A zirconium metal-organic framework with SOC topological net for catalytic peptide bond hydrolysis

Nanoproteases: Alternatives to Natural Protease for Biotechnological Applications

Some nanomaterials with intrinsic protease-like activity have the advantages of good stability, biosafety, low price, large-scale preparation and unique property of nanomaterials, which are promising alternatives for natural proteases in various applications. An especial term, "nanoprotease", has been coined to stress the intrinsic proteolytic property of these nanomaterials. As a new generation of artificial proteases, they have become a burgeoning field, attracting many researchers to design and synthesize high performance nanoproteases. In this review, we summarize recent progress on all types of nanoproteases with regard of their activity, mechanism and application and introduce a new and effective strategy for engineering high-performance nanoproteases. In addition, we discuss the challenges and opportunities of nanoprotease research in the future.

Biphenyl tetracarboxylic acid-based metal-organic frameworks: a case of topology-dependent thermal expansion

The large inherent flexibility and highly modular nature of metal-organic frameworks (MOFs) make them ideal candidates for the study of negative thermal expansion (NTE). Among diverse organic ligands, the biphenyl unit, which can unrestrictedly rotate along its C-C single bond, can largely enhance the structural flexibility. Herein, we explored the thermal expansion behaviors of four indium biphenyl tetracarboxylates (BPTCs). Owing to the different dihedral angles of BPTC ligands and coordination mode of In3+, they show distinct topologies: InOF-1 (nti), InOF-2 (unc), InOF-12 (pts) and InOF-13 (nou). Intriguingly, it is found that the thermal expansion is highly dependent on the specific topology. The MOFs featuring mononuclear nodes show normal positive thermal expansion (PTE), and the magnitudes of coefficients follow the trend of InOF-2 < InOF-12 < InOF-13, inversely related to averaged molecular volumes. In contrast, the InOF-1, composed of a 1D chain of corner-shared InO6 octahedrons, shows pronounced NTE. Detailed high-resolution synchrotron powder X-ray diffraction and lattice dynamic analyses shed light on the fact that NTE in the InOF-1 is a synergy effect of the spring-like distortion of the inorganic 1D helical chain and twisting of the BPTC ligands. The present work shows how the topological arrangement of building blocks governs the thermal expansion behaviors.

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.

Experimental Demonstration of Topological Catalysis for CO2 Electroreduction

The past decade has witnessed substantial progress in understanding nontrivial band topology and discovering exotic topological materials in condensed-matter physics. Recently, topological physics has been further extended to the chemistry discipline, leading to the emergence of topological catalysis. In principle, the topological effect is detectable in catalytic reactions, but no conclusive evidence has been reported yet. Herein, by precisely manipulating the topological surface state (TSS) of Bi2Se3 nanosheets through thickness control and the application of a magnetic field, we provide direct experimental evidence to illustrate topological catalysis for CO2 electroreduction. With and without the cooperation of TSS, CO2 is mainly reduced into liquid fuels (HCOOH and H2C2O4) and CO, exhibiting high (up to 90% at -1.1 V versus reversible hydrogen electrode) and low Faradaic efficiency (FE), respectively. Theoretically, the product and FE difference can be attributed to the TSS-regulated adsorption of key intermediates and the reduced barrier of the potential-determining step. Our work demonstrates the inherent correlation between band topology and electrocatalysis, paving a new avenue for designing high-performance catalysts.

Reactivity of metal-oxo clusters towards biomolecules: from discrete polyoxometalates to metal-organic frameworks

Metal-oxo clusters hold great potential in several fields such as catalysis, materials science, energy storage, medicine, and biotechnology. These nanoclusters of transition metals with oxygen-based ligands have also shown promising reactivity towards several classes of biomolecules, including proteins, nucleic acids, nucleotides, sugars, and lipids. This reactivity can be leveraged to address some of the most pressing challenges we face today, from fighting various diseases, such as cancer and viral infections, to the development of sustainable and environmentally friendly energy sources. For instance, metal-oxo clusters and related materials have been shown to be effective catalysts for biomass conversion into renewable fuels and platform chemicals. Furthermore, their reactivity towards biomolecules has also attracted interest in the development of inorganic drugs and bioanalytical tools. Additionally, the structural versatility of metal-oxo clusters allows for the efficiency and selectivity of the biomolecular reactions they promote to be readily tuned, thereby providing a pathway towards reaction optimization. The properties of the catalyst can also be improved through incorporation into solid supports or by linking metal-oxo clusters together to form Metal-Organic Frameworks (MOFs), which have been demonstrated to be powerful heterogeneous catalysts. Therefore, this review aims to provide a comprehensive and critical analysis of the state of the art on biomolecular transformations promoted by metal-oxo clusters and their applications, with a particular focus on structure-activity relationships.

