Preparation, characterization and activity of tea polyphenols-zinc complex

The zinc-complexes of tea polyphenols (TP), including (−)-epigallocatechin gallate (EGCG), were prepared with zinc chloride at pH 6.5 in the absence of oxygen. The complexes were characterized with field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), ultraviolet–visible (UV–vis), fourier transform infrared (FTIR), 1H nuclear magnetic resonance (1H NMR) spectroscopy and thermogravimetric analysis (TGA), and their antioxidant and antibacterial activities were studied. The results showed that TP/EGCG complexed with zinc ion in the B-ring at 1:1, and the thermal stability of the complexes was better than that of TP/EGCG, and the scavenging activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and superoxide radicals and the antibacterial activities against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) were significantly stronger than those of EGCG/TP. We speculated that the complexation with zinc ion might enhance the thermal stability, the antioxidant activity and the antibacterial activity of TP/EGCG. It can be expected that the zinc-complexes of TP/EGCG will have a bright prospect for their potent biological activity.