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1. Rapid mechanochemical encapsulation of biocatalysts into robust metal–organic frameworks

   https://doi.org/10.1038/s41467-019-12966-0  

   Wei, Tz-Han ; Wu, Shi-Hong ; Huang, Yi-Da ; Lo, Wei-Shang ; Williams, Benjamin P. ; Chen, Sheng-Yu ; Yang, Hsun-Chih ; Hsu, Yu-Shen ; Lin, Zih-Yin ; Chen, Xin-Hua ; et al ( November 2019 , Nature Communications)

   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.

    

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2. A general Ca-MOM platform with enhanced acid-base stability for enzyme biocatalysis

   https://doi.org/https://doi.org/10.1016/j.checat.2021.03.001  

   Pan, Y. ; Li, Q. ; Li, H. ; Farmakes, J. ; Ugrinov, A. ; Zhu, X. ; Lai, Z. ; Chen, B. ; Yang, Z. ( April 2021 , Chem catalysis)

   null (Ed.)

   Co-precipitation of enzymes in metal-organic frameworks is a unique enzyme-immobilization strategy but is challenged by weak acid-base stability. To overcome this drawback, we discovered that Ca2+ can co-precipitate with carboxylate ligands and enzymes under ambient aqueous conditions and form enzyme@metal-organic material composites stable under a wide range of pHs (3.7–9.5). We proved this strategy on four enzymes with varied isoelectric points, molecular weights, and substrate sizes—lysozyme, lipase, glucose oxidase (GOx), and horseradish peroxidase (HRP)—as well as the cluster of HRP and GOx. Interestingly, the catalytic efficiency of the studied enzymes was found to depend on the ligand, probing the origins of which resulted in a correlation among enzyme backbone dynamics, ligand selection, and catalytic efficiency. Our approach resolved the long-lasting stability issue of aqueous-phase co-precipitation and can be generalized to biocatalysis with other enzymes to benefit both research and industry. 

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3. One-pot synthesis of enzyme@metal–organic material (MOM) biocomposites for enzyme biocatalysis

   https://doi.org/DOI https://doi.org/10.1039/D1GC00775K  

   Pan, Y. ; Li, H. ; Lenertz, M. ; Han, Y. ; Ugrinov, A. ; Kilin, D. ; Chen, B. ; Yang, Z. ( March 2021 , Green chemistry)

   null (Ed.)

   Metal–organic frameworks/materials (MOFs/MOMs) are advanced enzyme immobilization platforms that improve biocatalysis, materials science, and protein biophysics. A unique way to immobilize enzymes is co-crystallization/co-precipitation, which removes the limitation on enzyme/substrate size. Thus far, most enzyme@MOF composites rely on the use of non-sustainable chemicals and, in certain cases, heavy metals, which not only creates concerns regarding environmental conservation but also limits their applications in nutrition and biomedicine. Here, we show that a dimeric compound derived from lignin, 5,5′-dehydrodivanillate (DDVA), co-precipitates with enzymes and low-toxicity metals, Ca2+ and Zn2+, and forms stable enzyme@Ca/Zn–MOM composites. We demonstrated this strategy on four enzymes with different isoelectric points (IEPs), molecular weights, and substrate sizes. Furthermore, we found that all enzymes displayed slightly different but reasonable catalytic efficiencies upon immobilization in the Ca–DDVA and Zn–DDVA MOMs, as well as reasonable reusability in both composites. We then probed the structural basis of such differences using a representative enzyme and found enhanced restriction of enzymes in Zn–DDVA than in Ca–DDVA, which might have caused the activity difference. To the best of our knowledge, this is the first aqueous-phase, one-pot synthesis of a lignin-derived “green” enzyme@MOF/MOM platform that can host enzymes without any limitations on enzyme IEP, molecular weight, and substrate size. The different morphologies and crystallinities of the composites formed by Ca–DDVA and Zn–DDVA MOMs broaden their applications depending on the problem of interest. Our approach of enzyme immobilization not only improves the sustainability/reusability of almost all enzymes but also reduces/eliminates the use of non-sustainable resources. This synthesis method has a negligible environmental impact while the products are non-toxic to living things and the environment. The biocompatibility also makes it possible to carry out enzyme delivery/release for nutritional or biomedical applications via our “green” biocomposites. 

