We show that an enzyme maintains its biological function under a wider range of conditions after being embedded in metal-organic framework (MOF) microcrystals via a de novo approach. This enhanced stability arises from confinement of the enzyme molecules in the mesoporous cavities in the MOFs, which reduces the structural mobility of enzyme molecules. We embedded catalase (CAT) into zeolitic imidazolate frameworks (ZIF-90 and ZIF-8), and then exposed both embedded CAT and free CAT to a denature reagent (i.e., urea) and high temperatures (i.e., 80 °C). The embedded CAT maintains its biological function in the decomposition of hydrogen peroxide even when exposed to 6 M urea and 80 °C, with apparent rate constants k (s) of 1.30 × 10 and 1.05 × 10, respectively, while free CAT shows undetectable activity. A fluorescence spectroscopy study shows that the structural conformation of the embedded CAT changes less under these denaturing conditions than free CAT.
Metal–organic frameworks (MOFs) have recently garnered consideration as an attractive solid substrate because the highly tunable MOF framework can not only serve as an inert host but also enhance the selectivity, stability, and/or activity of the enzymes. Herein, we demonstrate the advantages of using a mechanochemical strategy to encapsulate enzymes into robust MOFs. A range of enzymes, namely β-glucosidase, invertase, β-galactosidase, and catalase, are encapsulated in ZIF-8, UiO-66-NH2, or Zn-MOF-74 via a ball milling process. The solid-state mechanochemical strategy is rapid and minimizes the use of organic solvents and strong acids during synthesis, allowing the encapsulation of enzymes into three prototypical robust MOFs while maintaining enzymatic biological activity. The activity of encapsulated enzyme is demonstrated and shows increased resistance to proteases, even under acidic conditions. This work represents a step toward the creation of a suite of biomolecule-in-MOF composites for application in a variety of industrial processes.
The formation of biofunctionalized metal–organic frameworks (MOFs) by growing them on a variety of macromolecular biological species, particularly on enzymes and living cells, offers exciting opportunities for a wide range of applications, including biocatalysis, biosensing, and diagnoses. MOFs are commonly subjected to biofunctionalization and biomimetic mineralization, owing to their good chemical and thermal stabilities and easy preparation in aqueous medium under ambient conditions. The functionalization of MOFs with biological substances, such as enzymes, nonenzymatic proteins, and living cells promotes the formation of MOF‐based biocomposites which retain the biological functions of the embedded biological substances. The most common method to construct these biofunctionalized MOFs is either by directly growing the MOF on the biological moiety or by postsynthetic modification of the exterior surface of the MOF with the desired biological species. In particular, hierarchically porous MOFs (containing both mesopores and micropores) are ideal candidates for hosting enzymes and for the translocation of nonenzymatic proteins. This review covers various advanced strategies for developing MOF‐based biocomposites for a wide range of bioapplications, such as biomedical storage, tumor cell targeting, and drug delivery. The influence of MOFs on the biological activity of living cells and future prospects for developing novel MOF‐based biorefinery are discussed.
Applying
metal–organic frameworks (MOFs) on the surface
of other materials to form multifunctional materials has recently
attracted great attention; however, directing the MOF overgrowth is
challenging due to the orders of magnitude differences in structural
dimensions. In this work, we developed a universal strategy to mediate
MOF growth on the surface of metal nanoparticles (NPs), by taking
advantage of the dynamic nature of weakly adsorbed capping agents.
During this colloidal process, the capping agents gradually dissociate
from the metal surface, replaced in situ by the MOF.
The MOF grows to generate a well-defined NP-MOF interface without
a trapped capping agent, resulting in a uniform core–shell
structure of one NP encapsulated in one single-crystalline MOF nanocrystal
with specific facet alignment. The concept was demonstrated by coating
ZIF-8 and UiO-66-type MOFs on shaped metal NPs capped by cetyltrimethylammonium
surfactants, and the formation of the well-defined NP-MOF interface
was monitored by spectroscopies. The defined interface outperforms
ill-defined ones generated via conventional methods, displaying a
high selectivity to unsaturated alcohols for the hydrogenation of
an α,β-unsaturated aldehyde. This strategy opens a new
route to create aligned interfaces between materials with vastly different
structural dimensions.
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