Mimicking catalase and catecholase enzymes by copper(II)-containing complexes

An imidazolate-bridged copper(II)-zinc(II) complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(2-aminoethyl)amine perchlorate (denoted as “Cu,Zn complex”) and a simple copper(II) complex (Cu(II)-tris(2-aminoethyl) amine chloride (“Cu-tren”) were prepared and immobilised on silica gel (by hydrogen or covalent bonds) and montmorillonite (by ion exchange). The immobilised substances were characterised by FT-IR spectroscopy and their thermal characteristics were also studied. The obtained materials were tested in two probe reactions: catalytic oxidation of 3,5-di-tert-butyl catechol (DTBC) (catecholase activity) and the decomposition of hydrogen peroxide (catalase activity). It was found that the catecholase activity of the Cu,Zn complex increased considerably upon immobilization on silica gel via hydrogen bonds and intercalation by ion exchange among the layers of montmorillonite. The imidazolate-bridged copper(II)-zinc(II) complex and its immobilised versions were inactive in hydrogen peroxide decomposition. The Cu(II)-tris(2-aminoethyl)amine chloride complex displayed good catalase activity; however, immobilisation could not improve it.     

Synthesis,Characterization, and Catalytic Activity of New Cu(II) Complexes of Schiff Base: Effective Catalysts for Decolorization of Acid Red 37 Dye Solution

In this paper, three new Cu(II) Schiff base complexes with three different anions (acetate, chloride, and nitrate) were successfully synthesized and characterized by elemental analysis, mass spectra, molar conductance, FT‐IR, NMR,UV–vis spectroscopy, magnetic moment, ESR, and thermal analysis. The catalytic performances of these complexes in decolorization of azo dye, Acid Red 37, were evaluated. Copper(II) complexes were found to be an efficient catalyst for decolorization of Acid Red 37 in the presence of hydrogen peroxide. The catalytic investigation revealed that the Cu(II) complex with acetate anion (complex 1 ) performed the highest catalytic activity. The kinetics of the decolorization of AR37 with this catalyst was studied, and the observed rate constant was determined. The effects of different reaction parameters such as catalyst dosage, solution pH, initial concentration of H₂O₂, dye solution, and reaction temperature on the reaction rate constant were studied. The best reacting conditions should be catalyst dosage = 0.004 g, initial pH 4.0, [H₂O₂]₀ = 0.8 M, and [AR37]₀ = 1.16 M at temperature 25°C. Under these conditions, about 99% of AR37 was decolorized within 60 min. The results indicated that the Cu(II) complex with the acetate anion is a promising catalyst for wastewater treatment.     

Selective oxidation of sulfides and oxidative bromination of organic substrates catalyzed by polymer anchored Cu(II) complex

A new polymer-anchored Cu(II) complex has been synthesized and characterized. The catalytic performance of the complex has been tested for the oxidation of sulfides and in oxidative bromination reaction with hydrogen peroxide as the oxidant. Sulfides have been selectively oxidized to the corresponding sulfoxides in excellent yields and in the presence of KBr as the bromine source, organic substrates have been selectively converted to mono bromo substituted compounds using polymer-anchored Cu(II) catalyst. This catalyst showed excellent catalytic activity, high selectivity, and recyclability. The polymer-anchored Cu(II) catalyst could be easily recovered by filtration and reused more than five times without appreciable loss of its initial activity.     

Hydrogen peroxide formation upon oxidation of oxalic acid in presence and absence of oxygen and of manganese(II)--III. Iron(III) and copper(II) as retarders

The formation of considerable amounts of hydrogen peroxide upon the slow addition of various oxidizing agents to oxalic acid in dilute sulphuric acid in the presence of oxygen and Mn(II) is greatly retarded in the presence of Fe(III) or Cu(II). With hydrogen peroxide as oxidizing agent and a trace of Fe(II) there is considerable decomposition of peroxide, under a nitrogen atmosphere, after a few hours at 25 degrees in light (from a tungsten lamp), and less decomposition in the dark. This decomposition is decreased by Mn(II) and also when the original mixture contains Fe(III). With oxygen as the oxidizing agent Fe(II) is about 100 times as effective an inhibitor of peroxide formation as Fe(III). With all oxidizing agents used, Cu(II) is some 6-10 times more effective as a retarder than Fe(III). The inhibition is accounted for by the reaction Fe(III) [or Cu(II)] + CO(-)(2) --> Fe(II) [or Cu(I)] + CO(2).     

