Electrochemical behavior of iron(III) complexes with aminohydroxamic acids

Abstract

The electrochemical reduction of various aminohydroxamate complexes of iron(III), such as alanine-, serine-, lysine-, histidine- and glutamo-γ-hydroxamate, has been investigated in aqueous solution by cyclic voltammetry on hanging mercury drop electrodes to determine the mechanism involved in the electron transfer processes. In all the studied cases the iron(III) complexes, with the exception of histidinehydroxamate, have been found to undergo reversible reductions followed by irreversible chemical reactions (EC mechanism). Rate constants for the irreversible dissociation of iron(II) complexes were calculated. The typical quasi-reversible pattern for the reduction of histidinehydroxamate was attributed to the different coordination mode. The observed differences in redox potentials between the investigated complexes suggest that the electronic effect of the substituent on the carbonyl group, involved in the coordination to the iron center, may modify the donor properties of the oxygen atoms of the hydroxamate moiety. The potentials determined at physiological pH are in the range of biological reducing agents, which makes these compounds potential siderophore models.