Quasi-reversible Process Research Articles

Electronic structure and reactivity studies of a nonsymmetric one-electron oxidized CuII bis-phenoxide complex

The tetradentate mixed imino/amino phenoxide ligand (N-(3,5-di-tert-butylsalicylidene)-N′-(2-hydroxyl-3,5-di-tert-butylbenzyl))-trans-1,2-cyclohexanediamine (salalen) was complexed with CuII, and the resulting Cu complex (2) was characterized by a number of experimental techniques and theoretical calculations. Two quasi-reversible redox processes for 2, as observed by cyclic voltammetry, demonstrated the potential stability of oxidized forms, and also the increased electron-donating ability of the salalen ligand in comparison to the salen analogue. The electronic structure of the one-electron oxidized [2]+ was studied in detail, and Cu K-edge X-ray Absorption Spectroscopy (XAS) measurements confirmed a CuII-phenoxyl radical complex in solution. Resonance Raman (rR) and variable temperature 1H NMR studies, coupled with theoretical calculations, showed that [2]+ is a triplet (S=1) CuII-phenoxyl radical species, with localization of the radical on the more electron-rich aminophenoxide. Attempted isolation of X-ray quality crystals of [2]+ afforded [2H]+, with a protonated phenol bonded to CuII, and an additional H-bonding interaction with the SbF6− counterion. Stoichiometric reaction of dilute solutions of [2]+ with benzyl alcohol showed that the complex reacts in a similar manner as the oxidized CuII-salen analogue, and does not exhibit a substrate-binding pre-equilibrium as observed for the oxidized bis-aminophenoxide CuII-salan derivative.

Voltammetric behavior of Mammeisin (MA) at a glassy carbon electrode and its interaction with Bovine Serum Albumin (BSA)

The electrochemical oxidation of Mammeisin (MA) was studied in a solution containing acetone and 0.1M phosphate buffer +0.1M KCl (pH=5.3) at a glassy carbon electrode (GCE), using cyclic (CV) and square wave voltammetry (SWV). MA showed a quasi-reversible process, which is pH dependent and that involves the exchange of two electrons and two protons. The oxidation product was adsorbed by the electrode surface to form a film that blocks active sites over repetitive cyclic. Moreover, the interaction of MA and bovine serum albumin (BSA) was studied by CV and SWV at different pHs (5.4, 7.2, 9.5). As a result of the affinity binding with BSA, electrochemically inactive complex was formed. In addition, the oxidation potential of MA in the presence of BSA depends on the pH. The diffusion coefficients of both free and bound MA were estimated from the cyclic voltammetry data using the method developed by Randles-Sevich (Df=9.85×10−5cm2s−1 and Db=1.27×10−9cm2s−1) and the binding constant of MA-BSA complex, K=3.47×102Lmol−1, was obtained.

Voltammetric and spectroscopic studies of the interaction between copper (II) ions with the pesticide carbendazim and its effect in the soil

The pesticide carbendazim (MBC) has nitrogen and oxygen in their structure which can interact with metal ions. This work evaluated the interaction between copper (II) ions with the pesticide carbendazim. The results obtained by cyclic voltammetry (CV) in 0.4 mol L−1 Britton-Robinson (BR) buffer (pH 4.0), under glass carbon electrode (GCE) to the MBC, showed an oxidation peak at 1.02 V and a reduction peak at 0.78 V vs Ag/AgCl, with characteristics of a quasi-reversible process controlled by the diffusion of the species in solution. For the Cu2+ metal ions, two reduction peaks were observed at − 0.26 and − 0.11 V and an oxidation peak at 0.04 V vs Ag/AgCl, with characteristics of a quasi-reversible process, controlled by the diffusion of the species in solution. In the interaction between carbendazim and copper metal ion, the formation of an oxidation peak around 0.60 V vs Ag/AgCl and a reduction peak around 0.08 V was observed, in a 1:1 ratio (Cu2+:MBC) in solution, suggesting that a new compound was formed. Complex formation was confirmed by UV-Vis spectroscopy, where changes were observed in the MBC absorption band and Cu2+ d-d band, suggesting the formation of a MBC-Cu complex. Analyses with the soil samples showed that after 30 min of the presence of the carbendazim solution in the soil, the pesticide had around 80% of its initial concentration adsorbed. When carbendazim is in the presence of the Cu2+ ion, about 62% of the pesticide is adsorbed, indicating that complexation influences adsorption of the species in the soil studied.

