水相中5-（嘌呤-6-巯基）邻苯二酚衍生物的电化学合成

本文报道了6-巯基嘌呤存在时在水相中通过阳极氧化邻苯二酚来电化学合成5-(嘌呤-6-巯基)邻苯二酚衍生物。循环伏安法和控制电位电解的结果表明该类化合物的形成为EC过程,即邻苯二酚衍生物原料先是被电化学氧化成对应的邻苯醌衍生物,该醌非常活泼,进一步与6-巯基嘌呤发生迈克尔加成反应,原位转化生成化合物3a-3d。该工作进一步证明了水相中邻苯醌衍生物的电化学合成与原位转化是合成邻苯二酚衍生物的重要方法。     

A Penicillamine Biosensor Based on Tyrosinase Immobilized on Nano‐Au/ PAMAM Dendrimer Modified Gold Electrode

Gold electrodes were modified with submonolayers of 3‐mercaptopropionic acid and further reacted with poly(amidoamine) (PAMAM) dendrimers to obtain thin films. The high affinity of PAMAM dendrimer for nano‐Au with its amine groups was used to realize the role of nano‐Au as an intermediator to immobilize the enzyme of tyrosinase. The characterization of the modified electrode was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy (AFM). Tyrosinase can catalyze the oxidation of catechol to o‐benzoquinone. When penicillamine was added to the solution, it reacted with o‐benzoquinone to form the corresponding thioquinone derivatives, which resulted in decrease of the reduction current of o‐benzoquinone. Based on this, a new electrochemical sensor for determination of penicillamine has been developed.     

Estimation of homogeneous rate constants of reaction of electrochemically generated ortho‐benzoquinones with 1,3‐indandione

Electrochemical oxidation of some catechol derivatives has been studied in the presence of 1,3‐indandione as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate the participation of electrochemically produced o‐benzoquinones in the Michael reaction with 1,3‐indandione to form the corresponding new catechol derivatives. On the basis of the EC mechanism, the observed homogeneous rate constants (k_obs) of reaction of produced o‐benzoquinones with 3‐indandione were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 605–613, 2007     

聚苯胺颗粒电极的制备与其电化学行为

采用循环伏安法,以含苯胺(An)的硫酸溶液为电解质,采用循环伏安技术在Pt微盘电极上得到随机、不连续沉积的聚苯胺(PAn)微颗粒和PAn膜.实验结果表明:H2SO4浓度、苯胺浓度、电位扫描上限和扫速对电化学合成随机、不连续沉积的PAn微颗粒具有重要影响.不连续随机沉积的PAn微颗粒电极与PAn膜电极在锂离子(Li-ion)电池电解质溶液中的行为有明显差异,不连续随机沉积的PAn微颗粒电极可以清楚地得到氧化还原电流峰,而PAn膜电极无法形成清晰的氧化还原电流峰.采用较缓慢扫描速度更有利于形成良好"结晶"的不连续PAn颗粒电极,该种电极可以同时具有高比能量和可逆性能.     

Nucleophilic Addition of Thiaproline to Electrochemically Derived o‐Quinone,Application to the Sensitive Voltammetric Detection of Thiaproline

The mechanism of electrochemical behavior of catechol in the presence of thiaproline is investigated by cyclic voltammetry, controlled‐potential coulometry and spectrophotometric tracing of the reaction coordinate. The results indicate that thiaproline participate in with an ECEC mechanism in a nucleophilic (Michael) addition to o‐quinone. Effect of pH of buffer solution on reaction pathway is studied and showed that addition of thiaproline to the o‐quinone is performed only in solutions with pHs higher than 5. These results indicate that the addition of thiaproline is occurred first from amine functional group. In the second step, the addition of carboxylate group of thiaproline to C‐5 of catechol results the final product with a lactone ring in its structure. Observation of two isosbestic point in absorption spectrum during the progress of the electrolysis together with the FT‐IR results for final product can be presented as evidence for two step addition of thiaproline to catechol. Final product, due to the electron donor property of thiaproline, more easily oxidized respect to the former catechol and as a result, a new redox couple is obtained for this compound in lower potentials. The easier anodic oxidation of addition product (relative to catechol) caused to an increase in anodic current for catechol, which is proportional to the thiaproline concentration. The differential pulse voltammetry (DPV) is applied as a sensitive voltammetric method for the detection of thiaproline. A linear range from 5×10^?8 to 5×10^?6 M with a detection limit of 1×10^?8 M is resulted for thiaproline. With respect to the reversibility of the electrochemical reactions in the mechanism, and also more facile oxidation of the addition products, the square‐wave voltammetry is presented as a method with considerably more sensitivity for the detection of sub‐micromolar amounts of thiaproline. The advantageous properties of the voltammetric method for thiaproline detection lie in its excellent catalytic activity, sensitivity and simplicity.     

