Antimicrobial Activity of Anionic Bis(-Heterocyclic Carbene) Silver Complexes.

The antimicrobial properties of a series of anionic bis(carbene) silver complexes Na[Ag(NHC)] were investigated (- and , where NHC is a 2,2'-(imidazol-2-ylidene)dicarboxylate-type -heterocyclic carbene). The complexes were synthesized by the interaction of imidazolium dicarboxylate compounds with silver oxide in the presence of aqueous sodium hydroxide. Complexes , were characterized analytically and spectroscopically, and the ligand precursor and complexes and were structurally identified by X-ray diffraction methods. The anions of and , [Ag(NHC)], showed a typical linear disposition of C-Ag-C atoms and an uncommonly eclipsed conformation of carbene ligands. The antimicrobial properties of complexes -, which contains chiral (- and ) and non-chiral derivatives (,,), were evaluated against Gram-negative bacteria, and , and a Gram-positive bacterium, . From the observed values of the minimal inhibitory concentration and minimal bactericidal concentration, complexes and showed the best antimicrobial activity against all strains. An interesting chirality-antimicrobial relationship was found, and eutomer showed better activity than its enantiomer against the three bacteria. Furthermore, these complexes were investigated experimentally and theoretically by Ag nuclear magnetic resonance, and the electronic and steric characteristics of the dianionic carbene ligands were also examined.