Reactivity of DPPH• in the Oxidation of Catechol and Catechin
Reactivity of DPPH• in the Oxidation of Catechol and Catechin
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DOI：
10.1002/kin.20542
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发表时间：
2011-03-01
影响因子：
1.5
通讯作者：
Yeh, Andrew
中科院分区：
文献类型：
--
作者：
Chen, Wei-Lin;Li, Wei-Shuen;Yeh, Andrew
在 pH 5.5-7.5、mu = 0.10 M [(n-Bu)(4)N]ClO4、T = 25 ℃ 的不同比例的 CH3OH/H2O 混合溶剂中，对 dpph（中心点）自由基还原邻苯二酚和儿茶素进行了动力学研究。水性溶剂中的氧化速率常数 k(H2O) 由以下线性图外推得到：每个 pH 值下的特定速率常数 k 与 % H2O 的关系图。对于两种类黄酮，观察到 k(H2O) 和 1/[H+] 之间存在线性关系，其中 k(H2O) = k(1)K(a1)/[H+]，其中 K-a1 是儿茶酚环上的第一个酸解离常数，k(1) 是单阴性物质 HX- 的氧化速率常数。对于邻苯二酚和儿茶素，从图的斜率获得的 k(1) 值分别为 (8.2 +/- 0.2) x 10(5) 和 (6.1 +/- 0.1) x 10(5) M-1 s(-1)。根据外球电子转移反应的Marcus理论对该反应进行分析，得到dpph(中心点)/dpphH电偶的自交换速率常数值为3.7×10(3)M-1s(-1)。 (C) 2011 年 Wiley 期刊公司 Int J Chem Kinet 43: 147-153, 2011
A kinetic study of the reduction of pyrocatechol and catechin by dpph(center dot) radical has been carried out in various ratios of CH3OH/H2O mixed solvent at pH 5.5-7.5, mu = 0.10 M [(n-Bu)(4)N]ClO4, and T = 25 degrees C. The rate constants of oxidation in aqueous solvent, k(H2O), were obtained from the extrapolation of the linear plots of the specific rate constants k vs. % H2O plots at each pH value. A linear relationship between k(H2O) and 1/[H+] was observed for both flavonoids with k(H2O) = k(1)K(a1)/[H+], where K-a1 was the first acid dissociation constant on the catechol ring and k(1) is the rate constant of the oxidation of the mononegative species HX-. The values of k(1) obtained from the slopes of the plots are (8.2 +/- 0.2) x 10(5) and (6.1 +/- 0.1) x 10(5) M-1 s(-1) for pyrocatechol and catechin, respectively. The analysis of the reaction on the basis of Marcus theory for an outer-sphere electron transfer reaction yielded a value of 3.7 x 10(3) M-1 s(-1) for the self-exchange rate constant of dpph(center dot)/dpphH couple. (C) 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 147-153, 2011