Trypsin-Immobilized Metal-Organic Framework as a Biocatalyst In Proteomics Analysis

Buffer Effects in Zirconium-Based UiO Metal-Organic Frameworks (MOFs) That Influence Enzyme Immobilization and Catalytic Activity in Enzyme/MOF Biocatalysts

Novel biocatalysts that feature enzymes immobilized onto solid supports have recently become a major research focus in an effort to create more sustainable and greener chemistries in catalysis. Many of these novel biocatalyst systems feature enzymes immobilized onto metal-organic frameworks (MOFs), which have been shown to increase enzyme activity, stability, and recyclability in industrial processes. While the strategies used for immobilizing enzymes onto MOFs can vary, the conditions always require a buffer to maintain the functionality of the enzymes during immobilization. This report brings attention to critical buffer effects important to consider when developing enzyme/MOF biocatalysts, specifically for buffering systems containing phosphate ions. A comparative analysis of different enzyme/MOF biocatalysts featuring horseradish peroxidase and/or glucose oxidase immobilized onto the MOFs UiO-66, UiO-66-NH₂, and UiO-67 using a noncoordinate buffering system (MOPSO buffer) and a phosphate buffering system (PBS) show that phosphate ions can have an inhibitory effect. Previous studies utilizing phosphate buffers for enzyme immobilization onto MOFs have shown Fourier transform infrared (FT-IR) spectra that have been assigned stretching frequencies associated with enzymes after immobilization. Analyses and characterizations using zeta potential measurements, scanning electron microscopy, Brunauer-Emmett-Teller surface area, powder X-ray diffraction, Energy Dispersive X-ray Spectroscopy, and FT-IR show concerning differences in enzyme loading and activity based on the buffering system used during immobilization.

Nanobiohybrids: Synthesis strategies and environmental applications from micropollutants sensing and removal to global warming mitigation

Micropollutants contamination and global warming are critical environmental issues that require urgent attention due to natural and anthropogenic activities posing serious threats to human health and ecosystems. However, traditional technologies (such as adsorption, precipitation, biodegradation, and membrane separation et al.) are facing challenges of low utilization efficiency of oxidants, poor selectivity, and complex in-situ monitoring operations. To address these technical bottlenecks, nanobiohybrids, synthesized by interfacing the nanomaterials and biosystems, have recently emerged as eco-friendly technologies. In this review, we summarize the synthesis approaches of nanobiohybrids and their utilization as emerging environmental technologies for addressing environmental problems. Studies demonstrate that enzymes, cells, and living plants can be integrated with a wide range of nanomaterials including reticular frameworks, semiconductor nanoparticles and single-walled carbon nanotubes. Moreover, nanobiohybrids demonstrate excellent performance for micropollutant removal, carbon dioxide conversion, and sensing of toxic metal ions and organic micropollutants. Therefore, nanobiohybrids are expected to be environmental friendly, efficient, and cost-effective techniques for addressing environmental micropollutants issues and mitigating global warming, benefiting both humans and ecosystems alike.

Covalent Organic Framework Cladding on Peptide-Amphiphile-Based Biomimetic Catalysts

Peptide-based biomimetic catalysts are promising materials for efficient catalytic activity in various biochemical transformations. However, their lack of operational stability and fragile nature in non-aqueous media limit their practical applications. In this study, we have developed a cladding technique to stabilize biomimetic catalysts within porous covalent organic framework (COF) scaffolds. This methodology allows for the homogeneous distribution of peptide nanotubes inside the COF (TpAzo and TpDPP) backbone, creating strong noncovalent interactions that prevent leaching. We synthesized two different peptide-amphiphiles, C₁₀FFVK and C₁₀FFVR, with lysine (K) and arginine (R) at the C-termini, respectively, which formed nanotubular morphologies. The C₁₀FFVK peptide-amphiphile nanotubes exhibit enzyme-like behavior and efficiently catalyze C-C bond cleavage in a buffer medium (pH 7.5). We produced nanotubular structures of TpAzo-C₁₀FFVK and TpDPP-C₁₀FFVK through COF cladding by using interfacial crystallization (IC). The peptide nanotubes encased in the COF catalyze C-C bond cleavage in a buffer medium as well as in different organic solvents (such as acetonitrile, acetone, and dichloromethane). The TpAzo-C₁₀FFVK catalyst, being heterogeneous, is easily recoverable, enabling the reaction to be performed for multiple cycles. Additionally, the synthesis of TpAzo-C₁₀FFVK thin films facilitates catalysis in flow. As control, we synthesized another peptide-amphiphile, C₁₀FFVR, which also forms tubular assemblies. By depositing TpAzo COF crystallites on C₁₀FFVR nanotubes through IC, we produced TpAzo-C₁₀FFVR nanotubular structures that expectedly did not show catalysis, suggesting the critical role of the lysines in the TpAzo-C₁₀FFVK.

