Artykuły w czasopismach: „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.

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M. Silaev, Michael. "Kinetics of Free-Radical Addition Processes by the Nonbranched-Chain Mechanism". Journal of Advance Research in Applied Science (ISSN: 2208-2352) 3, nr 10 (31.10.2016): 01–19. http://dx.doi.org/10.53555/nnas.v3i10.645.

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Five reaction schemes are suggested for the initiated nonbranched-chain addition of free radicals to the multiple bonds of the unsaturated compounds. The proposed schemes include the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in these schemes involves three or four types of free radicals. One of them is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the suggested schemes, nine rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. These equations provide good fits for the nonmonotonic (peaking) dependences of the formation rates of the molecular products (1:1 adducts) on the concentration of the unsaturated component in binary systems consisting of a saturated component (hydrocarbon, alcohol, etc.) and an unsaturated component (alkene, allyl alcohol, formaldehyde, or dioxygen). The unsaturated compound in these systems is both a reactant and an autoinhibitor generating low-reactive free radicals. A similar kinetic description is applicable to the nonbranched-chain process of the free-radical hydrogen oxidation, in which the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant). The energetics of the key radical-molecule reactions is considered.

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Stirk, Krista M., L. K. Marjatta Kiminkinen i Hilkka I. Kenttamaa. "Ion-molecule reactions of distonic radical cations". Chemical Reviews 92, nr 7 (listopad 1992): 1649–65. http://dx.doi.org/10.1021/cr00015a008.

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Silaev, M. M. "Competition Kinetics of the Nonbranched-Chain Addition of Free Radicals to Olefins, Formaldehyde, and Oxygen". International Journal of Chemical Engineering 2011 (2011): 1–19. http://dx.doi.org/10.1155/2011/830610.

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Five reaction schemes are suggested for the initiated nonbranched-chain addition of free radicals to the multiple bonds of alkenes, formaldehyde, and oxygen. The schemes include reactions competing with chain propagation through a reactive free radical. The chain evolution stage in these schemes involves three or four types of free radicals. One of them— , , , , or —is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the suggested schemes, nine rate equations containing one to three parameters to be determined directly are set up using quasi-steady-state treatment. These equations provide good fits for the nonmonotonic (peaking) dependences of the formation rates of the molecular addition products (1 : 1 adducts) on the concentration of the unsaturated component in liquid homogeneous binary systems consisting of a saturated component (hydrocarbon, alcohol, etc.) and an unsaturated component (olefin, formaldehyde, or dioxygen). The unsaturated compound in these systems is both a reactant and an autoinhibitor generating low-reactive free radicals. A similar kinetic description is applicable to nonbranched-chain free-radical hydrogen oxidation. The energetics of the key radical-molecule reactions is considered.

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Wojnárovits, László, i Erzsébet Takács. "Rate constants of dichloride radical anion reactions with molecules of environmental interest in aqueous solution: a review". Environmental Science and Pollution Research 28, nr 31 (4.06.2021): 41552–75. http://dx.doi.org/10.1007/s11356-021-14453-w.

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AbstractNatural waters, water droplets in the air at coastal regions and wastewaters usually contain chloride ions (Cl-) in relatively high concentrations in the milimolar range. In the reactions of highly oxidizing radicals (e.g., •OH, •NO3, or SO4•-) in the nature or during wastewater treatment in advanced oxidation processes the chloride ions easily transform to chlorine containing radicals, such as Cl•, Cl2•-, and ClO•. This transformation basically affects the degradation of organic molecules. In this review about 400 rate constants of the dichloride radical anion (Cl2•-) with about 300 organic molecules is discussed together with the reaction mechanisms. The reactions with phenols, anilines, sulfur compounds (with sulfur atom in lower oxidation state), and molecules with conjugated electron systems are suggested to take place with electron transfer mechanism. The rate constant is high (107–109 M-1 s-1) when the reduction potential the one-electron oxidized species/molecule couple is well below that of the Cl2•-/2Cl- couple.

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Shiels, Oisin J., P. D. Kelly, Stephen J. Blanksby, Gabriel da Silva i Adam J. Trevitt. "Barrierless Reactions of Three Benzonitrile Radical Cations with Ethylene". Australian Journal of Chemistry 73, nr 8 (2020): 705. http://dx.doi.org/10.1071/ch19606.

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Reactions of three protonated benzonitrile radical cations with ethylene are investigated. Product branching ratios and reaction kinetics, measured using ion-trap mass spectrometry, are reported and mechanisms are developed with support from quantum chemical calculations. Reactions proceed via pre-reactive van der Waals complexes with no energy barrier (above the reactant energy) and form radical addition and addition–elimination product ions. Rate coefficients are 4-dehydrobenzonitrilium: 1.72±0.01×10−11 cm3 molecule−1 s−1, 3-dehydrobenzonitrilium: 1.85±0.01×10−11 cm3 molecule−1 s−1, and 2-dehydrobenzonitrilium: 5.96±0.06×10−11 cm3 molecule−1 s−1 (with±50% absolute uncertainty). A ring-closure mechanism involving the protonated nitrile substituent is proposed for the 2-dehydrobenzonitrilium case and suggests favourable formation of the protonated indenimine cation.

