Ab initio molecular dynamics of the reaction of quercetin with superoxide radical

Energy Technology Data Exchange (ETDEWEB)

Lespade, Laure, E-mail: l.lespade@ism.u-bordeaux1.fr

2016-08-22

Highlights: • Ab initio molecular dynamics is performed to describe the reaction of quercetin and superoxide. • The reaction occurs near the sites 4′ and 7 when the system contains sufficiently water molecules. • The difference of reactivity of superoxide compared to commonly used radicals as DPPH{sup ·} or ABTS{sup ·+} is explained. - Abstract: Superoxide plays an important role in biology but in unregulated concentrations it is implicated in a lot of diseases such as cancer or atherosclerosis. Antioxidants like flavonoids are abundant in plant and are good scavengers of superoxide radical. The modeling of superoxide scavenging by flavonoids from the diet still remains a challenge. In this study, ab initio molecular dynamics of the reaction of the flavonoid quercetin toward superoxide radical has been carried out using Car–Parrinello density functional theory. The study has proven different reactant solvation by modifying the number of water molecules surrounding superoxide. The reaction consists in the gift of a hydrogen atom of one of the hydroxyl groups of quercetin to the radical. When it occurs, it is relatively fast, lower than 100 fs. Calculations show that it depends largely on the environment of the hydroxyl group giving its hydrogen atom, the geometry of the first water layer and the presence of a certain number of water molecules in the second layer, indicating a great influence of the solvent on the reactivity.

An ion cooling and state characterization apparatus for studies of molecular ion dissociative interactions

International Nuclear Information System (INIS)

Deng, Shihu; Vane, C R; Bannister, M E; Havener, C C; Meyer, F W; Krause, H F; Hettich, R L; Goeringer, D E; Van Berkel, G J

2009-01-01

An experimental capability is being developed at the Oak Ridge National Laboratory Multi-Charged Ion Research Facility (ORNL MIRF) to enable stored cooling and state characterization of molecular ions of essentially any mass. Ions selected from a variety of available sources are injected from the side into a 1.5 meter long electrostatic mirror trap, where excited internal states are cooled by radiative cooling. An electron beam target located near the middle of the ion-trap region, coupled with neutral fragment imaging detector systems at each end of the trap, permits state-specific studies of electron-molecular ion dissociation.

Interface tuning of current-induced cooling in molecular circuits

Czech Academy of Sciences Publication Activity Database

Foti, Giuseppe; Vázquez, Héctor

2017-01-01

Roč. 121, č. 2 (2017), s. 1082-1088 ISSN 1932-7447 R&D Projects: GA ČR GA15-19672S Institutional support: RVO:68378271 Keywords : current-induced heating and cooling * molecular junction * Carbene Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 4.536, year: 2016

Adsorbate-driven cooling of carbene-based molecular junctions

Czech Academy of Sciences Publication Activity Database

Foti, Giuseppe; Vázquez, Héctor

2017-01-01

Roč. 8, Oct (2017), s. 2060-2068 ISSN 2190-4286 R&D Projects: GA ČR GA15-19672S EU Projects: European Commission(XE) 702114 - HEATEXMOL Institutional support: RVO:68378271 Keywords : adsorbate * carbene * current-induced heating and cooling * molecular junction * vibrations Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.127, year: 2016

Free radical reactions of isoxazole and pyrazole derivatives of hispolon: kinetics correlated with molecular descriptors.

Science.gov (United States)

Shaikh, Shaukat Ali M; Barik, Atanu; Singh, Beena G; Modukuri, Ramani V; Balaji, Neduri V; Subbaraju, Gottumukkala V; Naik, Devidas B; Priyadarsini, K Indira

2016-12-01

Hispolon (HS), a natural polyphenol found in medicinal mushrooms, and its isoxazole (HI) and pyrazole (HP) derivatives have been examined for free radical reactions and in vitro antioxidant activity. Reaction of these compounds with one-electron oxidant, azide radicals ([Formula: see text]) and trichloromethyl peroxyl radicals ([Formula: see text]), model peroxyl radicals, studied by nanosecond pulse radiolysis technique, indicated formation of phenoxyl radicals absorbing at 420 nm with half life of few hundred microseconds (μs). The formation of phenoxyl radicals confirmed that the phenolic OH is the active centre for free radical reactions. Rate constant for the reaction of these radicals with these compounds were in the order k HI ≅ k HP  >   k HS . Further the compounds were examined for their ability to inhibit lipid peroxidation in model membranes and also for the scavenging of 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical and superoxide ([Formula: see text]) radicals. The results suggested that HP and HI are less efficient than HS towards these radical reactions. Quantum chemical calculations were performed on these compounds to understand the mechanism of reaction with different radicals. Lower values of adiabatic ionization potential (AIP) and elevated highest occupied molecular orbital (HOMO) for HI and HP compared with HS controlled their activity towards [Formula: see text] and [Formula: see text] radicals, whereas the contribution of overall anion concentration was responsible for higher activity of HS for DPPH, [Formula: see text], and lipid peroxyl radical. The results confirm the role of different structural moieties on the antioxidant activity of hispolon derivatives.

Multiscale QM/MM molecular dynamics study on the first steps of guanine damage by free hydroxyl radicals in solution.

Science.gov (United States)

Abolfath, Ramin M; Biswas, P K; Rajnarayanam, R; Brabec, Thomas; Kodym, Reinhard; Papiez, Lech

2012-04-19

Understanding the damage of DNA bases from hydrogen abstraction by free OH radicals is of particular importance to understanding the indirect effect of ionizing radiation. Previous studies address the problem with truncated DNA bases as ab initio quantum simulations required to study such electronic-spin-dependent processes are computationally expensive. Here, for the first time, we employ a multiscale and hybrid quantum mechanical-molecular mechanical simulation to study the interaction of OH radicals with a guanine-deoxyribose-phosphate DNA molecular unit in the presence of water, where all of the water molecules and the deoxyribose-phosphate fragment are treated with the simplistic classical molecular mechanical scheme. Our result illustrates that the presence of water strongly alters the hydrogen-abstraction reaction as the hydrogen bonding of OH radicals with water restricts the relative orientation of the OH radicals with respect to the DNA base (here, guanine). This results in an angular anisotropy in the chemical pathway and a lower efficiency in the hydrogen-abstraction mechanisms than previously anticipated for identical systems in vacuum. The method can easily be extended to single- and double-stranded DNA without any appreciable computational cost as these molecular units can be treated in the classical subsystem, as has been demonstrated here. © 2012 American Chemical Society

Adiabatic Cooling for Rovibrational Spectroscopy of Molecular Ions

DEFF Research Database (Denmark)

Fisher, Karin

2017-01-01

The field of cold molecular ions is a fast growing one, with applications in high resolution spectroscopy and metrology, the search for time variations of fundamental constants, cold chemistry and collisions, and quantum information processing, to name a few. The study of single molecular ions...... is attractive as it enables one to push the limits of spectroscopic accuracy. Non-destructive spectroscopic detection of molecular ions can be achieved by co-trapping with an easier to detect atomic ion. The ion chain has coupled motion, and transitions which change both the internal and motional states...... to the measured heating rates, almost perfectly fitting existing heating rate theory. Further, the same model successfully predicted the heating rates of the in-phase mode of a two-ion crystal, indicating that we can use it to predict the heating rates in experiments on molecule-atom chains. Adiabatic cooling...

A path integral molecular dynamics study of the hyperfine coupling constants of the muoniated and hydrogenated acetone radicals

Energy Technology Data Exchange (ETDEWEB)

Oba, Yuki; Kawatsu, Tsutomu; Tachikawa, Masanori, E-mail: tachi@yokohama-cu.ac.jp [Quantum Chemistry Division, Yokohama City University, Seto 22-2, Kanazawa-ku, Yokohama 236-0027 (Japan)

2016-08-14

The on-the-fly ab initio density functional path integral molecular dynamics (PIMD) simulations, which can account for both the nuclear quantum effect and thermal effect, were carried out to evaluate the structures and “reduced” isotropic hyperfine coupling constants (HFCCs) for muoniated and hydrogenated acetone radicals (2-muoxy-2-propyl and 2-hydoxy-2-propyl) in vacuo. The reduced HFCC value from a simple geometry optimization calculation without both the nuclear quantum effect and thermal effect is −8.18 MHz, and that by standard ab initio molecular dynamics simulation with only the thermal effect and without the nuclear quantum effect is 0.33 MHz at 300 K, where these two methods cannot distinguish the difference between muoniated and hydrogenated acetone radicals. In contrast, the reduced HFCC value of the muoniated acetone radical by our PIMD simulation is 32.1 MHz, which is about 8 times larger than that for the hydrogenated radical of 3.97 MHz with the same level of calculation. We have found that the HFCC values are highly correlated with the local molecular structures; especially, the Mu—O bond length in the muoniated acetone radical is elongated due to the large nuclear quantum effect of the muon, which makes the expectation value of the HFCC larger. Although our PIMD result calculated in vacuo is about 4 times larger than the measured experimental value in aqueous solvent, the ratio of these HFCC values between muoniated and hydrogenated acetone radicals in vacuo is in reasonable agreement with the ratio of the experimental values in aqueous solvent (8.56 MHz and 0.9 MHz); the explicit presence of solvent molecules has a major effect on decreasing the reduced muon HFCC of in vacuo calculations for the quantitative reproduction.

A path integral molecular dynamics study of the hyperfine coupling constants of the muoniated and hydrogenated acetone radicals

International Nuclear Information System (INIS)

Oba, Yuki; Kawatsu, Tsutomu; Tachikawa, Masanori

2016-01-01

The on-the-fly ab initio density functional path integral molecular dynamics (PIMD) simulations, which can account for both the nuclear quantum effect and thermal effect, were carried out to evaluate the structures and “reduced” isotropic hyperfine coupling constants (HFCCs) for muoniated and hydrogenated acetone radicals (2-muoxy-2-propyl and 2-hydoxy-2-propyl) in vacuo. The reduced HFCC value from a simple geometry optimization calculation without both the nuclear quantum effect and thermal effect is −8.18 MHz, and that by standard ab initio molecular dynamics simulation with only the thermal effect and without the nuclear quantum effect is 0.33 MHz at 300 K, where these two methods cannot distinguish the difference between muoniated and hydrogenated acetone radicals. In contrast, the reduced HFCC value of the muoniated acetone radical by our PIMD simulation is 32.1 MHz, which is about 8 times larger than that for the hydrogenated radical of 3.97 MHz with the same level of calculation. We have found that the HFCC values are highly correlated with the local molecular structures; especially, the Mu—O bond length in the muoniated acetone radical is elongated due to the large nuclear quantum effect of the muon, which makes the expectation value of the HFCC larger. Although our PIMD result calculated in vacuo is about 4 times larger than the measured experimental value in aqueous solvent, the ratio of these HFCC values between muoniated and hydrogenated acetone radicals in vacuo is in reasonable agreement with the ratio of the experimental values in aqueous solvent (8.56 MHz and 0.9 MHz); the explicit presence of solvent molecules has a major effect on decreasing the reduced muon HFCC of in vacuo calculations for the quantitative reproduction.

Molecular Mobility of n-Ethylene Glycol Dimethacrylate Glass Formers Upon Free Radical Polymerization

Science.gov (United States)

Plaza, Maria Teresa Viciosa

When a liquid upon cooling avoids crystallization, it enters the supercooled state. If the temperature continues to decrease, the consequent increase of viscosity is reflected in the molecular mobility in such a way that the characteristic relaxation times of cooperative motions become of the same order of the experimentally accessible timescales. Further cooling finally transforms the highly viscous liquid into a glass, in which only local motions are allowed. The monomers n-ethylene glycol dimethacrylate (n-EGDMA) for n =1 to 4, that constitutes the object of this study, easily circumvent crystallization, being good candidates to study the molecular mobility in both supercooled and glassy states. Dielectric Relaxation Spectroscopy (DRS) was the technique chosen to obtain detailed information about their molecular mobility (Chapters 1 and 2). The first part of this work consisted in the dielectric characterization of the relaxation processes present above and below the glass transition temperature (Tg), which shifts to higher values with the molecular weight ( Mw), result confirmed by Differential Scanning Calorimetry (DSC). While the cooperative alpha-process associated to the glass transition, and the secondary beta process, depend on Mw, the other found secondary process, gamma, seems to be independent from this factor (Chapter 3). In the next Chapters different strategies were carried out in order to clarify the mechanisms in the origin of these two secondary relaxations (beta and gamma), and to learn about its respective relation with the main a relaxation. Monitoring the real time isothermal free radical polymerization of TrEGDMA by Temperature Modulated Differential Scanning Calorimetry (TMDSC), carried out at temperatures below the gamma T of the final polymer network, we shown among others two important features: i) the vitrification of the polymer in formation leads to relatively low degrees of conversion, and ii) the unreacted monomer is expelled from

Thermal histories of chondrules in solar nebula shocks, including the effect of molecular line cooling

Science.gov (United States)

Morris, Melissa A.

Chondrules are millimeter-sized, silicate (mostly ferromagnesian) igneous spheres found within chondritic meteorites. They are some of the oldest materials in our Solar System, having formed within a few million years of its birth. Chondrules were melted at high temperature (over 1800 K), while they were free-floating objects in the early solar nebula. Their petrology and chemistry constrain their formation, especially their thermal histories. Chondrules provide some of the most powerful constraints on conditions in the solar nebula. Models in which chondrule precursors melted by passage through solar nebula shocks are very promising, and meet most constraints on chondrule formation in broad brush. However, these models have been lacking in some of the relevant physics. Previous shock models have used incorrect approximations to the input radiation boundary condition, and the opacity of solids has been treated simply. Most important, a proper treatment of cooling due to molecular line emission has not been included. In this thesis, the shock model is significantly improved in order to determine if it remains consistent with observational constraints. The appropriate boundary condition for the input radiation and the proper method for calculation of the opacity of solids are determined, and a complete treatment of molecular line cooling due to water is included. Previous estimates of the effect of line cooling predicted chondrule cooling rates in excess of 10,000 K per hour. However, once molecular line cooling due to water was incorporated into the full shock model, it was found that line cooling has a minimal effect on the thermal histories of gas and chondrules. This behavior is attributed mostly to the thermal buffering of the gas due to hydrogen dissociation and recombination, which tends to keep the gas temperature at approximately 2000 K until the column densities of water become optically thick to line emission. Chondrule cooling rates in the range of 10

Radical scavenging activity of crude polysaccharides from Camellia sinensis

Directory of Open Access Journals (Sweden)

Yang Fan

2011-01-01

Full Text Available A preparation of crude polysaccharides (TPS was isolated from Camellia sinensis by precipitation and ultrafiltration. TPS1, TPS2, and TPS3 had molecular weights of 240, 21.4, and 2.46 kDa, respectively. The radical scavenging activities of TPS were evaluated by DPPH free radical, hydroxyl radical and superoxide radical scavenging. These results revealed that TPS exhibited strong radical scavenging activity in a concentration-dependent manner. TPS3 with lowest molecular weight showed a higher radical scavenging activity.

Involvement of free radicals followed by the activation of phospholipase A2 in the mechanism that underlies the combined effects of methamphetamine and morphine on subacute toxicity or lethality in mice: Comparison of the therapeutic potential of fullerene, mepacrine, and cooling

International Nuclear Information System (INIS)

Mori, Tomohisa; Ito, Shinobu; Namiki, Mizuho; Suzuki, Tadashi; Kobayashi, Shizuko; Matsubayashi, Kenji; Sawaguchi, Toshiko

2007-01-01

An increase in polydrug abuse is a major problem worldwide. The coadministration of methamphetamine and morphine increased subacute toxicity or lethality in rodents. However, the underlying mechanisms by which lethality is increased by the coadministration of methamphetamine and morphine are not yet fully understood. Coadministered methamphetamine and morphine induced lethality by more than 80% in BALB/c mice, accompanied by the rupture of cells in the kidney and liver, and an increase in poly (ADP-ribose) polymerase (PARP)-immunoreactive cells in the heart, kidney and liver. The lethal effect and the increase in the incidence of rupture or PARP-immunoreactive cells induced by the coadministration of methamphetamine and morphine was significantly attenuated by pretreatment with mepacrine (phospholipase A 2 inhibitor) or fullerene (a radical scavenger), or by cooling from 30 to 90 min after drug administration. Furthermore, based on the results of the electron spin resonance spin-trapping technique, hydroxyl radicals were increased by the administration of methamphetamine and morphine, and these increased hydroxyl radicals were potently attenuated by fullerene and cooling. These results suggest that hydroxyl radicals plays an important role in the increased lethality induced by the coadministration of methamphetamine plus morphine. The potency of cooling or drugs for decreasing the subacute toxicity or lethality induced by the coadministration of methamphetamine and morphine was in the order fullerene = cooling > mepacrine. These results indicate that fullerene and cooling are beneficial for preventing death that is induced by the coadministration of methamphetamine and morphine

Effect of concentration and molecular weight of chitosan and its derivative on the free radical scavenging ability.

Science.gov (United States)

Li, Huili; Xu, Qing; Chen, Yun; Wan, Ajun

2014-03-01

Chitosan is a biodegradable and biocompatible natural scaffold material, which has numerous applications in biomedical sciences. In this study, the in vitro antioxidant activity of chitosan scaffold material was investigated by the chemiluminescence signal generated from the hydroxyl radical (•OH) scavenging assay. The scavenging mechanism was also discussed. The results indicated that the free radical scavenging ability of chitosan scaffold material significantly depends on the chitosan concentration and shows interesting kinetic change. Within the experimental concentration range, the optimal concentration of chitosan was 0.2 mg/mL. The molecular weight of chitosan also attributed to the free radical scavenging ability. Comparison between chitosan and its derivative found that carboxymethyl chitosan possessed higher scavenging ability. Copyright © 2013 Society of Plastics Engineers.

Generation and detection of the cyclohexadienyl radical in phosphonium ionic liquids.

Science.gov (United States)

Lauzon, J M; Arseneau, D J; Brodovitch, J C; Clyburne, J A C; Cormier, P; McCollum, B; Ghandi, K

2008-10-21

The formation of the cyclohexadienyl radical, C(6)H(6)Mu, in ionic and molecular solvents has been compared. This is the first time that a muoniated free radical is reported in an ionic liquid. In marked contrast to molecular liquids, free radical generation in ionic liquids is significantly enhanced. Comparison of the hyperfine interactions in the ionic liquid and in molecular solvents and with theoretical calculations, suggests significant and unforeseen solvent interaction with the cyclohexadienyl radical.

An experimental and ab initio study of the electronic spectrum of the jet-cooled F{sub 2}BO free radical

Energy Technology Data Exchange (ETDEWEB)

Grimminger, Robert; Clouthier, Dennis J., E-mail: dclaser@uky.edu [Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055 (United States); Sheridan, Phillip M. [Department of Chemistry and Biochemistry, Canisius College, Buffalo, New York 14208 (United States)

2014-04-28

We have studied the B{sup ~} {sup 2}A{sub 1}–X{sup ~} {sup 2}B{sub 2} laser-induced fluorescence (LIF) spectrum of the jet-cooled F{sub 2}BO radical for the first time. The transition consists of a strong 0{sub 0}{sup 0} band at 446.5 nm and eight weak sequence bands to shorter wavelengths. Single vibronic level emission spectra obtained by laser excitation of individual levels of the B{sup ~} state exhibit two electronic transitions: a very weak, sparse B{sup ~}–X{sup ~} band system in the 450–500 nm region and a stronger, more extensive set of B{sup ~} {sup 2}A{sub 1}–A{sup ~} {sup 2}B{sub 1} bands in the 580–650 nm region. We have also performed a series of high level ab initio calculations to predict the electronic energies, molecular structures, vibrational frequencies, and rotational and spin-rotation constants in the X{sup ~} {sup 2}B{sub 2}, A{sup ~2}B{sub 1} and B{sup ~} {sup 2}A{sub 1} electronic states as an aid to the analysis of the experimental data. The theoretical results have been used as input for simulations of the rotationally resolved B{sup ~} {sup 2}A{sub 1}–X{sup ~} {sup 2}B{sub 2} 0{sub 0}{sup 0} LIF band and Franck-Condon profiles of the LIF and single vibronic level emission spectra. The agreement between the simulations obtained with purely ab initio parameters and the experimental spectra validates the geometries calculated for the ground and excited states and the conclusion that the radical has C{sub 2v} symmetry in the X{sup ~}, A{sup ~}, and B{sup ~} states. The spectra provide considerable new information about the vibrational energy levels of the X{sup ~} and A{sup ~} states, but very little for the B{sup ~} state, due to the very restrictive Franck-Condon factors in the LIF spectra.

Cation radicals of xanthophylls.

Science.gov (United States)

Galinato, Mary Grace I; Niedzwiedzki, Dariusz; Deal, Cailin; Birge, Robert R; Frank, Harry A

2007-10-01

Carotenes and xanthophylls are well known to act as electron donors in redox processes. This ability is thought to be associated with the inhibition of oxidative reactions in reaction centers and light-harvesting pigment-protein complexes of photosystem II (PSII). In this work, cation radicals of neoxanthin, violaxanthin, lutein, zeaxanthin, beta-cryptoxanthin, beta-carotene, and lycopene were generated in solution using ferric chloride as an oxidant and then studied by absorption spectroscopy. The investigation provides a view toward understanding the molecular features that determine the spectral properties of cation radicals of carotenoids. The absorption spectral data reveal a shift to longer wavelength with increasing pi-chain length. However, zeaxanthin and beta-cryptoxanthin exhibit cation radical spectra blue-shifted compared to that of beta-carotene, despite all of these molecules having 11 conjugated carbon-carbon double bonds. CIS molecular orbital theory quantum computations interpret this effect as due to the hydroxyl groups in the terminal rings selectively stabilizing the highest occupied molecular orbitals of preferentially populated s-trans-isomers. The data are expected to be useful in the analysis of spectral results from PSII pigment-protein complexes seeking to understand the role of carotene and xanthophyll cation radicals in regulating excited state energy flow, in protecting PSII reaction centers against photoinhibition, and in dissipating excess light energy absorbed by photosynthetic organisms but not used for photosynthesis.

Cool C-shocks and high-velocity flows in molecular clouds

International Nuclear Information System (INIS)

Smith, M.D.; Brand, P.W.J.L.

1990-01-01

C-shocks can be driven through dense clouds when the neutrals and magnetic field interact weakly due to a paucity of ions. We develop a method for calculating C-shock properties with the aim of interpreting the observed high-velocity molecular hydrogen. A high Mach number approximation, corresponding to low temperatures, is employed. Under strong cooling conditions the flow is continuous even though a subsonic region may be present downstream. Analytic expressions for the maximum temperature, dissociation fraction, self-ionization level and J-shock transition are derived. (author)

Radiation-induced damage in T4 bacteriophage: the effect of superoxid radicals and molecular oxygen. Progress report, December 1, 1977--November 30, 1978

International Nuclear Information System (INIS)

Samuni, A.; Chevion, M.; Halpern, Y.S.; Ilan, Y.A.; Czapski, G.

1978-01-01

The sensitivity of T4 bacteriophage towards γ irradiation has been studied in phosphate buffer suspensions. The spectrum of the water radicals was controlled by a careful choice of the appropriate saturating gas and the addition of radical scavengers. Thus, it was possible to distinguish between the effects of molecular oxygen and the superoxide radicals formed through its reactions. About 90 percent of the damage was caused by the water radicals formed in the bulk suspensions. These probably affected the phage proteins; only the remainder of the damage involved the viral DNA. The oxygen enhancement ratio observed was not connected in any way with the formation of the superoxide radicals. The results confirmed that the OH radicals are the reactive species, while e - /sub aq/ as well as the superoxide radical do not contribute to the radiodamage

A Free-Radical Pathway to Hydrogenated Phenanthrene in Molecular Clouds-Low Temperature Growth of Polycyclic Aromatic Hydrocarbons.

Science.gov (United States)

Thomas, Aaron M; Lucas, Michael; Yang, Tao; Kaiser, Ralf I; Fuentes, Luis; Belisario-Lara, Daniel; Mebel, Alexander M

2017-08-05

The hydrogen-abstraction/acetylene-addition mechanism has been fundamental to unravelling the synthesis of polycyclic aromatic hydrocarbons (PAHs) detected in combustion flames and carbonaceous meteorites like Orgueil and Murchison. However, the fundamental reaction pathways accounting for the synthesis of complex PAHs, such as the tricyclic anthracene and phenanthrene along with their dihydrogenated counterparts, remain elusive to date. By investigating the hitherto unknown chemistry of the 1-naphthyl radical with 1,3-butadiene, we reveal a facile barrierless synthesis of dihydrophenanthrene adaptable to low temperatures. These aryl-type radical additions to conjugated hydrocarbons via resonantly stabilized free-radical intermediates defy conventional wisdom that PAH growth is predominantly a high-temperature phenomenon and thus may represent an overlooked path to PAHs as complex as coronene and corannulene in cold regions of the interstellar medium like in the Taurus Molecular Cloud. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

EPR spin trapping of protein radicals

DEFF Research Database (Denmark)

Davies, Michael Jonathan; Hawkins, Clare Louise

2004-01-01

Electron paramagnetic resonance (EPR) spin trapping was originally developed to aid the detection of low-molecular-mass radicals formed in chemical systems. It has subsequently found widespread use in biology and medicine for the direct detection of radical species formed during oxidative stress...... tumbling radicals are often broad and relatively poor in distinctive features, a number of techniques have been developed that allow a wealth of information to be obtained about the nature, site, and reactions of such radicals. This article summarizes recent developments in this area and reviews selected...... examples of radical formation on proteins....

A simple approach to CO cooling in molecular clouds

Science.gov (United States)

Whitworth, A. P.; Jaffa, S. E.

2018-03-01

Carbon monoxide plays an important role in interstellar molecular clouds, both as a coolant, and as a diagnostic molecule. However, a proper evaluation of the cooling rate due to CO requires a determination of the populations of many levels, the spontaneous and stimulated radiative de-excitation rates between these levels, and the transfer of the emitted multi-line radiation; additionally, this must be done for three isotopologues. It would be useful to have a simple analytic formulation that avoided these complications and the associated computational overhead; this could then be used in situations where CO plays an important role as a coolant, but the details of this role are not the main concern. We derive such a formulation here, by first considering the two asymptotic forms that obtain in the limits of (a) low volume-density and optical depth, and (b) high volume-density and optical depth. These forms are then combined in such a way as to fit the detailed numerical results from Goldsmith & Langer (1978, ApJ, 222, 881; hereafter GL78). The GL78 results cover low temperatures, and a range of physical conditions where the interplay of thermal and sub-thermal excitation, optical-depth effects, and the contributions from rare isotopologues, are all important. The fit is obtained using the Metropolis-Hastings method, and reproduces the results of GL78 well. It is a purely local and analytic function of state — specifically a function of the density, ρ, isothermal sound speed, a, CO abundance, XCO, and velocity divergence, ∇ṡυ. As an illustration of its use, we consider the cooling layer following a slow steady non-magnetic planar J-shock. We show that, in this idealised configuration, if the post-shock cooling is dominated by CO and its isotopologues, the thickness of the post-shock cooling layer is very small and approximately independent of the pre-shock velocity, υo, or pre-shock isothermal sound speed, ao.

Molecular weight growth in Titan's atmosphere: branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes.

Science.gov (United States)

Kirk, Benjamin B; Savee, John D; Trevitt, Adam J; Osborn, David L; Wilson, Kevin R

2015-08-28

The reaction of small hydrocarbon radicals (i.e.˙CN, ˙C2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC[triple bond, length as m-dash]C˙), a likely product from the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (-H = 27%, -CH3 = 73%) and (-H = 14%, -CH3 = 86%), respectively. Together, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.

Vibronic Spectroscopy of the Phenylcyanomethyl Radical

Science.gov (United States)

Mehta, Deepali N.; Kidwell, Nathanael M.; Zwier, Timothy S.

2011-06-01

Resonance stabilized radicals (RSRs) are thought to be key intermediates in the formation of larger molecules in planetary atmospheres. Given the nitrogen-rich atmosphere of Titan, and the prevalence of nitriles there, it is likely that nitrile and isonitrile RSRs could be especially important in pathways leading to the formation of more complex nitrogen-containing compounds and the aerosols ("tholins") that are ultimately produced. In this talk, the results of a gas phase, jet-cooled vibronic spectroscopy study of the phenylcyanomethyl radical (C_6H_5.{C}HCN), the nitrogen-containing analog of the 1-phenylpropargyl radical, will be presented. A resonant two color photon ionization spectrum over the range 21,350-22,200 Cm-1 (450.0-468.0 nm) has been recorded, and the D_0-D_1 origin band has been tentatively identified at 21,400 Cm-1. Studies identifying the ionization threshold, and characterizing the vibronic structure will also be presented. An analogous study of the phenylisocyanomethyl radical, C_6H_5.{C}HNC, is currently being pursued for comparison with that of phenylcyanomethyl radical.

Radical production in biological systems

International Nuclear Information System (INIS)

Johnson, J.R.; Akabani, G.

1994-10-01

This paper describes our effort to develop a metric for radiation exposure that is more fundamental than adsorbed dose and upon which a metric for exposure to chemicals could be based. This metric is based on the production of radicals by the two agents. Radicals produced by radiation in biological systems commonly assumed to be the same as those produced in water despite the presence of a variety of complex molecules. This may explain why the extensive efforts to describe the relationship between energy deposition (track structure) and molecular damage to DNA, based on the spectrum of radicals produced, have not been successful in explaining simple biological effects such as cell killing. Current models assume that DNA and its basic elements are immersed in water-like media and only model the production and diffusion of water-based radicals and their interaction with DNA structures; these models lack the cross sections associated with each macro-component of DNA and only treat water-based radicals. It has been found that such models are not realistic because DNA is not immersed in pure water. A computer code capable of simulating electron tracks, low-energy electrons, energy deposition in small molecules, and radical production and diffusion in water like media has been developed. This code is still in at a primitive stage and development is continuing. It is being used to study radical production by radiation, and radical diffusion and interactions in simple molecular systems following their production. We are extending the code to radical production by chemicals to complement our PBPK modeling efforts. It therefore has been developed primarily for use with radionuclides that are in biological materials, and not for radiation fields

Donor free radical explosive composition

Science.gov (United States)

Walker, Franklin E. [15 Way Points Rd., Danville, CA 94526; Wasley, Richard J. [4290 Colgate Way, Livermore, CA 94550

1980-04-01

An improved explosive composition is disclosed and comprises a major portion of an explosive having a detonation velocity between about 1500 and 10,000 meters per second and a minor amount of a donor additive comprising an organic compound or mixture of organic compounds capable of releasing low molecular weight free radicals or ions under mechanical or electrical shock conditions and which is not an explosive, or an inorganic compound or mixture of inorganic compounds capable of releasing low molecular weight free radicals or ions under mechanical or electrical shock conditions and selected from ammonium or alkali metal persulfates.

Formation of stable radicals during perfluoroalkane radiolysis

International Nuclear Information System (INIS)

Allayarov, S.R.; Demidov, S.V.; Kiryukhin, D.P.; Mikhajlov, A.I.; Barkalov, I.M.

1984-01-01

Accumulation and stabilization kinetics of perfluoroalkyls during α-radiolysis ( 60 Co) of perfluoralkanes (PFA) in a wide temperature range for different PFA fractions differing in the average molecular weight, is investigated. It is noted that low temperature (PFA) radiolysis (77 K) is of a linear nature of accumulation of stabilized radicals up to doses of approximately 700 KGy. In the case of PFA radiolysis at 300 K radiation yields of stable radicals are somewhat lower than at 47 K and at doses of 200-300 KGy, their accumulation ceases. It is shown that kinetics of formation and accumulation of stable radicals does not depend on molecular mass and PFA fraction viscosity. Perfluoroalkyl stability is explained by intra molecular conformation spheric insulation of the free valency. Perfluoroalkyl stability in different PFA fractions in a wide time range in different media is investigated

Unexpected mobility of OH+ and OD+ molecular ions in cooled helium gas

International Nuclear Information System (INIS)

Isawa, R; Yamazoe, J; Tanuma, H; Ohtsuki, K

2012-01-01

Mobilities of OH + and OD + ions in cooled helium gas have been measured at gas temperature of 4.3 K. Measured mobilities of both ions as a function of an effective temperature T eff show a minimum around 80 K, and they are approaching to the polarization limits at very low T eff . These findings will be related to the extremely strong anisotropy of the interaction potential between the molecular ion and helium atom.

On the quantification of the dissolved hydroxyl radicals in the plasma-liquid system using the molecular probe method

Science.gov (United States)

Ma, Yupengxue; Gong, Xinning; He, Bangbang; Li, Xiaofei; Cao, Dianyu; Li, Junshuai; Xiong, Qing; Chen, Qiang; Chen, Bing Hui; Huo Liu, Qing

2018-04-01

Hydroxyl (OH) radical is one of the most important reactive species produced by plasma-liquid interactions, and the OH in liquid phase (dissolved OH radical, OHdis) takes effect in many plasma-based applications due to its high reactivity. Therefore, the quantification of the OHdis in a plasma-liquid system is of great importance, and a molecular probe method usually used for the OHdis detection might be applied. Herein, we investigate the validity of using the molecular probe method to estimate the [OHdis] in the plasma-liquid system. Dimethyl sulfoxide is used as the molecular probe to estimate the [OHdis] in an air plasma-liquid system, and usually the estimation of [OHdis] is deduced by quantifying the OHdis-induced derivative, the formaldehyde (HCHO). The analysis indicates that the true concentration of the OHdis should be estimated from the sum of three terms: the formed HCHO, the existing OH scavengers, and the H2O2 formed from the OHdis. The results show that the measured [HCHO] needs to be corrected since the HCHO consumption is not negligible in the plasma-liquid system. We conclude from the results and the analysis that the molecular probe method generally underestimates the [OHdis] in the plasma-liquid system. If one wants to obtain the true concentration of the OHdis in the plasma-liquid system, one needs to know the consumption behavior of the OHdis-induced derivatives, the information of the OH scavengers (such as hydrated electron, atomic hydrogen besides the molecular probe), and also the knowledge of the H2O2 formed from the OHdis.

Ring-Expansion/Contraction Radical Crossover Reactions of Cyclic Alkoxyamines: A Mechanism for Ring Expansion-Controlled Radical Polymerization

Directory of Open Access Journals (Sweden)

Atsushi Narumi

2018-06-01

Full Text Available Macrocyclic polymers present an important class of macromolecules, displaying the reduced radius of gyration or impossibility to entangle. A rare approach for their synthesis is the ring expansion-controlled radical “vinyl” polymerization, starting from a cyclic alkoxyamine. We here describe ring-expansion radical crossover reactions of cyclic alkoxyamines which run in parallel to chain-propagation reactions in the polymerization system. The radical crossover reactions extensively occurred at 105–125 °C, eventually producing high molecular weight polymers with multiple inherent dynamic covalent bonds (NOC bonds. A subsequent ring-contraction radical crossover reaction and the second ring-expansion radical crossover reaction are also described. The major products for the respective three stages were shown to possess cyclic morphologies by the molecular weight profiles and the residual ratios for the NOC bonds (φ in %. In particular, the high φ values ranging from ca. 80% to 98% were achieved for this cyclic alkoxyamine system. This result verifies the high availability of this system as a tool demonstrating the ring-expansion “vinyl” polymerization that allows them to produce macrocyclic polymers via a one-step vinyl polymerization.

Mechanistic Insights into Radical-Mediated Oxidation of Tryptophan from ab Initio Quantum Chemistry Calculations and QM/MM Molecular Dynamics Simulations.

Science.gov (United States)

Wood, Geoffrey P F; Sreedhara, Alavattam; Moore, Jamie M; Wang, John; Trout, Bernhardt L

2016-05-12

An assessment of the mechanisms of (•)OH and (•)OOH radical-mediated oxidation of tryptophan was performed using density functional theory calculations and ab initio plane-wave Quantum Mechanics/Molecular Mechanics (QM/MM) molecular dynamics simulations. For the (•)OH reactions, addition to the pyrrole ring at position 2 is the most favored site with a barrierless reaction in the gas phase. The subsequent degradation of this adduct through a H atom transfer to water was intermittently observed in aqueous-phase molecular dynamics simulations. For the (•)OOH reactions, addition to the pyrrole ring at position 2 is the most favored pathway, in contrast to the situation in the model system ethylene, where concerted addition to the double bond is preferred. From the (•)OOH position 2 adduct QM/MM simulations show that formation of oxy-3-indolanaline occurs readily in an aqueous environment. The observed transformation starts from an initial rupture of the O-O bond followed by a H atom transfer with the accompanying loss of an (•)OH radical to solution. Finally, classical molecular dynamics simulations were performed to equate observed differential oxidation rates of various tryptophan residues in monoclonal antibody fragments. It was found that simple parameters derived from simulation correlate well with the experimental data.

Spectroscopy, Kinetics, and Dynamics of Combustion Radicals

Energy Technology Data Exchange (ETDEWEB)

Nesbitt, David J. [Research/Professor

2013-08-06

Spectroscopy, kinetics and dynamics of jet cooled hydrocarbon transients relevant to the DOE combustion mission have been explored, exploiting i) high resolution IR lasers, ii) slit discharge sources for formation of jet cooled radicals, and iii) high sensitivity detection with direct laser absorption methods and near the quantum shot noise limit. What makes this combination powerful is that such transients can be made under high concentrations and pressures characteristic of actual combustion conditions, and yet with the resulting species rapidly cooled (T ≈10-15K) in the slit supersonic expansion. Combined with the power of IR laser absorption methods, this provides novel access to spectral detection and study of many critical combustion species.

Free radical hydrogen atom abstraction from saturated hydrocarbons: A crossed-molecular-beams study of the reaction Cl + C{sub 3}H{sub 8} {yields} HCl + C{sub 3}H{sub 7}

Energy Technology Data Exchange (ETDEWEB)

Blank, D.A.; Hemmi, N.; Suits, A.G.; Lee, Y.T. [Lawrence Berkeley National Lab., CA (United States)

1997-04-01

The abstraction of hydrogen atoms from saturated hydrocarbons are reactions of fundamental importance in combustion as well as often being the rate limiting step in free radical substitution reactions. The authors have begun studying these reactions under single collision conditions using the crossed molecular beam technique on beamline 9.0.2.1, utilizing VUV undulator radiation to selectively ionize the scattered hydrocarbon free radical products (C{sub x}H{sub 2x+1}). The crossed molecular beam technique involves two reactant molecular beams fixed at 90{degrees}. The molecular beam sources are rotatable in the plane defined by the two beams. The scattered neutral products travel 12.0 cm where they are photoionized using the VUV undulator radiation, mass selected, and counted as a function of time. In the authors initial investigations they are using halogen atoms as protypical free radicals to abstract hydrogen atoms from small alkanes. Their first study has been looking at the reaction of Cl + propane {r_arrow} HCl + propyl radical. In their preliminary efforts the authors have measured the laboratory scattering angular distribution and time of flight spectra for the propyl radical products at collision energies of 9.6 kcal/mol and 14.9 kcal/mol.

The Rise of Radicals in Bioinorganic Chemistry

OpenAIRE

Gray, Harry B.; Winkler, Jay R.

2016-01-01

Prior to 1950, the consensus was that biological transformations occurred in two-electron steps, thereby avoiding the generation of free radicals. Dramatic advances in spectroscopy, biochemistry, and molecular biology have led to the realization that protein-based radicals participate in a vast array of vital biological mechanisms. Redox processes involving high-potential intermediates formed in reactions with O_2 are particularly susceptible to radical formation. Clusters of tyrosine (Tyr) a...

Allylthioketone Mediated Free Radical Polymerization of Methacrylates

Directory of Open Access Journals (Sweden)

Feng Zhong

2017-11-01

Full Text Available By combination of high trapping free radical efficiency of the thioketone and resonance of the allylic radical, a new type of mediating agent, 1,3,3-triphenylprop-2-ene-1-thione (TPPT has been successfully synthesized, and then is used to study controlled free radical polymerization of methacrylates. Very stable TPPT radicals at the end of poly(methyl methacrylate (PMMA are detected in the polymerization of MMA using TPPT and AIBN as the control agent and initiator. The MALDI-TOF MS spectra are used to identify terminal groups of the resultant poly(glycidyl methacrylate (PGMA, and major component of the obtained polymer has the structure, (CH32(CNC-PGMA-C7H9O3. Chain extension reaction tests ascertain formation of the dead polymers during the polymer storage and purification process of the polymers. Owing to very slow fragmentation reaction of the TPPT-terminated polymethacrylate radical and addition reaction of this radical with a primary radical, the growing chain radicals are difficult to be regenerated, leading to an unobvious change of the molecular weight with monomer conversion. The molecular weights of polymers can be controlled by the ratios of monomer/initiator and TPPT/initiator. However, the first order kinetics of the polymerization and the polymers with narrow polydispersity are obtained, and these phenomena are discussed. This study provides useful information on how to design a better controlling agent.

Aerosol Fragmentation Driven by Coupling of Acid-Base and Free-Radical Chemistry in the Heterogeneous Oxidation of Aqueous Citric Acid by OH Radicals.

Science.gov (United States)

Liu, Matthew J; Wiegel, Aaron A; Wilson, Kevin R; Houle, Frances A

2017-08-10

A key uncertainty in the heterogeneous oxidation of carboxylic acids by hydroxyl radicals (OH) in aqueous-phase aerosol is how the free-radical reaction pathways might be altered by acid-base chemistry. In particular, if acid-base reactions occur concurrently with acyloxy radical formation and unimolecular decomposition of alkoxy radicals, there is a possibility that differences in reaction pathways impact the partitioning of organic carbon between the gas and aqueous phases. To examine these questions, a kinetic model is developed for the OH-initiated oxidation of citric acid aerosol at high relative humidity. The reaction scheme, containing both free-radical and acid-base elementary reaction steps with physically validated rate coefficients, accurately predicts the experimentally observed molecular composition, particle size, and average elemental composition of the aerosol upon oxidation. The difference between the two reaction channels centers on the reactivity of carboxylic acid groups. Free-radical reactions mainly add functional groups to the carbon skeleton of neutral citric acid, because carboxylic acid moieties deactivate the unimolecular fragmentation of alkoxy radicals. In contrast, the conjugate carboxylate groups originating from acid-base equilibria activate both acyloxy radical formation and carbon-carbon bond scission of alkoxy radicals, leading to the formation of low molecular weight, highly oxidized products such as oxalic and mesoxalic acid. Subsequent hydration of carbonyl groups in the oxidized products increases the aerosol hygroscopicity and accelerates the substantial water uptake and volume growth that accompany oxidation. These results frame the oxidative lifecycle of atmospheric aerosol: it is governed by feedbacks between reactions that first increase the particle oxidation state, then eventually promote water uptake and acid-base chemistry. When coupled to free-radical reactions, acid-base channels lead to formation of low molecular

Measurements of Free Radical in Vitamin E-Doped Ultra-High Molecular Weight Polyethylene: Dependence on Materials Processing and Irradiation Environments

International Nuclear Information System (INIS)

Ridley, M. D.

2006-01-01

In an effort to combat oxidation of the load-bearing, polyethylene (PE) components of total hip- and knee-joint replacement devices, antioxidant such as vitamin E (α-Tocopherol (α-T)) has been introduced into polymer matrix. In this study we investigated effect of α-T on free radicals in medical grade ultra-high molecular weight polyethylene (UHMWPE), GUR 1020 resin. Since oxidation resistance depends on radical reaction, we used electron spin resonance (ESR) technique for direct detection of free radicals before and after irradiation. High concentration (20% by vol.) of α-T was used so its ESR signal (due to α-T-O degree radical) could be distinguished among the overwhelming signals due to PE radicals. Two groups of samples were investigated. In one group, samples were prepared from blends of α-T and UHMWPE powder (α-T-P), and in the second group, from compression molded blocks (α-T-B). In each group, samples were γ-irradiated in sealed packages filled with N 2 , or in open air, and free radicals were measured in open air environment as a function of time. Also included in this study were α-T, and powder resin and compression molded blocks without any α-T. Following irradiation in air, α-T-P and α-T produced identical ESR spectra showing characteristic feature of α-T-O degree radical. Absence of PE radicals in the ESR signals suggests quenching/repairing of PE radicals by α-T in presence of oxygen. However, when irradiation was performed in N 2 , ESR signals of α-T-P exhibited superimposed resonance lines due to PE and α-T-O degree radicals. Furthermore, presence of a-T or α-T-O degree radicals did not prevent subsequent oxidation of PE radicals in producing stable, oxygen-induced radicals (OIR). Post-irradiation oxidation index measured by FTIR, however, did not show any difference between these samples. Compression molded samples, with or without α-T, produced ESR spectra showing features characteristics of PE radicals only, and there was no

Molecular Dynamics Simulations of Collisional Cooling and Ordering of Multiply Charged Ions in a Penning Trap

International Nuclear Information System (INIS)

Holder, J.P.; Church, D.A.; Gruber, L.; DeWitt, H.E.; Beck, B.R.; Schneider, D.

2000-01-01

Molecular dynamics simulations are used to help design new experiments by modeling the cooling of small numbers of trapped multiply charged ions by Coulomb interactions with laser-cooled Be + ions. A Verlet algorithm is used to integrate the equations of motion of two species of point ions interacting in an ideal Penning trap. We use a time step short enough to follow the cyclotron motion of the ions. Axial and radial temperatures for each species are saved periodically. Direct heating and cooling of each species in the simulation can be performed by periodically rescaling velocities. Of interest are Fe 11+ due to a EUV-optical double resonance for imaging and manipulating the ions, and Ca 14+ since a ground state fine structure transition has a convenient wavelength in the tunable laser range

Glutathione--hydroxyl radical interaction: a theoretical study on radical recognition process.

Directory of Open Access Journals (Sweden)

Béla Fiser

Full Text Available Non-reactive, comparative (2 × 1.2 μs molecular dynamics simulations were carried out to characterize the interactions between glutathione (GSH, host molecule and hydroxyl radical (OH(•, guest molecule. From this analysis, two distinct steps were identified in the recognition process of hydroxyl radical by glutathione: catching and steering, based on the interactions between the host-guest molecules. Over 78% of all interactions are related to the catching mechanism via complex formation between anionic carboxyl groups and the OH radical, hence both terminal residues of GSH serve as recognition sites. The glycine residue has an additional role in the recognition of OH radical, namely the steering. The flexibility of the Gly residue enables the formation of further interactions of other parts of glutathione (e.g. thiol, α- and β-carbons with the lone electron pair of the hydroxyl radical. Moreover, quantum chemical calculations were carried out on selected GSH/OH(• complexes and on appropriate GSH conformers to describe the energy profile of the recognition process. The relative enthalpy and the free energy changes of the radical recognition of the strongest complexes varied from -42.4 to -27.8 kJ/mol and from -21.3 to 9.8 kJ/mol, respectively. These complexes, containing two or more intermolecular interactions, would be the starting configurations for the hydrogen atom migration to quench the hydroxyl radical via different reaction channels.

The molecular dynamics simulation of structure and transport properties of sheared super-cooled liquid metal

International Nuclear Information System (INIS)

Wang Li; Liu Xiangfa; Zhang Yanning; Yang Hua; Chen Ying; Bian Xiufang

2003-01-01

Much more attention has been paid to the microstructure of liquid metal under non-ordinary condition recently. In this Letter, the pair correlation function (PCF), together with internal energy of sheared super-cooled liquid Co as a function of temperature has been calculated by molecular dynamics simulation based upon the embedded atom method (EAM) and analyzed compared to that under normal condition. The finding indicates that there exist three obvious peaks of PCF for liquid Co; while as the shear stress is applied to the liquid, the first and second peaks of PCF become lower, the third peak disappeared. The concentric shell structure representing short-range order of liquid still exists, however, it is weakened by the addition of shear stress, leading to the increases of disordering degree of liquid metal. The curves of energy versus temperature suggest the higher crystalline temperature compared to that under normal condition at the same cooling rate. In addition, the viscosity of super-liquid Co is calculated by non-equilibrium molecular dynamics (NEMD)

Structural modification of the skin barrier by OH radicals: a reactive molecular dynamics study for plasma medicine

International Nuclear Information System (INIS)

Van der Paal, J; Verlackt, C C; Yusupov, M; Neyts, E C; Bogaerts, A

2015-01-01

While plasma treatment of skin diseases and wound healing has been proven highly effective, the underlying mechanisms, and more generally the effect of plasma radicals on skin tissue, are not yet completely understood. In this paper, we perform ReaxFF-based reactive molecular dynamics simulations to investigate the interaction of plasma generated OH radicals with a model system composed of free fatty acids, ceramides, and cholesterol molecules. This model system is an approximation of the upper layer of the skin (stratum corneum). All interaction mechanisms observed in our simulations are initiated by H-abstraction from one of the ceramides. This reaction, in turn, often starts a cascade of other reactions, which eventually lead to the formation of aldehydes, the dissociation of ceramides or the elimination of formaldehyde, and thus eventually to the degradation of the skin barrier function. (paper)

Deciphering free-radical code of radiation effects

International Nuclear Information System (INIS)

Volovyk, S.; Bazyka, D.; Loganovsky, K.; Bebeshko, V.

2007-01-01

Complete text of publication follows. Objective: Ionizing radiation is fundamental environmental factor for life origin and evolution. Free radicals, primordial 'sea' for life conceiving and existence, induced by cosmic and terrestrial background radiation, are evolutionally archetypal, ubiquitous, and omnipotent in physiological- pathophysiological dichotomy. Classical free-radical paradigm in radiation biology and medicine, focused in essence on oxidative damage, needs new conceptualization and generalization. Methods: Suggested novel insights into free radicals dual immanent nature and functions in organism systems are based on original concepts of radicals dynamic charge transfer (CT) - redox ambivalence (interactional nucleo-, electro-, and ambiphilicity spectrum); pertinent chemical reactivity and selectivity delocalization model; physiological functional ambivalence and complementarity, and dynamic free-radical homeostasis. Results: Subtle perturbations in radicals CT spatiotemporal homeodynamics, in responsive signaling / controlling networks, concomitant alterations in genes expression, transcription, and apoptosis, redox control of mitochondrial ET chain, telomere/telomerase balance, DNA CT, circadian clock, hemispheric biochemical dominance/accentuation, including alteration of nitric oxide-superoxide complementarity, membranes permeability, neurotransmission pattern, synaptic circuitry, etc under radiation exposure have more fundamental impact on organism systems (especially CNS and CVS) deterioration than simple radicals inflicted oxidative (nitrosative) damage of cellular constituents. Conclusions: This novel conceptualization of free-radical paradigm constitutes new dimension in deciphering molecular mechanisms of radiation effects on subtle borderline norm-pathology and continuity-discontinuity dichotomy in organisms systems disorders - CT(redox)omics, which involves investigation of CT, redox, and spin states of free radicals, DNA bases

Implications of recent research on microstructure modifications, through heat-related processing and trait alteration to bio-functions, molecular thermal stability and mobility, metabolic characteristics and nutrition in cool-climate cereal grains and other types of seeds with advanced molecular techniques.

Science.gov (United States)

Ying, Yuguang; Zhang, Huihua; Yu, Peiqiang

2018-02-16

The cutting-edge synchrotron radiation based and globar-sourced vibrational infrared microspectroscopy have recently been developed. These novel techniques are able to reveal structure features at cellular and molecular levels with the tested tissues being intact. However, to date, the advanced techniques are unfamiliar or unknown to food and feed scientists and have not been used to study the molecular structure changes in cool-climate cereal grain seeds and other types of bio-oil and bioenergy seeds. This article aims to provide some recent research in cool-climate cereal grains and other types of seeds on molecular structures and metabolic characteristics of carbohydrate and protein, and implication of microstructure modification through heat-related processing and trait alteration to bio-functions, molecular thermal stability and mobility, and nutrition with advanced molecular techniques- synchrotron radiation based and globar-sourced vibrational infrared microspectroscopy in the areas of (1) Inherent microstructure of cereal grain seeds; (2) The nutritional values of cereal grains; (3) Impact and modification of heat-related processing to cereal grain; (4) Conventional nutrition evaluation methodology; (5) Synchrotron radiation-based and globar-sourced vibrational (micro)-spectroscopy for molecular structure study and molecular thermal stability and mobility, and (6) Recent molecular spectroscopic technique applications in research on raw, traits altered and processed cool-climate cereal grains and other types of seeds. The information described in this article gives better insights of research progress and update in cool-climate cereal grains and other seeds with advanced molecular techniques.

Radiation-induced damage in E. coli B: The effect of superoxide radicals and molecular oxygen. Progress report, December 1, 1978--November 30, 1979

International Nuclear Information System (INIS)

Samuni, A.; Czapski, G.

The roles of superoxide radicals and of molecular oxygen in the radiodamage of E. coli B suspended in dilute phosphate buffer were studied. The presence of high concentrations of polyethylene glycol in the γ-irradiated cell suspensions, had no effect on bacterial radiosensitivity. This indicates that the damage was primarily endogenous, i.e. originated intracellularly. Saturation of the cell suspensions with N 2 O doubled the radiosensitivity, thus indicating that OH radicals are responsible for the majority of the damage (indirect radiation effect). The presence of oxygen either in the absence or presence of N 2 O brought about roughly a three-fold increase in the radiosensitivity. Since in the presence of N 2 O all e - /sub aq/ are scavenged by the nitrous oxide rather than by oxygen, this shows that superoxide radicals play no role in the bacterial radiodamage. Our results substantiate the attribution of the oxygen effect to a direct interaction of O 2 with the hydroxyl-radical-damaged sites on vital biomolecules, and exclude any significant contribution of e - /sub aq/ and superoxide radicals to the cellular radiodamage

Cellular and Molecular Mechanisms of the Production of Free Radicals during Exercise and Their Function on Skeletal Muscles

Directory of Open Access Journals (Sweden)

2017-06-01

Full Text Available Physical activity is an integral part of human life. Among significant biological changes during physical activity are increase of metabolism and production of free radicals. Free radical can be defined as molecule or molecular fragments containing unpaired electron in the outer orbital, which react with nearby molecules to obtain stability. These highly reactive molecules have various deleterious effects, such as reduced force generation and increased muscle atrophy. There is evidence that ROS produced during exercise has positive adaptation effects. ROS production leads to increased expression of the anti-oxidants. These molecules, by neutralizing free radicals, neutralize the negative effects of ROS. In addition, exercise-induced ROS leads to the expression of PGC-1α  protein, having a significant impact on various aspects of cell metabolism, mitochondrial biogenesis and cellular respiration as well as metabolism of fat and glucose. This paper provides an overview of the evidence to date on the effects of ROS on exercising muscle. These aspects include the sources of ROS, their positive and negative cellular effects,  role of antioxidants, and ROS-dependent adaptations of muscle cells in response to physical exercise

Living atom transfer radical polymerization of 4-acetoxystyrene

DEFF Research Database (Denmark)

Gao, Bo; Chen, Xianyi; Ivan, Bela

1997-01-01

Living atom transfer radical polymerization (ATRP) of 4-acetoxystyrene (1), a protected 4-vinylphenol, leading to poly(4-acetoxystyrene) with well-defined molecular weight and narrow molecular weight distribution was carried out in bulk with a,a'-dibromoxylene(2)/CuBr/2,2-bipyridine(bpy) as initi......Living atom transfer radical polymerization (ATRP) of 4-acetoxystyrene (1), a protected 4-vinylphenol, leading to poly(4-acetoxystyrene) with well-defined molecular weight and narrow molecular weight distribution was carried out in bulk with a,a'-dibromoxylene(2)/CuBr/2,2-bipyridine......(bpy) as initiating system. A linear (M) over bar(n), versus monomer conversion plot was found in good accordance with the theoretical line, indicating 100% initiating efficiency. The polymerization is first order in respect to monomer up to about 70% monomer conversion. Deviations from linearity at higher conversion...

Studies of radiation-produced radicals and radical ions. Progress report, June 1, 1981-August 31, 1982

International Nuclear Information System (INIS)

Williams, T.F.

1982-01-01

The discovery and characterization of novel radical ions produced by the γ irradiation of solids continues to be a fertile field for investigation. This Progress Report describes the generation and ESR identification of several new paramagnetic species, some of which have long been sought as important intermediates in radiation chemistry. We have also contributed to a general theoretical problem in ESR spectroscopy. Solid-state studies of electron attachment reactions, both non-dissociative and dissociative, reveal interesting structural and chemical information about the molecular nature of these processes for simple compounds. In particular, ESR measurements of the spin distribution in the products allow a fairly sharp distinction to be drawn between radical anions and radical-anion pairs or adducts. Dimer radical anion formation can also take place but the crystal structure plays a role in this process, as expected. Some radical anions undergo photolysis to give radical-anion pairs which may then revert back to the original radical anion by a thermal reaction. The chemistry of these reversible processes is made more intricate by a competing reaction in which the radical abstracts a hydrogen atom from a neighboring molecule. However, the unraveling of this complication has also served to extend our knowledge of the role of quantum tunneling in chemical reactions. The results of this investigation testify to the potential of solid-state techniques for the study of novel and frangible radical ions. Progress in this field shows no sign of abating, as witness the recent discovery of perfluorocycloalkane radical anions and alkane radical cations

Helium-cooled nuclear reactor

International Nuclear Information System (INIS)

Longton, P.B.; Cowen, H.C.

