Electrochemical Behaviour of Isoflavones Genistein and Biochanin A at a Glassy Carbon Electrode

The electrochemical behaviour of genistein and biochanin A was studied at a glassy carbon electrode by cyclic, differential pulse and square wave voltammetry. Genistein undergoes three irreversible, pH dependent oxidation reactions with the transfer of one electron and one proton from each hydroxyl group. The formation of two electroactive products that undergo reversible redox reactions was observed. Biochanin A undergoes two irreversible, pH dependent reactions due to the oxidation of the two hydroxyl groups. The electrochemical behaviour of the chemical analogue daidzein was also investigated. The electroactive centres of genistein and biochanin A were identified and their oxidation mechanisms discussed.     

Sorbic Acid and Its Degradation Products: Electrochemical Characterization

The electrochemical redox behavior of sorbic acid (SA), an important food preservative, was investigated at a glassy carbon electrode using cyclic, differential pulse, and squarewave voltammetry over a wide pH range. The oxidation of SA is an irreversible, diffusion-controlled, and pH-independent process that occurs with the transfer of only one electron and does not involve the formation of any electroactive oxidation product. Adsorption of SA at GCE electrodes was also observed. Following incubation in different pH electrolytes, the degradation of SA was electrochemically detected by the appearance of a new oxidation peak at lower potential value. The degradation products, formed homogenously in solution, undergo irreversible oxidation and lead to the formation of two oxidation products that strongly adsorb on the electrode surface and are reversibly oxidized. SA degradation was also confirmed using HPLC and UV-Vis spectrophotometry. A mechanism for oxidation of SA and its degradation products in aqueous solutions was proposed.     

Redox Mechanisms of Nodularin and Chemically Degraded Nodularin

The electrochemical behaviour of Nodularin (NOD), a hepatotoxic cyclic pentapeptide, was studied at a glassy carbon electrode. NOD electrochemical oxidation is an irreversible, pH‐independent process, involving the transfer of one electron. Upon incubation in different pH electrolytes, chemical degradation of NOD was electrochemically detected by the appearance of a new oxidation peak. The chemically degraded NOD (cdNOD), undergoes an irreversible, pH‐dependent oxidation, and its redox products are reversibly oxidised. The charge transfer properties of cdNOD as well as of its redox metabolites were investigated. Mechanisms for NOD oxidation, NOD chemical degradation and oxidation of cdNOD and its metabolites were proposed.     

Anodic behavior of clioquinol at a glassy carbon electrode

Clioquinol is an antifungal, antiprotozoal and an Alzheimer's disease drug with cytotoxic activity toward human cancer cells. The electrochemical behavior of clioquinol and its oxidation product was studied using cyclic, differential pulse and square-wave voltammetry over a wide pH range on a glassy carbon electrode. The results revealed that the oxidation of clioquinol is an irreversible pH-dependent process that proceeds with the transfer of one electron and one proton in an adsorption-controlled mechanism and results in the formation of a main oxidation product, which adsorbs very strongly on the glassy carbon surface. The charge transfer coefficient was calculated as 0.64. The adsorbed oxidation product presented reversible redox behavior, with two electron and two proton transfer. The electrochemical oxidation of clioquinol as a phenolic compound involves the formation of a phenoxy radical which reacts in at least two ways: in one pathway the radical initiates polymerization, the products remaining at the electrode surface, and in the other the radical is oxidized to a quinone-like structure. A mechanism for the oxidation of clioquinol is proposed.     

Electrochemical Oxidation of Rutin

An electrochemical investigation of rutin oxidation on a glassy carbon electrode was carried out using cyclic voltammetry, differential pulse voltammetry and square‐wave voltammetry over a wide pH interval. The electrochemical oxidation is a complex process, which proceeds in a cascade mechanism, related with the 4‐hydroxyl groups of the rutin molecule. The catechol 3′,4′‐dihydroxyl group is the first to be oxidized by a two‐electron – two‐proton reversible oxidation reaction, followed by an irreversible oxidation reaction due to the 5,7‐dihydroxyl group. Both mechanisms are pH dependent. An adsorption process is also observed and the oxidation products block the electrode surface.     