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Balucani, Nadia. "Gas-phase prebiotic chemistry in extraterrestrial environments". Proceedings of the International Astronomical Union 5, H15 (listopad 2009): 682–83. http://dx.doi.org/10.1017/s1743921310010938.

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AbstractA variety of molecular species up to complex polyatomic molecules/radicals have been identified in many extraterrestrial gaseous environments, including interstellar clouds, cometary comae and planetary atmospheres. Amongst the identified molecules/radicals, a large percentage are organic in nature and encompass also prebiotic molecules. Different types of microscopic processes are believed to be involved in their formation, including surface processes, ion- and radical- molecule reactions. A thorough characterization of such a complex chemistry relies on a multi-disciplinary approach, where the observations are complemented by accurate chemical modeling. Unfortunately, a literature survey reveals that only a small percentage of the elementary reactions considered in the available models have been characterized in laboratory experiments. In this contribution, a brief overview will be given of recent experimental techniques that have allowed us to reach a better description of neutral-neutral gas-phase reactions, which might be responsible for the formation of simple prebiotic molecules.

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BRÜCK, Thomas B., Maria Francesca GERINI, Enrico BACIOCCHI i Patricia J. HARVEY. "Oxidation of thioanisole and p-methoxythioanisole by lignin peroxidase: kinetic evidence of a direct reaction between compound II and a radical cation". Biochemical Journal 374, nr 3 (15.09.2003): 761–66. http://dx.doi.org/10.1042/bj20030487.

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The reaction of H2O2 with thioanisole and p-methoxythioanisole catalysed by lignin peroxidase from Phanerochaete chrysosporium has been studied spectrophotometrically under turnover and single turnover conditions with a stopped-flow apparatus. Pre-formed lignin peroxidase compounds I and II are each able to react with the sulphides to form a sulphide radical cation. The radical cation is then converted into the sulphoxide either by reaction with the medium or by reaction with compound II. This is the first report of a direct reaction between compound II and the substrate radical cation. With thioanisole, significant enantiomeric selectivity and high oxygen incorporation in the sulphoxide are obtained because compound II is preferentially reduced by the enzyme-bound thioanisole radical cation compared with the neutral substrate. By contrast, with p-methoxythioanisole, the data imply formation of an intermediate ternary complex comprising compound II, radical cation and neutral substrate, such that a chain of electron transfer reactions starting from neutral molecule and progressing to oxidized haem via substrate radical cation is facilitated, yielding the native enzyme and two molecules of p-methoxythioanisole radical cation as products. The reactions of compounds I and II with sulphides imply flexing of the apoprotein moiety during catalysis.

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XIE, HONG-BIN, YI-HONG DING i CHIA-CHUNG SUN. "RADICAL-MOLECULE REACTIONS HCO/HOC + C2H4: A MECHANISTIC STUDY". Journal of Theoretical and Computational Chemistry 04, nr 04 (grudzień 2005): 1029–55. http://dx.doi.org/10.1142/s0219633605001994.

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A detailed computational study is performed on the radical-molecule reactions between HCO/HOC and ethylene ( C 2 H 4) at the Gaussian-3//B3LYP/6-31G(d) level. For the HCO + C 2 H 4 reaction, the most favorable pathway is the direct C -addition forming the intermediate H 2 CCH 2 CHO , followed by a 1,2- H -shift leading to H 3 CCHCHO . Subsequently, there are two highly competitive dissociation pathways for H 3 CCHCHO : one is the formation of the direct H -extrusion product H 2 CCHCHO + H , and the other is the formation of C 2 H 5 + CO via the intermediate H 3 CCH 2 CO . The overall reaction barrier is 14.1 and 14.6 kcal/mol respectively, at the G3B3 level. The quasi-direct H -donation process to produce C 2 H 5 + CO with the barrier 16.5 kcal/mol is less competitive. Thus, only at higher temperatures, the HCO + C 2 H 4 reaction could play a role. In contrast, the HOC + C 2 H 4 reaction just need to overcome a small barrier 2.0 kcal/mol to generate C 2 H 5 + CO via the quasi-direct H -donation mechanism. This is suggestive of the potential importance of the HOC + C 2 H 4 reaction in combustion processes. However, the direct C -addition channel is much less competitive. The present kinetic data and orbital analysis show that the HCO radical has much higher reactivity than HOC , although the latter is more energetic. Till now, no kinetic study on the HOC radical has been reported, the present study can provide useful information on understanding the reactivity and depletion mechanism of the energetic HOC radical.

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Lochmann, Christine, Thomas F. M. Luxford, Samanta Makurat, Andriy Pysanenko, Jaroslav Kočišek, Janusz Rak i Stephan Denifl. "Low-Energy Electron Induced Reactions in Metronidazole at Different Solvation Conditions". Pharmaceuticals 15, nr 6 (2.06.2022): 701. http://dx.doi.org/10.3390/ph15060701.

