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Artykuły w czasopismach na temat "Radical‐ Molecule Reactions"
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Silaev, Michael M. "KINETIC EQUATIONS FOR RADICAL-CHAIN OXIDATION INVOLVING PROCESS-INHIBITING ALKYL (OR HYDRO)TETRAOXYL FREE RADICAL". American Journal of Applied Sciences 05, nr 06 (30.06.2023): 29–48. http://dx.doi.org/10.37547/tajas/volume05issue06-07.
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The derivation of kinetic equations for the oxidation processes by the free-radical nonbranched-chain mechanism is shown. This derivation is based on the proposed reaction scheme for the initiated addition of free radicals to the multiple bond of the molecular oxygen includes the addition reaction of the peroxyl free radical to the oxygen molecule to form the tetraoxyl free radical. This reaction competes with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which – alkyl(or hydro)tetraoxyl – is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. The rate equations (containing one to three parameters to be determined directly) are deduced using the quasi-steady-state treatment. These kinetic equations were used to describe the γ-induced nonbranched-chain processes of free-radical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing various amounts of oxygen at 296 K. The ratios of rate constants of competing reactions and rate constants of addition reactions to the molecular oxygen are defined. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoinhibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. It is shown that a maximum in these curves arises from the competition between hydrocarbon (or hydrogen) molecules and dioxygen for reacting with the emerging peroxyl 1:1 adduct radical. From the energetic standpoint possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule gas-phase reactions is considered.
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Xie, Hong-Bin, Yi-Hong Ding i Chia-Chung Sun. "Ylidic radical-molecule reactions". Journal of Computational Chemistry 27, nr 5 (15.04.2006): 545–51. http://dx.doi.org/10.1002/jcc.20362.
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Chen, Pu, Huawen Huang, Qi Tan, Xiaochen Ji i Feng Zhao. "Recent Advances in Molecule Synthesis Involving C-C Bond Cleavage of Ketoxime Esters". Molecules 28, nr 6 (15.03.2023): 2667. http://dx.doi.org/10.3390/molecules28062667.
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The synthetic strategies of oxime derivatives participating in radical-type reactions have been rapidly developed in the last few decades. Among them, the N–O bond cleavage of oxime esters leading to formation of nitrogen-centered radicals triggers adjacent C–C bond cleavage to produce carbon-centered free radicals, which has been virtually used in organic synthesis in recent years. Herein, we summarized the radical reactions involving oxime N–O bond and C–C bond cleavage through this special reaction form, including those from acyl oxime ester derivatives and cyclic ketoxime ester derivatives. These contents were systematically classified according to different reaction types. In this review, the free radical reactions involving acyl oxime esters and cyclic ketoxime esters after 2021 were included, with emphasis on the substrate scope and reaction mechanism.
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Silaev, Michael M. "OXYGEN AS OXIDANT AND ANTIOXIDANT". EPH - International Journal of Applied Science 1, nr 2 (27.06.2015): 21–32. http://dx.doi.org/10.53555/eijas.v1i2.3.
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New reaction scheme is suggested for the initiated nonbranched-chain addition of free radicals to the multiple bond of the molecular oxygen. The scheme includes the addition reaction of the peroxyl free radical to the oxygen molecule to form the tetraoxyl free radical. This reaction competes with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which (tetraoxyl) is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the proposed scheme rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. The kinetic description with use the obtained rate equations is applied to the γ-induced nonbranched-chain processes of the freeradical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing different amounts of oxygen at 296 K. The ratios of rate constants of competing reactions and rate constants of addition reactions to the molecular oxygen are defined. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. From the energetic standpoint possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule gas-phase reactions is considered.
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Holze, Rudolf. "Radical Intermediates in Electrochemical Polymer-Forming Reactions". Collection of Czechoslovak Chemical Communications 65, nr 6 (2000): 899–923. http://dx.doi.org/10.1135/cccc20000899.
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The role of organic radicals in the formation of functional polymers, in particular intrinsically conducting polymers, is reviewed. New results recently obtained with in situ spectroscopic methods illustrating the influence of the molecular structure of monomers (aniline and substituted anilines) in the behaviour of radical intermediates are presented. The stabilising influence of substituents at various positions of the aniline molecule is evaluated and compared based on conceivable structures of reaction intermediates.
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Chumakov, Anton A., Valentina N. Batalova, Yuriy G. Slizhov i Tamara S. Minakova. "VERIFICATION OF NON-CATALYTIC HYDROGEN PEROXIDE DISPROPORTIONATION MECHANISM BY THERMODYNAMIC ANALYSIS OF ONE-ELECTRON REDOX REACTIONS". IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 60, nr 6 (19.07.2017): 40. http://dx.doi.org/10.6060/tcct.2017606.5529.
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There is two-electron transfer during the process of hydrogen peroxide decomposition into water and oxygen. The detailed mechanism of non-catalytic hydrogen peroxide disproportionation is not verified until now. We assumed that any poly-electron redox process is a complex and consists of one-electron redox reactions. We have formulated equations of possible one-electron transfers during hydrogen peroxide disproportionation. Based on known laws and equations of thermochemistry we calculated standard thermodynamic functions for a total reaction and each one-elect-ron redox reaction using reference values of standard thermodynamic functions of reagents and products of reactions. Results show that the total reaction leads to significant decrease in Gibbs free energy -246.0 kJ/mol in gas phase but there is increase +39.9 kJ/mol in Gibbs free energy during the first proposed step. It is substantiation for known dependence of hydrogen peroxide dismutation kinetics at thermal, photochemical or catalytic activation. The first proposed step of non-catalytic process is one-electron plus one-proton transfer in thermally or photochemically activated dimeric hydrogen peroxide associate (H2O2)2 with simultaneous generation of hydroperoxyl HO2• and hydroxyl HO• free radicals and water molecule. There is thermodynamic argumentation for radical chain mechanism of hydrogen peroxide disproportionation after the activation. We made the graphic illustration of thermodynamically supported scheme of non-catalytic hydrogen peroxide decomposition. There is a cyclic alternation of two radical-molecular interactions during the hydrogen peroxide chain decomposition. The hydroxyl radical generates the hydroperoxyl radi-cal from a hydrogen peroxide molecule and then the hydroperoxyl radical interacts with a next hydrogen peroxide molecule followed by the hydroxyl radical generation. Interactions between the homonymic or heteronymic free radicals are the reactions of chain breaking.Forcitation:Chumakov A.A., Batalova V.N., Slizhov Yu.G., Minakova T.S. Verification of non-catalytic hydrogen peroxide disproportionation mechanism by thermodynamic analysis of one-electron redox reactions. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 6. P. 40-44.
