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)(2)X(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 HAu(CN)(2)Cl(2)]. Reaction of trans-Au(CN)(2)X(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.