How Can Proteins Enter the Interior of a MOF? Investigation of Cytochrome c Translocation into a MOF Consisting of Mesoporous Cages with Microporous Windows

Metal-organic frameworks for precise inclusion of single-stranded DNA and transfection in immune cells

Effective transfection of genetic molecules such as DNA usually relies on vectors that can reversibly uptake and release these molecules, and protect them from digestion by nuclease. Non-viral vectors meeting these requirements are rare due to the lack of specific interactions with DNA. Here, we design a series of four isoreticular metal-organic frameworks (Ni-IRMOF-74-II to -V) with progressively tuned pore size from 2.2 to 4.2 nm to precisely include single-stranded DNA (ssDNA, 11–53 nt), and to achieve reversible interaction between MOFs and ssDNA. The entire nucleic acid chain is completely confined inside the pores providing excellent protection, and the geometric distribution of the confined ssDNA is visualized by X-ray diffraction. Two MOFs in this series exhibit excellent transfection efficiency in mammalian immune cells, 92% in the primary mouse immune cells (CD4+ T cell) and 30% in human immune cells (THP-1 cell), unrivaled by the commercialized agents (Lipo and Neofect).

Non-viral vectors are important for transfection but can be limited in the uptake, protection and release of ssDNA. Here, the authors report on the design of metal-organic-framework vectors with precisely controlled pore geometry and demonstrate the vector in the transfection of immune cells.

Hybridization of MOFs and polymers

Metal-organic frameworks (MOFs) have received much attention because of their attractive properties. They show great potential applications in many fields. An emerging trend in MOF research is hybridization with flexible materials, which is the subject of this review. Polymers possess a variety of unique attributes, such as softness, thermal and chemical stability, and optoelectrical properties that can be integrated with MOFs to make hybrids with sophisticated architectures. Hybridization of MOFs and polymers is producing new and versatile materials that exhibit peculiar properties hard to realize with the individual components. This review article focuses on the methodology for hybridization of MOFs and polymers, as well as the intriguing functions of hybrid materials.

Cu(I) Coordination Polymers as the Green Heterogeneous Catalysts for Direct C-H Bonds Activation of Arylalkanes to Ketones in Water with Spatial Confinement Effect

To develop coordination polymers (CPs) as catalysts to selectively catalyze the reaction of C-H bond activation of arylalkanes to their homologous ketones, three new Cu(I)-based coordination polymers (Cu^I-CPs) [CuI(aas-TPB)]_n (1), [CuBr(ass-TPB)CH₃CN]_n (2), and {[Cu(ass-TPB)]Cl}_n (3) (TPB = N,N,N-tris(3-pyridinyl)-1,3,5-benzenetricarboxamide) were synthesized. Structural variations from a herringbone fashion one-dimensional framework of 1 to a two-dimensional framework of 2 containing a 48-membered macrocycle and a cationic three-dimensional framework of 3 filled with Cl^- anions were observed arising from the different halogen ions (I^-, Br^-, and Cl^-). 1-3 were used as the green heterogeneous catalysts to catalyze direct C-H bond activation reactions of arylalkanes to ketones under mild reaction conditions with water as solvent. Handy product separation, convenient reaction procedures, and recyclability of these catalysts make the catalytic system fascinating. Moreover, the Cu^I-CPs performed the reaction with high regioselectivity due to the unique spatial confinement effect of CPs.

