Iron(III) complexation by new aminocarboxylate chelators - Thermodynamic and kinetic studies

The complexation of Fe-III by new tetradentate and pentadentate aminocarboxylate chelators, designed to protect cells against iron-catalysed oxidative damage, was investigated. Ferric iron complexes of N,N'-bis(3,4,5-trimethoxybenzyl) ethylenediamine-N,N'-diacetic acid (L1), N,N'-dibenzylethylenediamine-N,N'-diacetic acid (L2) and [N-(2-hydroxybenzyl)-N'-benzylethylenediamine-N,N'-diacetic acid] (L3) have been characterized in aqueous solution by potentiometric, UV/Vis spectrophotometric and cyclic voltammetric measurements. The parent Ligand, ethylenediamine-N,N'-diacetic acid (L4), has also been studied. As expected, the presence of a hard phenolate donor group in L3 significantly enhances the affinity for iron while decreasing the potential of the Fe-III/Fe-II redox couple compared to L1 or L2. Kinetics studies have provided the kinetic rate constants related to the formation and the dissociation of the ferric complex with L3. The results reveal a fast Fe-III uptake, which is a favorable feature for a biological use of this type of ligand. Overall, these results demonstrate the pertinence of the use of such ligands to protect biological tissues against oxidative stress.