Hydrolytic nanozymes: Preparation, properties, and applications

Hydrolytic nanozymes, as promising alternatives to hydrolytic enzymes, can efficiently catalyze the hydrolysis reactions and overcome the operating window limitations of natural enzymes. Moreover, they exhibit several merits such as relatively low cost, easier recovery and reuse, improved operating stability, and adjustable catalytic properties. Consequently, they have found relevance in practical applications such as organic synthesis, chemical weapon degradation, and biosensing. In this review, we highlight recent works addressing the broad topic of the development of hydrolytic nanozymes. We review the preparation, properties, and applications of six types of hydrolytic nanozymes, including AuNP-based nanozymes, polymeric nanozymes, surfactant assemblies, peptide assemblies, metal and metal oxide nanoparticles, and MOFs. Last, we discuss the remaining challenges and future directions. This review will stimulate the development and application of hydrolytic nanozymes.

Polyoxometalates as Potential Artificial Enzymes toward Biological Applications

Artificial enzymes, as alternatives to natural enzymes, have attracted enormous attention in the fields of catalysis, biosensing, diagnostics, and therapeutics because of their high stability and low cost. Polyoxometalates (POMs), a class of inorganic metal oxides, have recently shown great potential in mimicking enzyme activity due to their well-defined structure, tunable composition, high catalytic efficiency, and easy storage properties. This review focuses on the recent advances in POM-based artificial enzymes. Different types of POMs and their derivatives-based mimetic enzyme functions are covered, as well as the corresponding catalytic mechanisms (where available). An overview of the broad applications of representative POM-based artificial enzymes from biosensing to theragnostic is provided. Insight into the current challenges and the future directions for POMs-based artificial enzymes is discussed.

Enhancing the Properties of Yttria-Stabilized Zirconia Composites with Zeolitic Imidazolate Framework-Derived Nanocarbons

Ceramic matrix composites (CMCs) reinforced with nanocarbon have attracted significant interest due to their potential to enhance mechanical, thermal, and electrical properties. Although the investigation of carbon-based materials such as graphene and carbon nanotubes as additives for advanced ceramics has been widespread, the utilization of metal-organic framework (MOF)-derived nanocarbons in CMCs remains largely unexplored. We extended our previous proof-of-concept investigations by demonstrating the effectiveness of a different type of MOF-derived carbon as a reinforcing phase in an alternative ceramic matrix. We employed spark plasma sintering (SPS) to consolidate yttria-stabilized zirconia (YSZ) and zeolitic imidazolate framework (ZIF-67) powder blends at 1300 °C and a uniaxial pressure of 50 MPa. YSZ serves as the ceramic matrix, whereas ZIF-67 serves as the nanocarbon source. The composite exhibits a highly significant improvement in fracture toughness with an increase of up to 13% compared to that of the YSZ monolith. The formation of ZIF-derived nanocarbon interlayers is responsible for the observed enhancement in ductility, which can be attributed to their ability to facilitate energy dissipation during crack propagation and inhibit grain growth. Furthermore, the room-temperature electrical conductivity of the sintered samples demonstrates a substantial improvement, primarily due to the in situ formation of nanocarbon-based fillers, reaching an impressive 27 S/m with 10 wt % ZIF-67 content. Based on the results, it can be inferred that the incorporation of in situ MOF-derived nanocarbons into CMCs leads to a substantial improvement in both the mechanical and electrical properties.

Oriented Self-assembly of Flexible MOFs Nanocrystals into Anisotropic Superstructures with Homogeneous Hydrogels Behaviors

Building of metal-organic frameworks (MOFs) homogeneous hydrogels made by spontaneous crystallization remains a significant challenge. Inspired by anisotropically structured materials in nature, an oriented super-assembly strategy to construct micro-scale MOFs superstructure is reported, in which the strong intermolecular interactions between zirconium-oxygen (Zr─O) cluster and glutamic acid are utilized to drive the self-assembly of flexible nanoribbons into pumpkin-like microspheres. The confined effect between water-flexible building blocks and crosslinked hydrogen networks of superstructures achieved a mismatch transformation of MOFs powders into homogeneous hydrogels. Importantly, the elastic and rigid properties of hydrogels can be simply controlled by precise modulation of coordination and self-assembly for anisotropic superstructure. Experimental results and theoretical calculations demonstrates that MOFs anisotropic superstructure exhibits dynamic double networks with a superior water harvesting capacity (119.73 g g-1 ) accompanied with heavy metal removal (1331.67 mg g-1 ) and strong mechanical strength (Young's modulus of 0.3 GPa). The study highlights the unique possibility of tailoring MOFs superstructure with homogeneous hydrogel behavior for application in diverse fields.

Green, Safe, and Reliable Synthesis of Bimetallic MOF-808 Nanozymes With Enhanced Aqueous Stability and Reactivity for Biological Applications

Bimetallic metal-organic frameworks (MOFs) are promising nanomaterials whose reactivity towards biomolecules remains challenging due to issues related to synthesis, stability, control over metal oxidation state, phase purity, and atomic level characterization. Here, these shortcomings are rationally addressed through development of a synthesis of mixed metal Zr/Ce-MOFs in aqueous environment, overcoming significant hurdles in the development of MOF nanozymes, sufficiently stable on biologically relevant conditions. Specifically, a green and safe synthesis of Zr/Ce-MOF-808 is reported in water/acetic acid mixture which affords remarkably water-stable materials with reliable nanozymatic reactivity, including MOFs with a high Ce content previously reported to be unstable in water. The new materials outperform analogous bimetallic MOF nanozymes, showcasing that rational synthesis modifications could impart outstanding improvements. Further, atomic-level characterization by X-ray Absorption Fine Structure (XAFS) and X-ray Diffraction (XRD) confirmed superior nanozymes arise from differences in the synthetic method, which results in aqueous stable materials, and Ce incorporation, which perturbs the ligand exchange dynamics of the material, and could ultimately be used to fine tune the intrinsic MOF reactivity. Similar rational strategies which leverage metals in a synergistic manner should enable other water-stable bimetallic MOF nanozymes able to surpass existing ones, laying the path for varied biotechnological applications.

High Peroxidase-Mimicking Metal-Organic Frameworks Decorated with Platinum Nanozymes for the Colorimetric Detection of Acetylcholine Chloride and Organophosphorus Pesticides via Enzyme Cascade Reaction

The sensitive detection of acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) is very important for the protection of human health. Herein, a hybrid material, Pt NPs/Fe-MOF, consisting of a metal-organic framework (MIL-88B-NH2, Fe-MOF) decorated with platinum nanoparticles (Pt NPs), was prepared first and exhibited remarkably improved and excellent peroxidase-mimicking activity compared to the Fe-MOF material resulting from the synergistic catalysis effect between Fe-MOF and Pt NPs, which can effectively catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to generate a blue product (oxidized TMB, oxTMB). Interestingly, in the presence of AChE and acetylcholinesterase, the peroxidase-mimicking activity from Pt NPs/Fe-MOF was inhibited obviously, and thus, a colorimetric sensing platform for AChE can be constructed; more importantly, after the addition of OPs, this nanozyme activity can be recovered, inducing the further successful construction of a sensitive colorimetric sensing platform for OPs. The related sensing mechanism and condition optimization were studied, and the as-prepared Pt NPs/Fe-MOF nanozyme-based colorimetric method for AChE and OP detection displayed superior analytical performances with wide linearities and low detection limits. Furthermore, the designed method offers satisfactory real application ability. We expect the as-proposed Pt NPs/Fe-MOF nanozyme-based colorimetric sensing platform for AChE and OPs via the enzyme cascade reaction to show great potential application.

