a silicon-dioxide surface was reduced to a minimum value of only one-third of the value obtained on relatively active nickel and platinum surfaces. This is the result of its low catalytic efficiency. Ionization energy was recovered on both the active and the inactive surfaces, indicating that this energy either was released many times faster than the recombination energy or was not controlled by the surface composition.

  17. Peroxidase-Like Catalytic Activity of Ag3PO4 Nanocrystals Prepared by a Colloidal Route

    Science.gov (United States)

    Liu, Yuanjun; Zhu, Guoxing; Yang, Jing; Yuan, Aihua; Shen, Xiaoping

    2014-01-01

    Nearly monodispersed Ag3PO4 nanocrystals with size of 10 nm were prepared through a colloidal chemical route. It was proven that the synthesized Ag3PO4 nanoparticles have intrinsic peroxidase-like catalytic activity. They can quickly catalyze oxidation of the peroxidase substrate 3, 3, 5, 5-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue color. The catalysis reaction follows Michaelis-Menten kinetics. The calculated kinetic parameters indicate a high catalytic activity and the strong affinity of Ag3PO4 nanocrystals to the substrate (TMB). These results suggest the potential applications of Ag3PO4 nanocrystals in fields such as biotechnology, environmental chemistry, and medicine. PMID:25271632

  18. Synthesis of Iron Nanoparticles Using Azadirachta indica Extract and Its Catalytic Activity Toward Nitrophenol Reduction.

    Science.gov (United States)

    Karthikeyan, C; Ranjani, M; Kim, Ae Rhan; Yoo, Dong Jin; Kumar, G Gnana

    2016-03-01

    A simple, hasty and eco-friendly approach for the synthesis of iron nanoparticles has been developed using the medicinally important Azadirachta indica extract, which act as both reducing and stabilizing agent. The formation and morphological properties of iron nanoparticles as a function of metallic precursor and Azadirachta indica extract concentration have been investigated. The influence of solvent over the size and texture of iron nanoparticles has also been evaluated in detail. The thermal behavior of prepared nanoparticles was identified from thermogravimetric analysis. Furthermore, the catalytic activity of prepared iron nanoparticles toward the reduction of p-nitrophenol was analyzed and the reduction process was occurred within 30 sec. The cost and time efficient biosynthesis process and excellent catalytic activity of the prepared iron nanoparticles construct this protocol attractive.

  19. ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

    Energy Technology Data Exchange (ETDEWEB)

    Biener, M M; Biener, J; Wichmann, A; Wittstock, A; Baumann, T F; Baeumer, M; Hamza, A V

    2011-03-24

    Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

  20. Catalytic Activity of Oxidized Carbon Black and Graphene Oxide for the Crosslinking of Epoxy Resins

    Directory of Open Access Journals (Sweden)

    Maria Rosaria Acocella

    2017-04-01

    Full Text Available This article compares the catalytic activities of oxidized carbon black (oCB and graphene oxide (eGO samples on the kinetics of a reaction of diglycidyl ether of bisphenol A (DGEBA with a diamine, leading to crosslinked insoluble networks. The study is mainly conducted by rheometry and Differential Scanning Calorimetry (DSC. Following the same oxidation procedure, CB samples are more efficiently oxidized than graphite samples. For instance, CB and graphite samples with high specific surface areas (151 and 308 m2/g, as oxidized by the Hummers’ method, exhibit O/C wt/wt ratios of 0.91 and 0.62, respectively. Due to the higher oxidation levels, these oCB samples exhibit a higher catalytic activity toward the curing of epoxy resins than fully exfoliated graphene oxide.

  1. A Structural Hinge in Eukaryotic MutY Homologues Mediates Catalytic Activity and Rad9-Rad1-Hus1 Checkpoint Complex Interactions

    Energy Technology Data Exchange (ETDEWEB)

    P Luncsford; D Chang; G Shi; J Bernstein; A Madabushi; D Patterson; A Lu; E Toth

    2011-12-31

    The DNA glycosylase MutY homologue (MYH or MUTYH) removes adenines misincorporated opposite 8-oxoguanine as part of the base excision repair pathway. Importantly, defects in human MYH (hMYH) activity cause the inherited colorectal cancer syndrome MYH-associated polyposis. A key feature of MYH activity is its coordination with cell cycle checkpoint via interaction with the Rad9-Rad1-Hus1 (9-1-1) complex. The 9-1-1 complex facilitates cell cycle checkpoint activity and coordinates this activity with ongoing DNA repair. The interdomain connector (IDC, residues 295-350) between the catalytic domain and the 8-oxoguanine recognition domain of hMYH is a critical element that maintains interactions with the 9-1-1 complex. We report the first crystal structure of a eukaryotic MutY protein, a fragment of hMYH (residues 65-350) that consists of the catalytic domain and the IDC. Our structure reveals that the IDC adopts a stabilized conformation projecting away from the catalytic domain to form a docking scaffold for 9-1-1. We further examined the role of the IDC using Schizosaccharomyces pombe MYH as model system. In vitro studies of S. pombe MYH identified residues I261 and E262 of the IDC (equivalent to V315 and E316 of the hMYH IDC) as critical for maintaining the MYH/9-1-1 interaction. We determined that the eukaryotic IDC is also required for DNA damage selection and robust enzymatic activity. Our studies also provide the first evidence that disruption of the MYH/9-1-1 interaction diminishes the repair of oxidative DNA damage in vivo. Thus, preserving the MYH/9-1-1 interaction contributes significantly to minimizing the mutagenic potential of oxidative DNA damage.

  2. Photocatalytic activity of PANI loaded coordination polymer composite materials: Photoresponse region extension and quantum yields enhancement via the loading of PANI nanofibers on surface of coordination polymer

    Energy Technology Data Exchange (ETDEWEB)

    Cui, Zhongping; Qi, Ji; Xu, Xinxin, E-mail: xuxx@mail.neu.edu.cn; Liu, Lu; Wang, Yi, E-mail: yiwang67@163.com

    2013-09-15

    To enhance photocatalytic property of coordination polymer in visible light region, polyaniline (PANI) loaded coordination polymer photocatalyst was synthesized through in-situ chemical oxidation of aniline on the surface of coordination polymer. The photocatalytic activity of PANI loaded coordination polymer composite material for degradation of Rhodamine B (RhB) was investigated. Compared with pure coordination polymer photocatalyst, which can decompose RhB merely under UV light irradiation, PANI loaded coordination polymer photocatalyst displays more excellent photocatalytic activity in visible light region. Furthermore, PANI loaded coordination polymer photocatalyst exhibits outstanding stability during the degradation of RhB. - Graphical abstract: PANI loaded coordination polymer composite material, which displays excellent photocatalytic activity under visible light was firstly synthesized through in-situ chemical oxidation of aniline on surface of coordination polymer. Display Omitted - Highlights: • This PANI loaded coordination polymer composite material represents the first conductive polymer loaded coordination polymer composite material. • PANI/coordination polymer composite material displays more excellent photocatalytic activity for the degradation of MO in visible light region. • The “combination” of coordination polymer and PANI will enable us to design high-activity, high-stability and visible light driven photocatalyst in the future.

  3. Catalytic activity of CuOn-La2O3/gamma-Al2O3 for microwave assisted ClO2 catalytic oxidation of phenol wastewater.

    Science.gov (United States)

    Bi, Xiaoyi; Wang, Peng; Jiang, Hong

    2008-06-15

    In order to develop a catalyst with high activity and stability for microwave assisted ClO2 catalytic oxidation, we prepared CuOn-La2O3/gamma-Al2O3 by impregnation-deposition method, and determined its properties using BET, XRF, XPS and chemical analysis techniques. The test results show that, better thermal ability of gamma-Al2O3 and high loading of Cu in the catalyst can be achieved by adding La2O3. The microwave assisted ClO2 catalytic oxidation process with CuOn-La2O3/gamma-Al2O3 used as catalyst was also investigated, and the results show that the catalyst has an excellent catalytic activity in treating synthetic wastewater containing 100 mg/L phenol, and 91.66% of phenol and 50.35% of total organic carbon (TOC) can be removed under the optimum process conditions. Compared with no catalyst process, CuOn-La2O3/gamma-Al2O3 can effectively degrade contaminants in short reaction time and with low oxidant dosage, extensive pH range. The comparison of phenol removal efficiency in the different process indicates that microwave irradiation and catalyst work together to oxidize phenol effectively. It can therefore be concluded from results and discussion that CuOn-La2O3/gamma-Al2O3 is a suitable catalyst in microwave assisted ClO2 catalytic oxidation process.

  4. Effect of preparation procedures on catalytic activity and selectivity of copper-based mixed oxides in selective catalytic oxidation of ammonia into nitrogen and water vapour

    Science.gov (United States)

    Jabłońska, Magdalena; Nocuń, Marek; Gołąbek, Kinga; Palkovits, Regina

    2017-11-01

    The selective oxidation of ammonia into nitrogen and water vapour (NH3-SCO) was studied over Cu-Mg(Zn)-Al-(Zr) mixed metal oxides, obtained by coprecipitation and their subsequent calcination. The effect of acid-base properties of Cu-Mg-Al-Ox on catalytic activity was investigated by changing the Mg/Al molar ratio. Other Cu-containing oxides were prepared by rehydration of calcined Mg-Al hydrotalcite-like compounds or thermal decomposition of metal nitrate precursors. XRD, BET, NH3-TPD, H2-TPR, XPS, FTIR with adsorption of pyridine and CO as well as TEM techniques were used for catalysts characterization. The results of catalytic tests revealed a crucial role of easily reducible highly dispersed copper oxide species to obtain enhanced activity and N2 selectivity in NH3-SCO. The selective catalytic reduction of NO by NH3 (NH3-SCR) and in situ DRIFT of NH3 sorption indicated that NH3-SCO proceeds according to the internal selective catalytic reduction mechanism (i-SCR).

  5. Synthesis of high active catalytic systems based on double molybdenum carbides

    OpenAIRE

    Dolmatov Vladimir; Kuznetsov Sergey; Rebrov Evgeny; Schouten Jacob Cornelis

    2015-01-01

    A new two-stage synthesis of double molybdenum and nickel carbides and high active and stable catalytic coatings of nickelpromoter molybdenum carbide in molten salts is developed. The first stage includes the formation of molybdenum–nickel alloys by an electrolytic method and currentless transfer in chloride melts. The second stage consists in the carbonization of the alloys in chloride-carbonate melt under various synthesis conditions. The stabilities of the nickel-promoter catalyti...

  6. Investigation into the morphology and structure of magnetic bentonite nanocomposites with their catalytic activity

    Science.gov (United States)

    Wan, Dong; Wang, Guanghua; Li, Wenbing; Wei, Xiaobi

    2017-08-01

    Al pillared bentonite-Fe3O4 nanocomposites (Fe3O4/Al-B) with controllable Fe3O4 particle sizes and loadings were synthesized by a simple in situ oxidation-precipitation method. The obtained samples were characterized by XRD, SEM, TEM, FTIR, XPS, VSM and N2 sorption. These results suggested that Fe3O4 was chemically anchored to the bentonite sheets via Fe-O-Si bonds, resulting in the formation of secondary pore structure. Three types of structure of Fe3O4/Al-B nanocomposites were proposed at different Fe3O4 loadings, varying from 40 to 80 wt%. The catalytic activity of the Fe3O4/Al-B nanocomposites was investigated in the heterogeneous Fenton-like oxidation of rhodamine B (RhB). The 50 nm Fe3O4/Al-B nanocomposite showed enhanced degradation of RhB over the control catalyst, benefited from its greater surface area and pore volume. The highest catalytic activity was found to be at Fe3O4 loading of 60 wt%, which was attributed to the synergistic effects between both increased surface area and formed Fe-O-Si bonds. These findings offer a better understanding on structural and morphological relationships of Fe3O4/Al-B nanocomposites with their heterogeneous Fenton-like catalytic activity.

  7. A distinct atomic structure-catalytic activity relationship in 3-10 nm supported Au particles.

    Science.gov (United States)

    Petkov, Valeri; Ren, Yang; Shan, Shiyao; Luo, Jin; Zhong, Chuan-Jian

    2014-01-07

    Bulk Au is very inert but Au nanoparticles less than 5 nm in size have been found to be catalytically active for several reactions, in particular for low-temperature oxidation of CO. Using high-energy X-ray diffraction coupled with atomic pair distribution function analysis and computer simulations we determine the structure of 3 nm and 10 nm Au particles supported on titania and silica as typical representatives of reducible and irreducible supports, respectively. We find that the synthesis protocol adopted in our work affects strongly and differently the structure of the Au nanoparticles on the different supports. This leads to clearly distinct dependences of the catalytic activity of the nanoparticles on their size. In the case of the silica support the catalytic activity of Au nanoparticles increases and in the case of the titania support it decreases with decreasing nanoparticle size. The experimental results are considered in terms of current theoretical predictions and found to be in good accord with them.

  8. A microreactor array for spatially resolved measurement of catalytic activity for high-throughput catalysis science

    Energy Technology Data Exchange (ETDEWEB)

    Kondratyuk, Petro; Gumuslu, Gamze; Shukla, Shantanu; Miller, James B; Morreale, Bryan D; Gellman, Andrew J

    2013-04-01

    We describe a 100 channel microreactor array capable of spatially resolved measurement of catalytic activity across the surface of a flat substrate. When used in conjunction with a composition spread alloy film (CSAF, e.g. Pd{sub x}Cu{sub y}Au{sub 1-x-y}) across which component concentrations vary smoothly, such measurements permit high-throughput analysis of catalytic activity and selectivity as a function of catalyst composition. In the reported implementation, the system achieves spatial resolution of 1 mm{sup 2} over a 10×10 mm{sup 2} area. During operation, the reactant gases are delivered at constant flow rate to 100 points of differing composition on the CSAF surface by means of a 100-channel microfluidic device. After coming into contact with the CSAF catalyst surface, the product gas mixture from each of the 100 points is withdrawn separately through a set of 100 isolated channels for analysis using a mass spectrometer. We demonstrate the operation of the device on a Pd{sub x}Cu{sub y}Au{sub 1-x-y} CSAF catalyzing the H{sub 2}-D{sub 2} exchange reaction at 333 K. In essentially a single experiment, we measured the catalytic activity over a broad swathe of concentrations from the ternary composition space of the Pd{sub x}Cu{sub y}Au{sub 1-x-y} alloy.

  9. Direct Visualization of Catalytically Active Sites at the FeO-Pt(111) Interface

    Energy Technology Data Exchange (ETDEWEB)

    Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; Bai, Yunhai; Merte, L. R.; Lammich, Lutz; Besenbacher, Fleming; Mavrikakis, Manos; Wendt, Stefen

    2015-08-25

    Within the area of surface science, one of the “holy grails” is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O2 and CO environments revealed catalytic activity occurring at the FeO-Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO-Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. The presented STM results are in accord with DFTþU calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically.

  10. Regulating Water-Reduction Kinetics in Cobalt Phosphide for Enhancing HER Catalytic Activity in Alkaline Solution.

    Science.gov (United States)

    Xu, Kun; Ding, Hui; Zhang, Mengxing; Chen, Min; Hao, Zikai; Zhang, Lidong; Wu, Changzheng; Xie, Yi

    2017-07-01

    Electrochemical water splitting to produce hydrogen renders a promising pathway for renewable energy storage. Considering limited electrocatalysts have good oxygen-evolution reaction (OER) catalytic activity in acid solution while numerous economical materials show excellent OER catalytic performance in alkaline solution, developing new strategies that enhance the alkaline hydrogen-evolution reaction (HER) catalytic activity of cost-effective catalysts is highly desirable for achieving highly efficient overall water splitting. Herein, it is demonstrated that synergistic regulation of water dissociation and optimization of hydrogen adsorption free energy on electrocatalysts can significantly promote alkaline HER catalysis. Using oxygen-incorporated Co 2 P as an example, the synergistic effect brings about 15-fold enhancement of alkaline HER activity. Theory calculations confirm that the water dissociation free energy of Co 2 P decreases significantly after oxygen incorporation, and the hydrogen adsorption free energy can also be optimized simultaneously. The finding suggests the powerful effectiveness of synergetic regulation of water dissociation and optimization of hydrogen adsorption free energy on electrocatalysts for alkaline HER catalysis. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Direct Single-Enzyme Biomineralization of Catalytically Active Ceria and Ceria–Zirconia Nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Curran, Christopher D.; Lu, Li; Jia, Yue; Kiely, Christopher J.; Berger, Bryan W.; McIntosh, Steven

    2017-02-21

    Biomineralization is an intriguing approach to the synthesis of functional inorganic materials for energy applications whereby biological systems are engineered to mineralize inorganic materials and control their structure over multiple length scales under mild reaction conditions. Herein we demonstrate a single-enzyme-mediated biomineralization route to synthesize crystalline, catalytically active, quantum-confined ceria (CeO2–x) and ceria–zirconia (Ce1–yZryO2–x) nanocrystals for application as environmental catalysts. In contrast to typical anthropogenic synthesis routes, the crystalline oxide nanoparticles are formed at room temperature from an otherwise inert aqueous solution without the addition of a precipitant or additional reactant. An engineered form of silicatein, rCeSi, as a single enzyme not only catalyzes the direct biomineralization of the nanocrystalline oxides but also serves as a templating agent to control their morphological structure. The biomineralized nanocrystals of less than 3 nm in diameter are catalytically active toward carbon monoxide oxidation following an oxidative annealing step to remove carbonaceous residue. The introduction of zirconia into the nanocrystals leads to an increase in Ce(III) concentration, associated catalytic activity, and the thermal stability of the nanocrystals.

  12. Effect of the synthetic method on the catalytic activity of alumina: Epoxidation of cyclohexene

    Energy Technology Data Exchange (ETDEWEB)

    Valderruten, N.E., E-mail: nevalderruten@icesi.edu.co [Departamento de Ciencias Químicas, Universidad Icesi, Cali (Colombia); Peña, W.F.; Ramírez, A.E. [Departamento de Química, Universidad del Cauca, Popayán (Colombia); Rodríguez-Páez, J.E. [Departamento de Física, Universidad del Cauca, Popayán (Colombia)

    2015-02-15

    Graphical abstract: Temperature influence on percent conversion and selectivity in the epoxidation of cyclohexene using commercial alumina as a catalyst. - Highlights: • Aluminum oxide was synthesized using Pechini method. • The alumina obtained showed a mix of boehmite and γ-alumina phases. • We research an economically feasible method to obtain alumina for use as a catalyst. • Alumina obtained by Pechini showed high percent conversion and/or selectivity. • The best results were 78% conversion and 78% selectivity to epoxidation reactions. - Abstract: Al{sub 2}O{sub 3} was prepared from different inorganic precursors via the Pechini method and compared with Al{sub 2}O{sub 3} prepared by the sol–gel method. Structural characterization of these materials was carried out by FTIR, X-ray diffraction (XRD), N{sub 2} adsorption at −196 °C and transmission electron microscopy (TEM). The solids were tested in the epoxidation of cyclohexene and a difference in their catalytic activities was observed. The characterization results indicate that the samples prepared by Pechini have a mixture of γ-alumina and boehmite, a condition favoring catalytic activity, whereas the sol–gel sample is less crystalline due to higher boehmite content. These results indicate that both the nature of the precursor and the method of synthesis strongly affect the catalytic activity of Al{sub 2}O{sub 3}.

  13. Dinuclear Lanthanide (III) coordination polymers in a domino reaction

    OpenAIRE

    Loukopoulos, Edward; Griffiths, Kieran; Akien, Geoffrey R.; Kourkoumelis, Nikolaos; Abdul-Sada, Alaa; Kostakis, George E.

    2015-01-01

    A systematic study was performed to further optimise the catalytic room-temperature synthesis of trans-4,5- diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere. For this purpose, a series of dinuclear lanthanide (III) coordination polymers were synthesised using a dianionic\\ud Schiff base and their catalytic activities were investigated.

  14. Probing the electrostatics of active site microenvironments along the catalytic cycle for Escherichia coli dihydrofolate reductase.

    Science.gov (United States)

    Liu, C Tony; Layfield, Joshua P; Stewart, Robert J; French, Jarrod B; Hanoian, Philip; Asbury, John B; Hammes-Schiffer, Sharon; Benkovic, Stephen J

    2014-07-23

    Electrostatic interactions play an important role in enzyme catalysis by guiding ligand binding and facilitating chemical reactions. These electrostatic interactions are modulated by conformational changes occurring over the catalytic cycle. Herein, the changes in active site electrostatic microenvironments are examined for all enzyme complexes along the catalytic cycle of Escherichia coli dihydrofolate reductase (ecDHFR) by incorporation of thiocyanate probes at two site-specific locations in the active site. The electrostatics and degree of hydration of the microenvironments surrounding the probes are investigated with spectroscopic techniques and mixed quantum mechanical/molecular mechanical (QM/MM) calculations. Changes in the electrostatic microenvironments along the catalytic environment lead to different nitrile (CN) vibrational stretching frequencies and (13)C NMR chemical shifts. These environmental changes arise from protein conformational rearrangements during catalysis. The QM/MM calculations reproduce the experimentally measured vibrational frequency shifts of the thiocyanate probes across the catalyzed hydride transfer step, which spans the closed and occluded conformations of the enzyme. Analysis of the molecular dynamics trajectories provides insight into the conformational changes occurring between these two states and the resulting changes in classical electrostatics and specific hydrogen-bonding interactions. The electric fields along the CN axes of the probes are decomposed into contributions from specific residues, ligands, and solvent molecules that make up the microenvironments around the probes. Moreover, calculation of the electric field along the hydride donor-acceptor axis, along with decomposition of this field into specific contributions, indicates that the cofactor and substrate, as well as the enzyme, impose a substantial electric field that facilitates hydride transfer. Overall, experimental and theoretical data provide evidence for

  15. Bioinspired catalytic generation of high-valent cobalt-oxo species by the axially coordinated CoPc on pyridine-functionalized MWCNTs for the elimination of organic contaminants

    Science.gov (United States)

    Li, Nan; Wang, Ying; Wu, Chenren; Lu, Wangyang; Pei, Kemei; Chen, Wenxing

    2018-03-01

    Enzymes have always been a source of inspiration for the design and improvement of catalysts. Many examples are occurring in heme/non-heme metalloenzymes with the generation of active high-valent metal-oxo intermediates that are controlled by the surrounding amino acids/protein and axial residue ligands, facilitating the efficient oxidation of substrates in biochemical processes. Here, the high-valent cobalt-oxo species have been formed during the heterolysis of H2O2 activated by the bioinspired catalyst, axially coordinated cobalt phthalocyanine (CoPc) on pyridine-functionalized multi-walled carbon nanotubes (MWCNTs-Py), characterized by ultraviolet-visible and X-ray photoelectron spectroscopy. Formation process of the active cobalt-oxo species has been further confirmed by electrospray ionization mass spectrometry analysis and the results from the density functional theory (B3LYP/6-311G) calculations. Such high-valent cobalt-oxo species exhibit high reactivity and enough persistence for the oxidation of the target substrate, C.I. Acid Red 1. The oxidation products are nearly biodegradable small molecules identified by ultra-performance liquid chromatography/high-definition mass spectrometry. This strategy provides a foundation on developing efficient and persistent catalytic system, in particular oxidation processes based on the complex catalysts with N4 macrocycle structures.

  16. Fluorine- and Nitrogen-Codoped MoS2 with a Catalytically Active Basal Plane.

    Science.gov (United States)

    Wang, Yuanzhe; Liu, Shanshan; Hao, Xianfeng; Zhou, Junshuang; Song, Dandan; Wang, Dong; Hou, Li; Gao, Faming

    2017-08-23

    Two-dimensional molybdenum disulfide (2D MoS2) has drawn persistent interests as one of the most promising alternatives to Pt catalysts for the hydrogen evolution reaction (HER). It is generally accepted that the edge sites of 2D MoS2 are catalytically active but the basal planes are inert. Activating the MoS2 basal plane is an obvious strategy to enhance the HER activity of this material. However, few approaches have sought to activate the basal plane. Here, for the first time, we demonstrate that the inert basal planes can be activated via the synergistic effects of nitrogen and fluorine codoping. Our first-principles calculations reveal that nitrogen in the basal plane of the fluorine- and nitrogen-codoped MoS2 (NF-MoS2) can act as a new active and further tuneable catalytic site. The as-prepared NF-MoS2 catalyst exhibited an enormously enhanced HER activity compared to that of pure MoS2 and N-doped MoS2 due to the chemical codoping effect. This work will pave a novel pathway for enhancing the HER activity using the synergistic effects of chemical codoping.

  17. μ-reactor measurements of catalytic activity of mass selected nano-particles

    DEFF Research Database (Denmark)

    Riedel, Jakob Nordheim

    The work of this thesis revolves around catalytic activity measurements of nano-particles tested using a μ-reactor platform, developed and produced at DTU, in a collaboration between CINF and Nanotech. The thesis contains the results from two separate research projects; both utilising μ-reactors ......The work of this thesis revolves around catalytic activity measurements of nano-particles tested using a μ-reactor platform, developed and produced at DTU, in a collaboration between CINF and Nanotech. The thesis contains the results from two separate research projects; both utilising μ......-reactors in combination with surface science techniques and computer simulations. The first project described is a study of hydrogen dissociation on mono-disperse platinum clusters. The second project studies methanation from carbon monoxide and hydrogen on nano-particles of nickel-iron alloys. The second study is a work...... stable. DFT simulations demonstrated that even a single oxygen atom binds strongly to SiO2-supported Pt8 clusters and changes the morphology and chemical properties of the cluster. Catalytic methanation reaction from CO and H2 was studied on Ni75Fe25 nano-particles with sizes 3.5nm, 5nm, 7nm and 9nm...

  18. Halide-Enhanced Catalytic Activity of Palladium Nanoparticles Comes at the Expense of Catalyst Recovery

    Directory of Open Access Journals (Sweden)

    Azzedine Bouleghlimat

    2017-09-01

    Full Text Available In this communication, we present studies of the oxidative homocoupling of arylboronic acids catalyzed by immobilised palladium nanoparticles in aqueous solution. This reaction is of significant interest because it shares a key transmetallation step with the well-known Suzuki-Miyaura cross-coupling reaction. Additives can have significant effects on catalysis, both in terms of reaction mechanism and recovery of catalytic species, and our aim was to study the effect of added halides on catalytic efficiency and catalyst recovery. Using kinetic studies, we have shown that added halides (added as NaCl and NaBr can increase the catalytic activity of the palladium nanoparticles more than 10-fold, allowing reactions to be completed in less than half a day at 30 °C. However, this increased activity comes at the expense of catalyst recovery. The results are in agreement with a reaction mechanism in which, under conditions involving high concentrations of chloride or bromide, palladium leaching plays an important role. Considering the evidence for analogous reactions occurring on the surface of palladium nanoparticles under different reaction conditions, we conclude that additives can exert a significant effect on the mechanism of reactions catalyzed by nanoparticles, including switching from a surface reaction to a solution reaction. The possibility of this switch in mechanism may also be the cause for the disagreement on this topic in the literature.

  19. The non-catalytic domains of Drosophila katanin regulate its abundance and microtubule-disassembly activity.

    Directory of Open Access Journals (Sweden)

    Kyle D Grode

    Full Text Available Microtubule severing is a biochemical reaction that generates an internal break in a microtubule and regulation of microtubule severing is critical for cellular processes such as ciliogenesis, morphogenesis, and meiosis and mitosis. Katanin is a conserved heterodimeric ATPase that severs and disassembles microtubules, but the molecular determinants for regulation of microtubule severing by katanin remain poorly defined. Here we show that the non-catalytic domains of Drosophila katanin regulate its abundance and activity in living cells. Our data indicate that the microtubule-interacting and trafficking (MIT domain and adjacent linker region of the Drosophila katanin catalytic subunit Kat60 cooperate to regulate microtubule severing in two distinct ways. First, the MIT domain and linker region of Kat60 decrease its abundance by enhancing its proteasome-dependent degradation. The Drosophila katanin regulatory subunit Kat80, which is required to stabilize Kat60 in cells, conversely reduces the proteasome-dependent degradation of Kat60. Second, the MIT domain and linker region of Kat60 augment its microtubule-disassembly activity by enhancing its association with microtubules. On the basis of our data, we propose that the non-catalytic domains of Drosophila katanin serve as the principal sites of integration of regulatory inputs, thereby controlling its ability to sever and disassemble microtubules.

  20. Facile and green synthesis of cellulose nanocrystal-supported gold nanoparticles with superior catalytic activity.

    Science.gov (United States)

    Yan, Wei; Chen, Chang; Wang, Ling; Zhang, Dan; Li, Ai-Jun; Yao, Zheng; Shi, Li-Yi

    2016-04-20

    The emphasis of science and technology shifts toward environmentally friendly and sustainable resources and processes. Herein, we report a facile, one-pot and green synthesis of biomaterial-supported gold nanoparticles (AuNPs) with superior catalytic activity. Cellulose nanocrystal (CNC)-supported AuNPs were prepared by heating the aqueous mixture of HAuCl4, CNCs and polyethylene glycol, avoiding toxic chemicals, extreme condition and complicated procedure. The resultant CNC-supported AuNPs exhibited catalytic activities for the reduction of 4-nitrophenol by sodium borohydride. The maximum apparent rate constant reached 1.47×10(-2)s(-1), and the turnover frequency reached 641h(-1). The superior catalytic performance can be ascribed to the large amount of highly dispersed AuNPs with few nanometers in size which are loaded on CNCs. About 90% of the AuNPs are smaller than 10nm, and nearly 60% of the AuNPs are smaller than 5nm. The synthesis is eco-friendly, facile and low-cost, thus has great potential for industrial and medical applications. Copyright © 2015 Elsevier Ltd. All rights reserved.

  1. Structural, optical and photo-catalytic activity of nanocrystalline NiO thin films

    Energy Technology Data Exchange (ETDEWEB)

    Al-Ghamdi, Attieh A. [Center of Nanotechnology, King Abdulaziz University, Jeddah (Saudi Arabia); Abdel-wahab, M. Sh., E-mail: mshabaan90@yahoo.com [Center of Nanotechnology, King Abdulaziz University, Jeddah (Saudi Arabia); Materials Science and Nanotechnology Department, Faculty of Postgraduate Studies for Advanced Sciences, Beni-Suef University, Beni-Suef (Egypt); Farghali, A.A. [Materials Science and Nanotechnology Department, Faculty of Postgraduate Studies for Advanced Sciences, Beni-Suef University, Beni-Suef (Egypt); Chemistry Department, Faculty of Science, Beni-Suef University, Beni-Suef (Egypt); Hasan, P.M.Z. [Center of Nanotechnology, King Abdulaziz University, Jeddah (Saudi Arabia)

    2016-03-15

    Highlights: • Synthesis of nanocrystalline NiO thin films with different thicknesses using DC magnetron sputtering technique. • Effect of film thickness and particle size on photo-catalytic degradation of methyl green dye under UV light was studied. • The deposited NiO thin films are efficient, stable and possess high photo-catalytic activity upon reuse. - Abstract: Physical deposition of nanocrystalline nickel oxide (NiO) thin films with different thickness 30, 50 and 80 nm have been done on glass substrate by DC magnetron sputtering technique and varying the deposition time from 600, 900 to 1200 s. The results of surface morphology and optical characterization of these films obtained using different characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), photoluminescence (PL) and UV–vis spectrophotometry provide important information like formation of distinct nanostructures in different films and its effect on their optical band gap which has decreased from 3.74 to 3.37 eV as the film thickness increases. Most importantly these films have shown very high stability and a specialty to be recycled without much loss of their photo-catalytic activity, when tested as photo-catalysts for the degradation of methyl green dye (MG) from the wastewater under the exposure of 18 W energy of UV lamp.

  2. Investigating the role of chain and linker length on the catalytic activity of an H 2 production catalyst containing a β-hairpin peptide

    Energy Technology Data Exchange (ETDEWEB)

    Reback, Matthew L.; Ginovska, Bojana; Buchko, Garry W.; Dutta, Arnab; Priyadarshani, Nilusha; Kier, Brandon L.; Helm, Monte L.; Raugei, Simone; Shaw, Wendy J.

    2016-06-02

    Building on our recent report of an active H2 production catalyst [Ni(PPh2NProp-peptide)2]2+ (Prop=para-phenylpropionic acid, peptide (R10)=WIpPRWTGPR-NH2, p=D-proline, and P2N=1-aza-3,6-diphosphacycloheptane) that contains structured -hairpin peptides, here we investigate how H2 production is effected by: (1) the length of the hairpin (eight or ten residues) and (2) limiting the flexibility between the peptide and the core complex by altering the length of the linker: para-phenylpropionic acid (three carbons) or para-benzoic acid (one carbon). Reduction of the peptide chain length from ten to eight residues increases or maintains the catalytic current for H2 production for all complexes, suggesting a non-productive steric interaction at longer peptide lengths. While the structure of the hairpin appears largely intact for the complexes, NMR data are consistent with differences in dynamic behavior which may contribute to the observed differences in catalytic activity. Molecular dynamics simulations demonstrate that complexes with a one-carbon linker have the desired effect of restricting the motion of the hairpin relative to the complex; however, the catalytic currents are significantly reduced compared to complexes containing a three-carbon linker as a result of the electron withdrawing nature of the -COOH group. These results demonstrate the complexity and interrelated nature of the outer coordination sphere on catalysis.

  3. Block copolymer hollow fiber membranes with catalytic activity and pH-response

    KAUST Repository

    Hilke, Roland

    2013-08-14

    We fabricated block copolymer hollow fiber membranes with self-assembled, shell-side, uniform pore structures. The fibers in these membranes combined pores able to respond to pH and acting as chemical gates that opened above pH 4, and catalytic activity, achieved by the incorporation of gold nanoparticles. We used a dry/wet spinning process to produce the asymmetric hollow fibers and determined the conditions under which the hollow fibers were optimized to create the desired pore morphology and the necessary mechanical stability. To induce ordered micelle assembly in the doped solution, we identified an ideal solvent mixture as confirmed by small-angle X-ray scattering. We then reduced p-nitrophenol with a gold-loaded fiber to confirm the catalytic performance of the membranes. © 2013 American Chemical Society.

  4. Preparation, Characterization and Catalytic Activity of Nickel Molybdate (NiMoO4 Nanoparticles

    Directory of Open Access Journals (Sweden)

    Hicham Oudghiri-Hassani

    2018-01-01

    Full Text Available Nickel molybdate (NiMoO4 nanoparticles were synthesized via calcination of an oxalate complex in static air at 500 °C. The oxalate complex was analyzed by thermal gravimetric analysis (TGA and Fourier transform infrared spectroscopy (FTIR. The as-synthesized nickel molybdate was characterized by Brunauer–Emmett–Teller technique (BET, X-ray diffraction (XRD, and transmission electron microscopy (TEM and its catalytic efficiency was tested in the reduction reaction of the three-nitrophenol isomers. The nickel molybdate displays a very high activity in the catalytic reduction of the nitro functional group to an amino. The reduction progress was controlled using Ultraviolet-Visible (UV-Vis absorption.

  5. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

    Science.gov (United States)

    Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

    2016-05-24

    Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

  6. Metal ion coordination in the E. coli Nudix hydrolase dihydroneopterin triphosphate pyrophosphatase: New clues into catalytic mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Hill, Shannon E.; Nguyen, Elaine; Ukachukwu, Chiamaka U.; Freeman, Dana M.; Quirk, Stephen; Lieberman, Raquel L.; Boggon, Titus J.

    2017-07-25

    Dihydroneopterin triphosphate pyrophosphatase (DHNTPase), a member of the Mg2+ dependent Nudix hydrolase superfamily, is the recently-discovered enzyme that functions in the second step of the pterin branch of the folate biosynthetic pathway in E. coli. DHNTPase is of interest because inhibition of enzymes in bacterial folate biosynthetic pathways is a strategy for antibiotic development. We determined crystal structures of DHNTPase with and without activating, Mg2+-mimicking metals Co2+ and Ni2+. Four metal ions, identified by anomalous scattering, and stoichiometrically confirmed in solution by isothermal titration calorimetry, are held in place by Glu56 and Glu60 within the Nudix sequence motif, Glu117, waters, and a sulfate ion, of which the latter is further stabilized by a salt bridge with Lys7. In silico docking of the DHNTP substrate reveals a binding mode in which the pterin ring moiety is nestled in a largely hydrophobic pocket, the β-phosphate activated for nucleophilic attack overlays with the crystallographic sulfate and is in line with an activated water molecule, and remaining phosphate groups are stabilized by all four identified metal ions. The structures and binding data provide new details regarding DHNTPase metal requirements, mechanism, and suggest a strategy for efficient inhibition.

  7. A short cross-linker activates human P-glycoprotein missing a catalytic carboxylate.

    Science.gov (United States)

    Loo, Tip W; Clarke, David M

    2017-12-01

    P-glycoprotein (P-gp) is an ATP-dependent drug pump that protects us from toxic agents and confers multidrug resistance. It has a tweezer-like structure with each arm consisting of a transmembrane domain (TMD) and a nucleotide-binding domain (NBD). Drug substrates bind to sites within the TMDs to activate ATPase activity by promoting a tweezer-like closing of the gap between the NBDs. The catalytic carboxylates may be critical for NBD movements because the E556Q(NBD1) or E1201Q(NBD2) mutation inhibited drug-stimulated ATPase activity. If the catalytic carboxylates were components of the mechanism to bring the NBDs together, then we predicted that insertion of a flexible cross-linker between the arms would increase ATPase activity of the mutants. We found that cross-linking (between L175C(TMD1) and N820C(TMD2)) with a short flexible cross-linker (7.8Å maximum) restored high levels of drug-stimulated ATPase activity of the E556Q or E1201Q mutants. Cross-linking with a longer cross-linker (22Å maximum) however, did not restore activity. Cross-linking could not rescue all ATPase deficient mutants. For example, cross-linking L175C/N820C with short or long cross-linkers did not activate the H-loop mutants H587A or H1232A or the Walker A K433M or K1076M mutants. The results suggest that the E556 and E1201 catalytic carboxylates are part of a spring-like mechanism that is required to facilitate movements between the open and closed conformations of P-gp during ATP hydrolysis. Copyright © 2017 Elsevier Inc. All rights reserved.

  8. Coordinating the activities of a planner and an execution agent

    Science.gov (United States)

    Tate, Austin

    1989-01-01

    A research program was defined that will explore the link between planning and execution systems. A simple scenario was defined in which a very capable off-line planning system interacts with the user and a smaller, less capable, on-line real-time system executing plans and reacting to faults. However, the on-line execution system may have a more flexible representation of the plans it is executing. This imbalance in the capabilities of the two agents involved should clarify some of the research objectives and give an experimental framework for the work. The task is to investigate the knowledge representations and communication protocols needed to link a user stating some requirements for a task to be carried out through a planning system to the (remote) execution agent that can carry out the user's wishes. The notion that a single representation can encapsulate the expression of the user's requirements, the capabilities for action, the communication to the execution agent, the successful or faulty response from the execution agent and the means of keeping the user informed, is examined. Methods of creating plan patches to update the plans separately held by each of the parties involved to keep them in step as they each react to changing circumstances in real-time is investigated. This involves the specification of plan patch attachment points that can be understood by the recipient. Transaction based methods are also investigated for coordinating the activities of the planner with those of the execution agent and user. The trial application area for the research is in the command and control of an advanced Earth Observation Space Platform.

  9. α-Helical Peptide-Gold Nanoparticle Hybrids: Synthesis, Characterization, and Catalytic Activity.

    Science.gov (United States)

    Tomizaki, Kin-Ya; Yamaguchi, Yuichi; Tsukamoto, Naoyuki; Imai, Takahito

    2017-12-13

    Gold nanoparticles are promising nanomaterials for catalytic reactions, sensing/imaging systems, photonic/plasmonic devices, and electronics because of their unique physical and chemical properties. To date, significant catalytic activities of gold nanoparticles have been reported for reactions such as carbon monooxide oxidation and 4-nitrophenol reduction, and diverse gold nanoparticle morphologies such as nanospheres, wires, rods, and cubes have been achieved using a variety of capping/stabilizing organic molecules. Very recently, we designed a -sheet-forming peptide that accommodates HAuCl4 in the cavities of peptide self-assemblies and provided ultrathin gold nanoribbons 50-100 nm wide, several nanometers high, and microns long, without the need for external reductants in the aqueous medium. However, there are few reports on the simultaneous assembly of peptides forming secondary structures and metallic nanoparticles into peptide-metallic particle hybrids under mild aqueous conditions and demonstration of their use as catalysts. Furthermore, the gold nanoribbon surfaces are covered with -sheet structures, disrupting the access of substrates to the active sites, thereby possibly inhibiting their catalytic activity. We here report (i) the design, synthesis, and characterization of a new template peptide, RU025, that tends to form an -helical conformation and self-assembles into network nanoarchitectures in aqueous solution through possibly hydrophobic and electrostatic interactions, (ii) the characterization of gold seed crystals synthesized by mixing RU025 and HAuCl4, (iii) the characterization of peptide-gold nanoparticle hybrids directed by crystal growth with NaBH4 and showing its dependence on the conditions used for nucleation, and (iv) the catalytic activities of the hybrids towards the reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH4. The size and morphology of gold nanoparticles can be tuned in the nanometer range by

  10. Characterization of ferromagnetic sludge-based activated carbon and its application in catalytic ozonation of p-chlorobenzoic acid.

    Science.gov (United States)

    Lu, Siying; Liu, Yongze; Feng, Li; Sun, Zhongen; Zhang, Liqiu

    2017-03-09

    In order to solve the separation problem of powdered sludge-based activated carbon (SAC), a series of novel ferromagnetic sludge-based activated carbons (FMSACs, with different iron content 2.3, 4.3, and 9.5 wt%) with a good magnetic separation ability were prepared through co-precipitation method in this study. The structure and physicochemical properties of FMSACs and their catalytic ozonation performance on the removal of p-chlorobenzoic acid (p-CBA) were investigated. The saturation magnetization (Ms) of FMSACs was determined in the range of 0.3674-5.7992 emu g-1, and experiments confirmed that these FMSACs could be easily separated by magnetic fields. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that magnetite and maghemite were the main magnetic phases in FMSACs. Comparing with ozonation alone and SAC catalytic ozonation, the presence of 2.3 wt% - FMSAC improved the degradation of p-CBA during catalytic ozonation from 44 and 70 to 80%. The tertiary butanol inhibition experiment indicated that FMSACs catalytic ozonation process followed hydroxyl radical reaction mechanism. Furthermore, after six repetitive catalytic ozonation runs, 2.3 wt% - FMSAC still showed relatively high catalytic activity for the removal of p-CBA. Consequently, the novel FMSACs with magnetic separation ability and catalytic performance provide a practical pathway for the sludge utilization.

  11. Importance of the oxygen bond strength for catalytic activity in soot oxidation

    DEFF Research Database (Denmark)

    Christensen, Jakob M.; Grunwaldt, Jan-Dierk; Jensen, Anker D.

    2016-01-01

    (loose contact) the rate constants for a number of catalytic materials outline a volcano curve when plotted against their heats of oxygen chemisorption. However, the optima of the volcanoes correspond to different heats of chemisorption for the two contact situations. In both cases the activation...... oxidation. The optimum of the volcano curve in loose contact is estimated to occur between the bond strengths of α-Fe2O3 and α-Cr2O3. Guided by an interpolation principle FeaCrbOx binary oxides were tested, and the activity of these oxides was observed to pass through an optimum for an FeCr2Ox binary oxide...

  12. Chelating ruthenium phenolate complexes: synthesis, general catalytic activity, and applications in olefin metathesis polymerization.

    Science.gov (United States)

    Kozłowska, Anna; Dranka, Maciej; Zachara, Janusz; Pump, Eva; Slugovc, Christian; Skowerski, Krzysztof; Grela, Karol

    2014-10-20

    Cyclic Ru-phenolates were synthesized, and these compounds were used as olefin metathesis catalysts. Investigation of their catalytic activity pointed out that, after activation with chemical agents, these catalysts promote ring-closing metathesis (RCM), enyne and cross-metathesis (CM) reactions, including butenolysis, with good results. Importantly, these latent catalysts are soluble in neat dicyclopentadiene (DCPD) and show good applicability in ring-opening metathesis polymeriyation (ROMP) of this monomer. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. The Contribution of Non-catalytic Carbohydrate Binding Modules to the Activity of Lytic Polysaccharide Monooxygenases*

    Science.gov (United States)

    Crouch, Lucy I.; Labourel, Aurore; Walton, Paul H.; Davies, Gideon J.; Gilbert, Harry J.

    2016-01-01

    Lignocellulosic biomass is a sustainable industrial substrate. Copper-dependent lytic polysaccharide monooxygenases (LPMOs) contribute to the degradation of lignocellulose and increase the efficiency of biofuel production. LPMOs can contain non-catalytic carbohydrate binding modules (CBMs), but their role in the activity of these enzymes is poorly understood. Here we explored the importance of CBMs in LPMO function. The family 2a CBMs of two monooxygenases, CfLPMO10 and TbLPMO10 from Cellulomonas fimi and Thermobispora bispora, respectively, were deleted and/or replaced with CBMs from other proteins. The data showed that the CBMs could potentiate and, surprisingly, inhibit LPMO activity, and that these effects were both enzyme-specific and substrate-specific. Removing the natural CBM or introducing CtCBM3a, from the Clostridium thermocellum cellulosome scaffoldin CipA, almost abolished the catalytic activity of the LPMOs against the cellulosic substrates. The deleterious effect of CBM removal likely reflects the importance of prolonged presentation of the enzyme on the surface of the substrate for efficient catalytic activity, as only LPMOs appended to CBMs bound tightly to cellulose. The negative impact of CtCBM3a is in sharp contrast with the capacity of this binding module to potentiate the activity of a range of glycoside hydrolases including cellulases. The deletion of the endogenous CBM from CfLPMO10 or the introduction of a family 10 CBM from Cellvibrio japonicus LPMO10B into TbLPMO10 influenced the quantity of non-oxidized products generated, demonstrating that CBMs can modulate the mode of action of LPMOs. This study demonstrates that engineered LPMO-CBM hybrids can display enhanced industrially relevant oxygenations. PMID:26801613

  14. Catalytic oxidation of pulping effluent by activated carbon-supported heterogeneous catalysts.

    Science.gov (United States)

    Yadav, Bholu Ram; Garg, Anurag

    2016-01-01

    The present study deals with the non-catalytic and catalytic wet oxidation (CWO) for the removal of persistent organic compounds from the pulping effluent. Two activated carbon-supported heterogeneous catalysts (Cu/Ce/AC and Cu/Mn/AC) were used for CWO after characterization by the following techniques: temperature-programmed reduction, Fourier transform infrared spectroscopy and thermo-gravimetric analysis. The oxidation reaction was performed in a batch high-pressure reactor (capacity = 0.7  L) at moderate oxidation conditions (temperature = 190°C and oxygen pressure = 0.9 MPa). With Cu/Ce/AC catalyst, the maximum chemical oxygen demand (COD), total organic carbon (TOC) and lignin removals of 79%, 77% and 88% were achieved compared to only 50% removal during the non-catalytic process. The 5-day biochemical oxygen demand (BOD5) to COD ratio (a measure for biodegradability) of the pulping effluent was improved to 0.52 from an initial value of 0.16. The mass balance calculations for solid recovered after CWO reaction showed 8% and 10% deduction in catalyst mass primarily attributed to the loss of carbon and metal leaching. After the CWO process, carbon deposition was also observed on the recovered catalyst which was responsible for around 3-4% TOC reduction.

  15. Catalytically active and hierarchically porous SAPO-11 zeolite synthesized in the presence of polyhexamethylene biguanidine

    KAUST Repository

    Liu, Yan

    2014-03-01

    Hierarchically porous SAPO-11 zeolite (H-SAPO-11) is rationally synthesized from a starting silicoaluminophosphate gel in the presence of polyhexamethylene biguanidine as a mesoscale template. The sample is well characterized by XRD, N2 sorption, SEM, TEM, NMR, XPS, NH3-TPD, and TG techniques. The results show that the sample obtained has good crystallinity, hierarchical porosity (mesopores at ca. 10nm and macropores at ca. 50-200nm), high BET surface area (226m2/g), large pore volume (0.25cm3/g), and abundant medium and strong acidic sites (0.36mmol/g). After loading Pt (0.5wt.%) on H-SAPO-11 by using wet impregnation method, catalytic hydroisomerization tests of n-dodecane show that the hierarchical Pt/SAPO-11 zeolite exhibits high conversion of n-dodecane and enhanced selectivity for branched products as well as reduced selectivity for cracking products, compared with conventional Pt/SAPO-11 zeolite. This phenomenon is reasonably attributed to the presence of hierarchical porosity, which is favorable for access of reactants on catalytically active sites. The improvement in catalytic performance in long-chain paraffin hydroisomerization over Pt/SAPO-11-based catalyst is of great importance for its industrial applications in the future. © 2013 Elsevier Inc.

  16. Catalytic Degradation of Ortho-Chlorophenol Using Activated Carbon Modified by Different Methods

    Directory of Open Access Journals (Sweden)

    Yang Zheng

    2018-01-01

    Full Text Available The performance of activated carbon (AC modified by different methods was compared for its catalytic degradation of ortho-chlorophenol (o-CP. For the chemically treated AC, the catalytic effect of AC–NH3·H2O was superior to the other catalysts examined, having an o-CP removal efficiency of 82.2% at 330 °C. For the metal-modified catalysts, AC–V and AC–Co showed similar removal performances of 93.2% at 330 °C. N2 adsorption-desorption isotherms, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS, and gas chromatography—mass spectrometry (GC-MS analyses were used to characterize the reaction products, and different reaction mechanisms were proposed for both AC–NH3·H2O and AC–V according to the results. Complete oxidative degradation of o-CP was achieved by AC–V, with AC–NH3·H2O leading to the formation of additional dioxins. It can be deduced that a risk of dioxin synthesis and escape during the regeneration process is possible when nitrogen-modified carbon is used in selective catalytic reduction (SCR denitrification reactions, especially in the presence of chlorine atoms, benzene rings, and oxygen.

  17. Preparation of Rh/Ni Bimetallic Nanoparticles and Their Catalytic Activities for Hydrogen Generation from Hydrolysis of KBH4

    Directory of Open Access Journals (Sweden)

    Liqiong Wang

    2017-04-01

    Full Text Available ISOBAM–104 protected Rh/Ni bimetallic nanoparticles (BNPs of 3.1 nm in diameter were synthesized by a co–reduction method with a rapid injection of KBH4 solution. The catalytic activities of as–prepared BNPs for hydrogen generation from hydrolysis of a basic KBH4 solution were evaluated. Ultraviolet–visible spectrophotometry (UV–Vis, transmission electron microscopy (TEM, and high–resolution transmission electron microscopy (HRTEM were employed to characterize the structure, particle size, and chemical composition of the resultant BNPs. Catalytic activities for hydrolysis of KBH4 and catalytic kinetics of prepared BNPs were also investigated. It was shown that Rh/Ni BNPs displayed much higher catalytic activities than that of Rh or Ni monometallic nanoparticles (MNPs, and the prepared Rh10Ni90 BNPs possessed the highest catalytic activities with a value of 11580 mol–H2·h−1·mol–Rh−1. The high catalytic activities of Rh/Ni BNPs could be attributed to the electron transfer effect between Rh and Ni atoms, which was confirmed by a density functional theory (DFT calculation. The apparent activation energy for hydrogen generation of the prepared Rh10Ni90 BNPs was about 47.2 ± 2.1kJ/mol according to a kinetic study.

  18. Enhanced catalytic activity without the use of an external light source using microwave-synthesized CuO nanopetals

    Directory of Open Access Journals (Sweden)

    Govinda Lakhotiya

    2017-05-01

    Full Text Available We report enhanced catalytic activity of CuO nanopetals synthesized by microwave-assisted wet chemical synthesis. The catalytic reaction of CuO nanopetals and H2O2 was studied with the application of external light source and also under dark conditions for the degradation of the hazardous dye methylene blue. The CuO nanopetals showed significant catalytic activity for the fast degradation of methylene blue and rhodamine B (RhB under dark conditions, without the application of an external light source. This increased catalytic activity was attributed to the co-operative role of H2O2 and the large specific surface area (≈40 m2·g−1 of the nanopetals. We propose a detail mechanism for this fast degradation. A separate study of the effect of different H2O2 concentrations for the degradation of methylene blue under dark conditions is also illustrated.

  19. Coordination of physicians' operational activities : a Contingency perspective

    NARCIS (Netherlands)

    Broekhuis, Manda; van Donk, Dirk Pieter

    2011-01-01

    Purpose - The purpose of this paper is to investigate the impact of three different dimensions of customer-induced uncertainty and task uncertainty on the mix of physicians' coordination practices. Design/methodology/approach - An improvement and research project are combined resulting in 16 case

  20. Synthesis and catalytic properties of a series of cobalt porphyrins as cytochrome P450 model: the effect of substituents on the catalytic activity.

    Science.gov (United States)

    Hu, Bingcheng; Sun, Chengguo; Deng, Quanzhi; Liu, Zuliang

    2013-08-01

    A series of cobalt porphyrins derived from hemin was prepared as cytochrome P450 models. Effects of substituents at the cobalt deuteroporphyrin-propionate side chains are investigated in oxidation of toluene with air to benzaldehyde and benzyl alcohol without the use of solvent and sacrificial co-reductant. The catalytic activity of cobalt porphyrins depends on the type of substituents. When the electron-withdrawing groups like -Cl, -Br, were introduced into the double propionate side chains, they can increase the catalyst stability and selectivity to benzaldehyde. In comparison with these electron-withdrawing groups, the electron-donor groups, such as -CH 3 , -S-S- and -NH 2 groups, can improve their catalytic activities. Moreover, the electron-donor group containing an unpaired electron (such as -S-S-, -NH 2 ) is benefit for improving its catalytic efficiency and promoting the electron delivery. It can be concluded that the double propionate side chains in the deuteroporphyrin complex may participate in oxidation process and effect electron transfer from the high-valent metalloporphyrin species to the substrate.