Electrodeposition of Catechol on Glassy Carbon Electrode and Its Electrocatalytic Activity Toward NADH Oxidation

Catechol can be oxidized electrochemically to its corresponding o‐benzoquinone. The electrogenerated quinone can be deposited by cycling the potential at the surface of glassy carbon electrodes. We have studied the electrochemical features of films derived from catechol by cyclic voltammetry. The electrodeposited film shows stable reversible redox response, dependent on pH as anticipated for quinone/catechol functionalities. Glassy carbon electrodes covered with a film derived from catechol exhibit catalytic activity in the electrooxidation of NADH at a low potential. The catalytic current is proportional to the concentration of NADH over the range 0.02–0.34 mM.     

Electrochemical dissolution of chalcopyrite studied by voltammetry of immobilized microparticles

The characteristics of anodic electrochemical dissolution of chalcopyrite (CuFeS₂) powder in hydrochloric acid medium with sodium chloride have been studied. Cyclic voltammetry and chronopotentiometry of immobilized microparticles using paraffin-impregnated graphite electrode was employed. Present work is focused on electrochemical identification of chalcopyrite cathodic and anodic reaction products within the potential range of −0.7 to +0.8 V (vs. SCE) in hydrochloric acid solution containing sodium chloride and/or copper(II) chloride.     

Voltammetry of a Novel Antimycobacterial Agent 1‐Hydroxy‐N‐(4‐nitrophenyl)naphthalene‐2‐carboxamide in a Single Drop of a Solution

The aim of this study is the development of a miniaturized voltammetric method for the determination of an antimycobacterial agent 1‐hydroxy‐N‐(4‐nitrophenyl)naphthalene‐2‐carboxamide (HNN) in a single drop (20 μL) of a solution by cathodic and anodic voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate its redox properties followed by the optimization of differential pulse voltammetric determination in a regular 10 mL volume. The optimal medium for the analytical application of both cathodic and anodic voltammetry was found to be Britton‐Robinson buffer pH 7.0 and dimethyl sulfoxide (9 : 1, v/v). HNN gave one cathodic peak at around −0.6 V and one anodic peak at around +0.2 V vs. Ag|AgCl (3 mol L⁻¹ KCl) reference electrode. Determination of HNN in a 10 mL volume gave the limit of quantification around 10 nmol L⁻¹ by both adsorptive stripping anodic and cathodic voltammetry. Afterwards, miniaturized voltammetric methods in a single drop of solution (20 μL) were investigated. This approach requested some modifications of the cell design and voltammetric procedures. A novel method of removing dissolved oxygen in a single drop had to be developed and tested. Developed miniaturized voltammetric methods gave parameters comparable to the determination of HNN in 10 mL. The applicability of the miniaturized method was verified by the determination of HNN in a drop of a bacterial growth medium.     

