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     

Cathodic stripping voltammetry of copper-complexed reactive dyes at a hanging mercury drop electrode: Reactive violet 5

Reactive Violet 5 and its hydrolysis product, which is produced as a side product in the dyeing process, can be determined in an admixture at sub-ppb levels by cathodic stripping voltammetry because the potentials of their azo reduction peaks are separated sufficiently. For both dyes, at intermediate pH values the azo peak is preceded by a complexed -copper reduction peak at a less negative potential, which aids the identification of the dyes. The use of pH 6 EDTA buffer removes the complexed-copper peak, as does the use of an acidic buffer (pH < 3). This unusual use of EDTA as a pH buffer facilitates the determination of mixtures of the dye and its hydrolysis product.     

Voltammetric studies of the activity of an electrode made of a graphite-epoxy composite in redox reactions of ascorbic acid and hydroquinone

The potentials of the anodic peak of ascorbic acid oxidation and the potential differences of anodic and cathodic peaks (ΔE _p) of the hydroquinone/benzoquinone redox system at an electrode made of a graphite-epoxy composite are determined in weakly acidic and neutral supporting electrolytes by direct and cyclic voltammetry. The results obtained are compared with thermodynamic values and with the available values of these parameters at different solid electrodes for the above-mentioned redox systems. The effect of aging of the surface of electrodes made of graphite-epoxy composites on the potentials and peak currents of the anodic oxidation of ascorbic acid are studied. It is demonstrated that the regeneration of the electrode surface by mechanically cutting thin layers is important for reducing the δE _p value of the hydroquinone/benzoquinone redox system down to 28–30 mV in supporting electrolytes with pH 2.0 and 7.0. This value is typical of thermodynamically reversible electrode reactions involving two-electron transfer at 20–25°C.     

Investigation of corrosion of a rotating iron electrode in HNO3 by in-situ Raman spectroscopy

Iron products resulting during reduction/oxidation processes in 0.15 M HNO₃ and 0.02 M HNO₃ with and without excess of supporting electrolyte are detected by Raman spectroscopy. The presence of ferrous species close to Fe depend on local pH changes and hydrodynamic conditions. Pre-corroded electrodes may be covered by Fe₃O₄ during cathodic treatment. The resulting oxides and hydroxides are not easily removable on stationary electrodes either at passivation potentials or during a slow reduction at −0.9 V vs. SCE. Simultaneous reduction of NO⁻₃ to HNO₂ also influences the corrosion process.     

Electrochemical Polymerization of Methylene Green

The electrochemical polymerization of methylene green has been carried out using cyclic voltammetry. The electrolytic solution consisted of 4° 10^?3 mol/L methylene green, 0.1 mol/L NaNO₃ and 1 × 10^?2 mol/L sodium tetraborate with pH 11.0. The temperature for polymerization is controlled at 60°C. The scan potential is set between ?0.2 and 1.2 V (vs. Ag/AgCl with saturated KCl solution). There are an anodic peak and a cathodic peak on the cyclic voltammogram of poly (methylene green) at pH≤3.8. Both peak potentials shift towards negative potentials with increasing pH value, and their peak currents decrease with increasing pH value. Poly (methylene green) has a good electrochemical activity and stability in aqueous solutions with pH≤3.8. The UV‐Visible spectrum and FTIR spectrum of poly (methylene green) are different from those of methylene green.     

Electrochemical synthesis,characterisation and comparative study of new conducting polymers from amino-substituted naphthalene sulfonic acids

Conducting polymers have been synthesised electrochemically from 4-amino-3-hydroxynaphthalene-1-sulfonic acid (4A3HN1SA), 4-aminonaphthalene-1-sulfonic acid (4AN1SA) and 7-amino-4-hydroxynaphthalene-2-sulfonic acid (7A4HN2SA) on glassy carbon electrodes. The influence of the positive potential limit on the potential cycling polymerisation of 4A3HN1SA was studied, and a sufficiently high potential limit allowed better film growth. Under similar polymerisation conditions, the three monomers showed different radical formation potentials and different voltammetric peak profiles. The effects of scan rate and solution pH on the electrochemical properties of the polymers were investigated, in the range between 10 and 200 mV s^?1, all the modified electrodes showing a surface-confined electrode process. In the pH range from 2.0 to 9.0, the anodic peak potentials decreased linearly with increasing pH for all the three modified electrodes. The modified electrodes were characterised by electrochemical impedance spectroscopy in pH 4.0 and 7.0 buffer solutions. The results showed a more porous poly(7A4HN2SA) film, which is less affected by pH change than the other two films. Scanning electron microscopy of the polymer films also showed significant differences in their morphologies.     

