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

<div><p>A series of new imidazolium salts (<b>1–4</b>) as <i>N</i>-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 (<b>5–8</b>). All compounds were characterized by physico-chemical and spectroscopic techniques. The molecular structures of <b>1</b> and <b>5</b> 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 <b>5–8</b> displayed good antibacterial activities on <i>Staphylococcus aureus</i> (ATCC 12600) and <i>Escherichia coli</i> (ATCC 11303) compared with the salts. Furthermore, it was observed that with increase in chain length at <i>N</i>-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, <b>5</b> and <b>8</b> were efficient in promoting the cleavage of nucleic acids in the presence of H₂O₂.</p>