Strategy for Low Background‐Current Levels in the Electrochemical Biosensors Using Horse‐Radish Peroxidase Labels

This article describes an electrochemical strategy to achieve low background‐current levels in horse‐radish peroxidase (HRP)‐based electrochemical immunosensors. The strategy consists of (i) the use of an HRP substrate/product redox couple whose formal potential is high and (ii) the use of an electrode that shows moderate electrocatalytic activity for the redox couple. The strategy is proved by a model biosensor using a catechol/o‐benzoquinone redox couple and an indium tin oxide (ITO) electrode. The combined effect of high formal potential and moderate electrocatalytic activity allows o‐benzoquinone electroreduction with minimal catechol electrooxidation and H₂O₂ electroreduction. The detection limit for mouse‐IgG is 100 pg/mL.     

Sensitive Electrochemical Determination of Catechol with a Graphene Modified Carbon Ionic Liquid Electrode

In this paper a graphene (GR) modified carbon ionic liquid electrode (CILE) was fabricated and used as the voltammetric sensor for the sensitive detection of catechol. Due to the specific physicochemical characteristics of GR such as high surface area, excellent conductivity and good electrochemical properties, the modified electrode exhibits rapid response and strong catalytic activity with high stability toward the electrochemical oxidation of catechol. A pair of well‐defined redox peaks appeared with the anodic and the cathodic peak potential located at 225 mV and 133 mV (vs.SCE) in pH 6.5 phosphate buffer solution, respectively. Electrochemical behaviors of catechol on the GR modified CILE were carefully investigated and the electrochemical parameters were calculated with the results of the electrode reaction standard rate constant (k_s) as 1.24 s^?1, the charge transfer coefficient (α) as 0.4 and the electron transfer number (n) as 2. Under the selected conditions the differential pulse voltammetric peak current increased linearly with the catechol concentrations in the range from 1.0 × 10^‐7 to 7.0 × 10^?4mol L‐1 with the detection limit as 3.0 × 10^?8mol L‐1 (3σ). The proposed method was further applied to the synthetic waste water samples determination with satisfactory results     

酸性介质中碘离子在铂电极上的电化学氧化行为

采用循环伏安法研究了酸性介质中碘离子在铂电极上不同电位区间, 不同酸度下的电化学反应行为. 结果表明, 当极化电位较低(小于0.6 V(vs Hg/Hg2SO4))时, 碘离子在铂电极上发生2I--2e→I2电氧化反应, 反应产物通过I2+I-=I-3被进一步溶解, 整个反应属于E-C(electrochemical-chemical)模式. 电氧化过程中可以形成碘膜, 其也可以被碘离子溶解. 当极化电位升高至0.6 V(vs Hg/Hg2SO4)或以上时, 碘离子会直接电氧化为高价态碘化合物, I-+3H2O→IO-3+6H++6e, 而析出的碘膜并不发生再氧化反应; 在电化学还原过程中, 出现了两个还原峰, 分别对应于I2、I-3的还原反应; 在无碘膜时, 碘离子电氧化过程受溶液中碘离子的液相扩散步骤控制; 碘膜形成后, 主要受碘膜中碘离子的固相扩散控制; 酸度对于碘离子的电化学氧化过程有很大的影响, 其线性极化曲线的起峰电位及电流峰值电位均随酸浓度升高而负移.     

Electrocatalytic Oxidation of Paracetamol on Ni and NiCu Alloy Modified Glassy Carbon Electrode

In this study we investigated the electrocatalytic oxidation of anti‐inflammatory drug (paracetamol) on Nickel and Nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) in alkaline solution. These electrodes prepared by galvanostatic method and different electrochemical techniques such as cyclic voltammetry and chronoamperometry were used to track the oxidation process and its kinetics. From Voltammetric studies we concluded that in the presence of drugs the anodic peak current of low valences Nickel species increased, followed by a decrease in the corresponding cathodic current peak. This indicates that drugs were oxidized on the redox mediator which was immobilized on the electrode surface via an electrocatalytic mechanism. Using Laviron's equation, the values of α and k_s for the immobilized redox species were determined. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of paracetamol was found in agreement with the values obtained from CV measurements.     