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4. MOF-Enabled Ion-Regulating Gel Electrolyte for Long-Cycling Lithium Metal Batteries Under High Voltage

   https://doi.org/10.1002/smll.202106225  

   Fu, Xuewei ; Hurlock, J. Matthew ; Ding, Chenfeng ; Li, Xiaoyu ; Zhang, Qiang ; Zhong, Wei-Hong ( December 2021 , Small)

   High-voltage lithium metal batteries (LMBs) are a promising high-energy density energy storage system. However, their practical implementations are impeded by short lifespan due to uncontrolled lithium dendrite growth, narrow electrochemical stability window, and safety concerns of liquid electrolytes. Here, a porous composite aerogel is reported as the gel electrolyte (GE) matrix, made of metal–organic framework (MOF)@bacterial cellulose (BC), to enable long-life LMBs under high voltage. The effectiveness of suppressing dendrite growth is achieved by regulating ion deposition and facilitating ion conduction. Specifically, two hierarchical mesoporous Zr-based MOFs with different organic linkers, that is, UiO-66 and NH2-UiO-66, are embedded into BC aerogel skeletons. The results indicate that NH2-UiO-66 with anionphilic linkers is more effective in increasing the Li+ transference number; the intermolecular interactions between BC and NH2-UiO-66 markedly increase the electrochemical stability. The resulting GE shows high ionic conductivity (≈1 mS cm−1), high Li+ transference number (0.82), wide electrochemical stability window (4.9 V), and excellent thermal stability. Incorporating this GE in a symmetrical Li cell successfully prolongs the cycle life to 1200 h. Paired with the Ni-rich LiNiCoAlO2 (Ni: Co: Al = 8.15:1.5:0.35, NCA) cathode, the NH2-UiO-66@BC GE significantly improves the capacity, rate performance, and cycle stability, manifesting its feasibility to operate under high voltage. 

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5. Expanding the “library” of Metal-Organic Frameworks (MOFs) for enzyme biomineralization

   Jordahl, Drew Jordahl ; Armstrong, Zoe ; Li, Qiaobin ; Gao, Runxiang ; Liu, Wei ; Johnson, Kelley ; Brown, William ; Scheiwiller, Allison ; Feng, Li ; Ugrinov, Angel ; et al ( October 2022 , ACS applied materials interfaces)

   Farha, Omar (Ed.)

   Metal-Organic Frameworks (MOFs) are advanced platforms for enzyme immobilization. Enzymes can be entrapped via either diffusion (into pre-formed MOFs) or co-crystallization. Enzyme co-crystallization with specific metals/ligands in the aqueous phase, also known as biomineralization, minimizes the enzyme loss as compared to organic phase co-crystallization, removes the size limitation on enzymes and substrates, and can potentially broaden the application of enzyme@MOF composites. However, not all enzymes are stable/functional in the presence of excess metal ions and/or ligands currently available for co-crystallization. Furthermore, most current biomineralization-based MOFs have limited (acid-) pH stability, making it necessary to explore other metal-ligand combinations that can also immobilize enzymes. Here, we report our discovery on the combination of five metal ions and two ligands that can form biocomposites with two model enzymes differing in size and hydrophobicity in the aqueous phase under ambient conditions. Surprisingly, most of the formed composites are single- or multi- phase crystals even though the reaction phase is aqueous, with the rest as amorphous powders. All 20 enzyme@MOF composites showed good to excellent reusability, and were stable under weakly acidic pHs. The stability under weakly basic conditions depended on the selection of enzyme and metal-ligand combinations, yet for both enzymes, 3-4 MOFs offered decent stability under basic conditions. This work initiates the expansion of the current “library” of metal-ligand selection for encapsulating/biomineralizing large enzymes/enzyme clusters, leading to customized encapsulation of enzymes according to enzymes stability, functionality, and optimal pH. 

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