Abstract
Second-order rate constants, k 5, for H-atom abstraction by phenoxyl radicals from five tocopherol (vitami E) derivatives have been measured spectrophotometrically at 25.0°C by the stopped-flow method, as a model reaction of tocopherols with unstable free radicals (LOO •, LO •, and HO •) in biological systems. Three new tocopherol derivatives with a five-membered heterocyclic ring were found to be 1.9–2.1 times more active than the α-tocopherol which has the highest antioxidant activity among natural tocopherols. The proton hyperfine splittings for the five tocopheroxyl radicals derived from these tocopherols by the reaction with phenoxyl were also determined by ESR measurements.
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