1975-01-01

In helium cooled HTR's there is a by-pass circuit for cleaning purposes in addition to the main cooling circuit. This is to remove such impurities as hydrogen, methane, carbon monoxide and water from the coolant. In this system, part of the coolant successively flows first through an oxidation bed of copper oxide and an absorption bed of silica gel, then through activated charcoal or a molecular sieve. The hydrogen and carbon monoxide impurities are absorbed and the dry gas is returned to the main cooling circuit. To lower the hydrogen/water ratio without increasing the hydrogen fraction in the main cooling circuit, some of the hydrogen fraction converted into water is added to the cooling circuit. This is done, inter alia, by bypassing the water produced in the oxidation bed before it enters the absorption bed. The rest of the by-pass circuit, however, also includes an absorption bed with a molecular sieve. This absorbs the oxidized carbon monoxide fraction. In this way, such side effects as the formation of additional methane, carburization of the materials of the by-pass circuit or loss of graphite are avoided. (DG/RF) [de

The Analytical Potential Energy Function of NH Radical Molecule in External Electric Field

International Nuclear Information System (INIS)

Wu Dong-Lan; Tan Bin; Wan Hui-Jun; Xie An-Dong; Ding Da-Jun

2015-01-01

The geometric structures of an NH radical in different external electric fields are optimized by using the density functional B3P86/cc-PV5Z method, and the bond lengths, dipole moments, vibration frequencies and IR spectrum are obtained. The potential energy curves are gained by the CCSD (T) method with the same basis set. These results indicate that the physical property parameters and potential energy curves may change with the external electric field, especially in the reverse direction electric field. The potential energy function of zero field is fitted by the Morse potential, and the fitting parameters are in good accordance with the experimental data. The potential energy functions of different external electric fields are fitted adopting the constructed potential model. The fitted critical dissociation electric parameters are shown to be consistent with the numerical calculation, and the relative errors are only 0.27% and 6.61%, hence the constructed model is reliable and accurate. The present results provide an important reference for further study of the molecular spectrum, dynamics and molecular cooling with Stark effect. (paper)

Ultracold molecules for the masses: Evaporative cooling and magneto-optical trapping

Science.gov (United States)

Stuhl, B. K.

While cold molecule experiments are rapidly moving towards their promised benefits of precision spectroscopy, controllable chemistry, and novel condensed phases, heretofore the field has been greatly limited by a lack of methods to cool and compress chemically diverse species to temperatures below ten millikelvin. While in atomic physics these needs are fulfilled by laser cooling, magneto-optical trapping, and evaporative cooling, until now none of these techniques have been applicable to molecules. In this thesis, two major breakthroughs are reported. The first is the observation of evaporative cooling in magnetically trapped hydroxyl (OH) radicals, which potentially opens a path all the way to Bose-Einstein condensation of dipolar radicals, as well as allowing cold- and ultracold-chemistry studies of fundamental reaction mechanisms. Through the combination of an extremely high gradient magnetic quadrupole trap and the use of the OH Λ-doublet transition to enable highly selective forced evaporation, cooling by an order of magnitude in temperature was achieved and yielded a final temperature no higher than 5mK. The second breakthrough is the successful application of laser cooling and magneto-optical trapping to molecules. Motivated by a proposal in this thesis, laser cooling of molecules is now known to be technically feasible in a select but substantial pool of diatomic molecules. The demonstration of not only Doppler cooling but also two-dimensional magneto-optical trapping in yttrium (II) oxide, YO, is expected to enable rapid growth in the availability of ultracold molecules—just as the invention of the atomic magneto-optical trap stimulated atomic physics twenty-five years ago.

Measurements of free radical in vitamin E-doped ultra-high molecular weight polyethylene: Dependence on materials processing and irradiation environments

Energy Technology Data Exchange (ETDEWEB)

Ridley, M.D. [Department of Physics, Biomaterials Research Laboratory, University of Memphis, 216 Manning Hall, Memphis, TN 38152 (United States); Jahan, M.S. [Department of Physics, Biomaterials Research Laboratory, University of Memphis, 216 Manning Hall, Memphis, TN 38152 (United States)], E-mail: mjahan@memphis.edu

2007-12-15

Ultra-high molecular weight polyethylene (UHMWPE), doped with vitamin E ({alpha}-tocopherol ({alpha}-T)), was irradiated with gamma rays in nitrogen (N{sub 2}) or air, and the resulting free radicals were detected in air using an electron spin resonance (ESR) technique. Two groups of samples were investigated. In one group, samples were prepared from blends of {alpha}-T (20 wt%) and UHMWPE powder (PPE-{alpha}-T) and, in the other, from compression molded blocks (CMPE-{alpha}-T). The CMPE-{alpha}-T blocks contained 0% (control), 0.5%, 1.0%, 10.0%, 15.0%, 20.0% and 25.0% {alpha}-T by weight. When irradiation was performed in air, the ESR spectrum of powder samples showed the presence of only vitamin E radical (tocopheroxyl, {alpha}-T-O{sup {center_dot}}), and there was no detectable signal due to PE radicals (alkyl/allyl). Most likely, all PE radicals were quenched by vitamin E during irradiation in air. However, when irradiation was performed in N{sub 2}, composite ESR spectra showed the presence of both PE and {alpha}-T-O{sup {center_dot}} radicals. Compared to the control (PPE, 0% {alpha}-T) PE radicals in PPE-20% {alpha}-T were found to be significantly reduced or quenched by {alpha}-T. The presence of {alpha}-T in powder samples, however, did not affect the long-term (71 days in this study) oxidation behavior of the PE radicals. Compression molded samples, with and without {alpha}-T, produced identical ESR spectra irrespective of their irradiation environment N{sub 2} or air. However, radical concentration, measured immediately after irradiation, was found to be an order of magnitude less in CMPE-{alpha}-T than in the control (CMPE-0% {alpha}-T). They also evidenced identical structural changes in the respective ESR spectra during subsequent oxidation for 24 days in open air. These observations suggest that {alpha}-T can effectively quench a significant fraction of PE radicals during irradiation, but has no measurable effect on subsequent reactions. No

Theory of tapered laser cooling

International Nuclear Information System (INIS)

Okamoto, Hiromi; Wei, J.

1998-01-01

A theory of tapered laser cooling for fast circulating ion beams in a storage ring is constructed. The authors describe the fundamentals of this new cooling scheme, emphasizing that it might be the most promising way to beam crystallization. The cooling rates are analytically evaluated to study the ideal operating condition. They discuss the physical implication of the tapering factor of cooling laser, and show how to determine its optimum value. Molecular dynamics method is employed to demonstrate the validity of the present theory

Structure evolution during the cooling and coalesced cooling processes of Cu-Co bimetallic clusters

International Nuclear Information System (INIS)

Li Guojian; Wang Qiang; Li Donggang; Lue Xiao; He Jicheng

2008-01-01

Constant-temperature molecular dynamics with general EAM was employed to study the structure evolutions during the cooling and coalesced cooling processes of Cu-Co bimetallic clusters. It shows that the desired particle morphologies and structures can be obtained by controlling the composition and distribution of hetero atoms during synthesis process

Pressure and cooling rate effect on polyhedron clusters in Cu-Al alloy by using molecular dynamics simulation

Science.gov (United States)

Celik, Fatih Ahmet

2014-10-01

In this study, the microstructural evolution of crystal-type and icosahedral (icos)-type polyhedrons in Cu-50 at%Al alloy based on the embedded atom method (EAM) model is studied at two cooling rates under normal and high pressures by using the molecular dynamics (MD) simulation method. The cluster-type index method (CTIM) which describes icos and defective icos polyhedrons and the new cluster-type index method (CTIM-2) which describes crystal-type polyhedrons have been used to perform polyhedron analysis in the model alloy system. The results of our simulations demonstrate that the effects of the cooling rate and pressure play an important role in the numbers of polyhedrons and their structures in the system.

Pressure and cooling rate effect on polyhedron clusters in Cu–Al alloy by using molecular dynamics simulation

Energy Technology Data Exchange (ETDEWEB)

Celik, Fatih Ahmet, E-mail: facelik@beu.edu.tr

2014-10-01

In this study, the microstructural evolution of crystal-type and icosahedral (icos)-type polyhedrons in Cu–50 at%Al alloy based on the embedded atom method (EAM) model is studied at two cooling rates under normal and high pressures by using the molecular dynamics (MD) simulation method. The cluster-type index method (CTIM) which describes icos and defective icos polyhedrons and the new cluster-type index method (CTIM-2) which describes crystal-type polyhedrons have been used to perform polyhedron analysis in the model alloy system. The results of our simulations demonstrate that the effects of the cooling rate and pressure play an important role in the numbers of polyhedrons and their structures in the system.

Radical production in the radiolysis of benzene

International Nuclear Information System (INIS)

LaVerne, J.A.; Araos, M.S.

1998-01-01

Complete text of publication follows. Benzene is the prototypical aromatic compound and yet the radiation chemistry of the radicals formed in its radiolysis is not well understood. Temporal information on the yield of phenyl radical, the major radical produced in the radiolysis, is important for understanding the radiation chemistry of many other types of aromatic compounds including some polymers. The effects of track structure on the production of phenyl radicals have been examined using iodine-scavenging techniques. The variation of the yields of iodobenzene and the other major molecular products such as biphenyl as a function of iodine concentration gives a good indication of the competition kinetics occurring in particle tracks. Experimental results of the scavenger experiments will be shown and their implications in the radiolysis of condensed hydrocarbons will be discussed

New concepts for molecular magnets

Science.gov (United States)

Pilawa, Bernd

1999-03-01

Miller and Epstein (1994) define molecular magnets as magnetic materials which are prepared by the low-temperature methods of the preparative chemistry. This definition includes molecular crystals of neutral radicals, radical salts and charge transfer complexes as well as metal complexes and polymers with unpaired spins (Dormann 1995). The challenge of molecular magnets consists in tailoring magnetic properties by specific modifications of the molecular units. The combination of magnetism with mechanical or electrical properties of molecular compounds promise materials of high technical interest (Gatteschi 1994a and 1994b, Möhwald 1996) and both the chemical synthesis of new molecular materials with magnetic properties as well as the physical investigation and explanation of these properties is important, in order to achieve any progress. This work deals with the physical characterization of the magnetic properties of molecular materials. It is organized as follows. In the first part molecular crystals of neutral radicals are studied. After briefly discussing the general magnetic properties of these materials and after an overview over the physical principles of exchange interaction between organic radicals I focus on the interplay between the crystallographic structure and the magnetic properties of various derivatives of the verdazyl and nitronyl nitroxide radicals. The magnetic properties of metal complexes are the subject of the second part. After an overview over the experimental and theoretical tools which are used for the investigation of the magnetic properties I shortly discuss the exchange coupling of transition metal ions and the magnetic properties of complexes of two and three metal ions. Special emphasis is given to spin cluster compounds. Spin cluster denote complexes of many magnetic ions. They are attractive as building blocks of molecular magnets as well as magnetic model compounds for the study of spin frustration, molecular super

Correlation between inter-spin interaction and molecular dynamics of organic radicals in organic 1D nanochannels

Energy Technology Data Exchange (ETDEWEB)

Kobayashi, Hirokazu [Department of Chemistry, College of Humanities and Sciences, Nihon University 3-25-40, Sakura-jo-sui, Setagaya-ku, Tokyo, 156-8550 (Japan)

2015-12-31

One-dimensional (1D) molecular chains of 4-substituted-2,2,6,6-tetramethyl-1-piperidinyloxyl (4-X-TEMPO) radicals were constructed in the crystalline 1D nanochannels of 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) used as a template. The ESR spectra of CLPOT inclusion compounds (ICs) using 4-X-TEMPO were examined on the basis of spectral simulation using EasySpin program package for simulating and fitting ESR spectra. The ESR spectra of [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC were isotropic in the total range of temperatures. The peak-to-peak line width (ΔB{sub pp}) became monotonically narrower from 2.8 to 1.3 mT with increase in temperature in the range of 4.2–298 K. The effect of the rotational diffusion motion of TEMPO radicals in the CLPOT nanochannels for the inter-spin interaction of the [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC was found to be smaller than the case of [(TPP){sub 2}−(TEMPO){sub 1.0}] IC (TPP = tris(o-phenylenedioxy)cyclotriphosphazene) reported in our previous study. The ΔB{sub pp} of the [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC in the whole range of temperatures was much narrower than the estimation to be based on the Van Vleck’s formula for the second moment of the rigid lattice model where the electron spin can be considered as fixed; 11 mT of Gaussian line-width component. This suggests the possibility of exchange narrowing in the 1D organic-radical chains of the [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC. On the other hand, the ESR spectra of [(CLPOT){sub 2}-(MeO-TEMPO){sub 0.41}] IC (MeO-TEMPO = 4-methoxy-TEMPO) were reproduced by a superposition of major broad isotropic adsorption line and minor temperature-dependent modulated triplet component. This suggests that the IC has the part of 1D organic-radical chains and MeO-TEMPO molecules isolated in the CLPOT nanochannels.

Role of free radicals in radiation chemical aging

Energy Technology Data Exchange (ETDEWEB)

Greenstock, C L

1986-01-01

Ionizing radiation initiates chemical changes in DNA, phospholipid membranes and other critical cell targets, that, if allowed to accumulate unrepaired, may lead to aging and other chronic effects. The chemical effects are free radical mediated, the principal damaging species being radical OH and to a lesser extent O2-anion radical and the molecular product H/sub 2/O/sub 2/. Many compounds can act in combination with ionizing radiation, to amplify the potential oxidative stress. Chemicals, ultra-violet light, lipid peroxides and their breakdown products may increase the extent of acute and chronic radiobiological effects.

Interotex-innovative gas equipment for heating and cooling

Energy Technology Data Exchange (ETDEWEB)

Winnington, T.L. [Interotex Ltd. (United Kingdom); Moore, N. [British Gas plc (United Kingdom); Valle, F.; Sanz, J. I. [Gas Natural SDG S.A. (Spain); Chavarri, J.M. [Fagor Electrodomesticos S. Coop. (Spain); Uselton, R. [Lennox Industries Inc. (United States)

1997-10-01

Conventionally, cooling technology for the residential market is provided by electrically driven vapour re-compression systems. But lately, due to the Montreal Protocol - restricting the utilisation of ozone depleting substances - and to the high peak demand in electricity, created by electrical air conditioning systems, there is a commercial opportunity for gas fired air conditioning appliances. This paper describes the development programme for a radical new absorption technology, from the theoretical studies, through the experimental programme, to the building, commissioning and installation of demonstration machines. It also includes an analysis of the world-wide residential cooling market and the opportunities available to manufacturers and gas utilities to introduce new gas heating and cooling technology, capable of competing effectively with electrical systems. (au)

Growth kinetics and properties of ZnO/ZnMgO heterostructures grown by radical-source molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Ivanov, S.V. [Institute of Semiconductor Technology, Technical University Braunschweig, Hans-Sommer-Str. 66, 38106 Braunschweig (Germany); Ioffe Physico-Technical Institute, Polytekhnicheskaya Street 26, 194021 St. Petersburg (Russian Federation); El-Shaer, A.; Bakin, A.; Waag, A. [Institute of Semiconductor Technology, Technical University Braunschweig, Hans-Sommer-Str. 66, 38106 Braunschweig (Germany); Shubina, T.V.; Listoshin, S.B. [Ioffe Physico-Technical Institute, Polytekhnicheskaya Street 26, 194021 St. Petersburg (Russian Federation)

2007-07-01

A phenomenological approach to quantitative description of Zn(Mg)O growth by radical-source molecular beam epitaxy, based on the experimental studies of RHEED intensity oscillations, has been developed. It allows a precise control of growth rate, composition and stoichiometry at any growth temperature, Along with optimization of a growth initiation procedure on a c-sapphire, it is necessary condition for fabrication of high quality ZnO epilayers and ZnO/ZnMgO heterostructures in a wide Mg composition range. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Colorless to purple-red switching electrochromic anthraquinone imides with broad visible/near-IR absorptions in the radical anion state: simulation-aided molecular design.

Science.gov (United States)

Chen, Fengkun; Zhang, Jie; Jiang, Hong; Wan, Xinhua

2013-07-01

The large redshift of near-infrared (NIR) absorptions of nitro-substituted anthraquinone imide (Nitro-AQI) radical anions, relative to other AQI derivatives, is rationalized based on quantum chemical calculations. Calculations reveal that the delocalization effects of electronegative substitution in the radical anion states is dramatically enhanced, thus leading to a significant decrease in the HOMO-LUMO band gap in the radical anion states. Based on this understanding, an AQI derivative with an even stronger electron-withdrawing dicyanovinyl (di-CN) substituent was designed and prepared. The resulting molecule, di-CN-AQI, displays no absorption in the Vis/NIR region in the neutral state, but absorbs intensively in the range of λ=700-1000 (λmax ≈860 nm) and λ=1100-1800 nm (λmax ≈1400 nm) upon one-electron reduction; this is accompanied by a transition from a highly transmissive colorless solution to one that is purple-red. The relationship between calculated radical anionic HOMO-LUMO gaps and the electron-withdrawing capacity of the substituents is also determined by employing Hammett parameter, which could serve as a theoretical tool for further molecular design. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nitroxyl free radicals formed from hindered amine light stabilizers under 60Co γ-ray irradiation

International Nuclear Information System (INIS)

Wang Huiliang; Chen Wenxiu

2006-01-01

Nitroxyl free radicals formed from several low molecular weight (LMW) hindered amine light stabilizers (HALS) under 60 Co γ-ray irradiation was studied with electron spin resonance (ESR) spectroscopy. All the HALSs irradiated in air formed nitroxyl free radicals under irradiation in air. For most of the HALSs, concentration of the nitroxyl free radicals increased linearly and quickly with absorbed dose in 0-10 kGy range, but increased slowly, or even kept constant, with doses of greater than 10 kGy. Concentration of nitroxyl free radicals formed from LMW HALS was usually higher than high molecular weight HALS. Tetramethyl HALS was easier to form nitroxyl free radicals than pentamethyl HLAS. Concentration of nitroxyl free radicals formed from the samples irradiated in oxygen was about two times higher than that the samples irradiated in air. Mechanisms of the nitroxyl free radical formation from the γ-ray irradiated HALSs were was discussed. (authors)

Watson-Crick Base Pair Radical Cation as a Model for Oxidative Damage in DNA.

Science.gov (United States)

Feketeová, Linda; Chan, Bun; Khairallah, George N; Steinmetz, Vincent; Maitre, Philippe; Radom, Leo; O'Hair, Richard A J

2017-07-06

The deleterious cellular effects of ionizing radiation are well-known, but the mechanisms causing DNA damage are poorly understood. The accepted molecular events involve initial oxidation and deprotonation at guanine sites, triggering hydrogen atom abstraction reactions from the sugar moieties, causing DNA strand breaks. Probing the chemistry of the initially formed radical cation has been challenging. Here, we generate, spectroscopically characterize, and examine the reactivity of the Watson-Crick nucleobase pair radical cation in the gas phase. We observe rich chemistry, including proton transfer between the bases and propagation of the radical site in deoxyguanosine from the base to the sugar, thus rupturing the sugar. This first example of a gas-phase model system providing molecular-level details on the chemistry of an ionized DNA base pair paves the way toward a more complete understanding of molecular processes induced by radiation. It also highlights the role of radical propagation in chemistry, biology, and nanotechnology.

Transformations of dissolved organic matter induced by UV photolysis, Hydroxyl radicals, chlorine radicals, and sulfate radicals in aqueous-phase UV-Based advanced oxidation processes.

Science.gov (United States)

Varanasi, Lathika; Coscarelli, Erica; Khaksari, Maryam; Mazzoleni, Lynn R; Minakata, Daisuke

2018-05-15

Considering the increasing identification of trace organic contaminants in natural aquatic environments, the removal of trace organic contaminants from water or wastewater discharge is an urgent task. Ultraviolet (UV) and UV-based advanced oxidation processes (AOPs), such as UV/hydrogen peroxide (UV/H 2 O 2 ), UV/free chlorine and UV/persulfate, are attractive and promising approaches for the removal of these contaminants due to the high reactivity of active radical species produced in these UV-AOPs with a wide variety of organic contaminants. However, the removal efficiency of trace contaminants is greatly affected by the presence of background dissolved organic matter (DOM). In this study, we use ultrahigh resolution mass spectrometry to evaluate the transformation of a standard Suwanee River fulvic acid DOM isolate in UV photolysis and UV-AOPs. The use of probe compounds allows for the determination of the steady-state concentrations of active radical species in each UV-AOP. The changes in the H/C and O/C elemental ratios, double bond equivalents, and the low-molecular-weight transformation product concentrations of organic acids reveal that different DOM transformation patterns are induced by each UV-AOP. By comparison with the known reactivities of each radical species with specific organic compounds, we mechanistically and systematically elucidate the molecular-level DOM transformation pathways induced by hydroxyl, chlorine, and sulfate radicals in UV-AOPs. We find that there is a distinct transformation in the aliphatic components of DOM due to HO• in UV/H 2 O 2 and UV/free chlorine. Cl• induced transformation of olefinic species is also observed in the UV/free chlorine system. Transformation of aromatic and olefinic moieties by SO 4 •- are the predominant pathways in the UV/persulfate system. Copyright © 2018 Elsevier Ltd. All rights reserved.

Electron beam treatment with radical scavengers/enhancers

International Nuclear Information System (INIS)

Gehringer, P.

1994-08-01

E-beam treatment of low level contaminated groundwater is best apt to demonstrate the role of scavengers and enhancers, respectively because groundwater already contains some scavengers as natural solutes. The action of ionizing radiation to water is known to result in the formation of ions, molecular and free radical species. For low level contaminations of groundwater (pollutant concentration aqu - and H are of interest for pollutant decomposition. The pollutants have to compete for the free radical species with the natural solutes. 10 figures are discussed. (author)

Radiation-induced polymerisation of 2,3-dihydrofuran: free-radical or cationic mechanism?

International Nuclear Information System (INIS)

Janovsky, Igor; Naumov, Sergej; Knolle, Wolfgang; Mehnert, Reiner

2005-01-01

Concentrated (10 mol%) solutions of 2,3-dihydrofuran in CFCl 2 CF 2 Cl matrix were irradiated at 77 K and several intermediates (dimer radical cation, dihydrofuryl radical, and polymer radicals) were observed by low-temperature EPR spectroscopy. The irradiated solutions yielded after melting a polymeric product, which was characterised by IR spectroscopy and gel permeation chromatography. The polydisperse polymer is assumed to be formed mainly by a cationic process initiated by a dimer carbocation. The free-radical mechanism via the dihydrofuryl radical leads to low molecular weight oligomers only. Quantum chemical calculations support the interpretation of the experimental results

Avoiding fractional electrons in subsystem DFT based ab-initio molecular dynamics yields accurate models for liquid water and solvated OH radical

International Nuclear Information System (INIS)

Genova, Alessandro; Pavanello, Michele; Ceresoli, Davide

2016-01-01

In this work we achieve three milestones: (1) we present a subsystem DFT method capable of running ab-initio molecular dynamics simulations accurately and efficiently. (2) In order to rid the simulations of inter-molecular self-interaction error, we exploit the ability of semilocal frozen density embedding formulation of subsystem DFT to represent the total electron density as a sum of localized subsystem electron densities that are constrained to integrate to a preset, constant number of electrons; the success of the method relies on the fact that employed semilocal nonadditive kinetic energy functionals effectively cancel out errors in semilocal exchange–correlation potentials that are linked to static correlation effects and self-interaction. (3) We demonstrate this concept by simulating liquid water and solvated OH • radical. While the bulk of our simulations have been performed on a periodic box containing 64 independent water molecules for 52 ps, we also simulated a box containing 256 water molecules for 22 ps. The results show that, provided one employs an accurate nonadditive kinetic energy functional, the dynamics of liquid water and OH • radical are in semiquantitative agreement with experimental results or higher-level electronic structure calculations. Our assessments are based upon comparisons of radial and angular distribution functions as well as the diffusion coefficient of the liquid.

Avoiding fractional electrons in subsystem DFT based ab-initio molecular dynamics yields accurate models for liquid water and solvated OH radical.

Science.gov (United States)

Genova, Alessandro; Ceresoli, Davide; Pavanello, Michele

2016-06-21

In this work we achieve three milestones: (1) we present a subsystem DFT method capable of running ab-initio molecular dynamics simulations accurately and efficiently. (2) In order to rid the simulations of inter-molecular self-interaction error, we exploit the ability of semilocal frozen density embedding formulation of subsystem DFT to represent the total electron density as a sum of localized subsystem electron densities that are constrained to integrate to a preset, constant number of electrons; the success of the method relies on the fact that employed semilocal nonadditive kinetic energy functionals effectively cancel out errors in semilocal exchange-correlation potentials that are linked to static correlation effects and self-interaction. (3) We demonstrate this concept by simulating liquid water and solvated OH(•) radical. While the bulk of our simulations have been performed on a periodic box containing 64 independent water molecules for 52 ps, we also simulated a box containing 256 water molecules for 22 ps. The results show that, provided one employs an accurate nonadditive kinetic energy functional, the dynamics of liquid water and OH(•) radical are in semiquantitative agreement with experimental results or higher-level electronic structure calculations. Our assessments are based upon comparisons of radial and angular distribution functions as well as the diffusion coefficient of the liquid.

Molecular models of zinc phthalocyanines: semi-empirical molecular orbital computations and physicochemical properties studied by molecular mechanics simulations

International Nuclear Information System (INIS)

Gantchev, Tsvetan G.; van Lier, Johan E.; Hunting, Darel J.

2005-01-01

To build 3D-molecular models of Zinc-phthalocyanines (ZnPc) and to study their diverse chemical and photosensitization properties, we performed quantum mechanical molecular orbital (MO) semi-empirical (AM1) computations of the ground, excited singlet and triplet states as well as free radical (ionic) species. RHF and UHF (open shell) geometry optimizations led to near-perfect symmetrical ZnPc. Predicted ionization potentials (IP), electron affinities (EA) and lowest electronic transitions of ZnPc are in good agreement with the published experimental and theoretical data. The computation-derived D 4h /D 2h -symmetry 3D-structures of ground and excited states and free radicals of ZnPc, together with the frontier orbital energies and Mulliken electron population analysis enabled us to build robust molecular models. These models were used to predict important chemical-reactivity entities such as global electronegativity (χ), hardness (η) and local softness based on Fukui-functions analysis. Examples of molecular mechanics (MM) applications of the 3D-molecular models are presented as approaches to evaluate solvation free energy (ΔG 0 ) solv and to estimate ground- and excited- state oxidation/reduction potentials as well as intermolecular interactions and stability of ground and excited state dimers (exciplexes) and radical ion-pairs

Applied quantum chemistry: Spectroscopic detection and characterization of the F2BS and Cl2BS free radicals in the gas phase

International Nuclear Information System (INIS)

Jin, Bing; Clouthier, Dennis J.; Sheridan, Phillip M.

2015-01-01

In this and previous work [D. J. Clouthier, J. Chem. Phys. 141, 244309 (2014)], the spectroscopic signatures of the X 2 BY (X = H, halogen, Y = O, S) free radicals have been predicted using high level ab initio theory. The theoretical results have been used to calculate the electronic absorption and single vibronic level (SVL) emission spectra of the radicals under typical jet-cooled conditions. Using these diagnostic predictions, the previously unknown F 2 BS and Cl 2 BS free radicals have been identified and characterized. The radicals were prepared in a free jet expansion by subjecting precursor mixtures of BF 3 or BCl 3 and CS 2 vapor to an electric discharge at the exit of a pulsed molecular beam valve. The B ~2 A 1 –X ~ 2 B 2 laser-induced fluorescence spectra were found within 150 cm −1 of their theoretically predicted positions with vibronic structure consistent with our Franck-Condon simulations. The B ~2 A 1 state emits down to the ground state and to the low-lying A ~2 B 1 excited state and the correspondence between the observed and theoretically derived SVL emission Franck-Condon profiles was used to positively identify the radicals and make assignments. Excited state Coriolis coupling effects complicate the emission spectra of both radicals. In addition, a forbidden component of the electronically allowed B ~ –X ~ band system of Cl 2 BS is evident, as signaled by the activity in the b 2 modes in the spectrum. Symmetry arguments indicate that this component gains intensity due to a vibronic interaction of the B ~2 A 1 state with a nearby electronic state of 2 B 2 symmetry

Radical fashion and radical fashion innovation

NARCIS (Netherlands)

Zhang, D.; Benedetto, Di A.C.

2010-01-01

This is a study of the related concepts of radical fashion and radical fashion innovation. Radical fashions are defined here as those that may never enter the market at all, and exist primarily on runway shows, in exhibitions and in publicity; by contrast, radical fashion innovations may be very

High resolution spectroscopy of jet cooled phenyl radical: The ν{sub 1} and ν{sub 2} a{sub 1} symmetry C–H stretching modes

Energy Technology Data Exchange (ETDEWEB)

Chang, Chih-Hsuan; Nesbitt, David J. [JILA, National Institute of Standards and Technology, University of Colorado, Boulder, Colorado 80309, USA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (United States)

2016-07-28

A series of CH stretch modes in phenyl radical (C{sub 6}H{sub 5}) has been investigated via high resolution infrared spectroscopy at sub-Doppler resolution (∼60 MHz) in a supersonic discharge slit jet expansion. Two fundamental vibrations of a{sub 1} symmetry, ν{sub 1} and ν{sub 2}, are observed and rotationally analyzed for the first time, corresponding to in-phase and out-of-phase symmetric CH stretch excitation at the ortho/meta/para and ortho/para C atoms with respect to the radical center. The ν{sub 1} and ν{sub 2} band origins are determined to be 3073.968 50(8) cm{sup −1} and 3062.264 80(7) cm{sup −1}, respectively, which both agree within 5 cm{sup −1} with theoretical anharmonic scaling predictions based on density functional B3LYP/6-311g++(3df,3dp) calculations. Integrated band strengths for each of the CH stretch bands are analyzed, with the relative intensities agreeing remarkably well with theoretical predictions. Frequency comparison with previous low resolution Ar-matrix spectroscopy [A. V. Friderichsen et al., J. Am. Chem. Soc. 123, 1977 (2001)] reveals a nearly uniform Δν ≈ + 10-12 cm{sup −1} blue shift between gas phase and Ar matrix values for ν{sub 1} and ν{sub 2}. This differs substantially from the much smaller red shift (Δν ≈ − 1 cm{sup −1}) reported for the ν{sub 19} mode, and suggests a simple physical model in terms of vibrational mode symmetry and crowding due to the matrix environment. Finally, the infrared phenyl spectra are well described by a simple asymmetric rigid rotor Hamiltonian and show no evidence for spectral congestion due to intramolecular vibrational coupling, which bodes well for high resolution studies of other ring radicals and polycyclic aromatic hydrocarbons. In summary, the combination of slit jet discharge methods with high resolution infrared lasers enables spectroscopic investigation of even highly reactive combustion and interstellar radical intermediates under gas phase, jet-cooled

The free radical process for the polymer surface treated by radio frequency plasma

International Nuclear Information System (INIS)

Ma Yuguang; Yang Meiling; Shen Jiacong; Zheng Yingguang

1992-01-01

The formation and translation of the free radicals on the polymer surface treated by plasmas were studied and observed by ESR measurement. The results show that C-C bond split was main reaction in the process of the polymer irradiated by plasma, by which a stable alkyl free radical was formed. When alkyl free radical contacted with air, they translate into peroxide radical instantaneously. The peroxide radical was not as stable as radical in vacuum, they can react each other to form some polar-groups on polymer surface. The interaction between the peroxide free radical and polymer chain was correlative not only to the structure of polymer but also to the molecular motion of the polymer chain. The nature of plasma treating polymer surface was that the peroxide radicals were led onto polymer surface

Insertion of molecular oxygen into a palladium(II) methyl bond: a radical chain mechanism involving palladium(III) intermediates.

Science.gov (United States)

Boisvert, Luc; Denney, Melanie C; Hanson, Susan Kloek; Goldberg, Karen I

2009-11-04

The reaction of (bipy)PdMe(2) (1) (bipy = 2,2'-bipyridine) with molecular oxygen results in the formation of the palladium(II) methylperoxide complex (bipy)PdMe(OOMe) (2). The identity of the product 2 has been confirmed by independent synthesis. Results of kinetic studies of this unprecedented oxygen insertion reaction into a palladium alkyl bond support the involvement of a radical chain mechanism. Reproducible rates, attained in the presence of the radical initiator 2,2'-azobis(2-methylpropionitrile) (AIBN), reveal that the reaction is overall first-order (one-half-order in both [1] and [AIBN], and zero-order in [O(2)]). The unusual rate law (half-order in [1]) implies that the reaction proceeds by a mechanism that differs significantly from those for organic autoxidations and for the recently reported examples of insertion of O(2) into Pd(II) hydride bonds. The mechanism for the autoxidation of 1 is more closely related to that found for the autoxidation of main group and early transition metal alkyl complexes. Notably, the chain propagation is proposed to proceed via a stepwise associative homolytic substitution at the Pd center of 1 with formation of a pentacoordinate Pd(III) intermediate.

ESR study on free radicals trapped in crosslinked polytetrafluoroethylene (PTFE)

International Nuclear Information System (INIS)

Oshima, Akihiro; Tabata, Yoneho; Seguchi, Tadao

1997-01-01

Free radicals in crosslinked PTFE which formed by 60 Co γ-rays irradiation at 77 K and at room temperature were studied by electron spin resonance (ESR) spectroscopy. The crosslinked PTFE specimens with different crosslinking density were prepared by electron beam irradiation in the molten state. The ESR spectra observed in the irradiated crosslinked PTFE are much different from those in non-crosslinked PTFE (virgin); a broad singlet component increases with increasing the crosslinking density, G-value of radicals is much higher in crosslinked PTFE than in non-crosslinked one. Free radicals related to the broad component are trapped in the non-crystalline region of crosslinked PTFE and rather stable at room temperature, whereas radicals trapped in amorphous non-crosslinked PTFE are unstable at room temperature. It is thought that most of free radicals trapped in the crosslinked PTFE are formed in the crosslinked amorphous region. The trapped radicals decays around 383 K (110 o C) due to the molecular motion of α-relaxation. (Author)

Preparation of molecularly imprinted nanoparticles with superparamagnetic susceptibility through atom transfer radical emulsion polymerization for the selective recognition of tetracycline from aqueous medium

International Nuclear Information System (INIS)

Dai, Jiangdong; Pan, Jianming; Xu, Longcheng; Li, Xiuxiu; Zhou, Zhiping; Zhang, Rongxian; Yan, Yongsheng

2012-01-01

Highlights: ► Atom transfer radical emulsion polymerization is a “living” and green technique. ► Nanoparticles can overcome mass transfer limitations and improve accessibility. ► Molecular imprinted nanoparticles with magnetic property for fast separation. ► The performance of imprinted nanoparticles was investigated in detail. ► Nanoparticles were used to selective recognize Tetracycline from water medium. - Abstract: In the work, we reported an effective method for the preparation of molecularly imprinted nanoparticles with superparamagnetic susceptibility through atom transfer radical emulsion polymerization (ATREP), and then as-prepared magnetic molecularly imprinted nanoparticles (MMINs) were evaluated as adsorbents for selective recognition of tetracycline (TC) molecules from aqueous medium. The resulting nanoparticles were characterized by FT-IR, TGA, VSM, SEM and TEM. The results demonstrated MMINs with a narrow diameter distribution were cross-linked with modified Fe 3 O 4 particles, composed of imprinted layer and exhibited good magnetic sensitivity, magnetic and thermal stability. Batch rebinding studies were carried out to determine the specific adsorption equilibrium, kinetics, and selective recognition. The estimated adsorption capacity of MMINs towards TC by the Langmuir isotherm model was 12.10 mg g −1 at 298 K, which was 6.33 times higher than that of magnetic non-molecularly imprinted nanoparticles (MNINs). The kinetic property of MMINs was well-described by the pseudo-second-order rate equation. The results of selective recognition experiments demonstrated outstanding affinity and selectivity towards TC over competitive antibiotics. The reusability of MMINs showed no obviously deterioration at least five repeated cycles in performance. In addition, the MMINs prepared were successfully applied to the extraction of TC from the spiked pork sample.

Molecular design of high performance fused heteroacene radical cations: A DFT study

International Nuclear Information System (INIS)

Kawabata, Hiroshi; Ohmori, Shigekazu; Matsushige, Kazumi; Tachikawa, Hiroto

2008-01-01

Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation of fused furan oligomer, denoted by F(n) where n means number of furan rings in the oligomer, to elucidate the electronic structures at ground and low-lying excited states. A polymer of fused furan was also investigated using one-dimensional periodic boundary condition (PBC) for comparison. It was found that the reorganization energy of radical cation of F(n) from vertical hole trapping point to its relaxed structure is significantly small. Also, the reorganization energy decreased gradually with increasing n, indicating that F(n) has an effective hole transport property. It was found that the cation radical of F(n) has a low energy band at near IR region, which is strongly correlated to hole conductivity. The relation between the electronic states and hole conductivity was discussed on the basis of theoretical calculations

ESR Study of the polyvinyl alcohol gamma-ray induced free-radicals

International Nuclear Information System (INIS)

Rosas S, E.

1994-01-01

This work reports the findings of the molecular weight effect on the electron spin resonance saturation curve of the gamma-ray irradiated polyvinyl alcohol, G-RIPVA. It has been noted that Pva of a lower molecular weight, between 13,000-23,000, show some noticeable differences in the electron spin resonance, ESR, response as a function of the gamma-ray dose in the 1-100 k Gy range than the one reported in the literature with molecular weight of 108,000. Results show a linear response in the log-log plot of the dose vs ESR signal intensity for samples based on G-RIPVA of the lower molecular weight as contrasted with the non-linear ESR response of G-RIPVA of higher molecular weight in the above named dose range. Such a result has been assumed to arise from the shorter molecular chains for the case of the lower molecular weight samples making this to increase the production of Pva free radicals with respect to the absorbed studied doses. Also, a discussion on the nature and stability of the Pva free radicals will be given. (Author)

Nitroxide radicals formed in situ as polymer chain growth regulators

International Nuclear Information System (INIS)

Kolyakina, Elena V; Grishin, Dmitry F

2009-01-01

Published data on controlled synthesis of macromolecules using nitroxide radicals, formed in situ during polymerization, as polymer chain growth regulators are systematized and generalized. The attention is focused on the mechanism of polymer chain growth control during reversibly inhibited radical homopolymerization and the effect of structure of precursors and regulating additives on the polymerization kinetics of monomers of different nature and the molecular-mass characteristics of the polymers thus formed. The key methods for generation of nitroxide radicals directly during polymerization are considered. The prospects for development and practical use of these approaches for the synthesis of new polymeric materials are evaluated.

Molecules cooled below the Doppler limit

Science.gov (United States)

Truppe, S.; Williams, H. J.; Hambach, M.; Caldwell, L.; Fitch, N. J.; Hinds, E. A.; Sauer, B. E.; Tarbutt, M. R.

2017-12-01

Magneto-optical trapping and sub-Doppler cooling have been essential to most experiments with quantum degenerate gases, optical lattices, atomic fountains and many other applications. A broad set of new applications await ultracold molecules, and the extension of laser cooling to molecules has begun. A magneto-optical trap (MOT) has been demonstrated for a single molecular species, SrF, but the sub-Doppler temperatures required for many applications have not yet been reached. Here we demonstrate a MOT of a second species, CaF, and we show how to cool these molecules to 50 μK, well below the Doppler limit, using a three-dimensional optical molasses. These ultracold molecules could be loaded into optical tweezers to trap arbitrary arrays for quantum simulation, launched into a molecular fountain for testing fundamental physics, and used to study collisions and chemistry between atoms and molecules at ultracold temperatures.

Free radicals, oxygen and radiosensitizing drugs: a very brief introduction

International Nuclear Information System (INIS)

Willson, R.

1981-01-01

A review is presented of the historical aspects of the search for radiation sensitizing drugs. Metronidazole, Flagyl and misonidazole are undergoing clincial trials as the result of basic free radical and cellular research. Studies at the molecular, biochemical and cellular levels are described. From the information obtained it now appears that several processes may be involved in sensitization: interference with charge recombination due to a sensitizer having a high electron affinity; an increase in the yield of oxidizing hydroxyl radicals by electron sequestration; interference with radical combination reactions due to a sensitizer having a high one electron oxidation potential; oxidation or organic radicals so fixing them; formation of products which are toxic; and changes in the biochemistry of the cell. 106 references, 4 figures

Resonance Raman and quantum chemical studies of short polyene radical cations

DEFF Research Database (Denmark)

Keszthelyi, T.; Wilbrandt, R.; Bally, T.

1997-01-01

,3,5-hexatriene have been studied. The radical cations were generated radiolytically in a glassy Freon matrix and investigated by optical absorption and resonance Raman spectroscopy. Ab initio and density functional molecular-orbital calculations have been carried out to predict equilibrium structures...... and to assist assignment of the resonance Raman spectra. A new and improved scaled quantum mechanical force field for the butadiene radical cation was also determined. The presence of more than one rotamer was observed in all the polyene radical cations we investigated. (C) 1997 Elsevier Science B.V....

1,2-Fluorine Radical Rearrangements: Isomerization Events in Perfluorinated Radicals.

Science.gov (United States)

Van Hoomissen, Daniel J; Vyas, Shubham

2017-11-16

Devising effective degradation technologies for perfluoroalkyl substances (PFASs) is an active area of research, where the molecular mechanisms involving both oxidative and reductive pathways are still elusive. One commonly neglected pathway in PFAS degradation is fluorine atom migration in perfluoroalkyl radicals, which was largely assumed to be implausible because of the high C-F bond strength. Using density functional theory calculations, it was demonstrated that 1,2-F atom migrations are thermodynamically favored when the fluorine atom migrated from a less branched carbon center to a more branched carbon center. Activation barriers for these rearrangements were within 19-29 kcal/mol, which are possible to easily overcome at elevated temperatures or in photochemically activated species in the gas or aqueous phase. It was also found that the activation barriers for the 1,2-F atom migration are lowered as much as by 10 kcal/mol when common oxidative degradation products such as HF assisted the rearrangements or if the resulting radical center was stabilized by vicinal π-bonds. Natural bond orbital analyses showed that fluorine moves as a radical in a noncharge-separated state. These findings add an important reaction to the existing knowledge of mechanisms for PFAS degradation and highlights the fact that 1,2-F atom shifts may be a small channel for isomerization of these compounds, but upon availability of mineralization products, this isomerization process could become more prominent.

Engineering radical polymer electrodes for electrochemical energy storage

Science.gov (United States)

Nevers, Douglas R.; Brushett, Fikile R.; Wheeler, Dean R.

2017-06-01

In principle a wide range of organic materials can store energy in the form of reversible redox conversions of stable radicals. Such chemistry holds great promise for energy storage applications due to high theoretical capacities, high rate capabilities, intrinsic structural tunability, and the possibility of low-cost "green" syntheses from renewable sources. There have been steady improvements in the design of organic radical polymers, in which radicals are incorporated into the backbone and/or as pendant groups. This review highlights opportunities for improved redox molecule and polymer design along with the key challenges (e.g., transport phenomena, solubility, and reaction mechanisms) to transitioning known organic radicals into high-performance electrodes. Ultimately, organic-based batteries are still a nascent field with many open questions. Further advances in molecular design, electrode engineering, and device architecture will be required for these systems to reach their full potential and meet the diverse and increasing demands for energy storage.

Free radicals in chemical carcinogenesis.

Science.gov (United States)

Clemens, M R

1991-12-15

During the past decade, remarkable progress has been made in our understanding of cancer-causing agents, mechanisms of cancer formation and the behavior of cancer cells. Cancer is characterized primarily by an increase in the number of abnormal cells derived from a given normal tissue, invasion of adjacent tissues by these abnormal cells, and lymphatic or blood-borne spread of malignant cells to regional lymph nodes and to distant sites (metastasis). It has been estimated that about 75-80% of all human cancers are environmentally induced, 30-40% of them by diet. Only a small minority, possibly no more than 2% of all cases, result purely from inherent genetic changes. Several lines of evidence confirm that the fundamental molecular event or events that cause a cell to become malignant occur at the level of the DNA and a variety of studies indicate that the critical molecular event in chemical carcinogenesis is the interaction of the chemical agent with DNA. The demonstration that DNA isolated from tumor cells can transfect normal cells and render them neoplastic provides direct proof that an alteration of the DNA is responsible for cancer. The transforming genes, or oncogenes, have been identified by restriction endonuclease mapping. One of the characteristics of tumor cells generated by transformation with viruses, chemicals, or radiation is their reduced requirement for serum growth factors. A critical significance of electrophilic metabolites of carcinogenes in chemical carcinogenesis has been demonstrated. A number of "proximate" and "ultimate" metabolites, especially those of aromatic amines, were described. The "ultimate" forms of carcinogens actually interact with cellular constituents to cause neoplastic transformation and are the final metabolic products in most pathways. Recent evidence indicates that free radical derivatives of chemical carcinogens may be produced both metabolically and nonenzymatically during their metabolism. Free radicals carry no

CONCERNING CHAIN GROWTH SPECIFIC REACTION RATE AS A PART OF THE PROCESS OF METHYL METHACRYLATE MASS RADICAL POLYMERIZATION

Directory of Open Access Journals (Sweden)

A. A. Sultanova

2017-02-01

Full Text Available It is the chain growth specific reaction rate that was determined for the process of methyl methacrylate mass radical polymerization within the temperature range of 40–900 С in quasi-steady approximation by means of Monte Carlo method. The theoretical model of radical polymerization was developed taking the gel effect into account. Computer software was developed that enables to imitate radical polymerization process taking gel effect into account within the minimum run time. The programme was tested on asymptotic examples as well as was applied for methyl methacrylate mass radical polymerization. The programme makes it possible to calculate monomer conversion, molecular mass variation, molecular-mass distribution, etc.

Radical S-adenosylmethionine (SAM) enzymes in cofactor biosynthesis: a treasure trove of complex organic radical rearrangement reactions.

Science.gov (United States)

Mehta, Angad P; Abdelwahed, Sameh H; Mahanta, Nilkamal; Fedoseyenko, Dmytro; Philmus, Benjamin; Cooper, Lisa E; Liu, Yiquan; Jhulki, Isita; Ealick, Steven E; Begley, Tadhg P

2015-02-13

In this minireview, we describe the radical S-adenosylmethionine enzymes involved in the biosynthesis of thiamin, menaquinone, molybdopterin, coenzyme F420, and heme. Our focus is on the remarkably complex organic rearrangements involved, many of which have no precedent in organic or biological chemistry. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Redundant Sb condensation on GaSb epilayers grown by molecular beam epitaxy during cooling procedure

International Nuclear Information System (INIS)

Arpapay, B.; Şahin, S.; Arıkan, B.; Serincan, U.

2014-01-01

The effect of four different cooling receipts on the surface morphologies of unintentionally-doped GaSb epilayers on GaSb (100) substrates grown by molecular beam epitaxy is reported. Those receipts include three different Sb beam equivalent pressure (BEP) levels and two different termination temperatures. Surface morphologies of epilayers were examined by wet etching, surface profiler, atomic force microscopy, scanning electron microscopy and Raman spectroscopy. The results demonstrate that during the cooling period, a Sb BEP of 4.00 × 10 −4 Pa at a termination temperature of 400 °C induces a smooth surface without Sb condensation whereas same Sb BEP at a termination temperature of 350 °C forms a 300 nm thick Sb layer on the surface. In addition, it is revealed that by applying a wet etching procedure and using a surface profiler it is possible to identify this condensed layer from the two-sloped feature of mesa profile. - Highlights: • Sb beam flux termination temperature is crucial for redundant Sb condensation. • Sb beam flux level has a role on the thickness of redundant condensed Sb layer. • Redundant Sb layer thickness can be measured by two-sloped mesa structure

Preparation of molecularly imprinted nanoparticles with superparamagnetic susceptibility through atom transfer radical emulsion polymerization for the selective recognition of tetracycline from aqueous medium

Energy Technology Data Exchange (ETDEWEB)

Dai, Jiangdong; Pan, Jianming; Xu, Longcheng; Li, Xiuxiu [School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); Zhou, Zhiping [School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Zhang, Rongxian [School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); Yan, Yongsheng, E-mail: djdxxx123@163.com [School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); State Key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing, 100191 (China)

2012-02-29

Highlights: Black-Right-Pointing-Pointer Atom transfer radical emulsion polymerization is a 'living' and green technique. Black-Right-Pointing-Pointer Nanoparticles can overcome mass transfer limitations and improve accessibility. Black-Right-Pointing-Pointer Molecular imprinted nanoparticles with magnetic property for fast separation. Black-Right-Pointing-Pointer The performance of imprinted nanoparticles was investigated in detail. Black-Right-Pointing-Pointer Nanoparticles were used to selective recognize Tetracycline from water medium. - Abstract: In the work, we reported an effective method for the preparation of molecularly imprinted nanoparticles with superparamagnetic susceptibility through atom transfer radical emulsion polymerization (ATREP), and then as-prepared magnetic molecularly imprinted nanoparticles (MMINs) were evaluated as adsorbents for selective recognition of tetracycline (TC) molecules from aqueous medium. The resulting nanoparticles were characterized by FT-IR, TGA, VSM, SEM and TEM. The results demonstrated MMINs with a narrow diameter distribution were cross-linked with modified Fe{sub 3}O{sub 4} particles, composed of imprinted layer and exhibited good magnetic sensitivity, magnetic and thermal stability. Batch rebinding studies were carried out to determine the specific adsorption equilibrium, kinetics, and selective recognition. The estimated adsorption capacity of MMINs towards TC by the Langmuir isotherm model was 12.10 mg g{sup -1} at 298 K, which was 6.33 times higher than that of magnetic non-molecularly imprinted nanoparticles (MNINs). The kinetic property of MMINs was well-described by the pseudo-second-order rate equation. The results of selective recognition experiments demonstrated outstanding affinity and selectivity towards TC over competitive antibiotics. The reusability of MMINs showed no obviously deterioration at least five repeated cycles in performance. In addition, the MMINs prepared were successfully

ESR investigation of the reactions of glutathione, cysteine and penicillamine thiyl radicals: competitive formation of RSOcenter dot, Rcenter dot, RSSRcenter dot-. , and RSScenter dot

Energy Technology Data Exchange (ETDEWEB)

Becker, David; Swarts, Steven; Champagne, Mark; Sevilla, M D

1988-05-01

The reactions of cysteine, glutathione and penicillamine thiyl radicals with oxygen and their parent thiols in frozen solutions have been elucidated with e.s.r. The major sulfur radicals observed are: (1) thiyl radicals, RS center dot; (2) disulfide radical anions, RSSR anion radicals; (3) perthiyl radicals, RSS center dot and upon introduction of oxygen; (4) sulfinyl radicals, RSO center dot, where R represents the remainder of the cysteine, glutathione or penicillamine moiety. The radical product observed depends on pH, concentration of thiol, and presence or absence of molecular oxygen. The sulfinyl radical is a ubiquitous intermediate, peroxyl radical attack on thiols may lead to sulfinyl radicals. The authors elaborate the observed reaction sequences that lead to sulfinyl radicals and, using /sup 17/O isotopic substitution studies, demonstrate the oxygen atom in sulfinyl radicals originates from dissolved molecular oxygen. The glutathione radical is found to abstract hydrogen from the ..cap alpha..-carbon position on the cysteine residue of glutathione to form a carbon-centred radical.

Development of linear free energy relationships for aqueous phase radical-involved chemical reactions.

Science.gov (United States)

Minakata, Daisuke; Mezyk, Stephen P; Jones, Jace W; Daws, Brittany R; Crittenden, John C

2014-12-02

Aqueous phase advanced oxidation processes (AOPs) produce hydroxyl radicals (HO•) which can completely oxidize electron rich organic compounds. The proper design and operation of AOPs require that we predict the formation and fate of the byproducts and their associated toxicity. Accordingly, there is a need to develop a first-principles kinetic model that can predict the dominant reaction pathways that potentially produce toxic byproducts. We have published some of our efforts on predicting the elementary reaction pathways and the HO• rate constants. Here we develop linear free energy relationships (LFERs) that predict the rate constants for aqueous phase radical reactions. The LFERs relate experimentally obtained kinetic rate constants to quantum mechanically calculated aqueous phase free energies of activation. The LFERs have been applied to 101 reactions, including (1) HO• addition to 15 aromatic compounds; (2) addition of molecular oxygen to 65 carbon-centered aliphatic and cyclohexadienyl radicals; (3) disproportionation of 10 peroxyl radicals, and (4) unimolecular decay of nine peroxyl radicals. The LFERs correlations predict the rate constants within a factor of 2 from the experimental values for HO• reactions and molecular oxygen addition, and a factor of 5 for peroxyl radical reactions. The LFERs and the elementary reaction pathways will enable us to predict the formation and initial fate of the byproducts in AOPs. Furthermore, our methodology can be applied to other environmental processes in which aqueous phase radical-involved reactions occur.

Enantioselective cyclizations and cyclization cascades of samarium ketyl radicals

Science.gov (United States)

Kern, Nicolas; Plesniak, Mateusz P.; McDouall, Joseph J. W.; Procter, David J.

2017-12-01

The rapid generation of molecular complexity from simple starting materials is a key challenge in synthesis. Enantioselective radical cyclization cascades have the potential to deliver complex, densely packed, polycyclic architectures, with control of three-dimensional shape, in one step. Unfortunately, carrying out reactions with radicals in an enantiocontrolled fashion remains challenging due to their high reactivity. This is particularly the case for reactions of radicals generated using the classical reagent, SmI2. Here, we demonstrate that enantioselective SmI2-mediated radical cyclizations and cascades that exploit a simple, recyclable chiral ligand can convert symmetrical ketoesters to complex carbocyclic products bearing multiple stereocentres with high enantio- and diastereocontrol. A computational study has been used to probe the origin of the enantioselectivity. Our studies suggest that many processes that rely on SmI2 can be rendered enantioselective by the design of suitable ligands.

Oxidation of benzene by radiolytically produced OH radicals. [x rays

Energy Technology Data Exchange (ETDEWEB)

Klein, G W; Schuler, R H [Carnegie-Mellon Univ., Pittsburgh, Pa. (USA)

1978-01-01

The radiolysis of N/sub 2/O saturated-aqueous solutions of benzene-/sup 14/C has been examined using radio-liquid chromatographic methods to follow the quantitative aspects of the reactions of hydroxycyclohexadienyl radicals. In the absence of a radical oxidant, at least five important products are produced. The total yield of 5.8 observed for the incorporation of benzene into products accounts for essentially all of the radicals initially produced from the water. Dimeric products predominate with a total yield of 4.1. Phenol is produced with a yield of only 0.8 indicating a disproportionation/combination ratio for hydroxycyclohexadienyl radicals of < = 0.4. In the presence of 2mM ferricyanide the hydroxycyclohexadienyl radicals are quantitatively oxidized to phenol with no trace (< 1%) remaining of dimeric or other high molecular weight products. The initial yield for phenol formation (6.0 molecules/100 eV) provides a measure for OH production in N/sub 2/O saturated aqueous solutions.

Structure reactivity relationship in the reaction of DNA guanyl radicals with hydroxybenzoates

Energy Technology Data Exchange (ETDEWEB)

Do, Trinh T.; Tang, Vicky J.; Aguilera, Joseph A. [Department of Radiology University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610 (United States); Milligan, Jamie R., E-mail: jmilligan@ucsd.ed [Department of Radiology University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610 (United States)

2010-11-15

In DNA, guanine bases are the sites from which electrons are most easily removed. As a result of hole migration to this stable location on guanine, guanyl radicals are major intermediates in DNA damage produced by the direct effect of ionizing radiation (ionization of the DNA itself and not through the intermediacy of water radicals). We have modeled this process by employing gamma irradiation in the presence of thiocyanate ions, a method which also produces single electron oxidized guanyl radicals in plasmid DNA in aqueous solution. The stable products formed in DNA from these radicals are detected as strand breaks after incubation with the FPG protein. When a phenolic compound is present in the solution during gamma irradiation, the formation of guanyl radical species is decreased by electron donation from the phenol to the guanyl radical. We have quantified the rate of this reaction for four different phenolic compounds bearing carboxylate substituents as proton acceptors. A comparison of the rates of these reactions with the redox strengths of the phenolic compounds reveals that salicylate reacts ca. 10-fold faster than its structural analogs. This observation is consistent with a reaction mechanism involving a proton coupled electron transfer, because intra-molecular transfer of a proton from the phenolic hydroxyl group to the carboxylate group is possible only in salicylate, and is favored by the strong 6-membered ring intra-molecular hydrogen bond in this compound.

Electronic states of aryl radical functionalized graphenes: Density functional theory study

Science.gov (United States)

Tachikawa, Hiroto; Kawabata, Hiroshi

2016-06-01

Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz) n (n = 1-4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR-(Bz) n (n = 1-4) showed that the aryl radical binds to the carbon atom of GR, and a C-C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol-1 at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol-1. The electronic states of GR-(Bz) n were examined on the basis of theoretical results.

Reactions of the radical cations of aliphatic aldehydes in freon matrices

International Nuclear Information System (INIS)

Belevskij, V.N.; Belopushkin, S.I.; Feldman, V.I.

