The tridentate Schiff base ligand o-vanillin salicylhydrazone was derived from aromatic o-vanillin and isonicotinic acid hydrazide, and its Fe(III) and Ni(II) coordination polymers ((FeHLCl2·H2O)n and (Ni2L2phen2)n, H2L = o-vanillin salicylhydrazone, phen = 1,10-phenanthroline) were prepared and fully characterized. The crystal structures of both complexes were determined by X-ray single-crystal diffraction. The interaction of the free ligand H2L and the corresponding complexes with herring sperm DNA (HS-DNA) was estimated by absorption and emission titration methods, which revealed that the compounds interacted with HS-DNA through an intercalation mode. The binding of the compounds with bovine serum albumin (BSA) protein investigated using UV-visible and fluorescence spectroscopic methods indicated that strong binding interaction exists between the complexes and BSA compared to the ligand H2L. The alterations in the secondary structure of the protein by the complexes were confirmed by synchronous fluorescence spectroscopic studies. Molecular docking calculations revealed that the complexes bind through extensive hydrogen bonding, hydrophobic and van der Waals interactions with DNA and BSA. Investigation of their antioxidative properties showed that the polymeric Ni(II) complex has a strong radical scavenging potency against nitric oxide and superoxide anion radicals. Further, in vitro cytotoxicity studies of the ligand H2L and its complexes found that the Ni(II) complex exhibited substantial anticancer activity against human lung adenocarcinoma cell lines A549 with an IC50 value of 11.67 μM, and has shown higher activity than the well-known anticancer drug cisplatin.
