Mechanism of Chicoric Acid Electrochemical Oxidation and Identification of Oxidation Products by Liquid Chromatography and Mass Spectrometry

Electrochemical oxidation of chicoric acid (ChA) was investigated using cyclic voltammetry and chronoamperometry at a glassy carbon electrode. Chicoric acid generates single quasi‐reversible redox wave in cyclic voltammetry over a wide pH range, and an ECEC‐dimerization mechanism is proposed. Effect of glutathione (GSH) on the electrochemical oxidation of chicoric acid (ChA) was investigated in Britton−Robinson buffer solution. Ultra‐high performance liquid chromatography (UPLC) coupled with mass spectrometry (MS) was used to show that the naturally occurring chicoric acid (ChA) underwent an electrochemical oxidation in the presence of glutathione (GSH) to form mono‐, bi‐, tri‐, and four‐glutathione conjugates of chicoric acid and a mono‐glutathione conjugate of a chicoric acid dimer. The obtained results are useful for understanding and predicting the oxidative degradation pathway of chicoric acid.     

Electrochemical Oxidation of Catechols in the Presence of Triethyl Phosphite

The mechanism of electrochemical oxidation of catechol and some of its derivatives have been studied in the presence of triethyl phosphite as a nucleophile in aqueous solution. Voltammetric studies indicate that the quinones derived from catechol, and its derivatives, participate in Michael addition reaction with triethyl phosphite. The reaction mechanism consists of electron transfer followed by a chemical reaction which is named as an EC mechanism. The homogeneous rate constants (k_obs) were estimated by comparing the experimental cyclic voltammograms with the digitally simulated voltammograms based on EC mechanism. Also the effects of nucleophile concentration and substituted group of catechols on voltammetric behavior and the rate constants of chemical reactions were examined.     

Electrochemical Oxidation of Donepezil and Its Voltammetric Determination at Gold Electrode

The oxidative ability of donepezil, a frequently prescribed drug for the treatment of Alzheimer’s disease is reported for the first time at a gold electrode. It was oxidized by cyclic voltammetry and determined by square wave voltammetry in phosphate buffer electrolyte. Electrochemical degradation of donepezil was carried out by long term potential cycling. The identification and characterization of the major product, isolated by preparative high performance liquid chromatography, was performed by high resolution mass spectrometry and 1D and 2D nuclear magnetic resonance spectroscopy. Donepezil hydroxy derivative was identified as the major electrochemical oxidation product from donepezil.     

Ni纳米催化剂的制备及其对葡萄糖电催化氧化的研究

采用等体积浸渍和程序升温还原的方法制备了不同Ni含量的Ni/AC纳米催化剂,并对其进行了形貌和结构表征。采用三电极体系和循环伏安法在碱性溶液中进行了其对葡萄糖催化氧化的电化学测试。结果表明,Ni/AC/GCE(修饰在玻碳电极上的Ni/AC)催化剂对葡萄糖有较强的电催化氧化作用。其中,20%的Ni/AC/GCE对葡萄糖电催化氧化作用最强,且随着葡萄糖浓度增加,响应电流显著增大,二者呈线性相关。20%Ni/AC/GCE催化剂对葡萄糖催化氧化的线性响应范围为0.2~6.5 mmol/L,相关系数为0.999,响应灵敏度是13.15μA/(mmol/L),最低检测限为35μmol/L。稳定性测试结果表明,20%Ni/AC/GCE有着良好的稳定性,每隔两天测试,运行三周后其响应电流仍能维持在95%以上。     

Cyclic Voltammetric Study of the Oxidation of Catechols in the Presence of Cyanide Ion

Electrochemical oxidation of catechols has been studied in the presence of cyanide ion as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate that the participation of catechols in the Michael reaction with cyanide ion to form the corresponding o‐dihydroxybenzonitrile. Based on an EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results.     

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.     

Elucidation of the Electrochemical Oxidation Pathway of Ammonia in Dimethylformamide and the Room Temperature Ionic Liquid, 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide

The direct electrochemical oxidation of ammonia has been examined in both the organic solvent dimethylformamide (DMF) and the room temperature ionic liquid 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][N(Tf)₂]. The corresponding voltammetric responses have been shown to be similar in each solvent with a broad oxidative wave occurring upon the introduction of ammonia to the solution and the appearance of a new reductive wave following the oxidation. The oxidative reaction process has been examined and a suitable reaction pathway has been deduced, corresponding to the formation of ammonium cations after oxidation of the ammonia. A linear response of limiting current against vol% ammonia was observed in both DMF and [EMIM][N(Tf)₂], suggesting potential application for analytical methods.     

