Concurrent general acid and general base catalysis in the hydrolysis of an imidate ester. 3. Ethyl N-p-nitrophenylformimidate

1979 ◽  
Vol 101 (21) ◽  
pp. 6277-6282 ◽  
Author(s):  
Yin-Nan Lee ◽  
Gaston L. Schmir
Keyword(s):  
Base Catalysis ◽  
General Base ◽  
General Acid ◽  
Hydrolysis Of

scholarly journals pH-dependence and structure–activity relationships in the papain-catalysed hydrolysis of anilides

1971 ◽  
Vol 124 (1) ◽  
pp. 117-122 ◽  
Author(s):  
G. Lowe ◽  
Y. Yuthavong
Keyword(s):  
Acid Catalysis ◽  
Ph Dependence ◽  
Base Catalysis ◽  
General Base ◽  
Structure Activity ◽  
Equilibrium Binding ◽  
General Acid ◽  
Leaving Group ◽  
Hydrolysis Of ◽  
Equilibrium Binding Constant

The pH-dependence of the Michaelis–Menten parameters for the papain-catalysed hydrolysis of N-acetyl-l-phenylalanylglycine p-nitroanilide was determined. The equilibrium binding constant, Ks, is independent of pH between 3.7 and 9.3, whereas the acylation constant, k+2, shows bell-shaped pH-dependence with apparent pKa values of 4.2 and 8.2. The effect of substituents in the leaving group on the acylation constant of the papain-catalysed hydrolysis of hippuryl anilides and N-acetyl-l-phenylalanylglycine anilides gives rise in both series to a Hammett ρ value of -1.04. This indicates that the enzyme provides electrophilic, probably general-acid, catalysis, as well as the nucleophilic or general-base catalysis previously found. A mechanism involving a tetrahedral intermediate whose formation is general-base-catalysed and whose breakdown is general-acid-catalysed seems most likely. The similarity of the Hammett ρ values appears to exclude facilitated proton transfer as a means through which the specificity of papain is expressed.

Concurrent general acid and general base catalysis in the hydrolysis of an imidate ester. 2. Bifunctional catalysis

1979 ◽  
Vol 101 (11) ◽  
pp. 3026-3035 ◽  
Author(s):  
Yin-Nan Lee ◽  
Gaston L. Schmir
Keyword(s):  
Base Catalysis ◽  
Bifunctional Catalysis ◽  
General Base ◽  
General Acid ◽  
Hydrolysis Of

Concurrent general acid and general base catalysis in the hydrolysis of an imidate ester. I. Monofunctional catalysis

1978 ◽  
Vol 100 (21) ◽  
pp. 6700-6707 ◽  
Author(s):  
Yin-Nan Lee ◽  
Gaston L. Schmir
Keyword(s):  
Base Catalysis ◽  
General Base ◽  
General Acid ◽  
Hydrolysis Of

Micellar catalysis of organic reactions. VIII. Kinetic studies of the hydrolysis of 2-acetyloxybenzoic acid (aspirin) in the presence of micelles

1982 ◽  
Vol 35 (7) ◽  
pp. 1357 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Aqueous Solution ◽  
Cetyltrimethylammonium Bromide ◽  
Cetylpyridinium Chloride ◽  
Kinetic Studies ◽  
Base Catalysis ◽  
Plateau Region ◽  
General Base ◽  
Mechanism Of Hydrolysis ◽  
Ph Range ◽  
Hydrolysis Of

The hydrolysis of 2-acetyloxybenzoic acid in the pH range 6-12 has been studied in the presence of micelles of cetyltrimethylammonium bromide (ctab) and cetylpyridinium chloride (cpc). In the plateau region (pH 6-8) the hydrolysis is inhibited by the presence of micelles, while in the region where the normal BAC2 hydrolysis (pH > 9) occurs the reaction is catalysed by micelles of ctab and cpc. The mechanism of hydrolysis in the plateau region is shown to involve general base catalysis by the adjacent ionized carboxy group both in the presence and absence of micelles. This reaction is inhibited in the presence of micelles because the substrate molecules are solubilized into the micelle and water is less available in this environment than in normal aqueous solution.

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