Synthesis, Characterization and Antimicrobial properties of Methylbenzyl and Nitrobenzyl containing Imidazolium-based Silver N-Heterocyclic Carbenes

A series of imidazolium-based novel ionic liquids (ILs) containing methylbenzyl and nitrobenzyl substituents were prepared and further converted to neutral as well as ionic silver complexes. The ILs and their Ag-NHCs (N-Heterocyclic Carbenes) were successfully characterized by NMR, FT-IR, and EI-MS studies. The ILs and Ag-NHCs were screened for antimicrobial activity based on the zone of inhibition, Minimum Inhibitory Concentration (MIC) determination, and stability studies against Salmonella enterica and Staphylococcus aureus. The neutral complex NS-32 ((1-((2′-cyano-[1,1′-biphenyl]-4-yl)methyl)-3-(4-nitrobenzyl)-2,3-dihydroimidazol-2-yl)silver bromide) was the most active with MIC of 25 μM and showed efficient growth inhibition of bacterial pathogens even up to 21 d. The complex NS-32 was further monitored for cell wall disruption by scanning electron microscopy (SEM). The photomicrographs of bacterial cells obtained by SEM after treatment of NS-32 with S. enterica and S. aureus showed rupture of a cell wall, thus proving it to be the site of action and ultimately having inhibitory effects on the microbial cell growth.