Anodic Oxidation of Serine Anion on Smooth and Platinized Platinum

The anodic oxidation of serine anion on smooth (Pt) and platinized (Pt(Pt)) platinum electrodes is studied by the methods of cyclic and linear voltammetry, rotating disk electrode, coulometry, and reflectance IR spectroscopy. On both electrodes, the potential regions of electrochemical transformation of this amino acid are determined. It is shown that electrooxidation of serine proceeds with abstraction of 4 and 2 electrons on Pt and Pt(Pt) electrodes, respectively. It is found that the anodic oxidation of serine anions proceeds from the adsorbed state; a possible kinetic scheme of this process is proposed.     

Electrochemical oxidation of benzaldehyde and hydroxybenzaldehydes in acetonitrile on platinum and glassy carbon electrodes

The electrochemical oxidation of benzaldehyde and four hydroxybenzaldehydes was studied on platinum and glassy carbon electrodes in acetonitrile. A considerable difference was observed in electrooxidation performed on platinum and glassy carbon electrodes. All hydroxy derivatives fouled the glassy carbon electrode, but platinum was passivated only by the electrooxidation of 3-hydroxybenzaldehyde, highlighting the crucial role of the position of the substituent relative to the hydroxy group. On the glassy carbon electrode, the formation of the corresponding benzoyl radical could have taken place, which promoted the buildup of polymers on the electrode surface.     

Electrochemical oxidation of tertiary phosphines in the presence of camphene

Anodic oxidation of tertiary phosphines (tripropyl-, tributyl-, and triphenylphosphine) in the presence of a bicyclic alkene (camphene) on a platinum and a glassy carbon electrodes was studied. For the first time the voltammetric characteristics of the process of camphene anodic oxidation were obtained. The electrochemical reactions with alkyl and aromatic phosphine were found to be dissimilar. The results of preparative electrooxidation of trialkylphosphines showed that in the course of electrolysis the tertiary phosphine cation-radicals generated on the anode enter into two concurrent reactions: (1) with the parent phosphine to form eventually trialkylphosphonium salts and trialkylphosphine oxides presumably as complex compounds and (2) with camphene to form trialkylcamphenylphosphonium salts and probably phosphonium salts with a monocyclic substituent. Preparative electrochemical oxidation of triphenylphosphine in the presence of camphene affords almost exclusively either triphenylphosphine oxide (in the experiment with platinum anode) or the triphenylphosphine oxide complex with perchloric acid (at the electrolysis on a glassy carbon anode).     

Catalytic phenomena during the methanol oxidation at platinum electrodes in contact with solid polymer electrolytes

The methanol electrooxidation at platinum-gauze electrodes contacting a solid polymer electrolyte is studied in water and sulfuric-acid solutions by voltammetry in a broad potential range and by measuring steady-state currents and electrode coverages with chemisorbed species at low anodic potentials. The specific rate of the methanol oxidation in these systems is higher than that of similar platinum electrodes in liquid electrolytes. The catalytic action depends on the measurements conditions and the electrode potential. Reasons for catalytic effects at different potentials are discussed.     

Electrochemical behavior of hydrazine at mechanically renewed solid electrodes

The electrooxidation of hydrazine was studied at metallic wire electrodes made of Co, Ni, Ag, Cu, and a graphite-epoxy composite by anodic and cyclic voltammetry with a linear potential sweep in alkaline-supporting electrolytes. Electrode working surfaces were regenerated by mechanically cutting a thin 0.5-μm layer in situ before each polarization cycle. The effects of the electrode material and the renewal of its surface on the parameters of anodic voltammograms of hydrazine were demonstrated. Hydrazine anodic peaks obtained at clean surfaces of electrodes fabricated from Ni, Ag, and a graphite-epoxy composite and also peaks at the potentials of the oxide formation on Ni and Cu electrodes can be used as analytical signals for the voltammetric determination of hydrazine.     

