A SYNERGISTIC APPROACH TO KINETIC AND MECHANISTIC STUDIES OF REGENERATION OF β-CAROTENE FROM TERT-BUTOXYL RADICAL INDUCED β-CAROTENE RADICAL CATION BY CHLOROGENIC ACID

The rates of oxidation of β-carotene and chlorogenic acid by tert-butoxyl radicals (t-BuO^·) were studied by measuring the absorbance of β-carotene at 491 nm and chlorogenic acid at 328 nm spectrophotometrically. Radicals (t-BuO^·) were generated by the photolysis of tert-butyl hydroperoxide (t-BuOOH) 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 were determined in the absence and presence of varying concentrations of β-carotene. An increase in the concentration of β-carotene was found to decrease the rate of oxidation of chlorogenic acid, suggesting that β-carotene and chlorogenic acid competed for t-BuO^· radicals. The quantum yields (f_expt) were 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-BuO^· radicals only, the quantum yields (f_cal) were theoretically calculated. f_expt and f_cal values suggested that chlorogenic acid not only protected β-carotene from t-BuO^· radicals, but also regenerated β-carotene from β-carotene radical cation, formed by the reaction of β-carotene with t-BuO^·radicals. Results indicated a possible synergistic interaction between chlorogenic acid and β-carotene in which 35.4% of β-carotene was regenerated by chlorogenic acid.