Reticular Chemistry in Its Chiral Form: Axially Chiral Zr(IV)-Spiro Metal-Organic Framework as a Case Study

The interplay of primary organic ligands and inorganic secondary building units (SBUs) has led to a continual boom of reticular chemistry, particularly metal-organic frameworks (MOFs). Subtle variations of organic ligands can have a significant impact on the ultimate structural topology and consequently, the material's function. However, the role of ligand chirality in reticular chemistry has rarely been explored. In this work, we report the organic ligand chirality-controlled synthesis of two zirconium-based MOFs (Spiro-1 and Spiro-3) with distinct topological structures as well as a temperature-controlled formation of a kinetically stable phase (Spiro-4) based on the carboxylate-functionalized inherently axially chiral 1,1'-spirobiindane-7,7'-phosphoric acid ligand. Specifically, Spiro-1 is a homochiral framework comprising only enantiopure S-spiro ligands and has a unique 4,8-connected sjt topology with large 3D interconnected cavities, while Spiro-3 contains equal amounts of S- and R-spiro ligands, resulting in a racemic framework of 6,12-connected edge-transitive alb topology with narrow channels. Interestingly, the kinetic product Spiro-4 obtained with racemic spiro ligands is built of both hexa- and nona-nuclear zirconium clusters acting as 9- and 6-connected nodes, respectively, giving rise to a newly discovered azs net. Notably, the preinstalled highly hydrophilic phosphoric acid groups combined with large cavity, high porosity, and outstanding chemical stability endow Spiro-1 with remarkable water vapor sorption performance, whereas Spiro-3 and Spiro-4 show poor performances due to inappropriate pore systems and structural fragility upon the water adsorption/desorption process. This work highlights the important role of ligand chirality in manipulating the framework topology and function and would further enrich the development of reticular chemistry.

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

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

Fluorescence immunosensor based on functional nanomaterials and its application in tumor biomarker detection

An immunosensor is defined as an analytical device that detects the binding of an antigen to its specific antibody by coupling an immunochemical reaction to the surface of a device called a transducer. Fluorescence immunosensing is one of the most promising immunoassays at present, and has the advantages of simple operation, fast response and high stability. A traditional fluorescence immunosensor often uses an enzyme-labelled antibody as a recognition unit and an organic dye as a fluorescence probe, so it is easily affected by environmental factors with low sensitivity. Nanomaterials have unique photostability, catalytic properties and biocompatibility, which open up a new path for the construction of stable and sensitive fluorescence immunosensors. This paper briefly introduces different kinds of immunosensors and the role of nanomaterials in the construction of immunosensors. The significance of fluorescent immunosensors constructed from functional nanomaterials to detect tumor biomarkers was analyzed, and the strategies to further improve the performance of fluorescent immunosensors and their future development trend were summarized.

Promising advances in nanobiotic-based formulations for drug specific targeting against multidrug-resistant microbes and biofilm-associated infections

Antimicrobial agents and alternative strategies to combat bacterial infections have become urgent due to the rapid development of multidrug-resistant bacteria caused by the misuse and overuse of antibiotics, as well as the ineffectiveness of antibiotics against difficult-to-treat infectious diseases. Nanobiotics is one of the strategies being explored to counter the increase in antibiotic-resistant bacteria. Nanobiotics are antibiotic molecules encapsulated in nanoparticles or artificially engineered pure antibiotics that are ≤ 100 nm in size in at least one dimension. Formulation scientists recognize nanobiotic delivery systems as an effective strategy to overcome the limitations associated with conventional antibiotic therapy. This review highlights the general mechanisms by which nanobiotics can be used to target resistant microbes and biofilm-associated infections. We focus on the design elements, properties, characterization, and toxicity assessment of organic nanoparticles, inorganic nanoparticle and molecularly imprinted polymer-based nano-formulations that can be designed to improve the efficacy of nanobiotic formulation.

Acridine based metal-organic framework host-guest featuring efficient photoelectrochemical-type photodetector and white LED

A novel metal-organic framework (MOF) host-guest material [Cd₃(EtOIPA)₄(HAD)₂]·H₂O has been successfully synthesized by the reaction of 5-ethoxyisophthalic acid (EtOIPA), acridine (AD) and Cd(II) salts under hydrothermal conditions. Structurally, the title MOF possesses a trinucleate Cd(II) based 2D double-layer with the protonated AD cations as the template encapsulated into the grids. The combination of experiments and theoretical calculations reveals that the orderly arrangement of EtOIPA dimers, protonated AD cations and trinucleate Cd(II) clusters generates highly delocalized π-electron channels with a prolonged exciton lifetime. The MOF powders show bright yellow emission with a long lifetime of 50.63 ns. Photoelectrochemical measurements reveal a high photocurrent density ratio of 290 between light and dark conditions at 0 V bias potential, making it a perfect self-driven photodetector. By coating the yellow phosphor on a commercially available blue LED, a high performance white LED with CIE, CCT and CRI values of (0.325, 0.336), 88.2 and 5844 K, respectively can be obtained.