A new tetradentate diimine-dioxime ligand containing a donor set of N-4, and its homo-, heterodinuclear and homotrinuclear copper(II) complexes were prepared and characterized on the basis of their elemental analysis, FT-IR, H-1 and C-13 NMR spectra, molar conductivity and magnetic moment measurements. The extraction ability of N,N ''-bis[1-biphenyl-2-hydroxyimino-1-ethylidene]-diethylenetriamine was also evaluated in chloroform by using several transition metal picrates such as Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), U(II) and Hg(II). It has been seen that the ligand shows strong binding ability toward the copper(II) ion. Moreover, the catalytic activities of the complexes for the disproportionation of hydrogen peroxide were investigated in the presence of imidazole. The synthesized complexes display efficiency in the disproportion reactions of hydrogen peroxide, producing water and dioxygen in catalase-like activity. The interaction between these complexes and DNA has also been investigated by agarose gel electrophoresis. We found that the homo- and heterodinuclear copper complexes can cleave supercoiled pBR322 DNA to nicked and linear forms. The dinuclear complexes including phenanthroline (2-4), with H2O2 as a co-oxidant, exhibited the strongest cleaving activity. (C) 2009 Elsevier Ltd. All rights reserved.