Micellar catalysis of organic reactions. Part 37. A comparison of the catalysis of ester and amide hydrolysis by copper-containing micelles

1997 ◽  
Vol 75 (2) ◽  
pp. 202-206 ◽  
Author(s):  
Trevor J. Broxton ◽  
Abdulla Nasser
Keyword(s):  
Metal Ion ◽  
Cetyltrimethylammonium Bromide ◽  
Acid Group ◽  
Ester Hydrolysis ◽  
Reaction Centre ◽  
Rate Determining Step ◽  
Amide Hydrolysis ◽  
Low Concentrations ◽  
Triton X ◽  
Hydrolysis Of

The hydrolysis of a number of nitroactivated esters and amides has been studied in the presence of copper-containing metallomicelles at neutral pH. The relative rates of hydrolysis in the pure metallomicelle and in co-micelles with either cetyltrimethylammonium bromide (ctab) or Triton X-100 depends on the hydrophobicity of the substrate and whether it is completely solubilized by the copper micelle. Thus it depends on the concentration of the copper micelle. At low concentrations of copper micelle (0.2 mM) where the substrate is incompletely solubilized, the reaction is faster when 2 mM ctab is added. At higher concentrations (>0.6 mM) where the substrate may be almost completely solubilized by the copper micelle, the reaction is slower when 2 mM ctab is added. For ester hydrolysis the presence of either a carboxylic acid group or a heterocyclic nitrogen atom close to the reaction centre resulted in much larger catalysis by the metallomicelle than for model compounds without these additional groups. It is postulated that these groups coordinate with the metal ion and thus present the reaction centre close to a metal-bound hydroxyl resulting in a significant increase in the rate of bond formation, which is the rate-determining step for ester hydrolysis. For amide hydrolysis the presence of a carboxyl group ortho to the reaction centre did not lead to larger catalysis by the copper micelle than for the compound without this group. This difference is attributed to the different rate-determining steps for amide and for ester hydrolysis. Keywords: metallomicelles, ester and amide hydrolysis.

scholarly journals The roles of phospholipase D and a GTP-binding protein in guanosine 5′-[γ-thio]triphosphate-stimulated hydrolysis of phosphatidylcholine in rat liver plasma membranes

1990 ◽  
Vol 272 (3) ◽  
pp. 749-753 ◽  
Author(s):  
K M Hurst ◽  
B P Hughes ◽  
G J Barritt
Keyword(s):  
Rat Liver ◽  
Phospholipase D ◽  
Plasma Membranes ◽  
Regulatory Protein ◽  
Gtp Binding ◽  
Liver Plasma Membranes ◽  
Low Concentrations ◽  
Rat Liver Plasma Membranes ◽  
Triton X ◽  
Hydrolysis Of

1. Guanosine 5′-[gamma-thio]triphosphate (GTP[S]) stimulated by 50% the rate of release of [3H]choline and [3H]phosphorylcholine in rat liver plasma membranes labelled with [3H]choline. About 70% of the radioactivity released in the presence of GTP[S] was [3H]choline and 30% was [3H]phosphorylcholine. 2. The hydrolysis of phosphorylcholine to choline and the conversion of choline to phosphorylcholine did not contribute to the formation of [3H]choline and [3H]phosphorylcholine respectively. 3. The release of [3H]choline from membranes was inhibited by low concentrations of SDS or Triton X-100. Considerably higher concentrations of the detergents were required to inhibit the release of [3H]phosphorylcholine. 4. Guanosine 5′-[beta gamma-imido]triphosphate and guanosine 5′-[alpha beta-methylene]triphosphate, but not adenosine 5′-[gamma-thio]-triphosphate, stimulated [3H]choline release to the same extent as did GTP[S]. The GTP[S]-stimulated [3H]choline release was inhibited by guanosine 5′-[beta-thio]diphosphate, GDP and GTP but not by GMP. 5. It is concluded that, in rat liver plasma membranes, (a) GTP[S]-stimulated hydrolysis of phosphatidylcholine is catalysed predominantly by phospholipase D with some contribution from phospholipase C, and (b) the stimulation of phosphatidylcholine hydrolysis by GTP[s] occurs via a GTP-binding regulatory protein.

scholarly journals Phosphomonoesterase hydrolysis of polyphosphoinositides in rat kidney: Properties and subcellular localization of the enzyme system

1975 ◽  
Vol 150 (3) ◽  
pp. 537-551 ◽  
Author(s):  
P H Cooper ◽  
J N Hawthorne
Keyword(s):  
Phosphatase Activity ◽  
Metal Ion ◽  
Rat Kidney ◽  
Gradient Centrifugation ◽  
Sodium Deoxycholate ◽  
Subcellular Fractionation ◽  
Kidney Cortex ◽  
Ph Optimum ◽  
Triton X ◽  
Hydrolysis Of

Tthe properties of diphosphoinositide and triphosphoinositide phosphatases from rat kidney homogenate were studied in an assay system in which non-specific phosphatase activity was eliminated. The enzymes were not completely metal-ion dependent and were activated by Mg2+. The detergent sodium deoxycholate, Triton X-100 and Cutscum inhibited the reaction; cetyltrimethylammonium bromide only activated when added with the subtrates and in the presence Mg2+. Both enzymes had a pH optimum of 7.5. Ca2+ and Li+ both activated triphosphoinositide phosphatase, but Ca2+ inhibited and L+ had little effect on diphosphoinositide phosphatase. Cyclic AMP had no effect on either enzyme. The enzymes were three times more active in kidney cortex than in the medulla. On subcellular fractionation of kidney-cortex homogenates by differential and density-gradient centrifugation, the distribution of the enzymes resembled that of thiamin pyrophosphatase (assayed in the absence of ATP), suggesting localization in the Golgi complex. However, the distribution differed from that of the liver Golgimarker galactosyltransferase. Activities of both diphosphoinositide and triphosphoinositide phosphatases and thiamin pyrophosphatase were low in purified brush-border fragments. Further experiments indicate that at least part of the phosphatase activity is soluble.

A comparison of the mechanisms of hydrolysis of benzimidates, esters, and amides in sulfuric acid media

2005 ◽  
Vol 83 (9) ◽  
pp. 1391-1399 ◽  
Author(s):  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Isotope Effects ◽  
Ester Hydrolysis ◽  
Water Molecules ◽  
Acid Media ◽  
Tetrahedral Intermediate ◽  
Amide Hydrolysis ◽  
Solvent Isotope ◽  
Reaction Media ◽  
Hydrolysis Of

The mechanisms given in textbooks for both ester and amide hydrolysis in acid media are in need of revision. To illustrate this, benzimidates were chosen as model compounds for oxygen protonated benzamides. In aqueous sulfuric acid media they hydrolyze either by a mechanism involving attack of two water molecules at the carbonyl carbon to give a neutral tetrahedral intermediate directly, as in ester hydrolysis, or by an SN2 attack of two water molecules at the alkyl group of the alkoxy oxygen to form the corresponding amide, or by both mechanisms, depending on the structure of the benzimidate. The major line of evidence leading to these conclusions is the behavior of the excess acidity plots resulting from the rate constants obtained for the hydrolyses as functions of acid concentration and temperature. The first of these mechanisms is in fact very similar to one found for the hydrolysis of benzamides, as inferred from: (1) similar excess acidity plot behaviour; and (2) the observed solvent isotope effects for amide hydrolysis, which are fully consistent with the involvement of two water molecules, but not with one or with three (or more). This mechanism starts out as essentially the same one as that found for ester hydrolysis under the same conditions. Differences arise because the neutral tetrahedral intermediate, formed directly as a result of the protonated substrate being attacked by two water molecules (not one), possesses an easily protonated nitrogen in the amide and benzimidate cases, explaining both the lack of 18O exchange observed for amide hydrolysis and the irreversibility of the reaction. Protonated tetrahedral intermediates are too unstable to exist in the reaction media; in fact, protonation of an sp3 hybridized oxygen to put a full positive charge on it is extremely difficult. (This means that individual protonated alcohol or ether species are unlikely to exist in these media either.) Thus, the reaction of the intermediate going to product or exchanged reactant is a general-acid-catalyzed process for esters. For amide hydrolysis, the situation is complicated by the fact that another, different, mechanism takes over in more strongly acidic media, according to the excess acidity plots. Some possibilities for this are given.Key words: esters, amides, benzimidates, hydrolysis, excess acidity, mechanism, acid media.

Kinetics of the metal ion catalyzed ester hydrolysis of O-acetyl di-2-pyridyl ketoxime

1985 ◽  
Vol 24 (19) ◽  
pp. 3088-3090 ◽  
Author(s):  
Junghun Suh ◽  
Myunghyun Paik Suh ◽  
Jae Don Lee
Keyword(s):  
Metal Ion ◽  
Ester Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of

Micellar catalysis of organic reactions. Part 33. Amide hydrolysis in neutral solution in the presence of a copper-containing micelle

1993 ◽  
Vol 71 (5) ◽  
pp. 670-673 ◽  
Author(s):  
Trevor J. Broxton ◽  
Robin A. Coa
Keyword(s):  
Cetyltrimethylammonium Bromide ◽  
Cupric Chloride ◽  
Buffer Concentration ◽  
Neutral Solution ◽  
Hydroxide Ion ◽  
Amide Hydrolysis ◽  
Mechanism Of Reaction ◽  
Rate Of Reaction ◽  
Hydrolysis Of ◽  
Micelle Surface

The hydrolysis of 5-nitro-2-(trifluoroacetylamino)benzoic acid (1) has been studied at pH 7 in water and in the presence of micelles of cetyltrimethylammonium bromide (ctab) and of copper-containing micelles formed from the reaction of N,N,N′-trimethyl-N′-hexadecylethylenediamine and cupric chloride. It has been found that the hydrolysis of 1 is inhibited by micelles of ctab but strongly catalysed by the copper-containing micelle at this pH. At a higher pH where the hydroxide ion reaction becomes important the reaction is catalysed by micelles of ctab as well, but the catalysis is stronger by the copper-containing micelle. The effect of added sodium chloride on the rate of reaction is shown to be larger for reaction in the presence of ctab than for reaction in the presence of the copper micelles. Also reported are the effects of the buffer concentration on the rate of reaction at various pH for both micelles. It is concluded that the mechanism of reaction in the copper-containing micelle involves a metal-bound hydroxyl rather than a free hydroxide ion loosely associated with the cationic micelle surface. It is interesting that the catalysis of this reaction by the copper-containing micelle is large enough to allow amide hydrolysis at a reasonable rate at neutral pH at ambient temperature.

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