Modulating the Biofunctionality of Metal–Organic-Framework-Encapsulated Enzymes through Controllable Embedding Patterns

Embedding an enzyme within a MOF as exoskeleton (enzyme@MOF) offers new opportunities to improve the inherent fragile nature of the enzyme, but also to impart novel biofunctionality to the MOF. Despite the remarkable stability achieved for MOF-embedded enzymes, embedding patterns and conversion of the enzymatic biofunctionality after entrapment by a MOF have only received limited attention. Herein, we reveal how embedding patterns affect the bioactivity of an enzyme encapsulated in ZIF-8. The enzyme@MOF can maintain high activity when the encapsulation process is driven by rapid enzyme-triggered nucleation of ZIF-8. When the encapsulation is driven by slow coprecipitation and the enzymes are not involved in the nucleation of ZIF-8, enzyme@MOF tends to be inactive owing to unfolding and competing coordination caused by the ligand, 2-methyl imidazole. These two embedding patterns can easily be controlled by chemical modification of the amino acids of the enzymes, modulating their biofunctionality.     

Metal–Organic Framework Crystal–Glass Composite Membranes with Preferential Permeation of Ethane

Metal–organic framework (MOF) glass is an easy to process and self-supported amorphous material that is suitable for fabricating gas separation membranes. However, MOF glasses, such as ZIF-62 and ZIF-4 have low porosity, which makes it difficult to obtain membranes with high permeance. Here, a self-supported MOF crystal–glass composite (CGC) membrane was prepared by melt quenching a mixture of ZIF-62 as the membrane matrix and ZIF-8 as the filler. The conversion of ZIF-62 from crystal to glass and the simultaneous partial melting of ZIF-8 facilitated by the melt state of ZIF-62 make the CGC membrane monolithic, eliminating non-selective grain boundaries and improving selectivity. The thickness of CGC membrane can be adjusted to fabricate a membrane without the need of a support substrate. CGC membranes exhibit a C₂H₆ permeance of 41 569 gas permeation units (GPU) and a C₂H₆/C₂H₄ selectivity of 7.16. The CGC membrane has abundant pores from the glassy state of ZIF-62 and the crystalline ZIF-8, which enables high gas permeance. ZIF-8 has preferential adsorption for C₂H₆ and promotes C₂H₆ transport in the membrane, and thus the GCG membrane exhibits ultrahigh C₂H₆ permeance and good C₂H₆/C₂H₄ selectivity.     

Mn3O4/金属有机骨架材料活化过一硫酸盐降解水中难降解有机污染物罗丹明B

锰氧化物是一类环境友好型材料,可以有效活化过一硫酸盐(PMS)降解水中难降解有机污染物.但是锰氧化物在单独使用时容易出现严重的团聚现象,进而降低其对PMS的催化活性,不利于水中污染物的降解.因此,人们通常将锰氧化物负载于多孔的载体材料上.金属有机骨架材料(MOFs)因具有巨大的比表面积和温和的制备条件而广受关注.本文采用温和的溶剂热法首次成功制备了Mn3O4与MOF的复合材料Mn3O4/ZIF-8,并通过X射线衍射、扫描电镜、透射电镜、X射线光电子能谱和红外光谱等手段对其进行了表征,探究了Mn3O4/ZIF-8的形成机理.考察了Mn3O4负载量对Mn3O4/ZIF-8催化性能的影响,以及Mn3O4/ZIF-8投加量、PMS投加量、初始罗丹明B(RhB)浓度和反应温度对RhB去除效果的影响,同时探究了Mn3O4/ZIF-8的重复使用性能,分析了RhB的降解途径、去除机理以及最终的降解副产物.结果表明,边长为50?150 nm的片状Mn3O4均匀分散在粒径为250 nm的六边形ZIF-8的外表面;当Mn3O4负载量为0.5时,所制备的复合材料0.5-Mn/ZIF-120活化PMS对RhB的降解效果最好,反应60 min时RhB降解率可达到99.4%,且Mn的浸出量可以忽略不计.在该体系中,RhB的降解过程符合一级动力学反应方程,其降解速率常数随催化剂和PMS投加量的增加、反应温度的提高和初始RhB浓度的减小而增大.在0.5-Mn/ZIF-120催化剂投加量为0.4 g/L、PMS投加量为0.3 g/L、初始RhB浓度为10 mg/L、初始溶液pH为5.18及室温(23oC)条件下,水中RhB的降解率在40 min时即可达到98%.淬灭实验表明,该体系中HO?起主导作用,而其主要来源于活化PMS所产生的SO4–?.此外,通过简单的二次水冲洗方式对0.5-Mn/ZIF-120催化剂进行回收使用,在连续5次循环使用后仍然可见较高的催化活性和稳定性,RhB的去除率保持在96%以上,且Mn的浸出百分率始终低于5%.     