Copper catalysts based on fiberglass supports for hydrocarbon oxidation reactions with the participation of hydrogen peroxide

Copper-containing catalysts were prepared by the adsorption of the ammonia complexes of Cu(II) on the surface of a silicate fiberglass material followed by the thermal and oxidative treatment of the samples. The states of copper after the adsorption of ammonia complexes and in the prepared samples were characterized using electronic diffuse reflectance spectroscopy. The catalytic activity of the samples in hydrogen peroxide decomposition and cyclohexane oxidation reactions was studied. It was found that molecular oxygen can be involved in the radical process of hydrogen peroxide oxidation. Based on spectroscopic data, it was hypothesized that partially reduced Cu(I)–Cu(O) compounds are active species in the catalysts of this type.     

SYNTHESIS, CHARACTERIZATION AND CATALYTIC ACTIVITY OF N,N''-BIS(3-ALLYL SALICYLIDENE)ETHYLENEDIAMINE COBALT(II) SCHIFF BASE COMPLEX ANCHORED ON A NEW POLYMER SUPPORT

A new chelating polymer support has been prepared by suspension copolymeriz a tion of synthesized N,N'-bis(3-allyl salicylidene)ethylenediamine monomer Schiff base (N,N'-BSEDA) with styrene (St) and divinylbenzene (DVB) using azobisisobutyronitrile (AIBN) as initiator in the presence of poly(vinyl alcohol). The content and complexation ability of monomer Schiff base (N,N'-BSEDA) for cobalt(II) ions in prepared crosslinked polymer beads have shown dependence on the amount of DVB used in reaction mixture. The amount of monomer Schiff base (N,N'-BSEDA) in crosslinked beads showed a substantial decreasing trend at high concentration of DVB in the reaction mixture (＞ 1.5 mol dm-3), hence the efficiency of complexation (EC%) and cobalt(II) ion loading (EL%) of polymer beads showed a decreasing trend. The structure of monomer Schiff base (N,N'-BSEDA) and its cobalt(II) complex on polymer support was elucidated by IR, UV and magnetic measurements. The catalytic activity of polymer bound cobalt(Ⅱ) Schiff base complex was evaluated by analyzing kinetic data of decomposition of hydrogen peroxide in the presence of either supported cobalt (II) complex or free cobalt(II) complex. The activation energy for the decomposition of hydrogen peroxide by polymer supported cobalt(II)complex was found to be low (33.37 kJ mol-l) in comparison with unsupported cobalt(II) complex (56.35 kJ mol-1). On the basis of experimental observations, reaction steps are proposed and a suitable rate expression derived.     

CATALASE MIMIC WITH Fe (II) METALLOMICELLE

The effect of Fe (II) metallomicelle as a model of catalase, which was formed by adding surfactants (CTAB, SDS, LSS, Brij35) in Fe (II) -trien complex of molar ratios 1: 500 on the decomposition of hydrogen peroxide was investigated at 20°C and 30°C in pH 10 using KI-color and UV Spectrophotometry. A kinetic model for metallomicellar catalysis was proposed. The association constant of the ternary complex K and the rate constant of the decomposition of hydrogen peroxide k3 were obtained. The results indicate that the metallomicelles making up of Fe (II) metal complex and cationic or nonionic surfactants have obvious catalysis on the decomposition of hydrogen peroxide, but the metallomicelles making up of Fe (II) metal complex and anionic or zwitterionic surfactants have inhibition on this reaction.     

Electrocatalytic reduction of Molecular Oxygen with a Copper (II) Coordination Polymer

Oxygen reduction at the polarized water/1,2-dichloroethane (DCE) interface catalyzed by a Cu (II) coordination polymer (Cu–pol) was studied with two lipophilic electron donors ferrocene (Fc) and tetrathiafulvalene (TTF). The results of the ion transfer voltammetry and two-phase shake flask experiments suggest proceeding of the catalytic reaction as proton-coupled electron transfer reduction of oxygen to hydrogen peroxide and water. In this process, while the protons supplied from the aqueous phase, the electrons provided from the organic phase by the weak electron donor, Fc. The O₂ molecule takes a superoxide structure with Cu–pol which resulted to hydrogen peroxide or water on reduction. Furthermore, the results revealed that the apparent rate constant of TTF + Cu-pol is higher than that of Fc + Cu-pol system due to the faster kinetic reaction of TTF with respect to Fc.     

Catalytic Activity of 3d-Metal Coordination Compounds with Diphenylthiocarbazide

The catalytic activity of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), and Cu(II) diphenylthiocarbazide complexes in decomposition of hydrogen peroxide was studied. The activation energies of this reaction were correlated with the strength of ligand bonding to the metal atom in the catalyst molecule.     