Polyoxometalate-metal organic framework-lipase: An efficient green catalyst for synthesis of benzyl cinnamate by enzymatic esterification of cinnamic acid

Iron-carboxylate (MIL-100(Fe)) and HKUST-1 (Cu₃(BTC)₂, BTC=1,3,5-benzenetricarboxylic acid) as nanoporous metal organic framework supports were compared for immobilization of porcine pancreatic lipase (PPL). These immobilizations improved thermal, pH and operational stability of PPL compared to the soluble enzyme. Stability of MIL-100(Fe) was better than HKUST-1 as support. MIL-100(Fe) encapsulated Keggin phosphotungstic acid H₃PW₁₂O₄₀ (PW) (PW@MIL-100(Fe)) was synthesized to develop novel enzyme immobilized system and characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) and Barrett Joyner Halenda (BJH) analysis. Relative activity for immobilized lipase on PW@MIL-100(Fe) was more than MIL-100(Fe) in pH range of 3-9. At the elevated temperature of 70°C, the PW@MIL-100(Fe) was the most stable one. PW@MIL-100(Fe)/PPL substrate exhibited the higher stability at 4°C and 25°C, along with other supports. Moreover, PW@MIL-100(Fe) was chosen as the best support for immobilization of PPL and was also applied for the synthesis of benzyl cinnamate by enzymatic esterification of cinnamic acid. The immobilized enzyme retained 90.4% of its initial activity during synthesis of benzyl cinnamate after 5 successive catalytic rounds and reached 80.0% yield after 8 reuses.

Pore Environment Control and Enhanced Performance of Enzymes Infiltrated in Covalent Organic Frameworks

In the drive toward green and sustainable methodologies for chemicals manufacturing, biocatalysts are predicted to have much to offer in the years to come. That being said, their practical applications are often hampered by a lack of long-term operational stability, limited operating range, and a low recyclability for the enzymes utilized. Herein, we show how covalent organic frameworks (COFs) possess all the necessary requirements needed to serve as ideal host materials for enzymes. The resultant biocomposites of this study have shown the ability boost the stability and robustness of the enzyme in question, namely lipase PS, while also displaying activities far outperforming the free enzyme and biocomposites made from other types of porous materials, such as mesoporous silica and metal-organic frameworks, exemplified in the kinetic resolution of the alcohol assays performed. The ability to easily tune the pore environment of a COF using monomers bearing specific functional groups can improve its compatibility with a given enzyme. As a result, the orientation of the enzyme active site can be modulated through designed interactions between both components, thus improving the enzymatic activity of the biocomposites. Moreover, in comparison with their amorphous analogues, the well-defined COF pore channels not only make the accommodated enzymes more accessible to the reagents but also serve as stronger shields to safeguard the enzymes from deactivation, as evidenced by superior activities and tolerance to harsh environments. The amenability of COFs, along with our increasing understanding of the design rules for stabilizing enzymes in an accessible fashion, gives great promise for providing "off the shelf" biocatalysts for synthetic transformations.

A general and efficient approach for tuning the crystal morphology of classical MOFs

The size/morphology-controlled synthesis of classical MOFs with 2-methylimidazole (2-MI) as a coordination modulator.

An efficient approach for enhancing the catalytic activity of Ni-MOF-74 via a relay catalyst system for the selective oxidation of benzylic C–H bonds under mild conditions

A facile and efficient approach for enhancing the catalytic activity of Ni-MOF-74 via a relay catalysis strategy with [bmim]Br was developed, which is excellent for the selective oxidation of benzylic C–H bond under mild conditions.

Immobilization of cellulase proteins on zeolitic imidazolate framework (ZIF-8)/polyvinylidene fluoride hybrid membranes

ZIF-8/PVDF hybrid membranes have been applied in cellulase immobilization for the first time, which improves cellulase stability with preserved activity.

Synthesis, functionalization, and applications of metal–organic frameworks in biomedicine

Metal–organic frameworks (MOFs), also known as coordination polymers, have attracted extensive research interest in the past few decades due to their unique physical structures and potentially vast applications.

Stable metal–organic frameworks as a host platform for catalysis and biomimetics

Recent years have witnessed the exploration and synthesis of an increasing number of metal–organic frameworks (MOFs). The utilization of stable MOFs as a platform for catalysis and biomimetics is discussed.