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Novikova, Anna A., i Mikhail E. Soloviev. "QUANTUM CHEMICAL STUDY OF OXIDATION REACTIONS IN UNSATURATED HYDROCARBONS". IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 60, nr 7 (24.08.2017): 14. http://dx.doi.org/10.6060/tcct.2017607.5516.
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In this article quantum-chemical calculations using DFT B3LYP/cc-pvdz method was used for the investigation of changes in thermodynamic functions of reactions of oxidation of unsaturated hydrocarbons such as heptane and heptadiene as low-molecular models of hydrocarbon residues of lipids. The effect of the position of the reaction center relative to the double bonds and conformations of double bonds on reactivity of the compounds in reactions of hydrogen abstraction by the hydroxyl radical, dioxygen accession and chain propagation were analyzed. By comparison of changes in thermodynamic functions of reactions it was shown that hydrocarbons with cis- conformations of double bonds are characterized with higher reactivity in reactions of hydrogen abstraction but peroxi-radicals of these conformers are more stable. The changes in thermodynamic functions of reaction of hydrogen abstraction for diene according to the calculation are smaller comparing with olefins. This is due to the difference in the stability of the radicals formed. The stability of hydrocarbon radicals of dienes in comparison with olefins is explained by their planar structure with electron density of unpaired electron delocalized between five carbon atoms. The emergence of such pentadienil-type radicals is the cause of a higher oxidation of dienes compared with olefins. The analysis of molecular structures of peroxi-radicals of dienes shows that after accepting dioxygen by hydrocarbon radical the isomerization takes place. According calculations it is preferable for the dioxygen molecule not to join with the central carbon atom from which the hydrogen atom has been abstracted but to attack the double bond joining with C2 carbon atom. During the isomerization the double bond moves to the center of the molecule forming thus the conjugated pair with the other double bond. Comparison of thermodynamic functions of reaction for cis- and trans- isomers shows that cis-trans isomerization is possible during the dioxygen accession to the hydrocarbon radical. These results are in good agreement with the experimental data published earlier.Forcitation:Novikova A.A., Soloviev M.E. Quantum chemical study of oxidation reactions in unsaturated hydrocarbons. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 7. P. 14-20.
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Iuga, Cristina, C. Ignacio Sainz-Díaz i Annik Vivier-Bunge. "Hydroxyl radical initiated oxidation of formic acid on mineral aerosols surface: a mechanistic, kinetic and spectroscopic study". Environmental Chemistry 12, nr 2 (2015): 236. http://dx.doi.org/10.1071/en14138.
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Environmental context The presence of air-borne mineral dust containing silicates in atmospheric aerosols should be considered in any exploration of volatile organic compound chemistry. This work reports the mechanisms, relative energies and kinetics of free-radical reactions with formic acid adsorbed on silicate surface models. We find that silicate surfaces are more likely to act as a trap for organic radicals than to have a catalytic effect on their reactions. Abstract Heterogeneous reactions of atmospheric volatile organic compounds on aerosol particles may play an important role in atmospheric chemistry. Silicate particles are present in air-borne mineral dust in atmospheric aerosols, and radical reactions can be different in the presence of these mineral particles. In this work, we use quantum-mechanical calculations and computational kinetics to explore the reaction of a hydroxyl free radical with a formic acid molecule previously adsorbed on several models of silicate surfaces. We find that the reaction is slower and takes place according to a mechanism that is different than the one in the gas phase. It is especially interesting to note that the reaction final products, which are the formyl radical attached to the cluster surface, and a water molecule, are much more stable than those formed in the gas phase, the overall reaction being highly exothermic in the presence of the surface model. This suggests that the silicate surface is a good trap for the formed formyl radical. In addition, we have noted that, if a second hydroxyl radical approaches the adsorbed formyl radical, the formation of carbonic acid on the silicate surface is a highly exothermic and exergonic process. The carbonic acid molecule remains strongly attached to the surface, thus blocking CO2 formation in the formic acid oxidation reaction. The spectroscopic properties of the systems involved in the reaction have been calculated, and interesting frequency shifts have been identified in the main vibration modes.
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Bordina, Galina E., Nadezhda P. Lopina, Gleb S. Parshin, Alexey A. Andreev i Ilya A. Nekrasov. "Mechanism of light polymerization of composites". Russian Journal of Dentistry 26, nr 2 (4.09.2022): 163–70. http://dx.doi.org/10.17816/1728-2802-2022-26-2-163-170.
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BACKGROUND: The article presents a review of the chemical aspects of the reaction of light polymerization of composites in dental practice. This reaction refers to free radical polymerization reactions, with photons as activators. In dentistry, composites are classified as chemically cured, light cured, doubly cured, and thermally cured. This depends on the origin of the activation energy of free radical polymerization of methacrylates. Chemically, dental composites are usually a mixture of four main components: an organic polymer matrix, an inorganic filler, an appret compound, a binder matrix and filler, and an initiatoraccelerator system. The radical polymerization process includes four main stages. The first stage is activation; in the case of light cured dental composites, it is photoactivation. In this case, a photoinitiator molecule is excited, for example, camphorquinone, which is widely used in the production of dental composite materials. If a free radical is formed, the polymerization process is similar for all composite materials based on a methacrylate organic matrix. The only difference is exactly how free radicals are formed and the rate of their formation. Under the influence of light quanta, the carbon atom of the ketone group of camphorquinone passes into an excited state, which allows the excited photoinitiator molecule to interact with two methacrylate molecules by a double bond. The double bond gives one electron to the excited camphorquinone molecule, and the second electron acts as a free radical agent; in other words, a macroradical is formeda monomer molecule that can attach other monomer molecules to itself.
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Koyanagi, Kohei, Yoshinori Takashima, Takashi Nakamura, Hiroyasu Yamaguchi i Akira Harada. "Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent". Beilstein Journal of Organic Chemistry 12 (22.11.2016): 2495–502. http://dx.doi.org/10.3762/bjoc.12.244.
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Supramolecular catalysts have received a great deal of attention because they improve the selectivity and efficiency of reactions. Catalysts with host molecules exhibit specific reaction properties and recognize substrates via host–guest interactions. Here, we examined radical polymerization reactions with a chain transfer agent (CTA) that has α-cyclodextrin (α-CD) as a host molecule (α-CD-CTA). Prior to the polymerization of N,N-dimethylacrylamide (DMA), we investigated the complex formation of α-CD with DMA. Single X-ray analysis demonstrated that α-CD includes DMA inside its cavity. When DMA was polymerized in the presence of α-CD-CTA using 2,2'-azobis[2-(2-imidazolin-2-yl)propane dihydrochloride (VA-044) as an initiator in an aqueous solution, poly(DMA) was obtained in good yield and with narrow molecular weight distribution. In contrast, the polymerization of DMA without α-CD-CTA produced more widely distributed polymers. In the presence of 1,6-hexanediol (C6 diol) which works as a competitive molecule by being included in the α-CD cavity, the reaction yield was lower than that without C6 diol.
