Metal-Organic Frameworks from Edible Natural Products

Electrostatically Dominated Pre-Organization in Cyclodextrin Metal-Organic Frameworks

Electrostatic interactions between oppositely charged entities play a key role in pre-organizing substrates and stabilizing transition states of reactions in enzymes. The use of electrostatic interactions to pre-organize ions in nanoconfined pores, however, has not been investigated to its full potential. Herein, we describe how carboxylate anions can be pre-organized at the behest of their electrostatic interactions with K+ cations in nanoconfined tunnels present in γ-cyclodextrin metal-organic frameworks, i.e., CD-MOFs. Several carboxylate anions, which are all much smaller than the cavities of the tunnels, were visualized by X-ray crystallography when nanoconfined in CD-MOFs, despite the large voids present in the tunnels. These anions were found to be aligned within a planar array defined by four K+ cations, positioned around the periphery of the tunnels. The strong electrostatic interactions between the carboxylate anions and the K+ cations dictate the orientation of the anions and override the influence of all other possible noncovalent bonding interactions between them and the tunnels. Consequently, the aligned pairs of γ-cyclodextrin rings constituting the tunnels become distorted, resulting in them having lower symmetry and fewer disordered carboxylate anions in the solid state. Our findings offer a transformative strategy for controlling the packing and orientation of ions in nanoconfined environments.

Enhanced ammonia-sensitive intelligent films based on a metal-organic framework for accurate shrimp freshness monitoring

Sensitive intelligent films can be used to accurately monitor food freshness. In this study, a cellulose acetate curcumin-loaded cyclodextrin (CD)-based metal-organic framework intelligent film (CA-Cur@CD-MOF) was developed to monitor shrimp freshness at different spoilage stages in real time. The mechanical, barrier, optical, and ammonia-sensitive properties of this film were studied. Notably, this film demonstrated effective ammonia-sensitive color development, reaching a ΔE value of 8.5 in 2 min under an ammonia atmosphere of approximately 0.4 mM. This intelligent film exhibits good DPPH free radical scavenging ability, high thermal stability, and excellent theoretical limit of detection (LOD). Interestingly, shrimp can be classified as "fresh", "sub-fresh", and "spoilage" during the monitoring of shrimp freshness. Furthermore, a significant correlation (R2 = 0.9641) was observed between the TVB-N and ΔE value for this film. Therefore, this intelligent film is promising for the real-time monitoring of freshness of shrimp and other protein-rich foods.

Cyclic Oxothiomolybdates: Building Blocks for Cyclodextrin-Based Open Frameworks

Desolvation processes, though common in self-assembled biological structures, are rarely evidenced and utilized in the design of crystalline architectures. In this study, we introduce a novel approach using the [Mo8S8O8(OH)8(guest)]2- complex, formed by the self-condensation of four [MoV 2O2S2]2- fragments around a guest unit (MoVIO6H4 or oxalate), as a chaotropic scaffold for crystallizing hybrid organic-inorganic systems with natural cyclodextrins. Our findings reveal that β-cyclodextrin (β-CD) facilitates the formation of host-guest complexes, while α-cyclodextrin (α-CD) induces the formation of a Kagome-type structure with significant voids. These new compounds were thoroughly characterized using X-ray diffraction (both powder and single-crystal), N2 adsorption, elemental and thermogravimetric analysis. Additionally, solution studies using 1H NMR titration and small-angle X-ray scattering (SAXS) demonstrated pre-association of the building units in solution. These results enhance our understanding of the design principles for supramolecular structures composed of inorganic polyanions and cyclodextrins.

γ-Cyclodextrin-metal organic framework as a carrier for trans-N-p-coumaroyltyramine: A study of drug solubability, stability, and inhibitory activity against α-glucosidase

γ-Cyclodextrin-based metal-organic frameworks (γ-CD-MOF) were successfully synthesized using the solvent diffusion method and applied as carriers for trans-N-p-coumaroyltyramine (N-p-t-CT, NCT) to study the solubability, stability, sustained release and inhibitory activity against α-glucosidase. The solubilization effect of γ-CD-MOF on N-p-t-CT was performed using impregnation (NCT@CD-MOF-1) and co-crystallization (NCT@CD-MOF-2) methods. X-ray diffraction, scanning electron microscope (SEM), fourier transform infrared spectrometer (FTIR), and N2 adsorption/desorption were used to characterize the MOFs before and after loading NCT. The results showed that NCT@CD-MOF-2 had a better solubability for N-p-t-CT, 145.03 μg/mg of drug loading capacity could be achieved, and the solubility of NCT@CD-MOF-2 in water was 366 times higher than free N-p-t-CT. In addition, the stabilities of N-p-t-CT under temperature, UV light and pH conditions were greatly improved after encapsulation in γ-CD-MOF. Furthermore, NCT@CD-MOFs had a sustained release of N-p-t-CT over an extended period in vitro due to the primary encapsulation in pore structures. Notably, γ-CD-MOF loaded with N-p-t-CT showed superior inhibitory activity against α-glucosidase compared to free N-p-t-CT. Cytotoxicity studies demonstrated that NCT@CD-MOF-2 had low toxicity in vitro and perfect biocompatibility with HL-7702 cells, and γ-CD-MOF could reduce the toxicity of free N-p-t-CT at higher concentrations.

