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首页> 外文期刊>Chemistry: A European journal >Extraordinary radical scavengers: 4-mercaptostilbenes
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Extraordinary radical scavengers: 4-mercaptostilbenes

机译：非凡的自由基清除剂：4-巯基对苯二酚

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In the past decade, there was a great deal of interest and excitement in developing more active antioxidants and cancer chemoprevention agents than resveratrol, a naturally occurring stilbene. In this work, eight resveratrol-directed 4-mercaptostilbenes were constructed based on the inspiration that thiophenol should be a stronger radical scavenger than phenol, and their reaction rates with galvinoxyl (GO.) and 2,2-diphenyl-1-picrylhydrazyl (DPPH.) radicals in methanol and ethyl acetate were measured by using stopped-flow UV/Vis spectroscopy at 25 °C. Kinetic analysis demonstrates that 4-mercaptostilbenes are extraordinary radical scavengers, and the substitution of the 4-SH group for the 4-OH group in the stilbene scaffold is an important strategy to improve the radical-scavenging activity of resveratrol. Surprisingly, in methanol, some of the 4-mercaptostilbenes are 10 ~4-times more active than resveratrol, dozens of times to hundreds of times more effective than known antioxidants (α-tocopherol, ascorbic acid, quercetin, and trolox). The detailed radical-scavenging mechanisms were discussed based on acidified-kinetic analysis. Addition of acetic acid remarkably reduced the GO. and DPPH. radical-scavenging rates of the 4-mercaptostilbenes in methanol, a solvent that supports ionization, suggesting that the reactions proceed mainly through a sequential proton loss electron transfer mechanism. In contrast, an interesting acid-promoted kinetics was observed for the reactions of the 4-mercaptostilbenes with DPPH. in ethyl acetate, a solvent that weakly supports ionization. The increased ratio in rates is closely correlated with the electron-rich environment in the molecules, suggesting that the acceleration could benefit from the contribution of the electron transfer from the 4-mercaptostilbenes and DPPH.. However, the addition of acetic acid had no influence on the GO.-scavenging rates of the 4-mercaptostilbenes in ethyl acetate, due to the occurrence of the direct hydrogen atom transfer. Our results show that the radical-scavenging activity and mechanisms of 4-mercaptostilbenes depends significantly on the molecular structure and acidity, the nature of the attacking radical, and the ionizing capacity of the solvent.
机译：在过去的十年中，与天然白藜芦醇白藜芦醇相比，开发出更多的活性抗氧化剂和癌症化学预防剂引起了极大的兴趣和兴奋。在这项工作中，基于以下启示构建了八种白藜芦醇导向的4-巯基对苯二酚：硫酚应是比苯酚更强的自由基清除剂，并且它们与galvinoxyl（GO。）和2,2-二苯基-1-picylhydrazyl（DPPH）的反应速率通过在25°C下使用停止流UV / Vis光谱法测量甲醇和乙酸乙酯中的自由基。动力学分析表明4-巯基对苯二酚是非凡的自由基清除剂，用4-SH基取代二苯乙烯骨架中的4-OH基是提高白藜芦醇清除自由基活性的重要策略。出乎意料的是，在甲醇中，一些4-巯基对苯二酚的活性是白藜芦醇的10到4倍，比已知的抗氧化剂（α-生育酚，抗坏血酸，槲皮素和trolox）的效力高数十倍至数百倍。基于酸化动力学分析讨论了详细的自由基清除机理。加入乙酸显着降低了GO。和DPPH。 4-巯基对苯二酚在甲醇中的自由基清除速率，甲醇是一种支持电离的溶剂，表明反应主要通过顺序的质子损失电子转移机理进行。相反，对于4-巯基对苯二酚与DPPH的反应，观察到了有趣的酸促进动力学。乙酸乙酯中的一种溶剂，弱支持电离。比率的增加与分子中富电子的环境密切相关，这表明加速可得益于4-巯基对苯二酚和DPPH的电子转移作用。但是，乙酸的添加没有影响由于直接氢原子转移的发生，对4-巯基对苯二酚在乙酸乙酯中的GO-清除速率的影响。我们的结果表明4-巯基对苯二酚的自由基清除活性和机理在很大程度上取决于分子结构和酸度，攻击自由基的性质以及溶剂的电离能力。

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