Rozprawy doktorskie na temat "Radical‐ Molecule Reactions"
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Cline, Taylor Scott. "Investigation of Water-Molecule Complexes and Their Catalytic Effect on Important Atmospheric Reactions". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3990.
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This dissertation is a collection of works that investigates issues related to environmental chemistry. The first portion of this research explores the role of water vapor on the kinetics of important atmospheric reactions. Work is presented on the self-reaction of β-hydroxyethyl peroxy radical (β-HEP) and the catalytic increase in reaction rate by water vapor. β-HEP serves as a model system for investigating the possible role of water vapor in perturbing the kinetics and product branching ratio of atmospheric reactions of other alkyl peroxy radicals. The self-reaction rate coefficient of β-HEP was investigated between 276-296 K with 1.0 × 10^15 to 2.5 × 10^17 molecules cm^-3 of water vapor at 200 Torr total pressure by slow-flow laser flash photolysis coupled with UV time-resolved spectroscopy and long-path, wavelength-modulated, diode-laser spectroscopy. The overall disproportionation rate constant is expressed as the product of temperature-dependent and water vapor-dependent terms giving k(T,H2O) = 7.8 × 10^-14 (e^8.2 ^(±2.5) ^kJ/RT)(1 + 1.4 × 10^-34 × e^92 ^(±11) ^kJ/RT[H2O]). The results suggest that formation of a β--HEP-H2O complex is responsible for the observed water vapor enhancement of the self-reaction rate coefficient. Complex formation is supported with computational results identifying three local energy minima for the β--HEP-H2O complex. Both the temperature range and water vapor concentrations used were chosen because of their significance to conditions in the troposphere. As the troposphere continues to get warmer and wetter, more complexes with water will form, which in turn may perturb the kinetics and product branching ratios of atmospheric reactions. Future studies are proposed for the reaction of β-HEP + NO leading to NO2 formation. A laser-induced fluorescence cell was designed, built, and tested in preparation for studies of NO2 formation. Additionally Harriott-cell optics were manufactured and tested to detect HO2 using two-tone frequency-modulated diode-laser spectroscopy. In a related work, the breakdown of the environmental contaminants polychlorinated biphenyls (PCB's) was investigated using a new method. A new method for analyzing anaerobic digestion is also presented. The degradation rate and efficiency of digestion processes are typically measured by introducing a substrate or pollutant into a digester and then monitoring the effluents for the pollutant or substrate, a costly and slow process. A new method for rapid measurement of the rates and efficiencies of anaerobic degradation of pollutants and lignocellulose substrates from various pretreatments is described. The method uses micro-reactors (10-30 mL) containing a mixed culture of anaerobic bacteria obtained from a working anaerobic digester. The rates of degradation and metabolism of pollutants are measured in parallel sets of micro-reactors. Measurements of metabolic rate and pollutant degradation simultaneously is an effective means of rapidly examining pollutant degradation on a micro-scale. Calorimetric measurements alone allow rapid, relative evaluation of various substrate pretreatment methods. Finally calorimetric and electrophoretic methods were used to further knowledge in analytical techniques applied to important problems. In the last section of this dissertation the thermal and photolytic breakdown of promethazine hydrochloride is reported. Promethazine hydrochloride is a mediation that is commonly used as an antihistamine, a sedative, and an antiemetic, and to treat motion sickness. Perivascular extravasation, unintentional intra-arterial injection and intraneuronal or perineuronal infiltration may lead to irreversible tissue damage if the drug is not properly diluted or is administered too quickly. Data on the stability of promethazine hydrochloride diluted in sodium chloride 0.9% are lacking. This study evaluates the thermal and photolytic degradation of promethazine hydrochloride concentrations of 250 µg/mL and 125 µg/mL diluted in sodium chloride 0.9% over a period of 9 days. Degradation rates of promethazine hydrochloride were determined under UV-light, fluorescent light, and no light at various temperatures and concentrations to determine medication stability. The shelf-life (<10% degradation) at 25°C under normal fluorescent lights is 4.9 days, at 25°C protected from light, 6.6 days, and at 7°C in the dark, 8.1 days. These results may increase patient safety by improving current protocols for intravenous promethazine administration
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Kuresepi, Salen. "Alternative mechanisms in skin allergy processes : contribution of radical reactions from the molecule to the tissue". Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF010/document.
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L’allergie de contact est une pathologie touchant de 15 à 20 % de la population occidentale. A l’heure actuelle il n’existe aucun traitement, la seule façon efficace de prévention étant l’éviction totale des allergènes. Les tests de sensibilisation de nouvelles molécules avant leur mise sur le marché ont été réalisés sur l’animal jusqu’à l’interdiction dans le 7ème amendement à la directive Européenne concernant l’industrie cosmétique. Dans ce contexte il est primordial de développer des méthodes alternatives. Ce travail de thèse propose d’analyser la problématique de l’allergie de contact en allant de la molécule au tissu pour les allergènes réagissant par voie radicalaire :In chemico : étude de la réactivité des hydroperoxydes allyliques vis-à-vis des acides aminés par la RMNIn situ : études de radicaux issus de ces composés sur des épidermes humains reconstitués par RPEIn cellulo : étude du stress oxydant sur les cellules dendritiques et la voie de signalisation Keap1/Nrf2/AREAllergic contact dermatitis is a pathology affecting 15 to 20% of the Western population. Until now no treatment exists, the prevention is the eviction of allergens. In the past, tests concerning new molecules for the market were tested on animals until the prohibition in the 7th amendment of the European directive concerning the cosmetics industry. In this context it is essential to develop alternative methods to assess the allergenic potential of chemicals.This manuscript proposes to analyze the problem of the allergic contact dermatitis from the molecule to the tissue for allergens reacting through radical mechanisms:In chemico: study of the reactivity profile of allylic hydroperoxides toward amino acids by NMRIn situ: radical intermediates formation on reconstructed human epidermis from allylic hydroperoxides by EPR In cellulo: study of the oxidative stress from allylic hydroperoxides on dendritic cells trough the Keap1/Nrf2/ARE sensor pathway
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BOCHEREL, PASCAL. "Etude par la methode c. R. E. S. U. De reactions neutre-neutre (radical-radical et radical-molecule) a temperature ultra-basse (de 13 a 295 k)". Rennes 1, 1995. http://www.theses.fr/1995REN10058.
