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Fast Deactivation (fast + deactivation)
Selected AbstractsAcidosis Impairs the Protective Role of hERG K+ Channels Against Premature StimulationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 10 2010B.Sc., CHUN YUN DU M.B. Acidosis and the hERG K+ Channel.,Introduction: Potassium channels encoded by human ether-à-go-go-related gene (hERG) underlie the cardiac rapid delayed rectifier K+ channel current (IKr). Acidosis occurs in a number of pathological situations and modulates a range of ionic currents including IKr. The aim of this study was to characterize effects of extracellular acidosis on hERG current (IhERG), with particular reference to quantifying effects on IhERG elicited by physiological waveforms and upon the protective role afforded by hERG against premature depolarizing stimuli. Methods and Results: IhERG recordings were made from hERG-expressing Chinese Hamster Ovary cells using whole-cell patch-clamp at 37°C. IhERG during action potential (AP) waveforms was rapidly suppressed by reducing external pH from 7.4 to 6.3. Peak repolarizing current and steady state IhERG activation were shifted by ,+6 mV; maximal IhERG conductance was reduced. The voltage-dependence of IhERG inactivation was little-altered. Fast and slow time-constants of IhERG deactivation were smaller across a range of voltages at pH 6.3 than at pH 7.4, and the contribution of fast deactivation increased. A modest acceleration of the time-course of recovery of IhERG from inactivation was observed, but time-course of activation was unaffected. The amplitude of outward IhERG transients elicited by premature stimuli following an AP command was significantly decreased at lower pH. Computer simulations showed that after AP repolarization a subthreshold stimulus at pH 7.4 could evoke an AP at pH 6.3. Conclusion: During acidosis the contribution of IhERG to action potential repolarization is reduced and hERG may be less effective in counteracting proarrhythmogenic depolarizing stimuli. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1160-1169) [source] Integration of methanation into the hydrogenation process of benzoic acidAICHE JOURNAL, Issue 1 2009Baoning Zong Abstract The traditional industrial process for hydrogenation of benzoic acid to cyclohexanecarboxylic acid (CCA) has drawbacks of low-activity and fast deactivation of the Pd/C catalyst due to the poisoning of CO arising from the decarboxylation of CCA. A novel rapidly quenched skeletal NiCrFe promoter (RQ NiCrFe) is developed for the methanation of CO to harmless CH4. Evaluations in bench-scale autoclave and in traditional industrial equipment verified that RQ NiCrFe was very effective in promoting the activity of the Pd/C catalyst in the hydrogenation of benzoic acid. In order to solve the catalyst recycle and separation problem introduced by RQ NiCrFe, the industrial process was modified by incorporating a hydraulic cyclone and a magnetic separator to the separation unit. The modified process showed merits of lower costs of catalyst and operation, higher productivity, and better product purity than the traditional process. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Carbon nanotube-supported bimetallic palladium,gold electrocatalysts for electro-oxidation of formic acidPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010Cheng-Han Chen Abstract It is known that palladium-based catalysts are initially very active in direct formic acid oxidation but they suffer from fast deactivation caused by a strongly adsorbed CO intermediate. Reactivation of the catalysts involving application of anodic potential may cause palladium dissolution. The aim of the present study is to increase the stability and performance of palladium-based catalysts in direct formic acid fuel cells (DFAFCs). Preparation and characterization of palladium/multiwalled carbon nanotubes (Pd/MWCNTs) and towards formic acid oxidation via different treatments are described. The catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV). It was shown that the Pd and Pd,Au MWCNTs supported catalysts after reduction in H2,Ar at 200,°C (R200 treatment) were highly active in formic acid electro-oxidation, whereas the catalysts after heating in argon at 250,°C (C250 treatment) were inactive. The catalysts after hydrogen treatment have smaller metal particles and better contact with MWCNTs support. CV, simulating reactivation of the catalysts, showed that the Pd catalyst suffers from severe Pd dissolution, whereas for the Pd,Au selective leaching of Pd is considerably slower. [source] Catalytic decomposition of methane over supported Ni catalysts with different particle sizesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Sun Yunfei Abstract Methane decomposition on ,-Al2O3 -supported Ni catalysts, as a method for the production of carbon nanofibers (CNFs) and CO-free hydrogen, has been investigated to show the effect of catalyst particle size on the rate and yield of CNFs formation. The catalysts were prepared by deposition,precipitation with different calcination temperature ranging from 725 to 1025 K so as to have different initial particle sizes. The results show that catalysts with smaller initial particle sizes had higher initial growth rate but experienced fast deactivation. The lifetime of the catalyst, ending at the inflection point on the rate curve of CNFs growth, could well represent the yield of CNFs of the catalyst, and the maximal yield of CNFs was achieved on the Ni catalysts calcinated at 823 K and with a particle size of around 56 nm. However, the diameters of the grown CNFs were not directly related to the initial size of the catalysts, because of particle sintering and breaking during catalyst reduction or CNFs formation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Triplet Excitation Scavenging in Films of Conjugated PolymersCHEMPHYSCHEM, Issue 7 2009Sarah Schols Abstract Nonvertical triplet energy transfer in solid conjugated polymer films is demonstrated for the first time using 1,3,5,7-cyclooctatetraene, a compound that can efficiently quench the phosphorescence of polyfluorene without affecting its fluorescence (see spectra). The results suggest that nonvertical triplet scavengers might be promising candidates for controlling the triplet concentration in fluorescent high-brightness organic devices. Phosphorescence and delayed fluorescence of polyfluorene polymer films doped with cyclooctatetraene (COT) and anthracene are studied by means of time-resolved photoluminescence (PL) measurements. The occurrence of an anomalous nonvertical triplet energy transfer in solid conjugated polymer films is demonstrated for the first time employing the "nonvertical" COT triplet acceptor, which appears to behave similarly to conventional vertical triplet acceptors, such as anthracene. Both dopant molecules are found to efficiently quench the host phosphorescence of the polymer without affecting the host fluorescence,this can be attributed to the large singlet,triplet (S1,T1) splitting of these molecules. This S1,T1 splitting is exceptionally large in COT due to its low-lying relaxed triplet state, which is capable of accepting host triplet excitations. In contrast to anthracene, the triplet lifetime of the COT molecules is reasonably short, thus making a fast deactivation of the triplet excitations possible. This suggests that nonvertical triplet scavengers might be promising candidates for quenching the host triplet excitations in future electrically pumped fluorescence organic lasers, which suffer from excessive triplet-state losses. [source] | ||||||||||