Esterase models

In the following sections, the present status of the investigation on esterase models will be described. 

Hayama et al.132 discussed the catalytic effects of silver ion-polyacrylic add systems toward the hydrolyses of 2,4-dinitrophenylvinylacetate 84 (DNPVA) by using the weak nudeophilicity of carboxylic groups and the change-transfer interactions between olefinie esters and silver ions133Metal complexes of basic polyelectrolytes are also stimulating as esterase models. Hatano etal. 34, 13S) reported that some copper(II)-poly-L-lysine complexes were active for the hydrolyses of amino acid esters, such as D- and L-phenylalanine methyl ester 85 (PAM). They... 

When esterase models are designed, several important and fundamental problems have to be solved. Systematic studies on other interactions, such as hydrogen-bonding and charge-transfer type forces have not been fully performed. Furthermore, various cooperative actions between different kinds of interactions, e. g. the correlation between the attraction of substrate and repulsion of a product by a polyelectrolyte catalyst, has not yet been carried. 

Acidic proteinoids accelerate the hydrolysis of the unnatural substrate, p-nitrophenyl acetate 7,8). P-Nitrophenyl acetate has been used as a substrate for both natural esterases and esterase models. The imidazole ring of histidine is involved in the active site of a variety of enzymes, including hydrolytic enzymes. Histidine residues of proteinoid play a key role in the hydrolysis, the contribution to activity of residues of lysine and arginine is minor, and no activity is observed for proteinoid containing no basic amino acid 7). 

Sheehan and co-woricers prepared a pentapeptide, L-Thr-L-AlarL er-L-His-L-Asp as an esterase model, from a viewpoint that three amino acids (serine, histidine and aspartic acid) are involved at the actne site (131,132). The rate constant for the penti ptide f 7,1.5 sec (pH 7.73,25.5 ) is greater than 0.25 M sec for... 

Even if this does not reflect the swollen state porosity, it would lead to increased diffusional limitations and a larger specific surface area. The photopolymers probably have a more open pore structure in the swollen state giving the template more rapid access to the sites, which are in this case confined to a smaller surface area. The difference in the conversion of pendant double bonds, and thereby the difference in cross-linking densities between the two types of materials, is probably also a factor that comes into play. An increase in chain flexibility at the sites is likely to cause an increase in the template adsorption-desorption rate coefficients. In this context it is interesting to note that increased rate enhancements were observed upon controlled hydrolysis of the polymer backbone of an imprinted esterase model [73]. 

O2 binding for monooxygenase models Nucleophile binding for esterase model... 

Hydrolysis of esters by CD hydroxyls within complexes has intensively been studied as esterase models. Heretofore, much effort has been devoted by using a-CD, B CD and their derivatives. Y-CD may be an unsuitable host for usual substrates because of the large cavity size. We have studied the spacer effect of the appended naphthalene moiety of 2 on its catalytic activity in ester hydrolysis of p- and m-nitropheny-acetates and compared the behavior with that of the corresponding 3-CD derivative 5. 

Hine, J., Khan, M.N. Internal amine-assisted attack of alcoholic hydroxyl group on esters serine esterase models. Indian J. Chem. 1992, 31B, 427-435 and references cited therein. 

Synthetic Polyelectrolytes as Models of Nucleic Acids and Esterases... 

The field of synthetic enzyme models encompasses attempts to prepare enzymelike functional macromolecules by chemical synthesis [30]. One particularly relevant approach to such enzyme mimics concerns dendrimers, which are treelike synthetic macromolecules with a globular shape similar to a folded protein, and useful in a range of applications including catalysis [31]. Peptide dendrimers, which, like proteins, are composed of amino acids, are particularly well suited as mimics for proteins and enzymes [32]. These dendrimers can be prepared using combinatorial chemistry methods on solid support [33], similar to those used in the context of catalyst and ligand discovery programs in chemistry [34]. Peptide dendrimers used multivalency effects at the dendrimer surface to trigger cooperativity between amino acids, as has been observed in various esterase enzyme models [35]. 

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