New polyaza macrobicyclic binucleating ligands and their binuclear copper(II) complexes: Electrochemical, catalytic and DNA cleavage studies

A new symmetrical polyaza macrocyclic binucleating ligand L-1 and its permethylated derivative ligand L-2 have been synthesized by using the precursor compound 2-[2-(2,6-diformyl-4-methylphenoxy)propoxyl]-5-methylisophthalaldehyde and bis(aminoethyl) amine. The molecular structure of the precursor compound and the ligand L-2 were determined by the single crystal XRD method. The ligands L-1 and L2 were treated with two equivalents of Cu(ClO4)(2) center dot 6H(2)O to afford the new binuclear complexes [Cu2L1(mu-OH)(ClO4)(2)](ClO4) (1) and [Cu2L2(mu-OH)(ClO4)(2)](ClO4) (2), respectively. Both the complexes were characterized by elemental and spectral methods. A cyclic voltammetric investigation of these Cu(II) complexes show a quasireversible followed by an irreversible one electron reduction processes around E-pc(1) = -0.59 V, -0.55 V and E-pc(2) = -1.07 V, -1.02 V. ESR spectra of the copper(II) complexes 1 and 2 show a broad signal at g = 2.08 and 2.10, and mu(eff) values of 1.43 and 1.46 BM, respectively, which convey a spin-spin interaction between the two copper(II) ions. The initial rate (V-in) for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the binuclear Cu(II) complexes 1 and 2 are 1.15 X 10(-4) and 1.66 x 10(-4) Ms-1 respectively. Both the complexes remarkably promote the hydrolytic cleavage of super-coiled plasmid DNA under physiological conditions in the presence of H2O2 at pH 7.2 and 37 degrees C. The reaction profile for the complex 1 mediated reaction displayed approximately pseudo-first-order kinetic behavior, with k(obs) similar to 0.07 min(-1) and R-2 = 0.984. (C) 2008 Elsevier Ltd. All rights reserved.