Mixed ligand copper(II) complexes of diimine co-ligands: Synthesis, characterization, DNA binding and DNA cleavage activity

Abstract

Four mixed ligand copper(II) complexes having general formula [Cu(acox)(diimine)]2+1–4, (acox is acenaphthylene-1,2-dione dioxime) have been synthesised and characterized by suitable analytical techniques. The diimine ligands used for the isolation of complexes are bipyridine (bpyn 1), phenanthroline (phne, 2), phenanthroline-5,6-dione (5,6-dione, 3) and dipyridoquinoxaline (dpqn, 4). The degree of binding affinity of complexes with DNA has been assessed using UV–Visible absorption spectroscopic technique, which reveals that the complex that possesses dpqn ligand binds with DNA more strongly than its analogue complexes. The planar geometry of dpqn ligand assists the intercalation of complex partially in between the nucleobases of DNA. On the other hand, the higher hydrophobicity of 5,6-dione in 3 is accountable for its higher DNA-binding affinity than that of bpyn and phne complexes. The trend of DNA binding affinity of complexes observed by ethidium bromide displacement assay and viscosity studies attest the results observed in absorption spectral titration of complexes with DNA. All the four Cu(II) complexes cleave supercoiled plasmid DNA in ACN/Tris(HCl)-NaCl buffer in the absence of an activating agent. Also, these complexes display prominent DNA cleavage activity in presence of hydrogen peroxide and the results indicated that the DNA-cleaving ability of complexes varies in the order 4 > 3 > 2 > 1, and the highest ability of 4 in H2O2 to cleave DNA indicates that it could be developed as efficient chemical nuclease.