DNA binding, protein interaction, radical scavenging and cytotoxic activity of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde(2′-hydroxybenzoyl)hydrazone and its Cu(II) complexes: A structure activity relationship study

Two new copper(II) complexes have been synthesized by reacting 2-oxo-1,2-dihydroquinoline-3-carbaldehyde(2′-hydroxybenzoyl)hydrazone (H2L) (1) with CuCl2·2H2O or Cu(NO3)2·3H2O, in order to obtain a clear picture on the role of counter ion in the biological properties of the complexes so obtained. Single-crystal X-ray diffraction studies revealed that both the complexes [CuCl(HL)(H2O)]·CH3OH (2) and [Cu(HL)(CH3OH)2]NO3 (3) have square pyramidal geometry with the ligand coordinating through uni-negative tridentate ONO− fashion. The UV–Vis and fluorescence spectroscopy experimental evidences strongly suggested that the ligand and the two Cu(II) complexes could interact with calf thymus DNA (CT-DNA) through intercalation. The interactions of the compounds to bovine serum albumin (BSA) were investigated by UV–Vis, fluorescence and synchronous fluorescence spectra. The results indicated that all the three compounds could quench the intrinsic fluorescence of BSA in a static quenching way. Investigations of antioxidative properties showed that all the compounds have strong radical scavenging properties. Cytotoxic studies showed that the two copper(II) complexes exhibited effective cytotoxic activity against HeLa cancer cells. Overall, the complex 3 has exhibited better biological activity than that of the complex 2 and the ligand.