Electrochemistry of cytochrome P450 BM3 in sodium dodecyl sulfate films

Direct electrochemistry of the cytochrome P450 BM3 heme domain (BM3) was achieved by confining the protein within sodium dodecyl sulfate (SDS) films on the surface of basal-plane graphite (BPG) electrodes. Cyclic voltammetry revealed the heme FeIII/II redox couple at -330 mV (vs Ag/AgCl, pH 7.4). Up to 10 V/s, the peak current was linear with the scan rate, allowing us to treat the system as surface-confined within this regime. The standard heterogeneous rate constant determined at 10 V/s was estimated to be 10 s-1. Voltammograms obtained for the BM3-SDS-BPG system in the presence of dioxygen exhibited catalytic waves at the onset of FeIII reduction. The altered heme reduction potential of the BM3-SDS-graphite system indicates that SDS is likely bound in the enzyme active-site region. Compared to other P450-surfactant systems, we find redox potentials and electron-transfer rates that differ by approximately 100 mV and >10-fold, respectively, indicating that the nature of the surfactant environment has a significant effect on the observed heme redox properties.     

Simultaneous Detection of Peracetic Acid and Hydrogen Peroxide by Amperometry at Pt and Au Electrodes

Based on preliminary voltammetric investigations at both Pt and Au electrodes in aqueous solutions buffered at different pH values in the range 0–10, two possible profitable triple‐pulse amperometric approaches were developed for determining simultaneously peroxyacetic acid (PAA) and hydrogen peroxide present in the same samples. At both surfaces a pulsed waveform applied at rotating‐disc electrodes was adopted to take advantage on one hand of the optimized signal reproducibility achieved by this potential multistep antifouling approach and on the other hand of the constant thickness of the diffusion layer, which is necessary when the recording of time‐independent currents is desired. At a rotating‐disc Pt electrode an anodic selective signal was indeed recorded for H₂O₂ alone, while PAA contents could be inferred only from the difference of convenient signals, since at all pHs explored its sole cathodic reaction could be observed at potentials coincident with those proper for the reduction of H₂O₂ too. The same pulse approach at Au electrodes instead provided totally independent signals for the two analytes considered, thus proving to be suitable for their independent detection. In fact, H₂O₂ alone undergoes anodic oxidation also at this surface, while the reduction of PAA occurs at potentials less cathodic than those required for H₂O₂. At both electrodes, the best results turned out to be achieved at pH 0 in terms of both precision (±2–4%) and detection limits (0.2–0.3 mM), as well as of linear range which extended for about three orders of magnitude. The kinetics of the equilibrium involving the generation of H₂O₂ from the reaction of PAA with water was also evaluated, since it was suspected of making unreliable the proposed amperometric approaches.     

Cyclic and stripping voltammetry of Se(+4) and Se(−2) at the HMDE in acidic media

Electroreduction of Se(+4) and electrooxidation of Se(?2) were studied at mercury electrodes in acidic media and an improved mechanism of the reduction process was proposed. This mechanism takes into account the fact that the reduction path is concentration-dependent. At lower concentrations of Se(+4), mercury selenide and hydrogen selenide are formed at various potentials. At higher Se(+4) concentrations the electrode quickly becomes covered by a rigid deposit of mercury selenide and then the reduction starts to proceed to elemental selenium. Another form of selenium was formed in the vicinity of the mercury surface due to a chemical reaction between H₂SeO₃ and H₂Se. Oxidation of hydrogen selenide proceeds similarly, in the sense that after coverage of the electrode surface by a deposit of mercury selenide the oxidation starts to proceed to elemental selenium. The cathodic stripping peak of mercury selenide can be obtained down to 2 × 10^?8M of Se(+4), but this peak is often split and therefore the determination of traces of Se(+4) by the cathodic stripping technique is cumbersome.     