Post-Synthetic Surface Modification of Metal-Organic Frameworks and Their Potential Applications

Metal-organic frameworks (MOFs) are porous hybrid materials with countless potential applications. Most of these rely on their porous structure, tunable composition, and the possibility of incorporating and expanding their functions. Although functionalization of the inner surface of MOF crystals has received considerable attention in recent years, methods to functionalize selectively the outer crystal surface of MOFs are developed to a lesser extent, despite their importance. This article summarizes different types of post-synthetic modifications and possible applications of modified materials such as: catalysis, adsorption, drug delivery, mixed matrix membranes, and stabilization of porous liquids.

Nanoscale MOFs in nanomedicine applications: from drug delivery to therapeutic agents

Metal-organic frameworks (MOFs) hold great promise for widespread applications in biomedicine and nanomedicine. MOFs are one of the most fascinating nanocarriers for drug delivery, benefiting from their high porosity and facile modification. Furthermore, the tailored components of MOFs can be therapeutic agents for various treatments, including drugs as organic ligands of MOFs, active metal as central metal ions of MOFs, and their combinations as carrier-free MOF-based nanodrug. In this review, the advances in delivery systems and applications as therapeutic agents for nanoscale MOF-based materials are summarized. The challenges of MOFs in clinical translation and the future directions in the field of MOFs therapy are also discussed. We hope that more researchers will focus their attention on advancing and translating MOF-based nanodrugs into pre-clinical and clinical applications.

Comparison of covalent and in situ immobilization of Candida antarctica lipase A on a flexible nanoporous material

In this study, Candida antarctica lipase A, which has a unique applicability for the conversion of highly branched and bulky substrates, was subjected to immobilization on the flexible nanoporous MIL-53(Fe) by two approaches: covalent coupling and in situ immobilization method. The pre-synthesized support under ultrasound irradiation was incubated with N,N-dicyclohexylcarbodiimide to mediate the covalent attachment between the carboxylic groups on the support surface and amino groups of enzyme molecules. The in situ immobilization in which the enzyme molecules directly were embedded into the metal-organic framework was performed under mild operating conditions in a facile one-step manner. Both immobilized derivatives of the enzyme were characterized by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, FT-IR spectra, and energy-dispersive X-ray spectroscopy. In the in situ immobilization method, the enzyme molecules were efficiently encapsulated within the support with a high loading capacity (220 ± 5 mg/g support). On the other hand, the covalent attachment resulted in immobilizing much lower concentrations of the enzyme (20 ± 2.2 mg/g support). Although both immobilized derivatives of lipase showed broader pH and temperature tolerance relative to the soluble enzyme, the biocatalyst, which was prepared through in situ method, was more stable at elevated temperatures than the covalently immobilized lipase. Furthermore, in situ immobilized derivatives of Candida antarctica lipase A could be efficiently reused for at least eight cycles (> 70% of retained activity). In contrast, its covalently immobilized counterpart showed a drastic decrease in activity after five cycles (less than 10% of retained activity at the end of 6 rounds).

Enzyme-Linked Metal Organic Frameworks for Biocatalytic Degradation of Antibiotics

Metal organic frameworks (MOFs) are multi-dimensional network of crystalline material held together by bonding of metal atoms and organic ligands. Owing to unique structural, chemical, and physical properties, MOFs has been used for enzyme immobilization to be employed in different catalytic process, including catalytic degradation of antibiotics. Immobilization process other than providing large surface provides enzyme with enhanced stability, catalytic activity, reusability, and selectivity. There are various approaches of enzyme immobilization over MOFs including physical adsorption, chemical bonding, diffusion and in situ encapsulation. In situ encapsulation is one the best approach that provides extra stability from unfolding and denaturation in harsh industrial conditions. Presence of antibiotic in environment is highly damaging for human in particular and ecosystem in general. Different methods such as ozonation, oxidation, chlorination and catalysis are available for degradation or removal of antibiotics from environment, however these are associated with several issues. Contrary to these, enzyme immobilized MOFs are novel system to be used in catalytic degradation of antibiotics. Enzyme@MOFs are more stable, reusable and more efficient owing to additional support of MOFs to natural enzymes in well-established process of photocatalysis for degradation of antibiotics aimed at environmental remediation. Prime focus of this review is to present catalytic degradation of antibiotics by enzyme@MOFs while outlining their synthetics approaches, characterization, and mechanism of degradation. Furthermore, this review highlights the significance of enzyme@MOFs system for antibiotics degradation in particular and environmental remediation in general. Current challenges and future perspective of research in this field are also outlined along with concluding comments.

