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

A new symmetrical polyaza macrocyclic binucleating ligand L1 and its permethylated derivative ligand L2 have been synthesized by using the precursor compound 2-[2-(2,6-diformyl-4-methylphenoxy)propoxy]-5-methylisophthalaldehyde and bis(aminoethyl) amine. The molecular structure of the precursor compound and the ligand L2 were determined by the single crystal XRD method. The ligands L1 and L2 were treated with two equivalents of Cu(ClO4)2 · 6H2O to afford the new binuclear complexes [Cu2L1(μ-OH)(ClO4)2](ClO4) (1) and [Cu2L2(μ-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 Epc1 = −0.59 V, −0.55 V and Epc2 = −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 μeff values of 1.43 and 1.46 BM, respectively, which convey a spin–spin interaction between the two copper(II) ions. The initial rate (Vin) for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the binuclear Cu(II) complexes 1 and 2 are 1.15 × 10−4 and 1.66 × 10−4 Ms−1 respectively. Both the complexes remarkably promote the hydrolytic cleavage of supercoiled plasmid DNA under physiological conditions in the presence of H2O2 at pH 7.2 and 37 °C. The reaction profile for the complex 1 mediated reaction displayed approximately pseudo-first-order kinetic behavior, with kobs ∼ 0.07 min−1 and R2 = 0.984.

Graphical abstractA new symmetrical polyaza macrocyclic binucleating ligand L1 and its permethylated derivative ligand L2 have been synthesized by using the precursor compound 2-[2-(2,6-diformyl-4-methylphenoxy)propoxy]-5-methylisophthalaldehyde and bis(aminoethyl) amine. The molecular structure of the precursor compound and the ligand L2 were determined by the single crystal XRD method. The ligands L1 and L2 were treated with two equivalents of Cu(ClO4)2 · 6H2O to afford the new binuclear complexes [Cu2L1(μ-OH)(ClO4)2](ClO4) (1) and [Cu2L2(μ-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 process around Epc1 = −0.59 V and −0.55 V, and Epc2 = −1.07 V and −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 μeff values of 1.43 and 1.46 BM, respectively, which convey a spin–spin interaction between the two copper(II) ions. The initial rate (Vin) for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the binuclear Cu(II) complexes 1 and 2 are 1.15 × 10−4 and 1.66 × 10−4 Ms−1, respectively. Both the complexes remarkably promote the hydrolytic cleavage of supercoiled plasmid DNA under physiological conditions in the presence of H2O2 at pH 7.2 and 37 °C. The reaction profile for the complex 1 mediated reaction displayed approximately pseudo-first-order kinetic behavior, with kobs ∼ 0.07 min−1 and R2 = 0.984.Figure optionsDownload full-size imageDownload as PowerPoint slide