Exploring benzene Ru(II) complexes of 2-subsitituted quinoline/napthyridine ligands: Synthesis, biomacromolecular binding and DFT investigations

Abstract

This work reports the synthesis of 2-substituted quinoline/napthyridine ligands by a Friedländer condensation which are employed for the synthesis of half-sandwich benzene ruthenium(II) complexes having formula [(benzene)RuIIL(N∩N)Cl]+. These complexes have been characterized spectroscopically by IR, UV, 1H, and 13C NMR, HR-MS and SC-XRD techniques. The interaction of the [2]PF6 with ct-DNA and HSA have been evaluated using UV–Vis absorption spectroscopy. The binding constants for ct-DNA - [2]PF6 and HSA - [2]PF6 complex were found to be in the order of 104 M–1, which suggests that HSA can transport the complex toward the potential target sites. Furthermore, competitive displacement assay and viscosity measurement reflect that the [2]PF6 binds to the groove region of DNA. Moreover, molecular docking studies with HSA and DNA corroborated the outcome of experimental binding studies, underscoring the potential of these Ru(II) complexes as potential candidates for various biological activities. DFT studies reveal the existence of strong hydrogen bonds (about -35 kJ/mol) between the hydrogens of the -NH2 group (of the cationic part of the complex) and the counter anions (Cl− and PF6−). The existence of NH···Cl− and NH···F (of PF6−) hydrogen bonds in [2]Cl and in [2]PF6 were confirmed with the help of atom-in-molecule (AIM) and non-covalent interaction index (NCI) analysis. The negative H(rc) values obtained from AIM analysis indicates the partial covalent character of the NH···Cl− and N-H···F (of PF6−) hydrogen bonded interaction in [2]Cl and [2]PF6 complexes.