Heterogeneous electron-transfer kinetic parameters of metalloproteins as studied by channel-flow hydrodynamic voltammetry

Channel-flow hydrodynamic voltammetry was used to study the direct electron-transfer reactions of two metalloproteins, myoglobin and cytochrome c, under steady-state conditions at methyl viologen modified (MVM) gold foil electrodes. Utilization of a dual working electrode cell with this technique permitted determination of the heterogeneous electron-transfer kinetics for both the reduction and oxidation of myoglobin. The formal heterogeneous electron-transfer rate constants in pH 7.00 phosphate buffered solutions were found to be 8.9 (±1.5)×10⁻⁵ cm s⁻¹ for the reduction, and 7.7 (±1.2)×10⁻⁵ cm s⁻¹ for the reoxidation of myoglobin. The transfer coefficient values obtained were 0.21 (±0.01) for the reductive (α) and 0.82 (±0.01) for the oxidative (1−α) electrode reactions. Ionic strength and pH dependences were observed in these direct electron-transfer reactions. Collective current efficiency measurements in the myoglobin experiments indicated that an overall simple charge-transfer process occurred at the respective electrode interfaces. A formal rate constant of 3.4 (±0.2)×10⁻⁵ cm s⁻¹ with a transfer coefficient of 0.25 (±0.01) for the reduction (α) of cytochrome c was obtained by this hydrodynamic technique. The use of channel-flow hydrodynamic voltammetry in characterizing an electrode reaction as well as an interpretation of the data presented are discussed.     

343 - Heterogeneous electron transfer kinetics of sperm whale myoglobin

Very little information has been reported describing the heterogeneous electron transfer kinetics of biological molecules at electrodes. We report here the first application of a recently developed spectroelectrochemical technique to the measurement of the heterogeneous electron transfer kinetics of a biological molecule, sperm whale myoglobin, at a methyl viologen modified gold minigrid electrode. The overpotential dependence of the heterogeneous electron transfer rate constant for the reduction of myoglobin at this surface gives rise to values of the formal heterogeneous electron transfer rate constant [k^o′_f,h = 3.88 (± 0.07) × 10⁻¹¹ cm/s] and the transfer coefficient [α = 0.88 (± 0.01)] for this electrocatalyzed process. The importance of studying the heterogeneous electron transfer kinetics of biological molecules lies in the fact that many physiological electron transfer reactions occur heterogeneously. Though myoglobin does not function in this manner physiologically, our initial study has been directed at this molecule owing to its stability and ready availability. It is expected that this technique will be applied to other optically transparent electrodes and other biological molecules thereby providing new insights into understanding biological redox reactions.     

Study on electrode process of myoglobin at a polymerized Toluidine Blue film electrode

This paper reports the use of an electrochemically polymerized Toluidine Blue (TB) filmelectrode.The film on platinum electrode surface was analyzed with ESCA.The heterogeneouselectron transfer processes of myoglobin at the polymerized TB film electrode have been investigatedusing in situ UV-visible spectroelectrochemistry.The formal potential(E°′)and electron transfernumber(n)of myoglobin were calculated as E°′=0.045 V(vs.NHE)and n=0.99.The exhaustivereduction and oxidation electrolyses are achieved in 130 s and 110 s respectively,during a potential stepbetween-0.4 V and+0.4 V.A formal heterogeneous electron transfer rate constant(ksh)of 1.09×10~(-4) cm/s and a transfer coefficient(α)of 0.47 were obtained by cyclic voltabsorptometry,whichindicated that myoglobin underwent a quasi-reversible electrode process at the polymerized TB filmelectrode.     

A study of the electrochemical behavior of an oxadiazole derivative electrodeposited on multi-wall carbon nanotube-modified electrode and its application as a hydrazine sensor

In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT−GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k _s, and the charge transfer coefficient, α, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4 ± 0.5 s⁻¹ and 0.51, respectively at pH = 7.0. The obtained results indicate that hydrazine peak potential at OMWCNT−GCE shifted for 14, 109, and 136 mV to negative values as compared with oxadiazole-modified GCE, MWCNT−GCE, and activated GCE surface, respectively. The electron transfer coefficient, α, and the heterogeneous rate constant, k′, for the oxidation of hydrazine at OMWCNT−GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0 μM and 10.0 to 400.0 μM and detection limit of 0.17 μM for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT−GCE was shown to be successfully applied to determine hydrazine in various water samples.

