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Electrochemical Experiments (electrochemical + experiment)
Selected AbstractsCopper-containing nitrite reductase from Pseudomonas chlororaphis DSM 50135FEBS JOURNAL, Issue 12 2004Evidence for modulation of the rate of intramolecular electron transfer through nitrite binding to the type 2 copper center The nitrite reductase (Nir) isolated from Pseudomonas chlororaphis DSM 50135 is a blue enzyme, with type 1 and type 2 copper centers, as in all copper-containing Nirs described so far. For the first time, a direct determination of the reduction potentials of both copper centers in a Cu-Nir was performed: type 2 copper (T2Cu), 172 mV and type 1 copper (T1Cu), 298 mV at pH 7.6. Although the obtained values seem to be inconsistent with the established electron-transfer mechanism, EPR data indicate that the binding of nitrite to the T2Cu center increases its potential, favoring the electron-transfer process. Analysis of the EPR spectrum of the turnover form of the enzyme also suggests that the electron-transfer process between T1Cu and T2Cu is the fastest of the three redox processes involved in the catalysis: (a) reduction of T1Cu; (b) oxidation of T1Cu by T2Cu; and (c) reoxidation of T2Cu by NO2,. Electrochemical experiments show that azurin from the same organism can donate electrons to this enzyme. [source] Widening the Voltammetric Window Using Regular Arrays of Microdisk ElectrodesELECTROANALYSIS, Issue 16 2007Francois Abstract This work explores, through mathematical modeling and numerical simulation, the use of regular arrays of microdisk electrodes wired in parallel as a means to increase the width of the electrochemical window in which one can carry out electrochemical experiments. [source] Optical Measurements of Platinum Based Electrocatalysts for the Electrooxidation of Methanol,FUEL CELLS, Issue 1-2 2003K. Gruber Abstract In a combinatorial electrochemistry experiment quinine was used as a pH sensitive fluorescing indicator to detect the catalytic activity of methanol oxidation catalysts. During electrochemical experiments the surface of the electrode array was monitored with a CCD camera. The dependence of the intensity of the fluorescence on the applied potential was used as an analytical tool; to investigate the electrochemical performance of Pt based electrocatalysts, for the electrooxidation of methanol, in both short and long term tests. [source] P450-catalyzed vs. electrochemical oxidation of haloperidol studied by ultra-performance liquid chromatography/electrospray ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 9 2010Tove Johansson Mali'n The metabolites formed via the major metabolic pathways of haloperidol in liver microsomes, N -dealkylation and ring oxidation to the pyridinium species, were produced by electrochemical oxidation and characterized by ultra-performance liquid chromatography/electrospray ionization mass spectrometry (UPLC/ESI-MS). Liver microsomal incubations and electrochemical oxidation in the presence of potassium cyanide (KCN) resulted in two diastereomeric cyano adducts, proposed to be generated from trapping of the endocyclic iminium species of haloperidol. Electrochemical oxidation of haloperidol in the presence of KCN gave a third isomeric cyano adduct, resulting from trapping of the exocyclic iminium species of haloperidol. In the electrochemical experiments, addition of KCN almost completely blocked the formation of the major oxidation products, namely the N -dealkylated products, the pyridinium species and a putative lactam. This major shift in product formation by electrochemical oxidation was not observed for the liver microsomal incubations where the N -dealkylation and the pyridinium species were the major metabolites also in the presence of KCN. The previously not observed dihydropyridinium species of haloperidol was detected in the samples, both from electrochemical oxidation and the liver microsomal incubations, in the presence of KCN. The presence of the dihydropyridinium species and the absence of the corresponding cyano adduct lead to the speculation that an unstable cyano adduct was formed, but that cyanide was eliminated to regenerate the stable conjugated system. The formation of the exocyclic cyano adduct in the electrochemical experiments but not in the liver microsomal incubations suggests that the exocyclic iminium intermediate, obligatory in the electrochemically mediated N -dealkylation, may not be formed in the P450-catalyzed reaction. Copyright © 2010 John Wiley & Sons, Ltd. [source] Gold-coated fused-silica sheathless electrospray emitters based on vapor-deposited titanium adhesion layersRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2003Stefan Nilsson Gold-coated fused-silica electrospray (ES) emitters based on vapor-deposited adhesion layers of titanium have been manufactured to investigate the possibilities of producing durable ES emitters applicable in chip-based analytical devices. The stabilities of the emitters were studied by both electrospray and electrochemical experiments and a marked increase in the emitter lifetime, compared to that for Cr/Au coated emitters, was found for the Ti/Au emitters in the ES durability tests. This indicates that Ti (rather than Cr) adhesion layers should be used in association with large-scale fabrication of ES emitters by vapor-deposition techniques. The lifetime of about 500,700 hours also allowed the Ti/Au-coated emitter to be used as an integrated part of a capillary liquid chromatography column coupled to a mass spectrometer in a series of LC/MS experiments. The Ti/Au coating was further studied by electrochemical techniques and scanning electron microscopy in conjunction with X-ray spectroscopy. It is shown that the eventual failure of the Ti/Au emitters in ES experiments was due to an almost complete detachment of the gold layer. Experimental evidence suggests that the detachment of the gold coating was due to a reduced adhesion to the titanium layer during oxidation in positive electrospray. Most likely, this was caused by the formation of an oxide layer on the titanium film. It is thus shown that unlimited emitter stabilities are not automatically obtained even if the metallic adhesion layer is stabilized by an oxide formation under positive electrospray conditions. Copyright © 2003 John Wiley & Sons, Ltd. [source] A Mechanically Interlocked BundleCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2004Jovica D. Badji Abstract The prototype of an artificial molecular machine consisting of a trisammonium tricationic component interlocked with a tris(crown ether) component to form a molecular bundle with averaged C3v symmetry has been designed and synthesized. The system is based on noncovalent interactions, which include 1) N+H,,,O hydrogen bonds; 2) CH,,,O interactions between the CH2NH2+CH2 protons on three dibenzylammonium-ion-containing arms, which are attached symmetrically to a benzenoid core, and three dibenzo[24]crown-8 macrorings fused onto a triphenylene core; and 3) ,,,,, stacking interactions between the aromatic cores. The template-directed synthesis of the mechanically interlocked, triply threaded bundle involves post- assembly covalent modification, that is, the efficient conversion of three azide functions at the ends of the arms of the bound and threaded trication into bulky triazole stoppers, after 1,3-dipolar cycloaddition with di- tert -butylacetylenedicarboxylate to the extremely strong 1:1 adduct that is formed in dichloromethane/acetonitrile (3:2), on account of a cluster effect associated with the paucivalent adduct. Evidence for the averaged C3v symmetry of the molecular bundle comes from absorption and luminescence data, as well as from electrochemical experiments, 1H NMR spectroscopy, and mass spectrometry. The photophysical properties of the mechanically interlocked bundle are very similar to those of the superbundle that precedes the formation of the bundle in the process of supramolecular assistance to covalent synthesis. Although weak non-nucleophilic bases (e.g., nBu3N and iPr2NEt) fail to deprotonate the bundle, the strong tBuOK does, as indicated by both luminescence and 1H NMR spectroscopy. While deprotonation undoubtedly loosens up the interlocked structure of the molecular bundle by replacing relatively strong N+H,,,O hydrogen bonds by much weaker NH,,,O ones, the ,,,,, stacking interactions ensure that any structural changes are inconsequential, particularly when the temperature of the solution of the neutral molecular bundle in dichloromethane is cooled down to considerably below room temperature. [source] | ||||||||||