Hydrolase mimic via second coordination sphere engineering in metal-organic frameworks for environmental remediation

A novel fluorescent sensor for highly sensitive detection of ascorbic acid in food based on inhibiting phosphatase-like activity of Zr-based MOF

Nanozyme-based sensors for detecting ascorbic acid (AA) generally depend on the reducibility of the analyte. However, these sensors are susceptible to interference from reducing substances in food. Herein, a novel fluorescent sensor for AA detection was developed based on inhibiting the phosphatase-like activity of a Zr-based metal-organic framework (Zr-CAU-28). Hydroxyl-rich AA molecules adsorb on the surface of Zr-CAU-28 through hydrogen bonding with [Zr6O4(OH)4] cluster, leading to a decrease in the relative content of terminal hydroxyl groups within the catalytic sites. The constructed sensor exhibits a wide detection range (0.08-11 μg·mL-1) and low detection limit of 0.025 μg·mL-1. Potential interfering studies demonstrated the good selectivity of the sensor. Moreover, the fluorescent sensor can effectively detect AA in juices and vitamin C tablets, with the recovery rate ranging from 96.25 % to 108.50 %. This work represents the first application of phosphatase mimics for AA detection, offering a new strategy for food analysis.

Metal-organic framework-based tunable platform for the immobilization of lipase with enhanced activity in non-aqueous systems

Nowadays, metal-organic frameworks (MOFs) have been emerged as an efficient platform for enzyme immobilization due to their high porosity, tunability, and chemical versatility. In this study, a series of hybrid lipase@NKMOF-101-M (M = Mg, Mn, Zn, Co, or Ni) biocatalysts were constructed through a facile in situ encapsulation method, and the encapsulation and immobilization of lipase in MOFs were carefully validated. The catalytic activity of lipase@NKMOF-101-Mn was 2-fold higher than that of lipase@ZIF-8 and 3-fold higher than that of lipase@MCM-41 due to its excellent dispersibility and hydrophobicity in hexane. The reduced Km value demonstrated a superior affinity of lipase@NKMOF-101s toward to the substrate in non-aqueous reaction system. Moreover, the effects of MOF particle size, metal ions, and enzyme distribution on the catalytic performance of the immobilized lipase were systematically investigated. The results demonstrated that as the particle size of lipase@NKMOF-101s decreased, the apparent enzyme activity increased dramatically. Metal ions in MOFs exhibited activation effect toward to enzyme activity and an approximate 12-fold increase in activity was achieved when transesterification was performed using lipase@NKMOF-101-Mn compared with free lipase. Notably, lipase@NKMOF-101-Co and lipase@NKMOF-101-Ni exhibited substrate selectivity owing to the specific distribution of the lipase in the MOF carriers. Lipase@NKMOF-101s can maintain >80 % of its initial activity even after 5 recycles and a long-term storage (30 days). Consequently, NKMOF-101 is a tunable and sustainable platform for the construction of enzyme@MOFs biocatalysts with superior catalytic performance.

From Nanozymes to Multi-Purpose Nanomaterials: The Potential of Metal-Organic Frameworks for Proteomics Applications

Metal-organic frameworks (MOFs) have the potential to revolutionize the biotechnological and medical landscapes due to their easily tunable crystalline porous structure. Herein, the study presents MOFs' potential impact on proteomics, unveiling the diverse roles MOFs can play to boost it. Although MOFs are excellent catalysts in other scientific disciplines, their role as catalysts in proteomics applications remains largely underexplored, despite protein cleavage being of crucial importance in proteomics protocols. Additionally, the study discusses evolving MOF materials that are tailored for proteomics, showcasing their structural diversity and functional advantages compared to other types of materials used for similar applications. MOFs can be developed to seamlessly integrate into proteomics workflows due to their tunable features, contributing to protein separation, peptide enrichment, and ionization for mass spectrometry. This review is meant as a guide to help bridge the gap between material scientists, engineers, and MOF chemists and on the other side researchers in biology or bioinformatics working in proteomics.

