Reactivity of dpph? in the oxidation of catechol and catechin

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Title:	Reactivity of dpph? in the oxidation of catechol and catechin
Authors:	Chen, W.-L., Li, W.-S., Fu, P.-J., Yeh, A.
Contributors:	Department of Chemistry, Tunghai University
Date:	2011
Issue Date:	2013-05-14T09:01:08Z (UTC)
Abstract:	A kinetic study of the reduction of pyrocatechol and catechin by dpph ? radical has been carried out in various ratios of CH 3OH/H2O mixed solvent at pH 5.5-7.5, μ = 0.10 M [(n-Bu)4N]ClO4, and T = 25°C. The rate constants of oxidation in aqueous solvent, kH2O, were obtained from the extrapolation of the linear plots of the specific rate constants k vs. % H 2O plots at each pH value. A linear relationship between k H2O and 1/[H+] was observed for both flavonoids with kH2O = k1Ka1/[H+], where K a1 was the first acid dissociation constant on the catechol ring and k1 is the rate constant of the oxidation of the mononegative species HX-. The values of k1 obtained from the slopes of the plots are (8.2 ± 0.2) × - 105 and (6.1 ± 0.1) × - 105 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 × - 103 M-1 s-1 for the self-exchange rate constant of dpph?/dpphH couple. ? 2011 Wiley Periodicals, Inc.
Relation:	International Journal of Chemical Kinetics Volume 43, Issue 3, March 2011, Pages 147-153
Appears in Collections:	[Department of Chemistry ] Periodical Articles

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