Antioxidant activity of Ferrozine-iron-amino acid complexes

Amino acid-Fe(II)-chelator complexes exhibit strong antioxidant activity. Taking advantage of the unique spectral characteristics of the complexes formed when Ferrozine (Fz) is used as the chelator, we now show that the primary blue complex (epsilon(max) at 632 nm) decomposes by two independent pathways: (i) a nonoxidative pathway involving dissociation of the amino acid component and formation of a purple complex (epsilon(max) at 562 nm) and (ii) an oxidative pathway leading to Fe(III) and colorless products. Quantitative conversion of the blue to purple complex yields an isosbestic point (i.p.) at 601 nm, whereas no i.p. is formed during quantitative oxidation of the blue complex. However, under some experimental conditions, decomposition of the blue product occurs by both pathways, leading to occurrence of a clean i.p. at wavelengths varying from 601 to 574 nm. Results of simulation experiments, confirmed by direct analysis, demonstrate that shifts in the i.p. reflect differences in the fractions of blue compound that decompose by the oxidative and nonoxidative pathways. Indeed, the fraction of blue that is converted to the purple complex is readily deduced from the wavelength of the i.p. These results suggest that identification of a physiological chelator that can replace Ferrozine in amino acid-iron complexes might have important physiological and pharmacological applications.