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Metronidazole belongs to the class of nitroimidazole molecules and has been considered as a potential radiosensitizer for radiation therapy. During the irradiation of biological tissue, secondary electrons are released that may interact with molecules of the surrounding environment. Here, we present a study of electron attachment to metronidazole that aims to investigate possible reactions in the molecule upon anion formation. Another purpose is to elucidate the effect of microhydration on electron-induced reactions in metronidazole. We use two crossed electron/molecular beam devices with the mass-spectrometric analysis of formed anions. The experiments are supported by quantum chemical calculations on thermodynamic properties such as electron affinities and thresholds of anion formation. For the single molecule, as well as the microhydrated condition, we observe the parent radical anion as the most abundant product anion upon electron attachment. A variety of fragment anions are observed for the isolated molecule, with NO2− as the most abundant fragment species. NO2− and all other fragment anions except weakly abundant OH− are quenched upon microhydration. The relative abundances suggest the parent radical anion of metronidazole as a biologically relevant species after the physicochemical stage of radiation damage. We also conclude from the present results that metronidazole is highly susceptible to low-energy electrons.

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Dong, Hao, Yi-hong Ding i Chia-chung Sun. "Radical−Molecule Reactions HCO/HOC + C2H2: Mechanistic Study". Journal of Physical Chemistry A 109, nr 51 (grudzień 2005): 11941–55. http://dx.doi.org/10.1021/jp0442854.

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Wang, De-Quan, Ji-Lai Li, Xu-Ri Huang, Cai-Yun Geng i Chia-Chung Sun. "Diatomic radical–molecule reactions CN+HONO: Mechanistic study". Journal of Molecular Structure: THEOCHEM 857, nr 1-3 (maj 2008): 20–26. http://dx.doi.org/10.1016/j.theochem.2008.01.030.

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Sandhiya, Lakshmanan, Harish Jangra i Hendrik Zipse. "Molecule‐Induced Radical Formation (MIRF) Reactions—A Reappraisal". Angewandte Chemie International Edition 59, nr 16 (21.02.2020): 6318–29. http://dx.doi.org/10.1002/anie.201912382.

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Kawai, Shigeki, Ondřej Krejčí, Tomohiko Nishiuchi, Keisuke Sahara, Takuya Kodama, Rémy Pawlak, Ernst Meyer, Takashi Kubo i Adam S. Foster. "Three-dimensional graphene nanoribbons as a framework for molecular assembly and local probe chemistry". Science Advances 6, nr 9 (luty 2020): eaay8913. http://dx.doi.org/10.1126/sciadv.aay8913.

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Recent advances in state-of-the-art probe microscopy allow us to conduct single molecular chemistry via tip-induced reactions and direct imaging of the inner structure of the products. Here, we synthesize three-dimensional graphene nanoribbons by on-surface chemical reaction and take advantage of tip-induced assembly to demonstrate their capability as a playground for local probe chemistry. We show that the radical caused by tip-induced debromination can be reversibly terminated by either a bromine atom or a fullerene molecule. The experimental results combined with theoretical calculations pave the way for sequential reactions, particularly addition reactions, by a local probe at the single-molecule level decoupled from the surface.

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Michail, Karim, Naif Aljuhani i Arno G. Siraki. "The interaction of diamines and polyamines with the peroxidase-catalyzed metabolism of aromatic amines: a potential mechanism for the modulation of aniline toxicity". Canadian Journal of Physiology and Pharmacology 91, nr 3 (marzec 2013): 228–35. http://dx.doi.org/10.1139/cjpp-2012-0253.

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Synthetic and biological amines such as ethylenediamine (EDA), spermine, and spermidine have not been previously investigated in free-radical biochemical systems involving aniline-based drugs or xenobiotics. We aimed to study the influence of polyamines in the modulation of aromatic amine radical metabolites in peroxidase-mediated free radical reactions. The aniline compounds tested caused a relatively low oxidation rate of glutathione in the presence of horseradish peroxidase (HRP), and H2O2; however, they demonstrated marked oxygen consumption when a polyamine molecule was present. Next, we characterized the free-radical products generated by these reactions using spin-trapping and electron paramagnetic resonance (EPR) spectrometry. Primary and secondary but not tertiary polyamines dose-dependently enhanced the N-centered radicals of different aniline compounds catalyzed by either HRP or myeloperoxidase, which we believe occurred via charge transfer intermediates and subsequent stabilization of aniline-derived radical species as suggested by isotopically labeled aniline. Aniline/peroxidase reaction product(s) were monitored at 435 nm by kinetic spectrophotometry in the presence and absence of a polyamine additive. Using gas chromatography – mass spectrometry, the dimerziation product of aniline, azobenzene, was significantly amplified when EDA was present. In conclusion, di- and poly-amines are capable of enhancing the formation of aromatic-amine-derived free radicals, a fact that is expected to have toxicological consequences.

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Quiclet-Sire, Béatrice, i Samir Z. Zard. "Some aspects of radical cascade and relay reactions". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, nr 2200 (kwiecień 2017): 20160859. http://dx.doi.org/10.1098/rspa.2016.0859.

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The ability to create carbon–carbon bonds is at the heart of organic synthesis. Radical processes are particularly apt at creating such bonds, especially in cascade or relay sequences where more than one bond is formed, allowing for a rapid assembly of complex structures. In the present brief overview, examples taken from the authors' laboratory will serve to illustrate the strategic impact of radical-based approaches on synthetic planning. Transformations involving nitrogen-centred radicals, electron transfer from metallic nickel and the reversible degenerative exchange of xanthates will be presented and discussed. The last method has proved to be a particularly powerful tool for the intermolecular creation of carbon–carbon bonds by radical additions even to unactivated alkenes. Various functional groups can be brought into the same molecule in a convergent manner and made to react together in order to further increase the structural complexity. One important benefit of this chemistry is the so-called RAFT/MADIX technology for the manufacture of block copolymers of almost any desired architecture.