1985-01-01

ESR spectra of γ-irradiated solutions of acetic and propionic aldehydes in freon-11 and freon-113 affected by aldehyde concentration, temperature, and the action of light were studied. It is shown that the radical cations are converted into neutral radicals, and the cations CHsub(3)CHsub(2)CHOsup(+). are converted to RCO and CHsub(3)CHCHO due to ion-molecular reactions of proton transfer of hydrogen atom transfer. (author)

A rational approach to the modulation of the dynamics of the magnetisation in a dysprosium-nitronyl-nitroxide radical complex.

Science.gov (United States)

Poneti, Giordano; Bernot, Kevin; Bogani, Lapo; Caneschi, Andrea; Sessoli, Roberta; Wernsdorfer, Wolfgang; Gatteschi, Dante

2007-05-14

A control of the dynamics of the magnetisation is chemically achieved in a ring-like Dy-radical based molecule, allowing the estimation of the quantum tunneling frequency with a (4)He-cooled susceptometer.

Sympathetic cooling and crystallization of ions in a linear Paul trap

International Nuclear Information System (INIS)

Drewsen, M.; Bowe, P.; Hornekaer, L.; Brodersen, C.; Schiffer, J.P.; Hangst, J.S.; Schiffer, J.P.

1999-01-01

Coulomb crystals, containing up to a few hundred ions of which more than 50% were cooled sympathetically by the Coulomb interaction with laser cooled Mg + ions, have been produced in a linear Paul trap. By controlling the balance of the radiation pressure from the two cooling lasers, the Coulomb crystals could be segregated according to ion species. Previous studies of ion crystals and molecular dynamics simulations suggest that the temperature may be around 10 mK or lower. The obtained results indicate that a wide range of atomic and molecular ions, which due to their internal structures are not amenable to direct laser cooling, can be effectively cooled and localized (crystallized) in linear Paul traps. For high resolution spectroscopy of such ions this may turn out to be very useful. copyright 1999 American Institute of Physics

Studies on the self-catalyzed Knoevenagel condensation, characterization, DPPH radical scavenging activity, cytotoxicity, and molecular properties of 5-arylidene-2,2-dimethyl-1,3-dioxane-4,6-diones using single crystal XRD and DFT techniques

Science.gov (United States)

Suresh Kumar, G. S.; Antony Muthu Prabhu, A.; Bhuvanesh, N.

2014-10-01

We have studied the self-catalyzed Knoevenagel condensation, spectral characterization, DPPH radical scavenging activity, cytotoxicity, and molecular properties of 5-arylidene-2,2-dimethyl-1,3-dioxane-4,6-diones using single crystal XRD and DFT techniques. In the absence of any catalyst, a series of novel 5-arylidene-2,2-dimethyl-1,3-dioxane-4,6-diones were synthesized using Meldrum’s acid and formylphenoxyaliphatic acid(s) in water. These molecules are arranged in the dimer form through intermolecular H-bonding in the single crystal XRD structure. Compounds have better DPPH radical scavenging activity and cytotoxicity against A431 cancer cell line. The optimized molecular structure, natural bond orbital analysis, electrostatic potential map, HOMO-LUMO energies, molecular properties, and atomic charges of these molecules have been studied by performing DFT/B3LYP/3-21G(*) level of theory in gas phase.

The Rise of Radicals in Bioinorganic Chemistry.

Science.gov (United States)

Gray, Harry B; Winkler, Jay R

2016-10-01

Prior to 1950, the consensus was that biological transformations occurred in two-electron steps, thereby avoiding the generation of free radicals. Dramatic advances in spectroscopy, biochemistry, and molecular biology have led to the realization that protein-based radicals participate in a vast array of vital biological mechanisms. Redox processes involving high-potential intermediates formed in reactions with O 2 are particularly susceptible to radical formation. Clusters of tyrosine (Tyr) and tryptophan (Trp) residues have been found in many O 2 -reactive enzymes, raising the possibility that they play an antioxidant protective role. In blue copper proteins with plastocyanin-like domains, Tyr/Trp clusters are uncommon in the low-potential single-domain electron-transfer proteins and in the two-domain copper nitrite reductases. The two-domain muticopper oxidases, however, exhibit clusters of Tyr and Trp residues near the trinuclear copper active site where O 2 is reduced. These clusters may play a protective role to ensure that reactive oxygen species are not liberated during O 2 reduction.

Understanding Molecular-Ion Neutral Atom Collisions for the Production of Ultracold Molecular Ions

Science.gov (United States)

2014-02-03

SECURITY CLASSIFICATION OF: This project was superseded and replaced by another ARO-funded project of the same name, which is still continuing. The goal...cooled atoms," IOTA -COST Workshop on molecular ions, Arosa, Switzerland. 5. E.R. Hudson, "Sympathetic cooling of molecules with laser cooled

Properties of aqueous systems relevant to the SCWR via molecular dynamics simulations

Energy Technology Data Exchange (ETDEWEB)

Kallikragas, D. [Trent Univ., Dept. of Chemistry, Peterborough, Ontario (Canada); Guzonas, D. [Canadian Nuclear Laboratories, Chalk River, Ontario (Canada); Svishchev, I., E-mail: isvishchev@trentu.ca [Trent Univ., Dept. of Chemistry, Peterborough, Ontario (Canada)

2015-06-15

Supercritical water (SCW) is the intended heat transfer fluid in the proposed GEN-IV supercritical water cooled reactor (SCWR). The oxidative environment poses challenges in choosing appropriate design materials and understanding the behaviour of SCW at the nanoscale within crevices of the passivation layer is needed for developing a control strategy to minimize corrosion. Molecular dynamics simulations have been employed to investigate molecular structure and diffusion of water and chloride in nanometer-spaced iron hydroxide surfaces. Results demonstrate that water is more likely to accumulate on the surface at low-density conditions. The effect of confinement on the water structure diminishes with as little as 20 Å of surface separation. Clustering and the accumulation of water at the surface imply that the SCWR will be most susceptible to pitting corrosion and stress corrosion cracking. A parameterized equation is provided that gives the diffusion coefficients of {sub O2}, H{sub 2}, and OH radical in high temperature and SCW. (author)

Modeling of the Reaction Mechanism of Enzymatic Radical C–C Coupling by Benzylsuccinate Synthase

Directory of Open Access Journals (Sweden)

Maciej Szaleniec

2016-04-01

Full Text Available Molecular modeling techniques and density functional theory calculations were performed to study the mechanism of enzymatic radical C–C coupling catalyzed by benzylsuccinate synthase (BSS. BSS has been identified as a glycyl radical enzyme that catalyzes the enantiospecific fumarate addition to toluene initiating its anaerobic metabolism in the denitrifying bacterium Thauera aromatica, and this reaction represents the general mechanism of toluene degradation in all known anaerobic degraders. In this work docking calculations, classical molecular dynamics (MD simulations, and DFT+D2 cluster modeling was employed to address the following questions: (i What mechanistic details of the BSS reaction yield the most probable molecular model? (ii What is the molecular basis of enantiospecificity of BSS? (iii Is the proposed mechanism consistent with experimental observations, such as an inversion of the stereochemistry of the benzylic protons, syn addition of toluene to fumarate, exclusive production of (R-benzylsuccinate as a product and a kinetic isotope effect (KIE ranging between 2 and 4? The quantum mechanics (QM modeling confirms that the previously proposed hypothetical mechanism is the most probable among several variants considered, although C–H activation and not C–C coupling turns out to be the rate limiting step. The enantiospecificity of the enzyme seems to be enforced by a thermodynamic preference for binding of fumarate in the pro(R orientation and reverse preference of benzyl radical attack on fumarate in pro(S pathway which results with prohibitively high energy barrier of the radical quenching. Finally, the proposed mechanism agrees with most of the experimental observations, although the calculated intrinsic KIE from the model (6.5 is still higher than the experimentally observed values (4.0 which suggests that both C–H activation and radical quenching may jointly be involved in the kinetic control of the reaction.

The properties and Roles of Resonance-Stabilized Radicals in Photochemical Pathways in Titan's Atmosphere

Science.gov (United States)

Sebree, Joshua A.; Kidwell, Nathan; Zwier, Timothy

2010-11-01

In recent years, the Cassini satellite has been providing details about the composition of Titan's atmosphere. Recent data has shown the existence of polycyclic aromatic hydrocarbons (PAHs) at higher altitudes than previously expected including masses tentatively ascribed to naphthalene and anthracene. The formation of indene (C9H9) and naphthalene (C10H8), the simplest PAHs, and their derivatives are of great interest as similar mechanisms may lead to the formation of larger fused-ring systems. In recent years it has been proposed that resonance-stabilized radicals (RSRs) may play an important role as intermediates along these pathways. RSRs gain extra stability by delocalizing the unpaired electron through a neighboring conjugated π-system. Because of this extra stability, RSRs are able to build up in concentration, allowing for the creation of larger, more complex systems through their recombination with other RSRs. Mass-selective UV-visible spectra of two RSRs, phenylallyl and benzylallenyl radicals, have been recorded under jet-cooled conditions. These two radicals, while sharing the same radical conjugation, have unique properties. The roles these radicals may play in the formation of fused ring systems will be discussed along with recent photochemical results on reaction pathways starting from benzylallene through the benzylallenyl radical.

A combined crossed molecular beam and theoretical investigation of the reaction of the meta-tolyl radical with vinylacetylene--toward the formation of methylnaphthalenes.

Science.gov (United States)

Yang, Tao; Muzangwa, Lloyd; Kaiser, Ralf I; Jamal, Adeel; Morokuma, Keiji

2015-09-07

Crossed molecular beam experiments and electronic structure calculations on the reaction of the meta-tolyl radical with vinylacetylene were conducted to probe the formation of methyl-substituted naphthalene isomers. We present the compelling evidence that under single collision conditions 1- and 2-methylnaphthalene can be formed without an entrance barrier via indirect scattering dynamics through a bimolecular collision of two non-PAH reactants: the meta-tolyl radical and vinylacetylene. The electronic structure calculations, conducted at the UCCSD(T)-F12b/cc-pVDZ//UM06-2x/cc-pVTZ + ZPE(UM06-2x/cc-pVTZ) level of theory, reveal that this reaction is initiated by the barrierless addition of the meta-tolyl radical to the terminal vinyl carbon (C1) of vinylacetylene, via a van-der-Waals complex implying that this mechanism can play a key role in forming methyl-substituted PAHs in low temperature extreme environments such as the low temperature interstellar medium and hydrocarbon-rich atmospheres of planets and their moons in the outer solar system. The reaction mechanism, proposed from the C11H11 potential energy surface, involves a sequence of isomerizations involving hydrogen transfer and ring closure, followed by hydrogen dissociation, which eventually leads to 1- and 2-methylnaphthalene in an overall exoergic process.

Polarized proton spin density images the tyrosyl radical locations in bovine liver catalase

Directory of Open Access Journals (Sweden)

Oliver Zimmer

2016-09-01

Full Text Available A tyrosyl radical, as part of the amino acid chain of bovine liver catalase, supports dynamic proton spin polarization (DNP. Finding the position of the tyrosyl radical within the macromolecule relies on the accumulation of proton polarization close to it, which is readily observed by polarized neutron scattering. The nuclear scattering amplitude due to the polarization of protons less than 10 Å distant from the tyrosyl radical is ten times larger than the amplitude of magnetic neutron scattering from an unpaired polarized electron of the same radical. The direction of DNP was inverted every 5 s, and the initial evolution of the intensity of polarized neutron scattering after each inversion was used to identify those tyrosines which have assumed a radical state. Three radical sites, all of them close to the molecular centre and the haem, appear to be equally possible. Among these is tyr-369, the radical state of which had previously been proven by electron paramagnetic resonance.

Time-resolved proton polarisation (TPP) images tyrosyl radical sites in bovine liver catalase.

Science.gov (United States)

Zimmer, Oliver; Jouve, Hélène M.; Stuhrmann, Heinrich B.

2017-05-01

A differentiation between dynamic polarised protons close to tyrosyl radical sites in catalase and those of the bulk is achieved by time-resolved polarised neutron scattering. Three radical sites, all of them being close to the molecular centre and the heme, appear to be equally possible. Among these is tyr-369 the radial site of which had previously been proven by EPR.

Imidazoline and imidazolidine nitroxides as controlling agents in nitroxide-mediated pseudoliving radical polymerization

Science.gov (United States)

Edeleva, M. V.; Marque, S. R. A.; Bagryanskaya, E. G.

2018-04-01

Controlled, or pseudoliving, radical polymerization provides unique opportunities for the synthesis of structurally diverse polymers with a narrow molecular-weight distribution. These reactions occur under relatively mild conditions with broad tolerance to functional groups in the monomers. The nitroxide-mediated pseudoliving radical polymerization is of particular interest for the synthesis of polymers for biomedical applications. This review briefly describes one of the mechanisms of controlled radical polymerization. The studies dealing with the use of imidazoline and imidazolidine nitroxides as controlling agents for nitroxide-mediated pseudoliving radical polymerization of various monomers are summarized and analyzed. The publications addressing the key steps of the controlled radical polymerization in the presence of imidazoline and imidazolidine nitroxides and new approaches to nitroxide-mediated polymerization based on protonation of both nitroxides and monomers are considered. The bibliography includes 154 references.

Relationship between protein molecular structural makeup and metabolizable protein supply to dairy cattle from new cool-season forage corn cultivars

Science.gov (United States)

Abeysekara, Saman; Khan, Nazir A.; Yu, Peiqiang

2018-02-01

Protein solubility, ruminal degradation and intestinal digestibility are strongly related to their inherent molecular makeup. This study was designed to quantitatively evaluate protein digestion in the rumen and intestine of dairy cattle, and estimate the content of truly metabolizable protein (MP) in newly developed cool-season forage corn cultivars. The second objective was to quantify protein inherent molecular structural characteristics using advance molecular spectroscopic technique (FT/IR-ATR) and correlate it to protein metabolic characteristics. Six new cool-season corn cultivars, including 3 Pioneer (PNR) and 3 Hyland (HL), coded as PNR-7443R, PNR-P7213R, PNR-7535R, HL-SR06, HL-SR22, HL-BAXXOS-RR, were evaluated in the present study. The metabolic characteristics, MP supply to dairy cattle, and energy synchronization properties were modeled by two protein evaluation models, namely, the Dutch DVE/OEB system and the NRC-2001 model. Both models estimated significant (P contents of microbial protein (MCP) synthesis and truly absorbable rumen undegraded protein (ARUP) among the cultivars. The NRC-2001 model estimated significant (P content and degraded protein balance (DPB) among the cultivars. The contents MCP, ARUP and MP were higher (P < 0.05) for cultivar HL-SR06, resulting in the lowest (P < 0.05) DPB. However, none of the cultivars reached the optimal target hourly effective degradability ratio [25 g N g/kg organic matter (OM)], demonstrating N deficiency in the rumen. There were non-significant differences among the cultivars in molecular-spectral intensities of protein. The amide I/II ratio had a significant correlation with ARUP (r = - 0.469; P < 0.001) and absorbable endogenous protein (AECPNRC) (P < 0.001; r = 0.612). Similarly, amide-II area had a weak but significant correlation (r = 0.299; P < 0.001) with RUP and ARUP, and with AECPNRC (P < 0.001; r = 0.411). Except total digestible nutrients and AECPNRC, the amide-I area did not show significant

The first radical-based spintronic memristors: Towards resistive RAMs made of organic magnets

Science.gov (United States)

Goss, Karin; Krist, Florian; Seyfferle, Simon; Hoefel, Udo; Paretzki, Alexa; Dressel, Martin; Bogani, Lapo; Institut Fuer Anorganische Chemie, University of Stuttgart Collaboration; 1. Physikalisches Institut, University of Stuttgart Team

2014-03-01

Using molecules as building blocks for electronic devices offers ample possibilities for new device functionalities due to a chemical tunability much higher than that of standard inorganic materials, and at the same time offers a decrease in the size of the electronic component down to the single-molecule level. Purely organic molecules containing no metallic centers such as organic radicals can serve as an electronic component with magnetic properties due to the unpaired electron in the radical state. Here we present memristive logic units based on organic radicals of the nitronyl-nitroxide kind. Integrating these purely molecular units as a spin coated layer into crossbar arrays, electrically induced unipolar resistive switching is observed with a change in resistance of up to 100%. We introduce a model based on filamentary reorganization of molecules of different oxidation state revealing the importance of the molecular nature for the switching properties. The major role of the oxidation state of these paramagnetic molecules introduces a magnetic field dependence to the device functionality, which goes along with magnetoresistive charactistics observed for the material. These are the first steps towards a spintronic implementation of organic radicals in electronic devices.

A graphene Zener-Klein transistor cooled by a hyperbolic substrate

Science.gov (United States)

Yang, Wei; Berthou, Simon; Lu, Xiaobo; Wilmart, Quentin; Denis, Anne; Rosticher, Michael; Taniguchi, Takashi; Watanabe, Kenji; Fève, Gwendal; Berroir, Jean-Marc; Zhang, Guangyu; Voisin, Christophe; Baudin, Emmanuel; Plaçais, Bernard

2018-01-01

The engineering of cooling mechanisms is a bottleneck in nanoelectronics. Thermal exchanges in diffusive graphene are mostly driven by defect-assisted acoustic phonon scattering, but the case of high-mobility graphene on hexagonal boron nitride (hBN) is radically different, with a prominent contribution of remote phonons from the substrate. Bilayer graphene on a hBN transistor with a local gate is driven in a regime where almost perfect current saturation is achieved by compensation of the decrease in the carrier density and Zener-Klein tunnelling (ZKT) at high bias. Using noise thermometry, we show that the ZKT triggers a new cooling pathway due to the emission of hyperbolic phonon polaritons in hBN by out-of-equilibrium electron-hole pairs beyond the super-Planckian regime. The combination of ZKT transport and hyperbolic phonon polariton cooling renders graphene on BN transistors a valuable nanotechnology for power devices and RF electronics.

Probing Intermolecular Electron Delocalization in Dimer Radical Anions by Vibrational Spectroscopy

International Nuclear Information System (INIS)

Mani, Tomoyasu; Brookhaven National Laboratory; Grills, David C.

2017-01-01

Delocalization of charges is one of the factors controlling charge transport in conjugated molecules. It is considered to play an important role in the performance of a wide range of molecular technologies, including organic solar cells and organic electronics. Dimerization reactions are well-suited as a model to investigate intermolecular spatial delocalization of charges. And while dimerization reactions of radical cations are well investigated, studies on radical anions are still scarce. Upon dimerization of radical anions with neutral counterparts, an electron is considered to delocalize over the two molecules. By using time-resolved infrared (TRIR) detection coupled with pulse radiolysis, we show that radical anions of 4-n-hexyl-4'-cyanobiphenyl (6CB) undergo such dimerization reactions, with an electron equally delocalized over the two molecules. We have recently demonstrated that nitrile ν(C≡N) vibrations respond to the degree of electron localization of nitrile-substituted anions: we can quantify the changes in the electronic charges from the neutral to the anion states in the nitriles by monitoring the ν(C≡N) IR shifts. In the first part of this article, we show that the sensitivity of the ν(C≡N) IR shifts does not depend on solvent polarity. In the second part, we describe how probing the shifts of the nitrile IR vibrational band unambiguously confirms the formation of dimer radical anions, with K dim = 3 × 10 4 M –1 . IR findings are corroborated by electronic absorption spectroscopy and electronic structure calculations. We find that the presence of a hexyl chain and the formation of π–π interactions are both crucial for dimerization of radical anions of 6CB with neutral 6CB. Our study provides clear evidence of spatial delocalization of electrons over two molecular fragments.

Kinetics of molecular transformations in connective tissue hyaluronic acid

International Nuclear Information System (INIS)

Phillips, G.O.

1990-01-01

When exposed to ionizing radiations or inflammatory disease, the glycosaminolycan component of connective tissue is preferentially degraded, probably by a free-radical mediate pathway. The resulting changes in molecular structure adversely change the properties of the matrix. Rooster comb hyaluronic acid of high molecular weight was used to investigate the mechanisms of these structural changes at macro and molecular level. Intrinsic viscosity and gel permeation chromatography measurements are suitable for demonstrating that random chain session occurs. Fast kinetic techniques are necessary to identify the mechanisms of single strand breaks. Pulse conductivity and low-angle laser light scattering pulse radiolysis can quantify the rate and yield of strand breaks. Competitive radical scavenging methods have also allowed the quantification of the rate of spontaneous and alkali-catalyzed hydrolysis of a-hydroxy radicals on polysaccharide chains, which control molecular structure changes

Ultraviolet photodissociation dynamics of the benzyl radical.

Science.gov (United States)

Song, Yu; Zheng, Xianfeng; Lucas, Michael; Zhang, Jingsong

2011-05-14

Ultraviolet (UV) photodissociation dynamics of jet-cooled benzyl radical via the 4(2)B(2) electronically excited state is studied in the photolysis wavelength region of 228 to 270 nm using high-n Rydberg atom time-of-flight (HRTOF) and resonance enhanced multiphoton ionization (REMPI) techniques. In this wavelength region, H-atom photofragment yield (PFY) spectra are obtained using ethylbenzene and benzyl chloride as the precursors of benzyl radical, and they have a broad peak centered around 254 nm and are in a good agreement with the previous UV absorption spectra of benzyl. The H + C(7)H(6) product translational energy distributions, P(E(T))s, are derived from the H-atom TOF spectra. The P(E(T)) distributions peak near 5.5 kcal mol(-1), and the fraction of average translational energy in the total excess energy, , is ∼0.3. The P(E(T))s indicate the production of fulvenallene + H, which was suggested by recent theoretical studies. The H-atom product angular distribution is isotropic, with the anisotropy parameter β ≈ 0. The H/D product ratios from isotope labeling studies using C(6)H(5)CD(2) and C(6)D(5)CH(2) are reasonably close to the statistical H/D ratios, suggesting that the H/D atoms are scrambled in the photodissociation of benzyl. The dissociation mechanism is consistent with internal conversion of the electronically excited benzyl followed by unimolecular decomposition of the hot benzyl radical on the ground state.

Radical inactivation of a biological sulphydryl molecule

International Nuclear Information System (INIS)

Lin, W.S.; Lal, M.; Gaucher, G.M.; Armstrong, D.A.

1977-01-01

Reactive species produced from the free radical-induced chain oxidation of low molecular weight sulphydryl-containing molecules in aerated solutions deactivate the sulphydryl-containing enzyme papain, forming both reparable mixed disulphides and non-reparable products. This inactivation is highly efficient for penicillamine and glutathione, but almost negligible with cysteine, which is a protector of papain for [cysteine] / [papain] >= 5 under all conditions used. In the case of glutathione, superoxide dismutase caused only a small reduction in the inactivation and peroxide yields were small, implying that the deactivating species are not .O 2 - but RSOO. radicals or products from them. For penicillamine, however, dimutase was highly effective and the peroxide yields were relatively large, demonstrating that .O 2 - or a radical with similar capabilities for forming H 2 O 2 and being deactivated by dismutase was involved. Although in the presence of dismutase penicillamine is a better protector of non-reparable papain inactivation than glutathione, it suffers from a deficiency in that the papain-penicillamine mixed disulphide, which is always formed, cannot be repaired by spontaneous reaction with RSH molecules. (author)

Inclusion of molecular biotherapies with radical radiotherapy: modeling of combined modality treatment schedules

International Nuclear Information System (INIS)

Jones, Bleddyn; Dale, Roger G.

1999-01-01

Purpose: The use of molecular biology based therapies concurrently with radical radiotherapy is likely to offer potential benefits, but there is relatively little use of classical radiobiology in the rationale for such applications. The biological mechanisms that govern the outcomes of radiotherapy need to be completely understood before rational application and optimization of such adjuvant biotherapies with radiotherapy. Methods and Materials: Existing biomathematical models of radiotherapy can be used to explore the possible impact of biotherapies that modify tumor proliferation rates and/or radiosensitivity parameters during radiotherapy. Equations that show how to incorporate biotherapies with the linear-quadratic model of radiation cell kill are presented. Also considered are changes in tumor physiology, such as improved blood flow with enhanced delivery of biotherapy to the tumor cells and accelerated clonogen repopulation during radiotherapy. Monte Carlo random sampling methods are used to simulate these effects in heterogenous tumor populations with variation in radiosensitivities, clonogen numbers, and doubling times, as well as variations in repopulation onset rates and in vascular perfusion rates with time. Results: The time onset and duration of exposure of each type of biotherapy during radical radiotherapy can influence the predicted tumor cure probabilities in subtle ways. In general, the efficacy of biotherapies that radiosensitize will depend upon the number of radiotherapy fractions that are sensitized and the change in blood flow with time during radiotherapy. Biotherapies that control repopulation will depend not only on the duration of exposure but also, where accelerated repopulation occurs, on the time at which biotherapy is initiated during radiotherapy. From the ranges of radiobiological parameters and biotherapy efficacies assumed for exploratory examples, large changes of tumor control probability (TCP) are encountered in individual

Formation and determination of perinaphthenyl radical and PCAH in combustion processes

Energy Technology Data Exchange (ETDEWEB)

Franceschi, A [Univ., Pisa, Italy; Gerbaz, G P; Mangolini, S

1976-09-01

The concentration profiles of polycyclic aromatic hydrocarbons (PCAH) and perinaphthenyl radical along a vertical flow reactor have been determined for fuel rich premixed flames of n-heptane with small fractions of other hydrocarbons, methanol, and nitrogen oxide. It has been found that there is a strict relation between the concentrations of the higher molecular weight PCAH, which are the main components of soluble fraction of soot, and the perinaphthenyl radical. The aromatic ring of the fuel supplying the reactor plays the most significant role in the formation of PCAH and perinaphthenyl radical. Furthermore their concentrations increase passing from benzene toluene and, lastly, to mesitylene, because the energy of the C(arom)--C(alif) bond is lower than that of the C(arom)--C(arom) bond. The promoting action of methanol, when added to benzene, in the formation of PCAH and perinaphthenyl radical could be explained by the increased presence of CH/sub 3/ . radicals, which, can overcome the inhibiting action of OH. radicals. The contrary happens when methanol is added to toluene, because CH/sub 3/. coming from alcohol represents only a small fraction of the overall concentration, while the oxidant activity of OH. is prevailing. Finally the strong action of NO in reducing the free radical concentration has been pointed out.

Comparing Positively and Negatively Charged Distonic Radical Ions in Phenylperoxyl Forming Reactions.

Science.gov (United States)

Williams, Peggy E; Marshall, David L; Poad, Berwyck L J; Narreddula, Venkateswara R; Kirk, Benjamin B; Trevitt, Adam J; Blanksby, Stephen J

2018-06-04

In the gas phase, arylperoxyl forming reactions play a significant role in low-temperature combustion and atmospheric processing of volatile organic compounds. We have previously demonstrated the application of charge-tagged phenyl radicals to explore the outcomes of these reactions using ion trap mass spectrometry. Here, we present a side-by-side comparison of rates and product distributions from the reaction of positively and negatively charge tagged phenyl radicals with dioxygen. The negatively charged distonic radical ions are found to react with significantly greater efficiency than their positively charged analogues. The product distributions of the anion reactions favor products of phenylperoxyl radical decomposition (e.g., phenoxyl radicals and cyclopentadienone), while the comparable fixed-charge cations yield the stabilized phenylperoxyl radical. Electronic structure calculations rationalize these differences as arising from the influence of the charged moiety on the energetics of rate-determining transition states and reaction intermediates within the phenylperoxyl reaction manifold and predict that this influence could extend to intra-molecular charge-radical separations of up to 14.5 Å. Experimental observations of reactions of the novel 4-(1-carboxylatoadamantyl)phenyl radical anion confirm that the influence of the charge on both rate and product distribution can be modulated by increasing the rigidly imposed separation between charge and radical sites. These findings provide a generalizable framework for predicting the influence of charged groups on polarizable radicals in gas phase distonic radical ions. Graphical Abstract.

Periodic thermodynamics of laser-driven molecular motor

International Nuclear Information System (INIS)

Li Dan; Zheng Wenwei; Wang Zhisong

2008-01-01

Operation of a laser-driven nano-motor inevitably generates a non-trivial amount of heat, which can possibly lead to instability or even hinder the motor's continual running. This work quantitatively examines the overheating problem for a recently proposed laser-operated molecular locomotive. We present a single-molecule cooling theory, in which molecular details of the locomotive system are explicitly treated. This theory is able to quantitatively predict cooling efficiency for various candidates of molecular systems for the locomotive, and also suggests concrete strategies for improving the locomotive's cooling. It is found that water environment is able to cool the hot locomotive down to room temperature within 100 picoseconds after photon absorption. This cooling time is a few orders of magnitude shorter than the typical time for laser operation, effectively preventing any overheating for the nano-locomotive. However, when the cooling is less effective in non-aqueous environment, residual heat may build up. A continuous running of the motor will then lead to a periodic thermodynamics, which is a common character of many laser-operated nano-devices

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

Energy Technology Data Exchange (ETDEWEB)

Tilocca, Antonio [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)

2013-09-21

A set of molecular dynamics simulations were performed to investigate the effect of cooling rate and system size on the medium-range structure of melt-derived multicomponent silicate glasses, represented by the quaternary 45S5 Bioglass composition. Given the significant impact of the glass degradation on applications of these materials in biomedicine and nuclear waste disposal, bulk structural features which directly affect the glass dissolution process are of particular interest. Connectivity of the silicate matrix, ion clustering and nanosegregation, distribution of ring and chain structural patterns represent critical features in this context, which can be directly extracted from the models. A key issue is represented by the effect of the computational approach on the corresponding glass models, especially in light of recent indications questioning the suitability of conventional MD approaches (that is, involving melt-and-quench of systems containing ∼10{sup 3} atoms at cooling rates of 5-10 K/ps) when applied to model these glasses. The analysis presented here compares MD models obtained with conventional and nonconventional cooling rates and system sizes, highlighting the trend and range of convergence of specific structural features in the medium range. The present results show that time-consuming computational approaches involving much lower cooling rates and/or significantly larger system sizes are in most cases not necessary in order to obtain a reliable description of the medium-range structure of multicomponent glasses. We identify the convergence range for specific properties and use them to discuss models of several glass compositions for which a possible influence of cooling-rate or size effects had been previously hypothesized. The trends highlighted here represent an important reference to obtain reliable models of multicomponent glasses and extract converged medium-range structural features which affect the glass degradation and thus their

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

International Nuclear Information System (INIS)

Tilocca, Antonio

2013-01-01

A set of molecular dynamics simulations were performed to investigate the effect of cooling rate and system size on the medium-range structure of melt-derived multicomponent silicate glasses, represented by the quaternary 45S5 Bioglass composition. Given the significant impact of the glass degradation on applications of these materials in biomedicine and nuclear waste disposal, bulk structural features which directly affect the glass dissolution process are of particular interest. Connectivity of the silicate matrix, ion clustering and nanosegregation, distribution of ring and chain structural patterns represent critical features in this context, which can be directly extracted from the models. A key issue is represented by the effect of the computational approach on the corresponding glass models, especially in light of recent indications questioning the suitability of conventional MD approaches (that is, involving melt-and-quench of systems containing ∼10 3 atoms at cooling rates of 5-10 K/ps) when applied to model these glasses. The analysis presented here compares MD models obtained with conventional and nonconventional cooling rates and system sizes, highlighting the trend and range of convergence of specific structural features in the medium range. The present results show that time-consuming computational approaches involving much lower cooling rates and/or significantly larger system sizes are in most cases not necessary in order to obtain a reliable description of the medium-range structure of multicomponent glasses. We identify the convergence range for specific properties and use them to discuss models of several glass compositions for which a possible influence of cooling-rate or size effects had been previously hypothesized. The trends highlighted here represent an important reference to obtain reliable models of multicomponent glasses and extract converged medium-range structural features which affect the glass degradation and thus their application

Microwave and millimeter wave astrochemistry: Laboratory studies of transition metal-containing free radicals and spectroscopic observations of molecular interstellar environments

Science.gov (United States)

Adande, Gilles Rapotchombo

Progress in our understanding of the chemical composition of the interstellar medium leans both on laboratory analyses of high resolution rotational spectra from molecules that may be present in these regions, and on radio astronomical observations of molecular tracers to constrain astrochemical models. Due to the thermodynamic conditions in outer space, some molecules likely to be found in interstellar regions in relevant abundances are open shell radicals. In a series of laboratory studies, the pure rotational spectra of the transition metal containing radicals sulfur species ScS, YS, VS and ZnSH were obtained for the first time. In addition to accurate and precise rest frequencies for these species, bonding characteristics were determined from fine and hyperfine molecular parameters. It was found that these sulfides have a higher degree of covalent bonding than their mostly ionic oxide counterparts. Isomers and isotope ratios are excellent diagnostic tools for a variety of astrochemical models. From radio observations of isotopes of nitrile species, the galactic gradient of 14N/15N was accurately established. A further study of this ratio in carbon rich asymptotic giant branch stars provided observational evidence for an unknown process in J type carbon stars, and highlighted the need to update stellar nucleosynthesis models. Proper radiative transfer modeling of the emission spectra of interstellar molecules can yield a wealth of information about the abundance and distribution of these species within the observed sources. To model the asymmetric emission of SO and SO2 in oxygen-rich supergiants, an in-house code was developed, and successfully applied to gain insight into circumstellar sulfur chemistry of VY Canis Majoris. It was concluded that current astrochemistry kinetic models, based on spherical symmetry assumptions, need to be revisited.

Laser spectroscopy of hydrocarbon radicals

Energy Technology Data Exchange (ETDEWEB)

Chen, P. [Harvard Univ., Cambridge, MA (United States)

1993-12-01

The author reports the application of supersonic jet flash pyrolysis to the specific preparation of a range of organic radicals, biradicals, and carbenes in a skimmed molecular beam. Each species was produced cleanly and specifically, with little or no secondary reactions by the thermal dissociation of appropriately designed and synthesized organic precursors. Photoelectron spectra of the three isomeric C{sub 3}H{sub 2} carbenes, ortho-benzyne, and the {alpha},3-dehydrotoluene biradical, were used to establish adiabatic ionization potentials for use in thermochemical determinations.

Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations.

Science.gov (United States)

Deng, Lu; Du, Jincheng

2018-01-14

Borosilicate glasses form an important glass forming system in both glass science and technologies. The structure and property changes of borosilicate glasses as a function of thermal history in terms of cooling rate during glass formation and simulation system sizes used in classical molecular dynamics (MD) simulation were investigated with recently developed composition dependent partial charge potentials. Short and medium range structural features such as boron coordination, Si and B Q n distributions, and ring size distributions were analyzed to elucidate the effects of cooling rate and simulation system size on these structure features and selected glass properties such as glass transition temperature, vibration density of states, and mechanical properties. Neutron structure factors, neutron broadened pair distribution functions, and vibrational density of states were calculated and compared with results from experiments as well as ab initio calculations to validate the structure models. The results clearly indicate that both cooling rate and system size play an important role on the structures of these glasses, mainly by affecting the 3 B and 4 B distributions and consequently properties of the glasses. It was also found that different structure features and properties converge at different sizes or cooling rates; thus convergence tests are needed in simulations of the borosilicate glasses depending on the targeted properties. The results also shed light on the complex thermal history dependence on structure and properties in borosilicate glasses and the protocols in MD simulations of these and other glass materials.

Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations

Science.gov (United States)

Deng, Lu; Du, Jincheng

2018-01-01

Borosilicate glasses form an important glass forming system in both glass science and technologies. The structure and property changes of borosilicate glasses as a function of thermal history in terms of cooling rate during glass formation and simulation system sizes used in classical molecular dynamics (MD) simulation were investigated with recently developed composition dependent partial charge potentials. Short and medium range structural features such as boron coordination, Si and B Qn distributions, and ring size distributions were analyzed to elucidate the effects of cooling rate and simulation system size on these structure features and selected glass properties such as glass transition temperature, vibration density of states, and mechanical properties. Neutron structure factors, neutron broadened pair distribution functions, and vibrational density of states were calculated and compared with results from experiments as well as ab initio calculations to validate the structure models. The results clearly indicate that both cooling rate and system size play an important role on the structures of these glasses, mainly by affecting the 3B and 4B distributions and consequently properties of the glasses. It was also found that different structure features and properties converge at different sizes or cooling rates; thus convergence tests are needed in simulations of the borosilicate glasses depending on the targeted properties. The results also shed light on the complex thermal history dependence on structure and properties in borosilicate glasses and the protocols in MD simulations of these and other glass materials.

Quantitative investigation of free radicals in bio-oil and their potential role in condensed-phase polymerization.

Science.gov (United States)

Kim, Kwang Ho; Bai, Xianglan; Cady, Sarah; Gable, Preston; Brown, Robert C

2015-03-01

We report on the quantitative analysis of free radicals in bio-oils produced from pyrolysis of cellulose, organosolv lignin, and corn stover by EPR spectroscopy. Also, we investigated their potential role in condensed-phase polymerization. Bio-oils produced from lignin and cellulose show clear evidence of homolytic cleavage reactions during pyrolysis that produce free radicals. The concentration of free radicals in lignin bio-oil was 7.5×10(20)  spin g(-1), which was 375 and 138 times higher than free-radical concentrations in bio-oil from cellulose and corn stover. Pyrolytic lignin had the highest concentration in free radicals, which could be a combination of carbon-centered (benzyl radicals) and oxygen-centered (phenoxy radicals) organic species because they are delocalized in a π system. Free-radical concentrations did not change during accelerated aging tests despite increases in molecular weight of bio-oils, suggesting that free radicals in condensed bio-oils are stable. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Computational studies of free radical-scavenging properties of phenolic compounds.

Science.gov (United States)

Alov, Petko; Tsakovska, Ivanka; Pajeva, Ilza

2015-01-01

For more than half a century free radical-induced alterations at cellular and organ levels have been investigated as a probable underlying mechanism of a number of adverse health conditions. Consequently, significant research efforts have been spent for discovering more effective and potent antioxidants / free radical scavengers for treatment of these adverse conditions. Being by far the most used antioxidants among natural and synthetic compounds, mono- and polyphenols have been the focus of both experimental and computational research on mechanisms of free radical scavenging. Quantum chemical studies have provided a significant amount of data on mechanisms of reactions between phenolic compounds and free radicals outlining a number of properties with a key role for the radical scavenging activity and capacity of phenolics. The obtained quantum chemical parameters together with other molecular descriptors have been used in quantitative structure-activity relationship (QSAR) analyses for the design of new more effective phenolic antioxidants and for identification of the most useful natural antioxidant phenolics. This review aims at presenting the state of the art in quantum chemical and QSAR studies of phenolic antioxidants and at analysing the trends observed in the field in the last decade.

Micrococcus radiodurans surface exonuclease. Dimer to monomer conversion by ionizing radiation-generated aqueous free radicals

Energy Technology Data Exchange (ETDEWEB)

Mitchel, R E.J.

1980-01-01

Micrococcus radiodurans possesses an exonuclease firmly bound to a middle cell wall membrane layer. Aqueous OH/sup -/ radicals generated chemically or by ionizing radiation cause the immediate release of this enzyme into the surrounding medium. The enzyme is located in a hydrophobic site and can also be released by aqueous n-butanol. When extracted by this solvent it is a non-covalently linked dimer and has a molecular weight of 260,000 as determined by gel filtration. When released by radiation generated OH/sup -/ radicals, the enzyme initially appears in solution as the dimer but is rapidly split by further aqueous radical attack into two 130,000 molecular weight subunits. Hydroxyl radicals are most effective but reducing radicals are also able to monomerize the enzyme. Only the released dimer enzyme is subject to free radical monomerization. Bound dimer enzyme is not split prior to release. No detectable loss of activity or change in catalytic properties accompanies the free radical cleavage of the enzyme. Both subunits of the dimer enzyme possess a tightly bound metal ion (probably Ca/sup 2 +/) required for activity. The monomer but not the dimer enzyme will bind to an anion exchanger. The monomer is susceptible to loss of its metal ion, and consequent inactivation, when exposed to the exchanger in the absence of Ca/sup 2 +/. Besides providing information on some of the immediate non-lethal effects of ionizing radiation, the behavior of this enzyme system demonstrates a potential cellular mechanism by which internally or externally generated free radicals could be utilized by the cell to control various enzymic reactions.

Single-molecule electronics: Cooling individual vibrational modes by the tunneling current.

Science.gov (United States)

Lykkebo, Jacob; Romano, Giuseppe; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C

2016-03-21

Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, which typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular "heat sink" where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the "cooling mode," given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions.

Effect of solid phase on the selectivity of alkyl radical formation by gamma-irradiation of branched alkanes

International Nuclear Information System (INIS)

Koizumi, Hitoshi; Hashino, Masatoshi; Ichikawa, Tsuneki; Yoshida, Hiroshi

1992-01-01

ESR and electron spin echo measurements of alkyl radicals generated by γ-irradiation of glassy and crystalline branched alkanes C 10 ∼ C 13 have been carried out to elucidate the effect of molecular structure and solid phase on the selectivity of alkyl radical formation. Alkyl radicals generated and stabilized at 77 K in the glassy alkanes are secondary penultimate radicals. Tertiary radicals and secondary radicals other than the penultimate one are not generated either by hydrogen abstraction or from ionized or excited molecules. In the crystalline alkanes, however, a small amount of secondary internal radicals are generated in addition to the predominant formation of the secondary penultimate radicals. It is concluded that the detachment of C-H hydrogen preferentially takes place at the location where the motion of carbon atoms assisting the detachment of the C-H hydrogen easily occurs. (author)

Mechanism and kinetics in reactions of caffeic acid with radicals by pulse radiolysis and calculation

International Nuclear Information System (INIS)

Li, Xifeng; Cai, Zhongli; Katsumura, Yosuke

2000-01-01

The interaction of caffeic acid with e aq - , (CH 3 ) 2 (OH) CCH 2 · , CO 2 ·- , H · , ·OH and N 3 · radicals were studied by γ-, pulse radiolysis and molecular orbital calculation. UV-visible spectra of electron/·OH adducts, semi-quinone radicals of caffeic ions, and the stable products from the reactions were derived. The rate constants were determined. The attacked sites and the most favorable structures of the transient radicals were predicted. Reaction mechanisms were proposed. (author)

Hydroxyl-radical-induced oxidation of cyclic dipeptides: Reactions of free peptide radicals and their peroxyl radicals

International Nuclear Information System (INIS)

Mieden, O.J.

1989-01-01

In the course of this study investigations were carried out into the reactions of hydroxyl radicals and hydrogen atoms with cyclic dipeptides as well as the subsequent reactions of peptide radicals and their peroxyl radicals in aqueous solution. The radiolysis products formed in the absence and presence of oxygen or transient metal complexes were characterized and determined on a quantitative basis. The linking of information from product analyses to the kinetic data for transient species obtained by time-resolving UV/VIS and conductivity measurements (pulse radiolysis) as well as computer-assisted simulations of individual events during the reaction permitted an evaluation of the mechanisms underlying the various processes and an identification of interim products with short life-times, which did or did not belong to the group of radicals. Through the characterization of key reactions of radicals and peroxyl radicals of this substance class a major advance has been made towards a better understanding of the role of radicals in the peptide compound and the mechanisms involved in indirect radiation effects on long-chain peptides and proteins. (orig.) [de

A radical approach to radical innovation

NARCIS (Netherlands)

D. Deichmann (Dirk); J.C.M. van den Ende (Jan)

2014-01-01

textabstractInnovation pays. Amazon, Apple, Facebook, Google – nearly every one of today’s most successful companies has a talent for developing radical new ideas. But how best to encourage radical initiative taking from employees, and does their previous success or failure at it play a role?

Radicalization In Pakistan And The Spread Of Radical Islam In Pakistan

Directory of Open Access Journals (Sweden)

Bahir ahmad

2015-08-01

Full Text Available ABSTRACT It is pertinent to mention that radicalism is not intrinsic to Islam and radical interpretations of the religion or for that matter may occur within any way of life and religion Saikal 2003 and yet the question remains as to why Muslims in certain geographical regions have more radical approaches towards their religion and also that what are the causes of such radicalization. Becoming a radical Muslim is not even a matter of a day nor is it a sudden process. There are several reasons behind making a person radical peaceful angry smiling or tolerant. For knowing the reason behind radicalization or radicals persons one has to understand the causes. Tracing these causes is one of the ways to eliminate such behavior. The first step in the elimination of the radical sentiments in a person is to develop peace in his personality Fair Malhotra amp Shapiro 2010. The chapter which has been addressed here is going to shed light on the roots and symptoms of the radicalism. There will be a brief discussion on how the roots of radicalism can be traced and can be eliminated. The assessment and discussion will be conducted on the parameters of the economy media politics and theology from social cultural point of view. According to the analysis of Ahrari 2000 political factor is one of the major and direct factors which have resulted in causing of the radicalism. These factors however intertwine with one another. Radical actions cannot take place only because of the political factors.

The chemistry of separations ligand degradation by organic radical cations

International Nuclear Information System (INIS)

Mezyk, S.P.; Horne, G.P.; Mincher, B.J.; Zalupski, P.R.; Cook, A.R.; Wishart, J.F.

2016-01-01

Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexing agents and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R"."+), carbon-centered radicals (R".), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R"."+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with 2 ligands: CMPO and TODGA. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved. (authors)

Development of radiation-resisting high molecular-weight materials

International Nuclear Information System (INIS)

Nakagawa, Tsutomu

1976-01-01

The excellent radiation-resisting polyvinyl chloride developed at the opportunity of the research on the relationships between the protection of living body and the polymer-technological protection from radiation is reviewed. The report is divided into four main parts, namely 1) the change in the molecular arrangement of market-available, high molecular-weight materials by gamma-ray irradiation, 2) the protection of high molecular-weight materials from radiation, 3) the relationships between the biological radiation-protective substances and the change to radiation-resisting property of synthesized high molecular-weight substances, and 4) the development of the radiation-resisting high molecular-weight materials as metal-collecting agents. Attention is paid to the polyvinyl chloride having N-methyl-dithio-carbamate radical (PMD), synthesized by the author et. al., that has excellent radiation-resisting property. PMD has some possibility to form thiol- and amino-radicals necessary to protect living things from radiation. It is believed that the protection effects of N-methyl-dithio-carbamate radical are caused by the relatively stable S radical produced by the energy transfer. PMD film is suitable for the irradiation of foods, because it hardly changes the permeability of oxygen and carbon dioxide. PMD produces mercaptide or chelate. A new metal-collecting agent (PSDC) having reactivity with the metallic ions with radiation-resisting property was developed, which is derived from polyvinyl chloride and sodium N-methyl-N-carboxy-methyl-dithio-carbamate. (Iwakiri, K.)

Separation of photo-induced radical pair in cryptochrome to a functionally critical distance

DEFF Research Database (Denmark)

Solov'yov, Ilia; Domratcheva, Tatiana; Schulten, Klaus

2014-01-01

Cryptochrome is a blue light receptor that acts as a sensor for the geomagnetic field and assists many animals in long-range navigation. The magnetoreceptor function arises from light-induced formation of a radical pair through electron transfer between a flavin cofactor (FAD) and a triad...... of tryptophan residues. Here, this electron transfer is investigated by quantum chemical and classical molecular dynamics calculations. The results reveal how sequential electron transfer, assisted by rearrangement of polar side groups in the cryptochrome interior, can yield a FAD-Trp radical pair state...... step can overcome in speed both recombination (electron back-transfer) and proton transfer involving the radical pair reached after primary electron transfer....

Phosphite radicals and their reactions. Examples of redox, substitution, and addition reactions

International Nuclear Information System (INIS)

Schaefer, K.; Asmus, K.D.

1980-01-01

Phosphite radicals HPO 3 - and PO 3 2 -, which exist in an acid-base equilibrium with pK = 5.75, are shown to take part in various types of reactions. In the absence of scavengers, they disappear mainly by second-order disproportionation and combination; a first-order contribution to the decay is also indicated. HPO 3 - and PO 3 2 - are good reductants toward electron acceptors such as tetranitromethane. In this reaction phosphate and C(NO 2 ) 3 - are formed. Phosphite radicals can, however, also act as good oxidants, e.g., toward thiols and thiolate ions. These reactions lead to the formation of RS. radicals which were identified either directly, as in the case of penicillamine, through the optical absorption of PenS. or more indirectly through equilibration of RS. with RS- to the optically absorbing RSSR-. disulfide radical anion. A homolytic substitution reaction (S/sub H/2) occurs in the reaction of the phosphite radicals with aliphatic disulfides, yielding RS. radicals and phosphate thioester RSPO 3 2 -. Lipoic acid, as an example of a cyclic disulfide, is reduced to the corresponding RSSR-. radical anion and also undergoes the S/sub H/2 reaction with about equal probability. An addition reaction is observed between phosphite radicals and molecular oxygen. The resulting peroxo phosphate radicals establish an acid-base equilibrium HPO 5 - . reversible PO 5 2- . + H+ with a pK = 3.4. Absolute rate constants were determined for all reactions discussed

“Jihad Cool/Jihad Chic”: The Roles of the Internet and Imagined Relations in the Self-Radicalization of Colleen LaRose (Jihad Jane

Directory of Open Access Journals (Sweden)

Caroline Joan S. Picart

2015-04-01

Full Text Available The internet provides the means through which a “self-activating terrorist” may first self-radicalize through some imaginary or sympathetic connection with an organized terrorist network. Additionally, the internet allows such a self-activating terrorist to move into the stage of radical violent action. The internet serves both functions by providing the lone wolf with not only a rhetorical medium for self-justification and communication through the use of “monster talk” and its converse, the rhetoric about the “good citizen,” but it is also a source for relatively inexpensive and more unpredictable technologies of mass destruction. Crucial to this analysis is the distinction between radicalization of thought and radicalization of action, as a theoretical rhetoric of radicalization does not automatically convert into a rhetoric of radical action unless there are catalysts at work. The internet, as well as imagined relations cemented by the rhetorics of “jihadi cool” or “jihadi chic,” function as these crucial catalysts, galvanizing monster talk into monstrous action. The article focuses specifically on the case of self-activating terrorist Colleen LaRose to analyze how different factors—mental, psychological, social, and economic—interact with imaginative elements, such as surrogate father-mentor-lover relations for LaRose, and contribute to the formation of a self-activating terrorist, and what ultimately motivates and galvanizes her to move from a rhetoric of radical talk to a rhetoric of radical action, using Silber and Bhatt’s model of radicalization as an initial heuristic. In the case of Colleen LaRose, the romance of “jihadi chic” or “jihadi cool” (the converse of the rhetoric of the monstrous “infidel” or “lone wolf terrorist” was an essential factor to her self-radicalization. It is this imagined status of “jihadi chic” or “jihadi cool” (that nevertheless must somehow have a look of �

Spectroscopic Parameter and Molecular Constant Investigations on Low-Lying States of BeF Radical

Directory of Open Access Journals (Sweden)

Jin Feng Sun

2012-02-01

Full Text Available The potential energy curves (PECs of X2Σ+, A2Πr and B2Σ+ states of BeF radical have been investigated using the complete active space self-consistent-field (CASSCF method, followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI approach at the correlation-consistent basis sets, cc-pV5Z for Be and aug-cc-pV6Z for F. Based on the PECs of X2Σ+, A2Πr and B2Σ+ states, the spectroscopic parameters (De, Re, ωe, ωeχe, αe and Be have also been determined in the present work. With the PECs determined at the present level of theory, vibrational states have been predicted for each state when the rotational quantum number J equals zero (J = 0. The vibrational levels, inertial rotation and centrifugal distortion constants are determined for the three states, and the classical turning points are also calculated for the X2Σ+ state. Compared with the available experiments and other theories, it can be seen that the present spectroscopic parameter and molecular constant results are more fully in agreement with the experimental findings.

Photoisomerization and photodissociation dynamics of reactive free radicals

Energy Technology Data Exchange (ETDEWEB)

Bise, Ryan T. [Univ. of California, Berkeley, CA (United States)

2000-08-01

The photofragmentation pathways of chemically reactive free radicals have been examined using the technique of fast beam photofragment translational spectroscopy. Measurements of the photodissociation cross-sections, product branching ratios, product state energy distributions, and angular distributions provide insight into the excited state potential energy surfaces and nonadiabatic processes involved in the dissociation mechanisms. Photodissociation spectroscopy and dynamics of the predissociative $\\tilde{A}$²A₁ and $\\tilde{B}$²A₂ states of CH₃S have been investigated. At all photon energies, CH₃ + S(³P_j), was the main reaction channel. The translational energy distributions reveal resolved structure corresponding to vibrational excitation of the CH₃ umbrella mode and the S(³P_j) fine-structure distribution from which the nature of the coupled repulsive surfaces is inferred. Dissociation rates are deduced from the photofragment angular distributions, which depend intimately on the degree of vibrational excitation in the C-S stretch. Nitrogen combustion radicals, NCN, CNN and HNCN have also been studied. For all three radicals, the elimination of molecular nitrogen is the primary reaction channel. Excitation to linear excited triplet and singlet electronic states of the NCN radical generates resolved vibrational structure of the N₂ photofragment. The relatively low fragment rotational excitation suggests dissociation via a symmetric C_2V transition state. Resolved vibrational structure of the N₂ photofragment is also observed in the photodissociation of the HNCN radical. The fragment vibrational and rotational distributions broaden with increased excitation energy. Simple dissociation models suggest that the HNCN radical isomerizes to a cyclic intermediate (c-HCNN) which then dissociates via a tight cyclic

Formation of Hydroxylamine from Ammonia and Hydroxyl Radicals

Science.gov (United States)

Krim, Lahouari; Zins, Emilie-Laure

2014-06-01

In the interstellar medium, as well as in icy comets, ammonia may be a crucial species in the first step toward the formation of amino-acids and other prebiotic molecules such as hydroxylamine (NH2OH). It is worth to notice that the NH3/H2 ratio in the ISM is 3 10-5 compared the H2O/H2 one which is only 7 10-5. Using either electron-UV irradiations of water-ammonia ices or successive hydrogenation of solid nitric oxide, laboratory experiments have already shown the feasibility of reactions that may take place on the surface of ice grains in molecular clouds, and may lead to the formation of this precursor. Herein is proposed a new reaction pathway involving ammonia and hydroxyl radicals generated in a microwave discharge. Experimental studies, at 3 and 10 K, in solid phase as well as in neon matrix have shown that this reaction proceed via a hydrogen abstraction, leading to the formation of NH2 radical, that further recombine with hydroxyl radical to form hydroxylamine, under non-energetic conditions.

Isolation and characterisation of in vitro and cellular free radical scavenging peptides from corn peptide fractions.

Science.gov (United States)

Wang, Liying; Ding, Long; Wang, Ying; Zhang, Yan; Liu, Jingbo

2015-02-16

Corn gluten meal, a corn processing industry by-product, is a good source for the preparation of bioactive peptides due to its special amino acid composition. In the present study, the in vitro and cellular free radical scavenging activities of corn peptide fractions (CPFs) were investigated. Results indicated that CPF1 (molecular weight less than 1 kDa) and CPF2 (molecular weight between 1 and 3 kDa) exhibited good hydroxyl radical, superoxide anion radical and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonicacid) diammonium salt (ABTS) radical scavenging activity and oxygen radical absorbance capacity (ORAC). Meanwhile, the in vitro radical scavenging activity of CPF1 was slightly higher than that of CPF2. Both CPF1 and CPF2 also exhibited significant cytoprotective effects and intracellular reactive oxygen species scavenging activity in Caco-2 cells exposed to hydrogen peroxide (H2O2). The amino acid composition analysis revealed that the CPF were rich in hydrophobic amino acids, which comprised of more than 45% of total amino acids. An antioxidant peptide sequence of Tyr-Phe-Cys-Leu-Thr (YFCLT) was identified from CPF1 using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI TOF/TOF MS). The YFCLT exhibited excellent ABTS radical scavenging activity with a 50% effective concentration (EC50) value of 37.63 µM, which was much lower than that of Trolox. In conclusion, corn gluten meal might be a good source to prepare antioxidant peptides.

Manipulating radicals: Using cobalt to steer radical reactions

OpenAIRE

Chirilă, A.

2017-01-01

This thesis describes research aimed at understanding and exploiting metallo-radical reactivity and explores reactions mediated by square planar, low-spin cobalt(II) complexes. A primary goal was to uncover novel reactivity of discrete cobalt(III)-bound carbene radicals generated upon reaction of the cobalt(II) catalysts with carbene precursors. Another important goal was to replace cobalt(II)-porphyrin catalysts with cheaper and easier to prepare metallo-radical analogues. Therefore the cata...

Free radical inactivation of trypsin

International Nuclear Information System (INIS)

Cudina, Ivana; Jovanovic, S.V.