A Haloalkane Dehalogenase DhaA Nanoparticle Based on Pullulan Conjugation and Polyethyleneimine Adsorption

Haloalkane dehalogenase DhaA is a member of the α/β-hydrolase superfamily and can degrade the halogenated compounds. However, the enzyme could not tolerate harsh and extreme environmental conditions, such as high temperature, extreme pH, and hypersaline, which limits its practical applications. Pullulan is a hydrophilic polysaccharide and acts as an additive to improve the enzyme stability. Polyethyleneimine (PEI) is a protein stabilizer and a polymer with a high density of ionizable amino groups. In the present study, DhaA was covalently conjugated with acetylated pullulan and adsorbed with PEI by electrostatic interactions to form nanoparticles (PEI-pullulan-DhaA). As compared with DhaA, PEI-pullulan-DhaA essentially maintained the enzymatic activity of DhaA, along with slight change in the kinetic parameters and enzyme conformation. The conjugated pullulan tends to form a large hydrated layer around DhaA. PEI, a cationic polymer, generated an amphiphilic microenvironment around DhaA. Pullulan conjugation and PEI adsorption could significantly improve the stability of DhaA against high temperature and low pH by structural stabilization of DhaA. PEI-pullulan-DhaA could also tolerate the hypersaline, organic solvents, and long-term storage. Thus, PEI-pullulan-DhaA has a strong environmental stability and is promising for industrial and environmental applications.

Polysaccharides-Directed Biomineralization of Enzymes in Hierarchical Zeolite Imidazolate Frameworks for Electrochemical Detection of Phenols

Biomineralization of enzymes inside rigid metal-organic frameworks (MOFs) is appealing due to its biocompatibility and simplicity. However, this strategy has hitherto been limited to microporous MOFs, leading to low apparent enzymatic activity. In this study, polysaccharide sodium alginate is introduced during the biomineralization of enzymes in zeolitic imidazolate frameworks (ZIFs) to competitively coordinate with metal ions, which endows the encapsulated enzyme with a 7-fold higher activity than that in microporous ZIFs. Mechanism investigation showed that the introduction of alginate generates hierarchical porous structures and enhances the hydrophilicity, which contributes to the enhanced activity of the enzyme. Moreover, the porous ZIFs protect the embedded tyrosinase under detrimental conditions, which allows for the fast detection of phenol, with the limit of detection of 0.03 mM (S/N = 3). Engineering the enzyme with MOFs to enhance its activity and stability is anticipated to extend its application in biocatalysis and biosensors.

Mimic metalloenzymes with atomically dispersed Fe sites in covalent organic framework membranes for enhanced CO2 photoreduction

The massive CO2 emissions from continuous increases in fossil fuel consumption have caused disastrous environmental and ecological crises. Covalent organic frameworks (COFs) hold the potential to convert CO2 and water into value-added chemicals and O2 to mitigate this crisis. However, their activity and selectivity are very low under conditions close to natural photosynthesis. In this work, inspired by the photosynthesis process in natural leaves, we successfully anchored atomically dispersed Fe sites into interlayers of the photoactive triazine-based COF (Fe-COF) membrane to serve as a mimic metalloenzyme for the first time. It is found that under gas-solid conditions and no addition of any photosensitizer and sacrificial reagent, the highly crystalline Fe-COF membrane shows a record high CO2 photoreduction performance with a CO production of 3972 μmol g-1 in a 4 h reaction, ∼100% selectivity of CO, and excellent cycling stability (at least 10 cycles). In such a remarkable photocatalytic CO2 conversion, the atomically dispersed Fe sites with high catalytic activity significantly reduce the formation energy barrier of key *CO2 and *COOH intermediates, the high-density triazine moieties supply more electrons to the iron catalytic center to promote CO2 reduction, and the homogeneous COF membrane greatly improves the electron/mass transport. Thus, this work opens a new window for the design of highly efficient photocatalysts and provides new insights into their structure-activity relationship in CO2 photocatalytic reduction.