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26

Hansen, Jaron C., i Joseph S. Francisco. "Radical–Molecule Complexes: Changing Our Perspective on the Molecular Mechanisms of Radical–Molecule Reactions and their Impact on Atmospheric Chemistry". ChemPhysChem 3, nr 10 (18.10.2002): 833–40. http://dx.doi.org/10.1002/1439-7641(20021018)3:10<833::aid-cphc833>3.0.co;2-0.

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Song, Chun Lian, Shao Gang Pi, Chuan Song Wang i Mei Duo Liu. "Reactive Process Research of Cornstalk Hydrolysis to Sugar on Micro-Stream Discharge". Advanced Materials Research 233-235 (maj 2011): 785–88. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.785.

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In order to further study the mechanism of hydrolysis reactions to sugars using cornstalk on plasma, preliminary study of reactive process are carried out. Model compounds of cornstalk components are chosen and hydrolyzed on plasma. Activation energy of elementary reactions, which are single-molecule reactions, free radical reactions and bimolecular reactions, are calculated by bond energy percentage rules. Elementary reactions and preliminary reaction mechanism model, which cornstalk hydrolyzes to sugars on plasma are identified.

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28

Moore, Benjamin N., Stephen J. Blanksby i Ryan R. Julian. "Ion–molecule reactions reveal facile radical migration in peptides". Chemical Communications, nr 33 (2009): 5015. http://dx.doi.org/10.1039/b907833a.

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Li, Ji-Lai, Cai-Yun Geng, Xu-Ri Huang i Chia-Chung Sun. "Atomic radical—molecule reactions F + CH3C≡CH: mechanistic study". Theoretical Chemistry Accounts 117, nr 3 (19.09.2006): 417–29. http://dx.doi.org/10.1007/s00214-006-0169-2.

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30

Barnabas, Mary V., i Alexander D. Trifunac. "Ion—molecule reactions of tetramethylethylene radical cations in zeolites". Chemical Physics Letters 193, nr 4 (maj 1992): 298–304. http://dx.doi.org/10.1016/0009-2614(92)85671-v.

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STIRK, K. M., L. K. M. KIMINKINEN i H. I. KENTTAEMAA. "ChemInform Abstract: Ion-Molecule Reactions of Distonic Radical Cations." ChemInform 24, nr 22 (20.08.2010): no. http://dx.doi.org/10.1002/chin.199322312.

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32

Savee, John D., Ewa Papajak, Brandon Rotavera, Haifeng Huang, Arkke J. Eskola, Oliver Welz, Leonid Sheps, Craig A. Taatjes, Judit Zádor i David L. Osborn. "Direct observation and kinetics of a hydroperoxyalkyl radical (QOOH)". Science 347, nr 6222 (5.02.2015): 643–46. http://dx.doi.org/10.1126/science.aaa1495.

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Oxidation of organic compounds in combustion and in Earth’s troposphere is mediated by reactive species formed by the addition of molecular oxygen (O2) to organic radicals. Among the most crucial and elusive of these intermediates are hydroperoxyalkyl radicals, often denoted “QOOH.” These species and their reactions with O2 are responsible for the radical chain branching that sustains autoignition and are implicated in tropospheric autoxidation that can form low-volatility, highly oxygenated organic aerosol precursors. We report direct observation and kinetics measurements of a QOOH intermediate in the oxidation of 1,3-cycloheptadiene, a molecule that offers insight into both resonance-stabilized and nonstabilized radical intermediates. The results establish that resonance stabilization dramatically changes QOOH reactivity and, hence, that oxidation of unsaturated organics can produce exceptionally long-lived QOOH intermediates.

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33

Brigiano, Flavio Siro, Yannick Jeanvoine, Antonio Largo i Riccardo Spezia. "The formation of urea in space". Astronomy & Astrophysics 610 (luty 2018): A26. http://dx.doi.org/10.1051/0004-6361/201731610.

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Context. Many organic molecules have been observed in the interstellar medium thanks to advances in radioastronomy, and very recently the presence of urea was also suggested. While those molecules were observed, it is not clear what the mechanisms responsible to their formation are. In fact, if gas-phase reactions are responsible, they should occur through barrierless mechanisms (or with very low barriers). In the past, mechanisms for the formation of different organic molecules were studied, providing only in a few cases energetic conditions favorable to a synthesis at very low temperature. A particularly intriguing class of such molecules are those containing one N–C–O peptide bond, which could be a building block for the formation of biological molecules. Urea is a particular case because two nitrogen atoms are linked to the C–O moiety. Thus, motivated also by the recent tentative observation of urea, we have considered the synthetic pathways responsible to its formation. Aims. We have studied the possibility of forming urea in the gas phase via different kinds of bi-molecular reactions: ion-molecule, neutral, and radical. In particular we have focused on the activation energy of these reactions in order to find possible reactants that could be responsible for to barrierless (or very low energy) pathways. Methods. We have used very accurate, highly correlated quantum chemistry calculations to locate and characterize the reaction pathways in terms of minima and transition states connecting reactants to products. Results. Most of the reactions considered have an activation energy that is too high; but the ion-molecule reaction between NH2OHNH2OH2+ and formamide is not too high. These reactants could be responsible not only for the formation of urea but also of isocyanic acid, which is an organic molecule also observed in the interstellar medium.