Graphical Abstract

A comprehensive review on bio-mimicked multimolecular frameworks and supramolecules as scaffolds for enzyme immobilization

Immobilization depicts a propitious route to optimize the catalytic performances, efficient recovery, minimizing autocatalysis, and also augment the stabilities of enzymes, particularly in unnatural environments. In this opinion, supramolecules and multimolecular frameworks have captivated immense attention to achieve profound controllable interactions between enzyme molecules and well-defined natural or synthetic architectures to yield protein bioconjugates with high accessibility for substrate binding and enhanced enantioselectivities. This scholastic review emphasizes the possibilities of associating multimolecular complexes with biological entities via several types of interactions, namely covalent interactions, host-guest complexation, π - π ${\rm{\pi }}-{\rm{\pi }}$ interactions, intra/inter hydrogen bondings, electrostatic interactions, and so forth offers remarkable applications for the modulations of enzymes. The potential synergies between artificial supramolecular structures and biological systems are the primary concern of this pedagogical review. The majority of the research primarily focused on the dynamic biomolecule-responsive supramolecular assemblages and multimolecular architectures as ideal platforms for the recognition and modulation of proteins and cells. Embracing sustainable green demeanors of enzyme immobilizations in a quest to reinforce site-selectivity, catalytic efficiency, and structural integrality of enzymes are the contemporary requirements of the biotechnological sectors that instigate the development of novel biocatalytic systems.

Immobilization of Lipase in Cu-BTC MOF with Enhanced Catalytic Performance for Resolution of N-hydroxymethyl Vince Lactam

Metal-organic frameworks (MOFs) can be used as the immobilization carriers to protect the physicochemical properties of enzymes and improve their catalytic performance. Herein, we report an in situ co-precipitation method to immobilize lipase from Candida sp. 99-125 in Cu-BTC MOF (BTC = 1, 3, 5-benzene tricarboxylic acid, H₃BTC). Characterizations of the immobilized lipase (lipase@Cu-BTC) have confirmed the entrapment of lipase molecules in Cu-BTC MOF. The immobilized lipase has been successfully applied for resolving N-hydroxymethyl vince lactam (N-HMVL) and its catalytic activity is five times that of native enzyme. More importantly, we found that Cu-BTC MOF can afford powerful protection for enzyme in nearly dry organic solvent and endow the immobilized lipase with excellent reusability and storage stability. Our present study may widen the application of immobilized enzyme with MOF as the immobilized carrier.

Synthesis and Biomedical Applications of Highly Porous Metal-Organic Frameworks

In this review, aspects of the synthesis, framework topologies, and biomedical applications of highly porous metal-organic frameworks are discussed. The term "highly porous metal-organic frameworks" (HPMOFs) is used to denote MOFs with a surface area larger than 4000 m² g^-1. Such compounds are suitable for the encapsulation of a variety of large guest molecules, ranging from organic dyes to drugs and proteins, and hence they can address major contemporary challenges in the environmental and biomedical field. Numerous synthetic approaches towards HPMOFs have been developed and discussed herein. Attempts are made to categorise the most successful synthetic strategies; however, these are often not independent from each other, and a combination of different parameters is required to be thoroughly considered for the synthesis of stable HPMOFs. The majority of the HPMOFs in this review are of special interest not only because of their high porosity and fascinating structures, but also due to their capability to encapsulate and deliver drugs, proteins, enzymes, genes, or cells; hence, they are excellent candidates in biomedical applications that involve drug delivery, enzyme immobilisation, gene targeting, etc. The encapsulation strategies are described, and the MOFs are categorised according to the type of biomolecule they are able to encapsulate. The research field of HPMOFs has witnessed tremendous development recently. Their intriguing features and potential applications attract researchers' interest and promise an auspicious future for this class of highly porous materials.

