Biocatalysis hybrid enzymes

Applications of sol-gel-processed interphase catalysts. Chemical Reviews, 102, 3543-3578. Pierre, A.C. (2004) The sol-gel encapsulation of enzymes. Biocatalysis and Biotransformation, 22, 145-170. Shchipunov, Yu.A. (2003) Sol-gel derived biomaterials of silica and carrageenans. Journal of Colloid and Interface Science, 268, 68-76. Shchipunov Yu.A. and Karpenko T.Yu. (2004) Hybrid polysaccharide-silica nanocomposites prepared by the sol-gel technique. Langmuir, 20, 3882-3887. 

Macroporous substrates with interconnected voids can be used as platforms for biomacromolecule separation and enzyme immobilization. These assemblies are likely to find application in biocatalysis and bioassays. The inorganic framework can provide a robust substrate, while their large and abundant pores allow the transportation of biomolecules. The availability of various morphologies for macroporous materials provides another level of control over the function of the hybrids. 

An interesting alternative that combines the advantages of both classical and quantum mechanics is to use hybrid QM/MM models, first introduced by Arieh Warshel for modeling enzymatic reactions [7]. Here, the chemical species at the active site are treated using high-level (and therefore expensive) QM models, which are coupled to a force field that describes the reaction environment. Hybrid models can thus take into account solvent effects in homogeneous catalysis, support structure and interface effects in heterogeneous catalysis, and enzyme structure effects in biocatalysis. 

One of the inherent advantages of enzymes is the ability to discriminate between stereoisomers, often generating products with ena-tiomeric excesses (i.e., of over 98%). Judicious application of biocatalysis can also reduce the number of chemical steps needed to synthesize certain drugs, leading to hybrid chemoenzymatic processes with lower costs and less waste. The range of enzymes used in the synthesis of chiral intermediates has expanded beyond esterases and acylases and... 

Biocatalysis is a key route to both natural and non-natural polysaccharide structures. Research in this area is particularly rich and generally involves at least one of the following three synthetic approaches 1) isolated enzyme, 2) whole-cell, and 3) some combination of chemical and enzymatic catalysts (i.e. chemoenzymatic methods) (87-90). Two elegant examples that used cell-fi-ee enzymatic catalysts were described by Makino and Kobayashi (25) and van der Vlist and Loos (27). Indeed, for many years, Kobayashi has pioneered the use of glycosidic hydrolases as catalysts for polymerizations to prepare polysaccharides (88,91). In their paper, Makino and Kobayashi (25) made new monomers and synthesized unnatural hybrid polysaccharides with regio- and stereochemical-control. Van der Vlist and Loos (27) made use of tandem reactions catalyzed by two different enzymes in order to prepare branched amylose. One enzyme catalyzed the synthesis of linear structures (amylose) where the second enzyme introduced branches. In this way, artificial starch can be prepared with controlled quantities of branched regions. 

If formation of macroporous hcaieycomb structures using polymers, nanocomposites, and hybrids have been described, only few examples of honeycomb films based on new building blocks introduced via the different methods described above have been recently achieved as functional materials. Indeed, functional honeycomb film with self-assembled Horseradish peroxidase (HRP) enzyme nanogels at the pore walls for biocatalysis can be mentioned for clinical diagnostic kits and for immunoassays [193]. 

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