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Tong, L., i Y. J. Shi. "Gas-phase reaction chemistry of 1,1-dimethyl-1-silacyclobutane as a precursor gas in the hot-wire chemical vapor deposition process — Formation of tetramethylsilane and trimethylsilane". Canadian Journal of Chemistry 89, nr 1 (styczeń 2011): 19–26. http://dx.doi.org/10.1139/v10-147.

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The secondary gas-phase reaction products of 1,1-dimethyl-1-silacyclobutane (DMSCB) and its isotopomer, 1,1-di(perdeuteratedmethyl)-1-silacyclobutane (DMSCB-d6), in a hot-wire chemical vapour deposition reactor were investigated using vacuum UV laser single photon ionization with time-of-flight mass spectrometry. Dimethylsilylene, one of the primary decomposition products, undergoes π-type addition across the double and triple C–C bond and an insertion reaction into the Si–H bond. A short-chain reaction mechanism, initiated by methyl radicals produced in the primary decomposition, is found to exist for both the source DMSCB molecule and its stable secondary products. The formation of tetramethylsilane and trimethylsilane via the reaction of 1,1-dimethylsilene with a methyl radical and an H2 molecule, respectively, has been demonstrated. These are two new reaction channels involving 1,1-dimethylsilene in secondary gas-phase reactions.

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35

Borges dos Santos, Rui M., Benedito J. Costa Cabral i José A. Martinho Simões. "Bond-dissociation enthalpies in the gas phase and in organic solvents: Making ends meet". Pure and Applied Chemistry 79, nr 8 (1.01.2007): 1369–82. http://dx.doi.org/10.1351/pac200779081369.

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Solvent effects are responsible for the difference between gas- and solution-phase bond-dissociation enthalpies (BDEs), and are thus crucial for understanding reactivity in solution. While solvation effects can be negligible (e.g., in reactions involving carbon-centered radicals), they may be rather significant (e.g., when oxygen-centered radicals are formed). This paper reviews a number of models which have been proposed to deal with the difference between the solvation energetics of a radical and its parent molecule. It is concluded that the radical-solvent interaction may be larger than previously anticipated.

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36

Clemen, Martin, i Jürgen Grotemeyer. "Subsequent radical fragmentation reactions of N,N-diethylamino-substituted azobenzene derivatives in a Fourier transform ion cyclotron resonance mass spectrometer using collision-induced dissociation and photodissociation". European Journal of Mass Spectrometry 23, nr 6 (31.08.2017): 359–68. http://dx.doi.org/10.1177/1469066717729275.

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The fragmentation behavior of N, N-diethylamino-substituted azobenzene derivatives is investigated by high-resolving mass spectrometry using a Fourier transform ion cyclotron resonance mass spectrometer. Former investigations by photodissociation as well as collision-induced dissociation experiments used to induce a loss of C3H8 from the diethylamino group. The position of the additional proton in [M + H]+ ions is important due to the sequences of radical fragmentation reactions. Two possibilities arise. First, a charge is located at the azo group leading to a methyl radical loss. The second possibility is that the charge has been located on the aniline nitrogen of the molecule resulting in an ethyl radical loss. Only o-ethyl red has shown the overall loss of C3H8 in a two-step radical reaction mechanism. Nevertheless, p-ethyl red and ethyl yellow have shown systematic fragmentation reactions as well. Loss of C3H8 has not been likely regarding both these molecules. All experimental findings together with quantum chemical calculations as well as kinetic calculations support the proposed fragmentation mechanisms of the three azo dyes.

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37

Liu, Dongping, Ina T. Martin, Jie Zhou i Ellen R. Fisher. "Radical-surface interactions during film deposition: A sticky situation?" Pure and Applied Chemistry 78, nr 6 (1.01.2006): 1187–202. http://dx.doi.org/10.1351/pac200678061187.

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Our imaging of radicals interacting with surfaces (IRIS) method was used to investigate radical-surface reactions during low-temperature plasma-enhanced chemical vapor deposition (PECVD) processes. Special emphasis was placed on the analysis of surface reactivities for CH, SiH, CN, NH, NH2, CF2, and SiCl2 radicals during film growth. The effects of plasma parameters, such as radio frequency (rf) power and gas composition, substrate temperature, and substrate bias on radical-surface reactivity were analyzed. Different radicals exhibit different behavior at the surface of a depositing film. Specifically, CH, SiH, and CN are "sticky", with high surface reactivities. In contrast, other species such as NH, CF2, and SiCl2 do not stick to the surface of growing films and, in some cases are actually generated at the surface of the depositing film. Different plasma systems and parameters can have an effect on the stickiness of some of these species. Our IRIS measurements indicate a molecule's surface sticking probability may also be related to the molecule's electronic configuration and stability, with the most reactive species being molecules with a doublet electron configuration. In contrast, the singlet species examined here tend to be generated at the surface during film deposition. Our results also indicate that when a molecule scatters with greater than 100 % probability, it is likely to be strongly affected by energetic ion bombardment of the film surface.