Role of Molecular Modification and Protein Folding in the Nucleation and Growth of Protein-Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are a class of porous nanomaterials that have been extensively studied as enzyme immobilization substrates. During in situ immobilization, MOF nucleation is driven by biomolecules with low isoelectric points. Investigation of how biomolecules control MOF self-assembly mechanisms on the molecular level is key to designing nanomaterials with desired physical and chemical properties. Here, we demonstrate how molecular modifications of bovine serum albumin (BSA) with fluorescein isothiocyanate (FITC) can affect MOF crystal size, morphology, and encapsulation efficiency. Final crystal properties are characterized using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), fluorescent microscopy, and fluorescence spectroscopy. To probe MOF self-assembly, in situ experiments were performed using cryogenic transmission electron microscopy (cryo-TEM) and X-ray diffraction (XRD). Biophysical characterization of BSA and FITC-BSA was performed using ζ potential, mass spectrometry, circular dichroism studies, fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The combined data reveal that protein folding and stability within amorphous precursors are contributing factors in the rate, extent, and mechanism of crystallization. Thus, our results suggest molecular modifications as promising methods for fine-tuning protein@MOFs' nucleation and growth.

Confining enzymes in porous organic frameworks: from synthetic strategy and characterization to healthcare applications

Enzymes are a class of natural catalysts with high efficiency, specificity, and selectivity unmatched by their synthetic counterparts and dictate a myriad of reactions that constitute various cascades in living cells. The development of suitable supports is significant for the immobilization of structurally flexible enzymes, enabling biomimetic transformation in the extracellular environment. Accordingly, porous organic frameworks, including metal organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen-bonded organic frameworks (HOFs), have emerged as ideal supports for the immobilization of enzymes because of their structural features including ultrahigh surface area, tailorable porosity, and versatile framework compositions. Specially, organic framework-encased enzymes have shown significant enhancement in stability and reusability, and their tailorable pore opening provides a gatekeeper-like effect for guest sieving, which is beneficial for mimicking intracellular biocatalysis processes. This immobilization technique brings new insight into the development of next-generation enzyme materials and shows huge potential in healthcare applications, such as biomarker diagnosis, biostorage, and cancer and antibacterial therapies. In this review, we describe the state-of-the-art strategies for the structural immobilization of enzymes using the well-explored MOFs and burgeoning COFs and HOFs as scaffolds, with special emphasis on how these porous framework-confined technologies can provide a favorable microenvironment for mimicking natural biocatalysis. Subsequently, advanced characterization techniques for enzyme conformation, the effect of the confined microenvironment on the activity of enzymes, and the emerging healthcare applications will be surveyed.

Emerging advances and current applications of nanoMOF-based membranes for water treatment

Metal-organic frameworks (MOFs) are significantly tunable materials that can be exploited in a wide range of applications. In recent years, a large number of studies have been focused on synthesizing nano-scale MOFs (nanoMOFs), thus taking advantage of these unique materials in various applications, especially those that are only possible at nano-scale. One of the technologies where nanoMOF materials occupy a central role is the membrane technology as one of the most efficient separation techniques. Therefore, numerous reports can be found on the enhancement of the physicochemical properties of polymeric membranes by using nanoMOFs, leading to remarkably improved performance. One of the most considerable applications of these nanoMOF-based membranes is in water treatment systems, because freshwater scarcity is now an undeniable crisis facing humanity. In this in-depth review, the most prominent synthesis and post-synthesis methods for the fabrication of nanoMOFs are initially discussed. Afterwards, different nanoMOF-based composite membranes such as thin-film nanocomposites (TFN) and mixed-matrix membranes (MMM) and their various fabrication methods are reviewed and compared. Then, the impacts of using MOFs-based membranes for water purification through growing metal-organic frameworks crystals on the support materials and utilization of metal-organic frameworks as fillers in mixed matrix membrane (MMM) are highlighted. Finally, a summary of pros and cons of using nanoMOFs in membrane technology for water treatment purposes and clear future prospects and research potentials are presented.

Fragmented α-Amylase into Microporous Metal-Organic Frameworks as Bioreactors

This work presents an efficient and facile strategy to prepare an α-amylase bioreactor. As enzymes are quite large to be immobilized inside metal-organic frameworks (MOFs), the tertiary and quaternary structures of α-amylase were first disrupted using a combination of urea, dithiothreitol (DTT), and iodoacetamide (IAA). After losing its tertiary structure, the unfolded proteins can now penetrate into the microporous MOFs, affording fragmented α-amylase@MOF bioreactors. Among the different MOFs evaluated, UiO-66 gave the most promising potential due to the size-matching effect of the α-helix of the fragmented α-amylase with the pore size of UiO-66. The prepared bioreactor exhibited high yields of small carbohydrate (maltose) even when reused up to 15 times (>80% conversion).

