Synthesis, characterization and antimicrobial activity of water-soluble silver(I) complexes of metronidazole drug and selected counter-ions

A series of water-soluble silver(I) complexes of the type [Ag(MTZ)(2)X] [MTZ = 1-(2-hydroxyethyl)-2-methyl-5-nitro-1H-imidazole (metronidazole drug); X = NO3-, ClO4-, CF3COO-, BF4- and CH3SO3-] was synthesised by the reactions of various Ag(I) salts with metronidazole (MTZ). All the complexes were characterized by ESI-MS spectrometry, solution NMR (H-1 and C-13) and IR spectroscopy, and elemental analysis. Further evidence for the formation and molecular structure of all the complexes was provided by X-ray single-crystal crystallography. The different counter ions affect the crystal packing of the complexes and thus have an impact on the final geometries. The antimicrobial activities of the complexes against two Gram-positive strains: Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228, three Gram-negative strains: Pseudomonas aeruginosa ATCC 15442, Escherichia coli ATCC 25922, Proteus hauseri ATCC 13315 and yeast Candida albicans ATCC 10231 were evaluated and compared with antibacterial and antifungal properties of appropriate silver salts, metronidazole and silver sulfadiazine drugs. The newly synthesized compounds exhibited significant antibacterial activity against Gram-positive bacteria, better than the referenced silver sulfadiazine. The best active silver(I)-metronidazole complex contains a methanesulphonate counter-ion. Moreover, the complex inhibited the growth of yeast Candida albicans at a concentration 3-fold lower than that required for silver sulfadiazine. In addition, the complexes containing a tetrafluoroborate and a perchlorate as counter-ions were characterized as effective antibacterial agents against the tested Gram-negative bacteria.