Kinetics and mechanism of the addition of water and ring-opening of 2-methyl- and 2-aryl-4H-3,1-benzoxazines to 2-aminobenzyl esters in the acidic pH range; change in rate-limiting step with buffer concentration and evidence for a tetrahedral carbonyl addition intermediate

1997 ◽  
pp. 1503-1510 ◽  
Author(s):  
Wendy J. Dixon ◽  
Frank Hibbert ◽  
Judith F. Mills
Keyword(s):  
Ring Opening ◽  
Kinetics And Mechanism ◽  
Acidic Ph ◽  
Buffer Concentration ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Range Change ◽  
Carbonyl Addition ◽  
Ph Range ◽  
Rate Limiting

scholarly journals A study of the oxidation of butan-1-ol and propan-2-ol by nicotinamide-adenine dinucleotide catalysed by yeast alcohol dehydrogenase.

1975 ◽  
Vol 147 (3) ◽  
pp. 541-547 ◽  
Author(s):  
C J Dickenson ◽  
F M Dickinson
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ternary Complexes ◽  
Kinetics Of Oxidation ◽  
Yeast Alcohol Dehydrogenase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Ph Range ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Flow Experiments

1. The kinetics of oxidation of butan-1-ol and propan-2-ol by NAD+, catalysed by yeast alcohol dehydrogenase, were studied at 25 degrees C from pH 5.5 to 10, and at pH 7.05 from 14 degrees to 44 degrees C, 2. Under all conditions studied the results are consistent with a mechanism whereby some dissociation of coenzyme from the active enzyme-NAD+-alcohol ternary complexes occurs, and the mechanism is therefore not strictly compulsory order. 3. A primary 2H isotopic effect on the maximum rates of oxidation of [1-2H2]butan-1-ol and [2H7]propan-2-ol was found at 25 degrees C over the pH range 5.5-10. Further, in stopped-flow experiments at pH 7.05 and 25 degrees C, there was no transient formation of NADH in the oxidation of butan-1-ol and propan-2-ol. The principal rate-limiting step in the oxidation of dependence on pH of the maximum rates of oxidation of butan-1-ol and propan-2-ol is consisten with the possibility that histidine and cysteine residues may affect or control catalysis.

Kinetics and mechanism of methanolysis of benzoyl derivatives of substituted phenylureas and phenylthioureas

1984 ◽  
Vol 49 (9) ◽  
pp. 2103-2110 ◽  
Author(s):  
Jaromír Kaválek ◽  
Said El Bahaie ◽  
Vojeslav Štěrba
Keyword(s):  
Nitrogen Atom ◽  
Steric Hindrance ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Kinetics And Mechanism ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Order Of Magnitude ◽  
Rate Limiting ◽  
Derivatives Of

The methanolysis rate constants and dissociation constants have been measured of benzoyl derivatives of substituted phenylureas and phenylthioureas. The dissociation constants of the thio derivatives are higher by 1 order of magnitude and the rate constants are higher by 2 orders of magnitude than the respective values of the oxygen analogues. Logarithms of the rate and dissociation constants have been correlated with the Hammet σ constant; the ρ constant of the methanolysis of the oxygen derivatives is almost 2x higher than that of the thio derivatives, which is explained by a change in the rate-limiting step. Methylation of the phenyl nitrogen atom increases the acidity by almost 2 orders of magnitude. This effect is due obviously to steric hindrance to the conjugation with the adjacent carbonyl or thiocarbonyl group.

Kinetics and Mechanism of Cyclization of N-(2-Methoxycarbonylphenyl)-N-methylsulfonamide to 1-Methyl-(1H)-2,1,3-benzothiadiazine-4(3H)-one-2,2-dioxide

1992 ◽  
Vol 57 (6) ◽  
pp. 1282-1290 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Potassium Hydroxide ◽  
Kinetics And Mechanism ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Conjugate Acid ◽  
Cyclization Kinetics ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Cyclic Intermediate

The cyclization kinetics of N-(2-methoxycarbonylphenyl)-N-methylsulfonamide to 1-methyl-(1H)-2,1,3-benzothiadiazine-4(3H)-one-2,2-dioxide have been studied in glycinamide, morpholine, and butylamine buffers and in solutions of potassium hydroxide. The rate-limiting step consists in splitting off of the proton from the cyclic intermediate formed from the anion of the starting substrate. The value of the Bronsted coefficient β decreases with increasing pKa value of the conjugate acid of buffer. The calculated pKa value of the cyclic intermediate is 9.3.