  1. Catalytic performance of activated carbon supported cobalt catalyst for CO2 reforming of CH4.

    Science.gov (United States)

    Zhang, Guojie; Su, Aiting; Du, Yannian; Qu, Jiangwen; Xu, Ying

    2014-11-01

    Syngas production by CO2 reforming of CH4 in a fixed bed reactor was investigated over a series of activated carbon (AC) supported Co catalysts as a function of Co loading (between 15 and 30wt.%) and calcination temperature (Tc=300, 400 or 500°C). The catalytic performance was assessed through CH4 and CO2 conversions and long-term stability. XRD and SEM were used to characterize the catalysts. It was found that the stability of Co/AC catalysts was strongly dependent on the Co loading and calcination temperature. For the loadings (25wt.% for Tc=300°C), stable activities have been achieved. The loading of excess Co (>wt.% 25) causes negative effects not only on the performance of the catalysts but also on the support surface properties. In addition, the experiment showed that ultrasound can enhance and promote dispersion of the active metal on the carrier, thus improving the catalytic performance of the catalyst. The catalyst activity can be long-term stably maintained, and no obvious deactivation has been observed in the first 2700min. After analyzing the characteristics, a reaction mechanism for CO2 reforming of CH4 over Co/AC catalyst was proposed. Copyright © 2014 Elsevier Inc. All rights reserved.

  2. Superior acidic catalytic activity and stability of Fe-doped HTaWO6 nanotubes

    KAUST Repository

    Liu, He

    2017-07-26

    Fe-doped HTaWO6 (H1-3xFexTaWO6, x = 0.23) nanotubes as highly active solid acid catalysts were prepared via an exfoliation-scrolling-exchange process. The specific surface area and pore volume of undoped nanotubes (20.8 m2 g-1, 0.057 cm3 g-1) were remarkably enhanced through Fe3+ ion-exchange (>100 m2 g-1, 0.547 cm3 g-1). Doping Fe ions into the nanotubes endowed them with improved thermal stability due to the stronger interaction between the intercalated Fe3+ ions and the host layers. This interaction also facilitated the preservation of effective Brønsted acid sites and the generation of new acid sites. The integration of these functional roles resulted in Fe-doped nanotubes with high acidic catalytic activities in the Friedel-Crafts alkylation of anisole and the esterification of acetic acid. Facile accessibility to active sites, generation of effective Brønsted acid sites, high stability of the tubular structure and strong acid sites were found to synergistically contribute to the excellent acidic catalytic efficiency. Additionally, the activity of cycled nanocatalysts can be easily recovered through annealing treatment.

  3. Green Synthesis and Catalytic Activity of Gold Nanoparticles Synthesized by Artemisia capillaris Water Extract

    Science.gov (United States)

    Lim, Soo Hyeon; Ahn, Eun-Young; Park, Youmie

    2016-10-01

    Gold nanoparticles were synthesized using a water extract of Artemisia capillaris (AC-AuNPs) under different extract concentrations, and their catalytic activity was evaluated in a 4-nitrophenol reduction reaction in the presence of sodium borohydride. The AC-AuNPs showed violet or wine colors with characteristic surface plasmon resonance bands at 534 543 nm that were dependent on the extract concentration. Spherical nanoparticles with an average size of 16.88 ± 5.47 29.93 ± 9.80 nm were observed by transmission electron microscopy. A blue shift in the maximum surface plasmon resonance was observed with increasing extract concentration. The face-centered cubic structure of AC-AuNPs was confirmed by high-resolution X-ray diffraction analysis. Based on phytochemical screening and Fourier transform infrared spectra, flavonoids, phenolic compounds, and amino acids present in the extract contributed to the reduction of Au ions to AC-AuNPs. The average size of the AC-AuNPs decreased as the extract concentration during the synthesis was increased. Higher 4-nitrophenol reduction reaction rate constants were observed for smaller sizes. The extract in the AC-AuNPs was removed by centrifugation to investigate the effect of the extract in the reduction reaction. Interestingly, the removal of extracts greatly enhanced their catalytic activity by up to 50.4 %. The proposed experimental method, which uses simple centrifugation, can be applied to other metallic nanoparticles that are green synthesized with plant extracts to enhance their catalytic activity.

  4. Fibrous nano-silica supported ruthenium (KCC-1/Ru): A sustainable catalyst for the hydrogenolysis of alkanes with good catalytic activity and lifetime

    KAUST Repository

    Fihri, Aziz

    2012-07-06

    We have shown that fibrous nanosilica (KCC-1) can serve as a suitable support for the synthesis of highly dispersed ruthenium (Ru) nanoparticles. The resulting KCC-1/Ru catalyst displayed superior activity for the hydrogenolysis of propane and ethane at atmospheric pressure and at low temperature. The high catalytic activity was due to the formation of Ru-nanoparticles with an active size range (1-4 nm) and the presence of hexagonal-shaped particles with several corners and sharp edges possessing reactive atoms with lowest coordination numbers. The catalyst was stable with an excellent lifetime and no sign of deactivation, even after eight days. This enhanced stability may be due to the fibrous nature of KCC-1 which restricts Ostwald ripening of Ru nanoparticles. © 2012 American Chemical Society.

  5. LASER INDUCED SELECTIVE ACTIVATION UTILIZING AUTO-CATALYTIC ELECTROLESS PLATING ON POLYMER SURFACE

    DEFF Research Database (Denmark)

    Zhang, Yang; Nielsen, Jakob Skov; Tang, Peter Torben

    2009-01-01

    . Characterization of the deposited copper layer was used to select and improve laser parameters. Several types of polymers with different melting points were used as substrate. Using the above mentioned laser treatment, standard grades of thermoplastic materials such as ABS, SAN, PE, PC and others have been......This paper presents a new method for selective micro metallization of polymers induced by laser. An Nd: YAG laser was employed to draw patterns on polymer surfaces using a special set-up. After subsequent activation and auto-catalytic electroless plating, copper only deposited on the laser tracks...

  6. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

    Science.gov (United States)

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

    2016-02-01

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology.

  7. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

    Science.gov (United States)

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

    2016-01-01

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology. PMID:26861509

  8. Relief of autoinhibition by conformational switch explains enzyme activation by a catalytically dead paralog

    Energy Technology Data Exchange (ETDEWEB)

    Volkov, Oleg A.; Kinch, Lisa; Ariagno, Carson; Deng, Xiaoyi; Zhong, Shihua; Grishin, Nick; Tomchick, Diana R.; Chen, Zhe; Phillips, Margaret A.

    2016-12-15

    Catalytically inactive enzyme paralogs occur in many genomes. Some regulate their active counterparts but the structural principles of this regulation remain largely unknown. We report X-ray structures ofTrypanosoma brucei S-adenosylmethionine decarboxylase alone and in functional complex with its catalytically dead paralogous partner, prozyme. We show monomericTbAdoMetDC is inactive because of autoinhibition by its N-terminal sequence. Heterodimerization with prozyme displaces this sequence from the active site through a complex mechanism involving acis-to-transproline isomerization, reorganization of a β-sheet, and insertion of the N-terminal α-helix into the heterodimer interface, leading to enzyme activation. We propose that the evolution of this intricate regulatory mechanism was facilitated by the acquisition of the dimerization domain, a single step that can in principle account for the divergence of regulatory schemes in the AdoMetDC enzyme family. These studies elucidate an allosteric mechanism in an enzyme and a plausible scheme by which such complex cooperativity evolved.

  9. Catalytic destruction of chloramine to nitrogen using chlorination and activated carbon--case study.

    Science.gov (United States)

    Kochany, J; Lipczynska-Kochany, E

    2008-04-01

    The paper presents the results of laboratory and pilot studies on the removal of chloramine from potable water using chlorination with a less-than-breakpoint dosage of chlorine, followed by treatment with catalytic activated carbon. The effect of the chlorine-to-nitrogen ratio, temperature, and carbon contact time were investigated to optimize conditions for chloramines removal and minimize the production of ammonia. Results demonstrated that prechlorination of water, followed by treatment with catalytic activated carbon, can degrade monochloramine to nitrogen gas as a main product. For all chlorine-to-ammonia ratios studied, the observed rates of monochloramine removal were higher at a temperature of 20 degrees C than they were at 5 degrees C. Generation of ammonia was slightly higher at the lower temperature. However, at both temperatures, practically all monochloramine was destroyed, and only insignificant amounts of ammonia were formed when a chlorine-to-ammonia ratio of 7:1 was applied. The described method is simple and cost-effective, because it eliminates the requirement of removal of ammonia, typically formed during the treatment of chloramines with activated carbon.

  10. Synthesis and electro-catalytic activity of Pt-Co nanoflowers

    Science.gov (United States)

    Su, Yanqiu; Yu, Xiaofei; Li, Lanlan; Dong, Lili; Yan, Hui; Zhao, Jianling

    2017-07-01

    The study of metallic nanoflowers has attracted more and more attention because of their larger surface areas and active sites, which could be applied for surface-sensitive areas. Despite these excellent characteristics, it is still very hard to synthesize noble metal nanoflowers as the flower-like structure is apt to change into some more stable shapes which are covered by lower energy surfaces. In this study, Pt-Co nanoflowers were successfully synthesized by a two-step method via the reaction between Co nanoparticles and Pt precursor. From the transmission electron microscopy (TEM) images, it could be seen clearly that the products possessed a flower-like nanostructure. The morphology of the final products depended on a number of parameters, such as the reaction time and the reaction temperature. Based on the experimental results and theoretical calculation, the formation of nanoflowers could be attributed to the galvanic replacement reaction between Co nanoparticles and Pt precursor. In addition, the electrochemical catalytic activity of Pt-Co nanoflowers toward methanol oxidation was also evaluated in comparison with that of commercial Pt black. Owing to the special structure, the electro-catalytic activity and stability of Pt-Co nanoflowers were much better than those of commercial Pt black.

  11. Active site structure and catalytic mechanism of phosphodiesterase for degradation of intracellular second messengers

    Science.gov (United States)

    Zhan, Chang-Guo

    2002-03-01

    Phosphodiesterases are clinical targets for a variety of biological disorders, because this superfamily of enzymes regulate intracellular concentration of cyclic nucleotides that serve as the second messengers playing a critical role in a variety of physiological processes. Understanding structure and mechanism of a phosphodiesterase will provide a solid basis for rational design of the more efficient therapeutics. Although a three-dimensional X-ray crystal structure of the catalytic domain of human phosphodiesterase 4B2B was recently reported, it was uncertain whether a critical bridging ligand in the active site is a water molecule or a hydroxide ion. The identity of this bridging ligand has been determined by performing first-principles quantum chemical calculations on models of the active site. All the results obtained indicate that this critical bridging ligand in the active site of the reported X-ray crystal structure is a hydroxide ion, rather than a water molecule, expected to serve as the nucleophile to initialize the catalytic degradation of the intracellular second messengers.

  12. Interface modulation of bacteriogenic Ag/AgCl nanoparticles by boosting the catalytic activity for reduction reactions using Co2+ ions.

    Science.gov (United States)

    Zhou, Hao; Che, Lin; Guo, Xuyun; Wang, Xue; Zhan, Jingjing; Wu, Minghuo; Hu, Yufeng; Yi, Xianliang; Zhang, Xuwang; Liu, Lifen

    2017-05-02

    Boosting the low catalytic activity of bacteriogenic Ag/AgCl nanoparticles (NPs) by adding Co2+ in a model reaction, i.e. p-nitrophenol (PNP) reduction, was observed. Under optimal conditions, Co-Ag/AgCl NPs show an apparent rate constant (kapp) of 0.0837 s-1 upon PNP reduction. Considering the trace amount of Co-Ag/AgCl NPs used in catalysis (about 1.2 μg), the activity parameter κ (which is the ratio of kapp and catalyst mass) can reach more than 6.97 × 104 s-1 g-1, which is 214-fold higher than that of pristine Ag/AgCl NPs. Meanwhile, this κ value is also the highest value reported to date. In addition, the biogenic Co-Ag/AgCl NPs exhibit superior catalytic activities over other substrates, such as m-nitrophenol, o-nitrophenol, methyl orange and rhodamine B. The activity enhancement mechanism is supposed to be that Co2+ acts as a Lewis acid, and coordinates with the surface peptides to affect the electric field distribution at the Ag/AgCl NP interface.

  13. Synthesis, crystal structure and catalytic effect on thermal decomposition of RDX and AP: An energetic coordination polymer [Pb{sub 2}(C{sub 5}H{sub 3}N{sub 5}O{sub 5}){sub 2}(NMP)·NMP]{sub n}

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jin-jian [School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Yancheng Teachers College, Yancheng 224002 (China); Liu, Zu-Liang, E-mail: liuzl@mail.njust.edu.cn [School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Cheng, Jian [School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Yancheng Teachers College, Yancheng 224002 (China); Fang, Dong, E-mail: fangdong106@163.com [Yancheng Teachers College, Yancheng 224002 (China)

    2013-04-15

    An energetic lead(II) coordination polymer based on the ligand ANPyO has been synthesized and its crystal structure has been got. The polymer was characterized by FT-IR spectroscopy, elemental analysis, DSC and TG-DTG technologies. Thermal analysis shows that there are one endothermic process and two exothermic decomposition stages in the temperature range of 50–600 °C with final residues 57.09%. The non-isothermal kinetic has also been studied on the main exothermic decomposition using the Kissinger's and Ozawa–Doyle's methods, the apparent activation energy is calculated as 195.2 KJ/mol. Furthermore, DSC measurements show that the polymer has significant catalytic effect on the thermal decomposition of ammonium perchlorate. - Graphical abstract: An energetic lead(II) coordination polymer of ANPyO has been synthesized, structurally characterized and properties tested. Highlights: ► We have synthesized and characterized an energetic lead(II) coordination polymer. ► We have measured its molecular structure and thermal decomposition. ► It has significant catalytic effect on thermal decomposition of AP.

  14. 75 FR 15496 - Agency Information Collection (Care Coordination Home Telehealth (CCHT)) Activity Under OMB Review

    Science.gov (United States)

    2010-03-29

    ...).'' SUPPLEMENTARY INFORMATION: Title: Care Coordination Home Telehealth (CCHT) Patient Satisfaction Survey, VA Form 10-0481. OMB Control Number: 2900-New (CCHT). Type of Review: New collection. Abstract: Patients... AFFAIRS Agency Information Collection (Care Coordination Home Telehealth (CCHT)) Activity Under OMB Review...

  15. The Botrytis cinerea xylanase Xyn11A contributes to virulence with its necrotizing activity, not with its catalytic activity

    Directory of Open Access Journals (Sweden)

    González Celedonio

    2010-02-01

    Full Text Available Abstract Background The Botrytis cinerea xylanase Xyn11A has been previously shown to be required for full virulence of this organism despite its poor contribution to the secreted xylanase activity and the low xylan content of B. cinerea hosts. Intriguingly, xylanases from other fungi have been shown to have the property, independent of the xylan degrading activity, to induce necrosis when applied to plant tissues, so we decided to test the hypothesis that secreted Xyn11A contributes to virulence by promoting the necrosis of the plant tissue surrounding the infection, therefore facilitating the growth of this necrotroph. Results We show here that Xyn11A has necrotizing activity on plants and that this capacity is conserved in site-directed mutants of the protein lacking the catalytic activity. Besides, Xyn11A contributes to the infection process with the necrotizing and not with the xylan hydrolyzing activity, as the catalytically-impaired Xyn11A variants were able to complement the lower virulence of the xyn11A mutant. The necrotizing activity was mapped to a 30-amino acids peptide in the protein surface, and this region was also shown to mediate binding to tobacco spheroplasts by itself. Conclusions The main contribution of the xylanase Xyn11A to the infection process of B. cinerea is to induce necrosis of the infected plant tissue. A conserved 30-amino acids region on the enzyme surface, away from the xylanase active site, is responsible for this effect and mediates binding to plant cells.

  16. Synthesis, spectral and catalytic activity of some Manganese(II) bis-benzimidazole diamide complexes

    Science.gov (United States)

    Mohapatra, Subash Chandra; Hundal, M. S.; Mathur, Pavan

    2011-09-01

    Four Mn(II) complexes bound to a neutral bis-benzimidazole diamide ligand N,N'-bis(2-methyl benzimidazolyl 2,2'-oxy-diethanamide) (GBOA) have been synthesized and characterized. Anionic ligand associated with the complexes varies as Cl - CH 3COO -, SCN - and ClO 4-. X-ray structure of one of the complexes [Mn(GBOA) 2(H 2O) 2]Cl 2·4H 2O was solved and shows that the Mn(II) ion is hexacoordinate. Two equatorial positions are occupied by benzimidazole imine nitrogen atoms while the other two sites are occupied by amide carbonyl oxygens. The imine nitrogen and carbonyl oxygens are bound to Mn(II) by different arms of the two ligands while axial sites are occupied by two water molecules. Two Cl - anions are outside the coordination sphere and form an extensive 3D H-bonded network. Axially distorted octahedral geometry is confirmed for all the four complexes by low temperature EPR spectroscopy. Distortion parameter D was found to be similar for [Mn(GBOA) 2(H 2O) 2]Cl 2·4H 2O and [Mn(GBOA) 2(H 2O) 2]·(CH 3COO) 2·H 2O. Cyclic voltammograms have been obtained for all the four complexes and E1/2 values are dependant on the anionic ligand being in the coordination sphere or outside. [Mn(GBOA) 2(H 2O) 2]Cl 2·4H 2O and [Mn(GBOA) 2(H 2O) 2]·(CH 3COO) 2·H 2O carry out the selective oxidation of N-benzyldimethylamine, and 1-methyl-pyrollidine to their respective carbonyl products with catalytic efficiency of 35-50%.

  17. Precursor type affecting surface properties and catalytic activity of sulfated zirconia

    Directory of Open Access Journals (Sweden)

    Zarubica Aleksandra R.

    2007-01-01

    Full Text Available Zirconium-hydroxide precursor samples are synthesized from Zr-hydroxide, Zr-nitrate, and Zr-alkoxide, by precipitation/impregnation, as well as by a modified sol-gel method. Precursor samples are further sulphated for the intended SO4 2- content of 4 wt.%, and calcined at 500-700oC. Differences in precursors’ origin and calcination temperature induce the incorporation of SO4 2- groups into ZrO2 matrices by various mechanisms. As a result, different amounts of residual sulphates are coupled with other structural, as well as surface properties, resulting in various catalytic activities of sulphated zirconia samples. Catalyst activity and selectivity are a complex synergistic function of tetragonal phase fraction, sulphates contents, textural and surface characteristics. Superior activity of SZ of alkoxide origin can be explained by a beneficial effect of meso-pores owing to a better accommodation of coke deposits.

  18. Effect of citrate on Aspergillus niger phytase adsorption and catalytic activity in soil

    Science.gov (United States)

    Mezeli, Malika; Menezes-Blackburn, Daniel; Zhang, Hao; Giles, Courtney; George, Timothy; Shand, Charlie; Lumsdon, David; Cooper, Patricia; Wendler, Renate; Brown, Lawrie; Stutter, Marc; Blackwell, Martin; Darch, Tegan; Wearing, Catherine; Haygarth, Philip

    2015-04-01

    Current developments in cropping systems that promote mobilisation of phytate in agricultural soils, by exploiting plant-root exudation of phytase and organic acids, offer potential for developments in sustainable phosphorus use. However, phytase adsorption to soil particles and phytate complexion has been shown to inhibit phytate dephosphorylation, thereby inhibiting plant P uptake, increasing the risk of this pool contributing to diffuse pollution and reducing the potential benefits of biotechnologies and management strategies aimed to utilise this abundant reserve of 'legacy' phosphorus. Citrate has been seen to increase phytase catalytic efficiency towards complexed forms of phytate, but the mechanisms by which citrate promotes phytase remains poorly understood. In this study, we evaluated phytase (from Aspergillus niger) inactivation, and change in catalytic properties upon addition to soil and the effect citrate had on adsorption of phytase and hydrolysis towards free, precipitated and adsorbed phytate. A Langmuir model was fitted to phytase adsorption isotherms showing a maximum adsorption of 0.23 nKat g-1 (19 mg protein g-1) and affinity constant of 435 nKat gˉ1 (8.5 mg protein g-1 ), demonstrating that phytase from A.niger showed a relatively low affinity for our test soil (Tayport). Phytases were partially inhibited upon adsorption and the specific activity was of 40.44 nKat mgˉ1 protein for the free enzyme and 25.35 nKat mgˉ1 protein when immobilised. The kinetics of adsorption detailed that most of the adsorption occurred within the first 20 min upon addition to soil. Citrate had no effect on the rate or total amount of phytase adsorption or loss of activity, within the studied citrate concentrations (0-4mM). Free phytases in soil solution and phytase immobilised on soil particles showed optimum activity (>80%) at pH 4.5-5.5. Immobilised phytase showed greater loss of activity at pH levels over 5.5 and lower activities at the secondary peak at pH 2

  19. An approach to establish the uncertainty budget of catalytic activity concentration measurements in a reference laboratory.

    Science.gov (United States)

    Rami, Laura; Canalias, Francesca

    2015-04-01

    Reference laboratories providing reference services recognized by the Joint Committee for Traceability in Laboratory Medicine (JCTLM) must be accredited as calibration laboratories according to ISO 17025 and ISO 15195. These standards require laboratories to establish an uncertainty budget, in which the uncertainty contributions of the relevant uncertainty components are specified. We present a model to estimate the measurement uncertainty of creatine kinase catalytic activity concentration results obtained by IFCC primary reference measurement procedure. The measurement uncertainty has been estimated by following the next steps: 1) specification of the measurand; 2) identification of the most relevant uncertainty sources; 3) estimation of standard uncertainties by either type A or type B evaluation; 4) estimation of combined uncertainty while taking into account sensitivity coefficients, as well as existence of correlated uncertainty sources; and 5) estimation of expanded uncertainty with a defined coverage probability. The estimated expanded uncertainty was 2.2% (k=2). Uncertainty sources with a significant contribution to the measurement uncertainty were the following: pH adjustment (0.68%), absorbance accuracy (0.48%), wavelength adjustment (0.20%), reaction temperature (0.19%), volume fraction of sample (0.15%) and absorbance linearity (0.06%). The present model is an approach to establish the uncertainty budget of primary reference procedures for the measurement of the catalytic activity concentration of enzymes, and aims at being an example to be followed by other reference laboratories, as well as by laboratories that carry out primary reference measurement procedures.

  20. Biorefining of platinum group metals from model waste solutions into catalytically active bimetallic nanoparticles.

    Science.gov (United States)

    Murray, Angela J; Zhu, Ju; Wood, Joe; Macaskie, Lynne E

    2018-03-01

    Bacteria can fabricate platinum group metal (PGM) catalysts cheaply, a key consideration of industrial processes and waste decontaminations. Biorecovery of PGMs from wastes is promising but PGM leachates made from metallic scraps are acidic. A two-step biosynthesis 'pre-seeds' metallic deposits onto bacterial cells benignly; chemical reduction of subsequent metal from acidic solution via the seeds makes bioscaffolded nanoparticles (NPs). Cells of Escherichia coli were seeded using Pd(II) or Pt(IV) and exposed to a mixed Pd(II)/Pt(IV) model solution under H 2 to make bimetallic catalyst. Its catalytic activity was assessed in the reduction of Cr(VI), with 2 wt% or 5 wt% preloading of Pd giving the best catalytic activity, while 1 wt% seeds gave a poorer catalyst. Use of Pt seeds gave less effective catalyst in the final bimetallic catalyst, attributed to fewer and larger initial seeds as shown by electron microscopy, which also showed a different pattern of Pd and Pt deposition. Bimetallic catalyst (using cells preloaded with 2 wt% Pd) was used in the hydrogenation of soybean oil which was enhanced by ~fourfold using the bimetallic catalyst made from a model waste solution as compared to 2 wt% Pd preloaded cells alone, with a similar selectivity to cis C18:1 product as found using a Pd-Al 2 O 3 commercial catalyst. © 2018 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.

  1. Catalytic oxidation of S(IV) in seawater slurries of activated carbon

    Energy Technology Data Exchange (ETDEWEB)

    B.F. Vidal; P. Ollero; F.J. Gutierrez Ortiz; R. Arjona [University of Seville, Sevilla (Spain). Department of Chemical and Environmental Engineering

    2005-07-01

    Flue gas desulfurization (FGD) by means of SO{sub 2} absorption in seawater is a well-known process with a main drawback; due to the low S(IV) oxidation rate at the low pH values of the absorption tower effluent, a large oxidation basin is required. Laboratory reactor tests, in which a commercially available activated carbon was used, showed a significant catalytic effect. It is shown that the kinetic equation for the catalytic oxidation of S(IV), in seawater slurries of activated carbon, is first-order with respect to S(IV) and zero-order with respect to oxygen. The dependence of the kinetic constant with respect to pH, temperature, and catalyst size particles were also obtained. The study showed that using an appropriated size and concentration of catalyst, it is possible to reach, at pH = 4, S(IV), oxidation rates similar to those obtained at pH = 6 without catalyst. Operating at pH = 4 requires less seawater flow rate in the oxidation basin than at pH = 6. Thus, the volume of the water treatment plant can be reduced too. The space requirements and both the capital and the operating cost are lower, a critical issue concerning the retrofitting of existing power stations. 12 refs., 9 figs., 3 tabs.

  2. Molecular dynamics characterization of five pathogenic factor X mutants associated with decreased catalytic activity

    KAUST Repository

    Abdel-Azeim, Safwat

    2014-11-11

    Factor X (FX) is one of the major players in the blood coagulation cascade. Upon activation to FXa, it converts prothrombin to thrombin, which in turn converts fibrinogen into fibrin (blood clots). FXa deficiency causes hemostasis defects, such as intracranial bleeding, hemathrosis, and gastrointestinal blood loss. Herein, we have analyzed a pool of pathogenic mutations, located in the FXa catalytic domain and directly associated with defects in enzyme catalytic activity. Using chymotrypsinogen numbering, they correspond to D102N, T135M, V160A, G184S, and G197D. Molecular dynamics simulations were performed for 1.68 μs on the wild-type and mutated forms of FXa. Overall, our analysis shows that four of the five mutants considered, D102N, T135M, V160A, and G184S, have rigidities higher than those of the wild type, in terms of both overall protein motion and, specifically, subpocket S4 flexibility, while S1 is rather insensitive to the mutation. This acquired rigidity can clearly impact the substrate recognition of the mutants.

  3. Enhancing catalytic activity of a hybrid xylanase through single substitution of Leu to Pro near the active site.

    Science.gov (United States)

    Wang, Qian; Zhao, Li-Li; Sun, Jian-Yi; Liu, Jian-Xin; Weng, Xiao-Yan

    2012-03-01

    A modified error-prone PCR and high-throughout screening system based on 96-well plate were employed to improve catalytic activity of a hybrid xylanase (ATx). The mutant (FSI-A124) with enhanced activity was further heterologously expressed in Pichia pastoris under the control of GAP promoter. The recombinant xylanase driven by the Saccharomyces cerevisiae α-mating factor was secreted into culture medium. After growth in YPD medium for 96 h, xylanase activity in the culture supernatant reached 66.1 U ml(-1), which was 2.92 times as that of its parent. 6 × His-tagged purification increased the specific activity to 1557.61 U mg(-1). The optimum temperature and pH of recombinant xylanase were 55°C and 6.0, respectively. A single amino acid substitution (L49P) was observed within sequence of the mutant. Insight of the three dimensional structure revealed that proline possibly produced weaker hydrogen bond, van der Waals force and hydrophobic interaction with other residues nearby than leucine, especially for V174, contributing to the flexibility of catalytic residue E177. In this study, FSI-A124 exhibited higher xylanase activity but poorer thermostability than its parent, indicating that activity and stability might be negatively correlated.

  4. Preparation and characterization of polyaniline/manganese dioxide composites and their catalytic activity.

    Science.gov (United States)

    Gemeay, Ali H; El-Sharkawy, Rehab G; Mansour, Ikhlas A; Zaki, Ahmed B

    2007-04-15

    This paper is devoted to the preparation of polyaniline/MnO2 (PANI/MnO2) composites via chemical oxidation of aniline in H2SO4 medium using beta-MnO2 as an oxidant. The parameters affecting the polymerization reaction are considered. These parameters are [aniline], amount of beta-MnO2, stirring time, and polymerization temperature. SEM, FT-IR, XRD, and TGA techniques are used to characterize the resulting composites. XRD measurements reveal the distortion of the crystal structure of beta-MnO2 after the polymerization reaction. Thus, the XRD pattern of PANI is predominating. The crystalline composites are obtained using higher molar ratio of [Ox]/[ANI] and at higher temperature. Increasing the amount of beta-MnO2 led to an increase in the acidic character of the obtained composites due to adsorption of excess H+ on the oxide surface. The thermal stability of the composites decreased with increasing both [aniline] and stirring time, while it increased with increasing amount of beta-MnO2. The applications of the composites in the oxidative degradation of Direct Red 81, Acid Blue 92, and Indigo Carmine dyes exhibited good catalytic activity in the presence of H2O2 as an oxidant. The reactions followed first-order kinetics and the rate constants were determined. The degradation reaction involved the catalytic action of the PANI counterpart of the composite toward H2O2 decomposition, which can lead to the generation of HO radicals as a highly efficient oxidant attacking the target dyes. The detailed kinetic studies and the mechanism of these catalytic reactions are under consideration in our group.

  5. Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms.

    Science.gov (United States)

    Koval, Iryna A; Selmeczi, Katalin; Belle, Catherine; Philouze, Christian; Saint-Aman, Eric; Gautier-Luneau, Isabelle; Schuitema, Anna Maria; van Vliet, Marcel; Gamez, Patrick; Roubeau, Olivier; Lüken, Matthias; Krebs, Bernt; Lutz, Martin; Spek, Anthony L; Pierre, Jean-Louis; Reedijk, Jan

    2006-08-07

    We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.

  6. Synthesis, characterization, hydrolase and catecholase activity of a dinuclear iron(III) complex: Catalytic promiscuity.

    Science.gov (United States)

    Camargo, Tiago P; Maia, Fernanda F; Chaves, Cláudia; de Souza, Bernardo; Bortoluzzi, Adailton J; Castilho, Nathalia; Bortolotto, Tiago; Terenzi, Hernán; Castellano, Eduardo E; Haase, Wolfgang; Tomkowicz, Zbigniew; Peralta, Rosely A; Neves, Ademir

    2015-05-01

    Herein, we report the synthesis and characterization of the new di-iron(III) complex [(bbpmp)(H2O)(Cl)Fe(III)(μ-Ophenoxo)Fe(III)(H2O)Cl)]Cl (1), with the symmetrical ligand 2,6-bis{[(2-hydroxybenzyl)(pyridin-2-yl)methylamino]methyl}-4-methylphenol (H3bbpmp). Complexes 2 with the unsymmetrical ligand H2bpbpmp - {2-[[(2-hydroxybenzyl)(2-pyridylmethyl)]aminomethyl]-6-bis(pyridylmethyl) aminomethyl}-4-methylphenol and 3 with the ligand L(1)=4,11-dimethyl-1,8-bis{2-[N-(di-2-pyridylmethyl)amino]ethyl}cyclam were included for comparison purposes. Complex 1 was characterized through elemental analysis, X-ray crystallography, magnetochemistry, electronic spectroscopy, electrochemistry, mass spectrometry and potentiometric titration. The magnetic data show a very weak antiferromagnetic coupling between the two iron centers of the dinuclear complex 1 (J=-0.29cm(-1)). Due to the presence of labile coordination sites in both iron centers the hydrolysis of both the diester model substrate 2,4-BDNPP and DNA was studied in detail. Complex 1 was also able to catalyze the oxidation of the substrate 3,5-di-tert-butylcatechol (3,5-DTBC) to give the corresponding quinone, and thus it can be considered as a catalytically promiscuous system. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. Dinuclear and mononuclear manganese(IV)-radical complexes and their catalytic catecholase activity.

    Science.gov (United States)

    Mukherjee, Soumen; Weyhermüller, Thomas; Bothe, Eberhard; Wieghardt, Karl; Chaudhuri, Phalguni

    2004-11-21

    Seven o-aminophenol ligands based on aniline and m-phenylenediamine, which act as mono- and di-nucleating non-innocent ligands, respectively, together with their seven Mn(IV)-complexes, 1-7 are described. One of them, 1, is dinuclear and 2-7 are mononuclear, in which the ligands are coordinated in their oxidized o-iminobenzosemiquinone radical forms. The crystal structures of 1 and 3 were determined by X-ray diffraction and the electronic structures were established by various physical methods including EPR and variable-temperature (2-290 K) susceptibility measurements. Electrochemical measurements (CV and SQW) indicate primarily ligand-centered redox processes. The Mn(IV)-radical complexes, 1-7, catalyze the oxidation of 3,5-di-tert-butylcatechol with molecular oxygen as the sole oxidant to afford 3,5-di-tert-butylquinone quantitatively under mild conditions to mimic the function of the copper-containing enzyme catechol oxidase. An "on-off" mechanism of the radicals without redox participation of the metal center is proposed for the catalytic oxidation process. Complex 1 is found to be a good catalyst for oxidative C-C coupling of hindered phenols to diphenoquinones.

  8. Understanding the catalytic activity of gold nanoparticles through multi-scale simulations

    DEFF Research Database (Denmark)

    Brodersen, Simon Hedegaard; Vej-Hansen, Ulrik Grønbjerg; Larsen, Britt Hvolbæk

    2011-01-01

    We investigate how the chemical reactivity of gold nanoparticles depends on the cluster size and shape using a combination of simulation techniques at different length scales, enabling us to model at the atomic level the shapes of clusters in the size range relevant for catalysis. The detailed......-coordinated active sites is found, and their reactivities are extracted from models based on Density Functional Theory calculations. This enables us to determine the chemical activity of clusters in the same range of particle sizes that is accessible experimentally. The variation of reactivity with particle size...... is in excellent agreement with experiments, and we conclude that the experimentally observed trends are mostly explained by the high reactivity of under-coordinated corner atoms on the gold clusters. Other effects, such as the effect of the substrate, may influence the reactivities significantly, but the presence...

  9. Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining.

    Science.gov (United States)

    Buurmans, Inge L C; Ruiz-Martínez, Javier; Knowles, William V; van der Beek, David; Bergwerff, Jaap A; Vogt, Eelco T C; Weckhuysen, Bert M

    2011-09-18

    Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials.

  10. Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining

    Science.gov (United States)

    Buurmans, Inge L. C.; Ruiz-Martínez, Javier; Knowles, William V.; van der Beek, David; Bergwerff, Jaap A.; Vogt, Eelco T. C.; Weckhuysen, Bert M.

    2011-11-01

    Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials.

  11. Relationships between physical activity, physical fitness, somatic fitness, and coordination along childhood and adolescence

    Directory of Open Access Journals (Sweden)

    João Paulo Saraiva

    2010-12-01

    Full Text Available The two main goals of this review were to understand how the relationships between physical activity, physical fitness, somatic fitness, and coordination are established along the motor development of children and adolescents, and how they would influence their future lives. The web based bibliographic database B-On was searched for peer-reviewed publications during the last decade (2000 to 2009. Search criteria included all articles on relationships between any two of the above named factors. Although different methodological designs and variables were found as markers for the same factor, overall results suggested the existence of a clear positive relationship among physical activity, physical fitness, somatic fitness, and coordination from childhood to adolescence, with a special relevance for the relationship between physical activity and coordination. It was also noted a renewed interest on physical activity and motor coordination developmental characteristics and relationships as well as on their lifelong health effects.

  12. Relationships between physical activity, physical fitness, somatic fitness, and coordination along childhood and adolescence

    Directory of Open Access Journals (Sweden)

    J.P. Saraiva

    2010-01-01

    Full Text Available The two main goals of this review were to understand how the relationships between physical activity, physical fitness, somatic fitness, and coordination are established along the motor development of children and adolescents, and how they would influence their future lives. The web based bibliographic database B-On was searched for peer-reviewed publications during the last decade (2000 to 2009. Search criteria included all articles on relationships between any two of the above named factors. Although different methodological designs and variables were found as markers for the same factor, overall results suggested the existence of a clear positive relationship among physical activity, physical fitness, somatic fitness, and coordination from childhood to adolescence, with a special relevance for the relationship between physical activity and coordination. It was also noted a renewed interest on physical activity and motor coordination developmental characteristics and relationships as well as on their lifelong health effects.

  13. Factors Controlling the Redox Activity of Oxygen in Perovskites: From Theory to Application for Catalytic Reactions

    Directory of Open Access Journals (Sweden)

    Chunzhen Yang

    2017-05-01

    Full Text Available Triggering the redox reaction of oxygens has become essential for the development of (electro catalytic properties of transition metal oxides, especially for perovskite materials that have been envisaged for a variety of applications such as the oxygen evolution or reduction reactions (OER and ORR, respectively, CO or hydrocarbons oxidation, NO reduction and others. While the formation of ligand hole for perovskites is well-known for solid state physicists and/or chemists and has been widely studied for the understanding of important electronic properties such as superconductivity, insulator-metal transitions, magnetoresistance, ferroelectrics, redox properties etc., oxygen electrocatalysis in aqueous media at low temperature barely scratches the surface of the concept of oxygen ions oxidation. In this review, we briefly explain the electronic structure of perovskite materials and go through a few important parameters such as the ionization potential, Madelung potential, and charge transfer energy that govern the oxidation of oxygen ions. We then describe the surface reactivity that can be induced by the redox activity of the oxygen network and the formation of highly reactive surface oxygen species before describing their participation in catalytic reactions and providing mechanistic insights and strategies for designing new (electro catalysts. Finally, we give a brief overview of the different techniques that can be employed to detect the formation of such transient oxygen species.

  14. Multiple functionalities of Ni nanoparticles embedded in carboxymethyl guar gum polymer: catalytic activity and superparamagnetism

    Energy Technology Data Exchange (ETDEWEB)

    Sardar, Debasmita [Department of Chemistry, University of Calcutta, 92 A.P.C. Road, Kolkata 700009 (India); Sengupta, Manideepa; Bordoloi, Ankur [Nano Catalysis, Catalytic Conversion and Process Division, CSIR—Indian Institute of Petroleum (IIP), Mohkampur, Dehradun 248005 (India); Ahmed, Md. A.; Neogi, S.K.; Bandyopadhyay, Sudipta [Department of Physics, University of Calcutta, 92 A.P.C. Road, Kolkata 700009 (India); Jain, Ruchi; Gopinath, Chinnakonda S. [Catalysis Division and Center of Excellence on Surface Science, CSIR—National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008 (India); Bala, Tanushree, E-mail: tanushreebala@gmail.com [Department of Chemistry, University of Calcutta, 92 A.P.C. Road, Kolkata 700009 (India)

    2017-05-31

    Highlights: • Ni nanoparticles were synthesized in polymer to form Ni-Polymer composite. • Ni nanoparticles retain their superparamagnetism in the composite. • Ni-Polymer composites showed catalytic activity. - Abstract: Composites comprising of metallic nanoparticles in polymer matrices have allured significant importance due to multifunctionalities. Here a simple protocol has been described to embed Ni nanoparticles in carboxymethyl guar gum (CMGG) polymer. The composite formation helps in the stabilization of Ni nanoparticles which are otherwise prone towards aerial oxidation. Further the nanoparticles retain their superparamagnetic nature and catalytic capacity. Ni-Polymer composite catalyses the reduction of 4-Nitrophenol to 4-Aminophenol very efficiently in presence of NaBH{sub 4}, attaining a complete conversion under some experimental conditions. Ni-Polymer composite is well characterized using UV–vis spectroscopy, FTIR, XPS, powder XRD, TGA, SEM and TEM. A detailed magnetic measurement using superconducting quantum interference device-vibrating sample magnetometer (SQUID-VSM) reveals superparamagnetic behaviour of the composite.

  15. Dinuclear manganese complexes for water oxidation: evaluation of electronic effects and catalytic activity.

    Science.gov (United States)

    Arafa, Wael A A; Kärkäs, Markus D; Lee, Bao-Lin; Åkermark, Torbjörn; Liao, Rong-Zhen; Berends, Hans-Martin; Messinger, Johannes; Siegbahn, Per E M; Åkermark, Björn

    2014-06-28

    During recent years significant progress has been made towards the realization of a sustainable and carbon-neutral energy economy. One promising approach is photochemical splitting of H2O into O2 and solar fuels, such as H2. However, the bottleneck in such artificial photosynthetic schemes is the H2O oxidation half reaction where more efficient catalysts are required that lower the kinetic barrier for this process. In particular catalysts based on earth-abundant metals are highly attractive compared to catalysts comprised of noble metals. We have now synthesized a library of dinuclear Mn2(II,III) catalysts for H2O oxidation and studied how the incorporation of different substituents affected the electronics and catalytic efficiency. It was found that the incorporation of a distal carboxyl group into the ligand scaffold resulted in a catalyst with increased catalytic activity, most likely because of the fact that the distal group is able to promote proton-coupled electron transfer (PCET) from the high-valent Mn species, thus facilitating O-O bond formation.

  16. The stability and catalytic activity of W13@Pt42 core-shell structure.

    Science.gov (United States)

    Huo, Jin-Rong; Wang, Xiao-Xu; Li, Lu; Cheng, Hai-Xia; Su, Yan-Jing; Qian, Ping

    2016-10-19

    This paper reports a study of the electronic properties, structural stability and catalytic activity of the W13@Pt42 core-shell structure using the First-principles calculations. The degree of corrosion of W13@Pt42 core-shell structure is simulated in acid solutions and through molecular absorption. The absorption energy of OH for this structure is lower than that for Pt55, which inhibits the poison effect of O containing intermediate. Furthermore we present the optimal path of oxygen reduction reaction catalyzed by W13@Pt42. Corresponding to the process of O molecular decomposition, the rate-limiting step of oxygen reduction reaction catalyzed by W13@Pt42 is 0.386 eV, which is lower than that for Pt55 of 0.5 eV. In addition by alloying with W, the core-shell structure reduces the consumption of Pt and enhances the catalytic efficiency, so W13@Pt42 has a promising perspective of industrial application.

  17. Green Synthesis of Smart Metal/Polymer Nanocomposite Particles and Their Tuneable Catalytic Activities

    Directory of Open Access Journals (Sweden)

    Noel Peter Bengzon Tan

    2016-03-01

    Full Text Available Herein we report a simple and green synthesis of smart Au and Ag@Au nanocomposite particles using poly(N-isopropylacrylamide/polyethyleneimine (PNIPAm/PEI core-shell microgels as dual reductant and templates in an aqueous system. The nanocomposite particles were synthesized through a spontaneous reduction of tetrachloroauric (III acid to gold nanoparticles at room temperature, and in situ encapsulation and stabilization of the resultant gold nanoparticles (AuNPs with amine-rich PEI shells. The preformed gold nanoparticles then acted as seed nanoparticles for further generation of Ag@Au bimetallic nanoparticles within the microgel templates at 60 °C. These nanocomposite particles were characterized by TEM, AFM, XPS, UV-vis spectroscopy, zeta-potential, and particle size analysis. The synergistic effects of the smart nanocomposite particles were studied via the reduction of p-nitrophenol to p-aminophenol. The catalytic performance of the bimetallic Ag@Au nanocomposite particles was 25-fold higher than that of the monometallic Au nanoparticles. Finally, the controllable catalytic activities of the Au@PNIPAm/PEI nanocomposite particles were demonstrated via tuning the solution pH and temperature.

  18. Green synthesis, characterization and catalytic activity of silver nanoparticles using Cassia auriculata flower extract separated fraction

    Science.gov (United States)

    Muthu, Karuppiah; Priya, Sethuraman

    2017-05-01

    Cassia auriculata L., the flower aqueous extract was fractionated by separating funnel using n-hexane (A1), chloroform (A2), ethyl acetate (A3) and triple distilled water (A4). The A4 fraction was concentrated and determined the presence of preliminary phytochemicals such as tannins, flavonoids, glycosides, carbohydrates and polyphenolic compounds. These phytochemical compounds acted as reducing as well as a stabilizing agent in the green synthesis of Ag NPs from aqueous silver ions. Initially, the colour change and UV-vis absorbance surface Plasmon resonance strong, wide band located at 435 nm has confirmed the synthesis of Ag NPs. The X-ray diffraction (XRD) pattern of Ag NPs shows a face-centered cubic crystal structure. The observed values were calculated by Debye-Scherrer equation to theoretical confirms the particle size of 18 nm. The surface morphology of Ag NPs was viewed by HRTEM, the particles are spherical and triangle shapes with sizes from 10 to 35 nm. Further, the Ag NPs was effective catalytic activity in the reduction of highly environmental polluted organic compounds of 4-nitrophenol and methyl orange. The green synthesis of Ag NPs seems to eco-friendly, cost-effective, conventional one spot synthesis and greater performance of catalytic degradation of environmentally polluted organic dyes.

  19. Effect of substrate (ZnO morphology on enzyme immobilization and its catalytic activity

    Directory of Open Access Journals (Sweden)

    Huang Xuelei

    2011-01-01

    Full Text Available Abstract In this study, zinc oxide (ZnO nanocrystals with different morphologies were synthesized and used as substrates for enzyme immobilization. The effects of morphology of ZnO nanocrystals on enzyme immobilization and their catalytic activities were investigated. The ZnO nanocrystals were prepared through a hydrothermal procedure using tetramethylammonium hydroxide as a mineralizing agent. The control on the morphology of ZnO nanocrystals was achieved by varying the ratio of CH3OH to H2O, which were used as solvents in the hydrothermal reaction system. The surface of as-prepared ZnO nanoparticles was functionalized with amino groups using 3-aminopropyltriethoxysilane and tetraethyl orthosilicate, and the amino groups on the surface were identified and calculated by FT-IR and the Kaiser assay. Horseradish peroxidase was immobilized on as-modified ZnO nanostructures with glutaraldehyde as a crosslinker. The results showed that three-dimensional nanomultipod is more appropriate for the immobilization of enzyme used further in catalytic reaction.

  20. Chlorinated aromatics from combustion: influence of chlorine, combustion conditions, and catalytic activity.

    Science.gov (United States)

    Oberg, T; Ohrström, T

    2003-09-01

    Research on the formation of chlorinated aromatics in combustion processes has mainly taken place in the laboratory. Previous attempts to correlate observation data from commercial plants have been inconclusive. This study reports on the outcome of an industrial experiment in a full-scale afterburner. The influence of chlorine input, combustion temperature, and catalytic activity was investigated in a factorial design with two blocks. Polychlorinated benzenes, dibenzo-p-dioxins, and dibenzofurans were formed both at combustion temperatures and below 400 degrees C. The results show that all three experimental factors have statistically significant impact on the formation and release of these toxic byproducts. The quantitative dependence between chlorine input and the occurrence of chlorinated aromatics is of particular interest due to previous controversy. The purpose with this study was to ensure that the installation of a boiler for energy recovery would not cause elevated emissions of chlorinated aromatics. The experiment demonstrated that this risk is probably low, since the presence of catalytic material or an increase in chlorine input is required for this to happen. A general conclusion was that industrial experimentation employing the principles of statistical design could improve the validity in recommendations regarding commercial plant operation.

  1. Disproportionation of hydrogen peroxide in the presence of coordination compounds of manganese (II) with glycine

    Energy Technology Data Exchange (ETDEWEB)

    Batyr, D.G.; Isak, V.G.; Kil' mininov, S.V.

    1988-01-01

    It has been established that the effective decomposition of hydrogen peroxide takes place in the presence of coordination compounds of manganese (II) with glycine (Gly). The catalytically active species is the complex (MnGly/sub 3/)/sup 2 +/.

  2. Loss of Catalytic Activity in the E134D, H67A, and H349A Mutants of DapE: Mechanistic Analysis with QM/MM Investigation.

    Science.gov (United States)

    Dutta, Debodyuti; Mishra, Sabyashachi

    2016-11-17

    In the fight against bacterial infections and antibiotic resistance, the dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase (DapE) is a potentially safe target enzyme. The role of the Glu134, His67, and His349 residues in the binding and hydrolysis of N-succinyl-l,l-diaminopimelic acid (SDAP) is investigated by employing molecular dynamics simulation and hybrid quantum mechanical-molecular mechanical (MM) calculations of the E134D, H67A, and H349A mutants of DapE. The free energy of substrate binding obtained from the MM-Poisson-Boltzmann surface area approach correctly reproduced the experimentally observed ordering of substrate affinity, that is, E134D > wt > H67A > H349A. The mechanism of catalytic action by the E134D mutant is elucidated by structurally and energetically characterizing the intermediates and the transition states along the reaction pathway. The rate-determining step in the general acid-base hydrolysis reaction by the E134D mutant is found to be the nucleophilic attack step, which involves an activation energy barrier 10 kcal/mol greater than that in the wild-type (wt)-DapE. This explains the 3 orders of magnitude decrease in the experimentally determined kcat value for the E134D mutant compared to that of wt-DapE. In the H67A and H349A mutants, the Glu134 residue undergoes a conformational change and exhibits a strong coordination with the metal centers. This not only results in a weaker substrate binding in the two histidine mutants but also hinders the activation of the catalytic water molecule, which constitutes the first step of the substrate hydrolysis by DapE. This leads to an effective quenching of the catalytic activity in the H67A and H349A mutants.

  3. Muscle activity during functional coordination training: implications for strength gain and rehabilitation

    DEFF Research Database (Denmark)

    Jørgensen, Marie Birk; Andersen, Lars Louis; Kirk, Niels

    2010-01-01

    The purpose of this study was to evaluate if different types, body positions, and levels of progression of functional coordination exercises can provide sufficiently high levels of muscle activity to improve strength of the neck, shoulder, and trunk muscles. Nine untrained women were familiarized...... training can be performed with a muscle activity sufficient for strength gain. Functional coordination training may therefore be a good choice for prevention or rehabilitation of musculoskeletal pain or injury in the neck, shoulder, or trunk muscles....

  4. Activated macrophage survival is coordinated by TAK1 binding proteins.

    Directory of Open Access Journals (Sweden)

    September R Mihaly

    Full Text Available Macrophages play diverse roles in tissue homeostasis and immunity, and canonically activated macrophages are critically associated with acute inflammatory responses. It is known that activated macrophages undergo cell death after transient activation in some settings, and the viability of macrophages impacts on inflammatory status. Here we report that TGFβ- activated kinase (TAK1 activators, TAK1-binding protein 1 (TAB1 and TAK1-binding protein 2 (TAB2, are critical molecules in the regulation of activated macrophage survival. While deletion of Tak1 induced cell death in bone marrow derived macrophages even without activation, Tab1 or Tab2 deletion alone did not profoundly affect survival of naïve macrophages. However, in lipopolysaccharide (LPS-activated macrophages, even single deletion of Tab1 or Tab2 resulted in macrophage death with both necrotic and apoptotic features. We show that TAB1 and TAB2 were redundantly involved in LPS-induced TAK1 activation in macrophages. These results demonstrate that TAK1 activity is the key to activated macrophage survival. Finally, in an in vivo setting, Tab1 deficiency impaired increase of peritoneal macrophages upon LPS challenge, suggesting that TAK1 complex regulation of macrophages may participate in in vivo macrophage homeostasis. Our results demonstrate that TAB1 and TAB2 are required for activated macrophages, making TAB1 and TAB2 effective targets to control inflammation by modulating macrophage survival.

  5. Mechanical bending induced catalytic activity enhancement of monolayer 1 T'-MoS2 for hydrogen evolution reaction

    Science.gov (United States)

    Shi, Wenwu; Wang, Zhiguo; Fu, Yong Qing

    2017-09-01

    In this paper, mechanisms behind enhancement of catalytic activity of MoS2 mono-layer (three atomic layers) for hydrogen evolution reaction (HER) by mechanically applying bending strain were investigated using density functional theory. Results showed that with the increase of bending strains, the Gibbs free energy for hydrogen adsorption on the MoS2 mono-layer was decreased from 0.18 to -0.04 eV and to 0.13 eV for the bend strains applied along the zigzag and armchair directions, respectively. The mechanism for the enhanced catalytic activity comes from the changes of density of electronic states near the Fermi energy level, which are induced by the changes of the Mo-S and Mo-Mo bonds upon bending. This report provides a new design methodology to improve the catalytic activity of catalysts based on two-dimensional transition metal dichalcogenides through a simple mechanical bending.

  6. Extending Thymidine Kinase Activity to the Catalytic Repertoire of Human Deoxycytidine Kinase

    Energy Technology Data Exchange (ETDEWEB)

    Hazra, Saugata; Sabini, Eliszbetta; Ort, Stephan; Konrad, Manfred; Lavie, Arnon; (UIC); (MXPL-G)

    2009-03-04

    Salvage of nucleosides in the cytosol of human cells is carried out by deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1). Whereas TK1 is only responsible for thymidine phosphorylation, dCK is capable of converting dC, dA, and dG into their monophosphate forms. Using structural data on dCK, we predicted that select mutations at the active site would, in addition to making the enzyme faster, expand the catalytic repertoire of dCK to include thymidine. Specifically, we hypothesized that steric repulsion between the methyl group of the thymine base and Arg104 is the main factor preventing the phosphorylation of thymidine by wild-type dCK. Here we present kinetic data on several dCK variants where Arg104 has been replaced by select residues, all performed in combination with the mutation of Asp133 to an alanine. We show that several hydrophobic residues at position 104 endow dCK with thymidine kinase activity. Depending on the exact nature of the mutations, the enzyme's substrate preference is modified. The R104M-D133A double mutant is a pyrimidine-specific enzyme due to large K{sub m} values with purines. The crystal structure of the double mutant R104M-D133A in complex with the L-form of thymidine supplies a structural explanation for the ability of this variant to phosphorylate thymidine and thymidine analogs. The replacement of Arg104 by a smaller residue allows L-dT to bind deeper into the active site, making space for the C5-methyl group of the thymine base. The unique catalytic properties of several of the mutants make them good candidates for suicide-gene/protein-therapy applications.

