The ligand unwrapping/rewrapping pathway that exchanges metals in S-acetylated, hexacoordinate N(2)S(2)O(2) complexes

The effect of S-acetylation in MN(2)S(2) complexes on metal exchange reactivity was examined in a series of MN(2)S(2)O(2) complexes. While clean exchange processes do not occur for the MN(2)S(2) derivatives where formation of S-bridged aggregates predominate, acetylation permits the metal exchange with hierarchy that follows the Irving–Williams series of stability for first row transition metals: Fe(2+) < Co(2+) < Ni(2+) < Cu(2+) > Zn(2+). The rate determining step consistent with kinetic parameters depends on both M and M′, supporting a mechanism of exchange that involves ligand unwrapping/rewrapping process as earlier defined by Margerum et al. for M(EDTA) systems. The enhanced metal exchange deriving from S-acetylation is of significance to probes and detection of cysteine-S metallo-proteins and metallo-enzyme active sites, and highlights a new role for S-acetylation.