title: One- and two-electron oxidation reactions of trolox by peroxynitrite.
abstract: One and two electron oxidation reactions of peroxynitrite with trolox, an analogue of vitamin E were studied. Kinetics of the reaction was studied using a single mixing stopped-flow spectrometer in the pH range from 6 to 11 and the products were analyzed by HPLC/HPIC. One-electron oxidation reaction produced the phenoxyl radical of trolox having a characteristic absorption spectrum in the 300-500 nm region with absorption maximum at 430 nm. The rate constant for the formation of the trolox radical at 430 nm was determined to be 1.8 x 10(5) M(-1) s(-1). At low concentration of peroxynitrite the radical did not show any noticeable decay in the time scale of 20-50 s. However, when the concentration of peroxynitrite was increased, there was an appreciable increase in the decay of the trolox radical due to its reaction with excess peroxynitrite yielding a bimolecular rate constant of 6.0 x 10(3) M(-1) s(-1) for the reaction of trolox radical with peroxynitrite. The released nitrite and nitrate anions, and the two-electron oxidation product quinone produced as a result of these reactions, were estimated using ion chromatography and HPLC analysis. By following the changes in the yields of nitrite and quinone as a function of peroxynitrite concentration and from the above determined rate parameters, the relative importance of the one and two electron processes has been discussed.
authors.affiliation: Radiation Chemistry & Chemical Dynamics Division, and Applied Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India. kindira@apsara.barc.ernet.in
authors.forename: K I
authors.initials: KI
authors.lastname: Priyadarsini
authors.forename: S
authors.initials: S
authors.lastname: Kapoor
authors.forename: D B
authors.initials: DB
authors.lastname: Naik
mesh_terms: D016227:Benzoquinones / Q000032:analysis / Q000737:chemistry*; D002839:Chromans / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004579:Electron Transport; D007700:Kinetics; D009566:Nitrates / Q000032:analysis / Q000737:chemistry*; D009570:Nitriles / Q000032:analysis / Q000737:chemistry*; D010084:Oxidation-Reduction; D013053:Spectrophotometry / Q000379:methods; D014810:Vitamin E / Q000031:analogs & derivatives
chemical_list: D016227:Benzoquinones; D002839:Chromans; D009566:Nitrates; D009570:Nitriles; D014810:Vitamin E; C039642:peroxynitric acid; C004532:quinone; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid