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.
It
has been reported that the biological functions of enzymes could
be altered when they are encapsulated in metal–organic frameworks
(MOFs) due to the interactions between them. Herein, we probed the
interactions of catalase in solid and hollow ZIF-8 microcrystals.
The solid sample with confined catalase is prepared through a reported
method, and the hollow sample is generated by hollowing the MOF crystals,
sealing freestanding enzymes in the central cavities of hollow ZIF-8.
During the hollowing process, the samples were monitored by small-angle
X-ray scattering (SAXS) spectroscopy, electron microscopy, powder
X-ray diffraction (PXRD), and nitrogen sorption. The interfacial interactions
of the two samples were studied by infrared (IR) and fluorescence
spectroscopy. IR study shows that freestanding catalase has less chemical
interaction with ZIF-8 than confined catalase, and a fluorescence
study indicates that the freestanding catalase has lower structural
confinement. We have then carried out the hydrogen peroxide degradation
activities of catalase at different stages and revealed that the freestanding
catalase in hollow ZIF-8 has higher activity.
A UiO-66 analog was synthesized in 100 s using water-assisted grinding. The linker solubility suggested that tetrafluorobenzene-1,4-dicarboxylic acid was the best linker. Zr-metal-organic framework nanocrystals displayed good topologies and hydrophobicities, and high water/thermal stabilities. The less amorphous complex led to higher porosities and pore volumes with a 60 min grinding time.
The incompatibility between the anode and the cathode chemistry limits the used of Mg as an anode. This issue may be addressed by separating the anolyte and the catholyte with a membrane that only allows for Mg2+ transport. Mg‐MOF‐74 thin films were used as the separator for this purpose. It was shown to meet the needs of low‐resistance, selective Mg2+ transport. The uniform MOF thin films supported on Au substrate with thicknesses down to ca. 202 nm showed an intrinsic resistance as low as 6.4 Ω cm2, with the normalized room‐temperature ionic conductivity of ca. 3.17×10−6 S cm−1. When synthesized directly onto a porous anodized aluminum oxide (AAO) support, the resulting films were used as a standalone membrane to permit stable, low‐overpotential Mg striping and plating for over 100 cycles at a current density of 0.05 mA cm−2. The film was effective in blocking solvent molecules and counterions from crossing over for extended period of time.
An oxidative linker cleaving (OLC) process was developed
for surgical
manipulation of the engraving process within single crystalline MOFs
particles. The strategy relies on selective degradation of 2,5-dihydroxyterephthalic
acid linker into small molecular fragments by oxidative ring-opening
reactions, resulting in controllable scissoring of framework. By regulation
of the generation and diffusion of oxidative species, the core MOFs
will undergo divergent etching routes, producing a series of single
crystalline hollow and yolk–shell MOF structures. In addition,
the OLC process can be initiated and localized around the pre-embedded
Pd NPs through on-site catalytic generation of oxidative species,
leading to solitary confinement of multiple NPs within one single
crystalline MOF particle, namely, a multi-yolk–shell structure.
This unique architecture can effectively protect NPs from agglomeration
while realizing size selective catalysis at the same time.
We studied coordination-dependent surfactant binding on shaped MOF nanocrystals. Cetyltrimethylammonium bromide (CTAB) on the surface of ZIF-8 was used as a model system. Infrared spectroscopic analysis and molecular dynamics simulations reveal different coordination environments for Zn nodes on {100} and {110} facets, resulting in different CTAB adsorption. We found that we are able to fine-tune the ratio of {100} and {110} facets in the nanocrystals. We also observed that once the MOF nanocrystals are enclosed by pure {110} facets growth along the {100} facets is terminated because the MOF nanocrystal has no surface area for CTAB adsorption. Growth can then be reinitiated through the etching of these rhombic dodecahedral nanocrystals to form a small amount of undercoordinated sites. This work represents the first systematic study of the design principles underpinning the synthesis of shaped MOF nanocrystals.
Here we design an interface between
a metal nanoparticle (NP) and
a metal–organic framework (MOF) to activate an inert CO2 carboxylation reaction and in situ monitor its unconventional
regioselectivity at the molecular level. Using a Kolbe–Schmitt
reaction as model, our strategy exploits the NP@MOF interface to create
a pseudo high-pressure CO2 microenvironment over the phenolic
substrate to drive its direct C–H carboxylation at ambient
conditions. Conversely, Kolbe–Schmitt reactions usually demand
high reaction temperature (>125 °C) and pressure (>80 atm).
Notably,
we observe an unprecedented CO2 meta-carboxylation of an
arene that was previously deemed impossible in traditional Kolbe–Schmitt
reactions. While the phenolic substrate in this study is fixed at
the NP@MOF interface to facilitate spectroscopic investigations, free
reactants could be activated the same way by the local pressurized
CO2 microenvironment. These valuable insights create enormous
opportunities in diverse applications including synthetic chemistry,
gas valorization, and greenhouse gas remediation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.