  7. Effect of the dispersants on Pd species and catalytic activity of supported palladium catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Yue [Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205 (China); Yang, Xiaojun, E-mail: 10100201@wit.edu.cn [Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205 (China); Cao, Shuo, E-mail: cao23@email.sc.edu [North America R& D Center, Clariant BU Catalysts, Louisville, 40209, KY (United States); Zhou, Jie [Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205 (China); Wu, Yuanxin [Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205 (China); School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Han, Jinyu [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Yan, Zhiguo [Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205 (China); Zheng, Mingming [Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, Hubei Key Laboratory of Oilcrops Lipid Chemistry and Nutrition, Wuhan 430062 (China)

    2017-04-01

    Highlights: • Polyvinyl alcohol (PVA) inhibited the sintering and reduction of Pd nanoparticles. • Activity was improved for supported Pd catalysts with PVA modified method. • PVA modified method minimized the catalyst deactivation. • This work provides an insight of the regeneration strategies for Pd catalysts. - Abstract: A series of supported palladium catalysts has been prepared through the precipitation method and the reduction method, using polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) as dispersants. The effects of the dispersants on the properties of catalysts were evaluated and the catalytic performance of the new materials was investigated for the oxidative carbonylation of phenol to diphenyl carbonate (DPC). The catalysts as prepared were also characterized by the X-ray diffraction (XRD), transmission electron microscope (TEM), Brunner-Emmet-Teller (BET) measurements and X-ray photoelectron spectroscopy (XPS) techniques. The results show that the addition of the dispersants had no effect on the crystal phase of the catalysts. However, the dispersion of Pd particles was improved when the dispersants were used. Moreover, the particle sizes of Pd nanoparticles modified by PVA were smaller than those modified by PVP. The catalysts prepared using the dispersants gave better yields of DPC than the catalysts prepared without the dispersants. The highest yield of DPC was 17.9% with the PVA-Red catalyst. The characterization results for the used catalysts showed that the Pd species in the PVA-Red catalyst remained mostly divalent and the lattice oxygen species were consumed during the reaction, which could lead to the higher catalytic activity of the PVA-Red catalyst. The experimental results confirm that PVA effectively inhibited the sintering and reduction of active Pd species in the oxidative carbonylation of phenol.

  8. Preparation of silver nanoparticles/polydopamine functionalized polyacrylonitrile fiber paper and its catalytic activity for the reduction 4-nitrophenol

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Shixiang, E-mail: shixianglu@bit.edu.cn [School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 – IEMN, Lille F-59000 (France); Yu, Jianying; Cheng, Yuanyuan [School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Wang, Qian; Barras, Alexandre [Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 – IEMN, Lille F-59000 (France); Xu, Wenguo [School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Szunerits, Sabine [Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 – IEMN, Lille F-59000 (France); Cornu, David [Institut Européen des Membranes, UMR 5635, Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), CNRS, Université Montpellier 2, 276 rue de la Galéra, Montpellier 34000 (France); Boukherroub, Rabah, E-mail: rabah.boukherroub@iemn.univ-lille1.fr [Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 – IEMN, Lille F-59000 (France)

    2017-07-31

    Graphical abstract: Illustration of the preparation of Ag nanoparticles coated paper and its catalytic application for 4-nitrophenol reduction into the corresponding 4-aminophenol. - Highlights: • Polyacrylonitrile paper was functionalized with polydopamine and Ag nanoparticles. • Polydopamine coating layer played both reductive and adhesive roles. • The composite material displayed good catalytic activity for 4-nitrophenol reduction. • The process was environmentally benign and facile. - Abstract: The study reports on the preparation of polyacrylonitrile fiber paper (PANFP) functionalized with polydopamine (PD) and silver nanoparticles (Ag NPs), named as Ag NPs/PD/PANFP. The composite material was obtained via a simple two-step chemical process. First, a thin polydopamine layer was coated onto the PANFP surface through immersion into an alkaline dopamine (pH 8.5) aqueous solution at room temperature. The reductive properties of polydopamine were further exploited for the deposition of Ag NPs. The morphology and chemical composition of the composite material were characterized using scanning electron microscopy (SEM), X-ray diffraction pattern (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of the nanocomposite was evaluated for the reduction of 4-nitrophenol using sodium borohydride (NaBH{sub 4}) at room temperature. The Ag NPs/PD/PANFP displayed good catalytic performance with a full reduction of 4-nitrophenol into the corresponding 4-aminophenol within 30 min. Moreover, the composite material exhibited a good stability up to 4 cycles without a significant loss of its catalytic activity.

  9. Investigating the effects of alkali metal Na addition on catalytic activity of HZSM-5 for methyl mercaptan elimination

    Science.gov (United States)

    Yu, Jie; He, Dedong; Chen, Dingkai; Liu, Jiangping; Lu, Jichang; Liu, Feng; Liu, Pan; Zhao, Yutong; Xu, Zhizhi; Luo, Yongming

    2017-10-01

    Na-modified HZSM-5 catalysts with different Na loading amounts were prepared by incipient-wetness impregnation method and their catalytic activities for methyl mercaptan catalytic elimination were analyzed. XRD, N2 adsorption-desorption, NH3-TPD, CO2-TPD and FT-IR measurements were carried out to investigate the effects of modification of alkali metal Na on the physicochemical properties of the HZSM-5 zeolite catalyst. Research results illustrated that the introduction of alkali metal Na can improve catalytic activity for CH3SH catalytic elimination. CH3SH can be almost completely converted over 3%-Na/HZSM-5 at 450 °C compared to pure HZSM-5 at 600 °C based on our experimental results and the results from previous research. The improved catalytic activity could be attributed to the regulated acid-base properties of the HZSM-5 catalysts by doping with alkali metal Na. High alkali concentration treatment, however, may destroy the framework structure of the catalyst sample, thus causing the poor stability performance of the obtained catalyst.

  10. Effect of nitrogen-containing impurities on the activity of perovskitic catalysts for the catalytic combustion of methane.

    Science.gov (United States)

    Buchneva, Olga; Gallo, Alessandro; Rossetti, Ilenia

    2012-11-05

    LaMnO(3), either pure or doped with 10 mol % Sr, has been prepared by flame pyrolysis in nanostructured form. Such catalysts have been tested for the catalytic flameless combustion of methane, achieving very high catalytic activity. The resistance toward poisoning by some model N-containing impurities has been checked in order to assess the possibility of operating the flameless catalytic combustion with biogas, possibly contaminated by S- or N-based compounds. This would be a significant improvement from the environmental point of view because the application of catalytic combustion to gas turbines would couple improved energy conversion efficiency and negligible noxious emissions, while the use of biogas would open the way to energy production from a renewable source by means of very efficient technologies. A different behavior has been observed for the two catalysts; namely, the undoped sample was more or less heavily poisoned, whereas the Sr-doped sample showed slightly increasing activity upon dosage of N-containing compounds. A possible reaction mechanism has been suggested, based on the initial oxidation of the organic backbone, with the formation of NO. The latter may adsorb more or less strongly depending on the availability of surface oxygen vacancies (i.e., depending on doping). Decomposition of NO may leave additional activated oxygen species on the surface, available for low-temperature methane oxidation and so improving the catalytic performance.

  11. Coordinated sensing and active repair for self-healing

    Science.gov (United States)

    Hurley, D. A.; Huston, D. R.

    2011-02-01

    Self-repairing structural systems have the potential for improved performance ranges and lifetimes over conventional systems. Self-healing materials are not a new phenomenon and have been used in automotive and aeronautical applications for over a century. The bulk of these systems operate by using damage to directly initiate a repair response without any supervisory coordination. Integrating sensing and supervisory control technologies with self-healing may improve the safety and reliability of critical components and structures. This project illustrates the benefit of an integrated sensing, control, and self-healing system using laboratory scale test beds. A thermoplastic polymer embedded with resistive heating wires acts as the self-healing material. Damage is detected using an electro-optical sensing scheme based on photoresistors and a PC handling control duties. As damage occurs it is detected, located, and characterized. The key to this project is the integration of sensor feedback to control healing so that repairs are executed, monitored, and completed on the basis of continuous sensor data. This proof-of-concept prototype can likely be expanded and improved with alternative sensor options, self-healing materials, and system architecture.

  12. Study of nitric oxide catalytic oxidation on manganese oxides-loaded activated carbon at low temperature

    Science.gov (United States)

    You, Fu-Tian; Yu, Guang-Wei; Wang, Yin; Xing, Zhen-Jiao; Liu, Xue-Jiao; Li, Jie

    2017-08-01

    Nitric oxide (NO) is an air pollutant that is difficult to remove at low concentration and low temperature. Manganese oxides (MnOx)-loaded activated carbon (MLAC) was prepared by a co-precipitation method and studied as a new catalyst for NO oxidation at low temperature. Characterization of MLAC included X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption/desorption and X-ray photoelectron spectroscopy (XPS). Activity tests demonstrated the influence of the amount of MnOx and the test conditions on the reaction. MLAC with 7.5 wt.% MnOx (MLAC003) exhibits the highest NO conversion (38.7%) at 1000 ppm NO, 20 vol.% O2, room temperature and GHSV ca. 16000 h-1. The NO conversion of MLAC003 was elevated by 26% compared with that of activated carbon. The results of the MLAC003 activity test under different test conditions demonstrated that NO conversion is also influenced by inlet NO concentration, inlet O2 concentration, reaction temperature and GHSV. The NO adsorption-desorption process in micropores of activated carbon is fundamental to NO oxidation, which can be controlled by pore structure and reaction temperature. The activity elevation caused by MnOx loading is assumed to be related to Mn4+/Mn3+ ratio. Finally, a mechanism of NO catalytic oxidation on MLAC based on NO adsorption-desorption and MnOx lattice O transfer is proposed.

  13. Nanocasted synthesis of the mesostructured LaCoO3 perovskite and its catalytic activity in methane combustion.

    Science.gov (United States)

    Wang, Yangang; Wang, Yanqin; Liu, Xiaohui; Guo, Yun; Guo, Yanglong; Lu, Guanzhong

    2009-02-01

    Extremely high surface area, mesostructured LaCoO3 perovskite has been synthesized by nanocasting from mesoporous cubic (Ia3d) vinyl silica. Thus-prepared material was characterized by XRD, TEM, and N2-sorption, and its catalytic property was also tested in methane combustion. The catalytic results demonstrated that thus-prepared mesostructured LaCoO3 perovskite had higher activity than the conventional bulk LaCoO3 perovskite prepared by citrate method. Further analysis showed that both the high surface area and the existence of high valent cobalt ions (Co4+, XPS analysis) were contributed to the high activity.

  14. Thiol peroxidase-like activity of some intramolecularly coordinated ...

    Indian Academy of Sciences (India)

    Diselenides (13) and (14) with dimethylaminomethyl- or nitro-donor groups in close proximity to selenium, show much better thiol peroxidase-like activities compared to diselenides 10-12 with amide donor groups. Cyclic voltammetry study of diselenides 10-12 derived from redox-active ferrocenamide has been carried out.

  15. Beyond Therapy Dogs: Coordinating Large-Scale Finals Week Activities

    Science.gov (United States)

    Flynn, Holly

    2017-01-01

    Finals week activities have become increasingly popular in academic libraries in the last few years, but what is a library to do when it is not allowed to have therapy dogs? This column examines a progression of increasingly popular activities at Michigan State University Libraries. Included is an assessment of what makes them popular, our…

  16. Catalytic Activity and Photophysical Properties of Biomolecules Immobilized on Mesoporous Silica

    DEFF Research Database (Denmark)

    Ikemoto, Hideki

    hybrid materials used for further study. One metalloenzyme, horseradish peroxidase(HRP), was immobilized on rod-shaped SBA-15 by physical adsorption. The catalytic activity of free and immobilized enzyme was first compared at room temperature. Details of the enzyme kinetics including the apparent...... 2 (LH2) from purple photosynthetic bacteria was immobilized on SBA-15 with hexagonally ordered cylindrical pores or on MCF-type mesoporous silica with disordered cage-like mesopores. To identify the location of LH2, spherical particles with small or large pores were tested for the adsorption of LH2....... LH2 was adsorbed to the particles with large pores, while little LH2 was adsorbed to the particles with small pores. Subsequent observation with fluorescence microscopy confirmed that LH2 is adsorbed in the pores of mesoporous silica. The conjugates of LH2 and mesoporous silica were studiedby steady...

  17. Nickel(II) complexes containing thiosemicarbazone and triphenylphosphine: Synthesis, spectroscopy, crystallography and catalytic activity

    Science.gov (United States)

    Priyarega, S.; Kalaivani, P.; Prabhakaran, R.; Hashimoto, T.; Endo, A.; Natarajan, K.

    2011-09-01

    Four new Ni(II) complexes of the general formula [Ni(PPh 3)(L)] (L = dibasic tridentate ligand derived from 4-diethylamino-salicylaldehyde and thiosemicarbazide or 4-N-substituted thiosemicarbazide) have been reported. The new complexes have been synthesized and characterized by analytical and spectroscopic (IR, electronic, 1H NMR and 31P NMR) techniques. Molecular structure of one of the complexes has been determined by X-ray crystallography. The complex, [Ni(PPh 3)(L4)] (H 2L4 = thiosemicarbazone prepared from 4-diethylamino-salicylaldehyde and 4-phenylthiosemicarbazide) crystallized in monoclinic space group with two molecules per unit cell and has the dimensions of a = 13.232(6) Å, b = 10.181(5) Å, c = 13.574(7) Å, α = 90°, β = 98.483(2)° and γ = 90°. Catalytic activity of the complexes has been explored for aryl-aryl coupling reaction.

  18. Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation.

    Science.gov (United States)

    Birkner, Nancy; Nayeri, Sara; Pashaei, Babak; Najafpour, Mohammad Mahdi; Casey, William H; Navrotsky, Alexandra

    2013-05-28

    Previous measurements show that calcium manganese oxide nanoparticles are better water oxidation catalysts than binary manganese oxides (Mn3O4, Mn2O3, and MnO2). The probable reasons for such enhancement involve a combination of factors: The calcium manganese oxide materials have a layered structure with considerable thermodynamic stability and a high surface area, their low surface energy suggests relatively loose binding of H2O on the internal and external surfaces, and they possess mixed-valent manganese with internal oxidation enthalpy independent of the Mn(3+)/Mn(4+) ratio and much smaller in magnitude than the Mn2O3-MnO2 couple. These factors enhance catalytic ability by providing easy access for solutes and water to active sites and facile electron transfer between manganese in different oxidation states.

  19. Phoenix dactylifera L. leaf extract phytosynthesized gold nanoparticles; controlled synthesis and catalytic activity.

    Science.gov (United States)

    Zayed, Mervat F; Eisa, Wael H

    2014-01-01

    A green synthesis route was reported to explore the reducing and capping potential of Phoenix dactylifera extract for the synthesis of gold nanoparticles. The processes of nucleation and growth of gold nanoparticles were followed by monitoring the absorption spectra during the reaction. The size and morphology of these nanoparticles was typically imaged using transmission electron microscopy (TEM). The particle size ranged between 32 and 45 nm and are spherical in shape. Fourier transform infrared (FTIR) analysis suggests that the synthesized gold nanoparticles might be stabilized through the interactions of hydroxyl and carbonyl groups in the carbohydrates, flavonoids, tannins and phenolic acids present in P. dactylifera. The as-synthesized Au colloids exhibited good catalytic activity for the degradation of 4-nitrophenol. Copyright © 2013 Elsevier B.V. All rights reserved.

  20. Stereoselective Catalytic Synthesis of Active Pharmaceutical Ingredients in Homemade 3D-Printed Mesoreactors.

    Science.gov (United States)

    Rossi, Sergio; Porta, Riccardo; Brenna, Davide; Puglisi, Alessandra; Benaglia, Maurizio

    2017-04-03

    3D-printed flow reactors were designed, fabricated from different materials (PLA, HIPS, nylon), and used for a catalytic stereoselective Henry reaction. The use of readily prepared and tunable 3D-printed reactors enabled the rapid screening of devices with different sizes, shapes, and channel dimensions, aimed at the identification of the best-performing reactor setup. The optimized process afforded the products in high yields, moderate diastereoselectivity, and up to 90 % ee. The method was applied to the continuous-flow synthesis of biologically active chiral 1,2-amino alcohols (norephedrine, metaraminol, and methoxamine) through a two-step sequence combining the nitroaldol reaction with a hydrogenation. To highlight potential industrial applications of this method, a multistep continuous synthesis of norephedrine has been realized. The product was isolated without any intermediate purifications or solvent switches. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation

    Science.gov (United States)

    Birkner, Nancy; Nayeri, Sara; Pashaei, Babak; Najafpour, Mohammad Mahdi; Casey, William H.; Navrotsky, Alexandra

    2013-01-01

    Previous measurements show that calcium manganese oxide nanoparticles are better water oxidation catalysts than binary manganese oxides (Mn3O4, Mn2O3, and MnO2). The probable reasons for such enhancement involve a combination of factors: The calcium manganese oxide materials have a layered structure with considerable thermodynamic stability and a high surface area, their low surface energy suggests relatively loose binding of H2O on the internal and external surfaces, and they possess mixed-valent manganese with internal oxidation enthalpy independent of the Mn3+/Mn4+ ratio and much smaller in magnitude than the Mn2O3-MnO2 couple. These factors enhance catalytic ability by providing easy access for solutes and water to active sites and facile electron transfer between manganese in different oxidation states. PMID:23667149

  2. Catalytic Activity of Sulfated and Phosphated Catalysts towards the Synthesis of Substituted Coumarin

    Directory of Open Access Journals (Sweden)

    Nagi R. E. Radwan

    2018-01-01

    Full Text Available New modified acidic catalysts were prepared from the treatment of silica, titania and silica prepared from hydrolyzed tetraethyl orthosilicate (TEOS with sulfuric and phosphoric acid. The sulfated and phosphated silica synthesized from TEOS were calcined at 450 and 650 °C. These catalysts were characterized by X-ray diffraction (XRD, Fourier-transform infrared spectroscopy (FTIR, transmission electron microscope (TEM, and scanning electron microscope (SEM. The surface areas, total pore volume, and mean pore radius of the acidic catalysts were investigated, while the pore size distribution was determined by the Barrett, Joyner and Halenda (BJH method. The catalytic activity of the sulfated and phosphated silica and/or titania were examined with the Pechmann condensation reaction, in which different phenols reacted with ethyl acetoacetate as a neat reaction to obtain the corresponding coumarin derivatives. The results indicated that the treatment of the catalysts with sulfuric or phosphoric acid led to a decrease in the phases’ crystallinity to a certain degree. The morphology and the structure of the acidified catalysts were examined and their particle size was calculated. Furthermore, the amount of the used catalysts played a vital role in controlling the formation of the products as well as their performance was manipulated by the number and nature of the active acidic sites on their surfaces. The obtained results suggested that the highest catalytic conversion of the reaction was attained at 20 wt % of the catalyst and no further increase in the product yield was detected when the amount of catalyst exceeded this value. Meanwhile the phenol molecules were a key feature in obtaining the final product.

  3. Mechanistic insight into the hydrazine decomposition on Rh(111): effect of reaction intermediate on catalytic activity.

    Science.gov (United States)

    Deng, Zhigang; Lu, Xiaoqing; Wen, Zengqiang; Wei, Shuxian; Liu, Yunjie; Fu, Dianling; Zhao, Lianming; Guo, Wenyue

    2013-10-14

    Periodic density functional theory (DFT) calculations have been performed to systematically investigate the effect of reaction intermediate on catalytic activity for hydrazine (N2H4) decomposition on Rh(111). Reaction mechanisms via intramolecular and NH2-assisted N2H4 decompositions are comparatively analyzed, including adsorption configuration, reaction energy and barrier of elementary step, and reaction network. Our results show that the most favorable N2H4 decomposition pathway starts with the initial N-N bond scission to the NH2 intermediate, followed by stepwise H stripping from adsorbed N2Hx (x = 1-4) species, and finally forms the N2 and NH3 products. Comparatively, the stepwise intramolecular dehydrogenation via N2H4→ N2H3→ N2H2→ N2H → N2, and N2H4→ NH2→ NH → N with or without NH2 promotion effect, are unfavorable due to higher energy barriers encountered. Energy barrier analysis, reaction rate constants, and electronic structures are used to identify the crucial competitive route. The promotion effect of the NH2 intermediate is structurally reflected in the weakening of the N-H bond and strengthening of the N-N bond in N2Hx in the coadsorption system; it results intrinsically from the less structural deformation of the adsorbate, and weakening of the interaction between dehydrogenated fragment and departing H in transition state. Our results highlight the crucial effect of reaction intermediate on catalytic activity and provide a theoretical approach to analyze the effect.

  4. Synthesis, characterization and catalytic activity of carbon-silica hybrid catalyst from rice straw

    Science.gov (United States)

    Janaun, J.; Safie, N. N.; Siambun, N. J.

    2016-07-01

    The hybrid-carbon catalyst has been studied because of its promising potential to have high porosity and surface area to be used in biodiesel production. Silica has been used as the support to produce hybrid carbon catalyst due to its mesoporous structure and high surface area properties. The chemical synthesis of silica-carbon hybrid is expensive and involves more complicated preparation steps. The presence of natural silica in rice plants especially rice husk has received much attention in research because of the potential as a source for solid acid catalyst synthesis. But study on rice straw, which is available abundantly as agricultural waste is limited. In this study, rice straw undergone pyrolysis and functionalized using fuming sulphuric acid to anchor -SO3H groups. The presence of silica and the physiochemical properties of the catalyst produced were studied before and after sulphonation. The catalytic activity of hybrid carbon silica acid catalyst, (H-CSAC) in esterification of oleic acid with methanol was also studied. The results showed the presence of silica-carbon which had amorphous structure and highly porous. The carbon surface consisted of higher silica composition, had lower S element detected as compared to the surface that had high carbon content but lower silica composition. This was likely due to the fact that Si element which was bonded to oxygen was highly stable and unlikely to break the bond and react with -SO3H ions. H-CSAC conversions were 23.04 %, 35.52 % and 34.2 7% at 333.15 K, 343.15 K and 353.15 K, respectively. From this research, rice straw can be used as carbon precursor to produce hybrid carbon-silica catalyst and has shown catalytic activity in biodiesel production. Rate equation obtained is also presented.

  5. Residue Phe112 of the Human-Type Corrinoid Adenosyltransferase (PduO) Enzyme of Lactobacillus reuteri Is Critical to the Formation of the Four-Coordinate Co(II) Corrinoid Substrate and to the Activity of the Enzyme

    Energy Technology Data Exchange (ETDEWEB)

    Mera, Paola E.; St. Maurice, Martin; Rayment, Ivan; Escalante-Semerena, Jorge C.; UW

    2009-06-08

    ATP:Corrinoid adenosyltransferases (ACAs) catalyze the transfer of the adenosyl moiety from ATP to cob(I)alamin via a four-coordinate cob(II)alamin intermediate. At present, it is unknown how ACAs promote the formation of the four-coordinate corrinoid species needed for activity. The published high-resolution crystal structure of the ACA from Lactobacillus reuteri (LrPduO) in complex with ATP and cob(II)alamin shows that the environment around the alpha face of the corrin ring consists of bulky hydrophobic residues. To understand how these residues promote the generation of the four-coordinate cob(II)alamin, variants of the human-type ACA enzyme from L. reuteri (LrPduO) were kinetically and structurally characterized. These studies revealed that residue Phe112 is critical in the displacement of 5,6-dimethylbenzimidazole (DMB) from its coordination bond with the Co ion of the ring, resulting in the formation of the four-coordinate species. An F112A substitution resulted in a 80% drop in the catalytic efficiency of the enzyme. The explanation for this loss of activity was obtained from the crystal structure of the mutant protein, which showed cob(II)alamin bound in the active site with DMB coordinated to the cobalt ion. The crystal structure of an LrPduO(F112H) variant showed a DMB-off/His-on interaction between the corrinoid and the enzyme, whose catalytic efficiency was 4 orders of magnitude lower than that of the wild-type protein. The analysis of the kinetic parameters of LrPduO(F112H) suggests that the F112H substitution negatively impacts product release. Substitutions of other hydrophobic residues in the Cbl binding pocket did not result in significant defects in catalytic efficiency in vitro; however, none of the variant enzymes analyzed in this work supported AdoCbl biosynthesis in vivo.

  6. Flexible coordination of stationary and mobile conversations with gaze: Resource allocation among multiple joint activities

    Directory of Open Access Journals (Sweden)

    Eric Mayor

    2016-10-01

    Full Text Available Gaze is instrumental in coordinating face-to-face social interactions. But little is known about gaze use when social interactions co-occur with other joint activities. We investigated the case of walking while talking. We assessed how gaze gets allocated among various targets in mobile conversations, whether allocation of gaze to other targets affects conversational coordination, and whether reduced availability of gaze for conversational coordination affects conversational performance and content. In an experimental study, pairs were videotaped in four conditions of mobility (standing still, talking while walking along a straight-line itinerary, talking while walking along a complex itinerary, or walking along a complex itinerary with no conversational task. Gaze to partners was substantially reduced in mobile conversations, but gaze was still used to coordinate conversation via displays of mutual orientation, and conversational performance and content was not different between stationary and mobile conditions. Results expand the phenomena of multitasking to joint activities.

  7. Active DC Bus Signaling Control Method for Coordinating Multiple Energy Storage Devices in DC Microgrid

    OpenAIRE

    Li, Fulong; Lin, Zhengyu; Qian, Zhongnan; Wu, Jiande

    2017-01-01

    This paper will be presented in 2017 Second IEEE International Conference on DC Microgrids (ICDCM) on 28th June 2017. Abstract: Management of multiple energy storage devices in a DC microgrid is a challenge. Conventional method, such as droop control, cannot ensure accurate current sharing in coordinating multiple battery banks, which limits the DC microgrid system performance. This paper proposed an active DC bus signaling (ADBS) method to coordinate multiple battery banks in a DC microg...

  8. COMPARISON OF CATALYTIC ACTIVITIES BOTH FOR SELECTIVE OXIDATION AND DECOMPOSITION OF AMMONIA OVER Fe/HZβ CATALYST

    Directory of Open Access Journals (Sweden)

    YELİZ ÇETİN

    2016-11-01

    Full Text Available Ammonia is one of the syngas contaminants that must be removed before using the syngas downstream applications. The most promising hot-gas clean-up techniques of ammonia are selective catalytic oxidation (SCO and catalytic decomposition. In this study, the catalytic activities over Zeolite Hβ supported iron catalyst (Fe/HZβ were compared both for the two catalytic routes. For SCO experiments; temperature (300-550 °C, O2 (2000-6000 ppmv and (0-10% H2 concentrations were investigated with the presence of 800 ppm NH3 in each of the final gas mixture. In the second route, catalytic ammonia decomposition experiments were carried out with H2 in balance N2 (0-30% containing 800 ppm NH3 at 700°C and 800°C. In the SCO, NH3 conversions were increased with increasing reaction temperatures with the absence of H2 in the reaction mixture. With 10% H2, it was shown that NH3 conversions increased with decreasing the reaction temperature. This was interpreted as the competing H2 and NH3 oxidations over the catalyst. On the other hand, in the catalytic decomposition, thermodynamic equilibrium conversion of almost 100% was attained at both 700 and 800 °C. Upon H2 addition, all conversions decreased. The decrease in conversion seemed to be linear with inlet hydrogen concentration. Hydrogen was seen to inhibit ammonia decomposition reaction. It was shown that Fe/HZβ catalyst is better to use for catalytic decomposition of NH3 in syngas rather than SCO of NH3 in spite of higher reaction temperatures needed in the decomposition reaction.

  9. Catalytic activity of various pepsin reduced Au nanostructures towards reduction of nitroarenes and resazurin

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Bhagwati; Mandani, Sonam; Sarma, Tridib K., E-mail: tridib@iiti.ac.in [Indian Institute of Technology Indore, Discipline of Chemistry, School of Basic Sciences (India)

    2015-01-15

    Pepsin, a digestive protease enzyme, could function as a reducing as well as stabilizing agent for the synthesis of Au nanostructures of various size and shape under different reaction conditions. The simple tuning of the pH of the reaction medium led to the formation of spherical Au nanoparticles, anisotropic Au nanostructures such as triangles, hexagons, etc., as well as ultra small fluorescent Au nanoclusters. The activity of the enzyme was significantly inhibited after its participation in the formation of Au nanoparticles due to conformational changes in the native structure of the enzyme which was studied by fluorescence, circular dichroism (CD), and infra red spectroscopy. However, the Au nanoparticle-enzyme composites served as excellent catalyst for the reduction of p-nitrophenol and resazurin, with the catalytic activity varying with size and shape of the nanoparticles. The presence of pepsin as the surface stabilizer played a crucial role in the activity of the Au nanoparticles as reduction catalysts, as the approach of the reacting molecules to the nanoparticle surface was actively controlled by the stabilizing enzyme.

  10. Catalytic activity of various pepsin reduced Au nanostructures towards reduction of nitroarenes and resazurin

    Science.gov (United States)

    Sharma, Bhagwati; Mandani, Sonam; Sarma, Tridib K.

    2015-01-01

    Pepsin, a digestive protease enzyme, could function as a reducing as well as stabilizing agent for the synthesis of Au nanostructures of various size and shape under different reaction conditions. The simple tuning of the pH of the reaction medium led to the formation of spherical Au nanoparticles, anisotropic Au nanostructures such as triangles, hexagons, etc., as well as ultra small fluorescent Au nanoclusters. The activity of the enzyme was significantly inhibited after its participation in the formation of Au nanoparticles due to conformational changes in the native structure of the enzyme which was studied by fluorescence, circular dichroism (CD), and infra red spectroscopy. However, the Au nanoparticle-enzyme composites served as excellent catalyst for the reduction of p-nitrophenol and resazurin, with the catalytic activity varying with size and shape of the nanoparticles. The presence of pepsin as the surface stabilizer played a crucial role in the activity of the Au nanoparticles as reduction catalysts, as the approach of the reacting molecules to the nanoparticle surface was actively controlled by the stabilizing enzyme.

  11. An artificial heme-enzyme with enhanced catalytic activity: evolution, functional screening and structural characterization.

    Science.gov (United States)

    Vitale, Rosa; Lista, Liliana; Cerrone, Corinne; Caserta, Giorgio; Chino, Marco; Maglio, Ornella; Nastri, Flavia; Pavone, Vincenzo; Lombardi, Angela

    2015-05-07

    Synthetic proteins represent useful tools for reproducing metalloprotein functions in minimal, well-defined scaffolds. Herein, we describe the rational refinement of function into heme-protein models from the Mimochrome family. Originally designed to mimic the bis-His cytochrome b, the Mimochrome structure was modified to introduce a peroxidase-like activity, by creating a distal cavity on the heme. The success with the first asymmetric system, Mimochrome VI (MC6), gave the opportunity to explore further modifications in order to improve the catalytic activity. Starting from ferric MC6, single amino acid substitutions were introduced in the peptide chains to obtain four compounds, which were screened for peroxidase activity. The detailed structural and functional analysis of the best analogue, Fe(III)-E(2)L(TD)-MC6, indicates that an arginine residue in proximity to the heme-distal site could assist with catalysis by favoring the formation of the intermediate "compound I", thus mimicking R(38) in HRP. This result highlights the potential of using small scaffolds for exploring the main factors that tune the heme-protein activity, and for programming new desired functions.

  12. Cytochrome c oxidase loses catalytic activity and structural integrity during the aging process in Drosophila melanogaster

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Jian-Ching; Rebrin, Igor [Department of Pharmacology and Pharmaceutical Sciences, University of Southern California, Los Angeles, CA 90033 (United States); Klichko, Vladimir; Orr, William C. [Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275 (United States); Sohal, Rajindar S., E-mail: sohal@usc.edu [Department of Pharmacology and Pharmaceutical Sciences, University of Southern California, Los Angeles, CA 90033 (United States)

    2010-10-08

    Research highlights: {yields} Cytochrome c oxidase loses catalytic activity during the aging process. {yields} Abundance of seven nuclear-encoded subunits of cytochrome c oxidase decreased with age in Drosophila. {yields} Cytochrome c oxidase is specific intra-mitochondrial site of age-related deterioration. -- Abstract: The hypothesis, that structural deterioration of cytochrome c oxidase (CcO) is a causal factor in the age-related decline in mitochondrial respiratory activity and an increase in H{sub 2}O{sub 2} generation, was tested in Drosophila melanogaster. CcO activity and the levels of seven different nuclear DNA-encoded CcO subunits were determined at three different stages of adult life, namely, young-, middle-, and old-age. CcO activity declined progressively with age by 33%. Western blot analysis, using antibodies specific to Drosophila CcO subunits IV, Va, Vb, VIb, VIc, VIIc, and VIII, indicated that the abundance these polypeptides decreased, ranging from 11% to 40%, during aging. These and previous results suggest that CcO is a specific intra-mitochondrial site of age-related deterioration, which may have a broad impact on mitochondrial physiology.

  13. Enhanced catalytic activity and inhibited biofouling of cathode in microbial fuel cells through controlling hydrophilic property

    Science.gov (United States)

    Li, Da; Liu, Jia; Wang, Haiman; Qu, Youpeng; Zhang, Jie; Feng, Yujie

    2016-11-01

    The hydrophilicity of activated carbon cathode directly determines the distribution of three-phase interfaces where oxygen reduction occurs. In this study, activated carbon cathodes are fabricated by using hydrophobic polytetrafluoroethylene (PTFE) and amphiphilic LA132 at various weight ratio to investigate the effect of hydrophilic property on cathode performance. Contact angle tests confirm the positive impact of LA132 content on hydrophilicity. Cathode with 67 wt% LA132 content shows the highest electrochemical activity as exchange current density increases by 71% and charge transfer resistance declines by 44.6% compared to that of PTFE cathode, probably due to the extended reaction interfaces by optimal hydrophilicity of cathode so that oxygen reduction is facilitated. As a result, the highest power density of 1171 ± 71 mW m-2 is obtained which is 14% higher than PTFE cathode. In addition to the hydrophilicity, this cathode had more negative charged surface of catalyst layer, therefore the protein content of cathodic biofilm decreased by 47.5%, indicating the effective bacterial inhibition when 67 wt% LA132 is used. This study shows that the catalytic activity of cathode is improved by controlling proper hydrophilicity of cathode, and that biofilm can be reduced by increasing hydrophilicity and lowering the surface potential.

  14. Beyond the active site: the impact of the outer coordination sphere on electrocatalysts for hydrogen production and oxidation.

    Science.gov (United States)

    Ginovska-Pangovska, Bojana; Dutta, Arnab; Reback, Matthew L; Linehan, John C; Shaw, Wendy J

    2014-08-19

    outer coordination sphere enhances proton movement and results in lower catalytic overpotentials for H2 oxidation, while achieving water solubility in some cases. Amino acids with acidic and basic side chains concentrate substrate around catalysts for H2 production, resulting in up to 5-fold enhancements in rate. The addition of a structured peptide in an H2 production catalyst limited the structural freedom of the amino acids nearest the active site, while enhancing the overall rate. Enhanced stability to oxygen or extreme conditions such as strongly acidic or basic conditions has also resulted from an amino acid based outer coordination sphere. From the "top-down" approach, others have achieved water solubility and photocatalytic activity by associating this core complex with photosystem-I. Collectively, by use of this well understood core, the role of individual and combined features of the outer coordination sphere are starting to be understood at a mechanistic level. Common mechanisms have yet to be defined to predictably control these processes, but our growing knowledge in this area is essential for the eventual mimicry of enzymes by efficient molecular catalysts for practical use.

  15. Study of nitric oxide catalytic oxidation on manganese oxides-loaded activated carbon at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    You, Fu-Tian [Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen (China); University of Chinese Academy of Sciences, Beijing (China); Yu, Guang-Wei, E-mail: gwyu@iue.ac.cn [Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen (China); Wang, Yin, E-mail: yinwang@iue.ac.cn [Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen (China); Xing, Zhen-Jiao [Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen (China); Liu, Xue-Jiao; Li, Jie [Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen (China); University of Chinese Academy of Sciences, Beijing (China)

    2017-08-15

    Highlights: • Loading manganese oxides on activated carbon effectively promotes NO oxidation. • NO adsorption-desorption on activated carbon is fundamental to NO oxidation. • A high Mn{sup 4+}/Mn{sup 3+} ratio contributes to NO oxidation by promoting lattice O transfer. - Abstract: Nitric oxide (NO) is an air pollutant that is difficult to remove at low concentration and low temperature. Manganese oxides (MnO{sub x})-loaded activated carbon (MLAC) was prepared by a co-precipitation method and studied as a new catalyst for NO oxidation at low temperature. Characterization of MLAC included X-ray diffraction (XRD), scanning electron microscopy (SEM), N{sub 2} adsorption/desorption and X-ray photoelectron spectroscopy (XPS). Activity tests demonstrated the influence of the amount of MnO{sub x} and the test conditions on the reaction. MLAC with 7.5 wt.% MnO{sub x} (MLAC003) exhibits the highest NO conversion (38.7%) at 1000 ppm NO, 20 vol.% O{sub 2}, room temperature and GHSV ca. 16000 h{sup −1}. The NO conversion of MLAC003 was elevated by 26% compared with that of activated carbon. The results of the MLAC003 activity test under different test conditions demonstrated that NO conversion is also influenced by inlet NO concentration, inlet O{sub 2} concentration, reaction temperature and GHSV. The NO adsorption-desorption process in micropores of activated carbon is fundamental to NO oxidation, which can be controlled by pore structure and reaction temperature. The activity elevation caused by MnO{sub x} loading is assumed to be related to Mn{sup 4+}/Mn{sup 3+} ratio. Finally, a mechanism of NO catalytic oxidation on MLAC based on NO adsorption-desorption and MnO{sub x} lattice O transfer is proposed.

  16. Evaluation of Performance Catalytic Ozonation Process with Activated Carbon in the Removal of Humic Acids from Aqueous Solutions

    Directory of Open Access Journals (Sweden)

    Gh. Asgari

    2011-01-01

    Full Text Available Introduction & Objective: In recent years, the use of alternative disinfectants and the control of natural organic matters are two approaches that are typically applied in water treatment utilities to reduce the formation of chlorinated disinfection by-products. Catalytic ozonation is a new technology used to promote the efficiency of ozonation. The goal of this study was to survey the feasibility application of activated carbon as a catalyst in ozonation process for removal of humic acids from aqueous solution. Materials & Methods: This experimental study has been done in laboratory of water and wastewater chemistry, Tarbiat Modarres University. The solid structure and chemical composition of activated carbon were analyzed by X-ray fluorescence (XRF. Ozonation and catalytic ozonation experiments were performed in a semi-batch reactor and the mass of ozone produced was measured by iodometric titration methods. Concentration changes of humic acid in samples with a concentration of 15 mg/l were determined by using spectrophotometer at an absorbance wavelength of 254 nm. To evaluate the performance of catalytic ozonation in humic acid removal, total organic carbon and trihalomethane formation potential were evaluated and the results were analyzed by Excel software. Results: Catalytic ozone results showed that using activated carbon as a catalyst increased humic acid decomposition up to 11 times and removal efficiency increased with increasing pH (4-12 and catalyst dosage (0.25-1.5 g/250cc. The experimental results showed that catalytic ozonation was most effective in less time (10 min with considerable efficiency (95% compared to the sole ozonation process (SOP. Conclusion: The results indicated that the catalytic ozonation process, compared to SOP, was less affected by radical scavenger, and total organic carbon, and trihalomethane formation potential removal achieved were 30% and 83%, respectively. (Sci J Hamadan Univ Med Sci 2011;17(4:25-33

  17. Synthesis, characterization and catalytic activity of highly ordered hexagonal and cubic composite monoliths.

    Science.gov (United States)

    El-Safty, Sherif A

    2008-03-15

    Design of nanocatalysts for efficient heterogeneous catalytic systems is needed to high ingredients for environmental cleanup of organic pollutant species. Here, well-defined order NiO-silica monolithic catalysts with hexagonal P6mm and cubic Pm3n mesostructures were successfully fabricated by using an instant direct-templating method of lyotropic and microemulsion phases of Brij 76 (C18H37(OCH2CH2)10 OH, C18EO 10). Ordered hexagonal P6mm NiO/HOM-2 monoliths could be fabricated in lyotropic system of Brij 76 at phase composition domains of TMOS/Brij 76 (50 wt%). However, periodically ordered cubic Pm3n NiO-supported monoliths were synthesized in microemulsion system formed by addition of C12-alkane to the hexagonal phase domains. This synthetic strategy also revealed that the NiO particles were well-dispersed into the silicate pore surface matrices of mesostructures. Monolithic NiO-silica composites with 2D hexagonal and 3D cubic geometries and with large particle morphologies show promise to act as catalysts. The current study revealed evidence of the advantages of nanoscale pore geometry and shape, and particle morphology of the supported silica monoliths in the design of nanocatalysts that can efficiently enhance the catalytic functionality in terms of stability, reversibility and reactivity. Furthermore, a key finding in our study was that 2D hexagonal and 3D cubic mesostructured NiO-silica catalysts retained the specific activity towards the oxidation reaction even after several regeneration/reuse cycles. Significant study of the mechanistic cyclization of the organic reactant using the density functional (DFT) calculations provided evidence of the key components of conformations of the functional model during the formation of the oxidation product.

  18. Helicobacter Catalase Devoid of Catalytic Activity Protects the Bacterium against Oxidative Stress.

    Science.gov (United States)

    Benoit, Stéphane L; Maier, Robert J

    2016-11-04

    Catalase, a conserved and abundant enzyme found in all domains of life, dissipates the oxidant hydrogen peroxide (H2O2). The gastric pathogen Helicobacter pylori undergoes host-mediated oxidant stress exposure, and its catalase contains oxidizable methionine (Met) residues. We hypothesized catalase may play a large stress-combating role independent of its classical catalytic one, namely quenching harmful oxidants through its recyclable Met residues, resulting in oxidant protection to the bacterium. Two Helicobacter mutant strains (katAH56A and katAY339A) containing catalase without enzyme activity but that retain all Met residues were created. These strains were much more resistant to oxidants than a catalase-deletion mutant strain. The quenching ability of the altered versions was shown, whereby oxidant-stressed (HOCl-exposed) Helicobacter retained viability even upon extracellular addition of the inactive versions of catalase, in contrast to cells receiving HOCl alone. The importance of the methionine-mediated quenching to the pathogen residing in the oxidant-rich gastric mucus was studied. In contrast to a catalase-null strain, both site-change mutants proficiently colonized the murine gastric mucosa, suggesting that the amino acid composition-dependent oxidant-quenching role of catalase is more important than the well described H2O2-dissipating catalytic role. Over 100 years after the discovery of catalase, these findings reveal a new non-enzymatic protective mechanism of action for the ubiquitous enzyme. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  19. Effect of oxidation and catalytic reduction of trace organic contaminants on their activated carbon adsorption.

    Science.gov (United States)

    Schoutteten, Klaas V K M; Hennebel, Tom; Dheere, Ellen; Bertelkamp, Cheryl; De Ridder, David J; Maes, Synthia; Chys, Michael; Van Hulle, Stijn W H; Vanden Bussche, Julie; Vanhaecke, Lynn; Verliefde, Arne R D

    2016-12-01

    The combination of ozonation and activated carbon (AC) adsorption is an established technology for removal of trace organic contaminants (TrOCs). In contrast to oxidation, reduction of TrOCs has recently gained attention as well, however less attention has gone to the combination of reduction with AC adsorption. In addition, no literature has compared the removal behavior of reduction vs. ozonation by-products by AC. In this study, the effect of pre-ozonation vs pre-catalytic reduction on the AC adsorption efficiency of five TrOCs and their by-products was compared. All compounds were susceptible to oxidation and reduction, however the catalytic reductive treatment proved to be a slower reaction than ozonation. New oxidation products were identified for dinoseb and new reduction products were identified for carbamazepine, bromoxynil and dinoseb. In terms of compatibility with AC adsorption, the influence of the oxidative and reductive pretreatments proved to be compound dependent. Oxidation products of bromoxynil and diatrizoic acid adsorbed better than their parent TrOCs, but oxidation products of atrazine, carbamazepine and dinoseb showed a decreased adsorption. The reductive pre-treatment showed an enhanced AC adsorption for dinoseb and a major enhancement for diatrizoic acid. For atrazine and bromoxynil, no clear influence on adsorption was noted, while for carbamazepine, the reductive pretreatment resulted in a decreased AC affinity. It may thus be concluded that when targeting mixtures of TrOCs, a trade-off will undoubtedly have to be made towards overall reactivity and removal of the different constituents, since no single treatment proves to be superior to the other. Copyright © 2016 Elsevier Ltd. All rights reserved.

  20. A graphene-based smart catalytic system with superior catalytic performances and temperature responsive catalytic behaviors.

    Science.gov (United States)

    Qi, Junjie; Lv, Weipeng; Zhang, Guanghui; Li, Yang; Zhang, Guoliang; Zhang, Fengbao; Fan, Xiaobin

    2013-07-21

    We have successfully developed a unique graphene-based smart catalytic system which consists of the graphene supported Au-Pt bimetallic nanocatalyst with a well-defined core-shell structure and a dextran-based temperature-responsive polymer. The unique catalytic system possesses excellent catalytic performances and the catalytic activities could be readily switched on or off at different temperature windows.

  1. [Effect of coordinational germanium compounds on enzyme synthesis and activity].

    Science.gov (United States)

    Seĭfullina, I I; Martsinko, E E; Batrakova, O A; Borzova, N V; Ivanko, E V; Varbanets, L D

    2002-01-01

    Germanium complexes (IV) with succinic (H2Suc), oxyethyliminodiacetic (H2Oeida) and iminodisuccinic (H4Ids) acids as well as homo- and heteroligand germanium complexes (IV)--products of interaction of triammonium salt of oxyethylidendiphosphonic acid ((NH4)3HL) and oxyacids: tartaric (H4Tart), citric (H4Citr), trioxyglutaric (H4Toglut) acids have been synthesized. Composition of the obtained complexes: [Ge(OH)2(NaSuc)2].2H2O (I); [Ge(OH) (Oeida).H2O].H2O (II); [Ge(OH)2(NaHIds)2] (III); [Ge(OH)2(NH4)3HL) (H2Tart)] (IV); [Ge(OH)2(NH4)3HL) (H2Citr)] (V); [Ge(OH)2(NH4)3HL) (H2Toglut)] (VI); [Ge(OH)2((NH4)2HL)2] (VII); [Ge (OH)2((NH4)2HL)2] (VII); [Ge(OH)2 (H2O)2(NH4) HL] (VIII) has been determined. The capability of the synthesized compounds has been studied to affect synthesis and activity of the following enzymes: collagenase, alpha-N-acetylgalactosaminidase (alpha-GalNAc-ase) and alpha-galactosidase (alpha-Gal-ase). It has been established that the complexes II-VIII activate biosynthesis of alpha-Gal-ase and alpha-GalNAc-ase, while germanium dioxide (IX) and complex I possess considerable inhibiting effect on synthesis of the above enzymes. It has been also established that all the compounds except for IV increased the activity of both alpha-Gal-ase and alpha-GalNAc-ase. All the considered complexes demonstrated similar reaction with respect to collagenase: they inhibited both synthesis and activity.

  2. 1.2.5. Synthesis, crystal structure and catalytic activity of 2-methoxycarbonylethyldichlorotin hydroxide

    Directory of Open Access Journals (Sweden)

    Wenchao Ding, Han Lu, Wugai An, Xu Yingying, Laijin Tian*

    2014-04-01

    Full Text Available Abstract: 2-methoxycarbonylethyldichlorotin hydroxide, CH3OCOCH2CH2SnCl2(OH ( 1, has been synthesized by hydrolysis reaction and characterized by elemental analysis, FTIR, 1H NMR spectroscopy, and X-ray single crystal diffraction. Compound  1 is a centrosymmetric dimmer, and the tin atom approximates to octahedral geometry via an intramolecular carbonyl- to-tin coordination and hydroxo-bridging. The compound display high selectivity and good catalysis activity on the transesterification reaction of ethyl acetoacetate with an alcohol. Supporting information: FT-IR, 1H NMR, X-Ray, GC/MS analyses, Cif file. 

  3. One-step and rapid synthesis of porous Pd nanoparticles with superior catalytic activity toward ethanol/formic acid electrooxidation

    Science.gov (United States)

    Hong, Wei; Fang, Youxing; Wang, Jin; Wang, Erkang

    2014-02-01

    Porous Pd nanoparticles are successfully prepared by a rapid, one-step, and efficient route with high yield in aqueous solution. The developed method is very simple, just by mixing sodium tetrachloropalladate, polyvinylpyrrolidone and hydroquinone and heated at 70 °C for 15 min. The structure and composition are analyzed by transmission electron microscope, selected-area electron diffraction, inductively coupled plasma optical emission spectrometer, X-ray diffraction, energy dispersive X-ray spectrum and X-ray photoelectron spectroscopy. Electrochemical catalytic measurement results prove that the as synthesized porous Pd nanoparticles exhibit superior catalytic activity towards ethanol and formic acid electrooxidation.

  4. Inhibition of the ATPase activity of the catalytic portion of ATP synthases by cationic amphiphiles.

    Science.gov (United States)

    Datiles, Manuel J; Johnson, Eric A; McCarty, Richard E

    2008-04-01

    Melittin, a cationic, amphiphilic polypeptide, has been reported to inhibit the ATPase activity of the catalytic portions of the mitochondrial (MF1) and chloroplast (CF1) ATP synthases. Gledhill and Walker [J.R. Gledhill, J.E. Walker. Inhibition sites in F1-ATPase from bovine heart mitochondria, Biochem. J. 386 (2005) 591-598.] suggested that melittin bound to the same site on MF1 as IF1, the endogenous inhibitor polypeptide. We have studied the inhibition of the ATPase activity of CF1 and of F1 from Escherichia coli (ECF1) by melittin and the cationic detergent, cetyltrimethylammonium bromide (CTAB). The Ca2+- and Mg2+-ATPase activities of CF1 deficient in its inhibitory epsilon subunit (CF1-epsilon) are sensitive to inhibition by melittin and by CTAB. The inhibition of Ca2+-ATPase activity by CTAB is irreversible. The Ca2+-ATPase activity of F1 from E. coli (ECF1) is inhibited by melittin and the detergent, but Mg2+-ATPase activity is much less sensitive to both reagents. The addition of CTAB or melittin to a solution of CF1-epsilon or ECF1 caused a large increase in the fluorescence of the hydrophobic probe, N-phenyl-1-naphthylamine, indicating that the detergent and melittin cause at least partial dissociation of the enzymes. ATP partially protects CF1-epsilon from inhibition by CTAB. We also show that ATP can cause the aggregation of melittin. This result complicates the interpretation of experiments in which ATP is shown to protect enzyme activity from inhibition by melittin. It is concluded that melittin and CTAB cause at least partial dissociation of the alpha/beta heterohexamer.

  5. Fabrication and Catalytic Activity of Thermally Stable Gold Nanoparticles on Ultrastable Y (USY Zeolites

    Directory of Open Access Journals (Sweden)

    Keiko Iida

    2013-07-01

    Full Text Available Au was deposited on ultrastable Y (USY zeolites using an ion-exchange method. Up to 5.5 wt% Au was introduced into the NH4-form of USY zeolites. In contrast, deposition of Au hardly took place on the H- and Na-forms of Y-type zeolites, NH4-forms of mordenite, and ZSM-5. Treatment of the Au-loaded USY zeolite in a H2 atmosphere, afforded Au0 nanoparticles. These particles were thermally stable even at 973 K, where their mean particle diameter was 3.7 nm. In contrast, highly aggregated Au particles were observed after thermal treatment at temperatures lower than 523 K, followed by storage in air for a month. The resulting particle sizes were in good correlation with the IR band intensity of the adsorbed CO and the catalytic activity of Au in the aerobic oxidation of benzyl alcohol. The Au nanoparticles showed highest activity when the Au/USY zeolite was thermally treated at 673–973 K. A negligible deactivation was observed after repeating the reaction at least 12 times. In the case of Au/TiO2 catalyst prepared by the deposition-precipitation method, the highest activity was observed at 573 K, which was lower than the temperature used for the Au/USY zeolites. This study demonstrated the potential use of the NH4-form of USY zeolites for supporting Au.

  6. Balancing Catalytic Activity and Interface Energetics of Electrocatalyst-Coated Photoanodes for Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Xu, Zhe; Wang, Haoyu; Wen, Yunzhou; Li, Wenchao; Sun, Chuyu; He, Yuting; Shi, Zhan; Pei, Lang; Chen, Yongda; Yan, Shicheng; Zou, Zhigang

    2018-01-31

    For photoelectrochemical (PEC) water splitting, the interface interactions among semiconductors, electrocatalysts, and electrolytes affect the charge separation and catalysis in turn. Here, through the changing of the bath temperature, Co-based oxygen evolution catalysts (OEC) with different crystallinities were electrochemically deposited on Ti-doped Fe 2 O 3 (Ti-Fe 2 O 3 ) photoanodes. We found: (1) the OEC with low crystallinity is highly ion-permeable, decreasing the interactions between OEC and photoanode due to the intimate interaction between semiconductor and electrolyte; (2) the OEC with high crystallinity is nearly ion-impermeable, is beneficial to form a constant buried junction with semiconductor, and exhibits the low OEC catalytic activity; and (3) the OEC with moderate crystallinity is partially electrolyte-screened, thus contributing to the formation of ideal band bending underneath surface of semiconductor for charge separation and the highly electrocatalytic activity of OEC for lowering over-potentials of water oxidation. Our results demonstrate that to balance the water oxidation activity of OEC and OEC-semiconductor interface energetics is crucial for highly efficient solar energy conversion; in particular, the energy transducer is a semiconductor with a shallow or moderate valence-band level.

