Synthesis and characterization of dimeric Schiff base Co^II, Ni^II, Cu^II complexes for their catalytic application of aerobic oxidation of alcohol and interaction with biomolecules

Three new transition metal (Co(II), Ni(II) and Cu(II)) complexes of Schiff's base ligand were prepared in situ by refluxing stoichiometric amounts of respective metal salts with 2-hydroxy-1-naphthaldehyde and 2-picolylamine. The structural feature of the synthesized complexes was derived from spectral (FT-IR, UV–Vis and ESI-mass) studies and elemental analysis. The single crystal X-ray diffraction analysis of complex 3 showed the structure as dimeric form [Cu(2-hnppa)Cl]₂ and each copper atom is penta-coordinated. The calculated τ value of [Cu(2-hnppa)Cl]₂ was 0.25 (where α = 157.84 and β = 172.18) indicating the square pyramidal geometry. Binding of these complexes (1–3) with calf thymus DNA was investigated by UV–Vis, fluorescence, viscosity measurements and computer aided molecular docking studies and the K_b value of complexes 1–3 were 2.4 × 10⁵, 5.9 × 10⁵ and 2.0 × 10⁴M⁻¹, respectively. The relative binding energies of the metal complexes 1–3 docked with DNA were −151.82, −151.86 and −151.80 eV, respectively. Complexes (1–3) exhibited a good binding capability with bovine serum albumin (BSA) with relatively high binding constant values. The complexes also act as a catalyst that enables efficient aerobic oxidation of a broad range of alcohols (benzyl alcohol, n-octanol) to the corresponding aldehydes at room temperature with ambient air as the oxidant.