Synthesis,characterization and biological studies of some Co(II), Ni(II) and Cu(II) complexes derived from indole-3-carboxaldehyde and glycylglycine as Schiff base ligand

The Schiff base ligand derived from indole-3-carboxaldehyde(indal) and glycylglycine(glygly) were synthesized and characterized by elemental analysis, IR, electronic spectrum, ¹H NMR and mass spectrum. Co(II), Ni(II) and Cu(II)–indal-glygly Schiff base complexes were synthesized and characterized by elemental analysis, molar conductance, IR, electronic spectra, magnetic measurements, ESR, electrochemical studies, TGA, DSC analysis, XRD and SEM. Conductance measurements indicate that the above complexes are 1:1 electrolytes. IR spectral data show that the ligand is tridentate and the binding sites are azomethine nitrogen, peptide nitrogen and carboxylato oxygen atoms. Electronic spectral measurements indicate tetrahedral geometry for Co(II) and Ni(II) complexes and square planar geometry for Cu(II) complex. Magnetic measurements show weak ferromagnetic behaviour for Co(II) and Ni(II) complexes and paramagnetic behaviour for Cu(II) complex. ESR spectral data shows the ionic link between metal and the Schiff base ligand. The metal complexes are found to be stabilized in the unusual oxidation states of the metal ion during electrolysis. Thermal analysis of the complex indicates that the decomposition takes place in three steps. IR and thermal studies indicate that the fourth position would be occupied by a water molecule in complexes. XRD shows that the complexes have the crystallite size of 31, 40 and 67 nm, respectively. The surface morphology of the complexes was studied by SEM. The antimicrobial activity of the ligand and its complexes were screened by Kirby Bayer Disc Diffusion method. DNA cleavage studies were performed for metal–Schiff base complexes in presence of hydrogen peroxide as oxidant.     

Catalytic activity of binuclear planar copper(II) complexes for the decomposition of hydrogen peroxide

Planar binuclear copper(II) complexes generally showed high catalytic activities for the decomposition of hydrogen peroxide compared with the relevant planar mononuclear copper(II) complexes. This result was explained on the assumption that the two-electron transfer occurs between H₂O₂ molecules via an intervening binuclear copper(II) complex.     

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 di‐imine 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 × 10^?3 to 8.1 × 10^?3 mol L^?1 resulted in increased oxygen formation. Increasing the pH from 7 to 11 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, [Cu₂(apip)₂im]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. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 472–479, 2001     

Kinetics and mechanism of decomposition of hydrogen peroxide in the presence of manganese(III) porphyrins

The kinetics of homogeneous decomposition of hydrogen peroxide in the presence of manganese complexes with anionic ligands and various aromatic macrocycles were studied by the volumetric method. Ionmolecular mechanism was proposed on the basis of spectrophotometric data for catalytic decomposition of hydrogen peroxide with participation of manganese(III) porphyrins. The catalytic activity of the porphyrin complexes was higher by a factor of 1.5–3 than the activity of the corresponding solvate complexes with anionic ligands. The catalytic activity of porphyrin manganese complexes can be controlled by variation of the electronic structure of the macroring and the nature of anionic ligand coordinated at the apical position.     

Functional monomers and polymers. LIX. Properties and function of Cu(II) complexes of the copolymers having pendant sulfide and imidazolyl groups

The Cu(II) complexes of copolymers having pendant sulfide and imidazolyl groups were prepared by a free radical copolymerization of ethylvinylsulfide with vinylimidazole, and their properties and function were studied spectrophotometrically in comparison with those of poly[4(5)-vinylimidazole]. The complexes were found to be effective as catalysts for the oxidation of hydroquinone. Visible and ESR spectra of the Cu(II)-copolymer complexes were similar to those of the Cu(II)-homopolymer complexes, while the catalytic activity for the oxidation was different between these complex systems. A rapid reaction followed by a slow reaction, particularly at high ethylvinylsulfide content in the copolymers, was observed in the Cu(II)-copolymer complex systems, but a continuous reaction proportional to the reaction time was observed in the Cu(II)-homopolymer complex systems. The reoxidation rate of Cu(I) to Cu(II) complex, which was little affected by the concentration of imidazolyl group, decreased with a rise of the ethylvinylsulfide content in the copolymer. It was suggested that the sulfur atom of the sulfide group was weakly coordinated to Cu(II) but strongly to Cu(I), and an electron transfer reaction from substrate to the Cu(II) complex was increased, while reoxidation reaction of the Cu(I) complex was decreased in the copolymer complex systems.     

Efficient epoxidation reaction of terminal olefins with hydrogen peroxide catalyzed by an iron (II) complex

A highly active iron (II) complex that catalyzed epoxidation of terminal olefins with hydrogen peroxide was described. The catalytic system displayed excellent catalytic ability for the selective oxidation of terminal olefins to epoxides with high selectivity (up to 97.8%) in CH₃CN at 25?°C. The catalytic activity of three similarly structural iron (II) complexes was comparatively studied. The effect of various auxiliary ligands on epoxidation was investigated in detail.     