Voltammetric Oxidation of Drugs of Abuse II. Codeine and Metabolites

The oxidation of codeine on glassy carbon electrodes has been studied in detail using differential pulse voltammetry. The results obtained using a glassy carbon electrode clearly show a much more complex oxidation mechanism than that previously reported when platinum and gold electrodes were used. To clarify the codeine oxidative profile, several metabolites and analogues of this alkaloid, codeine N‐oxide, norcodeine, dihydrocodeine, acetylcodeine and 6‐chlorodesoxycodeine, were synthesized and studied. It was deduced that the anodic waves observed in codeine oxidation are related to the presence of methoxy, hydroxy and tertiary amine groups. Due to the similarity of potentials at which these oxidative processes take place, at some pHs an overlap of peaks occurs and only one anodic wave is observed.     

Kinetics and mechanism of glucose electrooxidation on different electrode-catalysts: Part II. Effect of the nature of the electrode and the electrooxidation mechanism

A comparative study has been made of glucose electrooxidation on electrodes made of metals of group VIII, Ag, Au, Cu and glassy carbon as well as of phthalocyanines and porphyrins of cobalt, manganese and iron. It is found that considerable electrooxidation currents are observed for iridium and rhodium (group VIII), and for gold and copper (the copper subgroup). In neutral and alkaline solutions, glucose electrooxidation rates on gold considerably exceed those on platinum.Investigations have been carried out into the main regularities of glucose electrooxidation on a gold electrode in a wide range of potentials, glucose concentrations and pH values. The effect of chloride ions, gluconic acid and amino acids on glucose electrooxidation on gold have been studied.Proceeding from the direct comparison of adsorption data with polarization data obtained under the same conditions, a mechanism of glucose electrooxidation on platinum has been suggested. It is also shown that the mechanism of glucose electrooxidation on gold is similar, in many respects, to that on platinum.     

Square Wave Stripping Voltammetry of Unlabeled Single‐ and Double‐Stranded DNAs

We show that, in difference to previously applied electrochemical methods working with stationary electrodes, square wave voltammetry produces well‐developed peaks II_SW (specific for dsDNA) and III_SW yielded by ssDNA at hanging mercury drop electrode (HMDE) and solid amalgam electrodes (SAEs). Using these peaks various kinds of DNA structural transitions can be studied, including unwinding of dsDNA at negatively charged electrode surfaces. The sensitivity of the DNA analysis is much better than that obtained with guanine oxidation signals at carbon electrodes. Both carbon electrodes and SAEs appear attractive as transducers in label‐free RNA and DNA sensors.     

Adsorption and Electrooxidation of DNA at Glassy Carbon Electrodes Modified with Multiwall Carbon Nanotubes Dispersed in Glucose Oxidase

We are proposing for the first time the successful immobilization of DNA at glassy carbon electrodes (GCE) modified with carbon nanotubes (CNT) dispersed in glucose oxidase (GOx) (GCE/CNT‐GOx) either by direct adsorption or by layer‐by‐layer self‐assembling using polydiallyldimethylamine (PDDA). The presence of GOx allows an efficient dispersion of CNT and gives a most favorable environment that promotes the adsorption and makes possible a more sensitive electrooxidation of DNA. The PDDA incorporated in the self‐assembled architecture largely facilitates the adsorption and electrooxidation of dsDNA and the adsorbed layer can be successfully used for evaluating the interaction of DNA with methylene blue.     

Anodic Stripping Determination of Pt (IV) Based on the Anodic Oxidation of Cu from the Intermetallic Phase of Cu3Pt

It is shown that platinum can be determined by anodic stripping voltammetry at the peak of selective electrooxidation of copper from intermetallic phase with platinum of Cu₃Pt composition. The composition of intermetallic copper-platinum phase formed on the electrode during pre-electrolysis was calculated on the amount of potential displacement (ΔЕ) of copper electrooxidation.     

Use of Cationic Surfactants Film Carbon Paste Electrodes Modified with Multiwalled Carbon Nanotubes in Electrochemical Analysis of dsDNA

Direct electrochemistry of dsDNA based on the enhancement effect of cationic surfactants such as dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) was achieved by using a carbon paste electrode modified with multiwalled carbon nanotubes (MWCNTs/CPE) as the basal electrode. The results indicated that the dsDNA molecules have been adsorbed quite strongly on the cationic surfactants’ film and very well developed peaks which were attributed to the oxidation of guanine residues on the dsDNA molecule structure were obtained from both electrodes. The electrochemical behavior of dsDNA at the surface of the modified electrodes was also evaluated. Based on the signal of guanine, under the optimal conditions, very low levels of dsDNA were detected following short accumulation times with detection limits of 0.650 mg L^?1 and 0.119 mg L^?1 for DTAB/MWCNTs/CPE and TTAB/MWCNTs/CPE, respectively.     