Cysteamine-modified ZIF-8 colloidal building blocks: Direct assembly of nanoparticulate MOF films on gold surfaces via thiol chemistry

Chemical modification of metal organic framework (MOF) nanocrystal colloids was used to endow them with chemical affinity for gold substrates. Modified nanocrystals were then used as building blocks for rapid and selective self-assembly of porous films. Cysteamine (Cys, 2-aminoetanethiol) was chosen as both chemical modulator and functionalizing agent of Zeolite Imidazolate Framework-8 (ZIF-8) MOF nanocrystals. Important parameters such as the impact of the modulator on the range of nanocrystals stability, size, polydispersity, morphology, and crystalline structure were assessed via both, small and wide angle x-ray scattering (SAXS and WAXS). Cysteamine modified ZIF-8 nanocrystals were assembled into films over conductive Au substrates and film growth was followed in-situ with Quartz Crystal Microbalance (QCM). Thiol moieties exposed out of the ZIF-8 surface after cysteamine modification, results in the formation of thiol bonds with Au conductive substrates as shown via Cyclic Voltammetry experiments. The strategy here presented allows for the synthesis of pre-designed building blocks for MOF films on metal surfaces.     

Catalytically Active Hollow Fiber Membranes with Enzyme-Embedded Metal–Organic Framework Coating

Metal–organic frameworks (MOFs) are suitable enzyme immobilization matrices. Reported here is the in situ biomineralization of glucose oxidase (GOD) into MOF crystals (ZIF-8) by interfacial crystallization. This method is effective for the selective coating of porous polyethersulfone microfiltration hollow fibers on the shell side in a straightforward one-step process. MOF layers with a thickness of 8 μm were synthesized, and fluorescence microscopy and a colorimetric protein assay revealed the successful inclusion of GOD into the ZIF-8 layer with an enzyme concentration of 29±3 μg cm⁻². Enzymatic activity tests revealed that 50 % of the enzyme activity is preserved. Continuous enzymatic reactions, by the permeation of β-d -glucose through the GOD@ZIF-8 membranes, showed a 50 % increased activity compared to batch experiments, emphasizing the importance of the convective transport of educts and products to and from the enzymatic active centers.     

ZIF-8 degrades in cell media,serum, and some—but not all—common laboratory buffers

ABSTRACT

Drug delivery using metal-organic frameworks (MOF) has elicited interest in their biocompatibility; however, few studies have been conducted on their stability in common buffers, cell media, and blood proteins. In particular, the use of ZIF-8, a MOF interconnected by Zn and methylimidazole, has been frequently employed. In this study, we tested single crystals of ZIF-8 with common laboratory buffers, cell media, and serum, and noted several issues. Buffers containing phosphate and bicarbonate alter the appearance and composition of ZIF-8; however, these buffers do not appear to cause cargo to leak out even when the ZIF-8 itself is displaced by phosphates. On the other hand, serum dissolves ZIF-8, causing premature cargo release. Our results show that ZIF-8 undergoes surface chemistry changes that may affect the interpretation of cellular uptake and cargo release data. On the other hand, it provides a rational explanation as to how ZIF-8 neatly dissolves in vivo.     