     

A Novel Electrochemical Glassy Carbon Electrode Modified with Carbon Black and Glyceline Deep Eutectic Solvent within a Crosslinked Chitosan Film for Simultaneous Determination of Acetaminophen and Diclofenac

Glyceline, reline, or ethaline deep eutectic solvents and carbon black nanoparticles within a crosslinked chitosan film are investigated as glassy carbon electrode modifiers for the first time. The selected 5 mg mL⁻¹ glyceline modified GCE was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Simultaneous determination of acetaminophen and diclofenac by differential pulse adsorptive stripping voltammetry (DPAdSV) presented limits of detection of 2.6×10⁻⁸ and 5.2×10⁻⁸ mol L⁻¹ for acetaminophen and diclofenac, respectively, in pharmaceutical and biological samples. The obtained results were compared with those obtained by HPLC at a confidence level of 95 %.     

Square‐Wave Voltammetry of the Molybdenum‐1,10 Phenanthroline‐Fulvic Acids Complex: Redox Kinetics Measurements

The reduction process of molybdenum in the presence of fulvic acids and phenanthroline was investigated by square-wave voltammetry (SWV). The mixed-ligand complex of molybdenum exhibits a pronounced tendency to adsorb onto the mercury electrode surface. The electrode reaction proceeds as a surface process in which both components of the redox couple are firmly confined to the electrode surface. The kinetics of the electrode reaction is studied utilizing the properties of “split SW peaks” and “quasireversible maximum”. The kinetic parameters obtained with two different square-wave voltammetric methods are in good agreement. In 0.5 mol/L NaCl solution with pH 2.5 the kinetic parameters are: standard rate constant k_s=8±2 s⁻¹, cathodic electron transfer coefficient α=0.41±0.05, and number of exchanged electrons n=2. The SW kinetic measurements are confirmed by cyclic voltammetric method.     

Time Resolved Direct Determination of Arsenate in the Presence of Arsenite on Pencil Graphite Electrode Modified by Graphene Oxide and Zirconium

Trace amount of arsenate in the presence of arsenite was determined directly on pencil graphite electrode modified by graphene oxide and zirconium (Zr−G−PGE). The layer‐by‐layer modification of PGE was characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Key point of the developed method was quick adsorption of arsenate than arsenite on the Zr−G−PGE. In optimal conditions, the Zr−G−PGE was applied for determination of arsenate using differential pulse voltammetry in a linear range 0.10–40.0 μg L⁻¹ with a limit of determination of 0.12±0.01 μg L⁻¹. The sensitivity of the electrode was 1.36±0.07 μA/μg L⁻¹. The modified electrode was used to measure the concentration of arsenate in the river water. A recovery test was performed by introducing 10 μg L⁻¹ arsenate into the rivers water in order and acceptable data of average recovery of 101.2 % was obtained. From the experimental results, the as‐prepared electrode can provide a satisfactory method for direct determination of arsenate in real samples.     

Determination of Cytochrome C,in Solution and in The Adsorbed State,by Differential Pulse Voltammetry (DPV).

Abstract

We carried out the determination of cytochrome C, in solution and in the adsorbed state, using differential pulse voltammetry (DPV). The results obtained with DPV were compared with those obtained using cyclic voltammetry (CV). The influence of the nature of the electrodic material and of the different promoters was shown. It was also demonstrated that the electron transfer in solution and in the adsorbed state is quasi-reversible.

Cytochrome C was determined at a concentration of 1.0 × 10^?5 mol L^?1 which was more one decade lower than that obtained by cyclic voltammetry. The linearity range was more than two decades.     

Electrochemical Behaviour Study and Determination of Guanine, 6‐Thioguanine,Acyclovir and Gancyclovir on Fluorine‐doped SnO2 Electrode. Application in Pharmaceutical Preparations

