Synthesis, Cytotoxicity and Antibacterial Studies of p-Methoxybenzyl-Substituted and Benzyl-Substituted N-Heterocyclic Carbene-Silver Complexes

p-Methoxybenzyl-substituted and benzyl-substituted N-heterocyclic carbene (NHC) [(3a-c) and (6a-c)] precursors were synthesised from the reaction of 1H-imidazole (1a), 4,5-dichloro-1H-imidazole (1b), and 1H-benzimidazole (1c) with p-methoxybenzyl bromide (2) and benzyl bromide (5). These NHC precursors were then treated with silver(I) acetate to yield the NHC-silver complexes [1,3-bis(4-methoxybenzyl)imidazol-2-ylidene]silver(I) acetate (4a), [4,5-dichloro-1,3-bis(4-methoxybenzyl)imidazol-2-ylidene]silver(I) acetate (4b), [1,3-bis(4-methoxybenzyl)benzimidazol-2-ylidene]silver(I) acetate (4c), (1,3-dibenzylimidazol-2-ylidene)silver (I) acetate (7a), (1,3-dibenzyl-4,5-dichloroimidazol-2-ylidene)silver(I) acetate (7b), and (1,3-dibenzylbenzimidazol-2-ylidene)silver(I) acetate (7c), respectively. The NHC precursor 3c, four NHC-silver complexes 4c and 7a-c were characterised by single-crystal X-ray diffraction method. The preliminary antibacterial activity of all the compounds was studied against Gram-negative bacteria Escherichia coli, and Gram-positive bacteria Staphylococcus aureus using the Kirby-Bauer disk-diffusion method. Almost all the NHC-silver complexes have shown high antibacterial activity compared to the NHC precursors. In addition, the NHC-silver complexes had their cytotoxicity investigated through MTT-based preliminary in vitro testing on the Caki-1 cell lines in order to determine their IC50 values. NHC-silver complexes 4a-c and 7a-c were found to have IC50 values of 7.3 (+/-6), 12.7 (+/-3), 25.2 (+/-5), 2.5 (+/-3), 10.8 (+/-4) and 12.5 (+/-4) mu M respectively on the Caki-1 cell line.