Pulse polarograpmc study of the electrochemical reduction of lucigenin in aqueous medium

The electrochemical reduction of lucigenin (bis-N-methylacridinium nitrate) in aqueous solution was studied by normal pulse polarography, normal pulse polarography with differential detection of the current, and differential pulse polarography with cathodic and anodic pulses at several pulse amplitudes. The effects of pH and lucigenin concentration were studied. In confirmation of an earlier d.c. polarographic study, lucigenin is shown to be reduced in two separate one-electron steps. An adsorption peak accompanies the first step, while the second, below pH 3.5, is catalytic owing to chemical regeneration of the intermediate reduction product at the electrode surface.     

桑色素极谱行为的研究

研究了桑色素在pH=1～14的水溶液中的极谱行为. 于不同pH范翻内得列了四个还原波. 研究证实在pH<4条件下获得的P_1波为表面催化氢波. 其余三个波为不同形态桑色素的单电子吸附还原波, 并伴有随后化学反应过程. 测得在单分子层饱和吸附条件下, 每一个桑色素分子所占汞电极面积为1.36 nm.     

Cathodic adsorptive stripping voltammetric studies on lamivudine: an antiretroviral drug

The electrochemical reduction and adsorption of lamivudine, a systemic antiviral drug, were studied in a phosphate buffer medium at a hanging mercury drop electrode (HMDE). Cyclic voltammetry studies showed one well-defined reduction peak in the potential range from -1.2 to -1.8 V under different pH conditions, but the best results were obtained at pH 3.4. The reduction was irreversible and exhibited diffusion-controlled adsorption. The response was evaluated with respect to preconcentration time, pH effect, accumulation potential, accumulation time, and scan rate. The number of electrons transferred in the reduction process was calculated and the probable reduction mechanism was proposed. A systemic study of the experimental parameters that affect the square-wave stripping response was carried out and experimental conditions were optimized.     

Glycine adsorption on a mercury electrode modified by neodymium

Ranges of neodymium reduction potentials in aqueous solutions of potassium chloride at pH = 2 and in solutions containing glycine were determined by differential pulse polarography. The glycine complex with neodymium is not formed in the range of the amino acid concentration 0.001–0.12 M. Glycine adsorption on a mercury electrode and on an electrode modified with neodymium was studied by the cyclic voltammetry method.     

Determination of Trace Levels of Medroprogesterone Acetate in the Presence of KIO3 by Adsorptive-Catalytic Stripping Voltammetry

A adsorptive-catalytic stripping voltammetry has received considerable attention in recent years. However,the method has been used to only a limited extent of inorganic ions. And no method for organic compounds has been reported so far. In this paper,the adsorptive properties of Medroprogesterone Acetate(MPA) on a hanging mercury electrode and the mechanism of catalytic wave in the presence of KIO₃ were studied. A new sensitive adsorptive-catalytic stripping voltammetry for the determination of MPA is proposed based on the combination of adsorptive accumulation of MPA with the regeneration of the reactant MPA by the homogeneous catalytic reaction between KIO₃ and intermediate radical HMPA formed in the reduction process of MPA. The dual amplification resulting from adsorptive-catalytic effects produces excellent sensitivity. The adsorptive-catalytic stripping process of MPA differs from inorganic ions in catalytic mechanism. The catalytic current is produced by the chemical reaction between KIO₃ and HMPA, instead of the catalytic current of complexation produced at the mercury electrode surface.     

Formation and electrochemical characterization of 6-thioguanosine monolayers on the mercury surface

The interfacial and electrochemical behavior of 6-thioguanosine-6-thioguanine riboside (6TGR)-on a hanging mercury drop electrode was studied with ac and cyclic voltammetry in a solution of 0.1 M Na(2)SO(4) and 0.01 M sodium acetate buffer at pH 4.3. A self-assembled monolayer (SAM) of chemisorbed 6TGR molecules formed under determined adsorption conditions was characterized. A low-density monolayer of chemisorbed 6TGR molecules and a condensed monolayer of physisorbed ones, which are successively formed by reduction of the SAM, were also studied.     

钴(II)-丁二酮肟-亚硝酸盐体系极谱催化波的机理研究

在氨性底液(PH8)中, 钴(II)-丁二酮肟(DMG)-亚硝酸盐体系产生高灵敏的极谱催化波. 利用吸附伏安法, 测定下限可达1×10^-^1^1mol.dm^-^3Co. 我们用多种电化学方法和紫外可见分光光度法证明, 吸附在汞电极表面的[NH4]2[Co(DMG)2(NO2)2]是有很高电活性的混配化合物, 在复杂的电还原过程中, 不仅Co(II)和DMG被催化还原, 而且NO2^-也被催化还原, 从而产生很大的催化电流, 本文再一次证明, “活性钴"在催化波的形成过程中起着重要的作用.     

