Antimicrobial activities of bis-(N-alkylbenzimidazole)-cobalt(II) and zinc (II) complexes

Eight benzimidazole precursors (L), namely 1-allyl-benzimidazole, 1-methallyl-benzimidazole, 1-isopropyl-benzimidazole, 1-(3-methyloxetan-3-yl)methyl-benzimidazole, 1-allyl-5,6-dimethyl-benzimidazole, 1-methallyl-5,6- dimethyl-benzimidazole, 1-isopropyl-5,6-dimethyl-benzimidazole and 1-(3-methyloxetan-3-yl)methyl-5,6- dimethyl-benzimidazole, were coordinated to cobalt(II) and zinc(II) cations to form complexes of the type [MCl2L2]. Single-crystal X-ray structures were determined for two cobalt(II) and for one zinc(II) complexes and confirmed their tetrahedral molecular geometry. The antibacterial and antifungal activities of these two series of cobalt(II) and zinc(II) complexes were studied against Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae), Gram-positive (Staphylococcus aureus, methicillin-resistant S. aureus and Enterococcus faecalis) bacteria and fungal strains (Candida albicans and Candida glabrata). Overall, cobalt(II) complexes were more effective than the zinc(II) complexes against all microorganisms. The most significant results were obtained with the two dichloro-bis(1-allyl-5,6-dimethylbenzimidazole)-cobalt(II) and dichloro-bis(1-methallyl-5,6-dimethylbenzimidazole)-cobalt(II) complexes against Candida albicans and Candida glabrata fungi with measured minimal inhibitory concentrations as low as 0.024 μmol/mL, values close to those obtained with the commercially available drug Flucanozole (0.020 μmol/mL).