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Voltammetry Experiments (voltammetry + experiment)
Selected AbstractsBioelectrochemical Characterization of Horseradish and Soybean PeroxidasesELECTROANALYSIS, Issue 21 2009Marco Frasconi Abstract Heme peroxidase are ubiquitous enzymes catalyzing the oxidation of a broad range of substrates by hydrogen peroxide. In this paper the bioelectrochemical characterization of horseradish peroxidase (HRP) and soybean peroxidase (SBP), belonging to class III of the plant peroxidase superfamily, was studied. The homogeneous reactions between peroxidases and some common redox mediators in the presence of hydrogen peroxide have been carried out by cyclic voltammetry. The electrochemical characterization of the reactions involving enzyme, substrate and mediators concentrations allowed us to calculate the kinetic parameters for the substrate,enzyme reaction (KMS) and for the redox mediator,enzyme reaction (KMM). A full characterization of the direct electron transfer kinetic parameters between the electrode and enzyme active site was also performed by opportunely modeling data obtained from cyclic voltammetry and square wave voltammetry experiments. The experimental data obtained with immobilized peroxidases show enhanced direct electron transfer and excellent electrocatalytical performance for H2O2. Despite the structural similarities and common catalytic cycle, HRP and SBP exhibit differences in their substrate affinity and catalytic efficiency. Basing on our results, it can be concluded that peroxidase from soybean represents an interesting alternative to the classical and largely employed one obtained from horseradish as biorecognition element of electrochemical mediated biosensors. [source] Electroanalytical Determination of Promethazine Hydrochloride in Pharmaceutical Formulations on Highly Boron-Doped Diamond Electrodes Using Square-Wave Adsorptive VoltammetryELECTROANALYSIS, Issue 18 2008Francisco, Wirley Abstract The electrochemical oxidation of promethazine hydrochloride was made on highly boron-doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78,V for 30 seconds. The square-wave adsorptive voltammetry results obtained in BR buffer showed two well-defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH,4.0, frequency of 50,s,1, step of 2,mV, and amplitude of 50,mV. Under these conditions, linear responses were obtained for concentrations from 5.96×10,7 to 4.76×10,6,mol L,1, and calculated detection limits of 2.66×10,8,mol L,1 (8.51,,g L,1) for peak 1 and of 4.61×10,8,mol L,1 (14.77,,g L,1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method. [source] Quantized Double-Layer Charging of Rhodium2057(Tridecylamine)321 Clusters Using Differential Pulse and Cyclic Voltammetry,ADVANCED MATERIALS, Issue 2 2007A. Kakade Rhodium nanoclusters show a series of quantized double-layer-charging events in solution-phase voltammetry at room temperature (see figure). The unusual variation in the FWHM for both the cathodic and anodic regions in differential pulse voltammetry experiments can be explained by several complex factors including reorganization and disproportionation of charged clusters coupled with electron-transfer processes pertaining to the Rh,Rh bonds. [source] Preparation and study of cellulose acetate membranes modified with linear polymers covalently bonded to Starburst polyamidoamine dendrimersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008J. Ledesma-García Abstract Novel ion-selective membranes were prepared by means of the noncovalent modification of a cellulose acetate (CA) polymer with either poly(ethylene- alt -maleic anhydride) or poly(allylamine hydrochloride) chains covalently linked to Starburst amine-terminated polyamidoamine (PAMAM) dendrimers generations 4 and 3.5, respectively. Linear polymer incorporation within the porous CA membrane was performed with mechanical forces, which resulted in modified substrates susceptible to covalent adsorption of the relevant dendritic materials via the formation of amide bonds with a carbodiimide activation agent. The membranes thus prepared were characterized by chemical, physical, and spectroscopic measurements, and the results indicate that the dendrimer peripheral functional groups were the species that participated in the ion-exchange events. The prepared materials were also evaluated for their ion-exchange permeability with sampled current voltammetry experiments involving cationic and anionic species {[Ru(NH3)6]3+ and [Fe(CN6)]3,, respectively} as redox probe molecules under different pH conditions. As expected, although permeability was favored by opposite charges between the dendrimer and the electroactive probe, a clear blocking effect took place when the charge in the dendritic polymer and the electroactive complex was the same. Electrochemical impedance spectroscopy measurements, on the other hand, showed that the PAMAM-modified membranes were characterized by good selectivity and low resistance values for multivalent ions compared to a couple of commercial ion-exchange membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Highly Conjugated p -Quinonoid ,-Extended Tetrathiafulvalene Derivatives: A Class of Highly Distorted Electron DonorsCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2004Marta C. Díaz Abstract A new class of ,-extended TTF-type electron donors (11,a,c) has been synthesized by Wittig,Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10,a,c). In cyclic voltammetry experiments, donors 11,a,c reveal a single, electrochemically irreversible oxidation,yielding the corresponding dicationic products,at relatively low oxidation potentials (,0.7,0.8 V). Theoretical calculations, performed at the DFT level (B3,P86/6-31,G*), predict a highly-folded C2h structure for 11,a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO,LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11,a.+ retains the folded C2h structure predicted for the neutral molecule as the most stable conformation, the dication 11,a2+ has a fully aromatic D2 structure, formed by an orthogonal 9,9,-bianthryl central unit to which two singly-charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical-induced one-electron oxidation of 11,a,c was shown to lead to the radical cation species (11,a,c.+), which were found to disproportionate with generation of the respective dication species (11,a,c2+) and the neutral molecules (11,a,c). Una nueva familia de moléculas dadoras de electrones de tipo TTF , -extendido, altamente conjugadas, (11,a,c) se han sintetizado mediante la reacción de olefinación de Wittig,Horner de la biantrona (9) con fosfonatos de 1,3-ditiol (10,a,c). En los experimentos de voltamperometría cíclica, los dadores 11,a,c muestran una única onda de oxidación electroquímicamente irreversible,dando lugar a los productos dicatiónicos,a potenciales relativamente bajos (,0.7,0.8 V). Cálculos teóricos, llevados a cabo a nivel DFT (B3,P86/6-31,G*), predicen una estructuraC2haltamente distorsionada para 11,a. La molécula adopta una conformación en forma de doble mariposa para aliviar el impedimento estérico. Los cálculos sugieren que la transferencia de carga intramolecular asociada a la transición HOMO,LUMO es responsable de la banda de absorción observada por encima de 400 nm en el espectro electrónico. El catión radical 11,a.+retiene la estructura C2hplegada predicha para la molécula neutra como la conformación más estable. Por el contrario, el dicatión 11,a2+muestra una estructuraD2totalmente aromática,formada por una unidad central de 9,9,-biantrilo ortogonal, unida a los anillos cargados de ditiol. Los profundos cambios conformacionales que experimentan los compuestos 11 tras la oxidación explican sus propiedades electroquímicas. Medidas de radiólisis de pulso, esto es, la oxidación monoelectrónica de 11,a,c inducida por radicales, conduce a las especies catión radical (11,a,c.+), las cuales dismutan para generar las respectivas especies dicatiónicas (11,a,c2+) y la molécula neutra (11,a,c). [source] Redox Properties of Mixed Lutetium/Yttrium Nitride Clusterfullerenes: Endohedral LuxY3,xN@C80(I) (x=0,3) CompoundsCHEMPHYSCHEM, Issue 7 2009Ján Tarábek Dr. Abstract The complex redox behavior of mixed lutetium/yttrium nitride clusterfullerenes of the series LuxY3,xN§C80(Ih, x=0,3) (see figure) results in up to three irreversible reduction steps. A reduction mechanism is proposed based on fast-scan and square-wave voltammetry experiments combined with simulations of the voltammograms. The redox behavior of mixed lutetium/yttrium nitride clusterfullerenes of the series LuxY3,xN@C80(Ih, x=0,3) is studied for the first time by means of cyclic voltammetry, fast-scan cyclic voltammetry, square-wave voltammetry, and electron paramagnetic resonance (EPR) spectroelectrochemistry. A reversible single-electron-transfer process, which does not result in an EPR signal, is detected during the anodic oxidation sweep of cyclic voltammetry experiments performed at different temperatures (296 and 360 K). The cathodic reduction sweep reveals a rather complex response for all the four clusterfullerenes,with up to three irreversible reduction steps. By correlating the results of fast-scan and square-wave voltammetry and combining them with simulations of the voltammograms, we are able to propose a reduction mechanism for the LuxY3,xN@C80(I) (x=0,3) fullerenes. [source] | |||||||||||||