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Electrode Reaction (electrode + reaction)
Selected AbstractsElectrode Reactions of Catechol at Tyrosinase-Immobilized Latex SuspensionsELECTROANALYSIS, Issue 8 2004Patsamon Rijiravanich Abstract Tyrosinase was immobilized on polystyrene latex particles in order to control amounts of the enzyme. The tyrosinase-coated latex particles were composed of the core polystyrene and four successive coating layers: polystyrene sulfonate, polyallylamine, tyrosinase and polyallylamine again, built up by the layer-by-layer technique. They showed catalytic currents for the enzymatic oxidation of catechol to o -quinone. The enzyme activity per particle was evaluated as 2.3×10,7 units from UV absorption of o -quinone. The relation between the catalytic current and the concentration of catechol leads to a Michaelis-Menten type kinetic equation. The layer-by-layer method was found to have a deactivating effect on enzyme catalysis. In spite of this, the catechol oxidation current was larger than the current from free tyrosinase at a common value of enzyme units per volume. This is ascribed to strong adsorption of the latex particles on the electrode, leading to the enhancement of the local concentration of tyrosinase. [source] Charge and Mass Transfer Across the Metal/Solution InterfaceISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008Eliezer Gileadi Electrode reactions are characterized by charge transfer across the interface. The charge can be carried by electrons or by ions. It is shown here that when both mass and charge cross the interface, the charge must be carried by the ionic species, not by the electrons, as a result of the very large difference in the time scale for electron and ion transfer. A prime example of charge transfer by ions is metal deposition. It is proposed that ion transfer occurs by migration of the ions across the interface, under the influence of the high electrostatic field in the double layer. The rate constants observed for metal deposition are comparable to those for outer-sphere charge transfer. These unexpectedly high rate constants for metal deposition are explained by a model in which removal of the solvation shell and reduction of the effective charge on the metal ion occur in many small steps, and a make-before-break mechanism exists, which lowers the total Gibbs energy of the system as it moves along the reaction coordinate from the initial to the final state. [source] Cathodic Stripping Voltammetry of Uracil.ELECTROANALYSIS, Issue 1 2009Experimental, Theoretical Study Under Conditions of Square-Wave Voltammetry Abstract The electrode mechanism of uracil at a hanging mercury drop electrode (HMDE) is studied under cathodic stripping square-wave voltammetric mode owing to the cathodic dissolution of a sparingly soluble compound formed between the electrode material and uracil. The experimental results can be partly explained in the light of the recent theory for cathodic stripping processes of insoluble salts under conditions of square-wave voltammetry. It is established that the electrode reaction is complicated by attractive interactions between the deposited species of the insoluble compound. To elucidate the electrode mechanism completely a novel theoretical model is developed considering adsorption of the reacting analyte and lateral interactions between species of the insoluble compound. With the help of numerical simulations the effect of interactions is studied in detail, emphasizing the properties of the response that can be used as diagnostic criteria for recognition of the type of interaction forces. Theoretically predicted voltammetric properties agree well with the experimental results enabling clarification of the complex electrode mechanism of uracil at HMDE. [source] Isolation of Solid Solution Phases in Size-Controlled LixFePO4 at Room TemperatureADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Genki Kobayashi Abstract State-of-the-art LiFePO4 technology has now opened the door for lithium ion batteries to take their place in large-scale applications such as plug-in hybrid vehicles. A high level of safety, significant cost reduction, and huge power generation are on the verge of being guaranteed for the most advanced energy storage system. The room-temperature phase diagram is essential to understand the facile electrode reaction of LixFePO4 (0,<,x,<,1), but it has not been fully understood. Here, intermediate solid solution phases close to x,=,0 and x,=,1 have been isolated at room temperature. Size-dependent modification of the phase diagram, as well as the systematic variation of lattice parameters inside the solid-solution compositional domain closely related to the electrochemical redox potential, are demonstrated. These experimental results reveal that the excess capacity that has been observed above and below the two-phase equilibrium potential is largely due to the bulk solid solution, and thus support the size-dependent miscibility gap model. [source] Acid decomposition of omeprazole in the absence of thiol: A differential pulse polarographic study at the static mercury drop electrode (SMDE)JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2006Ali M. Qaisi Abstract The reactions of omeprazole, a potent proton pump inhibitor (PPI), were investigated in the absence of a nucleophile. Reactions were monitored, using differential pulse polarography (DPP) at the static mercury drop electrode (SMDE), in solutions buffered to pH values ranging from 2.0 to 8.0. The fast, sensitive, and selective electrochemical technique facilitated to repeat recordings of successive voltammograms [peak current (nA) vs. peak potential (volts vs. Ag/AgCl saturated with 3.0 