Synthesis and antimicrobial properties of cycloheptyl substituted benzimidazolium salts and their silver(I) carbene complexes

Due to increasing infections caused by microbes, there is an urgent need for the development of new effective antimicrobial agents. Silver-N-heterocyclic carbene (silver-NHC) complexes are a new class of antimicrobial agents. In this study, we aimed to synthesize highly lipophilic silver-NHC complexes. Four new complexes were synthesized by the reaction of the corresponding benzimidazolium salts and Ag2O in dichloromethane at room temperature. The synthesized compounds were characterized by H-1 NMR, C-13 NMR, IR and elemental analysis. The antimicrobial performances of benzimidazolium salts and silver complexes were tested against the standard bacterial strains Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungi Candida albicans and Candida tropicalis. Minimum inhibitory concentrations (MICs) of all compounds were determined. The obtained data demonstrate that all benzimidazolium salts and silver complexes inhibit the growth of bacteria and fungi. Silver complexes are more active than the corresponding benzimidazolium salts (MIC: 6.25 mu g/mL for Gram-positive bacteria and fungi).