scholarly journals Kinetic studies on the acid hydrolysis of the methyl ketoside of unsubstituted and O-acetylated N-acetylneuraminic acid

1973 ◽  
Vol 133 (4) ◽  
pp. 623-628 ◽  
Author(s):  
A. Neuberger ◽  
Wendy A. Ratcliffe
Keyword(s):  
Sialic Acid ◽  
Acid Hydrolysis ◽  
Model Compound ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Neuraminic Acid ◽  
Acetylneuraminic Acid ◽  
Rate Of Hydrolysis ◽  
Ph Range ◽  
Hydrolysis Of

The hydrolysis of the model compound 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl-α-d-neuraminic acid and neuraminidase (Vibrio cholerae) closely resembled that of the O-acetylated sialic acid residues of rabbit Tamm–Horsfall glycoprotein. This confirmed that O-acetylation was responsible for the unusually slow rate of acid hydrolysis of O-acetylated sialic acid residues observed in rabbit Tamm–Horsfall glycoprotein and their resistance to hydrolysis by neuraminidase. The first-order rate constant of hydrolysis of 2-methyl-N-acetyl-α-d-neuraminic acid by 0.05m-H2SO4 was 56-fold greater than that of 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl -α-d-neuraminic acid. Kinetic studies have shown that in the pH range 1.00–3.30, the observed rate of hydrolysis of 2-methyl-N-acetyl-α-d-neuraminic acid can be attributed to acid-catalysed hydrolysis of the negatively charged CO2− form of the methyl ketoside.

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.

Open-chain nitrogen compounds. Part XV. A kinetic study of the hydrolysis of 1-aryl-3-aryloxymethyl-3-methyltriazenes and related triazenes

1992 ◽  
Vol 70 (8) ◽  
pp. 2224-2233 ◽  
Author(s):  
Keith Vaughan ◽  
Donald L. Hooper ◽  
Marcus P. Merrin
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Buffer System ◽  
Open Chain ◽  
Nucleophilic Displacement ◽  
Ether Oxygen ◽  
Rate Of Hydrolysis ◽  
Electron Withdrawing Group ◽  
Ph Range ◽  
Kinetics Of

The kinetics of hydyrolysis of a series of 1-aryl-3-aryloxymethyl-3-methyltriazenes, Ar-N=N-NMe-CH2OAr′, was studied over the pH range 2–7.5. Reactions were followed by the change in UV absorbance spectra of the triazenes. The aryloxymethyltriazenes decompose more slowly at pH 7.5 than the hydroxymethyltriazenes, Ar-N=NMe-CH2OH; the hydrolysis is favoured by the presence of an electron-withdrawing group in Ar′. A mixed isopropanol/buffer system was developed in order to improve solubility of the aryloxymethyl triazenes. Lowering the pH caused an increase in the rate of hydrolysis and under strongly acidic conditions an electron-withdrawing group in Ar′ actually slows down the reaction. A Hammett plot of the pseudo-first-order rate constant, kobs, is curved, indicating that two or more mechanisms operate simultaneously and that the contribution of each mechanism is substituent-dependent. A plot of kobs vs. [buffer] is linear; the slope of the plot affords the rate constant, kb for the buffer-catalyzed reaction for each substituent. A Hammett plot of kb vs. σ is linear with ρ = +0.55, suggesting that the buffer-catalyzed reaction involves nucleophilic displacement of the phenoxy group by the buffer anion. Further analysis afforded the specific acid-catalyzed rate constants, [Formula: see text], for each substituent; this component of the reaction has a negative ρ, consistent with a mechanism involving protonation at the ether oxygen. The postulation that specific acid catalysis is a component of the reaction mechanism was confirmed by the observation of a solvent deuterium isotope effect, 2.28 > kH/kD > 1.60. Only the p-NO2 and p-CN phenyloxymethyltriazenes showed any spontaneous decomposition.

