Encapsulation of enzymes in metal–organic frameworks (MOFs) is often obstructed by the small size of the orifices typical of most reported MOFs, which prevent the passage of larger‐size enzymes. Here, the preparation of hierarchical micro‐ and mesoporous Zn‐based MOFs via the templated emulsification method using hydrogels as a template is presented. Zinc‐based hydrogels featuring a 3D interconnecting network are first produced via the formation of hydrogen bonds between melamine and salicylic acid in which zinc ions are well distributed. Further coordination with organic linkers followed by the removal of the hydrogel template produces hierarchical Zn‐based MOFs containing both micropores and mesopores. These new MOFs are used for the encapsulation of glucose oxidase and horseradish peroxidase to prove the concept. The immobilized enzymes exhibit a remarkably enhanced increased operational stability and enzymatic activity with a kcat/km value of 85.68 mm s–1. This value is 7.7‐fold higher compared to that found for the free enzymes in solution, and 2.7‐fold higher than enzymes adsorbed on conventional microporous MOFs. The much higher catalytic activity of the mesoporous conjugate for Knoevenagel reactions is demonstrated, since the large pores enable easier access to the active sites, and compared with that observed for catalysis using microporous MOFs.
Magnetic multi-enzyme nanosystems have been prepared via co-precipitation of enzymes and metalorganic framework HKUST-1 precursors in the presence of magnetic Fe 3 O 4 nanoparticles. The spatial co-localization of two enzymes was achieved using a layer-by-layer positional assembly strategy.Glucose oxidase (GOx) and horseradish peroxidase (HRP) were used as the model enzymes for cascade biocatalysis. By controlling the spatial positions of enzymes, three bienzyme nanosystems GOx@HRP@HKUST-1@Fe 3 O 4 , GOx-HRP@HKUST-1@Fe 3 O 4 and HRP@GOx@HKUST-1@Fe 3 O 4 were prepared in which GOx and HRP containing layers were in close proximity, either encapsulated in the HKUST-1 inner layer, or immobilized on the HKUST-1 outer shell, or randomly distributed in the two MOF layers. Their properties were characterized by transmission electron microscopy, energydispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, and zeta potential measurements. The highest activity was observed at pH ¼ 6 and a temperature of 20 C. Thanks to the favorable positioning of enzymes, the GOx@HRP@HKUST-
Dimerization
of cyclodextrin (CD) molecules is an elementary step
in the construction of CD-based nanostructured materials. Cooperative
binding of CD cavities to guest molecules facilitates the dimerization
process and, consequently, the overall stability and assembly of CD
nanostructures. In the present study, all three dimerization modes
(head-to-head, head-to-tail, and tail-to-tail) of β-CD molecules
and their binding to three isoflavone drug analogues (puerarin, daidzin,
and daidzein) were investigated in explicit water surrounding using
molecular dynamics simulations. Total and individual contributions
from the binding partners and solvent environment to the thermodynamics
of these binding reactions are quantified in detail using free energy
calculations. Cooperative drug binding to two CD cavities gives an
enhanced binding strength for daidzin and daidzein, whereas for puerarin
no obvious enhancement is observed. Head-to-head dimerization yields
the most stable complexes for inclusion of the tested isoflavones
(templates) and may be a promising building block for construction
of template-stabilized CD nanostructures. Compared to the case of
CD monomers, the desolvation of CD dimers and entropy changes upon
complexation prove to be influential factors of cooperative binding.
Our results shed light on key points of the design of CD-based supramolecular
assemblies. We also show that structure-based calculation of binding
thermodynamics can quantify stabilization caused by cooperative effects
in building blocks of nanostructured materials.
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