Redox and ligand exchange reactions of potential gold(I) and gold(III)-cyanide metabolites under biomimetic conditions

Biomimetic pathways for the oxidation of [Au(CN) 2] −, a gold metabolite, and further cyanation of the gold(III) products to form Au(CN) 4 − were investigated using 13C NMR and UV–Visible spectroscopic methods. Hypochlorite ion, an oxidant released during the oxidative burst of immune cells, was employed. The reaction generates mixed dicyanoaurate(III) complexes, trans-[Au(CN) 2X 2] −, where X − represents equilibrating hydroxide and chloride ligands, and establishes the chemical feasibility of dicyanoaurate oxidation by OCl − to gold(III) species. This oxidation reaction suggests a new procedure for synthesis of H[Au(CN) 2Cl 2]. Reaction of trans-[Au(CN) 2X 2] − (X −=Cl − and Br −) or [AuCl 4] − with HCN in aqueous solution at pH 7.4 leads directly to [Au(CN) 4] − without detection of the anticipated [Au(CN) x X 4− x ] −intermediates, which is attributed to the cis- and trans-accelerating effects of the cyanides. The reduction of [Au(CN) 4] − by glutathione and other thiols is a complex, pH-dependent process that proceeds through two intermediates and ultimately generates [Au(CN) 2] −. These studies provide further insight into the possible mechanisms of an immunogenically generated gold(I)/gold(III) redox cycle in vivo.