Antidiabetic Drug Metformin Oxidation and in situ Interaction with dsDNA Using a dsDNA‐electrochemical Biosensor

The antidiabetic drug metformin (MET) is one of a group of emerging pharmaceutical drug contaminants in the wastewater treatment plants. The electrochemical behaviour of MET?Cu(II) complex by differential pulse and square wave voltammetry, in a wide pH range, at a glassy carbon electrode modified with a carbon black dihexadecylphosphate film (CB?DHP/GCE), was investigated. The MET?Cu(II) complex oxidation showed one pH‐dependent process, which leads to the formation of an oxidation product, being oxidized at a lower potential. The electroanalytical MET?Cu(II) complex detection limit, LOD=0.63 μM, and quantification limit, LOQ=2.09 μM, were obtained, and the MET?Cu(II) complex determination in wastewater samples collected from a senior residence effluent, using the CB?DHP/GCE, was achieved. Considering MET toxicity, the electrochemical evaluation of MET?dsDNA interaction, in incubated solutions and using dsDNA‐electrochemical biosensors, following the changes in the oxidation peaks of guanosine and adenosine residues electrochemical currents, was also investigated. The MET?dsDNA interaction mechanism, for shorter times, occurs by the binding of MET molecules in the minor grooves of the dsDNA, and for long times, the stabilization of the MET?dsDNA complex, causing a local distortion and/or unwinding of dsDNA morphology, is described. However, MET did not promote DNA oxidative damage.     

Electrochemical Oxidation of Quercetin

The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square‐wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3′,4′‐dihydroxyl electron‐donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible.     

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.     

硫代硫酸盐在铂电极上的电化学氧化行为

用循环伏安法测定了硫代硫酸盐在铂电极上的电化学氧化行为, 结果表明, 其电化学氧化行为与体系的pH和扫描速度密切相关. 当pH为5~6时, 硫代硫酸盐的循环伏安曲线出现三个氧化峰, 峰电位分别在0.05 V、0.58 V和1.02 V附近, 随pH值升高和扫描速度的降低, 0.05 V附近的氧化峰逐渐变得明显, 同时各氧化峰的峰电位与扫描速度的对数, 峰电流与扫描速度的平方根均成很好的线性关系；当pH为8~9时, 硫代硫酸盐的循环伏安曲线出现三个明显的氧化峰, 峰电位分别在0.05 V、0.91 V和1.22 V附近. 随扫描速度降低, 循环伏安曲线出现交叉, 体系呈现明显的电化学振荡行为；但当pH=10时, 1.22 V附近的氧化峰消失. 硫代硫酸盐的电化学氧化行为非常复杂, 电化学氧化机制随体系pH的变化而变化.     

Electrochemical oxidation of guanosine and adenosine: Two convergent pathways

We herein explore a novel route for oxidative stress in DNA by using electrochemistry as mimicking tool. Essentially, the electrochemical oxidation of guanine and adenine nucleosides and oligo-homo-nucleotides at pyrolytic graphite electrodes in neutral and alkaline aqueous solutions was studied. Under these experimental conditions all these compounds give rise to an adsorbed product not previously described, which was electrochemically and kinetically characterized. The virtually identical kinetic and electrochemical features exhibited by the oxidized compounds generated from all precursors strongly suggest a common species arising from both adenine and guanine derivatives. Supported by DFT calculations, we propose two convergent pathways for the electrochemical oxidation of adenosine and guanosine. Those calculations indicate that the common oxidized base product forms stable H-bond base pairs with both thymine and cytosine.     

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.     

次亚磷酸根离子在多晶铂电极上氧化的原位红外光谱研究

次亚磷酸根离子在多晶铂电极上氧化的原位红外光谱研究;电氧化;电催化;SNIFTIRS     

Solid State Electrochemical Oxidation Mechanisms Of Morin in Aqueous Media

The mechanism of electrochemical oxidation of morin has been studied using cyclic, differential pulse and square‐wave voltammetry techniques in aqueous electrolyte with solid, insoluble morin hydrate mechanically transferred to a glassy carbon electrode surface, over a wide pH range. The oxidation mechanism proceeds in sequential steps, related with the hydroxyl groups in the three aromatic rings and the oxidation is pH dependent over part of the pH range the oxidation potentials are shifted to lower values with increasing pH. Oxidation of the 2′,4′dihydroxy moiety at the B ring of morin occurs first, at very low positive potentials, and is a one electron one proton reversible reaction. The hydroxyl groups oxidized at more positive potentials were shown to undergo an irreversible oxidation reaction.     