Mesoporous Metal-Organic Frameworks with Exceptionally High Working Capacities for Adsorption Heat Transformation

Pore size is one of the most important parameters of adsorbents, and mesoporous materials have received intense attention for large guests. Here, a series of mesoporous coordination polymers underlying a new framework prototype for fast expansion of pore size is reported and the profound effect of pore size on adsorption heat transformation is demonstrated. Three isostructural honeycomb-like frameworks are designed and synthesized by combining ditopic linear metal oxalate chains and triangular tris-pyridine ligands. Changing the ligand bridging length from 5.5 to 8.6 and 9.9 Å gives rise to effective pore diameter from 20 to 33 and 37 Å, surface area from 2096 to 2630 and 2749 m² g^-1 , and pore volume from 1.19 to 1.93 and 2.36 cm³ g^-1 , respectively. By virtue of the unique and tunable isotherm shape of mesopores, exceptionally large working capacity up to 1.19 g g^-1 or 0.38 g cm^-3 for adsorption heat transformation can be achieved using R-134a (1,1,1,2-tetrafluroethane) as a working fluid.

High efficiency and long-term intracellular activity of an enzymatic nanofactory based on metal-organic frameworks

Enhancing or restoring enzymatic function in cells is highly desirable in applications ranging from ex vivo cellular manipulations to enzyme replacement therapies in humans. However, because enzymes degrade in biological milieus, achieving long-term enzymatic activities can be challenging. Herein we report on the in cellulo properties of nanofactories that consist of antioxidative enzymes encapsulated in metal-organic frameworks (MOFs). We demonstrate that, while free enzymes display weak activities for only a short duration, these efficient nanofactories protect human cells from toxic reactive oxygen species for up to a week. Remarkably, these results are obtained in spite of the nanofactories being localized in lysosomes, acidic organelles that contain a variety of proteases. The long-term persistence of the nanofactories is attributed to the chemical stability of MOF in low pH environment and to the protease resistance provided by the protective cage formed by the MOF around the encapsulated enzymes.

A facile strategy for enzyme immobilization with highly stable hierarchically porous metal-organic frameworks

Metal-organic frameworks (MOFs) have drawn extensive research interest as candidates for enzyme immobilization owing to their tunable porosity, high surface area, and excellent chemical/thermal stability. Herein, we report a facile and universal strategy for enzyme immobilization using highly stable hierarchically porous metal-organic frameworks (HP-MOFs). The HP-MOFs were stable over a wide pH range (pH = 2-11 for HP-DUT-5) and met the catalysis conditions of most enzymes. The as-prepared hierarchical micro/mesoporous MOFs with mesoporous defects showed a superior adsorption capacity towards enzymes. The maximum adsorption capacity of HP-DUT-5 for glucose oxidase (GOx) and uricase was 208 mg g^-1 and 225 mg g^-1, respectively. Furthermore, we constructed two multi-enzyme biosensors for glucose and uric acid (UA) by immobilizing GOx and uricase with horseradish peroxidase (HRP) on HP-DUT-5, respectively. These sensors were efficiently applied in the colorimetric detection of glucose and UA and showed good sensitivity, selectivity, and recyclability.

In situ hybridization of enzymes and their metal-organic framework analogues with enhanced activity and stability by biomimetic mineralisation

By incorporating Cytochrome c (peroxidase, Cyt c) into a skeleton of its corresponding synthetic MOF analogue (peroxidase mimic, CuBDC), approximately 12-fold catalytic efficiency (k_cat/K_M) enhancement is observed compared to free Cyt c. Meanwhile, the shield endowed by CuBDC prevents encapsulated enzymes from deactivation by trypsin digestion, thermal treatment and long-term storage in vitro. This concept of combining enzymes and their MOF mimics with enhanced enzymatic activity and stability may provide new insights into the design of highly active, stable enzyme-MOF composite catalysts and holds promise for applications in biocatalysis, biosensing and drug delivery systems.

Strategies for Improving the Functionality of Zeolitic Imidazolate Frameworks: Tailoring Nanoarchitectures for Functional Applications

Zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs) built with tetrahedral metal ions and imidazolates, offer permanent porosity and high thermal and chemical stabilities. While ZIFs possess some attractive physical and chemical properties, it remains important to enhance their functionality for practical application. Here, an overview of the extensive strategies which have been developed to improve the functionality of ZIFs is provided, including linker modifications, functional hybridization of ZIFs via the encapsulation of guest species (such as metal and metal oxide nanoparticles and biomolecules) into ZIFs, and hybridization with polymeric matrices to form mixed matrix membranes for industrial gas and liquid separations. Furthermore, the developed strategies for achieving size and shape control of ZIF nanocrystals are considered, which are important for optimizing the textural characteristics as well as the functional performance of ZIFs and their derived materials/hybrids. Moreover, the recent trends of using ZIFs as templates for the derivation of nanoporous hybrid materials, including carbon/metal, carbon/oxide, carbon/sulfide, and carbon/phosphide hybrids, are discussed. Finally, some perspectives on the potential future research directions and applications for ZIFs and ZIF-derived materials are offered.

Integration of Biomolecules with Metal-Organic Frameworks

Owing to the progressive development of metal-organic-frameworks (MOFs) synthetic processes and considerable potential applications in last decade, integrating biomolecules into MOFs has recently gain considerable attention. Biomolecules, including lipids, oligopeptides, nucleic acids, and proteins have been readily incorporated into MOF systems via versatile formulation methods. The formed biomolecule-MOF hybrid structures have shown promising prospects in various fields, such as antitumor treatment, gene delivery, biomolecular sensing, and nanomotor device. By optimizing biomolecule integration methods while overcoming existing challenges, biomolecule-integrated MOF platforms are very promising to generate more practical applications.

Metal-Organic Frameworks at the Biointerface: Synthetic Strategies and Applications

Many living organisms are capable of producing inorganic materials of precisely controlled structure and morphology. This ubiquitous process is termed biomineralization and is observed in nature from the macroscale (e.g., formation of exoskeletons) down to the nanoscale (e.g., mineral storage and transportation in proteins). Extensive research efforts have pursued replicating this chemistry with the overarching aims of synthesizing new materials of unprecedented physical properties and understanding the complex mechanisms that occur at the biological-inorganic interface. Recently, we demonstrated that a class of porous materials termed metal-organic frameworks (MOFs) can spontaneously form on protein-based hydrogels via a process analogous to natural matrix-mediated biomineralization. Subsequently, this strategy was extended to functional biomacromolecules, including proteins and DNA, which have been shown to seed and accelerate crystallization of MOFs. Alternative strategies exploit co-precipitating agents such as polymers to induce MOF particle formation thus facilitating protein encapsulation within the porous crystals. In these examples the rigid molecular architecture of the MOF was found to form a protective coating around the biomacromolecule offering improved stability to external environments that would normally lead to its degradation. In this way, the MOF shell mimics the protective function of a biomineralized exoskeleton. Other methodologies have also been explored to encapsulate enzymes within MOF structures, including the fabrication of polycrystalline hollow MOF microcapsules that preserve the original enzyme functionality over several batch reaction cycles. The potential to design MOFs of varied pore size and chemical functionality has underpinned studies describing the postsynthesis infiltration of enzymes into MOF pore networks and bioconjugation strategies for the decoration of the MOF outer surface, respectively. These methods and configurations allow for customized biocomposites. MOF biocomposites have been extended from simple proteins to complex biological systems including viruses, living yeast cells, and bacteria. Indeed, a noteworthy result was that cells encapsulated within a crystalline MOF shell remain viable after exposure to a medium containing lytic enzymes. Furthermore, the cells can adsorb nutrients (glucose) through the MOF shell but cease reproducing until the MOF casing is removed, at which point normal cellular activity is fully restored. The field of MOF biocomposites is expansive and rapidly developing toward different applied research fields including protection and delivery of biopharmaceuticals, biosensing, biocatalysis, biobanking, and cell and virus manipulation. This Account describes the current progress of MOFs toward biotechnological applications highlighting the different strategies for the preparation of biocomposites, the developmental milestones, the challenges, and the potential impact of MOFs to the field.

