DFT/TD-DFT calculation, photophysical properties, DNA/protein binding and catecholase activity of chelating ligand based trigonal bipyramidal copper(II) complexes

Abstract

Cu(II) complexes [Cu(L)(bipy)]ClO4 (1) and [Cu(L)(phen)]ClO4 (2) (where HL = 2-[(3-Methylamino-propylimino)-methyl]-phenol, bipy = 2,2′-bipyridine and phen = 1,10-phenanthroline) have been synthesized and characterized by single crystal X-ray diffraction studies, FT-IR spectra, ESI-MS, electronic absorption, and emission spectroscopy. Both the Cu(II) complexes are mononuclear with five coordinated distorted trigonal bipyramidal geometries and the π-conjugated bipy and phen favor the formation of 2D supramolecular structures with CH … π and π … π interactions. DFT/TD-DFT calculations were performed using B3LYP, B3PW91 and MPW1PW91 functionals to explain the experimentally observed molecular structure and electronic absorption spectral properties. Complexes are active for catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) in presence of molecular oxygen. Interactions of complexes with bovine serum albumins (BSA) and human serum albumins (HSA) have been studied by electronic absorption and emission spectroscopy and the calculated values of binding constants are 6.91 × 105 L mol−1 (1-BSA), 6.16 × 105 L mol−1 (1-HSA), 6.57 × 105 L mol−1 (2-BSA) and 3.80 × 105 L mol−1 (2-HSA). Electronic absorption and fluorescence spectroscopic studies reveal that interactions of complexes with CT-DNA occur through intercalative binding mode.