Electrochemical studies of guanosine in DMF and detection of its radical cation in a scanning electrochemical microscopy nanogap experiment

This communication reports the findings of the investigation of the electrochemical (EC) oxidation of the important bimolecular guanosine (Gs) by scanning electrochemical microscopy (SECM) using carbon fiber ultramicroelectrodes (CF-UMEs) as the probe and substrate. The first attempt is to try to gain a steady-state voltammogram for EC oxidation of Gs at the CF-UME probe in aqueous buffer solutions with three different pH values. Experimental results indicate that due to serious adsorption of Gs on the CF-UME surface, an "S-shaped" steady-state voltammetric curve, which is required for SECM studies, cannot be obtained in aqueous solutions. To solve this adsorption problem, a series of experiments for studying the EC behavior of Gs in DMF are carried out. A well-defined "S-shaped" steady-state cyclic voltammogram (CV) could be achieved at the CF-UME in DMF containing 0.1M TBAPF6 as the supporting electrolyte. By combining several EC techniques, including cyclic voltammetry at glassy carbon (GC) macroelectrode and CF-UMEs, and chronoamperometry, the general chemical characteristics and EC behavior of Gs in DMF solution are studied. Furthermore, SECM detection of Gs*+, the radical cation of Gs electrogenerated in its first oxidation, is carried out by using feedback and tip generation/substrate collection modes in a nanogap configuration. Gs*+ has been electrochemically detected for the first time, with an estimated lifetime of 相似文献   

On‐Line Electrochemistry/Electrospray Ionization Mass Spectrometry (EC/ESI‐MS) for the Generation and Identification of Nucleotide Oxidation Products

The oxidation behavior of DNA and RNA nucleotides is studied by an on‐line set‐up consisting of an electrochemical thin‐layer cell (EC) directly coupled to electrospray ionization mass spectrometry (ESI‐MS). This set‐up allows the generation of nucleotide oxidation products in the electrochemical cell at increasing potentials. Moreover, the products are determined directly, without isolation or derivatization steps, by electrospray ionization time of flight mass spectrometry (ESI‐ToF/MS). The dependence of the mass spectra on the applied potential is displayed as ‘mass voltammograms’. An advanced set‐up, consisting of the electrochemical cell coupled to electrospray ionization tandem mass spectrometry (EC/ESI‐MS/MS) allows further structure elucidation based on fragmentation experiments. The electrochemical conversion is performed using a boron doped diamond (BDD) working electrode, which is known to generate hydroxyl radicals at high potentials. The capability of the EC‐MS system to generate highly relevant oxidation products which also occur upon oxidative damage in vivo is demonstrated in this study by the formation of well known biomarkers for DNA damage, including 2′‐deoxy‐8‐oxo‐guanosine 5′‐monophosphate.     

中性介质中L-丝氨酸在Pt电极上解离吸附和氧化的原位FTIR研究

运用电化学循环伏安(CV)和原位红外反射光谱(in situ FTIRS)研究了中性介质中L-丝氨酸在Pt电极上的解离吸附和氧化过程. 结果表明, 在中性溶液中, 以两性离子形式存在的丝氨酸可以在很低的电位下(-0.6 V, vs. SCE)在Pt电极表面发生解离吸附, 生成强吸物种一氧化碳(COL)、(COB)和氰负离子(CN-). 研究结果还表明, 当电位低于0.7 V(vs. SCE)时, CN-能稳定存在于电极表面, 抑制丝氨酸的进一步反应. 在更高电位时则主要为丝氨酸分子的氧化过程.     

Electrochemical behaviors of guanosine on carbon ionic liquid electrode and its determination

The electrochemical behaviors of guanosine on the ionic liquid of N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (CPE) was studied in this paper and further used for guanosine detection. Guanosine showed an adsorption irreversible oxidation process on the carbon ionic liquid electrode (CILE) with the oxidation peak potential located at 1.12 V (vs. SCE) in a pH 4.5 Britton-Robinson (B-R) buffer solution. Compared with that on the traditional carbon paste electrode, small shift of the oxidation peak potentials appeared but with a great increment of the oxidation peak current on the CILE, which was due to the presence of ionic liquid in the modified electrode adsorbed the guanosine on the surface and promoted the electrochemical response. The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n), and the electrode reaction standard rate constant (k_s) were calculated as 0.74, 1.9 and 1.26 × 10⁻⁴ s⁻¹, respectively. Under the optimal conditions the oxidation peak current showed a good linear relationship with the guanosine concentration in the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol/L by cyclic voltammetry with the detection limit of 2.61 × 10⁻⁷ mol/L (3σ). The common coexisting substances showed no interferences to the guanosine oxidation. The CILE showed good ability to distinguish the electrochemical response of guanosine and guanine in the mixture solution. The urine samples were further detected by the proposed method with satisfactory results.     

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.     

电化学氧化和臭氧化预处理酸性化工废水的效能研究

保持一定酸度条件下对比了电化学氧化和臭氧氧化预处理酸性化工废水的效能（废水原pH 0.85）. 结果表明,在废水中添加2 g·L^-1 NaCl电化学氧化预处理效果较佳,30 mA·cm^-2条件下电解20 min后水样的CODCr（化学需氧量）去除率达43.4%,BOD₅/COD_Cr（生化需氧量与化学需氧量的比值）值从原来的0.034上升至0.14,可生化性明显提高. 单独臭氧化仅在pH 7.0才能取得一定的预处理效能. Ti(Ⅳ)/O₃/H₂O₂高级氧化体系在pH 2.85条件下亦有较好的预处理效果,16 min后水样COD_Cr去除率达22.9%,BOD₅/COD_Cr值则提高至0.072.     