Green synthesis of enzyme/metal-organic framework composites with high stability in protein denaturing solvents

OBJECTIVES

Enzyme/metal-organic framework composites with high stability in protein denaturing solvents were reported in this study.

RESULTS

Encapsulation of enzyme in metal-organic frameworks (MOFs) via co-precipitation process was realized, and the generality of the synthesis was validated by using cytochrome c, horseradish peroxidase, and Candida antarctica lipase B as model enzymes. The stability of encapsulated enzyme was greatly increased after immobilization on MOFs. Remarkably, when exposed to protein denaturing solvents including dimethyl sulfoxide, dimethyl formamide, methanol, and ethanol, the enzyme/MOF composites still preserved almost 100% of activity. In contrast, free enzymes retained no more than 20% of their original activities at the same condition. This study shows the extraordinary protecting effect of MOF shell on increasing enzyme stability at extremely harsh conditions.

CONCLUSION

The enzyme immobilized in MOF exhibited enhanced thermal stability and high tolerance towards protein denaturing organic solvents.

Deciphering the Structural Relationships of Five Cd-Based Metal-Organic Frameworks

The one-pot reaction of Cd(NO₃)₂·4H₂O and 5-(6-(hydroxymethyl)pyridin-3-yl)isophthalic acid (H₂L) in DMF/H₂O (DMF = N,N-dimethylformamide) produced a two-dimensional (2D) metal-organic framework (MOF) of [Cd(L)(H₂O)₂] (A) bearing aqua-bridged Cd centers, accompanied by two three-dimensional (3D) MOFs [Cd(L)(DMF)_0.5] (B) and [Cd(L)] (C). Removing the bridging aqua molecules of A by heating led to the formation of an additional 3D MOF of [Cd(L)] (D) in a single-crystal to single-crystal (SCSC) manner. The search for the preceding compound that could convert to A resulted in the isolation of a 2D MOF [Cd(L)(DMF)] (E) that readily converted to A in water, but with the loss of single crystallinity. Upon excitation at 350 nm, A, D, E, and the ligand H₂L fluoresced at 460 nm, 468 nm, 475 nm, and 411 nm, respectively. The fluorescence of A could be used for the selective detection of Fe³⁺ in water down to 0.58 ppm. This quenching was not affected by the presence of other common metal ions.

Shielding against Unfolding by Embedding Enzymes in Metal-Organic Frameworks via a de Novo Approach

We show that an enzyme maintains its biological function under a wider range of conditions after being embedded in metal-organic framework (MOF) microcrystals via a de novo approach. This enhanced stability arises from confinement of the enzyme molecules in the mesoporous cavities in the MOFs, which reduces the structural mobility of enzyme molecules. We embedded catalase (CAT) into zeolitic imidazolate frameworks (ZIF-90 and ZIF-8), and then exposed both embedded CAT and free CAT to a denature reagent (i.e., urea) and high temperatures (i.e., 80 °C). The embedded CAT maintains its biological function in the decomposition of hydrogen peroxide even when exposed to 6 M urea and 80 °C, with apparent rate constants k_obs (s^-1) of 1.30 × 10^-3 and 1.05 × 10^-3, respectively, while free CAT shows undetectable activity. A fluorescence spectroscopy study shows that the structural conformation of the embedded CAT changes less under these denaturing conditions than free CAT.

