Zn–polyphenol chelation: complexes with quercetin, (+)-catechin, and derivatives: I optical and NMR studies

The complexation of Zn2+ by quercetin, (+)-catechin and several derivatives has been investigated in the aim to determine the stoichiometry and the stereospecificity and its influence on their antioxidant properties. These studies have been conducted under anaerobic conditions in hydro-organic solvents buffered at pH 7 using UV–Vis and 1H NMR spectroscopies. From the evolution of the spectra of the flavonoids with the concentration of ZnAc their stoichiometry and the coordination sites were determined.