Twin-electrode thin-layer electrochemistry. Kinetics of second-order disproportionation of uranium(V) by decay of steady-state current

1966 ◽  
Vol 38 (13) ◽  
pp. 1881-1887 ◽  
Author(s):  
Bruce. McDuffie ◽  
Charles N. Reilley
Keyword(s):  
Steady State ◽  
Thin Layer ◽  
Second Order ◽  
Steady State Current ◽  
Kinetics Of

Substrate interactions in the human type IIa sodium-phosphate cotransporter (NaPi-IIa)

2005 ◽  
Vol 288 (5) ◽  
pp. F969-F981 ◽  
Author(s):  
Leila V. Virkki ◽  
Ian C. Forster ◽  
Jürg Biber ◽  
Heini Murer
Keyword(s):  
Steady State ◽  
Sodium Phosphate ◽  
Complete Removal ◽  
Xenopus Laevis Oocytes ◽  
Charge Movement ◽  
Steady State Current ◽  
Transport Cycle ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
State Charge

We have characterized the kinetics of substrate transport in the renal type IIa human sodium-phosphate cotransporter (NaPi-IIa). The transporter was expressed in Xenopus laevis oocytes, and steady-state and pre-steady-state currents and substrate uptakes were characterized by voltage-clamp and isotope flux. First, by measuring simultaneous uptake of a substrate (32Pi, 22Na) and charge in voltage-clamped oocytes, we established that the human NaPi-IIa isoform operates with a Na:Pi:charge stoichiometry of 3:1:1 and that the preferred transported Pi species is HPO42−. We then probed the complex interrelationship of substrates, pH, and voltage in the NaPi-IIa transport cycle by analyzing both steady-state and pre-steady-state currents. Steady-state current measurements show that the apparent HPO42− affinity is voltage dependent and that this voltage dependency is abrogated by lowering the pH or the Na+ concentration. In contrast, the voltage dependency of the apparent Na+ affinity increased when pH was lowered. Pre-steady-state current analysis shows that Na+ ions bind first and influence the preferred orientation of the transporter in the absence of Pi. Pre-steady-state charge movement was partially suppressed by complete removal of Na+ from the bath, by reducing extracellular pH (both in the presence and absence of Na+), or by adding Pi (in the presence of 100 mM Na). None of these conditions suppressed charge movement completely. The results allowed us to modify previous models for the transport cycle of NaPi-II transporters by including voltage dependency of HPO42− binding and proton modulation of the first Na+ binding step.

Effect of Anodizing Voltage on the Growth Kinetics of Porous Anodic Alumina on Al-0.5 wt% Mn Alloys

2013 ◽  
Vol 795 ◽  
pp. 56-59 ◽  
Author(s):  
C.H. Voon ◽  
Mohd Nazree Derman ◽  
U. Hashim ◽  
K.R. Ahmad
Keyword(s):  
Steady State ◽  
Current Efficiency ◽  
Current Density ◽  
Dielectric Breakdown ◽  
Oxide Growth ◽  
Nucleation Process ◽  
Manganese Alloy ◽  
Steady State Current ◽  
Pore Nucleation ◽  
Kinetics Of

In this study, the effect of anodizing voltage on the current density versus time transient, oxide mass and the current efficiency of anodizing of aluminium manganese alloy was reported. It was found that the anodizing voltage facilitated the pore nucleation process and increased the steady state current density. However, when the anodizing voltage is 70V, dielectric breakdown occurred. The current density versus time transient for anodizing conducted at 30 to 60 V were typical while the shape was unusual for anodizing conducted at 70 V. The rate of oxide growth increased as a function of anodizing voltage. The current efficiency of anodizing increased as the anodizing increased from 30V to 70V.

