Triphenylphosphine Thiolate Gold(I) Complexes with Redox-Active Schiff Bases: Synthesis, Electrochemical Properties, and Biological Activity

Abstract

New gold(I) phosphine thiolate complexes [(Ph3P)Au(SLn)] I–V with Schiff bases LnSH containingredox-active catechol, phenol, or quinone methide moieties were synthesized and characterized. Themolecular structure of compound I in the crystalline state was established by X-ray diffraction (CCDCno. 2237815). The electrochemical behavior of compounds I–V was studieв by cyclic voltammetry. The proposedelectrooxidation mechanism of the complexes involves the Au–S bond cleavage, the disulfide formation,as well as the oxidation of the redox active group of the ligand. In the cathode region, complexes I–IIItend to form relatively stable monoanionic species. The radical scavenging activity of complexes decreases incomparison to free ligands in the reactions with synthetic radicals and the CUPRAC test. Compounds I, II,IV, and V have no clear-cut effect on the promoted DNA damage; however, they show antioxidant actionin the non-enzymatic lipid peroxidation of rat liver homogenate. Compounds I–V demonstrate a weak antibacterialactivity against Staphylococcus aureus strains. The gold(I) complexes cytotoxicity was studied againstA-549, MCF-7, and HTC-116 cancer cell lines using MTT assay. The test compounds are characterized byhigher selectivity to certain types of cells than the sulfur-containing Schiff bases. The presence of quinonemethide moiety in the ligand in case of V significantly increases the cytotoxicity against all of the cell lines.