Enhancing the Electrochemical Energy Storage of Metal-Organic Frameworks: Linker Engineering and Size Optimization

The electric conductivity and charge transport efficiency of metal-organic frameworks (MOFs) dictate the effective utilization of built-in redox centers and electrochemical redox kinetics and therefore electrochemical performance. Reticular chemistry and the tunable microcosmic shape of MOFs allow for improving their electric conductivity and charge transfer efficiency. Herein, we synthesized two Ni-MOFs (Ni-tdc-bpy and Ni-tdc-bpe) by the solvothermal reaction of Ni2+ ions with 2,5-thiophenedicarboxylic acid (H2tdc) in the presence of conjugated 4,4'-bipyridyl (bpy) and 1,2-di(4-pyridyl)ethylene (bpe) coligands, respectively. We also synthesized two thinning Ni-MOFs (Ni-tdc-bpy(0.5) and Ni-tdc-bpe(0.5)) by adjusting the amounts of bpy and bpe, respectively. Experimental investigations revealed that linker engineering by tuning the delocalization of the N-donor dipyridyl coligands and size optimization by controlling the amount of the coligand rendered the Ni-MOF with significantly improved electrical conductivity and charge transport efficiency. Among them, Ni-tdc-bpe(0.5) possessing the bpe coligand with more strong delocalization and an optimized size exhibited an enhanced specific capacitance of 650 F g-1 at 0.5 A g-1. Moreover, the hybrid supercapacitor constructed from Ni-tdc-bpe(0.5) and activated carbon delivered an excellent energy density of 33.6 Wh kg-1 at a power density of 232.6 W kg-1.

Versatile electrospun cobalt-doped carbon films for rapid antibiotic degradation

This study presents a novel approach to water contamination remediation by developing cobalt-doped carbon nanofiber films using electrospun ZIF-67 precursors, aiming to degrade tetracycline hydrochloride (TCH) and other antibiotics. This method uniquely combines the advantages of metal-organic frameworks (MOFs) and electrospinning to enhance catalytic performance, demonstrating significant innovation in environmental catalysis. The research systematically evaluated the impact of various factors on the catalytic activity of carbonized PAN@ZIF-67 films (CPZF), including carbonization temperature, ZIF-67 content, and PMS dosage. Notably, the CPZF catalyst with 11% ZIF-67 content (named as CPZF-11%) achieved an impressive 99.7% degradation of TCH within just 10 min under visible light and PMS activation, highlighting its superior catalytic efficiency. The study revealed that CPZF-11% exhibited excellent stability and recyclability, maintaining near 100% degradation rates even after six cycles. This catalytic performance is attributed to the synergistic effect of photogenerated electrons and PMS activation, leading to the formation of reactive oxygen species (ROS) such as sulfate radicals and singlet oxygen. The research further elucidated the degradation pathways and intermediate products through quenching experiments and electron paramagnetic resonance (EPR) analysis. The findings demonstrate the broad applicability of CPZF/Vis/PMS in various water matrices, including tap water and wastewater, underscoring its potential for real-world applications in wastewater treatment. This innovative integration of MOFs and electrospinning offers a promising strategy for developing efficient, recyclable, and high-performance catalysts for environmental remediation.

Spatiotemporal Proximity-Enhanced Biocatalytic Cascades Within Metal-Organic Frameworks for Wearable and Theranostic Applications

Enzymatic catalysis, particularly multi-enzyme cascade catalytic, is often limited by the spatial and temporal separation of enzymes and their signal substrates. Herein, a facile method for producing a spatiotemporal proximity-enhanced biocatalytic cascade system is introduced by encasing enzymes within metal-organic frameworks (MOFs) that are modulated with sulfonic acid-functionalized signal substrates. The modulated behavior relies on the sulfonic acid groups coordinated with Zn2+. As a proof of concept, by utilizing 2,2'-Azinobis (3-ethylbenzothiazoline-6-sulfonic acid ammonium salt) (ABTS), a widely-used signal substrate for horseradish peroxidase, two-enzyme/substrate, and three-enzyme/substrate MOFs, which demonstrated a 7.4- and 10.2-fold increase in biocatalytic efficiency over free systems are successfully synthesized. Incorporating the synthesized MOFs into homemade wearable patches and in vivo settings, noninvasive sweat glucose colorimetric detection and photoacoustic imaging-guided photothermal tumor therapy are enabled, respectively. This advancement stems from the newly established coordinative bonds between Zn2+ centers and substrates' sulfonic acid groups, which negates the need for additional signal substrates, thereby not only enhancing but also streamlining bioapplication processes.