Voltammetric studies of the interaction between lead metal ion and the methyl parathion pesticide

In this work, the interaction of the pesticide methyl parathion (MP) with the lead metal ion was evaluated using a carbon electrode reused from a zinc battery. MP showed a reduction peak around − 0.57 V, with characteristics of irreversible processes, followed by a redox pair at 0.02 and 0.04 V. For the Pb2+ ion was observed a redox pair with the peaks at − 0.65 and − 0.44 V, with characteristics of quasi-reversible process. The evaluation of the MP interaction with the metal ion was performed by anodic stripping voltammetry and by UV-Vis spectroscopy. The studies indicated the formation of a new species in solution with a stripping peak at − 0.60 V, as well as a pronounced effect on the stripping peak of the methyl parathion. Since this change is in the hydroxylamine redox couple, it suggests that the interaction is through the sulfur atom present in the parathion molecule. Through titration studies, was suggested a possible 1:2 Pb:MP stoichiometry for the complex formed. Langmuir linearization algorithms of titration data with the metal allowed us to calculate the stability constant for the Pb:MP complex (log K′ = 7.6).The confirmation of the interaction between the species in solution was evidenced by UV-Vis spectroscopy, with the reduction of the MP absorption band at 282 nm.

Hemoglobin becomes electroactive upon interaction with surface-protected Au nanoparticles

In this work, we report on the electrochemical behavior of bioconjugates prepared with gold nanoparticles (AuNP) capped with three different molecular layers (citrate anions, 6-mercaptopurine and ω-mercaptoundecanoic acid) and the protein hemoglobin (Hb). Freshly formed bioconjugates are deposited on a glassy carbon electrode and assayed for electroactivity. A pair of redox peaks with formal potential at −0.37V is obtained, in contrast with the free Hb protein that is inactive on the glassy carbon substrate. The redox response is typical for quasi-reversible processes allowing the determination of the electron transfer rate constant for the three bioconjugates. Additional evidence of the structural integrity of protein upon forming the bioconjugate is obtained by monitoring the electrochemical response of the Hb heme Fe(III)/Fe(II) redox couple as a function of solution pH. Moreover, the Hb forming the protein corona around the AuNPs show good electrocatalytic activity for the reduction of hydrogen peroxide and oxygen. It has been found that only the first layer of Hb surrounding the AuNPs are electroactive, although some part of the second layer also contribute, pointing to the role of the AuNP in the electrochemical response.

Electrodeposition of Pb from PbO in urea and 1-butyl-3-methylimidazolium chloride deep eutectic solutions

In this work, urea and 1-butyl-3-methylimidazolium chloride (urea-BMIC) deep eutectic solutions were used as electrolytes for electrodeposition of lead from lead oxide. The electrochemical behavior of Pb (II) ions was investigated by cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques at 353–373K. Cyclic voltammograms and chronopotentiograms indicate that the reduction of Pb (II) ions to Pb is a diffusion-controlled quasi-reversible process and it proceeds via one step two-electron transfer process at −0.38V (vs. Ag). The diffusion coefficient of Pb (II) ions increases from 3.22×10−8cm2s−1 to 1.49×10−7cm2s−1 as temperature increases from 353K to 373K. The activation energy for diffusion is determined to be 83.93kJmol−1. In addition, results from chronoamperometry show that lead deposition involves in a three-dimensional instantaneous nucleation and diffusion-controlled growth. On the other hand, the electrodeposit on a Cu substrate was pure Pb as confirmed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Scanning electron microscopy (SEM) image indicated that a uniform, dense, and non-dendritic coating with grain size of 3μm in diameter was prepared by potentiostatic electrolysis at −0.4V (vs. Ag). The optimized current efficiency (96.17%) and energy consumption (0.11kWhkg−1) was obtained by potentiostatic electrolysis at −0.4V (vs. Ag) and 373K from urea-BMIC deep eutectic solutions containing 0.072moldm−3 PbO.

A Study on Voltametric Electro-kinetic Mechanism of Catechol at l-glutamic Acid-Carbon Paste Sensor

Quinones and quinoles, the pervasive components of living organism, perform different biochemical and physiological activities. These compounds have found their widespread applications as life saving drugs in cancer chemotherapy, antioxidant, anti bacterial and antifungal agents. These contribute as components of biological electron transfer chains located indifferent body parts. Electrochemical redox behavior of catechol using cyclic and differential pulse voltammetry at the surface of ℓ-glutamic acid modified carbon paste sensor was observed quite sensitive. There was a remarkable increase in the magnitude of both peak currents of catechol at the surface of modified electrode as compared to that of bare carbon paste electrode. Optimizations of working parameters for both techniques have been performed to perk up the working efficiency during experimentation. The electrochemical process occurs under both the diffusion and adsorption controlled conditions. The kinetic parameters such as heterogeneous electron transfer rate constant for electrode process (K<sub>h</sub>), diffusion coefficient (D), standard rate constant of surface reaction (k°), electron transfer coefficient (α) and the average surface concentrations of electro-active species (χ<sub>1</sub>&χ<sub>2</sub>) at the electro-chemical barriers catechol/o-quinone radical and o-quinone radical/o-quinone were calculated. The calculated value of K<sub>h</sub> lie in close vicinity to limiting value of a complete irreversible process and in far range of quasi-reversible process. In the higher range of applied scan rates at lower potentials of the used potential window, the forward scan revealed the formation of well stable reaction intermediate, at relatively slower rate. This is the rate determining step of the oxidation process but in case of reduction pulse of the same scan rate, there is no indication of any reduction intermediate moieties. The chemical process during electrochemical oxidation of catechol follows pseudo first order kinetics. Furthermore, a two step oxidation, Electronic-Chemical-Electronic-Chemical reactions (ECEC) mechanism has been proposed and single step reduction has been observed for the coupled redox process at the sensor/analyte interface.

Solvent and electrode influence on electrochemical forming of poly-Fe(III)-aminophenylporphyrin films

Fe(III)-complexes of amino-substituted tetraphenylporphyrins obtained from solutions in organic solvents: dichloromethane, ethanol, and dimethyl sulfoxide have been electropolymerized. The solvents’ effects on deposition and surface morphology of the obtained polyporphyrin film have been determined. It is only possible to obtain a polyporphyrin film from DMSO solutions through electrochemical activation of electropolymerization by a superoxide anion radical (O[Formula: see text]. The activation effect of the dissolved oxygen becomes evident in porphyrin interaction with the superoxide anion radical (O[Formula: see text] that is synthesized in DMSO thanks to the quasi-reversible redox process. The size of particles forming the film is lowest when the film is deposited from DMSO and highest when it is deposited from dichloromethane. Therefore, the ratio of polyporphyrin phase grain growth rate to the nucleation rate has the highest value when the film is deposited from dichloromethane. Such films have the most developed surfaces, while those deposited from ethanol are the smoothest. If the film is deposited on an ITO-electrode, the particles forming the surface are a little larger than in the case of deposition on Pt, which is explained by a slower nucleation on the ITO surface. FeClT([Formula: see text]-NH2Ph)P-based films obtained from ethanol and dichloromethane have negative photo-EMF values, which indicates that the [Formula: see text]-type films have semiconductor properties.

