Mineralization‐Inspired Synthesis of Magnetic Zeolitic Imidazole Framework Composites

Research Progress of Metal-Organic Frameworks as Drug Delivery Systems

Metal-organic frameworks (MOFs) are composite crystalline materials created through the coordination of metal ions and organic ligands. MOFs have attracted extensive attention in the biomedical field based on the advantages of internal porosity, customizable porosity, and facile surface modification. This review examines the utilization of MOFs in drug delivery systems, focusing on the research progress from the aspects of coloading drug systems, intelligent responsive carriers, biological macromolecule stabilizers, self-driving micro/nanomotors, and multifunctional living carriers. In addition, the current challenges the research faces are also discussed. The review aims to provide a reference for the further application of MOFs as advanced drug delivery systems.

Reprogramming Tumor-Associated Macrophages with a Se-Based Core-Satellite Nanoassembly to Enhance Cancer Immunotherapy

Tumor-associated macrophages (TAMs), as the most prevalent immune cells in the tumor microenvironment, play a pivotal role in promoting tumor development through various signaling pathways. Herein, we have engineered a Se@ZIF-8 core-satellite nanoassembly to reprogram TAMs, thereby enhancing immunotherapy outcomes. When the nanoassembly reaches the tumor tissue, selenium nanoparticles and Zn2+ are released in response to the acidic tumor microenvironment, resulting in a collaborative effort to promote the production of reactive oxygen species (ROS). The generated ROS, in turn, activate the nuclear factor κB (NF-κB) signaling pathway, driving the repolarization of TAMs from M2-type to M1-type, effectively eliminating cancer cells. Moreover, the nanoassembly can induce the immunogenic death of cancer cells through excess ROS to expose calreticulin and boost macrophage phagocytosis. The Se@ZIF-8 core-satellite nanoassembly provides a potential paradigm for cancer immunotherapy by reversing the immunosuppressive microenvironment.

Recent advances in metal-organic frameworks for stimuli-responsive drug delivery

After entering the human body, drugs for treating diseases, which are prone to delivery and release in an uncontrolled manner, are affected by various factors. Based on this, many researchers utilize various microenvironmental changes encountered during drug delivery to trigger drug release and have proposed stimuli-responsive drug delivery systems. In recent years, metal-organic frameworks (MOFs) have become promising stimuli-responsive agents to release the loaded therapeutic agents at the target site to achieve more precise drug delivery due to their high drug loading, excellent biocompatibility, and high stimuli-responsiveness. The MOF-based stimuli-responsive systems can respond to various stimuli under pathological conditions at the site of the lesion, releasing the loaded therapeutic agent in a controlled manner, and improving the accuracy and safety of drug delivery. Due to the changes in different physical and chemical factors in the pathological process of diseases, the construction of stimuli-responsive systems based on MOFs has become a new direction in drug delivery and controlled release. Based on the background of the rapidly increasing attention to MOFs applied in drug delivery, we aim to review various MOF-based stimuli-responsive drug delivery systems and their response mechanisms to various stimuli. In addition, the current challenges and future perspectives of MOF-based stimuli-responsive drug delivery systems are also discussed in this review.

Co-Immobilization of Laccase and Mediator into Fe-Doped ZIF-8 Significantly Enhances the Degradation of Organic Pollutants

Co-immobilization of laccase and mediator 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) for wastewater treatment could simultaneously achieve the reusability of laccase and avoid secondary pollution caused by the toxic ABTS. Herein, Fe-induced mineralization was proposed to co-immobilize laccase and ABTS into a metal-organic framework (ZIF-8) within 30 min. Immobilized laccase (Lac@ZIF-8-Fe) prepared at a 1:1 mass ratio of Fe2+ to Zn2+ exhibited enhanced catalytic efficiency (2.6 times), thermal stability, acid tolerance, and reusability compared to free laccase. ABTS was then co-immobilized to form Lac+ABTS@ZIF-8-Fe (ABTS = 261.7 mg/g). Lac@ZIF-8-Fe exhibited significantly enhanced bisphenol A (BPA) removal performance over free laccase due to the local substrate enrichment effect and improved enzyme stability. Moreover, the Lac+ABTS@ZIF-8-Fe exhibited higher BPA removal efficiency than the free laccase+ABTS system, implying the presence of a proximity effect in Lac+ABTS@ZIF-8-Fe. In the successive malachite green (MG) removal, the MG degradation efficiency by Lac@ZIF-8-Fe was maintained at 96.6% at the fifth reuse with only an extra addition of 0.09 mM ABTS in each cycle. As for Lac+ABTS@ZIF-8-Fe, 58.5% of MG was degraded at the fifth cycle without an extra addition of ABTS. Taken together, this research has provided a novel strategy for the design of a co-immobilized laccase and ABTS system for the degradation of organic pollutants.