Enhanced Activity of Enzyme Immobilized on Hydrophobic ZIF-8 Modified by Ni2+ Ions

The development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework-8 (ZIF-8) has been proved to be an effective platform for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF-8 carrier by using Ni²⁺ ions as anchor (ZIF-8@PEP-Ni). By contrast, the direct coating of PEP on the surface of ZIF-8 (ZIF-8@PEP) generated significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF-8@PEP-Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA cm⁻², which is much lower than the 690 and 919 mV overpotential values of ZIF-8@PEP and PEP, respectively.     

Metal Organic Framework Cubosomes

We demonstrate a general strategy for the synthesis of ordered bicontinuous-structured metal organic frameworks (MOFs) by using polymer cubosomes (PCs) with a double primitive structure (Im m symmetry) as the template. The filling of MOF precursors in the open channel of PCs, followed by their coordination and removal of the template, generates MOF cubosomes with a single primitive topology (Pm m) and average mesopore diameters of 60–65 nm. Mechanism study reveals that the formation of ZIF-8 cubosomes undergoes a new MOF growth process, which involves the formation of individual MOF seeds in the template, their growth and eventual fusion into the cubosomes. Their growth kinetics follows the Avrami equation with an Avrami exponent of n=3 and a growth rate of k=1.33×10⁻⁴, indicating their fast 3D heterogeneous growth mode. Serving as a bioreactor, the ZIF-8 cubosomes show high loading of trypsin enzyme, leading to a high catalytic activity in the proteolysis of bovine serum albumin.     

Preparation and characterization of ZIF-8 and ZIF-67 incorporated poly(vinylidene fluoride) membranes for pervaporative separation of methanol/water mixtures

Metal–organic frameworks (MOFs) are made up of metal centers and organic binders with larger surface area and distinct pore structures. Particularly significant advancement in MOF membranes has been achieved in three different directions: preparation of MOF membranes with larger surface area, improving the membrane performance by surface modification, and its usage with added features. However, its significance has not been completely known and concluded yet. MOF membranes are used in a variety of membrane-based separation like gas permeation, nanofiltration, pervaporation, membrane distillation, etc. This research aims to synthesize MOFs (ZIF-8 and ZIF-67) and MOF membranes (ZIF-8/PVDF and ZIF-67/PVDF) and used them in the pervaporative separation of the methanol/water mixture. MOFs and MOF membranes were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetry analysis. Methanol/water mixtures were be used to study the performance of the prepared membranes. A study on the process parameters such as temperature (40, 45, 50, and 55°C), feed pressure (4, 8, 12, and 16 psi), and feed composition (10%, 20%, 30%, and 40% of water) was carried out to examine the effect of each process parameters for pure membrane. In contrast, Taguchi screening design was used to screen the most influential process variable. The optimized conditions based on Taguchi screening method were 55°C, 12 psi, and 40 %vol of water in feed. The obtained total flux of 425 L/m²h was observed for M3 membrane. As feed temperature increased, the total flux of all three membranes was increased.     

Growing ZIF-8 Seeds on Charged COF Substrates toward Efficient Propylene-Propane Separation Membranes

We report a covalent organic framework (COF) induced seeding strategy to fabricate metal–organic framework (MOF) membranes. Contrary to graphene oxide nuclei-depositing substrate, COF substrate has uniform pore size, high microporosity and abundant functional groups. We designed a series of charged COF nanosheets to induce the formation of ZIF-8@COF nanosheet seeds with high aspect ratio over 150, which were readily processed into a compact and uniform seed layer. The resulting ZIF-8 membranes with thickness down to 100 nm exhibit an ultrahigh C₃H₆/C₃H₈ separation performance and superior long-term stability. Our strategy is also validated by fabricating ultrathin ZIF-67 and UiO-66 membranes.     

Metal–Organic Framework Disintegrants: Enzyme Preparation Platforms with Boosted Activity

An enzyme formulation using customized enzyme activators (metal ions) to directly construct metal–organic frameworks (MOFs) as enzyme protective carriers is presented. These MOF carriers can also serve as the disintegrating agents to simultaneously release enzymes and their activators during biocatalysis with boosted activities. This highly efficient enzyme preparation combines enzyme immobilization (enhanced stability, easy operation) and homogeneous biocatalysis (fast diffusion, high activity). The MOF serves as an ion pump that continuously provides metal ion activators that greatly promote the enzymatic activities (up to 251 %). This MOF–enzyme composite demonstrated an excellent protective effect against various perturbation environments. A mechanistic investigation revealed that the spontaneous activator/enzyme release and ion pumping enable enzymes to sufficiently interact with their activators owing to the proximity effects, leading to a boost in biocatalytic performance.     

Metal–organic frameworks as efficient materials for drug delivery: Synthesis,characterization, antioxidant,anticancer, antibacterial and molecular docking investigation

Metal–organic framework (MOF) nano particles are a class of promising porous nano materials for biomedical applications. Owing to its high loading potential and pH-sensitive degradation, most promising of the MOFs is the zeolitic imidazolate crystal framework (ZIF-8), a progressive useful material for small molecule distribution. Doxorubicin (DOX), designated as a classical drug, was jobwise entrapped in ZIF-8 nano particles. ZIF-8 nano particles, as a novel carrier, were used to monitor the release of the anticancer drug DOX and prevent it from dissipating before reaching its goal. ZIF-8 nano particles with encapsulated DOX (DOX@ZIF-8) can be synthesized in a single pot by incorporation of DOX into the reaction mixture. MOFs and the designed drug delivery (DOX@ZIF-8) system were characterized by Fourier transfer infrared, scanning electron microscopy, N₂ sorption isotherm and X-ray diffraction. The impact of MOFs and the engineered drug delivery system on the viability of human breast and liver cancer cell lines was evaluated. The loaded drug was released at pH 5 faster than at pH 7.4. The nano particles of ZIF-8 showed low cytotoxicity, while DOX@ZIF-8 showed high cytotoxicity to HepG-2 and MCF-7 cells compared with free DOX at the equivalent concentration of DOX of >12.5 μg/ml. These findings indicate that DOX@ZIF-8 nano particles are a promising method for the delivery of cancer cells to drugs. Furthermore, ZIF-8, DOX and encapsulated DOX@ZIF-8 compounds were screened for their potential antibacterial activities against pathogenic bacteria compared with standard antibiotics by the agar well diffusion technique. The results demonstrate that the DOX@ZIF-8 exhibits a strong inhibition zone against Gram-negative strains (Escherichia coli) in comparison with the reference drug gentamycin. The docking active site interactions were evaluated to predict the binding between DOX with the receptor of breast cancer 3hb5-oxidoreductase and liver cancer 2h80-lipid binding protein for anticancer activity.     

Post-Synthetic Modification of ZIF-8 Crystals and Films through UV Light Photoirradiation: Impact on the Physicochemical Behavior of the MOF

The physicochemical modification of Metal-Organic Frameworks (MOFs) is a current challenge in the search to improve their performance in different technological applications. In this work we analyze the post-synthetic modification of ZIF-8 crystals and films through a simple and clean treatment that involves the exposure to a UV lamp under environmental conditions. It is demonstrated that a short treatment alters the MOF structure and chemistry, providing a modified ZIF-8 due to partial disconnections of its structure which increase the amount of terminal surface species such as Zn−OH and −C=N-H, but without compromising the overall MOF structure, specific surface area or thermal stability. Additionally, it leads to changes in several properties of the ZIF-8, such as its capacity to accumulate charge through pseudocapacitive processes, its interaction with nitric oxide and its light absorption behavior. This strategy of modifying ZIF-8 without the use of chemicals through a gentle disconnection of its own structure could open new perspectives of post-functionalization of crystals and films of ZIF-8 to be used in a wide range of applications.     