Fast multipoint immobilization of lipase through chiral L-proline on a MOF as a chiral bioreactor

In this paper, we describe the facile preparation of a chiral catalyst by the combination of the amino acid, l-proline (Pro), and the enzyme, porcine pancreas lipase (PPL), immobilized on a microporous metal-organic framework (PPL-Pro@MOF). The multipoint immobilization of PPL onto the MOF is made possible with the aid of Pro, which also provided a chiral environment for enhanced enantioselectivity. The application of the microporous MOF is pivotal in maintaining the catalytic activity of PPL, wherein it prevented the leaching of Pro during the catalytic reaction, leading to the enhanced activity of PPL. The prepared biocatalyst was applied in asymmetric carbon-carbon bond formation, demonstrating the potential of this simple approach for chemical transformations.

Proline-Modified UIO-66 as Nanocarriers to Enhance Candida rugosa Lipase Catalytic Activity and Stability for Electrochemical Detection of Nitrofen

Immobilization can be used to improve the stability of lipases and enhances lipase recovery and reusability, which increases its commercial value and industrial applications. Nevertheless, immobilization frequently causes conformational changes of the lipases, which decrease lipase catalytic activity. in the present work, we synthesized UIO-66 and grafted UIO-66 crystals with proline for immobilization of Candida rugosa lipase (CRL). As indicated by steady-state fluorescence microscopy, grafting of proline onto UIO-66 crystals induced beneficial conformational change in CRL. CRL immobilized on UIO-66/Pro (CRL@UIO-66/Pro) demonstrated higher enzyme activity and better recyclability than that immobilized on UIO-66 (CRL@UIO-66) in both hydrolysis (CRL@UIO-66/Pro: 0.34 U; CRL@UIO-66: 0.15 U) and transesterification (CRL@UIO-66/Pro: 0.93 U; CRL@UIO-66: 0.25 U) reactions. The higher values of k_cat and k_cat/K_m of CRL@UIO-66/Pro also showed that it had better catalytic efficiency as compared to CRL@UIO-66. It is also worth noting that CRL@UIO-66/Pro (0.93 U) demonstrated a much higher transesterification activity as compared to free CRL (0.11 U), indicating that UIO-66/Pro has increased the solvent stability of CRL. Both CRL@UIO-66 and CRL@UIO-66/Pro were also used for the fabrication of biosensors for nitrofen with a wide linear range (0-100 μM), lower limit of detection, and good recovery rate.

Lipase Immobilization on Macroporous ZIF-8 for Enhanced Enzymatic Biodiesel Production

Immobilization of enzyme on metal-organic frameworks (MOFs) has drawn increasing interest owing to their many well-recognized characteristics. However, the pore sizes of MOFs (mostly micropores and mesopores) limit their application for enzyme immobilization to a great extent owing to the large size of enzyme molecules. Synthesis of MOFs with macropores would therefore solve this problem, typically encountered with conventional MOFs. In this work, macroporous zeolitic imidazolate frameworks (ZIF-8), referred to as M-ZIF-8, were synthesized and used for immobilization of Aspergillus niger lipase (ANL). Immobilization efficiency using M-ZIF-8 and enzymatic catalytic performance for biodiesel preparation were investigated. The immobilized ANL on M-ZIF-8 (ANL@M-ZIF-8) showed higher enzymatic activity (6.5-fold), activity recovery (3.8-fold), thermal stability (1.4- and 3.4-fold at 80 and 100 °C, respectively), reusability (after five cycles, 68% of initial activity was maintained), and porosity than ANL on conventional ZIF-8 (ANL/ZIF-8). In addition, by using ANL@M-ZIF-8 for catalyzing a biodiesel production reaction, a higher fatty acid methyl ester yield was achieved.

Harnessing the biocatalytic attributes and applied perspectives of nanoengineered laccases-A review