1988-01-01

Reactivities of free radical oxidants, radical OH, Br2-anion radical and Cl 3 COO radical and a reductant, CO2-anion radical, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20 0 C. Highly reactive free radicals, radical OH, Br2-anion radical and CO2-anion radical, react with trypsin at diffusion controlled rates. Moderately reactive trichloroperoxy radical, k(Cl 3 COO radical + trypsin) preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by radical OH, Br2-anion radical and CO2-anion radical are low, G(inactivation) = 0.6-0.8, which corresponds to ∼ 10% of the initially produced radicals. In contrast, Cl 3 COO radical inactivates trypsin with ∼ 50% efficiency, i.e. G(inactivation) = 3.2. (author)

Magnetic trapping of buffer-gas-cooled chromium atoms and prospects for the extension to paramagnetic molecules

International Nuclear Information System (INIS)

Bakker, Joost M; Stoll, Michael; Weise, Dennis R; Vogelsang, Oliver; Meijer, Gerard; Peters, Achim

2006-01-01

We report the successful buffer-gas cooling and magnetic trapping of chromium atoms with densities exceeding 10 12 atoms per cm 3 at a temperature of 350 mK for the trapped sample. The possibilities of extending the method to buffer-gas cool and magnetically trap molecules are discussed. To minimize the most important loss mechanism in magnetic trapping, molecules with a small spin-spin interaction and a large rotational constant are preferred. Both the CrH ( 6 Σ + ground state) and MnH ( 7 Σ + ) radicals appear to be suitable systems for future experiments

Application of numerical methods to the determination of molecular wave functions

International Nuclear Information System (INIS)

Douady, Jerome

1969-01-01

A simplified SCF Method is developed. The wave function of molecular systems and spin densities in the case of free radicals are computed from geometrical data. This method, including at the beginning a delocalization of electrons over all the molecular system, two methods which clear out bonding and anti-bonding interactions have been studied and programmed: a) overlap population analysis, b) localisation of molecular orbitals. These methods have been carried out in the case of organic compounds and free radicals. (author) [fr

The chemistry of separations ligand degradation by organic radical cations

Energy Technology Data Exchange (ETDEWEB)

Mezyk, S.P.; Horne, G.P. [California State University at Long Beach, Long Beach, CA 90840 (United States); Mincher, B.J.; Zalupski, P.R. [Idaho National Laboratory, Idaho Falls, ID 83415 (United States); Cook, A.R.; Wishart, J.F. [Chemistry Department, Brookhaven National Laboratory, New York, 11973 (United States)

2016-07-01

Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexing agents and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R{sup .+}), carbon-centered radicals (R{sup .}), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R{sup .+} as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with 2 ligands: CMPO and TODGA. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved. (authors)

Absolute photoionization cross-section of the methyl radical.

Science.gov (United States)

Taatjes, Craig A; Osborn, David L; Selby, Talitha M; Meloni, Giovanni; Fan, Haiyan; Pratt, Stephen T

2008-10-02

The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; sigma(CH3)(10.2 eV) = (5.7 +/- 0.9) x 10(-18) cm(2) and sigma(CH3)(11.0 eV) = (6.0 +/- 2.0) x 10(-18) cm(2). The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 +/- 2.0) x 10(-18) cm(2) at 10.460 eV, (5.5 +/- 2.0) x 10(-18) cm(2) at 10.466 eV, and (4.9 +/- 2.0) x 10(-18) cm(2) at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.

Mass spectrometric characterization of a pyrolytic radical source using femtosecond ionization

Energy Technology Data Exchange (ETDEWEB)

Frey, H M; Beaud, P; Mischler, B; Radi, P P; Tzannis, A P; Gerber, T [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1997-06-01

Radicals play, as reactive species, an important role in the chemistry of combustion. In contrast to atmospheric flames where spectra are congested due to high vibrational and rotational excitation, experiments in the cold environment of a molecular beam (MB) yield clean spectra that can be easily attributed to one species by Resonantly Enhanced Multi Photon Ionization (REMP). A pyrolytic radical source has been set up. To characterize the efficiency of the source `soft` ionization with femto second pulses is applied which results in less fragmentation, simplifying the interpretation of the mass spectrum. (author) figs., tabs., refs.

Cool diffusion flames of butane isomers activated by ozone in the counterflow

KAUST Repository

Alfazazi, Adamu

2018-02-02

Ignition in low temperature combustion engines is governed by a coupling between low-temperature oxidation kinetics and diffusive transport. Therefore, a detailed understanding of the coupled effects of heat release, low-temperature oxidation chemistry, and molecular transport in cool flames is imperative to the advancement of new combustion concepts. This study provides an understanding of the low temperature cool flame behavior of butane isomers in the counterflow configuration through the addition of ozone. The initiation and extinction limits of butane isomers’ cool flames have been investigated under a variety of strain rates. Results revealed that, with ozone addition, establishment of butane cool diffusion flames was successful at low and moderate strain rates. iso-Butane has lower reactivity than n-butane, as shown by higher fuel mole fractions needed for cool flame initiation and lower extinction strain rate limits. Ozone addition showed a significant influence on the initiation and sustenance of cool diffusion flames; as ozone-less cool diffusion flame of butane isomers could not be established even at high fuel mole fractions. The structure of a stable n-butane cool diffusion flame was qualitatively examined using a time of flight mass spectrometer. Numerical simulations were performed using a detailed chemical kinetic model and molecular transport to simulate the extinction limits of the cool diffusion flames of the tested fuels. The model qualitatively captured experimental trends for both fuels and ozone levels, but over-predicted extinction limits of the flames. Reactions involving low-temperature species predominantly govern extinction limits of cool flames. The simulations were used to understand the effects of methyl branching on the behavior of n-butane and iso-butane cool diffusion flames.

Electronic structure of 2,5,8-tri-tert-butylphenalenyl radical studied by He(I) photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Kubota, Mari [School of Medicine, Keio University, Hiyoshi-4, Kohoku, Yokohama 223-8521 (Japan)], E-mail: marik@hc.cc.keio.ac.jp; Kobayashi, Tsunetoshi [School of Medicine, Keio University, Hiyoshi-4, Kohoku, Yokohama 223-8521 (Japan); Kubo, Takashi; Nakasuji, Kazuhiro [Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

2008-09-15

Phenalenyl radical is an odd-alternant hydrocarbon radical of high symmetry, D{sub 3h} and is extremely attractive as the constituent of molecular magnets. But it has not been characterized in detail. Recently, 2,5,8-tri-tert-butylphenalenyl radical has successfully been synthesized. In this work the gas phase He(I) photoelectron spectrum of this radical has been measured and analyzed with the aid of UHF MO and RHF MO SECI calculations. The first band has been assigned to the ionization from the SO-{pi}-MO of the neutral radical. The second band group has been ascribed to the ionized states relevant to three triplet ionic states and one singlet ionic state of the monocation, the third band group being ascribed to the two singlet ionic states of the monocation.

Mechanism and kinetics in reactions of caffeic acid with radicals by pulse radiolysis and calculation

Energy Technology Data Exchange (ETDEWEB)

Li, Xifeng; Cai, Zhongli; Katsumura, Yosuke [Tokyo Univ., Tokai, Ibaraki (Japan). Nuclear Engineering Research Lab

2000-03-01

The interaction of caffeic acid with e{sub aq}{sup -}, (CH{sub 3}){sub 2}(OH) CCH{sub 2}{sup {center_dot}}, CO{sub 2}{sup {center_dot}}{sup -}, H{sup {center_dot}}, {center_dot}OH and N{sub 3}{sup {center_dot}} radicals were studied by {gamma}-, pulse radiolysis and molecular orbital calculation. UV-visible spectra of electron/{center_dot}OH adducts, semi-quinone radicals of caffeic ions, and the stable products from the reactions were derived. The rate constants were determined. The attacked sites and the most favorable structures of the transient radicals were predicted. Reaction mechanisms were proposed. (author)

Mechanistic investigations of novel photoinitiators for radical polymerization

International Nuclear Information System (INIS)

Griesser, M.

2012-01-01

Nowadays, there is a wide variety of photoinitiators (PIs) available for radical polymerizations. A common example are two-component (Type II) systems such as benzophenone and tertiary amines. However these systems also suffer from problems due to bimolecularity. These include the possible back electron transfer (BET) leading to deactivation, as well as the solvent cage effect, occurring in highly viscous media. The aim of this thesis was to investigate the reaction mechanism of several photoinitiating systems, which show superior performance. Moreover, they exhibit additional benefits such as circumvention of oxygen inhibition by decarboxylation. Thereby this work helps to understand the molecular basis of the performance of different PI systems. In vestigated PIs included benzaldoxime esters, covalently linked benzophenone and N-phenylglycine as well as derivatives of both systems. Furthermore a PI based on benzophenone extended by ethynyl moeities is discussed. The main tool in this investigation was photo-CIDNP (chemically induced dynamic nuclear polarization), an NMR based technique for studying radical reactions. A complementary view was obtained with TR-EPR (time-resolved electron paramagnetic resonance), which provides direct information about the active radical species. The results were further compared with quantum mechanical calculations (DFT) of the magnetic properties of the radicals. The theoretical approach was further applied to other paramagnetic species such as donor-acceptor systems. (author) [de

Thermodynamic and kinetic analysis of the reaction between biological catecholamines and chlorinated methylperoxy radicals

Science.gov (United States)

Dimić, Dušan S.; Milenković, Dejan A.; Marković, Jasmina M. Dimitrić; Marković, Zoran S.

2018-05-01

The antiradical potency of catecholamines (dopamine, epinephrine, norepinephrine, L-DOPA), metabolites of dopamine (homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid) and catechol towards substituted methylperoxy radicals is investigated. The thermodynamic parameters, together with the kinetic approach, are used to determine the most probable mechanism of action. The natural bond orbital and quantum theory of atoms in molecules are utilised to explain the highest reactivity of trichloromethylperoxy radical. The preferred mechanism is dependent both on the thermodynamic and kinetic parameters . The number of chlorine atoms on radical, the presence of intra-molecular hydrogen bond and number of hydroxy groups attached to the aromatic ring significantly influence the mechanism. The results suggest that sequential proton loss electron transfer (SPLET) is the most probable for reaction with methylperoxy and hydrogen atom transfer (HAT) for reaction with trichloromethylperoxy radicals, with a gradual transition between SPLET and HAT for other two radicals. Due to the significant deprotonation of molecules containing the carboxyl group, the respective anions are also investigated. The HAT and SPLET mechanisms are highly competitive in reaction with MP radical, while the dominant mechanism towards chlorinated radicals is HAT. The reactions in methanol and benzene are also discussed.

Monolayer graphene dispersion and radiative cooling for high power LED

Science.gov (United States)

Hsiao, Tun-Jen; Eyassu, Tsehaye; Henderson, Kimberly; Kim, Taesam; Lin, Chhiu-Tsu

2013-10-01

Molecular fan, a radiative cooling by thin film, has been developed and its application for compact electronic devices has been evaluated. The enhanced surface emissivity and heat dissipation efficiency of the molecular fan coating are shown to correlate with the quantization of lattice modes in active nanomaterials. The highly quantized G and 2D bands in graphene are achieved by our dispersion technique, and then incorporated in an organic-inorganic acrylate emulsion to form a coating assembly on heat sinks (for LED and CPU). This water-based dielectric layer coating has been formulated and applied on metal core printed circuit boards. The heat dissipation efficiency and breakdown voltage are evaluated by a temperature-monitoring system and a high-voltage breakdown tester. The molecular fan coating on heat dissipation units is able to decrease the equilibrium junction temperature by 29.1 ° C, while functioning as a dielectric layer with a high breakdown voltage (>5 kV). The heat dissipation performance of the molecular fan coating applied on LED devices shows that the coated 50 W LED gives an enhanced cooling of 20% at constant light brightness. The schematics of monolayer graphene dispersion, undispersed graphene platelet, and continuous graphene sheet are illustrated and discussed to explain the mechanisms of radiative cooling, radiative/non-radiative, and non-radiative heat re-accumulation.

Monolayer graphene dispersion and radiative cooling for high power LED

International Nuclear Information System (INIS)

Hsiao, Tun-Jen; Eyassu, Tsehaye; Henderson, Kimberly; Kim, Taesam; Lin, Chhiu-Tsu

2013-01-01

Molecular fan, a radiative cooling by thin film, has been developed and its application for compact electronic devices has been evaluated. The enhanced surface emissivity and heat dissipation efficiency of the molecular fan coating are shown to correlate with the quantization of lattice modes in active nanomaterials. The highly quantized G and 2D bands in graphene are achieved by our dispersion technique, and then incorporated in an organic-inorganic acrylate emulsion to form a coating assembly on heat sinks (for LED and CPU). This water-based dielectric layer coating has been formulated and applied on metal core printed circuit boards. The heat dissipation efficiency and breakdown voltage are evaluated by a temperature-monitoring system and a high-voltage breakdown tester. The molecular fan coating on heat dissipation units is able to decrease the equilibrium junction temperature by 29.1 ° C, while functioning as a dielectric layer with a high breakdown voltage (>5 kV). The heat dissipation performance of the molecular fan coating applied on LED devices shows that the coated 50 W LED gives an enhanced cooling of 20% at constant light brightness. The schematics of monolayer graphene dispersion, undispersed graphene platelet, and continuous graphene sheet are illustrated and discussed to explain the mechanisms of radiative cooling, radiative/non-radiative, and non-radiative heat re-accumulation. (paper)

EPR and optical spectroscopic studies of neutral free radicals in an adamantane matrix

International Nuclear Information System (INIS)

Jordan, J.E.

1975-03-01

Recent work in our laboratory has demonstrated that neutral free radicals produced by x-irradiation and trapped in adamantane exhibit exceedingly long lifetimes because of the lack of rapid diffusion in the solid matrix. This observation and the fact that samples can be pressed into pellets with high optical transparency in the visible and near uv regions of the spectrum suggested to us that this unique matrix might be used for studying the optical properties of free radicals. The results of a wide variety of experiments of this type are described in this thesis. These include experiments in which secondary free radicals are produced by photoinduced decomposition of primary free radicals by selective irradiation with visible light, the observation of strong optical absorption spectra of free radicals at room temperature using a Cary 14 spectrophotometer, the finding that certain free radicals exhibit strong, visible fluorescence when irradiated with uv light, and the discovery that the absorption intensity of multiplicity-forbidden transition in singlet and doublet state species is enhanced relative to spin-allowed transitions by at least three orders of magnitude. An analysis of these results in terms of molecular orbital theory is given, and experiments designed to obtain the epr spectra of electronically-excited states of free radicals are described

Optimizing the multicycle subrotational internal cooling of diatomic molecules

Science.gov (United States)

Aroch, A.; Kallush, S.; Kosloff, R.

2018-05-01

Subrotational cooling of the AlH+ ion to the miliKelvin regime, using optimally shaped pulses, is computed. The coherent electromagnetic fields induce purity-conserved transformations and do not change the sample temperature. A decrease in a sample temperature, manifested by an increase of purity, is achieved by the complementary uncontrolled spontaneous emission which changes the entropy of the system. We employ optimal control theory to find a pulse that stirs the system into a population configuration that will result in cooling, upon multicycle excitation-emission steps. The obtained optimal transformation was shown capable to cool molecular ions to the subkelvins regime.

Synthesis of Well-defined Amphiphilic Block Copolymers by Organotellurium-Mediated Living Radical Polymerization (TERP).

Science.gov (United States)

Kumar, Santosh; Changez, Mohammad; Murthy, C N; Yamago, Shigeru; Lee, Jae-Suk

2011-10-04

Low-molecular weight amphiphilic diblock copolymers, polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP), and (P2VP-b-PS) with different block ratios were synthesized for the first time via organotellurium-mediated living radical polymerization (TERP). For both the homo- and block copolymerizations, good agreement between the theoretical, and experimental molecular weights was found with nearly 100% yield in every case. The molecular weight distribution for all the samples ranged between 1.10 and 1.24, which is well below the theoretical lower limit of 1.50 for a conventional free radical polymerization. Furthermore, a very simple approach to producing highly dense arrays of titania nanoparticles (TiO2 ) is presented using a site-selective reaction of titanium tetraisopropoxide within the P2VP domains of micellar film of P2VP-b-PS in toluene through the sol-gel method. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Conversion of alkyl radicals to allyl radicals in irradiated single crystal mats of polyethylene

International Nuclear Information System (INIS)

Fujimura, T.; Hayakawa, N.; Kuriyama, I.

1978-01-01

The decay of alkyl radicals, the conversion of alkyl radicals to allyl radicals and the trapping of allyl radicals in irradiated single crystal mats of polyethylene have been studied by electron spin resonance (e.s.r.). It has been suggested that in the crystal core alkyl radicals react with trans-vinylene double bonds and are converted into trans-vinylene allyl radicals; at the crystal surface, alkyl radicals react with vinyl end groups and are converted into allyl radicals with vinyl end groups. The decay of radical pairs and the formation of trans-vinylene double bonds are discussed. (author)

Guest Editorial: Processes of Radicalization and De-Radicalization

Directory of Open Access Journals (Sweden)

Donatella Della Porta

2012-05-01

Full Text Available The study of radicalization and de-radicalization, understood as processes leading towards the increased or decreased use of political violence, is central to the question of how political violence emerges, how it can be prevented, and how it can be contained. The focus section of this issue of the International Journal of Conflict and Violence addresses radicalization and de-radicalization, seeking to develop a more comprehensive understanding of the processes, dynamics, and mechanisms involved and taking an interdisciplinary approach to overcome the fragmentation into separate disciplines and focus areas. Contributions by Pénélope Larzillière, Felix Heiduk, Bill Kissane, Hank Johnston, Christian Davenport and Cyanne Loyle, Veronique Dudouet, and Lasse Lindekilde address repressive settings, legitimacy, institutional aspects, organizational outcomes, and dynamics in Europe, Asia, Africa, and North and South America.

Metal-catalyzed living radical polymerization and radical polyaddition for precision polymer synthesis

Energy Technology Data Exchange (ETDEWEB)

Mizutani, M; Satoh, K [Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Kamigaito, M, E-mail: kamigait@apchem.nagoya-u.ac.j

2009-08-01

The metal-catalyzed radical addition reaction can be evolved into two different polymerization mechanisms, i.e.; chain- and step-growth polymerizations, while both the polymerizations are based on the same metal-catalyzed radical formation reaction. The former is a widely employed metal-catalyzed living radical polymerization or atom transfer radical polymerization of common vinyl monomers, and the latter is a novel metal-catalyzed radical polyaddition of designed monomer with an unconjugated C=C double bond and a reactive C-Cl bond in one molecule. The simultaneous ruthenium-catalyzed living radical polymerization of methyl acrylate and radical polyaddition of 3-butenyl 2-chloropropionate was achieved with Ru(Cp*)Cl(PPh{sub 3}){sub 2} to afford the controlled polymers, in which the homopolymer segments with the controlled chain length were connected by the ester linkage.

Effect of Free Radicals & Antioxidants on Oxidative Stress: A Review

Directory of Open Access Journals (Sweden)

Ashok Shinde

2012-01-01

Full Text Available Recently free radicals have attracted tremendous importance in the field of medicine including dentistry and molecular biology. Free radicals can be either harmful or helpful to the body. When there is an imbalance between formation and removal of free radicals then a condition called as oxidative stress is developed in body. To counteract these free radicals body has protective antioxidant mechanisms which have abilities to lower incidence of various human morbidities and mortalities. Many research groups in the past have tried to study and confirm oxidative stress. Many authors also have studied role of antioxidants in reducing oxidative stress. They have come across with controversial results and furthermore it is not yet fully confirmed whether oxidative stress increases the need for dietary antioxidants. Recently, an association between periodontitis and cardiovascular disease has received considerable attention. Various forms of antioxidants have been introduced as an approach to fight dental diseases and improve general gingival health. The implication of oxidative stress in the etiology of many chronic and degenerative diseases suggests that antioxidant therapy represents a promising avenue for treatment. This study was conducted with the objective of reviewing articles relating to this subject. A Pub Med search of all articles containing key words free radicals, oxidative stress, and antioxidants was done. A review of these articles was undertaken.

Radical abundance how a revolution in nanotechnology will change civilization

CERN Document Server

Drexler, K Eric

2013-01-01

K. Eric Drexler is the founding father of nanotechnology--the science of engineering on a molecular level. In Radical Abundance, he shows how rapid scientific progress is about to change our world. Thanks to atomically precise manufacturing, we will soon have the power to produce radically more of what people want, and at a lower cost. The result will shake the very foundations of our economy and environment. Already, scientists have constructed prototypes for circuit boards built of millions of precisely arranged atoms. The advent of this kind of atomic precision promises to change the way we make things--cleanly, inexpensively, and on a global scale. It allows us to imagine a world where solar arrays cost no more than cardboard and aluminum foil, and laptops cost about the same. A provocative tour of cutting edge science and its implications by the field's founder and master, Radical Abundance offers a mind-expanding vision of a world hurtling toward an unexpected future.

Effect of TEMPO-oxidization and rapid cooling on thermo-structural properties of nanocellulose.

Science.gov (United States)

Mhd Haniffa, Mhd Abd Cader; Ching, Yern Chee; Chuah, Cheng Hock; Yong Ching, Kuan; Nazri, Nik; Abdullah, Luqman Chuah; Nai-Shang, Liou

2017-10-01

Recently, surface functionality and thermal property of the green nanomaterials have received wide attention in numerous applications. In this study, microcrystalline cellulose (MCC) was used to prepare the nanocrystalline celluloses (NCCs) using acid hydrolysis method. The NCCs was treated with TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl)oxy radical]-oxidation to prepare TEMPO-oxidized NCCs. Cellulose nanofibrils (CNFs) also prepared from MCC using TEMPO-oxidation. The effects of rapid cooling and chemical treatments on the thermo-structural property studies of the prepared nanocelluloses were investigated through FTIR, thermogravimetric analysis-derivative thermogravimetric (TGA-DTG), and XRD. A posteriori knowledge of the FTIR and TGA-DTG analysis revealed that the rapid cooling treatment enhanced the hydrogen bond energy and thermal stability of the TEMPO-oxidized NCC compared to other nanocelluloses. XRD analysis exhibits the effect of rapid cooling on pseudo 2 I helical conformation. This was the first investigation performed on the effect of rapid cooling on structural properties of the nanocellulose. Copyright © 2017 Elsevier Ltd. All rights reserved.

Free radical scavenging activity of coenzyme Q measured by a chemiluminescent assay

International Nuclear Information System (INIS)

Battino, Maurizio; Ferri, Elida; Girotti, Stefano; Lenaz, Giorgio

1991-01-01

Involvement of coenzyme Q (CoQ) in anti-oxydant activities, in addition to its major redox role, has frequently been suggested in recent years. In order to elucidate if CoQ could really be engaged in scavenging free radicals produced endogenously in a biological system, an experimental system was developed in which beef heart mitochondria in the presence of a saturating NADH concentration and of rotenone produce free radicals. The presence of oxygen-reactive forms was easily detected by a luminol-dependent chemiluminescence process. The chemi-luminescence assay showed that short-chain CoQ homologues can act as pro-oxidants, enhancing free radical effects, while exogenous coenzyme Q 10 could scavenge free radicals, especially at very low concentration. In this system, exogenous CoQ 10 was more effective than α-tocopherol at the same concentration in scavenging free radicals. The molecular mechanism that leads to this activity is still unclear, but these results are of biochemical importance because they indicate that CoQ may act as an anti=oxidant in situations mimicking physiopathological conditions. This direct chemiluminescent method is promising for studies of biochemical processes which involve active oxygen species. (author). 24 refs.; 4 figs

The effect of non-equilibrium metal cooling on the interstellar medium

Science.gov (United States)

Capelo, Pedro R.; Bovino, Stefano; Lupi, Alessandro; Schleicher, Dominik R. G.; Grassi, Tommaso

2018-04-01

By using a novel interface between the modern smoothed particle hydrodynamics code GASOLINE2 and the chemistry package KROME, we follow the hydrodynamical and chemical evolution of an isolated galaxy. In order to assess the relevance of different physical parameters and prescriptions, we constructed a suite of 10 simulations, in which we vary the chemical network (primordial and metal species), how metal cooling is modelled (non-equilibrium versus equilibrium; optically thin versus thick approximation), the initial gas metallicity (from 10 to 100 per cent solar), and how molecular hydrogen forms on dust. This is the first work in which metal injection from supernovae, turbulent metal diffusion, and a metal network with non-equilibrium metal cooling are self-consistently included in a galaxy simulation. We find that properly modelling the chemical evolution of several metal species and the corresponding non-equilibrium metal cooling has important effects on the thermodynamics of the gas, the chemical abundances, and the appearance of the galaxy: the gas is typically warmer, has a larger molecular-gas mass fraction, and has a smoother disc. We also conclude that, at relatively high metallicity, the choice of molecular-hydrogen formation rates on dust is not crucial. Moreover, we confirm that a higher initial metallicity produces a colder gas and a larger fraction of molecular gas, with the low-metallicity simulation best matching the observed molecular Kennicutt-Schmidt relation. Finally, our simulations agree quite well with observations that link star formation rate to metal emission lines.

Magnetic trapping of buffer-gas-cooled chromium atoms and prospects for the extension to paramagnetic molecules

Energy Technology Data Exchange (ETDEWEB)

Bakker, Joost M [Humboldt Universitaet zu Berlin, Institut fuer Physik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Stoll, Michael [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany); Weise, Dennis R [Universitaet Konstanz, Fachbereich Physik, 78457 Constance (Germany); Vogelsang, Oliver [Universitaet Konstanz, Fachbereich Physik, 78457 Konstanz (Germany); Meijer, Gerard [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany); Peters, Achim [Humboldt Universitaet zu Berlin, Institut fuer Physik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

2006-10-14

We report the successful buffer-gas cooling and magnetic trapping of chromium atoms with densities exceeding 10{sup 12} atoms per cm{sup 3} at a temperature of 350 mK for the trapped sample. The possibilities of extending the method to buffer-gas cool and magnetically trap molecules are discussed. To minimize the most important loss mechanism in magnetic trapping, molecules with a small spin-spin interaction and a large rotational constant are preferred. Both the CrH ({sup 6}{sigma}{sup +} ground state) and MnH ({sup 7}{sigma}{sup +}) radicals appear to be suitable systems for future experiments.

Modeling and Proposed Molecular Mechanism of Hydroxyurea Through Docking and Molecular Dynamic Simulation to Curtail the Action of Ribonucleotide Reductase.

Science.gov (United States)

Iman, Maryam; Khansefid, Zeynab; Davood, Asghar

2016-01-01

Ribonucleotide Reductase (RNR) is an important anticancer chemotherapy target. It has main key role in DNA synthesis and cell growth. Therefore several RNR inhibitors, such as hydroxyurea, have entered the clinical trials. Based on our proposed mechanism, radical site of RNR protein reacts with hydroxyurea in which hydroxyurea is converted into its oxidized form compound III, and whereby the tyrosyl radical is converted into a normal tyrosine residue. In this study, docking and molecular dynamics simulations were used for proposed molecular mechanism of hydroxyurea in RNR inhibition as anticancer agent. The binding affinity of hydroxyurea and compound III to RNR was studied by docking method. The docking study was performed for the crystal structure of human RNR with the radical scavenger Hydroxyurea and its oxidized form to inhibit the human RNR. hydroxyurea and compound III bind at the active site with Tyr-176, which are essential for free radical formation. This helps to understand the functional aspects and also aids in the development of novel inhibitors for the human RNR2. To confirm the binding mode of inhibitors, the molecular dynamics (MD) simulations were performed using GROMACS 4.5.5, based upon the docked conformation of inhibitors. Both of the studied compounds stayed in the active site. The results of MD simulations confirmed the binding mode of ligands, accuracy of docking and the reliability of active conformations which were obtained by AutoDock. MD studies confirm our proposed mechanism in which compound III reacts with the active site residues specially Tyr-176, and inhibits the radical generation and subsequently inhibits the RNR enzyme.

The atomic coilgun and single-photon cooling

Energy Technology Data Exchange (ETDEWEB)

Libson, Adam, E-mail: alibson@physics.utexas.edu; Bannerman, Stephen Travis; Clark, Robert J.; Mazur, Thomas R.; Raizen, Mark G. [University of Texas at Austin, Center for Nonlinear Dynamics and Department of Physics (United States)

2012-12-15

As the simplest atom, hydrogen has a unique role as a testing ground of fundamental physics. Precision measurements of the hydrogen atomic structure provide stringent tests of current theory, while tritium is an excellent candidate for studies of {beta}-decay and possible measurement of the neutrino rest mass. Furthermore, precision measurement of antihydrogen would allow for tests of fundamental symmetries. Methods demonstrated in our lab provide an avenue by which hydrogen isotopes can be trapped and cooled to near the recoil limit. The atomic coilgun, which we have demonstrated with metastable neon and molecular oxygen, provides a general method of stopping a supersonic beam of any paramagnetic species. This tool provides a method by which hydrogen and its isotopes can be magnetically trapped at around 100 mK using a room temperature apparatus. Another tool developed in our laboratory, single-photon cooling, allows further cooling of a trapped sample to near the recoil limit. This cooling method has already been demonstrated on a trapped sample of rubidium. We report on the progress of implementing these methods to trap and cool hydrogen isotopes, and on the prospects for using cold trapped hydrogen for precision measurements.

Excitation energies, photoionization cross sections, and asymmetry parameters of the methyl and silyl radicals.

Science.gov (United States)

Velasco, A M; Lavín, C; Dolgounitcheva, O; Ortiz, J V

2014-08-21

Vertical excitation energies of the methyl and silyl radicals were inferred from ab initio electron propagator calculations on the electron affinities of CH3(+) and SiH3(+). Photoionization cross sections and angular distribution of photoelectrons for the outermost orbitals of both CH3 and SiH3 radicals have been obtained with the Molecular Quantum Defect Orbital method. The individual ionization cross sections corresponding to the Rydberg channels to which the excitation of the ground state's outermost electron gives rise are reported. Despite the relevance of methyl radical in atmospheric chemistry and combustion processes, only data for the photon energy range of 10-11 eV seem to be available. Good agreement has been found with experiment for photoionization cross section of this radical. To our knowledge, predictions of the above mentioned photoionization parameters on silyl radical are made here for the first time, and we are not aware of any reported experimental measurements. An analysis of our results reveals the presence of a Cooper minimum in the photoionization of the silyl radical. The adequacy of the two theoretical procedures employed in the present work is discussed.

Free radical reactions of hematoporphyrin: a pulse radiolysis study

International Nuclear Information System (INIS)

Ahmed, Mohammed; Guleria, Apurav; Singh, Ajay K.; Sarkar, S.K.

2011-01-01

Radiation chemistry of porphyrin derivatives has been given much attention in recent years. Although till date photo dynamic therapy (PDT) with Hematoporphyrin (HP) has already proved its effectiveness in the treatment of cancer, the molecular mechanisms by which this therapy-destroys tumour cells as well as its optimal physical parameters are still not fully understood. Thus it becomes necessary to understand the interaction of different free radicals with HP. Pulse radiolysis studies have been performed to understand the interaction of different free radicals with HP. The product formation along with bleaching and presence of a number of transients makes it difficult to pin point the mode and site of free radical attack. The radiation-induced formation of various transients (HP-OH, HO - , HP + ) in aqueous solution was investigated at various pHs by pulse radiolysis technique by means of N 3 , O - and CCl 3 O 2 radicals with and without triethyl-amine, under different dose conditions. The observed intermediates are characterized by their kinetic and spectroscopic data. The absorption spectrum of each transient could be differentiated from each other by their absorption maxima, extinction coefficients and kinetics. A clear indication of product formation has also been observed by employing continuous electron pulse and the solution shows a green coloration. It is conceivable that under certain conditions, similar transients may be produced when HP is used as a sensitizer in radiation chemotherapy of cancer patients. Our study may throw some light into the breakdown mechanism of haemoglobin to BV in addition to the understanding of free radical interaction of HP. (author)

Turbine airfoil cooling system with cooling systems using high and low pressure cooling fluids

Science.gov (United States)

Marsh, Jan H.; Messmann, Stephen John; Scribner, Carmen Andrew

2017-10-25

A turbine airfoil cooling system including a low pressure cooling system and a high pressure cooling system for a turbine airfoil of a gas turbine engine is disclosed. In at least one embodiment, the low pressure cooling system may be an ambient air cooling system, and the high pressure cooling system may be a compressor bleed air cooling system. In at least one embodiment, the compressor bleed air cooling system in communication with a high pressure subsystem that may be a snubber cooling system positioned within a snubber. A delivery system including a movable air supply tube may be used to separate the low and high pressure cooling subsystems. The delivery system may enable high pressure cooling air to be passed to the snubber cooling system separate from low pressure cooling fluid supplied by the low pressure cooling system to other portions of the turbine airfoil cooling system.

Radical Change by Entrepreneurial Design

National Research Council Canada - National Science Library

Roberts, Nancy C

1998-01-01

.... How radical change in public policy has occurred in the past is then documented. We find examples of radical change by chance, radical change by consensus, radical change by learning, and radical change by entrepreneurial design...

Novel Water Soluble Chitosan Derivatives with 1,2,3-Triazolium and Their Free Radical-Scavenging Activity.

Science.gov (United States)

Li, Qing; Sun, Xueqi; Gu, Guodong; Guo, Zhanyong

2018-03-28

Chitosan is an abundant and renewable polysaccharide, which exhibits attractive bioactivities and natural properties. Improvement such as chemical modification of chitosan is often performed for its potential of providing high bioactivity and good water solubility. A new class of chitosan derivatives possessing 1,2,3-triazolium charged units by associating "click reaction" with efficient 1,2,3-triazole quaternization were designed and synthesized. Their free radical-scavenging activity against three free radicals was tested. The inhibitory property and water solubility of the synthesized chitosan derivatives exhibited a remarkable improvement over chitosan. It is hypothesized that triazole or triazolium groups enable the synthesized chitosan to possess obviously better radical-scavenging activity. Moreover, the scavenging activity against superoxide radical of chitosan derivatives with triazolium (IC 50 radical-scavenging assay, the same pattern were observed, which should be related to the triazolium grafted at the periphery of molecular chains.

Spin-selective recombination reactions of radical pairs: Experimental test of validity of reaction operators

Energy Technology Data Exchange (ETDEWEB)

Maeda, Kiminori [Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford (United Kingdom); Liddell, Paul; Gust, Devens [Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, 85287-1604 (United States); Hore, P. J. [Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford (United Kingdom)

2013-12-21

Spin-selective reactions of radical pairs are conventionally modelled using an approach that dates back to the 1970s [R. Haberkorn, Mol. Phys. 32, 1491 (1976)]. An alternative approach based on the theory of quantum measurements has recently been suggested [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010)]. We present here the first experimental attempt to discriminate between the two models. Pulsed electron paramagnetic resonance spectroscopy has been used to investigate intramolecular electron transfer in the radical pair form of a carotenoid-porphyrin-fullerene molecular triad. The rate of spin-spin relaxation of the fullerene radical in the triad was found to be inconsistent with the quantum measurement description of the spin-selective kinetics, and in accord with the conventional model when combined with spin-dephasing caused by rotational modulation of the anisotropic g-tensor of the fullerene radical.

Infrared Emission Spectrum of the Hydroxyl Radical: A Novel Experiment in Molecular Spectroscopy.

Science.gov (United States)

Henderson, Giles; And Others

1982-01-01

Describes an experiment in which parameters from an "ab-initio" potential are used to calculate vibrational-rotational energy levels and construct a "stick spectrum" for the overtone emission of the hydroxyl radical. Provides background information on ab-initio spectrum, experimental procedures, and analysis of data. (Author/JN)

Hydro-chemical study of the evolution of interstellar pre-biotic molecules during the collapse of molecular clouds

International Nuclear Information System (INIS)

Majumdar, Liton; Das, Ankan; Chakrabarti, Sandip K.; Chakrabarti, Sonali

2012-01-01

One of the stumbling blocks for studying the evolution of interstellar molecules is the lack of adequate knowledge about the rate coefficients of various reactions which take place in the interstellar medium and molecular clouds. Some theoretical models of rate coefficients do exist in the literature for computing abundances of complex pre-biotic molecules. So far these have been used to study the abundances of these molecules in space. However, in order to obtain more accurate final compositions in these media, we have calculated the rate coefficients for the formation of some of the most important interstellar pre-biotic molecules by using quantum chemical theory. We use these rates inside our hydro-chemical model to examine the chemical evolution and final abundances of pre-biotic species during the collapsing phase of a proto-star. We find that a significant amount of various pre-biotic molecules could be produced during the collapse phase of a proto-star. We thoroughly study the formation of these molecules via successive neutral-neutral and radical-radical/radical-molecular reactions. We present the time evolution of the chemical species with an emphasis on how the production of these molecules varies with the depth of a cloud. We compare the formation of adenine in interstellar space using our rate-coefficients and using those obtained from existing theoretical models. Formation routes of the pre-biotic molecules are found to be highly dependent on the abundances of the reactive species and the rate coefficients involved in the reactions. The presence of grains strongly affects the abundances of the gas phase species. We also carry out a comparative study between different pathways available for the synthesis of adenine, alanine, glycine and other molecules considered in our network. Despite the huge abundances of the neutral reactive species, production of adenine is found to be strongly dominated by the radical-radical/radical-molecular reaction pathways

The games radicals play : special issue on free radicals and radical ions

OpenAIRE

Walton, J.C.; Williams, F.

2015-01-01

Chemistry and Physics have aptly been described as “most excellent children of Intellect and Art” [1]. Both these “children” engage with many playthings, and molecules rank as one of their first favorites, especially radicals, which are amongst the most lively and exciting. Checking out radicals dancing to the music of entropy round their potential energy ballrooms is surely both entertaining and enlightening. Radicals’ old favorite convolutions are noteworthy, but the new styles, modes and a...

Time resolved resonance Raman spectra of anilino radical and aniline radical cation

International Nuclear Information System (INIS)

Tripathi, G.N.R.; Schuler, R.H.

1987-01-01

We report, in this paper, submicrosecond time resolved resonance Raman spectra of anilino radical and its radical cation as observed in pulse radiolytic studies of the oxidation of aniline in aqueous solution. By excitation in resonance with the broad and weak electronic transition of anilino radical at 400 nm (ε--1250 M -1 cm -1 ) we have observed, for the first time, the vibrational features of this radical. The Wilson ν 8 /sub a/ ring stretching mode at 1560 cm -1 is most strongly resonance enhanced. The ν 7 /sub a/ CN stretching band at 1505 cm -1 , which is shifted to higher frequency by 231 cm -1 with respect to aniline, is also prominent. The frequency of this latter mode indicates that the CN bond in the radical has considerable double bond character. The Raman spectrum of aniline radical cation, excited in resonance with the --425 nm electronic absorption (ε--4000 M -1 cm -1 ), shows features which are similar to phenoxyl radical. Most of the observed frequencies of this radical in solution are in good agreement with vibrational energies determined by recent laser photoelectron spectroscopic studies in the vapor phase. The bands most strongly enhanced in the resonance Raman spectrum are, however, weak in the photoelectron spectrum. While the vibrational frequencies observed for anilino radical and its isoelectronic cation are quite similar, the resonance enhancement patterns are very different. In particular the ν 14 b 2 mode of anilino radical observed at 1324 cm -1 is highly resonance enhanced because of strong vibronic coupling between the 400 nm 2 A 2 -- 2 B 1 and the higher 2 B 1 -- 2 B 1 electronic transitions

Radical cation spectroscopy of substituted alkyl phenyl ketones via tunnel ionization

Energy Technology Data Exchange (ETDEWEB)

Bohinski, Timothy; Moore Tibbetts, Katharine [Center for Advanced Photonics Research, Temple University, Philadelphia, PA 19122 (United States); Department of Chemistry, Temple University, Philadelphia, PA 19122 (United States); Munkerup, Kristin [Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø (Denmark); Tarazkar, Maryam [Center for Advanced Photonics Research, Temple University, Philadelphia, PA 19122 (United States); Department of Chemistry, Temple University, Philadelphia, PA 19122 (United States); Romanov, Dmitri A. [Center for Advanced Photonics Research, Temple University, Philadelphia, PA 19122 (United States); Department of Physics, Temple University, Philadelphia, PA 19122 (United States); Matsika, Spiridoula [Department of Chemistry, Temple University, Philadelphia, PA 19122 (United States); Levis, Robert J., E-mail: rjlevis@temple.edu [Center for Advanced Photonics Research, Temple University, Philadelphia, PA 19122 (United States); Department of Chemistry, Temple University, Philadelphia, PA 19122 (United States)

2014-10-17

Highlights: • Infrared strong field spectroscopy on (o, m, p)-methylacetophenone was performed. • Electronic resonance in the radical cations at 1370 nm produces benzoyl fragment. • Magnitude of resonance feature increases from ortho to meta to para isomer. • Hydrogen interactions and moment of inertia account for the trend across isomers. - Abstract: Mass spectra are measured for 2′-, 3′- and 4′-(ortho, meta and para) methyl substituted alkyl phenyl ketones excited at wavelengths ranging from 1200 to 1500 nm in the strong field regime. The selective loss of a methyl group from the acetyl group of the parent molecular ion upon excitation at ∼1370 nm is attributed to an electronic resonance between ground D{sub 0} and excited D{sub 2} state of the radical cation. Depletion of the parent molecular ion is enhanced as the methyl substituent is moved from the 2′ to 3′ to 4′ position on the phenyl ring with respect to the acetyl group. The phenyl-acetyl dihedral angle is the relevant coordinate enabling excitation to the dissociative D{sub 2} state. Calculations on the radical cation of 2′-methylacetophenone show two stable geometries with dihedral angles of 7 degrees and 63 degrees between the phenyl and acetyl groups. The barrier to rotation for the 2′ isomer limits population transfer to the D{sub 2} state. In contrast, calculations on the radical cations of 3′- and 4′-methylacetophenone reveal no rotational barrier to prevent population transfer to the excited state, which is consistent with the enhanced dissociation yield in comparison with the 2′ substitution. The enhanced dissociation of the 4′ isomer as compared to the 3′ isomer is attributed to its lower moment of inertia about the dihedral angle.

Molecular Mechanisms behind Free Radical Scavengers Function against Oxidative Stress

Directory of Open Access Journals (Sweden)

Fereshteh Ahmadinejad

2017-07-01

Full Text Available Accumulating evidence shows that oxidative stress is involved in a wide variety of human diseases: rheumatoid arthritis, Alzheimer’s disease, Parkinson’s disease, cancers, etc. Here, we discuss the significance of oxidative conditions in different disease, with the focus on neurodegenerative disease including Parkinson’s disease, which is mainly caused by oxidative stress. Reactive oxygen and nitrogen species (ROS and RNS, respectively, collectively known as RONS, are produced by cellular enzymes such as myeloperoxidase, NADPH-oxidase (nicotinamide adenine dinucleotide phosphate-oxidase and nitric oxide synthase (NOS. Natural antioxidant systems are categorized into enzymatic and non-enzymatic antioxidant groups. The former includes a number of enzymes such as catalase and glutathione peroxidase, while the latter contains a number of antioxidants acquired from dietary sources including vitamin C, carotenoids, flavonoids and polyphenols. There are also scavengers used for therapeutic purposes, such as 3,4-dihydroxyphenylalanine (L-DOPA used routinely in the treatment of Parkinson’s disease (not as a free radical scavenger, and 3-methyl-1-phenyl-2-pyrazolin-5-one (Edaravone that acts as a free radical detoxifier frequently used in acute ischemic stroke. The cell surviving properties of L-DOPA and Edaravone against oxidative stress conditions rely on the alteration of a number of stress proteins such as Annexin A1, Peroxiredoxin-6 and PARK7/DJ-1 (Parkinson disease protein 7, also known as Protein deglycase DJ-1. Although they share the targets in reversing the cytotoxic effects of H2O2, they seem to have distinct mechanism of function. Exposure to L-DOPA may result in hypoxia condition and further induction of ORP150 (150-kDa oxygen-regulated protein with its concomitant cytoprotective effects but Edaravone seems to protect cells via direct induction of Peroxiredoxin-2 and inhibition of apoptosis.

Intramolecular transformation of thiyl radicals to α-aminoalkyl radicals: 'ab initio' calculations on homocystein

International Nuclear Information System (INIS)

Chhun, S.; Berges, J.; Bleton, V.; Abedinzadeh, Z.

2000-01-01

One-electron oxidation of thiols by oxidizing radicals leads to the formation of thiyl radical and carbon-centered radicals. It has been shown experimentally that in the absence of oxygen, the thiyl radicals derived from certain thiols of biological interest such as glutathion, cysteine and homocysteine decay rapidly by intramolecular rearrangement reactions into the carbon-centered radical. In the present work we have investigated theoretically the structure and the stability of thiyl and carbon-centered radicals of homocysteine in order to check the possibility of this rearrangement. (author)

Free radical transfer in polymers

International Nuclear Information System (INIS)

Sonntag, C. von; Bothe, E.; Ulanski, P.

1998-01-01

For the present study of free-radical transfer in polymers pulse radiolysis and product studies have been carried out in aqueous solutions using thus far only the water-soluble polymers polyacrylic acid, polymethacrylic acid and polyvinyl alcohol. When OH radicals, generated in the radiolysis of N 2 O-saturated aqueous solutions, react with polymers the lifetime of the polymer radical thus created very much depends on the number of radicals per polymer chain. When there are a large number of radicals per chain their bimolecular decay may be faster than the corresponding (diffusion controlled) decay of monomeric radicals, but when the macromolecule contains only few or even just one radical their lifetime is considerably prolonged. Highly charged polymers such as polyacrylic acid at high pH attain a rod-like conformation which again favors a long lifetime of the radicals. Under such conditions, radical transfer reactions can occur. For example, in polyacrylic acid OH radicals generate two kinds of radicals side by side. The radical in β-position to the carboxylate group converts into the thermodynamically more stable α-radicals by an H-transfer reaction as can be followed by spectrophotometry. Besides radical transfer reactions β-fragmentation reactions occur causing chain scission. Such reactions can be followed in a pulse radiolysis experiment by conductometry, because counter ions are released upon chain scission. Such a process is especially effective in the case of polymethacrylic acid, where it results in a chain depolymerization. An intramolecular H-abstraction is also observed in the γ-radiolysis of polyacrylic acid with the corresponding peroxyl radicals. This causes a chain reaction to occur. The resulting hydroperoxides are unstable and decarboxylate given rise to acetylacetone-like products. In polyvinyl alcohol the peroxyl radicals in α-position to the alcohol function undergo HO 2 -elimination. This prevents a scission of the polymer chain in the

Atomic size effect on critical cooling rate and glass formation

International Nuclear Information System (INIS)

Jalali, Payman; Li Mo

2005-01-01

Atomic size effect on critical cooling rate and glass formability in a model binary system is investigated using molecular dynamics simulation. To isolate atomic size effect from the rest of the factors that critically influence the glass formation, a hard sphere model is employed in conjunction with a newly developed densification method. The glass formability is defined as a set of optimal conditions that result in the slowest cooling rate of the glass-forming liquid. Critical cooling rates are identified from extensive molecular dynamics simulations. A kinetic glass-forming diagram is mapped out that marks the boundary between the glass-forming regions and competing crystalline phases in terms of the parameters of the atomic size ratio and alloy concentration. It is found that the potency of the atomic size difference on glass formation is influenced greatly by the competing metastable and equilibrium crystalline phases in the system, and the kinetic processes leading to the formation of these phases. The mechanisms of the atomic size effect on topological instability of crystal packing and glass formation are discussed

COOL: A code for Dynamic Monte Carlo Simulation of molecular dynamics

Science.gov (United States)

Barletta, Paolo

2012-02-01

Cool is a program to simulate evaporative and sympathetic cooling for a mixture of two gases co-trapped in an harmonic potential. The collisions involved are assumed to be exclusively elastic, and losses are due to evaporation from the trap. Each particle is followed individually in its trajectory, consequently properties such as spatial densities or energy distributions can be readily evaluated. The code can be used sequentially, by employing one output as input for another run. The code can be easily generalised to describe more complicated processes, such as the inclusion of inelastic collisions, or the possible presence of more than two species in the trap. New version program summaryProgram title: COOL Catalogue identifier: AEHJ_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHJ_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1 097 733 No. of bytes in distributed program, including test data, etc.: 18 425 722 Distribution format: tar.gz Programming language: C++ Computer: Desktop Operating system: Linux RAM: 500 Mbytes Classification: 16.7, 23 Catalogue identifier of previous version: AEHJ_v1_0 Journal reference of previous version: Comput. Phys. Comm. 182 (2011) 388 Does the new version supersede the previous version?: Yes Nature of problem: Simulation of the sympathetic process occurring for two molecular gases co-trapped in a deep optical trap. Solution method: The Direct Simulation Monte Carlo method exploits the decoupling, over a short time period, of the inter-particle interaction from the trapping potential. The particle dynamics is thus exclusively driven by the external optical field. The rare inter-particle collisions are considered with an acceptance/rejection mechanism, that is, by comparing a random number to the collisional probability

Spatio-temporal bio-radical processes: the state of the art and new challenges

International Nuclear Information System (INIS)

Gauduel, Y.A.

2013-01-01

The course of ultrafast elementary bio-molecular damage governed by low energy electrons can be carefully investigated in the pre-thermal regime. During this specific regime, the energy of partially localized electron is still higher than the thermal energy kT (0.025 eV) but its interaction potential with molecules is directly dependent on the state density fluctuations of the environment. In presence of water molecules two well-defined non-equilibrium low-energy electron configurations, 2p-like excited pre-hydrated electron and electron-radical pair, represent very interesting quantum entities for the real-time investigation of their interactions with bio-molecular environments. In the framework of nonadiabatic trajectories, quantum branching ratios of low energy electron pathways are highly influenced by time-dependent water caging effects. The investigation of ultrafast concerted processes with low energy localized electrons contributes to the concept of tenuous borderline between direct and indirect molecular damage at the local order. The quantum character of very-short lived low-energy electron in a pre-hydrated configuration (infrared 2p-like excited electron) provides a unique sub-nano-metric probe to spatially explore early radiation damage on biologically relevant molecules. For the first time, femto-bio-radical investigations performed in aqueous environments give correlated spatial and temporal information on bio-molecular damage triggered by ultrafast low energy electron attachments. In the future, this innovative approach would be applied to more complex bio-molecular architectures such as DNA or protein complexes

Iron and iron derived radicals

International Nuclear Information System (INIS)

Borg, D.C.; Schaich, K.M.

1987-04-01

We have discussed some reactions of iron and iron-derived oxygen radicals that may be important in the production or treatment of tissue injury. Our conclusions challenge, to some extent, the usual lines of thought in this field of research. Insofar as they are born out by subsequent developments, the lessons they teach are two: Think fast! Think small! In other words, think of the many fast reactions that can rapidly alter the production and fate of highly reactive intermediates, and when considering the impact of competitive reactions on such species, think how they affect the microenvironment (on the molecular scale) ''seen'' by each reactive molecule. 21 refs., 3 figs., 1 tab

Improved Mechanical Performance Fracture Properties and Reliability of Radical-Cured Thermosets

Energy Technology Data Exchange (ETDEWEB)

Redline, Erica Marie [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Bolintineanu, Dan S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lane, J. Matthew [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Stevens, Mark J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Alam, Todd M. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Celina, Mathias C. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2016-10-01

The aim of this study was to alter polymerization chemistry to improve network homogeneity in free-radical crosslinked systems. It was hypothesized that a reduction in heterogeneity of the network would lead to improved mechanical performance. Experiments and simulations were carried out to investigate the connection between polymerization chemistry, network structure and mechanical properties. Experiments were conducted on two different monomer systems - the first is a single monomer system, urethane dimethacrylate (UDMA), and the second is a two-monomer system consisting of bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) in a ratio of 70/30 BisGMA/TEGDMA by weight. The methacrylate systems were crosslinked using traditional radical polymeriza- tion (TRP) with azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) as an initiator; TRP systems were used as the control. The monomers were also cross-linked using activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) as a type of controlled radical polymerization (CRP). FTIR and DSC were used to monitor reac- tion kinetics of the systems. The networks were analyzed using NMR, DSC, X-ray diffraction (XRD), atomic force microscopy (AFM), and small angle X-ray scattering (SAXS). These techniques were employed in an attempt to quantify differences between the traditional and controlled radical polymerizations. While a quantitative methodology for characterizing net- work morphology was not established, SAXS and AFM have shown some promising initial results. Additionally, differences in mechanical behavior were observed between traditional and controlled radical polymerized thermosets in the BisGMA/TEGDMA system but not in the UDMA materials; this finding may be the result of network ductility variations between the two materials. Coarse-grained molecular dynamics simulations employing a novel model of the CRP reaction were carried out for

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. IV. Effects of additives on Polymer molecular weight

International Nuclear Information System (INIS)

Watanabe, T.; Suwa, T.; Okamoto, J.; Machi, S.

1979-01-01

Poly(tetrafluoroethylene)(PTFE) of high molecular weight, 4.5 x 10 7 , was incidentally obtained at earlier study of an emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. In order to clarify this phenomenon, the effects of additives, in particular radical scavengers, on the molecular weight of PTFE and its polymerization behavior were studied. It was found that the molecular weight of PTFE is increased by the addition of hydroquinone, benzoquinone, α-pinene, dl-limonene, and ethylenediamine but is decreased by oxygen and triethylamine. A PTFE latex with molecular weight higher than 2 x 10 7 was obtained in the presence of hydroquinone. It is concluded that additives such as hydroquinone and benzaquinone, which rapidly scavenge the primary radicals (OH, H, and e/sub aq/ - ) in the aqueous phase but not the growing polymer radicals in PTFE particles, are most effective in increasing the molecular weight

Post-irradiation chemical reactions during devitrification of molecular matrices (review)

International Nuclear Information System (INIS)

Barkalov, I.M.; Kiryukhin, D.P.

1993-01-01

At temperatures above the melting point (mp) a material is in a thermodynamic equilibrium state, in which any thermodynamic function of state (specific volume, enthalpy, and entrophy) is governed unambiguously by the temperature, pressure, etc. At temperatures below the mp, the material is converted to another equilibrium state, i.e., a crystal. However, during rapid cooling, a state of a nonequilibrium supercooled liquid can be obtained. Further cooling of this state below the glass-transition temperature, T g1 , leads to the additional formation of a nonequilibrium solid amorphous state, often simply called glass. In the vitreous state, species are capable of only vibrational and small-scale rotational motions. The translational mobility that is characteristic of the liquid state is completely lost. Very important for what follows is the fact that the transition from a supercooled liquid to the vitreous state or the reverse transition (devitrification) is accompanied by a sharp change of properties: the viscosity changes by 10-15 orders of magnitude, the modulus of elasticity changes 10-1000 fold, the coefficient of thermal expansion changes 10-100 fold, etc. Most impressive is the gigantic viscosity jump in the narrow temperature-dependent glass-transition region. This means that the molecular mobility governing the chemical-transformation dynamics undergoes a sharp change in this region. The nature of the chemical process during passage through the glass-softening region should change because of a sharp change of the mobility of the reactants, with a huge change of molecular mobility being attained by a temperature change of only a few degrees. During radiolysis of vitreous matrices, active species of radical and ionic nature are formed. This review discusses the recombination reactions of radiolysis products during heating to the supercooled state

Development of a new free radical absorption capacity assay method for antioxidants: aroxyl radical absorption capacity (ARAC).

Science.gov (United States)

Nagaoka, Shin-ichi; Nagai, Kanae; Fujii, Yuko; Ouchi, Aya; Mukai, Kazuo

2013-10-23

A new free radical absorption capacity assay method is proposed with use of an aroxyl radical (2,6-di-tert-butyl-4-(4'-methoxyphenyl)phenoxyl radical) and stopped-flow spectroscopy and is named the aroxyl radical absorption capacity (ARAC) assay method. The free radical absorption capacity (ARAC value) of each tocopherol was determined through measurement of the radical-scavenging rate constant in ethanol. The ARAC value could also be evaluated through measurement of the half-life of the aroxyl radical during the scavenging reaction. For the estimation of the free radical absorption capacity, the aroxyl radical was more suitable than the DPPH radical, galvinoxyl, and p-nitrophenyl nitronyl nitroxide. The ARAC value in tocopherols showed the same tendency as the free radical absorption capacities reported previously, and the tendency was independent of an oxygen radical participating in the scavenging reaction and of a medium surrounding the tocopherol and oxygen radical. The ARAC value can be directly connected to the free radical-scavenging rate constant, and the ARAC method has the advantage of treating a stable and isolable radical (aroxyl radical) in a user-friendly organic solvent (ethanol). The ARAC method was also successfully applied to a palm oil extract. Accordingly, the ARAC method would be useful in free radical absorption capacity assay of antioxidative reagents and foods.

Legionella confirmation in cooling tower water

Science.gov (United States)

Farhat, Maha; Shaheed, Raja A.; Al-Ali, Haidar H.; Al-Ghamdi, Abdullah S.; Al-Hamaqi, Ghadeer M.; Maan, Hawraa S.; Al-Mahfoodh, Zainab A.; Al-Seba, Hussain Z.