Synthesis and Characterization of a New Cobaloxime-Terpyridine Compound

A new cobaloxime was synthesized by the reaction of cobalt chloride and diphenylglyoxime in methanol, followed by the addition of 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine, pytpy. This complex was characterized by UV–Vis spectroscopy, 1H-NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction analysis. In cyclic voltammetry experiments an irreversible reduction wave assigned to Co(III)/Co(II) at Ecp = −0.31 V vs. Ag/AgCl and a quasi-reversible process assigned to the Co(II)/Co(I) reduction at −0.72 V vs. Ag/AgCl were observed. The crystal of the complex belongs to the triclinic space group P1 with a = 12.4698(6) Å, b = 14.1285(8) Å, c = 15.5801(8) Å, α = 109.681(4)°, β = 112.975(4)°, γ = 81.67(96.414(4)°3)°, V = 2284.0(2) Å3, Z = 2, Dc = 1.408 mg·m−3, μ = 0.66 mm−1, F(000) = 996, and final R1 = 0.0564, ωR2 = 0.1502.

A new zinc coordination polymer in (10, 3)-d framework with unusual redox property

A new coordination polymer, [Zn(H1dimb)(Cl)]n (1) (H1dimb = 2,5-di (1H-imidazol-1-yl)benzoate), is obtained by hydrothermal synthesis and characterized by single crystal X-ray diffraction data and elemental analysis. Compound 1 crystallizes in the orthorhombic space group Pccn, and its structure exhibits a rarely observed ultimate racemic 3D network with 2-fold interpenetrating (10, 3)-d (or utp) topology due to the presence of alternating arrays of left- and right-handed helices. Thermo-gravimetric analysis (TGA) data for 1 reveals that the metal-organic framework (MOF) is thermally stable up to 350 °C under a N2 atmosphere. Compound 1 also possesses interesting photoluminescent properties as expected for Zn2+ complexes of aromatic ligands. Photoemission spectra measured in the solid state reveal a very strong emission band centered at 417 nm. Cyclic voltammetric data reveal that the compound exhibits quasi reversible two-electron redox process in acidic aqueous solution and the surprising electrochemical behavior is attributed to the Zn/Zn2+ process.

ELECTROCHEMICAL AND PHOTO-ELECTROCHEMICAL PROCESSES OF METHYLENE BLUE OXIDATION BY Ti/TiO2 ELECTRODES MODIFIED WITH FE-ALLOPHANE

This work reports the degradation of methylene blue (MB) on Ti/TiO2 and Ti/TiO2/Fe-allophane electrodes in a pH 3 using 0.1 M Na2SO4 as support electrolyte. SEM micrographs show a homogeneous distribution of TiO2 over the whole electrode surface forming nanotubes and nanopores. Fe-allophane modified electrode shows the formation of large-grains agglomerate on the electrode surface due to allophane, which provides a greater surface area to the electrode due to meso and micropore structures. Preliminary cyclic voltammetry show that Ti/TiO2 has the typical voltammetric response due to Ti(III)/Ti(IV) pair. Diffusional problems were observed through of the film when the electrode is modified with Fe-allophane modifying the quasi-reversible process Ti(III)/Ti(IV). Different kind of methodologies in the degradation process were used: Electrochemistry (EC), Photochemistry (PC), Photoelectrochemistry (PEC) and Adsorption (Ads). These methods were developing to discard any reaction or interaction that is not of interest. On Ti/TiO2 with PC and Ads methodologies was not observed any activity to MB degradation showing that is not photosensitive and that the interaction between this and surface electrode is low. But with EC and PEC degradation to 55% is reached after 3 hours of electrolysis. With Ti/TiO2-Fe-allophane electrodes are observed a higher activity for all methodologies. The PC and Ads methods show that the MB degradation reaches to ~20 % of the initial concentration. As mentioned above, the PC and Ads processes no show degradation on Ti/TiO2, therefore the degradation it only due to the adsorption of MB in/on allophane coat behaving as concentrator matrix. A lower improvement is observed with EC process when is incorporated Ti/TiO2-Fe-allophane is due to the barrier of the electrode surface by oxidation products. With PEC is reached the higher degradation value of ~88 %, showing an improvement of the degradation with the presence of Fe-allophane. The results indicate that the main role of Fe-allophane on the electrode is similar to a concentrator matrix.

Development of a novel electrochemical sensor based on cobalt(II) complex useful in the detection of dopamine in presence of ascorbic acid and uric acid

[(Co(bdmpzm)2(NCS)2] (bdmpzm=bis(3,5-dimethylpyrazol-1-yl)methane) was synthesized and combined with single walled carbon nanotubes (SWCNT) and nafion on a screen printed carbon electrode (SPCE). The electrocatalytic activity of modified electrode (Nafion-SWCNT-[Co(bdmpzm)2(NCS)2]/SPCE) was evaluated for dopamine (DA) oxidation. Anodic and cathodic peak were seen to 0.42V.and0.29V respectively, showed a much more quasi-reversible process, (∆V 0.128) compared with the electrode without cobalt complex. The detection limit (3σ/b) for dopamine was 0.095μmol L−1. The studies of reproducibility determined as relative standard deviation (RSD) was 2.5%.(n=5) with four different electrodes. The repeatability were 1.5% (n=5) The new sensor was used in the quantify DA in human urine with an average recovery between 83.0 and 93.0%.

Redox-Switchable New Phthalocyanines Containing Hydrazono-Thiazole-Carboxylate Fragments: Synthesis, Electrochemical, Spectroelectrochemical and Electrocolorimetric Investigation.

New phthalonitrile compound with Schiff base, carbothioamide and thiazole moieties as substituents and its corresponding metal-free and metallophthalocyanines (Zn(II), Ni(II), Co(II), and Cu(II)) were synthesized and characterized for the first time. The solubilities of these novel phthalocyanines were high in organic solvents. The redox properties of the compounds have been researched by cyclic voltammetry, square wave voltammetry, controlled-potential coulometry and in situ spectroelectrochemistry in dimethylsulfoxide. The compounds displayed metal and/or phthalocyanine ring-based, generally reversible or quasi-reversible reduction and oxidation processes. The effect of aggregation on the redox behavior of these complexes was also discussed. In general, decreased intensity and broadening in the main Q absorption band and the appearance of a new blue-shifted band confirmed the presence of H-type aggregates in the solutions of the complexes 4, 6 and 8 in DMSO/TBAP. The color changes associated with the redox processes and electrogenerated anionic and cationic redox species were also recorded with in situ electrocolorimetric measurements. In situ UV-vis spectral and associated color changes monitored during the reduction processes of the complexes suggested their applicability in the fields of the electrochemical technologies.

Au@AuPt nanoparticles embedded in B-doped graphene: A superior electrocatalyst for determination of rutin

A hydrothermal approach was used to prepare B-doped graphene with B2O3 as reductant and boron source. Results reveal that the boron atoms have been successfully embedded into graphene with a high content of a total B species (2.85at.%). Then, B-doped graphene was exfoliated further into monolayer nanosheet by impregnating Au@AuPt core-shell nanoparticles (Au@AuPt NPs) because boron atom creates a net positive charge, which facilitates Au@AuPt NPs adsorption to form Au@AuPt NPs/B-doped graphene hybrid nanocatalysts. After that, the Au@AuPt NPs/B-doped hybrid suspension was dropped on glassy carbon electrode for sensing rutin. In this way, the dispersed carboxyl units of B-doped graphene can form hydrogen bonding with the phenolic hydroxyl groups of rutin, making rutin enrich easily on modified electrode surface to enhance the electrochemical response. At the same time, its electrochemical mechanism on the modified electrode was elucidated using cyclic voltammetry. It was found that its electrochemical behavior on modified electrode surface was a surface-controlled quasi-reversible process, and the charge transfer coefficient (α) and electron transfer number (n) were 0.296 and 2, respectively. This electrochemical sensor for rutin provided a wide linear response range of 2.00×10−9–4.00×10−6M with the detection limit (S/N=3) of 2.84×10−10M. The proposed method was applied successfully to selective determination of rutin in Tablets with acceptable recovery range (97.23–101.65%).

Electrodeposition of Zinc from Zinc Oxide in 2:1 Urea/1-Butyl-3-methylimidazolium Chloride Ionic Liquid

In this study, zinc oxide (ZnO) was dissolved in 2:1 mole ratio of urea/1-butyl-3-methylimidazolium chloride (urea-BMIC) ionic liquids and electrochemically reduced to metallic zinc (Zn) on the cathode. The electrochemical behavior of zinc species in the urea-BMIC-ZnO ionic liquids was investigated by cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques at 373 K using a tungsten working electrode and silver reference electrode. The cyclic voltammograms and chronopotentiograms indicate that the reduction of zinc species to metallic Zn is a diffusion-controlled quasi-reversible process and it proceeds via an apparent two-electron transfer process on tungsten working electrode. From the chronoamperometric analysis, zinc deposition in urea-BMIC involves in a three-dimensional instantaneous nucleation and diffusion-controlled growth at 373 K. The value of diffusion coefficient of zinc species in the urea-BMIC (molar ratio 2:1) ionic liquids at 373 K is 4.39 × 10−9 cm2·s−1. Zinc coatings were prepared on copper substrates at various current densities (constant current electrolysis) and different cathodic potentials (constant potential electrolysis). SEM micrograph indicated that a uniform, dense, and compact coating was produced by potentiostatic electrolysis at −1.1 V (vs. Ag). In addition, the obtained electrodeposit on the Cu substrate was metallic Zn as confirmed by XRD pattern and EDS spectrum. The optimized current efficiency (99.24%) and energy consumption (3.29 kWh/kg) was obtained by potentiostatic electrolysis at −1.1 V (vs. Ag) and 383 K in urea-BMIC ionic liquids containing 0.49 mmol/mL ZnO.

Higher order derivative voltammetry for reversible and irreversible electrode processes under spherical diffusion

Theoretical expressions for the first, second and third derivatives of voltammetric curves are analytically derived for reversible, quasi-reversible, and irreversible processes under spherical diffusion. The shapes of the curves are analyzed n terms of peak-potentials, peak-currents, and peak-widths, and the differences and ratios among them. The results obtained with spherical electrodes are compared with those with the planar electrodes, which exhibits striking differences between two electrodes. Derived parameters – such as ratios of peak-currents (ipa/ipc), and ratios of half-peak-widths (W½a/W½c), and ratios of the differences in peak potentials (ΔEpa/ΔEpc), for various derivatives are analyzed. As electrode sphericity increases, these ratios (i. e., measures of symmetry in the curves) for a quasi-reversible and irreversible electron transfer process approaches to one, which is the same as that for a simple reversible electrode process on a planar electrode. Namely, the asymmetry which was exhibited on planar electrodes for quasi and irreversible processes disappears on a spherical electrode. This suggests that the planar electrode is better suited for kinetic study of slower electron transfer than spherical electrodes for this derivative approach.

