One- and Two-Electron Oxidation Reactions of Trolox by Peroxynitrite

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.