Synthesis, crystal structures, DNA binding and cleavage activity of water soluble mono and dinuclear copper(II) complexes with tridentate ligands

•Water soluble mono and dinuclear copper(II) complexes are reported.•In mononuclear complex copper has distorted square pyramidal structure.•In dinuclear complex copper atoms are bridged with phenolate oxygen atoms.•Mononuclear complexes bind DNA more strongly than dinuclear complexes.•Dinuclear complexes exhibit higher nuclease activity.

Water soluble mono and dinuclear copper(II) complexes of novel tridentate ligands have been synthesized and characterized by spectroscopic methods and single crystal X-ray diffraction analysis. X-ray crystallographic studies reveal that the structure of mononuclear copper(II) complex with 2-[1-(methylamino-ethylimino)-ethyl]-phenol [Cu(HAPMEN)(H2O)2]NO3 has distorted square pyramidal structure whereas the dinuclear complex with 2-[1-(proylamino-ethylimino)-methyl]-phenol [Cu(SAPEN)]2(ClO4)2 has square planar geometry. Electrochemical behavior of these complexes was investigated by cyclic voltammetric studies. The complexes show quasi reversible cyclic voltammetric responses for the Cu(II)/Cu(I) couple. The binding properties of these complexes with calf-thymus DNA have been investigated by using absorption spectrophotometry. Mono nuclear complexes show unusually high binding affinity possible due to presence the labile aqua ligands. Cleavage activities of these complexes have been investigated on double stranded pBR 322 plasmid DNA by gel electrophoresis experiments under different conditions. Dinuclear complexes exhibit higher nuclease activity when compared with those of mononuclear complexes. The studies indicate that the cleavage of DNA takes place by oxidative mechanism in the presence of oxidant (H2O2).

Graphical abstractWater soluble mono and dinuclear copper(II) complexes are reported. In mononuclear complex copper is 5-coordinate and has distorted square pyramidal structure while in dinuclear complex it is only 4-coordinate containing phenolate bridging atoms. The complexes cleave DNA quite efficiently by oxidative mechanism. Mononuclear complexes bind DNA more strongly than corresponding dinuclear complexes possibly due to the labile aqua ligands. Dinuclear complexes exhibit higher nuclease activity when compared with corresponding/related mononuclear complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide