Synthesis of new dinuclear dicopper(II) and dinickel(II) complexes. The kinetics of catechol oxidase and electrochemistry of a dicopper(II) complex

Abstract

A new dinuclear ligand L¢, ethylene[OO¢-bis-salicylidene-b-diketone] bearing two symmetrical coordination sites was synthesized by the condensation of salicylaldehyde and acetylacetone, L, with 1,2-dibromoethane under reflux. The ligand L¢ in a 1:1 ratio was treated with CuCl 2 and NiCl 2 to yield the complexes, tetrachloro bis[OO¢-bissalicylidene-b-diketone copper(II)] and bis[OO¢-bis-salicylidene-b-diketone nickel(II)] chloride. The complexes were subsequently characterized by spectroscopic techniques, elemental analysis, i.r., 1 H-n.m.r., 13 C-n.m.r., u.v.-vis., e.p.r. spectroscopy, and conductance measurements. The conductance measurements in DMF reveal that the Cu II complex is covalent while the Ni II complex is ionic and the spectral data support the Cu II complex to be distorted octahedral whereas the Ni II complex has square-planar geometry.The dioxygen binding was studied spectrophotometrically by the oxidation of tetrachloro bis[OO¢-bissalicylidene-b-diketone copper(II)] with pyrocatechol in the presence of oxygen. The kinetic experiments were performed with the copper complex in DMF by monitoring the increase in absorbance over time at pH 8.0 in the presence of pyrocatechol at 25°C. The kinetic parameters V max and K M were determined on the Michaelis-Menten Approach.Redox behavior of the dinuclear copper(II) complex was investigated by cyclic voltammetry in the presence of O 2 with the pyrocatechol (substrate) and also without the substrate. The large difference in potentials E 0 is indicative of reversible oxygen binding of the complex and distinct catalytic activity.

Synthesis, structural and spectroscopic characterization and biomimetic properties of new copper, manganese, zinc complexes: Identification of possible superoxide-dismutase mimics bearing hydroxyl radical generating/scavenging abilities

“…Among the most successful metalcomplexes possessing SOD activity, dinuclear metal complexes [11,12] have received much attention considering that in nature various enzymes containing dinuclear metal active centres exist and are able to bind oxygen and catalyze the transformation of reactive intermediates. As part of this ongoing search for new therapeutic antioxidant agents, we have decided to start a systematic study on copper, zinc and manganese complexes containing heterocyclic N-donor ligands, also able to form dinuclear species, followed by investigations on their superoxide scavenging activity [13][14][15][16].…”

Cu(II) complexes as receptor molecules for development of new chloride sensors

“…1. Cu(II) complex 1 has been synthesized by the method reported in literature [36], whereas Cu(II) complex 2 has been synthesized by following method: to a solution of the ligand LH 2 (0.5 g, 1 mmol) in dichloromethane (25 cm 3 ) was added CuCl 2 ·2H 2 O (0.3 g, 2 mmol) in MeOH in 1:2 molar ratio. The colored product was isolated by slow evaporation of the resultant mixture, filtered, washed with hexane and dried in vacuo.…”