New 4′-(4-chlorophenyl)-2,2′:6′,2″-terpyridine ruthenium(II) complexes: Synthesis, characterization, interaction with DNA/BSA and cytotoxicity studies

In this study, we have developed a series of new monofunctional Ru(II) complexes of the general formula mer-[Ru(Cl-Ph-tpy)(N-N)Cl]Cl in which Cl-Ph-tpy is 4′-(4-chlorophenyl)-2,2′:6′,2″-terpyridine, N-N is a bidentate chelating ligand (1,2-diaminoethane (en, 1), 1,2-diaminocyclohexane (dach, 2) or 2,2′-bipyridine (bpy, 3)). All complexes were fully characterized by elemental analysis and spectroscopic techniques (IR, UV–Vis, 1D and 2D NMR). Their chemical behavior in aqueous solution was studied by UV–Vis and NMR spectroscopy showing that all compounds are relatively labile leading to the formation of the corresponding aqua species 1aq–3aq. Their DNA binding ability was evaluated by UV–Vis spectroscopy, fluorescence quenching measurements and viscosity measurements. Competitive studies with ethidium bromide (EB) showed that the complexes can displace DNA-bound EB, suggesting strong competition with EB (K_sv = 1.1–2.7 × 10⁴ M^− 1). These experiments show that the ruthenium complexes interact with DNA via intercalation. The complexes bind to serum protein albumin displaying relatively high binding constants (K_sv = 10⁴–10⁵ M^− 1). Compound 3 displayed from high to moderate cytotoxicity against two cancer cell lines HeLa and A549 (with IC₅₀ ca. 12.7 μM and 53.8 μM, respectively), while complexes 1 and 2 showed only moderate cytotoxicity (with IC₅₀ ca. 84.8 μM and 96.3 μM, respectively) against HeLa cells. The cell cycle analysis (by flow cytometry) of HeLa and A549 cells treated with complex 3 shows minor changes on the cell cycle phase distribution.