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Ce memoire presente l'etude experimentale de reactions neutre-neutre (molecule-radical et radical-radical) sur un grand intervalle de temperature allant de la temperature ambiante jusqu'a des temperatures extremement basses de l'ordre de 10 k. Ce type de reaction est tres important d'un point de vue astrochimique, dans l'etude d'atmospheres planetaires et dans la confrontation avec la theorie. La technique c. R. E. S. U. (cinetique de reaction en ecoulement supersonique uniforme) permettant d'avoir un ecoulement uniforme de temperature tres basse et la technique plp-lif (pulse de photolyse laser-fluorescence induite par laser) ont permis les premieres etudes de reactions avec les radicaux cn, oh et ch a des temperatures aussi basses que 13 k. Les coefficients de vitesse des reactions de cn avec o#2 et de cn avec nh#3 croissent de facon monotone quand la temperature diminue. Ces mesures confrontees a la theorie montrent que l'on doit inclure, en plus des interactions a longue portee, celles a courte portee. Les premieres etudes de la reaction du radical oh avec trois butenes sont utiles pour une meilleure comprehension des pollutions de l'atmosphere terrestre. La forte dependance negative en temperature du coefficient de vitesse de la reaction du radical oh avec hbr a fait apparaitre une sous estimation du coefficient de vitesse aux temperatures regnant dans la stratosphere terrestre. Ceci a une incidence dans le cycle de l'ozone. Les premieres mesures du coefficient de vitesse de la reaction de oh avec no en fonction de la temperature et de la pression sont utiles dans l'etude d'atmospheres planetaires, notamment celle de la terre. Les premieres etudes de reactions entre le radical ch et plusieurs molecules et radicaux neutres indiquent que ch reagit rapidement a tres basse temperature. L'etude spectroscopique des radicaux cn et oh a montre que l'ecoulement supersonique presente un reel equilibre thermodynamique
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Le, Picard Sébastien. "Etude de la cinetique de reactions bimoleculaires (atome-molecule) et termoleculaires (radical-molecule) a ultra basse temperature (23-295 k) par la technique cresu". Rennes 1, 1998. http://www.theses.fr/1998REN10130.
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Ce memoire reporte l'etude experimentale de la cinetique de divers processus reactionnels entre especes neutres en phase gazeuse a tres basses temperatures (jusqu'a 23 k). La connaissance de la vitesse de ces processus dans ces conditions extremes est utile a la comprehension de la synthese des molecules dans le milieu interstellaire et dans les atmospheres planetaires froides. La dependance en temperature de la vitesse de reactions permet egalement de faire progresser nos connaissances des mecanismes reactionnels. Le dispositif experimental utilise combine la technique aerodynamique cresu (cinetique de reaction en ecoulement supersonique uniforme), qui permet de generer un jet de gaz de tres basse temperature a l'equilibre thermodynamique, et la technique plp-lif (photolyse laser pulsee - fluorescence induite par laser), qui permet de mesurer la vitesse des reactions impliquant des atomes ou des radicaux et des molecules neutres. Les reactions d'association entre le radical ch et les molecules n#2 et co ont ainsi ete etudiees a 53 k afin d'etendre la connaissance de la cinetique de ces reactions a des temperatures pertinentes pour differentes atmospheres extra-terrestres. Les coefficients de vitesse de deux reactions impliquant des atomes (al + o#2 alo + o et si + o#2 sio + o) ont ete mesures pour la premiere fois en dessous de la temperature ambiante (entre 23 et 295 k). La vitesse de ces deux reactions augmente lorsque la temperature diminue et la dependance en temperature de la premiere reaction a ete reproduite de maniere satisfaisante par une theorie de capture tenant compte des interactions a longue portee entre les reactants. Enfin, l'etude de la relaxation dans la structure fine de l'atome al (#2p#j) par collisions avec l'argon a ete effectuee entre 44 et 137 k. Completee par une etude theorique, elle a permis de caracteriser le potentiel d'interaction entre al et ar. Les eventuelles implications astrophysiques de l'ensemble de ces mesures ont egalement fait l'objet de discussions tout au long de ce memoire.
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Hannachi, Hassen. "Etudes cinetiques sous conditions atmospheriques simulees des reactions de composes carbonyles avec oh', o::(3), no'::(3) : consequences sur la chimie de basse troposphere". Paris 7, 1986. http://www.theses.fr/1986PA077213.
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Atkinson, Dean Bruce. "Radical-molecule reaction dynamics in the low temperature regime". Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187401.
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The temperature dependence of the rate coefficient of radical-molecule reactions is studied using novel flow techniques. The methodology makes use of the cooling extant in uniform and free supersonic expansions to produce low temperature (90-250 K in the uniform expansion and near 1 K in the free jet) environments which are not at chemical equilibrium. The design of the axisymmetric Laval nozzles, which are integral in producing the uniform supersonic expansion, is reviewed in depth. The experimental details pertinent to the characterization and operation of the pulsed uniform supersonic expansion flow reactor are considered. The application of free jet flows for the study of radical-molecule reactions at temperatures near I K is also discussed. The rate coefficient of the atmospherically important termolecular reactions OH + NO and OH + NO₂ were investigated at several temperatures between approximately 100 and 250 K and pressures between 0.1 and 10. The results are found to be well fit by a simple k = CT⁻ⁿ dependence suggested by statistical unimolecular theory within the collision complex model. The suggested variation of the reaction, OH + NO, is k = 7.0(±2.0) X 10⁻³¹ (T/300 K)^(2.6±0.3) over the range 90 to 550 K. The reaction, OH + N02, displayed falloff behavior in the pressure range studied here, so recommendation of the absolute low pressure rate coefficient awaits further pressure dependent study. The purely bimolecular reaction, OH + HBr, has been studied at temperatures between 76 and 242 K using the pulsed uniform supersonic expansion flow reactor and near 1 K using the free jet flow reactor. This reaction displays a complex temperature dependence not well predicted by current dynamical theory. The results are evaluated in the light of previously obtained rate coefficients, generally at higher temperatures, and of theoretical predictions of the absolute value and temperature dependence of the rate coefficient. Impact on the modeling of low temperature environments is discussed.
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Black, J. F. "REMPI studies of molecular reaction dynamics". Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379012.
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Jonušas, Mindaugas. "Study of photo-induced and radical reactions between CH4 and NH3 : astrochemical applications". Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS048/document.
