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.

Studies in Solvolysis. Part VII. The Neutral Hydrolysis of Methyl Perchlorate

1975 ◽  
Vol 53 (20) ◽  
pp. 3106-3115 ◽  
Author(s):  
Ross Elmore Robertson ◽  
Adrianna Annesa ◽  
John Marshall William Scott
Keyword(s):  
Heat Capacity ◽  
Carbon Atom ◽  
Temperature Dependence ◽  
Thermodynamic Parameters ◽  
Isotope Effect ◽  
Perchlorate Ion ◽  
Rate Of Hydrolysis ◽  
Leaving Groups ◽  
Hydrolysis Of

The temperature dependence of the rate of hydrolysis of methyl perchlorate has been measured and the entropy (ΔS≠), enthalpy (ΔH≠), and heat capacity (ΔCp≠) of activation calculated. The measurements confirm that the perchlorate ion is superior to all other leaving groups in water. The isotope effect related to the hydrolysis of methyl-d3 perchlorate has been measured at three temperatures and shown to be inverse. The thermodynamic parameters and the isotope effect were examined with respect to the mechanism of substitution at a primary carbon atom.

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.

scholarly journals Mechanism of acyl transfer by the class A serine β-lactamase of Streptomyces albus G

1991 ◽  
Vol 279 (1) ◽  
pp. 213-221 ◽  
Author(s):  
J Lamotte-Brasseur ◽  
G Dive ◽  
O Dideberg ◽  
P Charlier ◽  
J M Frère ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Amide Bond ◽  
Carbonyl Carbon Atom ◽  
Cephalosporin C ◽  
Beta Lactamase ◽  
Beta Lactam ◽  
Carbonyl Carbon ◽  
Class A ◽  
Streptomyces Albus ◽  
Hydrolysis Of

Optimization by energy minimization of stable complexes occurring along the pathway of hydrolysis of benzylpenicillin and cephalosporin C by the Streptomyces albus G beta-lactamase has highlighted a proton shuttle that may explain the catalytic mechanism of the beta-lactamases of class A. Five residues, S70, S130, N132, T235 and A237, are involved in ligand binding. The gamma-OH group of T235 and, in the case of benzylpenicillin, the gamma-OH group of S130 interact with the carboxylate group, on one side of the ligand molecule. The side-chain NH2 group of N132 and the carbonyl backbone of A237 interact with the exocyclic CONH amide bond, on the other side of the ligand. The backbone NH groups of S70 and A237 polarize the carbonyl group of the scissile beta-lactam amide bond. Four residues, S70, K73, S130 and E166, and two water molecules, W1 and W2, perform hydrolysis of the bound beta-lactam compound. E166, via W1, abstracts the proton from the gamma-OH group of S70. While losing its proton, the O-gamma atom of S70 attacks the carbonyl carbon atom of the beta-lactam ring and, concomitantly, the proton is delivered back to the adjacent nitrogen atom via W2, K73 and S130, thus achieving formation of the acyl-enzyme. Subsequently, E166 abstracts a proton from W1. While losing its proton, W1 attacks the carbonyl carbon atom of the S70 ester-linked acyl-enzyme and, concomitantly, re-entry of a water molecule W'1 replacing W1 allows E166 to deliver the proton back to the same carbonyl carbon atom, thus achieving hydrolysis of the beta-lactam compound and enzyme recovery. The model well explains the differences found in the kcat. values for hydrolysis of benzylpenicillin and cephalosporin C by the Streptomyces albus G beta-lactamase. It also explains the effects caused by site-directed mutagenesis of the Bacillus cereus beta-lactamase I [Gibson, Christensen & Waley (1990) Biochem J. 272, 613-619].

