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Unstructured confinement of enzyme is created in Metal–Organic Frameworks. The orientation and backbone dynamics of the trapped enzyme are determined, essential for biocatalyst design and fundamental enzyme studies under confinement.

 

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. 

Exponential growth in the field of covalent–organic frameworks (COFs) is emanating from the direct correlation between designing principles and desired properties. The comparison of catalytic activity between single‐pore and dual‐pore COFs is of importance to establish structure–function relationship. Herein, the synthesis of imine‐linked dual‐pore [(BPyDC)]_x%‐ETTA COFs (x = 0%, 25%, 50%, 75%, 100%) with controllable bipyridine content is fulfilled by three‐component condensation of 4,4′,4″,4′″‐(ethene‐1,1,2,2‐tetrayl)tetraaniline (ETTA), 4,4′‐biphenyldialdehyde, and 2,2′‐bipyridyl‐5,5′‐dialdehyde in different stoichiometric ratio. The strong coordination of bipyridine moieties of [(BPyDC)]_x%‐ETTA COFs with palladium imparts efficient catalytic active sites for selective functionalization of sp²CH bond to CX (X = Br, Cl) or CO bonds in good yield. To broaden the scope of regioselective CH functionalization, a wide range of electronically and sterically substituted substrates under optimized catalytic condition are investigated. A comparison of the catalytic activity of palladium decorated dual‐pore frameworks with single‐pore imine‐linked Pd(II) @ Py‐2,2′‐BPyDC framework  is undertaken. The finding of this work provides a sporadic example of chelation‐assisted CH functionalization and disclosed an in‐depth comparison of the relationship between superior catalytic activity and core properties of rationally designed imine linked frameworks.

 

A photoactive porphyrinic metal−organic framework (MOF) has been prepared by exchanging Ti into a Zr‐based MOF precursor. The resultant mixed‐metal Ti/Zr porphyrinic MOF demonstrates much‐improved efficiency for gas‐phase CO₂photoreduction into CH₄and CO under visible‐light irradiation using water vapor compared to the parent Zr‐MOF. Insightful studies have been conducted to probe the photocatalysis processes. This work provides the first example of gas‐phase CO₂photoreduction into methane without organic sacrificial agents on a MOF platform, thereby paving an avenue for developing MOF‐based photocatalysts for application in CO₂photoreduction and other types of photoreactions.

 

Polymer structure and conformational dynamics are essential to polymer macroscopic properties, but are challenging to probe. We report here a synthetic pathway to chemically add a nitroxide moiety onto block polymers in a mild, aqueous environment and demonstrate its use in a series of polymeric micelles using Electron Paramagnetic Resonance (EPR) spectroscopy. The micelles were characterized with several analytical approaches and EPR findings were in general consistent with other approaches. Upon exposure to organic solvents, the line shape changes reflected the micelle swelling and EPR spectral simulations revealed structural information of the swelled micelles. The label introduced via our method can be cleaved and replaced with other probes to report different information site‐specifically. The mild conditions facilitate the future use of EPR in solving biopolymer problems. In combination with other labeling approaches, one can perform polymer spin labeling with different chemistry, so that various information about polymers can be obtained site‐specifically. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2017,55, 1770–1782