Immobilization on Metal-Organic Framework Engenders High Sensitivity for Enzymatic Electrochemical Detection

The protection effect of metal-organic framework (MOF) provides high stability for immobilized enzyme. The small cavities of MOFs, however, usually result in decreased apparent substrate affinity and enzymatic activity of immobilized enzyme, compared to native enzyme. We synthesized zeolitic imidazolate framework-8 (ZIF-8) with a combination of mesoporous and microporous channels for cytochrome c (Cyt c) immobilization. Compared with native Cyt c, the immobilized Cyt c displayed increased apparent substrate affinity (Michaelis constant K_m reduced by ∼50%), ∼128% increased enzymatic activity, and 1.4-fold increased sensitivity in the enzymatic electrochemical detection of H₂O₂. The immobilized Cyt c-coated screen-printed electrode was applied for the fast detection of residual H₂O₂ in microliter food samples such as milk and beer, making it promising for the development of efficient biosensors.

Investigation of the Mesoporous Metal-Organic Framework as a New Platform To Study the Transport Phenomena of Biomolecules

Mesoporous materials, Tb-mesoMOF and MCM-41, were used to study the transport phenomena of biomolecules entering the interior pores from solution. Vitamins B₁₂ and B₂ were successfully encapsulated into these mesoporous materials, whereas Tb-mesoMOF (0.33 g of B₁₂/g, 0.01 g of B₂/g) adsorbed a higher amount of vitamin per mass than MCM-41 (0.21 g of B₁₂/g, 0.002 g of B₂/g). The diffusion mechanism of the biomolecules entering Tb-mesoMOF was evaluated using a mathematical model. The Raman spectroscopy studies showed vitamin B₁₂ has been encapsulated within Tb-mesoMOF's pores, and evaluation of the peak shifts indicated strong interactions linking vitamin B₁₂'s pyrroline moiety with Tb-mesoMOF's triazine and benzoate rings. Because of these stronger interactions between the vitamins and Tb-mesoMOF, longer egress times were observed than with MCM-41.

Mesoporous Metal-Organic Framework with Well-Defined Cruciate Flower-Like Morphology for Enzyme Immobilization

Metal-organic frameworks (MOFs) have recently emerged as a promising candidates for the immobilization of enzymes due to their diversified structures and porosity. However, a lack of good size and morphological control over the as-prepared MOFs has limited their practical applications in some cases. Herein, instead of zeolitic imidazolate framework-8 (ZIF-8) with the standard rhombic dodecahedral morphology, we successfully synthesize a novel mesoporous catalase@ZIF composite with cruciate flower-like morphology by embedding catalase molecules into uniformly sized ZIF crystals. With extraordinarily large mesopore size and high protein loading capacity, the catalase@ZIF composites with cruciate flower-like morphology exhibit 400% higher activity than that of catalase@ZIF composites with conventional rhombic dodecahedral morphology, and show higher reusability than conventional rhombic dodecahedral morphology. More importantly, we demonstrate for the first time that the biomacromolecules (proteins) can not directly regulate the crystal size, morphology, and crystallinity of ZIF-8. Moreover, the crystal morphology of ZIF has primary dependence on concentrations of 2-methylimidazole and Zn²⁺ ions, and can be directly controlled by adjusting concentrations of Zn²⁺ ions while keeping the high concentration of 2-methylimidazole.

Enzyme–MOF (metal–organic framework) composites

This review summarizes the syntheses and applications of metal–organic framework (MOF)–enzyme composites with specific emphasis on the merits MOFs bring to the immobilized enzymes.

Immobilization of lysozyme proteins on a hierarchical zeolitic imidazolate framework (ZIF-8)

A hierarchical zeolitic imidazolate framework-8 containing micropores and mesopores showed superior adsorption activity than micro-ZIF-8 towards enzyme proteins.

Synthesis, structure and luminescence properties of two Cd(ii)/M(i) (M = K, Rb) interpenetrated heterometallic frameworks based on giant double-walled cages

Two isostructural 2-fold interpenetrated double-walled frameworks based on a rare heterometallic nested cage-within-cage motif were synthesized.

