Kinetics Of Free Radical Reactions Research Articles

Possibility of determination of the level of antioxidants in human body using spectroscopic methods

In this work, the processes of antioxidant defence against aggressive free radicals in human body were investigated theoretically; and the existing methods of diagnosis of oxidative stress and disturbance of antioxidant activity were reviewed. Also, the kinetics of free radical reactions in the oxidation of luminol and interaction antioxidants (such as chlorophyll in the multicomponent system of plant's leaves and ubiquinone) with the UV radiation were investigated experimentally by spectroscopic method. The results showed that this method is effective for recording the luminescence of antioxidants, free radicals, chemiluminescent reactions and fluorescence. In addition these results reveal new opportunities for the study of the antioxidant activity and antioxidant balance in a multicomponent system by allocating features of the individual components in spectral composition. A creation of quality control method for drugs, that are required for oxidative stress diagnosis, is a promising direction in the development of given work.

Hydroxyl radical initiated oxidation of formic acid on mineral aerosols surface: a mechanistic, kinetic and spectroscopic study

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.

Antioxidant capacity of Ugni molinae fruit extract on human erythrocytes: an in vitro study.

Ugni molinae is an important source of molecules with strong antioxidant activity widely used as a medicinal plant in Southern Chile-Argentina. Total phenol concentration from its fruit extract was 10.64 ± 0.04 mM gallic acid equivalents. Analysis by means of HPLC/MS indicated the presence of the anthocyanins cyanidin and peonidin, and the flavonol quercitin, all in glycosylated forms. Its antioxidant properties were assessed in human erythrocytes in vitro exposed to HClO oxidative stress. Scanning electron microscopy showed that HClO induced an alteration in erythrocytes from a normal shape to echinocytes; however, this change was highly attenuated in samples containing U. molinae extracts. It also had a tendency in order to reduce the hemolytic effect of HClO. In addition, X-ray diffraction experiments were performed in dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine bilayers, classes of lipids preferentially located in the outer and inner monolayers, respectively, of the human erythrocyte membrane. It was observed that U. molinae only interacted with DMPC. Results by fluorescence spectroscopy on DMPC large unilamellar vesicles and isolated unsealed human erythrocyte membranes also showed that it interacted with the erythrocyte membrane and DMPC. It is possible that the location of U. molinae components into the membrane outer monolayer might hinder the diffusion of HClO and of free radicals into cell membranes and the consequent decrease of the kinetics of free radical reactions.

Tree structure for intermolecular hydrogen abstraction from hydrocarbons (C/H) and generic rate constant rules for abstraction by vinyl radical

AbstractModeling of complex reaction systems is necessary in the design, analysis, and optimization of many technologically important processes such as pyrolysis, steam cracking, coking, partial oxidation, and combustion. The complexity in kinetic modeling of all these processes is introduced both by the feed, which is a hydrocarbon mixture, and the high reactivity of radical intermediates. Recent advances in automated mechanism generation tools, although capable of establishing the complex reaction network, pose a big challenge of assigning rate parameters for all the reactions or devising appropriate estimation rules for all reaction classes in the network. The kinetics of free radical reactions dictates the chemistry of technologically important thermal processes. Intermolecular hydrogen abstraction by radicals is one of the dominant reaction types and constitutes a major part (often >50%) in any thermal reaction network owing to their profound effect on product distribution. While abstraction reactions by H atoms (and to some extent by methyl radicals) have been studied extensively in the past, the abstraction kinetics by vinyl radical is less explored even though vinyl radicals play an important role in molecular weight growth chemistry and in predicting acetylene concentrations in pyrolysis and fuel‐rich hydrocarbon flames. This study presents the hierarchical tree structure for intermolecular hydrogen abstraction by vinyl radicals from {C/H} molecules and provides generic rate rules that account for most of the variation in CH bond energy in the family of aliphatic, aromatic, naphthenic, olefinic, and aromatic naphtheno hydrocarbons. Reaction classes developed in this work are still dictated by immediate neighbors within the spirit of group additivity, although some efforts were made to access the effect of non–next neighbors on generic rate parameters. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 327–349, 2012