Electrochemical Degradation of the Pesticide Dimethenamid‐P at Gold,DSA Platinum and Ruthenium Oxide Electrodes in Different Electrolytes

For the first time the electrochemical degradation of the pesticide dimethenamid‐P was studied. Its direct electrochemical degradation, using potential cycling at a gold electrode, was performed by cyclic voltammetry and HPLC analysis of electrolyte after 72 h showed 56.8 % of degradation. HPLC‐MS indicates the formation of degradation products through the elimination of chlorine atom and C? N bond cleavage. By indirect electrolysis using DSA Ti/PtOx and DSA Ti/RuO₂ electrodes during 30 minutes 87.2 % and 88.3 % of dimethenamid‐P was degradated, respectively. The high percentage of degradation of dimethenamid‐P was achieved with non time consuming, simple and cheap electrochemical processes.     

谷胱甘肽、表面活性剂共存体系对青蒿素过氧键稳定性的影响

青蒿素的过氧桥键是其抗疟作用的关键部位。采用循环伏安法研究了谷胱甘肽、表面活性剂共存体系对青蒿素过氧键稳定性的影响。实验表明,当青蒿素浓度为1.0mmol/L,谷胱甘肽浓度≥2.0×10-5mol/L时,加入阳离子表面活性剂(1.0×10-5mol/L,DBDAB),在体系中形成了谷胱甘肽-青蒿素-DBDAB三元加合物,该加合物在-0.88V电位下还原,其还原峰电位比游离青蒿素的还原峰电位负移了240mV,其还原反应活化能升高了46·3kJ/moL,使青蒿素的过氧键更趋稳定;而阴离子表面活性剂对体系没有影响。进一步探讨了该三元加合物形成的电极机理。     

Kinetic Study of the Oxidation of Catechols in the Presence of Some Aza‐crown Ethers by Digital Simulation of Cyclic Voltammograms

The electrochemical oxidation of catechols ( 1 ) have been studied in the presence of diaza‐18‐crown‐6 (DA18C6) ( 3a ), diaza‐15‐crown‐5 (DA15C5) ( 3b ), and aza‐15‐crown‐5 (A15C5) ( 3c ) as nucleophiles in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate the participation of electrochemically generated o‐benzoquinones ( 2 ) in Michael‐type reaction with aza‐crown ethers ( 3 ) to form the corresponding new o‐benzoquinone‐aza‐crown ether adducts ( 5 ). Based on ECE mechanism, the observed homogeneous rate constants (k_obs) of the reaction of o‐bezoquinones ( 2 ) with aza‐crown ethers ( 3 ) were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated observed homogeneous rate constants (k_obs) was found to vary in the order DA18C6>DA15C5>A15C5.     

在抗坏血酸存在下用L-赖氨酸修饰玻碳电极测定多巴胺

采用电化学氧化法制备了L-广赖氮酸单分子层修饰玻碳电极,研究了多巴胺（DA）和抗坏血酸（AA）在该电极上的电化学行为。结果表明,L-广赖氨酸单分子层修饰玻碳电极不仅能改善多巴胺和抗坏血酸的电化学行为,而且能将多巴胺和抗坏血酸二者在裸电极上的完全重叠的单氧化峰分开成为两个完全独立的氧化峰,循环伏安（CV）图上峰间距为507mV,差分脉冲伏安（DPV）图上峰间距为460mV,由此可实现在AA的共存下对样品中的DA进行选择性测定。     

Voltammetric Study of Aminopurines on Pencil Graphite Electrode in the Presence of Copper Ions

Electrochemical oxidations of aminopurines (adenine, 2‐aminopurine, 2,6‐diaminopurine) and their complexes with Cu(I) on a pencil graphite electrode were investigated by means of linear sweep voltammetry (LSV) and elimination voltammetry with linear scan (EVLS). The anodic process of the Cu(I)‐aminopurine complex, corresponding to the oxidation of Cu(I) to Cu(II), takes place in the potential range between 0.4 and 0.5 V (vs. Ag/AgCl/3 M KCl). At more positive potentials the aminopurines provide voltammetric peaks resulting from the oxidation of the purine ring. The stability of the accumulated complex layer was investigated by the adsorptive transfer stripping technique.     

Oxidation of Sulfides with Pyridinium Tribromide in the Presence of Hydrated Silica Gel

A variety of sulfides have been oxidized to sulfoxides utilizing pyridinium tribromide in the presence of hydrated silica gel in a non‐aqueous media. A combination of pyridinium tribromide and hydrated silica gel releases molecular bromine slowly in the reaction, affecting the oxidation. Hydrated silica gel also promotes decomposition of the bromosulfonium intermediate to the product. This procedure employs non‐aqueous media for the first time in such a reaction.     

