scholarly journals The mechanism of the solvolysis of p-methoxybenzyl chloride in aqueous acetone containing pyridine or thiourea. Evidence for concurrent substitution by unimolecular and bimolecular processes

1979 ◽  
Vol 57 (19) ◽  
pp. 2646-2651 ◽  
Author(s):  
Alan Queen
Keyword(s):  
Aqueous Acetone ◽  
Rate Of Reaction ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The overall rate of reaction of p-methoxybenzyl chloride with 70% aqueous acetone is increased by the addition of pyridine but the rate of hydrolysis is decreased. Comparison of these data with those for benzhydryl chloride under the same conditions shows that the rate of hydrolysis of p-methoxybenzyl chloride is less than the rate of ionisation. These results are discussed in terms of concurrent operation of the SN1 mechanism and a bimolecular process. Similar results are obtained when thiourea is used instead of pyridine.

Electrostatic, Polar, and steric factors in the Acid Hydrolysis of the Dipeptides

1957 ◽  
Vol 10 (3) ◽  
pp. 256 ◽  
Author(s):  
RJL Martin
Keyword(s):  
Carbon Atom ◽  
Water Molecule ◽  
Peptide Bond ◽  
Bimolecular Reaction ◽  
Carbonyl Carbon Atom ◽  
Rate Of Reaction ◽  
Steric Factors ◽  
Rate Of Hydrolysis ◽  
Reaction With Water ◽  
Hydrolysis Of

Published kinetic data concerning the rates of hydrolysis of dipeptides are discussed and interpreted in terms of the expected electrostatic, polar, and steric influences of the constituent groups. The evidence is consistent with a reaction mechanism in which a proton is first added reversibly to the peptide nitrogen, and the amide cation so formed reacts at the carbonyl carbon atom with a water molecule in a rate-controlling bi molecular substitution. Substitution at the glycyl carbon atom of the parent substance glycylglycine will alter the steric hindrance to substitution by the water molecule. On the other hand, the polar effect of these substituents will be small and will have little influence on the rate of reaction. Substituents at the glycine carbon atom introduce polar factors only with little evidence of steric effects. This absence of a steric effect applies both to the formation of the amide cation and to the substitution by the water. Electron repelling groups decrease the rate of hydrolysis and must be considered to have a greater effect on decreasing the electron accession to the peptide nitrogen necessary for the rupture of the bend than on increasing the concentration of the amide cation. Electron attracting substituents act in the reverse manner. There is some evidence for a small amount of steric compression between groups on either side of the peptide bond for the bimolecular reaction with water.

SOLVOLYSIS OF ALKYL CHLOROSULFATES: PART I. REACTION OF n-PROPYL CHLOROSULFATE WITH NUCLEOPHILES

1965 ◽  
Vol 43 (3) ◽  
pp. 547-555 ◽  
Author(s):  
E. Buncel ◽  
J. P. Millington
Keyword(s):  
Aqueous Dioxane ◽  
Halide Ions ◽  
Leaving Group ◽  
Rate Of Reaction ◽  
Previous Proposal ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Chlorine Bond ◽  
Bimolecular Mechanism

The effect of various reagents on the rate of hydrolysis of n-propyl chlorosulfate in 10 M aqueous dioxane is reported. Halide ions increase the rate of reaction (I− > Br− > Cl−) but perchlorate is without effect. Hydroxide and pyrrolidine have a strong accelerating effect, but only at higher concentrations. These observations support a bimolecular mechanism: rate-determining displacement by nucleophile on carbon, with OSO2Cl− as the leaving group. The present results are not in accord with a previous proposal that alkyl chlorosulfates react by rate-determining sulfur–chlorine bond fission followed by fast displacement by nucleophile on carbon.

Substituent Effects on the Micelle-Catalysed and Uncatalysed Basic Hydrolysis of a Series of Substituted N-Methyl-p-toluanilides

1979 ◽  
Vol 32 (8) ◽  
pp. 1717 ◽  
Author(s):  
TJ Broxton ◽  
NW Duddy
Keyword(s):  
Substituent Effects ◽  
Cationic Micelles ◽  
Mechanism Of Reaction ◽  
Rate Of Reaction ◽  
Hammett Correlation ◽  
Rate Of Hydrolysis ◽  
Linear Plot ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Reaction In Water

The rate of hydrolysis of a series of substituted N-methyl-p-toluanilides has been measured in water and in the presence of cationic micelles [cetyltrimethylammonium bromide (ctab)]. A Hammett correlation of the rates of hydrolysis gave a curved Hammett plot for the reaction in water (k2,W) but a linear plot for the rate of reaction at optimal concentrations of ctab (k2,max) and for derived rate constants within the micelle (k2,m) These results are discussed in terms of the mechanism of reaction, and for two compounds a micelle-induced change of mechanism is indicated.

