Organophosphate Detoxification and Acetylcholinesterase Reactivation Triggered by Zeolitic Imidazolate Framework Structural Degradation.

Organophosphate (OP) toxicity is related to inhibition of acetylcholinesterase (AChE) activity, which plays a key role in the neurotransmission process. In this work, we report the ability of different zinc zeolitic imidazolate frameworks (ZIFs) to behave as potential antidotes against OP poisoning. The Zn-L coordination bond (L = purine, benzimidazole, imidazole, or 2-methylimidazole) is sensitive to the G-type nerve agent model compounds diisopropylfluorophosphate (DIFP) and diisopropylchlorophosphate, leading to P-X (X = F or Cl) bond breakdown into nontoxic diisopropylphosphate. P-X hydrolysis is accompanied by ZIF structural degradation (Zn-imidazolate bond hydrolysis), with the concomitant release of the imidazolate linkers and zinc ions representing up to 95% of ZIF particle dissolution. The delivered imidazolate nucleophilic attack on the OP@AChE adduct gives rise to the recovery of AChE enzymatic function. P-X bond breakdown, ZIF structural degradation, and AChE reactivation are dependent on imidazolate linker nucleophilicity, framework topology, and particle size. The best performance is obtained for 20 nm nanoparticles (NPs) of Zn(2-methylimidazolate)2 (sod ZIF-8) exhibiting a DIFP degradation half-life of 2.6 min and full recovery of AChE activity within 1 h. 20 nm sod ZIF-8 NPs are not neurotoxic, as proven by in vitro neuroblastoma cell culture viability tests.

Polymorphism and orientation control of copper-dicarboxylate metal-organic framework thin films through vapour- and liquid-phase growth.

Precise control over the crystalline phase and crystallographic orientation within thin films of metal-organic frameworks (MOFs) is highly desirable. Here, we report a comparison of the liquid- and vapour-phase film deposition of two copper-dicarboxylate MOFs starting from an oriented metal hydroxide precursor. X-ray diffraction revealed that the vapour- or liquid-phase reaction of the linker with this precursor results in different crystalline phases, morphologies, and orientations. Pole figure analysis showed that solution-based growth of the MOFs follows the axial texture of the metal hydroxide precursor, resulting in heteroepitaxy. In contrast, the vapour-phase method results in non-epitaxial growth with uniplanar texture only.

Targeting telomerase utilizing zeolitic imidazole frameworks as non-viral gene delivery agents across different cancer cell types.

Telomerase, a ribonucleoprotein coded by the hTERT gene, plays an important role in cellular immortalization and carcinogenesis. hTERT is a suitable target for cancer therapeutics as its activity is highly upregulated in most of cancer cells but absent in normal somatic cells. Here, by employing the two Metal-Organic Frameworks (MOFs), viz. ZIF-C and ZIF-8, based biomineralization we encapsulate Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)/Cas9 plasmid system that targets hTERT gene (CrhTERT) in cancer cells. When comparing the two biocomposites, ZIF-C shows the better loading capacity and cell viability. The loaded plasmid in ZIF-C is highly protected against enzymatic degradation. CrhTERT@ZIF-C is efficiently endocytosed by cancer cells and the subcellular release of CrhTERT leads to telomerase knockdown. The resultant inhibition of hTERT expression decreases cellular proliferation and causing cancer cell death. Furthermore, hTERT knockdown shows a significant reduction in tumour metastasis and alters protein expression. Collectively we show the high potential of ZIF-C-based biocomposites as a promising general tool for gene therapy of different types of cancers.

Fabrication of 3D Oriented MOF Micropatterns with Anisotropic Fluorescent Properties.

