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 C-13 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- gold(III) species. This oxidation reaction suggests a new procedure for synthesis of H[Au(CN)(2)Cl-2]. Reaction of trans-[Au(CN)(2)X-2](-) (X-=Cl- and Br-) or [AuCl4](-) with HCN in aqueous solution at pH 7.4 leads directly to [Au(CN)(4)](-) without detection of the anticipated [Au(CN)(x)X4-x](-) intermediates, which is attributed to the cis- and trans-accelerating effects of the cyanides. The reduction of [Au(CN)(2)](-) 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. (C) 2001 Elsevier Science BN. All rights reserved.