The mechanism of the reaction of diphenylketene with bases in aqueous solution: nucleophilic attack versus general base catalysis of ketene hydration

1992 ◽  
Vol 114 (14) ◽  
pp. 5643-5646 ◽  
Author(s):  
J. Andraos ◽  
A. J. Kresge
Keyword(s):  
Aqueous Solution ◽  
Base Catalysis ◽  
Nucleophilic Attack ◽  
General Base ◽  
Mechanism Of The Reaction

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.

Kinetics and mechanism of the bromination of phenols in aqueous solution. Evidence of general base catalysis of bromine attack

1990 ◽  
Vol 68 (10) ◽  
pp. 1769-1773 ◽  
Author(s):  
Oswald S. Tee ◽  
N. Rani Iyengar
Keyword(s):  
Aqueous Solution ◽  
Kinetics And Mechanism ◽  
Base Catalysis ◽  
Hydroxyl Group ◽  
Molecular Bromine ◽  
Electrophilic Attack ◽  
General Base ◽  
Carboxylate Anions

The reactions of bromine with phenol, 4-bromophenol, and 4-methylphenol (p-cresol) in aqueous solution are catalyzed by carboxylate anions, confirming the suggestions of earlier work. The results are consistent with deprotonation of the phenol hydroxyl group by a general base occurring at more or less the same time as electrophilic attack by molecular bromine. Possible origins of the general base catalysis are discussed. Combined with earlier results, the present findings suggest that a protonated cyclohexadienone is not a mandatory intermediate in phenol bromination; it can be avoided in both the formation of and enolization of the cyclohexadienone intermediate by general catalysis. Keywords: bromination, phenol, mechanism, catalysis, kinetics.

scholarly journals Classification of the nucleolytic ribozymes based upon catalytic mechanism

F1000Research ◽  
2019 ◽  
Vol 8 ◽  
pp. 1462
Author(s):  
David M.J. Lilley
Keyword(s):  
Catalytic Mechanism ◽  
Base Catalysis ◽  
Nucleophilic Attack ◽  
Rna Cleavage ◽  
Hydroxyl Groups ◽  
Acid Base ◽  
General Base ◽  
Cleavage Reactions ◽  
Mechanistic Basis

The nucleolytic ribozymes carry out site-specific RNA cleavage reactions by nucleophilic attack of the 2′-oxygen atom on the adjacent phosphorus with an acceleration of a million-fold or greater. A major part of this arises from concerted general acid–base catalysis. Recent identification of new ribozymes has expanded the group to a total of nine and this provides a new opportunity to identify sub-groupings according to the nature of the general base and acid. These include nucleobases, hydrated metal ions, and 2′-hydroxyl groups. Evolution has selected a number of different combinations of these elements that lead to efficient catalysis. These differences provide a new mechanistic basis for classifying these ribozymes.

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.

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