Abstract

SYNERGISTIC INTERACTION OF CHLOROGENIC ACID WITH PHOTOCHEMICALLY GENERATED tert-BUTOXYL RADICAL INDUCED ASCORBIC ACID RADICALS – A KINETIC APPROACH TO REGENERATION OF ASCORBIC ACID

G Vijayalakshmi*, M Adinarayana & P Jayaprakash Rao

Abstract

The rates of oxidation of ascorbic acid and chlorogenic acid (CGA) by tert-butoxyl radicals (t-BuO) were studied by measuring the absorbance of ascorbic acid at 265 nm and CGA at 328 nm spectrophotometrically. Radicals (t-BuO) were generated by the photolysis of tert-butyl hydroperoxide (t-BuOOH) in presence of tertbutyl alcohol to scavenge OH radicals. The rates and the quantum yields () of oxidation of CGA by t-BuO radicals were determined in the absence and presence of varying concentrations of ascorbic acid. An increase in the concentration of ascorbic acid was found to decrease the rate of oxidation of CGA, suggesting that ascorbic acid and CGA competed for t-BuO radicals. From the competition kinetics, the rate constant for the ascorbic acid reaction with t-BuO radicals was calculated to be 6.65  109 dm3 mol-1 s-1. The quantum yields (expt) were 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 (cal) were theoretically calculated. expt and cal values suggested that ascorbic acid not only protected CGA from t-BuO radicals, but also regenerated CGA from CGA radical, formed by the reaction of CGA with t- BuO radicals. Results indicated a possible synergistic interaction between CGA and ascorbic acid in which 59.9 % of CGA was regenerated by ascorbic acid. Keywords: Chlorogenic acid, ascorbic acid, regeneration, synergism, tert-butoxyl radicals, oxidation.

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