Catalytically active group

In homogeneous catalysis, the catalytically active species is dissolved in the reaction medium and is present uniformly throughout the system. However, with resin catalysis, the catalytically active groups are anchored to the matrix and in the solvent-resin system are located at the surface of and within the body of the resin bead only. Ion exchangers are, in fact, particulate active. species and when used as catalysts combine with the physical and mechanical benefits of heterogeneous catalysts (Pitochelli, 1980). 

Scheme 18. Introduction of a catalytically active group on the dendrimer surface...

Shukla GC, Padgett RA. A catalytically active group II intron domain 5 can function in the U12-dependent spliceosome. Mol. Cell 2002 9 1145-1150. 

From the previous examples it is apparent that simple imprinting with a transition state analogue does not lead to cavities with sufficient catalytic activity in addition, catalytically active groups have to be placed in proper position within the cavity. This is also true for catalytic antibodies since it was shown that for, example, a guanidinium group (of the amino acid L-arginine) plays an important role in the catalysis of the basic hydrolysis of esters by a catalytic antibody. 

In contrast to the core-functionalized systems, periphery-functionalized dendrimers have their catalytically active groups located at the surface of the den-... 

The possibility to tailor-make MIPs towards a desired selectivity in combination with the high stability of the materials under a broad range of conditions has rendered MIPs attractive for the development of synthetic enzymes [243, 244]. A popular strategy has been to imprint a transition state analog to obtain a polymer that reduces the activation energy of the reaction. Catalytically active groups are often included in the polymer network. This approach has been applied towards ester and amide hydrolysis reactions [245, 246]. Examples of other reactions where MIPs have been utilized as enzyme mimics are isomerization [247], transamination [248], Diels-Alder reaction [249], 3-elimination [250] and regioselective cycloaddition [251]. 

The micelle carries catalytically active groups and acts as a catalyst. 

The reason is that the minerals serve as a shield physically protecting cellulose fibers from cellulolytic enzymes diffusing into the matrix. At pH 7.5-9, the enzymes have 10-1000 times lower activity, depending on the types of the enzymes, pH, and the dissociation constants of catalytically active groups in the enzyme active center. 

Macromolecular metal complexes of dendrimers have a number of properties, which make them promising for use in catalysis. Firstly, they are relatively readily separable from the reaction products by precipitation with a poor solvent or by membrane filtration. Secondly, the introduction of catalytically active sites into dendrimers is controllable in this they resemble terminally functionalized polymers. The dendrimer structure allows us to purposefully introduce catalytically active groups into the dendrimer core, onto the outer surface, or in intermediate positions. The introduction of cataljdically active groups to the outer surface makes them accessible to reaction and enables us to obtain a catalyst that has a high metal content owing to the dendrimer structure. The introduction of catalytically active... 

Macromolecular metal complexes of soluble dendrimers with catalytically active groups on their surface have been used in hydrogenation [112, 113], Kharasch addition [114], Heck reactions and hydroformylation [115-118], metathesis of unsaturated compounds [119-121], oxidation [122], etc. The use of dendrimers in most cases enabled catalyst reuse and also influenced the activity and selectivity of the processes. 

Sisido studied the influence of catalytically active groups distribution in the chain on the rate of the reaction. He considered three cases ... 

Another often applied approach to enzyme mimics is imprinting a polymer containing catalytically active groups with a substrate analogue. For example, a polymer containing Co(II)-imidazole complexes imitating the active site of the phosphotriesterase enzyme was designed... 

The preceding derivations relate to a multichain mechanism with one catalytically active group per enzyme molecule. If the enzyme molecule has N equally and quite independently active groups, then Equation (19-54) is modified to... 

This forms an ideal basis for the synthesis of enzyme models since naturally occurring material with built-in complexing ability can be used. Surprisingly effective methods have been developed for the reasonably selective functionalization of the primary hydroxyl groups allowing the incorporation of various catalytically active groups. In some cases recognition of enantiomers or enantioselective syntheses have been involved. All this work has been competently and extensively reviewed and hence need not be rediscussed here. 

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