The Effects of Amines on the Esterase Activities of Thrombin and Thrombokinase and on Several Clotting Tests

1974 ◽  
Vol 31 (02) ◽  
pp. 309-318
Author(s):  
Phyllis S Roberts ◽  
Raphael M Ottenbrite ◽  
Patricia B Fleming ◽  
James Wigand
Keyword(s):  
Choline Chloride ◽  
Polymerization Process ◽  
Ammonium Bromide ◽  
Bovine Thrombin ◽  
One Stage ◽  
Human Proteins ◽  
Rate Of Hydrolysis ◽  
The One ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Summary1. Choline chloride, 0.1 M (in 0.25 M Tris. HCl buffer, pH 7.4 or 8.0, 37°), doubles the rate of hydrolysis of TAME by bovine thrombokinase but has no effect on the hydrolysis of this ester by either human or bovine thrombin. Only when 1.0 M or more choline chloride is present is the hydrolysis of BAME by thrombokinase or thrombin weakly inhibited. Evidence is presented that shows that these effects are due to the quaternary amine group.2. Tetramethyl ammonium bromide or chloride has about the same effects on the hydrolysis of esters by these enzymes as does choline chloride but tetra-ethyl, -n.propyl and -n.butyl ammonium bromides (0.1 M) are stronger accelerators of the thrombokinase-TAME reaction and they also accelerate, but to a lesser degree, the thrombin-TAME reaction. In addition, they inhibit the hydrolysis of BAME by both enzymes. Their effects on these reactions, however, do not follow any regular order. The tetraethyl compound is the strongest accelerator of the thrombokinase-TAME reaction but the tetra-ethyl and -butyl compounds are the strongest accelerators of the thrombin-TAME reaction. The ethyl and propyl compounds are the best (although weak) inhibitors of the thrombokinase-BAME and the propyl compound of the thrombin-BAME reactions.3. Tetra-methyl, -ethyl, -n.propyl and -n.butyl ammonium bromides (0.01 M) inhibit the clotting of fibrinogen by thrombin (bovine and human proteins) at pH 7.4, imidazole or pH 6.1, phosphate buffers and they also inhibit, but to a lesser degree, a modified one-stage prothrombin test. In all cases the inhibition increases regularly as the size of the alkyl group increases from methyl to butyl. Only the ethyl com pound (0.025 M but not 0.01 M), however, significantly inhibits the polymerization of bovine fibrin monomers. It was concluded that inhibition of the fibrinogen-thrombin and the one-stage tests by the quaternary amines is not due to any effect of the com pounds on the polymerization process but probably due to inhibition of thrombin’s action on fibrinogen by the quaternary amines.

The effect of polymeric and model imidazolium halides on the rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid

1985 ◽  
Vol 50 (4) ◽  
pp. 845-853 ◽  
Author(s):  
Miloslav Šorm ◽  
Miloslav Procházka ◽  
Jaroslav Kálal
Keyword(s):  
Catalyst Concentration ◽  
Low Molecular Weight ◽  
Imidazolium Chloride ◽  
First Order ◽  
Nitrobenzoic Acid ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Ethanol In Water ◽  
Direct Attack

The course of hydrolysis of an ester, 4-acetoxy-3-nitrobenzoic acid catalyzed with poly(1-methyl-3-allylimidazolium bromide) (IIa), poly[l-methyl-3-(2-propinyl)imidazolium chloride] (IIb) and poly[l-methyl-3-(2-methacryloyloxyethyl)imidazolium bromide] (IIc) in a 28.5% aqueous ethanol was investigated as a function of pH and compared with low-molecular weight models, viz., l-methyl-3-alkylimidazolium bromides (the alkyl group being methyl, propyl, and hexyl, resp). Polymers IIb, IIc possessed a higher activity at pH above 9, while the models were more active at a lower pH with a maximum at pH 7.67. The catalytic activity at the higher pH is attributed to an attack by the OH- group, while at the lower pH it is assigned to a direct attack of water on the substrate. The rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid is proportional to the catalyst concentration [IIc] and proceeds as a first-order reaction. The hydrolysis depends on the composition of the solvent and was highest at 28.5% (vol.) of ethanol in water. The hydrolysis of a neutral ester, 4-nitrophenyl acetate, was not accelerated by IIc.

Kinetics of hydrolysis of peroxodisulphate ions in acidic medium to peroxomonosulphuric acid

1981 ◽  
Vol 46 (5) ◽  
pp. 1229-1236 ◽  
Author(s):  
Jan Balej ◽  
Milada Thumová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Acidic Medium ◽  
Measured Data ◽  
Molar Ratios ◽  
Starting Solution ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The rate of hydrolysis of S2O82- ions in acidic medium to peroxomonosulphuric acid was measured at 20 and 30 °C. The composition of the starting solution corresponded to the anolyte flowing out from an electrolyser for production of this acid or its ammonium salt at various degrees of conversion and starting molar ratios of sulphuric acid to ammonium sulphate. The measured data served to calculate the rate constants at both temperatures on the basis of the earlier proposed mechanism of the hydrolysis, and their dependence on the ionic strength was studied.

