FURTHER STUDIES ON THE KINETICS AND MECHANISM OF THE COPPER-IMIDAZOLE CATALYSED DECOMPOSITION OF HYDROGEN PEROXIDE

Abstract

The catalytic decomposition of hydrogen peroxide in the presence of the tetrakis(imidazole)copper(II) complex was investigated. The kinetics, based on the rates of oxygen evolution, indicated that a ternary copper(I1)-imidazole-peroxo complex is involved in the rate-determining step. The equilibrium constant for the coordination of hydrogen peroxide to the cupric ion, and the acid dissociation constant for the coordinated H202 ligand were calculated as 1.7 M¹ and 2.1 × 10⁹ M, respectively. The ternary complex undergoes intramolecular electron transfer, with k = 4 s¹, generating Cu(1) species which can react with hydrogen peroxide or dioxygen, returning to the catalytic cycle. A complete mechanism is proposed, based on the kinetics of oxygen and on the electrocatalytic behdviour observed for the copperimidazole complexes under a dioxygen atmosphere.     

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     

The kinetics of complex formation between Ti(IV) and hydrogen peroxide

The kinetics of the formation of the titanium‐peroxide [TiO²⁺₂] complex from the reaction of Ti(IV)OSO₄ with hydrogen peroxide and the hydrolysis of hydroxymethyl hydroperoxide (HMHP) were examined to determine whether Ti(IV)OSO₄ could be used to distinguish between hydrogen peroxide and HMHP in mixed solutions. Stopped‐flow analysis coupled to UV‐vis spectroscopy was used to examine the reaction kinetics at various temperatures. The molar absorptivity (ε) of the [TiO²⁺₂] complex was found to be 679.5 ± 20.8 L mol^?1 cm^?1 at 405 nm. The reaction between hydrogen peroxide and Ti(IV)OSO₄ was first order with respect to both Ti(IV)OSO₄ and H₂O₂ with a rate constant of 5.70 ± 0.18 × 10⁴ M^?1 s^?1 at 25°C, and an activation energy, E_a = 40.5 ± 1.9 kJ mol^?1. The rate constant for the hydrolysis of HMHP was 4.3 × 10^?3 s^?1 at pH 8.5. Since the rate of complex formation between Ti(IV)OSO₄ and hydrogen peroxide is much faster than the rate of hydrolysis of HMHP, the Ti(IV)OSO₄ reaction coupled to time‐dependent UV‐vis spectroscopic measurements can be used to distinguish between hydrogen peroxide and HMHP in solution. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 457–461, 2007     

Effect of different dimethylphenols on the interactions with Ni2+-exchanged montmorillonite

The influence of different steric and electronic properties of 2,4-; 2,5-; and 3,5- dimethylphenols (2,4-; 2,5-; and 3,5- DMP, respectively) on Ni²⁺-montmorillonite (Ni²⁺-MMT) (I) were studied. The results of X-ray diffraction show that the observed changes of the basal spacing were due to the intercalation of phenol derivatives into the interlayer space of montmorillonite. The existence of one peak at ~1,633 cm^?1 in the IR spectra of sample Ni²⁺-MMT + 2,4-DMP (II) and Ni²⁺-MMT + 2,5-DMP (III) and shift of this peaks to higher frequency indicate that 2,4-DMP and 2,5-DMP exist in the interlayer space of Ni²⁺-MMT in the protonated form. The two bands at ~1,622 and 1,597 cm^?1 in the sample Ni²⁺-MMT + 3,5-DMP (IV) indicate that 3,5-DMP may be also directly coordinated to Ni²⁺ cations. The different interactions of phenol derivatives in the silicate interlayers will be connected with different position of methyl groups on the phenol ring.     

Indirect Spectrophotometric Determination of Vanadium(IV) by Flow Injection Analysis Based on the Redox Reaction with Copper(II) in the Presence of Neocuproine

Abstract

An indirect photometric method with a continuous-flow analysis is presented for the determination of trace amounts of vanadium(IV). It is based on the redox reaction of copper(II) with vanadium(1V) in the presence of neocuproine. In the presence of neocuproine, copper(I1) is reduced easily by vanadium(I V) to a copper(1)-neocuproine complex, which shows a n absorption maximum at 454 nm. By measuring t h e absorbance of the complex at this wavelength, vanadium(1V) in t h e range 2×10^?6 - 8 × mol dm^?5 mol dm^?3 can be determined at a rate of 120 samples h^?1. The fractional determination of vanadium(1V) and iron(I1) is also studied.     

