New palladium(ii) and platinum(ii) complexes with an ONS donor azo-thioether pincer ligand: synthesis, characterization, protein binding study and in vitro cytotoxicity

Abstract

New Pd(II) and Pt(II) complexes, [Pd(L)Cl] (1) and [Pt(L)Cl] (2), with an O,N,S donor azo-thioether pincer ligand (HL) are synthesized and thoroughly characterized by spectroscopic techniques. X-Ray structures of the complexes revealed the distorted square planar geometry around the central metal ions. Electronic structures and spectral properties are interpreted by DFT and TDDFT calculations. Interaction of the complexes with CT-DNA and BSA proteins is studied by absorption and fluorescence methods. Fluorescence titration revealed that the complexes strongly quench DNA bound ethidium bromide (EB) as well as the intrinsic fluorescence of BSA protein through static quenching. The high binding constants (K_b) obtained from the DNA binding studies promoted in vitro cytotoxicity assays of the complexes in various human cancer cell lines (colon cancer cell line HCT116, lung cancer cell line A549 and liver cancer cell line HepG2). The half maximal inhibitory concentrations (IC₅₀) of complexes 1 and 2 are found to be less compared to cisplatin.