Electrochemical polarisation and galvanic couple behaviour of the primary phase of 55% Al–Zn coating investigated using band microelectrodes (BME) and band microelectrode arrays

Electrochemical polarisation experiments have shown that anodic dissolution processes on Al–40% Zn alloys are significantly enhanced in chloride compared to sulfate-based electrolytes. The aluminium content of the alloys allowed passive behaviour to be observed in sulfate electrolyte even in the presence of zinc-rich precipitates on the surface. Electrolyte pH affected cathodic processes, which was attributed to the rate of proton reduction and the passivity of the surface. Monitoring the OCP of the alloy band during polarisation of neighbouring zinc electrodes in band microelectrode (BME) arrays showed that generation of alkaline pH at the zinc electrodes affected the OCP of the alloy when the inter-electrode spacing was 10, 50, and 200 μm. Where elements of a BME array were close enough to interact via mass transport, the overall galvanic behaviour of the cell was found to be anodic or cathodic, whereas the alloy was consistently cathodic with respect to zinc in galvanic cells at larger separations. Dedicated to the 80th birthday of Keith B. Oldham.     

Redox reaction characteristics of ferritin-immobilized onto poly(l-lysine)-modified indium oxide electrodes

Ferritin-immobilized poly(l-lysine)-modified electrodes showed well-defined redox waves representing ferritin. Cathodic and anodic peak currents obtained from cyclic voltammograms were proportional to potential sweep rates. From charge flow values during oxidation or reduction reactions calculated by peak areas in cyclic voltammograms, and the surface coverage of ferritin, reacted iron atoms per ferritin molecule were calculated. Obtained numbers of reacted iron atoms were significantly smaller than expected values from iron atoms at ferrihydrite core surfaces of ferritin, which would be caused by the rate-determining ion flow through ion channels of ferritin to compensate for charges in the ferritin cavity. Anodic and cathodic peak potentials in cyclic voltammograms were significantly dependent on cationic species in the solution, though voltammetric shapes and peak currents were independent of cations. From the obtained results that structural changes in ferritin were not detected by fluorescent spectra, it is thought that the cationic dependence on ferritin redox peak potentials is caused by ferritin cores.     

The determination of some 2-thiobarbiturates by cathodic stripping voltammetry

Pulse polarography and cyclic voltammetry are employed in studies of the electrochemical behaviour of 5-ethyl-5'-(l-methylbutyl)-2-thiobarbituric acid (I), l-methyl-5-ethyl-5'-(l-methylpropyl)-2-thiobarbituric acid (II) and l,3-dimethyl-5-ethyl-5'-p-chlorophenyl)-2-thiobarbituric acid (III) in the pH range 4–12. All three compounds show anodic and cathodic waves or peaks in this pH range. Compounds (I) and (II) are oxidized at mercury indicator electrodes to produce mercury salts which can adsorb thereon and are thus amenable to cathodic stripping voltammetric analysis (c.s.v.) down to concentrations of the order of 10^-6 M, which is superior to the sensitivities obtained by differential pulse polarography (d.p.p.) based on a reduction peak. Compound (III) oxidizes to produce sulphur which is subsequently plated as HgS. Again the sensitivity of the c.s.v. method is of the order of lO^-6 M and analytically superior to d.p.p. The optimum pH for the three determinations is 8. The determination of (II) in the presence of its oxygenated analogue and metabolite, phemitone, and the effect of chloride ions are reported.     

Electrochemical,chemical and spectrophotometric investigation of the copper(II)-bicinchoninic acid reagent used for protein measurements

The use of a reagent containing copper (II), bicinchoninic acid (BCA) and tartrate buffered at pH 11.25 was studied voltammetrically, coulometrically, spectrophotometrically and chemically. The reagent exhibits three cathodic waves at rotating platinum disk and rotating glassy carbon electrodes. The two more-positive cathodic waves correspond to electrochemical reduction to copper (I)-bisbicinchoninate, Cu(BCA)₂^3?. The third cathodic wave is caused by reduction to metallic copper. A reaction mechanism is proposed that shows the major chemical species in the solution and the electrochemical reaction products. Voltammetric and chemical studies indicate that the reagent should be used with care for protein assays because it is subject to multiple chemical interferences.     

