Dose‐, time‐and lipophilicity‐dependent silver(I)–N‐heterocyclic carbene complexes: Synthesis, characterization and interaction with plasmid and Aedes albopictus DNA

Four new Ag(I)–N-heterocyclic carbene (NHC) complexes (5–8) bearing symmetrically substituted NHC ligands have been synthesized starting from the corresponding benzimidazolium bromide salts which are accessible in a single step from N-substituted benzimidazoles (N-alkyl and N-aryl) and subsequently reacted with the basic metal source Ag2O in acetonitrile–methanol. These compounds were characterized using elemental analyses, 1H NMR, 13C NMR, Fourier transform infrared and UV–visible spectroscopic techniques, and molar conductivity. Single-crystal structural studies for complex 5 show that the Ag(I) centre has a perfectly linear C–Ag–C coordination, with quasi-parallel pairs of aromatic benzimidazole planes. All the complexes interact with Aedes albopictus DNA via intercalation mode by a large hypochromicity of 22 and 27% and smaller hypochromicity of 16 and 19%. Furthermore, all complexes exhibit efficient DNA cleavage activity via a non-oxidative mechanistic pathway. The DNase activities of the test compounds revealed a time- and concentration-dependent activity pattern. The Ag(I)–NHC complexes showed considerably higher DNA cleavage activity compared to their respective benzimidazolium salts at a lower concentration. The DNA cleavage of these complexes changed from a moderate effect to a good one, corresponding to the increasing lipophilicity order of the complexes as 5 < 6 < 7 < 8 (1.02, 1.05, 1.78 and 2.06 for 5–8, respectively). This order is further corroborated with the DNA binding study, but with the exception of complex 5, which shows a better binding ability for DNA (Kb = 3.367 × 106) than complexes 6–8 (6.982 × 105, 8.376 × 105 and 1.223 × 106, respectively).