Micropatterning crystalline materials with oriented pores is necessary for the fabrication of devices with anisotropic properties. Crystalline and porous metal-organic frameworks (MOFs) are ideal materials as their chemical and structural mutability enables precise tuning of functional properties for applications ranging from microelectronics to photonics. Herein, a patternable oriented MOF film is designed: by using a photomask under X-ray exposure, the MOF film decomposes in the irradiated areas, remaining intact in the unexposed regions. The MOF film acts simultaneously as a resist and as functional porous material. While the heteroepitaxial growth from aligned Cu(OH)2 nanobelts is used to deposit oriented MOF films, the sensitivity to radiation is achieved by integrating a brominated dicarboxylate ligand (Br2 BDC) into a copper-based MOF Cu2 L2 DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane; L = BDC/Br2 BDC). The lithographed samples act as diffraction gratings upon irradiation with a laser, thus confirming the quality of the extended MOF micropattern. Furthermore, the oriented MOF patterns are functionalized with fluorescent dyes. As a result, by rotating the polarization angle of the laser excitation, the alignment of the dye in the MOF is demonstrated. By controlling the functional response to light, this MOF patterning protocol can be used for the microfabrication of optical components for photonic devices.

App-based quantification of crystal phases and amorphous content in ZIF biocomposites.

The performance of zeolitic imidazolate frameworks (ZIFs) as protective hosts for proteins in drug delivery or biocatalysis strongly depends on the type of crystalline phase used for the encapsulation of the biomacromolecule (biomacromolecule@ZIF). Therefore, quantifying the different crystal phases and the amount of amorphous content of ZIFs is becoming increasingly important for a better understanding of the structure-property relationship. Typically, crystalline ZIF phases are qualitatively identified from diffraction patterns. However, accurate phase examinations are time-consuming and require specialized expertise. Here, we propose a calibration procedure (internal standard ZrO2) for the rapid and quantitative analysis of crystalline and amorphous ZIF phases from diffraction patterns. We integrated the procedure into a user-friendly web application, named ZIF Phase Analysis, which facilitates ZIF-based data analysis. As a result, it is now possible to quantify i) the relative amount of various common crystal phases (sodalite, diamondoid, ZIF-CO3-1, ZIF-EC-1, U12 and ZIF-L) in biomacromolecule@ZIF biocomposites based on Zn2+ and 2-methylimidazole (HmIM) and ii) the crystalline-to-amorphous ratio. This new analysis tool will advance the research on ZIF biocomposites for drug delivery and biocatalysis.

Unraveling the timescale of the structural photo-response within oriented metal-organic framework films.

Fundamental knowledge on the intrinsic timescale of structural transformations in photo-switchable metal-organic framework films is crucial to tune their switching performance and to facilitate their applicability as stimuli-responsive materials. In this work, for the first time, an integrated approach to study and quantify the temporal evolution of structural transformations is demonstrated on an epitaxially oriented DMOF-1-on-MOF film system comprising azobenzene in the DMOF-1 pores (DMOF-1/AB). We employed time-resolved Grazing Incidence Wide-Angle X-Ray Scattering measurements to track the structural response of the DMOF-1/AB film upon altering the length of the azobenzene molecule by photo-isomerization (trans-to-cis, 343 nm; cis-to-trans, 450 nm). Within seconds, the DMOF-1/AB response occurred fully reversible and over several switching cycles by cooperative photo-switching of the oriented DMOF-1/AB crystallites as confirmed further by infrared measurements. Our work thereby suggests a new avenue to elucidate the timescales and photo-switching characteristics in structurally responsive MOF film systems.

Combining a Genetically Engineered Oxidase with Hydrogen-Bonded Organic Frameworks (HOFs) for Highly Efficient Biocomposites.

Enzymes incorporated into hydrogen-bonded organic frameworks (HOFs) via bottom-up synthesis are promising biocomposites for applications in catalysis and sensing. Here, we explored synthetic incorporation of d-amino acid oxidase (DAAO) with the metal-free tetraamidine/tetracarboxylate-based BioHOF-1 in water. N-terminal enzyme fusion with the positively charged module Zbasic2 strongly boosted the loading (2.5-fold; ≈500 mg enzyme gmaterial-1 ) and the specific activity (6.5-fold; 23 U mg-1 ). The DAAO@BioHOF-1 composites showed superior activity with respect to every reported carrier for the same enzyme and excellent stability during catalyst recycling. Further, extension to other enzymes, including cytochrome P450 BM3 (used in the production of high-value oxyfunctionalized compounds), points to the versatility of genetic engineering as a strategy for the preparation of biohybrid systems with unprecedented properties.