Trace Level Determination of Hydrogen Peroxide at a Carbon Ceramic Electrode Modified with Copper Oxide Nanostructures

An electrochemical sensor was developed for determination of hydrogen peroxide based on nanocopper oxides modified carbon sol‐gel or carbon ceramic electrode (CCE). The modified electrode was prepared by electrodeposition of metallic copper on the CCE surface and derivatized in situ to copper oxides nanostructures and characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The modified electrode responded linearly to the hydrogen peroxide (H₂O₂) concentration over the range 0.78–193.98 µmol L^?1 with a detection limit of 71 nmol L^?1 (S/N=3) and the sensitivity of 0.697 A mol^?1 L cm^?2. This electrode was used as selective amperometric sensor for determination of H₂O₂ contents in hair coloring creams.     

Feasibility of low-voltage cathodic electroluminescence at oxide-covered aluminum electrodes for trace metal determinations in aqueous solutions

Metal-catalyzed electroluminescence is generated at an oxide-covered aluminum electrode during the reduction of oxygen, potassium peroxodisulfate, and especially hydrogen peroxide in aqueous solutions. The feasibility of this electroluminescence for the determination of copper (5 × 10^?9 M) and thallium (> 10^?10 M) is demonstrated.     

Amperometric Glucose Biosensor Based on the Deposition of Copper and Glucose Oxidase onto Glassy Carbon Transducer

ABSTRACT

The performance of a first generation glucose amperometric biosensor based on the entrapment of glucose oxidase (GOx) within a net of copper electrodeposited onto activated glassy carbon electrode, is described. The copper electrodeposited offers an efficient electrocatalytic activity towards the reduction of enzymatically-liberated hydrogen peroxide, allowing for a fast and sensitive glucose quantification. The influence of the electrodeposition conditions (pH, potential, time, copper salt and enzyme concentrations) on the response of the bioelectrode was evaluated from the amperometric signals of hydrogen peroxide and glucose. The combination of copper electrodeposition with a nation membrane allows an excellent selectivity towards easily oxidizable compounds such as uric and ascorbic acids at an operating potential of -0.050 V. The response is linear up to 2.0 × 10^?2 M glucose, the detection limit being 1.2 × 10^?3 M.     

Stopped-flow injection determination of copper(II) at the ng ml−1 level

A stopped-flow injection method for the determination of copper(II) in the range 0.2–300 ng ml^?1 is proposed, based on the catalytic effect of this ion on the 2,2'-dipyridylketone hydrazone/hydrogen peroxide reaction. The oxidation product shows an intense blue fluorescence that is monitored at λ_ex = 350 nm, λ_em = 427 nm. The sampling rate (72 h^?1), r.s.d. (1.4%) and the lack of interference from most foreign ions, allowed application of the method to the determination of copper in foods and blood serum.     

Kinetic determination of traces of manganese(II) by its catalytic effect on the oxidation of acid blue 45 with hydrogen peroxide

A catalytic method is described for the determination of trace amounts of manganese(II) based on its catalytic effect on the hydrogen peroxide oxidation of an anthraquinone dye, Acid blue 45 (C.I. 63010). The reaction is followed spectrophotometrically by measuring the rate of change in absorbance of the dye at 595 nm. The calibration graph (rate constant (tg α) vs. manganese concentration) is linear in the range 4–25 ng Mn ml^?1, the relative standard deviation being 1.9% at the 13 ng Mn ml^?1 level. There are few interferences. The kinetic parameters of the reaction were investigated and the role of hydrogen peroxide and hydrogencarbonate ions is discussed.     