Antioxidant activity of free radical reactions inhibitors, applied to the dressing material for wound healing

Antioxidant activity (AA) of inhibitors of free radical reactions (FRR) (dieton, mexidol, trypsin), applied to the dressing material for wound healing was studied using a model system containing suspension of laminated liposomes, formed from the fraction of total chicken yolk phospholipids. Lipid peroxidation (LPO) of liposome membranes was initiated by addition of Fe2+ ions. The kinetics of FRR was monitored by coumarin enhanced chemiluminescence (CL). AA of the inhibitors was determined by their ability to intercept aqueous and hydrophobic free radicals and chelate Fe2+ ions. Their ability to intercept radicals reduced in the following order: dieton > trypsin > mexidol. We have also found previously unknown ability of mexidol to interact with Fe2+ and to eliminate the FRR catalyst. Studying AA of the FRR inhibitors in the two-components mixture, containing dieton and mexidol, we have observed the multifunctional effect: dieton increased the duration of latent period of CL by intersepting lipid peroxyl radicals, while mexidol, decreased this parameter by interacting with Fe2+, i.e. mexidol masked the action of dieton. Study of AA of two-components mixture, containing mexidol and trypsin has demonstrated the same multifunctional effect. In the two-component mixture, containing trypsin and dieton, the inhibitors exhibit synergistic action. All the antioxidant properties of these FRR inhibitors were also preserved in the three component mixture. Thus, the mixture dieton, mexidol and trypsin, possesses high AA, that validates their use in the dressing materials employed for wound healing.

Protective effect of Ugni molinae Turcz against oxidative damage of human erythrocytes

Ugni molinae Turcz, also known as “Murtilla”, is a plant that grows in the south of Chile. Infusions of its leaves have long been used in traditional native herbal medicine. The chemical composition of the leaves indicates the presence of polyphenols, which have antioxidant properties. In the present work, the antioxidant properties of U. molinae were evaluated in human erythrocytes exposed in vitro to oxidative stress induced by HClO. The experiments were carried out by scanning electron microscopy (SEM) and hemolysis measurements. The SEM observations showed that HClO induced a morphological alteration in the red blood cells from a discoid to an echinocytic form. According to the bilayer couple hypothesis, the formation of echinocytes indicates that HClO was inserted in the outer leaflet of the erythrocyte membrane. However, a concentration as low as 10 μM gallic acid equivalents (GAE) U. molinae aqueous extract neutralized the shape change effect of HClO applied in a concentration as high as 0.25 mM. The significant protection of U. molinae aqueous extract was also shown in the hemolysis experiments. In fact, very low concentrations of the extract considerably reduced the deleterious capacity of HClO to induce hemolysis in red blood cells. It is concluded that the location of the extract components into the membrane bilayer and the resulting restriction on its fluidity might hinder the diffusion of HClO and its consequent damaging effects. This conclusion can also imply that this restriction could apply to the diffusion of free radicals into cell membranes and the subsequent decrease of the kinetics of free radical reactions.

ChemInform Abstract: Kinetics of Free Radical Reactions of Some Biologically Important Compounds as Studied by Pulse Radiolysis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Kinetics of Free Radical Reactions of Some Biologically Important Compounds as Studied by Pulse Radiolysis

Kinetics of Free Radical Reactions of Some Biologically Important Compounds as Studied by Pulse Radiolysis

Radiolabelling Studies of Free Radicals Using Muonium (The Second Hydrogen Radioisotope)

An overview is presented of the way various spectroscopic/radioisotopic-labelling methods (MuSR), in which free radicals are labelled with the light hydrogen radioisotope muonium, may be employed in the study of free radical reaction kinetics and dynamics. Specifically considered are: the reaction rates of thiyl radicals and related species in relation to biological membrane damage; the dynamics of radicals sorbed in solid catalysts and in activated carbons and other porous particulate materials of environmental significance; reacting gas-phase systems; mechanisms for the formation of muon (muonium) labelled radicals, and the study of radical stabilisation and reactivity.