  7. Antitumour, antimicrobial and catalytic activity of gold nanoparticles synthesized by different pH propolis extracts

    Energy Technology Data Exchange (ETDEWEB)

    Gatea, Florentina; Teodor, Eugenia Dumitra, E-mail: eu-teodor@yahoo.com [National Institute for Biological Sciences, Centre of Bioanalysis (Romania); Seciu, Ana-Maria [National Institute for Biological Sciences, Cellular and Molecular Biology Department (Romania); Covaci, Ovidiu Ilie [SARA Pharm Solutions (Romania); Mănoiu, Sorin [National Institute for Biological Sciences, Cellular and Molecular Biology Department (Romania); Lazăr, Veronica [University of Bucharest, Faculty of Biology (Romania); Radu, Gabriel Lucian [University “Politehnica” Bucharest, Faculty of Applied Chemistry and Materials Science (Romania)

    2015-07-15

    The Romanian propolis was extracted in five different media, respectively, in water (pH 6.8), glycine buffer (pH 2.5), acetate buffer (pH 5), phosphate buffer (pH 7.4) and carbonate buffer (pH 9.2). The extracts presented different amounts of flavonoids and phenolic acids, increasing pH leading to higher concentrations of active compounds. Five variants of gold nanoparticles suspensions based on different pH Romanian propolis aqueous extracts were successfully synthesized. The obtained nanoparticles presented dimensions between 20 and 60 nm in dispersion form and around 18 nm in dried form, and different morphologies (spherical, hexagonal, triangular). Fourier transform infrared spectroscopy proved the attachment of organic compounds from propolis extracts to the colloidal gold suspensions and X-ray diffraction certified that the suspensions contain metallic gold. The obtained propolis gold nanoparticles do not exhibit any antibacterial or antifungal activity, but presented different catalytic activities and toxicity on tumour cells.

  8. Acrylonitrile irreversibly inactivates glyceraldehyde-3-phosphate dehydrogenase by alkylating the catalytically active cysteine 149.

    Science.gov (United States)

    Campian, E Cristian; Cai, Jian; Benz, Frederick W

    2002-08-15

    Acrylonitrile (AN) is a vinyl monomer used in the production of synthetic fibers, rubber and plastics. AN is acutely toxic but its mechanism of toxicity remains to be established. AN is metabolized to cyanide in vivo but cyanide production alone cannot explain acute AN toxicity. Previous work in our laboratory has shown that AN can alkylate highly reactive cysteine residues in proteins. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a critical enzyme involved in glycolysis, has a catalytically active cysteine 149 in its active site. We report that AN irreversibly inhibits GAPDH with second-order rate constants, at pH 7.4, of 3.7 and 9.2 M(-1) s(-1) at 25 and 37 degrees C, respectively. A combination of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) and electrospray ionization-mass spectrometry-mass spectrometry (ESI-MS-MS) was used to show that AN inactivates GAPDH by covalently binding to cysteine 149 in the active site of the enzyme. Inactivation of GAPDH by AN would be expected to impair glycolytic ATP production and when coupled with the inhibition of mitochondrial ATP synthesis by the AN metabolite cyanide would result in metabolic arrest. The brain can withstand metabolic arrest for only a few minutes thus these combined actions may account for the acute toxicity of AN in vivo.

  9. Mechanism of TRIM25 Catalytic Activation in the Antiviral RIG-I Pathway

    Directory of Open Access Journals (Sweden)

    Jacint G. Sanchez

    2016-08-01

    Full Text Available Antiviral response pathways induce interferon by higher-order assembly of signaling complexes called signalosomes. Assembly of the RIG-I signalosome is regulated by K63-linked polyubiquitin chains, which are synthesized by the E3 ubiquitin ligase, TRIM25. We have previously shown that the TRIM25 coiled-coil domain is a stable, antiparallel dimer that positions two catalytic RING domains on opposite ends of an elongated rod. We now show that the RING domain is a separate self-association motif that engages ubiquitin-conjugated E2 enzymes as a dimer. RING dimerization is required for catalysis, TRIM25-mediated RIG-I ubiquitination, interferon induction, and antiviral activity. We also provide evidence that RING dimerization and E3 ligase activity are promoted by binding of the TRIM25 SPRY domain to the RIG-I effector domain. These results indicate that TRIM25 actively participates in higher-order assembly of the RIG-I signalosome and helps to fine-tune the efficiency of the RIG-I-mediated antiviral response.

  10. Antitumour, antimicrobial and catalytic activity of gold nanoparticles synthesized by different pH propolis extracts

    Science.gov (United States)

    Gatea, Florentina; Teodor, Eugenia Dumitra; Seciu, Ana-Maria; Covaci, Ovidiu Ilie; Mănoiu, Sorin; Lazăr, Veronica; Radu, Gabriel Lucian

    2015-07-01

    The Romanian propolis was extracted in five different media, respectively, in water (pH 6.8), glycine buffer (pH 2.5), acetate buffer (pH 5), phosphate buffer (pH 7.4) and carbonate buffer (pH 9.2). The extracts presented different amounts of flavonoids and phenolic acids, increasing pH leading to higher concentrations of active compounds. Five variants of gold nanoparticles suspensions based on different pH Romanian propolis aqueous extracts were successfully synthesized. The obtained nanoparticles presented dimensions between 20 and 60 nm in dispersion form and around 18 nm in dried form, and different morphologies (spherical, hexagonal, triangular). Fourier transform infrared spectroscopy proved the attachment of organic compounds from propolis extracts to the colloidal gold suspensions and X-ray diffraction certified that the suspensions contain metallic gold. The obtained propolis gold nanoparticles do not exhibit any antibacterial or antifungal activity, but presented different catalytic activities and toxicity on tumour cells.

  11. Synthesis of Co/N-HNTs composites and investigation on its catalytic activity for H{sub 2} generation

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Dongcui; Cheng, Zhilin; Nan, Zhaodong, E-mail: zdnan@yzu.edu.cn

    2016-11-01

    Co/N-HNTs composites were synthesized via a one-pot solvothermal method, where amine functional halloysite nanotubes (N-HNTs) were used as support materials. Effects of sulfosuccinate sodium salt (AOT), an anionic surfactant, on morphology and dispersibility of Co particles anchored at the N-HNTs were studied. The dispersibility of the Co particles was promoted with the increase of the AOT concentration. The as-obtained composite was used as a catalyst to generate H{sub 2} gas by hydrolysis of NaBH{sub 4} solution. The catalytic activity of the composite was significantly enhanced than the pure Co and Co/graphene composite at the same experimental conditions reported by our laboratory, and the catalyst was conveniently separated from the solution by a magnet. The catalytic activity was enhanced when the dispersibility of the Co particles was improved at the surface of the N-HNTs and the Co content contained in the composite was lowed. At the same time, the Co particles anchored at the inner surface of the N-HNTs resulted in higher catalytic activity, where the Co particles may bond with nitrogen atoms. The activation energy for the hydrolysis of NaBH{sub 4} was calculated to be about 15.42 kJ mol{sup −1}. The catalyst can be continuously used for four times with about the same catalytic activity. - Highlights: • Co/N-HNTs composites are synthesized. • The dispersibility and morphology of the Co particles anchored at the N-HNTs are modified by AOT. • The composite shows higher catalytic activity for production H{sub 2} gas.

  12. Physical Activity and Fitness in Children with Developmental Coordination Disorder: A Systematic Review

    Science.gov (United States)

    Rivilis, Irina; Hay, John; Cairney, John; Klentrou, Panagiota; Liu, Jian; Faught, Brent E.

    2011-01-01

    Developmental coordination disorder (DCD) is a neurodevelopmental condition characterized by poor motor proficiency that interferes with a child's activities of daily living. Activities that most young children engage in such as running, walking, and jumping are important for the proper development of fitness and overall health. However, children…

  13. Can Gymnastic Teacher Predict Leisure Activity Preference among Children with Developmental Coordination Disorders (DCD)?

    Science.gov (United States)

    Engel-Yeger, Batya; Hanna-Kassis, Amany; Rosenblum, Sara

    2012-01-01

    The aims of the study were to analyze: (1) whether significant differences exist between children with typical development and children with developmental coordination disorders (DCD) in their preference to participate in leisure activities (2) whether the teacher estimation of activity form (TEAF) evaluation predicts participation preference.…

  14. Rapid and enhanced activation of microporous coordination polymers by flowing supercritical CO.sub.2

    Science.gov (United States)

    Matzger, Adam J.; Liu, Baojian; Wong-Foy, Antek G.

    2016-07-19

    Flowing supercritical CO.sub.2 is used to activate metal organic framework materials (MOF). MOFs are activated directly from N,N-dimethylformamide (DMF) thus avoiding exchange with a volatile solvent. Most MCPs display increased surface areas directly after treatment although those with coordinatively unsaturated metal centers benefit from additional heating.

  15. Comparing Activity Patterns, Biological, and Family Factors in Children with and without Developmental Coordination Disorder

    Science.gov (United States)

    Beutum, Monique Natalie; Cordier, Reinie; Bundy, Anita

    2013-01-01

    The association between motor proficiency and moderate to vigorous physical activity (MVPA) suggests children with developmental coordination disorder (DCD) may be susceptible to inactivity-related conditions such as cardiovascular diseases. The aim of this study was to compare children with and without DCD on physical activity patterns, activity…

  16. Coordination of Fictive Motor Activity in the Larval Zebrafish Is Generated by Non-Segmental Mechanisms

    Science.gov (United States)

    Wiggin, Timothy D.; Peck, Jack H.; Masino, Mark A.

    2014-01-01

    The cellular and network basis for most vertebrate locomotor central pattern generators (CPGs) is incompletely characterized, but organizational models based on known CPG architectures have been proposed. Segmental models propose that each spinal segment contains a circuit that controls local coordination and sends longer projections to coordinate activity between segments. Unsegmented/continuous models propose that patterned motor output is driven by gradients of neurons and synapses that do not have segmental boundaries. We tested these ideas in the larval zebrafish, an animal that swims in discrete episodes, each of which is composed of coordinated motor bursts that progress rostrocaudally and alternate from side to side. We perturbed the spinal cord using spinal transections or strychnine application and measured the effect on fictive motor output. Spinal transections eliminated episode structure, and reduced both rostrocaudal and side-to-side coordination. Preparations with fewer intact segments were more severely affected, and preparations consisting of midbody and caudal segments were more severely affected than those consisting of rostral segments. In reduced preparations with the same number of intact spinal segments, side-to-side coordination was more severely disrupted than rostrocaudal coordination. Reducing glycine receptor signaling with strychnine reversibly disrupted both rostrocaudal and side-to-side coordination in spinalized larvae without disrupting episodic structure. Both spinal transection and strychnine decreased the stability of the motor rhythm, but this effect was not causal in reducing coordination. These results are inconsistent with a segmented model of the spinal cord and are better explained by a continuous model in which motor neuron coordination is controlled by segment-spanning microcircuits. PMID:25275377

  17. Active Coordinated Operation of Distribution Network System for Many Connections of Distributed Generators

    Science.gov (United States)

    Hayashi, Yasuhiro; Kawasaki, Shoji; Matsuki, Junya; Wakao, Shinji; Baba, Junpei; Hojo, Masahide; Yokoyama, Akihiko; Kobayashi, Naoki; Hirai, Takao; Oishi, Kohei

    Recently, total number of distributed generators (DGS) such as photovoltaic generation system and wind turbine generation system connected to an actual distribution network increases drastically. The distribution network connected with many distributed generators must be operated keeping reliability of power supply, power quality and loss minimization. In order to accomplish active distribution network operation to take advantage of many connections of DGS, a new coordinated operation of distribution system with many connections of DGS is necessary. In this paper, the authors propose a coordinated operation of distribution network system connected with many DGS by using newly proposed sectionalizing switches control, sending voltage control and computation of available DG connection capability. In order to check validity of the proposed coordinated operation of distribution system, numerical simulations using the proposed coordinated distribution system operation are carried out in a practical distribution network model.

  18. Determining the Catalytic Activity of Transition Metal-Doped TiO2 Nanoparticles Using Surface Spectroscopic Analysis

    Science.gov (United States)

    Yang, Sena; Lee, Hangil

    2017-11-01

    The modified TiO2 nanoparticles (NPs) to enhance their catalytic activities by doping them with the five transition metals (Cr, Mn, Fe, Co, and Ni) have been investigated using various surface analysis techniques such as scanning electron microscopy (SEM), Raman spectroscopy, scanning transmission X-ray microscopy (STXM), and high-resolution photoemission spectroscopy (HRPES). To compare catalytic activities of these transition metal-doped TiO2 nanoparticles (TM-TiO2) with those of TiO2 NPs, we monitored their performances in the catalytic oxidation of 2-aminothiophenol (2-ATP) by using HRPES and on the oxidation of 2-ATP in aqueous solution by taking electrochemistry (EC) measurements. As a result, we clearly investigate that the increased defect structures induced by the doped transition metal are closely correlated with the enhancement of catalytic activities of TiO2 NPs and confirm that Fe- and Co-doped TiO2 NPs can act as efficient catalysts.

  19. Bifunctional Molecular Photoswitches Based on Overcrowded Alkenes for Dynamic Control of Catalytic Activity in Michael Addition Reactions.

    Science.gov (United States)

    Pizzolato, Stefano F; Collins, Beatrice S L; van Leeuwen, Thomas; Feringa, Ben L

    2017-05-02

    The emerging field of artificial photoswitchable catalysis has recently shown striking examples of functional light-responsive systems allowing for dynamic control of activity and selectivity in organocatalysis and metal-catalysed transformations. While our group has already disclosed systems featuring first generation molecular motors as the switchable central core, a design based on second generation molecular motors is lacking. Here, the syntheses of two bifunctionalised molecular switches based on a photoresponsive tetrasubstituted alkene core are reported. They feature a thiourea substituent as hydrogen-donor moiety in the upper half and a basic dimethylamine group in the lower half. This combination of functional groups offers the possibility for application of these molecules in photoswitchable catalytic processes. The light-responsive central cores were synthesized by a Barton-Kellogg coupling of the prefunctionalized upper and lower halves. Derivatization using Buchwald-Hartwig amination and subsequent introduction of the thiourea substituent afforded the target compounds. Control of catalytic activity in the Michael addition reaction between (E)-3-bromo-β-nitrostyrene and 2,4-pentanedione is achieved upon irradiation of stable-(E) and stable-(Z) isomers of the bifunctional catalyst 1. Both isomers display a decrease in catalytic activity upon irradiation to the metastable state, providing systems with the potential to be applied as ON/OFF catalytic photoswitches. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Catalytic dehydrogenation of isobutane in the presence of hydrogen over Cs-modified Ni2P supported on active carbon

    Science.gov (United States)

    Xu, Yanli; Sang, Huanxin; Wang, Kang; Wang, Xitao

    2014-10-01

    In this article, an environmentally friendly non-noble-metal class of Cs-Ni2P/active carbon (AC) catalyst was prepared and demonstrated to exhibit enhanced catalytic performance in isobutane dehydrogenation. The results of activity tests reveal that Ni/AC catalyst was highly active for isobutane cracking, which led to the formation of abundant methane and coke. After the introduction of phosphorus through impregnation with ammonium di-hydrogen phosphate and H2-temperature programmed reduction, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene and stability of catalyst increased remarkably. The characterization results indicate that, after the addition of phosphorous, the improvement of dehydrogenation selectivity is ascribed to the partial positive charges carried on Ni surface in Ni2P particles, which decreases the strength of Nisbnd C bond between Ni and carbonium-ion intermediates and the possibility of excessive dehydrogenation. In addition, Cs-modified Ni2P/AC catalysts display much higher catalytic performance as compared to Ni2P/AC catalyst. Cs-Ni2P-6.5 catalyst has the highest catalytic performance, and the selectivity to isobutene higher than 93% can be obtained even after 4 h reaction. The enhancement in catalytic performance of the Cs-modified catalysts is mainly attributed to the function of Cs to improve the dispersion of Ni2P particles, transfer electron from Cs to Ni, and decrease acid site number and strength.

  1. Electrochemical sensing chemical oxygen demand based on the catalytic activity of cobalt oxide film.

    Science.gov (United States)

    Wang, Jinqi; Wu, Can; Wu, Kangbing; Cheng, Qin; Zhou, Yikai

    2012-07-29

    Cobalt oxide sensing film was in situ prepared on glassy carbon electrode surface via constant potential oxidation. Controlling at 0.8 V in NaOH solution, the high-valence cobalt catalytically oxidized the reduced compounds, decreasing its surface amount and current signal. The current decline was used as the response signal of chemical oxygen demand (COD) because COD represents the summation of reduced compounds in water. The surface morphology and electrocatalytic activity of cobalt oxide were readily tuned by variation of deposition potential, time, medium and Co(2+) concentration. As confirmed from the atomic force microscopy measurements, the cobalt oxide film, that prepared at 1.3 V for 40 s in pH 4.6 acetate buffer containing 10 mM Co(NO(3))(2), possesses large surface roughness and numerous three-dimensional structures. Electrochemical tests indicated that the prepared cobalt oxide exhibited high electrocatalytic activity to the reduced compounds, accompanied with strong COD signal enhancement. As a result, a novel electrochemical sensor with high sensitivity, rapid response and operational simplicity was developed for COD. The detection limit was as low as 1.1 mg L(-1). The analytical application was studied using a large number of lake water samples, and the accuracy was tested by standard method. Copyright © 2012 Elsevier B.V. All rights reserved.

  2. Biologically active Phytophthora mating hormone prepared by catalytic asymmetric total synthesis

    Science.gov (United States)

    Harutyunyan, Syuzanna R.; Zhao, Zhijian; den Hartog, Tim; Bouwmeester, Klaas; Minnaard, Adriaan J.; Feringa, Ben L.; Govers, Francine

    2008-01-01

    A Phytophthora mating hormone with an array of 1,5-stereogenic centers has been synthesized by using our recently developed methodology of catalytic enantioselective conjugate addition of Grignard reagents. We applied this methodology in a diastereo- and enantioselective iterative route and obtained two of the 16 possible stereoisomers of Phytophthora hormone α1. These synthetic stereoisomers induced the formation of sexual spores (oospores) in A2 mating type strains of three heterothallic Phytophthora species, P. infestans, P. capsici, and P. nicotianae but not in A1 mating type strains. The response was concentration-dependent, and the oospores were viable. These results demonstrate that the biological activity of the synthetic hormone resembles that of the natural hormone α1. Mating hormones are essential components in the sexual life cycle of a variety of organisms. For plant pathogens like Phytophthora, sexual reproduction is important as a source of genetic variation. Moreover, the thick-walled oospores are the most durable propagules that can survive harsh environmental conditions. Sexual reproduction can thus greatly affect disease epidemics. The availability of synthetic compounds mimicking the activity of Phytophthora mating hormone will be instrumental for further unravelling sexual reproduction in this important group of plant pathogens. PMID:18559862

  3. Controlling catalytic activity of gold cluster on MgO thin film for water splitting

    Science.gov (United States)

    Ding, Zijing; Yan, Lei; Li, Zi; Ma, Wei; Lu, Gang; Meng, Sheng

    2017-09-01

    We propose that supported gold clusters on MgO thin film can potentially serve as an efficient photocatalyst for water splitting. The catalytic activity of the gold cluster is enhanced by excess electrons occupying its quantum well states (QWSs) and can be controlled by varying the oxide thickness, introducing defects/doping in the substrate, and modulating the plasmonic response of the Au cluster. We find that the bonding between the water molecule and certain QWSs can significantly reduce the water splitting energy barrier in its ground state. More importantly, the water splitting is nearly spontaneous when the QWS is photoexcited. First-principles real-time electron dynamics simulations reveal that the excited QWS in the supported gold cluster has a long lifetime on the scale of picoseconds. Generation of activated hydrogen atoms is predicted to occur spontaneously following photoexcitation, and the yield of H2 gas is maintained by enriching hydrogen concentration without poisoning the catalyst. These results illustrate promising routes for promoting photocatalysis via engineering the energy levels of supported metal clusters.

  4. Adenylate kinase from Streptococcus pneumoniae is essential for growth through its catalytic activity

    Directory of Open Access Journals (Sweden)

    Trung Thanh Thach

    2014-01-01

    Full Text Available Streptococcus pneumoniae (pneumococcus infection causes more than 1.6 million deaths worldwide. Pneumococcal growth is a prerequisite for its virulence and requires an appropriate supply of cellular energy. Adenylate kinases constitute a major family of enzymes that regulate cellular ATP levels. Some bacterial adenylate kinases (AdKs are known to be critical for growth, but the physiological effects of AdKs in pneumococci have been poorly understood at the molecular level. Here, by crystallographic and functional studies, we report that the catalytic activity of adenylate kinase from S. pneumoniae (SpAdK serotype 2 D39 is essential for growth. We determined the crystal structure of SpAdK in two conformations: ligand-free open form and closed in complex with a two-substrate mimic inhibitor adenosine pentaphosphate (Ap5A. Crystallographic analysis of SpAdK reveals Arg-89 as a key active site residue. We generated a conditional expression mutant of pneumococcus in which the expression of the adk gene is tightly regulated by fucose. The expression level of adk correlates with growth rate. Expression of the wild-type adk gene in fucose-inducible strains rescued a growth defect, but expression of the Arg-89 mutation did not. SpAdK increased total cellular ATP levels. Furthermore, lack of functional SpAdK caused a growth defect in vivo. Taken together, our results demonstrate that SpAdK is essential for pneumococcal growth in vitro and in vivo.

  5. Single‐molecule mechanochemical characterization of E. coli pol III core catalytic activity

    Science.gov (United States)

    Naufer, M. Nabuan; Murison, David A.; Rouzina, Ioulia; Beuning, Penny J.

    2017-01-01

    Abstract Pol III core is the three‐subunit subassembly of the E. coli replicative DNA polymerase III holoenzyme. It contains the catalytic polymerase subunit α, the 3′ → 5′ proofreading exonuclease ε, and a subunit of unknown function, θ. We employ optical tweezers to characterize pol III core activity on a single DNA substrate. We observe polymerization at applied template forces F  30 pN. Both polymerization and exonucleolysis occur as a series of short bursts separated by pauses. For polymerization, the initiation rate after pausing is independent of force. In contrast, the exonucleolysis initiation rate depends strongly on force. The measured force and concentration dependence of exonucleolysis initiation fits well to a two‐step reaction scheme in which pol III core binds bimolecularly to the primer‐template junction, then converts at rate k 2 into an exo‐competent conformation. Fits to the force dependence of k init show that exo initiation requires fluctuational opening of two base pairs, in agreement with temperature‐ and mismatch‐dependent bulk biochemical assays. Taken together, our results support a model in which the pol and exo activities of pol III core are effectively independent, and in which recognition of the 3′ end of the primer by either α or ε is governed by the primer stability. Thus, binding to an unstable primer is the primary mechanism for mismatch recognition during proofreading, rather than an alternative model of duplex defect recognition. PMID:28263430

  6. Facile and Green Synthesis of Palladium Nanoparticles-Graphene-Carbon Nanotube Material with High Catalytic Activity

    Science.gov (United States)

    Sun, Tai; Zhang, Zheye; Xiao, Junwu; Chen, Chen; Xiao, Fei; Wang, Shuai; Liu, Yunqi

    2013-01-01

    We report a facile and green method to synthesize a new type of catalyst by coating Pd nanoparticles (NPs) on reduced graphene oxide (rGO)-carbon nanotube (CNT) nanocomposite. An rGO–CNT nanocomposite with three-dimensional microstructures was obtained by hydrothermal treatment of an aqueous dispersion of graphene oxide (GO) and CNTs. After the rGO–CNT composites have been dipped in K2PdCl4 solution, the spontaneous redox reaction between the GO–CNT and PdCl42− led to the formation of nanohybrid materials consisting rGO–CNT decorated with 4 nm Pd NPs, which exhibited excellent and stable catalytic activity: the reduction of 4-nitrophenol to 4-aminophenol using NaBH4 as a catalyst was completed in only 20 s at room temperature, even when the Pd content of the catalyst was 1.12 wt%. This method does not require rigorous conditions or toxic agents and thus is a rapid, efficient, and green approach to the fabrication of highly active catalysts. PMID:23982312

  7. Hierarchical nano-on-micro copper with enhanced catalytic activity towards electro-oxidation of hydrazine

    Science.gov (United States)

    Yan, Xiaodong; Liu, Yuan; Scheel, Kyle R.; Li, Yong; Yu, Yunhua; Yang, Xiaoping; Peng, Zhonghua

    2018-01-01

    The electrochemical properties of catalyst materials are highly dependent on the materials structure and architecture. Herein, nano-on-micro Cu electrodes are fabricated by growing Cu microcrystals on Ni foam substrate, followed by introducing Cu nanocrystals onto the surface of the Cu microcrystals. The introduction of Cu nanocrystals onto the surface of Cu microcrystals is shown to dramatically increase the electrochemically active surface area and thus significantly enhances the catalytic activity of the catalyst electrode towards electro-oxidation of hydrazine. The onset potential (-1.04 V vs. Ag/AgCl) of the nano-on-micro Cu electrode is lower than those of the reported Cu-based catalysts under similar testing conditions, and a current density of 16 mA·cm-2, which is 2 times that of the microsized Cu electrode, is achieved at a potential of -0.95 V vs. Ag/AgCl. Moreover, the nano-on-micro Cu electrode demonstrates good long-term stability.

  8. Preparation of carbon-supported Bi/Ti composites and its catalytic activity under solar irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Peng; Wu, Yanlin; Shi, Jin; Liu, Dan; Dong, Wenbo, E-mail: wbdong@fudan.edu.cn

    2014-02-15

    Carbon-supported photocatalysts of Bi/Ti oxides (Bi/Ti-C) were synthesized by a facile sol–gel process. Carbon was mounted as support substrate by controlling calcination temperature. The as-prepared materials were characterized through X-ray diffraction, and the N{sub 2} adsorption–desorption isotherm and surface texture of Bi/Ti-C at 673 K were observed by scanning electron microscopy and transmission electron microscopy. Characterization results revealed that BiOCl was the major phase of the catalytic composites, and that Bi/Ti-673 K was endowed with the porous structure of the coated C. The photocatalytic degradation activity of these samples to Rhodamine B was determined through ultraviolet-visible spectrophotometry. The composite prepared at 673 K demonstrated the highest photocatalytic efficiency. The addition of C avoided the need to modify the surface area of the crystals. In addition, the photocatalytic activities of the Bi/Ti composites were significantly improved by the compounded microstructure.

  9. Nanostructured Samarium Doped Fluorapatites and Their Catalytic Activity towards Synthesis of 1,2,4-Triazoles

    Directory of Open Access Journals (Sweden)

    Kranthi Kumar Gangu

    2016-09-01

    Full Text Available An investigation was conducted into the influence of the amino acids as organic modifiers in the facile synthesis of metal incorporated fluorapatites (FAp and their properties. The nanostructured Sm doped fluorapatites (Sm-FAp were prepared by a co-precipitation method using four different amino acids, namely glutamic acid, aspartic acid, glycine and histidine. The materials were characterized by various techniques including X-ray diffraction (XRD, Fourier transform infra-red spectroscopy (FT-IR, field emission scanning electron microscopy (FE-SEM, energy-dispersive X-ray spectroscopy (EDX, high resolution transmission electron microscopy (HR-TEM, N2-adsorption/desorption isotherm, temperature programmed desorption (TPD and fluorescence spectrophotometry. Under similar conditions, Sm-FAp prepared using different amino acids exhibited distinctly different morphological structures, surface area and pore properties. Their activity as catalysts was assessed and Sm-FAp/Glycine displayed excellent efficiency in the synthesis of 1,2,4-triazole catalyzing the reaction between 2-nitrobenzaldehyde and thiosemicarbazide with exceptional selectivity and 98% yield in a short time interval (10 min. The study provides an insight into the role of organic modifiers as controllers of nucleation, growth and aggregation which significantly influence the nature and activity of the catalytic sites on Sm-FAp. Sm-FAp could also have potential as photoactive material.

  10. Strong catalytic activity of iron nanoparticles on the surfaces of reduced olivine

    Science.gov (United States)

    Tucker, William C.; Quadery, Abrar H.; Schulte, Alfons; Blair, Richard G.; Kaden, William E.; Schelling, Patrick K.; Britt, Daniel T.

    2018-01-01

    It is demonstrated that olivine powders heated to subsolidus temperatures in reducing conditions can develop significant concentrations of 10-50 nm diameter Fe nanoparticles on grain surfaces and that these display strong catalytic activity not observed in powders without Fe nanoparticles. Reduced surfaces were exposed to NH3, CO, and H2, volatiles that may be present on the surfaces of comet and volatile-rich asteroids. In the case of NH3 exposure, rapid decomposition was observed. When exposed to a mixture of CO and H2, significant coking of the mineral surfaces occurred. Analysis of the mineral grains after reaction indicated primarily the presence of graphene or graphitic carbon. The results demonstrate that strong chemical activity can be expected at powders that contain nanophase Fe particles. This suggests space-weathered mineral surfaces may play an important role in the synthesis and processing of organic species. This processing may be part of the weathering processes of volatile-rich but atmosphereless solar-system bodies.

  11. Iridium-decorated multiwall carbon nanotubes and its catalytic activity with Shell 405 in hydrazine decomposition

    Science.gov (United States)

    Prasad, V.; Vasanthkumar, M. S.

    2015-10-01

    Iridium-functionalized multiwalled carbon nanotubes (Ir-MWNT) are the future catalyst support material for hydrazine fuel decomposition. The present work demonstrates decoration of iridium particle on iron-encapsulated multiwalled carbon nanotubes (MWNT) by wet impregnation method in the absence of any stabilizer. Electron microscopy studies reveal the coated iridium particle size in the range of 5-10 nm. Elemental analysis by energy dispersive X-ray diffraction confirms 21 wt% of Ir coated over MWNT. X-ray photoelectron spectroscopy (XPS) shows 4f5/2 and 4f7/2 lines of iridium and confirms the metallic nature. The catalytic activity of Ir-MWNT/Shell 405 combination is performed in 1 N hydrazine micro-thrusters. The thruster performance shows increase in chamber pressure and decrease in chamber temperature when compared to Shell 405 alone. This enhanced performance is due to high thermal conducting nature of MWNTs and the presence of Ir active sites over MWNTs.

  12. Catalytic Activity of Mono- and Bi-Metallic Nanoparticles Synthesized via Microemulsions

    Directory of Open Access Journals (Sweden)

    Ramona Y.G. König

    2014-07-01

    Full Text Available Water-in-oil (w/o microemulsions were used as a template for the synthesis of mono- and bi-metallic nanoparticles. For that purpose, w/o-microemulsions containing H2PtCl6, H2PtCl6 + Pb(NO32 and H2PtCl6 + Bi(NO3, respectively, were mixed with a w/o-microemulsion containing the reducing agent, NaBH4. The results revealed that it is possible to synthesize Pt, PtPb and PtBi nanoparticles of ~3–8 nm in diameter at temperatures of about 30°C. The catalytic properties of the bimetallic PtBi and PtPb nanoparticles were studied and compared with monometallic platinum nanoparticles. Firstly, the electrochemical oxidation of formic acid to carbon monoxide was investigated, and it was found that the resistance of the PtBi and PtPb nanoparticles against the catalyst-poisoning carbon monoxide was significantly higher compared to the Pt nanoparticles. Secondly, investigating the reduction of 4-nitrophenol to 4-aminophenol,we found that the bimetallic NPs are most active at 23 °C, while the order of the activity changes at higher temperatures, i.e., that the Pt nanoparticles are the most active ones at 36 and 49 °C. Furthermore, we observed a strong influence of the support, which was either a polymer or Al2O3. Thirdly, for the hydrogenation of allylbenzene to propylbenzene, the monometallic Pt NPs turned out to be the most active catalysts, followed by the PtPb and PtBi NPs. Comparing the two bimetallic nanoparticles, one sees that the PtPb NPs are significantly more active than the respective PtBi NPs.

  13. Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale.

    Science.gov (United States)

    Shan, Shiyao; Petkov, Valeri; Prasai, Binay; Wu, Jinfang; Joseph, Pharrah; Skeete, Zakiya; Kim, Eunjoo; Mott, Derrick; Malis, Oana; Luo, Jin; Zhong, Chuan-Jian

    2015-12-07

    The ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites is essential for understanding the correlation between the atomic structure and catalytic properties, enabling the preparation of efficient nanoalloy catalysts by design. Herein we describe a study of CO oxidation over PdCu nanoalloy catalysts focusing on gaining insights into the correlation between the atomic structures and catalytic activity of nanoalloys. PdCu nanoalloys of different bimetallic compositions are synthesized as a model system and are activated by a controlled thermochemical treatment for assessing their catalytic activity. The results show that the catalytic synergy of Pd and Cu species evolves with both the bimetallic nanoalloy composition and temperature of the thermochemical treatment reaching a maximum at a Pd : Cu ratio close to 50 : 50. The nanoalloys are characterized structurally by ex situ and in situ synchrotron X-ray diffraction, including atomic pair distribution function analysis. The structural data show that, depending on the bimetallic composition and treatment temperature, PdCu nanoalloys adopt two different structure types. One features a chemically ordered, body centered cubic (B2) type alloy consisting of two interpenetrating simple cubic lattices, each occupied with Pd or Cu species alone, and the other structure type features a chemically disordered, face-centered cubic (fcc) type of alloy wherein Pd and Cu species are intermixed at random. The catalytic activity for CO oxidation is strongly influenced by the structural features. In particular, it is revealed that the prevalence of chemical disorder in nanoalloys with a Pd : Cu ratio close to 50 : 50 makes them superior catalysts for CO oxidation in comparison with the same nanoalloys of other bimetallic compositions. However, the catalytic synergy can be diminished if the Pd50Cu50 nanoalloys undergo

  14. Catalytic reaction pathway for the mitogen-activated protein kinase ERK2.

    Science.gov (United States)

    Prowse, C N; Hagopian, J C; Cobb, M H; Ahn, N G; Lew, J

    2000-05-23

    The structural, functional, and regulatory properties of the mitogen-activated protein kinases (MAP kinases) have long attracted considerable attention owing to the critical role that these enzymes play in signal transduction. While several MAP kinase X-ray crystal structures currently exist, there is by comparison little mechanistic information available to correlate the structural data with the known biochemical properties of these molecules. We have employed steady-state kinetic and solvent viscosometric techniques to characterize the catalytic reaction pathway of the MAP kinase ERK2 with respect to the phosphorylation of a protein substrate, myelin basic protein (MBP), and a synthetic peptide substrate, ERKtide. A minor viscosity effect on k(cat) with respect to the phosphorylation of MBP was observed (k(cat) = 10 +/- 2 s(-1), k(cat)(eta) = 0.18 +/- 0.05), indicating that substrate processing occurs via slow phosphoryl group transfer (12 +/- 4 s(-1)) followed by the faster release of products (56 +/- 4 s(-1)). At an MBP concentration extrapolated to infinity, no significant viscosity effect on k(cat)/K(m(ATP)) was observed (k(cat)/K(m(ATP)) = 0.2 +/- 0.1 microM(-1) s(-1), k(cat)/K(m(ATP))(eta) = -0.08 +/- 0.04), consistent with rapid-equilibrium binding of the nucleotide. In contrast, at saturating ATP, a full viscosity effect on k(cat)/K(m) for MBP was apparent (k(cat)/K(m(MBP)) = 2.4 +/- 1 microM(-1) s(-1), k(cat)/K(m(MBP))(eta) = 1.0 +/- 0.1), while no viscosity effect was observed on k(cat)/K(m) for the phosphorylation of ERKtide (k(cat)/K(m(ERKtide)) = (4 +/- 2) x 10(-3) microM(-1) s(-1), k(cat)/K(m(ERKtide))(eta) = -0.02 +/- 0.02). This is consistent with the diffusion-limited binding of MBP, in contrast to the rapid-equilibrium binding of ERKtide, to form the ternary Michaelis complex. Calculated values for binding constants show that the estimated value for K(d(MBP)) (/= 1.5 mM). The dramatically higher catalytic efficiency of MBP in comparison to that

  15. Association between physical activity and motor skills and coordination in Portuguese children

    OpenAIRE

    Lopes, Luís; Lopes, Vítor P.; Santos, Rute; Pereira,Beatriz

    2011-01-01

    Nowadays, there is growing evidence in literature that Health benefits from regular physical activity (PA). The variance in PA among children is caused by a number of factors including their motor abilities and coordination. The aim of the study was to analyse the relation between usual PA and gross motor abilities and motor coordination in children aged 6 to 7 years. The sample comprised 21 children, aged in average 6,38±0,50 years. Physical activity was accessed by accelerometry, gross moto...

  16. Mesoporous Silica Supported Pd-MnOx Catalysts with Excellent Catalytic Activity in Room-Temperature Formic Acid Decomposition

    Science.gov (United States)

    Jin, Min-Ho; Oh, Duckkyu; Park, Ju-Hyoung; Lee, Chun-Boo; Lee, Sung-Wook; Park, Jong-Soo; Lee, Kwan-Young; Lee, Dong-Wook

    2016-09-01

    For the application of formic acid as a liquid organic hydrogen carrier, development of efficient catalysts for dehydrogenation of formic acid is a challenging topic, and most studies have so far focused on the composition of metals and supports, the size effect of metal nanoparticles, and surface chemistry of supports. Another influential factor is highly desired to overcome the current limitation of heterogeneous catalysis for formic acid decomposition. Here, we first investigated the effect of support pore structure on formic acid decomposition performance at room temperature by using mesoporous silica materials with different pore structures such as KIE-6, MCM-41, and SBA-15, and achieved the excellent catalytic activity (TOF: 593 h-1) by only controlling the pore structure of mesoporous silica supports. In addition, we demonstrated that 3D interconnected pore structure of mesoporous silica supports is more favorable to the mass transfer than 2D cylindrical mesopore structure, and the better mass transfer provides higher catalytic activity in formic acid decomposition. If the pore morphology of catalytic supports such as 3D wormhole or 2D cylinder is identical, large pore size combined with high pore volume is a crucial factor to achieve high catalytic performance.

  17. Recurrently connected and localized neuronal communities initiate coordinated spontaneous activity in neuronal networks.

    Science.gov (United States)

    Lonardoni, Davide; Amin, Hayder; Di Marco, Stefano; Maccione, Alessandro; Berdondini, Luca; Nieus, Thierry

    2017-07-01

    Developing neuronal systems intrinsically generate coordinated spontaneous activity that propagates by involving a large number of synchronously firing neurons. In vivo, waves of spikes transiently characterize the activity of developing brain circuits and are fundamental for activity-dependent circuit formation. In vitro, coordinated spontaneous spiking activity, or network bursts (NBs), interleaved within periods of asynchronous spikes emerge during the development of 2D and 3D neuronal cultures. Several studies have investigated this type of activity and its dynamics, but how a neuronal system generates these coordinated events remains unclear. Here, we investigate at a cellular level the generation of network bursts in spontaneously active neuronal cultures by exploiting high-resolution multielectrode array recordings and computational network modelling. Our analysis reveals that NBs are generated in specialized regions of the network (functional neuronal communities) that feature neuronal links with high cross-correlation peak values, sub-millisecond lags and that share very similar structural connectivity motifs providing recurrent interactions. We show that the particular properties of these local structures enable locally amplifying spontaneous asynchronous spikes and that this mechanism can lead to the initiation of NBs. Through the analysis of simulated and experimental data, we also show that AMPA currents drive the coordinated activity, while NMDA and GABA currents are only involved in shaping the dynamics of NBs. Overall, our results suggest that the presence of functional neuronal communities with recurrent local connections allows a neuronal system to generate spontaneous coordinated spiking activity events. As suggested by the rules used for implementing our computational model, such functional communities might naturally emerge during network development by following simple constraints on distance-based connectivity.

  18. Recurrently connected and localized neuronal communities initiate coordinated spontaneous activity in neuronal networks.

    Directory of Open Access Journals (Sweden)

    Davide Lonardoni

    2017-07-01

    Full Text Available Developing neuronal systems intrinsically generate coordinated spontaneous activity that propagates by involving a large number of synchronously firing neurons. In vivo, waves of spikes transiently characterize the activity of developing brain circuits and are fundamental for activity-dependent circuit formation. In vitro, coordinated spontaneous spiking activity, or network bursts (NBs, interleaved within periods of asynchronous spikes emerge during the development of 2D and 3D neuronal cultures. Several studies have investigated this type of activity and its dynamics, but how a neuronal system generates these coordinated events remains unclear. Here, we investigate at a cellular level the generation of network bursts in spontaneously active neuronal cultures by exploiting high-resolution multielectrode array recordings and computational network modelling. Our analysis reveals that NBs are generated in specialized regions of the network (functional neuronal communities that feature neuronal links with high cross-correlation peak values, sub-millisecond lags and that share very similar structural connectivity motifs providing recurrent interactions. We show that the particular properties of these local structures enable locally amplifying spontaneous asynchronous spikes and that this mechanism can lead to the initiation of NBs. Through the analysis of simulated and experimental data, we also show that AMPA currents drive the coordinated activity, while NMDA and GABA currents are only involved in shaping the dynamics of NBs. Overall, our results suggest that the presence of functional neuronal communities with recurrent local connections allows a neuronal system to generate spontaneous coordinated spiking activity events. As suggested by the rules used for implementing our computational model, such functional communities might naturally emerge during network development by following simple constraints on distance-based connectivity.

  19. CARE Coordinated Accelerator Research in Europe: integrating activity implemented as integrated infrastructure initiative

    CERN Document Server

    Aleksan, R

    2009-01-01

    The main objective of the CARE project was to generate a structured and integrated European area in the field of accelerator research and related R&D. A set of integrating activities involving the largest European infrastructure laboratories and their user communities “active in accelerator R&D”, including industrial partners was established with the following general objectives: 1) To optimise the use of existing infrastructures for improving the European knowledge on accelerator physics  By promoting a coherent and coordinated utilization and development of infrastructures and to facilitate the access to accelerators and test facilities for carrying accelerator studies  By understanding accelerator operation and reliability issues 2) To tackle new or state-of-the-art technologies in a more co-ordinated and collaborative approach  By developing a coherent and coordinated accelerator R&D program in Europe and carrying out joint R&D projects allowing one to enhance the existing (or...

  20. The relationship between segmental coordination, agility and physical activity in adolescents

    Directory of Open Access Journals (Sweden)

    Eliseo García Cantó

    2015-06-01

    Full Text Available Motor competence (MC may be related to youth physical activity (PA level. In the last few years, MC has been studied as a possible determinant of children PA level, but has not been widely studied in adolescents. To analyze the relationship between MC and PA level 533 adolescents (271 men and 261 women from the southeast of Spain were assessed. To register weekly PA was used the International Physical Activity Questionnaire (IPAQ and for the MC, four coordination tests including throw and catch test, eye-hand and eye-foot coordination tests and agility circuit. Data were analyzed using ANOVA and binary logistic regression. The overall MC is consistently related with PA level. Eye-hand coordination test and the agility test define more accurately the tendency to high PA level. Programs to promote PA and focused on MC should be emphasized from early ages to adolescence.

  1. Heterogeneous catalytic ozonation of dibutyl phthalate in aqueous solution in the presence of iron-loaded activated carbon.

    Science.gov (United States)

    Huang, Yuanxing; Cui, Chenchen; Zhang, Daofang; Li, Liang; Pan, Ding

    2015-01-01

    Iron-loaded activated carbon was prepared and used as catalyst in heterogeneous catalytic ozonation of dibutyl phthalate (DBP). The catalytic activity of iron-loaded activated carbon was investigated under various conditions and the mechanisms of DBP removal were deduced. Characterization of catalyst indicated that the iron loaded on activated carbon was mainly in the form of goethite, which reduced its surface area, pore volume and pore diameter. The presence of metals on activated carbon positively contributed to its catalytic activity in ozonation of DBP. Iron loading content of 15% and initial water pH of 8 achieved highest DBP removal among all the tried conditions. Catalyst dosage of 10 mg L(-1) led to approximately 25% of increase in DBP (initial concentration 2 mg L(-1)) removal in 60 min as compared with ozone alone, and when catalyst dosage increased to 100 mg L(-1), the DBP removal was further improved by 46%. Based on a comparison of reaction rates for direct and indirect transformation of DBP, the increased removal of DBP in this study likely occurred via transformation of ozone into hydroxyl radicals on the catalyst surface. Copyright © 2014 Elsevier Ltd. All rights reserved.

  2. Catalytic activity of active carbons impregnated before activation of pinewood sawdust and nutshells to be used on the control of atmospheric emissions.

    Science.gov (United States)

    Alvim-Ferraz, Maria da Conceição M; Gaspar, Carla Maria T B

    2005-03-17

    This work analyses the catalytic activity of metal oxides impregnated on activated carbons to be used for the complete oxidation of benzene present in atmospheric emissions. When the impregnation step is performed before CO2 activation, the knowledge about catalytic activity is as yet quite scarce, being the main objective of the study here reported. Pinewood sawdust and nutshells were recycled to produce the activated carbons. Non-expensive metal oxides (CoO, Co3O4 and CrO3) were impregnated. When the impregnation was performed before CO2 activation instead of after activation, at 523 K the kinetic constants were 3.6-4.3 times higher for sawdust carbons, and 2.1-2.7 times higher for nutshell carbons, due to a better metal oxide dispersion on higher mesopore areas and on wider micropores. With Co3O4 as catalyst, a benzene conversion of 90% was reached at a lower temperature than with CrO3 (472 and 558 K, respectively). The carbons impregnated before CO2 activation allowed very good conversions at temperatures that guarantee carbon stability (lower than 575 K). The results obtained led to the conclusion that activated carbon is a suitable support for metal oxide catalyst aiming the complete oxidation of benzene, mainly if an adequately porous texture is induced, proceeding to the impregnation before CO2 activation.

  3. Biosynthesis of gold nanoparticles using Capsicum annuum var. grossum pulp extract and its catalytic activity

    Science.gov (United States)

    Yuan, Chun-Gang; Huo, Can; Yu, Shuixin; Gui, Bing

    2017-01-01

    Biological synthesis approach has been regarded as a green, eco-friendly and cost effective method for nanoparticles preparation without any toxic solvents and hazardous bi-products during the process. This present study reported a facile and rapid biosynthesis method for gold nanoparticles (GNPs) from Capsicum annuum var. grossum pulp extract in a single-pot process. The aqueous pulp extract was used as biotic reducing agent for gold nanoparticle growing. Various shapes (triangle, hexagonal, and quasi-spherical shapes) were observed within range of 6-37 nm. The UV-Vis spectra showed surface plasmon resonance (SPR) peak for the formed GNPs at 560 nm after 10 min incubation at room temperature. The possible influences of extract amount, gold ion concentration, incubation time, reaction temperature and solution pH were evaluated to obtain the optimized synthesis conditions. The effects of the experimental factors on NPs synthesis process were also discussed. The produced gold nanoparticles were characterized by transform electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDS) and Fourier Transform infrared spectroscopy (FTIR). The results demonstrated that the as-obtained GNPs were well dispersed and stable with good catalytic activity. Biomolecules in the aqueous extract were responsible for the capping and stabilization of GNPs.

  4. CATALYTIC AND ELECTROCATALYTIC ACTIVITY OF Pt-Ru/C ELECTRODE FOR HYDROGEN OXIDATION IN ALKALINE

    Directory of Open Access Journals (Sweden)

    D. LABOU

    2008-07-01

    Full Text Available The kinetics of the oxidation of H2 on PtRu/C gas-diffusion electrode was studied by interfacing the electrode with aqueous electrolytes at different pH values. The conducting electrolytes were KOH and HClO4 aqueous solutions with different concentrations. It is shown that the nature of the aqueous electrolyte plays the role of an active catalyst support for the PtRu/C electrode which drastically affects its catalytic properties. During the aforementioned interaction, termed electrochemical metal support interaction (EMSI, the electrochemical potential of the electrons at the catalyst Fermi level is equalised with the electrochemical potential of the solvated electron in the aqueous electrolyte. The electrochemical experiments carried out at various pH values showed that the electrochemical promotion catalysis (EPOC is more intense when the catalyst-electrode is interfaced with electrolytes with high pH values where the OH– ionic conduction prevails. It was concluded that similar to the solid state electrochemical systems EPOC proceeds through the formation of a polar adsorbed promoting layer of , electrochemically supplied by the OH- species, at the three phase boundaries of the gas exposed gas diffusion catalyst-electrode surface.

  5. Biomimetic synthesis of silver nanoparticles and evaluation of their catalytic activity towards degradation of methyl orange

    Science.gov (United States)

    Manjari Mishra, Pravat; Bihari Pani, Khirod

    2017-11-01

    This paper described the significant effect of process variables like reductant concentrations, substrate concentration, reaction pH and reaction temperature on the size, morphology and yield of the silver nanoparticles (AgNPs) synthesized using aqueous leaf extract of a medicinal plant Momordica charantia (Bitter guard). By means of UV–vis spectroscopy, XRD analysis, TEM analysis and Fluorescence analysis, it is observed that the reaction solution containing 10‑3 M of AgNO3 of pH 5.3  +  10 ml of aqueous leaf extract at normal room temperature, was optimum for synthesis of stable, polydisperse, predominantly spherical AgNPs with average size of 12.15 nm. FT-IR and TEM studies confirmed the stability of AgNPs was due to the capping of phytoconstituents present in the leaf extract. The aqueous solution of leaf extract containing AgNPs showed remarkable catalytic activity towards degradation of methyl orange (MO) in aqueous medium.

  6. Enhanced stability and catalytic activity of bismuth nanoparticles by modified with porous silica

    Science.gov (United States)

    Chen, Kejun; Fan, Wenjie; Huang, Caijin; Qiu, Xiaoqing

    2017-11-01

    The present work reports that the elemental bismuth nanoparticles (Bi NPs) modified with silica can be obtained via in-situ reduction of bismuth oxide nanoparticles with porous silica coating layers. The as-synthesized samples were characterized by the powder X-ray diffraction, scanning electron microscope, transmission electron microscope, the Brunauer-Emmett-Teller surface areas and X-ray photoelectron spectroscopy. It is found that metallic bismuth nanoparticles are well covered by porous silica (Bi@SiO2) to form hybrids. Coating metallic bismuth nanoparticles with permeable silica makes it unsusceptible to agglomeration and deactivation, even if the metallic Bi NPs are stored in the oxygen-rich and aqueous atmospheres. Moreover, the synthesized samples can be employed as catalyst for reduction of p-nitrophenol into p-aminophenol. The optimal catalyst of Bi@SiO2-9.03 at% (9.03 = 100*nSi/nBi) exerts more satisfactory catalytic property and outstanding reusability than the bare metallic bismuth in this target reaction. The superior stability and enhanced activity enable the practical application of Bi NPs to be available and expedient.

  7. One pot synthesis of copper nanoparticles at room temperature and its catalytic activity

    Directory of Open Access Journals (Sweden)

    Nikhil V. Suramwar

    2016-11-01

    Full Text Available A facile reduction approach with sodium borohydride as a reducing agent and starch as a stabilizing agent leads to monodispersed Cu nanoparticles in aqueous medium at an ambient condition. The synthesized nanoparticles are highly pure with no traces of CuO found on surface. They are uniform in size in the range of 40–80 nm. The Cu nanoparticles have a FCC structure as characterized by powder X-ray diffraction (XRD. Transmission electron microscopy (TEM images show that they are arranged in a regular array which is separated by starch thin layer which controls the growth as well as stabilizes the Cu nanoparticles from air oxidation. The catalytic activity of prepared Cu nanomaterial was tested in Ullman reaction for the synthesis of biphenyl from iodobenzene. We have shown in this paper that the size as well as exposed surface area of the copper nanoparticles is responsible for the increase in yield of biphenyl up to 92%. This is higher compare to the 40% yield with the normal size copper powder under the same reaction condition.

  8. Preparation of Aun quantum clusters with catalytic activity in β-cyclodextrin polyurethane nanosponges.

    Science.gov (United States)

    Vasconcelos, Diego Andrade; Kubota, Tatiana; Santos, Douglas C; Araujo, Marcia V G; Teixeira, Zaine; Gimenez, Iara F

    2016-01-20

    Here we report the use of β-cyclodextrin polyurethane nanosponges cross-linked with 1,6-hexamethylene diisocyanate as a template for the preparation of Aun quantum clusters, by the core-etching of glutathione-capped Au nanoparticles. The study of temporal evolution of the core-etching process using different Au concentrations indicated that formation of Aun clusters embedded in the nanosponge is favored by the use of lower Au concentrations, since it began at shorter times and lead to higher cluster loading. An estimation of the number of Au atoms based on the maximum photoluminescence wavelength suggested that, depending on the Au concentration and the core etching time, clusters with 11-15 atoms were formed. After excluding the possibility of an inclusion complex formation, evaluation of the catalytic activity of nanosponge-loaded Aun clusters toward the reduction of 4-nitrophenol has shown that the reaction is catalyzed by the Aun clusters with no induction time, following the Langmuir-Hinshelwood kinetic model. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. PREPARATION, CHARACTERIZATION AND CATALYTIC ACTIVITY OF CuO/TS-1 ON BENZENE HYDROXYLATION REACTION

    Directory of Open Access Journals (Sweden)

    Nuni Widiarti

    2011-11-01

    Full Text Available CuO/TS-1 catalysts have been prepared and tested in the benzene hydroxylation. TS-1 was synthesized by hydrothermalmethod, while CuO/TS-1 was prepared by impregnation method using Cu(NO2.3H2O as precursor. Catalysts werecharacterized by using X-ray diffraction (XRD, infrared spectroscopy (IR, and N2 adsorption-desorption techniques.The catalytic activity was tested in the hydroxylation reaction of benzene. The products were analyzed using gaschromatography. Catalyst characterization by XRD and IR techniques have showed that the catalyst structure was aMFI type of zeolite. XRD pattern have showed the orthorombic structure and indicated the presence of CuOaggregation. The results of the pyridine adsorption have found that the acidity of TS-1 and CuO/TS-1 were a Lewis acidand it’s increased with an increasing amount of CuO loading. The results of nitrogen adsorption analysis have showeddecreasing of surface areas of catalyst with increasing amount of CuO loading. The optimum conditions of benzenehydroxylation was observed by 1%CuO/TS-1 catalyst at 70 °C, reaction time 2 h and acetic acid as the solvent yielded27.6% of phenol with phenol selectivity was 75.5%.