2018-01-01

Objectives: To investigate the presence of Legionella spp in cooling tower water. Legionella proliferation in cooling tower water has serious public health implications as it can be transmitted to humans via aerosols and cause Legionnaires’ disease. Methods: Samples of cooling tower water were collected from King Fahd Hospital of the University (KFHU) (Imam Abdulrahman Bin Faisal University, 2015/2016). The water samples were analyzed by a standard Legionella culture method, real-time polymerase chain reaction (RT-PCR), and 16S rRNA next-generation sequencing. In addition, the bacterial community composition was evaluated. Results: All samples were negative by conventional Legionella culture. In contrast, all water samples yielded positive results by real-time PCR (105 to 106 GU/L). The results of 16S rRNA next generation sequencing showed high similarity and reproducibility among the water samples. The majority of sequences were Alpha-, Beta-, and Gamma-proteobacteria, and Legionella was the predominant genus. The hydrogen-oxidizing gram-negative bacterium Hydrogenophaga was present at high abundance, indicating high metabolic activity. Sphingopyxis, which is known for its resistance to antimicrobials and as a pioneer in biofilm formation, was also detected. Conclusion: Our findings indicate that monitoring of Legionella in cooling tower water would be enhanced by use of both conventional culturing and molecular methods. PMID:29436561

Proceedings: Cooling tower and advanced cooling systems conference

International Nuclear Information System (INIS)

1995-02-01

This Cooling Tower and Advanced Cooling Systems Conference was held August 30 through September 1, 1994, in St. Petersburg, Florida. The conference was sponsored by the Electric Power Research Institute (EPRI) and hosted by Florida Power Corporation to bring together utility representatives, manufacturers, researchers, and consultants. Nineteen technical papers were presented in four sessions. These sessions were devoted to the following topics: cooling tower upgrades and retrofits, cooling tower performance, cooling tower fouling, and dry and hybrid systems. On the final day, panel discussions addressed current issues in cooling tower operation and maintenance as well as research and technology needs for power plant cooling. More than 100 people attended the conference. This report contains the technical papers presented at the conference. Of the 19 papers, five concern cooling tower upgrades and retrofits, five to cooling tower performance, four discuss cooling tower fouling, and five describe dry and hybrid cooling systems. Selected papers are indexed separately for inclusion in the Energy Science and Technology Database

Physiology of free radicals

Directory of Open Access Journals (Sweden)

Stevanović Jelka

2011-01-01

Full Text Available Free radicals imply that every atom, molecule, ion, group of atoms, or molecules with one or several non-paired electrons in outer orbital. Among these are: nitrogenoxide (NO•, superoxide-anion-radical (O2•-, hydroxyl radical (OH•, peroxyl radical (ROO•, alcoxyl radical (RO• and hydroperoxyl radical (HO2•. However, reactive oxygen species also include components without non-paired electrons in outer orbital (so-called reactive non-radical agents, such as: singlet oxygen (1O2, peroxynitrite (ONOO-, hydrogen-peroxide (H2O2, hypochloric acid (eg. HOCl and ozone (O3. High concentrations of free radicals lead to the development of oxidative stress which is a precondition for numerous pathological effects. However, low and moderate concentrations of these matter, which occur quite normally during cell metabolic activity, play multiple significant roles in many reactions. Some of these are: regulation of signal pathways within the cell and between cells, the role of chemoattractors and leukocyte activators, the role in phagocytosis, participation in maintaining, changes in the position and shape of the cell, assisting the cell during adaption and recovery from damage (e.g.caused by physical effort, the role in normal cell growth, programmed cell death (apoptosis and cell ageing, in the synthesis of essential biological compounds and energy production, as well as the contribution to the regulation of the vascular tone, actually, tissue vascularization.

Carbon-centered radicals in γ-irradiated bone substituting biomaterials based on hydroxyapatite.

Science.gov (United States)

Sadlo, Jaroslaw; Strzelczak, Grazyna; Lewandowska-Szumiel, Malgorzata; Sterniczuk, Marcin; Pajchel, Lukasz; Michalik, Jacek

2012-09-01

Gamma irradiated synthetic hydroxyapatite, bone substituting materials NanoBone(®) and HA Biocer were examined using EPR spectroscopy and compared with powdered human compact bone. In every case, radiation-induced carbon centered radicals were recorded, but their molecular structures and concentrations differed. In compact bone and synthetic hydroxyapatite the main signal assigned to the CO(2) (-) anion radical was stable, whereas the signal due to the CO(3) (3-) radical dominated in NanoBone(®) and HA Biocer just after irradiation. However, after a few days of storage of these samples, also a CO(2) (-) signal was recorded. The EPR study of irradiated compact bone and the synthetic graft materials suggest that their microscopic structures are different. In FT-IR spectra of NanoBone(®), HA Biocer and synthetic hydroxyapatite the HPO(4) (2-) and CO(3) (2-) in B-site groups are detected, whereas in compact bone signals due to collagen dominate.

Engineering a horseradish peroxidase C stable to radical attacks by mutating multiple radical coupling sites.

Science.gov (United States)

Kim, Su Jin; Joo, Jeong Chan; Song, Bong Keun; Yoo, Young Je; Kim, Yong Hwan

2015-04-01

Peroxidases have great potential as industrial biocatalysts. In particular, the oxidative polymerization of phenolic compounds catalyzed by peroxidases has been extensively examined because of the advantage of this method over other conventional chemical methods. However, the industrial application of peroxidases is often limited because of their rapid inactivation by phenoxyl radicals during oxidative polymerization. In this work, we report a novel protein engineering approach to improve the radical stability of horseradish peroxidase isozyme C (HRPC). Phenylalanine residues that are vulnerable to modification by the phenoxyl radicals were identified using mass spectrometry analysis. UV-Vis and CD spectra showed that radical coupling did not change the secondary structure or the active site of HRPC. Four phenylalanine (Phe) residues (F68, F142, F143, and F179) were each mutated to alanine residues to generate single mutants to examine the role of these sites in radical coupling. Despite marginal improvement of radical stability, each single mutant still exhibited rapid radical inactivation. To further reduce inactivation by radical coupling, the four substitution mutations were combined in F68A/F142A/F143A/F179A. This mutant demonstrated dramatic enhancement of radical stability by retaining 41% of its initial activity compared to the wild-type, which was completely inactivated. Structure and sequence alignment revealed that radical-vulnerable Phe residues of HPRC are conserved in homologous peroxidases, which showed the same rapid inactivation tendency as HRPC. Based on our site-directed mutagenesis and biochemical characterization, we have shown that engineering radical-vulnerable residues to eliminate multiple radical coupling can be a good strategy to improve the stability of peroxidases against radical attack. © 2014 Wiley Periodicals, Inc.

Radical-lanthanide ferromagnetic interaction in a T bIII bis-phthalocyaninato complex

Science.gov (United States)

Komijani, Dorsa; Ghirri, Alberto; Bonizzoni, Claudio; Klyatskaya, Svetlana; Moreno-Pineda, Eufemio; Ruben, Mario; Soncini, Alessandro; Affronte, Marco; Hill, Stephen

2018-02-01

Recent studies have highlighted the importance of organic ligands in the field of molecular spintronics, via which delocalized electron-spin density can mediate magnetic coupling to otherwise localized 4 f moments of lanthanide ions, which show tremendous potential for single-molecule device applications. To this end, high-field/high-frequency electron paramagnetic resonance (EPR) spectroscopy is employed to study a neutral terbium bis-phthalocyaninato metalorganic complex, [TbPc2 ] 0, with the aim of understanding the magnetic interaction between the Ising-like moment of the lanthanide ion and the unpaired spin density on the coordinating organic radical ligand. The measurements were performed on a previously unknown [TbPc2 ] 0 structural phase crystallizing in the Pnma space group. EPR measurements on powder samples of [TbPc2 ] 0 reveal an anisotropic spectrum, which is attributed to the spin-1/2 radical coupled weakly to the EPR-silent T bIII ion. Extensive double-axis rotation studies on a single crystal reveal two independent spin-1/2 signals with differently oriented (albeit identical) uniaxial g -tensors, in complete agreement with x-ray structural studies that indicate two molecular orientations within the unit cell. The easy-axis nature of the radical EPR spectra thus reflects the coupling to the Ising-like T bIII moment. This is corroborated by studies of the isostructural [YPc2 ] 0 analog (where Y is nonmagnetic yttrium), which gives a completely isotropic radical EPR signal. The experimental results for the terbium complex are well explained on the basis of an effective model that introduces a weak ferromagnetic Heisenberg coupling between an isotropic spin-1/2 and an anisotropic spin-orbital moment, J =6 , that mimics the known, strong easy-axis Tb ⋯P c2 crystal-field interaction.

Vinylcyclopropylacyl and polyeneacyl radicals. Intramolecular ketene alkyl radical additions in ring synthesis.

Science.gov (United States)

De Boeck, Benoit; Herbert, Nicola M A; Harrington-Frost, Nicole M; Pattenden, Gerald

2005-01-21

Treatment of a variety of substituted vinylcyclopropyl selenyl esters, e.g. 11, with Bu(3)SnH-AIBN in refluxing benzene leads to the corresponding acyl radical intermediates, which undergo rearrangement and intramolecular cyclisations via their ketene alkyl radical equivalents producing cyclohexenones in 50-60% yield. By contrast, treatment of conjugated triene selenyl esters, e.g. 32, with Bu(3)SnH-AIBN produces substituted 2-cyclopentenones via intramolecular cyclisations of their ketene alkyl radical intermediates. Under the same radical-initiating conditions the selenyl esters derived from o-vinylbenzoic acid and o-vinylcinnamic acid undergo intramolecular cyclisations producing 1-indanone and 5,6-dihydrobenzocyclohepten-7-one respectively in 60-70% yields. A tandem radical cyclisation from the alpha,beta,gamma,delta-diene selenyl ester 31 provides an expeditious synthesis of the diquinane 35 in 69% yield.

Controlled radical polymerization of an acrylamide containing L-alanine moiety via ATRP.

Science.gov (United States)

Rafiee, Zahra

2016-02-01

Homopolymerization of an optically active acrylamide having an amino acid moiety in the side chain, N-acryloyl-L-alanine (AAla) was carried out via atom transfer radical polymerization (ATRP) at room temperature using 2-hydroxyethyl-2'-methyl-2'-bromopropionate (HMB) or sodium-4-(bromomethyl)benzoate (SBB) as initiator in pure water, methanol/water mixture and pure methanol solvents. The polymerization reaction resulted in the optically active biocompatible amino acid-based homopolymer in good yield with narrow molecular weight distribution. The number average molecular weight increased with conversion and polydispersity was low. The structure and molecular weight of synthesized polymer were characterized by (1)H NMR, FT-IR spectroscopic techniques and size-exclusion chromatography.

Molecular typing of Legionella pneumophila from air-conditioning cooling waters using mip gene, SBT, and FAFLP methods.

Science.gov (United States)

Gong, Xiangli; Li, Juntao; Zhang, Ying; Hou, Shuiping; Qu, Pinghua; Yang, Zhicong; Chen, Shouyi

2017-08-01

Legionella spp. are important waterborne pathogens. Molecular typing has become an important method for outbreaks investigations and source tracking of Legionnaires. In a survey program conducted by the Guangzhou Center for Disease Control and Prevention, multiple serotypes Legionella pneumophila (L. pneumophila) were isolated from waters in air-conditioning cooling towers in urban Guangzhou region, China between 2008 and 2011. Three genotyping methods, mip (macrophage infectivity potentiator) genotyping, SBT (sequence-based typing), and FAFLP (fluorescent amplified fragment length polymorphism analysis) were used to type these waterborne L. pneumophila isolates. The three methods were capable of typing all the 134 isolates and a reference strain of L. pneumophila (ATCC33153), with discriminatory indices of 0.7034, 0.9218, and 0.9376, for the mip, SBT, and FAFLP methods respectively. Among the 9 serotypes of the 134 isolates, 10, 50, and 34 molecular types were detected by the mip, SBT, and FAFLP methods respectively. The mip genotyping and SBT typing are more feasible for inter-laboratory results sharing and comparison of different types of L. pneumophila. The SBT and FAFLP typing methods were rapid with higher discriminatory abilities. Combinations of two or more of the typing methods enables more accurate typing of Legionella isolates for outbreak investigations and source tracking of Legionnaires. Copyright © 2017 Elsevier B.V. All rights reserved.

Serum Hydroxyl Radical Scavenging Capacity as Quantified with Iron-Free Hydroxyl Radical Source

Science.gov (United States)

Endo, Nobuyuki; Oowada, Shigeru; Sueishi, Yoshimi; Shimmei, Masashi; Makino, Keisuke; Fujii, Hirotada; Kotake, Yashige

2009-01-01

We have developed a simple ESR spin trapping based method for hydroxyl (OH) radical scavenging-capacity determination, using iron-free OH radical source. Instead of the widely used Fenton reaction, a short (typically 5 seconds) in situ UV-photolysis of a dilute hydrogen peroxide aqueous solution was employed to generate reproducible amounts of OH radicals. ESR spin trapping was applied to quantify OH radicals; the decrease in the OH radical level due to the specimen’s scavenging activity was converted into the OH radical scavenging capacity (rate). The validity of the method was confirmed in pure antioxidants, and the agreement with the previous data was satisfactory. In the second half of this work, the new method was applied to the sera of chronic renal failure (CRF) patients. We show for the first time that after hemodialysis, OH radical scavenging capacity of the CRF serum was restored to the level of healthy control. This method is simple and rapid, and the low concentration hydrogen peroxide is the only chemical added to the system, that could eliminate the complexity of iron-involved Fenton reactions or the use of the pulse-radiolysis system. PMID:19794928

Molecular fountain.

Energy Technology Data Exchange (ETDEWEB)

Strecker, Kevin E.; Chandler, David W.

2009-09-01

A molecular fountain directs slowly moving molecules against gravity to further slow them to translational energies that they can be trapped and studied. If the molecules are initially slow enough they will return some time later to the position from which they were launched. Because this round trip time can be on the order of a second a single molecule can be observed for times sufficient to perform Hz level spectroscopy. The goal of this LDRD proposal was to construct a novel Molecular Fountain apparatus capable of producing dilute samples of molecules at near zero temperatures in well-defined user-selectable, quantum states. The slowly moving molecules used in this research are produced by the previously developed Kinematic Cooling technique, which uses a crossed atomic and molecular beam apparatus to generate single rotational level molecular samples moving slowly in the laboratory reference frame. The Kinematic Cooling technique produces cold molecules from a supersonic molecular beam via single collisions with a supersonic atomic beam. A single collision of an atom with a molecule occurring at the correct energy and relative velocity can cause a small fraction of the molecules to move very slowly vertically against gravity in the laboratory. These slowly moving molecules are captured by an electrostatic hexapole guiding field that both orients and focuses the molecules. The molecules are focused into the ionization region of a time-of-flight mass spectrometer and are ionized by laser radiation. The new molecular fountain apparatus was built utilizing a new design for molecular beam apparatus that has allowed us to miniaturize the apparatus. This new design minimizes the volumes and surface area of the machine allowing smaller pumps to maintain the necessary background pressures needed for these experiments.

Theoretical investigation of radical species formed from L-α-alanine under gamma-irradiation

International Nuclear Information System (INIS)

Simion, C.

2008-01-01

Gamma-irradiated L-α-alanine used in EPR-coupled dosimetry has a complex EPR spectrum at room temperature. Changing the temperature or other conditions of the irradiated samples leads to varied EPR spectrum, i.e., some components disappear and/or new ones are formed. We used both molecular mechanics (MM+) and semiempirical (AM1) methods to perform a theoretical investigation of the seven radical species that have been experimentally detected. We established their order of priority in the given simulation conditions (at 0 K, in vacuo). The formation stages advanced for these long-lived radical species were characterized by a theoretical determination of the reaction enthalpies. (author)

Radical transfer between proteins: role of tyrosine, tryptophan and protein peroxyl radicals

International Nuclear Information System (INIS)

Irwin, J.A.; Ostdal, H.; Davies, M.J.

1998-01-01

Reaction of the Fe(III) forms of the heme proteins myoglobin (Mb) and horseradish peroxidase (HRP) with H 2 O 2 gives rise to high-oxidation-state heme-derived species which can be described as a Fe(IV)-oxo porphyrin radical-cation ('Compound 1'). In the case of Mb, the Fe(IV)-oxo porphyrin radical-cation undergoes rapid electron transfer with the surrounding protein to give protein (globin)-derived radicals and an Fe(lV)-oxo species ('Compound 2'). The globin-derived radicals have been shown to be located at two (or more) sites: Tyr-103 or Trp-14, with the latter radical known to react with oxygen to give a Trp-derived peroxyl radical (Mb-Trp-OO*). With HRP, the Fe(lV)-oxo porphyrin radical-cation carries out two successive one-electron oxidation reactions at the exposed heme edge to give firstly 'Compound 2' [the Fe(lV)oxo species] and then the resting Fe(III) state of the enzyme. n this study we have investigated whether the Trp-14 peroxyl radical from Mb and the Compound 1 and 2 species from HRP (in the absence and presence of free Tyr) can oxidise amino acids, peptides and proteins. Such reactions constitute intermolecular protein-to-protein radical transfer reactions and hence protein chain-oxidation. We have also examined whether these oxidants react with antioxidants. Reaction of these heme-protein derived oxidants with amino acids, proteins and antioxidants has been carried out at room temperature for defined periods of time before freeze-quenching to 77K to halt reaction. The radical species present in the reaction system at the time of freezing were subsequently examined by EPR spectroscopy at 77K. Three free amino acids, Tyr, Trp and Cys (with Cys the least efficient) have been shown to react rapidly with Mb-Trp-OO*, as evidenced by the loss of the characteristic EPR features of Mb-Trp-OO* on inclusion of increasing concentrations of the amino acids. All other amino acids are much less reactive. Evidence has also been obtained for (inefficient) hydrogen

Novel Water Soluble Chitosan Derivatives with 1,2,3-Triazolium and Their Free Radical-Scavenging Activity

Directory of Open Access Journals (Sweden)

Qing Li

2018-03-01

Full Text Available Chitosan is an abundant and renewable polysaccharide, which exhibits attractive bioactivities and natural properties. Improvement such as chemical modification of chitosan is often performed for its potential of providing high bioactivity and good water solubility. A new class of chitosan derivatives possessing 1,2,3-triazolium charged units by associating “click reaction” with efficient 1,2,3-triazole quaternization were designed and synthesized. Their free radical-scavenging activity against three free radicals was tested. The inhibitory property and water solubility of the synthesized chitosan derivatives exhibited a remarkable improvement over chitosan. It is hypothesized that triazole or triazolium groups enable the synthesized chitosan to possess obviously better radical-scavenging activity. Moreover, the scavenging activity against superoxide radical of chitosan derivatives with triazolium (IC50 < 0.01 mg mL−1 was more efficient than that of derivatives with triazole and Vitamin C. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH and hydroxyl radical-scavenging assay, the same pattern were observed, which should be related to the triazolium grafted at the periphery of molecular chains.

Homegrown religious radicalization

DEFF Research Database (Denmark)

Khawaja, Iram

It has been reported that a growing number of youngsters from Western Europe are engaging in conflicts motivated by religious and political conflicts in the Middle East. This paper explores the reasons behind this seemingly religious radicalization from the point of view of the youngsters...... youngsters and parents of youngsters who have chosen a radicalized path in life. The paper will shed light on how the sense of and yearning for belonging and recognition have to be taken into account in our understanding of homegrown religious radicalization...

Formation and properties of radicals in γ-irradiated molecular compounds of urea with dicarboxylic acids

International Nuclear Information System (INIS)

Kasparov, M.S.; Trofimov, V.I.

1978-01-01

Radiation chemical yields of paramagnetic centres and their nature have been studied as well as secondary reactions in channel inclusion compounds of urea with sebacic acid and in mixed crystals of urea with succinic acid. In inclusion compounds of urea with sebacic acid the yield exceeds additive at 77 K. In mixed crystals of urea with succinic acid the yield at 77 K is equal to additive. In mixed crystals at all temperatures quazistationary concentrations of radicals are lower than in pure succinic acid. In inclusion compounds quazistationary concentration of radicals are higher than in pure sebacic acid. It has been shown that in solid two-component systems, when the nature of the components is identical, the matrix structure exerts an essential influence on the radiolysis of the system

Microbial analysis of meatballs cooled with vacuum and conventional cooling.

Science.gov (United States)

Ozturk, Hande Mutlu; Ozturk, Harun Kemal; Koçar, Gunnur

2017-08-01

Vacuum cooling is a rapid evaporative cooling technique and can be used for pre-cooling of leafy vegetables, mushroom, bakery, fishery, sauces, cooked food, meat and particulate foods. The aim of this study was to apply the vacuum cooling and the conventional cooling techniques for the cooling of the meatball and to show the vacuum pressure effect on the cooling time, the temperature decrease and microbial growth rate. The results of the vacuum cooling and the conventional cooling (cooling in the refrigerator) were compared with each other for different temperatures. The study shows that the conventional cooling was much slower than the vacuum cooling. Moreover, the microbial growth rate of the vacuum cooling was extremely low compared with the conventional cooling. Thus, the lowest microbial growth occurred at 0.7 kPa and the highest microbial growth was observed at 1.5 kPa for the vacuum cooling. The mass loss ratio for the conventional cooling and vacuum cooling was about 5 and 9% respectively.

Spin-polarized transport properties of a pyridinium-based molecular spintronics device

Science.gov (United States)

Zhang, J.; Xu, B.; Qin, Z.

2018-05-01

By applying a first-principles approach based on non-equilibrium Green's functions combined with density functional theory, the transport properties of a pyridinium-based "radical-π-radical" molecular spintronics device are investigated. The obvious negative differential resistance (NDR) and spin current polarization (SCP) effect, and abnormal magnetoresistance (MR) are obtained. Orbital reconstruction is responsible for novel transport properties such as that the MR increases with bias and then decreases and that the NDR being present for both parallel and antiparallel magnetization configurations, which may have future applications in the field of molecular spintronics.

ESR studies of radiation induced radical products from linoleic acid and linolenic acid and the radioprotective effect by α-tocopherol

International Nuclear Information System (INIS)

Zhu Younan; Tu Tiecheng; Dong Jirong; Zhang Jiashan; Li Nianyun

1993-01-01

Primary radicals from the γ-radiolysis of air-saturated linoleic acid and linolenic acid at 77 K, and the subsequent secondary radicals appeared during the course of variable temperature elevation were investigated by ESR. The ESR spectrum from samples irradiated and observed at 77 K shows the presence of the radical anion doublet arise from the electron adducts of the carboxy groups and the poorly resolved broad singlet results from some carbon-centered radicals. Annealing to approximately 125 K which allows for molecular oxygen migration results in the formation of peroxyl radicals. At 247 K, the ESR spectrum is a multi-line pattern which is attributable to structure of the α-carbon radical superimposed on the pentadienyl radicals. The ESR spectra from linoleic acid-α-tocopherol and linolenic acid-α-tocopherol binary systems irradiated at 77 K and recorded at 140 K or 215 K revealed the characteristic similarity to that from α-tocopherol alone, no trace of ESR signal from either peroxyl or the composite pattern from superposition of pentadienyl radical and α-carbon radicals can be found out. Therefore α-tocopherol has exerted radioprotection effect on peroxidation of linoleic acid and linolenic acid

Laparoscopic radical trachelectomy.

Science.gov (United States)

Rendón, Gabriel J; Ramirez, Pedro T; Frumovitz, Michael; Schmeler, Kathleen M; Pareja, Rene

2012-01-01

The standard treatment for patients with early-stage cervical cancer has been radical hysterectomy. However, for women interested in future fertility, radical trachelectomy is now considered a safe and feasible option. The use of minimally invasive surgical techniques to perform this procedure has recently been reported. We report the first case of a laparoscopic radical trachelectomy performed in a developing country. The patient is a nulligravid, 30-y-old female with stage IB1 adenocarcinoma of the cervix who desired future fertility. She underwent a laparoscopic radical trachelectomy and bilateral pelvic lymph node dissection. The operative time was 340 min, and the estimated blood loss was 100mL. There were no intraoperative or postoperative complications. The final pathology showed no evidence of residual disease, and all pelvic lymph nodes were negative. At 20 mo of follow-up, the patient is having regular menses but has not yet attempted to become pregnant. There is no evidence of recurrence. Laparoscopic radical trachelectomy with pelvic lymphadenectomy in a young woman who desires future fertility may also be an alternative technique in the treatment of early cervical cancer in developing countries.

Cooling techniques

International Nuclear Information System (INIS)

Moeller, S.P.

1994-01-01

After an introduction to the general concepts of cooling of charged particle beams, some specific cooling methods are discussed, namely stochastic, electron and laser cooling. The treatment concentrates on the physical ideas of the cooling methods and only very crude derivations of cooling times are given. At the end three other proposed cooling schemes are briefly discussed. (orig.)

Effect of Inhibitors on Atom Transfer Radical Polymerization of MMA

Institute of Scientific and Technical Information of China (English)

张鸿; 徐冬梅; 张可达

2005-01-01

Effect of a series of inhibitors as additives on atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with FeCl2/PPh3 as catalyst system was studied, including 2,4,6-trinitrophenol (TNP), 4-methoxyphenol (4-MP), hydroquinone (HQ) and nitrobenzene (NB). It was found that TNP was the only. efficient additive for ATRP among these inhibitors. In the presence of small amounts of TNP, the polymerization proceeded rapidly after induction period to yield the polymers with controlled molecular weights and narrow molecular weight distributions (MWD). The initiating efficiency of the modified catalyst system with TNP was increased. The mechanism was proposed and confirmed by the end group analysis of the polymer.

Radical Evil

Directory of Open Access Journals (Sweden)

Carlos Manrique

2007-12-01

Full Text Available There is an aporia in Kant’s analysis of evil: he defines radical evilas an invisible disposition of the will, but he also demands an inferential connection between visible evil actions and this invisible disposition. This inference,however, undermines the radical invisibility of radical evil according to Kant’s own definition of the latter. Noting how this invisibility of moral worth is a distinctive feature of Kant’s approach to the moral problem, the paper then asks why, in the Groundwork, he nonetheless forecloses a question about evil that seems to be consistent with this approach. It is argued that to account for this aporia and this foreclosure, one has to interrogate the way in which the category of religion orients Kant’s incipient philosophy of history in Die Religion.

Prevalence and Molecular Characteristics of Waterborne Pathogen Legionella in Industrial Cooling Tower Environments.

Science.gov (United States)

Li, Lijie; Qin, Tian; Li, Yun; Zhou, Haijian; Song, Hongmei; Ren, Hongyu; Li, Liping; Li, Yongguang; Zhao, Dong

2015-10-12

Cooling towers are a source of Legionnaires' disease. It is important from a public health perspective to survey industrial cooling towers for the presence of Legionella. Prospective surveillance of the extent of Legionella pollution was conducted at factories in Shijiazhuang, China between March 2011 and September 2012. Overall, 35.7% of 255 industrial cooling tower water samples showed Legionella-positive, and their concentrations ranged from 100 Colony-Forming Units (CFU)/liter to 88,000 CFU/liter, with an average concentration of 9100 CFU/liter. A total of 121 isolates were obtained. All isolates were L. pneumophila, and the isolated serogroups included serogroups 1 (68 isolates, 56.2%), 6 (25, 20.7%), 5 (12, 9.9%), 8 (8, 6.6%), 3 (6, 5.0%) and 9 (2, 1.6%). All 121 isolates were analyzed by pulsed-field gel electrophoresis (PFGE) and 64 different patterns were obtained. All 121 isolates were analyzed sequence-based typing (SBT), a full 7-allele profile was obtained from 117 isolates. One hundred and seventeen isolates were divided into 49 sequence types. Two virulence genes, lvh and rtxA, are analyzed by polymerase chain reaction (PCR). 92.6% (112/121) and 98.3% (119/121) isolates carried lvh and rtxA respectively and 90.9% (110/121) of tested isolates carried both genes. Our results demonstrated high prevalence and genetic polymorphism of L. pneumophila in industrial cooling tower environments in Shijiazhang, China, and the SBT and virulence gene PCR results suggested that the isolates were pathogenic. Improved control and prevention strategies are urgently needed.

Prevalence and Molecular Characteristics of Waterborne Pathogen Legionella in Industrial Cooling Tower Environments

Directory of Open Access Journals (Sweden)

Lijie Li

2015-10-01

Full Text Available Cooling towers are a source of Legionnaires’ disease. It is important from a public health perspective to survey industrial cooling towers for the presence of Legionella. Prospective surveillance of the extent of Legionella pollution was conducted at factories in Shijiazhuang, China between March 2011 and September 2012. Overall, 35.7% of 255 industrial cooling tower water samples showed Legionella-positive, and their concentrations ranged from 100 Colony-Forming Units (CFU/liter to 88,000 CFU/liter, with an average concentration of 9100 CFU/liter. A total of 121 isolates were obtained. All isolates were L. pneumophila, and the isolated serogroups included serogroups 1 (68 isolates, 56.2%, 6 (25, 20.7%, 5 (12, 9.9%, 8 (8, 6.6%, 3 (6, 5.0% and 9 (2, 1.6%. All 121 isolates were analyzed by pulsed-field gel electrophoresis (PFGE and 64 different patterns were obtained. All 121 isolates were analyzed sequence-based typing (SBT, a full 7-allele profile was obtained from 117 isolates. One hundred and seventeen isolates were divided into 49 sequence types. Two virulence genes, lvh and rtxA, are analyzed by polymerase chain reaction (PCR. 92.6% (112/121 and 98.3% (119/121 isolates carried lvh and rtxA respectively and 90.9% (110/121 of tested isolates carried both genes. Our results demonstrated high prevalence and genetic polymorphism of L. pneumophila in industrial cooling tower environments in Shijiazhang, China, and the SBT and virulence gene PCR results suggested that the isolates were pathogenic. Improved control and prevention strategies are urgently needed.

Radical constructivism: Between realism and solipsism

Science.gov (United States)

Martínez-Delgado, Alberto

2002-11-01

This paper criticizes radical constructivism of the Glasersfeld type, pointing out some contradictions between the declared radical principles and their theoretical and practical development. These contradictions manifest themselves in a frequent oscillation between solipsism and realism, despite constructivist claims to be an anti-realist theory. The paper also points out the contradiction between the relativism of the radical constructivist principles and the constructivist exclusion of other epistemological or educational paradigms. It also disputes the originality and importance of the radical constructivist paradigm, suggesting the idea of an isomorphism between radical constructivist theory and contemplative realism. In addition, some pedagogical and scientific methodological aspects of the radical constructivist model are examined. Although radical constructivism claims to be a rational theory and advocates deductive thinking, it is argued that there is no logical deductive connection between the radical principles of constructivism and the radical constructivist ideas about scientific research and learning. The paper suggests the possibility of an ideological substratum in the construction and hegemonic success of subjective constructivism and, finally, briefly advances an alternative realist model to epistemological and educational radical constructivism.

Modification of Ultra-High Vacuum Surfaces Using Free Radicals

CERN Document Server

Vorlaufer, G

2002-01-01

In ultra-high vacuum systems outgassing from vacuum chamber walls and desorption of surface adsorbates are usually the factors which determine pressure and residual gas composition. In particular in beam vacuum systems of accelerators like the LHC, where surfaces are exposed to intense synchrotron radiation and bombardment by energetic ions and electrons, surface properties like the molecular desorption yield or secondary electron yield can strongly influence the performance of the accelerator. Well-established treatment methods like vacuum bake-out or glow-discharge cleaning have been successfully applied in the past to condition ultra-high vacuum surfaces, but these methods are sometimes difficult to carry out, for example if the vacuum chambers are not accessible. In this work, an alternative treatment method is investigated. This method is based on the strong chemical reactivity of free radicals, electrically neutral fragments of molecules. Free radicals (in the case of this work, nitrogen and oxygen radi...

Molybdenum disulfide for ultra-low detection of free radicals: electrochemical response and molecular modeling

Science.gov (United States)

Gupta, Ankur; Rawal, Takat B.; Neal, Craig J.; Das, Soumen; Rahman, Talat S.; Seal, Sudipta

2017-06-01

Two-dimensional (2D) molybdenum disulfide (MoS2) offers attractive properties due to its band gap modulation and has led to significant research-oriented applications (i.e. DNA and protein detection, cell imaging (fluorescent label) etc.). In biology, detection of free radicals (i.e. reactive oxygen species and reactive nitrogen (NO*) species are very important for early discovery and treatment of diseases. Herein, for the first time, we demonstrate the ultra-low (pico-molar) detection of pharmaceutically relevant free radicals using MoS2 for electrochemical sensing. We present pico- to nano- molar level sensitivity in smaller MoS2 with S-deficiency as revealed by x-ray photoelectron spectroscopy. Furthermore, the detection mechanism and size-dependent sensitivity have been investigated by density functional theory (DFT) showing the change in electronic density of states of Mo atoms at edges which lead to the preferred adsorption of H2O2 on Mo edges. The DFT analysis signifies the role of size and S-deficiency in the higher catalytic activity of smaller MoS2 particles and, thus, ultra-low detection.

Effect of free radicals and cultivation media on radiation sensitivities of escherichia coli and related bacteria

International Nuclear Information System (INIS)

Ito, Hitoshi

2000-01-01

Effects of gamma-irradiation on some strains of Escherichia coli, Salmonella enteritidis and Staphylococcus aureus were investigated in the presence of N 2 , N 2 O and O 2 and with the hydroxyl radical (OH) scavengers glycerol, polyethylene glycerol and formate. Injured cell membrane of bacteria was detected using with MacConkey agar for E. coli and S. enteritidis and 7% NaCl Triptic soy agar for St. aureus instead of Tryptic soy agar for recovery medium. From this study, addition of glycerol significantly reduced the sensitivity in all of strains, and cell membrane was not injured significantly except in radiation sensitive strain E. coli A4-1. When superoxide radicals (O 2 ) were generated during irradiation in the presence of formate, injured cell membrane increased significantly in all of strains. However, molecular oxygen (O 2 ) and OH radicals also had some effects on the damage of cell membrane. These results suggest that most radiation induced cell lethality was responsible to the cooperative effects of intracellular OH radicals and O 2 on DNA with lessor effect of damage on cell membrane by O 2 radicals, O 2 and OH radicals. On the radiation sensitive strain of E. coli, cell lethality occurred significantly by the injury of cell membrane compared with other strains. (author)

Spin polarization and magnetic effects in radical reactions

International Nuclear Information System (INIS)

Salikhov, K.M.; Molin, Yu.N.; Sagdeev, R.Z.; Buchachenko, A.L.

1984-01-01

Studies on the effects of chemically induced dynamic nuclear and electron polarizations (CIDNP and CIDEP), and magnetic effects in radical reactions, have given rise to a new rapidly-progressing field of chemical physics. It came into being about ten years ago and has been attracting the ever-growing attention of researchers in related areas. The present book is a fairly all-embracing review of the state of affairs in this field. The book presents the physical background (both theoretical and experimental) of CIDNP and CIDEP, of the effects of an external magnetic field and magnetic nuclear moment (magnetic isotope effects) on radical reactions in solutions. Great attention has been paid to the application of chemical spin polarization and magnetic effects to solving various problems of chemical kinetics, structural chemistry, molecular physics, magnetobiology, and radiospectroscopy. The book will be useful for physicists, chemists and biologists employing CIDNP, CIDEP and magnetic effects in their investigations, as well as for researchers in related fields of chemical physics. The book can be also recommended for postgraduates and senior undergraduate students. (Auth.)

Salvage robotic radical prostatectomy

Directory of Open Access Journals (Sweden)

Samuel D Kaffenberger

2014-01-01

Full Text Available Failure of non-surgical primary treatment for localized prostate cancer is a common occurrence, with rates of disease recurrence ranging from 20% to 60%. In a large proportion of patients, disease recurrence is clinically localized and therefore potentially curable. Unfortunately, due to the complex and potentially morbid nature of salvage treatment, radical salvage surgery is uncommonly performed. In an attempt to decrease the morbidity of salvage therapy without sacrificing oncologic efficacy, a number of experienced centers have utilized robotic assistance to perform minimally invasive salvage radical prostatectomy. Herein, we critically evaluate the existing literature on salvage robotic radical prostatectomy with a focus on patient selection, perioperative complications and functional and early oncologic outcomes. These results are compared with contemporary and historical open salvage radical prostatectomy series and supplemented with insights we have gained from our experience with salvage robotic radical prostatectomy. The body of evidence by which conclusions regarding the efficacy and safety of robotic salvage radical prostatectomy can be drawn comprises fewer than 200 patients with limited follow-up. Preliminary results are promising and some outcomes have been favorable when compared with contemporary open salvage prostatectomy series. Advantages of the robotic platform in the performance of salvage radical prostatectomy include decreased blood loss, short length of stay and improved visualization. Greater experience is required to confirm the long-term oncologic efficacy and functional outcomes as well as the generalizability of results achieved at experienced centers.

Muoniated acyl and thioacyl radicals

International Nuclear Information System (INIS)

McKenzie, Iain; Brodovitch, Jean-Claude; Ghandi, Khashayar; Percival, Paul W.

2006-01-01

The product of the reaction of muonium with tert-butylisocyanate was previously assigned as the muoniated tert-butylaminyl radical (I. McKenzie, J.-C. Brodovitch, K. Ghandi, S. Kecman, P. W. Percival, Physica B 326 (2003) 76). This assignment is incorrect since the muon and 14 N hyperfine-coupling constants (hfcc) of this radical would have the opposite sign, which is in conflict with the experimental results. The radical is now reassigned as the muoniated N-tert-butylcarbamoyl radical, based on the similarities between the experimental muon and 14 N hfcc and hfcc calculated at the UB3LYP/6-311G(d,p)//UB3LYP/EPR-III level. The large zero-point energy in the N-Mu bond results in the dissociation barrier of the muoniated N-tert-butylcarbamoyl radical being above the combined energy of the reactants, in contrast to the N-tert-butylcarbamoyl radical where the dissociation barrier lies below the combined energy of the reactants. The reaction of muonium with tert-butylisothiocyanate produced both conformers of the muoniated N-tert-butylthiocarbamoyl radical and their assignment was based on the similarities between the experimental and calculated muon hfcc. These are the first acyl and thioacyl radicals to be directly detected by muon spin spectroscopy

Muoniated acyl and thioacyl radicals

Energy Technology Data Exchange (ETDEWEB)

McKenzie, Iain [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada); Brodovitch, Jean-Claude [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada); Ghandi, Khashayar [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada); Percival, Paul W. [TRIUMF and Department of Chemistry, 8888 University Drive, Simon Fraser University, Burnaby B.C., V5A 1S6 (Canada)]. E-mail: percival@sfu.ca

2006-03-31

The product of the reaction of muonium with tert-butylisocyanate was previously assigned as the muoniated tert-butylaminyl radical (I. McKenzie, J.-C. Brodovitch, K. Ghandi, S. Kecman, P. W. Percival, Physica B 326 (2003) 76). This assignment is incorrect since the muon and {sup 14}N hyperfine-coupling constants (hfcc) of this radical would have the opposite sign, which is in conflict with the experimental results. The radical is now reassigned as the muoniated N-tert-butylcarbamoyl radical, based on the similarities between the experimental muon and {sup 14}N hfcc and hfcc calculated at the UB3LYP/6-311G(d,p)//UB3LYP/EPR-III level. The large zero-point energy in the N-Mu bond results in the dissociation barrier of the muoniated N-tert-butylcarbamoyl radical being above the combined energy of the reactants, in contrast to the N-tert-butylcarbamoyl radical where the dissociation barrier lies below the combined energy of the reactants. The reaction of muonium with tert-butylisothiocyanate produced both conformers of the muoniated N-tert-butylthiocarbamoyl radical and their assignment was based on the similarities between the experimental and calculated muon hfcc. These are the first acyl and thioacyl radicals to be directly detected by muon spin spectroscopy.

Investigation of the O+allyl addition/elimination reaction pathways from the OCH2CHCH2 radical intermediate

International Nuclear Information System (INIS)

FitzPatrick, Benjamin L.; Lau, K.-C.; Butler, Laurie J.; Lee, S.-H.; Lin, Jim Jr-Min

2008-01-01

These experiments study the preparation of and product channels resulting from OCH 2 CHCH 2 , a key radical intermediate in the O+allyl bimolecular reaction. The data include velocity map imaging and molecular beam scattering results to probe the photolytic generation of the radical intermediate and the subsequent pathways by which the radicals access the energetically allowed product channels of the bimolecular reaction. The photodissociation of epichlorohydrin at 193.3 nm produces chlorine atoms and c-OCH 2 CHCH 2 radicals; these undergo a facile ring opening to the OCH 2 CHCH 2 radical intermediate. State-selective resonance-enhanced multiphoton ionization (REMPI) detection resolves the velocity distributions of ground and spin-orbit excited state chlorine independently, allowing for a more accurate determination of the internal energy distribution of the nascent radicals. We obtain good agreement detecting the velocity distributions of the Cl atoms with REMPI, vacuum ultraviolet (VUV) photoionization at 13.8 eV, and electron bombardment ionization; all show a bimodal distribution of recoil kinetic energies. The dominant high recoil kinetic energy feature peaks near 33 kcal/mol. To elucidate the product channels resulting from the OCH 2 CHCH 2 radical intermediate, the crossed laser-molecular beam experiment uses VUV photoionization and detects the velocity distribution of the possible products. The data identify the three dominant product channels as C 3 H 4 O (acrolein)+H, C 2 H 4 +HCO (formyl radical), and H 2 CO (formaldehyde)+C 2 H 3 . A small signal from C 2 H 2 O (ketene) product is also detected. The measured velocity distributions and relative signal intensities at m/e=27, 28, and 29 at two photoionization energies show that the most exothermic product channel, C 2 H 5 +CO, does not contribute significantly to the product branching. The higher internal energy onset of the acrolein+H product channel is consistent with the relative barriers en route to

Investigation of the O+allyl addition/elimination reaction pathways from the OCH2CHCH2 radical intermediate

Science.gov (United States)

Fitzpatrick, Benjamin L.; Lau, Kai-Chung; Butler, Laurie J.; Lee, Shih-Huang; Lin, Jim-Min, Jr.

2008-08-01

These experiments study the preparation of and product channels resulting from OCH2CHCH2, a key radical intermediate in the O+allyl bimolecular reaction. The data include velocity map imaging and molecular beam scattering results to probe the photolytic generation of the radical intermediate and the subsequent pathways by which the radicals access the energetically allowed product channels of the bimolecular reaction. The photodissociation of epichlorohydrin at 193.3 nm produces chlorine atoms and c-OCH2CHCH2 radicals; these undergo a facile ring opening to the OCH2CHCH2 radical intermediate. State-selective resonance-enhanced multiphoton ionization (REMPI) detection resolves the velocity distributions of ground and spin-orbit excited state chlorine independently, allowing for a more accurate determination of the internal energy distribution of the nascent radicals. We obtain good agreement detecting the velocity distributions of the Cl atoms with REMPI, vacuum ultraviolet (VUV) photoionization at 13.8 eV, and electron bombardment ionization; all show a bimodal distribution of recoil kinetic energies. The dominant high recoil kinetic energy feature peaks near 33 kcal/mol. To elucidate the product channels resulting from the OCH2CHCH2 radical intermediate, the crossed laser-molecular beam experiment uses VUV photoionization and detects the velocity distribution of the possible products. The data identify the three dominant product channels as C3H4O (acrolein)+H, C2H4+HCO (formyl radical), and H2CO (formaldehyde)+C2H3. A small signal from C2H2O (ketene) product is also detected. The measured velocity distributions and relative signal intensities at m/e=27, 28, and 29 at two photoionization energies show that the most exothermic product channel, C2H5+CO, does not contribute significantly to the product branching. The higher internal energy onset of the acrolein+H product channel is consistent with the relative barriers en route to each of these product channels

Rotationally inelastic scattering of methyl radicals with Ar and N{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Tkáč, Ondřej; Orr-Ewing, Andrew J., E-mail: a.orr-ewing@bristol.ac.uk [School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS (United Kingdom); Ma, Qianli; Dagdigian, Paul J., E-mail: pjdagdigian@jhu.edu [Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685 (United States); Stei, Martin [Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck (Austria)

2015-01-07

The rotationally inelastic scattering of methyl radical with Ar and N{sub 2} is examined at collision energies of 330 ± 25 cm{sup −1} and 425 ± 50 cm{sup −1}, respectively. Differential cross sections (DCSs) were measured for different final n′ rotational levels (up to n′ = 5) of the methyl radicals, averaged over k′ sub-levels, using a crossed molecular beam machine with velocity map imaging. For Ar as a collision partner, we present a newly constructed ab initio potential energy surface and quantum mechanical scattering calculations of state-resolved DCSs. These computed DCSs agree well with the measurements. The DCSs for both Ar and N{sub 2} collision partners are strongly forward peaked for all spectroscopic lines measured. For scattering angles below 60°, the theoretical CD{sub 3}–Ar DCSs show diffraction oscillations that become less pronounced as n′ increases, but these oscillations are not resolved experimentally. Comparisons are drawn with our recently reported DCSs for scattering of methyl radicals with He atoms.

Muonium and muonic radicals

International Nuclear Information System (INIS)

Burkhard, P.; Fischer, H.; Roduner, E.; Strub, W.; Geeson, D.; Symons, M.C.R.

1985-01-01

An energetic positive muon which is injected in a liquid sample of substrate molecules (S) creates an ionization track consisting of substrate cations (S + ) and electrons. Near the end of this track the muon may combine with an electron to form muonium (Mu) which is observable in inert liquids, but which reacts by addition to form a radical. Alternatively, the electron can add to S to form S - , which then combines with the muon to form the radical. Furthermore, instead of ending up in Mu or in a radical the muon may stay in a diamagnetic environment as a solvated muon, or as a muon substituting a proton in a molecule. Of interest in these schemes are the mechanisms and rates of formation of muonated radicals and in particular the rate constants for their reactions to products. Investigations are based on the observation of Mu and the radical by means of the μSR technique in transverse magnetic fields. (Auth.)

Study of the hydroxyl radical: Experimental advances in microwave spectroscopy, theoretical model and astrophysical consequences

International Nuclear Information System (INIS)

Destombes, Jean-Luc

1978-01-01

This research thesis mainly addresses the experimental and theoretical study of the hydroxyl radical, and the consequences of the obtained results in astrophysics which are studied with a model of pumping by the far infrared. After a recall of notions related to microwave spectroscopy and to molecular radio-astronomy, the author more particularly discusses different aspects of microwave spectroscopy in the interstellar environment and in laboratory. He also reviews different types of spectrometers for unsteady molecules. In the second part, he addresses issues related to the hydroxyl radical (OH): presentation of spectrometers, study of the reaction environment, study of the radical microwave spectrum, identification of transitions by frequency measurements. In the last parts, the author addresses some aspects of interstellar OH masers, and reports the application of some results to simple models of pumping by the far infra red

Flavonoids from Agrimonia pilosa Ledeb: Free Radical Scavenging and DNA Oxidative Damage Protection Activities and Analysis of Bioactivity-Structure Relationship Based on Molecular and Electronic Structures.

Science.gov (United States)

Zhu, Liancai; Chen, Jinqiu; Tan, Jun; Liu, Xi; Wang, Bochu

2017-02-26

To clarify the substantial basis of the excellent antioxidant capacity of Agrimonia pilosa Ledeb. Fourteen flavonoids were isolated and identified from Agrimonia pilosa Ledeb, seven of which have notable DPPH radical scavenging activities, i.e., catechin, luteolin, quercetin, quercitrin, hyperoside, rutin, luteolin-7- O -β-glucoside with IC 50 values of 5.06, 7.29, 4.36, 7.12, 6.34, 6.36 and 8.12 µM, respectively. The DNA nicking assay showed that five flavonoids from Agrimonia pilosa Ledeb-taxifolin, catechin, hyperoside, quercitrin and rutin-have good protective activity against DNA oxidative damage. Further, we analyzed the bioactivity-structure relationship of these 14 flavonoids by applying quantum theory. According to their O-H bond dissociation enthalpy (BDE), C ring's spin density and stable molecular structure, the relationship between their structures and radical scavenging capacities was evaluated and clarified. We found that among flavonoid aglycones from Agrimonia pilosa Ledeb, the O-H BDE of quercetin is lowest with the values of 69.02 and the O-H BDE of apigenin is highest with the values of 79.77. It is interesting that the O-H BDE value of isovitexin (78.55) with glycoside at C-6 position is lower than that of its aglycone (79.77) and vitexin (99.20) with glycoside at C-8 position. Further analysis indicated that the glycosidation of flavonoids at C-6 in the A-ring makes a more uniform distribution of spin density and improves the stability of free radicals leading to the increase in antioxidant capacity. Flavonoids with good antioxidant capacity might contribute to the pharmacological effects of Agrimonia pilosa Ledeb.

Flavonoids from Agrimonia pilosa Ledeb: Free Radical Scavenging and DNA Oxidative Damage Protection Activities and Analysis of Bioactivity-Structure Relationship Based on Molecular and Electronic Structures

Directory of Open Access Journals (Sweden)

Liancai Zhu

2017-02-01

Full Text Available To clarify the substantial basis of the excellent antioxidant capacity of Agrimonia pilosa Ledeb. Fourteen flavonoids were isolated and identified from Agrimonia pilosa Ledeb, seven of which have notable DPPH radical scavenging activities, i.e., catechin, luteolin, quercetin, quercitrin, hyperoside, rutin, luteolin-7-O-β-glucoside with IC50 values of 5.06, 7.29, 4.36, 7.12, 6.34, 6.36 and 8.12 µM, respectively. The DNA nicking assay showed that five flavonoids from Agrimonia pilosa Ledeb—taxifolin, catechin, hyperoside, quercitrin and rutin—have good protective activity against DNA oxidative damage. Further, we analyzed the bioactivity-structure relationship of these 14 flavonoids by applying quantum theory. According to their O-H bond dissociation enthalpy (BDE, C ring’s spin density and stable molecular structure, the relationship between their structures and radical scavenging capacities was evaluated and clarified. We found that among flavonoid aglycones from Agrimonia pilosa Ledeb, the O-H BDE of quercetin is lowest with the values of 69.02 and the O-H BDE of apigenin is highest with the values of 79.77. It is interesting that the O-H BDE value of isovitexin (78.55 with glycoside at C-6 position is lower than that of its aglycone (79.77 and vitexin (99.20 with glycoside at C-8 position. Further analysis indicated that the glycosidation of flavonoids at C-6 in the A-ring makes a more uniform distribution of spin density and improves the stability of free radicals leading to the increase in antioxidant capacity. Flavonoids with good antioxidant capacity might contribute to the pharmacological effects of Agrimonia pilosa Ledeb.

Cooling rate effects on structure of amorphous graphene

International Nuclear Information System (INIS)

Van Hoang, Vo

2015-01-01

Simple monatomic amorphous 2D models with Honeycomb structure are obtained from 2D simple monatomic liquids with Honeycomb interaction potential (Rechtsman et al., Phys. Rev. Lett. 95, 228301 (2005)) via molecular dynamics (MD) simulations. Models are observed by cooling from the melt at various cooling rates. Temperature dependence of thermodynamic and structural properties including total energy, mean ring size, mean coordination number is studied in order to show evolution of structure and thermodynamics upon cooling from the melt. Structural properties of the amorphous Honeycomb structures are studied via radial distribution function (RDF), coordination number and ring distributions together with 2D visualization of the atomic configurations. Amorphous Honeycomb structures contain a large amount of structural defects including new ones which have not been previously reported yet. Cooling rate dependence of structural properties of the obtained amorphous Honeycomb structures is analyzed. Although amorphous graphene has been proposed theoretically and/or recently obtained by the experiments, our understanding of structural properties of the system is still poor. Therefore, our simulations highlight the situation and give deeper understanding of structure and thermodynamics of the glassy state of this novel 2D material

Leghemoglobin-derived radicals. Evidence for multiple protein-derived radicals and the initiation of peribacteroid membrane damage

DEFF Research Database (Denmark)

Moreau, S; Davies, Michael Jonathan; Mathieu, C

1996-01-01

, with the consequent generation of lipid-derived radicals. The formation of such radicals may result in the depletion of membrane antioxidants and the initiation of lipid peroxidation. This transfer of damage from the heme center via the protein surface to neighboring membranes may be of considerable biological......-derived phenoxyl radical present at Tyr-133 in the soybean protein and Tyr-138 in the lupin protein. To obtain further information on these protein radicals and their potential interaction with the physiologically important peribacteroid membrane (which surrounds the microsymbiont in vivo), EPR spin trapping......); these radicals may be side chain- or alpha-carbon-derived, their exact sites have not been determined. Some of these radicals are on the protein surface and may be key intermediates in the formation of protein dimers. These radicals have been shown to be capable of reacting with peribacteroid membrane fractions...

Comparing Social Stories™ to Cool versus Not Cool

Science.gov (United States)

Leaf, Justin B.; Mitchell, Erin; Townley-Cochran, Donna; McEachin, John; Taubman, Mitchell; Leaf, Ronald

2016-01-01

In this study we compared the cool versus not cool procedure to Social Stories™ for teaching various social behaviors to one individual diagnosed with autism spectrum disorder. The researchers randomly assigned three social skills to the cool versus not cool procedure and three social skills to the Social Stories™ procedure. Naturalistic probes…

OKN-007 decreases free radical levels in a preclinical F98 rat glioma model.

Science.gov (United States)

Coutinho de Souza, Patricia; Smith, Nataliya; Atolagbe, Oluwatomisin; Ziegler, Jadith; Njoku, Charity; Lerner, Megan; Ehrenshaft, Marilyn; Mason, Ronald P; Meek, Bill; Plafker, Scott M; Saunders, Debra; Mamedova, Nadezda; Towner, Rheal A

2015-10-01

Free radicals are associated with glioma tumors. Here, we report on the ability of an anticancer nitrone compound, OKN-007 [Oklahoma Nitrone 007; a disulfonyl derivative of α-phenyl-tert-butyl nitrone (PBN)] to decrease free radical levels in F98 rat gliomas using combined molecular magnetic resonance imaging (mMRI) and immunospin-trapping (IST) methodologies. Free radicals are trapped with the spin-trapping agent, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), to form DMPO macromolecule radical adducts, and then further tagged by immunospin trapping by an antibody against DMPO adducts. In this study, we combined mMRI with a biotin-Gd-DTPA-albumin-based contrast agent for signal detection with the specificity of an antibody for DMPO nitrone adducts (anti-DMPO probe), to detect in vivo free radicals in OKN-007-treated rat F98 gliomas. OKN-007 was found to significantly decrease (P free radical levels detected with an anti-DMPO probe in treated animals compared to untreated rats. Immunoelectron microscopy was used with gold-labeled antibiotin to detect the anti-DMPO probe within the plasma membrane of F98 tumor cells from rats administered anti-DMPO in vivo. OKN-007 was also found to decrease nuclear factor erythroid 2-related factor 2, inducible nitric oxide synthase, 3-nitrotyrosine, and malondialdehyde in ex vivo F98 glioma tissues via immunohistochemistry, as well as decrease 3-nitrotyrosine and malondialdehyde adducts in vitro in F98 cells via ELISA. The results indicate that OKN-007 effectively decreases free radicals associated with glioma tumor growth. Furthermore, this method can potentially be applied toward other types of cancers for the in vivo detection of macromolecular free radicals and the assessment of antioxidants. Copyright © 2015. Published by Elsevier Inc.

Muonium-containing vinyl radicals

International Nuclear Information System (INIS)

Rhodes, C.J.; Symons, M.C.R.; Roduner, E.; Heming, M.

1987-01-01

Exposure of trimethylsilylacetylene and bis(trimethylsilyl)acetylene to positive muons gave radicals whose muon-electron hyperfine coupling constants establish that the corresponding vinyl radicals were formed. (author)

Dissociative Photoionization of the Elusive Vinoxy Radical.

Science.gov (United States)

Adams, Jonathan D; Scrape, Preston G; Lee, Shih-Huang; Butler, Laurie J

2017-08-24

These experiments report the dissociative photoionization of vinoxy radicals to m/z = 15 and 29. In a crossed laser-molecular beam scattering apparatus, we induce C-Cl bond fission in 2-chloroacetaldehyde by photoexcitation at 157 nm. Our velocity measurements, combined with conservation of angular momentum, show that 21% of the C-Cl photofission events form vinoxy radicals that are stable to subsequent dissociation to CH 3 + CO or H + ketene. Photoionization of these stable vinoxy radicals, identified by their velocities, which are momentum-matched with the higher-kinetic-energy Cl atom photofragments, shows that the vinoxy radicals dissociatively photoionize to give signal at m/z = 15 and 29. We calibrated the partial photoionization cross section of vinoxy to CH 3 + relative to the bandwidth-averaged photoionization cross section of the Cl atom at 13.68 eV to put the partial photoionization cross sections on an absolute scale. The resulting bandwidth-averaged partial cross sections are 0.63 and 1.3 Mb at 10.5 and 11.44 eV, respectively. These values are consistent with the upper limit to the cross section estimated from a study by Savee et al. on the O( 3 P) + propene bimolecular reaction. We note that the uncertainty in these values is primarily dependent on the signal attributed to C-Cl primary photofission in the m/z = 35 (Cl + ) time-of-flight data. While the value is a rough estimate, the bandwidth-averaged partial photoionization cross section of vinoxy to HCO + calculated from the signal at m/z = 29 at 11.53 eV is approximately half that of vinoxy to CH 3 + . We also present critical points on the potential energy surface of the vinoxy cation calculated at the G4//B3LYP/6-311++G(3df,2p) level of theory to support the observation of dissociative ionization of vinoxy to both CH 3 + and HCO + .

Radicals in arithmetic

NARCIS (Netherlands)

W.J. Palenstijn (Willem Jan)

2014-01-01

htmlabstractLet K be a field. A radical is an element of the algebraic closure of K of which a power is contained in K. In this thesis we develop a method for determining what we call entanglement. This describes unexpected additive relations between radicals, and is encoded in an entanglement

Free-radical-induced chain scission and cross-linking of polymers in aqueous solution. An overview

International Nuclear Information System (INIS)

Von Sonntag, C.