Modulation of Liposomal Membrane Fluidity by Flavonoids and Isoflavonoids

The polyphenolic structures of flavonoids and isoflavonoids confer them with the ability to scavenge free radicals and to chelate transition metals, a basis for their potent antioxidant abilities. Another possible contributory mechanism toward their antioxidant activities is their ability to stabilize membranes by decreasing membrane fluidity. In this study, the effects of representative flavonoids, isoflavonoids, and their metabolites on membrane fluidity and their preferential localization in the membrane were investigated using large unilamellar vesicles (LUVs) as the membrane models. These results were compared with those of cholesterol and α-tocopherol. Changes in fluorescence anisotropy values for a series of n-(9-anthroyloxy) fatty acid probes (n = 6, 12, 16) upon addition of the test compounds were used to monitor alterations in membrane fluidity at graded depths in lipid bilayer. The results of the study suggest that the flavonoids and isoflavonoids, similar to cholesterol and α-tocopherol, partition into the hydrophobic core of the membrane and cause a dramatic decrease in lipid fluidity in this region of the membrane. Localization of flavonoids and isoflavonoids into the membrane interiors and their resulting restrictions on fluidity of membrane components could sterically hinder diffusion of free radicals and thereby decrease the kinetics of free radical reactions.

Mechanism of inhibiting action of quinones in oxidizing polymers and model compounds

AbstractQuinones (Q) do not affect the liquid‐phase oxidation of hydrocarbons and retard the solid‐phase oxidation of polymers terminating chains in reactions with alkyl macroradicals. This difference is the result of specific influence of a polymer matrix on the kinetics of free radical reactions. Quinones were found to terminate chains in oxidizing polypropylene containing hydroperoxide groups by the reaction with hydroperoxyl radicals. This is the result of peroxide group's decomposition with hydrogen peroxide production and chain termination in the following reactions:magnified imageThe equilibrium reaction between hydroquinone (QH2) and quinonimine (QI) was evidenced to proceed as a chain reaction with chain propagation in reactions of •QH with QI and HQI• with QH2. Analysis of the reactions of quinone with phenols (ArOH)magnified imageproved that it can be important as an additional way of chain termination in oxidizing polymers and hydrocarbons at elevated temperatures.

Ultralow temperature kinetics of neutral–neutral reactions. The technique and results for the reactions CN+O2 down to 13 K and CN+NH3 down to 25 K

An entirely new experimental method is described which enables the rate constants of neutral–neutral gas-phase reactions to be measured at ultralow temperatures. The measurements are made by applying the pulsed laser photolysis (PLP), laser-induced fluorescence (LIF) technique of studying the kinetics of free radical reactions in the ultracold environment provided by the gas flow in a Cinétique de Réaction en Ecoulement Supersonique Uniforme (CRESU) apparatus. The experimental method is described in some detail and its application and limitations are discussed. Results are reported for the reactions of CN radicals with O2 and NH3. For reaction (1) between CN and O2 data are reported for the temperature range T=13–295 K and the rate constants are well-matched by the expression k1(T)=(2.49±0.17)×10−11 (T/298)(−0.63±0.04) cm3 molecule−1 s−1. For reaction (2) between CN and NH3, rate constants in the temperature range T=25–295 K fit the expression k2(T)=(2.77±0.67)×10−11 (T/298)(−1.14±0.15) cm3 molecule−1 s−1. The kinetic data are discussed in terms of the latest quantum chemical and reaction rate theories for these systems.

