Synthesis, structures, and novel antimicrobial activity of silver(I) halide complexes of imidazolidine-2-thiones

Abstract

In this paper, a series of silver(I) halide complexes of N-substituted-imidazolidine-2-thiones (L-NR, R = H, Me, Et) (reactants ratio: 1:3, M:L) are synthesized and characterized using analytical data, infrared spectroscopy, proton and carbon-13 NMR spectroscopy, single crystal X-ray crystallography and electron spray ionization mass spectrometry (ESI-MS). Mononuclear, trigonal planar [AgX(κ1S-L-NR)2] (X, R: Cl, Me, 1; Br, Me, 4) and tetrahedral [AgBr(κ1S-L-NEt)3] 5, dinuclear sulfur-bridged [Ag2Cl2(µ-S-L-NEt)2(κ1S-L-NEt)2] (2), and halogen-bridged [Ag2(µ-Br)2(κ1S-L-NH)4] (3) complexes, have been explored for their potential antimicrobial activity, including that of the previously reported ones, [AgBr(κ1S-L-NR)3] (R: Prn, 6; Bun, 7). Antimicrobial activity against Gram positive bacteria: Staphylococcus aureus (MTCC 740), Methicillin resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis (MTCC 435), Enterococcus faecalis (MTCC 439); Gram negative bacteria: Klebsiella pneumoniae (MTCC 109), Salmonella typhimurium (MTCC 98), Shigella flexneri (MTCC 1457) and a yeast, Candida albicans (MTCC 227) has been studied. Among the complexes investigated, several of them have shown high antimicrobial activity against MRSA, S. epidermidis and E. faecalis at low minimum inhibitory concentration (MIC) as compared to that of the reference drug gentamicin. The activity of complexes against Staphylococcus aureus, Shigella flexneri and Candida albicans, was either comparable or low vis-à-vis that of the corresponding reference compounds. The activity of the two allied complexes tested against K. pneumoniae and S. typhimurium was rather low. A three coordinate complex, [AgBr(κ1S-L-NMe)2] 4, with the highest percent cell viability of 96% followed by another dimeric complex, [Ag2(μ-Br)2(κ1S-L-NH)4] 3, have emerged the potential candidates for further studies.