Synthesis, structures, and ESI-mass studies of silver(I) derivatives of imidazolidine-2-thiones: Antimicrobial potential and biosafety evaluation.

The basic objective of this investigation is to explore potential metallo-organic antimicrobial agents based on silver-heterocyclic-2-thiones. In this respect, a series of silver(I) halide complexes with imidazolidine-2-thiones (L-NR, R=H, Me, Et, Prn, Bun, Ph), namely, mononuclear [AgX(L-NR)(PPh3)2] (X, R: Cl, Bu, 1; Br, Ph, 7); [AgX(L-NR)3] (Br, Bu, 5; Br, Prn, 8) and halogen bridged dinuclear [Ag2(μ-X)2(L-NR)2(PPh3)2] (Cl, Bun, 2; Cl, Ph, 3; Cl, Prn, 4; Br, Ph, 6) have been synthesized and characterized using modern techniques. The thio-ligands are terminally S-bonded in all the complexes. The in vitro antimicrobial potential and biosafety evaluation of the above complexes as well as that of previously reported analogous silver complexes has been studied against Gram positive bacteria, namely, Staphylococcus aureus (MTCC 740) and Methicillin resistant Staphylococcus aureus (MRSA), Gram negative bacteria Klebsiella pneumoniae (MTCC 109), Salmonella typhimurium (MTCC 98) and a yeast Candida albicans (MTCC 227). Most of the complexes tested have shown significant antimicrobial activity with low values of minimum inhibitory concentration (MIC). Significantly, the activity against MRSA is an important outcome of this investigation. Among complexes tested for their cytotoxicity using MTT [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay, some complexes showed low cellular toxicity with high percent cell viability. A dinuclear complex [Ag2(μ-Cl)2(L-NPh)2(PPh3)2] 3 with 93.3% cell viability emerges the most important candidate for further investigations.