Selective Analysis of Secondary Amines Using Liquid Chromatography with Electrochemical Detection (LC‐EC)

In a mixture of primary and secondary aliphatic amines, the primary amines were derivatized (masked) with o‐phthalaldehyde (OPA) followed by derivatization of the remaining secondary amines with ferrocenecarboxylic acid chloride (FAC). The “tagged” amines were analyzed by LC‐EC (liquid chromatography with electrochemical detection) using in‐series dual electrode detection. Chemically‐reversible oxidation of the FAC tagged secondary amines and their subsequent complementary oxidation and reduction signals coupled with chemically‐irreversible oxidation of OPA tagged primary amines provided the selectivity for quantitative secondary amine analysis. The procedure was also applied for the selective identification of fragment 4–11 (N‐terminus‐proline) of Substance P in the presence of other Substance P fragments with primary amino acids as their N‐termini.     

Electrochemical Polymerization of Methylene Green

The electrochemical polymerization of methylene green has been carried out using cyclic voltammetry. The electrolytic solution consisted of 4° 10^?3 mol/L methylene green, 0.1 mol/L NaNO₃ and 1 × 10^?2 mol/L sodium tetraborate with pH 11.0. The temperature for polymerization is controlled at 60°C. The scan potential is set between ?0.2 and 1.2 V (vs. Ag/AgCl with saturated KCl solution). There are an anodic peak and a cathodic peak on the cyclic voltammogram of poly (methylene green) at pH≤3.8. Both peak potentials shift towards negative potentials with increasing pH value, and their peak currents decrease with increasing pH value. Poly (methylene green) has a good electrochemical activity and stability in aqueous solutions with pH≤3.8. The UV‐Visible spectrum and FTIR spectrum of poly (methylene green) are different from those of methylene green.     

石墨电极上硫化钠的阳极氧化机理探索

电解硫化氢气体的碱性吸收液（Ｎａ２Ｓ表示）产生单质硫和氢气的研究是治理硫化氢废气的一种新方法［１ -７］,较之Ｃｌａｕｓ法有许多优点［３,４］,这对环境保护和资源回收均具有重要的实际意义．文献对硫化物水溶液电化学氧化机理的研究主要着重于在某些贵金属阳极上,包括某些硫化矿的湿法冶金反应过程的研究［８,９］,光电化学电池中使用多硫化物的研究［１０ -１３］,以及硫化物电解时产生单质硫的电催化活性研究［１４］等 ;但在石墨阳极上硫化物电化学氧化机理的研究报导却很少［３,４］．本文研究在石墨阳极上硫化钠水溶液…     

Voltammetric studies of the activity of an electrode made of a graphite-epoxy composite in redox reactions of ascorbic acid and hydroquinone

The potentials of the anodic peak of ascorbic acid oxidation and the potential differences of anodic and cathodic peaks (ΔE _p) of the hydroquinone/benzoquinone redox system at an electrode made of a graphite-epoxy composite are determined in weakly acidic and neutral supporting electrolytes by direct and cyclic voltammetry. The results obtained are compared with thermodynamic values and with the available values of these parameters at different solid electrodes for the above-mentioned redox systems. The effect of aging of the surface of electrodes made of graphite-epoxy composites on the potentials and peak currents of the anodic oxidation of ascorbic acid are studied. It is demonstrated that the regeneration of the electrode surface by mechanically cutting thin layers is important for reducing the δE _p value of the hydroquinone/benzoquinone redox system down to 28–30 mV in supporting electrolytes with pH 2.0 and 7.0. This value is typical of thermodynamically reversible electrode reactions involving two-electron transfer at 20–25°C.     

Electrochemical Oxidation of Catechols (=Benzene‐1,2‐diols) in the Presence of Benzoylacetonitrile: Synthesis of New Derivatives of 5,6‐Dihydroxybenzofuran

The electrochemical oxidation of catechol (=benzene‐1,2‐diol; 1a ) and some of its derivatives in H₂O/MeCN 1 : 1 containing benzoylacetonitrile (=β‐oxobenzenepropanenitrile; 3 ) as a nucleophile was studied by cyclic voltammetry and controlled‐potential coulometry. The voltammetric data showed that electrochemically generated o‐benzoquinones (=cyclohexa‐3,5‐diene‐1,2‐diones) from catechol ( 1a ) and 3‐methylcatechol ( 1b ) participate in a Michael‐addition reaction with 3 to form the corresponding 5,6‐dihydroxybenzofuran‐3‐carbonitrile 8 (Scheme 1). In this work, we report an efficient one‐pot method with high atom economy for the synthesis of new substituted 5,6‐dihydroxybenzofuran‐3‐carbonitriles in an undivided cell under ambient conditions.     

