A KINETIC AND MECHANISTIC APPROACH TO PROTECTION AND REPAIR OF TERT-BUTOXYL RADICALS INDUCED URACIL RADICALS BY CHLOROGENIC ACID

The rates of oxidation of uracil and chlorogenic acid (CGA) by tert-butoxyl radicals have been studied by measuring the absorbance of uracil at 258 nm and CGA at 328 nm spectrophotometrically. tert-butoxyl radicals are generated by the photolysis of tert-butyl hydroperoxide in presence of tert-butyl alcohol to scavenge ^·OH radicals. The rates and the quantum yields (f) of oxidation of CGA by t-BuO^·radicals have been determined in the absence and presence of varying concentrations of uracil. An increase in the concentration of uracil has been found to decrease the rate of oxidation of CGA suggesting that uracil and CGA compete for t-BuO^·radicals. Using competitive kinetic studies, the rate constant for the reaction of t-BuO^· radical with uracil has been found to be 4.43´ 10⁸ dm³ mol^-1 s^-1. The quantum yields (f_expt) have been calculated from the experimentally determined rates of oxidation of CGA under different experimental conditions. Assuming that CGA acts as a scavenger of t-BuO^·radicals only, the quantum yields (f_cal) have been theoretically calculated. f_expt and f_cal values suggest that CGA not only protects uracil from t-BuO^·radicals but also repairs uracil radicals formed by the reaction of uracil with t-BuO^·radicals.