Octahedral cobalt(III) complexes of the chloropentammine type. XIX. The preparation, properties, and reactions of some Chlorobenzylaminebis-(ethylenediamine)cobalt(III) salts and related complexes

1969 ◽  
Vol 22 (9) ◽  
pp. 1869 ◽  
Author(s):  
SC Chan ◽  
OW Lau
Keyword(s):  
Rate Constants ◽  
Open Chain ◽  
First Order ◽  
Benzyl Radical ◽  
Order Rate ◽  
Visible Spectra ◽  
Rate Of Reaction ◽  
Inductive Effects ◽  
Steric Factors ◽  
Hydrolysis Of

Salts of one isomeric series of chlorobenzylaminebis(ethylenediamine)- cobalt-(III) type of cations have been prepared using a variety of benzylamine derivatives as ligands. They are tentatively assigned a cis-configuration on the basis of their visible spectra. The first- order rate constants for their solvolytic aquation have been measured. Both resonance contributions and steric factors from the benzyl radical, as well as inductive effects of its substituents, all have negligibly small influences on the rate of reaction. The second-order rate constants for the hydrolysis of these cations by base have also been determined. The labilizing powers of the benzylamine ligands in this reaction are very similar to those of open-chain aliphatic amines, and significantly different from those of aromatic amines. To see if reactivities depend on the distance of separation between cobalt and the benzene ring, the experiments are extended to the chloro(β- phenylethylamine)bis(ethylenediamine)cobalt(III) type of complexes.

Direct Measurement of the Uncatalyzed Rate of Hydrolysis of a Peptide Bond

1996 ◽  
Vol 118 (23) ◽  
pp. 5498-5499 ◽  
Author(s):  
Rebecca A. R. Bryant ◽  
David E. Hansen
Keyword(s):  
Direct Measurement ◽  
Peptide Bond ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

A ribosomal-boand aminopeptidase in Escherichia coli B: substrate specificity

1970 ◽  
Vol 48 (12) ◽  
pp. 1292-1296 ◽  
Author(s):  
A. T. Matheson ◽  
A. J. Dick ◽  
F. Rollin
Keyword(s):  
Escherichia Coli ◽  
Substrate Specificity ◽  
Peptide Bond ◽  
Terminal Amino Acid ◽  
Strong Activity ◽  
E Coli ◽  
Rate Of Hydrolysis ◽  
Terminal Amino ◽  
Hydrolysis Of ◽  
Escherichia Coli B

The substrate specificity of the ribosomal-bound aminopeptidase from Escherichia coli B has been studied using di-, tri-, and tetrapeptides. The enzyme shows strong activity to leucyl, methionyl, threonyl, and lysyl peptides. Of the other dipeptides tested considerable hydrolysis was observed only if the C-terminal amino acid was leucine or methionine. In a given series of peptides the rate of hydrolysis of the N-terminal peptide bond increased as the size of the peptide increased. Although leucyi dipeptides were hydroiyzed more rapidly than the corresponding methionyl dipeptide the reverse was true with the tripeptides tested. No carboxypeptidase activity was observed and peptides containing D-amino acids were not hydroiyzed. The substrate specificity of the aminopeptidase was compared with the known N-terminal sequences of E. coli proteins to determine whether the enzyme may be involved in the removal of N-formylmethionyl from newly synthesized polypeptides.

Determination of the Tacticity of Poly(methyl methacrylate) by Hydrolysis Rate Measurements

1992 ◽  
Vol 57 (2) ◽  
pp. 349-356 ◽  
Author(s):  
František Mikeš ◽  
Jan Pecka
Keyword(s):  
Methyl Methacrylate ◽  
Ester Group ◽  
Hydrolysis Rate ◽  
Nucleophilic Attack ◽  
Carbonyl Carbon Atom ◽  
Poly Methyl Methacrylate ◽  
Carboxylic Groups ◽  
Simple Kinetic Model ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The rate of hydrolysis of poly(methyl methacrylate) increases with the content of meso(isotactic) diads in the polymer. The increase in the rate of hydrolysis of isotactic polymers is due to an intramolecular nucleophilic attack by the adjacent carboxylic ion on the carbonyl carbon atom in the ester group. An analysis of the content of sequences of variously arranged ester and carboxylic groups shows that the hydrolysis of s-poly(methyl methacrylate) is a random process, while i-poly(methyl methacrylate) is hydrolyzed gradually (by zip mechanism), starting from the carboxylate group formed by an external attack by hydroxylic ions. The kinetic data thus obtained cannot be interpreted in terms of a simple kinetic model. The tacticity of poly(methyl methacrylate) may be estimated from the dependence of the rate of hydrolysis on the content of meso diads determinated by NMR spectrometry. The rate of hydrolysis depends not only on the tacticity of the polymer, but probably also on its configurational sequence statistics.

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.

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