Electrochemical behaviour of 2,8-dihydroxyadenine at a glassy carbon electrode

The electrochemical behaviour of 2,8-dihydroxyadenine (2,8-DHA)- the main adenine oxidation product- has been investigated over a wide pH range at a glassy carbon electrode (GCE) using cyclic, differential pulse and square wave voltammetry. The oxidation of 2,8-DHA is a quasi-reversible process, pH dependent and occurs with the formation of a main oxidation product, P(2,8-DHA), that strongly adsorbs on the electrode surface. The reduction of 2,8-DHA also occurs and is a reversible process in the absence of molecular oxygen. In electrolytes with pH between 4 and 9 two consecutive reversible charge transfer reactions were identified. However, it was observed that O(2) interfered with the reductive electron transfer process of 2,8-DHA and that, in the presence of oxygen, the reduction of 2,8-DHA occurs at less negative potentials than in the absence of oxygen.     

Electrochemical Oxidation of Sulfasalazine at a Glassy Carbon Electrode

Sulfasalazine (SSZ) is a pharmaceutical compound used for the treatment of rheumatoid arthritis. The electrochemical oxidation of SSZ at a glassy carbon electrode was studied by cyclic, differential pulse and square wave voltammetry in a wide pH range. For electrolytes with pH<11.0, the oxidation is an irreversible, diffusion‐control, pH‐dependent process that involves the transfer of one electron and one proton from the hydroxyl group of the salicylic moiety. For pH>11.0 the oxidation is pH‐independent, and a pK_a≈11 was determined. The formation of a quinone‐like oxidation product that undergoes two electrons and two protons reversible redox reaction was observed. Also, UV‐vis spectra of SSZ were recorded as a function of supporting electrolytes pH. An electrochemical oxidation mechanism was proposed.     

Redox active surface films produced by electrooxidation of substituted indolysines

The electrochemical oxidation of substituted mono-and 3,3′-biindolysines is studied by methods of cyclic voltammetry and electron spin resonance (ESR) combined with in situ electrolysis. In acetonitrile, there occurs easy irreversible electrochemical oxidation and proceed processes of association of generated radical cations via unsubstituted positions of five-membered cycles. Polymeric products of oxidation of 2-arylindolysines, 3-indolysine-2-yl-quinoxalines, and 2,2′-diaryl-3,3′-biindolysines are obtained when cycling potential in the interval ?0.3 V → +0.8 V → ?1.3 V → ?0.3 V (Fc/Fc⁺). The products deposit on the electrode with the formation of redox-active films that are capable of undergoing reversible oxidation with the formation of stable paramagnetic states registered by the ESR method.     

头孢哌酮在玻碳电极上的电化学行为及检测方法

应用循环伏安法、线性扫描伏安法和微分脉冲伏安法研究头孢哌酮在玻碳电极上的电化学行为,建立了应用伏安法定量检测头孢哌酮的新方法。头孢哌酮的电极过程为受吸附控制的不可逆过程,电极反应转移电子数和转移质子数均为2。头孢哌酮在pH1.0的1mol/LH3PO4-NaOH介质中,在+0.13V(vs.Ag/AgCl)电位处产生一灵敏的氧化峰,应用微分脉冲伏安法进行测定,该峰电流值Ip与头孢哌酮质量浓度在5.05×10-7～1.01×10-4g/mL范围内有良好的线性关系(R=0.9996),检出限为4.95×10-9g/mL,样品测定平均加标回收率达99.50%,相对标准偏差(RSD)为3.17%。     

Mechanism of oxidation of 1-benzyl-1,4-dihydronicotinamide by the biologically active p-benzoquinone derivative, avarone, in a cationic micellar medium: An electrochemical approach

The electrochemical reduction of avarone (Q), an antitumor sesquiterpenoid quinone, was investigated at various pH in aqueous ethanol containing a cationic surfactant, cetyltrimethylammonium bromide (CTAB) by cyclic and rotating disc electrode voltammetry, using a glassy carbon electrode. Comparison of the electrochemical reduction of Q in presence of CTAB with the same process in a homogeneous water + ethanol solution shows an anodic shift of the reduction potential in the presence of CTAB; at pH > 9.5 and in presence of CTAB, two well-defined reduction peaks are observed, thus confirming one-electron reduction of Q, whereby the intermediate radical-anion is stabilized by the cationic micellar medium. The electrochemical oxidation of BNAH was investigated by cyclic voltammetry, and the anodic shift of the peak potential in presence of CTAB was observed. From the electrochemical behaviour of Q and BNAH, and the kinetics of the oxidation of BNAH with Q, it is suggested that the reaction takes place in two successive one-electron transfer steps. The application of the Marcus theory gives additional proof that, in this case, the first electron transfer is the rate determining step.     

