Novel, Biologically Imperative, Highly Versatile and Planar Systems: Synthesis, Characterization, Electrochemical Behavior, DNA Binding and Cleavage Properties of Substituted β-Diketimine Copper(II) and Zinc(II) Complexes with Dipyrido(3,2-a:2, 3 -c)phenazine Ligand

Novel copper(II) and zinc(II) complexes of the type [ML(dppz)]Cl2, [L = Schiff base derived from the condensation of 3-(3-phenyl-allylidene)-pentane-2,4-dione and para-substituted aniline; X = -NO2 (L1), -H (L2), -OH (L3) and -OCH3 (L4); dppz = dipyrido (3,2-a:2 ',3' -c)phenazine] were synthesized and characterized by various analytical and spectral techniques. The physico-chemical studies and spectral data indicated that all the complexes were monomeric and cationic with square-planar geometry. Spectroscopic data and viscosity measurements showed that the complexes intercalated to DNA with large binding constants. The substituted groups such as -NO2, -H, -OH and -OCH3 in aniline moiety influenced the observed trend in the redox potentials of the complexes. The peak potential separation and formal potential of complexes were independent of sweep rate or scan rate (ν) indicating a quasireversible one-electron redox process. In all the cases, ip was linear function of ν1/2, as expected for diffusion controlled process, and ipa/ipc ≈ 1 at all sweep rates. It was found that the decrease in ipc was due to the higher binding of copper complexes and slowly diffusing DNA. In the presence of a reducing agent like 3-mercaptopropionic acid (MPA), the chemical nuclease activity order of the copper complexes under dark reaction condition was -NO2 > -H > -OH > -OCH3. The hydrolytic cleavage of DNA by the zinc complexes was supported by the evidence from free radical quenching and T4 ligase ligation.