2002-01-01

Complete text of publication follows. In the radiolysis of N 2 O-saturated aqueous solutions OH are generated. In their reactions with polymers, they give rise to polymer-derived radicals. The kinetics of the formation and decay of these radicals are reviewed. The rate of reaction of a polymer with a reactive free radical is noticeably lower than that of an equivalent concentration of monomer due to the non-random distribution of the reaction sites. Once a larger number of radicals are formed on one polymer molecule, e.g. upon pulse radiolysis, close-by radicals recombine more rapidly while the more distant ones survive for much longer times than an equivalent concentration of freely diffusing radicals. Intermolecular cross-linking (between two polymer chains, increase in molecular weight) and intramolecular cross-linking (formation of small loops, no increase in polymer weight) are competing processes, and their relative yields thus depend on the dose rate and polymer concentration. Hydrogen-transfer reactions within the polymer, e.g. transformation of a secondary radical into a tertiary one, are common and facilitated by the high local density of reactive sites. Due to repulsive forces, the lifetime of radicals of charged polymers is substantially increased. This enables even relatively slow b-fragmentation reactions to become of importance. In the case of poly(methacrylic acid), where β-fragmentation is comparatively fast, this even leads to an unzipping, and as a consequence of the efficient release of methacrylic acid the situation of equilibrium polymerization is approached. Heterolytic β-fragmentation is possible when adequate leaving groups are available, e.g. in polynucleotides and DNA. In the presence of O 2 , chain scission occurs via oxyl radicals as intermediates. Some implications for technical applications are discussed

The scavenging of free radical and oxygen species activities and hydration capacity of collagen hydrolysates from walleye pollock ( Theragra chalcogramma) skin

Science.gov (United States)

Zhuang, Yongliang; Li, Bafang; Zhao, Xue

2009-06-01

Fish skin collagen hydrolysates (FSCH) were prepared from walleye pollock ( Theragra chalcogramma) using a mixture of enzymes, namely trypsin and flavourzyme. The degree of hydrolysis of the skin collagen was 27.3%. FSCH was mainly composed of low-molecular-weight peptides and the relative proportion of <1000Da fraction was 70.6%. Free radical and oxygen species scavenging activities of FSCH were investigated in four model systems, including diphenylpicrylhy-drazyl radical (DPPH), superoxide anion radical, hydroxyl radical and hydrogen peroxide model, and compared with that of a native antioxidant, reduced glutathione (GSH). FSCH was also evaluated by water-absorbing and water-holding capacity. The results showed that FSCH was able to scavenge free radical and oxygen species significantly and to enhance water-absorbing and water-holding capacity remarkably. Therefore, FSCH may have potential applications in the medicine and food industries.

Isomerization of Second-Generation Isoprene Peroxy Radicals: Epoxide Formation and Implications for Secondary Organic Aerosol Yields

Energy Technology Data Exchange (ETDEWEB)

D’Ambro, Emma L.; Møller, Kristian H.; Lopez-Hilfiker, Felipe D.; Schobesberger, Siegfried; Liu, Jiumeng; Shilling, John E.; Lee, Ben Hwan; Kjaergaard, Henrik G.; Thornton, Joel A.

2017-04-11

We report chamber measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation, where radical concentrations were systematically varied and the molecular composition of semi to low volatility gases and SOA were measured online. Using a detailed chemical mechanism, we find that to explain the behavior of low volatility products and SOA mass yields relative to input H2O2 concentrations, the second generation dihydroxy hydroperoxy peroxy radical (C5H11O6•) must undergo an intra-molecular H-shift with a net forward rate constant of order 0.1 s-1 or higher, consistent with quantum chemical calculations which suggest a net forward rate constant of 0.3-0.9 s-1. Furthermore, these calculations suggest the dominant product of this isomerization is a dihydroxy hydroperoxy epoxide (C5H10O5) which is expected to have a saturation vapor pressure ~2 orders of magnitude higher than the dihydroxy dihydroperoxide, ISOP(OOH)2 (C5H12O6), a major product of the peroxy radical reacting with HO2. These results provide strong constraints on the likely volatility distribution of isoprene oxidation products under atmospheric conditions and thus on the importance of non-reactive gas-particle partitioning of isoprene oxidation products as an SOA source.

Film cooling for a closed loop cooled airfoil

Science.gov (United States)

Burdgick, Steven Sebastian; Yu, Yufeng Phillip; Itzel, Gary Michael

2003-01-01

Turbine stator vane segments have radially inner and outer walls with vanes extending therebetween. The inner and outer walls are compartmentalized and have impingement plates. Steam flowing into the outer wall plenum passes through the impingement plate for impingement cooling of the outer wall upper surface. The spent impingement steam flows into cavities of the vane having inserts for impingement cooling the walls of the vane. The steam passes into the inner wall and through the impingement plate for impingement cooling of the inner wall surface and for return through return cavities having inserts for impingement cooling of the vane surfaces. At least one film cooling hole is defined through a wall of at least one of the cavities for flow communication between an interior of the cavity and an exterior of the vane. The film cooling hole(s) are defined adjacent a potential low LCF life region, so that cooling medium that bleeds out through the film cooling hole(s) reduces a thermal gradient in a vicinity thereof, thereby the increase the LCF life of that region.

Integrated Testing of a 4-Bed Molecular Sieve, Air-Cooled Temperature Swing Adsorption Compressor, and Sabatier Engineering Development Unit

Science.gov (United States)

Knox, James C.; Miller, Lee; Campbell, Melissa; Mulloth, Lila; Varghese, Mini

2006-01-01

Accumulation and subsequent compression of carbon dioxide that is removed from the space cabin are two important processes involved in a closed-loop air revitalization scheme of the International Space Station (ISS). The 4-Bed Molecular Sieve (4BMS) of ISS currently operates in an open loop mode without a compressor. The Sabatier Engineering Development Unit (EDU) processes waste CO2 to provide water to the crew. This paper reports the integrated 4BMS, air-cooled Temperature Swing Adsorption Compressor (TSAC), and Sabatier EDU testing. The TSAC prototype was developed at NASA Ames Research Center (ARC). The 4BMS was modified to a functionally flight-like condition at NASA Marshall Space Flight Center (MSFC). Testing was conducted at MSFC. The paper provides details of the TSAC operation at various CO2 loadings and corresponding performance of the 4BMS and Sabatier.

Multiple free-radical scavenging capacity in serum

Science.gov (United States)

Oowada, Shigeru; Endo, Nobuyuki; Kameya, Hiromi; Shimmei, Masashi; Kotake, Yashige

2012-01-01

We have developed a method to determine serum scavenging-capacity profile against multiple free radical species, namely hydroxyl radical, superoxide radical, alkoxyl radical, alkylperoxyl radical, alkyl radical, and singlet oxygen. This method was applied to a cohort of chronic kidney disease patients. Each free radical species was produced with a common experimental procedure; i.e., uv/visible-light photolysis of free-radical precursor/sensitizer. The decrease in free-radical concentration by the presence of serum was quantified with electron spin resonance spin trapping method, from which the scavenging capacity was calculated. There was a significant capacity change in the disease group (n = 45) as compared with the healthy control group (n = 30). The percent values of disease’s scavenging capacity with respect to control group indicated statistically significant differences in all free-radical species except alkylperoxyl radical, i.e., hydroxyl radical, 73 ± 12% (p = 0.001); superoxide radical, 158 ± 50% (p = 0.001); alkoxyl radical, 121 ± 30% (p = 0.005); alkylperoxyl radical, 123 ± 32% (p>0.1); alkyl radical, 26 ± 14% (p = 0.001); and singlet oxygen, 57 ± 18% (p = 0.001). The scavenging capacity profile was illustrated using a radar chart, clearly demonstrating the characteristic change in the disease group. Although the cause of the scavenging capacity change by the disease state is not completely understood, the profile of multiple radical scavenging capacities may become a useful diagnostic tool. PMID:22962529

Preoperative radiochemotherapy and radical surgery in comparison with radical surgery alone

International Nuclear Information System (INIS)

Mohr, C.; Schettler, D.; Bohndorf, W.

1994-01-01

A multicentric, randomized study of squamous cell carcinoma (SCC) of the oral cavity and the oropharynx has been undertaken by DOeSAK. The results after radical surgery alone have been compared with the results of combined preoperative radiochemotherapy followed by radical surgery. Patients with primary (biopsy proven) SCC of the oral cavity or the oropharynx with tumor nodes metastasis (TNM) stages T2-4, N0-3, M0 were included in the study. A total of 141 patients were treated by radical surgery alone, whereas 127 patients were treated by radical surgery preceded by preoperative radiochemotherapy. The pre-operative treatment consisted of conventionally fractioned irradiation on the primary and the regional lymph nodes with a total dose of 36 Gy (5 x 2 Gy per week) and low-dose cisplatin chemotherapy with 5 x 12.5 mg cisplatin per m 2 of body surface during the first week of treatment. Radical surgery according to be DOeSAK definitions (DOeSAK, 1982) was performed after a delay of 10-14 days. During the follow-up period, 28.2% of all patients suffered from locoregional recurrence, and 27.2% of the patients died. The percentages were higher after radical surgery alone for locoregional recurrence (31% and 15.6%) and for death (28% and 18.6%). The life-table analysis showed improved survival rates of 4.5% after 1 year and 8.3% after 2 years in the group of patients treated with combined therapy. The demonstrated improvement appeared to be significant with the Gehan-Wilcoxon test as well as with the log rank test below a P value of 5%. (au) (29 refs.)

Radicals in arithmetic

NARCIS (Netherlands)

Palenstijn, Willem Jan

2014-01-01

Let K be a field. A radical is an element of the algebraic closure of K of which a power is contained in K. In this thesis we develop a method for determining what we call entanglement. This describes unexpected additive relations between radicals, and is encoded in an entanglement group. We give

Radicalization as a Vector: Exploring Non-Violent and Benevolent Processes of Radicalization.

Directory of Open Access Journals (Sweden)

Ken Reidy

2018-03-01

Full Text Available Successful radicalization posits three outcomes: extremism, terrorism or both. As these are undesirable, radicalization is understood as wholly malevolent and governments work to prevent and/or stop it. Nonetheless, a handful of scholars have recognized that the same radicalization process which results in either outcome may, theoretically at least, also have beneficial outcomes such as environmental awareness or human rights. This article explores one such outcome. Based on interviews with British Muslim aid workers (n=6 operating in Jihadist conflict zones post Arab spring and using constructivist grounded theory, it illustrates how the research participants radicalized to humanitarianism which resulted in them assisting the most plighted of Muslims by deploying to the most wanton of areas: ones commonly referred to as Jihadist conflict zones. Evidently, these destinations are shared with Jihadists and given the array of other observable similarities (socio-demographics and [pre-]mobilization behaviours, these morally opposed groups become conflated by the security services. This is further compounded by the fact that Jihadists manipulate and/or impersonate aid workers so as to funnel people and funds. To distinguish both, this article documents the benevolent pathway of the research participants and juxtaposes it to scholarly knowledge on Jihadist pathways. Socialization was revealed to be the key distinguishing feature rather than descriptive risk factors (such as ideology or moral outrage because the process of radicalization was not found to be the start of the radicalized pathway. It concludes that benevolently radicalized Islamic groups constitute an effective means of pathway divergence for particular typologies by offering an attractive and prosocial alternative to Jihadism. This strengths-based preventative approach (“what’s right” takes the form of a community-centric market competitor to Jihadism rather than a problem

Radical cations of quadricyclane and norbornadiene in polar ZSM-5 matrices: Radical cation photochemical transformations without photons

International Nuclear Information System (INIS)

Barnabas, M.V.; Trifunac, A.D.

1994-01-01

Radical cations of quadricyclane (Q) and norbornadiene (NBD) are produced by γ-radiolysis in zeolites. In polar ZSM-5, only one radical cation is initially observed below 100K. Increasing the temperature above 200K gives rise to the cyclopentadiene radical cation. Higher temperatures (>360K) give rise to the cyclopenten-4-yl radical. The observation of cyclopentadiene radical cation implies the occurrence of the reverse Diels-Alder reaction. This is a thermally forbidden, photochemically allowed, process, which is made possible by the interaction of the polar zeolite matrix sites with parent NBD and Q radical cations

Divertor cooling device

International Nuclear Information System (INIS)

Nakayama, Tadakazu; Hayashi, Katsumi; Handa, Hiroyuki

1993-01-01

Cooling water for a divertor cooling system cools the divertor, thereafter, passes through pipelines connecting the exit pipelines of the divertor cooling system and the inlet pipelines of a blanket cooling system and is introduced to the blanket cooling system in a vacuum vessel. It undergoes emission of neutrons, and cooling water in the divertor cooling system containing a great amount of N-16 which is generated by radioactivation of O-16 is introduced to the blanket cooling system in the vacuum vessel by way of pipelines, and after cooling, passes through exit pipelines of the blanket cooling system and is introduced to the outside of the vacuum vessel. Radiation of N-16 in the cooling water is decayed sufficiently with passage of time during cooling of the blanket, thereby enabling to decrease the amount of shielding materials such as facilities and pipelines, and ensure spaces. (N.H.)

Cool colored coating and phase change materials as complementary cooling strategies for building cooling load reduction in tropics

International Nuclear Information System (INIS)

Lei, Jiawei; Kumarasamy, Karthikeyan; Zingre, Kishor T.; Yang, Jinglei; Wan, Man Pun; Yang, En-Hua

2017-01-01

Highlights: • Cool colored coating and PCM are two complementary passive cooling strategies. • A PCM cool colored coating system is developed. • The coating reduces cooling energy by 8.5% and is effective yearly in tropical Singapore. - Abstract: Cool colored coating and phase change materials (PCM) are two passive cooling strategies often used separately in many studies and applications. This paper investigated the integration of cool colored coating and PCM for building cooling through experimental and numerical studies. Results showed that cool colored coating and PCM are two complementary passive cooling strategies that could be used concurrently in tropical climate where cool colored coating in the form of paint serves as the “first protection” to reflect solar radiation and a thin layer of PCM forms the “second protection” to absorb the conductive heat that cannot be handled by cool paint. Unlike other climate zones where PCM is only seasonally effective and cool paint is only beneficial during summer, the application of the proposed PCM cool colored coating in building envelope could be effective throughout the entire year with a monthly cooling energy saving ranging from 5 to 12% due to the uniform climatic condition all year round in tropical Singapore.

Thermoelectric self-cooling for power electronics: Increasing the cooling power

International Nuclear Information System (INIS)

Martinez, Alvaro; Astrain, David; Aranguren, Patricia

2016-01-01

Thermoelectric self-cooling was firstly conceived to increase, without electricity consumption, the cooling power of passive cooling systems. This paper studies the combination of heat pipe exchangers and thermoelectric self-cooling, and demonstrates its applicability to the cooling of power electronics. Experimental tests indicate that source-to-ambient thermal resistance reduces by around 30% when thermoelectric self-cooling system is installed, compared to that of the heat pipe exchanger under natural convection. Neither additional electric power nor cooling fluids are required. This thermal resistance reaches 0.346 K/W for a heat flux of 24.1 kW/m"2, being one order of magnitude lower than that obtained in previous designs. In addition, the system adapts to the cooling demand, reducing this thermal resistance for increasing heat. Simulation tests have indicated that simple system modifications allow relevant improvements in the cooling power. Replacement of a thermoelectric module with a thermal bridge leads to 33.54 kW/m"2 of top cooling power. Likewise, thermoelectric modules with shorter legs and higher number of pairs lead to a top cooling power of 44.17 kW/m"2. These results demonstrate the applicability of thermoelectric self-cooling to power electronics. - Highlights: • Cooling power of passive systems increased. • No electric power consumption. • Applicable for the cooling of power electronics. • Up to 44.17 kW/m"2 of cooling power, one order of magnitude higher. • Source-to-ambient thermal resistance reduces by 30%.

CN radical in diffuse interstellar clouds

International Nuclear Information System (INIS)

Federman, S.R.; Danks, A.C.; Lambert, D.L.

1984-01-01

A survey of 15 lines of sight for the CN B 2 Σ + --X 2 Σ + interstellar absorption lines shows that the CN column density in diffuse interstellar clouds follows the relation log N(CN)proportionalm log N(H 2 ), where mroughly-equal3. This result is reproduced by a reaction network in which CN is produced primarily from C 2 by the neutral-neutral reaction C 2 +N → CN+C, and photodissociation is the main destruction pathway for the neutral molecules CH, C 2 , and CN. The CN radical is the first molecular species observed in diffuse clouds that requires a neutral-neutral reaction for its formation in the gas phase. The network also reproduces the observed ratio N(CN)/N(H 2 )

Study of free-radical centers in lignin with 2-mm band ESR spectroscopy

International Nuclear Information System (INIS)

Kuzina, S.I.; Demidov, S.V.; Brezgunov, A.Yu.; Poluehktov, O.G.; Grinberg, O.Ya.; Dubinskij, A.A.; Mikhajlov, A.I.; Lebedev, Ya.S.

1993-01-01

The nature of paramagnetic centers in pristine lignin and lignin, treated with molecular chlorine, aqueous solutions of acids and alkalis, and γ- and UV-irradiated, was studied with 2-mm band ESR spectroscopy. Most of the observed singlet ESR lines are accounted for by radicals with conjugated bonds. High reactivity of double bonds of polyconjugated systems was in the processes studied

NASA Applications of Molecular Nanotechnology

Science.gov (United States)

Globus, Al; Bailey, David; Han, Jie; Jaffe, Richard; Levit, Creon; Merkle, Ralph; Srivastava, Deepak

1998-01-01

Laboratories throughout the world are rapidly gaining atomically precise control over matter. As this control extends to an ever wider variety of materials, processes and devices, opportunities for applications relevant to NASA's missions will be created. This document surveys a number of future molecular nanotechnology capabilities of aerospace interest. Computer applications, launch vehicle improvements, and active materials appear to be of particular interest. We also list a number of applications for each of NASA's enterprises. If advanced molecular nanotechnology can be developed, almost all of NASA's endeavors will be radically improved. In particular, a sufficiently advanced molecular nanotechnology can arguably bring large scale space colonization within our grasp.

Youth De-Radicalization: A Canadian Framework

Directory of Open Access Journals (Sweden)

Hafal (Haval Ahmad

2017-09-01

Full Text Available Youth radicalization leading to violence has become a growing fear among Canadians, as terrorist attacks are carried out in Western states. Although Canada has suffered relatively fewer acts of violence, this fear has intensified and a de-radicalization strategy is needed in the Canadian context. In a qualitative case study methodology, interviews were conducted with school counsellors, religious leaders, and academics to explore solutions to youth radicalization. Youth de-radicalization approaches from the United Kingdom were analyzed and found that community-based initiatives were missing from programming. Social identity theory is used to explain that youth join radicalized groups to feel a sense of belonging and have to be provided an alternative and moderate group identity to de-radicalize. This study found youth de-radicalization in Canada is best served through a community collaboration approach.

Molecular Subgroup of Primary Prostate Cancer Presenting with Metastatic Biology.

Science.gov (United States)

Walker, Steven M; Knight, Laura A; McCavigan, Andrena M; Logan, Gemma E; Berge, Viktor; Sherif, Amir; Pandha, Hardev; Warren, Anne Y; Davidson, Catherine; Uprichard, Adam; Blayney, Jaine K; Price, Bethanie; Jellema, Gera L; Steele, Christopher J; Svindland, Aud; McDade, Simon S; Eden, Christopher G; Foster, Chris; Mills, Ian G; Neal, David E; Mason, Malcolm D; Kay, Elaine W; Waugh, David J; Harkin, D Paul; Watson, R William; Clarke, Noel W; Kennedy, Richard D

2017-10-01

Approximately 4-25% of patients with early prostate cancer develop disease recurrence following radical prostatectomy. To identify a molecular subgroup of prostate cancers with metastatic potential at presentation resulting in a high risk of recurrence following radical prostatectomy. Unsupervised hierarchical clustering was performed using gene expression data from 70 primary resections, 31 metastatic lymph nodes, and 25 normal prostate samples. Independent assay validation was performed using 322 radical prostatectomy samples from four sites with a mean follow-up of 50.3 months. Molecular subgroups were identified using unsupervised hierarchical clustering. A partial least squares approach was used to generate a gene expression assay. Relationships with outcome (time to biochemical and metastatic recurrence) were analysed using multivariable Cox regression and log-rank analysis. A molecular subgroup of primary prostate cancer with biology similar to metastatic disease was identified. A 70-transcript signature (metastatic assay) was developed and independently validated in the radical prostatectomy samples. Metastatic assay positive patients had increased risk of biochemical recurrence (multivariable hazard ratio [HR] 1.62 [1.13-2.33]; p=0.0092) and metastatic recurrence (multivariable HR=3.20 [1.76-5.80]; p=0.0001). A combined model with Cancer of the Prostate Risk Assessment post surgical (CAPRA-S) identified patients at an increased risk of biochemical and metastatic recurrence superior to either model alone (HR=2.67 [1.90-3.75]; pmolecular subgroup of primary prostate cancers with metastatic potential. The metastatic assay may improve the ability to detect patients at risk of metastatic recurrence following radical prostatectomy. The impact of adjuvant therapies should be assessed in this higher-risk population. Copyright © 2017 European Association of Urology. Published by Elsevier B.V. All rights reserved.

Experimental study of living free radical polymerization using trifunctional initiator and polymerization mediated by nitroxide

International Nuclear Information System (INIS)

Galhardo, Eduardo; Lona, Liliane M.F.

2009-01-01

Controlled free radical polymerization or living free radical polymerization has received increasing attention as a technique for the production of polymers with microstructure highly controlled. In particular, narrow molecular weight distributions are obtained with polydispersity very close to one. In this research it was investigate the controlled polymerization mediated by nitroxide, using a cyclic trifunctional peroxide. As long as we know, there are only publications in literature dealing with NMRP using mono- and bi-functional initiators. It was believed that the trifunctional peroxide can increase the rate of polymerization, since more free radicals are generated, if compared with initiators with lower functionality. Furthermore, the fact of the initiator be cyclic means that branches are not generated in the chains, which theoretically prevents an increase in polydispersity of the polymer. The effect of the dissociation constant of the trifunctional initiator in the velocity of the reaction was analyzed. (author)

N-Chlorosuccinimide (NCS): A Novel Initiator for Atom Transfer Radical Polymerization of Methyl Methacrylate

Institute of Scientific and Technical Information of China (English)

WANG,Xia-Yan; CHANG,Li-Qun; ZHOU,Hong; ZHANG,Ke-Da

2006-01-01

Atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was achieved, using N-chlorosuccinimide (NCS) as an initiator together with catalytic system CuCl/PMDETA (N,N,N',N',N"-pentamethyldiethyl-enetriamine), CuCl/MA5-DETA (N,N,N',N',N"-penta(methylacrylate)diethylenetriamine), and CuCl/bipy (bipy=2,2'-bipyridyl) respectively. The results indicated that the polymerization possessed typical controlled/living radical polymerization characteristics. The analysis for terminal group of obtained polymer by 1H NMR proved that NCS is an initiator for ATRP. In comparison with NBS, the polymerization rate was slower and the resulted polymer had narrower molecular weight distribution (MWD) when NCS was employed as the initiator.

Solvent driving force ensures fast formation of a persistent and well-separated radical pair in plant cryptochrome

DEFF Research Database (Denmark)

Lüdemann, Gesa; Solov'yov, Ilia; Kubar, Tomás

2015-01-01

upon the electron transfer. This approach allows us to follow the time evolution of the electron transfer in an unbiased fashion and to reveal the molecular driving force which ensures fast electron transfer in cryptochrome guaranteeing formation of a persistent radical pair suitable...

Effect of thermal treatment on potato starch evidenced by EPR, XRD and molecular weight distribution.

Science.gov (United States)

Bidzińska, Ewa; Michalec, Marek; Pawcenis, Dominika

2015-12-01

Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification. Copyright © 2015 John Wiley & Sons, Ltd.

Peroxyl radical reactions with carotenoids in microemulsions: Influence of microemulsion composition and the nature of peroxyl radical precursor.

Science.gov (United States)

El-Agamey, Ali; McGarvey, David J

2016-01-01

The reactions of acetylperoxyl radicals with different carotenoids (7,7'-dihydro-β-carotene and ζ-carotene) in SDS and CTAC microemulsions of different compositions were investigated using laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy. The primary objective of this study was to explore the influence of microemulsion composition and the type of surfactant used on the yields and kinetics of various transients formed from the reaction of acetylperoxyl radicals with carotenoids. Also, the influence of the site (hydrocarbon phases or aqueous phase) of generation of the peroxyl radical precursor was examined by using 4-acetyl-4-phenylpiperidine hydrochloride (APPHCl) and 1,1-diphenylacetone (11DPA) as water-soluble and lipid-soluble peroxyl radical precursors, respectively. LFP of peroxyl radical precursors with 7,7'-dihydro-β-carotene (77DH) in different microemulsions gives rise to the formation of three distinct transients namely addition radical (λmax=460 nm), near infrared transient1 (NIR, λmax=700 nm) and 7,7'-dihydro-β-carotene radical cation (77DH(•+), λmax=770 nm). In addition, for ζ-carotene (ZETA) two transients (near infrared transient1 (NIR1, λmax=660 nm) and ζ-carotene radical cation (ZETA(•+), λmax=730-740 nm)) are generated following LFP of peroxyl radical precursors in the presence of ζ-carotene (ZETA) in different microemulsions. The results show that the composition of the microemulsion strongly influences the observed yield and kinetics of the transients formed from the reactions of peroxyl radicals (acetylperoxyl radicals) with carotenoids (77DH and ZETA). Also, the type of surfactant used in the microemulsions influences the yield of the transients formed. The dependence of the transient yields and kinetics on microemulsion composition (or the type of surfactant used in the microemulsion) can be attributed to the change of the polarity of the microenvironment of the carotenoid. Furthermore, the nature of

Glutathione as a radical scavenger and the biological consequences of thiyl radical production

International Nuclear Information System (INIS)

Winterbourn, C.C.

1996-01-01

A large number of compounds that have toxic effects can be metabolised to free radicals and secondary reactive oxygen species. These may be directly damaging or affect cell function by altering regulatory mechanisms through changing redox status. Protection is provided by an integrated system of antioxidant defenses. This includes reduced glutathione (GSH), one of the functions of which is as a free radical scavenger. For GSH to be an effective radical scavenging antioxidant, therefore, it must act in concert with superoxide dismutase to remove the superoxide so generated. Superoxide is produced in a variety of metabolic processes. It is also a secondary product of radicals reacting with oxygen either directly or through GSH. The biological reactivity of superoxide has been the subject of much debate ever since the discovery of superoxide dismutase in 1968. It has more recently become apparent that its rapid reaction with nitric oxide to give peroxynitrite, and its ability to reversibly oxidise and inactivate iron sulphur enzymes, contribute to the toxicity of superoxide. Another mechanism that could be important involves addition reactions of superoxide with other radicals to give organic peroxides. This reaction, to form a tyrosine peroxide, has come to authors attention through the study of the scavenging of tyrosyl radicals by GSH. It is also shown that a tyrosine peroxide is a major product of the oxidation of tyrosine by neutrophils

Taking a radical position: Evidence for position specific radical representations in Chinese character recognition using masked priming ERP

Directory of Open Access Journals (Sweden)

I-Fan eSu

2012-09-01

Full Text Available In the investigation of orthographic representation of Chinese characters, one question that has stimulated much research is whether radicals (character components are specified for spatial position in a character (e.g. Ding, Peng, & Taft, 2004; Tsang & Chen, 2009. Differing from previous work, component or radical position information in this study is conceived in terms of relative frequency across different positions of characters containing it. A lexical decision task in a masked priming paradigm focusing on radicals with preferred position of occurrence was conducted. A radical position that encompasses more characters than other positions was identified to be the preferred position of a particular radical. The prime that was exposed for 96ms might share a radical with the target in the same or different positions. Moreover, the shared radical appeared either in its preferred or non-preferred position in the target. While response latencies only revealed the effect of graphical similarity, both effects of graphical similarity and radical position preference were found in the ERP results. The former effect was reflected in greater positivity in occipital P1 and greater negativity in N400 for radicals in different positions in prime and target characters. The latter effect manifested as greater negativity in occipital N170 and greater positivity in frontal P200 in the same time window elicited by radicals in their non-preferred position. Equally interesting was the reversal of the effect of radical position preference in N400 with greater negativity associated with radicals in preferred position. These findings identify the early ERP components associated with activation of position-specific radical representations in the orthographic lexicon, and reveal the change in the nature of competition from processing at the radical level to the lexical level.

Free Radicals and Extrinsic Skin Aging

Directory of Open Access Journals (Sweden)

Borut Poljšak

2012-01-01

Full Text Available Human skin is constantly directly exposed to the air, solar radiation, environmental pollutants, or other mechanical and chemical insults, which are capable of inducing the generation of free radicals as well as reactive oxygen species (ROS of our own metabolism. Extrinsic skin damage develops due to several factors: ionizing radiation, severe physical and psychological stress, alcohol intake, poor nutrition, overeating, environmental pollution, and exposure to UV radiation (UVR. It is estimated that among all these environmental factors, UVR contributes up to 80%. UV-induced generation of ROS in the skin develops oxidative stress, when their formation exceeds the antioxidant defence ability of the target cell. The primary mechanism by which UVR initiates molecular responses in human skin is via photochemical generation of ROS mainly formation of superoxide anion (O2−•, hydrogen peroxide (H2O2, hydroxyl radical (OH•, and singlet oxygen (1O2. The only protection of our skin is in its endogenous protection (melanin and enzymatic antioxidants and antioxidants we consume from the food (vitamin A, C, E, etc.. The most important strategy to reduce the risk of sun UVR damage is to avoid the sun exposure and the use of sunscreens. The next step is the use of exogenous antioxidants orally or by topical application and interventions in preventing oxidative stress and in enhanced DNA repair.

Radical reactions in vivo - an overview

International Nuclear Information System (INIS)

Saran, M.; Bors, W.

1990-01-01

Generation of radicals in vivo depends on metabolic activities. The reactions are usually influenced by (i) the presence and concentration of oxygen, (ii) the availability of transition metals (effects of binding and compartimentalization), (iii) the level of reductants and antioxidants (e.g. nutritional effects). The effects of radicals are thought to be due to (i) membrane damage (affecting passive or active transport through altered fluidity/function interrelationships, intercellular messenging through modifications in the synthesis of prostaglandins and leukotrienes); (ii) protein damage (e.g. affecting membrane transporters, channel proteins, receptor or regulatory proteins, immunomodulators); (iii) damage to DNA. Defense mechanisms consist of (i) prevention of the 'spreading' of primary damage by low molecular weight antioxidants (e.g. vitamin E, GSH, vitamin C, β-carotene, uric acid); (ii) prevention or limitation of 'secondary' damage by enzymes (e.g. GSH-peroxidase, catalase, superoxide dismutase, DT-diaphorase) and/or chelators; (iii) repair processes, e.g. lipid degradation/membrane repair enzymes (phospholipases, peroxidases, some transferases and reductases), protein disposal or repair enzymes (proteases, GSSG-reductase), DNA degradation or repair enzymes (exonucleases III, endonucleases III and IV, glycosylases, polymerases). Recent hypotheses on a messenging function of the superoxide anion O 2 - are discussed and possible implications of cross-reactions between O 2 - and nitric oxide (endothelium-derived relaxing factor EDRF) are shortly mentioned. (orig.)

Reaction between peroxynitrite and boronates: EPR spin-trapping, HPLC analyses, and quantum mechanical study of the free radical pathway

Science.gov (United States)

Sikora, Adam; Zielonka, Jacek; Lopez, Marcos; Dybala-Defratyka, Agnieszka; Joseph, Joy; Marcinek, Andrzej; Kalyanaraman, Balaraman

2013-01-01

Recently we showed that peroxynitrite (ONOO−) reacts directly and rapidly with aromatic and aliphatic boronic acids (k ≈ 106 M−1s−1). Product analyses and substrate consumption data indicated that ONOO− reacts stoichiometrically with boronates, yielding the corresponding phenols as the major product (~85–90%), and the remaining products (10–15%) were proposed to originate from free radical intermediates (phenyl and phenoxyl radicals). Here we investigated in detail the minor, free radical pathway of boronate reaction with ONOO−. The electron paramagnetic resonance (EPR) spin-trapping technique was used to characterize the free radical intermediates formed from the reaction between boronates and ONOO−. Using 2-methyl-2-nitrosopropane (MNP) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) spin traps, phenyl radicals were trapped and detected. Although phenoxyl radicals were not detected, the positive effects of molecular oxygen, and inhibitory effects of hydrogen atom donors (acetonitrile, and 2-propanol) and general radical scavengers (GSH, NADH, ascorbic acid and tyrosine) on the formation of phenoxyl radical-derived nitrated product, suggest that phenoxyl radical was formed as the secondary species. We propose that the initial step of the reaction involves the addition of ONOO− to the boron atom in boronates. The anionic intermediate undergoes both heterolytic (major pathway) and homolytic (minor pathway) cleavage of the peroxy (O-O) bond to form phenol and nitrite as a major product (via a non-radical mechanism), or a radical pair PhB(OH)2O•−…•NO2 as a minor product. It is conceivable that phenyl radicals are formed by the fragmentation of PhB(OH)2O•− radical anion. According to the DFT quantum mechanical calculations, the energy barrier for the dissociation of PhB(OH)2O•− radical anion to form phenyl radicals is only a few kcal/mol, suggesting rapid and spontaneous fragmentation of PhB(OH)2O•− radical anion

Chemical repair of trypsin-histidinyl radical

International Nuclear Information System (INIS)

Jovanovic, S.V.; Ruvarac, I.; Jankovic, I.; Josimovic, L.

1991-01-01

Oxyl radicals, such as hydroxyl, alkoxyl and peroxyl, react with biomolecules to produce bioradicals. Unless chemically repaired by suitable antioxidants, these bioradicals form stable products. This leads to loss of biological function of parent biomolecules with deleterious biological results, such as mutagenesis and cancer. Consequently, the understanding of the mechanisms of oxyl radical damage to biomolecules and chemical repair of such damage is crucial for the development of strategies for anticarcinogenesis and radioprotection. In this study the chemical repair of the histidinyl radical generated upon the trichloromethylperoxyl radical reaction with trypsin vas investigated by gamma radiolysis. The trypsin histidinyl radical is a resonance-stabilized heterocyclic free radical which was found to be unreactive with oxygen. The efficacy of the chemical repair of the trypsin-histidinyl radical by endogenous antioxidants which are electron donors (e.g. 5-hydroxytryptophan, uric acid) is compared to that of antioxidants which are H-atom donors (e. g. glutathione). 9 refs., 2 figs., 1 tab

Gnosticism and Radical Feminism

DEFF Research Database (Denmark)

Cahana, Jonathan

2016-01-01

and radical feminism would easily fall under this definition. There is, however, one major difference: since radical feminism is a relatively recent phenomenon which also benefited from modern modes of text production and preservation, almost all of the sources are still with us. This, in turn, may allow us...... to use radical feminism to make certain aspects of ancient Gnosticism re-emerge from their long submersion, provided that enough similarities can be independently drawn between the two phenomena to merit such a comparison. This paper therefore presents a comparison between concepts and positions...

Radical's view of sciences

International Nuclear Information System (INIS)

Mittal, J.P.

2004-01-01

Full text: General concept in radiation biology is that free radicals are highly reactive and they can damage vital cellular molecules leading to injurious effects. However, in this talk, evidence will be presented through the techniques of electron paramagnetic resonance ( EPR ) and pulse radiolysis that free radicals can be highly selective in their reaction with the target molecules. In addition, attempts will be made to present a brief account of emerging scenario of free radical generation, identification and their involvement in radiation damage mechanisms in chemical and biological systems

Fundamental studies of molecular multiphoton ionization

International Nuclear Information System (INIS)

Miller, J.C.; Compton, R.N.

1984-04-01

For several years the authors have performed fundamental studies of molecular multiphoton ionization (MPI). We will present a potpourri of techniques and results chosen to illustrate the interesting complexities of molecular MPI. Techniques used include time-of-flight mass spectroscopy, photoelectron spectroscopy, supersonic expansion cooling of molecular beams, harmonic generation, two-color laser MPI, and polarization spectroscopy. Whenever possible the relevance of these results to resonance ionization spectroscopy schemes will be delineated. 23 references, 10 figures

Gas Phase Molecular Dynamics

International Nuclear Information System (INIS)

Hall, G.E.; Prrese, J.M.; Sears, T.J.; Weston, R.E.

1999-01-01

The goal of this research is the understanding of elementary chemical and physical processes important in the combustion of fossil fuels. Interest centers on reactions involving short-lived chemical intermediates and their properties. High-resolution high-sensitivity laser absorption methods are augmented by high temperature flow-tube reaction kinetics studies with mass spectrometric sampling. These experiments provide information on the energy levels, structures and reactivity of molecular flee radical species and, in turn, provide new tools for the study of energy flow and chemical bond cleavage in the radicals in chemical systems. The experimental work is supported by theoretical and computational work using time-dependent quantum wave packet calculations that provide insights into energy flow between the vibrational modes of the molecule

Free cooling of hard-spheres with short and long range interactions

NARCIS (Netherlands)

Gonzalez Briones, Sebastián; Thornton, Anthony Richard; Luding, Stefan

2015-01-01

We study the stability, the clustering and the phase-diagram of free cooling granular gases. The systems consist of mono-disperse particles with additional non-contact (long-range) interactions, and are simulated here by the event-driven molecular dynamics algorithm with discrete (short-range

Oxidation and Free Radical Decay in Vitamin E-stabilized, Radiation Cross-linked UHMWPE

International Nuclear Information System (INIS)

Oral, E.

2006-01-01

A novel a-tocopherol (vitamin E, α-T)-stabilized, cross-linked ultra-high molecular weight polyethylene (UHMWPE) (αTPE) was developed for total joint arthroplasty as a bearing surface with low wear and improved mechanical properties. Accelerated aging showed α-T protects irradiated UHMWPE against oxidation. However, accelerated aging may not truly reflect in vivo and shelf oxidation. We used real-time aging to monitor the evolution of oxidation and free radical signals of α-T to determine the mechanism of oxidative stability. UHMWPE blocks (30x30x10 mm) were machined and γ-irradiated (85 kGy) in argon. The blocks were doped in α-T for 5 hours at 120 degree and homogenized for 64 hours at 120 degree in argon, packaged in vacuum and γ-sterilized (25 kGy). Samples were aged in air at room temperature, in air at 40 degree and in water at 40 degree. Measurements were at 1, 2, 3, 4 and 7 months. Sections cut from the aged blocks (150μm) were boiled in hexane overnight to extract free species and evaluated by FTIR. Oxidation indices were calculated by taking the area under the carbonyl peak and normalizing it to a skeletal peak. ESR was used to determine the content and type of free radicals. Control was 100-kGy irradiated, unstabilized UHMWPE. αTPE showed a small amount of oxidation, which stabilized after 2 months. This indicated that the decay of the hydroperoxides formed by the reaction of the residual free radicals with oxygen was exhausted by α-T due to its ability to scavenge free radicals. In contrast, control UHMWPE continued to oxidize because the residual free radicals likely continued to form hydroperoxides and additional free radicals, furthering the oxidation reactions. There was a shift in the free radical signature of both αTPE and control from the sextet alkyl/allyl radicals to a sharp singlet during aging. Most likely, trapped free radicals move along the crystal stems until they react with another free radical or until they reach the crystal

Fate of free radicals generated during one-electron reductions of 4-alkyl-1,4-peroxyquinols by cytochrome P-450

International Nuclear Information System (INIS)

Yumibe, N.P.; Thompson, J.A.

1988-01-01

Free radicals resulting from the one-electron reduction and subsequent homolytic cleavage of oxygen-oxygen bonds by heme proteins are likely to be responsible for some aspects of the toxicity of organic hydroperoxides. In the present work, effects of the 4-alkyl substituent of 2,6-di-tert-butyl-4-alkyl-4-hydroperoxycytohexa-2,5-dienones on radical production were investigated with microsomal cytochrome P-450 from rat liver. Quinoxy radicals from homolysis of the peroxyquinols underwent β-scission to produce a quinone and an alkyl radical, and this process occurred with increasing frequency as the stability of the alkyl radical increased. The fate of benzyl and 2-phenylethyl radicals generated from the appropriately substituted peroxyquinols was investigated also. The former was converted to benzyl alcohol, benzaldehyde, and toluene and the latter to 2-phenylethanol, phenylacetaldehyde, ethylbenzene, styrene, and benzaldehyde. Oxygen-18 labeling studies demonstrate that 80-85% of the benzyl alcohol incorporated oxygen from the hydroperoxide and the balance from molecular oxygen. This indicates that the predominant reaction pathway involved recombination between the benzyl radical and the iron-bound hydroxyl radical of the P-450 intermediate complex. By contrast, about 50% of 2-phenylethanol from the 2-phenylethyl radical incorporated oxygen from water and the balance from O 2 . Two alternative mechanisms are proposed to explain the formation of 2-phenylethanol that contained oxygen from water and the concurrent formation of styrene: (a) oxygen exchange of the P-450 intermediate with water, followed by hydrogen abstraction and radical recombination reactions with the P-450 complex, or (b) oxidation of the radical to the 2-phenylethyl cation followed by proton elimination and hydration

Fragmentation characteristics of the unstable [CH3 CO][radical sign] radicals generated by neutralization of [CH3CO]+ cations

Science.gov (United States)

Hop, C. E. C. A.; Holmes, J. L.

1991-03-01

The stability and fragmentation characteristics of [CH3 CO][radical sign] radicals, generated by vertical charge exchange between acetyl cations and permanent gases or metal vapours (He, Xe, NO, Cd, Na and K), were examined mass spectrometrically. Two dissociation reactions were observed, the losses of CH[radical sign]3 and H[radical sign]. The H[radical sign] loss reaction, the higher energy dissociation, became of greater importance as the exothermicity of the charge exchange was increased. Based on the analysis of the kinetic energy releases it was concluded that these decompositions arose from the population of two excited states of the [CH3 CO][radical sign] radical.

Molecular mechanisms of the direct radiation effects on the DNA: ESR spectroscopy for examining oriented fibres after X-ray exposure

International Nuclear Information System (INIS)

Voit, K.

1986-01-01

This thesis contains experiments, investigating molecular interactions between X radiation and DNA. ESR-spectra of the primary radicals are simulated. The types of secondary radicals are described. (AJ) [de

Legionnaires' Disease Outbreaks and Cooling Towers, New York City, New York, USA.

Science.gov (United States)

Fitzhenry, Robert; Weiss, Don; Cimini, Dan; Balter, Sharon; Boyd, Christopher; Alleyne, Lisa; Stewart, Renee; McIntosh, Natasha; Econome, Andrea; Lin, Ying; Rubinstein, Inessa; Passaretti, Teresa; Kidney, Anna; Lapierre, Pascal; Kass, Daniel; Varma, Jay K

2017-11-01

The incidence of Legionnaires' disease in the United States has been increasing since 2000. Outbreaks and clusters are associated with decorative, recreational, domestic, and industrial water systems, with the largest outbreaks being caused by cooling towers. Since 2006, 6 community-associated Legionnaires' disease outbreaks have occurred in New York City, resulting in 213 cases and 18 deaths. Three outbreaks occurred in 2015, including the largest on record (138 cases). Three outbreaks were linked to cooling towers by molecular comparison of human and environmental Legionella isolates, and the sources for the other 3 outbreaks were undetermined. The evolution of investigation methods and lessons learned from these outbreaks prompted enactment of a new comprehensive law governing the operation and maintenance of New York City cooling towers. Ongoing surveillance and program evaluation will determine if enforcement of the new cooling tower law reduces Legionnaires' disease incidence in New York City.

Metal-Diazo Radicals of α-Carbonyl Diazomethanes

Science.gov (United States)

Li, Feifei; Xiao, Longqiang; Liu, Lijian

2016-03-01

Metal-diazo radicals of α-carbonyl diazomethanes are new members of the radical family and are precursors to metal-carbene radicals. Herein, using electron paramagnetic resonance spectroscopy with spin-trapping, we detect diazo radicals of α-carbonyl diazomethanes, induced by [RhICl(cod)]2, [CoII(por)] and PdCl2, at room temperature. The unique quintet signal of the Rh-diazo radical was observed in measurements of α-carbonyl diazomethane adducts of [RhICl(cod)]2 in the presence of 5,5-dimethyl-pyrroline-1-N-oxide (DMPO). DFT calculations indicated that 97.2% of spin density is localized on the diazo moiety. Co- and Pd-diazo radicals are EPR silent but were captured by DMPO to form spin adducts of DMPO-N• (triplet-of-sextets signal). The spin-trapping also provides a powerful tool for detection of metal-carbene radicals, as evidenced by the DMPO-trapped carbene radicals (DMPO-C•, sextet signal) and 2-methyl-2-nitrosopropane-carbene adducts (MNP-C•, doublet-of-triplets signal). The transformation of α-carbonyl diazomethanes to metal-carbene radicals was confirmed to be a two-step process via metal-diazo radicals.

Chemical applications of molecular quantum theory

International Nuclear Information System (INIS)

Ungemach, S.R.

1977-09-01

Molecular systems of chemical interest are investigated with the aid of molecular quantum theory. The self-consistent field (SCF) method is used to predict the molecular structures of ClF 2 , ClF 4 and Cl 3 radicals, and the ions ClF 2 + , ClF 2 - , ClF 4 + and ClF 4 - . The ClF 2 and Cl 3 radicals are predicted to be bent with bond angles of 145.2 0 and 158.6 0 , respectively, while the ions ClF 2 + and ClF 2 - are predicted to be bent with a bond angle of 97.4 0 and linear, respectively. The geometry predictions for the ClF 4 radical and the ClF 4 + ion are found to be notably basis set dependent. The ClF 4 - ion is predicted to be square-planar. Multi-configuration self-consistent field (MCSCF) calculations have yielded the dipole moment function for the 1 sigma + state of HI, which qualitatively confirms the experimental finding that the dipole derivative at R/sub e/ is negative. The 2 sigma + F + H 2 potential energy surface is studied extensively with the configuration interaction (CI) method. The most complete calculations yield an activation energy of 2.74 kcal/mole and an exothermicity of 30.0 kcal/mole. The production of a potential energy surface of ''chemical accuracy'' for this system is found to be more difficult than previously believed. The simplest hydrophobic model, the water-methane system, is studied with the SCF method in order to determine the nature and magnitude of the interaction. The most favorable geometric arrangement corresponds to an attraction of 0.5 kcal/mole

Reaction between protein radicals and other biomolecules

DEFF Research Database (Denmark)

Østdal, H.; Davies, M.J.; Andersen, Henrik Jørgen

2002-01-01

The present study investigates the reactivity of bovine serum albumin (BSA) radicals towards different biomolecules (urate, linoleic acid, and a polypeptide, poly(Glu-Ala-Tyr)). The BSA radical was formed at room temperature through a direct protein-to-protein radical transfer from H(2)O(2....... Subsequent analysis showed a decrease in the concentration of urate upon reaction with the BSA radical, while the BSA radical in the presence of poly(Glu-Ala-Tyr) resulted in increased formation of the characteristic protein oxidation product, dityrosine. Reaction between the BSA radical and a linoleic acid...

Radical intermediates involved in the bleaching of the carotenoid crocin. Hydroxyl radicals, superoxide anions and hydrated electrons

International Nuclear Information System (INIS)

Bors, W.; Saran, M.; Michel, C.

1982-01-01

The participation of the primary radicals in the bleaching of aqueous solutions of the carotenoid crocin by ionizing radiation was investigated, employing both X-radiolysis and pulse radiolysis. The pulse-radiolytic data demonstrated a very rapid diffusion-controlled attack by both hydroxyl radicals (radicalsOH) and hydrated electrons (e - sub(aq)), while superoxide anions (O 2 - ) did not react at all. The site of the initial reaction of these radicals was not limited to the polyene chromophore. Slower secondary reactions involving crocin alkyl or peroxy radicals contribute mainly to the overall bleaching, in particular during steady-state irradiation. (author)

Total aerobic destruction of azo contaminants with nanoscale zero-valent copper at neutral pH: promotion effect of in-situ generated carbon center radicals.

Science.gov (United States)

Dong, Guohui; Ai, Zhihui; Zhang, Lizhi

2014-12-01

In this study, nanoscale zero-valent copper (nZVC) was synthesized with a facile solvothermal method and used for the aerobic removal of azo contaminants at neutral pH for the first time. We found that both Cu(I) and OH generated during the nZVC induced molecular oxygen activation process accounted for the rapid total destruction of azo contaminants in the nZVC/Air system, where nZVC could activate molecular oxygen to produce H2O2, and also release Cu(I) to break the -NN- bond of azo contaminants via the sandmeyer reaction for the generation of carbon center radicals. The in-situ generated carbon center radicals would then react with OH produced by the Cu(I) catalyzed decomposition of H2O2, resulting in the generation of low molecular weight organic acids and their subsequent mineralization. The indispensible role of Cu(I) catalyzed sandmeyer reaction and the promotion effect of in-situ generated carbon center radicals on the rapid total destruction of azo contaminants in the nZVC/Air system were confirmed by gas chromatography-mass spectrometry analysis. This study can deepen our understanding on the degradation of organic pollutant with molecular oxygen activated by zero valent metal, and also provide a new method to remove azo contaminants at neutral pH. Copyright © 2014 Elsevier Ltd. All rights reserved.

A very cool cooling system

CERN Multimedia

Antonella Del Rosso

2015-01-01

The NA62 Gigatracker is a jewel of technology: its sensor, which delivers the time of the crossing particles with a precision of less than 200 picoseconds (better than similar LHC detectors), has a cooling system that might become the precursor to a completely new detector technique.   The 115 metre long vacuum tank of the NA62 experiment. The NA62 Gigatracker (GTK) is composed of a set of three innovative silicon pixel detectors, whose job is to measure the arrival time and the position of the incoming beam particles. Installed in the heart of the NA62 detector, the silicon sensors are cooled down (to about -20 degrees Celsius) by a microfluidic silicon device. “The cooling system is needed to remove the heat produced by the readout chips the silicon sensor is bonded to,” explains Alessandro Mapelli, microsystems engineer working in the Physics department. “For the NA62 Gigatracker we have designed a cooling plate on top of which both the silicon sensor and the...

Formation of long-lived radicals on proteins by radical transfer from heme enzymes--a common process?

DEFF Research Database (Denmark)

Ostdal, H; Andersen, H J; Davies, Michael Jonathan

1999-01-01

concentrations were observed after limited digestion, although this effect was less marked with the HRP/H2O2/BSA system than with Fe(III)Mb/H2O2/BSA, consistent with different modes of radical transfer. More extensive digestion of BSA decreased the radical concentration to levels below those detected with native...... investigated using horseradish peroxidase (HRP)/H2O2, in the presence and absence of added tyrosine. Incubation of HRP with H2O2 and bovine or human serum albumins, in the presence and absence of tyrosine, gave long-lived albumin-derived radicals as detected by EPR spectroscopy. Evidence has been obtained...... for these albumin radicals being located on buried tyrosine residues on the basis of blocking experiments. The effect of protein conformation on radical transfer has been investigated using partial proteolytic digestion prior to protein oxidation. With HRP/H2O2/BSA and Fe(III)Mb/H2O2/BSA increased radical...

How to Cool the Planet by Jeff Goodell

Science.gov (United States)

Goodell, J.

2010-12-01

How to Cool the Planet is a narrative about the radical and controversial world of geoengineering - the deliberate, large-scale manipulation of the earth’s climate to reduce the risk of global warming. Unlike other books on this subject, it is not a polemic or historical review. It is the story of the author, a best-selling author and journalist for the New York Times Magazine, Rolling Stone, and other publications, to answer a not-so-simple question: is geoengineering a crazy idea or not? To answer this question, the author sets out on a quest to talk with - and test the sanity of - the leading scientists in this field, from David Keith, a physicist at the University of Calgary, to James Lovelock, independent scientist best known for his Gaia theory. Along the way, Goodell explores the science behind ideas like cloud brightening and the injection of sulfur particles into the stratosphere to deflect sunlight. But he is equally interested in the moral and ethical issues behind these ideas, as well the hopes and fears of the scientists who are exploring them. In the end, the book is a kind of radical experiment itself, exploring the not just the complexities of an emerging field of science, but the complexities of communicating such audacious thinking to non-scientific readers.

Femtosecond quantum dynamics and laser-cooling in thermal molecular systems

International Nuclear Information System (INIS)

Warmuth, C.

2000-01-01

This work deals with coherent and incoherent vibrational phenomena in thermal systems, wave packet motion and laser-cooling. In the first part, the principle of COIN (Coherence Observation by Interference Noise) has been applied as a new approach to measuring wave packet motion. In the experiment pairs of phase-randomized femtosecond pulses with relative delay-time τ prepare interference fluctuations in the excited state population, so the variance of the correlated fluorescence intensity directly mimics the dynamics of the propagating wave packet. The scheme is demonstrated by measuring the vibrational coherence of wave packet-motion in the B-state of gaseous iodine. The COIN-interferograms obtained recover propagation, recurrences, spreading, and revivals as the typical signature of wave packets. Due to the disharmony of the B-state-potential, fractional revivals have also been found showing the potential of the COIN-technique in quantum-dynamical research. In the second part the fluorescence lifetime of trans-stilbene, isolated and in the presence of 1 atm of Ar gas, respectively, was measured as a function of the detuning of the excitation frequency from the frequency of the 0-0-transition ω 0 . The lifetime was found to decrease on both sides of ω 0 , but the dependence of the lifetime on detuning in the presence of Ar gas is much weaker than for the isolated molecule. Both observations corroborate previous theoretical predictions of laser-cooling of thermal trans-stilbene upon excitation at the ω 0 frequency. The experimental results are in good agreement with theoretical analysis. (author)

Radical surgery compared with intracavitary cesium followed by radical surgery in cervical carcinoma stage IB

Energy Technology Data Exchange (ETDEWEB)

Tinga, D.J.; Bouma, J.; Aalders, J.G. (Dept. of Obstetrics and Gynaecology, State Univ. Hospital, Groningen (Netherlands)); Hollema, H. (Dept. of Pathology, State Univ. Hospital, Groningen (Netherlands))

1990-01-01

Forty-nine patients aged {le} 45 years, with cervical carcinoma stage IB ({le} 3 cm) were treated with either primary radical surgery (n = 26), or intracavitary irradiation followed by radical surgery (n = 23). With primary surgery, ovarian function had been preserved in 15 of the 25 patients, who were alive and well. Seven of the primary surgery patients were irradiated postoperatively and 2 others with a central recurrence were cured by irradiation. One other patient, who was not irradiated postoperatively, had an intestinal metastasis and died of the disease. If any of the adverse prognostic factors (as reported in the literature) had been considered as an indication for postoperative irradiation, 17 patients instead of 7 would have been irradiated after primary radical surgery. In the comparable group of 23 patients treated by intracavitary irradiation and radical surgery (and in 4 cases postoperative irradiation as well) there was no recurrence. There was no significant statistical difference between the treatment results in the cesium + surgery group and those who underwent primary radical surgery. Young patients with early cervical carcinoma without prognostic indicators for postoperative irradiation can benefit from primary radical surgery, because their ovarian function can be preserved. (authors).

Radical surgery compared with intracavitary cesium followed by radical surgery in cervical carcinoma stage IB

International Nuclear Information System (INIS)

Tinga, D.J.; Bouma, J.; Aalders, J.G.; Hollema, H.

1990-01-01

Forty-nine patients aged ≤ 45 years, with cervical carcinoma stage IB (≤ 3 cm) were treated with either primary radical surgery (n = 26), or intracavitary irradiation followed by radical surgery (n = 23). With primary surgery, ovarian function had been preserved in 15 of the 25 patients, who were alive and well. Seven of the primary surgery patients were irradiated postoperatively and 2 others with a central recurrence were cured by irradiation. One other patient, who was not irradiated postoperatively, had an intestinal metastasis and died of the disease. If any of the adverse prognostic factors (as reported in the literature) had been considered as an indication for postoperative irradiation, 17 patients instead of 7 would have been irradiated after primary radical surgery. In the comparable group of 23 patients treated by intracavitary irradiation and radical surgery (and in 4 cases postoperative irradiation as well) there was no recurrence. There was no significant statistical difference between the treatment results in the cesium + surgery group and those who underwent primary radical surgery. Young patients with early cervical carcinoma without prognostic indicators for postoperative irradiation can benefit from primary radical surgery, because their ovarian function can be preserved. (authors)

Free radicals in an Adamantane matrix. XI. Electron paramagnetic resonance study of conformations in the β-halo-tert-butyl radicals

International Nuclear Information System (INIS)

Lloyd, R.V.; Wood, D.E.