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38

AS, Shrikanth, i P. G. Jadar. "Anti-Oxidant effects of Swarnamakshika Bhasma : A Experimental Study". Journal of Ayurveda and Integrated Medical Sciences (JAIMS) 5, nr 04 (25.08.2020): 92–101. http://dx.doi.org/10.21760/jaims.5.4.16.

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Shodhana of Swarnamakshika carried out by Bharjana in Eranda Tila. Marana of Swarnamakshika by finely powdered Shudda Swarnamakshika was taken in a Khalvayantra. Then equal quantity of Shudda Gandhaka was added and triturated together till they become homogenous. To this mixture 100ml of Jambhira Rasa was added triturated well till it becomes semisolid consistency. The paste were made into shape of Chakrikas weighing 25gm and 8cm uniformly and kept for drying. Subjecting into 5 required number of Varahaputas. The present day lifestyle and food habits have increased the production of free radicals. These cytotoxic free radicals not only raise the oxidative stress but also play an important role in the immune-system dysfunction due to which the mankind is prone to various major ailments and it is now proved that diseases like Prameha, Pandu, Vatavyadhi etc. are free radical mediated ones. To tackle these free radicals our body needs antioxidants. An antioxidant is a molecule which is capable of inhibiting the oxidation of other molecules. Oxidation reactions can produce free radicals which in turn start chain reactions that damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates and inhibit other oxidation reactions. Many herbals drugs and compound herbal preparations have been screened for their antioxidant and immuno-modulatory properties but still there is a need for effective antioxidants. This dearth and also the fact that Swarnamakshika is being used in treating many of the free radical mediated diseases prompted us to take the present study which aims to validate the Antioxident effect of Swarnamakshika Bhasma scientifically and explain its probable mode of action at the cellular level.

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Zhang, Sheng Jian, i Ying Xian Zhao. "Kinetics and Selectivity of Cyclohexane Pyrolysis". Advanced Materials Research 455-456 (styczeń 2012): 540–48. http://dx.doi.org/10.4028/www.scientific.net/amr.455-456.540.

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Pyrolysis of cyclohexane was conducted with a plug-flow tube reactor at 873 K. The data of feed conversion fit first-order kinetics adequately, giving the apparent rate constant of 0.0092 s-1 . A chain mechanism of free radical reactions is proposed to interpret consumption of cyclohexane by four processes: homolysis of C-C bond (Path I) and homolysis of C-H bond (Path II ) in reaction chain initiation, H-abstraction of various radicals from feed molecule in reaction chain propagation (Path III ), and the process associated with coke formation (Path IV). The reaction path probability ratio of X I：X II：X III ：X IV was 0.5420: 0.0045 : 0.3897 : 0.0638.

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40

Kaur, Rupinder preet, Damanjit Kaur i Ritika Sharma. "Substituent effect on N–H bond dissociation enthalpies of carbamates: a theoretical study". Canadian Journal of Chemistry 93, nr 3 (marzec 2015): 279–88. http://dx.doi.org/10.1139/cjc-2014-0326.

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The present investigation deals with the study of the N–H bond dissociation enthalpies (BDEs) of the Y-substituted (NH2-C(=X)Y-R) and N-substituted ((R)(H)NC(=X)YH) carbamates (X, Y = O, S, Se; R = H, CH3, F, Cl, NH2), which have been evaluated using ab initio and density functional methods. The variations in N−H BDEs of these Y-substituted and N-substituted carbamates as the effect of substituent have been understood in terms of molecule stabilization energy (ME) and radical stabilization energy (RE), which have been calculated using the isodesmic reactions. The natural bond orbital analysis indicated that the electrodelocalization of the lone pairs of heteroatoms in the molecules and radicals affect the ME and RE values depending upon the type and site of substitution (whether N- or Y-). The variations in N−H BDEs depend upon the combined effect of molecule stabilization and radical stabilization by the various substituents.

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41

Dillon, T. J., i J. N. Crowley. "Direct detection of OH formation in the reactions of HO2 with CH3 C(O)O2 and other substituted peroxy radicals". Atmospheric Chemistry and Physics Discussions 8, nr 2 (11.04.2008): 7111–48. http://dx.doi.org/10.5194/acpd-8-7111-2008.

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Abstract. This work details the first direct observation of OH as a product from (R1): HO2+CH3C(O)O2→(products), which has generally been considered an atmospheric radical termination process. The technique of pulsed laser photolysis radical generation, coupled to calibrated laser induced fluorescence detection was used to measure an OH product yield for (R1) of (α1=0.5±0.2). This study of (R1) included the measurement of a rate coefficient k1(298 K)=1.4±0.5)×10-11cm3 molecule−1 s−1, substantially reducing the uncertainties in modelling this important atmospheric reaction. OH was also detected as a product from the reactions of HO2 with three other carbonyl-containing peroxy radicals, albeit at smaller yield, e.g. (R2): HO2+CH3C(O)CH2O2→(products), α2≈0.15. By contrast, OH was not observed (α<0.06) as a major product from reactions where carbonyl functionality was absent, e.g. HO2+HOCH2CH2O2 (R8), and HO2+CH3CH(OH)CH2O2 (R9).

