Stopped-Flow and Spectrophotometric Study on Radical Scavenging by Tea Catechins and the Model Compounds.
作者:Yasushi SENBA、Tsukasa NISHISHITA、Keiko SAITO、Hiroe YOSHIOKA、Hisashi YOSHIOKA
DOI:10.1248/cpb.47.1369
日期:——
Radical scavenging of four tea catechins, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg) and (-)-eppigallocatechin gallate (EGCg), and the model compounds of their partial structure was examined against the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical using stopped-flow and spectrophotometric methods. The number of DPPH radicals scavenged by a polyphenol molecule was larger than that of phenolic hydroxyl groups, suggesting that hydrogens which bond directly to the aromatic ring can also participate in radical scavenging. A model for the scavenging reaction was proposed in which the reaction proceeded with successive dehydrogenation from a polyphenol molecule. Analysis of the second order reaction rate constants and the activation parameters between DPPH and polyphenol at the early stage of the reaction showed that the values depended on the number of phenolic hydroxyl groups and their mutual position. Contribution of the A ring of catechins to the rate constants was estimated to be far smaller than that from the B ring. In the EGCg molecule, the B ring and the gallate group were not independent, but acted as a single group for DPPH radical scavenging.
对四种茶多酚(-)-表儿茶素(EC)、(-)-表没食子儿茶素(EGC)、(-)-表儿茶素没食子酸酯(ECg) 和(-)-表没食子儿茶素没食子酸酯(EGCg)及其部分结构的模型化合物, 用停流法和分光光度法研究了它们对1,1-二苯基-2-苦基肼基(DPPH)自由基的清除作用,发现一个多酚分子清除DPPH自由基的能力比羟基的数目强,说明直接与芳香环相连的氢原子也能参与自由基清除反应。提出了一个多酚分子连续脱氢的清除反应模型。研究了早期反应阶段DPPH和多酚的二级反应速率常数和活化参数,发现其数值与酚羟基数目及其相对位置有关。儿茶素A环对速率常数的贡献比B环小得多。在EGCg分子中,B环和没食子酸基团不是独立的,而是作为一个整体对DPPH自由基起清除作用。