Construction of Macroporous β-Glucosidase@MOFs by a Metal Competitive Coordination and Oxidation Strategy for Efficient Cellulose Conversion at 120 °C

Metal-organic frameworks (MOFs) have become promising accommodation for enzyme immobilization in recent years. However, the microporous nature of MOFs affects the accessibility of large molecules, resulting in a significant decline in biocatalysis efficiency. Herein, a novel strategy is reported to construct macroporous MOFs by metal competitive coordination and oxidation with induced defect structure using a transition metal (Fe²⁺) as a functional site. The feasibility of in situ encapsulating β-glucosidase (β-G) within the developed macroporous MOFs endows an enzyme complex (β-G@MOF-Fe) with remarkably enhanced synergistic catalysis ability. The 24 h hydrolysis rate of β-G@MOF-Fe (with respect to cellobiose) is as high as approximately 99.8%, almost 32.2 times that of free β-G (3.1%). Especially, the macromolecular cellulose conversion rate of β-G@MOF-Fe reached 90% at 64 h, while that of β-G@MOFs (most micropores) was only 50%. This improvement resulting from the expansion of pores (significantly increased at 50-100 nm) can provide enough space for the hosted biomacromolecules and accelerate the diffusion rate of reactants. Furthermore, unexpectedly, the constructed β-G@MOF-Fe showed a superior heat resistance of up to 120 °C, attributing to the new strong coordination bond (Fe²⁺-N) formation through the metal competitive coordination. Therefore, this study offers new insights to solve the problem of the high-temperature macromolecular substrate encountered in the actual reaction.

Co/N co-doped porous carbon as a catalyst for the degradation of RhB by efficient activation of peroxymonosulfate

We report on the preparation of Co/N-NPC_x/y with porous structure and excellent activation properties. The synthesis involves the preparation of Zn/Co-ZIF_x and the carbonization of Zn/Co-ZIF_x at a high temperature in an inert atmosphere. The volatilization of zinc during carbonization results in a porous structure, which is beneficial to the migration of pollutants. The sizes, specific surface areas, and pore size distribution of Co/N-NPC_x/y can be achieved by tuning Zn/Co ratio. The calcination temperatures mainly affect the crystalline phase, crystallinity, and magnetic properties of the as-prepared materials. The effects of the as-prepared materials properties and activation conditions on the Rhodamine B (RhB) degradation by PMS activation were investigated. Overall, it exhibited superior catalytic activity in PMS activation, as evidenced by almost complete removal of RhB (0.020 mM, 100 mL) by using 5 mg/L Co/N-NPC_0.5/900 and 1.250 mM PMS within 30 min. Furthermore, it confirmed the participation of SO₄^•-, •OH, and ¹O₂ in the catalytic reaction, and both SO₄^•- and ¹O₂ were the main reactive oxygen species that play a major role.

pH and H2S Dual-Responsive Magnetic Metal-Organic Frameworks for Controlling the Release of 5-Fluorouracil

Along with the increasing cancer incidence, developing suitable drug delivery systems (DDSs) is becoming urgent to control drug release and further enhance therapeutic efficiency. Herein, a Fe-Zn bimetallic MOF-derived ferromagnetic nanomaterial was synthesized by a one-step method. The successful preparation of ferromagnetic Fe-ZIF-8 was verified by scanning electron microscopy, powder X-ray diffraction, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, and physical property measurement system characterizations. Furthermore, the release behaviors of 5-FU from the ferromagnetic carrier were investigated in a simulative cancer microenvironment of PBS buffer solution (PBS = phosphate-buffered saline, pH = 5.8) and NaHS solution. The vehicle in PBS solution of pH = 5.8 and NaHS solution of 500 μM can rapidly release 5-FU with the cumulative release percentages of 68 and 36%, respectively, within two hundred minutes. The release mechanism in the weak acid environment can be mainly attributed to the decomposition of the Fe-ZIF-8. However, the strong interaction between Zn and Fe atoms in Fe-ZIF-8 and the S atom in H₂S plays an important role in the release process in the simulated H₂S cancer microenvironment. The investigation of release kinetic models indicates that the 5-FU release in the PBS solutions and NaHS solution of 500 μM can be accurately fitted by a second-degree polynomial model and first-order model, respectively. In addition, the decomposition products, zinc, iron, and 2-MeIM, are endogenous and show low toxicity values [LD₅₀ (Zn) = 0.35 g·kg^-1, LD₅₀ (Fe) = 30 g·kg^-1, and LD₅₀ (2-MeIM) = 1.4 g·kg^-1]. Therefore, the low-toxicity, pH and H₂S dual-stimuli-responsive, and ferromagnetic nature make the obtained Fe-ZIF-8 an ideal candidate in the field of bioactive molecule delivery.