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42

Dillon, T. J., i J. N. Crowley. "Direct detection of OH formation in the reactions of HO2 with CH3C(O)O2 and other substituted peroxy radicals". Atmospheric Chemistry and Physics 8, nr 16 (26.08.2008): 4877–89. http://dx.doi.org/10.5194/acp-8-4877-2008.

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Abstract. This work details the first direct observation of OH as a product from (R1): HO2+CH3C(O)O2→(products), which has generally been considered an atmospheric radical termination process. The technique of pulsed laser photolysis radical generation, coupled to calibrated laser induced fluorescence detection was used to measure an OH product yield for (R1) of α1(298 K)=(0.5±0.2). This study of (R1) included the measurement of a rate coefficient k1(298 K)=(1.4±0.5)×10−11cm3 molecule−1 s−1, substantially reducing the uncertainties in modelling this important atmospheric reaction. OH was also detected as a product from the reactions of HO2 with three other carbonyl-containing peroxy radicals, albeit at smaller yield, e.g. (R2): HO2+CH3C(O)CH2O2→(products), α2≈0.15. By contrast, OH was not observed (α<0.06) as a major product from reactions where carbonyl functionality was absent, e.g. HO2+HOCH2CH2O2 (R8), and HO2+CH3CH(OH)CH2O2 (R9).

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Renard, P., F. Siekmann, A. Gandolfo, J. Socorro, G. Salque, S. Ravier, E. Quivet i in. "Radical mechanisms of methyl vinyl ketone oligomerization through aqueous phase OH-oxidation: on the paradoxical role of dissolved molecular oxygen". Atmospheric Chemistry and Physics Discussions 13, nr 1 (28.01.2013): 2913–54. http://dx.doi.org/10.5194/acpd-13-2913-2013.

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Abstract. It is now accepted that one of the important pathways of Secondary Organic Aerosol (SOA) formation occurs through aqueous phase chemistry in the atmosphere. However, the liquid phase chemical mechanisms leading to macromolecules are still not well understood. For α-dicarbonyl precursors, such as methylglyoxal and glyoxal, radical reactions through OH-oxidation produce oligomers, irreversibly and faster than accretion reactions. Methyl vinyl ketone (MVK) was chosen in the present study as it is an α, β-unsaturated carbonyl that can undergo such reaction pathways in the aqueous phase and forms even high molecular weight oligomers. We present here experiments on the aqueous phase OH-oxidation of MVK, performed under atmospheric relevant conditions. Using NMR and UV absorption spectroscopy, high and ultra-high resolution mass spectrometry, we show that the fast formation of oligomers up to 1800 Da is due to radical oligomerization of MVK, and 13 series of oligomers (out of a total of 26 series) are identified. The influence of atmospherically relevant parameters such as temperature, initial concentrations of MVK and dissolved oxygen are presented and discussed. In agreement with the experimental observations, we propose a chemical mechanism of OH-oxidation of MVK in the aqueous phase that proceeds via radical oligomerization of MVK on the olefin part of the molecule. This mechanism highlights the paradoxical role of dissolved O2: while it inhibits oligomerization reactions, it contributes to produce oligomerization initiator radicals, which rapidly consume O2, thus leading to the supremacy of oligomerization reactions after several minutes of reaction. These processes, together with the large ranges of initial concentrations investigated (60–656 μM of dissolved O2 and 0.2–20 mM of MVK) show the fundamental role that O2 likely plays in atmospheric organic aerosol.

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Zhang, Yu, Bo Wei i Rongzhi Tang. "Theoretical Study on the Mechanisms, Kinetics, and Toxicity Evaluation of OH-Initiated Atmospheric Oxidation Reactions of Coniferyl Alcohol". Atmosphere 14, nr 6 (3.06.2023): 976. http://dx.doi.org/10.3390/atmos14060976.

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In this paper, we investigated the mechanisms, kinetics, and toxicity evaluation of the OH-initiated reaction of coniferyl alcohol (4-(3-hydroxy-1-propenyl)-2-methoxyphenol) in the atmosphere using theoretical calculations. The initial reaction of coniferyl alcohol with OH radicals had two pathways, H-abstraction and OH-addition reactions. The total reaction rate constants were 2.32 × 10−9 cm3 molecule−1 s−1 (in gas-phase) and 9.44 × 109 s−1 M−1 (in liquid-phase) for the preliminary reactions of coniferyl alcohol with OH radicals at 298 K, respectively, and the half-lives of the total reaction (including all initial H-abstraction and OH-addition reactions) of coniferyl alcohol with OH radical in the atmosphere, urban and remote clouds were 8.3 × 10−2 h, 5.83 × 103 h and 9.27 × 102 h, respectively. The temperature had a strong and positive influence on the initial reaction rate constant. The branching ratios of H-abstraction and OH-addition reactions were 3.68% and 97.69%, respectively, making the OH-addition reactions become dominant reactions. The ecotoxicity evaluation revealed that the toxicity levels of coniferyl alcohol and its products were similar and non-toxic. However, all these products have developmental toxicity, with most of them having no mutagenicity. Therefore, further attention should be paid to the oxidation process and product toxicity evaluation of coniferyl alcohol in the atmosphere.