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L'eau joue un rôle fondamental dans la photochimie du milieu interstellaire (MIS), à travers la formation d'espèces très réactives comme OH. Les radicaux OH peuvent par la suite interagir avec d'autres molécules hydrogénées pour reformer H2O par abstraction d'hydrogène: R-H + OH → R* + H2O. Dans le cadre de ce travail de thèse, nous avons étudié l'influence des photons VUV sur des analogues de glace interstellaire. Nous montrons que l'incorporation d'une petite quantité d'eau dans NH3 et CH4 glaces augmente considérablement la formation de radicaux réactifs comme NH2 et CH3 pendant le processus de photolyse et que le chauffage des glaces binaires irradiées telles que NH3-H2O et CH4-H2O conduit à la formation de NH2OH et d'espèces alcooliques plus complexes comme le propanol et le métoxyméthanol. Nous avons également entamé d'autres études en parallèle sur le l'évolution thermique des glaces de NH2OH d'une part et la formation de propanol par voies énergétiques (irradiation VUV) et non énergétique (réaction d'addition H) d'autre part afin de tenter d'expliquer la non-détection des ces espèces organiques dans le milieu interstellaire. L'étude des glaces mixtes irradiées NH3-CH4-H2O a montré la formation à basse température d'espèces plus exotiques en combinant les spectrométries IR et de masse. Nous avons réussi à identifier des composés organiques très complexes déjà détectés ou activement recherchés dans le MISWater plays a fundamental role in the photochemistry of the interstellar medium (ISM), through OH radical formation. OH radicals can interact with other H-containing species to form H2O through a hydrogen abstraction reaction: R-H + OH → R* + H2O. In this work, we have investigated the VUV processing on different interstellar ice analogs. We show that the incorporation of small amount of water in NH3 and CH4 ices greatly increases the formation of reactive NH2 and CH3 radicals during the photolysis processing. Thermal treatments of irradiated NH3-H2O and CH4-H2O ices lead to the formation of NH2OH and larger alcoholic species such as propanol and metoxymethanol. Further studies of thermal processing of NH2OH ice and formation of propanol through energetic (VUV irradiation) and non-energetic (surface H-addition reaction) processing were carried out in the context of this thesis in order to try explaining their non-detection in the interstellar medium. The study of the irradiated mixed NH3-CH4-H2O ices showed the formation of more exotic species by combining the IR and mass spectrometries. We managed to identify very large complex organic compounds already detected or tensively sought in the ISM
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Gunawan, Steven. "Enabling Chemistry to Expedite the Delivery of Pharmacologically Relevant Small Molecules". Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/265595.
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Operationally friendly protocols to produce libraries of novel small molecules with high molecular complexity are in huge demand for the interrogation of biological systems. As such, development of new MCRs and post-condensation modification of the MCR products have proven fruitful in the quest for new molecular probes and their expedited progression along the drug discovery value chain. The products thereof have found their way into numerous corporate compound collections. Crixivan (Indinavir), an antiretroviral, and Xylocaine (Lidocaine), a local anesthetic, are two examples of drugs derived from an MCR that have been marketed. The research topic of this dissertation encompasses the design and development of fifteen novel drug-like chemotypes in an operationally friendly, green, and expedited (≤ 3 synthetic operations) manner involving the Ugi MCR coupled with MAOS and high-throughput purification platforms. Over 500 drug-like small molecules (purity > 90% based on UV 214 nm and ELSD) have been synthesized, purified, and submitted to the NIH MLSMR for further biological evaluation against protein targets of interest. Furthermore, non-electrochemical carbamate oxidations enabling formation of N-acyliminium ion precursors, which are reactive intermediates that form the basis of a multitude of synthetic routes to natural products, have also been developed.
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Parry, D. J. "E.S.R. studies of the inter- and intra-molecular reactions of vinyl radicals". Thesis, University of York, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377283.
Pełny tekst źródłaKsiążki na temat "Radical‐ Molecule Reactions"
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P, Yu Byung, red. Free radicals in aging. Boca Raton: CRC Press, 1993.
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C, Gutteridge John M., red. Free radicals in biology and medicine. Wyd. 2. Oxford: Clarendon Press, 1989.
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C, Gutteridge John M., red. Free radicals in biology and medicine. Wyd. 3. Oxford: Clarendon Press, 1999.
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C, Gutteridge John M., red. Free radicals in biology and medicine. Oxford: Clarendon Press, 1985.
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G, Simic Michael, red. Oxygen radicals in biology and medicine. New York: Plenum Press, 1988.
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M, McCord Joe, i Bittar E. Edward, red. Oxyradicals in medical biology. Greenwich, Conn: JAI Press Inc., 1998.
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Nimmo, Samantha. Development of an experimental arrangement to investigate state-selected reactions between free radicals and diatomic molecules. Birmingham: University of Birmingham, 1994.
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Atkins, Peter. Reactions. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199695126.001.0001.
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Illustrated with remarkable new full-color images--indeed, one or more on every page--and written by one of the world's leading authorities on the subject, Reactions offers a compact, pain-free tour of the inner workings of chemistry. Reactions begins with the chemical formula almost everyone knows--the formula for water, H2O--a molecule with an "almost laughably simple chemical composition." But Atkins shows that water is also rather miraculous--it is the only substance whose solid form is less dense than its liquid (hence ice floats in water)--and incredibly central to many chemical reactions, as it is an excellent solvent, being able to dissolve gases and many solids. Moreover, Atkins tells us that water is actually chemically aggressive, and can react with and destroy the compounds dissolved in it, and he shows us what happens at the molecular level when water turns to ice--and when it melts. Moving beyond water, Atkins slowly builds up a toolkit of basic chemical processes, including precipitation (perhaps the simplest of all chemical reactions), combustion, reduction, corrosion, electrolysis, and catalysis. He then shows how these fundamental tools can be brought together in more complex processes such as photosynthesis, radical polymerization, vision, enzyme control, and synthesis. Peter Atkins is the world-renowned author of numerous best-selling chemistry textbooks for students. In this crystal-clear, attractively illustrated, and insightful volume, he provides a fantastic introductory tour--in just a few hundred colorful and lively pages - for anyone with a passing or serious interest in chemistry.
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Simic, Michael. Oxygen Radicals in Biology and Medicine. Springer London, Limited, 2012.
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Simic, Michael. Oxygen Radicals in Biology and Medicine. Springer London, Limited, 2013.
Znajdź pełny tekst źródłaCzęści książek na temat "Radical‐ Molecule Reactions"
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Werst, D. W., L. T. Percy i A. D. Trifunac. "Dissociation and Ion-Molecule Reactions of Alkane Radical Cations. Time-Resolved FDMR". W Organic Free Radicals, 233. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73963-7_116.