Evaluation of bathocuproine for the spectro-photometric determination of copper(I) in copper redox studies with applications in studies of natural waters

Copper(I) is determined at submicromolar levels in the presence of copper(II) in aqueous media by spectrophotometric measurement of the copper(I) complex of bathocuproine (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline). Copper(II) interference produced by reduction to copper(I) is described. Ethylenediamine can serve as a masking ligand to inhibit Cu(II) interference. The limit of detection is 1 × 10^?8 mol l^?1. Although this is not sensitive enough for use at natural copper concentrations, the procedure can be used in laboratory studies of copper redox processes at elevated levels in natural waters such as sea water. The dependence of results on pH and ionic strength was studied to evaluate the usefulness of the method in other aqueous systems.     

Mechanistic studies for modelling the metal ioncatalyzed tiron-hydrogen peroxide indicator reaction

Model building of kinetic-catalytic methods of determination is attempted for the tironhydrogen peroxide indicator reaction catalyzed by cobalt(II) and manganese(II) in alkaline medium. As a first approximation, rate equations for the metal ion-catalyzed reactions are derived from kinetic dependences on reagent concentrations and pH. More general models are obtained by considering the metal ion equilibria in the reaction mixture. For Co(II), a ternary tironhydrogen peroxideCo(II) complex was found to be responsible for the catalytic activity. As stability constants of peroxo (Co(II) complexes are unknown, only a qualitative approach can be given. Manganese catalyzes the indicator reaction in the presence of 1,10-phenanthroline or 2,2′-bipyridine. The initial rates under pseudo zero-order conditions in hydrogen peroxide and tiron correlate directly with the fraction of ternary activatortironMn(II) complex present. For bipyridine as activator, the rate constant is 1.31 × 10⁶ M^?1 min^?1 with respect to the ternary complex.     

Studies in fluorinated 1,3-diketones and related compounds Part XII. Synthesis and spectroscopic studies of some new polyfluorinated 1,3-diketones,and their copper 1,3-diketonates

New polyfluorinated 1,3-diketones have been prepared from polyfluorinated acetophenones and appropriate esters in the presence of sodamide. The corresponding copper 1,3-diketonates have been obtained by treating a methanolic solution of polyfluorinated 1,3-diketone with methanolic solution of copper acetate. The polyfluorinated 1,3-diketones have been characterized by elemental as well as by spectral studies, viz: I.R., ¹H N.M.R. and ¹⁹F N.M.R. In I.R., characteristic absorptions observed are: CF stretching bands (1300 ? 1000) cm^?1, CF deformation modes (900 ? 700 cm^?1) and intramolecular hydrogen bonding (3000 ? 2500 cm^?1). In ¹H N.M.R. methine ( = C$\text{H}$) signal is observed at δ 6.2 ? 6.8 ppm and enolic proton resonance signal at δ 13 ? 15 ppm indicating the presence of strong hydrogen bonding in such polyfluorinated 1,3-diketones.     

Kinetic spectrophotometric determination of indium/gallium mixtures

A kinetic method is presented for the determination of 0.5–5 μg ml^?1 gallium based on its activating effect on the copper(II)-catalyzed oxidation of 4,4′-dihydroxybenzophenone thiosemicarbazone by hydrogen peroxide. The reaction is monitored spectrophotometrically at 415 nm. Two sets of reaction conditions are established; one for the direct determination of gallium, and another, in which indium affects the gallium response, for determination of indium. Mixtures of these cations can be determined at μg ml^?1 levels and in gallium/indium ratios from 7.5:1 to 1:1.6, with an accuracy and precision of ca. 4.5%.     

Flow injection amperometric determination of hydrogen peroxide in household commercial products with a ruthenium oxide hexacyanoferrate modified electrode

Hydrogen peroxide was determined in oral antiseptic and bleach samples using a flow-injection system with amperometric detection. A glassy carbon electrode modified by electrochemical deposition of ruthenium oxide hexacyanoferrate was used as working electrode and a homemade Ag/AgCl (saturated KCl) electrode and a platinum wire were used as reference and counter electrodes, respectively. The electrocatalytic reduction process allowed the determination of hydrogen peroxide at 0.0 V. A linear relationship between the cathodic peak current and concentration of hydrogen peroxide was obtained in the range 10–5000 μmol L^?1 with detection and quantification limits of 1.7 (S/N?=?3) and 5.9 (S/N?=?10) μmol L^?1, respectively. The repeatability of the method was evaluated using a 500 μmol L^?1 hydrogen peroxide solution, the value obtained being 1.6% (n?=?14). A sampling rate of 112 samples h^?1 was achieved at optimised conditions. The method was employed for the quantification of hydrogen peroxide in two commercial samples and the results were in agreement with those obtained by using a recommended procedure.     