Enzyme encapsulation in metal–organic frameworks for applications in catalysis

Various methods for encapsulating enzymes in metal–organic frameworks are discussed and the catalytic activity of biocomposites prepared using these methods is highlighted.

Coupling two enzymes into a tandem nanoreactor utilizing a hierarchically structured MOF

A hierarchical porous metal-organic framework (MOF), PCN-888, containing three types of cavities was utilized to couple two enzymes into a tandem nanoreactor. The largest cavity (6.2 nm) can only accommodate one molecule of glucose oxidase (GOx). The intermediate cavity (5.0 nm) can accommodate one and only one molecule of horseradish peroxidase (HRP). The small cavity (2.0 nm) has sufficient size for neither GOx nor HRP, and remains open as a substrate diffusion pathway. The coupling of the two enzymes can only be achieved through a unique stepwise encapsulation with a specific order (GOx first, followed by HRP). The tandem nanoreactor shows excellent catalytic performances and negligible enzyme leaching. Its catalytic activity is well maintained within several catalytic cycles. Moreover, PCN-888 can provide protection to the encapsulated enzymes against trypsin digestion, indicating the in vitro and in vivo stability of the nanoreactor.

Smart Nanocomposites of Cu-Hemin Metal-Organic Frameworks for Electrochemical Glucose Biosensing

Herein, a smart porous material, Cu-hemin metal-organic-frameworks (Cu-hemin MOFs), was synthesized via assembling of Cu²⁺ with hemin to load glucose oxidase (GOD) for electrochemical glucose biosensing for the first time. The formation of the Cu-hemin MOFs was verified by scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, N₂ adsorption/desorption isotherms, UV-vis absorption spectroscopy, fluorescence spectroscopy, thermal analysis and electrochemical techniques. The results indicated that the Cu-hemin MOFs showed a ball-flower-like hollow cage structure with a large specific surface area and a large number of mesopores. A large number of GOD molecules could be successfully loaded in the pores of Cu-hemin MOFs to keep their bioactivity just like in a solution. The GOD/Cu-hemin MOFs exhibited both good performance toward oxygen reduction reaction via Cu-hemin MOFs and catalytic oxidation of glucose via GOD, superior to other GOD/MOFs and GOD/nanomaterials. Accordingly, the performance of GOD/Cu-hemin MOFs-based electrochemical glucose sensor was enhanced greatly, showing a wide linear range from 9.10 μM to 36.0 mM and a low detection limit of 2.73 μM. Moreover, the sensor showed satisfactory results in detection of glucose in human serum. This work provides a practical design of new electrochemical sensing platform based on MOFs and biomolecules.

Emerging Multifunctional Metal-Organic Framework Materials

Metal-organic frameworks (MOFs), also known as coordination polymers, represent an interesting type of solid crystalline materials that can be straightforwardly self-assembled through the coordination of metal ions/clusters with organic linkers. Owing to the modular nature and mild conditions of MOF synthesis, the porosities of MOF materials can be systematically tuned by judicious selection of molecular building blocks, and a variety of functional sites/groups can be introduced into metal ions/clusters, organic linkers, or pore spaces through pre-designing or post-synthetic approaches. These unique advantages enable MOFs to be used as a highly versatile and tunable platform for exploring multifunctional MOF materials. Here, the bright potential of MOF materials as emerging multifunctional materials is highlighted in some of the most important applications for gas storage and separation, optical, electric and magnetic materials, chemical sensing, catalysis, and biomedicine.

