Activation Energies for the Rate-Limiting Step in Water Photooxidation by Nanostructured α-Fe2O3and TiO2

2011 ◽  
Vol 133 (26) ◽  
pp. 10134-10140 ◽  
Author(s):  
Alexander J. Cowan ◽  
Christopher J. Barnett ◽  
Stephanie R. Pendlebury ◽  
Monica Barroso ◽  
Kevin Sivula ◽  
...  
Keyword(s):  
Activation Energies ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Water Photooxidation

Boron Diffusion Mechanism in Silicon Oxide Using AB Initio Methods

2000 ◽  
Vol 610 ◽  
Author(s):  
V. Zubkov ◽  
J. P. Senosiain ◽  
S. Aronowitz ◽  
V. Sukharev ◽  
C. B. Musgrave
Keyword(s):  
Density Functional ◽  
Silicon Oxide ◽  
Diffusion Mechanism ◽  
Activation Energies ◽  
Boron Diffusion ◽  
Functional Theory ◽  
Model Cluster ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

AbstractDensity functional theory was employed to explore the diffusion mechanism of boron in amorphous silicon oxide. The oxide was modeled with clusters of various sizes, and both neutral boron atoms and cations were considered. Three stable structures were found where B (or B+) was inserted into oxide: one in which B (or B+) is divalent and two in which B (or B+) is trivalent. Boron diffusion through silicon oxide proceeds as a sequence of B hops from one inserted position to another. For neutral boron the rate limiting step is B hop from one of trivalent structures to a divalent one with activation energies (Ea) in the range of 2.0-3.1 eV, depending on the model cluster. In the case of a cation the rate-limiting step is the B+ hop over the O atom in a divalent structure Si-B+-O-Si with calculated Ea of 2.4-2.8 eV. Experimental activation energies for B diffusion in silicon oxide are in the 2.3 - 4.2 eV range. Our results suggest that both neutral and cation boron can participate in B diffusion in oxide.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Kinetics and mechanism of cyclization of N-(2-methoxycarbonylphenyl)-N’-methylsulphonamide to 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

1991 ◽  
Vol 56 (8) ◽  
pp. 1701-1710 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Potassium Hydroxide ◽  
Acid Catalysis ◽  
Potassium Hydroxide Solution ◽  
Hydroxide Solution ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Cyclization Kinetics ◽  
Rate Limiting ◽  
Kinetics Of

The cyclization kinetics of N-(2-methylcarbonylphenyl)-N’-methylsulfonamide (IIb) into 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (Ib) has been studied in ethanolamine, morpholine, and butylamine buffers and in potassium hydroxide solution. The cyclization is subject to general base and general acid catalysis. The value of the Bronsted coefficient β is about 0.1, which indicates that splitting off of the proton from negatively charged tetrahedral intermediate represents the rate-limiting and thermodynamically favourable step. In the solutions of potassium hydroxide the cyclization of dianion of the starting ester IIb probably becomes the rate-limiting step.

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