Two-dimensional condensation of nucleic acid components at mercury film and gold electrodes

The adsorption of cytidine at the mercury film electrodes and at the Au (111) single crystal electrode has been investigated. Some kinetic aspects such as the influence of pH and temperature on the formation or dissolution of cytidine adlayer on the pyrolytic graphite electrode covered by a mercury film or on the Au (111) have been studied.     

Electrochemistry of diphenylditelluride at the hanging mercury drop electrode in a protic medium

The electrochemical behavior of diphenylditelluride, Phi2Te2, at a hanging mercury drop electrode has been studied in an aqueous-ethanol solution at pH 7 by means of cyclic and ac voltammetry. The appearance of two cathodic peaks has been attributed to the reversible reduction of the first and all the successive monolayers of a film of PhiTe-Hg, which is formed by adsorption of Phi2Te2 at the mercury/solution interface. The different electrochemical properties of such monolayers have been explained.     

The adsorption of acetylacetone at the mercury electrode

Adsorption of acetylacetone at the mercury electrode was studied in a wide pH range. Adsorption from acidic solutions is much stronger than the adsorption from basic solutions. The dependence of the differential capacity of the mercury electrode on the pH resembles the titration curve of acetylacetone. From such curves the pK of acetylacetone was calculated.     

甘草次酸的电化学研究

用单扫示波极谱法研究了甘草次酸在NaAc-HAc缓冲液中（pH4．0－5．5）的电化学行为和反应机理。甘草次酸于－1．53V（vs.SCE)(P1)左右有一个二阶示波导数峰（pH＝4．0－4．9）,峰高与甘草次酸浓度在0．4－6．3μg/mL范围内呈正比,检出限为0．2μg/mL;pH在5．00－5．53之间,甘草次酸有两个还原峰,其电位分别为－1．51V（P2）和－1．57V（P3)。实验证明甘草次酸的电极过程为不可逆的逐级电子转移过程,H2O2和羟基自由基可催化甘草次酸的还原峰。     

Adsorptive stripping square-wave voltammetric study of the degradation of lansoprazole in aqueous solutions

The adsorption and reduction behavior of lansoprazole has been studied by square-wave voltammetry at a hanging mercury drop electrode. A study of the variation in the reduction signal with solution variables, such as pH and concentration of lansoprazole, and instrumental variables, such as accumulation time and potential, frequency, pulse height and pulse amplitude, has resulted in optimization of the reduction signal for analytical purposes. The voltammetric procedure was successfully applied for rapid analysis of lansoprazole in stability studies without interference from the degradation products. It has also been used for the precise determination of lansoprazole in a pharmaceutical preparation.     

Voltammetric study of the redox behaviour of the Hg(II)/Hg(I)/Hg system at a rotating metal-ring/glassy-carbon disc electrode

The reduction of Hg(II) at a glassy-carbon electrode in various electrolytes has been studied by rotating ring-disc voltammetry. Reduction proceeds directly to metallic mercury in a single 2-electron step. However, at the foot of the wave, and only during the first reduction sweep after pretreatment of the electrode surface, a small amount of Hg(I) species is detected at the ring. The appearance of an Hg(I) intermediate is most pronounced in sulphuric acid solution. The reduction of Hg(II) is found to proceed irreversibly and to be of first order. At sufficiently negative potentials the reduction is convective-diffusion controlled. Stripping voltammetric experiments indicate that the dissolution of mercury gives Hg(II) in complexing electrolytes. In non-complexing electrolytes the initially formed Hg(II) reacts with mercury atoms on the electrode surface to give Hg(I). During electrodissolution, two stripping peaks may be observed as a result of underpotential adsorption of mercury on glassy carbon. The difference in peak potential between the adsorption (mono) layer peak and the bulk mercury peak has been related to the difference in work functions of the deposit (mercury) and substrate (carbon). A rotating glassy-carbon electrode has been used for the anodic stripping determination of mercury. When an appropriate amount of a cation such as cadmium(II) or copper(II) is added to the test solution, mercury down to 2 x 10(-9)M (0.4 ng ml ) can be determined in acidified thiocyanate electrolyte with a relative standard deviation of about 22%.     

pH effects on the reduction of bilirubin in aqueous media

The electrochemical reduction of bilirubin at the mercury electrode was studied in aqueous media embracing an extended pH range; a variety of electrochemical techniques was used. Reduction in neutral solution results in three waves—the first a reversible adsorption prewave, followed by a pH dependent, reversible, two electron wave and finally by a one electron irreversible wave. In basic solution, only two waves are discernable: the reversible adsorption prewave, followed by a three electron wave resulting from the coalescence of the second and third waves seen in neutral solution. Familiarity with the detailed electrochemistry of bilirubin reduction provides the prerequisite basis for developing a sensitive analytical method for its determination.     

