Zn-polyphenol chelation: complexes with quercetin, (+)-catechin, and derivatives: II Electrochemical and EPR studies

摘要

In this work, we have studied the formation of complexes between flavonols, (quercetin, rutin, quercitrin, kaempferol, luteolin, tamarixetim) and flavanols ((+)-catechin, (-)-epicatechin), flavanonol, (+)-taxifolin, and Zn acetate in two hydro-organic media at neutral pH in the absence of oxygen. The complexation was first studied by cyclic voltammetry. Then preparative electrolysis have been attempted followed by coulometry, UV-Vis optical absorption and circular dicroism spectroscopies for characterizing the oxidized compounds. Spectroelectrochemistries monitored either in the UV-Vis or in the EPR spectrometers at room temperature have been also used and we have identified o-semi-quinone intermediates in some cases. Different behaviour vis-a-vis the complexation by Zn2+ according to the molecular structures of these different families of polyphenols have been found. Some of them are more easily oxidizible. (C) 2004 Elsevier B.V. All rights reserved.