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.
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-NH
, 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.
Controlling the surface composition of shaped bimetallic nanoparticles could offer precise tunability of geometric and electronic surface structure for new nanocatalysts. To achieve this goal, a ...platform for studying the intermixing process in a shaped nanoparticle was designed, using multilayered Pd‐Ni‐Pt core–shell nanocubes as precursors. Under mild conditions, the intermixing between Ni and Pt could be tuned by changing layer thickness and number, triggering intermixing while preserving nanoparticle shape. Intermixing of the two metals is monitored using transmission electron microscopy. The surface structure evolution is characterized using electrochemical methanol oxidation. DFT calculations suggest that the low‐temperature mixing is enhanced by shorter diffusion lengths and strain introduced by the layered structure. The platform and insights presented are an advance toward the realization of shape‐controlled multimetallic nanoparticles tailored to each potential application.
Pd‐Ni‐Pt in the mix: A method for studying the intermixing process in a shaped nanoparticle was devised. It uses multilayered Pd‐Ni‐Pt core–shell nanocubes as precursors. Under mild conditions, the intermixing between Ni and Pt could be tuned by changing layer thickness and number, triggering intermixing while preserving nanoparticle shape.
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.
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.
A MOF thin film (down to 200 nm in thickness) is synthesized to enable selective Mg2+ transport with negligible crossover of the solvents and the counterions. When synthesized directly onto a porous anodized aluminum oxide (AAO) support, it permits stable, low overpotential Mg striping and plating. This work demonstrates that MOF thin film is a promising choice for future Mg battery applications.
DNAzymes are a promising class of bioinspired catalyst; however, their structural instability limits their potential. Herein, a method to stabilize DNAzymes by encapsulating them in a metal–organic ...framework (MOF) host is reported. This biomimetic mineralization process makes DNAzymes active under a wider range of conditions. The concept is demonstrated by encapsulating hemin‐G‐quadruplex (Hemin‐G4) into zeolitic imidazolate framework‐90 (ZIF‐90), which indeed increases the DNAzyme's structural stability. The stabilized DNAzymes show activities in the presence of Exonuclease I, organic solvents, or high temperature. Owing to its elevated stability and heterogeneous nature, it is possible to perform catalysis under continuous‐flow conditions, and the DNAzyme can be reactivated in situ by introducing K+. Moreover, it is found that the encapsulated DNAzyme maintains its high enantiomer selectivity, demonstrated by the sulfoxidation of thioanisole to (S)‐methyl phenyl sulfoxide. This concept of stabilizing DNAzymes expands their potential application in chemical industry.
Stabilizing DNAzymes: A method to stabilize DNAzymes by encapsulating them in a metal–organic framework (MOF) host is reported. The stabilized DNAzymes show activities in the presence of Exonuclease I, organic solvents, or high temperature. Owing to its elevated stability and heterogeneous phase, it is possible to perform catalysis under continuous‐flow conditions, and the DNAzyme can be reactivated in situ by introducing K+.
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 obs (s–1) of 1.30 × 10–3 and 1.05 × 10–3, 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.
Boron-containing materials are efficient catalysts for the oxidative dehydrogenation of propane to propylene, proceeding
via
radical intermediates. The radical mechanism is initiated by the solid ...surface and propagated in the gas phase. It has been hypothesized that the propylene selectivity could be increased by enhancing the gas-phase contributions by favoring the formation of
iso
- over
n
-propyl radical intermediates. Indeed, whereas
n
-propyl radicals can be converted to both propylene and ethylene,
iso
-propyl radicals yield exclusively propylene. In this contribution, we explore 3D printing to structure the hexagonal boron nitride (hBN) heterogeneous catalyst with high void space. 3D-printed hBN monoliths were found to exhibit a higher olefin selectivity and a higher
r
propylene
/
r
ethylene
ratio as compared to traditional pack beds of hBN pellets. Our kinetic studies indicate the increase of reaction order in propane from 1.5 to 2.3, implying the promotion of gas-phase reaction. This work does not only shows that 3D-structured catalysts lead to higher propylene selectivity, it also confirms the hypothesized reaction mechanism and illustrates the power of molecular insights in selective oxidation chemistry to improve the performance.
Graphical abstract
The development of a low temperature (−160 °C) NO adsorption technique is disclosed that avoids the chemical conversion of the probe molecule at room temperature. The observed IR peaks for Cu+(NO)2 ...and Cu2+(NO) species can be used to quantify the amount of exchanged copper species in a broad range of samples, including a wash‐coated honeycomb. Calibration curves for Cu+(NO)2 and Cu2+(NO) are determined for copper loadings up to 3.99 wt% with Silica‐to‐Alumina Ratio (SAR) of 16–22, and quantitative agreement with the complementary hydrogen Temperature Programmed Reduction (H2‐TPR) results is established. This methodology allows to identify different Cu species in Cu‐CHA, such as Z2Cu(II), Z1Cu(II)OH and Cu dimers, based on their distinct IR signatures. In addition, the perturbed T−O−T framework vibration – characterized at 400 °C – can also be used as a complimentary method to quantify Z2Cu(II) species.
Copper quantification: This work demonstrates that cryogenic NO‐IR is a facile technique to identify and quantify the exchanged copper species in Cu‐CHA. The observed IR peaks for Cu+(NO)2 and Cu2+(NO) species can be used to quantify the amount of exchanged copper species in a broad range of samples, including a wash‐coated honeycomb.
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