Catalytic hydrogen evolution in the presence of methylthiohydantoin-glycine and cobalt(II) ion: a study by cathodic stripping voltammetry at a hanging mercury drop electrode

The carbon-sulfur bond in methylthiohydantoin-glycine (MTH-Gly) is broken during the deposition on the mercury electrode at potentials around -0.1 V versus SCE, giving mercury sulfide which is detected by the characteristic cathodic peak at -0.7 V. If cobalt (II) is also present, the product of the deposition step is a mixture of mercury and cobalt sulfides. During the cathodic scan, the last one is reduced to a transient Co(0) species that catalyses the reduction of hydrogen ion to the hydrogen molecule by a mechanism alike to that emphasized for the Co(II)-sulfide ion system (F.G. B?nic?, N. Sp?taru, T. Sp?taru, Electroanalysis 9 (1997) 1341). This electrode process induces a cathodic peak at -1.4 V that enables the determination of MTH-Gly down to 10(-7) M in the borax buffer at pH 8.5. The possible extension of this method to other classes of organic sulfur compounds is briefly discussed.     

Influence of cyanide and sulphide ions on the reduction and reoxidation of cobalt(II) in thiocyanate solution at mercury electrodes

The process of reduction and reoxidation of cobalt(II) in thiocyanate solution at hanging mercury drop electrode has been investigated by cyclic voltammetric, chronoamperometric and anodic stripping methods. In 0.1 M NaSCN and 0.4 M NaClO₄ solution containing 1×10^?3M cobalt(II), the voltammogram on the first cycle at 0.05 V s^?1 gives a cathodic peak at ?1.06 V with hysteresis on reversal, and an anodic wave with a peak potential of ?0.28 V and with two shoulders near ?0.38 and ?0.45 V, respectively. Multicyclic voltammograms under the same conditions give a cathodic peak at ?0.90 V and an anodic peak at ?0.45 V. The reduction and reoxidation of cobalt(II) in thiocyanate solution is accelerated by the reduction products of thiocyanate ion, cyanide and sulphide ions, which are produced during the electroreduction of cobalt(II).A mechanism of reduction and reoxidation of cobalt(II) which involves a chemical reduction of thiocyanate ion by electroreduced metallic cobalt and takes into account cyanide and sulphide ions is proposed. The hysteresis on the cathodic wave is caused by the difference in reduction potentials of cobalt(II)-thiocyanate and-cyanide complexes. Cyclic voltammetric study of cobalt(II) in perchlorate solution containing trace amounts of cyanide and sulphide ions supports these conclusions.     

Mechanism and kinetics of electrode processes in systems comprising solid polyaluminate electrolyte

Cathodic reduction of organic semiconductors (charge-transfer complexes and radical-ion salts) at interfaces in Na(Hg)/β-Al₂O₃/organic semiconductor systems is studied by inversion voltammetry and chronopotentiometry. Formation of transition layer at the organic semiconductor/solid electrolyte interface is revealed. The mechanism of the charge transfer complex and radical-ion salt cathodic reduction depends on the potential scan rate; the cathodic process at nonmetal electrodes occurs under the conditions of double injection of electronic and ionic charge carriers to electrode bulk.     