Self-Assembly of Oriented Antibody-Decorated Metal-Organic Framework Nanocrystals for Active-Targeting Applications.

Antibody (Ab)-targeted nanoparticles are becoming increasingly important for precision medicine. By controlling the Ab orientation, targeting properties can be enhanced; however, to afford such an ordered configuration, cumbersome chemical functionalization protocols are usually required. This aspect limits the progress of Abs-nanoparticles toward nanomedicine translation. Herein, a novel one-step synthesis of oriented monoclonal Ab-decorated metal-organic framework (MOF) nanocrystals is presented. The crystallization of a zinc-based MOF, Zn2 (mIM)2 (CO3 ), from a solution of Zn2+ and 2-methylimidazole (mIM), is triggered by the fragment crystallizable (Fc) region of the Ab. This selective growth yields biocomposites with oriented Abs on the MOF nanocrystals (MOF*Ab): the Fc regions are partially inserted within the MOF surface and the antibody-binding regions protrude from the MOF surface toward the target. This ordered configuration imparts antibody-antigen recognition properties to the biocomposite and shows preserved target binding when compared to the parental antibodies. Next, the biosensing performance of the system is tested by loading MOF*Ab with luminescent quantum dots (QD). The targeting efficiency of the QD-containing MOF*Ab is again, fully preserved. The present work represents a simple self-assembly approach for the fabrication of antibody-decorated MOF nanocrystals with broad potential for sensing, diagnostic imaging, and targeted drug delivery.

On the completeness of three-dimensional electron diffraction data for structural analysis of metal-organic frameworks.

Three-dimensional electron diffraction (3DED) has been proven as an effective and accurate method for structure determination of nano-sized crystals. In the past decade, the crystal structures of various new complex metal-organic frameworks (MOFs) have been revealed by 3DED, which has been the key to understand their properties. However, due to the design of transmission electron microscopes (TEMs), one drawback of 3DED experiments is the limited tilt range of goniometers, which often leads to incomplete 3DED data, particularly when the crystal symmetry is low. This drawback can be overcome by high throughput data collection using continuous rotation electron diffraction (cRED), where data from a large number of crystals can be collected and merged. Here, we investigate the effects of improving completeness on structural analysis of MOFs. We use ZIF-EC1, a zeolitic imidazolate framework (ZIF), as an example. ZIF-EC1 crystallizes in a monoclinic system with a plate-like morphology. cRED data of ZIF-EC1 with different completeness and resolution were analyzed. The data completeness increased to 92.0% by merging ten datasets. Although the structures could be solved from individual datasets with a completeness as low as 44.5% and refined to a high precision (better than 0.04 Å), we demonstrate that a high data completeness could improve the structural model, especially on the electrostatic potential map. We further discuss the strategy adopted during data merging. We also show that ZIF-EC1 doped with cobalt can act as an efficient electrocatalyst for oxygen reduction reactions.

Stabilization of supramolecular membrane protein-lipid bilayer assemblies through immobilization in a crystalline exoskeleton.

Artificial native-like lipid bilayer systems constructed from phospholipids assembling into unilamellar liposomes allow the reconstitution of detergent-solubilized transmembrane proteins into supramolecular lipid-protein assemblies called proteoliposomes, which mimic cellular membranes. Stabilization of these complexes remains challenging because of their chemical composition, the hydrophobicity and structural instability of membrane proteins, and the lability of interactions between protein, detergent, and lipids within micelles and lipid bilayers. In this work we demonstrate that metastable lipid, protein-detergent, and protein-lipid supramolecular complexes can be successfully generated and immobilized within zeolitic-imidazole framework (ZIF) to enhance their stability against chemical and physical stressors. Upon immobilization in ZIF bio-composites, blank liposomes, and model transmembrane metal transporters in detergent micelles or embedded in proteoliposomes resist elevated temperatures, exposure to chemical denaturants, aging, and mechanical stresses. Extensive morphological and functional characterization of the assemblies upon exfoliation reveal that all these complexes encapsulated within the framework maintain their native morphology, structure, and activity, which is otherwise lost rapidly without immobilization.