In the recent past, numerous new types of nanostructured carriers, as support matrices, have been engineered to advance the traditional enzyme immobilization strategies. The current research aimed to develop a robust enzyme-based biocatalytic platform and its effective deployment in the industrial biotechnology sectors at large and catalysis area, in particular, as low-cost biocatalytic systems. Suitable coordination between the target enzyme molecules and surface pendent multifunctional entities of nanostructured carriers has led an effective and significant contribution in myriad novel industrial, biotechnological, and biomedical applications. As compared to the immobilization on planar two-dimensional (2-D) surface, the unique physicochemical, structural and functional attributes of nano-engineered matrices, such as high surface-to-volume ratio, surface area, robust chemical and mechanical stability, surface pendant functional groups, outstanding optical, thermal, and electrical characteristics, resulted in the concentration of the immobilized entity being substantially higher, which is highly requisite from applied bio-catalysis perspective. Besides inherited features, nanostructured materials-based enzyme immobilization aided additional features, such as (1) ease in the preparation or green synthesis route, (2) no or minimal use of surfactants and harsh reagents, (3) homogeneous and well-defined core-shell nanostructures with thick enzyme shell, and (4) nano-size can be conveniently tailored within utility limits, as compared to the conventional enzyme immobilization. Moreover, the growing catalytic needs can be fulfilled by multi-enzymes co-immobilization on these nanostructured materials-based support matrices. This review spotlights the unique structural and functional attributes of several nanostructured materials, including carbon nanotubes, graphene, and its derivate constructs, nanoparticles, nanoflowers, and metal-organic frameworks as robust matrices for laccase immobilization. The later half of the review focuses on the applied perspective of immobilized laccases for the degradation of emergent contaminants, biosensing cues, and lignin deconstruction and high-value products.

Metal-Organic Frameworks for Enzyme Immobilization: Beyond Host Matrix Materials

Enzyme immobilization in metal-organic frameworks (MOFs) as a promising strategy is attracting the interest of scientists from different disciplines with the expansion of MOFs' development. Different from other traditional host materials, their unique strengths of high surface areas, large yet adjustable pore sizes, functionalizable pore walls, and diverse architectures make MOFs an ideal platform to investigate hosted enzymes, which is critical to the industrial and commercial process. In addition to the protective function of MOFs, the extensive roles of MOFs in the enzyme immobilization are being well-explored by making full use of their remarkable properties like well-defined structure, high porosity, and tunable functionality. Such development shifts the focus from the exploration of immobilization strategies toward functionalization. Meanwhile, this would undoubtedly contribute to a better understanding of enzymes in regards to the structural transformation after being hosted in a confinement environment, particularly to the orientation and conformation change as well as the interplay between enzyme and matrix MOFs. In this Outlook, we target a comprehensive review of the role diversities of the host matrix MOF based on the current enzyme immobilization research, along with proposing an outlook toward the future development of this field, including the representatives of potential techniques and methodologies being capable of studying the hosted enzymes.

Facile Synthesis of Enzyme-Embedded Metal-Organic Frameworks for Size-Selective Biocatalysis in Organic Solvent

In situ immobilization of enzyme into metal-organic frameworks (MOFs) is performed through a one-step and facile method. Candida antarctica lipase B (CalB) is directly embedded in zeolitic imidazolate framework (ZIF)-8 by simply mixing an aqueous solution of 2-methylimidazole and zinc nitrate hexahydrate [Zn(NO₃)₂⋅6H₂O] containing CalB at room temperature. Due to the intrinsic micropores of ZIF-8, the obtained CalB@ZIF composite is successfully applied in size-selective transesterification reaction in organic solvent. CalB@ZIF not only shows much higher catalytic activity but also exhibits higher thermal stability than free CalB. Besides, the robust ZIF-8 shell also offers the hybrid composites excellent reusability.

Antibody Targeted Metal-Organic Frameworks for Bioimaging Applications

We report on the availability and chemical utility of primary amines within metal-organic frameworks (MOFs) for cell targeting. Primary amine groups represent one of the most versatile chemical moieties for conjugation to biologically relevant molecules, including antibodies and enzymes. Specifically, we used two different chemical conjugations schemes, utilizing the amino functionality on the organic linker: first, carbodiimide chemistry was used to link the primary amine to available carboxyl groups on the protein neutravidin; second, sulfhydryl cross-linking chemistry was used via Traut's reagent scheme. Importantly, this is the first report that documents this methodology implemented with MOF systems. Finally, the ability of the EpCAM antibody targeted MOFs to bind to a human epithelial cell line (A549), a common target for imaging studies, was confirmed with confocal microscopy.

Metal-Organic Frameworks: A Potential Platform for Enzyme Immobilization and Related Applications

Enzymes, as natural catalysts with remarkable catalytic activity and high region-selectivities, hold great promise in industrial catalysis. However, applications of enzymatic transformation are hampered by the fragility of enzymes in harsh conditions. Recently, metal-organic frameworks (MOFs), due to their high stability and available structural properties, have emerged as a promising platform for enzyme immobilization. Synthetic strategies of enzyme-MOF composites mainly including surface immobilization, covalent linkage, pore entrapment and in situ synthesis. Compared with free enzymes, most immobilized enzymes exhibit enhanced resistance against solvents and high temperatures. Besides, MOFs serving as matrixes for enzyme immobilization show extraordinary superiority in many aspects compared with other supporting materials. The advantages of using MOFs to support enzymes are discussed. To obtain a high enzyme loading capacity and to reduce the diffusion resistance of reactants and products during the reaction, the mesoporous MOFs have been designed and constructed. This review also covers the applications of enzyme-MOF composites in bio-sensing and detection, bio-catalysis, and cancer therapy, which is concerned with interdisciplinary nano-chemistry, material science and medical chemistry. Finally, some perspectives on reservation or enhancement of bio-catalytic activity of enzyme-MOF composites and the future of enzyme immobilization strategies are discussed.

