RESUMO
Objective To study the anti-oxidation properties of Zn2+-quercetin complexes .Methods The binding stoi-chiometric ratios and the binding constant of Zn2+ to quercetin were measured with UV-Vis spectroscopy .The binding sites on quercetin were determined via1 H NMR spectroscopy .The antioxidant activities of Zn2+-quercetin complexes were compared to quercetin by scavenging DPPH radical method .The binding ratio of Zn2+ to quercetin depends on neutralization of phenol groups of quercetin .Results The binding ratio of Zn2+ to quercetin is 1:2 when less than two OH groups were deprotonated . The binding ratio is 1:1 when more than three OH groups were deprotonated .The apparent binding constant is 2 .42 × 106 M -1 for the 1:1 Zn2+-quercetin complex .The 3′-OH and 4′-OH of quercetin are involved in the Zn2+ binding .The scavenging DPPH radical activity of Zn2+-quercetin complex is 2 .3 times of quercetin .Conclusion These results provide a new insight to expand applications of this traditional Chinese medicine .