Kinetic studies of antioxidant activity of new tocopherol model compounds in solution.
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概要
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The second-order rate constants <I>k</I><SUB>s</SUB> for the reaction of 10 kinds of tocopherol (vitamin E) model compounds with stable phenoxyl radical in ethanol have been measured at 25.0°C, using a stopped-flow spectrophotometer, as a model reaction of tocopherols with unstable free radicals (ROO·, RO·, and HO·) in biological systems. The absolute <I>k</I><SUB>s</SUB> values of α-, β-, γ-, and δ-tocopherol models are similar to or slightly smaller than those of the corresponding tocopherols having a long-phytyl-chain. The relative <I>k</I><SUB>s</SUB> values (α: β: γ: δ=100 : 53 : 50 : 24), that is, relative antioxidant activities, of α-, β-, γ-, and δ-tocopherol models are in good agreement with those (100 : 44 : 47 : 20) of α-, β-, γ-, and δ-tocopherols. The antioxidant activities of tocopherol models having two alkyl substituents, such as methyl, ethyl, isopropyl, and <I>t</I>-butyl groups, at ortho positions of OH group are similar to each other, suggesting that the effect of steric hindrance on the reaction rate is small. 5,7-Dimethyltocol model has quite similar rate constants with those of β- and γ-tocopherol models, whereas δ-tocopherol model is only ca. 24% as reactive as α-tocopherol model and tocol model is only ca. 10% as reactive as α-tocopherol model. The result indicates that the rate constants increase as the total electron donating capacity of the alkyl substituents at aromatic ring increases. For the tocopherol models log<I>k</I><SUB>s</SUB> was found to correlate with Σσ<SUP>+</SUP> substituent constants with a ρ<SUP>+</SUP> value of −1.0.
- 公益社団法人 日本化学会の論文
著者
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Mukai Kazuo
Department Of Chemistry Faculty Of Science Ehime University
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Uemoto Yuichi
Department of Chemistry, Faculty of Science, Ehime University
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Yokoyama Satoshi
Department of Chemistry, Faculty of Science, Ehime University
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Fukuda Kazuyuki
Department of Chemistry, Faculty of Science, Ehime University
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