Perspectives in inorganic and bioinorganic gold sulfur chemistry

A detailed picture of the chemical and electrochemical oxidation of a series of mononuclear and dinuclear phosphine Au(I) thiolates is presented. The medicinal implications of the results are illustrated by redox studies on the anti-rheumatoid drug, auranofin, [(2,3,4,6-tetra-acetyl-1-thio-beta-D-glucopyranosato)(triethylphosphine) gold(I)]. The phosphine Au(I) thiolate complexes undergo a broad irreversible oxidation in the range, +0.6 to +1.1 V, and a second irreversible oxidation at more positive potentials from +1.2 to +1.6 V (vs. SCE). Chemical oxidation of the Au(I) thiolate complexes with (Cp(2)Fe)(PF(6)) results in disulfide and tetragold(I) clusters with bridging thiolate ligands, except for the unusual nine Au(I) atoms cluster obtained by oxidation of [(dppm)Au(2)(p-SC(6)H(4)CH(3))(2) ]. Chemical oxidation of auranofin with (Cp(2)Fe)(PF(6)) results in disulfide and a cationic Au(I) cluster with bridging thiolate ligands, [(Et(3)PAu)(2)(mu-SATg)](2)(2+) , typical of mononuclear gold(I) thiolates. The Au(I) clusters react with disulfide to undergo thiolate/disulfide exchange. Comparative rates show clusters react much faster than the mononuclear complex, Ph(3)PAu(SC(6)H(4)CH(3)). A mechanism for the oxidation of auranofin and related complexes, and possible biological implications are discussed.