Synthesis, structural characterization of dinuclear copper(II) complexes based on Schiff base derived ligands and their impacts on DNA-binding affinities

Two binuclear copper (II) complexes ([Cu2(L1)2(Py)4] (1) and [Cu2(L2)2(Py)4] (2) where H2L1 (3-((2-hydroxybenzylidene)amino)benzoic acid and H2L2 (3-((2-hydroxy-5-nitrobenzylidene)amino)benzoic acid) have been synthesized and characterized by analytical and different spectroscopic technique. The X-ray diffraction analysis of both 1 and 2 complexes revealed that the geometry around the copper (II) centres are distorted square pyramidal. The crystal lattice in both 1 and 2 are stabilized by several types of intermolecular hydrogen bonds and & pi;...& pi; interactions. The intermolecular interactions on the crystal packing of 1 and 2 have been further studied by Hirshfeld surface analysis and corresponding 2D fingerprint plots. The interaction of 1 and 2 with calf thymus DNA (ct-DNA) have also been evaluated using absorption and fluorescence techniques and the result indicates that both 1 and 2 can bind to ct-DNA via an intercalative mode. The binding constant using absorption spectra between 1 with ct-DNA and 2 with ct-DNA have been found to be (10.3 & PLUSMN; 0.02) x 104 M-1 and (6.91 & PLUSMN; 0.01) x 104 M-1 respectively. Molecular docking studies also support the partial insertion of both 1 and 2 into the DNA backbone. Importantly, in Cu(II) complex 2, the Schiff base ligand possessing a significant electron withdrawing -NO2 group exhibits less interaction with ct-DNA compared to 1, containing less or no electron withdrawing character Schiff base.