Binuclear Biphenyl Organogold(III) Complexes: Synthesis, Photophysical and Theoretical Investigation, and Anticancer Activity

Abstract

A series of four binuclear complexes of general formula [(C^C)Au(Cl)(L^L)(Cl)Au(C^C)], where C^C is 4,4'-diterbutylbiphenyl and L^L is either a bridging diphosphine or 4,4'-bipyridine, are synthetized with 52 to 72 % yield and structurally characterized by X-ray diffraction. The use of the chelating 1,2-diphenylphosphinoethane ligand in a 1 : 2 (P^P):Au stoichiometry leads to the near quantitative formation of a gold double-complex salt of general formula [(C^C)Au(P^P)][(C^C^)AuCl₂ ]. The compounds display long-lived yellow-green phosphorescence with λ_em in the range of 525 to 585 nm in the solid state with photoluminescence quantum yields (PLQY) up to 10 %. These Au^III complexes are tested for their antiproliferative activity against lung adenocarcinoma cells A549 and results show that compounds 2 and 5 are the most promising candidates. The digold salt 5 shows anticancer activity between 66 and 200 nM on the tested cancer cell lines, whereas derivative 2 displays concentration values required to reduce by 50 % the cell viability (IC₅₀ ) between 7 and 11 μM. Reactivity studies of compound 5 reveal that the [(C^C)Au(P^P)]⁺ cation is stable in the presence of relevant biomolecules including glutathione suggesting a structural mechanism of action.

Keywords: antitumor agents; cytotoxicity; gold; luminescence; medicinal chemistry.