Heteroleptic complexes of hydrazone Scaffold of picolinoyl N- oxide and 2,4 dihydroxy phenyl moieties; evaluation of antioxidant activity, DNA and protein binding properties and in vitro antiproliferation studies

The present study deals with design and synthesis of new mononuclear Cu(II), Co(II), Ni(II) and Zn(II) metal complexes of hydrazone of 2-(2-(2,4-dihydroxybenzylidene)hydrazinecarbonyl)pyridine-1-oxide (H₂L), in a view to study their potential relevance for the biological applications. Structural aspects of the title compound (H₂L) and metal complexes synthesized were evaluated by spectral and analytical methods viz. ¹H NMR, ¹³C NMR, LC-MS, FT-IR, UV–Visible, SEM, EDX, Powder XRD, ESR, TGA and DTA. Ligational properties of H₂L were explored by employing pH metric equilibrium studies for recognizing metal ion binding potential donor sites, and further HyperChem 7.5 software for computing properties of frontier molecular orbitals to ascertain orientation of highest occupied molecular orbitals from which presumably electrons are donated to metal ion in complex formation. The affinity of all title compounds to bind with CT-DNA and the type of interaction, therein have been studied by conducting UV–VIS absorption and fluorescence emission titrations. The protein-binding ability of all metal complexes with two serum proteins (BSA and HSA) were explored by absorption titrations, and further fluorescence titrations for BSA binding were also performed. Antioxidant activity of the title compounds was carried out by the method of free radical scavenging using spectrophotometric technique. Additionally, cytotoxicity of all metal complexes and ligand was measured by CTG cell proliferation assay after treating them with MDA-MB-231 and SKOV-3 cell lines. The cell cycle arrest and apoptosis assay in above cell lines after treatment with title compounds were also investigated by flow cytometry. In addition, molecular docking studies at target CDK2 protein inferred binding affinity of the title compounds through non covalent bonding interactions.