to free enzymes in terms of enzyme reuse and separation of the reaction products. However, such chemical modifications often decrease enzymatic activity because of denaturation and hindrance of the reaction site. [1,2] Although fixation of enzymes in the cavities of mesoporous silicates and metal-organic frameworks by size fitting and physical interaction makes it possible to stabilize the encapsulated enzymes, this methodology leads to a slow diffusion of substrates to cavities containing immobilized enzymes. [3][4][5] Supramolecular polymer nanotubes, [6][7][8][9] formed by self-assembly of rationally designed amphiphilic molecules in water, are able to encapsulate and release enzymes and other proteins, which requires precise tuning of the size and surfaces composition of the nanochannels. [10][11][12] Nanotubes are useful for qualitative and quantitative analysis of proteins, [13][14][15] stabilization of proteins under harsh conditions, [16][17][18] acceleration of protein refolding, [19][20][21][22] and mimicking of proteins. [23] The use of nanotubes as solid supports in bioreactors is so far limited [24,25] because of the disadvantages such as an insufficient fixation of enzymes in addition to a slow diffusion of substrates to the nanochannels encapsulating enzymes.Herein we describe bioreactors based on enzymes encapsulated in photoresponsive transformable nanotubes and nanocoils end-capped with magnetic nanoparticles. In these bioreactors, morphological transformation from nanotubes to nanocoils initiates enzymatic reactions, which depend on the appearance of multiple narrow slits that allow penetration of substrates from the bulk solution. The use of magnetic nanoparticles enabled us to not only inhibit the release of encapsulated enzymes to the bulk solution but also magnetically recover the nanotubes after the enzymatic reactions. We found that these bioreactors stabilize encapsulated enzymes and have good kinetic performance, high reusability and recyclability, and size selectivity for the substrates.
Results and Discussion
Construction of Nanotubes and Structural AnalysisNanocoils sometimes appear as intermediates during the formation of nanotubes, which makes it difficult to selectively Self-assembly of asymmetric amphiphiles containing an azobenzene unit selectively produces molecular monolayer nanotubes, which can act as solid supports for enzymes without the use of chemical cross-linkers. Encapsulation of enzymes in nanotube channels and continuous capping of both open ends with magnetic nanoparticles allow us to construct bioreactors. Transformation of the nanotubes to nanocoils induced by the trans-to-cis isomerization of the azobenzene unit upon UV-light irradiation initiates catalysis due to the appearance of multiple narrow slits functioning as size-exclusion pathways for penetration of substrates from bulk solution. Kinetic performance of encapsulated enzymes is similar to that of free enzymes. Magnetic nanoparticles are very useful for inhibiting the release of encapsulated enzymes and c...
