Heterobimetallic o-vanillin functionalized complexes: In vitro DNA binding validation, cleavage activity and molecular docking studies of CuII–Sn2IV analogs

The heterobimetallic chemical entities 1–4 of o-vanillin functionalized Schiff base have been synthesized and characterized by elemental analysis and spectroscopic methods viz., UV–vis, IR, ESI–mass, NMR (in 2 and 4) and EPR (in 1 and 3). The NiII–Sn2IV analogs were synthesized only for structural elucidation by NMR spectroscopy. To evaluate the biological preference with the molecular target DNA, interaction of the CuII–Sn2IV entities 1 and 3 with CT DNA has been explored by employing various biophysical methods revealing the electrostatic mode of binding via oxygen of sugar–phosphate backbone of DNA helix. The Kb values of 1 and 3 were found to be 2.31 × 104 and 3.67 × 104 M−1, respectively suggesting the greater binding propensity of 3. Furthermore, site of action was ascertained by the interaction studies of 1 and 3 with 5′-AMP employing UV–vis titrations, 1H and 31P NMR studies which implicates the preferential selectivity of these complexes to N1 of adenosine moiety. Moreover, the antimicrobial activities of 1 and 3, revealed 3 as a good antimicrobial agent. The cleavage activity of 3 was evaluated by agarose gel electrophoresis assay with pBR322 DNA, revealing the involvement of singlet oxygen species via oxidative cleavage pathway. Additionally, 3 exhibited significant inhibitory effects on the catalytic activity of Topo I at a very low concentration, 15 μM, suggesting that 3 is an efficient catalytic inhibitor of human Topo I. The computer-aided molecular docking techniques were carried out to ascertain the mode of action toward the molecular target DNA and Topo I for 1 and 3.