Application of cyclodextrin-based metal-organic frameworks for multi-drug carriers: A combined experimental and simulation study

Combination therapy using multiple drugs has the potential for synergistic therapeutic effects and reduction in the administered dose. Furthermore, when combined with a drug delivery system, the therapeutic agents can effectively be targeted and delivered to the affected area. Therefore, a single carrier capable of encapsulating multiple drugs is of clinical significance. This study focused on cyclodextrin-based metal-organic frameworks (CD-MOFs) with high biocompatibility and hydrophobic and hydrophilic pores, because their amphiphilic pores should be suitable for encapsulating multiple drugs. First, the drug encapsulation ability of 5-fluorouracil (5FU) and ascorbic acid (ASC) into the γ-CD-MOF through experiments was compared with that of grand canonical Monte Carlo (GCMC) simulations. The drugs were suggested to encapsulate in the different pores of γ-CD-MOF depending on the hydrophilicity of the drug. In addition, the multi-drug encapsulation ability of the γ-CD-MOF was experimentally and numerically confirmed. In the simultaneous encapsulation experiments, the encapsulation amounts of 5FU and ASC were measured to be 0.0536 and 1.67 mol/mol, respectively. Also, the GCMC simulation demonstrated the simultaneous encapsulation of the two drugs, in which the loaded amounts of 5FU and ASC were calculated as 0.867 and 1.67 mol/mol, respectively. The encapsulation ability of multi-drug with hydrophilicity and hydrophobicity into the γ-CD-MOF was experimentally and numerically confirmed. The findings obtained in this study suggested that γ-CD-MOF will greatly contribute as a multi-drug carrier.

17O NMR Spectroscopy Reveals CO2 Speciation and Dynamics in Hydroxide-based Carbon Capture Materials

Carbon dioxide capture technologies are set to play a vital role in mitigating the current climate crisis. Solid-state 17O NMR spectroscopy can provide key mechanistic insights that are crucial to effective sorbent development. In this work, we present the fundamental aspects and complexities for the study of hydroxide-based CO2 capture systems by 17O NMR. We perform static density functional theory (DFT) NMR calculations to assign peaks for general hydroxide CO2 capture products, finding that 17O NMR can readily distinguish bicarbonate, carbonate and water species. However, in application to CO2 binding in two test case hydroxide-functionalised metal-organic frameworks (MOFs) - MFU-4l and KHCO3-cyclodextrin-MOF, we find that a dynamic treatment is necessary to obtain agreement between computational and experimental spectra. We therefore introduce a workflow that leverages machine-learning force fields to capture dynamics across multiple chemical exchange regimes, providing a significant improvement on static DFT predictions. In MFU-4l, we parameterise a two-component dynamic motion of the bicarbonate motif involving a rapid carbonyl seesaw motion and intermediate hydroxyl proton hopping. For KHCO3-CD-MOF, we combined experimental and modelling approaches to propose a new mixed carbonate-bicarbonate binding mechanism and thus, we open new avenues for the study and modelling of hydroxide-based CO2 capture materials by 17O NMR.

Olfactory Visualization Sensing Array Made with CelluMOFs to Predict Fruit Ripeness Using Deep Learning

