Factorial design analysis of the catalytic activity of di-imine copper(II) complexes in the decomposition of hydrogen peroxide

Factorial design analysis was applied to the study of the catalytic activity of diimine copper(II) complexes, in the decomposition of hydrogen peroxide. The studied complexes show a tridentate imine ligand (apip), derived from 2-acetylpyridine and 2-(2-aminoethyl)pyridine, and a hydroxo or an imidazole group at the fourth coordination site of the copper ion. The factorial design models for both [Cu(apip)imH](2+) and [Cu(apip)OH](+) were similar. increasing the peroxide concentration from 3.2 x 10(-3) to 8.1 x 10(-3) mol L-1 resulted in increased oxygen formation. Increasing the pH from 7 to I I also increased oxygen formation and had an effect about twice as large as the peroxide one. Both complexes also had an important interaction effect between peroxide concentration and pH. However, increasing the catalyst concentration led to a decrease in total oxygen formation. The obtained results were corroborated by further data, achieved by using the usual univariate method, and helped to elucidate equilibrium steps occurring in the studied systems. in very alkaline solutions, the studied [Cu(apip)imH](2+) complex can form the corresponding dinuclear species, [Cu-2(apip)(2)im](3+). While the mononuclear complex proved to be an efficient catalyst in hydrogen peroxide decomposition, the corresponding dinuclear compound seemed to be able to coordinate with the dioxygen molecule, inhibiting its observed release. (C) 2001 John Wiley & Sons. Inc.33847247

Keto-enolic equilibria of an isatin-Schiff base copper(II) complex and its reactivity toward carbohydrate oxidation

An interesting isatin-Schiff base copper(II) complex, [Cu(isapn)](ClO(4))(2) where isapn N,N'-[bis-(3,3'-indolin-2-one)]-1,3-diiminepropane, was prepared and characterized by different techniques, both in the solid state and in solution, and its reactivity toward carbohydrate oxidation was verified. The positive ion electrospray mass spectrum detects the complex as an isotopologue cluster of singly charged intact isatin-copper(I) ions of m/z 395 (for 65 Cu) with an isotopic pattern identical to that calculated for C(19)H(16)CuN(4)O(2)(+). Tandem mass spectrometry reveals an interesting and structurally diagnostic collision-induced dissociation behavior for this ionized complex, which is dominated by the cleavage of the N-(CH(2))(3)-AN propylene bridge. In aqueous solution, this complex undergoes a peculiar keto-enolic equilibrium, verified at different pH's by spectroscopic methods (u.v.-vis. and e.p.r.), with a corresponding pK(a) determined as 9.5. The e.p.r. parameter ratio g(parallel to)/A(parallel to) for this complex, in frozen MeOH/H(2)O (4: 1, v/v) solution at 77 K, changes from 188 cm in acidic medium (pH 2.5-3.0) to 118 cm in basic medium (pH 11), indicating a significant structural change from a distorted tetrahedral to a more tetragonal geometry around the copper ion. This compound was shown to catalyze the oxidation of hexoses ( glucose, fructose and galactose), in alkaline media, via reactive oxygen species, which were detected by using specific enzymes, and by e.p.r. spin trapping. The reaction was monitored at (25.0 +/- 0.1)degreesC by the consumption of oxygen, and showed first-order dependence on catalyst, followed by a saturation effect. First-order kinetics with respect to [OH(-)] concentration was also observed, indicating that enolization of the substrate as well as the metal-catalyzed enediol oxidation are the rate-determining steps.29549550

Infinite zig-zag and cyclic-tetranuclear isomeric imidazolate-bridged polynuclear copper(II) complexes: Magnetic properties, catalytic activity and electrospray mass and tandem mass spectrometry characterization

Two mononuclear copper(II) complexes 1 and 2 with the unsymmetrical tridentate ligands 2- and 4-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine have been prepared. In alkaline solution, deprotonation of the imidazole moiety. in 1 and 2 promotes self-assembly, which yielded two structurally different species. Depending on the binding site in the imidazole ring, a polymeric complex with an infinite zig-zag-chain 3, or a cyclic-tetranuclear complex 4 is formed, as shown by spectroscopic and spectrometric analysis. Herein, structural characterization of these isomeric polynuclear complexes was performed by electrospray mass (ESI-MS) and tandem mass spectrometric experiments (ESI-MS/MS). Each isomer was shown to be stable in methanolic solutions and to display unique mass spectra with characteristic multiply charged molecular and fragment ions, corroborating previous data by EPR measurements. Magnetic data in the solid state fit a typical curve for an one-dimensional infinite regular chain system, with J= -(32.4 +/- 1.2) cm(-1) and g = 2.03 for 3, and that of a cyclic-tetranuclear structure with J = -(55.5 +/- 0.4) cm(-1) and g = 2.29 for 4. In the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) by molecular oxygen, both complexes were shown to act as efficient catalysts, exhibiting very similar ratios: k(cat)/K-M = 9.12 x 10(6) mol(-1) dm(3) min(-1) for 3 and 8.73 x 10(6) mol(-1) dm(3) min(-1) for 4. These similar ratios indicate that interactions between the metal centres in 3 or 4 and the substrate in solution occur predominantly at the outside of the catalyst framework. (c) 2005 Elsevier B.V. All rights reserved.358133581359

Synthesis, structure and redox properties of an unexpected trinuclear copper(II) complex with aspartame: [Cu(apm)(2)Cu(mu-N,O : O '-apm)(2)(H2O)Cu(apm)(2)(H2O)]center dot 5H(2)O

Structural, magnetic and spectroscopic data of a new trinuclear copper(II) complex with the ligand aspartame (apm) are described. [Cu(apm)(2)CU(mu-N,O:O'-apm)(2)(H2O)Cu(apm)(2)(H2O)]-5H(2)O crystallizes in the triclinic system, space group P1 (#1) with a = 7.3300(1) angstrom, b = 15.6840(1) angstrom, c = 21.5280(1) angstrom, alpha = 93.02(1)degrees, beta = 93.21 (1)degrees, gamma = 92.66(1)degrees and Z = 1. Aspartame coordinates to Cu(II) through the carboxylate and beta-amino groups. The carboxylate groups of the two central ligands act as bidentate bridges in a syn-anti conformation while the carboxylate groups of the four peripheral ligands are monodentate in a syn conformation. The central copper ion is in a distorted square pyramidal geometry with the apical position being occupied by one oxygen atom of the water molecule. The two terminal copper(II) atoms are coordinated to the ligands in the same position but their coordination sphere differs from each other due to the fact that one copper atom has a water molecule in an apical position leading to an octahedral coordination sphere while the other copper atom is exclusively coordinated to aspartame ligands forming a distorted square pyramidal coordination sphere. Thermal analysis is consistent with the X-ray structure. EPR spectra and CV curves indicate a rupture of the trinuclear framework when this complex is dissolved in ethanol or DMF, forming a mononuclear species, with a tetragonal structure. (c) 2005 Elsevier B.V. All rights reserved