Studies of a photosynthetic photoelectrochemical cell using various electrodes

We have developed a photochemical cell using a combination of photosynthetic electron transport (photosystem I particles) and the photoreduction of a dye such as flavin mononucleotide (FMN) (6). The overall power conversion efficiency depends on the rate of charge transfer across the electrode surfaces in addition to the efficiency of the photosynthetic and photochemical reactions. For this reason, we studied the effect of varying the nature of the electrodes on the power developed. We found that reticulated vitreous carbon electrodes showed higher power conversion efficiencies than did nickel mesh, platinum, or SnO₂ glass. There are two reasons for this. First, the ratio of actual to apparent surface area is greater for RVC electrodes than for the others. Second, FMN and its photoproducts react better with carbon than platinum electrodes. Substituting RVC electrodes for platinum increased the power conversion efficiency from 1.0 to 3.9%. Platinizing platinum, nickel mesh, or brass electrodes also increased the power developed. However, the photopotential remained stable for several hours only for the platinized platinum electrodes.     

Mediated glucose biosensor based on polyvinylferrocene

Polyvinylferrocene (PVF) was electrochemically deposited on platinum and carbon electrodes to form a stable and resilient film. During cyclic voltammetry in phosphate buffer, the PVF film deposited on carbon electrodes exhibited anodic and cathodic peaks at 214 and 68 mV, respectively. Both types of electrodes, bearing electrodeposited PVF and crosslinked glucose oxidase, were responsive to glucose, but the carbon electrode appeared to provide a faster response and could determine glucose between 0.1 and 8 mM. When protected by a layer of polymer electrochemically formed from resorcinol and phenylenediamine, the mediated biosensors based on PVF-deposited carbon electrodes were capable of determining glucose up to 25 mM with a response time of 1 min, for at least 50 repeated analyses with good reproducibility. The presence of ambient oxygen, ascorbic acid (0.1 mM), and uric acid (0.5 mM) did not affect their performance. When applied for the determination of the glucose level in reconstituted human serum, the results agreed well with those of the reference hexokinase assay.     

Influence of percentage of guanine molecules, OH radicals, UV irradiation and temperature on electrooxidation of short synthetic oligonucleotides

The electrooxidation of short synthetic 20-nucleotides DNA sequences with various amount of guanine molecules has been studied in a wide temperature range by square wave voltammetry and the results were compared with UV-vis and CD spectra. A twofold increase of dsDNA voltammetric peak, related to an increase in the number of electrons transferred in the guanine electrooxidation process was found to begin at a temperature lower by circa 20 °C compared to the well known increase of the dsDNA absorbance upon denaturation. Since the dsDNA voltammetric peaks are related directly to the electrooxidation of guanine and adenine, early conformational changes in dsDNA are responsible for this effect. An increase in percentage of guanine in the DNA chains caused a delay in the conformational, predenaturation changes. An exception to this behavior was found for polyguanine (100% guanine). Interestingly, two distinct ranges of change in ellipticity in the CD spectra correlate well with the changes obtained by voltammetry. We have also checked the influence of OH radicals and UV irradiation on the dsDNA oxidation.     

Electropolymerization of Preadsorbed Layers of Some Azine Redox Dyes on Graphite

The redox-active azine dyes Nile blue A (NB) and Toluidine blue O (TB) were electropolymerized after preadsorption onto the surface of graphite electrodes by potential cycling, using an anodic scan limit of 0.9 or 1.0 V vs SCE, where irreversible electrooxidation of the dye proceeds, yielding polymerizable species. Electropolymerization of both dyes is followed by the progressive disappearance of the characteristic current peaks in the cyclic voltammograms, and formation of new ones, shifted by ca. 0.21 V to the positive direction. Also, a decrease and gradual disappearance of the characteristic luminescence at a maximum of 671 nm was observed during the electropolymerization of NB. The resulting electrodes, modified by electropolymerized derivatives of NB and TB, were shown to be able to catalyze the electrooxidation of the coenzyme NADH. Thus, the modified electrodes prepared can be used for amperometric detection of the reduced form of the coenzyme. Copyright 2000 Academic Press.     