Magnetic-Propelled Janus Yeast Cell Robots Functionalized with Metal-Organic Frameworks for Mycotoxin Decontamination

Cell robots that transform natural cells into active platforms hold great potential to enrich the biomedical prospects of artificial microrobots. Here, we present Janus yeast cell microrobots (JYC-robots) prepared by asymmetrically coating Fe₃O₄ nanoparticles (NPs) and subsequent in situ growth of zeolitic imidazolate framework-67 (ZIF-67) on the surface of yeast cells. The magnetic actuation relies on the Fe₃O₄ NPs wrapping. As the compositions of cell robots, the cell wall with abundant polysaccharide coupling with porous and oxidative ZIF-67 can concurrently remove mycotoxin (e.g., zearalenone (ZEN)). The magnetic propulsion accelerates the decontamination efficiency of JYC-robots against ZEN. Although yeast cells with fully coating of Fe₃O₄ NPs and ZIF-67 (FC-yeasts) show faster movement than JYC-robots, higher toxin-removal efficacy is observed for JYC-robots compared with that of FC-yeasts, reflecting the vital factor of the yeast cell wall in removing mycotoxin. Such design with Janus modification of magnetic NPs (MNPs) and entire coating of ZIF-67 generates active cell robot platform capable of fuel-free propulsion and enhanced detoxification, offering a new formation to develop cell-based robotics system for environmental remediation.

Magnetic zeolitic imidazolate frameworks composite as an efficient adsorbent for arsenic removal from aqueous solution

In this study, magnetic zeolitic imidazolate frameworks (ZIF-8) was prepared by a one-step method, where its evolution involved the coprecipitation reactions concomitant with the self-assembly reactions. Structural characterizations indicated that magnetic ZIF-8 showed irregular polyhedral morphology with a large specific surface area (696.5 m²/g) and saturation magnetization (4.31 emu/g). The as-prepared magnetic ZIF-8 enhanced the adsorption performance of As(III) and As(V), compared with bare Fe₃O₄. The pseudo second-order kinetic model (R² = 0.9627 and 0.9893 for As(III) and As(V), respectively) and the Langmuir model (R² = 0.9441 for As(III) and 0.9851 for As(V)) can fit the adsorption process well, confirming the nature of single-layer homogeneous chemisorption. The adsorption capacity was 30.87 and 17.51 mg/g, and their corresponding values of PC were 2.664 and 1.286 L/g, for As(III) and As(V), respectively. Solution pH showed an adverse effect on As(V) adsorption whereas no obvious effect on As(III). The ionic strength and coexisting ions had not obvious influence on adsorption of As(III) and As(V). The adsorption mechanism was explored and discussed based on the detailed spectroscopy analysis. This adsorbent can be recovered magnetically after use, which is promising for the practical application.

Stimuli-responsive metal-organic framework nanoparticles for controlled drug delivery and medical applications

Stimuli-responsive metal-organic framework nanoparticles, NMOFs, provide a versatile platform for the controlled release of drugs and biomedical applications. The porous structure of NMOFs, their biocompatibility, low toxicity, and efficient permeability turn the NMOFs into ideal carriers for therapeutic applications. Two general methods to gate the drug-loaded NMOFs and to release the loads were developed: by one method, the loaded NMOFs are coated or surface-modified with stimuli-responsive gates being unlocked in the presence of appropriate chemical (e.g., ions or reducing agents), physical (e.g., light or heat), or biomarker (e.g., miRNA or ATP) triggers. By a second approach, the drug-loaded NMOFs include encoded structural information or co-added agents to induce the structural distortion or stimulate the degradation of the NMOFs. Different chemical triggers such as pH changes, ions, ATP, or redox agents, and physical stimuli such as light or heat are applied to degrade the NMOFs, resulting in the release of the loads. In addition, enzymes, DNAzymes, and disease-specific biomarkers are used to unlock the gated NMOFs. The triggered release of drugs for cancer therapy, anti-blood clotting, and the design of autonomous insulin-delivery systems ("artificial pancreas") are discussed. Specifically, multi-drug carrier systems and functional NMOFs exhibiting dual and cooperative therapeutic functions are introduced. The future perspectives and applications of stimuli-responsive particles are addressed.

