Immobilized enzymes terms Links

The stability of lipase is one of its prominent properties that needs to be considered for improvement via immobilization. The long-term storage and thermal stability of any immobilized enzyme is dependent npon the (1) lipase interaction with the support, (2) binding position, (3) microenvironment, (4) chemical and physical structure of the support, (5) the properties of the spacer that links the lipase to the support, and (6) immobilization conditions. Hence, random immobilizations of the lipase usually do not improve the stability (Chibata et al., 1986 Hartmeier, 1985 Martinek et al., 1977). 

One approach to develop more biologically compatible surfaces for immobilizing proteins is to incorporate a matrix, such as a hydrogel, as an interface between the protein and the solid surface (Burnham et al. 2006). The entrapment of enzymes in a hydrogel layer provides excellent long-term stability and the possibility to adjust the polymer matrix to the specific needs of a certain enzyme. Hydrogels are useful for linking proteins to solid surfaces because their hydrophilic nature and porous structure can help to keep these labile molecules in the native functional state. 

One of the rare examples for the use of immobilized oxynitrilases has been published by Degussa [146]. The company investigated the asymmetric synthesis of (i )-cyanohydrins and used (i )-oxynitrilase, which had been cross-linked and subsequently polyvinyl alcohol-entrapped. The obtained immobilized lens-shaped biocatalysts were much more satisfying in terms of long-term stability and activity compared to the free enzyme and also showed less catalyst leaching than other enzyme supports. Moreover, the immobilization method is cheap, efficient, feasible on an industrial scale, and gives particles of defined size. The utility of these entrapped enzymes could be shown, as indicated in Scheme 57, in the synthesis of (i )-mandelonitrile (R)-175) from aldehyde 174. No catalyst deactivation was observed even after 20 cycles of reuse and yields as well as optical purities of (R)-175 remained constant within normal limits. 

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