DNA interaction and BSA binding of O-vanillin-based new Schiff base Co(III) and Ni(II) complexes: Theoretical, experimental, antibacterial and anticancer studies

Abstract

In the present work, two new mononuclear CoIII and NiII complexes containing H2valmea Schiff base ligand (H2valmea = 2-(((2-hydroxyethyl)imino)methyl)-6-methoxyphenol) were synthesized. X-ray crystallography, besides other techniques such as CHN, FT-IR and UV–Vis spectroscopy, determined the exact structures of both complexes. Bio-interactions (BSA and DNA binding), the antineoplastic ability and basal cell toxicity of complexes were investigated by various experimental and docking methods. Fluorescence emission and UV–Vis absorbance experiments confirmed the static mechanism in the interaction of both complexes with protein. Site marker competitive and tryptophan quenching experiments alongside docking studies revealed that CoIII complex preferred site I while NiII complex preferred site II of BSA. The main type of the complexes-protein interaction was hydrophobic forces, and FRET theory indicated that transferring energy was feasible for mononuclear complexes. Investigation of the complex-DNA interactions were done by absorption spectroscopy, ethidium bromide (EtBr) fluorescence displacement experiment, docking studies, cyclic voltammetry and viscosity measurements. All these studies suggested that NiII complex interacted with DNA by mainly intercalation mode of binding. In contrast, CoIII complex was a significantly weaker intercalator because it could not compete with EtBr in binding with DNA and revealed a lower MolDock score for intercalation than ethidium bromide in docking studies. These observations are confirmed by in vitro DNA mobility shift assay that indicated the strong inter-strand intercalation affinity of the NiII complex. Also, using the flow cytometry method, the apoptosis/necrosis pathway of the NiII complex was studied against A549 cells. The antibacterial assay showed the great bacteriocidal potency of NiII complex, while in the case of E.coli treatment, a moderate bacteriostatic behavior is seen.