A Structural Mimic of Carbonic Anhydrase in Zeolitic Imidazolate Frameworks via Trans-functionalization for Enhancing Hydrolytic Activity

Metal-organic frameworks (MOFs) have been widely considered as ideal platforms for the preparation of biomimetic catalysts, but it remains challenging to fabricate MOF-based enzyme-like catalysts with optimal activity. Here, we leverage the inherent flexibility of MOFs and propose a novel trans-functionalization strategy to construct a carbonic anhydrase (CA) mimic by the structural transformation from ZIF-L to ZIF-8. Theoretical and experimental results reveal that during the structural transformation, the hydroxyl group will preferentially coordinate with the interlayer Zn clusters to form the CA-like active center Zn-N3-OH. Therefore, more accessible active centers are generated on the as-prepared ZIF-8-OH, resulting in substantially enhanced catalytic activity in the hydrolysis of para-nitrophenyl acetate.

Molecular Insights into Sequence-Specific Protein Hydrolysis by a Soluble Zirconium-Oxo Cluster Catalyst

The development of catalysts for controlled fragmentation of proteins is a critical undertaking in modern proteomics and biotechnology. {Zr6O8}-based metal-organic frameworks (MOFs) have emerged as promising candidates for catalysis of peptide bond hydrolysis due to their high reactivity, stability, and recyclability. However, emerging evidence suggests that protein hydrolysis mainly occurs on the MOF surface, thereby questioning the need for their highly porous 3D nature. In this work, we show that the discrete and water-soluble [Zr6O4(OH)4(CH3CO2)8(H2O)2Cl3]+ (Zr6) metal-oxo cluster (MOC), which is based on the same hexamer motif found in various {Zr6O8}-based MOFs, shows excellent activity toward selective hydrolysis of equine skeletal muscle myoglobin. Compared to related Zr-MOFs, Zr6 exhibits superior reactivity, with near-complete protein hydrolysis after 24 h of incubation at 60 °C, producing seven selective fragments with a molecular weight in the range of 3-15 kDa, which are of ideal size for middle-down proteomics. The high solubility and molecular nature of Zr6 allow detailed solution-based mechanistic/interaction studies, which revealed that cluster-induced protein unfolding is a key step that facilitates hydrolysis. A combination of multinuclear nuclear magnetic resonance spectroscopy and pair distribution function analysis provided insight into the speciation of Zr6 and the ligand exchange processes occurring on the surface of the cluster, which results in the dimerization of two Zr6 clusters via bridging oxygen atoms. Considering the relevance of discrete Zr-oxo clusters as building blocks of MOFs, the molecular-level understanding reported in this work contributes to the further development of novel catalysts based on Zr-MOFs.

LaMg6Ga6S16: a chemical stable divalent lanthanide chalcogenide

Divalent lanthanide inorganic compounds can exhibit unique electronic configurations and physicochemical properties, yet their synthesis remains a great challenge because of the weak chemical stability. To the best of our knowledge, although several lanthanide monoxides epitaxial thin films have been reported, there is no chemically stable crystalline divalent lanthanide chalcogenide synthesized up to now. Herein, by using octahedra coupling tetrahedra single/double chains to construct an octahedral crystal field, we synthesized the stable crystalline La(II)-chalcogenide, LaMg6Ga6S16. The nature of the divalent La2+ cations can be identified by X-ray photoelectron spectroscopy, X-ray absorption near-edge structure and electron paramagnetic resonance, while the stability is confirmed by the differential thermal scanning, in-situ variable-temperature powder X-ray diffraction and a series of solid-state reactions. Owing to the particular electronic characteristics of La2+(5d1), LaMg6Ga6S16 displays an ultrabroad-band green emission at 500 nm, which is the inaugural instance of La(II)-based compounds demonstrating luminescent properties. Furthermore, as LaMg6Ga6S16 crystallizes in the non-centrosymmetric space group, P-6, it is the second-harmonic generation (SHG) active, possessing a comparable SHG response with classical AgGaS2. In consideration of its wider band gap (Eg = 3.0 eV) and higher laser-induced damage threshold (5×AgGaS2), LaMg6Ga6S16 is also a promising nonlinear optical material.

Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.