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Benson, Sidney W. "Some Problems of Structure and Reactivity in Free Radical and Molecule Reactions in the Gas Phase". W Advances in Photochemistry, 1–23. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2007. http://dx.doi.org/10.1002/9780470133323.ch1.
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Douberly, Gary E. "Infrared Spectroscopy of Molecular Radicals and Carbenes in Helium Droplets". W Topics in Applied Physics, 155–77. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-94896-2_4.
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AbstractThe helium droplet is an ideal environment to spectroscopically probe difficult to prepare molecular species, such as radicals, carbenes and ions. The quantum nature of helium at 0.4 K often results in molecular spectra that are sufficiently resolved to evoke an analysis of line shapes and fine-structure via rigorous “effective Hamiltonian” treatments. In this chapter, we will discuss general experimental methodologies and a few examples of successful attempts to efficiently dope helium droplets with organic molecular radicals or carbenes. In several cases, radical reactions have been carried out inside helium droplets via the sequential capture of reactive species, resulting in the kinetic trapping of reaction intermediates. Infrared laser spectroscopy has been used to probe the properties of these systems under either zero-field conditions or in the presence of externally applied, homogeneous electric or magnetic fields.
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Stufkens, D. J. "Light-Induced Radical Formation from Organometallic Complexes". W Selective Reactions of Metal-Activated Molecules, 267–76. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-662-00975-8_40.
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Linker, Torsten, Thomas Sommermann i Michael Maurer. "Transition-Metal-Mediated Radical Reactions: A Convenient Method for the Synthesis of 2-C-Branched Carbohydrates". W Selective Reactions of Metal-Activated Molecules, 147–50. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-662-00975-8_20.
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Dannenberg, J. J. "Theoretical Studies on the Reactions of Free Radicals". W Topics in Molecular Organization and Engineering, 221–31. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-2853-4_9.
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Hüttermann, Jürgen. "Radical Ions and Their Reactions in DNA and its Constituents". W Topics in Molecular Organization and Engineering, 435–62. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3750-8_17.
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Steenken, S. "One-Electron Redox Reactions Between Radicals and Molecules. Dominance of Inner-Sphere Mechanisms". W Free Radicals in Synthesis and Biology, 213–31. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0897-0_16.
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Leroy, G., D. Peeters, M. Sana i C. Wilante. "Thermochemistry and Kinetics of Ionic and Radical Reactions in the Gas Phase". W Topics in Molecular Organization and Engineering, 233–57. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-2853-4_10.
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Gutteridge, John M. C. "Signal, Messenger and Trigger Molecules from Free Radical Reactions and their Control by Antioxidants". W Signalling Mechanisms — from Transcription Factors to Oxidative Stress, 157–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-79675-3_14.
Pełny tekst źródłaStreszczenia konferencji na temat "Radical‐ Molecule Reactions"
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Marković, Svetlana, i Jelena Tošović. "CHLOROGENIC ACID – APPLICATION OF CONTEMPORARY DENSITY FUNCTIONALS TO A SINGLE MOLECULE". W 1st INTERNATIONAL Conference on Chemo and BioInformatics. Institute for Information Technologies, University of Kragujevac,, 2021. http://dx.doi.org/10.46793/iccbi21.081m.
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Although chlorogenic acid (5-O-caffeoylquinic acid, 5CQA) is a dietary phenol known for its pharmacological and nutritional properties, its structural features and mechanisms of oxidative action have not been completely elucidated. Clarification of the 5CQA structure was conducted by comparing the experimental and simulated IR, Raman, 1H-NMR, 13C-NMR, and UV spectra. For this purpose, a comprehensive conformational analysis of 5CQA was performed to reveal its most stable conformations in the gas-state and solution. Excellent agreement between all experimental and simulated spectra indicates correct arrangement of the atoms in the 5CQA molecule. In addition, the most stable conformation in solution coincides with that predicted with sophisticated NMR experiments. The quantum mechanics–based test for overall free-radical scavenging activity was applied for the investigation of antioxidative capacity of 5CQA relative to trolox (6-hydroxy-2,5,7,8- tetramethylchroman-2-carboxylic acid, Tx) as a reference compound. Hydrogen atom transfer (HAT), radical adduct formation (RAF), sequential proton loss electron transfer (SPLET), and single electron transfer – proton transfer (SET-PT) reactions of 5CQA and Tx with HO· and CH3OO· radicals were examined in benzene, pentyl ethanoate, and basic aqueous solutions. In non-polar solvents 5CQA reacts with HO· via HAT and RAF mechanisms, whereas HAT is the only reaction pathway with CH3OO·. At physiological conditions 5CQA exists in the form of monoanion and dianion. Both anionic forms undergo only HAT mechanism with CH3OO·. With HO·, the anions conform to the HAT, RAF, SPLET, and SET-PT mechanisms. Because all reactions of dianion are diffusion controlled, its contribution to scavenging HO· is comparable to that of more abundant monoanion. The calculated rate constant for overall reaction of 5CQA with HO· is in perfect agreement with the corresponding experimental value. The order of reactivity toward selected free radicals is the same in nonpolar and polar solutions: in comparison to Tx, 5CQA is more reactive toward HO·, but less reactive toward CH3OO·. Very good agreement between the experimental and calculated results confirms the ability of contemporary density functionals to quantify subtle physico-chemical interactions.
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Bethardy, Gregory A., Frederick J. Northrup i Robert G. Macdonald. "Time-resolved infrared absorption studies applied to the study of radical plus molecule reactions". W OE/LASE '94, redaktor John W. Hepburn. SPIE, 1994. http://dx.doi.org/10.1117/12.178095.
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Zhukovets, T. A., M. А. Khancheuski, I. V. Koktysh, E. I. Kvasyuk i A. G. Sysa. "ANTIOXIDANT EFFECTS OF EMOXYPINE AS ADJUVANT OF ANTI-CANCER DRUGS". W SAKHAROV READINGS 2021: ENVIRONMENTAL PROBLEMS OF THE XXI CENTURY. International Sakharov Environmental Institute of Belarusian State University, 2021. http://dx.doi.org/10.46646/sakh-2021-2-52-55.
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Antioxidants are known to minimize oxidative stress by interacting with free radicals produced as a result of cell aerobic reactions. Oxidative stress has long been linked to many diseases, especially tumours. Therefore, antioxidants play a crucial role in the prevention or management of free radical-related diseases. However, most of these antioxidants have anticancer effects only if taken in large doses. Therefore, the combined use of antioxidants with chemotherapeutic agents is an attractive strategy to combat various tumours. This article focuses on the antioxidant effect of emoxypine. The contribution of this molecule in enhancing the anticancer potentials of nelarabine will be demonstrated.
