Synthesis, characterization, computational and DNA interaction studies of mono- and dinuclear Ru(ii) complexes containing terpyridine and p-cymene ligands

Abstract

Herein, we present the development of three heteroleptic ruthenium complexes {two mononuclear [(tpy)Ru(phpy)Cl]ClO₄; [1], [(p-cym)Ru(phpy)Cl]ClO₄; [2], and a dinuclear [(tpy)RuCl(μ-phpy)Ru(p-cym)Cl](ClO₄)₂; [3]} using terpyridine (tpy), p-cymene (p-cym) and semi-flexible phenanthroline-pyrazine-based (phpy) ligands. The formation of 1–3 was confirmed by HRMS, and ¹H and ¹³C NMR spectroscopy. Furthermore, ¹H–¹H correlation spectroscopy was also done to support the possible assignment of the dinuclear 3. The redox and optical properties of the complexes were studied using cyclic voltammetry and UV-Vis spectroscopy. The DNA binding interaction study of the complexes was investigated utilizing the UV-Vis absorption titration and EB-displacement assay employing calf-thymus DNA (ct-DNA). The complexes display binding constants (K_b) of 5.5 × 10³ M⁻¹, 5.7 × 10³ M⁻¹ and 8.2 × 10³ M⁻¹ and the Stern–Volmer constants (K_SV) 2.7 × 10⁵ M⁻¹, 1.3 × 10⁴ M⁻¹, and 1.1 × 10⁵ M⁻¹ for 1, 2, and 3, respectively. The observed K_b and K_SV values are found to be governed by the rigidity, planarity and labile Cl⁻ functionality present in the complexes. The results demonstrate a moderately strong mixed mode of interaction between the complexes and CT-DNA and suggest their potential to act as good anticancer agents.