Design, synthesis, characterization and evaluation of the anticancer activity of water-soluble half-sandwich ruthenium(ii) arene halido complexes

The synthesis, detailed characterization, and investigation of the DNA- and BSA-binding affinity and cytotoxicity of three half-sandwich Ru(ii) arene chlorido complexes (1-3) are reported. Specifically, organometallic complexes [(eta(6)-p-cymene)(L-1)RuCl]Cl (1), [(eta(6)-p-cymene)(L-2)RuCl]Cl (2) and [(eta(6)-p-cymene)(L-3)RuCl]Cl (3) [L-1 = 2-(1H-benzo[d]imidazol-2-yl)quinolone, L-2 = 2-(quinolin-2-yl)benzo[d]oxazole, and L-3 = 2-(quinolin-2-yl)benzo[d]thiazole] were synthesized using [((eta(6)-p-cymene)Ru(mu-Cl)Cl)(2)] and L-1-L-3. All the complexes were characterized by various spectroscopic and analytical methods. Complex 1 was also characterized by single crystal X-ray diffraction analysis, the results of which are in-line with the piano-stool structure elucidated from the spectroscopic methods. Cyclic voltammetry of 1-3 showed good stability of the Ru(ii) state. The interactions of 1-3 with CT-DNA were investigated by UV-Vis studies and competitive binding with ethidium bromide (EthBr) using emission spectroscopy. Steady-state fluorescence quenching and synchronous fluorescence studies were performed to understand the interactions between 1-3 and bovine serum albumin (BSA). The geometry optimization of 1-3 was performed using the density functional theory (DFT). Complexes 1 and 2 were investigated for DNA binding using theoretical calculations. Molecule complexes 1-DNA and 2-DNA were huge (482-483 atoms, 2442 electrons) for any level of quantum chemical analysis. The semi-empirical PM6 method, which is more accurate than the force-field methods, was used, and the result suggested that several strong and weak electrostatic and intermolecular hydrogen bonding interactions exist between the outer edge of DNA and complexes 1 and 2. In addition, the in vitro cytotoxicity of L-1-L-3 and complexes 1-3 against a breast cancer cell line (MCF-7) was investigated by MTT cytotoxicity analyses. The studies performed here show that these complexes exhibit a good binding behavior with DNA and BSA and show good anticancer potency towards MCF-7 cells.