乙酰胆碱酯酶催化水解产物的电化学行为

报道了乙酰硫代胆碱水解产物硫代胆碱在玻碳电极上的电化学行为。以乙酰硫代胆碱作底物,在一定条件下乙酰胆碱酯酶催化底物水解,生成电活性物质硫代胆碱。利用循环伏安法和线性扫描伏安法研究了酶催化水解产物硫代胆碱在玻碳电极上的电化学行为。结果表明:在0.1mol/L的B-R缓冲溶液(pH7.0)中,硫代胆碱有一灵敏的氧化峰,峰电位EP=0.32V(vs.SCE);该体系属具有吸附性的不可逆过程。实验测得电子转移数为2,电极反应速率常数k=0.29s-1。     

Electrochemical Detection of Hydrazine Based on Electrospun Palladium Nanoparticle/Carbon Nanofibers

In this work, we developed an electrochemical method for the detection of hydrazine based on palladium nanoparticle/carbon nanofibers (Pd/CNFs). Pd/CNFs were prepared by electrospinning technique and subsequent thermal treatments. The electrocatalytic behaviors of Pd/CNFs modified glassy carbon electrode (Pd/CNF‐GCE) for hydrazine oxidation were evaluated by cyclic voltammetry (CV), an obvious and well‐defined oxidation peak appeared at ?0.32 V (vs. Ag/AgCl). The mechanism of the oxidation of hydrazine at Pd/CNF‐GCE was also studied, which demonstrated an irreversible diffusion‐controlled electrode process and a four‐electron transfer involved in the overall reaction. Furthermore, the wide linear range, low detection limit, good reproducibility and excellent storage stability were obtained utilizing differential pulse voltammetry (DPV).     

Electrochemical Redox Behavior of Omeprazole Using a Glassy Carbon Electrode

The electrochemical redox behavior of omeprazole (OMZ), a gastric acid pump inhibitor, was investigated at a glassy carbon electrode using cyclic, differential pulse and square‐wave voltammetry over a wide pH range. The pH‐dependent oxidation occurs in two irreversible consecutive charge transfer reactions. Adsorption of the nonelectroactive product was also observed. The first oxidation involves removal of one electron, followed by deprotonation and leads to the formation of a hydroxylated species. The second oxidation process is related to the hydroxyl and amino groups in the benzimidazole moiety. The reduction is irreversible, also pH‐dependent, and occurs in a single step at the sulfoxide group in a diffusion‐controlled mechanism. The diffusion coefficient of omeprazole was calculated to be D_OMZ=2.31×10^?6 cm² s^?1.     

1,3-二甲基-5-亚硝基-6-氨基脲嘧啶铂电极电化学加氢机理研究

采用稳态极化法、循环伏安法和恒电位库仑法对1,3-二甲基-5-亚硝基-6-氨基脲嘧啶在铂电极上的电化学加氢机理进行了研究,研究介质为硫酸和硫酸钾水溶液.结果表明,pH=3时,1,3-二甲基-5-亚硝基-6-氨基脲嘧啶在铂电极析氢电位(-600～-800mV,vs.饱和硫酸钾的硫酸亚汞参比电极)前,发生加氢还原反应,氢离子在铂电极表面得到电子生成原子态的氢参与反应.随着pH值降低,加氢反应速度增大,还原电位正移.在铂电极上的电化学加氢过程受扩散控制,增大搅拌速度和提高温度都可提高反应速度.     

Electrochemical oxidation mechanism of guanine and adenine using a glassy carbon microelectrode.

The electrochemical oxidation mechanism of guanine and adenine was investigated using a glassy carbon microelectrode and cyclic and differential pulse voltammetry. It is pH-dependent and the electron transfer process occurs in consecutive steps with the formation of strongly adsorbed dimers on the electrode surface for both compounds.     

