<span style="font-size:12.0pt;line-height:115%; font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language:HI">Kinetics of oxidation of thymine by <i>t</i>-butoxyl radical — Protection and repair by caffeic acid</span>

Abstract

The kinetics of oxidation of thymine and caffeic acid by <i>t-</i>BuO^• has been studied by the photolysis of <i>t</i>-butyl hydroperoxide in presence of <i>t</i>-butanol. The rates and the quantum

yields (φ) of oxidation of caffeic acid by <i>t-</i>BuO^• radicals have been determined by varying concentrations of thymine. An increase in [thymine] has been found to decrease the rate of

oxidation of caffeic acid suggesting that thymine and caffeic acid compete for <i>t-</i>BuO^• radicals. From competition kinetics, the rate constant of <i>t-</i>BuO^• - thymine reaction has been calculated to be 5.3×10⁷ dm³ mol^-1 s^-1. The experimentally determined quantum yields (φ_expt) and the calculated yields (φ_cal) of oxidation of caffeic acid, assuming that caffeic acid reacts only with <i>t-</i>BuO^• radicals, suggest that caffeic acid not only protects thymine from <i>t-</i>BuO^• radicals but also repairs thymine radicals formed by the reaction of <i>t-</i>BuO^• radicals.