Developing a colorimetry-based artificial scent screening system (i.e., an olfactory visual sensing system) with high sensitivity and accurate pattern recognition for detecting fruit ripeness remains challenging. In this work, we construct a flexible dye/CelluMOFs-based sensor array with improved sensitivity for on-site detection of characteristic gases of fruits and integrate a densely connected convolutional network (DenseNet) into the sensor array, enabling it to recognize unique scent fingerprints and categorize the ripeness of fruits. In the system, CelluMOFs are synthesized through in situ growth of γ-cyclodextrin metal-organic frameworks (γ-CD-MOFs) on flexible fiber filter paper to fabricate a uniform, flexible and porous dye/CelluMOFs sensitive membrane. Compared to the pristine filter paper, the CelluMOFs exhibit increased porosity with a 62 times higher specific surface area and a 3-fold increase in dye loading capacity after 12 h of adsorption. The prepared dye/CelluMOFs sensing film shows outstanding mechanical and detection stability with negligible deviation after 100 cycles of rubbing. The colorimetric visualization arrays with multiple colorimetric dye/CelluMOFs chips, enable the sensitive recognition and detection of nine kinds of characteristic fruit odors and achieve a high response at 8-1500 ppm of trans-2-hexenal, showcasing remarkably low gas detection thresholds. On the basis of the ppm-level limit of detection with high sensitivity, the fabricated colorimetric sensor arrays are typically used for in situ assessment of fruit ripeness by integrating DenseNet. This approach achieves a satisfactory classification accuracy of 99.09% on the validation set, enabling high-precision prediction of fruit ripeness levels.

Cyclodextrin supramolecular assembly confined luminescent materials

The macrocyclic supramolecular assembly confinement effect not only induces or extends the fluorescence/phosphorescence luminescence behavior of guest molecules but has also been widely applied in the research fields of chemistry, biology, and materials. This review primarily describes recent advances in cyclodextrin (CD) supramolecular assembly confined luminescent materials. Taking advantage of their hydrophobic cavity, CDs and their derivatives effectively encapsulate guest molecules and special functional groups or further assemble and polymerize to restrict the motion of guest chromophores, inducing and enhancing the luminescence behavior and realizing intelligent stimulus-responsive luminescence depending on changes in temperature, light, redox reactions and solvent polarity, which are successfully applied in targeted cell imaging, sensing, information encryption, anti-counterfeiting and flexible electronic light-emitting devices. With the emergence of new chromophores and CD primitives, spatial confinement within CD supramolecular assemblies will further realize the rapid development of supramolecular science and technology in circularly polarized luminescence, fluorescence/phosphorescence cascade energy transfer, light-harvesting energy-transfer systems and long persistent luminescent materials.

Cyclodextrin metal-organic framework@SiO2 nanocomposites for poorly soluble drug loading and release

The development of non-toxic drug carrier materials with high loading capacity, sustained release properties, stability, and biocompatibility holds significant medical value and potential for loading and releasing poorly soluble drugs. In this study, we synthesized a biocompatible, non-toxic, environmentally friendly CD-MOF porous material with high specific surface area and tunable structure. By incorporating SiO2 to enhance the stability of MOF materials, the synthesized CD-MOF@SiO2 material shows promising applications in drug delivery. The obtained CD-MOF@SiO2 nanocomposite was utilized as a carrier for the poorly soluble drug, folic acid. Characterization of the drug-loaded composite before and after drug loading was performed using scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, N2 adsorption-desorption, and X-ray diffraction analyses, showing improved stability as indicated by thermogravimetric analysis and derivative thermogravimetry data. UV spectrophotometry was used to investigate the loading and sustained release of folic acid under different conditions in PBS buffer, demonstrating that the well-structured CD-MOF@SiO2 material exhibits high drug loading and controllable release properties. The CD-MOF@SiO2 achieved a high drug loading efficiency (166.78%) and encapsulation rate (83.39%) for folic acid, leading to a significant increase in apparent solubility from 1.6 μg mL-1 in its free form to 21.74 mg mL-1, a 13 588-fold expansion. This work presents a novel, efficient, and highly valuable approach for the development of carrier materials for loading and releasing poorly soluble drugs.

Metal-organic frameworks in oral drug delivery

Metal-organic frameworks (MOFs) offer innovative solutions to the limitations of traditional oral drug delivery systems through their unique combination of metal ions and organic ligands. This review systematically examines the structural properties and principles of MOFs, setting the stage for their application in drug delivery. It discusses various classes of MOFs, including those based on zirconium, iron, zinc, copper, titanium, aluminum, potassium, and magnesium, assessing their drug-loading capacities, biocompatibility, and controlled release mechanisms. The effectiveness of MOFs is illustrated through case studies that highlight their capabilities in enhancing drug solubility, providing protection against the harsh gastrointestinal environment, and enabling precise drug release. The review addresses potential challenges, particularly the toxicity concerns associated with MOFs, and calls for further research into their biocompatibility and interactions with biological systems. It concludes by emphasizing the potential of MOFs in revolutionizing oral drug delivery, highlighting the critical need for comprehensive research to harness their full potential in clinical applications.

