Immobilization on solid supports

The concept of zeolite action was tested in a particular reaction where the enzyme is exposed from the beginning to an acidic environment the esterification of geraniol with acetic acid catalyzed by Candida antarctica lipase B immobilized on zeolite NaA [219]. Lipases have been used for the hydrolysis of triglycerides and due to their ambivalent hydrophobic/hydrophilic properties they are effective biocatalysts for the hydrolysis of hydrophobic substrates [220]. When water-soluble lipases are used in organic media they have to be immobilized on solid supports in order to exhibit significant catalytic activity. 

In conventional synthetic transformations, enzymes are normally used in aqueous or organic solvent at moderate temperatures to preserve the activity of enzymes. Consequently, some of these reactions require longer reaction times. In view of the newer developments wherein enzymes can be immobilized on solid supports [183], they are amenable to relatively higher temperature reaction with adequate pH control. The application of MW irradiation has been explored with two enzyme systems namely Pseudomonas lipase dispersed in Hyflo Super Cell and commercially available SP 435 Novozym (Candida antarctica lipase grafted on an acrylic resin). 

Enzymes are usually used in aqueous or organic media and the temperature is limited to 40 °C to preserve enzyme activity as a consequence the reactions need very long times. With enzymes immobilized on solid supports [80] it is possible to operate at higher temperatures. 

There are different strategies for making libraries wherein natural products skeletons have been constructed or immobilized on solid supports and subsequently derivatized ... 

Cyanogen bromide reacts with amino alcohols to give 2-aminooxazolines that condense in the presence of benzaldehyde and p-toluenesulfonic acid with loss of ammonia to give aza-bis(oxazolines) 173. Aza-bis(oxazohnes) such as 173 are emerging as a new and important class of chiral ligands for asymmetric processes with the added advantage that they can be immobilized on solid supports (Scheme 8.50). 

Glos and co-workers introduced the aza-bis(oxazolines) 258 and 259 (Fig. 9.78) as a new class of chiral C2-symmetric bis(oxazoline) ligands.These catalysts were used in various reactions such as enantioselective allylic substitution and cyclopropanation it was also shown that these new catalysts could easily be tethered to a polymeric support, as shown in structure 259, allowing for facile recovery of the catalyst. There have been other examples of bis(oxazoline) ligands immobilized on solid supports and their use in catalysis.These methods have shown mixed results. 

Immobilization. The fixing property of PEIs has previously been discussed. Another application of this property is enzyme immobilization (419). Enzymes can be bound by reactive compounds, eg, isothiocyanate (420) to the PEI skeleton, or immobilized on solid supports, eg, cotton by adhesion with the aid of PEIs. In every case, fixing considerably simplifies the performance of enzyme-catalyzed reactions, thus facilitating preparative work. This technique has been applied to glutaraldehyde-sensitive enzymes (421), a-glucose transferase (422), and pectin lyase, pectin esterase, and endopolygalacturonase (423). 

Superacids Immobilized on Solid Supports. The considerable success of Magic Acid and related superacids in solution chemistry and interest to extend the scope and utility of acid-catalyzed reactions, particularly hydrocarbon transformations, logically led to the attempts to adopt this chemistry to solid systems allowing heterogeneous catalytic processes. 

Pulido-Tofino, P, J.M. Barrero-Moreno, and M.C. Perez-Conde. 2000. Flow-through fluoroimmunosen-sor for isoproturon determination in agricultural foodstuff Evaluation of antibody immobilization on solid support. Anal. Chim. Acta 417 85-94. 

Immobilization on Solid Support of Selected Signature Libraries... 

Photosynthetic activities of cells and organelles can be stablised by immobilisation on solid supports (Hall et al., 1987, Gisby et al., 1987). Here we report the results of our studies on ammonia and hydrogen production by A, azollae immobilized on polyvinyl and polyurethane foams under different experimental conditions. We also present the morphological features of cells immobilized on solid supports as revealed by low temperature scanning electron microscopy. 

Metallocenes immobilized on solid support materials have been successfully introduced in industry as polymerization catalysts for the production of new application-oriented polymer materials. Industrial polymerizations, which are carried out either as a slurry process in liquid propylene or as a gas-phase process (Section 7.2.3), require that catalysts are in the form of solid grains or pellets soluble metallocene catalysts thus have to be supported on a solid carrier. 

Compound arrangement Spatially separable on a two-dimensional array Spatially separable on beads (beads in suspension or immobilized on solid support or in soft agar)... 

Several types of electrophilic selenium species have been immobilized on solid supports, for more convenient application to organic synthesis. These include selenenyl halides, " selenocyanates, and selenosulfonates. ... 

Benzisoselenazol-3(27T)-ones covalently immobilized on solid supports have been reported <2004ARK226>. The first 117 was obtained in the reaction of 3-aminopropyltriethoxysilane with dichloride 102 followed by the hydrolysis of the intermediate 116 formed. 4-Aminostyrene, treated with dichloride 102 in the presence of a,a -azobisisobutyronitrile (AIBN), gave, in a one-pot reaction, ebselen bound to a polyethylene chain 118. Another polymer-supported benzisoselenazol-3(2//)-one 119 was obtained by reacting dichloride 102 with 1-aminohexyl-amide gel (Scheme 42). 

Several types of solid catalysts have been explored for use in alkylation. Several groups have attempted to use hybrids (i.e., liquids that have been adsorbed or immobilized on solid supports), such as BF3/zeolites/aluminas, triflic acid on a carrier, H2SO4 on Si02, and so on. Since most have shown limited success, we restrict our discussion to the most promising true solid acid materials - zeolite catalysts. 

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