Heterostructured Au NPs/CdS/LaBTC MOFs Photoanode for Efficient Photoelectrochemical Water Splitting: Stability Enhancement via CdSe QDs to 2D-CdS Nanosheets Transformation

The electrochemical stability of MOFs in aqueous medium is most essential for MOFs based electrocatalysts for hydrogen production via water splitting. Since most MOFs suffer from instability issues in aqueous systems, there is enormous demand for electrochemically stable MOFs catalysts. Herein, we have developed a simple postsynthesis surface modification protocol for La (1,3,5-BTC) (H2O)6 metal-organic frameworks (LaBTC MOFs) using Mercaptopropionic acid (MPA), to attain electrochemical stability in aqueous mediums. The MPA treated LaBTC MOFs exhibited better stability than the bare LaBTC. Further, to facilitate light harvesting properties of LaBTC MOFs, Au nanoparticles (NPs) and CdSe quantum dots (QDs) are functionalized on LaBTC. The sensitization of LaBTC with Au NPs and CdSe QDs enhances the light harvesting properties of LaBTC in the visible region of solar spectrum. Using as a photoanode, the electrode generates the current density of ∼80 mA/cm(2) at 0.8 V (vs Ag/AgCl) during photoelectrochemical water splitting. The heterostructured LaBTC photoanode demonstrates the long-term stability for the period of 10 h. The electrode post-mortem analysis confirms the conversion of CdSe QDs into single crystalline 2D-CdS nanosheets. The present investigation reveals that CdS nanosheets together with SPR Au NPs improve the photoelectrochemical water splitting activity and stability of LaBTC MOFs.

Design of Laccase-Metal Organic Framework-Based Bioelectrodes for Biocatalytic Oxygen Reduction Reaction

Laccase in combination with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator is a well-known bioelectrocatalyst for the 4-electron oxygen reduction reactions (ORR). The present work deals with the first exploitation of mesoporous iron(III) trimesate-based metal organic frameworks (MOF) MIL-100(Fe) (MIL stands for materials from Institut Lavoisier) as a new and efficient immobilization matrix of laccase for the building up of biocathodes for ORR. First, the immobilization of ABTS in the pores of the MOF was studied by combining micro-Raman spectroscopy, X-ray powder diffraction (XRPD), and N2 porosimetry. The ABTS-MIL-100(Fe)-based modified electrode presents excellent properties in terms of charge transfer kinetics and ionic conductivity as well as a very stable and reproducible electrochemical response, showing that MIL-100(Fe) provides a suitable and stabilizing microenvironment for electroactive ABTS molecules. In a second step, laccase was further immobilized on the MIL-100(Fe)-ABTS matrix. The Lac-ABTS-MIL-100(Fe)-CIE bioelectrode presents a high electrocatalytic current density of oxygen reduction and a reproducible electrochemical response characterized by a high stability over a long period of time (3 weeks). These results constitute a significant advance in the field of laccase-based bioelectrocatalysts for ORR. According to our work, it appears that the high catalytic efficiency of Lac-ABTS-MIL-100(Fe) for ORR may result from a synergy of chemical and catalytic properties of MIL-100(Fe) and laccase.

Structural Evolution of Co-Based Metal Organic Frameworks in Pyrolysis for Synthesis of Core-Shells on Nanosheets: Co@CoOx@Carbon-rGO Composites for Enhanced Hydrogen Generation Activity

In this article, Co-based metal organic frameworks (MOFs) with two shapes were used as pyrolysis precursor to synthesize multilayer core-shells composites loaded on reduced graphene oxide (rGO) sheets. The core-shell structures were obtained by the formation of cores from metal ions and carbon shells from carbonization of ligands. Controllable oxidation of Co cores to CoOx shells generated multilayer core-shell structures anchored onto the surface of rGO sheets. The N-doped composites were obtained by adding poly vinylpyrrolidone. The multilayer core-shells composites exhibited superior catalytic activity toward hydrogen generation compared to their single layer counterparts. By using the N-doped multilayer composites, high hydrogen generation specific rate of 5560 mL min(-1) gCo(-1) was achieved at room temperature. The rGO sheets in composites improved their structure stability. These catalysts exhibited high stability after used five cycling. This synergistic strategy proposes simple, efficient, and versatile blue-prints for the fabrication of rGO composites from MOFs-based precursors.