An electroanalytical method using square wave voltammetry (SWV) is proposed for the quantification of Guanine (G), 6‐Thioguanine (TG), Acyclovir (Acy) and Ganciclovir (Gan) in different types of pharmacological samples. In addition, for the first time, a study of the electrochemical behavior (using cyclic voltammetry, CV) of guanine and its pharmacological derivatives on fluoride doped oxide (FTO) electrodes was carried out. The study of CV potential scanning demonstrated the charge transfer process was diffusion controlled and the diffusion coefficient was determined for all the studied products. Besides, electrochemical parameters, such as transfer coefficient, heterogeneous charge transfer constant and the number of electrons transferred (e) were determined namely, 4e for TG and 2e for G, Acy and Gan. SWV studies at pH 4 for G and 2 for TG, Acy and Gan showed linear ranges between 4.0×10⁻⁶ and 40.0×10⁻⁶ mol L⁻¹, with detection limits of 0.91×10⁻⁶ for G, and 1.50×10⁻⁶ for TG, 1.25×10⁻⁶ for Acy and 0.45×10⁻⁶ mol L⁻¹ for Gan. The method presents sensitivity and stability appropriate to be employed in quality control and routine quantification of drugs in pharmaceutical formulations.     

A study of the electrochemical behavior of an oxadiazole derivative electrodeposited on multi-wall carbon nanotube-modified electrode and its application as a hydrazine sensor

In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT?GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k _s, and the charge transfer coefficient, ??, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4?±?0.5?s^?1 and 0.51, respectively at pH?=?7.0. The obtained results indicate that hydrazine peak potential at OMWCNT?GCE shifted for 14, 109, and 136?mV to negative values as compared with oxadiazole-modified GCE, MWCNT?GCE, and activated GCE surface, respectively. The electron transfer coefficient, ??, and the heterogeneous rate constant, k??, for the oxidation of hydrazine at OMWCNT?GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0???M and 10.0 to 400.0???M and detection limit of 0.17???M for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT?GCE was shown to be successfully applied to determine hydrazine in various water samples.     

Electrochemical behavior of high-molecular-weight poly(ferrocenylsilane) films in aqueous electrolyte solutions

The electrochemical behavior of high-molecular-weight poly(ferrocenyldimethylsilane) films and poly(ferrocenylmethylphenylsilane) films, which contained about 2.8 × 10⁻⁶ mol cm⁻² ferrocene sites in eight kinds of aqueous electrolyte solutions, was investigated with cyclic voltammetry (CV). In some aqueous electrolyte solutions, the CV peak currents diminished gradually with an increase in the scanning times, whereas in other aqueous electrolyte solutions, stable and repeated cyclic voltammograms were obtained. The polymer films were poor-solvent-swollen in aqueous electrolyte solutions, and this resulted in a high resistivity of mass transfer and a slow rate of electrode reaction; therefore; quasireversible or irreversible CV processes were obtained. The kinetic parameters of the film-electrode processes, such as the surface transfer coefficient, the apparent diffusion coefficient, and the standard rate constant for electron transfer, for the two films in aqueous LiClO₄ solutions were measured, and the electrode process mechanism of the films was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2245–2253, 2004     

Electroactive porous films of myoglobin within calcium alginate

In this work, a novel two-step construction strategy for protein assembly films was proposed. The first step was the preparation of porous calcium alginate (CA) films by spraying calcium chloride (CaCl₂) solution over the mixture surface of sodium alginate and polyethylene glycol on various solid substrates. The second step involved the cast of myoglobin (Mb) onto the porous CA films and then formed the electroactive porous Mb-CA films. The nitrogen adsorption desorption isotherm, scanning electron microscope, alternating current impendence and cyclic voltammetry were used to characterize the porous films. Fully hydrated porous CA films had nearly 90 wt% water contents and UV–vis showed that Mb in the porous films retained its near native conformation at medium pH. The stable films modified on glassy carbon electrode demonstrated good electroactivity in protein-free buffer, which was originated from protein heme Fe(III)/Fe(II) redox couples. The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (k _s) and formal potential (E ^o′) were estimated by fitting the data of square-wave voltammetry with nonlinear regression analysis. It was observed that the formal potential of the Mb Fe(III)/Fe(II) couple in porous CA films shifted linearly between pH 4.0 and 11.0 with a slope of −52.7 mV/pH, suggesting that one proton transfer was coupled to each electron transfer in the electrochemical reaction. The porous Mb-CA films showed the electrocatalytic activity toward dioxygen, hydrogen peroxide, and nitrite with significant decreases in the electrode potential required, and exhibited good operational and storage stability, reproducibility and fast response time for H₂O₂ detection. It is showing the possible future application of the films for biosensors and biocatalysis.     

