A kinetic and mechanistic approach to protection and repair of tert-butoxyl radicals induced adenine radicals by chlorogenic acid

G. Vijayalakshmi, M. Adinaraya

Abstract

The rates of oxidation of adenine and chlorogenic acid by tert-butoxyl radicals have been studied by measuring the absorbance of adenine at 260 nm and chlorogenic acid 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 chlorogenic acid by t-BuO·radicals have been determined in the absence and presence of varying concentrations of adenine. An increase in the concentration of adenine has been found to decrease the rate of oxidation of chlorogenic acid suggesting that adenine and chlorogenic acid compete for t-BuO·radicals. From competition kinetics, the rate constant of chlorogenic acid reaction with adenine has been calculated to be 4.43 x 108 dm3 mol-1 s-1. The quantum yields ( f expt) have been calculated from the experimentally determined rates of oxidation of chlorogenic acid under different experimental conditions. Assuming that chlorogenic acid acts as a scavenger of t-butoxyl radicals only, the quantum yields ( f cal) have been theoretically calculated. f expt and f cal values suggest that chlorogenic acid not only protects adenine from t- BuO·radicals but also repairs adenine radicals formed by the reaction of adenine with t-BuO·radicals