M KCl)]. The DPP signals of omeprazole and its degradation products, believed to be due to sulfur functional group (the principal site of electrode reaction), gave advantages over the previously employed UV detection technique. The latter primarily relied on pyridine and benzimidazole analytical signals, which are common reaction products of PPI in aqueous acidic solutions. After peak identification, the resulting current (nA)-time (s) profiles, demonstrated that omeprazole undergoes degradation to form two main stable compounds, the first is the cyclic sulfenamide (D+), previously believed to be the active inhibitor of the H+, K+ -ATPase, the second is omeprazole dimer. This degradation is highly dependant on pH. Unlike previous studies which reported that the lifetime of D+ is few seconds, the cyclic sulfenamide (D+) was found to be stable for up to 5,20 min. The results further indicated that omeprazole converts into the cyclic sulfenamide in an irreversible reaction, consequently, D+ and sulfenic acid (an intermediate which rapidly converts into D+) were not interconvertable. The present work suggested that the sulfenic acid is the active inhibitor in vivo. In addition, the omeprazole reactions, in the absence of the thiol, were not as complicated as were previously reported. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:384,391, 2006 [source] Poly(4-hydroxyphenylacetic acid): A new material for immobilization of biomoleculesPOLYMER ENGINEERING & SCIENCE, Issue 10 2008Tatiana A.R. Silva The electrochemical modification, surface analysis, and electrochemical impedance spectroscopy of graphite electrodes modified with polymeric films derived from 4-hydroxyphenylacetic acid (4-HPA) were investigated. The electrooxidation and optimization of the immobilization of adenosine monophosphate (AMP) and guanosine monophosphate (GMP) onto poly(4-HPA) films at different pH values was carried out. Variation of the experimental conditions that influenced the electrode reaction, particularly the pH of the electrolytic solution, showed that the oxidation potentials of the immobilized AMP or GMP onto the modified electrodes decreased with increasing pH of the electrolyte. Higher oxidation current was obtained for AMP in phosphate buffer (pH 7.50) solution and GMP in acetate buffer (pH 4.50) solution. Film surface morphology and roughness in the absence or presence of AMP or GMP have been characterized by atomic force microscopy. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Comparison of the Electrochemical Behavior of the High Molecular Mass Cadmium Proteins in Arabidopsis thaliana and in Vegetable Plants on Using Preparative Native Continuous Polyacrylamide Gel Electrophoresis (PNC-PAGE)ELECTROANALYSIS, Issue 1 2006Bernd Kastenholz Abstract In Arabidopsis cytosol (supernatant) and in supernatants of vegetable plants high molecular mass cadmium proteins with molecular mass 200,kDa were isolated by using preparative native continuous polyacrylamide gel electrophoresis (PNC-PAGE). Because of a different electrochemical behavior of the Cd proteins in Arabidopsis and endive supernatants on using the same PAGE method, it is concluded that the high molecular mass cadmium proteins of Arabidopsis and endive possess different isoelectric points. Consequently, different chemical structures of the Cd proteins with molecular mass 200,kDa are present in Arabidopsis thaliana and in endive. During the electrophoretic separation of vegetable metalloproteins by using the Model 491 Prep Cell from BioRad, electroanalytical processes like electrode reactions may play an important role. [source] Early Polarographic Studies on ProteinsELECTROANALYSIS, Issue 13-14 2004Michael Heyrovsky Abstract The first effects of proteins observed with the dropping mercury electrode were catalytic, due to evolution of hydrogen in weakly alkaline solutions. Catalytic lowering of hydrogen overvoltage in presence of cobalt ions, the so-called Brdicka reaction, became the main means for polarographic study of proteins. Apart from that, polarography has been used for following proteins in their adsorption on the electrode surface, in their anodic reaction with mercury at positive potentials, in reduction of the disulfidic bonds of their components, in their complexation with metallic ions in the solution, in electrode reactions of their prosthetic groups and in antigen-antibody interactions. Our review is limited to applications of the dropping mercury electrode. [source] Recent advances in microdevices for electrochemical energy conversion and storageINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6-7 2007Gerardo Jose La O' Abstract The application of silicon microfabrication technologies to electrochemical devices allows reduction of overall device package to potentially increase volumetric power densities. This review first focuses on some exciting developments in microfuel cells, in particular, solid oxide fuel cells (SOFCs) and proton exchange membrane fuel cells (PEMFCs). The emphasis is given to innovative 2D processing methods, novel 2D architectures of microfuel cells, and demonstrated performance in terms of area power densities. Emerging 3D fabrication techniques that are potentially promising to produce 3D electrochemical devices such as 3D cell and stack architectures on the micrometer scale will then be discussed. Lastly this paper highlights some new opportunities in electrode kinetics studies enabled by microfabricated devices,investigation of scaling relationship between microelectrodes and electrochemical responses, which has led to improved fundamental understanding of electrode reactions and rate-limiting steps. Copyright © 2007 John Wiley & Sons, Ltd. [source] | |||||||||||||