New copper(II) µ-alkoxo-µ-carboxylato double-bridged complexes as models for the active site of catechol oxidase: synthesis, spectral characterization and DFT calculations.

A series of four copper(II) µ-Alkoxo-µ-carboxylato double bridged complexes, [{Cu2(L)}2][(µ-O2C-CO2] 1, [{Cu2(L)}2(µ-O2C-(CH2)CO2] 2, [{Cu2(L)}2(µ-O2C-CH2-CO2] 3 and [{Cu2(L)}2(µ-O2C-C6H4-CO2] 4 (H3L = 4-bromo-2-((E)-((3-(((E)-5-chloro-2-hydroxybenzylidene) amino)-2-hydroxypropyl) imino) methyl)-6-methoxyphenol and µ-dicarboxylate ions = oxalate, malonate, succinate and terephthalate) have been synthesized and characterized using several physicochemical techniques. The tridentate nature of H3L is interpreted from IR spectra. The Epr spectra of these complexes are characteristic of the quintet state (S = 2) in central features and the triplet state (S = 1) of these tetranuclear complexes. The electrochemical potential of these complexes was investigated using CV (cyclic voltammetry) and DPV (differential pulse voltammetry). All complexes showed quasi reversible reduction peaks in the cathodic region. To explore the stability of these complexes, quantum chemical parameters like electronegativity, ionization potential, electron affinity, global hardness and softness, and electrophilicity were estimated and discussed. The synthesized complexes have been designed as structural and functional models of the catechol oxidase enzymes to investigate the catecholase activity. Additionally, superoxide dismutase activity data of all complexes have also been evaluated and compared with known SOD mimics.

Unprecedented tetranuclear complexes with "weighing balance shaped" topology: single crystal structures, unusual EPR spectra, magnetic properties and antioxidant activity.

Using the 2-hydroxy-N'-[(E)-phenyl(pyridin-2-yl)methylidene]benzohydrazide ligand and dicarboxylate anions (succinate and malonate), two new copper(ii) complexes of formula [Cu4(µ-L)4(µ-CH2(COO)2)(H2O)3](NO3)2·4H2O (1) and [Cu4(µ-L)4(µ-CH2-CH2(COO)2)(H2O)](NO3)2] (2) have been synthesized and characterized by single crystal X-ray diffraction. Complexes 1 and 2 contain a dicarboxylate bridged tetranuclear Cu(ii) cationic unit with "weighing balance shaped" topology. These compounds have also been studied by variable temperature magnetic susceptibility measurements, X-band EPR spectroscopy and electrochemistry. The unprecedented tetranuclear copper complexes 1 and 2 exhibit antiferromagnetic interactions between adjacent copper(ii) centers with magnetic exchange coupling constants (J) of J1 = -6.8 cm-1, J2 = -20.6 cm-1 and g = 2.03 for 1 and J1 = -3.1 cm-1, J2 = -13.9 cm-1 and g = 2.02 for 2. The goal for our research work is to understand the factors that govern the stability of the Cu-O(-O-C-O-) bond towards reactive oxygen species (ROS) in Cu-containing mimics utilizing a systematic approach. The antioxidant superoxide dismutase measurements indicate that these complexes behave as superoxide dismutase mimics.