Solvolysis kinetics and mechanism of 3-methyl-1,3-thiazolidine-2,4-dione

1981 ◽  
Vol 46 (12) ◽  
pp. 3097-3103 ◽  
Author(s):  
Vladimír Macháček ◽  
Vojeslav Štěrba ◽  
Helena Zahradníčková
Keyword(s):  
Sodium Methoxide ◽  
Kinetics And Mechanism ◽  
Hydrolysis Kinetics ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Reaction Proceeds ◽  
One Step ◽  
Rate Limiting ◽  
Kinetics Of

The hydrolysis kinetics of 3-methyl-1,3-thiazolidine-2,4-dione have been studied in aqueous buffers and dilute NaOH solutions. The reaction proceeds via two base-catalyzed steps having different rates. In sodium methoxide solutions 3-methyl-1,3-thiazolidine-2,4-dione undergoes one-step methanolysis giving methyl thioglycolate anion as the final product. The rate-limiting step consists in decomposition of the anion CH3NCOSCH2COOCH3.

Kinetics and mechanism of solvolysis of substituted phenyl N-phenylbenzimidoesters

1987 ◽  
Vol 52 (5) ◽  
pp. 1285-1297
Author(s):  
Jaromír Kaválek ◽  
Ludmila Hejtmánková ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Kinetics And Mechanism ◽  
Reaction Products ◽  
Phenol Content ◽  
Aqueous Methanol ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of hydrochloric acid-catalyzed solvolysis of substituted phenyl and methyl N-phenylbenzimidoesters have been studied in methanol, 50 vol. % aqueous methanol, and 50 vol. % aqueous tetrahydrofurane, and the composition of the reaction products has been determined. The rate-limiting step consists in addition of water or methanol to the protonated substrate. The reaction of methyl N-phenylbenzimidoester with both water and methanol and that of substituted phenyl N-phenylbenzimidoesters with methanol produce aniline, the ester (or orthoester) and the corresponding phenol. The reaction of substituted phenyl N-phenylbenzimidoesters with water gives both the neutral tetrahedral intermediate (which is decomposed into phenol and anilide) and the protonated intermediate (which produces aniline and the ester). At the same proton concentration the phenol content increases with increasing value of the σ constant of the substituent.

Kinetics of Base-Catalysed Hydrolysis and Cyclisation of Substituted Acetamide and Benzamide O-(Phenoxycarbonyl)oximes

1999 ◽  
Vol 64 (10) ◽  
pp. 1641-1653 ◽  
Author(s):  
Jaromír Mindl ◽  
Jaromír Kaválek ◽  
Helena Straková ◽  
Vojeslav Štěrba
Keyword(s):  
Reaction Mechanism ◽  
Ph Dependence ◽  
Bond Formation ◽  
Reaction Step ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Substituted Benzamide ◽  
Ph Range ◽  
Rate Limiting ◽  
Kinetics Of

The reaction kinetics of acetamide O-(4-nitrophenoxycarbonyl)oxime have been studied in aqueous buffers at pH 2-11. At pH > 9, the pH dependence of kobs is linear with slope 1, the cyclisation to 3-methyl-1,2,4-oxadiazol-5(4H)-one and 4-nitrophenol being the only reaction. At pH < 7.5, the only reaction is the hydrolysis giving 4-nitrophenol and acetamidoxime. The dependence of kobs on pH has been used to determine the rate equation and to propose the reaction mechanism. The cyclisation kinetics of substituted benzamide O-(phenoxycarbonyl)oximes have been studied in the pH range from 9.25 to 11. The reaction mechanism has been proposed based on the ρ constants found. In the first reaction step, the proton is split off from the NH2 group; the subsequent, rate-limiting step involves simultaneous N-C bond formation and C-O bond splitting.

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
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