Metal–Organic Framework Disintegrants: Enzyme Preparation Platforms with Boosted Activity

An enzyme formulation using customized enzyme activators (metal ions) to directly construct metal–organic frameworks (MOFs) as enzyme protective carriers is presented. These MOF carriers can also serve as the disintegrating agents to simultaneously release enzymes and their activators during biocatalysis with boosted activities. This highly efficient enzyme preparation combines enzyme immobilization (enhanced stability, easy operation) and homogeneous biocatalysis (fast diffusion, high activity). The MOF serves as an ion pump that continuously provides metal ion activators that greatly promote the enzymatic activities (up to 251 %). This MOF–enzyme composite demonstrated an excellent protective effect against various perturbation environments. A mechanistic investigation revealed that the spontaneous activator/enzyme release and ion pumping enable enzymes to sufficiently interact with their activators owing to the proximity effects, leading to a boost in biocatalytic performance.     

ZIF-8基复合材料高效、稳定电催化还原CO2

电催化CO₂还原反应(eCO₂RR)受到催化剂本征活性以及传质的限制,导致材料的催化活性低、反应起始电位高等问题。我们以类沸石锌盐咪唑骨架(ZIF-8)材料为研究对象,探究了不同粒径ZIF-8材料的eCO₂RR性能。优选粒径为50 nm的ZIF-8材料,进一步引入碳纳米管(CNT)作为其导电基底材料,通过原位生长,构建了复合材料ZIF-8-50@CNT的多级孔结构和疏水界面。eCO₂RR实验结果表明,CNT的引入提高了催化剂的导电性,优化后的复合材料有效地降低了反应的起始电位。在-1.1 V(相对可逆氢电极(RHE))电位下,CO部分电流密度为15.6 mA·cm^-2,ZIF-8-50@CNT催化剂的比表面活性提升了3.5倍(相比ZIF-8-50),塔菲尔斜率降低到136 mV·dec^-1。并且产物CO的选择性和稳定性得到了提高,在宽电势窗口-0.9～-1.2 V(vs RHE)内,CO的法拉第效率(FE)保持在80%以上。在10 h稳定性测试中,催化剂活...     

ZIF-8基复合材料高效、稳定电催化还原CO2

电催化CO₂还原反应(eCO₂RR)受到催化剂本征活性以及传质的限制，导致材料的催化活性低、反应起始电位高等问题。我们以类沸石锌盐咪唑骨架(ZIF-8)材料为研究对象，探究了不同粒径ZIF-8材料的eCO₂RR性能。优选粒径为50 nm的ZIF-8材料，进一步引入碳纳米管(CNT)作为其导电基底材料，通过原位生长，构建了复合材料ZIF-8-50@CNT的多级孔结构和疏水界面。eCO₂RR实验结果表明，CNT的引入提高了催化剂的导电性，优化后的复合材料有效地降低了反应的起始电位。在-1.1 V (相对可逆氢电极(RHE))电位下，CO部分电流密度为15.6 mA·cm^-2，ZIF-8-50@CNT催化剂的比表面活性提升了3.5倍(相比ZIF-8-50)，塔菲尔斜率降低到136 mV·dec^-1。并且产物CO的选择性和稳定性得到了提高，在宽电势窗口-0.9~-1.2 V (vs RHE)内，CO的法拉第效率(FE)保持在80%以上。在10 h稳定性测试中，催化剂活性保持稳定，整体增强了复合材料eCO₂RR的性能。     

Modulation of metal-azolate frameworks for the tunable release of encapsulated glycosaminoglycans

Glycosaminoglycans (GAGs) are biomacromolecules necessary for the regulation of different biological functions. In medicine, GAGs are important commercial therapeutics widely used for the treatment of thrombosis, inflammation, osteoarthritis and wound healing. However, protocols for the encapsulation of GAGs in MOFs carriers are not yet available. Here, we successfully encapsulated GAG-based clinical drugs (heparin, hyaluronic acid, chondroitin sulfate, dermatan sulfate) and two new biotherapeutics in preclinical stage (GM-1111 and HepSYL proteoglycan) in three different pH-responsive metal-azolate frameworks (ZIF-8, ZIF-90, and MAF-7). The resultant GAG@MOF biocomposites present significant differences in terms of crystallinity, particle size, and spatial distribution of the cargo, which influences the drug-release kinetics upon applying an acidic stimulus. For a selected system, heparin@MOF, the released therapeutic retained its antithrombotic activity while the MOF shell effectively protects the drug from heparin lyase. By using different MOF shells, the present approach enables the preparation of GAG-based biocomposites with tunable properties such as encapsulation efficiency, protection and release.