High-Throughput Electron Diffraction Reveals a Hidden Novel Metal-Organic Framework for Electrocatalysis.

Metal-organic frameworks (MOFs) are known for their versatile combination of inorganic building units and organic linkers, which offers immense opportunities in a wide range of applications. However, many MOFs are typically synthesized as multiphasic polycrystalline powders, which are challenging for studies by X-ray diffraction. Therefore, developing new structural characterization techniques is highly desired in order to accelerate discoveries of new materials. Here, we report a high-throughput approach for structural analysis of MOF nano- and sub-microcrystals by three-dimensional electron diffraction (3DED). A new zeolitic-imidazolate framework (ZIF), denoted ZIF-EC1, was first discovered in a trace amount during the study of a known ZIF-CO3 -1 material by 3DED. The structures of both ZIFs were solved and refined using 3DED data. ZIF-EC1 has a dense 3D framework structure, which is built by linking mono- and bi-nuclear Zn clusters and 2-methylimidazolates (mIm- ). With a composition of Zn3 (mIm)5 (OH), ZIF-EC1 exhibits high N and Zn densities. We show that the N-doped carbon material derived from ZIF-EC1 is a promising electrocatalyst for oxygen reduction reaction (ORR). The discovery of this new MOF and its conversion to an efficient electrocatalyst highlights the power of 3DED in developing new materials and their applications.

Metal-Organic Framework-Based Enzyme Biocomposites.

Because of their efficiency, selectivity, and environmental sustainability, there are significant opportunities for enzymes in chemical synthesis and biotechnology. However, as the three-dimensional active structure of enzymes is predominantly maintained by weaker noncovalent interactions, thermal, pH, and chemical stressors can modify or eliminate activity. Metal-organic frameworks (MOFs), which are extended porous network materials assembled by a bottom-up building block approach from metal-based nodes and organic linkers, can be used to afford protection to enzymes. The self-assembled structures of MOFs can be used to encase an enzyme in a process called encapsulation when the MOF is synthesized in the presence of the biomolecule. Alternatively, enzymes can be infiltrated into mesoporous MOF structures or surface bound via covalent or noncovalent processes. Integration of MOF materials and enzymes in this way affords protection and allows the enzyme to maintain activity in challenge conditions (e.g., denaturing agents, elevated temperature, non-native pH, and organic solvents). In addition to forming simple enzyme/MOF biocomposites, other materials can be introduced to the composites to improve recovery or facilitate advanced applications in sensing and fuel cell technology. This review canvasses enzyme protection via encapsulation, pore infiltration, and surface adsorption and summarizes strategies to form multicomponent composites. Also, given that enzyme/MOF biocomposites straddle materials chemistry and enzymology, this review provides an assessment of the characterization methodologies used for MOF-immobilized enzymes and identifies some key parameters to facilitate development of the field.

Can 3D electron diffraction provide accurate atomic structures of metal-organic frameworks?

Many framework materials such as metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) are synthesized as polycrystalline powders, which are too small for structure determination by single crystal X-ray diffraction (SCXRD). Here, we show that a three-dimensional (3D) electron diffraction method, namely continuous rotation electron diffraction (cRED), can be used for ab initio structure determination of such materials. As an example, we present the complete structural analysis of a biocomposite, denoted BSA@ZIF-CO3-1, in which Bovine Serum Albumin (BSA) was encapsulated in a zeolitic imidazolate framework (ZIF). Low electron dose was combined with ultrafast cRED data collection to minimize electron beam damage to the sample. We demonstrate that the atomic structure obtained by cRED is as reliable and accurate as that obtained by single crystal X-ray diffraction. The high accuracy and fast data collection open new opportunities for investigation of cooperative phenomena in framework structures at the atomic level.

ZIF-C for targeted RNA interference and CRISPR/Cas9 based gene editing in prostate cancer.