  10. DNA/RNA hybrid substrates modulate the catalytic activity of purified AID.

    Science.gov (United States)

    Abdouni, Hala S; King, Justin J; Ghorbani, Atefeh; Fifield, Heather; Berghuis, Lesley; Larijani, Mani

    2018-01-01

    Activation-induced cytidine deaminase (AID) converts cytidine to uridine at Immunoglobulin (Ig) loci, initiating somatic hypermutation and class switching of antibodies. In vitro, AID acts on single stranded DNA (ssDNA), but neither double-stranded DNA (dsDNA) oligonucleotides nor RNA, and it is believed that transcription is the in vivo generator of ssDNA targeted by AID. It is also known that the Ig loci, particularly the switch (S) regions targeted by AID are rich in transcription-generated DNA/RNA hybrids. Here, we examined the binding and catalytic behavior of purified AID on DNA/RNA hybrid substrates bearing either random sequences or GC-rich sequences simulating Ig S regions. If substrates were made up of a random sequence, AID preferred substrates composed entirely of DNA over DNA/RNA hybrids. In contrast, if substrates were composed of S region sequences, AID preferred to mutate DNA/RNA hybrids over substrates composed entirely of DNA. Accordingly, AID exhibited a significantly higher affinity for binding DNA/RNA hybrid substrates composed specifically of S region sequences, than any other substrates composed of DNA. Thus, in the absence of any other cellular processes or factors, AID itself favors binding and mutating DNA/RNA hybrids composed of S region sequences. AID:DNA/RNA complex formation and supporting mutational analyses suggest that recognition of DNA/RNA hybrids is an inherent structural property of AID. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Protection of tobacco cells from oxidative copper toxicity by catalytically active metal-binding DNA oligomers.

    Science.gov (United States)

    Iwase, Junichiro; Furukawa, Hiroka; Hiramatsu, Takuya; Bouteau, François; Mancuso, Stefano; Tanaka, Kenichiro; Okazaki, Toshihiko; Kawano, Tomonori

    2014-03-01

    The impact of copper ions on the oxidative and calcium signal transductions, leading to cell death in plant cells, have been documented. Copper induces a series of biological and chemical reactions in plant cells including the oxidative burst reflecting the production of reactive oxygen species and the stimulation of calcium channel opening allowing a transient increase in cytosolic calcium concentrations. These early events, completed within a few minutes after the contact with copper, are known to trigger the development of cell death. The effects of DNA fragments with copper-binding motifs as novel plant cell-protecting agents were assessed using cell suspension cultures of transgenic tobacco (Nicotiana tabacum L., cell line BY-2) expressing the aequorin gene. The addition of GC-rich double-stranded DNA fragments, prior to the addition of copper ions, effectively blocked both the copper-induced calcium influx and cell death. In addition, the DNA-Cu complex examined was shown to possess superoxide-scavenging catalytic activity, suggesting that DNA-mediated protection of the cells from copper toxicity is due to the removal of superoxide. Lastly, a possible mechanism of DNA-Cu interaction and future applications of these DNA fragments in the protection of plant roots from metal toxicity or in aid of phyto-remediation processes are discussed.

  12. Bio-based phenols and fuel production from catalytic microwave pyrolysis of lignin by activated carbons.

    Science.gov (United States)

    Bu, Quan; Lei, Hanwu; Wang, Lu; Wei, Yi; Zhu, Lei; Zhang, Xuesong; Liu, Yupeng; Yadavalli, Gayatri; Tang, Juming

    2014-06-01

    The aim of this study is to explore catalytic microwave pyrolysis of lignin for renewable phenols and fuels using activated carbon (AC) as a catalyst. A central composite experimental design (CCD) was used to optimize the reaction condition. The effects of reaction temperature and weight hourly space velocity (WHSV, h(-1)) on product yields were investigated. GC/MS analysis showed that the main chemical compounds of bio-oils were phenols, guaiacols, hydrocarbons and esters, most of which were ranged from 71% to 87% of the bio-oils depending on different reaction conditions. Bio-oils with high concentrations of phenol (45% in the bio-oil) were obtained. The calorific value analysis revealed that the high heating values (HHV) of the lignin-derived biochars were from 20.4 to 24.5 MJ/kg in comparison with raw lignin (19 MJ/kg). The reaction mechanism of this process was analyzed. Copyright © 2014 Elsevier Ltd. All rights reserved.

  13. Role of the NC-loop in catalytic activity and stability in lipase from Fervidobacterium changbaicum.

    Directory of Open Access Journals (Sweden)

    Binchun Li

    Full Text Available Flexible NC-loops between the catalytic domain and the cap domain of the α/β hydrolase fold enzymes show remarkable diversity in length, sequence, and configuration. Recent investigations have suggested that the NC-loop might be involved in catalysis and substrate recognition in many enzymes from the α/β hydrolase fold superfamily. To foster a deep understanding of its role in catalysis, stability, and divergent evolution, we here systemically investigated the function of the NC-loop (residues 131-151 in a lipase (FClip1 from thermophilic bacterium Fervidobacterium changbaicum by loop deletion, alanine-scanning mutagenesis and site-directed mutagenesis. We found that the upper part of the NC-loop (residues 131-138 was of great importance to enzyme catalysis. Single substitutions in this region could fine-tune the activity of FClip1 as much as 41-fold, and any deletions from this region rendered the enzyme completely inactive. The lower part of the NC-loop (residues 139-151 was capable of enduring extensive deletions without loss of activity. The shortened mutants in this region were found to show both improved activity and increased stability simultaneously. We therefore speculated that the NC-loop, especially the lower part, would be a perfect target for enzyme engineering to optimize the enzymatic properties, and might present a hot zone for the divergent evolution of α/β hydrolases. Our findings may provide an opportunity for better understanding of the mechanism of divergent evolution in the α/β hydrolase fold superfamily, and may also guide the design of novel biocatalysts for industrial applications.

  14. Green Adeptness in the Synthesis and Stabilization of Copper Nanoparticles: Catalytic, Antibacterial, Cytotoxicity, and Antioxidant Activities

    Science.gov (United States)

    Din, Muhammad Imran; Arshad, Farhan; Hussain, Zaib; Mukhtar, Maria

    2017-12-01

    Copper nanoparticles (CuNPs) are of great interest due to their extraordinary properties such as high surface-to-volume ratio, high yield strength, ductility, hardness, flexibility, and rigidity. CuNPs show catalytic, antibacterial, antioxidant, and antifungal activities along with cytotoxicity and anticancer properties in many different applications. Many physical and chemical methods have been used to synthesize nanoparticles including laser ablation, microwave-assisted process, sol-gel, co-precipitation, pulsed wire discharge, vacuum vapor deposition, high-energy irradiation, lithography, mechanical milling, photochemical reduction, electrochemistry, electrospray synthesis, hydrothermal reaction, microemulsion, and chemical reduction. Phytosynthesis of nanoparticles has been suggested as a valuable alternative to physical and chemical methods due to low cytotoxicity, economic prospects, environment-friendly, enhanced biocompatibility, and high antioxidant and antimicrobial activities. The review explains characterization techniques, their main role, limitations, and sensitivity used in the preparation of CuNPs. An overview of techniques used in the synthesis of CuNPs, synthesis procedure, reaction parameters which affect the properties of synthesized CuNPs, and a screening analysis which is used to identify phytochemicals in different plants is presented from the recent published literature which has been reviewed and summarized. Hypothetical mechanisms of reduction of the copper ion by quercetin, stabilization of copper nanoparticles by santin, antimicrobial activity, and reduction of 4-nitrophenol with diagrammatic illustrations are given. The main purpose of this review was to summarize the data of plants used for the synthesis of CuNPs and open a new pathway for researchers to investigate those plants which have not been used in the past.

  15. Facile preparation of SERS and catalytically active Au nanostructures using furfuryl derivatives

    Science.gov (United States)

    Kim, Ki-Jung; Kim, Hyun-Chul; Park, Minsun; Huh, Seong

    2017-08-01

    Six different types of Au nanostructures with rough surfaces were readily prepared through the redox reactions between Au precursor, AuCl4-, and furfuryl derivatives without extra metal surface capping ligands, in deionized water at room temperature. Furfuryl alcohol (FA) or furfurylamine (FFA) was used as a sole reducing agent for the reduction of Au precursor. Both FA and FFA effectively polymerized during the redox reactions to form polyfuran polymers. These polymers are thought to act as surface capping ligands during the formation of Au nanostructures. Experiments were conducted with three different concentrations of each furfuryl derivative. Interestingly, Au particles prepared from the reaction with varying concentration of FA or FFA showed large differences in size, and revealed that the higher the ratios of [FA]/[AuCl4-] or [FFA]/[AuCl4-], the smaller the size of Au particles. The size of Au particles was in the range of 1 μm to under 30 nm. Among these samples, two nanostructured Au particles, AuFA-4 and AuFFA-1, deposited on a Si wafer by a simple drop-casting method, were revealed as highly active surface-enhanced Raman scattering (SERS) substrates for the detection of methylene blue (MB) and crystal violet (CV). High SERS enhancement factors (EFs) of 106 ∼ 108 for MB and CV were observed. Small size Au nanoparticles (AuFFA-2 and AuFFA-4) were also found to be very active for the catalytic hydrogenation of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 at room temperature. AuFFA-2 could be recycled eight times, without losing its activity.

  16. Forecasting the zeolite-containing catalyst activity in catalytic cracking technology taking into account the feedstock composition

    Science.gov (United States)

    Ivashkina, Elena; Nazarova, Galina; Shafran, Tatyana; Stebeneva, Valeriya

    2017-08-01

    The effect of the feedstock composition and the process conditions on the current catalyst activity in catalytic cracking technology using a mathematical model is performed in this research. The mathematical model takes into account the catalyst deactivation by coke for primary and secondary cracking reactions. The investigation results have shown that the feedstock has significant effect on the yield and the content of coke on the catalyst. Thus, the relative catalyst activity is significantly reduced by 7.5-10.7 %. With increasing the catalytic cracking temperature due to the catalyst flow temperature rising, the coke content and the yield per feedstock increase and the catalyst activity decreases by 5.3-7.7%. Rising the process temperature together with the catalyst circulation ratio contributes to increase of the coke yield per feedstock in the catalytic cracking and decrease of the coke content on the catalyst. It is connected with the catalyst flow rising to the riser and the contact time decreasing in the reaction zone. Also, the catalyst activity decreases in the range of 3.8-5.5% relatively to the regenerated catalyst activity (83 %).

  17. Developmental Exposure to Pesticides Alters Motor Activity and Coordination in Rats: Sex Differences and Underlying Mechanisms.

    Science.gov (United States)

    Gómez-Giménez, B; Felipo, V; Cabrera-Pastor, A; Agustí, A; Hernández-Rabaza, V; Llansola, M

    2018-02-01

    It has been proposed that developmental exposure to pesticides contributes to increasing prevalence of neurodevelopmental disorders in children, such as attention deficit with hyperactivity (ADHD) and to alterations in coordination skills. However, the mechanisms involved in these alterations remain unclear. We analyzed the effects on spontaneous motor activity and motor coordination of developmental exposure to a representative pesticide of each one of the four main chemical families: organophosphates (chlorpyrifos), carbamates (carbaryl), organochlorines (endosulfan), and pyrethroids (cypermethrin). Pesticides were administered once a day orally, in a sweet jelly, from gestational day 7 to post natal day 21. Spontaneous motor activity was assessed by an actimeter and motor coordination using the rotarod, when rats were adults. The effects were analyzed separately in males and females. Extracellular GABA in cerebellum and NMDA receptor subunits in hippocampus were assessed as possible underlying mechanisms of motor alterations. Motor coordination was impaired by developmental exposure to endosulfan, cypermethrin, and chlorpyrifos in females but not in males. The effect of endosulfan and cypermethrin would be due to increased extracellular GABA in cerebellum, which remains unaltered in male rats. Chlorpyrifos increased motor activity in males and females. Cypermethrin decreased motor activity mainly in males. In male rats, but not in females, expression of the NR2B subunit of NMDA receptor in hippocampus correlated with motor activity. These results show sex-specific effects of different pesticides on motor activity and coordination, associated with neurotransmission alterations. These data contribute to better understand the relationship between developmental exposure to the main pesticide families and motor disorders in children.

  18. Physical activity, physical fitness, gross motor coordination, and metabolic syndrome: focus of twin research in Portugal.

    Science.gov (United States)

    Maia, José António Ribeiro; Santos, Daniel; de Freitas, Duarte Luis; Thomis, Martine

    2013-02-01

    A very brief history of Portuguese twin research in sport and human movement sciences is presented. Recruitment procedures, zygosity determination, and phenotypes are given for twins and their parents from the mainland, and Azores and Madeira archipelagos. Preliminary findings are mostly related to physical activity, health-related physical fitness, gross motor coordination, neuromotor development, and metabolic syndrome traits.

  19. Developmental Coordination Disorder, Gender, and Body Weight: Examining the Impact of Participation in Active Play

    Science.gov (United States)

    Cairney, John; Kwan, Matthew Y. W.; Hay, John A.; Faught, Brent E.

    2012-01-01

    Background: To examine whether differences in participation in active play (PAP) can account for gender differences in the relationship between Developmental Coordination Disorder (DCD) and body weight/fat (BMI and percentage fat) in youth. Methods: A cross-sectional investigation of students in grades four through eight (n = 590). Height, weight…

  20. METHOD FOR DETERMINING THE SPATIAL COORDINATES IN THE ACTIVE STEREOSCOPIC SYSTEM

    Directory of Open Access Journals (Sweden)

    Valery V. Korotaev

    2014-11-01

    Full Text Available The paper deals with the structural scheme of active stereoscopic system and algorithm of its operation, providing the fast calculation of the spatial coordinates. The system includes two identical cameras, forming a stereo pair, and a laser scanner, which provides vertical scanning of the space before the system by the laser beam. A separate synchronizer provides synchronous operation of the two cameras. The developed algorithm of the system operation is implemented in MATLAB. In the proposed algorithm, the influence of background light is eliminated by interframe processing. The algorithm is based on precomputation of coordinates for epipolar lines and corresponding points in stereoscopic image. These data are used to quick calculation of the three-dimensional coordinates of points that form the three-dimensional images of objects. Experiment description on a physical model is given. Experimental results confirm the efficiency of the proposed active stereoscopic system and its operation algorithm. The proposed scheme of active stereoscopic system and calculating method for the spatial coordinates can be recommended for creation of stereoscopic systems, operating in real time and at high processing speed: devices for face recognition, systems for the position control of railway track, automobile active safety systems.

  1. A control architecture to coordinate distributed generators and active power filters coexisting in a microgrid

    DEFF Research Database (Denmark)

    Hashempour, Mohammad M.; Savaghebi, Mehdi; Quintero, Juan Carlos Vasquez

    2016-01-01

    This paper proposes a control architecture of distributed generators (DGs) inverters and shunt active power filters (APFs) in microgrids to compensate voltage harmonics in a coordinated way. For this, a hierarchical control structure is proposed that includes two control levels. The primary (local...

  2. A Control Architecture to Coordinate Distributed Generators and Active Power Filters Coexisting in a Microgrid

    DEFF Research Database (Denmark)

    Hashempour, Mohammad M.; Firoozabadi, Mehdi Savaghebi; Quintero, Juan Carlos Vasquez

    2016-01-01

    This paper proposes a control architecture of distributed generators (DGs) inverters and shunt active power filters (APFs) in microgrids to compensate voltage harmonics in a coordinated way. For this, a hierarchical control structure is proposed that includes two control levels. The primary (local...

  3. Catalytically-etched hexagonal boron nitride flakes and their surface activity

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Do-Hyun, E-mail: nanotube@korea.ac.kr [School of Electrical Engineering, Korea University, 5-ga, Anam-dong, Seongbuk-gu, Seoul 136-713 (Korea, Republic of); Lee, Minwoo; Ye, Bora [Green Manufacturing 3Rs R& D Group, Korea Institute of Industrial Technology, Ulsan 681-310 (Korea, Republic of); Jang, Ho-Kyun; Kim, Gyu Tae [School of Electrical Engineering, Korea University, 5-ga, Anam-dong, Seongbuk-gu, Seoul 136-713 (Korea, Republic of); Lee, Dong-Jin [New Functional Components Research Team, Korea Institute of Footware & Leather Technology, 152 Danggamseo-ro, Busanjin-gu, Busan 614-100 (Korea, Republic of); Kim, Eok-Soo [Green Manufacturing 3Rs R& D Group, Korea Institute of Industrial Technology, Ulsan 681-310 (Korea, Republic of); Kim, Hong Dae, E-mail: hdkim@kitech.re.kr [Green Manufacturing 3Rs R& D Group, Korea Institute of Industrial Technology, Ulsan 681-310 (Korea, Republic of)

    2017-04-30

    Highlights: • Hexagonal boron nitride flakes are etched at low temperature in air by catalysts. • The presence of transition metal oxides produces an etched structure in the flakes. • Etched surfaces become highly active due to vacancy defects formed in the flakes. - Abstract: Hexagonal boron nitride (h-BN) is a ceramic compound which is thermally stable up to 1000 °C in air. Due to this, it is a very challenging task to etch h-BN under air atmosphere at low temperature. In this study, we report that h-BN flakes can be easily etched by oxidation at 350 °C under air atmosphere in the presence of transition metal (TM) oxide. After selecting Co, Cu, and Zn elements as TM precursors, we simply oxidized h-BN sheets impregnated with the TM precursors at 350 °C in air. As a result, microscopic analysis revealed that an etched structure was created on the surface of h-BN flakes regardless of catalyst type. And, X-ray diffraction patterns indicated that the air oxidation led to the formation of Co{sub 3}O{sub 4}, CuO, and ZnO from each precursor. Thermogravimetric analysis showed a gradual weight loss in the temperature range where the weight of h-BN flakes increased by air oxidation. As a result of etching, pore volume and pore area of h-BN flakes were increased after catalytic oxidation in all cases. In addition, the surface of h-BN flakes became highly active when the h-BN samples were etched by Co{sub 3}O{sub 4} and CuO catalysts. Based on these results, we report that h-BN flakes can be easily oxidized in the presence of a catalyst, resulting in an etched structure in the layered structure.

  4. Developmental Coordination Disorder, Sex, and Activity Deficit over Time: A Longitudinal Analysis of Participation Trajectories in Children with and without Coordination Difficulties

    Science.gov (United States)

    Cairney, John; Hay, John A.; Veldhuizen, Scott; Missiuna, Cheryl; Faught, Brent E.

    2010-01-01

    Aim: Children with developmental coordination disorder (DCD) are known to participate in active play less than typically developing children. However, it is not known whether the activity deficit between children with and without DCD widens or diminishes over time. Method: Data were obtained from a large, prospective cohort study of children…

  5. Use of Inertial Central to Analyse Skill of Inter-Limb Coordination in Sport Activities

    Directory of Open Access Journals (Sweden)

    Caritu Yanis

    2011-12-01

    Full Text Available Kinematical movement analysis is regularly conducted through 3D video device, studying great number of parameters. The aim of this study is to focus on movement variability, following dynamical system perspectives, that is suitable through the use of inertial central to collect data in ecological context. This study gives two examples of sport activity (breaststroke swimming and rock climbing for which the motor skill was analysed through a macroscopic parameter, notably upper-lower limb coordination. The results showed higher intraindividual movement variability in experts while beginners used basic modes of coordination.

  6. Activating basal-plane catalytic activity of two-dimensional MoS2 monolayer with remote hydrogen plasma

    KAUST Repository

    Cheng, Chia-Chin

    2016-09-10

    Two-dimensional layered transition metal dichalcogenide (TMD) materials such as Molybdenum disufide (MoS2) have been recognized as one of the low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER). The crystal edges that account for a small percentage of the surface area, rather than the basal planes, of MoS2 monolayer have been confirmed as their active catalytic sites. As a result, extensive efforts have been developing in activating the basal planes of MoS2 for enhancing their HER activity. Here, we report a simple and efficient approach-using a remote hydrogen-plasma process-to creating S-vacancies on the basal plane of monolayer crystalline MoS2; this process can generate high density of S-vacancies while mainly maintaining the morphology and structure of MoS2 monolayer. The density of S-vacancies (defects) on MoS2 monolayers resulted from the remote hydrogen-plasma process can be tuned and play a critical role in HER, as evidenced in the results of our spectroscopic and electrical measurements. The H2-plasma treated MoS2 also provides an excellent platform for systematic and fundamental study of defect-property relationships in TMDs, which provides insights for future applications including electrical, optical and magnetic devices. © 2016 Elsevier Ltd.

  7. Identification of residues in the heme domain of soluble guanylyl cyclase that are important for basal and stimulated catalytic activity.

    Directory of Open Access Journals (Sweden)

    Padmamalini Baskaran

    Full Text Available Nitric oxide signals through activation of soluble guanylyl cyclase (sGC, a heme-containing heterodimer. NO binds to the heme domain located in the N-terminal part of the β subunit of sGC resulting in increased production of cGMP in the catalytic domain located at the C-terminal part of sGC. Little is known about the mechanism by which the NO signaling is propagated from the receptor domain (heme domain to the effector domain (catalytic domain, in particular events subsequent to the breakage of the bond between the heme iron and Histidine 105 (H105 of the β subunit. Our modeling of the heme-binding domain as well as previous homologous heme domain structures in different states point to two regions that could be critical for propagation of the NO activation signal. Structure-based mutational analysis of these regions revealed that residues T110 and R116 in the αF helix-β1 strand, and residues I41 and R40 in the αB-αC loop mediate propagation of activation between the heme domain and the catalytic domain. Biochemical analysis of these heme mutants allows refinement of the map of the residues that are critical for heme stability and propagation of the NO/YC-1 activation signal in sGC.

  8. Enhancement in the Catalytic Activity of Pd/USY in the Heck Reaction Induced by H2 Bubbling

    Directory of Open Access Journals (Sweden)

    Miki Niwa

    2010-12-01

    Full Text Available Pd was loaded on ultra stable Y (USY zeolites prepared by steaming NH4-Y zeolite under different conditions. Heck reactions were carried out over the prepared Pd/USY. We found that H2 bubbling was effective in improving not only the catalytic activity of Pd/USY, but also that of other supported Pd catalysts and Pd(OAc2. Moreover, the catalytic activity of Pd/USY could be optimized by choosing appropriate steaming conditions for the preparation of the USY zeolites; Pd loaded on USY prepared at 873 K with 100% H2O gave the highest activity (TOF = 61,000 h−1, which was higher than that of Pd loaded on other kinds of supports. The prepared Pd/USY catalysts were applicable to the Heck reactions using various kinds of substrates including bromo- and chloro-substituted aromatic and heteroaromatic compounds. Characterization of the acid properties of the USY zeolites revealed that the strong acid site (OHstrong generated as a result of steaming had a profound effect on the catalytic activity of Pd.

  9. Pt skin coated hollow Ag-Pt bimetallic nanoparticles with high catalytic activity for oxygen reduction reaction

    Science.gov (United States)

    Fu, Tao; Huang, Jianxing; Lai, Shaobo; Zhang, Size; Fang, Jun; Zhao, Jinbao

    2017-10-01

    The catalytic activity and stability of electrocatalyst is critical for the commercialization of fuel cells, and recent reports reveal the great potential of the hollow structures with Pt skin coat for developing high-powered electrocatalysts due to their highly efficient utilization of the Pt atoms. Here, we provide a novel strategy to prepare the Pt skin coated hollow Ag-Pt structure (Ag-Pt@Pt) of ∼8 nm size at room temperature. As loaded on the graphene, the Ag-Pt@Pt exhibits a remarkable mass activity of 0.864 A/mgPt (at 0.9 V, vs. reversible hydrogen electrode (RHE)) towards oxygen reduction reaction (ORR), which is 5.30 times of the commercial Pt/C catalyst, and the Ag-Pt@Pt also shows a better stability during the ORR catalytic process. The mechanism of this significant enhancement can be attributed to the higher Pt utilization and the unique Pt on Ag-Pt surface structure, which is confirmed by the density functional theory (DFT) calculations and other characterization methods. In conclusion, this original work offers a low-cost and environment-friendly method to prepare a high active electrocatalyst with cheaper price, and this work also discloses the correlation between surface structures and ORR catalytic activity for the hollow structures with Pt skin coat, which can be instructive for designing novel advanced electrocatalysts for fuel cells.

  10. Role of regulatory subunits and protein kinase inhibitor (PKI) in determining nuclear localization and activity of the catalytic subunit of protein kinase A.

    Science.gov (United States)

    Wiley, J C; Wailes, L A; Idzerda, R L; McKnight, G S

    1999-03-05

    Regulation of protein kinase A by subcellular localization may be critical to target catalytic subunits to specific substrates. We employed epitope-tagged catalytic subunit to correlate subcellular localization and gene-inducing activity in the presence of regulatory subunit or protein kinase inhibitor (PKI). Transiently expressed catalytic subunit distributed throughout the cell and induced gene expression. Co-expression of regulatory subunit or PKI blocked gene induction and prevented nuclear accumulation. A mutant PKI lacking the nuclear export signal blocked gene induction but not nuclear accumulation, demonstrating that nuclear export is not essential to inhibit gene induction. When the catalytic subunit was targeted to the nucleus with a nuclear localization signal, it was not sequestered in the cytoplasm by regulatory subunit, although its activity was completely inhibited. PKI redistributed the nuclear catalytic subunit to the cytoplasm and blocked gene induction, demonstrating that the nuclear export signal of PKI can override a strong nuclear localization signal. With increasing PKI, the export process appeared to saturate, resulting in the return of catalytic subunit to the nucleus. These results demonstrate that both the regulatory subunit and PKI are able to completely inhibit the gene-inducing activity of the catalytic subunit even when the catalytic subunit is forced to concentrate in the nuclear compartment.

  11. Sulfonate Ionic Liquid as a Stable and Active Catalyst for Levoglucosenone Production from Saccharides via Catalytic Pyrolysis

    Directory of Open Access Journals (Sweden)

    Jun-ichiro Hayashi

    2013-09-01

    Full Text Available In this study, various types of ionic liquids (ILs were examined for catalytic activity in the pyrolysis of cellulose for the production of levoglucosenone, which is a valuable and versatile compound for the synthesis of a variety of novel compounds. Cellulose was simply mixed with the ILs and subjected for the pyrolysis, typically at 300 °C, to produce volatile products, including levoglucosenone, separated from the ILs phase. The type of IL anion significantly affected the catalysis, and the use of ILs bearing sulfonate anion resulted in distinguished yields of levoglucosenone and IL recoveries for the reutilization. Detailed thermogravimetric analysis and discussion on properties of ILs revealed the active and thermally stable nature of the sulfonate ILs. Catalytic pyrolysis with those ILs was applied to the conversion of other saccharides composed of glucose molecules, resulting in a preferential formation of levoglucosenone but at low yields as compared to that from cellulose.

  12. Michael addition of dehydroalanine-containing MAPK peptides to catalytic lysine inhibits the activity of phosphothreonine lyase.

    Science.gov (United States)

    Zhang, Yuan; Yang, Ru; Huang, Juan; Liang, Qiujin; Guo, Yanmin; Bian, Weixiang; Luo, Lingfei; Li, Hongtao

    2015-11-30

    The phosphothreonine lyases OspF and SpvC irreversibly inactivate host dual-phosphorylated mitogen-activated protein kinases (MAPKs) [pThr-X-pTyr motif] through β-elimination. We found that dual-phosphorylated (pSer-X-pTyr) MAPK substrate peptides and their resulting catalytic products cross-link to OspF and SpvC. Mass spectrometry results revealed that these linkages form between lysine, which acts as a general base, and dehydroalanine (Dha) on catalytic products. The nucleophilic addition efficiency is dependent on the K136 residue being in a deprotonated state. Peptide cross-linking inhibits the activity of SpvC and blocks the inactivation of MAPK signaling by SpvC. Small compounds mimicking these sequences may act as phosphothreonine lyase inhibitors. Copyright © 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  13. Facet-dependent catalytic activity of platinum nanocrystals for triiodide reduction in dye-sensitized solar cells.

    Science.gov (United States)

    Zhang, Bo; Wang, Dong; Hou, Yu; Yang, Shuang; Yang, Xiao Hua; Zhong, Ju Hua; Liu, Jian; Wang, Hai Feng; Hu, P; Zhao, Hui Jun; Yang, Hua Gui

    2013-01-01

    Platinum (Pt) nanocrystals have demonstrated to be an effective catalyst in many heterogeneous catalytic processes. However, pioneer facets with highest activity have been reported differently for various reaction systems. Although Pt has been the most important counter electrode material for dye-sensitized solar cells (DSCs), suitable atomic arrangement on the exposed crystal facet of Pt for triiodide reduction is still inexplicable. Using density functional theory, we have investigated the catalytic reaction processes of triiodide reduction over {100}, {111} and {411} facets, indicating that the activity follows the order of Pt(111) > Pt(411) > Pt(100). Further, Pt nanocrystals mainly bounded by {100}, {111} and {411} facets were synthesized and used as counter electrode materials for DSCs. The highest photovoltaic conversion efficiency of Pt(111) in DSCs confirms the predictions of the theoretical study. These findings have deepened the understanding of the mechanism of triiodide reduction at Pt surfaces and further screened the best facet for DSCs successfully.

  14. The MOF-driven synthesis of supported palladium clusters with catalytic activity for carbene-mediated chemistry

    Science.gov (United States)

    Fortea-Pérez, Francisco R.; Mon, Marta; Ferrando-Soria, Jesús; Boronat, Mercedes; Leyva-Pérez, Antonio; Corma, Avelino; Herrera, Juan Manuel; Osadchii, Dmitrii; Gascon, Jorge; Armentano, Donatella; Pardo, Emilio

    2017-07-01

    The development of catalysts able to assist industrially important chemical processes is a topic of high importance. In view of the catalytic capabilities of small metal clusters, research efforts are being focused on the synthesis of novel catalysts bearing such active sites. Here we report a heterogeneous catalyst consisting of Pd4 clusters with mixed-valence 0/+1 oxidation states, stabilized and homogeneously organized within the walls of a metal-organic framework (MOF). The resulting solid catalyst outperforms state-of-the-art metal catalysts in carbene-mediated reactions of diazoacetates, with high yields (>90%) and turnover numbers (up to 100,000). In addition, the MOF-supported Pd4 clusters retain their catalytic activity in repeated batch and flow reactions (>20 cycles). Our findings demonstrate how this synthetic approach may now instruct the future design of heterogeneous catalysts with advantageous reaction capabilities for other important processes.

  15. CERTIFICATION REPORT The certification of the catalytic activity concentration of lactate dehydrogenase in ERM®-AD453k/IFCC

    OpenAIRE

    KUHLMANN JULIA; TOUSSAINT Brigitte; Schimmel, Heinz; Emons, Hendrik

    2016-01-01

    This report describes the production of ERM®-AD453k/IFCC, which is a material certified for the catalytic activity concentration of lactate dehydrogenase (LD). This material was produced in collaboration with the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) following ISO Guide 34:2009 [ ] and it is certified in accordance with ISO Guide 35:2006 [ ]. The starting material was a recombinant form of human LD isoenzyme 1 expressed in E. coli. It was produced, ...

  16. CERTIFICATION REPORT The certification of the catalytic activity concentration of alanine aminotransferase in ERM®-AD454k/IFCC

    OpenAIRE

    KUHLMANN JULIA; TOUSSAINT Brigitte; Schimmel, Heinz; Emons, Hendrik

    2016-01-01

    This report describes the production of ERM®-AD454k/IFCC, which is a material certified for the catalytic activity concentration of alanine aminotransferase (ALT). This material was produced in collaboration with the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) following ISO Guide 34:2009 [ ] and it is certified in accordance with ISO Guide 35:2006 [2]. The starting material was a recombinant form of human cytosolic ALT expressed in E. coli. It was produce...

  17. High catalytic activity of oriented 2.0.0 copper(I) oxide grown on graphene film

    OpenAIRE

    Primo, Ana; Esteve-Adell, Ivan; Blandez, Juan F.; Dhakshinamoorthy, Amarajothi; ?lvaro, Mercedes; Candu, Natalia; Coman, Simona M.; Parvulescu, Vasile I.; Garc?a, Hermenegildo

    2015-01-01

    Metal oxide nanoparticles supported on graphene exhibit high catalytic activity for oxidation, reduction and coupling reactions. Here we show that pyrolysis at 900 C under inert atmosphere of copper(II) nitrate embedded in chitosan films affords 1.1.1 facet-oriented copper nanoplatelets supported on few-layered graphene. Oriented (1.1.1) copper nanoplatelets on graphene undergo spontaneous oxidation to render oriented (2.0.0) copper(I) oxide nanoplatelets on few-layered graphen...

  18. Mononuclear Nickel(II Complexes with Schiff Base Ligands: Synthesis, Characterization, and Catalytic Activity in Norbornene Polymerization

    Directory of Open Access Journals (Sweden)

    Yi-Mei Xu

    2017-03-01

    Full Text Available The nickel(II catalyst has manifested higher catalytic activity compared to that of other late transition metal catalysts for norbornene polymerization. Therefore, several structurally similar trans-nickel(II compounds of N,O-chelate bidentate ligands were synthesized and characterized. Both the electronic effect and the steric hindrance influence polymerization. The molecular structures of 2, 4 and 5 were further confirmed by single-crystal X-ray diffraction.

  19. Improved surface-enhanced Raman and catalytic activities of reduced graphene oxide–osmium hybrid nano thin films

    OpenAIRE

    Kavitha, C.; Bramhaiah, K.; John, Neena S.; Aggarwal, Shantanu

    2017-01-01

    Reduced graphene oxide–osmium (rGO-Os) hybrid nano dendtrites have been prepared by simple liquid/liquid interface method for the first time. The method involves the introduction of phase-transfered metal organic precursor in toluene phase and GO dispersion in the aqueous phase along with hydrazine hydrate as the reducing agent. Dendritic networks of Os nanoparticles and their aggregates decorating rGO layers are obtained. The substrate shows improved catalytic and surface-enhanced activities...

  20. Improved surface-enhanced Raman and catalytic activities of reduced graphene oxide-osmium hybrid nano thin films

    Science.gov (United States)

    Kavitha, C.; Bramhaiah, K.; John, Neena S.; Aggarwal, Shantanu

    2017-09-01

    Reduced graphene oxide-osmium (rGO-Os) hybrid nano dendtrites have been prepared by simple liquid/liquid interface method for the first time. The method involves the introduction of phase-transfered metal organic precursor in toluene phase and GO dispersion in the aqueous phase along with hydrazine hydrate as the reducing agent. Dendritic networks of Os nanoparticles and their aggregates decorating rGO layers are obtained. The substrate shows improved catalytic and surface-enhanced activities comparable with previous reports. The catalytic activity was tested for the reduction of p-nitroaniline into p-phenyldiamine with an excess amount of NaBH4. The catalytic activity factors of these hybrid films are 2.3 s-1 g-1 (Os film) and 4.4 s-1 g-1 (rGO-Os hybrid film), which are comparable with other noble metal nanoparticles such as Au, Ag, but lower than Pd-based catalysts. Surface-enhanced Raman spectroscopy (SERS) measurements have been done on rhodamine 6G (R6G) and methylene blue dyes. The enhancement factor for the R6G adsorbed on rGO-Os thin film is 1.0 × 105 and for Os thin film is 7 × 103. There is a 14-fold enhancement observed for Os hybrids with rGO. The enhanced catalytic and SERS activities of rGO-Os hybrid thin film prepared by simple liquid/liquid interface method open up new challenges in electrocatalytic application and SERS-based detection of biomolecules.

  1. Movement-related activity in the periarcuate cortex of monkeys during coordinated eye and hand movements.

    Science.gov (United States)

    Kurata, Kiyoshi

    2017-09-20

    To determine the role of the periarcuate cortex during coordinated eye and hand movements in monkeys, the present study examined neuronal activity in this region during movement with the hand, eyes, or both as effectors toward a visuospatial target. Similar to the primary motor cortex (M1), the dorsal premotor cortex contained a higher proportion of neurons that were closely related to hand movements, whereas saccade-related neurons were frequently recorded from the frontal eye field (FEF). Interestingly, neurons that exhibited activity related to both eye and hand movements were recorded most frequently in the ventral premotor cortex (PMv), located between the FEF and M1. Neuronal activity in the periarcuate cortex was highly modulated during coordinated movements compared to either eye or hand movement only. Additionally, a small number of neurons were active specifically during one of the three task modes, which could be dissociated from the effector activity. In this case, neuron onset was either ahead of or behind the onset of eye and/or hand movement, and some neuronal activity lasted until reward delivery signaled successful completion of reaching. The present findings indicate that the periarcuate cortex, particularly the PMv, plays important roles in orchestrating coordinated movements from the initiation to the termination of reaching. Copyright © 2017, Journal of Neurophysiology.

  2. Hydrothermal synthesis, structure, heterogeneous catalytic activity and photoluminescent properties of a novel homoleptic Sm(III)-organic framework

    Energy Technology Data Exchange (ETDEWEB)

    Ay, Burak [Department of Chemistry, Arts and Science Faculty,Çukurova University, 01330 Adana (Turkey); Yildiz, Emel, E-mail: eeyildiz@cu.edu.tr [Department of Chemistry, Arts and Science Faculty,Çukurova University, 01330 Adana (Turkey); Felts, Ashley C.; Abboud, Khalil A. [Department of Chemistry, University of Florida, Gainesville, FL 32611 (United States)

    2016-12-15

    A novel metal-organic framework, (H{sub 2}pip){sub n}[Sm{sub 2}(pydc){sub 4}(H{sub 2}O){sub 2}]{sub n} (1) (H{sub 2}pydc=2,6-pyridinedicarboxylic acid, H{sub 2}pip=piperazine) has been synthesized under hydrothermal conditions and characterized by the elemental analysis, inductively coupled plasma (ICP) spectrometer, fourier transform infrared (FT-IR) spectra, thermogravimetric analysis (TGA), single crystal X-ray diffraction analysis and powder X-ray diffraction (PXRD). The structure of 1 was determined to be three-dimensional, linked along Sm-O-Sm chains. The asymmetric unit consisted of one singly anionic fragment consisting of Sm(III) coordinated to two H{sub 2}pydc ligands and one water, and one half of a protonated H{sub 2}pip, which sits on an inversion center. 1 exhibited luminescence emission bands at 534 nm at room temperature when excited at 440 nm. Its thermal behavior and catalytic performance were investigated and the selectivity was measured as 100% for the oxidation of thymol to thymoquinone. - Graphical abstract: A novel 3D lanthanide-organic framework has been synthesized under hydrothermal conditions. The thermal behavior and catalytic performance of 1 were investigated and its selectivity was measured as 100% for the oxidation of thymol to thymoquinone.

  3. Effect of structure and surface properties on the catalytic activity of nanodiamond in the conversion of 1,2-dichloroethane

    Science.gov (United States)

    Tveritinova, E. A.; Zhitnev, Yu. N.; Kulakova, I. I.; Maslakov, K. I.; Nesterova, E. A.; Kharlanov, A. N.; Ivanov, A. S.; Savilov, S. V.; Lunin, V. V.

    2015-04-01

    The catalytic activity of a detonation nanodiamond and its Ni-containing forms in the conversion of 1,2-dichloroethane is studied and compared with the activity of other carbon and nanocarbon materials: carbon nanotubes, "Dalan" synthetic diamond, and fluorinated graphite. The surface and structure of the carbon materials are characterized using XRD, diffuse reflectance IR spectroscopy, XPS, BET, and TPR. The catalytic properties of the materials are studied using the pulsed microcatalytic method. It is found that the synthetic diamond, the nanodiamond, and its Ni-containing forms are catalysts for dichloroethane conversion in a nitrogen atmosphere, where the main product is ethylene. It is noted that the catalytic activity of deactivated diamond catalysts is restored after hydrogen treatment. It is shown that the carbon structure of the nanodiamond and the "Dalan" synthetic diamond with hydrogen groups located on it plays a key role in the dichloroethane conversion. It is found that the nanodiamond acts simultaneously as a catalyst and an adsorbent of chlorine-containing products of dichloroethane conversion.

  4. Zn(II)-Coordinated Quantum Dot-FRET Nanosensors for the Detection of Protein Kinase Activity.

    Science.gov (United States)

    Lim, Butaek; Park, Ji-In; Lee, Kyung Jin; Lee, Jin-Won; Kim, Tae-Wuk; Kim, Young-Pil

    2015-07-23

    We report a simple detection of protein kinase activity using Zn(II)-mediated fluorescent resonance energy transfer (FRET) between quantum dots (QDs) and dye-tethered peptides. With neither complex chemical ligands nor surface modification of QDs, Zn(II) was the only metal ion that enabled the phosphorylated peptides to be strongly attached on the carboxyl groups of the QD surface via metal coordination, thus leading to a significant FRET efficiency. As a result, protein kinase activity in intermixed solution was efficiently detected by QD-FRET via Zn(II) coordination, especially when the peptide substrate was combined with affinity-based purification. We also found that mono- and di-phosphorylation in the peptide substrate could be discriminated by the Zn(II)-mediated QD-FRET. Our approach is expected to find applications for studying physiological function and signal transduction with respect to protein kinase activity.

  5. Synthesis, Characterization, and Antimicrobial Activities of Coordination Compounds of Aspartic Acid

    Directory of Open Access Journals (Sweden)

    T. O. Aiyelabola

    2016-01-01

    Full Text Available Coordination compounds of aspartic acid were synthesized in basic and acidic media, with metal ligand M : L stoichiometric ratio 1 : 2. The complexes were characterized using infrared, electronic and magnetic susceptibility measurements, and mass spectrometry. Antimicrobial activity of the compounds was determined against three Gram-positive and three Gram-negative bacteria and one fungus. The results obtained indicated that the availability of donor atoms used for coordination was a function of the pH of the solution in which the reaction was carried out. This resulted in varying geometrical structures for the complexes. The compounds exhibited a broad spectrum of activity and in some cases better activity than the standard.

  6. Regulation of expression and catalytic activity of Escherichia coli RsmG methyltransferase

    Science.gov (United States)

    Benítez-Páez, Alfonso; Villarroya, Magda; Armengod, M.-Eugenia

    2012-01-01

    RsmG is an AdoMet-dependent methyltransferase responsible for the synthesis of m7G527 in the 530 loop of bacterial 16S rRNA. This loop is universally conserved, plays a key role in ribosomal accuracy, and is a target for streptomycin binding. Loss of the m7G527 modification confers low-level streptomycin resistance and may affect ribosomal functioning. Here, we explore the mechanisms controlling RsmG expression and activity, which may somehow respond to the demand set by the amount of rRNA. We confirm that rsmG is the second member in a bicistronic operon and demonstrate that rsmG also has its own promoter, which appears, in actively growing cells, as a control device to offset both the relatively low stability of RsmG and inhibition of the operon promoter. RsmG levels decrease under conditions that down-regulate rRNA synthesis. However, coordination between rRNA and RsmG expression does not seem to occur at the level of transcription initiation. Instead, it might depend on the activity of an inverted repeated region, located between the rsmG promoter and ribosome binding site, which we show to work as a weak transcriptional terminator. To gain insights into the enzymatic mechanism of RsmG, highly conserved residues were mutated and the abilities of the resulting proteins to confer streptomycin resistance, to modify rRNA, and to bind AdoMet were explored. Our data demonstrate for the first time the critical importance of some residues located in the active site of Escherichia coli RsmG for the m7G modification process and suggest a role for them in rRNA binding and catalysis. PMID:22337945

  7. Theoretical explanation for the enhanced water-splitting catalytic activity in delithiated LiCoO2

    Science.gov (United States)

    Bajdich, Michal; Lu, Zhiyi; Norskov, Jens K.; Cui, Yi

    Layered LiCoO2 (LCO) is important battery material not well know for its electrochemical catalytic activity. On the other hand, layered 3 d -metal-oxyhydroxides, including CoOOH, are very active water-splitting (oxygen-evolution reaction, OER) catalysts in alkaline media with structure very similar to LCO. In this work, we use DFT+U calculations to explain the enhancement effect in OER catalytic activity in the electrochemically delithiated LCO (De-LCO). We analyze the surface stability and OER activity of the 5 most stable surface facets of LCO and the De-LCO, with 50% Li removed. Using standard thermodynamic approach of the theoretical OER overpotential, we show that all surface facets have more active sites under Li removal. Particularly, the non-polar facets are identified to be highly active and are further activated by the delithiation process, while the dominant (0001) surface has negligible activity. These findings are in very good agreement with our experimental investigation of LCO and De-LCO nanosheets and nanoparticles with well defined surface morphology.

  8. Catalytic activity and stability of glucose oxidase/horseradish peroxidase co-confined in macroporous silica foam.

    Science.gov (United States)

    Cao, Xiaodong; Li, Ying; Zhang, Zhiqiang; Yu, Jiachao; Qian, Jing; Liu, Songqin

    2012-12-21

    Investigation of the catalytic activity and stability of enzymes in confined nano/microspace provides valuable contributions to the fundamental understanding of biological reactions taking place on a mesoscopic scale within confined spaces. In this paper, macroporous silica foam (MSF) is used as a nanoreactor to co-confine glucose oxidase (GOD) and horseradish peroxidase (HRP). Then, the enzymatic cascade reactions, which act in tandem inside nanoreactors, for oxidation of glucose and 3,3',5,5'-tetramethylbenzidine (TMB) were studied. The catalytic kinetic parameters of apparent Michaelis constant (K(m)(app)) and maximum rate (V(max)) were obtained from Lineweaver-Burk plot by UV-vis spectrometry. Results showed that the catalytic activity of the co-confined enzymes is reduced compared to that of free enzymes in solution at room temperature. The stabilities of co-confined enzymes in denaturing agents, such as guanidinium chloride (GdmCl) and urea, were higher than those of free enzymes in solution. When employing a co-confined bienzyme system as a biosensor for the detection of glucose, a wider linear range of glucose was obtained for the co-confined bienzyme system than for free enzymes in solution.

  9. Preparation of silver nanoparticles/polydopamine functionalized polyacrylonitrile fiber paper and its catalytic activity for the reduction 4-nitrophenol

    Science.gov (United States)

    Lu, Shixiang; Yu, Jianying; Cheng, Yuanyuan; Wang, Qian; Barras, Alexandre; Xu, Wenguo; Szunerits, Sabine; Cornu, David; Boukherroub, Rabah

    2017-07-01

    The study reports on the preparation of polyacrylonitrile fiber paper (PANFP) functionalized with polydopamine (PD) and silver nanoparticles (Ag NPs), named as Ag NPs/PD/PANFP. The composite material was obtained via a simple two-step chemical process. First, a thin polydopamine layer was coated onto the PANFP surface through immersion into an alkaline dopamine (pH 8.5) aqueous solution at room temperature. The reductive properties of polydopamine were further exploited for the deposition of Ag NPs. The morphology and chemical composition of the composite material were characterized using scanning electron microscopy (SEM), X-ray diffraction pattern (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of the nanocomposite was evaluated for the reduction of 4-nitrophenol using sodium borohydride (NaBH4) at room temperature. The Ag NPs/PD/PANFP displayed good catalytic performance with a full reduction of 4-nitrophenol into the corresponding 4-aminophenol within 30 min. Moreover, the composite material exhibited a good stability up to 4 cycles without a significant loss of its catalytic activity.

  10. Tunable catalytic activities and selectivities of metal ion doped TiO2 nanoparticles--oxidation of organic compounds.

    Science.gov (United States)

    Wang, Anqi; Jing, Huanwang

    2014-01-21

    A series of metal ion doped TiO2 nanoparticles (M-TiO2, M = Cr(3+), Mn(2+), Fe(3+), V(5+), Zn(2+), Ni(2+), Ag(+), Cu(2+) and Co(2+)) were prepared by a facile co-precipitation approach and characterized by means of ICP-AES, N2 adsorption-desorption isotherms, XRD, TEM and HRTEM. Their catalytic performance was investigated via the oxidation of organic compounds. The variation of metal ion species and doping contents allowed tuning the catalytic properties of the M-TiO2. Among them, the catalyst Cu-10 displayed excellent activity (97.5%) in the oxidation of styrene and the selectivity of benzaldehyde was as high as 99.4%. Surprisingly, the product distribution of styrene oxidation experienced a reverse trend over the Co-TiO2 catalysts with different doping amounts of cobalt ions: Co-10 was in favor of forming benzaldehyde (80.2% selectivity), in contrast with Co-15, which produced styrene oxide as the dominant product (84.7% selectivity). The M-TiO2 catalysts also showed catalytic activities for the oxidation of benzyl alcohol and toluene to generate chlorine-free benzaldehyde in excellent selectivities (>99%).

  11. Ultrasonic Preparation of Nitrogen-doped TiO2 Nan crystalline Photo catalysts and Evaluation of Photo catalytic Activity

    Science.gov (United States)

    Zhang, Huifang; Lu, Zixin; Tang, Mengyao; Cao, Wenping; Cai, Kangni; Liu, Hanhu

    2017-12-01

    Pure TiO2 and N-doped nano-TiO2 photo catalysts were individually prepared following the sol-gel method under ultrasonic conditions. The photo catalytic decomposition of methyl orange (MO) solution under ultraviolet and visible light irradiation was used as a probe reaction to estimate their photo catalytic activities. The particle size, crystal structure, and optical properties of the prepared TiO2 were performed by X-ray diffraction, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The results suggest that ultrasound significantly reduced the size of the TiO2 particles, improved particle dispersion, which in turn improve the photo catalytic activity of TiO2 under ultraviolet light. Ultrasound also promoted the doping of non-metal nitrogen and markedly enhanced the visible light absorption capacity of the N-doped nano-TiO2. Compared with pure TiO2, the degradation rate for MO under visible light of U-N-TiO2 was increased by 70%.

  12. "Click" dendrimers: synthesis, redox sensing of Pd(OAc)2, and remarkable catalytic hydrogenation activity of precise Pd nanoparticles stabilized by 1,2,3-triazole-containing dendrimers.

    Science.gov (United States)

    Ornelas, Cátia; Aranzaes, Jaime Ruiz; Salmon, Lionel; Astruc, Didier

    2008-01-01

    "Click" dendrimers containing 1,2,3-triazolyl ligands that coordinate to PdII(OAc)2 have been synthesized in view of catalytic applications. Five of these dendrimers contain ferrocenyl termini directly attached to the triazole ligand in order to monitor the number of PdII that are introduced into the dendrimers by cyclic voltammetry. Reduction of the PdII-triazole dendrimers by using NaBH4 or methanol yields Pd nanoparticles (PdNPs) that are stabilized either by several dendrimers (G0, DSN) or by encapsulation inside a dendrimer (G1 and G2: DEN), as confirmed by TEM. Relative to PAMAM-DENs (PAMAM=poly(amidoamine)), the "click" DSNs and DENs show a remarkable efficiency and stability for olefin hydrogenation under ambient conditions of various substrates. The influence of the reductant of PdII bound to the dendrimers is dramatic, reduction with methanol leading to much higher catalytic activity than reduction with NaBH4. The most active NPs are shown to be those derived from dendrimer G1, and variation of its termini groups (ferrocenyl, alkyl, phenyl) allowed us to clearly delineate, optimize, and rationalize the role of the dendrimer frameworks on the catalytic efficiencies. Finally, hydrogenation of various substrates catalyzed by these PdNPs shows remarkable selectivity features.

  13. Activation of Al–Cu–Fe quasicrystalline surface: fabrication of a fine nanocomposite layer with high catalytic performance

    Directory of Open Access Journals (Sweden)

    Satoshi Kameoka

    2014-01-01

    Full Text Available A fine layered nanocomposite with a total thickness of about 200 nm was formed on the surface of an Al63Cu25Fe12 quasicrystal (QC. The nanocomposite was found to exhibit high catalytic performance for steam reforming of methanol. The nanocomposite was formed by a self-assembly process, by leaching the Al–Cu–Fe QC using a 5 wt% Na2CO3 aqueous solution followed by calcination in air at 873 K. The quasiperiodic nature of the QC played an important role in the formation of such a structure. Its high catalytic activity originated from the presence of highly dispersed copper and iron species, which also suppressed the sintering of nanoparticles.

  14. 3D hierarchical walnut-like CuO nanostructures: Preparation, characterization and their efficient catalytic activity for CO oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Weitang [Laboratory of Extreme Conditions Matter Properties, Southwest University of Science and Technology, Mianyang 621010 (China); Zhang, Yujuan [Laboratory of Extreme Conditions Matter Properties, Southwest University of Science and Technology, Mianyang 621010 (China); Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, CAEP, Mianyang, Sichuan 621900 (China); Duan, Tao, E-mail: duant@ustc.edu.cn [Laboratory of Extreme Conditions Matter Properties, Southwest University of Science and Technology, Mianyang 621010 (China); Zhu, Wenkun; Yi, Zao [Laboratory of Extreme Conditions Matter Properties, Southwest University of Science and Technology, Mianyang 621010 (China); Cui, Xudong, E-mail: xudcui@163.com [Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, CAEP, Mianyang, Sichuan 621900 (China)

    2016-07-15

    In this work, 3D hierarchical walnut-shaped, 2D nanosheet and 3D microspheres single phase CuO nanostructures are functioning as catalysts and supporting materials, differing from the conventional ways. The novel nanostructures were synthesized via hydrothermal method under a stainless steel autoclave. The as-prepared materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and H{sub 2} temperature-programmed reduction (H{sub 2}-TPR). The walnut-shaped structures with high O/Cu atomic ratio (1.22) exhibit high oxygen adsorption capacity and greatly enhanced catalytic activity. These results will be enrich the techniques for tuning the morphologies of metal oxide micro/nanostructures and open a new field in catalytic applications.

