Ligand-exchangeability of 2-coordinate phosphinegold(I) complexes with AuSP and AuNP cores showing selective antimicrobial activities against Gram-positive bacteria. Crystal structures of [Au(2-Hmpa)(PPh3)] and [Au(6-Hmna)(PPh3)] (2-H2mpa=2-mercaptopropionic acid, 6-H2mna=6-mercaptonicotinic acid)

Abstract Selective and effective antimicrobial activities against Gram-positive bacteria ( B. subtilis and/or S. aureus ) were found in 2-coordinate gold(I)–PPh 3 complexes with AuSP and AuNP cores, i.e. [Au(L)(PPh 3 )] (HL=2-H 2 mna [H 2 mna=mercaptonicotinic acid] 3 , d -H 2 pen [H 2 pen=penicillamine] 4 , d,l -H 2 pen 5 , 4-H 2 mba [H 2 mba=mercaptobenzoic acid] 8 , Hpz [Hpz=pyrazole] 9 , Him [Him=imidazole] 10 , 1,2,3-Htriz [Htriz=triazole] 11 , 1,2,4-Htriz 12 , Htetz [Htetz=tetrazole] 13 ), whereas no activity was observed in 2-coordinate AuSP core complexes [Au(2-Hmba)(PPh 3 )] 6 and [Au(3-Hmba)(PPh 3 )] 7 . The two novel AuSP core complexes, [Au(2-Hmpa)(PPh 3 )] [H 2 mpa=mercaptopropionic acid] 1 and [Au(6-Hmna)(PPh 3 )] 2 , were prepared and characterized by elemental analysis, FT-IR, TG/DTA, and ( 31 P, 1 H and 13 C) NMR spectroscopy. The crystal structures of 1 and 2 were determined as a supramolecular arrangement of the 2-coordinate AuSP core. Both 1 and 2 significantly showed antibacterial activities. As a model reaction of phosphinegold ( I ) complexes with the cysteine residue in the biological ligands, we examined if the ligand exchange reactions of the aromatic anions L 1 − in [Au(L 1 )(PPh 3 )] (HL 1 =6-H 2 mna 2 , 2-H 2 mna 3 , 2-H 2 mba 6 , Hpz 9 , Him 10 , 1,2,3-Htriz 11 , 1,2,4-Htriz 12 ) with aliphatic thiols HL 2 (HL 2 =2-H 2 mpa, d -H 2 pen) occurred under the mild conditions and, also, if the ‘reverse’ reactions, namely, the ligand exchange reactions of the thiolate anions in [Au(2-Hmpa)(PPh 3 )] 1 , [Au( d -Hpen)(PPh 3 )] 4 and [Au(2-Hmba)(PPh 3 )] 6 with the free ligands HL 1 took place under similar conditions. In this work, a relationship of the ligand-exchangeability among 2-coordinate gold(I) complexes ( 1 – 4 , 6 , 9 – 12 ) was revealed. Complex 6 was substitution-inert, whereas complexes 1 – 4 and 9 – 12 were substitution-labile. The ligand-exchangeability of Au–S and Au–N bonds in the 2-coordinate phosphinegold(I) complexes with AuSP and AuNP cores to form new AuSP cores, with retention of the Au–P bond, was closely related to the observed activities against Gram-positive bacteria, and the ease of the ligand-exchange reaction was strongly related to the intensity of the activities.