Electrochemical, magnetic, catalytic and DNA cleavage studies of binuclear copper(II) complexes derived from pendant substituted tetraaza macrobicyclic compartmental ligands

A series of macrobicyclic unsymmetrical binuclear copper(II) complexes of compartmental ligands were synthesized from the Schiff base condensation of 1,8[N,N′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}]-1,4,8,11- tetraaza-5,5,7,12,12,14-hexa methylcyclotetradecane with diamines like 1,2-diamino ethane, 1,3-diamino propane, 1,4-diaminobutane, 1,2-diaminobenzene and 1,8-diaminonaphthalene. The complexes were characterized by elemental and spectral analysis. Electrochemical studies of the copper(II) complexes show two irreversible one-electron reduction processes around E1pc = −0.70 to −1.10 V and E2pc = −0.98 to −1.36 V. ESR spectra of the binuclear copper(II) complexes show a broad signal at g = 2.10 and μeff values in the range 1.46–1.59 BM, which convey the presence of antiferromagnetic coupling. Cryomagnetic investigation of the binuclear complexes [Cu2L3(ClO4)](ClO4) and [Cu2L4(ClO4)](ClO4) show that the observed −2J values are 144 and 216 cm−1, respectively. The observed initial rate (Vin) for the catalytic hydrolysis of p-nitrophenyl phosphate by the binuclear copper(II) complexes were in the range 1.8 × 10−5 to 2.1 × 10−5 Ms−1. The initial rate (Vin) for the catalytic oxidation of catechol to o-quinone by the binuclear copper(II) complexes were in the range 2.7 × 10−5 to 3.5 × 10−5 Ms−1. The copper(II) complexes have been found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II.

Novel N-difunctionalised tetraaza macrocyclic ligands and their binuclear copper(II) complexes have been synthesized and characterized. Electrochemical studies indicate that the copper(II) complexes show two irreversible one-electron reduction processes. Catechol oxidation, phosphate hydrolysis and DNA cleavage studies show that the distorted complex has a higher catalytic activity than the other rigid complexes.Figure optionsDownload as PowerPoint slide