The Effect of the Buffering Capacity of the Supporting Electrolyte on the Electrochemical Oxidation of Dopamine and 4‐Methylcatechol in Aqueous and Nonaqueous Solvents

Dopamine was electrochemically oxidized in aqueous solutions and in the organic solvents N,N‐dimethyl‐formamide and dimethylsulfoxide containing varying amounts of supporting electrolyte and water, to form dopamine ortho‐quinone. It was found that the electrochemical oxidation mechanism in water and in organic solvents was strongly influenced by the buffering properties of the supporting electrolyte. In aqueous solutions close to pH 7, where buffers were not used, the protons released during the oxidation process were able to sufficiently change the localized pH at the electrode surface to reduce the deprotonation rate of dopamine ortho‐quinone, thereby slowing the conversion into leucoaminochrome. In N,N‐dimethylformamide and dimethylsulfoxide solutions, in the absence of buffers, dopamine was oxidized to dopamine ortho‐quinone that survived without further reaction for several minutes at 25 °C. The voltammetric data obtained in the organic solvents were made more complicated by the presence of HCl in commercial sources of dopamine, which also underwent an oxidation process.     

Captopril Electrochemical Oxidation on Fluorine‐Doped SnO2 Electrodes and Their Determination in Pharmaceutical Preparations

A novel application of fluorine‐doped tin oxide (FTO) electrodes is reported in the present work. To this end, the captopril electrochemical oxidation mechanism on FTO electrodes at various pH and its determination in pharmaceutical preparations was investigated. Captopril oxidation on FTO proceeds at pH between 2.0 and 4.0. The study revealed that interferences for captopril determination in pharmaceutical samples was totally suppressed using these electrode materials. Voltammetric survey showed an anodic peak at about 0.375 V (Ag|AgCl) for captopril oxidation, that takes place through an EC process at pH interval 2.0–4.0. The investigation demonstrated that captopril oxidation occurs through protonated species and these electroactive species interact by adsorption on FTO electrodes, with a large heterogeneous rate constant and a mechanism involving 1H⁺/1e^? in the global reaction. Moreover, a captopril sensor based upon FTO electrodes, with a linear range miliMolar, is proposed. These electrodes are promising candidates for the efficient electrochemical determination of captopril in pharmaceutical preparations.     

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.     

Pathways of Electrochemical Oxidation of Indolic Compounds

The electrochemical behaviour of indole and a group of indole‐containing compounds with a substituent at the C3 position, indol‐3‐acetamide (IAM), tryptamine, gramine, indole acetic acid (IAA), indole propionic acid (IPA), indole butyric acid (IBA) and tryptophan, was investigated at a glassy carbon electrode, in order to determine their oxidation pathways. Indole undergoes one irreversible pH dependent oxidation, whereas the oxidation process of indole derivatives was more complex, a two step, the oxidation at C2 position on the pyrrole ring followed by the hydroxylation at the C7 position of the benzene moiety of indoles, irreversible pH dependent oxidation.     

Electrochemical behaviour of rosmanol 9-ethyl ether,a diterpene lactone antioxidant isolated from sage

The electrochemical behaviour and mechanism of the redox process of the natural antioxidant rosmanol 9-ethyl ether, isolated fromSaliva officinalis L., were studied. The cyclic voltammograms of rosmanol 9-ethyl ether (R9EE), at characteristic pH values, and the electrochemical parameters for all investigated pH values were measured. Three characteristic pH regions, each with different behaviour of R9EE, were identified. In regions of pH < 4 and pH > 5 only one anodic peak appeared, whereas in the solutions of pH 4–5 two anodic peaks could be noted. The overall oxidation mechanism at pH < 4 is an e.H.e.H. oxidation mechanism, which as a final product gives a quinonic molecule. The influence of pH on the second oxidation peak potential tends towards zero in accordance with the preceding dissociation of the one of phenolic groups, thus suggesting an e.e.H. mechanism at pH > 5. This means that at the pH values expected in plant cells, R9EE has an unexpected structure, making this substance a potent antioxidant. Electrochemical and spectrophotometric measurements enabled us to establish an extremely low pK _a value (4.35) for R9EE.     

鸟嘌呤、鸟苷、鸟苷酸的电化学石英晶体微天平研究

利用电化学石英晶体微天平(EQCM)研究了鸟嘌呤、鸟苷和鸟苷酸在金电极上的电化学行为.结果表明,三种生物活性分子均能在1.1V电位被氧化,对应于它们所含的共同基团嘌呤环中CN键的氧化,根据氧化反应电量和质量的变化,求得电子转移数为4.氧化电流的大小次序为鸟苷酸>鸟苷>鸟嘌呤,这可能与三者在电极上的吸附量不同有关.