Synthesis and crystal structures of sterically tuned ether functionalized NHC-silver(I) complexes: antibacterial and nucleic acid interaction studies

A series of new imidazolium salts (1-4) as N-heterocyclic carbene (NHC) precursors have been synthesized by successive N-alkylation method. Reactions of these salts with Ag2O by varying the metal to salt ratio forms a series of new Ag(I)-NHC complexes (5-8). All compounds were characterized by physico-chemical and spectroscopic techniques. The molecular structures of 1 and 5 were characterized by single-crystal X-ray diffraction analysis. A comparative investigation of the bacterial growth inhibition potential of the salts and respective complexes indicates that 5-8 displayed good antibacterial activities on Staphylococcus aureus (ATCC 12600) and Escherichia coli (ATCC 11303) compared with the salts. Furthermore, it was observed that with increase in chain length at N-positions, the antibacterial activities also increased. Nuclease activity of the reported salts and Ag (I)-NHC complexes with nucleic acids (DNA and RNA) were also studied using agarose gel electrophoresis; the results show that the compounds do not have any apparent interaction with nucleic acids in the absence of hydrogen peroxide (H2O2). However, 5 and 8 were efficient in promoting the cleavage of nucleic acids in the presence of H2O2.