Spin Dynamics of the Anti-Aging Actions by NaturalAntioxidants

人体衰老是由脂质、蛋白质和核酸与活性氧和自由基反应引起的。天然抗氧化剂，如维生素E（α-，β-，γ-，δ-生育酚，TocH），泛醇，维生素C，多酚（黄酮，儿茶素）等，它存在于生物系统中，能迅速清除活性氧和自由基，保护衰老。本工作对上述天然抗氧化剂的清除自由基、再生生育酚和猝灭单线态氧的作用进行了动力学研究，得到了一些有趣的结果：1）维生素E清除花生四烯酸自由基的速率（k_s）采用停流分光光度计，通过改变pH值，在胶束溶液中测定α-、β-、γ-、δ-TocH和泛醇。已经阐明，泛醇在几种组织（心脏、肌肉、肝脏和脑）的线粒体和血清中分别显示出比α-生育酚更高和更低的自由基清除活性。 关于我们 2)本文测定了7种黄酮衍生物和4种儿茶素对单线态氧（^1O_2）的猝灭速率（K_Q），发现几种黄酮和儿茶素的K_Q值大于脂类、氨基酸和DNA的K_Q值。此外，这些值与α-和γ-生育酚、泛醇-10和质体醌醇模型的值相似，表明这些多酚可能通过猝灭^1O_2而有助于保护生物系统中的氧化损伤。（α-，β-，γ-，δ-TocH）在生物体系中的作用，用停流分光光度计研究了有机溶剂中维生素E自由基（α-，β-，γ-，δ-TocH，Toc）的生成和衰变反应动力学。通过比较实测曲线和微分方程数值计算得到的模拟曲线，确定了TOC生成和衰变反应的二级速率常数（k_f和2k_d）。在乙醇中，kf值按α-> β-~γ-> δ-TocH的顺序减小，2kd值按α-< β-< γ-< δ-Toc的顺序增大。在α-Toc.是为这些激进分子确定的。根据实验结果，讨论了α-、β-、γ-、δ-TOC自由基的衰变反应方案。4）用双混合停流分光光度计测定了维生素C再生天然维生素E的反应速率常数和活化能。维生素E自由基芳环上甲基取代的动力学效应表明，部分电荷转移在反应中起作用。由于未发现明显的氘动力学同位素效应，在本实验条件下隧道效应可能不起重要作用。少

Human aging is induced by the reaction of lipid, protein, and nucleic acid with active oxygens and free radicals. Natural antioxidants such as vitamin E (α-, β-, γ-, δ-tocopherol, TocH), ubiquinol, vitamin C, polyphenols (flavones, catechins) etc., which exist in biological systems, scavenge active oxygens and free radicals quickly, and protect the aging. In the present work, the kinetic studies of i) free-radical-scavenging action, ii) tocopherol-regeneration action, and iii) singlet-oxygen-quenching action with the above natural antioxidants were performed, and several interesting results were obtained.1) The aroxyl-radical-scavenging rates (k_s) of vitamin E (α-, β-, γ-, δ-TocH) and ubiquinol were measured in micellar solutions by varying pH, using stopped-flow spectrophotometer. It has been clarified that ubiquinol shows higher and lower free-radical-scavenging activity than a-tocopherol in mitochondria of several tissues (heart, muscle, liver and brain) and in serum, respectively. … More 2) Quenching rates (K_Q) of singlet oxygen (^1O_2) by 7 kinds of flavone derivatives and 4 kinds of catechins have been measured The K_Q values of several kinds of flavones and catechins were found to be larger than those of lipids, amino acids, and DNA. Further, these values are similar to those of a-and y-tocopherol, ubiquinol-10, and plastoquinol model, suggesting that these polyphenols may contribute to the protection of oxidative damage in biological systems, by quenching ^1O_2.3) In order to understand the dynamics of antioxidant actions of vitamin E (α-,β-, γ-, δ-TocH) in biological systems, kinetic study of the formation and decay reactions of vitamin E radicals (α-, β-, γ-, δ-tocopheroxyls, Toc) has been performed in organic solvents, using stopped-flow spectrophotometer. The second-order rate constants (k_f and 2k_d) for the formation and decay reactions of Toc were determined by comparing the observed curves with the simulation ones obtained by the numerical calculation of differential equations related to the above reactions. The k_f values decreased in the order of α-> β-~γ-> δ-TocH, and the 2kd values increased in the order of α-< β-< γ-< δ-Toc in ethanol. The wavelengths of absorption maxima (λmax^1) and molar extinction coefficients (ε_1) of the optical spectra (for example, i = 1~4 for α-Toc.) were determined for these radicals. The scheme of the decay reactions of α-, β-, γ-, δ-Toc radicals has been discussed based on the results obtained.4)The rate constant and activation energy of the regeneration reaction of natural vitamin E by vitamin C were determined with a double-mixingstopped-flow spectrophotometer. The kinetic effect ofmethyl substitution on the aromatic ring of vitamin E radical indicates that partial charge-transfer plays a role in the reaction Since a substantial deuterium kinetic isotope effect was not found, the tunneling effect may not play an important role under the present experimental conditions. Less