Iron-Mineralization-Induced Mesoporous Metal-Organic Frameworks Enable High-Efficiency Synergistic Catalysis of Natural/Nanomimic Enzymes

Metal-organic frameworks (MOFs) have become a promising accommodation for enzyme immobilization and protection. However, the integration of multienzymes into MOFs may result in compromise of individual enzymatic activity. In this work, we report an iron mineralization strategy to facilely construct a mesoporous MOF, possessing excellent peroxidase-mimic bioactivity. Furthermore, the feasibility of in situ encapsulating natural enzymes within the developed mesoporous MOF nanozymes endows these natural/nanomimic enzyme hybrids with remarkably enhanced synergistic catalysis ability. Such activity enhancement is mainly due to (1) the fast flux rate of substances through the interconnected mesoporous channels and (2) the simultaneously increased loading amount of enzymes and iron within the MOFs caused by the iron mineralization process.

Metal-organic frameworks for virus detection

Virus severely endangers human life and health, and the detection of viruses is essential for the prevention and treatment of associated diseases. Metal-organic framework (MOF), a novel hybrid porous material which is bridged by the metal clusters and organic linkers, has become a promising biosensor platform for virus detection due to its outstanding properties including high surface area, adjustable pore size, easy modification, etc. However, the MOF-based sensing platforms for virus detection are rarely summarized. This review systematically divided the detection platforms into nucleic acid and immunological (antigen and antibody) detection, and the underlying sensing mechanisms were interpreted. The nucleic acid sensing was discussed based on the properties of MOF (such as metal ion, functional group, geometry structure, size, porosity, stability, etc.), revealing the relationship between the sensing performance and properties of MOF. Moreover, antibodies sensing based on the fluorescence detection and antigens sensing based on molecular imprinting or electrochemical immunoassay were highlighted. Furthermore, the remaining challenges and future development of MOF for virus detection were further discussed and proposed. This review will provide valuable references for the construction of sophisticated sensing platform for the detection of viruses, especially the 2019 coronavirus.

Biodegradable Metal-Organic Framework-Based Microrobots (MOFBOTs)

Microrobots and metal-organic frameworks (MOFs) have been identified as promising carriers for drug delivery applications. While clinical applications of microrobots are limited by their low drug loading efficiencies and the poor degradability of the materials used for their fabrication, MOFs lack motility and targeted drug delivery capabilities. The combination of these two fields marks the beginning of a new era; MOF-based small-scale robots (MOFBOTs) for biomedical applications. Yet, biodegradability is a major hurdle in the field of micro- and nanoswimmers including small-scale robots. Here, a highly integrated MOFBOT that is able to realize magnetic locomotion, drug delivery, and selective degradation in cell cultures is reported for the first time. The MOF used in the investigations does not only allow a superior loading of chemotherapeutic drugs and their controlled release via a pH-responsive degradation but it also enables the controlled locomotion of enzymatically biodegradable gelatin-based helical microrobots under magnetic fields. The degradation of the integrated MOFBOT is observed after two weeks, when all its components fully degrade. Additionally, drug delivery studies performed in cancer cell cultures show reduced viability upon delivery of Doxorubicin within short time frames. This MOFBOT system opens new avenues for highly integrated fully biodegradable small-scale robots.

Carbodiimide-based synthesis of N-heterocycles: moving from two classical reactive sites to chemical bond breaking/forming reaction

Carbodiimides are a unique class of heterocumulene compounds that display distinctive chemical properties. The rich chemistry of carbodiimides has drawn increasing attention from chemists in recent years and has made them exceedingly useful compounds in modern organic chemistry, especially in the synthesis of N-heterocycles. This review has outlined the extensive application of carbodiimides in the synthesis of N-heterocycles from the 1980s to today. A wide range of reactions for the synthesis of various types of N-heterocyclic systems (three-, four-, five-, six-, seven-, larger-membered and fused heterocycles) have been developed on the basis of carbodiimides and their derivatives.

