The influence of amino acid ligands and vitamin C on the reduction potential of Fe (III): polarographic and electron spin resonance investigations.

The pH dependence of Fe(III)-amino acid complexes has been studied polarographically and by means of ESR spectroscopy. It could be shown that, at least, two complexes exist: one with a low molecular weight, ESR detectable at acid pH, and one with a high molecular weight at alkaline pH, ESR non detectable. The half wave potential of Fe(III) is lowered by amino acid ligands. The redox interaction of the Fe(III)-amino acid complexes with vitamin C results in a decrease of the ascorbyl radical concentration. Ascorbic acid also forms a complex with Fe(III) as indicated by a polarographic half wave potential near -0.55 V vs. S.C.E. at pH 7.