N-Heterocyclic carbene silver complexes: synthesis, characterization andin vitroantimicrobial studies

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Six new 2-morpholinoethyl and 2-diethylaminoethyl substituted N-heterocyclic carbene (NHC) silver complexes (2a-f) were synthesized from the reaction 1-(2-morpholinoethyl)-3-napthalenomethlbenzimidazolium chloride (1a), 1-(2-morpholinoethyl)-3-(2-methylbenzyl)benzimidazolium chloride (1b), 1-(2-morpholinoethyl)-3-(2,3,5,6-tetramethylbenzyl)benzimidazolium chloride (1c), [1-(2-diethylaminoethyl)-3-(3-methylbenzyl)benzimidazolium chloride (1d), [1-(2-diethylaminoethyl)-3-(2,3,5,6-tetramethylbenzyl)benzimidazolium chloride (1e), [1-(N,N-diethylethane)-3-(2,3,4,5,6-pentamethylbenzyl)benzimidazolium chloride (1f) with silver oxide (Ag2O) in dichloromethane at room temperature. These silver complexes were characterized by means of 1H NMR, 13C NMR, FT-IR spectroscopy and elemental analysis techniques. Also, [1-(N,N-diethylethane)-3-(2,3,4,5,6-pentamethylbenzyl)benzimidazol-2-ylidene]chlorosilver(I) complex (2f) was characterized by means of LC-MS and Maldi-MS methods. All silver complexes (2a-f) were screened for their in vitro antimicrobial activities against the following standard strains: Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungi Candida tropicalis, Candida albicans by using the microdilution broth method. These new compounds showed effective antimicrobial activities against gram-negative bacterial strains, gram-positive bacterial strains, and fungus. Also, ampicillin, ciprofloxacin, and fluconazole as the antibacterial standard drugs were used for comparison with synthesized new unsymmetrically substituted NHC silver complexes (2a-f).