Clinical and pre-clinical GAG-based biotherapeutics were encapsulated within three metal-azolate frameworks (ZIF-8, ZIF-90, and MAF-7). The resulting MOF biocomposites show different loading capacity, biopreservation properties and release profiles.     

A Novel of PTA/ZIF-8@Cellulose Aerogel Composite Materials for Efficient Photocatalytic Degradation of Organic Dyes in Water

A novel PTA/ZIF-8@CA composite material (PTA = phosphotungstic acid; CA = cellulose aerogel) with multilayer three-dimensional network structure was synthesized with cellulose aerogel as the framework and MOFs as the filler. The results showed that the degradation rates of methylene blue at δ = 10 ppm reached 99.8 % respectively in 30 min under the conditions of PTA/ZIF-8@CA input amount of 0.6 g · L^–1 and pH = 5. The degradation rate of rhodamine B at δ = 10 ppm reached 99.7 % in 60 min. This shows that PTA/ZIF-8@CA has excellent degradation efficiency and short-term performance. In addition, after 5 photocatalytic cycles, the degradation rates of methylene blue and rhodamine B by PTA/ZIF-8@CA were still 83.0 % and 82.5 %, respectively, reflecting that PTA/ZIF-8@CA has terrific photocatalysis stability.     

One-step fabrication of ZIF-8/polymer composite spheres by a phase inversion method for gas adsorption

This paper reports a phase inversion method for the preparation of macroporous polysulfone (PS) composite spheres through a single orifice spinneret. Surfactant F127 was pre-added in the polymer solution as a surface pore-forming agent, and different amount of zeolitic imidazolate framework-8 (ZIF-8) particles were incorporated to form the ZIF-8/polysulfone (ZIF-8/PS)-composite spheres. ZIF-8 and polymer acted as the adsorbent and binder in the final composite spheres, respectively. The fabrication conditions, such as the types of the surfactant, the amount of the surfactant, and ZIF-8 added in the polymer solution, were investigated. Nitrogen and carbon dioxide sorption analysis indicated the ZIF-8/PS composite spheres had similar properties as the pure ZIF-8 particles, and the active sites of ZIF-8 in the polymer composites were well exposed. The composite spheres exhibited advantages of easy handling and recycling over ZIF-8 particles, and this phase inversion method can be extended to prepare other polymer composite spheres.     

In Situ Enzyme Immobilization with Oxygen-Sensitive Luminescent Metal–Organic Frameworks to Realize “All-in-One” Multifunctions

Metal–organic frameworks (MOFs) for enzyme immobilization have already shown superior tunable and designable characteristics, however, their diverse responsive properties have rarely been exploited. In this work we integrated a responsive MOF into a MOF–enzyme composite with the purpose of designing an “all-in-one” multifunctional composite with catalytic and luminescence functions incorporated into a single particle. As a proof-of-concept, glucose oxidase (GOx) was encapsulated in situ within an oxygen (O₂)-sensitive, noble-metal-free, luminescent Cu^I triazolate framework (MAF-2), denoted as GOx@MAF-2. Owing to the rigid scaffold of MAF-2 and confinement effect, the GOx@MAF-2 composite showed significantly improved stability (shelf life of 60 days and heat resistance up to 80 °C) as well as good selectivity and recyclability. More importantly, owing to the O₂ sensitivity of MAF-2, the GOx@MAF-2 composite exhibited a rapid and reversible response towards dissolved O₂, thereby allowing direct and ratiometric sensing of glucose without the need for chromogenic substrates, cascade enzymatic reactions, or electrode systems. High sensitivity with a detection limit of 1.4 μm glucose was achieved, and the glucose levels in human sera were accurately determined. This strategy has led to a new application for MOFs that can be facilely extended to other MOF–enzyme composites due to the multifunctionality of MOFs.