Catalytic Activity of Copper(II) Enzyme-like Catalysts,Prepared by Molecular Imprinting Technique in Oxidation of Phenols

Summary: Molecularly imprinted polymer copper(II) catalysts were prepared by suspension polymerization of 4-vinylpyridine, trimethylolpropane trimethacrylate (series A) and additional monomer – acrylonitrile (series B) in the presence of Cu(II) ions and template: 4-metoxybenzyl alcohol; two samples were also prepared by surface molecular imprinting technique utilizing W/O emulsion. The catalytic activity was tested in model oxidation reactions of hydroquinone and 2,5-di-tert-butylhydroquinone using hydrogen peroxide. The imprinted catalysts were more effective in both reactions than non-imprinted but their activity strongly depended on Cu(II) loading. Surface imprinted samples showed the highest activity (L_H up to 100%).     

Studies on catalytic fluorescence formation with peroxidase-like metallotetrakis(N-methylpyridiniumyl) porphyrins

The relative ability of peroxidase-like metallotetrakis(N-methylpyridiniumyl)porphyrins [Me-TMPyP, Me = Mn(III), Fe(III), Co(III), Ni(II), Cu(II), and Zn(II)] to catalyse the hydrogen peroxide oxidation of homovanillic acid to a fluorescent dimer has been studied. The complexes of Mn, Fe and Co are effective catalysts in the reaction, but the complexes of Ni, Cu and Zn are not. The catalytic behaviour of Mn-TMPyP, Fe-TMPyP and Co-TMPyP has been compared with that of HRP in both enzymatic and kinetic analysis. The sequence of peroxidase-like catalytic activity is Mn-TMPyP> Co-TMPyP> Fe-TMPyP. The catalytic activity of Mn-TMPyP is 84% of that of HRP. These Me-TMPyP (Me = Mn, Fe, and Co) compounds are good substitutes for HRP in enzymatic analysis. Traces of hydrogen peroxide and glucose can be determined with the Me-TMPyP systems.     

Reaction of a copper(II)-nitrosyl complex with hydrogen peroxide: putative formation of a copper(I)-peroxynitrite intermediate

The reaction of a Cu(II)-nitrosyl complex (1) with hydrogen peroxide at -20 °C in acetonitrile results in the formation of the corresponding Cu(I)-peroxynitrite intermediate. The reduction of the Cu(II) center was monitored by UV-visible spectroscopic studies. Formation of the peroxynitrite intermediate has been confirmed by its characteristic phenol ring nitration reaction as well as isolation of corresponding Cu(I)-nitrate (2). On air oxidation, 2 resulted in the corresponding Cu(II)-nitrate (3). Thus, these results demonstrate a possible decomposition pathway for H(2)O(2) and NO through the formation of a peroxynitrite intermediate in biological systems.     

Synthesis,characterization, catalase functions and DNA cleavage studies of new homo and heteronuclear Schiff base copper(II) complexes

A new tetradentate diimine–dioxime ligand containing a donor set of N₄, and its homo-, heterodinuclear and homotrinuclear copper(II) complexes were prepared and characterized on the basis of their elemental analysis, FT-IR, ¹H and ¹³C NMR spectra, molar conductivity and magnetic moment measurements. The extraction ability of N,N′′-bis[1-biphenyl-2-hydroxyimino-1-ethylidene]-diethylenetriamine was also evaluated in chloroform by using several transition metal picrates such as Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II) and Hg(II). It has been seen that the ligand shows strong binding ability toward the copper(II) ion. Moreover, the catalytic activities of the complexes for the disproportionation of hydrogen peroxide were investigated in the presence of imidazole. The synthesized complexes display efficiency in the disproportion reactions of hydrogen peroxide, producing water and dioxygen in catalase-like activity. The interaction between these complexes and DNA has also been investigated by agarose gel electrophoresis. We found that the homo- and heterodinuclear copper complexes can cleave supercoiled pBR322 DNA to nicked and linear forms. The dinuclear complexes including phenanthroline (2–4), with H₂O₂ as a co-oxidant, exhibited the strongest cleaving activity.     

Studies of the Interaction of the Salicylideneserinatecopper(II) Complex with β-Cyclodextrin: Characterization and Reactivity of the Inclusion Compound

The compound formed by the copper-Schiff base complex salicylideneserinatecopper(II), [Cu(sal-ser)(H2O)], interacting with -cyclodextrin was prepared, and characterized in the solid state by infrared, UV-visible and EPR spectroscopies, X- ray diffraction, and thermoanalytical techniques. The catalytic activity of this compound, [Cu(sal-ser)CD], in the decomposition of hydrogen peroxide, and in the dismutation of superoxide radicals was also verified, in comparison with the reactivity of the free complex, in aqueous solution. In both cases, a decreasing in the reaction rate was observed for the CD-containing compound. The results of structural characterization, in addition to the substantial differences observed in the catalytic activities of the compounds, are indicative of partial insertion of the copper complex in the cavity of the oligosaccharide.