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Liu, Ruochen, Enke An i Kun Wu. "Theoretical Study on Chemical-Kinetic Characteristics of Oxy-Coal Mild Combustion". W ASME 2016 Power Conference collocated with the ASME 2016 10th International Conference on Energy Sustainability and the ASME 2016 14th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/power2016-59032.
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The chemical-kinetic characteristics of oxy-coal MILD combustion under different initial temperature and oxygen concentration were studied numerically. Aromatic benzene was considered representative for coal molecule. A unique reaction pathway under low oxygen concentration was obtained, the activation energy and reaction rate constant of involved elementary reactions were calculated through classic transition state theory (TST). The results show that low oxygen concentration and high temperature is advantageous for thickening flame front as well as slowing down flame propagation; as oxygen concentration and temperature increase, the global activation energy increases with greater slope; the decomposition of C5H5 dominates under high oxygen concentration, while the decomposition and oxidation of C5H5 become equally important as oxygen concentration decreases, leading to a new pathway that the complexity of overall chemical reactions develops; the radical CH2CHO is easily trigged under low oxygen concentration, its decomposition reaction dominates in the unique pathway C5H5→C5H4O→c-C4H5CH2CHO→CH3 due to larger activation energy, where more CO escapes. The simulation results have theoretical referencing value, laying foundations for the further practical work.
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Lesslie, Michael, Victor Ryzhov, J. Oomens, Giel Berden i Sandra Osburn. "COMBINING THE POWER OF IRMPD WITH ION-MOLECULE REACTIONS: THE STRUCTURE AND REACTIVITY OF RADICAL IONS OF CYSTEINE AND ITS DERIVATIVES". W 70th International Symposium on Molecular Spectroscopy. Urbana, Illinois: University of Illinois at Urbana-Champaign, 2015. http://dx.doi.org/10.15278/isms.2015.wg02.
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Bungay, Corey L., Thomas E. Tiwald i John A. Woollam. "Characterizing UV induced polymer degradation with spectroscopic ellipsometry". W Optical Interference Coatings. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/oic.1998.tuf.5.
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Polymers are susceptible to altered chemistry from UV radiation. The absorption of UV photons can promote breakage of important functional groups and structural bonds, such as C=C and C=O [1]. When an organic molecule absorbs UV radiation, it will be excited into higher energy states and possibly dissociate bonds. Dissociated radical species can then participate in additional reactions. Changes in chemistry may affect optical properties, which can have serious effects for polymers used in optical systems.
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Vijlee, Shazib Z., Igor V. Novosselov i John C. Kramlich. "Effects of Composition on the Flame Stabilization of Alternative Aviation Fuels in a Toroidal Well Stirred Reactor". W ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43014.
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The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of flame stabilization envelopes relative to the behavior of conventional fuels. Previous studies using the Toroidal Well Stirred Reactor (TWSR) found that synthetic alternatives to JP8 behave similarly in terms of lean flameout, but there is significant difference in the flameout behavior of a highly aliphatic fuel versus that of a highly aromatic fuel. Detailed computational fluid dynamics (CFD) and chemical reactor modeling (CRM) is necessary to understand differences in flame stabilization. The first portion of this study employs CFD models of the TWSR with reduced methane combustion chemistry. The models provide insight into the mechanism of flame stabilization inside the reactor as equivalence ratio is decreased to flameout. The CFD domain is expanded over earlier published TWSR CFD studies to capture previously unknown asymmetrical flame behavior. The Reynolds Stress Model (RSM) is used for turbulence closure, and the Eddy Dissipation Concept (EDC) model is used to include turbulence-chemistry interaction. The CFD results show that radical species (specifically OH) are transported around the reactor to interact with the incoming premixed fuel-air jet and initiate chain branching reactions. As the equivalence ratio decreases, and flameout is approached, the species concentration in the reactor becomes less homogenous. Radical production is delayed and eventually insufficient radical concentrations are available to ignite the incoming jet. The production and transport of radical species throughout the reactor are, thus, responsible for stabilizing the flame. CFD and PSR studies with methane agree that the radical behavior dictates blowout. The second portion of this study focuses on the importance of radical species in flame stabilization, but now employs a single perfectly stirred reactor (PSR) model, which allows the study of detailed chemistry for individual components of jet fuel. An aliphatic compound (iso-octane) and an aromatic compound (toluene) are used as investigative fuels to compare the differences in the chemical kinetic behavior of blowout for aliphatic versus aromatic fuel classes. The models show that the rates at which radical species (O, H, and OH) destroy the original fuel molecule are significantly different for iso-octane and toluene. During combustion, the radical destruction of toluene is much slower than for iso-octane at a constant temperature. In PSR systems, the toluene flame blows out at a higher temperature because a higher temperature is needed to provide sufficient radical concentrations and reaction rates to maintain a stable flame.
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Arathala, Parandaman, i Rabi Musah. "REACTION MECHANISM AND KINETICS OF THE GAS PHASE REACTIONS OF METHANE SULFONAMIDE WITH Cl RADICALS AND THE FATE OF CH2S(=O)2NH2 RADICAL". W 2022 International Symposium on Molecular Spectroscopy. Urbana, Illinois: University of Illinois at Urbana-Champaign, 2022. http://dx.doi.org/10.15278/isms.2022.fc07.
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Coombe, Robert D. "Azide reactions for advanced chemical lasers". W OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.wh1.
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An efficient short-wavelength chemical laser will be a device which couples a highly constrained chemical pumping mechanism with an atomic or molecular species whose spectroscopic characteristics are appropriate for lasing. Research in the past several years has identified a number of candidates (e.g., interhalogens, group VI atoms and molecules, CN, NO, and others) which are capable of lasing in the UV or visible regions. Recent work in our laboratory has sought means by which the very highly constrained reactions of azide radicals may be used to pump these known candidate systems. The electronic ground state of N3 correlates adiabatically to an excited N(2D) atom and a ground state N2 molecule. As a consequence, R + N3 reactions effectively proceed on excited state potential energy surfaces and are very strongly constrained to produce electronically excited metastable NR molecules. This view is supported by experimental studies of reactions of N3 with a number of first and second row atoms.1,2 The products of these reactions are useful as either energy storage agents or lasing species in a number of potential SWCL systems. N3 reactions can be operated in either continuous or pulsed modes. Pulsed experiments with these systems hold promise for early tests at reagent densities commensurate with measurable gain levels.
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Elapolu, Mohan S. R., i Alireza Tabarraei. "Stress Corrosion Cracking of Graphene". W ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23842.