THE ACID HYDROLYSIS OF GLYCOSIDES: I. GENERAL CONDITIONS AND THE EFFECT OF THE NATURE OF THE AGLYCONE

1964 ◽  
Vol 42 (6) ◽  
pp. 1456-1472 ◽  
Author(s):  
T. E. Timell
Keyword(s):  
Acid Hydrolysis ◽  
Equilibrium Concentration ◽  
Rate Coefficients ◽  
Acidity Function ◽  
Tertiary Alcohols ◽  
Conjugate Acid ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Opposing Effects ◽  
Hydrolysis Of

First-order rate coefficients and energies and entropies of activation have been determined for the acid-catalyzed hydrolysis of a number of methyl D-glycopyranosides and disaccharides. The relation between the logarithm of the rate coefficients and values for Hammett's acidity function was linear, although different for different acids. All compounds had entropies of activation indicating a unimolecular reaction mechanism. Glucosides of tertiary alcohols were hydrolyzed very rapidly, triethylmethyl β-D-glucopyranoside, for example, 30,000 times taster than the corresponding methyl compound.Increase in size of the aglycone caused a slight increase in the rate of hydrolysis of β-D-glucopyranosides, steric hindrance thus being of no significance. Electron-attracting substituents in the aglycone had little or no influence on the rate of hydrolysis, obviously because they would tend to lower the equilibrium concentration of the conjugate acid, while facilitating the subsequent heterolysis, the two opposing effects more or less cancelling out. These results were discussed in connection with recent studies on the acid hydrolysis of various phenyl glycopyranosides and with reference to the postulated occurrence of an activating inductive effect in oligo- and poly-saccharides containing carboxyl or other electronegative groups at C-5. It was concluded that there is little evidence for the existence of any such effect and that, for example, pseudoaldobiouronic acids should be hydrolyzed at the same rate as corresponding neutral disaccharides.

Kinetic studies of two-stage sulphuric acid hydrolysis of sugarcane bagasse

2015 ◽  
Vol 83 ◽  
pp. 850-858 ◽  
Author(s):  
Sachin Kumar ◽  
Pratibha Dheeran ◽  
Surendra P. Singh ◽  
Indra M. Mishra ◽  
Dilip K. Adhikari
Keyword(s):  
Acid Hydrolysis ◽  
Sulphuric Acid ◽  
Sugarcane Bagasse ◽  
Kinetic Studies ◽  
Two Stage ◽  
Hydrolysis Of

scholarly journals Acid Hydrolysis of Bromazepam Catalyzed by Micelles, Reverse Micelles, and Microemulsions

2015 ◽  
Vol 2015 ◽  
pp. 1-10
Author(s):  
Ferdousi Begum ◽  
M. Yousuf A. Mollah ◽  
M. Muhibur Rahman ◽  
Md. Abu Bin Hasan Susan
Keyword(s):  
Physicochemical Properties ◽  
Acid Hydrolysis ◽  
Reverse Micelles ◽  
Cetyltrimethylammonium Bromide ◽  
Order Rate Constant ◽  
Excellent Correlation ◽  
Initial Decrease ◽  
Droplet Sizes ◽  
Kinetics Of ◽  
Hydrolysis Of

Kinetics of the acid hydrolysis of bromazepam (Bz) has been investigated in micelles, reverse micelles, and microemulcions of cetyltrimethylammonium bromide (CTAB) by spectrophotometric method. The rate of the acid hydrolysis of Bz was found to be enhanced both below and above the critical micelle concentration (CMC) of CTAB in aqueous solution. The pseudo-first-order rate constant (k′) shows an initial decrease for both low and high H+concentrations. With further increase in [CTAB], at low [H+], thek′attains an almost constant value, while, at high [H+], thek′passes through a maximum and then decreases. The kinetic data for catalysis by micelles of CTAB was interpreted with the pseudophase ion exchange (PIE) model. In CTAB/cyclohexane/1-butanol/water microemulsions, as the water to surfactant ratio (wo) increases, the physicochemical properties and droplet sizes of microemulsions significantly change and distinct changes in reaction environment can be marked. The rate of the hydrolysis reaction exhibits excellent correlation with the physicochemical properties and droplet sizes of the microemulsions and reverse micelles of CTAB. At [H+] = 0.001 M, in reverse micelles and microemulsions of CTAB, thek′of the acid hydrolysis of Bz decreases sharply followed by a slight increase with increasingwo.