Electrocatalytic Characteristics of Ferrocenecarboxylic Acid Modified Carbon Paste Electrode in the Oxidation and Determination of L‐Cysteine

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenecarboxylic acid modified carbon paste electrode (FCMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L ‐cysteine is occurs at a potential about 580 mV less positive than that an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α and catalytic reaction rate constant, K′_h were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L ‐cysteine showed a linear dependent on the L ‐cysteine concentration and linear calibration curves were obtained in the ranges of 10^?5 M–10^?3 M and 4.1×10^?8 M–3.7×10^?5 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (2δ) were determined as 2.4×10^?6 M and 2.5×10^?8 M by CV and DPV methods. This method was also examined for determination of L ‐cysteine in some samples, such as Soya protein powder, serum of human blood by using recovery and standard addition methods.     

Electroactivated Disposable Pencil Graphite Electrode – New,Cost-effective,and Sensitive Electrochemical Detection of Bioflavonoid Hesperidin

In this paper, for the first time, electroactivated disposable pencil graphite electrode (ePGE) was used for the detection of bioflavonoid hesperidin with cyclic and differential pulse voltammetry. The electroactivation efficiency of the pencil graphite electrode (PGE) was examined employing electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) and the enhancement of electron transfer kinetics of the PGE after the electroactivation was found. Hesperidin is irreversibly oxidized on the ePGE and its oxidation was the most pronounced at pH=5.0. Two electrode processes were detected, on one hand, a mixed diffusion and adsorption control was observed for the first electrode process. On the other hand, only diffusion control was observed in the second electrode process. Linear dependence between the peak current and the hesperidin concentration was obtained in the concentration range from 5×10⁻⁷ mol dm⁻³ to 1×10⁻⁵ mol dm⁻³ and the determined lower limit of detection (LOD) was 2×10⁻⁷ mol dm⁻³. Moreover, hesperidin in pharmaceutical formulation (containing active substance, hesperidin, and excipients) was quantified using ePGE. A good correlation was obtained between experimentally obtained hesperidin concentration by voltammetric analysis and concentration determined by standard HPLC technique (R²=0.9462).     

Sensitive Superoxide Biosensor Based on Silicon Carbide Nanoparticles

Direct electron transfer of immobilized superoxide dismutase (Cu, Zn‐SOD) onto silicon carbide (SiC) nanoparticles displays a pair of well defined and nearly reversible redox peaks with formal potential (E°′) of −0.03 V in pH 7.4. The heterogeneous electron transfer rate constant (k_s) and surface coverage (Γ) of immobilized SOD are 11.0±0.4 s⁻¹ and 1.42×10⁻¹¹ mol cm⁻². Biosensor shows fast amperometric response (3s) with sensitivity and detection limit of 1.416 nA μM⁻¹, 1.66 μM, and 1.375 nA μM⁻¹, 2.1 μM for cathodically or anodically detection of superoxide, respectively. This biosensor also exhibits good stability, reproducibility and long life‐time.     

A comparison study of adsorptive transfer voltammetry and solution phase voltammetry for the determination of caffeic acid

This study reports a comparison of adsorptive transfer and solution phase voltammetric methods for the study of caffeic acid. For this purpose, a platform was prepared by the modification of glassy carbon electrodes (GCEs) with MWCNTs and samarium nanoparticles (SmNPs) by means of an ultrasonic bath. The surface morphology of the platform was characterized using SEM, EDX and XRD. The adsorptive transfer voltammetric method was based on the adsorption of caffeic acid (CFA) at the surface of the modified electrode by keeping it into a solution of CFA. Afterwards, the modified electrode was transferred with the adsorbed species in a cell containing only 0.1 mol L⁻¹ phosphate buffer solution (PBS) for the analysis. The current response of CFA was found to be linear over a concentration from 5.0 × 10⁻¹⁰ mol L⁻¹ to 1.0 × 10⁻⁷ mol L⁻¹. The values of the limit of detection (LOD) and limit of quantification (LOQ) were 2.0 × 10⁻¹⁰ mol L⁻¹ and 6.67 × 10⁻¹⁰ mol L⁻¹, respectively. The adsorptive transfer method using the modified electrode (SmNPs/MWCNTs/GCE) has successfully been applied to food samples for determining CFA. The solution phase voltammetry was carried out by dipping the electrode into a voltammetric cell containing CFA. The plot of peak currents was linear over the concentration range of 5.0 × 10⁻⁹ mol L⁻¹ –8.0 × 10⁻⁸ mol L⁻¹. The values of LOD and LOQ were 2.0 × 10⁻⁹ mol L⁻¹ and 6.67 × 10⁻⁹ mol L⁻¹ for CFA using a classical solution phase voltammetry at the proposed platform. It was shown that the LOD obtained at adsorptive transfer voltammetry was 10-fold lower when compared to classical solution phase voltammetry.     