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Abstract We use molecular dynamics (MD) simulations to study the stress corrosion cracking (SCC) of monolayer graphene sheets with an initial edge cracks. Two types of edge cracks are considered in the simulations; one with armchair edges and another one with zigzag edges. All the simulations are conducted at 300 K and the corrosive environment is O2 molecules. Tensile stresses are induced in the graphene sheet by applying mode–I loading. To understand the mechanism of the sub–critical crack growth during SCC, we expose the graphene sheets to O2 molecules at strains of 0.047 and 0.076. Our MD simulations capture the chemisorption process between the O2 molecules and pre–stressed graphene sheet. Oxygen molecules react with carbon radicals at the edges of the crack tip and gets adsorbed to the graphene surface. The atomic stresses in the vicinity of crack tip relaxes due to the adsorption of O2 molecule. Our results show that the reaction of O2 molecules with the carbon radicals at the crack tip can cause the failure of C–C bonds which leads to the sub critical cracking.
Raporty organizacyjne na temat "Radical‐ Molecule Reactions"
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Reisler, H. Reactions of Atoms and Radicals in Pulsed Molecular Beams. Office of Scientific and Technical Information (OSTI), kwiecień 2004. http://dx.doi.org/10.2172/838570.
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Kanner, Joseph, Edwin Frankel, Stella Harel i Bruce German. Grapes, Wines and By-products as Potential Sources of Antioxidants. United States Department of Agriculture, styczeń 1995. http://dx.doi.org/10.32747/1995.7568767.bard.
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Several grape varieties and red wines were found to contain large concentration of phenolic compounds which work as antioxidant in-vitro and in-vivo. Wastes from wine production contain antioxidants in large amounts, between 2-6% on dry material basis. Red wines but also white wines were found to prevent lipid peroxidation of turkey muscle tissues stored at 5oC. The antioxidant reaction of flavonoids found in red wines against lipid peroxidation were found to depend on the structure of the molecule. Red wine flavonoids containing an orthodihydroxy structure around the B ring were found highly active against LDL and membrane lipid peroxidation. The antioxidant activity of red wine polyphenols were also found to be dependent on the catalyzer used. In the presence of H2O2-activated myoglobin, the inhibition efficiency was malvidin 3-glucoside>catechin>malvidin>resveratol. However, in the presence of an iron redox cycle catalyzer, the order of effectiveness was resveratol>malvidin 3-glucoside = malvidin>catechin. Differences in protein binding were found to affect antioxidant activity in inhibiting LDL oxidation. A model protein such as BSA, was investigated on the antioxidant activity of phenolic compounds, grape extracts, and red wines in a lecithin-liposome model system. Ferulic acid followed by malvidin and rutin were the most efficient in inhibiting both lipid and protein oxidation. Catechin, a flavonal found in red-wines in relatively high concentration was found to inhibit myoglobin catalyzed linoleate membrane lipid peroxidation at a relatively very low concentration. This effect was studied by the determination of the by-products generated from linoleate during oxidation. The study showed that hydroperoxides are catalytically broken down, not to an alcohol but most probably to a non-radical adduct. The ability of wine-phenolics to reduce iron and from complexes with metals were also demonstrated. Low concentration of wine phenolics were found to inhibit lipoxygenase type II activity. An attempt to understand the bioavailability in humans of antocyanins from red wine showed that two antocyanins from red wine were found unchanged in human urine. Other antocyanins seems to undergo molecular modification. In hypercholesterolemic hamsters, aortic lipid deposition was significantly less in animals fed diets supplemented with either catechin or vitamin E. The rate of LDL accumulation in the carotid arteries was also significantly lower in the catechin and vitamin E animal groups. These results suggested a novel mechanism by which wine phenolics are associated with decreased risk of coronary heart diseases. This study proves in part our hypothesis that the "French Paradox" could be explained by the action of the antioxidant effects of phenolic compounds found at high concentration in red wines. The results of this study argue that it is in the interest of public health to increase the consumption of dietary plant falvonoids. Our results and these from others, show that the consumption of red wine or plant derived polyphenolics can change the antioxidant tone of animal and human plasma and its isolated components towards oxidative reactions. However, we need more research to better understand bioavailability and the mechanism of how polyphenolics affect health and disease.
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Kanner, Joseph, Mark Richards, Ron Kohen i Reed Jess. Improvement of quality and nutritional value of muscle foods. United States Department of Agriculture, grudzień 2008. http://dx.doi.org/10.32747/2008.7591735.bard.
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Food is an essential to our existence but under certain conditions it could become the origin to the accumulative health damages. Technological processes as heating, chopping, mincing, grounding, promote the lipid oxidation process in muscle tissues and meat foodstuffs. Lipid oxidation occurred rapidly in turkey muscle, intermediate in duck, and slowest in chicken during frozen storage. Depletion of tocopherol during frozen storage was more rapid in turkey and duck compared to chicken. These processes developed from lipid peroxides produce many cytotoxic compounds including malondialdehyde (MDA). The muscle tissue is further oxidized in stomach conditions producing additional cytotoxic compounds. Oxidized lipids that are formed during digestion of a meal possess the potential to promote reactions that incur vascular diseases. A grape seed extract (1% of the meat weight) and butylated hydroxytoluene (0.2% of the lipid weight) were each effective at preventing formation of lipid oxidation products for 3 hours during co-incubation with cooked turkey meat in simulated gastric fluid (SGF). Polyphenols in the human diet, as an integral part of the meal prevent the generation and absorption of cytotoxic compounds and the destruction of essential nutrients, eg. antioxidants vitamins during the meal. Polyphenols act as antioxidants in the gastrointestinal tract; they scavenge free radicals and may interact with reactive carbonyls, enzymes and proteins. These all reactions results in decreasing the absorption of reactive carbonyls and possible other cytotoxic compounds into the plasma. Consumptions of diet high in fat and red meat are contributory risk factors partly due to an increase production of cytotoxic oxidized lipid products eg. MDA. However, the simultaneously consumption of polyphenols rich foods reduce these factors. Locating the biological site of action of polyphenols in the in the gastrointestinal tract may explain the paradox between the protective effect of a highly polyphenols rich diet and the low bioavailability of these molecules in human plasma. It may also explain the "French paradox" and the beneficial effect of Mediterranean and Japanese diets, in which food products with high antioxidants content such as polyphenols are consumed during the meal.
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Blank, D. A., N. Hemmi, A. G. Suits i Y. T. Lee. 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}. Office of Scientific and Technical Information (OSTI), kwiecień 1997. http://dx.doi.org/10.2172/603612.
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