Kinetics of temperature-programmed reactivation of a hydrodesulphurization catalyst

1983 ◽  
Vol 48 (12) ◽  
pp. 3340-3355 ◽  
Author(s):  
Pavel Fott ◽  
Pavel Šebesta
Keyword(s):  
Carbon Dioxide ◽  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Thin Layer ◽  
Kinetic Parameters ◽  
Diffusion Region ◽  
Reaction Heat ◽  
Gaseous Products ◽  
Temperature Programmed ◽  
Kinetics Of

The kinetic parameters of reactivation of a carbonized hydrodesulphurization (HDS) catalyst by air were evaluated from combined thermogravimetric (TG) and differential thermal analysis (DTA) data. In addition, the gaseous products leaving a temperature-programmed reactor with a thin layer of catalyst were analyzed chromatographically. Two exothermic processes were found to take part in the reactivation, and their kinetics were described by 1st order equations. In the first process (180-400 °C), sulphur in Co and Mo sulphides is oxidized to sulphur dioxide; in the second process (300-540 °C), in which the essential portion of heat is produced, the deposited carbon is oxidized to give predominantly carbon dioxide. If the reaction heat is not removed efficiently enough, ignition of the catalyst takes place, which is associated with a transition to the diffusion region. The application of the obtained kinetic parameters to modelling a temperature-programmed reactivation is illustrated on the case of a single particle.

Kinetics of the reaction between hexamethylenediisocyanate and 1-pentanol

1983 ◽  
Vol 48 (11) ◽  
pp. 3279-3286
Author(s):  
Slavko Hudeček ◽  
Miloslav Bohdanecký ◽  
Ivana Hudečková ◽  
Pavel Špaček ◽  
Pavel Čefelín
Keyword(s):  
Liquid Chromatography ◽  
Rate Constants ◽  
Reversed Phase ◽  
Order Reaction ◽  
Second Order ◽  
Second Order Reaction ◽  
Reversed Phase Liquid Chromatography ◽  
Consecutive Reactions ◽  
Phase Liquid ◽  
Kinetics Of

The reaction between hexamethylenediisocyanate and 1-pentanol in toluene was studied by means of reversed-phase liquid chromatography. By employing this method, it was possible to determine all components of the reaction mixture including both products, i.e. N-(6-isocyanate hexyl)pentylcarbamate and N,N'-bis(pentyloxycarbonyl)hexamethylenediamine. Relations for the calculation of kinetic constants were derived assuming a competitive consecutive second-order reaction. It was demonstrated that the reaction involved in this case is indeed a second-order reaction, and the rate constants of the first and second consecutive reactions were determined.

Evidence for general base catalysis by protic solvents in a kinetic study of alcoholyses and hydrolyses of 1-(phenoxycarbonyl)pyridinium ions under both solvolytic and non-solvolytic conditions

2009 ◽  
Vol 74 (1) ◽  
pp. 43-55 ◽  
Author(s):  
Dennis N. Kevill ◽  
Byoung-Chun Park ◽  
Jin Burm Kyong
Keyword(s):  
Second Order ◽  
Base Catalysis ◽  
Substitution Reactions ◽  
Third Order ◽  
Methoxy Derivative ◽  
First Order ◽  
General Base ◽  
Protic Solvents ◽  
Kinetics Of ◽  
Pyridinium Ions

The kinetics of nucleophilic substitution reactions of 1-(phenoxycarbonyl)pyridinium ions, prepared with the essentially non-nucleophilic/non-basic fluoroborate as the counterion, have been studied using up to 1.60 M methanol in acetonitrile as solvent and under solvolytic conditions in 2,2,2-trifluoroethan-1-ol (TFE) and its mixtures with water. Under the non- solvolytic conditions, the parent and three pyridine-ring-substituted derivatives were studied. Both second-order (first-order in methanol) and third-order (second-order in methanol) kinetic contributions were observed. In the solvolysis studies, since solvent ionizing power values were almost constant over the range of aqueous TFE studied, a Grunwald–Winstein equation treatment of the specific rates of solvolysis for the parent and the 4-methoxy derivative could be carried out in terms of variations in solvent nucleophilicity, and an appreciable sensitivity to changes in solvent nucleophilicity was found.

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