“Fish‐in‐Net” Encapsulation of Enzymes in Macroporous Cages for Stable, Reusable, and Active Heterogeneous Biocatalysts

Abstract

There is currently great interest in enzyme immobilization to enhance enzyme stability and reusability, and to aid in separation from the reaction mixture, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] but immobilized enzymes on commonly used inorganic and organic solid supports show low activities. This is a result of the leaching of the enzymes from the solid supports and the limited conformational transitions available to the enzymes for chemical interaction on the supports. [1][2][3][4] Enzymes encapsulated by a sol-gel/polymer [3][4][5][6][7][8][9][10] show good activity, but the wide pore-size distribution in sol-gel/polymers cannot be well controlled, and this adversely influences the diffusion of reactants and products during biocatalysis to the detriment of their practical application. [3,4,16] Recently, a number of successful examples of good enzyme activity resulting from enzyme immobilization in uniform mesopores of ordered mesostructured materials have been reported. [14][15][16][17] However, enzyme immobilization in mesopores is limited by the pore size of the mesostructured materials, so that bulky enzymes or enzyme aggregates larger than the mesopores cannot be immobilized. A general and facile approach for the encapsulation of enzymes of various sizes in ordered mesoporous silica is reported here, where the enzymes are entrapped in macroporous cages connected by uniform mesoporous channels. These encapsulated enzymes show good activity, long-term stability, and excellent recycling characteristics. The concept of "fish-in-net" encapsulation of enzymes in ordered mesoporous silica under mild conditions is illustrated in Figure 1. Tetraethylorthosilicate (TEOS) was first assembled from a triblock ethylene oxide (EO)/propylene oxide (PO) copolymer surfactant ( EO 20 PO 70 EO 20 , P123) in ethanol. After evaporation of the ethanol and addition of glycerol, preformed precursors with ordered mesostructured silica particles were obtained in the glycerol solution, which is a non-denaturing solvent for enzymes. The preformed precursors were mixed with the enzyme solution under stirring at 4°C. During the interaction between the enzymes and the preformed precursors, active enzymes (acting as the "fish") were gradually entrapped in the "net" formed by the polymerization and condensation of the ordered mesostructured silica particles. After removal of the glycerol and water by evacuation, the xerogels with encapsulated enzymes were washed with ethanol and water several times to remove polymer surfactants in the mesopores. In contrast to the "ship-in-a-bottle" technique, [18] the enzymes in this work were used as templates for the

Biomimetic polymer-inorganic hybrid microcapsules for yeast alcohol dehydrogenase encapsulation

“…Specifically, in the field of biocatalysis, the development of versatile and efficient enzyme encapsulation matrices is of great importance for the preservation of enzyme stability and reusability, and for the facile isolation of the product from the reaction mixture [11][12][13][14][15][16][17][18]. Biopolymer-based microspheres and microcapsules have long been employed as enzyme encapsulation matrices, because of their low cost and superior biocompatibility.…”

Enzyme confined in silica-based nanocages for biocatalysis in a Pickering emulsion

“…However, nowadays it is still a great challenge to confine enzymes into the nanopores of mesoporous silicas with the aim of restraining the leakage of enzyme. 4 Duan and He have focused on the encapsulation of enzymes into the cylindrical nanochannels of MCM-41 and SBA-15 via silylation to reduce the size of pore opening after protein adsorption. 5 It was found that although this strategy could evidently inhibit protein leaching, it also considerably depressed the activities of immobilized enzymes.…”

Towards efficient chemical synthesis via engineering enzyme catalysis in biomimetic nanoreactors

“…[11][12][13] As a result, enzyme immobilization usually fails to maintain the intrinsic catalytic activity and selectivity of native enzymes, and/or afford adequate enzyme stability to meet the harsh reaction conditions in actual production processes, which poses great needs for engineering the support materials to offer a more propitious host environment to enzymes. [23][24][25][26][27][28][29][30][31] Additional merits associated with these nanoreactors include, permitting the biocatalytic process to be carried out in various media to transcend the limits of native enzymes preferring aqueous solution, and in favor of creating a permeationselective shell analogous to the biological membrane to govern reagent transportation. They harness plenty of benefits for enzyme immobilization, such as the suitable pore size (2 -50 nm, compatible with enzyme dimensions), large surface area and pore volume, open and well-connected porous networks, stable and robust pore wall, and good biocompatibility.…”