Electrochemistry of electropolymerized tetra (p-aminophenyl)porphyrin nickel film electrode and catalytic oxidation of acetaminophen

A polymer film of tetra(p-aminophenyl) porphyrin nickel was obtained at a glassy carbon electrode by a cyclic voltammetric method. Cyclic voltammograms of the film electrode exhibited two stable redox waves with anodic peak potential at 0.43V and cathodic peak potential at 0.30 V in 0.5M NaOH aqueous solution. The electrocatalytic characteristics of the film electrode were studied by cyclic voltammetry, a. c. impedance analysis and other methods. The oxidation peak current increased linearly with the addition of acetaminophen to the aqueous NaOH medium in the range 1 × 10^–6–2 × 10^–4 M acetaminophen. The performance of the electrode was verified by the determination of acetaminophen in a paracetamol preparation.     

Voltammetric Studies and Determination of Levodopa and Carbidopa in Pharmaceutical Products

In this paper, the possibility of analyzing levodopa and carbidopa by differential pulse voltammetry (DPV) utilizing a glassy carbon electrode in 0.1 mol L^?1 HClO₄ is reported. Cyclic voltammograms of levodopa show a redox couple with anodic and cathodic peak potentials at 0.58 V and 0.52 V (vs. Ag/AgCl), respectively. For carbidopa, there are two oxidation waves with maximum currents at 0.53 V and 1.02 V, without any cathodic counterpart at slow enough scan rate. Since in such conditions, the oxidation product of carbidopa does not undergo reduction, it is possible to analyze levodopa without interference. On the other hand, carbidopa can be determined between 0.85 V and 1.1 V in the presence of levodopa, coating the electrode with a Nafion film, which is selective for carbidopa. The developed methodology was applied to two different commercial samples of pharmaceutical products. The obtained data were compared with the results of the analysis by high performance liquid chromatography (HPLC) with UV detection, showing good correlation (relative errors changing between 0.4% and 3.5%) and absence of interference of the other components that accompanied the pharmaceuticals.     

Mechanistic Pathways and Identification of the Electrochemically Generated Oxidation Products of Flavonoid Eriodictyol in the Presence of Glutathione

The metabolic oxidation pathways of dietary flavonoid eriodictyol (Er) are not very well‐probed. In the present work, the electrochemical oxidation behavior of Er was studied in aqueous Britton‐Robinson (B‐R) buffer solution using cyclic voltammetry (CV), chronoamperometry (CA), and bulk‐electrolysis (BE). The oxidation products and reaction pathways of Er in the absence and the presence of glutathione (GSH) were proposed and identified in view of the results obtained by ultra‐high‐performance liquid chromatography coupled with mass spectrometry (UPLC‐MS). In the absence of GSH, eriodictyol shows one quasi‐reversible oxidation process at E_1/2=0.305 V, followed by a totally irreversible anodic peak at a more positive potential (E_p^a=1.05 V vs. Ag/AgCl, 3 M KCl). Putatively, the first process corresponds to the oxidation of the catechol moiety on the B ring of Er while the second one is attributed to the oxidation of the resorcinol moiety on the A ring. In the presence of GSH, however, the anodic oxidation of Er was proposed to be an ECEC‐type mechanism. The Er molecule first underwent a two‐electron oxidation coupled with loss of two‐proton to generate the corresponding quinone, which was either reduced to the original Er molecule by GSH, or further interacted with GSH to produce mono‐ and bi‐ glutathione conjugates of Er. The proposed mechanism was confirmed by digital simulation of the cyclic voltammograms.