  15. Activation of Al–Cu–Fe quasicrystalline surface: fabrication of a fine nanocomposite layer with high catalytic performance

    Science.gov (United States)

    Kameoka, Satoshi; Tanabe, Toyokazu; Satoh, Futami; Terauchi, Masami; Tsai, An Pang

    2014-01-01

    A fine layered nanocomposite with a total thickness of about 200 nm was formed on the surface of an Al63Cu25Fe12 quasicrystal (QC). The nanocomposite was found to exhibit high catalytic performance for steam reforming of methanol. The nanocomposite was formed by a self-assembly process, by leaching the Al–Cu–Fe QC using a 5 wt% Na2CO3 aqueous solution followed by calcination in air at 873 K. The quasiperiodic nature of theQC played an important role in the formation of such a structure. Its high catalytic activity originated from the presence of highly dispersed copper and iron species, which also suppressed the sintering of nanoparticles. PMID:27877642

  16. Activation of Al-Cu-Fe quasicrystalline surface: fabrication of a fine nanocomposite layer with high catalytic performance

    Science.gov (United States)

    Kameoka, Satoshi; Tanabe, Toyokazu; Satoh, Futami; Terauchi, Masami; Tsai, An Pang

    2014-02-01

    A fine layered nanocomposite with a total thickness of about 200 nm was formed on the surface of an Al63Cu25Fe12 quasicrystal (QC). The nanocomposite was found to exhibit high catalytic performance for steam reforming of methanol. The nanocomposite was formed by a self-assembly process, by leaching the Al-Cu-Fe QC using a 5 wt% Na2CO3 aqueous solution followed by calcination in air at 873 K. The quasiperiodic nature of the QC played an important role in the formation of such a structure. Its high catalytic activity originated from the presence of highly dispersed copper and iron species, which also suppressed the sintering of nanoparticles.

  17. Morphology-dependent catalytic activity of plasmonic MoO3‑x for hydrolytic dehydrogenation of ammonia borane

    Science.gov (United States)

    Gong, Jie; Li, Zhixue; Zhang, Ting; Chen, Runze; Zheng, Xiaoying; Zhang, Gaoke

    Series of plasmonic MoO3‑x particles have been prepared by a facile solvothermal method to produce hydrogen via hydrolytic dehydrogenation of ammonia borane. Interestingly, the as-prepared MoO3‑x particles present various morphologies, i.e. flower, schistose and nanorod by simply tuning the reaction temperature and solvent volume ratio of distilled water and acetic acid. More importantly, these MoO3‑x particles with different morphologies exhibit various catalytic performances of NH3BH3 under the irradiation of visible light. Particularly, the flower-like MoO3‑x microstructure possesses the best catalytic activity for hydrogen production probably owing to the relatively large surface area and strong LSPR in the visible region.

  18. Probing substrate interactions in the active tunnel of a catalytically deficient cellobiohydrolase (Cel7)

    DEFF Research Database (Denmark)

    Westh, Peter; Colussi, Francieli; Sørensen, Trine Holst

    2015-01-01

    to be addressed in molecular descriptions of processivity and its driving forces. Here, we have used titration calorimetry to study interactions of cellooligosaccharides (COS) and a catalytically deficient variant (E212Q) of the enzyme Cel7A from Trichoderma reesei. This enzyme has about 10 glucopyranose sub...

  19. Electrically active, doped monocrystalline silicon nanoparticles produced by hot wire thermal catalytic pyrolysis

    CSIR Research Space (South Africa)

    Scriba, MR

    2011-05-01

    Full Text Available Doped silicon nanoparticles have successfully been produced by hot wire thermal catalytic pyrolysis at 40 mbar and a filament temperature of 1800 °C, using a mixture of silane and diborane or phosphine. All particles are monocrystalline with shapes...

  20. Influence of Al content on textural properties and catalytic activity of ...

    Indian Academy of Sciences (India)

    As Al content is increased (nSi/nAl = 25), the hierarchical porous catalysts exhibited ... high Al content. In addition, we investigate the effect of increasing Al content in the initial gel on the textural and catalytic properties of the hierarchical porous aluminosilicate ..... pared successfully using polystyrene spheres as hard tem-.

  1. A top-down approach to prepare silicoaluminophosphate molecular sieve nanocrystals with improved catalytic activity.

    Science.gov (United States)

    Yang, Miao; Tian, Peng; Wang, Chan; Yuan, Yangyang; Yang, Yue; Xu, Shutao; He, Yanli; Liu, Zhongmin

    2014-02-21

    Silicoaluminophosphate SAPO-34 molecular sieve nanocrystals have been prepared by a post-synthesis milling and recrystallization method, which is further proven to be universally applicable to other SAPO molecular sieves. The obtained SAPO-34 with reduced Si enrichment on the external surface shows considerably improved catalytic performance in the MTO reaction.

  2. Separating Catalytic Activity at Edges and Terraces on Platinum: Hydrogen Dissociation

    NARCIS (Netherlands)

    Groot, I.M.N.; Kleyn, A.W.; Juurlink, L.B.F.

    2013-01-01

    Heterogeneous catalysis relies to a large extent on the reactivity of metal nanoparticles. The surface of these particles consists of atomically smooth terraces and edges. As local environments of atoms in edges and terraces are different, their catalytic ability varies. This severely complicates

  3. The Influence of Palladium on the Structure and Catalytic Activity of ...

    African Journals Online (AJOL)

    NJD

    nations exhausted from motor vehicles, catalytic converters are the industry's standard technology.1 Therefore, the ... two portions, one portion was reduced in 10 % hydrogen balanced with nitrogen gas at 850 °C for 1 h, ... hydrogen were carried out at 400 °C. Energy regions of the photoelectrons were scanned at a pass ...

  4. Boosting catalytic activity of metal nanoparticles for 4-nitrophenol reduction: Modification of metal naoparticles with poly(diallyldimethylammonium chloride)

    Energy Technology Data Exchange (ETDEWEB)

    You, Jyun-Guo; Shanmugam, Chandirasekar [Department of Chemistry, National Sun Yat-sen University, Taiwan (China); Liu, Yao-Wen; Yu, Cheng-Ju [Department of Applied Physics and Chemistry, University of Taipei, Taiwan (China); Tseng, Wei-Lung, E-mail: tsengwl@mail.nsysu.edu.tw [Department of Chemistry, National Sun Yat-sen University, Taiwan (China); School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Taiwan (China); Center for Nanoscience and Nanotechnology, National Sun Yat-sen University, Taiwan (China)

    2017-02-15

    Highlights: • The choice of capping ligand determines catalytic activity of metal nanocatalysts. • PDDA-capped metal nanoparticles electrostatically interact with 4-NP and BH4{sup −}. • PDDA-capped metal nanoparticles have good recyclability and large scalability. • PDDA-capped Pd nanoparticles show the highest rate constant and activity parameter. - Abstract: Most of the previously reported studies have focused on the change in the size, morphology, and composition of metal nanocatalysts for improving their catalytic activity. Herein, we report poly(diallyldimethylammonium chloride) [PDDA]-stabilized nanoparticles (NPs) of platinum (Pt) and palladium (Pd) as highly active and efficient catalysts for hydrogenation of 4-nitrophenol (4-NP) in the presence of NaBH4. PDDA-stabilized Pt and Pd NPs possessed similar particle size and same facet with citrate-capped Pt and Pd NPs, making this study to investigate the inter-relationship between catalytic activity and surface ligand without the consideration of the effects of particle size and facet. Compared to citrate-capped Pt and Pd NPs, PDDA-stabilized Pt and Pd NPs exhibited excellent pH and salt stability. PDDA could serve as an electron acceptor for metal NPs to produce the net positive charges on the metal surface, which provide strong electrostatic attraction with negatively charged nitrophenolate and borohydride ions. The activity parameter and rate constant of PDDA-stabilized metal NPs were higher than those of citrate-capped metal NPs. Compared to the previously reported Pd nanomaterials for the catalysis of NaBH4-mediated reduction of 4-NP, PDDA-stabilized Pd NPs exhibited the extremely high activity parameter (195 s{sup −1} g{sup −1}) and provided excellent scalability and reusability.

  5. Energy Efficient Catalytic Activation of Hydrogen peroxide for Green Chemical Processes: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Terrence J.; Horwitz, Colin

    2004-11-12

    A new, highly energy efficient approach for using catalytic oxidation chemistry in multiple fields of technology has been pursued. The new catalysts, called TAML® activators, catalyze the reactions of hydrogen peroxide and other oxidants for the exceptionally rapid decontamination of noninfectious simulants (B. atrophaeus) of anthrax spores, for the energy efficient decontamination of thiophosphate pesticides, for the facile, low temperature removal of color and organochlorines from pulp and paper mill effluent, for the bleaching of dyes from textile mill effluents, and for the removal of recalcitrant dibenzothiophene compounds from diesel and gasoline fuels. Highlights include the following: 1) A 7-log kill of Bacillus atrophaeus spores has been achieved unambiguously in water under ambient conditions within 15 minutes. 2) The rapid total degradation under ambient conditions of four thiophosphate pesticides and phosphonate degradation intermediates has been achieved on treatment with TAML/peroxide, opening up potential applications of the decontamination system for phosphonate structured chemical warfare agents, for inexpensive, easy to perform degradation of stored and aged pesticide stocks (especially in Africa and Asia), for remediation of polluted sites and water bodies, and for the destruction of chemical warfare agent stockpiles. 3) A mill trial conducted in a Pennsylvanian bleached kraft pulp mill has established that TAML catalyst injected into an alkaline peroxide bleach tower can significantly lower color from the effluent stream promising a new, more cost effective, energy-saving approach for color remediation adding further evidence of the value and diverse engineering capacity of the approach to other field trials conducted on effluent streams as they exit the bleach plant. 4) Dibenzothiophenes (DBTs), including 4,6-dimethyldibenzothiophene, the most recalcitrant sulfur compounds in diesel and gasoline, can be completely removed from model gasoline

  6. Catalytic Activity and Stability of Oxides: The Role of Near-Surface Atomic Structures and Compositions

    KAUST Repository

    Feng, Zhenxing

    2016-05-05

    δ oxide thin films, and the physical origin of segregation is discussed in comparison with (La1–ySry)2CoO4±δ/La1–xSrxCo0.2Fe0.8O3−δ. Sr enrichment in many electrocatalysts, such as La1–xSrxMO3−δ (M = Cr, Co, Mn, or Co and Fe) and Sm1–xSrxCoO3, has been probed using alternative techniques, including low energy ion scattering, secondary ion mass spectrometry, and X-ray fluorescence-based methods for depth-dependent, element-specific analysis. We highlight a strong connection between cation segregation and electrocatalytic properties, because cation segregation enhances oxygen transport and surface oxygen exchange kinetics. On the other hand, the formation of cation-enriched secondary phases can lead to the blocking of active sites, inhibiting oxygen exchange. With help from density functional theory, the links between cation migration, catalyst stability, and catalytic activity are provided, and the oxygen p-band center relative to the Fermi level can be identified as an activity descriptor. Based on these findings, we discuss strategies to increase a catalyst’s activity while maintaining stability to design efficient, cost-effective electrocatalysts.

  7. A Comparative Discussion of the Catalytic Activity and CO2-Selectivity of Cu-Zr and Pd-Zr (Intermetallic) Compounds in Methanol Steam Reforming

    National Research Council Canada - National Science Library

    Köpfle, Norbert; Mayr, Lukas; Schmidmair, Daniela; Bernardi, Johannes; Knop‐Gericke, Axel; Hävecker, Michael; Klötzer, Bernhard; Penner, Simon

    2017-01-01

      The activation and catalytic performance of two representative Zr-containing intermetallic systems, namely Cu-Zr and Pd-Zr, have been comparatively studied operando using methanol steam reforming (MSR) as test reaction...

  8. Augmentation of VAMP-catalytic activity of botulinum neurotoxin serotype B does not result in increased potency in physiological systems.

    Science.gov (United States)

    Elliott, Mark; Maignel, Jacquie; Liu, Sai Man; Favre-Guilmard, Christine; Mir, Imran; Farrow, Paul; Hornby, Fraser; Marlin, Sandra; Palan, Shilpa; Beard, Matthew; Krupp, Johannes

    2017-01-01

    Botulinum neurotoxins (BoNTs) are used extensively as therapeutic agents. Serotypes A and B are available as marketed products. Higher doses of BoNT/B are required to reach an efficacy similar to that of products containing BoNT/A. Advances in our understanding of BoNT/B mechanism of action have afforded the opportunity to make rational modifications to the toxin aimed at increasing its activity. Recently, a mutation in the light chain of BoNT/B (S201P) was described that increases the catalytic activity of the isolated BoNT/B light chain in biochemical assays. In this study, we have produced two full-length recombinant BoNT/B toxins in E.coli-one wild type (rBoNT/B1) and one incorporating the S201P mutation (rBoNT/B1(S201P)). We have compared the activity of these two molecules along with a native BoNT/B1 in biochemical cell-free assays and in several biological systems. In the cell-free assay, which measured light-chain activity alone, rBoNT/B1(S201P) cleaved VAMP-2 and VAMP-1 substrate with an activity 3-4-fold higher than rBoNT/B1. However, despite the enhanced catalytic activity of rBoNT/B1(S201P), there was no significant difference in potency between the two molecules in any of the in vitro cell-based assays, using either rodent spinal cord neurons or cortical neurons. Similarly in ex vivo tissue preparations rBoNT/B1(S201P) was not significantly more potent than rBoNT/B1 at inhibiting either diaphragm or detrusor (bladder) muscle activity in C57BL/6N and CD1 mice. Finally, no differences between rBoNT/B1 and rBoNT/B1(S201P) were observed in an in vivo digit abduction score (DAS) assay in C57BL/6N mice, either in efficacy or safety parameters. The lack of translation from the enhanced BoNT/B1(S201P) catalytic activity to potency in complex biological systems suggests that the catalytic step is not the rate-limiting factor for BoNT/B to reach maximum efficacy. In order to augment the efficacy of BoNT/B in humans, strategies other than enhancing light chain

  9. Embryo as an active granular fluid: stress-coordinated cellular constriction chains

    Science.gov (United States)

    Holcomb, Michael; Gao, Guo-Jie; Thomas, Jeffrey; Blawzdziewicz, Jerzy

    2016-11-01

    Mechanical stress plays an intricate role in gene expression in individual cells and sculpting of developing tissues. Motivated by our observation of the cellular constriction chains (CCCs) during the initial phase of ventral furrow formation in the Drosophila melanogaster embryo, we propose an active granular fluid (AGF) model that provides valuable insights into cellular coordination in the apical constriction process. In our model, cells are treated as circular particles connected by a predefined force network, and they undergo a random constriction process in which the particle constriction probability P is a function of the stress exerted on the particle by its neighbors. We find that when P favors tensile stress, constricted particles tend to form chain-like structures. In contrast, constricted particles tend to form compact clusters when P favors compression. A remarkable similarity of constricted-particle chains and CCCs observed in vivo provides indirect evidence that tensile-stress feedback coordinates the apical constriction activity.

  10. Catalytic activity of nuclear PLC-beta(1) is required for its signalling function during C2C12 differentiation.

    Science.gov (United States)

    Ramazzotti, Giulia; Faenza, Irene; Gaboardi, Gian Carlo; Piazzi, Manuela; Bavelloni, Alberto; Fiume, Roberta; Manzoli, Lucia; Martelli, Alberto M; Cocco, Lucio

    2008-11-01

    Here we report that PLC-beta(1) catalytic activity plays a role in the increase of cyclin D3 levels and induces the differentiation of C2C12 skeletal muscle cells. PLC-beta(1) mutational analysis revealed the importance of His(331) and His(378) for the catalysis. The expression of PLC-beta(1) and cyclin D3 proteins is highly induced during the process of skeletal myoblast differentiation. We have previously shown that PLC-beta(1) activates cyclin D3 promoter during the differentiation of myoblasts to myotubes, indicating that PLC-beta(1) is a crucial regulator of the mouse cyclin D3 gene. We show that after insulin treatment cyclin D3 mRNA levels are lower in cells overexpressing the PLC-beta(1) catalytically inactive form in comparison to wild type cells. We describe a novel signalling pathway elicited by PLC-beta(1) that modulates AP-1 activity. Gel mobility shift assay and supershift performed with specific antibodies indicate that the c-jun binding site is located in a cyclin D3 promoter region specifically regulated by PLC-beta(1) and that c-Jun binding activity is significantly increased by insulin and PLC-beta(1) overexpression. Mutation of AP-1 site decreased the basal cyclin D3 promoter activity and eliminated its induction by insulin and PLC-beta(1). These results hint at the fact that PLC-beta(1) catalytic activity signals a c-jun/AP-1 target gene, i.e. cyclin D3, during myogenic differentiation.

  11. Hierarchical Coordinated Control of Distributed Generators and Active Power Filters to Enhance Power Quality of Microgrids

    DEFF Research Database (Denmark)

    Savaghebi, Mehdi; Hashempour, Mohammad M.; Guerrero, Josep M.

    2014-01-01

    This paper addresses the coordinated control of distributed generators (DGs) inverters and active power filters (APFs) to compensate voltage harmonics in microgrids. For this, a hierarchical control system is proposed to mitigate voltage harmonic distortion. The hierarchical control structure...... includes two control levels: primary control and secondary control. Primary control consists of power controllers, selective virtual impedance loops and proportional-resonant (PR) voltage/current controllers. Secondary control manages the compensation of voltage harmonic distortion of sensitive load bus...

  12. Promotional effects of Titanium additive on the surface properties, active sites and catalytic activity of W/CeZrOx monolithic catalyst for the selective catalytic reduction of NOx with NH3

    Science.gov (United States)

    Xu, Haidi; Feng, Xi; Liu, Shuang; Wang, Yun; Sun, Mengmeng; Wang, Jianli; Chen, Yaoqiang

    2017-10-01

    CeZrTixO2 mixed oxides were prepared by a co-precipitation method, and serial WO3/CeZrTixO2 catalysts were prepared to investigate the influence of doping TiO2 into CeZrO2 on the catalytic performance of selective catalytic reduction of NOx with NH3. The activity results showed that the introduction of appropriate amount of TiO2 could effectively improve the catalytic performance. WO3/CeZrTi20O2 with 20 wt.% TiO2 showed better deNOx activity and sulfur/water vapor tolerance than W/CeZrO2. Several techniques, including N2 physisorption, XRD, XPS, H2-TPR, NH3-TPD and in situ DRIFTS, were employed to characterize catalysts. The results indicated that doping TiO2 led to the formation of cerium-zirconium-titanium solid solution with larger surface area. The interactions among metal oxides could enhance the redox properties of the catalyst, which was helpful to the improvement of the low-temperature NH3-SCR activity. Moreover, the addition of TiO2 promoted the adsorption and activation of NH3 and increased the reactivity of adsorbed nitrate species with NH3 species, which significantly affected the NH3-SCR performance. Finally, the results of in situ DRIFTS demonstrated that the NH3-SCR reaction mainly followed the Langmuir-Hinshelwood mechanism over W/CeZrO2 and W/CeZrTi20O2 catalysts at 200 °C.

  13. A "light-on" colorimetric assay for anion detection using the inhibitory effect of anions on the catalytic activity of metal nanoparticles for the degradation of methyl orange.

    Science.gov (United States)

    Lu, Lixia; Yang, Fan; Yang, Xiurong

    2014-12-07

    In this communication, we studied the inhibitory effects of anions on the catalytic activity of metal nanoparticles for the degradation of methyl orange (MO). Some anions have great affinity with specific metal nanoparticles, thus resulting in the change of surface state and inhibition of catalytic activity, which can be observed with the naked eye or manifested in the UV spectrum of MO for anion detection.

  14. Understanding Trends in Catalytic Activity: The Effect of Adsorbate-Adsorbate Interactions for CO Oxidation Over Transition Metals

    DEFF Research Database (Denmark)

    Grabow, Lars; Larsen, Britt Hvolbæk; Nørskov, Jens Kehlet

    2010-01-01

    Using high temperature CO oxidation as the example, trends in the reactivity of transition metals are discussed on the basis of density functional theory (DFT) calculations. Volcano type relations between the catalytic rate and adsorption energies of important intermediates are introduced...... and the effect of adsorbate-adsorbate interaction on the trends is discussed. We find that adsorbate-adsorbate interactions significantly increase the activity of strong binding metals (left side of the volcano) but the interactions do not change the relative activity of different metals and have a very small...... influence on the position of the top of the volcano, that is, on which metal is the best catalyst....

  15. Catalytic activity of refolded penicillin acylase subunits in aqueous solution and aerosol ot reversed micelles in octane.

    Science.gov (United States)

    Kabakov, V E; Klyachko, N L; Levashov, A V

    1994-08-01

    Refolded alpha and beta subunits of penicillin acylase were produced by gel-filtration under denaturing conditions followed by removal of urea through dialysis. Preparations of both renatured subunits hidrolysed specific substrate--phenylacetic acid p-nitroanilide in buffer and in the system of Aerosol OT reversed micelles, the alpha subunit being most catalytically active at Wo = 11.9, while the beta subunit--at Wo = 17.5. There was a good correlation between the position of the found maxima, the theoretically calculated optimal hydration degrees as well as the earlier reported profile of enzymatic activity for native enzyme in reversed micelles.

  16. Role of Carboxylate ligands in the Synthesis of AuNPs: Size Control, Molecular Interaction and Catalytic Activity

    KAUST Repository

    Aljohani, Hind Abdullah

    2016-05-22

    then describe the effect of the concentrations and of various type of the stabilizer, and the post-synthesis treatment on gold nanoparticles size. In Chapter 4, we focus on determining the nature of the interactions at molecular level between citrate (and other carboxylate-containing ligands) and AuNP in terms of the mode of coordination at the surface, and the formal oxidation state of Au when interacting with these negatively charged carboxylate ligands (i.e., LX- in the Green formalism). We achieve this by combining very advanced 13C CP/MAS, 23Na MAS and low-temperature SSNMR, high-resolution transmission electron microscopy (HRTEM) and density functional theory (DFT) calculations. A particular emphasis will be based on SS-NMR. In Chapter 5, we study the influence of pretreatment of 1% Au/TiO2 catalysts on the resulting activity in the oxidation of carbon monoxide, the effect of the concentration and the type of the ligands on the catalytic activity. The catalysts were characterized by TPO, XRD, and TEM spectroscopy.

  17. Synthesis, characterization and catalytic activity of indium substituted nanocrystalline Mobil Five (MFI) zeolite

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Kishor Kr. [Department of Chemistry, ADP College, Nagaon, Assam 782002 (India); Nandi, Mithun [Department of Chemistry, Gauhati University, Guwahati, Assam 781014 (India); Talukdar, Anup K., E-mail: anup_t@sify.com [Department of Chemistry, Gauhati University, Guwahati, Assam 781014 (India)

    2015-06-15

    Highlights: • In situ modification of the MFI zeolite by incorporation of indium. • The samples were characterized by XRD, FTIR, TGA, UV–vis (DRS), SAA, EDX and SEM. • The incorporation of indium was confirmed by XRD, FT-IR, UV–vis (DRS), EDX and TGA. • Hydroxylation of phenol reaction was studied on the synthesized catalysts. - Abstract: A series of indium doped Mobil Five (MFI) zeolite were synthesized hydrothermally with silicon to aluminium and indium molar ratio of 100 and with aluminium to indium molar ratios of 1:1, 2:1 and 3:1. The MFI zeolite phase was identified by XRD and FT-IR analysis. In XRD analysis the prominent peaks were observed at 2θ values of around 6.5° and 23° with a few additional shoulder peaks in case of all the indium incorporated samples suggesting formation of pure phase of the MFI zeolite. All the samples under the present investigation were found to exhibit high crystallinity (∼92%). The crystallite sizes of the samples were found to vary from about 49 to 55 nm. IR results confirmed the formation of MFI zeolite in all cases showing distinct absorbance bands near 1080, 790, 540, 450 and 990 cm{sup −1}. TG analysis of In-MFI zeolites showed mass losses in three different steps which are attributed to the loss due to adsorbed water molecules and the two types TPA{sup +} cations. Further, the UV–vis (DRS) studies reflected the position of the indium metal in the zeolite framework. Surface area analysis of the synthesized samples was carried out to characterize the synthesized samples The analysis showed that the specific surface area ranged from ∼357 to ∼361 m{sup 2} g{sup −1} and the pore volume of the synthesized samples ranged from 0.177 to 0.182 cm{sup 3} g{sup −1}. The scanning electron microscopy studies showed the structure of the samples to be rectangular and twinned rectangular shaped. The EDX analysis was carried out for confirmation of Si, Al and In in zeolite frame work. The catalytic activities of

  18. Fabrication of a PANI/CPs composite material: a feasible method to enhance the photocatalytic activity of coordination polymers.

    Science.gov (United States)

    Xu, Xin-Xin; Cui, Zhong-Ping; Qi, Ji; Liu, Xiao-Xia

    2013-03-21

    To improve the photocatalytic activity of a coordination polymer in the visible light region, polyaniline (PANI) was loaded onto its surface through a facile in situ chemical oxidation polymerization process. The resulting PANI loaded coordination polymer composite materials with excellent stability exhibit significantly higher photocatalytic activities than the pure coordination polymer photocatalyst on the degradation of methyl orange (MO) under visible light irradiation. This enhancement can be ascribed to the introduction of PANI on the surface of the coordination polymer, which leads to efficient separation of photogenerated electron-hole pairs as well as a significant expansion of the photoresponse region. Finally, we discussed the influence of acidity on the morphology and photocatalytic activity of the composite material. An optimal condition to obtain the PANI loaded coordination polymer composite material with excellent photocatalytic activity has been obtained.

  19. Mutational analysis of amino acid residues involved in catalytic activity of a family 18 chitinase from tulip bulbs.

    Science.gov (United States)

    Suzukawa, Keisuke; Yamagami, Takeshi; Ohnuma, Takayuki; Hirakawa, Hideki; Kuhara, Satoru; Aso, Yoichi; Ishiguro, Masatsune

    2003-02-01

    We expressed chitinase-1 (TBC-1) from tulip bulbs (Tulipa bakeri) in E. coli cells and used site-directed mutagenesis to identify amino acid residues essential for catalytic activity. Mutations at Glu-125 and Trp-251 completely abolished enzyme activity, and activity decreased with mutations at Asp-123 and Trp-172 when glycolchitin was the substrate. Activity changed with the mutations of Trp-251 to one of several amino acids with side-chains of little hydrophobicity, suggesting that hydrophobic interaction of Trp-251 is important for the activity. Molecular dynamics (MD) simulation analysis with hevamine as the model compound showed that the distance between Asp-123 and Glu-125 was extended by mutation of Trp-251. Kinetic studies of Trp-251-mutated chitinases confirmed these various phenomena. The results suggested that Glu-125 and Trp-251 are essential for enzyme activity and that Trp-251 had a direct role in ligand binding.

  20. Soluble porous coordination polymers by mechanochemistry: from metal-containing films/membranes to active catalysts for aerobic oxidation.

    Science.gov (United States)

    Zhang, Pengfei; Li, Haiying; Veith, Gabriel M; Dai, Sheng

    2015-01-14

    Soluble porous coordination polymers from mechanochemical synthesis are presented through a coordination polymerization between highly contorted, rigid tetraphenol and a broad variety of transition metal ions. These polymers can be easily cast as metal-containing films or freestanding membranes. Importantly, as-made coordination polymers are highly active and stable in the aerobic oxidation of allylic C-H bonds. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Catalytic Performance of Co3O4 on Different Activated Carbon Supports in the Benzyl Alcohol Oxidation

    Directory of Open Access Journals (Sweden)

    Misael Cordoba

    2017-12-01

    Full Text Available Co3O4 particles were supported on a series of activated carbons (G60, CNR, RX3, and RB3. Incipient wetness method was used to prepare these catalysts. The effect of the structural and surface properties of the carbonaceous supports during oxidation of benzyl alcohol was evaluated. The synthetized catalysts were characterized via IR, TEM, TGA/MS, XRD, TPR, AAS, XPS, and N2 adsorption/desorption isotherm techniques. Co3O4/G60 and Co3O4/RX3 catalysts have high activity and selectivity on the oxidation reaction reaching conversions above 90% after 6 h, without the presence of promoters. Catalytic performances show that differences in chemistry of support surface play an important role in activity and suggest that the presence of different ratios of species of cobalt and oxygenated groups on surface in Co3O4/G60 and Co3O4/RX3 catalysts, offered a larger effect synergic between both active phase and support increasing their catalytic activity when compared to the other tested catalysts.

  2. Tuning the geometry and biomimetic catalytic activity of manganese(III)-tetrabromocatecholate based robust platforms by introducing substitution at pyridine.

    Science.gov (United States)

    Jana, Narayan Ch; Brandão, Paula; Panja, Anangamohan

    2016-06-01

    The present report describes synthesis, characterization, crystal structures and catecholase activity of a series of five new manganese(III) complexes (1-5) derived from redox-noninnocent tetrabromocatecholate ligand in combination with different substituted pyridines. X-ray crystallography reveals that the geometry of manganese(III) centers in 1 and 2 is square pyramidal and they are pseudo-dimeric in the solid state resulting from the weak bonding of manganese(III) with a catecholate oxygen atom from the adjacent manganese(III) unit together with other weak interactions like hydrogen bonding and π⋯π stacking interactions. On the other hand, complexes 3-5 are discrete octahedral structures. All the complexes exhibit strong catecholase activity and their diverse catalytic activity can nicely be explained by the nature of substitution at pyridine ring - better electron donor inhibits the reduction of the metal center thereby lowering catecholase activity and vice versa (1 and 2 vs. 3-5). Besides the donor property of ancillary ligands, the structural distortion has also significant role in the biomimetic catalytic activity (1 vs. 2). Copyright © 2016 Elsevier Inc. All rights reserved.

  3. The proteolytic system of pineapple stems revisited: Purification and characterization of multiple catalytically active forms.

    Science.gov (United States)

    Matagne, André; Bolle, Laetitia; El Mahyaoui, Rachida; Baeyens-Volant, Danielle; Azarkan, Mohamed

    2017-06-01

    Crude pineapple proteases extract (aka stem bromelain; EC 3.4.22.4) is an important proteolytic mixture that contains enzymes belonging to the cysteine proteases of the papain family. Numerous studies have been reported aiming at the fractionation and characterization of the many molecular species present in the extract, but more efforts are still required to obtain sufficient quantities of the various purified protease forms for detailed physicochemical, enzymatic and structural characterization. In this work, we describe an efficient strategy towards the purification of at least eight enzymatic forms. Thus, following rapid fractionation on a SP-Sepharose FF column, two sub-populations with proteolytic activity were obtained: the unbound (termed acidic) and bound (termed basic) bromelain fractions. Following reversible modification with monomethoxypolyethylene glycol (mPEG), both fractions were further separated on Q-Sepharose FF and SP-Sepharose FF, respectively. This procedure yielded highly purified molecular species, all titrating ca. 1 mol of thiol group per mole of enzyme, with distinct biochemical properties. N-terminal sequencing allowed identifying at least eight forms with proteolytic activity. The basic fraction contained previously identified species, i.e. basic bromelain forms 1 and 2, ananain forms 1 and 2, and comosain (MEROPS identifier: C01.027). Furthermore, a new proteolytic species, showing similarities with basic bomelain forms 1 and 2, was discovered and termed bromelain form 3. The two remaining species were found in the acidic bromelain fraction and were arbitrarily named acidic bromelain forms 1 and 2. Both, acidic bromelain forms 1, 2 and basic bromelain forms 1, 2 and 3 are glycosylated, while ananain forms 1 and 2, and comosain are not. The eight protease forms display different amidase activities against the various substrates tested, namely small synthetic chromogenic compounds (DL-BAPNA and Boc-Ala-Ala-Gly-pNA), fluorogenic compounds

  4. Synthesis, structural characterization and microbial activity of 2D Ag(I)-5-aminoisophthalate coordination polymer with a new coordination mode

    Science.gov (United States)

    Günay, Handan; Çolak, Alper Tolga; Yeşilel, Okan Zafer; Tunç, Tuncay; Çolak, Ferdağ

    2015-11-01

    In this study, a novel polynuclear Ag(I)-5-aminoisophthalate complex [Ag(μ4-Haip)]n (1) (H2aip = 5-aminoisophthalic acid) has been synthesized. The molecular structure of this complex has been determined by the single crystal X-ray diffraction. The two-dimensional polynuclear complex is crystallized in the triclinic crystal system with space group P-1. The Ag(I) ion is four-coordinated by three carboxylate oxygen atoms of three different Haip ligands and one nitrogen atom in a distorted tetrahedral geometry. Furthermore, a novel coordination mode has shown by H2aip. This complex exhibits photoluminescence in the solid state at room temperature. Antimicrobial activity of complex was evaluated by the agar diffusion method. The complex showed antimicrobial activity against tested microorganism strains (Gram positive, gram negative bacteria, clinic isolate yeast and mold). Moreover this complex showed particularly high antifungal activity against yeast and mold.

  5. A computational study of the catalytic aerobic epoxidation of propylene over the coordinatively unsaturated metal-organic framework Fe3(btc)2: formation of propylene oxide and competing reactions.

    Science.gov (United States)

    Maihom, Thana; Sawangphruk, Montree; Probst, Michael; Limtrakul, Jumras

    2018-02-19

    The aerobic epoxidation of propylene over the metal-organic framework Fe 3 (btc) 2 (btc = 1,3,5-benzentricarboxylate) as catalyst has been investigated by means of density functional calculations. The mechanisms of the reaction towards propylene oxide, carbonylic products (acetone and propanal) and a pi-allyl radical were investigated to assess the efficiency of Fe 3 (btc) 2 for the selective formation of propylene oxide. Propylene oxide and carbonylic products are formed on Fe 3 (btc) 2 by proceeding via propyleneoxy intermediates in the first step. Subsequently, the intermediates can then either be transformed to propylene oxide by way of ring closure of the intermediate or to the carbonylic compounds of propanal and acetone via 1,2-hydride shift. The results show that the formation of propylene oxide is favored over the formation of carbonylic products mainly due to the activation barriers being 2-3 times smaller. The activation barriers for the formation of the propyleneoxy intermediates on the Fe 3 (btc) 2 catalyst for the first and second reaction cycle are also lower than the barriers obtained for the formation of the pi-allyl radical that acts as the precursor to combustion products. On the basis of these computational results, we therefore expect a high catalytic selectivity of the Fe 3 (btc) 2 catalyst with respect to the formation of propylene oxide. We also compared the catalytic activities of Fe 3 (btc) 2 and Cu 3 (btc) 2 . The activation energy of the rate-determining step is almost 2 times lower for Fe 3 (btc) 2 than that for Cu 3 (btc) 2 , due to a larger charge transfer from the catalytic site to the O 2 molecule in the case of Fe 3 (btc) 2 .

  6. Catalytic activity and effect of modifiers on Ni-based catalysts for the dry reforming of methane

    Energy Technology Data Exchange (ETDEWEB)

    Barroso-Quiroga, Maria Martha; Castro-Luna, Adolfo Eduardo [Facultad de Ingenieria y Ciencias Economico-Sociales INTEQUI-CONICET-UNSL, Av. 25 de Mayo 384 (5730) Villa Mercedes (S.L.) (Argentina)

    2010-06-15

    Ni catalysts supported on different ceramic oxides (Al{sub 2}O{sub 3}, CeO{sub 2}, La{sub 2}O{sub 3}, ZrO{sub 2}) were prepared by wet impregnation. The catalytic behavior toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain experimental conditions, and the catalyst supported on ZrO{sub 2} showed the highest stable activity during the period of time studied. The catalyst supported on CeO{sub 2} has a relatively good activity, but shows signs of deactivation after a certain time during the reaction. This catalyst was chosen to be studied after the addition of 0.5 wt% Li and K as activity modifiers. The introduction of the alkaline metals produces a reduction of the catalytic activity but a better stability over the reactant conversion time. The reverse water-gas shift reaction influences the global system of reactions, and as the results indicate, should be considered near equilibrium. (author)

  7. Coordinated activity of ventral tegmental neurons adapts to appetitive and aversive learning.

    Directory of Open Access Journals (Sweden)

    Yunbok Kim

    Full Text Available Our understanding of how value-related information is encoded in the ventral tegmental area (VTA is based mainly on the responses of individual putative dopamine neurons. In contrast to cortical areas, the nature of coordinated interactions between groups of VTA neurons during motivated behavior is largely unknown. These interactions can strongly affect information processing, highlighting the importance of investigating network level activity. We recorded the activity of multiple single units and local field potentials (LFP in the VTA during a task in which rats learned to associate novel stimuli with different outcomes. We found that coordinated activity of VTA units with either putative dopamine or GABA waveforms was influenced differently by rewarding versus aversive outcomes. Specifically, after learning, stimuli paired with a rewarding outcome increased the correlation in activity levels between unit pairs whereas stimuli paired with an aversive outcome decreased the correlation. Paired single unit responses also became more redundant after learning. These response patterns flexibly tracked the reversal of contingencies, suggesting that learning is associated with changing correlations and enhanced functional connectivity between VTA neurons. Analysis of LFP recorded simultaneously with unit activity showed an increase in the power of theta oscillations when stimuli predicted reward but not an aversive outcome. With learning, a higher proportion of putative GABA units were phase locked to the theta oscillations than putative dopamine units. These patterns also adapted when task contingencies were changed. Taken together, these data demonstrate that VTA neurons organize flexibly as functional networks to support appetitive and aversive learning.

  8. Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

    Directory of Open Access Journals (Sweden)

    Carmen Mejuto

    2015-12-01

    Full Text Available The coordination versatility of a 1,3,5-triphenylbenzene-tris-mesoionic carbene ligand is illustrated by the preparation of complexes with three different metals: rhodium, iridium and nickel. The rhodium and iridium complexes contained the [MCl(COD] fragments, while the nickel compound contained [NiCpCl]. The preparation of the tris-MIC (MIC = mesoionic carbene complex with three [IrCl(CO2] fragments, allowed the estimation of the Tolman electronic parameter (TEP for the ligand, which was compared with the TEP value for a related 1,3,5-triphenylbenzene-tris-NHC ligand. The electronic properties of the tris-MIC ligand were studied by cyclic voltammetry measurements. In all cases, the tris-MIC ligand showed a stronger electron-donating character than the corresponding NHC-based ligands. The catalytic activity of the tri-rhodium complex was tested in the addition reaction of arylboronic acids to α,β-unsaturated ketones.

  9. Light chain separated from the rest of the type a botulinum neurotoxin molecule is the most catalytically active form.

    Directory of Open Access Journals (Sweden)

    Nizamettin Gul

    Full Text Available Botulinum neurotoxins (BoNT are the most potent of all toxins. The 50 kDa N-terminal endopeptidase catalytic light chain (LC of BoNT is located next to its central, putative translocation domain. After binding to the peripheral neurons, the central domain of BoNT helps the LC translocate into cytosol where its proteolytic action on SNARE (soluble NSF attachment protein receptor proteins blocks exocytosis of acetyl choline leading to muscle paralysis and eventual death. The translocation domain also contains 105 Å -long stretch of ∼100 residues, known as "belt," that crosses over and wraps around the LC to shield the active site from solvent. It is not known if the LC gets dissociated from the rest of the molecule in the cytosol before catalysis. To investigate the structural identity of the protease, we prepared four variants of type A BoNT (BoNT/A LC, and compared their catalytic parameters with those of BoNT/A whole toxin. The four variants were LC + translocation domain, a trypsin-nicked LC + translocation domain, LC + belt, and a free LC. Our results showed that K(m for a 17-residue SNAP-25 (synaptosomal associated protein of 25 kDa peptide for these constructs was not very different, but the turnover number (k(cat for the free LC was 6-100-fold higher than those of its four variants. Moreover, none of the four variants of the LC was prone to autocatalysis. Our results clearly demonstrated that in vitro, the LC minus the rest of the molecule is the most catalytically active form. The results may have implication as to the identity of the active, toxic moiety of BoNT/A in vivo.

  10. Increased biomass yield of Lactococcus lactis by reduced overconsumption of amino acids and increased catalytic activities of enzymes.

    Directory of Open Access Journals (Sweden)

    Kaarel Adamberg

    Full Text Available Steady state cultivation and multidimensional data analysis (metabolic fluxes, absolute proteome, and transcriptome are used to identify parameters that control the increase in biomass yield of Lactococcus lactis from 0.10 to 0.12 C-mol C-mol(-1 with an increase in specific growth rate by 5 times from 0.1 to 0.5 h(-1. Reorganization of amino acid consumption was expressed by the inactivation of the arginine deiminase pathway at a specific growth rate of 0.35 h(-1 followed by reduced over-consumption of pyruvate directed amino acids (asparagine, serine, threonine, alanine and cysteine until almost all consumed amino acids were used only for protein synthesis at maximal specific growth rate. This balanced growth was characterized by a high glycolytic flux carrying up to 87% of the carbon flow and only amino acids that relate to nucleotide synthesis (glutamine, serine and asparagine were consumed in higher amounts than required for cellular protein synthesis. Changes in the proteome were minor (mainly increase in the translation apparatus. Instead, the apparent catalytic activities of enzymes and ribosomes increased by 3.5 times (0.1 vs 0.5 h(-1. The apparent catalytic activities of glycolytic enzymes and ribosomal proteins were seen to follow this regulation pattern while those of enzymes involved in nucleotide metabolism increased more than the specific growth rate (over 5.5 times. Nucleotide synthesis formed the most abundant biomonomer synthetic pathway in the cells with an expenditure of 6% from the total ATP required for biosynthesis. Due to the increase in apparent catalytic activity, ribosome translation was more efficient at higher growth rates as evidenced by a decrease of protein to mRNA ratios. All these effects resulted in a 30% decrease of calculated ATP spilling (0.1 vs 0.5 h(-1. Our results show that bioprocesses can be made more efficient (using a balanced metabolism by varying the growth conditions.

  11. Catalytic Activities of Fe3+- and Zn2+-Natural Zeolite on the Direct Cyclisation-Acetylation of (R-(+-Citronellal

    Directory of Open Access Journals (Sweden)

    Edy Cahyono

    2014-07-01

    Full Text Available Characterisation and catalytic ativities investigation of modified natural zeolite on cyclisation acetylation reaction of (R-(+-citronellal was performed. The experimental work involved isolation of (R-(+-citronellal from Java Citronella oil (Cymbopogon winterianus by vacuum fractional distillation, determination of its enantiomer, preparation and characterisation of different catalysts i.e. H-natural zeolite (H-Za, Fe3+-natural zeolite (Fe3+-Za, and Zn2+-natural zeolite (Zn2+-Za, followed by examination of catalytic activity and selectivity. Isolated citronellal contained 88.21% ee of (R-(+-citronellal. The main products of cyclisation-acetylation of (R-(+-citronellal was IPA (isopulegyl acetate and NIPA (neo-isopulegyl acetate. Although the highest yield of IPA and NIPA was obtained by Fe3+-Za catalyst (78.69% at 80oC and 120 min, the stereoselectivity of Fe3+-Za slightly lower than that of Zn2+-Za. Structure elucidation of citronellal and products was carried out by means of GC and GC-MS. Lewis acidity plays the role of acetyl ionic formation from acetic anhydride. The Activity and stereoselectivity of catalysts depended on Lewis acidity and cation distribution on the catalyst surface. © 2014 BCREC UNDIP. All rights reservedReceived: 18th December 2013; Revised: 9th April 2014; Accepted: 17th April 2014[ How to Cite: Cahyono, E., Muchalal, M., Triyono, T., Pranowo, H.D. (2014. Catalytic Activities of Fe3+- and Zn2+-Natural Zeolite on the Direct Cyclisation-Acetylation of (R-(+-Citronellal. Bulletin of Chemical Reaction Engineering & Catalysis, 9 (2: 128-135. (doi:10.9767/bcrec.9.2.5936.128-135 ][ Permalink/DOI: http://dx.doi.org/10.9767/bcrec.9.2.5936.128-135 ] 

  12. Defining the catalytic activity of nanoceria in the P23H-1 rat, a photoreceptor degeneration model.

    Directory of Open Access Journals (Sweden)

    Lily L Wong

    Full Text Available Inorganic catalytic nanoceria or cerium oxide nanoparticles (CeNPs are bona fide antioxidants that possess regenerative radical scavenging activities in vitro. Previously, we demonstrated that CeNPs had neuroprotective and anti-angiogenic properties in rodent retinal degeneration and neovascularization models. However, the cellular mechanisms and duration of the catalytic activity of CeNPs in preventing photoreceptor cell loss are still unknown. In this study, we sought to answer these questions using the P23H-1 rat, an autosomal dominant retinitis pigmentosa (adRP model.A single dose of either saline or CeNPs was delivered intravitreally into the eyes of P23H-1 rats at 2-3 weeks of age. Retinal functions were examined at 3 to 7 weeks post injection. We quantified retinal proteins by Western blot analyses and counted the number of apoptotic (TUNEL+ profiles in the outer nuclear layer (ONL of retinal sections. We measured free 8-isoprostanes to quantify lipid peroxidation in retinal tissues.We observed increased rod and cone cell functions up to three weeks post injection. Apoptotic cells were reduced by 46%, 56%, 21%, and 24% at 3, 7, 14, 21 days, respectively, after CeNPs injection compared to saline. Additionally, reduction of lipid peroxidation in the retinas of CeNPs-treated vs saline-treated animals was detected 14 days post injection.We validated that CeNPs were effective in delaying loss of photoreceptor cell function in an adRP rat model. This represents the fourth rodent retinal disease model that shows delay in disease progression after a single application of CeNPs. We further demonstrated that CeNPs slowed the rate of photoreceptor cell death. We deduced that the catalytic activity of CeNPs in vivo in this rat model to be undiminished for at least 7 days and then declined over the next 14 days after CeNPs administration.

  13. Ensemble perspective for catalytic promiscuity: calorimetric analysis of the active site conformational landscape of a detoxification enzyme.

    Science.gov (United States)

    Honaker, Matthew T; Acchione, Mauro; Sumida, John P; Atkins, William M

    2011-12-09

    Enzymological paradigms have shifted recently to acknowledge the biological importance of catalytic promiscuity. However, catalytic promiscuity is a poorly understood property, and no thermodynamic treatment has described the conformational landscape of promiscuous versus substrate-specific enzymes. Here, two structurally similar glutathione transferase (GST, glutathione S-transferase) isoforms with high specificity or high promiscuity are compared. Differential scanning calorimetry (DSC) indicates a reversible low temperature transition for the promiscuous GSTA1-1 that is not observed with substrate-specific GSTA4-4. This transition is assigned to rearrangement of the C terminus at the active site of GSTA1-1 based on the effects of ligands and mutations. Near-UV and far-UV circular dichroism indicate that this transition is due to repacking of tertiary contacts with the remainder of the subunit, rather than "unfolding" of the C terminus per se. Analysis of the DSC data using a modified Landau theory indicates that the local conformational landscape of the active site of GSTA1-1 is smooth, with barrierless transitions between states. The partition function of the C-terminal states is a broad unimodal distribution at all temperatures within this DSC transition. In contrast, the remainder of the GSTA1-1 subunit and the GSTA4-4 protein exhibit folded and unfolded macrostates with a significant energy barrier separating them. Their partition function includes a sharp unimodal distribution of states only at temperatures that yield either folded or unfolded macrostates. At intermediate temperatures the partition function includes a bimodal distribution. The barrierless rearrangement of the GSTA1-1 active site within a local smooth energy landscape suggests a thermodynamic basis for catalytic promiscuity.

  14. Structural Changes of Highly Active Pd/MeOx (Me = Fe, Co, Ni during Catalytic Methane Combustion

    Directory of Open Access Journals (Sweden)

    Dominik Seeburg

    2018-01-01

    Full Text Available Fe2O3, Co3O4 and NiO nanoparticles were prepared via a citrate method and further functionalized with Pd by impregnation. The pure oxides as well as Pd/Fe2O3, Pd/Co3O4, and Pd/NiO (1, 5 and 10 wt % Pd were employed for catalytic methane combustion under methane lean (1 vol %/oxygen rich (18 vol %, balanced with nitrogen conditions. Already, the pure metal oxides showed a high catalytic activity leading to complete conversion temperature of T100 ≤ 500 °C. H2-TPR (Temperature-programmed reduction experiments revealed that Pd-functionalized metal oxides exhibited enhanced redox activity compared to the pure oxides leading to improved catalytic combustion activity at lower temperatures. At a loading of 1 wt % Pd, 1Pd/Co3O4 (T100 = 360 °C outperforms 1Pd/Fe2O3 (T100 = 410 °C as well as 1Pd/NiO (T100 = 380 °C. At a loading of 10 wt % Pd, T100 could only be slightly reduced in all cases. 1Pd/Co3O4 and 1Pd/NiO show reasonable stability over 70 h on stream at T100. XPS (X-ray photoelectron spectroscopy and STEM (Scanning transmission electron microscopy investigations revealed strong interactions between Pd and NiO as well as Co3O4, respectively, leading to dynamic transformations and reoxidation of Pd due to solid state reactions, which leads to the high long-term stability.

  15. CERTIFICATION REPORT The certification of the catalytic activity concentration of creatine kinase in ERM®-AD455k/IFCC

    OpenAIRE

    KUHLMANN JULIA; TOUSSAINT Brigitte; Schimmel, Heinz; Emons, Hendrik

    2016-01-01

    This report describes the production of ERM®-AD455k/IFCC, which is a material certified for the catalytic activity concentration of creatine kinase (CK). This material was produced in collaboration with the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) following ISO Guide 34:2009 and it is certified in accordance with ISO Guide 35:2006. The starting material was a recombinant form of human CK isoenzyme MM (CK-MM) expressed in E. coli. It was produced, purif...

  16. Comparison of Two Preparation Methods on Catalytic Activity and Selectivity of Ru-Mo/HZSM5 for Methane Dehydroaromatization

    Directory of Open Access Journals (Sweden)

    Lucia M. Petkovic

    2014-01-01

    Full Text Available Catalytic performance of Mo/HZSM5 and Ru-Mo/HZSM5 catalysts prepared by vaporization-deposition of molybdenum trioxide and impregnation with ammonium heptamolybdate was analyzed in terms of catalyst activity and selectivity, nitrogen physisorption analyses, temperature-programmed oxidation of carbonaceous residues, and temperature-programmed reduction. Vaporization-deposition rendered the catalyst more selective to ethylene and coke than the catalyst prepared by impregnation. This result was assigned to lower interaction of molybdenum carbide with the zeolite acidic sites.

  17. Syntheses, characterizations, and catalytic activities of mesostructured aluminophosphates with tailorable acidity assembled with various preformed zeolite nanoclusters

    KAUST Repository

    Suo, Hongri

    2015-02-25

    © 2015, Springer Science+Business Media New York. A series of ordered hexagonal mesoporous zeolites have been successfully synthesized by the assembly of various preformed aluminosilicates zeolite (MFI, FAU, BEA etc.) with surfactants (cetyltrimethylammonium chloride) under hydrothermal conditions. These unique samples were further characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption, infrared spectroscopy. Characterization results showed that these samples contain primary and secondary structural building units of various zeolites, which may be responsible for their distinguished acidic strength, suggesting that the acidic strength of these mesoporous silicoaluminophosphates could be tailored and controlled. Furthermore, the prepared samples were catalytically active in the cracking of cumene.

  18. The masked cysteine residues in methylmalonyl-CoA mutase from Propionibacterium shermanii are essential for catalytic activity.

    Science.gov (United States)

    Roy, I

    1996-09-30

    Two masked cysteine residues have been reported in methylmalonyl-CoA mutase from Propionibacterium shermanii, Cys-535 in the alpha-subunit and Cys-517 in the beta-subunit, which are revealed only after reduction of the denatured enzyme with dithiothreitol. It has been postulated that these residues are involved in disulphide linkages to unknown thiols of low M(r). These two masked cysteine residues have been changed to an alanine, individually. Both the mutants, C535alphaA and C517betaA, were inactive. This shows that both these residues are essential for catalytic activity.

  19. Mechanistic Investigations of C-H Activations on Silica-Supported Co(ii) Sites in Catalytic Propane Dehydrogenation.

    Science.gov (United States)

    Estes, Deven P

    2017-04-26

    Catalytic reactions involving C-H bond activations are central to the chemical industry. One such example, alkane dehydrogenation, has recently become very important due to shortfalls in propene production and a large supply of cheap propane. However, current technologies are inefficient and have only moderate selectivity. In order to understand how to improve currently used catalysts, we must know more about the mechanism by which propane is dehydrogenated. We show here that Co(ii) sites on silica are good catalysts for the dehydrogenation of propane, having high activity and selectivity that is reasonably stable over the course of 10 h. Mechanistic investigations of this catalyst show that the main activation mechanism is most likely C-H activation by 1,2 addition.