Electrochemical Oxidation of Berberine and of Its Oxidation Products at a Glassy Carbon Electrode

The electrochemical behavior of berberine, an isoquinoline plant alkaloid with a wide spectrum of physiological effects, was studied at a glassy carbon electrode using cyclic, differential pulse and square‐wave voltammetry. The oxidation of berberine is a quasireversible, diffusion‐controlled process and occurred in a cascade mechanism with the formation of several oxidation products. The diffusion coefficient of berberine was calculated from cyclic voltammetry studies to be D=1.69×10^?6 cm² s^?1. The oxidation process of berberine is also pH dependent and the number of electrons and protons transferred was determined using differential pulse voltammetry. The formation of several oxidation products that adsorbed at the glassy carbon electrode surface was observed and their electrochemical behavior characterized. A mechanism for the oxidation of berberine at a glassy carbon electrode was proposed.     

Electrochemical Oxidation of Sanguinarine and of Its Oxidation Products at a Glassy Carbon Electrode – Relevance to Intracellular Effects

The electrochemical behavior of sanguinarine, a quaternary benzophenanthridine glycoside alkaloid with antimicrobial, anti‐inflammatory, antioxidant and/or immune‐stimulatory activities, was studied at a glassy carbon electrode using cyclic, differential pulse, and square wave voltammetry. The oxidation of sanguinarine is a quasireversible, diffusion‐controlled process and occurred in a cascade mechanism with the formation of several oxidation products which adsorbed at the electrode surface. The oxidation of sanguinarine is pH dependent and involves the transfer of the same number of electrons and protons. The adsorbed sanguinarine oxidation products are reversibly oxidized at the glassy carbon electrode surface and their oxidation for a wide range of pHs was also studied by differential pulse and square wave voltammetry. A mechanism for the oxidation of sanguinarine at glassy carbon electrode is proposed.     

耐尔兰A修饰碳纤维微柱电极的电化学性质研究

用循环伏安法将碳纤维柱电极表面官能团化，利用正负离子间的静电作用将耐尔兰Ａ修饰在碳纤维微柱电极（ＣＦＭＣＥ）表面，对该修饰电极的电化学性质进行研究，讨论了它的稳定性，测定了不同ＰＨ值下固定化耐尔兰Ａ电极反应的表现电子转移速率常数ｋ、电荷转移系数α以及参加电极反应的Ｈ＾＋数，实验表明：电极对血戏蛋白在ＣＦＭＣＥ上的还原有电催化作用。     

The anodic reactivity of 4,4′-dimethoxychalcone: a synthetic and mechanistic investigation

The anodic oxidation of the 4,4′-dimethoxychalcone (DMC) was investigated by different electrochemical methods at a platinum working electrode and in acetonitrile as a solvent. The DMC exhibited a single irreversible anodic peak around 1.6 V versus Ag/AgCl. On the time scale of cyclic voltammetry experiments, the highly reactive radical cation issued from the first electron transfer underwent a second order rate-limiting reaction. The potential imposed electrolyses of DMC led to the formation of a semi-conducting oligomer with 40 % yield. Using different physico-chemicals methods, the structural study confirmed the formation of an o-phenylenevinylene oligomer. The values of the corresponding optical and electrochemical band gaps were calculated to be 3.15 and 2.86 eV, respectively. Finally, a mechanism for the DMC electro-oligomerization was proposed on the basis of the obtained results.     

Electrochemical Behavior of Some Thiotriazoles in Aqueous‐Alcoholic Media at GCE

An electrochemical study related to the electrooxidation of 4‐amino‐3‐thio‐5‐methyl‐1,2,4‐triazole (I), 4‐amino‐3‐thio‐5‐phenyl‐1,2,4‐triazole (II) and 3‐thio‐5‐phenyl‐1,2,4‐triazole (III), in 10% v/v methanol‐acetate buffer pH 4.6 has been performed. A variety of electrochemical techniques such as differential pulse voltammetry, cyclic voltammetry, double‐potential step chronoamperometry, rotating‐disk electrode voltammetry and coulometry, were employed to clarify that the mechanism of the electrode process follows the oxidation of thiol compounds. All the compounds exhibit similar redox behavior under the given conditions. They display one irreversible oxidation peak, which is diffusion controlled. From the plot of current function in cyclic voltammetry and the ratio of i_c/i_a less than one in double‐potential step chronoamperometry, it was established that these compounds undergo an one electron oxidation followed by a dimerization process involving the formation of disulfide derivative (EC mechanism). The pK_a values were obtained by the dependence of limiting current and potential with in the wide pH interval. The transfer coefficients, the diffusion coefficients and rate constant of coupled chemical reaction were also reported. The substituent effects were also investigated.