硫酸存在时N-溴代苯二甲酰亚胺对甘露糖的胶束催化氧化

The kinetics of micellar-catalyzed oxidation of mannose by N-bromophthalimide was studied in the presence of sulfuric acid at 313 K. The orders of reaction with respect to [mannose], [oxidant], and [H+] were found to be fractional, first, and negative fractional order, respectively. Anionic micelles of sodiumdodecyl sulfate showed a partial inhibitory effect, while cationic micelles of cetyltrimethylammonium bromide increased the reaction rate with the same kinetic behavior. The reaction was catalyzed by cationic micelles, because of favorable electrostatic/thermodynamic/hydrophobic/hydrogen bonding between reactants and cationic micelles. Their catalytic roles are best explained by Berezin’s model. A variation of [phthalimide] showed that the rate of reaction decreased with increasing [phthalimide]. It was observed that, an increase of [mercuric acetate] had no effect on reaction velocity. The influence of salts on the reaction rate was also studied. The rate constant (kW ), binding constants (KS+KO), and corresponding activation parameters (Ea, ⊿H#, ⊿S#, and ⊿G#) were determined. A detailed mechanism with associated reaction kinetics is presented and discussed.     

1,4—二氢吡啶及其衍生物电化学反应机理的研究

研究了１１种１，４－二氢吡啶及其衍生物在乙腈溶剂中和铂盘电极上的电化学行为。实验结果表明：１，４－二氢吡啶及其衍生物在铂盘电极上的反应是受扩散和化学反应速率控制的两电子不可逆氧化过程，经连续两步失电子脱氢后形成相应的吡啶。用紫外吸收光谱电化学方法观测了电化学氧化过程。并与化学氧化产物的紫外光谱作了比较，证明１，４－二氢吡啶的电化学氧化产物与化学氧化产物一致。因此，电化学氧化是一种不需加化学试剂可使     

Dynamics of Electrocatalytic Oxidation of Ethylene Glycol,Methanol and Formic Acid at MWCNT Platform Electrochemically Modified with Pt/Ru Nanoparticles

Comparative electrocatalytic behavior of functionalized multiwalled carbon nanotubes (fMWCNTs) electrodecorated with Pt/Ru nanoparticles towards the oxidation of methanol (MeOH), ethylene glycol (EG) and formic acid (FA) has been investigated. The catalytic current density decreased approximately as MeOH≈EG>FA. Result revealed that BPPGE‐fMWCNT‐Pt/Ru tolerates CO poisoning for FA electrooxidation than when used for the oxidation of the EG or MeOH. Electrochemical impedance spectra are dependent on the oxidation potentials, with equivalent circuit models characteristic of adsorption‐controlled charge transfer kinetics. The results provide important insights into the electrochemical response of these small organic molecules useful in fuel cell technology.     

Investigation of Electrochemical Copolymerization of 1‐Naphthylamineaniline in the Presence of Various Organic Sulfonic Acids

The electrochemical and electro activity properties of poly(aniline‐co‐1‐naphthylamine) thin films have been investigated in the presence of various organic sulfonic acids. Homo and copolymer thin films are synthesized electrochemically, under cyclic voltammetric conditions in aqueous solution of organic sulfonic acids (1 M), viz p‐toluene‐sulfonic acid (P‐TSA), methane‐sulfonic acid (MSA), 5‐sulfosalicylic acid (5‐SSA), camphor‐sulfonic acid (CSA) and dodecylbenzene‐sulfonic acid (DBSA) (0.25 M) on glass carbon (GC) electrode at room temperature. The cyclic voltammograms (CVs) show that the current densities are strongly influenced by the size and acidity of the organic acids which are present in electrolyte. Electocopolymerization was carried out at different ratios of NPA to ANI (0.07, 0.05, 0.03, 0.02, 0.014). The formation of copolymer was proved by cyclic voltammogram study.     

Voltammetric Oxidation of Ambroxol and Application to Its Determination in Pharmaceuticals and in Drug Dissolution Studies

A detailed study of the electrochemistry of ambroxol at a glassy carbon electrode was carried out in the pH range 1.8–11.0 in aqueous solution using cyclic and differential pulse voltammetry. The compound was oxidized irreversibly at high positive potentials resulting in the formation of a chemical product at less positive potentials, which was more readily oxidized than the parent compound. In addition, a differential pulse voltammetric method was proposed for the determination of the drug in different pharmaceutical formulations, and in drug dissolution studies.