scholarly journals Further evidence for an allosteric model for ribonuclease

1976 ◽  
Vol 153 (2) ◽  
pp. 329-337 ◽  
Author(s):  
E J Walker ◽  
G B Ralston ◽  
I G Darvey
Keyword(s):  
Conformational Change ◽  
Equilibrium Dialysis ◽  
Kinetic Studies ◽  
Experimental Systems ◽  
Substrate Analogues ◽  
Multiple Binding ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Cyclic Cmp ◽  
Allosteric Model

Evidence is presented from three experimental systems to support the allosteric model of Walker et al. (1975) (Biochem. J. 147, 425-433) which explains the substrate-concentration-dependent transition observed in the RNAase (ribonuclease)-catalysed hydrolysis of 2‘:3’-cyclic CMP (cytidine 2‘:3’-cyclic monophosphate). 1. Kinetic studies of the initial rate of hydrolysis of 2‘:3’-cyclic CMP show that the midpoint of the transition shifts to lower concentrations of 2‘:3’-cyclic CMP in the presence of the substrate analogues 3′-CMP, 5′-CMP, 3′-AMP, 3′-UMP and Pi; 2′-CMP and 2′-UMP do not cause such a shift. 2. Trypsin-digestion studies show that a conformational change in RNAase to a form less susceptible to tryptic inactivation is induced in the presence of the substrate analogues 3′-CMP, 5′-CMP, 3′-AMP, and 3′-UMP. 2′-CMP, 2′-AMP and 2′-UMP do not induce this conformational change. 3. Equilibrium-dialysis experiments demonstrate the multiple binding of molecules of 3′-CMP, 3′-AMP and 5′-AMP to a molecule of RNAase. 2′-CMP binds the ratio 1:1 over the analogue concentration range studied.

Kinetic study on the acid hydrolysis of 1-aryl-2-phenyl-2-imidazolines. Basicity-rate of hydrolysis and structure relationships

1983 ◽  
Vol 20 (6) ◽  
pp. 1585-1588 ◽  
Author(s):  
Beatriz M. Fernández ◽  
Ana M. Reverdito ◽  
Isabel A. Perillo ◽  
Samuel Lamdan
Keyword(s):  
Kinetic Study ◽  
Acid Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

scholarly journals Oxidation–reduction reactions of simple hydroxamic acids and plutonium(IV) ions in nitric acid

2008 ◽  
Vol 96 (6) ◽  
Author(s):  
M. J. Carrott ◽  
O. D. Fox ◽  
G. LeGurun ◽  
C. J. Jones ◽  
C. Mason ◽  
...  
Keyword(s):  
Acid Hydrolysis ◽  
Kinetic Studies ◽  
Hydroxamic Acids ◽  
Single Cycle ◽  
Fuel Cycles ◽  
Oxidation Reduction ◽  
Advanced Fuel ◽  
Extraction Processes ◽  
The Stability ◽  
Hydrolysis Of

SummarySimple hydroxamic acids such as formo- and aceto-hydroxamic acids have been proposed as suitable reagents for the separation of either Pu and/or Np from U in modified or single cycle Purex based solvent extraction processes designed to meet the emerging requirements of advanced fuel cycles. The stability of these hydroxamic acids is dominated by their decomposition through acid hydrolysis. Kinetic studies of the acid hydrolysis of formo- and aceto-hydroxamic acids are reported in the absence and the presence of Pu(IV) ions. The slow reduction of these plutonium(IV) hydroxamate complexes to Pu(III) aquo-ions has been characterised by spectrophotometry and cyclic voltammetry. The reductions of Pu(IV) in the presence of FHA and AHA are consistent with a mechanism in which free hydroxamic acid in solution is hydrolysed whilst Pu(IV) ions remain fully complexed to hydroxamate ligands; then at some point close to a 1 : 1 Pu(IV) : XHA ratio, some free Pu

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