Kinetics of oxidation of adenosine by t-butoxyl radical: Protection and repair by caffeic acid

The kinetics of oxidation of adenosine and caffeic acid by t-BuO^? has been studied by the photolysis of t-BuOOH in the presence of t-BuOH. The rates and the quantum yields (φ) of oxidation of caffeic acid by t-BuO^? radicals have been determined in the absence and presence of varying concentrations of adenosine. An increase in the concentration of adenosine has been found to decrease the rate of oxidation of caffeic acid suggesting that adenosine and caffeic acid compete for t-BuO^? radicals. From competition kinetics, the rate constant of t-BuO^?–caffeic acid reaction has been calculated to be 8.15 × 10⁸ dm³ mol^?1 s^?1. The results of experimentally determined quantum yield (φ_exptl) values of oxidation of caffeic acid and the quantum yield values calculated (φ_cal) by assuming that caffeic acid reacts only with t-BuO^? radicals suggest that caffeic acid not only protects adenosine from t-BuO^? radicals but also repairs adenosine radicals formed by the reaction of t-BuO^? radicals. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 515–521, 2005