  20. Effect of lattice strain on the electro-catalytic activity of IrO2for water splitting.

    Science.gov (United States)

    Sun, Wei; Wang, Zhiqiang; Zaman, Waqas Qamar; Zhou, Zhenhua; Cao, Limei; Gong, Xue-Qing; Yang, Ji

    2018-01-23

    The lattice strain of IrO 2 plays a critical role in determining its OER activity. The Ir-O bond length change in IrO 6 coordination induces lattice strain. Increasing the annealing temperature results in a stretching strain along the c axis and a compressive strain on the a and b axes, leading to a larger c/a ratio. Enhancing the lattice strain decreases the c/a ratio, which is beneficial for improving OER activity.

  1. Catalytic activity vs. size correlation in platinum catalysts of PEM fuel cells prepared on carbon black by different methods

    Energy Technology Data Exchange (ETDEWEB)

    Nores-Pondal, F.J.; Granada, M.; Corti, H.R. [Departamento de Fisica de la Materia Condensada, Centro Atomico Constituyentes, Comision Nacional de Energia Atomica (CNEA), General Paz 1499, 1650 San Martin, Buenos Aires (Argentina); Vilella, I.M.J.; de Miguel, S.R.; Scelza, O.A. [Instituto de Investigaciones en Catalisis y Petroquimica (INCAPE), Facultad de Ingenieria Quimica (Universidad Nacional del Litoral) - CONICET, Santiago del Estero 2654, 3000 Santa Fe (Argentina); Troiani, H. [Departamento de Fisica, Centro Atomico Bariloche, Comision Nacional de Energia Atomica (CNEA), Av. Bustillo 9500, 8400 San Carlos de Bariloche (Argentina)

    2009-10-15

    In this work nanoparticulated platinum catalysts have been prepared on carbon Vulcan XC-72 using three methods starting with chloroplatinic acid as a precursor: (i) formic acid as a reductor agent; (ii) impregnation method followed by reduction in hydrogen atmosphere at moderated temperature; and (iii) microwave-assisted reduction in ethylene glycol. The catalytic and size studies were also performed on a commercial Pt catalyst (E-Tek, De Nora). The characterization of the particle size and distribution was performed by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD). The characterizations of the catalytic and electrocatalytic properties of the catalysts were determined by studying the cyclohexane dehydrogenation reaction (CHD) and the behavior under cyclic voltammetry (CV) in sulfuric acid solutions. The measured electrochemical activity, along with the hydrogen chemisorption of the catalysts allows the estimation of effective particle sizes, which are much larger than those measured by TEM and XRD. The catalysts prepared by reduction with formic acid and ethylene glycol (microwave-assisted) show electrochemical activities very close to those of the commercial catalyst, and are almost insensitive to the Pt dispersion or Pt particle size. The chemical activity in CHD correlates well with the metallic dispersion determined by hydrogen chemisorption, indicating similar accesibility of H{sub 2} and cyclohexane to the catalyst surface. (author)

  2. Evolutionary divergence in the catalytic activity of the CAM-1, ROR1 and ROR2 kinase domains.

    Directory of Open Access Journals (Sweden)

    Travis W Bainbridge

    Full Text Available Receptor tyrosine kinase-like orphan receptors (ROR 1 and 2 are atypical members of the receptor tyrosine kinase (RTK family and have been associated with several human diseases. The vertebrate RORs contain an ATP binding domain that deviates from the consensus amino acid sequence, although the impact of this deviation on catalytic activity is not known and the kinase function of these receptors remains controversial. Recently, ROR2 was shown to signal through a Wnt responsive, β-catenin independent pathway and suppress a canonical Wnt/β-catenin signal. In this work we demonstrate that both ROR1 and ROR2 kinase domains are catalytically deficient while CAM-1, the C. elegans homolog of ROR, has an active tyrosine kinase domain, suggesting a divergence in the signaling processes of the ROR family during evolution. In addition, we show that substitution of the non-consensus residues from ROR1 or ROR2 into CAM-1 and MuSK markedly reduce kinase activity, while restoration of the consensus residues in ROR does not restore robust kinase function. We further demonstrate that the membrane-bound extracellular domain alone of either ROR1 or ROR2 is sufficient for suppression of canonical Wnt3a signaling, and that this domain can also enhance Wnt5a suppression of Wnt3a signaling. Based on these data, we conclude that human ROR1 and ROR2 are RTK-like pseudokinases.

  3. New Ulvan-Degrading Polysaccharide Lyase Family: Structure and Catalytic Mechanism Suggests Convergent Evolution of Active Site Architecture.

    Science.gov (United States)

    Ulaganathan, ThirumalaiSelvi; Boniecki, Michal T; Foran, Elizabeth; Buravenkov, Vitaliy; Mizrachi, Naama; Banin, Ehud; Helbert, William; Cygler, Miroslaw

    2017-05-19

    Ulvan is a complex sulfated polysaccharide biosynthesized by green seaweed and contains predominantly rhamnose, xylose, and uronic acid sugars. Ulvan-degrading enzymes have only recently been identified and added to the CAZy ( www.cazy.org ) database as family PL24, but neither their structure nor catalytic mechanism(s) are yet known. Several homologous, new ulvan lyases, have been discovered in Pseudoalteromonas sp. strain PLSV, Alteromonas LOR, and Nonlabens ulvanivorans, defining a new family PL25, with the lyase encoded by the gene PLSV_3936 being one of them. This enzyme cleaves the glycosidic bond between 3-sulfated rhamnose (R3S) and glucuronic acid (GlcA) or iduronic acid (IdoA) via a β-elimination mechanism. We report the crystal structure of PLSV_3936 and its complex with a tetrasaccharide substrate. PLSV_3936 folds into a seven-bladed β-propeller, with each blade consisting of four antiparallel β-strands. Sequence conservation analysis identified a highly conserved region lining at one end of a deep crevice on the protein surface. The putative active site was identified by mutagenesis and activity measurements. Crystal structure of the enzyme with a bound tetrasaccharide substrate confirmed the identity of base and acid residues and allowed determination of the catalytic mechanism and also the identification of residues neutralizing the uronic acid carboxylic group. The PLSV_3936 structure provides an example of a convergent evolution among polysaccharide lyases toward a common active site architecture embedded in distinct folds.

  4. Active video gaming improves body coordination in survivors of childhood brain tumours

    DEFF Research Database (Denmark)

    Sabel, M.; Sjölund, A.; Broeren, J.

    2016-01-01

    Purpose: We investigated whether active video gaming (AVG) could bring about regular, enjoyable, physical exercise in children treated for brain tumours, what level of physical activity could be reached and if the children’s physical functioning improved. Methods: Thirteen children, aged 7–17 years...... survivors, home-based AVG, supported by a coach, was a feasible, enjoyable and moderately intense form of exercise that improved Body Coordination.Implications for Rehabilitation Childhood brain tumour survivors frequently have cognitive problems, inferior physical functioning and are less physically active...... compared to their healthy peers. Active video gaming (AVG), supported by Internet coaching, is a feasible home-based intervention in children treated for brain tumours, promoting enjoyable, regular physical exercise of moderate intensity. In this pilot study, AVG with Nintendo Wii improved Body...

  5. Catalytic asymmetric fluorinations.

    Science.gov (United States)

    Bobbio, Carla; Gouverneur, Véronique

    2006-06-07

    The appearance of structurally diverse fluorinating reagents displaying a large spectrum of reactivity has been critical to the development of the catalytic asymmetric fluorination processes known to date. In this article, we discuss how this area of research emerged and which strategies have allowed for the successful development of both nucleophilic and electrophilic catalytic enantioselective fluorinations. We also present the fundamental understanding of catalytic activity and enantioselectivity for the most efficient processes and highlight the first synthetic application with the preparation of a complex fluorinated target.

  6. Synthesis of chitosan supported palladium nanoparticles and its catalytic activity towards 2-nitrophenol reduction

    Energy Technology Data Exchange (ETDEWEB)

    Dhanavel, S.; Nivethaa, E. A. K.; Esther, G.; Stephen, A., E-mail: stephen-arum@hotmail.com [Material Science Centre, Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai-25 (India); Narayanan, V. [Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai 600 025 (India)

    2016-05-23

    Chitosan supported Palladium nanoparticles were synthesized by a simple cost effective chemical reduction method using NaBH{sub 4}. The prepared nanocomposite was characterized by X-Ray diffraction analysis, FESEM and Energy dispersive spectroscopy analysis of X-rays (EDAX). The catalytic performance of the nanocomposite was evaluated on the reduction of 2-Nitrophenol to the 2-Amino phenol with rate constant 1.08 × 10{sup −3} S{sup −1} by NaBH{sub 4} using Spectrophotometer.

  7. Preparation, characterization and catalytic activity of WO3 supported on sulfated tin oxide catalysts

    Directory of Open Access Journals (Sweden)

    M. Nasouh Alaya

    2017-02-01

    Catalytic application toward esterification of propionic acid with n-butanol was tested and the effect of various parameters, i.e., reaction temperature, reactant molar ratio, weight of the catalyst, WO3 loading and calcination temperature was also investigated. The highest conversion level was found for products loaded with 25 wt.%WO3 and calcined at 400 °C. Although both of Brønsted and Lewis acid sites are responsible for the reaction, the former acid sites found more effective on catalyzing the esterification reaction.

  8. Catalytic activity of Pd-doped Cu nanoparticles for hydrogenation as a single-atom-alloy catalyst.

    Science.gov (United States)

    Cao, Xinrui; Fu, Qiang; Luo, Yi

    2014-05-14

    The single atom alloy of extended surfaces is known to provide remarkably enhanced catalytic performance toward heterogeneous hydrogenation. Here we demonstrate from first principles calculations that this approach can be extended to nanostructures, such as bimetallic nanoparticles. The catalytic properties of the single-Pd-doped Cu55 nanoparticles have been systemically examined for H2 dissociation as well as H atom adsorption and diffusion, following the concept of single atom alloy. It is found that doping a single Pd atom at the edge site of the Cu55 shell can considerably reduce the activation energy of H2 dissociation, while the single Pd atom doped at the top site or in the inner layers is much less effective. The H atom adsorption on Cu55 is slightly stronger than that on the Cu(111) surface; however, a larger nanoparticle that contains 147 atoms could effectively recover the weak binding of the H atoms. We have also investigated the H atom diffusion on the 55-atom nanoparticle and found that spillover of the produced H atoms could be a feasible process due to the low diffusion barriers. Our results have demonstrated that facile H2 dissociation and weak H atom adsorption could be combined at the nanoscale. Moreover, the effects of doping one more Pd atom on the H2 dissociation and H atom adsorption have also been investigated. We have found that both the doping Pd atoms in the most stable configuration could independently exhibit their catalytic activity, behaving as two single-atom-alloy catalysts.

  9. Shared investment projects and forecasting errors: setting framework conditions for coordination and sequencing data quality activities.

    Science.gov (United States)

    Leitner, Stephan; Brauneis, Alexander; Rausch, Alexandra

    2015-01-01

    In this paper, we investigate the impact of inaccurate forecasting on the coordination of distributed investment decisions. In particular, by setting up a computational multi-agent model of a stylized firm, we investigate the case of investment opportunities that are mutually carried out by organizational departments. The forecasts of concern pertain to the initial amount of money necessary to launch and operate an investment opportunity, to the expected intertemporal distribution of cash flows, and the departments' efficiency in operating the investment opportunity at hand. We propose a budget allocation mechanism for coordinating such distributed decisions The paper provides guidance on how to set framework conditions, in terms of the number of investment opportunities considered in one round of funding and the number of departments operating one investment opportunity, so that the coordination mechanism is highly robust to forecasting errors. Furthermore, we show that-in some setups-a certain extent of misforecasting is desirable from the firm's point of view as it supports the achievement of the corporate objective of value maximization. We then address the question of how to improve forecasting quality in the best possible way, and provide policy advice on how to sequence activities for improving forecasting quality so that the robustness of the coordination mechanism to errors increases in the best possible way. At the same time, we show that wrong decisions regarding the sequencing can lead to a decrease in robustness. Finally, we conduct a comprehensive sensitivity analysis and prove that-in particular for relatively good forecasters-most of our results are robust to changes in setting the parameters of our multi-agent simulation model.

  10. Shared Investment Projects and Forecasting Errors: Setting Framework Conditions for Coordination and Sequencing Data Quality Activities

    Science.gov (United States)

    Leitner, Stephan; Brauneis, Alexander; Rausch, Alexandra

    2015-01-01

    In this paper, we investigate the impact of inaccurate forecasting on the coordination of distributed investment decisions. In particular, by setting up a computational multi-agent model of a stylized firm, we investigate the case of investment opportunities that are mutually carried out by organizational departments. The forecasts of concern pertain to the initial amount of money necessary to launch and operate an investment opportunity, to the expected intertemporal distribution of cash flows, and the departments’ efficiency in operating the investment opportunity at hand. We propose a budget allocation mechanism for coordinating such distributed decisions The paper provides guidance on how to set framework conditions, in terms of the number of investment opportunities considered in one round of funding and the number of departments operating one investment opportunity, so that the coordination mechanism is highly robust to forecasting errors. Furthermore, we show that—in some setups—a certain extent of misforecasting is desirable from the firm’s point of view as it supports the achievement of the corporate objective of value maximization. We then address the question of how to improve forecasting quality in the best possible way, and provide policy advice on how to sequence activities for improving forecasting quality so that the robustness of the coordination mechanism to errors increases in the best possible way. At the same time, we show that wrong decisions regarding the sequencing can lead to a decrease in robustness. Finally, we conduct a comprehensive sensitivity analysis and prove that—in particular for relatively good forecasters—most of our results are robust to changes in setting the parameters of our multi-agent simulation model. PMID:25803736

  11. Prevalence of Bimolecular Routes in the Activation of Diatomic Molecules with Strong Chemical Bonds (O2, NO, CO, N2) on Catalytic Surfaces.

    Science.gov (United States)

    Hibbitts, David; Iglesia, Enrique

    2015-05-19

    Dissociation of the strong bonds in O2, NO, CO, and N2 often involves large activation barriers on low-index planes of metal particles used as catalysts. These kinetic hurdles reflect the noble nature of some metals (O2 activation on Au), the high coverages of co-reactants (O2 activation during CO oxidation on Pt), or the strength of the chemical bonds (NO on Pt, CO and N2 on Ru). High barriers for direct dissociations from density functional theory (DFT) have led to a consensus that "defects", consisting of low-coordination exposed atoms, are required to cleave such bonds, as calculated by theory and experiments for model surfaces at low coverages. Such sites, however, bind intermediates strongly, rendering them unreactive at the high coverages prevalent during catalysis. Such site requirements are also at odds with turnover rates that often depend weakly on cluster size or are actually higher on larger clusters, even though defects, such as corners and edges, are most abundant on small clusters. This Account illustrates how these apparent inconsistencies are resolved through activations of strong bonds assisted by co-adsorbates on crowded low-index surfaces. Catalytic oxidations occur on Au clusters at low temperatures in spite of large activation barriers for O2 dissociation on Au(111) surfaces, leading to proposals that O2 activation requires low-coordination Au atoms or Au-support interfaces. When H2O is present, however, O2 dissociation proceeds with low barriers on Au(111) because chemisorbed peroxides (*OOH* and *HOOH*) form and weaken O-O bonds before cleavage, thus allowing activation on low-index planes. DFT-derived O2 dissociation barriers are much lower on bare Pt surfaces, but such surfaces are nearly saturated with CO* during CO oxidation. A dearth of vacant sites causes O2* to react with CO* to form *OOCO* intermediates that undergo O-O cleavage. NO-H2 reactions occur on Pt clusters saturated with NO* and H*; direct NO* dissociation requires vacant

  12. Substrate-mediated enhanced activity of Ru nanoparticles in catalytic hydrogenation of benzene

    KAUST Repository

    Liu, Xin

    2012-01-01

    The impact of carbon substrate-Ru nanoparticle interactions on benzene and hydrogen adsorption that is directly related to the performance in catalytic hydrogenation of benzene has been investigated by first-principles based calculations. The stability of Ru 13 nanoparticles is enhanced by the defective graphene substrate due to the hybridization between the dsp states of the Ru 13 particle with the sp 2 dangling bonds at the defect sites. The local curvature formed at the interface will also raise the Ru atomic diffusion barrier, and prohibit the particle sintering. The strong interfacial interaction results in the shift of averaged d-band center of the deposited Ru nanoparticle, from -1.41 eV for a freestanding Ru 13 particle, to -1.17 eV for the Ru/Graphene composites, and to -1.54 eV on mesocellular foam carbon. Accordingly, the adsorption energies of benzene are increased from -2.53 eV for the Ru/mesocellular foam carbon composites, to -2.62 eV on freestanding Ru 13 particles, to -2.74 eV on Ru/graphene composites. A similar change in hydrogen adsorption is also observed, and all these can be correlated to the shift of the d-band center of the nanoparticle. Thus, Ru nanoparticles graphene composites are expected to exhibit both high stability and superior catalytic performance in hydrogenation of arenes. © 2012 The Royal Society of Chemistry.

  13. Optimal coordinated voltage control in active distribution networks using backtracking search algorithm.

    Science.gov (United States)

    Tengku Hashim, Tengku Juhana; Mohamed, Azah

    2017-01-01

    The growing interest in distributed generation (DG) in recent years has led to a number of generators connected to a distribution system. The integration of DGs in a distribution system has resulted in a network known as active distribution network due to the existence of bidirectional power flow in the system. Voltage rise issue is one of the predominantly important technical issues to be addressed when DGs exist in an active distribution network. This paper presents the application of the backtracking search algorithm (BSA), which is relatively new optimisation technique to determine the optimal settings of coordinated voltage control in a distribution system. The coordinated voltage control considers power factor, on-load tap-changer and generation curtailment control to manage voltage rise issue. A multi-objective function is formulated to minimise total losses and voltage deviation in a distribution system. The proposed BSA is compared with that of particle swarm optimisation (PSO) so as to evaluate its effectiveness in determining the optimal settings of power factor, tap-changer and percentage active power generation to be curtailed. The load flow algorithm from MATPOWER is integrated in the MATLAB environment to solve the multi-objective optimisation problem. Both the BSA and PSO optimisation techniques have been tested on a radial 13-bus distribution system and the results show that the BSA performs better than PSO by providing better fitness value and convergence rate.

  14. PAK1 is a breast cancer oncogene that coordinately activates MAPK and MET signaling.

    Science.gov (United States)

    Shrestha, Y; Schafer, E J; Boehm, J S; Thomas, S R; He, F; Du, J; Wang, S; Barretina, J; Weir, B A; Zhao, J J; Polyak, K; Golub, T R; Beroukhim, R; Hahn, W C

    2012-07-19

    Activating mutations in the RAS family or BRAF frequently occur in many types of human cancers but are rarely detected in breast tumors. However, activation of the RAS-RAF-MEK-ERK MAPK pathway is commonly observed in human breast cancers, suggesting that other genetic alterations lead to activation of this signaling pathway. To identify breast cancer oncogenes that activate the MAPK pathway, we screened a library of human kinases for their ability to induce anchorage-independent growth in a derivative of immortalized human mammary epithelial cells (HMLE). We identified p21-activated kinase 1 (PAK1) as a kinase that permitted HMLE cells to form anchorage-independent colonies. PAK1 is amplified in several human cancer types, including 30--33% of breast tumor samples and cancer cell lines. The kinase activity of PAK1 is necessary for PAK1-induced transformation. Moreover, we show that PAK1 simultaneously activates MAPK and MET signaling; the latter via inhibition of merlin. Disruption of these activities inhibits PAK1-driven anchorage-independent growth. These observations establish PAK1 amplification as an alternative mechanism for MAPK activation in human breast cancer and credential PAK1 as a breast cancer oncogene that coordinately regulates multiple signaling pathways, the cooperation of which leads to malignant transformation.

  15. Boosting Chemical Stability, Catalytic Activity, and Enantioselectivity of Metal-Organic Frameworks for Batch and Flow Reactions.

    Science.gov (United States)

    Chen, Xu; Jiang, Hong; Hou, Bang; Gong, Wei; Liu, Yan; Cui, Yong

    2017-09-27

    A key challenge in heterogeneous catalysis is the design and synthesis of heterogeneous catalysts featuring high catalytic activity, selectivity, and recyclability. Here we demonstrate that high-performance heterogeneous asymmetric catalysts can be engineered from a metal-organic framework (MOF) platform by using a ligand design strategy. Three porous chiral MOFs with the framework formula [Mn2L(H2O)2] are prepared from enantiopure phosphono-carboxylate ligands of 1,1'-biphenol that are functionalized with 3,5-bis(trifluoromethyl)-, bismethyl-, and bisfluoro-phenyl substituents at the 3,3'-position. For the first time, we show that not only chemical stability but also catalytic activity and stereoselectivity of the MOFs can be tuned by modifying the ligand structures. Particularly, the MOF incorporated with -CF3 groups on the pore walls exhibits enhanced tolerance to water, weak acid, and base compared with the MOFs with -F and -Me groups. Under both batch and flow reaction systems, the CF3-containing MOF demonstrated excellent reactivity, selectivity, and recyclability, affording high yields and enantioselectivities for alkylations of indoles and pyrrole with a range of ketoesters or nitroalkenes. In contrast, the corresponding homogeneous catalysts gave low enantioselectivity in catalyzing the tested reactions.

  16. SIRT1 catalytic activity has little effect on tumor formation and metastases in a mouse model of breast cancer.

    Directory of Open Access Journals (Sweden)

    Katherine V Clark-Knowles

    Full Text Available The protein deacetylase SIRT1 has been implicated in the regulation of a large number of cellular processes that are thought to be required for cancer initiation and progression. There are conflicting data that make it unclear whether Sirt1 functions as an oncogene or tumor suppressor. To assess the effect of SIRT1 on the emergence and progression of mammary tumors, we crossed mice that harbor a point mutation that abolishes SIRT1 catalytic activity with mice carrying the polyoma middle T transgene driven by the murine mammary tumor virus promoter (MMTV-PyMT. The absence of SIRT1 catalytic activity neither accelerated nor blocked the formation of tumors and metastases in this model. There was a lag in tumor latency that modestly extended survival in Sirt1 mutant mice that we attribute to a delay in mammary gland development and not to a direct effect of SIRT1 on carcinogenesis. These results are consistent with previous evidence suggesting that Sirt1 is not a tumor promoter or a tumor suppressor.

  17. Catalytic activity of mono and bimetallic Zn/Cu/MWCNTs catalysts for the thermocatalyzed conversion of methane to hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Erdelyi, B. [Department of Physical Chemistry, Faculty of Science, P.J. Šafárik University, Moyzesova 11, 041 54 Košice (Slovakia); Institute of Physics, Faculty of Science, P.J. Šafárik University, Park Angelium 9, 040 01 Košice (Slovakia); Oriňak, A., E-mail: andrej.orinak@upjs.sk [Department of Physical Chemistry, Faculty of Science, P.J. Šafárik University, Moyzesova 11, 041 54 Košice (Slovakia); Oriňaková, R. [Department of Physical Chemistry, Faculty of Science, P.J. Šafárik University, Moyzesova 11, 041 54 Košice (Slovakia); Lorinčík, J. [Research Center Rez, Hlavní 130, 250 68 Husinec-Řež (Czech Republic); Jerigová, M. [Department of Physical Chemistry, Comenius University, Mlynská dolina 842 15 Bratislava 4 (Slovakia); Velič, D. [Department of Physical Chemistry, Comenius University, Mlynská dolina 842 15 Bratislava 4 (Slovakia); International Laser Centre, Ilkovičová 3, 841 01 Bratislava (Slovakia); Mičušík, M. [Polymer institute, Slovak Academy of Sciences, Dubravská cesta 9, 84541 Bratislava (Slovakia); and others

    2017-02-28

    Highlights: • Zn/Cu/MWCNTs catalyst with good activity. • Methane conversion to hydrogen with high effectivity. • ZnO/Cu responsible for catalytic activity. - Abstract: Mono and bimetallic multiwalled carbon nanotubes (MWCNTs) fortified with Cu and Zn metal particles were studied to improve the efficiency of the thermocatalytic conversion of methane to hydrogen. The surface of the catalyst and the dispersion of the metal particles were studied by scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS) and with energy-dispersive X-ray spectroscopy (EDS). It was confirmed that the metal particles were successfully dispersed on the MWCNT surface and XPS analysis showed that the Zn was oxidised to ZnO at high temperatures. The conversion of methane to hydrogen during the catalytic pyrolysis was studied by pyrolysis gas chromatography using different amounts of catalyst. The best yields of hydrogen were obtained using pyrolysis conditions of 900 °C and 1.2 mg of Zn/Cu/MWCNT catalyst for 1.5 mL of methane.The initial conversion of methane to hydrogen obtained with Zn/Cu/MWCNTs was 49%, which represent a good conversion rate of methane to hydrogen for a non-noble metal catalyst.

  18. Recovery of homogeneous polyoxometallate catalysts from aqueous and organic media by a mesoporous ceramic membrane without loss of catalytic activity.

    Science.gov (United States)

    Roy Chowdhury, Sankhanilay; Witte, Peter T; Blank, Dave H A; Alsters, Paul L; Ten Elshof, Johan E

    2006-04-03

    The recovery of homogeneous polyoxometallate (POM) oxidation catalysts from aqueous and non-aqueous media by a nanofiltration process using mesoporous gamma-alumina membranes is reported. The recovery of Q(12)[WZn(3)(ZnW(9)O(34))(2)] (Q=[MeN(n-C(8)H(17))(3)](+)) from toluene-based media was quantitative within experimental error, while up to 97 % of Na(12)[WZn(3)(ZnW(9)O(34))(2)] could be recovered from water. The toluene-soluble POM catalyst was used repeatedly in the conversion of cyclooctene to cyclooctene oxide and separated from the product mixture after each reaction. The catalytic activity increased steadily with the number of times that the catalyst had been recycled, which was attributed to partial removal of the excess QCl that is known to have a negative influence on the catalytic activity. Differences in the permeability of the membrane for different liquid media can be attributed to viscosity differences and/or capillary condensation effects. The influence of membrane pore radius on permeability and recovery is discussed.

  19. High catalytic activity of monometallic Ag, Cu nanostructures in the degradation of acid blue 113 dye: an electron relay effect

    Science.gov (United States)

    Udayabhaskar, R.; Mangalaraja, R. V.; Pandiyarajan, T.; Karthikeyan, B.; Mansilla, Héctor D.

    2017-09-01

    This report discusses the observed faster decoloration of an azo dye with an enhanced degradation rate constant achieved using metal nanostructures as a catalyst. Silver and copper nanostructures were synthesized by reducing the corresponding nitrate salts using hydrazine and hexamethylenetetramine (HMTA) in sodium hydroxide (NaOH) solution. The influence of HMTA was clearly evident from the scanning electron microscopy (SEM) images; with increasing concentration it caused agglomeration and the formation of net-like nanostructures. An x-ray diffraction study confirmed the formation of monometallic Ag and Cu nanostructures. The prepared nanostructures exhibited dipole and multipole surface plasmon resonance-related optical absorption bands which were size and shape dependent. The degradation of the azo dye acid blue 113 (AB113) in the presence of sodium borohydride (NaBH4) was taken as model system for studying the catalytic activity of the metal nanostructures. From the optical absorption spectral studies of dye degradation it was observed that the rate constant (k) was of the order of k Cu   >  k Ag   >  k no catalyst. From the dye degradation studies a high catalytic activity was observed for Cu nanostructures with a rate constant of 20.93  ×  10-4 s-1.

  20. Concurrent inhibition of kit- and FcepsilonRI-mediated signaling: coordinated suppression of mast cell activation

    DEFF Research Database (Denmark)

    Jensen, Bettina M; Beaven, Michael A; Iwaki, Shoko

    2008-01-01

    Although primarily required for the growth, differentiation, and survival of mast cells, Kit ligand (stem cell factor) is also required for optimal antigen-mediated mast cell activation. Therefore, concurrent inhibition of Kit- and FcepsilonRI-mediated signaling would be an attractive approach...... for targeting mast cell-driven allergic reactions. To explore this concept, we examined the effects of hypothemycin, a molecule that we identified as having such properties, in human and mouse mast cells. Hypothemycin blocked Kit activation and Kit-mediated mast cell adhesion in a similar manner to the well...... for a coordinated approach for the suppression of mast cell activation and provide a rationale for the development of compounds with a similar therapeutic profile....

  1. Coordinated activation of distinct Ca2+ sources and metabotropic glutamate receptors encodes Hebbian synaptic plasticity

    Science.gov (United States)

    Tigaret, Cezar M.; Olivo, Valeria; Sadowski, Josef H.L.P.; Ashby, Michael C.; Mellor, Jack R.

    2016-01-01

    At glutamatergic synapses, induction of associative synaptic plasticity requires time-correlated presynaptic and postsynaptic spikes to activate postsynaptic NMDA receptors (NMDARs). The magnitudes of the ensuing Ca2+ transients within dendritic spines are thought to determine the amplitude and direction of synaptic change. In contrast, we show that at mature hippocampal Schaffer collateral synapses the magnitudes of Ca2+ transients during plasticity induction do not match this rule. Indeed, LTP induced by time-correlated pre- and postsynaptic spikes instead requires the sequential activation of NMDARs followed by voltage-sensitive Ca2+ channels within dendritic spines. Furthermore, LTP requires inhibition of SK channels by mGluR1, which removes a negative feedback loop that constitutively regulates NMDARs. Therefore, rather than being controlled simply by the magnitude of the postsynaptic calcium rise, LTP induction requires the coordinated activation of distinct sources of Ca2+ and mGluR1-dependent facilitation of NMDAR function. PMID:26758963

  2. Enzyme activity effects of N-terminal His-tag attached to catalytic sub-unit of phosphoinositide-3-kinase.

    Science.gov (United States)

    Dickson, James M J; Lee, Woo-Jeong; Shepherd, Peter R; Buchanan, Christina M

    2013-11-05

    NTT (N-terminal tags) on the catalytic (p110) sub-unit of PI 3-K (phosphoinositol 3-kinase) have previously been shown to increase cell signalling and oncogenic transformation. Here we test the impact of an NT (N-terminal) His-tag on in vitro lipid and protein kinase activity of all class-1 PI 3-K isoforms and two representative oncogenic mutant forms (E545K and H1047R), in order to elucidate the mechanisms behind this elevated signalling and transformation observed in vivo. Our results show that an NT His-tag has no impact on lipid kinase activity as measured by enzyme titration, kinetics and inhibitor susceptibility. Conversely, the NT His-tag did result in a differential effect on protein kinase activity, further potentiating the elevated protein kinase activity of both the helical domain and catalytic domain oncogenic mutants with relation to p110 phosphorylation. All other isoforms also showed elevated p110 phosphorylation (although not statistically significant). We conclude that the previously reported increase in cell signalling and oncogenic-like transformation in response to p110 NTT is not mediated via an increase in the lipid kinase activity of PI 3-K, but may be mediated by increased p110 autophosphorylation and/or other, as yet unidentified, intracellular protein/protein interactions. We further observe that tagged recombinant protein is suitable for use in in vitro lipid kinase screens to identify PI 3-K inhibitors; however, we recommend that in vivo (including intracellular) experiments and investigations into the protein kinase activity of PI 3-K should be conducted with untagged constructs.

  3. The C Terminus of the Catalytic Domain of Type A Botulinum Neurotoxin May Facilitate Product Release from the Active Site*

    Science.gov (United States)

    Mizanur, Rahman M.; Frasca, Verna; Swaminathan, Subramanyam; Bavari, Sina; Webb, Robert; Smith, Leonard A.; Ahmed, S. Ashraf

    2013-01-01

    Botulinum neurotoxins are the most toxic of all compounds. The toxicity is related to a poor zinc endopeptidase activity located in a 50-kDa domain known as light chain (Lc) of the toxin. The C-terminal tail of Lc is not visible in any of the currently available x-ray structures, and it has no known function but undergoes autocatalytic truncations during purification and storage. By synthesizing C-terminal peptides of various lengths, in this study, we have shown that these peptides competitively inhibit the normal catalytic activity of Lc of serotype A (LcA) and have defined the length of the mature LcA to consist of the first 444 residues. Two catalytically inactive mutants also inhibited LcA activity. Our results suggested that the C terminus of LcA might interact at or near its own active site. By using synthetic C-terminal peptides from LcB, LcC1, LcD, LcE, and LcF and their respective substrate peptides, we have shown that the inhibition of activity is specific only for LcA. Although a potent inhibitor with a Ki of 4.5 μm, the largest of our LcA C-terminal peptides stimulated LcA activity when added at near-stoichiometric concentration to three versions of LcA differing in their C-terminal lengths. The result suggested a product removal role of the LcA C terminus. This suggestion is supported by a weak but specific interaction determined by isothermal titration calorimetry between an LcA C-terminal peptide and N-terminal product from a peptide substrate of LcA. Our results also underscore the importance of using a mature LcA as an inhibitor screening target. PMID:23779108

  4. Enhanced photo-catalytic activity of TiO2 films by removal of surface carbon impurities; the role of water vapor

    Science.gov (United States)

    Seo, Hyun Ook; Woo, Tae Gyun; Park, Eun Ji; Cha, Byeong Jun; Kim, Il Hee; Han, Sang Wook; Kim, Young Dok

    2017-10-01

    We have studied the photo-catalytic degradation of acetaldehyde over the surface of TiO2 films under UV light (365 nm) irradiation both at dry and humid air conditions using a high vacuum chamber equipped with on-line gas-chromatography as a batch-type reactor. Changes of TiO2 surfaces upon the photo-catalysis experiments were studied by X-ray photoelectron spectroscopy. The competitive adsorption of water and acetaldehyde resulted in the reduction of reaction rate of photo-catalytic degradation of acetaldehyde under the UV light irradiation. The photo-catalytic reaction rate of TiO2 films towards acetaldehyde mineralization increased when the photo-catalysis experiments were performed repeatedly and it was much more pronounced under humid conditions. Our XPS analysis revealed that carbon impurities on the surface of TiO2 films were removed by UV-light driven photo-catalytic mineralization under humid conditions. Water vapor facilitated the photo-catalytic removal of carbon impurities from TiO2 surface generating additional active sites of TiO2 which resulted in the enhanced photo-catalytic activity of TiO2 films.

  5. Catalytic hydrothermal treatment of pulping effluent using a mixture of Cu and Mn metals supported on activated carbon as catalyst.

    Science.gov (United States)

    Yadav, Bholu Ram; Garg, Anurag

    2016-10-01

    The present study was performed to investigate the performance of activated carbon-supported copper and manganese base catalyst for catalytic wet oxidation (CWO) of pulping effluent. CWO reaction was performed in a high pressure reactor (capacity = 0.7 l) at temperatures ranging from 120 to 190 °C and oxygen partial pressures of 0.5 to 0.9 MPa with the catalyst concentration of 3 g/l for 3 h duration. With Cu/Mn/AC catalyst at 190 °C temperature and 0.9 MPa oxygen partial pressures, the maximum chemical oxygen demand (COD), total organic carbon (TOC), lignin, and color removals of 73, 71, 86, and 85 %, respectively, were achieved compared to only 52, 51, 53, and 54 % removals during the non-catalytic process. Biodegradability (in terms of 5-day biochemical oxygen demand (BOD5) to COD ratio) of the pulping effluent was improved to 0.38 from an initial value of 0.16 after the catalytic reaction. The adsorbed carbonaceous fraction on the used catalyst was also determined which contributed meager TOC reduction of 3-4 %. The leaching test showed dissolution of the metals (i.e., Cu and Mn) from the catalysts in the wastewater during CWO reaction at 190 °C temperature and 0.9 MPa oxygen partial pressures. In the future, the investigations should focus on the catalyst reusability.

  6. Enhanced photo-catalytic activity of ordered mesoporous indium oxide nanocrystals in the conversion of CO2into methanol.

    Science.gov (United States)

    Gondal, M A; Dastageer, M A; Oloore, L E; Baig, U; Rashid, S G

    2017-07-03

    Ordered mesoporous indium oxide nanocrystal (m-In 2 O 3 ) was synthesized by nanocasting technique, in which highly ordered mesoporous silca (SBA-15) was used as structural matrix. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halanda (BJH) studies were carried out on m-In 2 O 3 and the results revealed that this material has a highly ordered mesoporous surface with reduced grain size, increased surface area and surface volume compared to the non porous indium oxide. The diffuse reluctance spectrum exhibited substantially improved light absorption efficiency in m-In 2 O 3 compared to normal indium oxide, however, no considerable change in the band gap energies of these materials was observed. When m-In 2 O 3 was used as a photo-catalyst in the photo-catalytic process of converting carbon dioxide (CO 2 ) into methanol under the pulsed laser radiation of 266-nm wavelengths, an enhanced photo-catalytic activity with the quantum efficiency of 4.5% and conversion efficiency of 46.3% were observed. It was found that the methanol production yield in this chemical process is as high as 485 µlg -1 h -1 after 150 min of irradiation, which is substantially higher than the yields reported in the literature. It is quite clear from the results that the introduction of mesoporosity in indium oxide, and the consequent enhancement of positive attributes required for a photo-catalyst, transformed photo-catalytically weak indium oxide into an effective photo-catalyst for the conversion of CO 2 into methanol.

  7. Hydrothermal synthesis, structure, heterogeneous catalytic activity and photoluminescent properties of a novel homoleptic Sm(III)-organic framework

    Science.gov (United States)

    Ay, Burak; Yildiz, Emel; Felts, Ashley C.; Abboud, Khalil A.

    2016-12-01

    A novel metal-organic framework, (H2pip)n[Sm2(pydc)4(H2O)2]n (1) (H2pydc=2,6-pyridinedicarboxylic acid, H2pip=piperazine) has been synthesized under hydrothermal conditions and characterized by the elemental analysis, inductively coupled plasma (ICP) spectrometer, fourier transform infrared (FT-IR) spectra, thermogravimetric analysis (TGA), single crystal X-ray diffraction analysis and powder X-ray diffraction (PXRD). The structure of 1 was determined to be three-dimensional, linked along Sm-O-Sm chains. The asymmetric unit consisted of one singly anionic fragment consisting of Sm(III) coordinated to two H2pydc ligands and one water, and one half of a protonated H2pip, which sits on an inversion center. 1 exhibited luminescence emission bands at 534 nm at room temperature when excited at 440 nm. Its thermal behavior and catalytic performance were investigated and the selectivity was measured as 100% for the oxidation of thymol to thymoquinone.

  8. Selection of head and whisker coordination strategies during goal-oriented active touch.

    Science.gov (United States)

    Schroeder, Joseph B; Ritt, Jason T

    2016-04-01

    In the rodent whisker system, a key model for neural processing and behavioral choices during active sensing, whisker motion is increasingly recognized as only part of a broader motor repertoire employed by rodents during active touch. In particular, recent studies suggest whisker and head motions are tightly coordinated. However, conditions governing the selection and temporal organization of such coordinated sensing strategies remain poorly understood. We videographically reconstructed head and whisker motions of freely moving mice searching for a randomly located rewarded aperture, focusing on trials in which animals appeared to rapidly "correct" their trajectory under tactile guidance. Mice orienting after unilateral contact repositioned their whiskers similarly to previously reported head-turning asymmetry. However, whisker repositioning preceded head turn onsets and was not bilaterally symmetric. Moreover, mice selectively employed a strategy we term contact maintenance, with whisking modulated to counteract head motion and facilitate repeated contacts on subsequent whisks. Significantly, contact maintenance was not observed following initial contact with an aperture boundary, when the mouse needed to make a large corrective head motion to the front of the aperture, but only following contact by the same whisker field with the opposite aperture boundary, when the mouse needed to precisely align its head with the reward spout. Together these results suggest that mice can select from a diverse range of sensing strategies incorporating both knowledge of the task and whisk-by-whisk sensory information and, moreover, suggest the existence of high level control (not solely reflexive) of sensing motions coordinated between multiple body parts. Copyright © 2016 the American Physiological Society.

  9. Social Activity and Cognitive Functioning Over Time: A Coordinated Analysis of Four Longitudinal Studies

    Directory of Open Access Journals (Sweden)

    Cassandra L. Brown

    2012-01-01

    Full Text Available Social activity is typically viewed as part of an engaged lifestyle that may help mitigate the deleterious effects of advanced age on cognitive function. As such, social activity has been examined in relation to cognitive abilities later in life. However, longitudinal evidence for this hypothesis thus far remains inconclusive. The current study sought to clarify the relationship between social activity and cognitive function over time using a coordinated data analysis approach across four longitudinal studies. A series of multilevel growth models with social activity included as a covariate is presented. Four domains of cognitive function were assessed: reasoning, memory, fluency, and semantic knowledge. Results suggest that baseline social activity is related to some, but not all, cognitive functions. Baseline social activity levels failed to predict rate of decline in most cognitive abilities. Changes in social activity were not consistently associated with cognitive functioning. Our findings do not provide consistent evidence that changes in social activity correspond to immediate benefits in cognitive functioning, except perhaps for verbal fluency.

  10. Functional independency between catalytic activity and subcellular targeting of polo-like kinase-1: phenotypes of ectopic overexpression of various mutants.

    Science.gov (United States)

    Ji, Jae-Hoon; Jang, Young-Joo

    2008-06-01

    The mammalian polo-like kinase-1 (Plk1) plays key role in the progression of the M-phase. As cells enter the M-phase, Plk1 is phosphorylated by an upstream kinase on Thr-210 in N-terminal region, which is essential for Plk1 activation. In addition to catalytic activation, the subcellular localization is also an important task for Plk1, and the C-terminal polo-boxes are responsible for Plk1 targeting. Although both catalytic activation and targeting might be essential and work concurrently, it is still unclear which process precedes the other in mitotic progression, and which is more essential for the function of Plk1 through the M-phase. In order to investigate this mechanism, this study introduced several point mutations in the catalytic and polo-box domains, and overexpressed these constructs in HeLa cells. Although the cellular effects by ectopic expression were different in the cells containing various Plk1 constructs, phosphorylation itself, not the catalytic activity, was found to be important for the progression of the M-phase. Plk1 phosphorylation was also responsible for targeting by polo-box, and compensated for the polo-box mutation. These results suggested that Plk1 is phosphorylated in the starting M-phase, and this phosphorylation induces polo-box targeting through a possible conformational change. In this situation, catalytic activation does not appear to be a critical factor for the function of Plk1.

  11. Nanocrystalline Ferrihydrite-Based Catalysts for Fischer-Tropsch Synthesis: Part II. Effects of Activation Gases on the Catalytic Performance.

    Science.gov (United States)

    Rhim, Geun Bae; Hong, Seok Yong; Park, Ji Chan; Jung, Heon; Rhee, Young Woo; Chun, Dong Hyun

    2016-02-01

    Fischer-Tropsch synthesis (FTS) was carried out over nanocrystalline ferrihydrite-based (Fe9O2(OH)23) catalysts activated by different reducing agents: syngas (H2+CO), CO, and H2. The syngas activation successfully changed the ferrihydrite-based catalysts into an active and stable catalytic structure with chi-carbide (Fe2.5 C) and epsilon'-carbide (Fe2.2 C). The crystal structure of the catalysts obtained by syngas activation was similar to the structure obtained by CO activation; this similarity was probably due to the peculiar reduction behavior of the ferrihydrite-based catalysts, which exhibit much greater reducibility in CO atmosphere than in H2 atmosphere. The performance of the catalysts activated by syngas was much higher than the performance of the catalysts activated by H2 and was comparable to the performance of the catalysts activated by CO. This strongly demonstrates that the ferrihydrite-based catalysts are advantageous for industrial FTS processes because syngas can be commonly used for both activation pre-treatment and subsequent reaction.

  12. What regulates the catalytic activities in AGE catalysis? An answer from quantum mechanics/molecular mechanics simulations.

    Science.gov (United States)

    Zhang, Yulai; Zhang, Hongxing; Zheng, Qingchuan

    2017-11-23

    The AGE superfamily (AGEs) is made up of kinds of isomerase which are very important both physiologically and industrially. One of the most intriguing aspects of AGEs has to do with the mechanism that regulates their activities in single conserved active pocket. In order to clarify the relationship among single conserved active pocket and two activities in AGEs, results for the epimerization activity catalyzed by RaCE and the isomerization activity catalyzed by SeYihS were obtained by using QM/MM umbrella sampling simulations and 2D-FES calculations. Our results show that both of them have similar enzyme-substrate combination mode for inner pyranose ring in single conserved active pocket even though they have different substrate specificity. This means that the pathways of ring opening catalyzed by them are similar. However, one non-conserved residue (Leu183 in RaCE, Met175 in SeYihS) in the active site, which has different steric hindrance, causes a small but effective change in the direction of ring opening in stage 1. And then this change will induce a fundamentally different catalytic activity for RaCE and SeYihS in stage 2. Our results give a novel viewpoint about the regulatory mechanism between CE and YihS in AGEs, and may be helpful for further experiments of rational enzyme design based on the (α/α)6-barrel basic scaffold.

  13. Modulated mechanism of phosphatidylserine on the catalytic activity of Naja naja atra phospholipase A2 and Notechis scutatus scutatus notexin.

    Science.gov (United States)

    Chiou, Yi-Ling; Lin, Shinne-Ren; Hu, Wan-Ping; Chang, Long-Sen

    2014-12-15

    Phosphatidylserine (PS) externalization is a hallmark for apoptotic death of cells. Previous studies showed that Naja naja atra phospholipase A2 (NnaPLA2) and Notechis scutatus scutatus notexin induced apoptosis of human cancer cells. However, NnaPLA2 and notexin did not markedly disrupt the integrity of cellular membrane as evidenced by membrane permeability of propidium iodide. These findings reflected that the ability of NnaPLA2 and notexin to hydrolyze membrane phospholipids may be affected by PS externalization. To address that question, this study investigated the membrane-interacted mode and catalytic activity of NnaPLA2 and notexin toward outer leaflet (phosphatidylcholine/sphingomyelin/cholesterol, PC/SM/Chol) and inner leaflet (phosphatidylserine/phosphatidylethanolamine/cholesterol, PS/PE/Chol) of plasma membrane-mimicking vesicles. PS incorporation promoted enzymatic activity of NnaPLA2 and notexin on PC and PC/SM vesicles, but suppressed NnaPLA2 and notexin activity on PC/SM/Chol and PE/Chol vesicles. PS incorporation increased the membrane fluidity of PC vesicles but reduced membrane fluidity of PC/SM, PC/SM/Chol and PE/Chol vesicles. PS increased the phospholipid order of all the tested vesicles. Moreover, PS incorporation did not greatly alter the binding affinity of notexin and NnaPLA2 with phospholipid vesicles. Acrylamide quenching studies and trinitrophenylation of Lys residues revealed that membrane-bound mode of notexin and NnaPLA2 varied with the targeted membrane compositions. The fine structure of catalytic site in NnaPLA2 and notexin in all the tested vesicles showed different changes. Collectively, the present data suggest that membrane-inserted PS modulates PLA2 interfacial activity via its effects on membrane structure and membrane-bound mode of NnaPLA2 and notexin, and membrane compositions determine the effect of PS on PLA2 activity. Copyright © 2014 Elsevier Ltd. All rights reserved.

  14. mTOR Ser-2481 autophosphorylation monitors mTORC-specific catalytic activity and clarifies rapamycin mechanism of action.

    Science.gov (United States)

    Soliman, Ghada A; Acosta-Jaquez, Hugo A; Dunlop, Elaine A; Ekim, Bilgen; Maj, Nicole E; Tee, Andrew R; Fingar, Diane C

    2010-03-12

    The mammalian target of rapamycin (mTOR) Ser/Thr kinase signals in at least two multiprotein complexes distinguished by their different partners and sensitivities to rapamycin. Acute rapamycin inhibits signaling by mTOR complex 1 (mTORC1) but not mTOR complex 2 (mTORC2), which both promote cell growth, proliferation, and survival. Although mTORC2 regulation remains poorly defined, diverse cellular mitogens activate mTORC1 signaling in a manner that requires sufficient levels of amino acids and cellular energy. Before the identification of distinct mTOR complexes, mTOR was reported to autophosphorylate on Ser-2481 in vivo in a rapamycin- and amino acid-insensitive manner. These results suggested that modulation of mTOR intrinsic catalytic activity does not universally underlie mTOR regulation. Here we re-examine the regulation of mTOR Ser-2481 autophosphorylation (Ser(P)-2481) in vivo by studying mTORC-specific Ser(P)-2481 in mTORC1 and mTORC2, with a primary focus on mTORC1. In contrast to previous work, we find that acute rapamycin and amino acid withdrawal markedly attenuate mTORC1-associated mTOR Ser(P)-2481 in cycling cells. Although insulin stimulates both mTORC1- and mTORC2-associated mTOR Ser(P)-2481 in a phosphatidylinositol 3-kinase-dependent manner, rapamycin acutely inhibits insulin-stimulated mTOR Ser(P)-2481 in mTORC1 but not mTORC2. By interrogating diverse mTORC1 regulatory input, we find that without exception mTORC1-activating signals promote, whereas mTORC1-inhibitory signals decrease mTORC1-associated mTOR Ser(P)-2481. These data suggest that mTORC1- and likely mTORC2-associated mTOR Ser-2481 autophosphorylation directly monitors intrinsic mTORC-specific catalytic activity and reveal that rapamycin inhibits mTORC1 signaling in vivo by reducing mTORC1 catalytic activity.

  15. The Nucleus of the Solitary Tract and the coordination of respiratory and sympathetic activities

    Directory of Open Access Journals (Sweden)

    Daniel B. Zoccal

    2014-06-01

    Full Text Available It is well known that breathing introduces rhythmical oscillations in the heart rate and arterial pressure levels. Sympathetic oscillations coupled to the respiratory activity have been suggested as an important homeostatic mechanism optimizing tissue perfusion and blood gas uptake/delivery. This respiratory-sympathetic coupling is strengthened in conditions of blood gas challenges (hypoxia and hypercapnia as a result of the synchronized activation of brainstem respiratory and sympathetic neurons, culminating with the emergence of entrained cardiovascular and respiratory reflex responses. Studies have proposed that the ventrolateral region of the medulla oblongata is a major site of synaptic interaction between respiratory and sympathetic neurons. However, other brainstem regions also play a relevant role in the patterning of respiratory and sympathetic motor outputs. Recent findings suggest that the neurons of the nucleus of the solitary tract (NTS, in the dorsal medulla, are essential for the processing and coordination of respiratory and sympathetic responses to hypoxia. The NTS is the first synaptic station of the cardiorespiratory afferent inputs, including peripheral chemoreceptors, baroreceptors and pulmonary stretch receptors. The synaptic profile of the NTS neurons receiving the excitatory drive from afferent inputs is complex and involves distinct neurotransmitters, including glutamate, ATP and acetylcholine. In the present review we discuss the role of the NTS circuitry in coordinating sympathetic and respiratory reflex responses. We also analyze the neuroplasticity of NTS neurons and their contribution for the development of cardiorespiratory dysfunctions, as observed in neurogenic hypertension, obstructive sleep apnea and metabolic disorders.

  16. Dynamic Shift Coordinated Control Based on Motor Active Speed Synchronization with the New Hybrid System

    Directory of Open Access Journals (Sweden)

    Ting Yan

    2017-01-01

    Full Text Available Considering the inherent disadvantages that severely affect driving comfortability during the shift process in HEVs, a dynamic shift coordinated control based on motor active speed synchronization is proposed to improve shift quality by reduction of shift vibration. The whole control scheme is comprised of three phases, preparatory phase, speed regulation phase, and synchronization phase, which are implemented consecutively in order. The key to inhibiting impact and jerk depends on the speed regulation phase, where motor active speed synchronization is utilized to reach the minimum speed difference between the two ends of synchronizer. A new hybrid system with superior performances is applied to present the validity of the adopted control algorithm during upshift or downshift, which can represent planetary gear system and conventional AMT shift procedure, respectively. Bench test, simulation, and road test results show that, compared with other methods, the proposed dynamic coordinated control can achieve shifting control in real time to effectively improve gear-shift comfort and shorten power interruption transients, with robustness in both conventional AMT and planetary gear train.

  17. Role of communication systems in coordinating supervising anesthesiologists' activities outside of operating rooms.

    Science.gov (United States)

    Smallman, Bettina; Dexter, Franklin; Masursky, Danielle; Li, Fenghua; Gorji, Reza; George, Dave; Epstein, Richard H

    2013-04-01

    Theoretically, communication systems have the potential to increase the productivity of anesthesiologists supervising anesthesia providers. We evaluated the maximal potential of communication systems to increase the productivity of anesthesia care by enhancing anesthesiologists' coordination of care (activities) among operating rooms (ORs). At hospital A, data for 13,368 pages were obtained from files recorded in the internal alphanumeric text paging system. Pages from the postanesthesia care unit were processed through a numeric paging system and thus not included. At hospital B, in a different US state, 3 of the authors categorized each of 898 calls received using the internal wireless audio system (Vocera(®)). Lower and upper 95% confidence limits for percentages are the values reported. At least 45% of pages originated from outside the ORs (e.g., 20% from holding area) at hospital A and at least 56% of calls (e.g., 30% administrative) at hospital B. In contrast, requests from ORs for urgent presence of the anesthesiologist were at most 0.2% of pages at hospital A and 1.8% of calls at hospital B. Approximately half of messages to supervising anesthesiologists are for activity originating outside the ORs being supervised. To use communication tools to increase anesthesia productivity on the day of surgery, their use should include a focus on care coordination outside ORs (e.g., holding area) and among ORs (e.g., at the control desk).

