Spectroscopic and pulse radiolysis studies of the antioxidant properties of (+) catechin: metal transition chelation and oxidizing radical scavenging

Catechin (5,7,3,4-tetrahydroxyflavan-3-ol, Cat), a compound suggested to give protection to living organisms both by direct scavenging of free radicals and metal chelation, was investigated in the presence of Zn(II) and Cu(II) ions by different techniques. The UV/vis, Raman and IR studies were useful to assess the chelation sites, the relevant interaction of Cat with Cu(II) ions, as well as the weak affinity with Zn(II). Cat acts as a bidentate ligand through the catechol moiety on B-ring, but the metal complex structure depends on the metal. In particular, some autoxidation processes may be involved in the formation of the Cu-Cat complexes. The protonation state of the B-ring plays an important role both in metal chelation and scavenging activity of Cat. Information on the reactivity of the free Cat towards oxidizing radicals with different redox properties were obtained by pulse radiolysis. In all cases the relatively stable phenoxyl radicals resulted to be formed.