1975-01-01

The β-halo-tert-butyl radicals were prepared by x-irradiation of the corresponding isobutyl halides in an adamantane matrix at 77 0 K and their conformations were determined by analysis of their EPR spectra. The radicals are nonplanar at the radical site, the fluoro and chloro radicals trans eclipsed and the bromo and iodo radicals gauche staggered with respect to the relative orientation of the carbon halogen bond and the direction of the singly occupied orbital. Vibration-rotation motions about the favored conformation are much larger for the fluoro radical than for the others. The rate of interconversion of the inequivalent methylene protons is approximately 1.5 x 10 9 sec -1 for the bromo radical at 202 0 K while it is too slow to measure for the iodo radical at the same temperature. The barrier to interconversion has a lower limit of 3 kcal/mol for the bromo radical and higher than that for the iodo radical. The halogen and proton hfsc in gauss and the g values for the XCH 2 C(CH 3 ) 2 radicals are: 19 F = 103.7, CH 2 = 10.4, CH 3 = 23.3, g = 2.0030 at 214 K; 35 Cl = 19.5, CH 2 = 6.3, CH 3 = 21.1, g = 2.0042 at 215 K; 81 Br = 6.7, CH 2 = 21.4, 42.7, CH 3 = 21.4, g = 2.0010 at 202 K; 127 I = 7.0, CH 2 = 21.9, 43.8, CH 3 = 21.9, g = 2.0009 at 208 K. The fluoro radical decays to nonradical products above 318 0 K, the chloro radical converts to 2-methyl allyl radical above 306 0 K, the bromo radical converts to tert-butyl radical by exchange with a matrix proton (or deuteron) at 209 0 K as does the iodo radical above 225 0 K. Photolysis with a Xe lamp converts the bromo and iodo radicals to nonradical products in less than the experimental time constant of 0.3 sec. The hypothesis is put forward that the nonplanarity and high barrier to rotation observed explain the retention of stereochemical configuration in reactions involving β-chloro, β-bromo, and β-iodo alkyl radicals. (auth)

17.9.3 Radical cations of diazo compounds

Science.gov (United States)

Davies, A. G.

This document is part of Subvolume E2 `Phosphorus-Centered Radicals, Radicals Centered on Other Heteroatoms, Organic Radical Ions' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

PHOTOGENERATION OF SINGLET OXYGEN AND FREE RADICALS IN DISSOLVED ORGANIC MATTER ISOLATED FROM THE MISSISSIPPI AND ATCHAFALAYA RIVER PLUMES

Science.gov (United States)

The photoreactivity to UV light of ultrafiltered dissolved organic matter (DOM) collected during cruises along salinity transects in the Mississippi and Atchafalaya River plumes was examined by measuring photogenerated free radicals and singlet molecular oxygen (1O2) photosensiti...

The dissociation of vibrationally excited CH3OSO radicals and their photolytic precursor, methoxysulfinyl chloride.

Science.gov (United States)

Alligood, Bridget W; Womack, Caroline C; Straus, Daniel B; Blase, Frances R; Butler, Laurie J

2011-05-21

The dissociation dynamics of methoxysulfinyl radicals generated from the photodissociation of CH(3)OS(O)Cl at 248 nm is investigated using both a crossed laser-molecular beam scattering apparatus and a velocity map imaging apparatus. There is evidence of only a single photodissociation channel of the precursor: S-Cl fission to produce Cl atoms and CH(3)OSO radicals. Some of the vibrationally excited CH(3)OSO radicals undergo subsequent dissociation to CH(3) + SO(2). The velocities of the detected CH(3) and SO(2) products show that the dissociation occurs via a transition state having a substantial barrier beyond the endoergicity; appropriately, the distribution of velocities imparted to these momentum-matched products is fit by a broad recoil kinetic energy distribution extending out to 24 kcal/mol in translational energy. Using 200 eV electron bombardment detection, we also detect the CH(3)OSO radicals that have too little internal energy to dissociate. These radicals are observed both at the parent CH(3)OSO(+) ion as well as at the CH(3)(+) and SO(2)(+) daughter ions; they are distinguished by virtue of the velocity imparted in the original photolytic step. The detected velocities of the stable radicals are roughly consistent with the calculated barriers (both at the CCSD(T) and G3B3 levels of theory) for the dissociation of CH(3)OSO to CH(3) + SO(2) when we account for the partitioning of internal energy between rotation and vibration as the CH(3)OSOCl precursor dissociates. © 2011 American Institute of Physics.

Inhibition of radiation-induced DNA strand breaks by hoechst 33258: OH-radical scavenging and DNA radical quenching

International Nuclear Information System (INIS)

Adhikary, A.; Bothe, E.; Von Sonntag, C.; Adhikary, A.

1997-01-01

The minor-groove-binding dye Hoechst 33258 has been found to protect pBR322 DNA in aqueous solution against radiation-induced single-strand breaks (ssb). This protective effect has been assumed to be largely due to the scavenging of the strand-break-generating OH radicals by Hoechst. From D 37 values for ssb at different Hoechst concentrations the value of the OH radical scavenging constant of DNA-bound Hoechst has been estimated at k Ho/DNA = 2.7 * 10 11 dm 3 mol -1 . This unexpectedly high value has led us to study the reactions of OH radicals with Hoechst in the absence and in the presence of double-stranded calf thymus DNA (ds DNA) by pulse radiolysis, and the formation of radiation-induced ssb by low angle laser light scattering. The D 37 /D 37 0 values at different Hoechst concentrations agree with the values obtained by Martin and al. and demonstrate the protection. However, this protection cannot be explained on the basis of OH radical scavenging alone using the above rate constants. There must, in addition, be some quenching of DNA radicals. Hoechst radicals are formed in the later ms time range, i.e a long time after the disappearance of the OH radicals. This delayed Hoechst radical formation has been assigned to a a reaction of DNA radicals with Hoechst, thereby inhibiting strand breakage. In confirmation, pulse radiolysis of aqueous solution of nucleotides in the presence of Hoechst yields a similar delayed Hoechst radical formation. The data indicate that in DNA the cross-section of this quenching has a diameter of 3 to 4 base pairs per Hoechst molecule. (N.C.)

Radical-Local Teaching and Learning

DEFF Research Database (Denmark)

Hedegaard, Mariane; Chaiklin, Seth

Radical-Local Teaching and Learning presents a theoretical perspective for analyzing and planning educational programmes for schoolchildren. To realize both general societal interests and worthwhile personal development, the content of educational programmes for children must be grounded in the l......Radical-Local Teaching and Learning presents a theoretical perspective for analyzing and planning educational programmes for schoolchildren. To realize both general societal interests and worthwhile personal development, the content of educational programmes for children must be grounded...... radical-local teaching and learning approach. The first half of the book introduces the idea of radical-local teaching and learning and develops the theoretical background for this perspective, drawing on the cultural-historical research tradition, particularly from Vygotsky, El'konin, Davydov......, and Aidarova. The second half of the book addresses the central concern of radical-local teaching and learning - how to relate educational practices to children's specific historical and cultural conditions. The experiment was conducted for an academic year in an afterschool programme in the East Harlem...

Electronic structure of Co islands grown on the {radical}3 x {radical}3-Ag/Ge(111) surface

Energy Technology Data Exchange (ETDEWEB)

Huang, Xiao-Lan; Chou, Chi-Hao; Lin, Chun-Liang; Tomaszewska, Agnieszka; Fu, Tsu-Yi, E-mail: phtifu@phy.ntnu.edu.tw

2011-09-30

By means of room temperature scanning tunneling spectroscopy (RT STS), we have studied the electronic structure of two different Ag/Ge(111) phases as well as Co islands grown on the {radical}3 x {radical}3-Ag/Ge (111) forming either {radical}13 x {radical}13 or 2 x 2 patterns. The spectrum obtained from 4 x 4-Ag/Ge(111) structure shows the existence of a shoulder at 0.7 V which is also present in the electronic structure of the Ge(111)-c2 x 8 and indicates donation of Ge electrons to electronic states of the Ag-driven phase. However, this fact is not supported by the electronic spectrum taken from the {radical}3 x {radical}3-Ag/Ge (111). The complexity of the Co-{radical}13 x {radical}13 islands bonding with the substrate is mirrored by a large number of peaks in their electronic spectra. The spectra obtained from the Co-2 x 2 islands which had grown on the step differ from those taken from Co-2 x 2 islands located along the edge of the terrace by a number of peaks at negative sample bias. This discrepancy is elucidated in terms of dissimilarities of Co-substrate interaction accompanying Co islands growth on different areas of the stepped surface.

Understanding political radicalization: The two-pyramids model.

Science.gov (United States)

McCauley, Clark; Moskalenko, Sophia

2017-04-01

This article reviews some of the milestones of thinking about political radicalization, as scholars and security officials struggled after 9/11 to discern the precursors of terrorist violence. Recent criticism of the concept of radicalization has been recognized, leading to a 2-pyramids model that responds to the criticism by separating radicalization of opinion from radicalization of action. Security and research implications of the 2-pyramids model are briefly described, ending with a call for more attention to emotional experience in understanding both radicalization of opinion and radicalization of action. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

Orgasm after radical prostatectomy

NARCIS (Netherlands)

Koeman, M; VanDriel, MF; Schultz, WCMW; Mensink, HJA

Objective To evaluate the ability to obtain and the quality of orgasm after radical prostatectomy, Patients and methods The orgasms experienced after undergoing radical prostatectomy were evaluated in 20 men (median age 65 years, range 56-76) using a semi-structured interview and a self-administered

Infrared surface temperature measurements for long pulse operation, and real time feedback control in Tore-Supra, an actively cooled Tokamak

Energy Technology Data Exchange (ETDEWEB)

Guilhem, D.; Adjeroud, B.; Balorin, C.; Buravand, Y.; Bertrand, B.; Bondil, J.L.; Desgranges, C.; Gauthier, E.; Lipa, M.; Messina, P.; Missirlian, M.; Mitteau, R.; Moulin, D.; Pocheau, C.; Portafaix, C.; Reichle, R.; Roche, H.; Saille, A.; Vallet, S

2004-07-01

Tore-Supra has a steady-state magnetic field using super-conducting magnets and water-cooled plasma facing components for high performances long pulse plasma discharges. When not actively cooled, plasma-facing components can only accumulate a limited amount of energy since the temperature increase continuously (T proportional to {radical}(t)) during the discharge until radiation cooling is equal to the incoming heat flux (T > 1800 K). Such an environment is found in most today Tokamaks. In the present paper we report the recent results of Tore-Supra, especially the design of the new generation of infrared endoscopes to measure the surface temperature of the plasma facing components. The Tore-Supra infrared thermography system is composed of 7 infrared endoscopes, this system is described in details in the paper, the new JET infrared thermography system is presented and some insights of the ITER set of visible/infrared endoscope is given. (authors)

O Behaviorismo Radical como filosofia da mente Radical Behaviorism as philosophy of mind

Directory of Open Access Journals (Sweden)

Carlos Eduardo Lopes

2003-01-01

Full Text Available O Behaviorismo Radical de B. F. Skinner é constantemente acusado de eliminar a mente de sua explicação do comportamento humano. Uma análise do livro The Concept of Mind, de Gilbert Ryle, sugere a possibilidade de defender a existência de uma mente relacional, diferente da categoria de existência da mente defendida em interpretações cartesianas (mente substancial. A análise de alguns textos de Skinner sugere que o conceito de uma mente relacional também pode ser defendido no Behaviorismo Radical. Esse fato, culminaria na possibilidade de que, além de filosofia da Ciência do Comportamento, o Behaviorismo Radical, também pode ser uma filosofia da mente, o que traria conseqüências ao estudo e à aplicação da Análise do Comportamento.B. F. Skinner's Radical Behaviorism has been repeatedly accused of eliminating the mind from its explanation of human behavior. An analysis of Gilbert Ryle's book, The Concept of Mind, suggests the possibility of defending the existence of a relational mind, different from the category of existence of mind defended in Cartesian interpretations (substantial mind. The analysis of some texts of Skinner suggests that the concept of a relational mind can also be defended in Radical Behaviorism. This fact would lead to the possibility that, beyond a philosophy of Behavior Science, Radical Behaviorism may also be a philosophy of mind, which would bring consequences to the study and application of Analysis of Behavior.

Molecular Insights into Variable Electron Transfer in Amphibian Cryptochrome

DEFF Research Database (Denmark)

Sjulstok, Emil; Lüdemann, Gesa; Kubař, Tomáš

2018-01-01

are mutated, radical-pair formation is still observed. In this study, we computationally investigate electron-transfer pathways in the X. laevis cryptochrome DASH by extensively equilibrating a previously established homology model using molecular dynamics simulations and then mutating key amino acids......Cryptochrome proteins are activated by the absorption of blue light, leading to the formation of radical pairs through electron transfer in the active site. Recent experimental studies have shown that once some of the amino acid residues in the active site of Xenopus laevis cryptochrome DASH...... involved in the electron transfer. The electron-transfer pathways are then probed by using tight-binding density-functional theory. We report the alternative electron-transfer pathways resolved at the molecular level and, through comparison of amino acid sequences for cryptochromes from different species...

Muonium radicals in benzene-styrene mixtures

International Nuclear Information System (INIS)

Ng, B.W.; Stadlbauer, J.W.; Walker, D.C.

1984-01-01

Muonium radicals were observed through their μ + SR precession frequencies in high transverse magnetic fields in pure benzene, pure styrene and their mixtures, all as liquids at room temperature. In benzene-styrene mixtures, the radicals obtained in each pure liquid are both present, so no slow (10 -9 -10 -5 s) intermolecular exchange occurs; but strong selectivity was found with the formation of the radical from styrene being about eight-times more probable than the radical from benzene. (Auth.)

Magnetocaloric Effect and Thermoelectric Cooling - A Synergistic Cooling Technology

Science.gov (United States)

2018-01-16

Thermoelectric Cooling - A Synergistic Cooling Technology Sb. GRANT NUMBER N00173-14-1-G016 Sc. PROGRAM ELEMENT NUMBER 82-2020-17 6. AUTHOR(S) 5d...Magnetocaloric Effect and Thermoelectric Cooling - A Synergistic Cooling Technology NRL Grant N00173-14-l-G016 CODE 8200: Spacecraft Engineering Department...82-11-0 1: Space and Space Systems Technology General Engineering & Research, L.L.C. Technical & Administrative point of contact: Dr. Robin

Laparoscopic radical cystectomy: key points

Directory of Open Access Journals (Sweden)

D. V. Perlin

2018-01-01

Full Text Available Background. Radical cystectomy remains the golden standard for treatment of muscle invasive bladder cancer. Objective: to duplicate with highest accuracy the open radical cystectomy procedure, which we successfully utilized earlier in our clinic, in the of laparoscopic conditions in order to preserve the advantages of minimally invasive procedures and retain the reliability of the tried and tested open surgery.Materials and methods. In the report were included 35 patients (27 men and 8 women with bladder cancer, who underwent laparoscopic radical cystectomy in Volgograd Regional Center of Urology and Nephrology between April 2013 and March 2016. Only the patients who had been submitted to full intracorporal ileal conduits were included.Results. The mean operative time was 378 minutes, the mean blood loss was 285 millilitres, the mean length of hospital stay was 12.4 days, only 20 % of patients required the narcotic anesthetics. The postoperative complication rate was 11.4 %. However, the majority of the patients were successfully treated with minimally invasive procedures. Generally, our results were similar to other reported studies.Conclusion. Laparoscopic radical cystectomy is a safe and efficient modality of treatment of bladder cancer. However, it needs more procedures and longer observation period to establish laparoscopic radical cystectomy as an alternative to open radical cystectomy.

WORKSHOP: Beam cooling

International Nuclear Information System (INIS)

Anon.

1994-01-01

Cooling - the control of unruly particles to provide well-behaved beams - has become a major new tool in accelerator physics. The main approaches of electron cooling pioneered by Gersh Budker at Novosibirsk and stochastic cooling by Simon van der Meer at CERN, are now complemented by additional ideas, such as laser cooling of ions and ionization cooling of muons

About the influence of lubricating-cooling agents on the cutting process

Directory of Open Access Journals (Sweden)

O.I. Sochko

2017-12-01

Full Text Available Set forth problem of necessity of increase of workability of metal. On the basis of generalization of researches at the area of physics – chemical mechanics of materials the offered hypothesis on the permanent activating of lubricating cooling technological facilities in the zone of cutting to hydrogen plasma, mechanism of her influence on the processes of deformation and destruction, and also reasonable new ways of formation of form of wares. It is in-process shown that lubricating – cooling technological facilities in it in the zone of destruction to the new phase state – hydrogen plasma. It is therefore consisted majority mainly of two elements – hydrogen and carbon, the basic changes of mechanical properties of solid are activated in the conditions of co-operating of body with an environment, it follows to link, with influence of nascent radically-active environment, but not from initial superficially – active. An ambiguousness in the estimation of reasons, at that arises up facilitation of processes of deformation and destructions of solids, that become deformed in different environments caused raising of system researches that is sanctified to this problem. As a result of chemical transformations of initial environment to the level of origin electric of active parts of hydrogen, possibility of their co-operating appears with ions and lone electrons of metal, that increases the electric field, to existing in the system «machine-tool – instrument – purveyance». Exactly co-operation electric of active structure of metal that arises up as a result of mechanical action, with the electric charged mixture of parts of hydrogen, id est an electron-electron, electron-ion and ion-ion, is able co-operation radically to change physical and mechanical properties of metal.

Spin trapping of radicals formed in gamma-irradiated methanol: effect of the irradiation temperature from 77K to 300K

International Nuclear Information System (INIS)

Schlick, S.; Kevan, L.

1976-01-01

The neutral radicals formed in gamma-irradiated methanol were studied by spin trapping with phenyl-t-butylnitrone (PBN) in an attempt to probe the primary neutral radicals formed. In the temperature range from approximately 157 K to 300 K both CH 2 OH and CH 3 O spin adducts are observed and their limiting ratio at high PBN concentrations is CH 2 OH/CH 3 O=1.5 over this temperature range. Below approximately 157 K this ratio increases exponentially with decreasing temperature with an apparent activation energy of 5.8 kJ/mole (1.4 kcal/mole); this is consistent with the finding that only CH 2 OH radicals are formed by gamma radiolysis at 77 K. Several possible models for the primary neutral radicals formed in gamma-irradiated methanol and their subsequent reactions as a function of irradiation temperature are discussed. It is suggested that the primary radical formation mechanisms are similar in the gas and liquid phases and become temperature dependent when molecular motion is arrested in the solid. (Auth.)

A study of the cool gas in the Large Magellanic Cloud. I. Properties of the cool atomic phase - a third H i absorption survey

Science.gov (United States)

Marx-Zimmer, M.; Herbstmeier, U.; Dickey, J. M.; Zimmer, F.; Staveley-Smith, L.; Mebold, U.

2000-02-01

The cool atomic interstellar medium of the Large Magellanic Cloud (LMC) seems to be quite different from that in the Milky Way. In a series of three papers we study the properties of the cool atomic hydrogen in the LMC (Paper I), its relation to molecular clouds using SEST-CO-observations (Paper II) and the cooling mechanism of the atomic gas based on ISO-[\\CII]-investigations (Paper III). In this paper we present the results of a third 21 cm absorption line survey toward the LMC carried out with the Australia Telescope Compact Array (ATCA). 20 compact continuum sources, which are mainly in the direction of the supergiant shell LMC 4, toward the surroundings of 30 Doradus and toward the eastern steep \\HI\\ boundary, have been chosen from the 1.4 GHz snapshot continuum survey of Marx et al. We have identified 20 absorption features toward nine of the 20 sources. The properties of the cool \\HI\\ clouds are investigated and are compared for the different regions of the LMC taking the results of Dickey et al. (survey 2) into account. We find that the cool \\HI\\ gas in the LMC is either unusually abundant compared to the cool atomic phase of the Milky Way or the gas is clearly colder (\\Tc\\ ~ 30 K) than that in our Galaxy (\\Tc\\ ~ 60 K). The properties of atomic clouds toward 30 Doradus and LMC 4 suggest a higher cooling rate in these regions compared to other parts of the LMC, probably due to an enhanced pressure near the shock fronts of LMC 4 and 30 Doradus. The detected cool atomic gas toward the eastern steep \\HI\\ boundary might be the result of a high compression of gas at the leading edge. The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.

ESR low-temperature investigations on water-containing biological substances to determine type, concentration and kinetics of the free radicals induced by irradiation with X-rays and β-radiation

International Nuclear Information System (INIS)

Fell, H.A.

1975-01-01

In the present work, ESR investigations on pure water and further biological interesting substances with high water content were carried out. In order to stabilize the free primary radicals occurring after irradiation, it was necessary to cool down the samples to the temperature of liquid helium. Methods were developed which enabled irradiation of the pure sample substance at this temperature to be performed. Two different kinds of radiation were applied, X-ray and β-radiation, and the results were compared with one another. The problem of transporting the irradiated sample from the place of irradiation to the measuring position maintaining 4.2 K was solved. A device was constructed to study the radical kinetics with whose assistance the samples can be brought to a pre-chosen temperature for a certain time. A calibration of the ESR spectrometer as well as the use of a secondary standard was necessary for the quantitative determination of the radical concentration. The type and concentration of the primary radicals occurring were investigated in the measured samples as well as the reduction of the radical concentration with increasing temperature determined. The measured values were compared with theoretical considerations. The effect of the radicals on biological systems at various temperatures was discussed. (orig./LH) [de

Radical chemistry of artemisinin

Energy Technology Data Exchange (ETDEWEB)

Denisov, Evgenii T; Solodova, S L; Denisova, Taisa G [Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region (Russian Federation)

2011-12-29

The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

Radical chemistry of artemisinin

Science.gov (United States)

Denisov, Evgenii T.; Solodova, S. L.; Denisova, Taisa G.

2010-12-01

The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

Radical chemistry of artemisinin

International Nuclear Information System (INIS)

Denisov, Evgenii T; Solodova, S L; Denisova, Taisa G

2010-01-01

The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

Radical chemistry of artemisinin

Energy Technology Data Exchange (ETDEWEB)

Denisov, Evgenii T; Solodova, S L; Denisova, Taisa G [Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region (Russian Federation)

2010-12-29

The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

Oxygen free radicals in rheumatoid arthritis

NARCIS (Netherlands)

P. Biemond (Pieter)

1986-01-01

textabstractCurrent knowledge strongly suggests that oxygen free radicals are involved in the pathogenesis of RA. Additional information about the mechanism of free radical attack is necessary in order to find out if interaction with the mechanism of free radical damage can be used in the treatment

Free radicals in health and disease

International Nuclear Information System (INIS)

Gonet, B.

1993-01-01

Free radicals appear in the cells as the result of exogenic factors (ionizing radiation, UV) or reactions naturally occurring in the cell. Free radical reactions may cause destruction of macromolecules (DNA, lipids, proteins). Free radical pathology is important in many diseases and aging processes in organisms

Radiative and mechanical feedback into the molecular gas of NGC 253

NARCIS (Netherlands)

Rosenberg, M. J. F.; Kazandjian, M. V.; van der Werf, P. P.; Israel, F. P.; Meijerink, R.; Weiß, A.; Requena-Torres, M. A.; Güsten, R.

Starburst galaxies are galaxies or regions of galaxies undergoing intense periods of star formation. Understanding the heating and cooling mechanisms in these galaxies can give us insight to the driving mechanisms that fuel the starburst. Molecular emission lines play a crucial role in the cooling

The structure and properties of free radicals: An electron spin resonance study of radiation damage to nucleic acid and protein components and to some sulfur-substituted derivitives

International Nuclear Information System (INIS)

Sagstuen, E.

1979-01-01

When cellular systems are exposed to ionizing radiation the long-term effects may range from minor disturbances to such dramatic changes as mutations and cell death. The processes leading to these macroscopical injuries are primarily confined at the molecular level. In all models aimed at a description of the action of radiation at the molecular level the formation of free radicals (which are species containing unpaired electrons) is a central concept. The technique of ESR spectroscopy is uniquely suited to study free radicals, as it is based on resonance absorption of energy by unpaired electrons in a magnetic field. ESR spectroscopy makes it possible to detect free radicals and, in some cases, to identify them. In order to study free radicals by ESR it is necessary to build up a sufficient number of unpaired spins in the sample (approximately 10 11 or more, depending on the shape of the resonance). This may be different techniques have been used to trap the induced radicals or to attain a sufficient steady state concentration level. A procedure which seems to contain a large amount of information is to irradiate at low temperatures, and, by subsequent heat-treatment of the sample to study the reactions and fate of the induced radicals. In this thesis single crystal studies of aromatic amino acids and pyrimidine derivitives together with some substituted purine derivitives are presented, and the results are discussed in relation to the present knowledge about radical formation in these classes of compounds. Single crystal studies of some sulfur-containing aromatic compounds have been presented with the purpose of shedding light on the electronic structure of sulfur-centred radicals. (JIW)

Free radicals in wood induced by γ-radiation

International Nuclear Information System (INIS)

Xu Honglin; Zhang Wenhui

1994-01-01

The free radicals in wood induced by γ-radiation were studied by electron spin resonance. The fine structure of the ESR signal from sawdust samples irradiated could be resolved into various radicals. These free radicals have a very long lifetime. The major spectrum for the free radicals will exponentially increased along with the radiation dose according to Y 1-Exp(-α a D). The intensity of radiation radicals is dependent on tree species. The stronger the intensity of mechanic free radicals is, the stronger the intensity of radiation free radicals

Dynamics of Peroxy and Alkenyl Radicals Undergoing Competing Rearrangements in Biodiesel Combustion

Energy Technology Data Exchange (ETDEWEB)

Dibble, Theodore S. [State Univ. of New York (SUNY), Syracuse, NY (United States)

2016-03-24

Biodiesel fuel is increasingly being used worldwide. Although we have a fair understanding of the molecular details of the chemistry of peroxy radicals derived from alkanes, biodiesel fuels contain ester and olefin groups which significantly impact the thermodynamics and kinetics of biodiesel ignition. The broader goal of this research is to carry out systematic computational studies of the elementary kinetics of the chemistry of ROO•, QOOH and •OOQOOH compounds that are models for biodiesel ignition.

Radical-Local Teaching and Learning

DEFF Research Database (Denmark)

Hedegaard, Mariane; Chaiklin, Seth

radical-local teaching and learning approach. The first half of the book introduces the idea of radical-local teaching and learning and develops the theoretical background for this perspective, drawing on the cultural-historical research tradition, particularly from Vygotsky, El'konin, Davydov......, and Aidarova. The second half of the book addresses the central concern of radical-local teaching and learning - how to relate educational practices to children's specific historical and cultural conditions. The experiment was conducted for an academic year in an afterschool programme in the East Harlem......Radical-Local Teaching and Learning presents a theoretical perspective for analyzing and planning educational programmes for schoolchildren. To realize both general societal interests and worthwhile personal development, the content of educational programmes for children must be grounded...

What is Radical Behaviorism? A Review of Jay Moore's Conceptual Foundations of Radical Behaviorism

Science.gov (United States)

Baum, William M

2011-01-01

B. F. Skinner founded both radical behaviorism and behavior analysis. His founding innovations included: a versatile preparation for studying behavior; explicating the generic nature of stimulus and response; a pragmatic criterion for defining behavioral units; response rate as a datum; the concept of stimulus control; the concept of verbal behavior; and explicating the explanatory power of contingencies. Besides these achievements, however, Skinner also made some mistakes. Subsequent developments in radical behaviorist thought have attempted to remedy these mistakes. Moore's book presents a “party line” version of radical behaviorism. It focuses narrowly on a few of Skinner's concepts (mostly mentalism and verbal behavior) and contains no criticism of his mistakes. In fact, Moore adds a few mistakes of his own manufacture; for example, he insists that the mental realm does not exist—an unprovable and distracting assertion. The book's portrayal of behavior analysis would have been current around 1960; it mentions almost none of the developments since then. It also includes almost no developments in radical behaviorism since Skinner. Moore's book would give an unwary reader a highly distorted picture of contemporary behavior analysis and radical behaviorism.

Experimental evaluation of cooling efficiency of the high performance cooling device

Science.gov (United States)

Nemec, Patrik; Malcho, Milan

2016-06-01

This work deal with experimental evaluation of cooling efficiency of cooling device capable transfer high heat fluxes from electric elements to the surrounding. The work contain description of cooling device, working principle of cooling device, construction of cooling device. Experimental part describe the measuring method of device cooling efficiency evaluation. The work results are presented in graphic visualization of temperature dependence of the contact area surface between cooling device evaporator and electronic components on the loaded heat of electronic components in range from 250 to 740 W and temperature dependence of the loop thermosiphon condenser surface on the loaded heat of electronic components in range from 250 to 740 W.

Experimental evaluation of cooling efficiency of the high performance cooling device

Energy Technology Data Exchange (ETDEWEB)

Nemec, Patrik, E-mail: patrik.nemec@fstroj.uniza.sk; Malcho, Milan, E-mail: milan.malcho@fstroj.uniza.sk [University of Žilina, Faculty of Mechanical Engineering, Department of Power Engineering, Univerzitna 1, 010 26 Žilina (Slovakia)

2016-06-30

This work deal with experimental evaluation of cooling efficiency of cooling device capable transfer high heat fluxes from electric elements to the surrounding. The work contain description of cooling device, working principle of cooling device, construction of cooling device. Experimental part describe the measuring method of device cooling efficiency evaluation. The work results are presented in graphic visualization of temperature dependence of the contact area surface between cooling device evaporator and electronic components on the loaded heat of electronic components in range from 250 to 740 W and temperature dependence of the loop thermosiphon condenser surface on the loaded heat of electronic components in range from 250 to 740 W.

Continuous all-optical deceleration of molecular beams

Science.gov (United States)

Jayich, Andrew; Chen, Gary; Long, Xueping; Wang, Anna; Campbell, Wesley

2014-05-01

A significant impediment to generating ultracold molecules is slowing a molecular beam to velocities where the molecules can be cooled and trapped. We report on progress toward addressing this issue with a general optical deceleration technique for molecular and atomic beams. We propose addressing the molecular beam with a pump and dump pulse sequence from a mode-locked laser. The pump pulse counter-propagates with respect to the beam and drives the molecules to the excited state. The dump pulse co-propagates and stimulates emission, driving the molecules back to the ground state. This cycle transfers 2 ℏk of momentum and can generate very large optical forces, not limited by the spontaneous emission lifetime of the molecule or atom. Importantly, avoiding spontaneous emission limits the branching to dark states. This technique can later be augmented with cooling and trapping. We are working towards demonstrating this optical force by accelerating a cold atomic sample.

Evidence for radical anion formation during liquid secondary ion mass spectrometry analysis of oligonucleotides and synthetic oligomeric analogues: a deconvolution algorithm for molecular ion region clusters.

Science.gov (United States)

Laramée, J A; Arbogast, B; Deinzer, M L

1989-10-01

It is shown that one-electron reduction is a common process that occurs in negative ion liquid secondary ion mass spectrometry (LSIMS) of oligonucleotides and synthetic oligonucleosides and that this process is in competition with proton loss. Deconvolution of the molecular anion cluster reveals contributions from (M-2H).-, (M-H)-, M.-, and (M + H)-. A model based on these ionic species gives excellent agreement with the experimental data. A correlation between the concentration of species arising via one-electron reduction [M.- and (M + H)-] and the electron affinity of the matrix has been demonstrated. The relative intensity of M.- is mass-dependent; this is rationalized on the basis of base-stacking. Base sequence ion formation is theorized to arise from M.- radical anion among other possible pathways.

Radical scavenging behavior of eriodictyol and fustin flavonoid compounds - A DFT study

Science.gov (United States)

Sadasivam, K.; Praveena, R.; Anbakzhakan, K.

2018-05-01

The density functional theory (DFT) protocol together with B3LYP/6-311G(d,p) level of theory has been utilized to explore and compare the structural features and molecular characteristics of two naturally occurring flavonoid compounds eriodictyol and fustin. The -OH bond dissociation energy (BDE) for all the radical species have been computed and interpreted in accordance with the radical scavenging activity. The ionization potential (IP) value of fustin flavonoid compound was found to be within the range of synthetic food additives. The polar nature and their capacity to polarise other atoms are established through the dipole moment analysis. Additionally, various parameters that are relevant to chemical potential such as electron affinity, hardness, softness, electro negativity and electrophilic index were calculated and analysed in the light of quercetin flavonoid compound in view of their antioxidant activity. The antioxidant capability of fustin is found to be superior to eriodictyol flavonoid.

Molecular dynamics simulations of nucleation and phase transitions in molecular clusters of hexafluorides

International Nuclear Information System (INIS)

Xu, S.

1993-01-01

Molecular dynamics simulations of nucleation and phase transitions in TeF 6 and SeF 6 clusters containing 100-350 molecules were carried out. Simulations successfully reproduced the crystalline structures observed in electron diffraction studies of large clusters (containing about 10 4 molecules) of the same materials. When the clusters were cooled, they spontaneously underwent the same bcc the monoclinic phase transition in simulations as in experiment, despite the million-fold difference in the time scales involved. Other transitions observed included melting and freezing. Several new techniques based on molecular translation and orientation were introduced to identify different condensed phases, to study nucleation and phase transitions, and to define characteristic temperatures of transitions. The solid-state transition temperatures decreased with cluster size in the same way as did the melting temperature, in that the depression of transition temperature was inversely proportional to the cluster radius. Rotational melting temperatures, as inferred from the rotational diffusion of molecules, coincided with those of the solid-state transition. Nucleation in liquid-solid and bcc-monoclinic transitions started in the interior of clusters on cooling, and at the surface on heating. Transition temperatures on cooling were always lower than those on heating due to the barriers to nucleation. Linear growth rates of nuclei in freezing were an order of magnitude lower than those in the bcc-monoclinic transition. Revealing evidence about the molecular behavior associated with phase changes was found. Simulations showed the formation of the actual transition complexes along the transition pathway, i.e., the critical nuclei of the new phase. These nuclei, consisting of a few dozen molecules, were distinguishable in the midst of the surrounding matter

Orthographic Skills Important to Chinese Literacy Development: The Role of Radical Representation and Orthographic Memory of Radicals

Science.gov (United States)

Yeung, Pui-sze; Ho, Connie Suk-han; Chan, David Wai-ock; Chung, Kevin Kien-hoa

2016-01-01

A 3-year longitudinal study among 239 Chinese students in Grades 2-4 was conducted to investigate the relationships between orthographic skills (including positional and functional knowledge of semantic radicals and phonetic radicals, and orthographic memory of radicals) and Chinese literacy skills (word reading, word spelling, reading…

The Games Radicals Play: Special Issue on Free Radicals and Radical Ions

Directory of Open Access Journals (Sweden)

John C. Walton

2015-02-01

Full Text Available Chemistry and Physics have aptly been described as “most excellent children of Intellect and Art” [1]. Both these “children” engage with many playthings, and molecules rank as one of their first favorites, especially radicals, which are amongst the most lively and exciting. Checking out radicals dancing to the music of entropy round their potential energy ballrooms is surely both entertaining and enlightening. Radicals’ old favorite convolutions are noteworthy, but the new styles, modes and arrangements appearing on the scene are even more interesting. Some of these are ephemeral and enjoy only a brief appearance, others are retro-types reappearing in new guises, still others are genuinely new and “go viral” in the scientific world. This Special Issue of Molecules contains the observations and reflections of a select group of chemists and physicists fascinated by this spectacle. It contains an eclectic mix reflecting on new modes and advances as well as on permutations and combinations that revive mature themes. [...

Cooling towers

International Nuclear Information System (INIS)

Boernke, F.

1975-01-01

The need for the use of cooling systems in power plant engineering is dealt with from the point of view of a non-polluting form of energy production. The various cooling system concepts up to the modern natural-draught cooling towers are illustrated by examples. (TK/AK) [de

Radical-pair based avian magnetoreception

Science.gov (United States)

Procopio, Maria; Ritz, Thorsten

2014-03-01

Behavioural experiments suggest that migratory birds possess a magnetic compass sensor able to detect the direction of the geomagnetic. One hypothesis for the basis of this remarkable sensory ability is that the coherent quantum spin dynamics of photoinduced radical pair reactions transduces directional magnetic information from the geomagnetic field into changes of reaction yields, possibly involving the photoreceptor cryptochrome in the birds retina. The suggested radical-pair based avian magnetoreception has attracted attention in the field of quantum biology as an example of a biological sensor which might exploit quantum coherences for its biological function. Investigations on such a spin-based sensor have focussed on uncovering the design features for the design of a biomimetic magnetic field sensor. We study the effects of slow fluctuations in the nuclear spin environment on the directional signal. We quantitatively evaluate the robustness of signals under fluctuations on a timescale longer than the lifetime of a radical pair, utilizing two models of radical pairs. Our results suggest design principles for building a radical-pair based compass sensor that is both robust and highly directional sensitive.

Clinical and molecular features of high-grade osteosarcoma

NARCIS (Netherlands)

Anninga, Jakob Klaas

2013-01-01

It can be concluded from this thesis that high-grade osteosarcoma is at clinical, pathological and molecular level a heterogeneous disease. To treat high-grade osteosarcoma, neo-adjuvant chemotherapy should be combined with radical surgery, irrespective the localization. There are only 4 effective

Observations of far-infrared molecular emission lines from the Orion molecular cloud

International Nuclear Information System (INIS)

Viscuso, P.J.

1986-01-01

The Orion Nebula has been the subject of intensive study for over one hundred years. Far-infrared (FIR) molecular line observations of CO in the shock region surrounding the infrared source IRc2 have suggested that the molecular hydrogen density in the shocked and post-shock gas is roughly 3 x 10 6 cm -3 . The temperature of this gas is on the order of 750-2000K. IRc2, like other nearby infrared sources within the Nebula, is thought to be a site of recent star formation. This object is apparently at the center of a massive bipolar molecular outflow of gas, which is producing a shock front where it meets the ambient molecular cloud surrounding IRc2. Study of such regions is important for the understanding of the chemical and physical processes that are involved in the formation of stars from molecular clouds. Recently, several far-infrared transitions among the low-lying levels of OH have been observed toward IRc2. OH is thought to be abundant, and it plays an important role in the chemical evolution of the shock and post-shock regions. The OH emission serves as a sensitive probe of the temperature and density for the shock-processed gas. A rigorous treatment of the radiative transfer of these measured transitions is performed using the escape probability formalism. From this analysis, the author determines the temperature of the OH-emitting region to be on the order of 40K. This suggests that the gas is part of the post-shock gas that has cooled sufficiently, most likely by way of radiative cooling by CO

Formation and spectroscopy of {alpha}-muoniated radicals

Energy Technology Data Exchange (ETDEWEB)

McKenzie, I.; Brodovitch, J.C.; Ghandi, K.; Kecman, S.; Percival, P.W

2003-02-01

Several novel {alpha}-muoniated radicals have been produced by the reaction of muonium with compounds containing diazo, isocyanate or carbene functional groups. In {alpha}-muoniated radicals the muon is attached directly to the radical centre; they can be formed either directly or indirectly via a {beta}-muoniated radical intermediate. The hyperfine coupling constants of the resulting radicals have been measured by transverse field muon spin rotation and muon avoided level-crossing resonance. The effect of muonium substitution was investigated for cases where ESR data are available for comparison.

Formation and spectroscopy of α-muoniated radicals

International Nuclear Information System (INIS)

McKenzie, I.; Brodovitch, J.C.; Ghandi, K.; Kecman, S.; Percival, P.W.

2003-01-01

Several novel α-muoniated radicals have been produced by the reaction of muonium with compounds containing diazo, isocyanate or carbene functional groups. In α-muoniated radicals the muon is attached directly to the radical centre; they can be formed either directly or indirectly via a β-muoniated radical intermediate. The hyperfine coupling constants of the resulting radicals have been measured by transverse field muon spin rotation and muon avoided level-crossing resonance. The effect of muonium substitution was investigated for cases where ESR data are available for comparison

Trapped ultracold molecular ions: candidates for an optical molecular clock for a fundamental physics mission in space

Science.gov (United States)

Roth, B.; Koelemeij, J.; Daerr, H.; Ernsting, I.; Jorgensen, S.; Okhapkin, M.; Wicht, A.; Nevsky, A.; Schiller, S.

2017-11-01

Narrow ro-vibrational transitions in ultracold molecules are excellent candidates for frequency references in the near-IR to visible spectral domain and interesting systems for fundamental tests of physics, in particular for a satellite test of the gravitational redshift of clocks. We have performed laser spectroscopy of several ro-vibrational overtone transitions υ = 0 → υ = 4 in HD+ ions at around 1.4 μm. 1+1 REMPD was used as a detection method, followed by measurement of the number of remaining molecules. The molecular ions were stored in a linear radiofrequency trap and cooled to millikelvin temperatures, by sympathetic cooling using laser-cooled Be+ ions simultaneously stored in the same trap.

Environmentally Persistent Free Radical (EPFRs) - Ambient Air Particulates, Soils and Fate of Some Pollutants

Science.gov (United States)

Lomnicki, S. M.

2017-12-01

Environmentally Persistent Free Radicals (EPFRs) are relatively recently discovered species that are present on ambient air particulates. Their origin is typically associated with the combustion borne PM, where in the cool zone of the combustion process aromatic precursors react with the metal centers of particulates forming surface-organic complex with radical characteristics. EPFRs have been found to be sufficiently resistant to be emitted from the combustion sources and persist in the ambient air on particulates. Their inhalation has been associated with severe health effects, and potentially are one of the major agents contributing the epidemiological risks of PM exposure. Interestingly, EPFRs can be formed not only at the elevated temperatures but also in ambient conditions, where the contact of precursor molecules with transition metal (but not only) domains can result in adsorbate complexes. In fact, EPFRs have been detected in the contaminated soils, or during the oil spill incidents. It is very likely, that the interaction of some molecules released to the air can result in the formation of EPFRs on the ambient air particulates in atmospheric conditions. These species can be a natural degradation by-products that lead to the formation of oxygenated organics in ambient atmosphere.

Restaurant food cooling practices.

Science.gov (United States)

Brown, Laura Green; Ripley, Danny; Blade, Henry; Reimann, Dave; Everstine, Karen; Nicholas, Dave; Egan, Jessica; Koktavy, Nicole; Quilliam, Daniela N

2012-12-01

Improper food cooling practices are a significant cause of foodborne illness, yet little is known about restaurant food cooling practices. This study was conducted to examine food cooling practices in restaurants. Specifically, the study assesses the frequency with which restaurants meet U.S. Food and Drug Administration (FDA) recommendations aimed at reducing pathogen proliferation during food cooling. Members of the Centers for Disease Control and Prevention's Environmental Health Specialists Network collected data on food cooling practices in 420 restaurants. The data collected indicate that many restaurants are not meeting FDA recommendations concerning cooling. Although most restaurant kitchen managers report that they have formal cooling processes (86%) and provide training to food workers on proper cooling (91%), many managers said that they do not have tested and verified cooling processes (39%), do not monitor time or temperature during cooling processes (41%), or do not calibrate thermometers used for monitoring temperatures (15%). Indeed, 86% of managers reported cooling processes that did not incorporate all FDA-recommended components. Additionally, restaurants do not always follow recommendations concerning specific cooling methods, such as refrigerating cooling food at shallow depths, ventilating cooling food, providing open-air space around the tops and sides of cooling food containers, and refraining from stacking cooling food containers on top of each other. Data from this study could be used by food safety programs and the restaurant industry to target training and intervention efforts concerning cooling practices. These efforts should focus on the most frequent poor cooling practices, as identified by this study.

Restaurant Food Cooling Practices†

Science.gov (United States)

BROWN, LAURA GREEN; RIPLEY, DANNY; BLADE, HENRY; REIMANN, DAVE; EVERSTINE, KAREN; NICHOLAS, DAVE; EGAN, JESSICA; KOKTAVY, NICOLE; QUILLIAM, DANIELA N.

2017-01-01

Improper food cooling practices are a significant cause of foodborne illness, yet little is known about restaurant food cooling practices. This study was conducted to examine food cooling practices in restaurants. Specifically, the study assesses the frequency with which restaurants meet U.S. Food and Drug Administration (FDA) recommendations aimed at reducing pathogen proliferation during food cooling. Members of the Centers for Disease Control and Prevention’s Environmental Health Specialists Network collected data on food cooling practices in 420 restaurants. The data collected indicate that many restaurants are not meeting FDA recommendations concerning cooling. Although most restaurant kitchen managers report that they have formal cooling processes (86%) and provide training to food workers on proper cooling (91%), many managers said that they do not have tested and verified cooling processes (39%), do not monitor time or temperature during cooling processes (41%), or do not calibrate thermometers used for monitoring temperatures (15%). Indeed, 86% of managers reported cooling processes that did not incorporate all FDA-recommended components. Additionally, restaurants do not always follow recommendations concerning specific cooling methods, such as refrigerating cooling food at shallow depths, ventilating cooling food, providing open-air space around the tops and sides of cooling food containers, and refraining from stacking cooling food containers on top of each other. Data from this study could be used by food safety programs and the restaurant industry to target training and intervention efforts concerning cooling practices. These efforts should focus on the most frequent poor cooling practices, as identified by this study. PMID:23212014

Unimolecular fragrmentations of the radical cation of the high-valent organometal oxide CH3ReO3 and its reactivity with ethylene in the gas phase

Science.gov (United States)

Schröder, Detlef; Herrmann, W. A.; Fischer, Richard W.; Schwarz, Helmut

1992-12-01

The unimolecular chemistry of CH3ReO[radical sign]+3 in the gas phase commences with a methyl migration to' generate CH3 OReO[radical sign]+2. This further undergoes multiple hydrogen migration to the metal centre to generate an intermediate which serves as a precursor for the elimination of both molecular hydrogen and of carbon monoxide. If CH3ReO[radical sign]+3 is reacted with ethylene, inter alia products are observed which point to a competition between an intramolecular metathesis reaction of the ethylene-inserted intermediate CH3CH2CH2ReO3[radical sign]+ and epoxidation of ethylene to generate c-C2H4O.

Cooling tower calculations

International Nuclear Information System (INIS)

Simonkova, J.

1988-01-01

The problems are summed up of the dynamic calculation of cooling towers with forced and natural air draft. The quantities and relations are given characterizing the simultaneous exchange of momentum, heat and mass in evaporative water cooling by atmospheric air in the packings of cooling towers. The method of solution is clarified in the calculation of evaporation criteria and thermal characteristics of countercurrent and cross current cooling systems. The procedure is demonstrated of the calculation of cooling towers, and correction curves and the effect assessed of the operating mode at constant air number or constant outlet air volume flow on their course in ventilator cooling towers. In cooling towers with the natural air draft the flow unevenness is assessed of water and air relative to its effect on the resulting cooling efficiency of the towers. The calculation is demonstrated of thermal and resistance response curves and cooling curves of hydraulically unevenly loaded towers owing to the water flow rate parameter graded radially by 20% along the cross-section of the packing. Flow rate unevenness of air due to wind impact on the outlet air flow from the tower significantly affects the temperatures of cooled water in natural air draft cooling towers of a design with lower demands on aerodynamics, as early as at wind velocity of 2 m.s -1 as was demonstrated on a concrete example. (author). 11 figs., 10 refs

Cooling optically levitated dielectric nanoparticles via parametric feedback

Science.gov (United States)

Neukirch, Levi; Rodenburg, Brandon; Bhattacharya, Mishkatul; Vamivakas, Nick

2015-05-01

The inability to leverage resonant scattering processes involving internal degrees of freedom differentiates optical cooling experiments performed with levitated dielectric nanoparticles, from similar atomic and molecular traps. Trapping in optical cavities or the application of active feedback techniques have proven to be effective ways to circumvent this limitation. We present our nanoparticle optical cooling apparatus, which is based on parametric feedback modulation of a single-beam gradient force optical trap. This scheme allows us to achieve effective center-of-mass temperatures well below 1 kelvin for our ~ 1 ×10-18 kg particles, at modest vacuum pressures. The method provides a versatile platform, with parameter tunability not found in conventional tethered nanomechanical systems. Potential applications include investigations of nonequilibrium nanoscale thermodynamics, ultra-sensitive force metrology, and mesoscale quantum mechanics and hybrid systems. Supported by the office of Naval Research award number N000141410442.

Semantic Radicals Contribute More Than Phonetic Radicals to the Recognition of Chinese Phonograms: Behavioral and ERP Evidence in a Factorial Study

Directory of Open Access Journals (Sweden)

Xieshun Wang

2017-12-01

Full Text Available The Chinese phonograms consist of a semantic radical and a phonetic radical. The two types of radicals have different functional contributions to their host phonogram. The semantic radical typically signifies the meaning of the phonogram, while the phonetic radical usually contains a phonological clue to the phonogram’s pronunciation. However, it is still unclear how they interplay with each other when we attempt to recognize a phonogram because previous studies rarely manipulated the functionality of the two types of radicals in a single design. Using a full factorial design, the present study aimed to probe this issue by directly manipulating the functional validity of the two types of radicals in a lexical decision task with both behavioral and event-related potential (ERP measurements. The results showed that recognition of phonograms which were related to their semantic radicals in meaning took a shorter reaction time, showed a lower error rate, and elicited a smaller P200 and a larger N400 than did recognition of those which had no semantic relation with their semantic radicals. However, the validity of phonetic radicals did not show any main effect or interaction with that of semantic radicals on either behavioral or ERP measurements. These results indicated that semantic radicals played a dominant role in the recognition of phonograms. Transparent semantic radicals, which provide valid semantic cues to phonograms, can facilitate the recognition of phonograms.

Pyrimidine nucleobase radical reactivity in DNA and RNA

Science.gov (United States)

Greenberg, Marc M.

2016-11-01

Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

Atomic and electronic structure transformations of silver nanoparticles under rapid cooling conditions.

Science.gov (United States)

Lobato, I; Rojas, J; Landauro, C V; Torres, J

2009-02-04

The structural evolution and dynamics of silver nanodrops Ag(2869) (4.4 nm in diameter) under rapid cooling conditions have been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modelled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique are used to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of 1.5625 × 10(13) K s(-1) the nanoparticles preserve an amorphous-like structure containing a large amount of 1551 and 1541 pairs which correspond to icosahedral symmetry. For a lower cooling rate (1.5625 × 10(12) K s(-1)), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and 1422 pairs which correspond to the face centred cubic and hexagonal close packed structures, respectively. The variations of the electronic density of states for the differently cooled nanoparticles are small, but in correspondence with the structural changes.

Quantification of hydroxyl radical produced during phacoemulsification.

Science.gov (United States)

Gardner, Jonathan M; Aust, Steven D

2009-12-01

To quantitate hydroxyl radicals produced during phacoemulsification with various irrigating solutions and conditions used in cataract surgery. Chemistry and Biochemistry Department, Utah State University, Logan, Utah, USA. All experiments were performed using an Infiniti Vision System phacoemulsifier with irrigation and aspiration. Hydroxyl radicals were quantitated using electron spin resonance spectroscopy and a spectrophotometric assay for malondialdehyde, which is formed by the oxidation of deoxyribose by the hydroxyl radical. Hydroxyl radical production increased during longitudinal-stroking phacoemulsification as power levels were increased in a nonlinear, nonexponential fashion. The detection of hydroxyl radical was reduced in irrigating solutions containing organic molecules (eg, citrate, acetate, glutathione, dextrose) and further reduced in Navstel, an irrigating solution containing a viscosity-modifying agent, hydroxypropyl methylcellulose. Hydroxyl radicals produced in settings representative of those used in phacoemulsification cataract surgery were quantitated using the deoxyribose method. Hydroxyl radical production was dependent on the level of ultrasound power applied and the irrigating solution used. Oxidative stress on the eye during phacoemulsification may be minimized by using irrigating solutions that contain organic molecules, including the viscosity-modifying agent hydroxypropyl methylcellulose, that can compete for reaction with hydroxyl radicals.

Free radicals in biology. Volume II

International Nuclear Information System (INIS)

Pryor, W.A.

1976-01-01

This volume continues the treatment of topics in free radical biology and free radical pathology from Volume I. In the first chapter, pyridinyl radicals, radicals which are models for those derived from NAD, are discussed. Pyridinyl radicals can be synthesized and isolated and directly studied in a number of chemical systems. The next chapter treats the role of glutathione in the cell. It is becoming even more apparent that this vital thiol controls a large number of important cellular functions. The GSH/GSSG balance has recently been implicated as a control for cellular development; this balance also may be important in relaying the effects of oxidants from one site to another in the body. The next chapter outlines the reactions of singlet oxygen; some of these involve free radicals and some do not. This reactive intermediate appears to be important both in photochemical smog and in cellular chemistry where singlet oxygen is produced by nonphotochemical processes. The production of free radicals from dry tissues, a controversial area with conflicting claims is reviewed. The next chapter outlines the current status of the studies of photochemical smog. The next two chapters treat specific reactive materials which are present in smog. The first discusses the chemistry of nitrogen oxides and ozone. The second chapter treats the chemistry of the peroxyacyl nitrites. These compounds, although present in only small concentration, are among the most toxic components of smog. The last two chapters treat radiation damage to proteins and radiation protection and radical reactions produced by radiation in nucleic acids

O conceito de mal radical The concept of radical evil

Directory of Open Access Journals (Sweden)

Adriano Correia

2005-01-01

Full Text Available A noção de mal radical aparece em Kant no contexto da discussão da religião nos limites da simples razão e busca dar conta da complexa relação entre o respeito pela lei moral e o amor-próprio na definição do móbil para a ação. Na busca por identificar o fundamento da propensão para o mal no homem, Kant se vê diante da dificuldade de ter de articular natureza e liberdade, e ainda que a noção de mal radical possa conservar algumas ambigüidades, permite conceber uma noção de responsabilidade compatível com uma inata propensão para o mal. Neste texto busco explicitar alguns passos fundamentais na construção do conceito por Kant.The concept of radical evil appears in Kant's theory when he discusses the religion in the limits of the mere reason and aims explain the complex relationship between respect for the moral law and the self-love, for establish the motive of the action. By aiming identify the basis of human inclination to evil, Kant is faced with the trouble of have to put nature and freedom in connection. Despite of the concept of radical evil retain some ambiguity, it allows conceive a notion of responsibility suitable to an inherent inclination to evil. In this paper is my purpose to explain some basic moments of Kantian formulation of that notion.

HPLC-ESR techniques for detection of complex trapped radicals

International Nuclear Information System (INIS)

Tu Tiecheng; Dong Jirong; Lin Nianyun; Xie Leidong; Liu Rengzhong

1992-01-01

High performance liquid chromatography (HPLC) and ESR combined examination of radical species is an advanced techniques for separation and identification of complex radical species. At SRCL, Waters 990 HPLC has been used to separate the complex trapped radicals and Varian E-112 ESR spectrometer to record the spectra of single trapped radicals after HPLC separation. The advantages of the combined techniques are described as bellow: HPLC is used to separate the long-lived complex trapped radicals derived from reaction of short-lived radicals with spin trap. ESR spectra from single trapped radicals, obtained following HPLC separation of complex trapped radicals, are recorded one by one and well resolved. The structures of short-lived radicals can be inferred from the ESR spectra of the long-lived trapped radicals

Scavenging of free-radical metabolites of aniline xenobiotics and drugs by amino acid derivatives: toxicological implications of radical-transfer reactions.

