Crystal structure, theoretical and experimental electronic structure and DNA/BSA protein interactions of nickel(II) N2O2 tetradentate Schiff base complexes

Abstract

Nickel(II) allyl arm Schiff base complexes ([NiL1] and [NiL2]) were synthesized and characterized by elemental analysis and ESI-MS, FT-IR, UV–Vis and 1H NMR spectral techniques. The structure of [NiL1] and [NiL2] were analyzed by single crystal X-ray crystallography reveal nickel complexes have slightly distorted square planar geometry around the metal ions. DFT calculations for [NiL1] and [NiL2] in gas phase were performed using SDD basis set for nickel atom and 6-311G(d,p) basis set for the remaining atoms and also at PW91/TZ2P/ZORA level. The electronic transitions of the complexes in acetonitrile were studied by TD-DFT calculations. The energy decomposition analysis was performed to understand the nature of bonding between Ni(II) and Schiff bases (H2L1 and H2L2) suggests that more covalent nature of bonding is in metal complexes. Hypochromism in absorption spectra, emission intensity decrease in EB-DNA complex and DNA viscosity increase by the addition of increasing concentration of the metal complex indicate intercalative mode of binding of the complex with DNA. The binding constants calculated are of the order of 105M−1. The BSA protein binding behavior with [NiL1] and [NiL2] were investigated using absorption and fluorescence titration experiments show alteration in protein’s microenvironment. Also, molecular docking studies were performed to understand the DNA-complex interactions.