Gene therapy is highly suited for prostate cancer (PC). Metal-organic-frameworks (MOFs) are potential gene delivery systems. Target-specific cytoplasmic and nuclear knockdown in host gene expression using ZIF-C is shown for the first time through RNAi and CRISPR/Cas9 based gene editing in PC cells. A green tea phytochemical coating enhances intracellular delivery.

Postsynthetic Metalated MOFs as Atomically Dispersed Catalysts for Hydroformylation Reactions.

A manganese-based metal-organic framework with dipyrazole ligands has been metalated with atomically dispersed Rh and Co species and used as a catalyst for the hydroformylation of styrene. The Rh-based materials exhibited excellent conversion at 80 °C with complete chemoselectivity, high selectivity for the branched aldehyde, high recyclability, and negligible metal leaching.

Fatty acids as biomimetic replication agents for luminescent metal-organic framework patterns.

Luminescent metal-organic frameworks (MOFs) are known to spontaneously self-assemble on human fingerprints. Here, we investigate the different chemical components of fingerprints and determine that MOF growth is predominantly induced by insoluble fatty acids. This finding shows that these simple biomolecules can be employed for the precise positioning of luminescent MOFs.

Continuous-Flow Synthesis of ZIF-8 Biocomposites with Tunable Particle Size.

Zeolitic imidazolate framework (ZIF) biocomposites show the capacity to protect and deliver biotherapeutics. To date, the progress in this research area is based on laboratory batch methods. Now, the first continuous flow synthetic method is presented for the encapsulation of a model protein (bovine serum albumin, BSA) and a clinical therapeutic (α1-antitrypsin, AAT) in ZIF-8. The in situ kinetics of nucleation, growth, and crystallization of BSA@ZIF-8 were studied by small-angle X-ray scattering. By controlling the injection time of ethanol, the particle growth could be quenched by ethanol-induced crystallization from amorphous particles to ZIF-8 crystals. The particle size of the biocomposite was tuned in the 40-100 nm range by varying residence time prior to introduction of ethanol. As a proof-of-concept, this procedure was used for the encapsulation of AAT in ZIF-8. Upon release of the biotherapeutic from the composite, the trypsin inhibitor function of AAT was preserved.

Enzyme Encapsulation in a Porous Hydrogen-Bonded Organic Framework.

Protection of biological assemblies is critical to applications in biotechnology, increasing the durability of enzymes in biocatalysis or potentially stabilizing biotherapeutics during transport and use. Here we show that a porous hydrogen-bonded organic framework (HOF) constructed from water-soluble tetra-amidinium (1·Cl4) and tetracarboxylate (2) building blocks can encapsulate and stabilize biomolecules to elevated temperature, proteolytic and denaturing agents, and extend the operable pH range for catalase activity. The HOF, which readily retains water within its framework structure, can also protect and retain the activity of enzymes such as alcohol oxidase, that are inactive when encapsulated within zeolitic imidazolate framework (ZIF) materials. Such HOF coatings could provide valid alternative materials to ZIFs: they are metal free, possess larger pore apertures, and are stable over a wider, more biologically relevant pH range.

Vapour-phase deposition of oriented copper dicarboxylate metal-organic framework thin films.

Copper dicarboxylate metal-organic framework films are deposited via chemical vapour deposition. Uniform films of CuBDC and CuCDC with an out-of-plane orientation and accessible porosity are obtained from the reaction of Cu and CuO with vaporised dicarboxylic acid linkers.

Enhanced Activity of Enzymes Encapsulated in Hydrophilic Metal-Organic Frameworks.

Encapsulation of biomacromolecules in metal-organic frameworks (MOFs) can preserve biological functionality in harsh environments. Despite the success of this approach, termed biomimietic mineralization, limited consideration has been given to the chemistry of the MOF coating. Here, we show that enzymes encapsulated within hydrophilic MAF-7 or ZIF-90 retain enzymatic activity upon encapsulation and when exposed to high temperatures, denaturing or proteolytic agents, and organic solvents, whereas hydrophobic ZIF-8 affords inactive catalase and negligible protection to urease.