Ultra-small gold nanoparticles embedded cyclodextrin metal-organic framework composite membrane to achieve antibacterial and humidity-responsive functions

Cyclodextrin metal-organic framework (CD-MOF) is an edible and porous material that can serve as a template for synthesizing small-sized metal nanoparticles. However, its highly hydrophilic nature has limited its wider application. Herein, ultra-small gold nanoparticles (U-AuNPs) were loaded into CD-MOF to produce a composite material Au@CD-MOF. The CD-MOF was utilized as a template to control the size of the AuNPs. The synthesized Au@CD-MOF was easily dispersible in aqueous medium and its released U-AuNPs exhibited effective water dispersion stability within 120 days. Additionally, compared to gold nanoparticles prepared using traditional methods (T-AuNPs), the U-AuNPs exhibited superior antibacterial properties. Furthermore, hydrophilic Au@CD-MOF was incorporated into a hydrophobic polydimethylsiloxane (PDMS) matrix (Au@CD-MOF/PDMS) to achieve a humidity-responsive antibacterial function. The composite membrane exhibited remarkable responsiveness to humidity, showing almost no release of U-AuNPs at 0 % humidity. However, it exhibited approximately 89 % release within 1 h, and complete release of U-AuNPs was observed within 4 h under 100 % humidity. These findings highlight the successful preparation of a humidity-responsive antibacterial composite membrane, which has great potential applications in various scenarios, particularly in the field of antibacterial food packaging.

Monomeric, Oligomeric, Polymeric, and Supramolecular Cyclodextrins as Catalysts for Green Chemistry

This review comprehensively covers recent developments of cyclodextrin-mediated chemical transformations for green chemistry. These cyclic oligomers of glucose are nontoxic, eco-friendly, and recyclable to accomplish eminent functions in water. Their most important feature is to form inclusion complexes with reactants, intermediates, and/or catalysts. As a result, their cavities serve as sterically restricted and apolar reaction fields to promote the efficiency and selectivity of reactions. Furthermore, unstable reagents and intermediates are protected from undesired side reactions. The scope of their applications has been further widened through covalent or noncovalent modifications. Combinations of them with metal catalysis are especially successful. In terms of these effects, various chemical reactions are achieved with high selectivity and yield so that valuable chemicals are synthesized from multiple components in one-pot reactions. Furthermore, cyclodextrin units are orderly assembled in oligomers and polymers to show their cooperation for advanced properties. Recently, cyclodextrin-based metal-organic frameworks and polyoxometalate-cyclodextrin frameworks have been fabricated and employed for unique applications. Cyclodextrins fulfill many requirements for green chemistry and should make enormous contributions to this growing field.

Symmetry-Breaking and Symmetry-Retaining Morphological Evolution of the Single Crystals of Cyclodextrin Metal-Organic Frameworks

The morphological symmetry-retaining and symmetry-breaking of single crystals of the γ-cyclodextrin metal-organic framework have been achieved via introducing lower symmetric β-cyclodextrins and α-cyclodextrins, respectively. β-cyclodextrins led to a morphological evolution with retained symmetry from cubic to rhombic dodecahedra, while α-cyclodextrins resulted in the original cubic crystal missing a vertex angle presenting symmetry-breaking behavior. The crystal structures of rhombic dodecahedra and angle-deficient crystals were confirmed through X-ray crystallography, and the mechanisms underlying the morphological transformation evolution were further analyzed. Our work not only provides a rare case realizing two different paths of morphological evolution in one system, but also encourages future efforts towards the evolution of artificial crystal systems in a natural way.

Unsymmetric Chiral Ligands for Large Metallo-Macrocycles: Selectivity of Orientational Self-Sorting

Nature uses various chiral and unsymmetric building blocks to form substantial and complex supramolecular assemblies. In contrast, the majority of organic ligands used in metallosupramolecular chemistry are symmetric and achiral. Here we extend the group of unsymmetric chiral bile acids used as a scaffold for organic bispyridyl ligands by employing chenodeoxycholic acid (CDCA), an epimer of the previously used ursodeoxycholic acid (UDCA). The epimerism, flexibility, and bulkiness of the ligands leads to large structural differences in coordination products upon reaction with Pd(NO3)2. The UDCA-bispyridyl ligand self-assembles quantitatively into a single crown-like Pd3L6 complex, whereas the CDCA ligand provides a mixture of coordination complexes of general formula PdnL2n, i.e., Pd2L4, Pd3L6, Pd4L8, Pd5L10, and even Pd6L12 containing an impressive 120 chiral centers. The coordination products were studied by a combination of analytical methods, with ion-mobility mass spectrometry (IM-MS) providing valuable details on their structure and allowed an effective separation of m/z 1461 to individual signals according to the arrival time distribution, thereby revealing four different ions of [Pd3L6(NO3)3]3+, [Pd4L8(NO3)4]4+, [Pd5L10(NO3)5]5+, and [Pd6L12(NO3)6]6+. The structures of all the complexes were modelled using DFT calculations. Finally, the challenges and conclusions in determining the specific structural identity of these unsymmetric species are discussed.