A Sensitive Visible Spectrophotometric Method for Copper Using Bis-Substituted Thiocarbamoyl Trisulfides

Abstract

Bis-substituted thiocarbamoyl disulfides (thiuram disulfides) were investigated as chromogenic reagents for the analysis of copper in trichloroacetic acid solutions. It was found that hydrogen peroxide speeded color development, increased color stability and enhanced color intensity in a trichloroacetic acid-alcohol matrix. In the presence of hydrogen peroxide, all copper complexes had molar absorptivities exceeding 30,000. Bis-pentamethylene thiocarbamoyl disulfide was selected as the best commerically available reagent of those investigated. The procedure is almost interference free, silver and mercury being the most serious interference. The sensitivity is 6 × 10^?3 micrograms/cm².     

Flow Injection Amperometric Determination of Hydrogen Peroxide at Low Level in Aqueous Solution

Abstract

A method is proposed for the flow-injection amperometric determination of hydrogen peroxide. Iodine is generated, by injecting hydrogen peroxide solution into an eluent 0.2 M in potassium iodide and 1 Min sulphuric acid and 5×10^?3M in Mo(VI) and is monitored at a platinum electrode that is being held at 0.1 V versus SCE. the rectilinearity range is from 10^?3?10^?6 M and the method is simple, accurate and compared favourably with the titrimetric method involving starch as indicator.     

Synthesis,magnetic properties,DNA binding and cleavage activity of a new oxalato bridged copper(II) complex

A novel oxalato‐bridged copper(II) complex has been prepared and structurally characterized: [Cu(bpa)(μ‐C₂O₄)].H₂O (bpa = bis(2‐pyridylmethyl) amine). In the complex, the copper ion is linked in an unusual μ_1,2,3‐C₂O₄^2? bridging mode, generating one‐dimensional zigzag chain disposition. Variable‐temperature magnetic susceptibility studies (2–300 K) reveal a weak ferromagnetic coupling, J = 0.63 cm^?1, between the copper ions. The interaction of the complex with CT‐DNA has been studied using UV–visible absorption and emission spectral methods, and the binding constant of the complex with CT‐DNA is K_app = 9 × 10⁴ m ^?1, which indicates that the interaction of the complex with DNA is a moderate intercalative mode. Furthermore, the complex cleaves supercoiled plasmid DNA efficiently in the presence of hydrogen peroxide. The mechanistic investigations suggest that the hydroxyl radical and singlet oxygen are involved in the DNA degradation. Copyright © 2012 John Wiley & Sons, Ltd.     

Study of the mimetic peroxidase-catalysed chemiluminescence reaction

The chemiluminescence behaviour of the reaction in which the Mn-TPPS₄ complex the mimetic enzyme of peroxidase [manganese tetrakis(sulphophenyl)porphine] acts as a catalyst for the oxidation of luminol by hydrogen peroxide was studied. The reaction product luminesces at 427 nm. Trace amounts of hydrogen peroxide and glucose can be determined with detection limits of 5.5 × 10^?9 and 2.7 × 10^?9 M, respectively. The characteristics of Mn-TPPS₄ were compared with those of horseradish peroxidase.     

Simultaneous semi-automatic catalytic titration of binary mixtures of mercury(II) with copper(II) or cadmium at the micromolar level

Copper(II) and mercury(II) act as catalyst and inhibitor, respectively, for the oxidation of 4,4'-dihydroxybenzophenone thiosemicarbazone by hydrogen peroxide in an ammonium chloride medium. The combination of these two effects and blocking of the catalytic cycle by EDTA are used as the basis for titrimetric methods for individual and simultaneous titrations of mercury and copper or cadmium, with catalytic end-point detection. Mixtures can be resolved in the mole ratio range 20.1–4.1 for Cu/Hg and 27.1–1.1 for Cd/Hg. Titrations are viable for 10^?7?10^?6 M mercury(II) and 10^?6-10^?5 M copper(II) or cadmium(II).