Pyridylbenzimidazole-Based Gold(III) Complexes: Lysozyme Metalation, DNA Binding Studies, and Biological Activity

The lysozyme binding affinity of new Au(III) complexes, bearing pyridylbenzimidazole ligands, was investigated by ESI-MS and UV/Vis. Metalation of lysozyme happened mainly by {Au}ⁿ⁺, {AuCl}^0/n+ and {AuCl₂}^n+/–. The appendage sulfonate group of pyridylbenzimidazole ligand system played a role in determining the products of interaction of HEWL with Au(III) complexes. The hydrophilic sulfonate group inhibited the ligand cleavage via the participation in several coulombic and H-bond interactions giving several AuLⁿ⁺ containing adduct peaks (L = 1-[(pyridin-2-yl) benzimidazole]-propyl-sulfonic acid). The stability of the complexes in presence of ascorbic acid was examined by UV/Vis and ¹³C NMR. To recognize if His15 side-chain is the metalation site of HEWL, the interactions between the complexes and imidazole, as a simple model of histidine, were investigated by ¹H and ¹³C NMR. The DNA binding studies of the complexes were reported. For this class of Au(III) complexes, it is preferred to decorate the pyridylbenzimidazole system with ethyl group rather than sulfonate and phthalimido group to have a complex with interesting antifungal activity against Candida albicans and Cryptococcus neoformans var. grubii. Au(III) complex, having sulfonate group, is noncytotoxic to non-malignant cells (human embryonic kidney cells (HEK293)), shows negligible hemoglobin release and is safe to the normal cells if applicable.