High Sensitive Sensor Based on Carbon Nanotube Electrode for Determination of Lanthanum in the Presence of Calcon Carboxylic Acid

In this paper we have investigated the electrochemical activity of lanthanum chloride (La (III)) in the presence of calcon carboxylic acid (CCA) using a multi-walled carbon nano tube/carbon paste electrode (CNT/CPE). The peak current increases linearly with increasing of the La (III) concentration. For this purpose, a few electrochemical methods such as cyclic, differential pulse voltammetry, linear sweep and hydrodynamic voltammetry, and chronoamperometry were used. The results show that calcon carboxylic acid as a ligand was useful for determination of La (III) and was able to improve its sensitivity. Cyclic voltammetry was used for study of reduction reaction of La (III) at the surface of modified electrode. The electrochemical parameters for La (III) at the surface of CNT/CPE, such as diffusion coefficient (D/ cm² s ^?1 = 5.26 × 10^?6), the electron transfer coefficient, (α = 0. 43), and the reduction rate constant, (k/ M s^?1 = 2.33 (±0.015) × 10²), were determined using voltammetry methods, which with the detection limit of La (III) by differential pulse voltammetry was found to be 1.3 nM. The combination of CCA with CNT as mediators in carbon paste electrode showed that this electrode is capable, sensitive, and simple to quantify La (III) in real samples with an average recovery of 97.64%.     

Electrochemical oxidation of 4‐tert‐butylcatechol in the presence of β‐cyclodextrin: Interplay between E and CE mechanisms

Electrochemical behavior of 4‐tert‐butylcatechol (H₂Q) in the presence of β‐cyclodextrin (β‐CD) was studied using cyclic voltammetry and hydrodynamic voltammetry. An electrochemical model in which both H₂Q and its oxidized form (Q) created inclusion complexes with β‐CD was proposed, and it was concluded that both free (as a result of complex‐dissociation reaction) and complex species could performed electron transfer. The heterogeneous rate constant for electron transfer of the inclusion complexes and their kinetic and thermodynamic parameters were obtained using digital simulation. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 507–513, 2012     

High‐Performance Electrocatalytic Activity of Palladium‐Copper Nanoalloy towards Methanol Electro‐oxidation in an Alkaline Medium

Nanoalloy of PdCu were synthesized with three different stoichiometry ratio (3 : 1, 1 : 1, 1 : 3) by simple co‐reduction process at 5 °C with Triton X‐100 as surface modifier. Morphology and composition of the synthesized catalyst were characterized by X‐ray diffraction (XRD), X‐ray photo electron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X‐ray analysis (EDAX) with selected area electron diffraction (SAED) techniques. Electrocatalytic activity and stability of the catalysts towards methanol oxidation reaction were verified in alkaline medium by cyclic voltammetry (CV) and chronoamperometry (CA). Observed results emphasis that PdCu nanoalloy in the 3 : 1 stoichiometric ratio shows better catalytic activity (778.98 mA mg⁻¹) and stability not only in the initial state (93.73 mA mg⁻¹) but also after 1800 s (8.61 mA mg⁻¹) among all other prepared catalysts.     

Development of an Electrochemical Sensor for Selective Determination of Dopamine Based on Molecularly Imprinted Poly(p-aminothiophenol) Polymeric Film

In this study, a molecularly imprinted electrochemical sensor (MIP/DA) was investigated for selective and sensitive determination of dopamine (DA) by electrochemical polymerization of p-aminothiophenol in the presence of DA on gold electrode. According to electrochemical behaviour of the sensor, gained through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), MIP/DA sensor showed distinctive electron transfer characteristics in comparison to the non-imprinted (NIP/DA) sensor. Besides the MIP/DA sensor showed high selectivity for dopamine through its analyte specific cavities. The sensor had a broad working range of 5.0×10⁻⁸–2.0×10⁻⁷ M with a limit of detection (LOD) of 1.8×10⁻⁸ M and the developed sensor was successfully applied for determination of dopamine in pharmaceutical samples.