Ziram herbicide determination using a polished silver solid amalgam electrode

The use of a polished silver solid amalgam electrode (p-AgSAE) and the square wave voltammetry (SWV) in the electroanalytical determination of Ziram herbicide in natural water samples is reported. The experimental and voltammetric parameters were optimized at 0.04molL−1 Brinton-Robinson buffer (pH 7.0), with a pulse potential frequency of 80s−1, pulse amplitude of 30mV, scan increment of 2mV and the cationic surfactant, cetyltrimethyl ammonium bromide, in the same molar ration of Ziram herbicide. In potential interval from −0.10V to −1.40V, the electrochemical redox process of Ziram occurred in two parts. In the first one, the Ziram complex is dissociated to anion radical and metallic cation, in a totally reversible redox process involving two electrons transfer. This electrons transfer, immediately initiate the subsequent reaction where the anion radical formed is converted to highly reactive dianion, in a reversible electron transfer. The dianion generated undergo an eletrophilic substituent by H+ ions, in a following chemical reaction. The second part corresponds to a quasi-reversible redox process from reduction reaction of the Zn+2 to metallic Zn. Analytical parameters such as: linearity range, equation of the analytical curves, coefficients determination, detection and quantification limits, recovery efficiency, and relative standard deviation for intraday and interday experiments were evaluated indicating that the voltammetric procedure using an p-AgSAE is suitable for determining any contamination by Ziram, minimising the toxic residues due to the use of liquid mercury or the adsorptive process relative to the use of other solid surfaces.

Synthesis, photophysical and electrochemical properties of novel hexadeca-substituted phthalocyanines bearing naphthoxy groups

The synthesis and characterization of a novel tetra-substituted phthalonitrile together with hexadeca-substituted metal-free and metallo phthalocyanines bearing naphthoxy groups in peripheral positions and hexyloxy groups in non-peripheral positions were described. Aggregation properties of phthalocyanine compounds were investigated in a concentration range of 1.4 × 10−5 M to 4 × 10−6 M. The energy transfer to phthalocyanine core and radiative decays of the naphthoxy emission and phthalocyanine core were examined. Electrochemistry of the complexes was studied with cyclic voltammetry and square wave voltammetry techniques. While zinc phthalocyanine (ZnPc) showed two phthalocyanine-based oxidation and two phthalocyanine-based reduction processes, cobalt phthalocyanine (CoPc) illustrated a metal-based and a phthalocyanine-based reductions and one metal-based and two phthalocyanine-based oxidation processes. Redox reactions of CoPcs are electrochemically and chemically reversible, while the reduction processes of ZnPc are reversible and the oxidation processes of ZnPc are quasi-reversible processes.

Study of redox behavior of Cu(II) and interaction of Cu(II) with lysine in the aqueous medium using cyclic voltammetry

Potassium chloride (0.1 M) and acetate buffer of different pH are used to study the redox behavior of Cu(II) ions in absence and presence of lysine amino acid. The potential window +1500 mV and -1000 mV was used to study the redox properties at solid glassy carbon electrode. Silver/silver chloride is used as a reference electrode and the counter electrode used is Pt. One pair of cathodic and anodic peaks for the Cu(II)/Cu(0) system is showed in cyclic voltammograms indicating the presence of two-electron transfer. The interaction between metal and ligand is supported by the shift of peak potential and charge transfer rate constant (k s ) values. Concentration effect of Cu(II) ions and solution pH effect on the interaction was also studied. The quasi-reversible process is indicated by a higher value of peak current ratio and peak potential separation (ΔE).

Electrochemical Characterization of Biochemically Active Cu(II) Mixed Ligand Complex with Histidine and Cysteine

AbstractCopper(II) complexes with cysteine and histidine, amino acids that coordinate copper(II) in human body, were investigated. Cu‐His and Cu‐Cys complexes were detected in pH range from 5.0 to 9.0 using voltammetric techniques. [CuHis2] complex reduces by two‐electron reversible process at ≈−0.40 V, while [CuCys] complex by one‐electron quasireversible process at −0.6 V, revealing strong adsorption at the electrode surface. When both amino acids are present in the solution, new peak appeared at −0.5 V, which corresponded to the [CuHisCys] complex reduction. Formation and characterization of mixed ligand complex was also supported by UV‐Vis spectra recorded at fixed histidine and various cysteine concentrations. Formation of [CuHisCys] complex in the solution was detected and stability constant calculated to amount to log KCuHisCys=16.9±0.3. This study was the first attempt to characterize formation of Cu(II) mixed ligand complexation process with biochemically important amino acids in electron transport and oxygenation reactions in human body.