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Wang, Ting, Xueqin Tao, Yi Xiao, Ganhua Qiu, Yun Yang i Benxia Li. "Charge separation and molecule activation promoted by Pd/MIL-125-NH2 hybrid structures for selective oxidation reactions". Catalysis Science & Technology 10, nr 1 (2020): 138–46. http://dx.doi.org/10.1039/c9cy01690b.

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The Pd/MIL-125-NH₂ hybrid photocatalyst exhibits great advantages in charge separation and molecule activation, with sufficient generation of both superoxide radical and singlet oxygen toward selective oxidation of organic molecules.

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46

Feng, Wan Yong, i Chava Lifshitz. "Ion/molecule reactions of naphthalene and 1-chloronaphthalene radical cations". International Journal of Mass Spectrometry and Ion Processes 152, nr 2-3 (luty 1996): 157–68. http://dx.doi.org/10.1016/0168-1176(95)04333-0.

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Grützmacher, Hans-Friedrich, i Michael Büchner. "Ion/Molecule Reactions of Isomeric Bromobutene Radical Cations with Ammonia". European Journal of Mass Spectrometry 10, nr 1 (luty 2004): 21–26. http://dx.doi.org/10.1255/ejms.622.

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Walker, H. M., D. Stone, T. Ingham, S. Vaughan, B. Bandy, M. Cain, R. L. Jones i in. "Nighttime measurements of HOx during the RONOCO project and analysis of the sources of HO2". Atmospheric Chemistry and Physics Discussions 15, nr 2 (30.01.2015): 2997–3061. http://dx.doi.org/10.5194/acpd-15-2997-2015.

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Abstract. Measurements of the radical species OH and HO2 were made using the Fluorescence Assay by Gas Expansion (FAGE) technique during a series of nighttime and daytime flights over the UK in summer 2010 and winter 2011. OH was not detected above the instrument's 1σ limit of detection during any of the nighttime flights or during the winter daytime flights, placing upper limits on [OH] of 1.8 × 106 molecule cm−3 and 6.4 × 105 molecule cm−3 for the summer and winter flights, respectively. HO2 reached a maximum concentration of 3.2 × 108 molecule cm−3 (13.6 pptv) during a nighttime flight on 20 July 2010, when the highest concentrations of NO3 and O3 were also recorded. Analysis of the rates of reaction of OH, O3, and the NO3 radical with measured alkenes indicates that the summer nighttime troposphere can be as important for the processing of VOCs as the winter daytime troposphere. Analysis of the instantaneous rate of production of HO2 from the reactions of O3 and NO3 with alkenes has shown that, on average, reactions of NO3 dominated nighttime production of HO2 during summer, and reactions of O3 dominated nighttime HO2 production during winter.

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Stevanovic, Jelka, Suncica Borozan, Slavoljub Jovic i Igor Ignjatovic. "Physiology of free radicals". Veterinarski glasnik 65, nr 1-2 (2011): 95–107. http://dx.doi.org/10.2298/vetgl1102095s.

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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.

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Dheandhanoo, Seksan, Leonard Forte, Arnold Fox i Diethard K. Bohme. "Ion-molecule reactions with carbon chain molecules: reactions with diacetylene and the diacetylene cation". Canadian Journal of Chemistry 64, nr 4 (1.04.1986): 641–48. http://dx.doi.org/10.1139/v86-104.

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Reactions of hydrocarbon and carbon/nitrogen ions with diacetylene and of the diacetylene radical cation with various molecules have been examined with a view to molecular growth by ion–molecule reaction. Measurements were performed with a Selected-Ion Flow Tube (SIFT) apparatus at 296 ± 2 K of the rate constants and product distributions for the reactions of C+, CH3+, C2H2+, C3H+, CN+, C2N+, and C2N2+ with C4H2 and of C4H2+ with H2, CO, C2H2, C2N2, and C4H2. Condensation and association reactions which build up the carbon content of the ion were observed to compete with charge transfer. For the reactions of CN+ and C2N2+ with C4H2 this growth involved the addition of cyanide to the carbon chain. The kinetics of protonation of diacetylene were also investigated. It was possible to bracket the proton affinity of diacetylene between the known proton affinities of HCN and CH3OH with a value for PA(C4H2) = 177 ± 5 kcal mol−1, which results in a heat of formation for C4H3+ of 305 ± 5 kcal mol−1. Numerous secondary association reactions were observed to form adduct ions in helium buffer gas at total pressures of a few tenths of a Torr with rates near the collision rate. This was the case for C6H4+ (C4H2+•C2H2), C7H5+ (C3H3+•C4H2), C8H4+ (C4H2+•C4H2), C8H5+ (C4H3+•C4H2), C9H3+ (C5H+•C4H2), C9H4+ (C5H2+•C4H2), C9H5 (C5H3+•C4H2), C10H4+ (C6H2+•C4H2), C10H5+ (C6H3+•C4H2), C11H7+ (C3H3+•(C4H2)2), C12H6+ (C4H2+•(C4H2)2), C9H3N+ (HC5N+•C4H2), and C10H4N+ (C2N+•(C4H2)2) where the reactants are indicated in parentheses. The observed high rates of association imply the formation of chemical bonds in the adduct ions but the structures of these ions were not resolved experimentally. In most instances there seems little basis for preferring acyclic over cyclic adduct ions.

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