| Research Abstract |
About 30 kinds of new tocopherol derivatives have been synthesized, and the rates of scavenging of substituted phenoxyl radical (PhO^<. >), k_2 and quenching of singlet oxygen ( ^1O_2), k_Q, by these tocopherols have been measured spectrophotometrically in ethanol. Both the log of the rate constants, k_2 and k_Q, were found to correlate with their peak oxidation potential, E_p. The quenching rates, k_Q, were found to be related linearly to the rates k_1 and k_2 of scavenging of peroxyl (LOO^<. >) (reported by Burton et al.) and phenoxyl (PhO^<. >) radicals by these tocopherols, respectively. Vitamin K_1-and K_3- hydroquinone and some estrogens were found to be several times more active than -tocopherol, respectively, which has the highest antioxidant activity among natural tocopherols Further, the second-order rate constants, k_<-1>, k_3, k_4, and k_6 for the reaction of vitamin E radical with i) lipid hydroperoxides (LOOH), ii) vitamin C, iii) ubiquinol, and iv) unsaturated fatty acid esters (LH), respectively, in solution have been measured. By comparing these rate constants, the mechanism of antioxidant and prooxidant actions of tocopherols in biomembranes and edible oils has been discussed.
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