Determination of cholride in natural and potable water samples byturbidimetric descrete-sample automatic analysis.

The reduction of the uranyl-mellitate complex at the dropping mercury electrode has been studied in aqueous and dimethyl sulfoxide solution. In aqueous solution, besides the reduction waves of the uranyl-mellitate complex, corresponding to the reduction of U(VI) to U(V), and of U(V) to U(III), an adsorption wave and a catalytic hydrogen wave were obtained; the species formed below pH 4.0 was UO₂(H₃A)^- and above pH 4.0 was UO₂(OH)(H₃A)^2-. In dimethyl sulfoxide solution, two well-defined waves were observed; the first wave is due to reduction of a uranyl-mellitate-DMSO complex, and the second to reduction of mellitic acid. The species involved are UO₂(DMSO)₆²⁺ below pH 2.2 and UO₂(H₃A)(DMSO)₅^-1 above pH 2.2. The activation energies of the reduction process were determined.     

Voltammetry of adsorbed cancerostatic actinomycins

A systematic study of the adsorption and association of the cancerostatic drug actinomycin-C₁ (ACT) at a hanging mercury drop electrode (HMDE) has been conducted using phase-sensitive a.c. voltammetry and cyclic voltammetry (CV). At all bulk concentrations, the adsorbed layer is transformed into a condensed film by the significant stacking forces acting between adjacent rings of the phenoxazone residues. The nucleation and growth mechanism is confirmed and the data are analysed using the Avrami equation. The adsorption parameters for the condensed film were evaluated at various pH values. In addition, the preparative electrochemical reduction of ACT was performed using the large-scale electrolysis and differential pulse polarography. The consequences for DNA interaction and membrane adsorption are discussed.     

Interfacial electrochemistry of hypophyseal polypeptide hormones

The adsorption and the electrode reaction of the cyclic polypeptide hormones oxytocin, desamino-oxytocin and vasopressin at the mercury/water interface was investigated by a.c. and d.c. polarography and by cyclic voltammetry. The saturation surface concentrations as obtained by the different methods under different potential oscillations, and at two pH values (2 and 6.6) varied between 3 × 10¹³ and 5 × 10¹³ molecules cm^-2. The kinetics of the adsorption—desorption reaction and of the electrode process was in every case the slowest for the non-charged desamino-oxytocin. Vasopressin behaved the most reversibly in a.c. polarography, while oxytocin showed the most reversible behavior in cyclic voltammetry. The difference in behavior is related to the difference in charge and hydrophobicity of the different polypeptides, affecting adsorption interactions and the catalytic reaction with the mercury surface.     

Hydrazones

The polarographic behavior of a number of N-benzylideneiminopyridinium iodides in aqueous alcohol buffer solutions was studied over a wide range of pH values. The mechanism of their reduction on a dropping mercury electrode and the factors affecting the cleavage of the N-N bond are discussed. The reduction product-the pyridinium ion-induces the catalytic evolution of hydrogen.     

Electrochemical behaviour of tilmicosin at the hanging mercury drop electrode

The electrochemical behaviour of tilmicosin (TIM) was investigated using cyclic voltammetry and square-wave voltammetry in Britton-Robinson buffers (pH 2–12). The voltammograms of TIM showed one-irreversible peak which attributed to reduction of the >C=C< group in the entire pH values. However, an additional peak was shown over the pH range 2.00 to 4.00. Its peak potential is more positive potential from that of >C=C< group, and its potential was not practically dependent on the pH. On the other hand, the peak potential of >C=C< group was shifted to the more negative values with increasing pH. According to the obtained voltammetric data, the probable reaction mechanism for the reduction of TIM was proposed. Moreover, the adsorption of TIM on the mercury electrode surface by means of square-wave adsorptive stripping voltammetry measurements is studied at different pH values. The peak current variations with the deposition time and TIM concentration were observed.     

Study on the adsorptive catalytic voltammetry of aloe-emodin at a carbon paste electrode

Recently, the studies and applications for the pola-rographic catalytic waves of organic compounds at dropping mercury electrode made considerable head-way. Tovopova et al.[1―4] reported the polarographic catalytic waves of the organic compounds containi…