Ultra-low temperature kinetics of neutral–neutral reactions: rate constants for the reactions of OH radicals with butenes between 295 and 23 K

The first experiments on the kinetics of reactions of the OH radical at temperatures below 80 K are reported. They have been carried out by applying the pulsed laser photolysis (PLP), laser-induced fluorescence (LIF) technique for studying the kinetics of free radical reactions in the ultra-cold environment provided by the gas flow in a CRESU (Cinetique de Reaction in Ecoulement Supersonique Uniforme) apparatus. This method has yielded rate constants for the reactions of OH with but-1-ene, (Z)-but-2-ene and (E)-but-2-ene at temperatures down to 23 K. The rate constants for all three reactions increase monotonically as the temperature is lowered and this dependence of the rate constants on temperature can be fitted to an empirical expression of the form (k/10–10 cm3 molecule–1 s–1)=a exp[b(T/298K)] with a and b equal to 5.2 and –2.8 for but-1-ene, 4.7 and –2.1 for (Z)-but-2-ene and 5.4 and –2.1 for (E)-but-2-ene.

The Parabolic Transition State Model and Resultant Nonlinear Correlations for the Kinetics of Free Radical Reactions

The transition state of a radical reaction may be treated as the point of intersection of two undisturbed potential curves, each of which characterises the energy of vibration of the atom attacked in either the initial molecule or that formed; a series of nonlinear equations of correlation has been derived for the dependence of the activation energy of a free radical abstraction reaction on the heat of reaction, the energy of triplet repulsion and the electronegativities of the atoms.

Fluorescence spectroscopy of organic reaction intermediates in solution using a commercial spectrofluorimeter

The fluorescence spectra of excited free radicals have been recorded using a pulsed laser to generate these reaction intermediates in the modified cell compartment of a commercial gated spectrofluorimeter. The technique, illustrated with data for the diphenylmethyl and diphenylhydroxymethyl radicals can also be applied to the study of the kinetics of free radical reactions.

ChemInform Abstract: TWO‐PARAMETER TAFT EQUATION IN KINETICS OF FREE RADICAL REACTIONS

Chemischer InformationsdienstVolume 7, Issue 7 Preparative Organic Chemistry ChemInform Abstract: TWO-PARAMETER TAFT EQUATION IN KINETICS OF FREE RADICAL REACTIONS I. B. AFANAS'EV, I. B. AFANAS'EVSearch for more papers by this author I. B. AFANAS'EV, I. B. AFANAS'EVSearch for more papers by this author First published: February 17, 1976 https://doi.org/10.1002/chin.197607127AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue7February 17, 1976 RelatedInformation

The two‐parameter taft equation in kinetics of free radical reactions

AbstractA new method was developed for the calculation of the resonance substituent constants of the two‐parameter Taft equation log ksub/k0=ρ*σ*+r*σr. It is based on a relationship between the spin density in free radicals and the rate constants of radical substitution reactions of CH3. Possibilities and limitations of the application of this correlation equation to the investigation of substitution and addition radical reactions are discussed.

Reactions of free radicals with aromatic compounds in the gaseous phase. I. Kinetics of the reaction of methyl radicals with toluene

The kinetics of abstraction of hydrogen atoms from the methyl group of the toluene molecule by methyl radicals at 430-540�K have been determined. The methyl radicals were produced by pyrolysis of di-t-butyl peroxide in a stirred-flow system. The kinetics ,agree substantially with those obtained by previous authors using photolytic methods for generating the methyl radicals. At toluene and methyl-radical concentrations of about 5 x 10-7 and 10-11 mole cm-3 respectively the benzyl radicals resulting from the abstraction disappear almost entirely by combination with methyl radicals at the methylenic position. In this respect the benzyl radical behaves differently from the iso-electronic phenoxy radical, which previous work has shown to combine with a methyl radical mainly at ring positions. The investigation illustrates the application of stirred-flow technique to the study of the kinetics of free-radical reactions.

1007. Kinetics of free-radical reactions in solution. Part I. Evaluation of rate constants for transfer reactions in systems with varying radical concentrations

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1008. Kinetics of free-radical reactions in solutions. Part II. The reaction of benzyl radicals with substituted toluenes

1008. Kinetics of free-radical reactions in solutions. Part II. The reaction of benzyl radicals with substituted toluenes