Studies in general acid and general base catalysis. Rate–acidity profiles for prototropic processes

1981 ◽  
Vol 59 (24) ◽  
pp. 3318-3318
Author(s):  
Ross Stewart ◽  
R. Srinivasan
Keyword(s):  
Base Catalysis ◽  
General Base ◽  
General Acid

not available

Deuterium exchange of C-methyl protons in lumazine derivatives

1970 ◽  
Vol 48 (2) ◽  
pp. 263-270 ◽  
Author(s):  
J. M. McAndless ◽  
Ross Stewart
Keyword(s):  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Acid Catalysis ◽  
Deuterium Exchange ◽  
Base Catalysis ◽  
Resonance Spectroscopy ◽  
Methyl Group ◽  
General Base ◽  
General Acid ◽  
Acid Catalyzed

Proton magnetic resonance spectroscopy has been used to examine the deuterium exchange of the methyl protons in two lumazine derivatives. The exchange occurs at the C-7 methyl group in 6,7,8-trimethyllumazine (2) and at the C-6 methyl group in 1,7-dihydro-6,7,8-trimethyllumazine (3). The former reaction is subject to both general acid- and general base-catalysis but the latter only to general acid-catalysis. Plausible mechanisms for the reactions of both compounds are advanced, involving in the case of 3, acid-catalyzed addition of water across the C6—N5 double bond.

Concurrent general-acid and general-base catalysis of esterification

1970 ◽  
Vol 92 (14) ◽  
pp. 4377-4382 ◽  
Author(s):  
Sheldon. Milstien ◽  
Louis Arthur. Cohen
Keyword(s):  
Base Catalysis ◽  
General Base ◽  
General Acid

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.

scholarly journals Mechanisms of RNA catalysis

2011 ◽  
Vol 366 (1580) ◽  
pp. 2910-2917 ◽  
Author(s):  
David M. J. Lilley
Keyword(s):  
Distinct Species ◽  
Base Catalysis ◽  
Nucleophilic Attack ◽  
Phosphoryl Transfer ◽  
Rna Catalysis ◽  
Rna Molecules ◽  
General Base ◽  
General Acid ◽  
Guanine And Adenine ◽  
Self Splicing

Ribozymes are RNA molecules that act as chemical catalysts. In contemporary cells, most known ribozymes carry out phosphoryl transfer reactions. The nucleolytic ribozymes comprise a class of five structurally-distinct species that bring about site-specific cleavage by nucleophilic attack of the 2′-O on the adjacent 3′-P to form a cyclic 2′,3′-phosphate. In general, they will also catalyse the reverse reaction. As a class, all these ribozymes appear to use general acid–base catalysis to accelerate these reactions by about a million-fold. In the Varkud satellite ribozyme, we have shown that the cleavage reaction is catalysed by guanine and adenine nucleobases acting as general base and acid, respectively. The hairpin ribozyme most probably uses a closely similar mechanism. Guanine nucleobases appear to be a common choice of general base, but the general acid is more variable. By contrast, the larger ribozymes such as the self-splicing introns and RNase P act as metalloenzymes.

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

General Acid and General Base Catalysis by the Monoanions of Dicarboxylic Acids

1967 ◽  
Vol 32 (7) ◽  
pp. 2229-2233 ◽  
Author(s):  
Gustav Lienhard ◽  
Frank Anderson
Keyword(s):  
Dicarboxylic Acids ◽  
Base Catalysis ◽  
General Base ◽  
General Acid

ChemInform Abstract: General-Acid and General-Base Catalysis of the Cleavage of α-D- Glucopyranosyl Fluoride

ChemInform ◽  
2010 ◽  
Vol 23 (5) ◽  
pp. no-no
Author(s):  
N. S. BANAIT ◽  
W. P. JENCKS
Keyword(s):  
Base Catalysis ◽  
General Base ◽  
General Acid

General-acid and general-base catalysis of the cleavage of .alpha.-D-glucopyranosyl fluoride

1991 ◽  
Vol 113 (21) ◽  
pp. 7958-7963 ◽  
Author(s):  
Narinder S. Banait ◽  
William P. Jencks
Keyword(s):  
Base Catalysis ◽  
General Base ◽  
General Acid
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