Hydrolysis of ester bonds

Staphylococcal nuclease Phosphoglycerides, hydrolysis of ester bond in, 204... 

Esterases form a wide family of enzymes that catalyze the hydrolysis of ester bonds. They are ubiquitously expressed in all tissues including the intestine, and are found in both microsomal and cytosolic fractions. Prueksaritonont et al. [6] have studied the metabolism of both p-nitrophenol acetate and acetylsalicylic acid by esterases from human intestinal microsomal and cytosolic systems, and the activity values were 2.76 pmol min-1 mg-1 and 0.96 nmol min-1 mg-1, respectively. Thus, the activity for the hydrolysis of p-nitrophenol acetate in human intestine approaches that in the liver. 

Both esters and amides undergo hydrolysis reactions. In a hydrolysis reaction, the ester or amide bond is cleaved, or split in two, to form two products. As mentioned earlier, the hydrolysis of an ester produces a carboxylic acid and an alcohol. The hydrolysis of an amide produces a carboxylic acid and an amine. There are two methods of hydrolysis acidic hydrolysis and basic hydrolysis. Both methods are shown in Figure 2.9. Hydrolysis usually requires heat. In acidic hydrolysis, the ester or amide reacts with water in the presence of an acid, such as H2SO4. In basic hydrolysis, the ester or amide reacts with the OH ion, from NaOH or water, in the presence of a base. Soap is made by the basic hydrolysis of ester bonds in vegetable oils or animal fats. 

Hydrolysis of Copolyamide-esters (CPAEs) by Lipase (jj,). CPAEs were synthesized by the amide-ester interchange reaction between polyamide and polyester. The length of the polyamide blocks was measured after hydrolysis of ester bonds in CPAE by alkali at 30 C. The infrared spectra after hydrolyzing ester bonds on CPAEs showed that the ester bonds were almost completely removed. The molecular weight distribution of polyamide blocks was examined by GPC (Table II). The following samples were used CPAE-1 (reaction time for synthesis, 1 hr) and CPAE-2 (reaction time, U hr) composed of nylon 6 and PCL at a 50/50 molar ratio, CPAE-3 (reaction time, 1 hr) and CPAE-U (reaction time,... 

AMP — A + P hydrolysis of ester bond - coupled to enei y-releasing processes... 

Lipases are widely distributed among animals, plants, and microorganisms. They catalyze the hydrolysis of ester bonds at the fat/water interface. The mechanism of the lipase-catalyzed hydrolysis of esters involves two consecutive steps [51]. First, the ester is attacked by a nucleophilic group of the enzyme - normally an OH of a serine or a SH of a cysteine - to form an acyl-enzyme intermediate with concomitant liberation of the alcohol moiety of the ester. The acyl-enzyme is subsequently attacked by a water molecule to give the product. 

Development of disagreeable odour and taste in fat or oil upon storage is called rancidity. Rancidity reactions may be due to hydrolysis of ester bonds (hydrolytic rancidity) or due to oxidation of uhsaturated fatty acids (oxidative rancidity). 

The considerations in the previous section need to be addressed and customized for every screening project. As an example, when we set out to develop a new library of esterases for synthetic chemistry use, we first needed to determine the criteria that would be used in the screening project. Esterases and lipases catalyze the hydrolysis of ester bonds as shown in Scheme 1 and are useful for reactions requiring different regioselectivities, chemoselectivities, and stereoselectivities depending on the enzyme s substrate specificities. 

Water, appearing in the system during forming polyene structures from the product of PETP thermal destruction - acetaldehyde, causes hydrolysis of ester bonds, increasing the rate of carboxyl groups formation. Besides, there takes place decrease of polymer relative viscosity [202]. 

To extract these pentoses there are different processes based on the nature of chemical bonds targeted acid-catalyzed hydrolysis of the glycosidic bond, hot alkaline hydrolysis of ester bonds between chains, or hydrolysis with biological catalysts. 

Among enzymes, lipases proved to be the most efficient for the in vitro polyester synthesis. Lipases or triacylglycerol acylhydrolases are water-soluble enzymes that catalyze the hydrolysis of ester bonds in water-insoluble, lipid substrates, and therefore comprise a subclass of the esterases. 

Chymotrypsin is an enzyme that catalyzes the hydrolysis of peptide bonds, with some specihcity for residues containing aromatic side chains. Chymotrypsin also cleaves peptide bonds at other sites, such as leucine, histidine, and glutamine, but with a lower frequency than at aromatic amino acid residues. It also catalyzes the hydrolysis of ester bonds. 

The reason why we used these polymers as trunk polymers is that the grafted side chains are easily isolated from the trunk polymer by hydrolysis of ester bonds, and characterization of grafted branches is possible. 

The hydrolytic degradation mechanism of these copolymers was qualitatively similar and can be described by the preferential hydrolysis of ester bonds fliroughout... 

The environmental fate of plasticizers results from their chemical constitution. Most of them contain the ester group and thus the hydrolysis of ester bond is the main reaction in aqueous medium. According to Wolfe et al. [9] it appears that this reaction at pH 7 may be too slow and is negligible (the half-life time exceeds 100 days). 

An antecedent of this peptidase mimic can be found in the bis-CD 33 developed earlier by Breslow (Figure 11). The two cavities are involved in the recognition of a dipeptide, such as Trp-Trp, with two hydrophobic groups, with an association constant of 2.5 x 10 which is increased by one order of magnitude when Zn(II) is also bound to the bipyridyl central bridge. Although the Cu(II) complex of 33 catalyzes the hydrolysis of ester bonds in hydrophobic substrates fitting into the cavities of the CDs, the hydrolysis of the amide bond in Trp-Trp was not reported. 

As water penetrates the matrix, hydrolysis of ester bonds occurs. 

Enzymes can also catalyze hydrolysis reactions which lead to the resorption of polymeric biomaterials. For example, proteolytic enzymes (proteases) catalyze the hydrolysis of peptide bonds (Fig. 6.1, Eq. 5) as well as the hydrolysis of ester bonds (Fig. 6.1, Eq. 6) [62]. 

The partial enzymatic hydrolysis of ester bonds on the surface of PET films or fibers resulting in changed surface properties has been quantified using a number of analytical methods (Table 1). Surface hydrophilicity can be assessed by contact... 

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