Control of the Porosity in Manganese Trimer-Based Metal-Organic Frameworks by Linker Functionalization

Manganese complexes have attracted significant interest in chemical industries and academic research for their application as catalysts owing to their ability to attain a variety of oxidation states. Generally, sterically bulky ligands are required to isolate molecular homogeneous catalysts in order to prevent decomposition. Herein, we capitalize on the catalytic properties of Mn and circumvent the instability of these complexes through incorporation of Mn-atoms into porous crystalline frameworks, such as metal-organic frameworks (MOFs). MOFs are able to enhance the stability of these catalysts while also providing accessibility to the Mn sites for enhanced reactivity. We solvothermally synthesized two trinuclear Mn-based MOFs, namely [Mn₃O(BDC)₃(H₂O)₃]_n (Mn-MIL-88, where H₂BDC = benzene-1,4-dicarboxylic acid) and [Mn₃O(BDC-Me₄)₃(H₂O)₃]_n (Mn-MIL-88-Me₄, where H₂BDC-Me₄ = 2,3,5,6-tetramethylterephthalic acid). Through comprehensive single-crystal X-ray diffraction, spectroscopic, and magnetic studies, we revealed that both MOFs are in a Mn(II/III) mixed-valence state instead of the commonly observed Mn(III) oxidation state. Furthermore, the use of a methylated linker (BDC-Me₄) allowed access to permanent porosity in Mn-MIL-88-Me₄, which is an analogue of the flexible MIL-88 family, yielding a catalyst for alcohol oxidation.

One-pot synthesis of trypsin-based magnetic metal-organic frameworks for highly efficient proteolysis

Immobilization of enzymes onto metal-organic frameworks (MOFs) through a biomimetic mineralization approach can preserve biological functionality in harsh environments. Despite the success of this approach, the alkaline environment of the reaction system, which is caused by the organic monomers of MOFs, makes it unsuitable for some pH-sensitive enzymes, especially for trypsin. Herein, we reported a facile approach for the one-pot synthesis of trypsin-immobilized magnetic zeolite imidazolate framework-8 (iron oxide@ZIF-8@trypsin), where the growth of ZIF-8 around the citric acid-modified iron oxide and immobilization of trypsin occurred simultaneously when the pH of the reaction system was changed to some extent. With a large specific surface area and a high enzyme loading capacity, the resultant iron oxide@ZIF-8@trypsin exhibited 2.6 times higher enzymatic activity than free trypsin. Moreover, it showed a favourable magnetic response (43 emu g^-1) which made the operation and recycling easy and convenient. In addition, iron oxide@ZIF-8@trypsin could be applied as an immobilized enzyme microreactor (IMER) to rapidly and efficiently digest proteins and complex human serum samples with satisfactory results, showing great promise for application in proteomic analysis.

Co-immobilization of an Enzyme System on a Metal-Organic Framework to Produce a More Effective Biocatalyst

In many respects, enzymes offer advantages over traditional chemical processes due to their decreased energy requirements for function and inherent greener processing. However, significant barriers exist for the utilization of enzymes in industrial processes due to their limited stabilities and inability to operate over larger temperature and pH ranges. Immobilization of enzymes onto solid supports has gained attention as an alternative to traditional chemical processes due to enhanced enzymatic performance and stability. This study demonstrates the co-immobilization of glucose oxidase (GOx) and horseradish peroxidase (HRP) as an enzyme system on Metal-Organic Frameworks (MOFs), UiO-66 and UiO-66-NH2, that produces a more effective biocatalyst as shown by the oxidation of pyrogallol. The two MOFs utilized as solid supports for immobilization were chosen to investigate how modifications of the MOF linker affect stability at the enzyme/MOF interface and subsequent activity of the enzyme system. The enzymes work in concert with activation of HRP through the addition of glucose as a substrate for GOx. Enzyme immobilization and leaching studies showed HRP/GOx@UiO-66-NH2 immobilized 6% more than HRP/GOx@UiO-66, and leached only 36% of the immobilized enzymes over three days in the solution. The enzyme/MOF composites also showed increased enzyme activity in comparison with the free enzyme system: the composite HRP/GOx@UiO-66-NH2 displayed 189 U/mg activity and HRP/GOx@UiO-66 showed 143 U/mg while the free enzyme showed 100 U/mg enzyme activity. This increase in stability and activity is due to the amine group of the MOF linker in HRP/GOx@UiO-66-NH2 enhancing electrostatic interactions at the enzyme/MOF interface, thereby producing the most stable biocatalyst material in solution. The HRP/GOx@UiO-66-NH2 also showed long-term stability in the solid state for over a month at room temperature.