A Fluorescent Zn(II)-Coordination Polymer: Selective Detection of Nitrofurantoin and Prevention of Peri-Implantitis after Ultrafine-Grained Titanium Implant by Reducing Inflammatory Cytokines Release

In the current research, a novel coordination polymer (CP) containing Zn(II) ions as nodes with the chemical formula of [Zn(IPT)₂]_n (1) has been produced via reaction of Zn(NO₃)₂·6H₂O with 5-(3-(1H-imidazol-1-yl)phenyl)-1H-tetrazolate (HIPT), a heterotopic imidazole-tetrazole-bifunctional ligand. The as-prepared complex 1 has been charactered via single crystal X-ray diffraction, elemental analysis, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and fourier transform infrared spectroscopy (FT-IR). Because of its outstanding luminescent performances and stability, the synthesized complex 1 is a kind of excellent material of luminescent sensor of nitrofurantoin (NFT) in the water. The value of K_sv for the complex 1 to NFT is about 1.4 × 10⁴ M^-1. For the treatment of the peri-implantitis with complex 1, the ELISA test was carried out to determine the levels of the inflammatory cytokines released into the gingival crevicular fluid. The results showed that the levels of the inflammatory cytokines could be significantly reduced by complex 1 treatment. In addition to this, the real time RT-PCR was also conducted, and the data suggested the signaling pathway of TLR-4-NF-κB activation was inhibited by complex 1.

Hierarchical porous and hydrophilic metal-organic frameworks with enhanced enzyme activity

Metal-organic frameworks (MOFs) for enzyme encapsulation-induced biomimetic mineralization under mild reaction conditions are commonly microporous and hydrophobic, which result in a rather high mass transfer resistance of the reactants and restrain the enzyme catalytic activity. Herein, we prepared a type of hierarchical porous and hydrophilic MOF through the biomimetic mineralization of enzymes, zinc ions, 2-methylimidazole, and lithocholic acid. The hierarchical porous structure accelerated the diffusion process of the reactants and the increased hydrophilicity conferred interfacial activity and increased the enzyme catalytic activity. The immobilized enzyme retained higher catalytic activity than the free enzyme and exhibited enhanced resistance to alkaline, organic, and high-temperature conditions. The nanobiocatalyst was reusable and showed long-term storage stability.

In-situ preparation of hollow cellulose nanocrystals/zeolitic imidazolate framework hybrid microspheres derived from Pickering emulsion

In situ interfacial growth of nanoparticles induced by a Pickering emulsion is recognized as a practical method for the fabrication of hollow composites. Herein, hybrid hollow microspheres were prepared using cellulose nanocrystals (CNCs) emulsified water-dodecane system as a template. The hybrid microspheres were composed of zeolitic imidazolate framework-8 (ZIF-8) shells and CNCs surface-layers. ZIF-8 crystals formed and grew at the oil-water interface with a low ligand/metal ion molar ratio. The composite microspheres owned rich porous structure with a high surface area of 1240 m² g^-1 and performed obvious hydrophilicity owing to the role of CNCs layers. The two characters offered CNCs/ZIF-8 composite materials with very prominent adsorption capacity towards dyes (1060.2 mg g^-1 for malachite green). Carbonization of CNCs/ZIF-8 composite materials afford ZIF-8 based materials more effective removal of methylene blue from water under sunlight, owing to the photocatalytic role of ZnO remained in carbonized product. This research paves the way to realize a variety of hollow CNCs/ZIFs hybrid materials for different application purposes.

Recent developments on zinc(ii) metal-organic framework nanocarriers for physiological pH-responsive drug delivery

The high storage capacities and excellent biocompatibilities of zinc(ii) metal-organic frameworks (Zn-MOFs) have made them outstanding candidates as drug delivery carriers. Recent studies on the pH-responsive processes based on carrier-drug interactions have proven them to be the most efficient and effective way to control the release profiles of drugs. To satisfy the ever-growing demand in cancer therapy, great efforts are being devoted to the development of methods to precisely control drug release and achieve targeted use of an active substance at the right time and place. In this review article, we discuss the diverse stimuli based on Zn-MOFs carriers that have been achieved upon external activation from single pH-stimulus-responsive or/and multiple pH-stimuli-responsive viewpoints. Also, the perspectives and future challenges in this type of carrier system are discussed.