Methanol electrooxidation on novel modified carbon paste electrodes with supported poly(isonicotinic acid) (sodium dodecyl sulfate)/Ni-Co electrocatalysts

Poly(isonicotinic acid) (PINA) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode (CPE). Ni(II) and Co(II) ions were incorporated into the electrode by immersion of the polymer-modified electrodes in Ni(II) and Co(II) ion solutions in different proportions. After the preparation of modified electrodes, their electrochemical behavior was studied by cyclic voltammetric experiments. Electrocatalytic oxidation of methanol at the surface of the modified electrodes was studied in 1?M NaOH solution. These modified electrodes exhibit high electrocatalytic activity and stability in alkaline solution, showing oxidation peaks at low potentials with high current densities. The electrooxidation of methanol was found to be more efficient on CPE/PINA(SDS)/Ni₈₀Co₂₀ than on CPE/PINA(SDS)/Ni and CPE/PINA(SDS)/Ni₅₀Co₅₀. The effects of various parameters such as scan rates and methanol concentration on the electrooxidation of methanol are also investigated.     

Model electrodes with defined mesoscopic structure

Model electrodes with defined mesoscopic structure were either generated by adsorption of surfactant stabilized metal clusters from colloidal solution on a support of gold or by electrochemical deposition of platinum on gold substrates. Both types of model electrodes were characterized by STM (scanning tunnelling microscopy), cyclic voltammetry and electrooxidation of adsorbed CO. The supported colloidal Pt as well as the electrochemically deposited Pt revealed different reactivities regarding the CO monolayer electrooxidation as compared to a polycrystalline Pt bulk electrode. In addition, in-situ FTIR (Fourier transformed infrared) spectroscopy was applied to characterize CO adsorbed on electrochemically deposited Pt on gold. Combined with the structural information from STM it seems likely that the differences regarding the catalytic properties of the model electrodes are due to different coverages of the substrate with catalyst particles. Received: 24 June 1996 / Revised: 29 November 1996 / Accepted: 4 December 1996     

聚邻甲苯胺的合成及物理化学性质

聚苯胺的导电性和电化学特性已被广泛地研究。最近,对苯胺衍生物的聚合物也开始了研究,如聚邻甲氧基苯胺、聚邻苯二胺和聚邻氨基酚,其中聚邻甲氧基苯胺是一种可溶性的导电高分子材料。为了探讨苯胺聚合的机理和苯胺上不同基团对聚苯胺性质的影响,我们使用了十六种苯     

铂和铱催化剂在中性电解液中对nh3电氧化性能

比较了Pt和Ir催化剂在中性NaCIO4电解液中对NH3氧化的电催化活性和选择性.发现NH3和NH4OH在Pt和Ir催化剂上的电氧化性能相似,因而可用NH4OH代替NH3进行研究.NH4OH在Pt和Ir催化剂上氧化峰峰电流密度与NH4OH浓度呈很好的线性关系,因而Pt和Ir均能作为控制电位电解型NH3传感器的催化剂.当NH4OH浓度为0.013 mol/L时,NH3在Pt和Ir催化剂上的氧化峰分别位于0.4和0.8 v,NH4OH在Pt催化剂上的氧化峰峰电位负于在Ir催化剂上的,这是Pt催化剂的优点,但NH4OH在Ir催化剂上的氧化峰峰电流密度为Pt催化剂上的2.5倍以上,说明NH4OH在Ir催化剂上的检测灵敏度远高于在Pt催化剂上的.而且CO对NH3在Ir催化剂上的检测没有干扰,但在Pt催化剂上有明显干扰.因此,初步的研究结果表明,Ir催化剂较适用于定电位电解型的NH3电化学传感器的阳极催化剂.     

铂微粒弥散的聚2，5－二甲氧基苯胺膜电极在甲醇电氧化中的催化行为

研究了电化学方法制备的铂微粒弥散的聚２，５－二甲氧基苯胺膜电极对甲醇电氧化的催化行为以及影响催化活性的主要因素。以ＸＰＳ、ＳＥＭ表征了这种电极材料的表面结构，结果表明，在酸性介质中，该膜电极对甲醇电氧化有高的催化活性和稳定性。