Study of the iron catechin complexes in dimethyl sulphoxide. Redox chemistry and interaction with superoxide radical anion in this medium.

The redox chemistry of catechin (catH(2)) and its iron complexes has been s tudied in dimethyl sulphoxide. In the absence of base a one-to-one iron (II )-catechin complex is formed which exhibits oxidation processes at 0.28, 0. 66, and 0.92 V vs SCE. These processes correspond to the oxidation of Fe(II ) to Fe(III), the formation of the quinonic form of the catechol moiety and the oxidation of another hydroxy group to a radical. In the presence of ba se a stable 1:1 complex is formed with oxidation processes that show up at +0.25, +0.64, and +0.88 V vs SCE. The voltammetric and spectroscopic charac terization of the species produced after the oxidation processes is describ ed. Upon interaction of the complex with superoxide radical anion in dimeth yl sulphoxide, the basic character of this radical anion causes the formati on of the monoanion of catechin leading to a more stable complex of iron(II ). The protonated superoxide disproportionates to molecular oxygen and pero xide, causing the oxidation of the metal ion. The addition of a second equi valent of superoxide oxidizes bound catechin to the corresponding semiquino ne. The formation of hydroxy radicals through Fenton chemistry does not tak e place because peroxide is consumed and the metal ion remains as a stable iron(III) complex.