Electrochemical Oxidation of ds‐DNA on Polypyrrole Nanofiber Modified Pencil Graphite Electrode

Preparation of a polypyrrole nanofiber (PPyNF) modified pencil graphite (PG) electrode and its usage in the electrochemical DNA biosensors was investigated. The electrodes (PPyNF/PG1 and PPyNF/PG2) were prepared from a solution containing 0.1 M pyrrole, 0.1 M Na₂CO₃ and 0.1 M LiCIO₄ by using potentiostatic and potentiodynamic methods. PPyNF/PG2 electrodes which were prepared by potentiostatic procedure showed higher responses for the oxidation of ds‐DNA than the PPyNF/PG1 electrodes prepared by potentiodynamic methods. Immobilization of the ds‐DNA on PG and PPyNF/PG surfaces was performed at a constant potential, +0.5 V, for 300 s in 0.5 M ABS (pH 4.8) containing 15 μg mL^?1 ds‐DNA and 20 mM LiCIO₄. The oxidation peak potentials of the ds‐DNA bases, guanine and adenine, were shifted to more cathodic values by using PPyNF/PG electrodes. The oxidation signal of the guanine base of ds‐DNA was decreased in the presence of methylene blue.     

Effect of solution pH on the electrochemical behavior of thiocarbamide at gold and platinum electrodes

The effect of solution pH on the electrochemical behavior of thiocarbamide at gold and platinum electrodes is studied by using cyclic voltammetry and quartz microgravimetry. It is shown that with the increasing of pH the half-wave potential of thiocarbamide oxidation shifts toward negative values in both cases. In the cathodic branches of the cyclic voltammograms, up to pH ≃ 4 the potential region of reduction of the thiocarbamide oxidation product remains practically unchanged; this allows concluding that the oxidation product is formamidine disulfide (at platinum) or its mixture with gold complex ions (at gold electrode). Further increasing of pH up to 9.5–10 results in the increase of the contribution of the reduction current of these ions to the cathodic signal. An explanation for this phenomenon is given. At the same time, new signals appear at E < −0.4 V; they may be interpreted as the current of elemental sulfur reduction. Increasing of pH over 10 leads to gold passivation by the elemental sulfur; this manifests itself as the electrode mass increase during the microgravimetry measurements. Introducing of sodium silicate (recommended in the literature as a solution stabilizer) to the solution does not eliminate the passivation of gold.     

Mechanism of nitrate electroreduction on Pt(100)

Kinetics and mechanism of nitrate anion reduction on the Pt(100) electrode in perchloric and sulfuric acid solutions are studied. Analysis of the results of electrochemical measurements (combination of potentiostatic treatment and cyclic voltammetry) and the data of in situ IR spectroscopy allow suggesting the following scheme of the nitrate reduction process on Pt(100) differing from that in the literature. If the potential of 0.85 V is chosen as the starting potential for a clean flame-annealed electrode surface and negativegoing (cathodic) potential sweep is applied, then an NO adlayer with the coverage of about 0.5 monolayer is formed on Pt(100) in the nitrate solution already at 0.6 V. The further decrease in the potential results in NO reduction to hydroxylamine or/and ammonia, desorbing products vacate the adsorption sites for nitrate and hydrogen adatoms. At E < 0.1 V, adsorbed hydrogen is mostly present on the surface. During positive-going (anodic) potential sweep, the process of nitrate reduction starts after partial hydrogen desorption, the cathodic peak of nitrate reduction to hydroxylamine or ammonia is observed at 0.32 V on cyclic voltammograms. The process of nitrate anion reduction continues up to 0.7 V; at higher potentials, the surface redox process with participation of hydroxylamine or ammonia (the anodic peak at 0.78 V) and nitrate (the cathodic peak at 0.74 V is due to nitrate reduction to NO on the vacant adsorption sites) occurs.     

卟啉化合物的电催化行为V.金属卟啉化合物电极上胱氨酸还原反应的动力学及反应机理研究

采用循环伏安法及带环的旋转圆盘电极技术,在经热处理的载于石墨粉上的四(对甲氧基苯基)卟啉钴(Co-TMPP/石墨)电极上研究了溶液pH值对胱氨酸还原反应的影响.实验结果表明,在不同pH值溶液中经热处理的Co-TMPP/石墨对 胱氨酸还原反应均有较好的催化活性且该电极上胱氨酸还原反应为不可逆的简单电荷传递反应.测出了不同pH值溶液中胱氨酸剂原反应的标准速度常数.当pH<4时,胱氨酸还原对[H^+]的反应级数为1;pH>9时,反应与[H^+]无关.提出了不同pH值溶液中胱氨酸还原反应的机理.