Science.gov (United States)

Michail, Karim; Baghdasarian, Argishti; Narwaley, Malyaj; Aljuhani, Naif; Siraki, Arno G

2013-12-16

We investigated a novel scavenging mechanism of arylamine free radicals by poly- and monoaminocarboxylates. Free radicals of arylamine xenobiotics and drugs did not react with oxygen in peroxidase-catalyzed reactions; however, they showed marked oxygen uptake in the presence of an aminocarboxylate. These free-radical intermediates were identified using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and electron paramagnetic resonance (EPR) spectrometry. Diethylenetriaminepentaacetic acid (DTPA), a polyaminocarboxylate, caused a concentration-dependent attenuation of N-centered radicals produced by the peroxidative metabolism of arylamines with the subsequent formation of secondary aliphatic carbon-centered radicals stemming from the cosubstrate molecule. Analogously, N,N-dimethylglycine (DMG) and N-methyliminodiacetate (MIDA), but not iminodiacetic acid (IDA), demonstrated a similar scavenging effect of arylamine-derived free radicals in a horseradish peroxidase/H2O2 system. Using human promyelocytic leukemia (HL-60) cell lysate as a model of human neutrophils, DTPA, MIDA, and DMG readily reduced anilinium cation radicals derived from the arylamines and gave rise to the corresponding carbon radicals. The rate of peroxidase-triggered polymerization of aniline was studied as a measure of nitrogen-radical scavenging. Although, IDA had no effect on the rate of aniline polymerization, this was almost nullified in the presence of DTPA and MIDA at half of the molar concentration of the aniline substrate, whereas a 20 molar excess of DMPO caused only a partial inhibition. Furthermore, the yield of formaldehyde, a specific reaction endproduct of the oxidation of aminocarboxylates by aniline free-radical metabolites, was quantitatively determined. Azobenzene, a specific reaction product of peroxidase-catalyzed free-radical dimerization of aniline, was fully abrogated in the presence of DTPA, as confirmed by GC/MS. Under aerobic conditions, a radical-transfer reaction

COMPUTATIONAL STUDY OF INTERSTELLAR GLYCINE FORMATION OCCURRING AT RADICAL SURFACES OF WATER-ICE DUST PARTICLES

International Nuclear Information System (INIS)

Rimola, Albert; Sodupe, Mariona; Ugliengo, Piero

2012-01-01

Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH . radical and H 3 O + surface defects. The coupling of incoming CO molecules with the surface OH . radicals on the ice clusters yields the formation of the COOH . radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol –1 and –22 kcal mol –1 , respectively. The COOH . radicals couple with incoming NH=CH 2 molecules (experimentally detected in the ISM) to form the NHCH 2 COOH . radical glycine through energy barriers of 12 kcal mol –1 , exceedingly high at ISM cryogenic temperatures. Nonetheless, when H 3 O + is present, one proton may be barrierless transferred to NH=CH 2 to give NH 2 =CH 2 + . This latter may react with the COOH . radical to give the NH 2 CH 2 COOH +. glycine radical cation which can then be transformed into the NH 2 CHC(OH) 2 +. species (the most stable form of glycine in its radical cation state) or into the NH 2 CHCOOH . neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh-physical conditions of the ISM may trigger reactions of cosmochemical interest. The relevance of surface H 3 O

Computational Study of Interstellar Glycine Formation Occurring at Radical Surfaces of Water-ice Dust Particles

Science.gov (United States)

Rimola, Albert; Sodupe, Mariona; Ugliengo, Piero

2012-07-01

Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH• radical and H3O+ surface defects. The coupling of incoming CO molecules with the surface OH• radicals on the ice clusters yields the formation of the COOH• radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol-1 and -22 kcal mol-1, respectively. The COOH• radicals couple with incoming NH=CH2 molecules (experimentally detected in the ISM) to form the NHCH2COOH• radical glycine through energy barriers of 12 kcal mol-1, exceedingly high at ISM cryogenic temperatures. Nonetheless, when H3O+ is present, one proton may be barrierless transferred to NH=CH2 to give NH2=CH2 +. This latter may react with the COOH• radical to give the NH2CH2COOH+• glycine radical cation which can then be transformed into the NH2CHC(OH)2 +• species (the most stable form of glycine in its radical cation state) or into the NH2CHCOOH• neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh-physical conditions of the ISM may trigger reactions of cosmochemical interest. The relevance of surface H3O+ ions to facilitate chemical

Cooling Tower Overhaul of Secondary Cooling System in HANARO

Energy Technology Data Exchange (ETDEWEB)

Park, Young Chul; Lee, Young Sub; Jung, Hoan Sung; Lim, In Chul [KAERI, Daejeon (Korea, Republic of)

2007-07-01

HANARO, an open-tank-in-pool type research reactor of 30 MWth power in Korea, has been operating normally since its initial criticality in February, 1995. For the last about ten years, A cooling tower of a secondary cooling system has been operated normally in HANARO. Last year, the cooling tower has been overhauled for preservative maintenance including fills, eliminators, wood support, water distribution system, motors, driving shafts, gear reducers, basements, blades and etc. This paper describes the results of the overhaul. As results, it is confirmed that the cooling tower maintains a good operability through a filed test. And a cooling capability will be tested when a wet bulb temperature is maintained about 28 .deg. C in summer and the reactor is operated with the full power.

Cooling Performance of ALIP according to the Air or Sodium Cooling Type

Energy Technology Data Exchange (ETDEWEB)

Ye, Huee-Youl; Yoon, Jung; Lee, Tae-Ho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2015-05-15

ALIP pumps the liquid sodium by Lorentz force produced by the interaction of induced current in the liquid metal and their associated magnetic field. Even though the efficiency of the ALIP is very low compared to conventional mechanical pumps, it is very useful due to the absence of moving parts, low noise and vibration level, simplicity of flow rate regulation and maintenance, and high temperature operation capability. Problems in utilization of ALIP concern a countermeasure for elevation of internal temperature of the coil due to joule heating and how to increase magnetic flux density of Na channel gap. The conventional ALIP usually used cooling methods by circulating the air or water. On the other hand, GE-Toshiba developed a double stator pump adopting the sodium-immersed self-cooled type, and it recovered the heat loss in sodium. Therefore, the station load factor of the plant could be reduced. In this study, the cooling performance with cooling types of ALIP is analyzed. We developed thermal analysis models to evaluate the cooling performance of air or sodium cooling type of ALIP. The cooling performance is analyzed for operating parameters and evaluated with cooling type. 1-D and 3-D thermal analysis model for IHTS ALIP was developed, and the cooling performance was analyzed for air or sodium cooling type. The cooling performance for air cooling type was better than sodium cooling type at higher air velocity than 0.2 m/s. Also, the air temperature of below 270 .deg. demonstrated the better cooling performance as compared to sodium.

Reactions of carbonate radical with cobalt(II) aminopolycarboxylates

International Nuclear Information System (INIS)

Mandal, P.C.; Bardhan, D.K.; Bhattacharyya, S.N.

1992-01-01

Reactions of carbonate (CO 3 - radical) and bicarbonate (HCO 3 radical) radicals generated by photolysis of a carbonate or bicarbonate solution at pH 11.2 and 8.5, respectively, with Co(II) complexes of iminodiacetic acid (IDA) and ethylenediaminetetraacetic acid (EDTA) have been studied. The rate constants for the reactions were in the order of 10 6 -10 7 dm 3 mol -1 s -1 . From the time-resolved spectroscopy of the products formed after reaction of CO 3 - radical or HCO 3 radical, it is observed that CO 3 - radical or HCO 3 radical oxidize the metal center to its higher oxidation state. (author) 26 refs.; 2 figs.; 1 tab

Self-Terminating, Oxidative Radical Cyclizations

Directory of Open Access Journals (Sweden)

Uta Wille

2004-05-01

Full Text Available The recently discovered novel concept of self-terminating, oxidative radical cyclizations, through which alkynes can be converted into carbonyl compounds under very mild reaction conditions using O-centered inorganic and organic radicals as oxidants, is described

Film cooling air pocket in a closed loop cooled airfoil

Science.gov (United States)

Yu, Yufeng Phillip; Itzel, Gary Michael; Osgood, Sarah Jane; Bagepalli, Radhakrishna; Webbon, Waylon Willard; Burdgick, Steven Sebastian

2002-01-01

Turbine stator vane segments have radially inner and outer walls with vanes extending between them. The inner and outer walls are compartmentalized and have impingement plates. Steam flowing into the outer wall plenum passes through the impingement plate for impingement cooling of the outer wall upper surface. The spent impingement steam flows into cavities of the vane having inserts for impingement cooling the walls of the vane. The steam passes into the inner wall and through the impingement plate for impingement cooling of the inner wall surface and for return through return cavities having inserts for impingement cooling of the vane surfaces. To provide for air film cooing of select portions of the airfoil outer surface, at least one air pocket is defined on a wall of at least one of the cavities. Each air pocket is substantially closed with respect to the cooling medium in the cavity and cooling air pumped to the air pocket flows through outlet apertures in the wall of the airfoil to cool the same.

Participation of oxidized sulfur center in intramolecular free radical processes in the model organic compounds of biological importance

International Nuclear Information System (INIS)

Pogocki, D.M.

2004-01-01

The pathogenesis of neurodegenerative diseases such as prion diseases (Creutzfeldt-Jacob disease) and Alzheimer's disease is strongly associated with the presence of β-amyloid peptide (βA) and prion protein (hPrP) in the brain tissue. Both macromolecules contain methionine (Met) residues. Their presence seems to be responsible for unique redox properties of βA and hPrP. These residues may undergo relatively easy autooxidation and/or metal-catalysed oxidation. The presented studies were focused on the potential function of Met residues as antioxidants or pro-oxidants and on their role in radical-mediated oxidation of peptides and proteins. The role of S-, O-, N- and C-centered radicals generated in various oligopeptides containing Met and relevant model compounds has been examined in detail with respect to formation of 2c-3e bonds, redox processes, fragmentation and their mutual interconversion. In order to achieve these goals several experimental radiation, photochemical, and molecular modelling methods were applied. The experimental and molecular modelling results show significant influence of functional neighbouring groups and conformational flexibility of a peptide backbone on the oxidative reduction pathway in oligopeptides containing single and multiple Met residues. The results presented here allow for better understanding of the known propensities of βA and hPrP to reduce transition metals and to form reactive oxygen species and free radicals. (author)

First-in-Human Ultrasound Molecular Imaging With a VEGFR2-Specific Ultrasound Molecular Contrast Agent (BR55) in Prostate Cancer: A Safety and Feasibility Pilot Study.

Science.gov (United States)

Smeenge, Martijn; Tranquart, François; Mannaerts, Christophe K; de Reijke, Theo M; van de Vijver, Marc J; Laguna, M Pilar; Pochon, Sibylle; de la Rosette, Jean J M C H; Wijkstra, Hessel

2017-07-01

BR55, a vascular endothelial growth factor receptor 2 (VEGFR2)-specific ultrasound molecular contrast agent (MCA), has shown promising results in multiple preclinical models regarding cancer imaging. In this first-in-human, phase 0, exploratory study, we investigated the feasibility and safety of the MCA for the detection of prostate cancer (PCa) in men using clinical standard technology. Imaging with the MCA was performed in 24 patients with biopsy-proven PCa scheduled for radical prostatectomy using a clinical ultrasound scanner at low acoustic power. Safety monitoring was done by physical examination, blood pressure and heart rate measurements, electrocardiogram, and blood sampling. As first-in-human study, MCA dosing and imaging protocol were necessarily fine-tuned along the enrollment to improve visualization. Imaging data were correlated with radical prostatectomy histopathology to analyze the detection rate of ultrasound molecular imaging with the MCA. Imaging with MCA doses of 0.03 and 0.05 mL/kg was adequate to obtain contrast enhancement images up to 30 minutes after administration. No serious adverse events or clinically meaningful changes in safety monitoring data were identified during or after administration. BR55 dosing and imaging were fine-tuned in the first 12 patients leading to 12 subsequent patients with an improved MCA dosing and imaging protocol. Twenty-three patients underwent radical prostatectomy. A total of 52 lesions were determined to be malignant by histopathology with 26 (50%) of them seen during BR55 imaging. In the 11 patients that were scanned with the improved protocol and underwent radical prostatectomy, a total of 28 malignant lesions were determined: 19 (68%) were seen during BR55 ultrasound molecular imaging, whereas 9 (32%) were not identified. Ultrasound molecular imaging with BR55 is feasible with clinical standard technology and demonstrated a good safety profile. Detectable levels of the MCA can be reached in patients

Free radicals and low-level photon emission in human pathogenesis: state of the art.

Science.gov (United States)

Van Wijk, Roeland; Van Wijk, Eduard P A; Wiegant, Fred A C; Ives, John

2008-05-01

Convincing evidence supports a role for oxidative stress in the pathogenesis of many chronic diseases. The model includes the formation of radical oxygen species (ROS) and the misassembly and aggregation of proteins when three tiers of cellular defence are insufficient: (a) direct antioxidative systems, (b) molecular damage repairing systems, and (c) compensatory chaperone synthesis. The aim of the present overview is to introduce (a) the basics of free radical and antioxidant metabolism, (b) the role of the protein quality control system in protecting cells from free radical damage and its relation to chronic diseases, (c) the basics of the ultraweak luminescence as marker of the oxidant status of biological systems, and (d) the research in human photon emission as a non-invasive marker of oxidant status in relation to chronic diseases. In considering the role of free radicals in disease, both their generation and their control by the antioxidant system are part of the story. Excessive free radical production leads to the production of heat shock proteins and chaperone proteins as a second line of protection against damage. Chaperones at the molecular level facilitate stress regulation vis-à-vis protein quali y control mechanisms. The manifestation of misfolded proteins and aggregates is a hallmark of a range of neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, amylotrophic lateral sclerosis, polyglutamine (polyQ) diseases, diabetes and many others. Each of these disorders exhibits aging-dependent onset and a progressive, usually fatal clinical course. The second part reviews the current status of human photon emission techniques and protocols for recording the human oxidative status. Sensitive photomultiplier tubes may provide a tool for non-invasive and continuous monitoring of oxidative metabolism. In that respect, recording ultraweak luminescence has been favored compared to other indirect assays. Several biological models have

Atomic and molecular adsorption on Rh(111)

DEFF Research Database (Denmark)

Mavrikakis, Manos; Rempel, J.; Greeley, Jeffrey Philip

2002-01-01

A systematic study of the chemisorption of both atomic (H, O, N, S, C), molecular (N-2, CO, NO), and radical (CH3, OH) species on Rh(111) has been performed. Self-consistent, periodic, density functional theory (DFT-GGA) calculations, using both PW91 and RPBE functionals, have been employed to de...

Oxidation of aromatic amines and diamines by OH radicals. Formation and ionization constants of amine cation radicals in water

International Nuclear Information System (INIS)

Hayon, E.; Rao, P.S.

1975-01-01

The one-electron oxidation by hydroxyl radicals of aromatic amines and diamines in water was studied using the fast-reaction technique of pulse radiolysis and kinetic absorption spectrophotometry. The following compounds were examined: N,N,N 1 ,N 1 - tetramethyl-p-phenylenediamine (TMPD), p-phenylenediamine (PD), N,N-dimethyl-p-phenylenediamene (DMPD), N,N,N 1 ,N 1 -tetramethylbenzidine (TMB), and diphenylamine (DPA). The main initial reaction of the OH radicals is suggested to be an addition to these compounds to give absorption spectra which absorb strongly in the visible and uv regions. These OH radical adducts decay by first-order kinetics and have lifetimes of approximately 5-50 μsec, dependent on the pH, buffer concentration, and the nature of the aromatic amines and diamines. They decay to give species with somewhat similar absorption spectra and extinction coefficients, which are very long lived in the absence of oxygen. The latter species are assigned to the cation radicals TMPD. + , PD. + , DMPD. + , TMB. + , and DPA. + . The OH radical adducts and the cation radicals have acid-base properties. The pK/sub a/ values of the cation radicals TMPDH. 2+ , PDH. 2+ , DMPDH. 2+ , TMBH. 2+ , and DPAH. 2+ were found to be 5.3, 5.9, 6.1, 5.1, and 4.2, respectively. The results indicate that these aromatic amines and diamines can be oxidized by free radicals to yield the corresponding cation radicals. (U.S.)

Intermediate Radical Termination Theory in Elucidation of RAFT Kinetics and Comparison to Experimental Data

Directory of Open Access Journals (Sweden)

M. Baqeri-Jagharq

2008-12-01

Full Text Available In current work a comprehensive mechanism based on intermediate radical termination theory is assumed for RAFT polymerization of styrene over cumyl dithiobenzoate as RAFT agent. Rate constants for addition (ka and fragmentation reactions (kf are set to 6×106 and 5×104 respectively, which lead to an equilibrium constant value of K = ka/kf = 1.2 x 102. Moment equations method was used to model this mechanism and the results were compared to experimental data to verify modeling. The effects of changing RAFT agent concentration on conversion, molecular weight and polydispersity index of the final product were investigated through the modeling. According to the results, the likelihood of living polymerization increases with raising RAFT agent concentration which leads to linearity of conversion and molecular weight curves and therefore lowering the polydispersity index and narrowing the molecular weight distribution.

Near-Infrared Free-Radical and Free-Radical-Promoted Cationic Photopolymerizations by In-Source Lighting Using Upconverting Glass.

Science.gov (United States)

Kocaarslan, Azra; Tabanli, Sevcan; Eryurek, Gonul; Yagci, Yusuf

2017-11-13

A method is presented for the initiation of free-radical and free-radical-promoted cationic photopolymerizations by in-source lighting in the near-infrared (NIR) region using upconverting glass (UCG). This approach utilizes laser irradiation of UCG at 975 nm in the presence of fluorescein (FL) and pentamethyldiethylene triamine (PMDETA). FL excited by light emitted from the UCG undergoes electron-transfer reactions with PMDETA to form free radicals capable of initiating polymerization of methyl methacrylate. To execute the corresponding free-radical-promoted cationic polymerization of cyclohexene oxide, isobutyl vinyl ether, and N-vinyl carbazole, it was necessary to use FL, dimethyl aniline (DMA), and diphenyliodonium hexafluorophosphate as sensitizer, coinitiator, and oxidant, respectively. Iodonium ions promptly oxidize DMA radicals formed to the corresponding cations. Thus, cationic polymerization with efficiency comparable to the conventional irradiation source was achieved. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Coherent electron cooling

Energy Technology Data Exchange (ETDEWEB)

Litvinenko,V.

2009-05-04

Cooling intense high-energy hadron beams remains a major challenge in modern accelerator physics. Synchrotron radiation is still too feeble, while the efficiency of two other cooling methods, stochastic and electron, falls rapidly either at high bunch intensities (i.e. stochastic of protons) or at high energies (e-cooling). In this talk a specific scheme of a unique cooling technique, Coherent Electron Cooling, will be discussed. The idea of coherent electron cooling using electron beam instabilities was suggested by Derbenev in the early 1980s, but the scheme presented in this talk, with cooling times under an hour for 7 TeV protons in the LHC, would be possible only with present-day accelerator technology. This talk will discuss the principles and the main limitations of the Coherent Electron Cooling process. The talk will describe the main system components, based on a high-gain free electron laser driven by an energy recovery linac, and will present some numerical examples for ions and protons in RHIC and the LHC and for electron-hadron options for these colliders. BNL plans a demonstration of the idea in the near future.

Man-portable personal cooling garment based on vacuum desiccant cooling

International Nuclear Information System (INIS)

Yang Yifan; Stapleton, Jill; Diagne, Barbara Thiané; Kenny, Glen P.; Lan, Christopher Q.

2012-01-01

A man-portable personal cooling garment based on the concept of vacuum desiccant cooling (VDC) was developed. It was demonstrated with cooling pads that a cooling capacity of 373.1 W/m 2 could be achieved in an ambient environment of 37 °C. Tests with human subjects wearing prototype cooling garments consisting of 12 VDC pads with an overall weight of 3.4 kg covering 0.4 m 2 body surface indicate that the garment could maintain a core temperature substantially lower than the control when the workload was walking on a treadmill of 2% inclination at 3 mph. The exercise was carried out in an environment of 40 °C and 50% relative humidity (RH) for 60 min. Tests also showed that the VDC garment could effectively reduce the metabolic heat accumulation in body with subject wearing heavily insulated nuclear, biological and chemical (NBC) suit working in the heat and allow the participant to work safely for 60 min, almost doubling the safe working time of the same participant when he wore NBC suit only. - Highlights: ► Heat stress mitigation is important for workers health, safety, and performance. ► Vacuum desiccant cooling (VDC) a novel concept for personal cooling. ► VDC garment man-portable and more efficient than commercial ice/pad vest. ► VDC garment suitable for personal cooling with NBC suit.

OH radical induced depolymerization of poly(methacrylic acid)

Science.gov (United States)

Ulanski, Piotr; Bothe, Eberhard; von Sonntag, Clemens

1999-05-01

Hydroxyl radicals (generated pulse radiolytically in dilute N 2O-saturated aqueous solutions) react with poly(methacrylic acid) producing two kinds of radicals. The primary radical is converted into a secondary one by H-abstraction ( k=3.5 × 10 2 s -1) as monitored by changes in the UV spectrum. Subsequently, the secondary radicals undergo chain scission ( k=1.8 s -1 at pH 7-9). This process has been followed both by spectrophotometry as well as by conductometry. In competition with the bimolecular decay of the radicals the ensuing end-chain radicals undergo efficient depolymerization resulting in the release of monomer. Since the lifetime of the radicals is much longer at high pH, where the polymer attains a rod-like conformation, depolymerization is most efficient in basic solution.

Laser cooling of solids

CERN Document Server

Petrushkin, S V

2009-01-01

Laser cooling is an important emerging technology in such areas as the cooling of semiconductors. The book examines and suggests solutions for a range of problems in the development of miniature solid-state laser refrigerators, self-cooling solid-state lasers and optical echo-processors. It begins by looking at the basic theory of laser cooling before considering such topics as self-cooling of active elements of solid-state lasers, laser cooling of solid-state information media of optical echo-processors, and problems of cooling solid-state quantum processors. Laser Cooling of Solids is an important contribution to the development of compact laser-powered cryogenic refrigerators, both for the academic community and those in the microelectronics and other industries. Provides a timely review of this promising field of research and discusses the fundamentals and theory of laser cooling Particular attention is given to the physics of cooling processes and the mathematical description of these processes Reviews p...

To cool, but not too cool: that is the question--immersion cooling for hyperthermia.

Science.gov (United States)

Taylor, Nigel A S; Caldwell, Joanne N; Van den Heuvel, Anne M J; Patterson, Mark J

2008-11-01

Patient cooling time can impact upon the prognosis of heat illness. Although ice-cold-water immersion will rapidly extract heat, access to ice or cold water may be limited in hot climates. Indeed, some have concerns regarding the sudden cold-water immersion of hyperthermic individuals, whereas others believe that cutaneous vasoconstriction may reduce convective heat transfer from the core. It was hypothesized that warmer immersion temperatures, which induce less powerful vasoconstriction, may still facilitate rapid cooling in hyperthermic individuals. Eight males participated in three trials and were heated to an esophageal temperature of 39.5 degrees C by exercising in the heat (36 degrees C, 50% relative humidity) while wearing a water-perfusion garment (40 degrees C). Subjects were cooled using each of the following methods: air (20-22 degrees C), cold-water immersion (14 degrees C), and temperate-water immersion (26 degrees C). The time to reach an esophageal temperature of 37.5 degrees C averaged 22.81 min (air), 2.16 min (cold), and 2.91 min (temperate). Whereas each of the between-trial comparisons was statistically significant (P < 0.05), cooling in temperate water took only marginally longer than that in cold water, and one cannot imagine that the 45-s cooling time difference would have any meaningful physiological or clinical implications. It is assumed that this rapid heat loss was due to a less powerful peripheral vasoconstrictor response, with central heat being more rapidly transported to the skin surface for dissipation. Although the core-to-water thermal gradient was much smaller with temperate-water cooling, greater skin and deeper tissue blood flows would support a superior convective heat delivery. Thus, a sustained physiological mechanism (blood flow) appears to have countered a less powerful thermal gradient, resulting in clinically insignificant differences in heat extraction between the cold and temperate cooling trials.

Electron spin resonance study of radicals in irradiated polyethylene

International Nuclear Information System (INIS)

Fujimura, Takashi

1979-02-01

In order to elucidate radiation effect in polyethylene, the nature and behavior of radicals produced in polyethylene and the model compound of polyethylene irradiated at 77 0 K were studied by using electron spin resonance. The structure of radical pairs, which are composed of two radicals produced very closely each other, was investigated in drawn polyethylene and the single crystal of n-eicosane. The radical pairs of intrachain type and interchain type were found in polyethylene and n-eicosane respectively. It was suggested that these two types of radical pairs are the precursors of double bonds and crosslinks respectively. The thermal decay reactions of radicals themselves produced in irradiated polyethylene were investigated. It was made clear that the short range distances between two radicals play an important role in the decay reaction of alkyl radicals at low temperatures. The trapping regions of radicals were studied and it was clarified that allyl radicals, which are produced by the reaction of alkyl radicals with double bonds, are trapped both in the crystalline and non-crystalline regions. (author)

Redox properties of free radicals

International Nuclear Information System (INIS)

Neta, P.

1981-01-01

Results of electron transfer reactions observed and monitored by pulse radiolysis are reported. This technique allows determination of the first one-electron reduction or oxidation of a compound rather than the overall two-electron transfer usually reported. Pulse radiolysis allows the determination of absolute rate constants for reactions of free radicals and helps elucidate the mechanisms involved. Studies using this technique to study radicals derived from quinones, nitro compounds, pyridines, phenols, and anilines are reported. Radicals of biochemical interest arising from riboflavin, ascorbic acid, vitamin K 3 , vitamin E, MAD + , porphyrins, etc. have also been studied

Hot wire radicals and reactions

International Nuclear Information System (INIS)

Zheng Wengang; Gallagher, Alan

2006-01-01

Threshold ionization mass spectroscopy is used to measure radical (and stable gas) densities at the substrate of a tungsten hot wire (HW) reactor. We report measurements of the silane reaction probability on the HW and the probability of Si and H release from the HW. We describe a model for the atomic H release, based on the H 2 dissociation model. We note major variations in silicon-release, with dependence on prior silane exposure. Measured radical densities versus silane pressure yield silicon-silane and H-silane reaction rate coefficients, and the dominant radical fluxes to the substrate

Performance characteristic of hybrid cooling system based on cooling pad and evaporator

Science.gov (United States)

Yoon, J. I.; Son, C. H.; Choi, K. H.; Kim, Y. B.; Sung, Y. H.; Roh, S. J.; Kim, Y. M.; Seol, S. H.

2018-01-01

In South Korea, most of domestic animals such as pigs and chickens might die due to thermal diseases if they are exposed to the high temperature consistently. In order to save them from the heat wave, numerous efforts have been carried out: installing a shade net, adjusting time of feeding, spraying mist and setting up a circulation fan. However, these methods have not shown significant improvements. Thus, this study proposes a hybrid cooling system combining evaporative cooler and air-conditioner in order to resolve the conventional problems caused by the high temperature in the livestock industry. The problem of cooling systems using evaporative cooling pads is that they are not effective for eliminating huge heat load due to their limited capacity. And, temperature of the supplied air cannot be low enough compared to conventional air-conditioning systems. On the other hand, conventional air-conditioning systems require relatively expensive installation cost, and high operating cost compared to evaporative cooling system. The hybrid cooling system makes up for the lack of cooling capacity of the evaporative cooler by employing the conventional air-conditioner. Additionally, temperature of supplied air can be lowered enough. In the hybrid cooling system, induced air by a fan is cooled by the evaporation of water in the cooling pad, and it is cooled again by an evaporator in the air-conditioner. Therefore, the more economical operation is possible due to additionally obtained cooling capacity from the cooling pads. Major results of experimental analysis of hybrid cooling system are as follows. The compressor power consumption of the hybrid cooling system is about 23% lower, and its COP is 17% higher than that of the conventional air-conditioners. Regarding the condition of changing ambient temperature, the total power consumption decreased by about 5% as the ambient temperature changed from 28.7°C to 31.7°C. Cooling capacity and COP also presented about 3% and 1

Synthesis and Characterization of Ethylenedithio-MPTTF-PTM Radical Dyad as a Potential Neutral Radical Conductor

DEFF Research Database (Denmark)

Souto, Manuel; Bendixen, Dan; Jensen, Morten

2016-01-01

During the last years there has been a high interest in the development of new purely-organic single-component conductors. Very recently, we have reported a new neutral radical conductor based on the perchlorotriphenylmethyl (PTM) radical moiety linked to a monopyrrolo-tetrathiafulvalene (MPTTF...

Spray cooling

International Nuclear Information System (INIS)

Rollin, Philippe.

1975-01-01

Spray cooling - using water spraying in air - is surveyed as a possible system for make-up (peak clipping in open circuit) or major cooling (in closed circuit) of the cooling water of the condensers in thermal power plants. Indications are given on the experiments made in France and the systems recently developed in USA, questions relating to performance, cost and environmental effects of spray devices are then dealt with [fr

An Experimental and Quantum Chemical Study of the Electronic Spectrum of the HBCl Free Radical

Science.gov (United States)

Gharaibeh, Mohammed A.; Nagarajan, Ramya; Clouthier, Dennis J.; Tarroni, Ricardo

2012-06-01

The chloroborane (HBCl) free radical has a complex electronic spectrum in the visible that involves a transition from a bent ground state to a linear excited state, both of which are the Renner-Teller components of what would be a ^2π state at linearity. We have used the synchronous-scan LIF and single vibronic level emission techniques to untangle the many overlapping vibronic bands and assign upper state K quantum numbers for jet-cooled HBCl and DBCl. The radicals were produced in a pulsed electric discharge jet using a precursor mixture of boron trichloride (BCl_3) and hydrogen or deuterium in high-pressure argon. As an important aid to understanding the data, the ground and excited state high level ab initio potential energy surfaces (PES) have been calculated and the vibrational levels obtained variationally. The calculated ground state levels are in excellent agreement with the emission data validating the quality of the PES. Aside from an approximately 100 cm-1 shift in the upper state electronic term value, the calculated excited state vibrational energy levels and isotope shifts match the LIF data very well, allowing the observed bands to be assigned with confidence.

Cooperative Magnetism in Crystalline N-Aryl-Substituted Verdazyl Radicals: First-Principles Predictions and Experimental Results.

Science.gov (United States)

Eusterwiemann, Steffen; Dresselhaus, Thomas; Doerenkamp, Carsten; Janka, Oliver; Niehaus, Oliver; Massolle, Anja; Daniliuc, Constantin G; Eckert, Hellmut; Pöttgen, Rainer; Neugebauer, Johannes; Studer, Armido

2017-05-02

We report on a series of eight diaryl-6-oxo-verdazyl radicals containing a tert-butyl group at the C(3) position with regard to their crystal structure and magnetic properties by means of magnetic susceptibility measurements in combination with quantum chemical calculations using a first-principles bottom-up approach. The latter method allows for a qualitative prediction and detailed analysis of the correlation between the solid-state architecture and magnetic properties. Although the perturbation in the molecular structure by varying the substituent on the N-aryl ring may appear small, the effects upon the structural parameters controlling intermolecular magnetic coupling interactions are strong, resulting in a wide spectrum of cooperative magnetic behavior. The non-substituted 1,5-diphenyl-tert-butyl-6-oxo-verdazyl radical features a ferromagnetic one-dimensional spin ladder type magnetic network-an extremely rarely observed phenomenon for verdazyl radicals. By varying substituents at the phenyl group, different non-isostructural compounds were obtained with widely different magnetic motifs ranging from linear and zigzag one-dimensional chains to potentially two-dimensional networks, from which we predict magnetic susceptibility data that are in qualitative agreement with experiments and reveal a large sensitivity to packing effects of the molecules. The present study advances the fundamental understanding between solid-state structure and magnetism in organically based radical systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Free radicals trapped in polyethylene matrix

International Nuclear Information System (INIS)

Shimada, S.; Maeda, M.; Hori, Y.; Kashiwabara, H.

1977-01-01

Two types of alkyl radicals were found to be trapped in irradiated crystals grown from polyethylene solution. One of them corresponds to the broad sextet pattern of the e.s.r. spectrum and the other corresponds to the sharp sextet pattern. The free radicals attributed to the broad sextet began to disappear at a lower temperature than the temperature at which the free radicals attributed to the sharp sextet disappeared. When butadiene molecules were brought into contact with the specimen, the decay of the free radicals corresponding to the broad sextet was accelerated. When the specimen was subjected to fuming nitric acid treatment, no broad sextet was observed. The mat of the crystals was aligned so that the c-axes of its crystallites were perpendicular to its surface. The broad sextet showed no anisotropy when the angle between the direction of applied magnetic field and that of the c-axis of the crystallite was varied. On the other hand, the sharp component of the spectrum showed apparent anisotropy. It can be concluded that the broad component comes from the free radicals trapped in the lamellar surface and the sharp component is attributed to the free radicals trapped in the inner part of the crystallite. (author)

Herbal medicine, radical scavenger and metal detoxification: bioinorganic, complexity and nano science perspectives

Science.gov (United States)

Sumitro, Sutiman B.; Alit, Sukmaningsih

2018-03-01

Developing Complexity Science and Nano Biological perspective giving the ideas of interfacing between modern physical and biological sciences for more comprehensive understanding of life. The study of bioinorganic is a trans-disciplinary, and will initiate the way to more comprehensive and better understanding life. We can talk about energy generation, motive forces and energy transfer at the level of macromolecules. We can then develop understanding biological behavior on nano size biological materials and its higher order using modern physics as well as thermodynamic law. This is a necessity to ovoid partial understanding of life that are not match with holism. In animal tissues, the accumulation or overwhelmed production of free radicals can damage cells and are believed to accelerate the progression of cancer, cardiovascular disease, and age-related diseases. Thus a guarded balance of radical species is imperative. Edward Kosower [1] proposed an idea of biradical in an aromatic organic compounds. Each of which having unpaired electrons. The magnetic force of this compound used for making agregation based on their magnetic characters. Bioinorganic low molecular weight complex compounds composing herbal medicine can bind toxic metals. This low molecular weight complex molecules then easily excerted the metals from the body, removing them from their either intracellular or extracellular existences. This bioinorganic chelation potential is now inspiring a new therapeutic strategies.

The role of melanin as protector against free radicals in skin and its role as free radical indicator in hair

Science.gov (United States)

Herrling, Thomas; Jung, Katinka; Fuchs, Jürgen

2008-05-01

Throughout the body, melanin is a homogenous biological polymer containing a population of intrinsic, semiquinone-like radicals. Additional extrinsic free radicals are reversibly photo-generated by UV and visible light. Melanin photochemistry, particularly the formation and decay of extrinsic radicals, has been the subject of numerous electron spin resonance (ESR) spectroscopy studies. Several melanin monomers exist, and the predominant monomer in a melanin polymer depends on its location within an organism. In skin and hair, melanin differs in content of eumelanin or pheomelanin. Its bioradical character and its susceptibility to UV irradiation makes melanin an excellent indicator for UV-related processes in both skin and hair. The existence of melanin in skin is strongly correlated with the prevention against free radicals/ROS generated by UV radiation. Especially in the skin melanin (mainly eumelanin) ensures the only natural UV protection by eliminating the generated free radicals/ROS. Melanin in hair can be used as a free radical detector for evaluating the efficacy of hair care products. The aim of this study was to investigate the suitability of melanin as protector of skin against UV generated free radicals and as free radical indicator in hair.

CSR: a new tool for storage and cooling of keV ion beams

Energy Technology Data Exchange (ETDEWEB)

Froese, Michael; Blaum, Klaus; Crespo Lopez-Urrutia, Jose; Fellenberger, Florian; Grieser, Manfred; Kaiser, Dirk; Lange, Michael; Laux, Felix; Menk, Sebastian; Orlov, Dmitry A.; Repnow, Roland; Schroeter, Claus D.; Schwalm, Dirk; Sieber, Thomas; Ullrich, Joachim; Varju, Jozef; Hahn, Robert von; Wolf, Andreas [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Heber, Oded; Rappaport, Michael; Toker, Jonathan; Zajfman, Daniel [Weizman Institute of Science, Rehovot (Israel)

2009-07-01

An electrostatic Cryogenic Storage Ring (CSR) is currently being built in Heidelberg, Germany. The current status and final design of this ring, with a focus on the optimized 2 K chamber cooling, precision chamber suspension, and pumping down to extremely low pressures via cryogenic vacuum chambers will be presented. This ring will allow long storage times of highly charged ion and polyatomic molecular beams with energies in the range of keV per charge-state. Combining the long storage times with vacuum chamber temperatures approaching 2 K, infrared-active molecular ions will be radiatively cooled to their rotational ground states. Many aspects of this concept were experimentally tested with a cryogenic trap for fast ion beams (CTF), which has already demonstrated the storage of fast ion beams in a large cryogenic device. An upcoming test will investigate the effect of pre-baking the cryogenic vacuum chambers to 600 K on the cryogenic vacuum and the ion beam storage.

Use of a vibrating plate to enhance natural convection cooling of a discrete heat source in a vertical channel

Energy Technology Data Exchange (ETDEWEB)

Florio, L.A.; Harnoy, A. [Department of Mechanical Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102 (United States)

2007-09-15

A numerical investigation was conducted into an alternative method of natural convection enhancement by the transverse oscillations of a thin short plate, strategically positioned in close proximity to a rectangular heat source. The heat source is attached to a mounting board in a vertical channel. Two-dimensional laminar flow finite element studies were carried out with the oscillation parameters, the oscillating plate-heat source mean clearance spacing, and the oscillating plate position varied. Significant cooling was found for displacement amplitudes of at least one-third of the mean clearance together with frequencies (Re/{radical}(Gr)) of over 2{pi} with the displacement being more critical to the cooling level. For the parameters investigated, up to a 52% increase in the local heat transfer coefficient relative to standard natural convection was obtained. The results indicate that this method can serve as a feasible, simpler, more energy and space efficient alternative to common methods of cooling for low power dissipating devices operating at conditions just beyond the reach of pure natural convection. (author)

Emergency reactor cooling device

International Nuclear Information System (INIS)

Arakawa, Ken.

1993-01-01

An emergency nuclear reactor cooling device comprises a water reservoir, emergency core cooling water pipelines having one end connected to a water feeding sparger, fire extinguishing facility pipelines, cooling water pressurizing pumps, a diesel driving machine for driving the pumps and a battery. In a water reservoir, cooling water is stored by an amount required for cooling the reactor upon emergency and for fire extinguishing, and fire extinguishing facility pipelines connecting the water reservoir and the fire extinguishing facility are in communication with the emergency core cooling water pipelines connected to the water feeding sparger by system connection pipelines. Pumps are operated by a diesel power generator to introduce cooling water from the reservoir to the emergency core cooling water pipelines. Then, even in a case where AC electric power source is entirely lost and the emergency core cooling system can not be used, the diesel driving machine is operated using an exclusive battery, thereby enabling to inject cooling water from the water reservoir to a reactor pressure vessel and a reactor container by the diesel drive pump. (N.H.)

Free radicals generated by radiolysis of aqueous solutions

International Nuclear Information System (INIS)

Schwarz, H.A.

1981-01-01

The free radicals produced in the radiolysis of aqueous solutions span the range of redox potentials from -2.9 to +2.65 volts. The identity and nature of these radicals were discussed. Most of the discussion was results obtained with low LET radiation sources ( 60 Co gamma radiation or electron accelerators). Water radiolysis provides the synthesis of many radicals and radical ions in aqueous solution. The primary radicals, e/sub aq/ - H, OH, are well characterized. The radical population can be made to be 90% pure OH (or O - ) if N 2 O solutions are irradiated, the remaining 10% being H atoms. 55% of the radicals can be converted to H atoms in acid solution or in neutral phosphate solutions(e/sub aq/ - reacts with H 2 PO 4- to produce H). The remaining 45% (OH radicals) are difficult to convert to H by reaction with H 2 , due to the slow rate of the reaction. About 100 atmospheres of H 2 are required to do the conversion in less than 10 - 6 sec. 3 figures, 3 tables. (DP)

Photoionization studies with molecular beams

International Nuclear Information System (INIS)

Ng, C.Y.

1976-09-01

A molecular beam photoionization apparatus which combines the advantages of both the molecular beam method with photoionization mass spectrometry has been designed and constructed for carrying out some unique photoionization experiments. Rotational cooling during the supersonic expansion has resulted in high resolution photoionization efficiency curves for NO, ICl, C 2 H 2 and CH 3 I. The analysis of these spectra has yielded ionization potentials for these molecules to an accuracy of +- 3 MeV. Detailed autoionization structures were also resolved. This allows the investigation of the selection rules for autoionization, and the identification of the Rydberg series which converge to the excited states of the molecular ions. The degree of relaxation for thermally populated excited states has been examined using NO and ICl as examples. As a result of adiabatic cooling, a small percentage of dimers is also formed during the expansion. The photoionization efficiency curves for (NO) 2 , ArICl, Ar 2 , Kr 2 and Xe 2 have been obtained near the thresholds. Using the known dissociation energies of the (NO) 2 , Ar 2 , Kr 2 and Xe 2 van der Waals molecules, the corresponding dissociation energies for NO-NO + , Ar 2 + , Kr 2 + , and Xe 2 + have been determined. The ionization mechanisms for this class of molecules are examined and discussed

Radical carbonylations using a continuous microflow system

Directory of Open Access Journals (Sweden)

Takahide Fukuyama

2009-07-01

Full Text Available Radical-based carbonylation reactions of alkyl halides were conducted in a microflow reactor under pressurized carbon monoxide gas. Good to excellent yields of carbonylated products were obtained via radical formylation, carbonylative cyclization and three-component coupling reactions, using tributyltin hydride or TTMSS as a radical mediator.

Radical-Mediated Enzymatic Polymerizations

Science.gov (United States)

Zavada, Scott R.; Battsengel, Tsatsral; Scott, Timothy F.

2016-01-01

Polymerization reactions are commonly effected by exposing monomer formulations to some initiation stimulus such as elevated temperature, light, or a chemical reactant. Increasingly, these polymerization reactions are mediated by enzymes―catalytic proteins―owing to their reaction efficiency under mild conditions as well as their environmental friendliness. The utilization of enzymes, particularly oxidases and peroxidases, for generating radicals via reduction-oxidation mechanisms is especially common for initiating radical-mediated polymerization reactions, including vinyl chain-growth polymerization, atom transfer radical polymerization, thiol–ene step-growth polymerization, and polymerization via oxidative coupling. While enzyme-mediated polymerization is useful for the production of materials intended for subsequent use, it is especially well-suited for in situ polymerizations, where the polymer is formed in the place where it will be utilized. Such polymerizations are especially useful for biomedical adhesives and for sensing applications. PMID:26848652

Effect of dose rate on radical and property of gelatin

International Nuclear Information System (INIS)

Geng Shengrong; Chen Yuxia; Zu Xiaoyan; Li Xin; Jiang Hongyou

2015-01-01

The gelatin was irradiated respectively in the range of 0-32 kGy by dose rates of 60 Gy/min 60 Co, 480 Gy/min 60 Co and 12000 Gy/min accelerator, and the relationships of the radical character and gelatin property with dose rate were investigated through electron spin resonance (ESR) and gelatin permeation chromatogram. The results show that there is weak ESR signal from unirradiated gelatin, but irradiated one presents typical double peak. The order of ESR signal intensity of gelatin with the same absorbed dosage from high to low is 60 Gy/min 60 Co, 480 Gy/min 60 Co and 12000 Gy/min accelerator. The linear relationship between ESR signal intensity from 60 Co irradiated gelatin and absorbed dose is y= 26.983x 2 +1 641.8x-205.69. The intrinsic viscosity, average relative molecular weight, gelatin strength and breaking elongation of irradiated gelatin from high to low are 480 Gy/min 60 Co, 12000 Gy/min accelerator and 60 Gy/min 60 Co. The protection mechanism of high dose rate radiation on gelatin degradation is that the production of effective long life free radicals reduces. (authors)

N-substituted-piperidines as Novel Anti-alzheimer Agents: Synthesis, antioxidant activity, and molecular docking study

Directory of Open Access Journals (Sweden)

Khairia M. Youssef

2018-06-01

Full Text Available Design, synthesis and evaluation of new acetylcholinesterase inhibitors by combining carbamoylpiperidine analogs containing nipecotic acid scaffold were described. Then, a series of hybrids have been developed by introducing Free radical scavengers. Molecular modeling was performed and structure activity relationships are discussed. Among the series, most potent compounds showed effective AchE inhibitions, high selectivity over butyrylcholinesterase and high radical scavenging activities. On the basis of this work, the ability of analogs containing nipecotic acid scaffold to serve in the design of N-benzyl-piperidine linked multipotent molecules for the treatment of Alzheimer Disease. Keywords: Synthesis, N-substituted-piperidines, Antioxidant activity, ATP chemiluminescence, Molecular modeling study

SELF-CONVERGENCE OF RADIATIVELY COOLING CLUMPS IN THE INTERSTELLAR MEDIUM

International Nuclear Information System (INIS)

Yirak, Kristopher; Frank, Adam; Cunningham, Andrew J.

2010-01-01

Isolated regions of higher density populate the interstellar medium (ISM) on all scales-from molecular clouds, to the star-forming regions known as cores, to heterogeneous ejecta found near planetary nebulae and supernova remnants. These clumps interact with winds and shocks from nearby energetic sources. Understanding the interactions of shocked clumps is vital to our understanding of the composition, morphology, and evolution of the ISM. The evolution of shocked clumps is well understood in the limiting 'adiabatic' case where physical processes such as self-gravity, heat conduction, radiative cooling, and magnetic fields are ignored. In this paper, we address the issue of evolution and convergence when one of these processes-radiative cooling-is included. Numeric convergence studies demonstrate that the evolution of an adiabatic clump is well captured by roughly 100 cells per clump radius. The presence of radiative cooling, however, imposes limits on the problem due to the removal of thermal energy. Numerical studies which include radiative cooling typically adopt the 100-200 cells per clump radius resolution. In this paper, we present the results of a convergence study for radiatively cooling clumps undertaken over a broad range of resolutions, from 12 to 1536 cells per clump radius, employing adaptive mesh refinement (AMR) in a two-dimensional axisymmetric geometry (2.5 dimensions). We also provide a fully three-dimensional simulation, at 192 cells per clump radius, which supports our 2.5 dimensional results. We find no appreciable self-convergence at ∼100 cells per clump radius as small-scale differences owing to increasingly resolving the cooling length have global effects. We therefore conclude that self-convergence is an insufficient criterion to apply on its own when addressing the question of sufficient resolution for radiatively cooled shocked clump simulations. We suggest the adoption of alternate criteria to support a statement of sufficient

Cooled-Spool Piston Compressor

Science.gov (United States)

Morris, Brian G.

1994-01-01

Proposed cooled-spool piston compressor driven by hydraulic power and features internal cooling of piston by flowing hydraulic fluid to limit temperature of compressed gas. Provides sufficient cooling for higher compression ratios or reactive gases. Unlike conventional piston compressors, all parts of compressed gas lie at all times within relatively short distance of cooled surface so that gas cooled more effectively.

Fluorescence lifetime measurement of radical ions

International Nuclear Information System (INIS)

Ichinose, Nobuyuki; Kinugasa, Jun-ichiro; Hagiri, Masahide; Nakayama, Toshihiro; Murakami, Hiroshi; Kishimoto, Maki; Daido, Hiroyuki

2004-01-01

One-photonic excitation of a charge transfer complex of hexamethoxybenzene (HMB) and nitrosonium tetrafluoroborate (NO + BF 4 - ) in acetonitrile afforded fluorescences emission from excited radical cation of HMB (HMB + *). Lifetime of the excited radical ion species was measured to be 7 ps by the pump-probe transient absorption technique. The lifetime was much shorter than that of free radical ion (63 ps), indicating the presence of an interaction between HMB + * and NO in the excited complex. (author)

Generation and propagation of radical reactions on proteins

DEFF Research Database (Denmark)

Hawkins, C L; Davies, Michael Jonathan

2001-01-01

The oxidation of proteins by free radicals is thought to play a major role in many oxidative processes within cells and is implicated in a number of human diseases as well as ageing. This review summarises information on the formation of radicals on peptides and proteins and how radical damage may...... be propagated and transferred within protein structures. The emphasis of this article is primarily on the deleterious actions of radicals generated on proteins, and their mechanisms of action, rather than on enzymatic systems where radicals are deliberately formed as transient intermediates. The final section...

Cooling towers

International Nuclear Information System (INIS)

Korik, L.; Burger, R.

1992-01-01

What is the effect of 0.6C (1F) temperature rise across turbines, compressors, or evaporators? Enthalpy charts indicate for every 0.6C (1F) hotter water off the cooling tower will require an additional 2 1/2% more energy cost. Therefore, running 2.2C (4F) warmer due to substandard cooling towers could result in a 10% penalty for overcoming high heads and temperatures. If it costs $1,250,000.00 a year to operate the system, $125,000.00 is the energy penalty for hotter water. This paper investigates extra fuel costs involved in maintaining design electric production with cooling water 0.6C (1F) to 3C (5.5F) hotter than design. If design KWH cannot be maintained, paper will calculate dollar loss of saleable electricity. The presentation will conclude with examining the main causes of deficient cold water production. State-of-the-art upgrading and methodology available to retrofit existing cooling towers to optimize lower cooling water temperatures will be discussed

Water cooling coil

Energy Technology Data Exchange (ETDEWEB)

Suzuki, S; Ito, Y; Kazawa, Y

1975-02-05

Object: To provide a water cooling coil in a toroidal nuclear fusion device, in which coil is formed into a small-size in section so as not to increase dimensions, weight or the like of machineries including the coil. Structure: A conductor arranged as an outermost layer of a multiple-wind water cooling coil comprises a hollow conductor, which is directly cooled by fluid, and as a consequence, a solid conductor disposed interiorly thereof is cooled indirectly.

Effect of closed loop cooling water transit time on containment cooling

International Nuclear Information System (INIS)

Smith, R.P.; Vossahlik, J.E.; Goodwin, E.F.

1996-01-01

Long term containment cooling analyses in nuclear plant systems are usually conducted assuming a quasi steady-state process, that is, a steady state evaluation of the cooling system is completed for each calculational step. In reality, fluid transport in the system, and heat addition to system components may affect the heat removal rate of the system. Transient effects occurring during system startup may affect the maximum temperatures experienced in the system. It is important to ensure that such transient effects do not affect operation of the system (e.g., cause a high temperature trip). To evaluate the effect of fluid transit delays, a closed loop cooling water system model has been developed that incorporates the fluid transport times when determining the closed loop cooling system performance. This paper describes the closed loop cooling system model as implemented in the CONTEMPT-LT/028 code. The evaluation of the transient temperature response of the closed loop cooling system using the model is described. The paper also describes the effect of fluid transit time on the overall containment cooling performance

Some reactions of oxidizing radicals with enzymes in aqueous solution

International Nuclear Information System (INIS)

Cundall, R.B.; Bisby, R.H.; Hoe, S.T.; Sims, H.E.; Anderson, R.F.

1979-01-01

A range of oxidizing radicals including some inorganic radical anions and the superoxide radical, can be generated by radiolysis of aqueous solutions. These radicals are more selective in their reactions with amino acids than the hydroxyl radical. Factors controlling the apparent reactivity of radical anions with proteins, such as free radical equilibria and ion-binding, are described. The superoxide radical inactivates papain by reaction with the cysteine residue. This reaction has been studied in solutions subjected to radiations of varying linear energy transfer. (Auth.)

Theoretical analysis of the performance of different cooling strategies with the concept of cool exergy

DEFF Research Database (Denmark)

Kazanci, Ongun Berk; Shukuya, Masanori; Olesen, Bjarne W.

2016-01-01

The whole chains of exergy flows for different cooling systems were compared. The effects of cooling demand (internal vs. external solar shading), space cooling method (floor cooling vs. air cooling with ventilation system), and the availability of a nearby natural heat sink (intake air for the v......The whole chains of exergy flows for different cooling systems were compared. The effects of cooling demand (internal vs. external solar shading), space cooling method (floor cooling vs. air cooling with ventilation system), and the availability of a nearby natural heat sink (intake air...... for the ventilation system being outdoor air vs. air from the crawl-space, and air-to-water heat pump vs. ground heat exchanger as cooling source) on system exergy performance were investigated. It is crucial to minimize the cooling demand because it is possible to use a wide range of heat sinks (ground, lake, sea......-water, etc.) and indoor terminal units, only with a minimized demand. The water-based floor cooling system performed better than the air-based cooling system; when an air-to-water heat pump was used as the cooling source, the required exergy input was 28% smaller for the floor cooling system. The auxiliary...

Long-lived gas-phase radicals from combustion

Energy Technology Data Exchange (ETDEWEB)

Kaneko, Takashi; Furusawa, Koji; Amano, Toshiji; Okubo, Yoichi; Tsuchiya, Jun' ichi; Yoshizawa, Fujiroku; Akutsu, Yoshiaki; Tamura, Masamitsu; Yoshida, Tadao (Univ. of Tokyo (Japan))

1989-04-20

On indoor air pollution or fire, it is feared that the gas-phase radicals from the combustion of inflammables or fuel seriously exert an influence on the organisms as harmful matter. The gas-phase radicals were studied using the electron spin resonance (ESR) spin-trapping technique. For the spin trap solution, 0.1 mol solution of {alpha}-phenyl-N-t-butylnitron in benzene was used. As a result, apparently long-lived and highly reactive oxygen-centered radicals were detected in the smoke from polyethylene, polypropylene, polystyrene, polymethylmethacrylate, cellulose, kerosene, benzene, acetone, methanol and butylalcohol. It is suggested that the production mechanism for the radicals should be different from olefin-NOx-air system reaction, which is considered for the radicals from cigarette smoke. 11 refs., 6 figs., 2 tabs.

The cooling of particle beams

International Nuclear Information System (INIS)

Sessler, A.M.

1994-10-01

A review is given of the various methods which can be employed for cooling particle beams. These methods include radiation damping, stimulated radiation damping, ionization cooling, stochastic cooling, electron cooling, laser cooling, and laser cooling with beam coupling. Laser Cooling has provided beams of the lowest temperatures, namely 1 mK, but only for ions and only for the longitudinal temperature. Recent theoretical work has suggested how laser cooling, with the coupling of beam motion, can be used to reduce the ion beam temperature in all three directions. The majority of this paper is devoted to describing laser cooling and laser cooling with beam coupling

[Research progress on free radicals in human body].

Science.gov (United States)

Wang, Q B; Xu, F P; Wei, C X; Peng, J; Dong, X D

2016-08-10

Free radicals are the intermediates of metabolism, widely exist in the human bodies. Under normal circumstances, the free radicals play an important role in the metabolic process on human body, cell signal pathway, gene regulation, induction of cell proliferation and apoptosis, so as to maintain the normal growth and development of human body and to inhibit the growth of bacteria, virus and cancer. However, when organic lesion occurs affected by external factors or when equilibrium of the free radicals is tipped in the human body, the free radicals will respond integratedly with lipids, protein or nucleic acid which may jeopardize the health of human bodies. This paper summarizes the research progress of the free radicals conducted in recent years, in relations to the perspective of the types, origins, test methods of the free radicals and their relationship with human's health. In addition, the possible mechanisms of environmental pollutants (such as polycyclic aromatic hydrocarbons) mediating oxidative stress and free radicals scavenging in the body were also summarized.

COMPUTATIONAL STUDY OF INTERSTELLAR GLYCINE FORMATION OCCURRING AT RADICAL SURFACES OF WATER-ICE DUST PARTICLES

Energy Technology Data Exchange (ETDEWEB)

Rimola, Albert; Sodupe, Mariona [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra (Spain); Ugliengo, Piero, E-mail: albert.rimola@uab.cat [Dipartimento di Chimica, NIS Centre of Excellence and INSTM (Materials and Technology National Consortium), UdR Torino, Universita di Torino, Via P. Giuria 7, 10125 Torino (Italy)

2012-07-20

Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH{sup .} radical and H{sub 3}O{sup +} surface defects. The coupling of incoming CO molecules with the surface OH{sup .} radicals on the ice clusters yields the formation of the COOH{sup .} radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol{sup -1} and -22 kcal mol{sup -1}, respectively. The COOH{sup .} radicals couple with incoming NH=CH{sub 2} molecules (experimentally detected in the ISM) to form the NHCH{sub 2}COOH{sup .} radical glycine through energy barriers of 12 kcal mol{sup -1}, exceedingly high at ISM cryogenic temperatures. Nonetheless, when H{sub 3}O{sup +} is present, one proton may be barrierless transferred to NH=CH{sub 2} to give NH{sub 2}=CH{sub 2}{sup +}. This latter may react with the COOH{sup .} radical to give the NH{sub 2}CH{sub 2}COOH{sup +.} glycine radical cation which can then be transformed into the NH{sub 2}CHC(OH){sub 2}{sup +.} species (the most stable form of glycine in its radical cation state) or into the NH{sub 2}CHCOOH{sup .} neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh

Universal crystal cooling device for precession cameras, rotation cameras and diffractometers

International Nuclear Information System (INIS)

Hajdu, J.; McLaughlin, P.J.; Helliwell, J.R.; Sheldon, J.; Thompson, A.W.

1985-01-01

A versatile crystal cooling device is described for macromolecular crystallographic applications in the 290 to 80 K temperature range. It utilizes a fluctuation-free cold-nitrogen-gas supply, an insulated Mylar crystal cooling chamber and a universal ball joint, which connects the cooling chamber to the goniometer head and the crystal. The ball joint is a novel feature over all previous designs. As a result, the device can be used on various rotation cameras, precession cameras and diffractometers. The lubrication of the interconnecting parts with graphite allows the cooling chamber to remain stationary while the crystal and goniometer rotate. The construction allows for 360 0 rotation of the crystal around the goniometer axis and permits any settings on the arcs and slides of the goniometer head (even if working at 80 K). There are no blind regions associated with the frame holding the chamber. Alternatively, the interconnecting ball joint can be tightened and fixed. This results in a set up similar to the construction described by Bartunik and Schubert where the cooling chamber rotates with the crystal. The flexibility of the systems allows for the use of the device on most cameras or diffractometers. THis device has been installed at the protein crystallographic stations of the Synchrotron Radiation Source at Daresbury Laboratory and in the Laboratory of Molecular Biophysics, Oxford. Several data sets have been collected with processing statistics typical of data collected without a cooling chamber. Tests using the full white beam of the synchrotron also look promising. (orig./BHO)

Analysis of dynamic enhancement of natural convection cooling by a discrete vibrating plate

Energy Technology Data Exchange (ETDEWEB)

Florio, L.A.; Harnoy, A. [New Jersey Institute of Technology, Department of Mechanical Engineering, Newark, NJ (United States)

2006-12-15

A dynamic means of locally enhancing laminar natural convection cooling in a vertical channel through the localized application of fluid oscillations is numerically investigated. The two-dimensional system considered for these purposes is a vertical channel with a small transversely oscillating plate placed near a constant heat flux channel wall. The flow and heat transfer in the system resulting from the combined effects of the natural convection and the oscillating plate were determined. The results indicate that for displacement amplitudes of at least one-third of the mean spacing and with dimensionless frequencies (Re/{radical}(Gr)) of at least 2{pi}, the local heat transfer coefficient can be enhanced by as much as 41%. (orig.)

Polymerization, shock cooling and ionization of liquid nitrogen

International Nuclear Information System (INIS)

Ross, M; Rogers, F

2005-01-01