Antimicrobial Properties of Amino-Acid-Derived N-Heterocyclic Carbene Silver Complexes.

Complexes {Ag[NHC]} (R = H, ; Me, and ; Pr, ; Bu, ), were prepared by treatment of imidazolium precursor compounds [Im] (2-(3-mesityl-1-imidazol-3-ium-1-yl)acetate, , ()-2-(3-mesityl-1-imidazol-3-ium-1-yl)acetate, -, and ()-2-methyl(3-mesityl-1-imidazol-3-ium-1-yl)acetate, , with AgO under appropriate conditions. They were characterised by analytical, spectroscopic (IR, H, and C NMR and polarimetry), and X-ray methods (). In the solid state, is a one-dimensional coordination polymer, in which the silver(I) cation is bonded to the carbene ligand and to the carboxylate group of a symmetry-related Ag[NHC] moiety. The coordination environment of the silver centre is well described by the DFT study of the dimeric model {Ag[NHC]}. The antimicrobial properties of these complexes were evaluated versus Gram-negative bacteria and . From the observed MIC and MBC values (minimal inhibitory concentration and minimal bactericidal concentration, respectively), complex showed the best antimicrobial properties (eutomer), which were significantly better than those of its enantiomeric derivative (distomer). Additionally, analysis of MIC and MBC values of - reveal a clear structure-antimicrobial effect relationship. Antimicrobial activity decreases when the steric properties of the R alkyl group in {Ag[NHC]} increase.