Polarographic study of hydrolysis of [8-lysine]vasopressin and its derivatives with blood serum of pregnant women

1980 ◽  
Vol 45 (4) ◽  
pp. 1099-1108 ◽  
Author(s):  
Mikuláš Chavko ◽  
Michal Bartík ◽  
Evžen Kasafírek
Keyword(s):  
Blood Serum ◽  
Pregnant Women ◽  
Degree Of Hydrolysis ◽  
Polarographic Study ◽  
Ph Optimum ◽  
Lysine Vasopressin ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Vasopressin Analogues

A polarographic study of the hydrolysis of [8-lysine]vasopressin and some hormonogens of the vasopressin series with the blood serum of women in the last week of pregnancy was studied. The dependence of hydrolysis on pH (pH optimum: 7.4-7.50, substrate concentration (Km 1.2 . 10-5M), pH stability and thermal stability were determined. The rate of hydrolysis of individual vasopressin analogues decreases in the order: [8-lysine]vasopressin > Nα-glycyl-prolyl[8-lysine]-vasopressin > Nα-leucyl-[8-lysine]vasopressin > Nα-alanyl-[8-lysine]vasopressin > Nα-phenyl alanyl-[8-lysine]vasopressin > Nα-diglycyl-[8-lysine]vasopressin > Nα-prolyl-[8-lysine]vasopressin > Nα-triglycyl-[8-lysine]vasopressin > Nα-sarcosyl-glycyl-[8-lysine]vasopressin. The degree of hydrolysis gradually increases to a multiple with the length of the pregnancy in consequence of the presence of oxytocine. However, vasopressin is also hydrolysed to a small extent with the enzymes from the blood sera of non-pregnant women. Under similar analytical conditions oxytocin was not hydrolysed with the sera of non-pregnant women and therefore oxytocin is a more suitable substrate than vasopressin for polarographic determination of serum oxytocinase.

Studies on the mechanism of acute inhibition of thyroglobulin hydrolysis by iodine

1985 ◽  
Vol 108 (4) ◽  
pp. 511-517 ◽  
Author(s):  
Nandalal Bagchi ◽  
Birdie Shivers ◽  
Thomas R. Brown
Keyword(s):  
Time Course ◽  
Period 2 ◽  
Iodotyrosine Deiodinase ◽  
Rate Of Hydrolysis ◽  
Underlying Mechanisms ◽  
Excess Iodide ◽  
Sites Of Action ◽  
Hydrolysis Of

Abstract. Iodine in excess is known to acutely inhibit thyroidal secretion. In the present study we have characterized the time course of the iodine effect in vitro and investigated the underlying mechanisms. Labelled thyroid glands were cultured in vitro in medium containing mononitrotyrosine, an inhibitor of iodotyrosine deiodinase. The rate of hydrolysis of labelled thyroglobulin was measured as the proportion of labelled iodotyrosines and iodothyronines recovered at the end of culture and was used as an index of thyroidal secretion. Thyrotrophin (TSH) administered in vivo acutely stimulated the rate of thyroglobulin hydrolysis. Addition of Nal to the culture medium acutely inhibited both basal and TSH-stimulated thyroglobulin hydrolysis. The effect of iodide was demonstrable after 2 h, maximal after 6 h and was not reversible upon removal of iodide. Iodide abolished the dibutyryl cAMP induced stimulation of thyroglobulin hydrolysis. Iodide required organic binding of iodine for its effect but new protein or RNA synthesis was not necessary. The inhibitory effects of iodide and lysosomotrophic agents such as NH4C1 and chloroquin on thyroglobulin hydrolysis were additive suggesting different sites of action. Iodide added in vitro altered the distribution of label in prelabelled thyroglobulin in a way that suggested increased coupling in the thyroglobulin molecule. These data indicate that 1) the iodide effect occurs progressively over a 6 h period, 2) continued presence of iodide is not necessary once the inhibition is established, 3) iodide exerts its action primarily at a post cAMP, prelysosomal site and 4) the effect requires organic binding of iodine, but not new RNA or protein synthesis. Our data are consistent with the hypothesis that excess iodide acutely inhibits thyroglobulin hydrolysis by increasing the resistance of thyroglobulin to proteolytic degradation through increased iodination and coupling.

Kinetic studies on the rate of hydrolysis of N-ethyl-N′-(dimethylaminopropyl)carbodiimide in aqueous solutions using mass spectrometry and capillary electrophoresis

2002 ◽  
Vol 310 (1) ◽  
pp. 122-124 ◽  
Author(s):  
Q Paula Lei ◽  
David H Lamb ◽  
Ron K Heller ◽  
Anthony G Shannon ◽  
Robert Ryall ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Capillary Electrophoresis ◽  
Aqueous Solutions ◽  
Kinetic Studies ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of
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