  18. Coordination chemistry controls the thiol oxidase activity of the B12-trafficking protein CblC.

    Science.gov (United States)

    Li, Zhu; Shanmuganathan, Aranganathan; Ruetz, Markus; Yamada, Kazuhiro; Lesniak, Nicholas A; Kräutler, Bernhard; Brunold, Thomas C; Koutmos, Markos; Banerjee, Ruma

    2017-06-09

    The cobalamin or B 12 cofactor supports sulfur and one-carbon metabolism and the catabolism of odd-chain fatty acids, branched-chain amino acids, and cholesterol. CblC is a B 12 -processing enzyme involved in an early cytoplasmic step in the cofactor-trafficking pathway. It catalyzes the glutathione (GSH)-dependent dealkylation of alkylcobalamins and the reductive decyanation of cyanocobalamin. CblC from Caenorhabditis elegans ( ce CblC) also exhibits a robust thiol oxidase activity, converting reduced GSH to oxidized GSSG with concomitant scrubbing of ambient dissolved O 2 The mechanism of thiol oxidation catalyzed by ce CblC is not known. In this study, we demonstrate that novel coordination chemistry accessible to ce CblC-bound cobalamin supports its thiol oxidase activity via a glutathionyl-cobalamin intermediate. Deglutathionylation of glutathionyl-cobalamin by a second molecule of GSH yields GSSG. The crystal structure of ce CblC provides insights into how architectural differences at the α- and β-faces of cobalamin promote the thiol oxidase activity of ce CblC but mute it in wild-type human CblC. The R161G and R161Q mutations in human CblC unmask its latent thiol oxidase activity and are correlated with increased cellular oxidative stress disease. In summary, we have uncovered key architectural features in the cobalamin-binding pocket that support unusual cob(II)alamin coordination chemistry and enable the thiol oxidase activity of ce CblC. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

  19. Physicochemical properties and catalytic activity of metal-carbon carrier composite materials

    Science.gov (United States)

    Kobotaeva, N. S.; Skorokhodova, T. S.; Razd'yakonova, G. I.; Poleshchuk, O. Kh.

    2017-07-01

    Composite metal-carbon materials are created on the basis of different kinds of carbon (multiwall carbon nanotubes, carbon black, Sibunit carbon-carbon material) and metals (Ag, Ni, Co), and their physicochemical and catalytic properties are investigated. It is shown that interaction between metals and carbon carriers proceeds not only with the functional groups on the surfaces of the carriers, but also through a system of-C-C-conjugated bonds. Silver deposited on the surface of a carbon carrier has a crystalline structure ( d cr = 10-15 nm), while nickel has an amorphous lamellar structure. Based on quantum-chemical calculations using the density functional theory, it is shown that cumene oxidation occurs via a homogeneous-heterogeneous mechanism.

  20. Synthesis, spectral studies and catalytic activity of ruthenium(II) complexes with organic amide ligands

    Energy Technology Data Exchange (ETDEWEB)

    Ashok, More; Prasad, Adapa V.S.S.; Ravinder, Vadde [Kakatiya University, Warangal (India). Dept. of Chemistry]. E-mail: ravichemku@rediffmail.com

    2007-07-01

    Twelve new hexacoordinated ruthenium(II) complexes with organic amides, [RuH(CO)(PPh{sub 3}){sub 2}(L{sub 2})], have been synthesized by treating the precursor, [RuH{sub 2}(CO)(PPh{sub 3}){sub 3}], with twelve different amide proligands separately. These complexes were characterized by elemental analysis and by UV-vis, IR, {sup 1}H, {sup 13}C and {sup 31}P NMR spectroscopies. Molecular formulae and octahedral structures have been tentatively proposed for the products. These complexes were found to be efficient in the catalytic reduction of NO{sub 2}-containing drugs such as chloramphenicol and metronidazole to their amino derivatives. The percent yields of the reduction products were determined spectrophotometrically. (author)

  1. Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials.

    Science.gov (United States)

    Hu, Xin-Ming; Rønne, Magnus H; Pedersen, Steen U; Skrydstrup, Troels; Daasbjerg, Kim

    2017-06-01

    In a comparative study of the electrocatalytic CO2 reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2 . This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Surface Characteristics and Catalytic Activity of Copper Deposited Porous Silicon Powder

    Directory of Open Access Journals (Sweden)

    Muhammad Yusri Abdul Halim

    2014-12-01

    Full Text Available Porous structured silicon or porous silicon (PS powder was prepared by chemical etching of silicon powder in an etchant solution of HF: HNO3: H2O (1:3:5 v/v. An immersion time of 4 min was sufficient for depositing Cu metal from an aqueous solution of CuSO4 in the presence of HF. Scanning electron microscopy (SEM analysis revealed that the Cu particles aggregated upon an increase in metal content from 3.3 wt% to 9.8 wt%. H2-temperature programmed reduction (H2-TPR profiles reveal that re-oxidation of the Cu particles occurs after deposition. Furthermore, the profiles denote the existence of various sizes of Cu metal on the PS. The Cu-PS powders show excellent catalytic reduction on the p-nitrophenol regardless of the Cu loadings.

  3. Architecture engineering toward highly active palladium integrated titanium dioxide yolk-double-shell nanoreactor for catalytic applications.

    Science.gov (United States)

    Liu, Baocang; Wang, Qin; Yu, Shengli; Jing, Peng; Liu, Lixia; Xu, Guangran; Zhang, Jun

    2014-10-21

    Rational design of the hierarchical architecture of a material with well controlled functionality is crucially important for improving its properties. In this paper, we present the general strategies for rationally designing and constructing three types of hierarchical Pd integrated TiO2 double-shell architectures, i.e. yolk-double-shell TiO2 architecture (Pd@TiO2/Pd@TiO2) with yolk-type Pd nanoparticles residing inside the central cavity of the hollow TiO2 structure; ultrafine Pd nanoparticles homogenously dispersed on both the external and internal surfaces of the inner TiO2 shell; and double-shell TiO2 architecture (@TiO2/Pd@TiO2) with Pd nanoparticles solely loaded on the external surface of the inner TiO2 shell, and double-shell TiO2 architecture (@TiO2@Pd@TiO2) with Pd nanoparticles dispersed in the interlayer space of double TiO2 shells, via newly developed Pd(2+) ion-diffusion and Pd sol impregnation methodologies. These architectures are well controlled in structure, size, morphology, and configuration with Pd nanoparticles existing in various locations. Owing to the variable synergistic effects arising from the location discrepancies of Pd nanoparticle in the architectures, they exhibit remarkable variations in catalytic activity. In particular, different from previously reported yolk-shell structures, the obtained yolk-double-shell Pd@TiO2/Pd@TiO2 architecture, which is revealed for the first time, possesses a uniform hierarchical structure, narrow size distribution, and good monodispersibility, and it creates two Pd-TiO2 interfaces on the external and internal surfaces of the inner TiO2 shell, leading to the strongest synergistic effect of Pd nanoparticles with TiO2 shell. Furthermore, the interlayer chamber between the double TiO2 shells connecting with the central cavity of the hollow TiO2 structure through the mesoporous TiO2 wall forms a nanoreactor for enriching the reactants and preventing the deletion of Pd nanoparticles during the reaction, thus

  4. Cytosolic entry of Shiga-like toxin a chain from the yeast endoplasmic reticulum requires catalytically active Hrd1p.

    Directory of Open Access Journals (Sweden)

    Shuyu Li

    Full Text Available BACKGROUND: Escherichia coli Shiga-like toxin 1 normally traffics to the endoplasmic reticulum (ER in sensitive mammalian cells from where the catalytic A chain (SLTxA1 dislocates to the cytosol to inactivate ribosomes. Currently, no molecular details of the dislocation process are available. To investigate the mechanism of the dislocation step we expressed SLTxA1 in the ER of Saccharomyces cerevisiae. METHODOLOGY AND PRINCIPAL FINDINGS: Using a combination of growth studies and biochemical tracking in yeast knock-out strains we show that SLTxA1 follows an ER-associated degradation (ERAD pathway to enter the cytosol in a step mediated by the transmembrane Hrd1p ubiquitin ligase complex. ER-to-cytosol dislocation of the bulk population of SLTxA1 requires Cdc48p and its ubiquitin-handling co-factor Npl4p, and this population of toxin is terminally dispatched by proteasomal degradation. A small sub-population of SLTxA1 uncouples from this classical ERAD pathway and recovers catalytic activity in the cytosol. The pathway that leads to toxicity is also Hrd1p-dependent but, unlike that for the related ricin A chain toxin, SLTxA1 dislocation does require the catalytic cysteine of Hrd1p. However it does not depend on canonical ubiquitylation since toxin variants lacking endogenous lysyl residues also utilize this pathway, and furthermore there is no requirement for a number of Cdc48p co-factors. CONCLUSIONS AND SIGNIFICANCE: The fraction of SLTxA1 that disengages from the ERAD pathway thus does so upstream of Cdc48p interactions and downstream of Hrd1p interactions, in a step that possibly involves de-ubiquitylation. Mechanistically therefore, the dislocation of this toxin is quite distinct from that of conventional ERAD substrates that are normally degraded, and the toxins partially characterised to date that do not require the catalytic cysteine of the major Hrd1p component of the dislocation apparatus.

  5. Difference in activity in the supplementary motor area depending on limb combination of hand-foot coordinated movements

    Directory of Open Access Journals (Sweden)

    Kento Nakagawa

    2016-10-01

    Full Text Available Periodic interlimb coordination shows lower performance when the ipsilateral hand and foot (e.g. right hand and right foot are simultaneously moved than when the contralateral hand and foot (e.g. right hand and left foot are simultaneously moved. The present study aimed to investigate how brain activity that is related to the dependence of hand-foot coordination on limb combination, using functional magnetic imaging (fMRI. Twenty-one right-handed subjects performed periodic coordinated movements of the ipsilateral or contralateral hand and foot in the same or opposite direction in the sagittal plane. Kinematic data showed that performance was lower for the ipsilateral hand-foot coordination than for the contralateral one. A comparison of brain activity between the same and opposite directions showed that there was a greater activation of supplemental motor area (SMA for ipsilateral hand-foot coordination as compared to that seen during contralateral hand-foot coordination. We speculate that this might reflect a difference in the degree of inhibition of the neural circuit that disrupts opposite directional movements between ipsilateral and contralateral hand-foot coordinated movements.

  6. SATB1 packages densely-looped, transciptionally-active chromatinfor coordinated expression of cytokine genes

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Shutao; Lee, Charles C.; Kohwi-Shigematsu, Terumi

    2006-05-23

    SATB1 is an important regulator of nuclear architecture that anchors specialized DNA sequences onto its cage-like network and recruits chromatin remodeling/modifying factors to control gene transcription. We studied the role of SATB1 in regulating the coordinated expression of Il5, Il4, and Il13 from the 200kb cytokine gene cluster region of mouse chromosome 11 during T-helper 2 (Th2)-cell activation. We show that upon cell activation, SATB1 is rapidly induced to form a unique transcriptionally-active chromatin structure that includes the cytokine gene region. Chromatin is folded into numerous small loops all anchored by SATB1, is histone H3 acetylated at lysine 9/14, and associated with Th2-specific factors, GATA3, STAT6, c-Maf, the chromatin-remodeling enzyme Brg-1, and RNA polymerase II across the 200kb region. Before activation, the chromatin displays some of these features, such as association with GATA3 and STAT6, but these were insufficient for cytokine gene expression. Using RNA interference (RNAi), we show that upon cell activation, SATB1 is not only required for chromatin folding into dense loops, but also for c-Maf induction and subsequently for Il4, Il5, and Il13 transcription. Our results show that SATB1 is an important determinant for chromatin architecture that constitutes a novel higher-order, transcriptionally-active chromatin structure upon Th2-cell activation.

  7. High catalytic activity achieved with a mixed manganese-iron site in protein R2 of Chlamydia ribonucleotide reductase.

    Science.gov (United States)

    Voevodskaya, Nina; Lendzian, Friedhelm; Ehrenberg, Anders; Gräslund, Astrid

    2007-07-24

    Ribonucleotide reductase (class I) contains two components: protein R1 binds the substrate, and protein R2 normally has a diferric site and a tyrosyl free radical needed for catalysis. In Chlamydia trachomatis RNR, protein R2 functions without radical. Enzyme activity studies show that in addition to a diiron cluster, a mixed manganese-iron cluster provides the oxidation equivalent needed to initiate catalysis. An EPR signal was observed from an antiferromagnetically coupled high-spin Mn(III)-Fe(III) cluster in a catalytic reaction mixture with added inhibitor hydroxyurea. The manganese-iron cluster in protein R2 confers much higher specific activity than the diiron cluster does to the enzyme.

  8. Novel Cage-Like Hexanuclear Nickel(II Silsesquioxane. Synthesis, Structure, and Catalytic Activity in Oxidations with Peroxides

    Directory of Open Access Journals (Sweden)

    Alexey N. Bilyachenko

    2016-05-01

    Full Text Available New hexanuclear nickel(II silsesquioxane [(PhSiO1.512(NiO6(NaCl] (1 was synthesized as its dioxane-benzonitrile-water complex (PhSiO1,512(NiO6(NaCl(C4H8O213(PhCN2(H2O2 and studied by X-ray and topological analysis. The compound exhibits cylinder-like type of molecular architecture and represents very rare case of polyhedral complexation of metallasilsesquioxane with benzonitrile. Complex 1 exhibited catalytic activity in activation of such small molecules as light alkanes and alcohols. Namely, oxidation of alcohols with tert-butylhydroperoxide and alkanes with meta-chloroperoxybenzoic acid. The oxidation of methylcyclohexane gave rise to the isomeric ketones and unusual distribution of alcohol isomers.

  9. A study on the morphology and catalytic activity of gold nanoparticles by the kinetic Monte Carlo simulation

    Science.gov (United States)

    He, Xiang; Chen, Zhao-Xu

    2016-05-01

    We studied the thermal-stability of supported Au nanoparticles on the substrates of different binding strength to gold by Monte Carlo simulations. It has been revealed that the stable Au morphology is determined by the temperature and the binding strength. When heated on the strongly-binding substrates, the Au nanoparticles would wet the substrate completely and form monolayer. The stable Au layered structure of few layers can be formed by the incomplete wetting of clusters on the intermediate-binding substrates. The simulation results are in good agreement with pertinent experimental and theoretical results. Based on the simulation results and experimental observations, we find the strong linkage between the top edge sites and the activity TOF of low-temperature CO oxidation. We conclude that the top edges sites of Au layered structures are possible reactive sites. This study may provide new perspective for controlling morphology and understanding catalytic activity of supported metallic clusters.

  10. Effect of dioxane on the binding of competitive inhibitor proflavin and catalytic activity of bovine pancreatic α-chymotrypsin

    Science.gov (United States)

    Sirotkin, V. A.; Mukhametzyanov, T. A.; Karmanova, Yu. V.

    2007-07-01

    The binding of competitive inhibitor proflavin by α-chymotrypsin in water-dioxane mixtures over the entire range of thermodynamic activities of water a w was studied. The data on the degree of binding of proflavin were compared to the results on the catalytic activity of the enzyme preliminary incubated in water-dioxane mixtures. An analysis of the behavior of the concentration dependences of these characteristics demonstrated that, at low a w values, the behavior of the interprotein contacts in the enzyme formed during its drying largely governs its functional properties, while at high a w values, they are determined by the interaction of the enzyme with the organic solvent. Interplay of these two factors is responsible for the observed complex shape of the isotherm of binding of proflavin, with the maximum degree of binding being attained at moderate a w values.

  11. Free-Standing Metal Oxide Nanoparticle Superlattices Constructed with Engineered Protein Containers Show in Crystallo Catalytic Activity.

    Science.gov (United States)

    Lach, Marcel; Künzle, Matthias; Beck, Tobias

    2017-12-11

    The construction of defined nanostructured catalysts is challenging. In previous work, we established a strategy to assemble binary nanoparticle superlattices with oppositely charged protein containers as building blocks. Here, we show that these free-standing nanoparticle superlattices are catalytically active. The metal oxide nanoparticles inside the protein scaffold are accessible for a range of substrates and show oxidase-like and peroxidase-like activity. The stable superlattices can be reused for several reaction cycles. In contrast to bulk nanoparticle-based catalysts, which are prone to aggregation and difficult to characterize, nanoparticle superlattices based on engineered protein containers provide an innovative synthetic route to structurally defined heterogeneous catalysts with control over nanoparticle size and composition. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. A Short Review on the Catalytic Activity of Hydrotalcite-Derived Materials for Dry Reforming of Methane

    Directory of Open Access Journals (Sweden)

    Radosław Dębek

    2017-01-01

    Full Text Available Nickel-containing hydrotalcite-derived materials have been recently proposed as promising materials for methane dry reforming (DRM. Based on a literature review and on the experience of the authors, this review focuses on presenting past and recent achievements on increasing activity and stability of hydrotalcite-based materials for DRM. The use of different NiMgAl and NiAl hydrotalcite (HT precursors, various methods for nickel introduction into HT structure, calcination conditions and promoters are discussed. HT-derived materials containing nickel generally exhibit high activity in DRM; however, the problem of preventing catalyst deactivation by coking, especially below 700 °C, is still an open question. The proposed solutions in the literature include: catalyst regeneration either in oxygen atmosphere or via hydrogasification; or application of various promoters, such as Zr, Ce or La, which was proven to enhance catalytic stability.

  13. Design of a Catalytic Active Site for Electrochemical CO2 Reduction with Mn(I)-Tricarbonyl Species.

    Science.gov (United States)

    Agarwal, Jay; Shaw, Travis W; Schaefer, Henry F; Bocarsly, Andrew B

    2015-06-01

    The design, synthesis, and assessment of a new manganese-centered catalyst for the electrochemical reduction of CO2 is described. The reported species, MnBr(6-(2-hydroxyphenol)-2,2'-bipyridine)(CO)3, includes a ligand framework with a phenolic proton in close proximity to the CO2 binding site, which allows for facile proton-assisted C-O bond cleavage. As a result of this modification, seven times the electrocatalytic current enhancement is observed compared to MnBr(2,2'-bipyridine)(CO)3. Moreover, reduction is possible at only 440 mV of overpotential. Theoretical computations suggest that the entropic contribution to the activation free energy is partially responsible for the increased catalytic activity. Experimental work, including voltammetry and product quantification from controlled potential electrolysis, suggests a key mechanistic role for the phenolic proton in the conversion of CO2 to CO.

  14. Enhancement of catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol through interfacial modification with heteropolymolybdates

    Science.gov (United States)

    Barczuk, Piotr J.; Lewera, Adam; Miecznikowski, Krzysztof; Zurowski, Artur; Kulesza, Pawel J.

    As evidenced from the increase of electrocatalytic currents measured under voltammetric and chronoamperometric conditions, the activity of bimetallic Pt-Ru and Pt-Sn nanoparticles towards oxidation of ethanol is increased by modification of their surfaces with ultra-thin films of phosphododecamolybdic acid (H 3PMo 12O 40). The enhancement effect has been most pronounced in a case of heteropolymolybdate-modified carbon-supported Pt-Sn catalysts. Independent high-resolution XPS measurements indicate the ability of heteropolymolybdates to stabilize tin (in bimetallic Pt-Sn particles) at higher oxidation states (presumably as tin oxo species). The overall activation effect may also be ascribed to changes in the morphology of catalytic films following modification with heteropolymolybdates. Presence of the polyoxometallate is also likely to increase of the interfacial population of reactive oxo groups in the vicinity of platinum centers.

  15. Enhancement of catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol through interfacial modification with heteropolymolybdates

    Energy Technology Data Exchange (ETDEWEB)

    Barczuk, Piotr J.; Lewera, Adam; Miecznikowski, Krzysztof; Zurowski, Artur; Kulesza, Pawel J. [Department of Chemistry, University of Warsaw, Pasteura 1, PL-02-093 Warsaw (Poland)

    2010-05-01

    As evidenced from the increase of electrocatalytic currents measured under voltammetric and chronoamperometric conditions, the activity of bimetallic Pt-Ru and Pt-Sn nanoparticles towards oxidation of ethanol is increased by modification of their surfaces with ultra-thin films of phosphododecamolybdic acid (H{sub 3}PMo{sub 12}O{sub 40}). The enhancement effect has been most pronounced in a case of heteropolymolybdate-modified carbon-supported Pt-Sn catalysts. Independent high-resolution XPS measurements indicate the ability of heteropolymolybdates to stabilize tin (in bimetallic Pt-Sn particles) at higher oxidation states (presumably as tin oxo species). The overall activation effect may also be ascribed to changes in the morphology of catalytic films following modification with heteropolymolybdates. Presence of the polyoxometallate is also likely to increase of the interfacial population of reactive oxo groups in the vicinity of platinum centers. (author)

  16. Transition Metal Ions in Zeolites: Coordination and activation of O2

    Science.gov (United States)

    Smeets, Pieter J.; Woertink, Julia S.; Sels, Bert F.; Solomon, Edward I.; Schoonheydt, Robert A.

    2010-01-01

    Zeolites containing transition metal ions (TMI) often show promising activity as heterogeneous catalysts in pollution abatement and selective oxidation reactions. In this paper, two aspects of research on the TMI Cu, Co and Fe in zeolites are discussed: (i) coordination to the lattice and (ii) activated oxygen species. At low loading, TMI preferably occupy exchange sites in six-membered oxygen rings (6MR) where the TMI preferentially coordinate with the oxygen atoms of Al tetrahedra. High TMI loadings result in a variety of TMI species formed at the zeolite surface. Removal of the extra-lattice oxygens during high temperature pretreatments can result in auto-reduction. Oxidation of reduced TMI sites often results in the formation of highly reactive oxygen species. In Cu-ZSM-5, calcination with O2 results in the formation of a species, which was found to be a crucial intermediate in both the direct decomposition of NO and N2O and the selective oxidation of methane into methanol. An activated oxygen species, called α-oxygen, is formed in Fe-ZSM5 and reported to be the active site in the partial oxidation of methane and benzene into methanol and phenol, respectively. However, this reactive α-oxygen can only be formed with N2O, not with O2. O2 activated Co intermediates in Faujasite (FAU) zeolites can selectively oxidize α-pinene and epoxidize styrene. In Co-FAU, CoIII superoxo and peroxo complexes are suggested to be the active cores, whereas in Cu and Fe-ZSM-5 various monomeric and dimeric sites have been proposed, but no consensus has been obtained. Very recently, the active site in Cu-ZSM-5 was identified as a bent [Cu-O-Cu]2+ core (Proc. Natl. Acad. Sci. USA 2009, 106, 18908-18913). Overall, O2 activation depends on the interplay of structural factors such as type of zeolite, size of the channels and cages and chemical factors such as Si/Al ratio and the nature, charge and distribution of the charge balancing cations. The presence of several different TMI sites

  17. Support effects on adsorption and catalytic activation of O2in single atom iron catalysts with graphene-based substrates.

    Science.gov (United States)

    Gao, Zheng-Yang; Yang, Wei-Jie; Ding, Xun-Lei; Lv, Gang; Yan, Wei-Ping

    2018-02-27

    The adsorption and catalytic activation of O 2 on single atom iron catalysts with graphene-based substrates were investigated systematically by density functional theory calculation. It is found that the support effects of graphene-based substrates have a significant influence on the stability of the single atom catalysts, the adsorption configuration, the electron transfer mechanism, the adsorption energy and the energy barrier. The differences in the stable adsorption configuration of O 2 on single atom iron catalysts with different graphene-based substrates can be well understood by the symmetrical matching principle based on frontier molecular orbital analysis. There are two different mechanisms of electron transfer, in which the Fe atom acts as the electron donor in single vacancy graphene-based substrates while the Fe atom mainly acts as the bridge for electron transfer in double vacancy graphene-based substrates. The Fermi softness and work function are good descriptors of the adsorption energy and they can well reveal the relationship between electronic structure and adsorption energy. This single atom iron catalyst with single vacancy graphene modified by three nitrogen atoms is a promising non-noble metal single atom catalyst in the adsorption and catalytic oxidation of O 2 . Furthermore, the findings can lay the foundation for the further study of graphene-based support effects and provide a guideline for the development and design of new non-noble-metal single atom catalysts.

  18. Identifying the Atomic-Level Effects of Metal Composition on the Structure and Catalytic Activity of Peptide-Templated Materials.

    Science.gov (United States)

    Merrill, Nicholas A; McKee, Erik M; Merino, Kyle C; Drummy, Lawrence F; Lee, Sungsik; Reinhart, Benjamin; Ren, Yang; Frenkel, Anatoly I; Naik, Rajesh R; Bedford, Nicholas M; Knecht, Marc R

    2015-12-22

    Bioinspired approaches for the formation of metallic nanomaterials have been extensively employed for a diverse range of applications including diagnostics and catalysis. These materials can often be used under sustainable conditions; however, it is challenging to control the material size, morphology, and composition simultaneously. Here we have employed the R5 peptide, which forms a 3D scaffold to direct the size and linear shape of bimetallic PdAu nanomaterials for catalysis. The materials were prepared at varying Pd:Au ratios to probe optimal compositions to achieve maximal catalytic efficiency. These materials were extensively characterized at the atomic level using transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, and atomic pair distribution function analysis derived from high-energy X-ray diffraction patterns to provide highly resolved structural information. The results confirmed PdAu alloy formation, but also demonstrated that significant surface structural disorder was present. The catalytic activity of the materials was studied for olefin hydrogenation, which demonstrated enhanced reactivity from the bimetallic structures. These results present a pathway to the bioinspired production of multimetallic materials with enhanced properties, which can be assessed via a suite of characterization methods to fully ascertain structure/function relationships.

  19. Ensemble averaged structure-function relationship for nanocrystals: effective superparamagnetic Fe clusters with catalytically active Pt skin.

    Science.gov (United States)

    Petkov, Valeri; Prasai, Binay; Shastri, Sarvjit; Park, Hyun-Uk; Kwon, Young-Uk; Skumryev, Vassil

    2017-10-19

    Practical applications require the production and usage of metallic nanocrystals (NCs) in large ensembles. Besides, due to their cluster-bulk solid duality, metallic NCs exhibit a large degree of structural diversity. This poses the question as to what atomic-scale basis is to be used when the structure-function relationship for metallic NCs is to be quantified precisely. We address the question by studying bi-functional Fe core-Pt skin type NCs optimized for practical applications. In particular, the cluster-like Fe core and skin-like Pt surface of the NCs exhibit superparamagnetic properties and a superb catalytic activity for the oxygen reduction reaction, respectively. We determine the atomic-scale structure of the NCs by non-traditional resonant high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Using the experimental structure data we explain the observed magnetic and catalytic behavior of the NCs in a quantitative manner. Thus we demonstrate that NC ensemble-averaged 3D positions of atoms obtained by advanced X-ray scattering techniques are a very proper basis for not only establishing but also quantifying the structure-function relationship for the increasingly complex metallic NCs explored for practical applications.

  20. Green synthesis and characterization of polyvinyl alcohol stabilized palladium nanoparticles: effect of solvent on diameter and catalytic activity

    Science.gov (United States)

    Chowdhury, Sreya Roy; Sarathi Roy, Partha; Bhattacharya, Swapan Kumar

    2017-06-01

    Global palladium nanoparticles of different average diameters in the range 2-19 nm have been synthesized at room temperature by the reduction of K2PdCl4 in aqueous alcohols of varying composition in presence of constant proportion of polyvinyl alcohol (PVA). The synthesized nanoparticles have been characterized by different spectroscopic, microscopic and electro analytical techniques like cyclic voltammetry, chronopotentiometry, and chronoamperometry. FTIR spectroscopy detects the effect of co-solvent composition on the particle-PVA interaction involving  -OH group of the latter. X-ray diffraction study shows that the nanoparticles have both face centred cubic and hexagonal crystalline structures which may influence the catalytic capability of the synthesized palladium quantum dots. The study reveals the influence of co-solvent (ethanol) composition in monitoring the average diameter and the nature of encapsulation of palladium nanoparticles which in turn help to monitor the electro-catalytic activity of the synthesized palladium nanoparticles in reference to oxidation of ethanol in alkaline medium.

  1. Selectivity of an Active Natural Zeolite in Catalytic Conversion Process of Bangkirai, Kruing and Kamper Woods Biofuel to Gasoline Fraction

    Directory of Open Access Journals (Sweden)

    Wega Trisunaryanti

    2010-06-01

    Full Text Available The selectivity of an active natural zeolite (ZAAH in catalytic conversion process of Bangkirai, Kruing and Kamper woods biofuels has been studied. The ZAAH catalyst was prepared from a natural zeolite (ZA treated with acids solution (1% HF and 6M HCI and hydrothermal then calcined at 500 °C and oxidized at 400 °C under nitrogen and oxygen gas stream, respectively. Characterizations of the catalysts including Si/Al ratio and acidity were determined by atomic adsorption spectroscopy (AAS and ammonia gas adsorption method, respectively. The conversion process was carried out in a flow reactor system at 400 °C, under N2 stream (20 mL/min. The biofuel was vaporized from the pyrolysis zone to the catalytic reactor. A liquid product was covered and analyzed by gas chromatograph (GC and that connected with mass spectroscopy (GC-MS. The characterization results showed that the Si/AI ratio and acidity of the ZAAH were higher than that of the ZA catalyst. The GC-MS data showed that the highest product selectivity was 2,4-dimethyl heptane and 1,2-dimethyl benzene. The total product selectivity using the ZAAH catalyst (bangkirai = 68.10%; kruing = 54.76%; kamper = 50.72% was higher than that of the ZA catalyst (bangkirai = 39.24%; kruing = 44.38%; kamper = 46.11%.

  2. Electrocatalytic CO2 Reduction with a Homogeneous Catalyst in Ionic Liquid: High Catalytic Activity at Low Overpotential.

    Science.gov (United States)

    Grills, David C; Matsubara, Yasuo; Kuwahara, Yutaka; Golisz, Suzanne R; Kurtz, Daniel A; Mello, Barbara A

    2014-06-05

    We describe a new strategy for enhancing the efficiency of electrocatalytic CO2 reduction with a homogeneous catalyst, using a room-temperature ionic liquid as both the solvent and electrolyte. The electrochemical behavior of fac-ReCl(2,2'-bipyridine)(CO)3 in neat 1-ethyl-3-methylimidazolium tetracyanoborate ([emim][TCB]) was compared with that in acetonitrile containing 0.1 M [Bu4N][PF6]. Two separate one-electron reductions occur in acetonitrile (-1.74 and -2.11 V vs Fc(+/0)), with a modest catalytic current appearing at the second reduction wave under CO2. However, in [emim][TCB], a two-electron reduction wave appears at -1.66 V, resulting in a ∼0.45 V lower overpotential for catalytic reduction of CO2 to CO. Furthermore, the apparent CO2 reduction rate constant, kapp, in [emim][TCB] exceeds that in acetonitrile by over one order of magnitude (kapp = 4000 vs 100 M(-1) s(-1)) at 25 ± 3 °C. Supported by time-resolved infrared measurements, a mechanism is proposed in which an interaction between [emim](+) and the two-electron reduced catalyst results in rapid dissociation of chloride and a decrease in the activation energy for CO2 reduction.

  3. The effects of exfoliation, organic solvents and anodic activation on the catalytic hydrogen evolution reaction of tungsten disulfide.

    Science.gov (United States)

    Liu, Wanglian; Benson, John; Dawson, Craig; Strudwick, Andrew; Raju, Arun Prakash Aranga; Han, Yisong; Li, Meixian; Papakonstantinou, Pagona

    2017-09-21

    The rational design of transition metal dichalcogenide electrocatalysts for efficiently catalyzing the hydrogen evolution reaction (HER) is believed to lead to the generation of a renewable energy carrier. To this end, our work has made three main contributions. At first, we have demonstrated that exfoliation via ionic liquid assisted grinding combined with gradient centrifugation is an efficient method to exfoliate bulk WS2 to nanosheets with a thickness of a few atomic layers and lateral size dimensions in the range of 100 nm to 2 nm. These WS2 nanosheets decorated with scattered nanodots exhibited highly enhanced catalytic performance for HER with an onset potential of -130 mV vs. RHE, an overpotential of 337 mV at 10 mA cm(-2) and a Tafel slope of 80 mV dec(-1) in 0.5 M H2SO4. Secondly, we found a strong aging effect on the electrocatalytic performance of WS2 stored in high boiling point organic solvents such as dimethylformamide (DMF). Importantly, the HER ability could be recovered by removing the organic (DMF) residues, which obstructed the electron transport, with acetone. Thirdly, we established that the HER performance of WS2 nanosheets/nanodots could be significantly enhanced by activating the electrode surface at a positive voltage for a very short time (60 s), decreasing the kinetic overpotential by more than 80 mV at 10 mA cm(-2). The performance enhancement was found to arise primarily from the ability of a formed proton-intercalated amorphous tungsten trioxide (a-WO3) to provide additional active sites and favourably modify the immediate chemical environment of the WS2 catalyst, rendering it more favorable for local proton delivery and/or transport to the active edge site of WS2. Our results provide new insights into the effects of organic solvents and electrochemical activation on the catalytic performance of two-dimensional WS2 for HER.

  4. Coordination of deep hip muscle activity is altered in symptomatic femoroacetabular impingement.

    Science.gov (United States)

    Diamond, Laura E; Van den Hoorn, Wolbert; Bennell, Kim L; Wrigley, Tim V; Hinman, Rana S; O'Donnell, John; Hodges, Paul W

    2017-07-01

    Diagnosis of femoroacetabular impingement (FAI) is increasing, yet the associated physical impairments remain poorly defined. This morphological hip condition can cause joint pain, stiffness, impaired function, and eventually hip osteoarthritis. This exploratory study compared coordination of deep hip muscles between people with and without symptomatic FAI using analysis of muscle synergies (i.e., patterns of activity of groups of muscles activated in synchrony) during gait. Fifteen individuals (11 males) with symptomatic FAI (clinical examination and imaging) and 14 age- and sex-comparable controls without morphological FAI underwent testing. Intramuscular fine-wire and surface electrodes recorded electromyographic activity of selected deep and superficial hip muscles. A non-negative matrix factorization algorithm extracted three synergies which were compared between groups. Information regarding which muscles were activated together in the FAI group (FAI group synergy vector) was used to reconstruct individual electromyography patterns and compare groups. Variance accounted for (VAF) by three synergies was less for the control (94.8 [1.4]%) than FAI (96.0 [1.0]%) group (p = 0.03). VAF of obturator internus was significantly higher in the FAI group (p = 0.02). VAF of the reconstructed individual electromyography patterns with the FAI or control group vector were significantly higher for the FAI group (p < 0.01). Following reconstruction, VAF of quadratus femoris was significantly more reduced in controls (p = 0.04), indicating greater between-subject variability. Coordination of deep hip muscles in the synergy related to hip joint control during early swing differed between groups. This phase involves movement towards the impingement position, which has relevance for the interpretation of synergy differences and potential clinical importance. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1494-1504, 2017

  5. Hydroxide-bridged dicopper complexes: the influence of secondary coordination sphere on structure and catecholase activity.

    Science.gov (United States)

    Bansal, Deepak; Gupta, Rajeev

    2017-04-05

    Amide-based ligands (H2L(1-6)) with assorted functional groups appended to them have been used for the synthesis of dicopper(ii) complexes 1-6 having a Cu(μ-OH)Cu core. The crystal structures of 1-6 show that while every Cu(ii) ion is ligated within the N3 pincer cavity of a potentially multidentate ligand, two Cu(ii) centers are bridged by a hydroxide group. Notably, the Cu(μ-OH)Cu core is encased within the secondary coordination sphere intricately created by the appended groups. While complexes 1 and 2 exhibit the presence of an H-bond acceptor in the proximity of the Cu(μ-OH)Cu core, complexes 3 and 4 display the occurrence of both the H-bond donor as well as H-bond acceptor groups in the vicinity of the Cu(μ-OH)Cu core. In contrast, complexes 5 and 6 present modified secondary coordination spheres around the Cu(μ-OH)Cu core with limited H-bonding interacting groups in 5 and no such groups in 6. We show that the extent of H-bonding by the appended groups modulates not only the Cu-OH bond distance, Cu(μ-OH)Cu angle and Cu-Cu separation but also the Cu(2+)/Cu(+) redox potential. All six complexes were utilized for their ability to oxidize 3,5-di-tert-butylcatechol, and the catecholase activity results have been correlated to the secondary coordination sphere created by the appended groups in all six complexes.

  6. Rhenium doping induced structural transformation in mono-layered MoS2 with improved catalytic activity for hydrogen evolution reaction

    Science.gov (United States)

    Shi, Wenwu; Wang, Zhiguo; Qing Fu, Yong

    2017-10-01

    This paper reports a new design methodology to improve catalytic activities of catalysts based on 2D transition metal dichalcogenides through elemental doping which induces structural transformations. Effects of rhenium (Re) doping on structural stability/phase transformation and catalytic activity of mono-layered trigonal prismatic (2H) MoS2 were investigated using density functional theory as one example. Results show that 2H-Mo1-x Re x S2 transforms into 1T‧-Mo1-x Re x S2MoS2 as the value of x is larger than 0.4, and the transfer of the electron from Re to Mo is identified as the main reason for this structural transformation. The 1T‧-Mo1-x Re x S2 shows a good catalytic activity for the hydrogen evolution reaction when 0.75  ⩽  x  ⩽  0.94.

  7. Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions.

    Science.gov (United States)

    Sahin, Ziya; Akkoς, Senem; İlhan, İlhan Özer; Kayser, Veysel

    2017-07-30

    Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from benzimidazolium salts. Detailed and generalized protocols are also presented for testing the catalytic activity of such complexes in arylation and Suzuki-Miyaura cross-coupling reactions. Representative results are shown for the catalytic activity of the four complexes in arylation and Suzuki-Miyaura type reactions. For each of the reactions investigated, at least one of the four complexes successfully catalyzed the reaction, qualifying them as promising candidates for catalysis of many carbon-carbon bond-forming reactions. The protocols presented are general enough to be adapted for the synthesis, purification and catalytic activity testing of new palladium N-heterocyclic carbene complexes.

  8. Sustainability of the Catalytic Activity of a Silica-Titania Composite (STC) for Long-Term Indoor Air Quality Control

    Science.gov (United States)

    Coutts, Janelle L.; Levine, Lanfang H.; Richards, Jeffrey T.

    2011-01-01

    TiO2-assisted photocatalytic oxidation (PCO) is an emerging technology for indoor air quality control and is also being evaluated as an alternative trace contaminant control technology for crew habitats in space exploration. Though there exists a vast range of literature on the development of photocatalysts and associated reactor systems, including catalyst performance and performance-influencing factors, the critical question of whether photocatalysts can sustain their initial catalytic activity over an extended period of operation has not been adequately addressed. For a catalyst to effectively serve as an air quality control product, it must be rugged enough to withstand exposure to a multitude of low concentration volatile organic compounds (VOCs) over long periods of time with minimal loss of activity. The objective of this study was to determine the functional lifetime of a promising photocatalyst - the silica-titania composite (STC) from Sol Gel Solutions, LLC in a real-world scenario. A bench-scale STC-packed annular reactor under continuous irradiation by a UV-A fluorescent black-light blue lamp ((lambda)max = 365 nm) was exposed to laboratory air continuously at an apparent contact time of 0.27 sand challenged with a known concentration of ethanol periodically to assess any changes in catalytic activity. Laboratory air was also episodically spiked with halocarbons (e.g., octafluoropropane), organosulfur compounds (e.g., sulfur hexafluoride), and organosilicons (e.g., siloxanes) to simulate accidental releases or leaks of such VOCs. Total organic carbon (TOC) loading and contaminant profiles of the laboratory air were also monitored. Changes in STC photocatalytic performance were evaluated using the ethanol mineralization rate, mineralization efficiency, and oxidation intermediate (acetaldehyde) formation. Results provide insights to any potential catalyst poisoning by trace halocarbons and organosulfur compounds.

  9. Phosphorylation of Ser-204 and Tyr-405 in human malonyl-CoA decarboxylase expressed in silkworm Bombyx mori regulates catalytic decarboxylase activity.

    Science.gov (United States)

    Hwang, In-Wook; Makishima, Yu; Suzuki, Tomohiro; Kato, Tatsuya; Park, Sungjo; Terzic, Andre; Chung, Shin-Kyo; Park, Enoch Y

    2015-11-01

    Decarboxylation of malonyl-CoA to acetyl-CoA by malonyl-CoA decarboxylase (MCD; EC 4.1.1.9) is a vital catalytic reaction of lipid metabolism. While it is established that phosphorylation of MCD modulates the enzymatic activity, the specific phosphorylation sites associated with the catalytic function have not been documented due to lack of sufficient production of MCD with proper post-translational modifications. Here, we used the silkworm-based Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid system to express human MCD (hMCD) and mapped phosphorylation effects on enzymatic function. Purified MCD from silkworm displayed post-translational phosphorylation and demonstrated coherent enzymatic activity with high yield (-200 μg/silkworm). Point mutations in putative phosphorylation sites, Ser-204 or Tyr-405 of hMCD, identified by bioinformatics and proteomics analyses reduced the catalytic activity, underscoring the functional significance of phosphorylation in modulating decarboxylase-based catalysis. Identified phosphorylated residues are distinct from the decarboxylation catalytic site, implicating a phosphorylation-induced global conformational change of MCD as responsible in altering catalytic function. We conclude that phosphorylation of Ser-204 and Tyr-405 regulates the decarboxylase function of hMCD leveraging the silkworm-based BmNPV bacmid expression system that offers a fail-safe eukaryotic production platform implementing proper post-translational modification such as phosphorylation.

  10. Preliminary X-ray crystallographic studies of BthTX-II, a myotoxic Asp49-phospholipase A{sub 2} with low catalytic activity from Bothrops jararacussu venom

    Energy Technology Data Exchange (ETDEWEB)

    Corrêa, L. C.; Marchi-Salvador, D. P. [Departamento de Física e Biofísica, Instituto de Biociências, UNESP, CP 510, CEP 18618-000, Botucatu-SP (Brazil); Cintra, A. C. O.; Soares, A. M. [Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, FCFRP, USP, Ribeirão Preto/SP (Brazil); Fontes, M. R. M., E-mail: fontes@ibb.unesp.br [Departamento de Física e Biofísica, Instituto de Biociências, UNESP, CP 510, CEP 18618-000, Botucatu-SP (Brazil)

    2006-08-01

    A myotoxic Asp49-PLA{sub 2} with low catalytic activity from B. jararacussu (BthTX-II) was crystallized in the monoclinic crystal system; a complete X-ray diffraction data set was collected and a molecular-replacement solution was obtained. The oligomeric structure of BthTX-II resembles those of the Asp49-PLA{sub 2} PrTX-III and all bothropic Lys49-PLA{sub 2}s. For the first time, a complete X-ray diffraction data set has been collected from a myotoxic Asp49-phospholipase A{sub 2} (Asp49-PLA{sub 2}) with low catalytic activity (BthTX-II from Bothrops jararacussu venom) and a molecular-replacement solution has been obtained with a dimer in the asymmetric unit. The quaternary structure of BthTX-II resembles the myotoxin Asp49-PLA{sub 2} PrTX-III (piratoxin III from B. pirajai venom) and all non-catalytic and myotoxic dimeric Lys49-PLA{sub 2}s. In contrast, the oligomeric structure of BthTX-II is different from the highly catalytic and non-myotoxic BthA-I (acidic PLA{sub 2} from B. jararacussu). Thus, comparison between these structures should add insight into the catalytic and myotoxic activities of bothropic PLA{sub 2}s.

  11. Coordinated activation of premotor and ventromedial prefrontal cortices during vicarious reward.

    Science.gov (United States)

    Shimada, Sotaro; Matsumoto, Madoka; Takahashi, Hidefumi; Yomogida, Yukihito; Matsumoto, Kenji

    2016-03-01

    The vicarious reward we receive from watching likable others obtaining a positive outcome is a pervasive phenomenon, yet its neural correlates are poorly understood. Here, we conducted a series of functional magnetic resonance imaging experiments to test the hypothesis that the brain areas responsible for action observation and reward processing work in a coordinated fashion during vicarious reward. In the first experiment (manipulation phase), the participant was instructed to cheer for a particular player in a two-player competitive game (Rock-Paper-Scissors). This manipulation made participants feel more unity with that player and resulted in unity-related activation in the premotor area during action observation. In the following main experiment, the participant witnessed the previously cheered-for or non-cheered-for player succeed in a new solitary game (a stopwatch game). The ventromedial prefrontal cortex (vmPFC) was activated when the cheered-for player succeeded in the game but not when the other player did. Interestingly, this vmPFC activation was functionally connected with premotor activation only during the cheered-for player's success. These results suggest that vicarious reward is processed in the vmPFC-premotor network, which is activated specifically by the success of the other person with whom the individual feels unity and closeness. © The Author (2015). Published by Oxford University Press.

  12. A new method for preparing highly active unsupported Mo sulfide. Catalytic activity for hydrogenolysis of 4-(1-naphthylmethyl)bibenzyl

    Energy Technology Data Exchange (ETDEWEB)

    Yoneyama, Yoshiharu; Song, Chunshan [Fuel Science Program and Applied Catalysis in Energy Laboratory, Pennsylvania State University, 206 Hosler Building, University Park, PA 16802 (United States)

    1999-04-06

    This paper reports on the catalytic activity of unsupported Mo sulfide (MoS{sub 2} like) catalysts which were prepared by a new and simple method comprised of decomposing ammonium tetrathiomolybdate (ATTM) in an organic solvent with added water under H{sub 2} pressure. Model compound reactions of 4-(1-naphthylmethyl)bibenzyl (NMBB) were carried out at 350-425C under H{sub 2} pressure in order to examine the activity of the Mo sulfide catalysts generated from ATTM with and without added water for C-C bond cleavage and hydrogenation of aromatic ring. The Mo sulfide catalysts generated from ATTM with added water were much more effective for C-C bond cleavage and hydrogenation of aromatic moieties at 350-425C than those from ATTM alone. Two-step tests revealed that the addition of water is effective for generating highly active Mo sulfide catalyst from ATTM, but water itself does not promote catalytic conversion. Removal of water after the decomposition of ATTM with added water at 350-400C under H{sub 2} pressure by hot purging gives highly active Mo sulfide catalyst. These results demonstrate that we have found a new and simple method for preparing highly active, dispersed (unsupported) Mo sulfide catalysts for hydroprocessing

  13. Conformation and catalytic activity of nickel-carbon cluster for ethanol dissociation in carbon nanotube synthesis: Ab initio molecular dynamics simulation

    Science.gov (United States)

    Fukuhara, Satoru; Shimojo, Fuyuki; Shibuta, Yasushi

    2017-07-01

    Conformation and catalytic activity of nickel-carbon binary clusters are investigated to shed light on important questions on the carbon nanotube growth. Carbon atoms tend to stay at the surface of the binary cluster and form carbon chains with increasing carbon concentration. The binary clusters have lower catalytic activity for ethanol dehydrogenation compared to pure nickel clusters due to the strong electron negativity of carbon atoms. Moreover, the Csbnd C bond dissociation in typical fragment molecules, which is a key reaction of carbon nanotube growth via alcohol CVD, is inhibited on the binary cluster due to the increase of the backward reaction.

  14. Iridium nanoparticles with high catalytic activity in degradation of acid red-26: an oxidative approach.

    Science.gov (United States)

    Goel, Anjali; Lasyal, Rajni

    2016-12-01

    Nanocatalysis using metal nanoparticles constitutes one of the emerging technologies for destructive oxidation of organics such as dyes. This paper deals with the degradation of acid red-26 (AR-26), an azo dye by hexacyanoferrate (abbreviated as HCF) (III) using iridium nanoparticles. UV-vis spectroscopy has been employed to obtain the details of the oxidative degradation of the selected dye. The effect of various operational parameters such as HCF(III) concentration, pH, initial dye concentration, catalyst and temperature was investigated systematically at the λmax, 507 nm, of the reaction mixture. Degradation kinetics follows the first order kinetic model with respect to AR-26 and Ir nano concentrations, while with respect to the HCF(III) concentration reaction it follows first order kinetics at lower concentrations, tending towards zero order at higher concentrations. Thermodynamic parameters have been calculated by studying the reaction rate at four different temperatures. The UV-vis, high performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS) analysis of degradation products showed the formation of carboxylic acid and substituted carboxylic acids as major degradation products, which are simple and less hazardous compounds. The big advantage of the present method is the recovery and reuse of iridium nanoparticles. Moreover, turnover frequencies for each catalytic cycle have been determined, indicating the long life span of Ir nanoparticles. Thus, the finding is a novel and highly economical alternative for environmental safety against pollution by dyes, and extendable for other contaminants as well.

  15. A New Energy-Saving Catalytic System: Carbon Dioxide Activation by a Metal/Carbon Catalyst.

    Science.gov (United States)

    Yun, Danim; Park, Dae Sung; Lee, Kyung Rok; Yun, Yang Sik; Kim, Tae Yong; Park, Hongseok; Lee, Hyunjoo; Yi, Jongheop

    2017-09-22

    The conversion of CO 2 into useful chemicals is an attractive method to reduce greenhouse gas emissions and to produce sustainable chemicals. However, the thermodynamic stability of CO 2 means that a lot of energy is required for its conversion into chemicals. Here, we suggest a new catalytic system with an alternative heating system that allows minimal energy consumption during CO 2 conversion. In this system, electrical energy is transferred as heat energy to the carbon-supported metal catalyst. Fast ramping rates allow high operating temperatures (T app =250 °C) to be reached within 5 min, which leads to an 80-fold decrease of energy consumption in methane reforming using CO 2 (DRM). In addition, the consumed energy normalized by time during the DRM reaction in this current-assisted catalysis is sixfold lower (11.0 kJ min -1 ) than that in conventional heating systems (68.4 kJ min -1 ). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Catalytic bioreactors and methods of using same

    Energy Technology Data Exchange (ETDEWEB)

    Worden, Robert Mark; Liu, Yangmu Chloe

    2017-07-25

    Various embodiments provide a bioreactor for producing a bioproduct comprising one or more catalytically active zones located in a housing and adapted to keep two incompatible gaseous reactants separated when in a gas phase, wherein each of the one or more catalytically active zones may comprise a catalytic component retainer and a catalytic component retained within and/or thereon. Each of the catalytically active zones may additionally or alternatively comprise a liquid medium located on either side of the catalytic component retainer. Catalytic component may include a microbial cell culture located within and/or on the catalytic component retainer, a suspended catalytic component suspended in the liquid medium, or a combination thereof. Methods of using various embodiments of the bioreactor to produce a bioproduct, such as isobutanol, are also provided.

  17. Catalytic activity of Ni complexed aminoclay towards the reduction of Cr(V), p-nitrophenol and fluorescein dye

    Science.gov (United States)

    Ranchani, A. Amala Jeya; Parthasarathy, V.; Devi, A. Anitha; Meenarathi, B.; Anbarasan, R.

    2017-09-01

    A green-colored Ni-complexed aminoclay (AC) was synthesized and its size and crystalline nature were confirmed by HRTEM images and XRD, respectively. The AC-Ni system was used as a catalyst towards the reduction of environmental pollutants like Cr(VI), fluorescein (Fluor) and nitrophenol (NiP) individually and also their mixture. The catalytic reduction of Cr(VI) was elaborately studied under different experimental conditions. The thermodynamic parameters were determined. The AC-Ni system exhibited lower energy of activation (E a) value. The apparent rate constant of individual components and their mixture was determined, analyzed and compared with the literature reports. The pollutants present in the mixture exhibited the lower k app value due to the complex formation.

  18. The deposition of Au-Pt core-shell nanoparticles on reduced graphene oxide and their catalytic activity.

    Science.gov (United States)

    Cui, Xiu; Wu, Shengnan; Jungwirth, Scott; Chen, Zhibing; Wang, Zhenghua; Wang, Lun; Li, Yongxin

    2013-07-26

    Au-Pt core-shell nanoparticles have been synthesized on a reduced graphene oxide (RGO) surface by an under-potential deposition (UPD) redox replacement technique, which involves redox replacement of a copper UPD monolayer by PtCl₄²⁻ that could be reduced and deposited simultaneously. Scanning electron microscopy (SEM) and electrochemical methods have been used to characterize the graphene decorated with Au-Pt core-shell nanoparticles. The electrochemical experiments show that the materials exhibit excellent catalytic activity towards the oxygen reduction reaction and the methanol oxidation reaction. It is believed that the high-performance of this new catalyst is due to the ultrathin Pt shell on the Au nanoparticles surface and the oxygen-containing functional groups on the RGO surface.

  19. Volume-confined synthesis of ligand-free gold nanoparticles with tailored sizes for enhanced catalytic activity

    Science.gov (United States)

    Shaik, Firdoz; Zhang, Weiqing; Niu, Wenxin; Lu, Xianmao

    2014-10-01

    Ligand-free Au nanoparticles with controlled sizes are synthesized via a volume-confined method. In this synthesis, mesoporous hollow silica shells (mHSS) are used as nano-containers for the impregnation of HAuCl4 solution before they are separated from the bulk solution. With a simple heating process, the Au precursor confined within the cavity of the isolated hollow shells is converted into ligand-free Au nanoparticles. The size of the Au nanoparticles can be tuned precisely by loading HAuCl4 solution of different concentrations, or by using mHSS with different cavity volumes. The ligand-free Au nanoparticles demonstrate superior catalytic activity than sodium citrate-capped Au nanoparticles.

  20. Catalytic activity of Ni complexed aminoclay towards the reduction of Cr(V), p-nitrophenol and fluorescein dye

    Science.gov (United States)

    Ranchani, A. Amala Jeya; Parthasarathy, V.; Devi, A. Anitha; Meenarathi, B.; Anbarasan, R.

    2017-11-01

    A green-colored Ni-complexed aminoclay (AC) was synthesized and its size and crystalline nature were confirmed by HRTEM images and XRD, respectively. The AC-Ni system was used as a catalyst towards the reduction of environmental pollutants like Cr(VI), fluorescein (Fluor) and nitrophenol (NiP) individually and also their mixture. The catalytic reduction of Cr(VI) was elaborately studied under different experimental conditions. The thermodynamic parameters were determined. The AC-Ni system exhibited lower energy of activation ( E a) value. The apparent rate constant of individual components and their mixture was determined, analyzed and compared with the literature reports. The pollutants present in the mixture exhibited the lower k app value due to the complex formation.