Metal-Organic Framework Nanocarriers for Drug Delivery in Biomedical Applications

Investigation of metal-organic frameworks (MOFs) for biomedical applications has attracted much attention in recent years. MOFs are regarded as a promising class of nanocarriers for drug delivery owing to well-defined structure, ultrahigh surface area and porosity, tunable pore size, and easy chemical functionalization. In this review, the unique properties of MOFs and their advantages as nanocarriers for drug delivery in biomedical applications were discussed in the first section. Then, state-of-the-art strategies to functionalize MOFs with therapeutic agents were summarized, including surface adsorption, pore encapsulation, covalent binding, and functional molecules as building blocks. In the third section, the most recent biological applications of MOFs for intracellular delivery of drugs, proteins, and nucleic acids, especially aptamers, were presented. Finally, challenges and prospects were comprehensively discussed to provide context for future development of MOFs as efficient drug delivery systems.

Hydrophobic pore space constituted in macroporous ZIF-8 for lipase immobilization greatly improving lipase catalytic performance in biodiesel preparation

BACKGROUND

During lipase-mediated biodiesel production, by-product glycerol adsorbing on immobilized lipase is a common trouble that hinders enzymatic catalytic activity in biodiesel production process. In this work, we built a hydrophobic pore space in macroporous ZIF-8 (named as M-ZIF-8) to accommodate lipase so that the generated glycerol would be hard to be adsorbed in such hydrophobic environment. The performance of the immobilized lipase in biodiesel production as well as its characteristics for glycerol adsorption were systematically studied. The PDMS (polydimethylsiloxane) CVD (chemical vapor deposition) method was utilized to get hydrophobic M-ZIF-8-PDMS with hydrophobic macropore space and then ANL (Aspergillus niger lipase) was immobilized on M-ZIF-8 and M-ZIF-8-PDMS by diffusion into the macropores.

RESULTS

ANL@M-ZIF-8-PDMS presented higher enzymatic activity recovery and better biodiesel production catalytic performance compared to ANL@M-ZIF-8. Further study revealed that less glycerol adsorption was observed through the hydrophobic modification, which may attribute to the improved immobilized lipase performance during biodiesel production and ANL@M-ZIF-8-PDMS remained more than 96% activity after five cycles' reuse. Through secondary structure and kinetic parameters' analysis, we found that ANL@M-ZIF-8-PDMS had lower extent of protein aggregation and twice catalytic efficiency (V _max/K _m) than ANL@M-ZIF-8.

CONCLUSIONS

Hydrophobic pore space constituted in macroporous ZIF-8 for lipase immobilization greatly improved lipase catalytic performance in biodiesel preparation. The hydrophobic modification time showed negligible influence on the reusability of the immobilized lipase. This work broadened the prospect of immobilization of enzyme on MOFs with some inspiration.

Iron and chromium MOFs as sustainable catalysts for transfer hydrogenation of carbonyl compounds and biomass conversions

Fe and Cr based MOFs (MIL-88B) act as efficient and reusable catalysts for transfer hydrogenation of carbonyl compounds including bio-derived substrates.

Engineering of Nanoscale Coordination Polymers with Biomolecules for Advanced Applications

Nanoscale coordination polymers (NCPs) have shown extraordinary advantages in various research areas due to their structural diversity and multifunctionality. Recently, integration of biomolecules with NCPs received extensive attention and the formed hybrid materials exhibit superior properties over the individual NCPs or biomolecules. In this review, the state-of-the-art of approaches to engineer NCPs with different types of guest biomolecules, such as amino acids, nucleic acids, enzymes and lipids are systematically introduced. Additionally, advanced applications of these biomolecule-NCP composites in the areas of sensing, catalysis, molecular imaging and therapy are thoroughly summarized. Finally, current challenges and prospects are also discussed.