XAS Investigation of biorelevant cobalt complexes in aqueous media

Abstract

Cobalt is an essential element of biological cycles involved in numerous metallobiomolecules, but it becomes a toxic element at high concentration or a radiotoxic element because of its use in the nuclear industry. “Molecular speciation” in biological media is an essential prerequisite to evaluate its chemical behaviour as well as its toxic or beneficial effects. In this scheme, we have focused on the coordination properties of the thiol-containing amino acid cysteine (Cys) and the pseudo-peptide N-(2-mercaptopropionyl)glycine (MPG) towards the Co²⁺ cation in aqueous media. XAS at the Co K edge and traditional spectroscopic techniques have been coupled in order to structurally characterize the cobalt coordination sphere. Oxidation states and geometries of the bis- and tris-cysteinato Co(III) complexes are in agreement with the literature data. In addition, bond lengths between the metallic centre and the donor atoms have been determined. The structure of a new dimeric N-(2-mercaptopropionyl)glycinato Co(II) complex in solution is also reported. The coordination of MPG to Co(II) through the thiolate and carboxylate functions is ascertained. This work provides fundamental structural information about biorelevant complexes of cobalt, which will contribute to our understanding of the chemical behaviour and the biological role of this radionuclide.