Protein binding affinity of biologically active thiourea based half-sandwich Ru(II) cymene complexes

Half-sandwich (η⁶-p-cymene) complexes bearing either neutral functionalized N,S-bidentate thiourea ligands or a mono-negative N,N-aminoquinoline ligand were screened for their antibacterial and antifungal activities as well as cell viability against non-malignant HEK293 (human embryonic kidney cells). The haemolysis parameters (HC₁₀ and HC₅₀) were determined to get some information about the compatibility of the toxic compounds with the blood components. The protein binding affinity of hen white egg lysozyme (HEWL), a model protein, towards the synthesized (η⁶-p-cymene) complexes was investigated by ESI-MS. Metalation of HEWL was achieved through both covalent and non-covalent modes of interaction. To recognize if the metalation site of HEWL is the His15 side chain, the reactions between the complexes and imidazole were theoretically and experimentally studied by quantum chemical calculations, UV–Vis and NMR. Exchange of the nitrogen coordination site of the thiourea ligand from the pyridine to the benzothiazole moiety induced higher potency against Staphylococcus aureus, Candida albicans and Cryptococcus neoformans var. grubii.