Solvolysis kinetics of ethyl 3-ethoxy-3-iminopropanoate

1986 ◽  
Vol 51 (3) ◽  
pp. 677-683 ◽  
Author(s):  
Jaromír Kaválek ◽  
Josef Panchartek ◽  
Tomáš Potěšil ◽  
Vojeslav Štěrba
Keyword(s):  
Water Molecule ◽  
Rate Constant ◽  
Hydrolysis Rate ◽  
Nucleophilic Attack ◽  
Tetrahedral Intermediate ◽  
Hydrolysis Rate Constant ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics have been studied of hydrolysis and methanolysis of ethyl 3-ethoxy-3-iminopropanoate. The methanolysis rate constant is lower than the hydrolysis rate constant by about 3 orders of magnitude. The rate-limiting step of the hydrolysis consists in the nucleophilic attack of the protonated substrate by a water molecule, whereas that of the methanolysis consists in the decomposition of tetrahedral intermediate which is several orders of magnitude slower than the decomposition of the intermediate formed in the hydrolysis.

Reaction kinetics of 1,2-diaminobenzene with ethyl 2-oxopropanoate and 2,3-butanedione

1988 ◽  
Vol 53 (12) ◽  
pp. 3154-3163 ◽  
Author(s):  
Jiří Klicnar ◽  
Jaromír Mindl ◽  
Ivana Obořilová ◽  
Jaroslav Petříček ◽  
Vojeslav Štěrba
Keyword(s):  
Reaction Kinetics ◽  
Acid Catalysis ◽  
Reaction Pathway ◽  
Hydroxide Ion ◽  
Tetrahedral Intermediate ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
General Acid ◽  
Rate Limiting ◽  
Kinetics Of

The reaction of 1,2-diaminobenzene with 2,3-butanedione is subject to general acid catalysis in acetate and phosphate buffers (pH 4-7). The rate-limiting step of formation of 2,3-dimethylquinoxaline consists in the protonation of dipolar tetrahedral intermediate. In the case of the reaction of 1,2-diaminobenzene with ethyl 2-oxopropanoate, the dehydration of carbinolamine gradually becomes rate-limiting with increasing pH in acetate buffers, whereas in phosphate buffers a new reaction pathway makes itself felt, viz. the formation of amide catalyzed by the basic buffer component and by hydroxide ion.

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.

Effect of Medium on Acid-Catalyzed Decomposition of N-(Phenylazo)-Substituted Nitrogen Heterocycles

1999 ◽  
Vol 64 (10) ◽  
pp. 1654-1672 ◽  
Author(s):  
Miroslav Ludwig ◽  
Iva Bednářová ◽  
Patrik Pařík
Keyword(s):  
Rate Constant ◽  
Principal Component ◽  
Catalyst Particle ◽  
Pivalic Acid ◽  
Linear Regression Method ◽  
Catalytic Rate Constant ◽  
Rate Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Four N-(phenylazo)-substituted saturated nitrogen heterocyclics were synthesized and their structure was confirmed by 1H and 13C NMR spectroscopy. The kinetics of their acid-catalyzed decomposition were studied at various concentrations of the catalyst (pivalic acid) in 40, 30, and 20% (v/v) aqueous ethanol at 25 °C. The values obtained for the observed rate constants were processed by the non-linear regression method according to the suggested kinetic models and by the method of principal component analysis (PCA). The interpretation of the results has shown that the acid-catalyzed decomposition of the heterocyclics under the conditions used proceeds by the mechanism of general acid catalysis, the proton being the dominant catalyst particle of the rate-limiting step. The decrease in the observed rate constant at higher concentrations of the catalyst was explained by the formation of a non-reactive complex composed of the undissociated acid and the respective N-(phenylazo)heterocycle. The effect of medium and steric effect of the heterocyclic moiety on the values of catalytic rate constant are discussed.

scholarly journals Coassembly of SecYEG and SecA Fully Restores the Properties of the Native Translocon

2018 ◽  
Vol 201 (1) ◽  
Author(s):  
Priya Bariya ◽  
Linda L. Randall
Keyword(s):  
Lipid Bilayers ◽  
Rate Constant ◽  
Apparent Rate Constant ◽  
Membrane Vesicles ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secretory System ◽  
Rate Limiting

ABSTRACTIn all cells, a highly conserved channel transports proteins across membranes. InEscherichia coli, that channel is SecYEG. Many investigations of this protein complex have used purified SecYEG reconstituted into proteoliposomes. How faithfully do activities of reconstituted systems reflect the properties of SecYEG in the native membrane environment? We investigated by comparing threein vitrosystems: the native membrane environment of inner membrane vesicles and two methods of reconstitution. One method was the widely used reconstitution of SecYEG alone into lipid bilayers. The other was our method of coassembly of SecYEG with SecA, the ATPase of the translocase. For nine different precursor species we assessed parameters that characterize translocation: maximal amplitude of competent precursor translocated, coupling of energy to transfer, and apparent rate constant. In addition, we investigated translocation in the presence and absence of chaperone SecB. For all nine precursors, SecYEG coassembled with SecA was as active as SecYEG in native membrane for each of the parameters studied. Effects of SecB on transport of precursors faithfully mimicked observations madein vivo. From investigation of the nine different precursors, we conclude that the apparent rate constant, which reflects the step that limits the rate of translocation, is dependent on interactions with the translocon of portions of the precursors other than the leader. In addition, in some cases the rate-limiting step is altered by the presence of SecB. Candidates for the rate-limiting step that are consistent with our data are discussed.IMPORTANCEThis work presents a comprehensive quantification of the parameters of transport by the Sec general secretory system in the threein vitrosystems. The standard reconstitution used by most investigators can be enhanced to yield six times as many active translocons simply by adding SecA to SecYEG during reconstitution. This robust system faithfully reflects the properties of translocation in native membrane vesicles. We have expanded the number of precursors studied to nine. This has allowed us to conclude that the rate constant for translocation varies with precursor species.

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.

Oxidation of 1- and 2-acetylnaphthalenes by iodate - a kinetic study

1990 ◽  
Vol 55 (6) ◽  
pp. 1535-1540 ◽  
Author(s):  
Prerepa Manikyamba
Keyword(s):  
Solvent Effect ◽  
Enol Form ◽  
Aqueous Methanol ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Carbonium Ion ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of oxidation of 1- and 2-acetylnaphthalenes by iodate in the presence of sulphuric acid in aqueous methanol has been studied. The reaction is first order with respect to both [iodate] and [acetylnaphthalene]. Solvent effect indicates a cation-dipole type of interaction in the rate limiting step. A mechanism is proposed with a slow attack of IO2+ on enol form of acetylnaphthalene forming an intermediate carbonium ion, which ultimately gives corresponding ω-hydroxyacetylnaphthalene. The higher reactivity of 2-acetyl isomer is attributed to the greater stability of the corresponding carbonium ion than that of 1-acetyl isomer.

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