Sustained-Release Hydrogen-Powered Bilateral Microneedles Integrating CD-MOFs for In Situ Treating Allergic Rhinitis

Glucocorticoids are widely used for treating allergic rhinitis, but conventional intranasal administration encounters unfavorable nasal cilia clearance and nasal mucosal barrier. Herein, a bilateral microneedle patch is fabricated for delivering cyclodextrin-based metal-organic frameworks (CD-MOF) encapsulating dexamethasone (DXMS) and paeonol (Pae), while NaH particles are mounted on the basal part of each microneedle. By intranasal administration, the microneedles are propelled into the nasal mucosa by NaH-generated hydrogen and then swell to form a hydrogel for sustainedly releasing drugs. The DXMS/Pae combination is demonstrated to be superior to more than the twofold dose of DXMS alone for improving allergic rhinitis in rats. It involves reducing mast cell degranulation and modulating Treg/Th17 cell homeostasis, whereas inhibiting Th1 to Th2 differentiation is associated with regulating the GATA3/T-bet pathway, as well as repairing epithelial barrier function by increasing MUC1 and downregulating periostin. In addition, this delivery system modulates the lipid metabolism of the nasal mucosa. Notably, the newly designed device significantly enhances the drug's therapeutic effect, and NaH-generated hydrogen may have the potential adjunctive therapeutic effect. Collectively, such an emerging microneedle-mediated nasal drug delivery creates a new form for alleviating immune inflammation and contributes a promising solution to reduce clinical glucocorticoid abuse.

Purification of gamma-cyclodextrin via selective coordination with potassium ions to form metal-organic frameworks

Efficient purification of gamma-cyclodextrin (γ-CD) is always challenging due to its structural similarity to other CDs and low crystallinity in water. In addressing this issue, an approach was proposed based on the formation mechanism of cyclodextrin metal-organic frameworks (CD-MOFs). This method involved the selective coordination of CDs mixture with potassium ions in water, facilitated by ethanol-induced crystallization, leading to the purification of γ-CD. The results showed that potassium ions enhanced γ-CD crystallization, and ethanol was crucial to selectively coordinating potassium ions with γ-CD. The characterizations revealed that the resulting CD-MOFs exhibited a small particle size, high surface area, and high thermal stability, and was identical to γ-CD-MOF, further indicating the final γ-CD with high purity. The separation factors of γ-CD/α-CD and γ-CD/β-CD were 309 and 260, respectively. Moreover, this method was validated through its application to the industrial enzymatic CDs mixture. The purification of γ-CD could achieve 99.99 ± 0.01 % after four crystallization cycles. Therefore, selectively coordinating with potassium ions to form MOFs provided a valuable reference for the purification of γ-CD and even the direct synthesis of γ-CD-MOF from CDs mixture. This advancement will also benefit the future production and application of γ-CD.

Cyclodextrin-based metal-organic frameworks transforming drug delivery

Cyclodextrin-based metal-organic frameworks (CD-MOFs) are gaining traction in the realm of drug delivery due to their inherent versatility and potential to amplify drug efficacy, specificity, and safety. This article explores the predominant preparation techniques for CD-MOFs, encompassing methods like vapor diffusion, microwave-assisted, and ultrasound hydrothermal approaches. Native CD-MOFs present compelling advantages in drug delivery applications. They can enhance drug loading capacity, stability, solubility, and bioavailability by engaging in diverse interactions with drugs, including host-guest, hydrogen bonding, and electrostatic interactions. Beyond their inherent properties, CD-MOFs can be customized as drug carriers through two primary strategies: co-crystallization with functional components and surface post-modifications. These tailored modifications pave the way for controlled release manners. They allow for slow and sustained drug release, as well as responsive releases triggered by various factors such as pH levels, glutathione concentrations, or specific cations. Furthermore, CD-MOFs facilitate targeted delivery strategies, like pulmonary or laryngeal delivery, enhancing drug delivery precision. Overall, the adaptability and modifiability of CD-MOFs underscore their potential as a versatile platform for drug delivery, presenting tailored solutions that cater to diverse biomedical and industrial needs.

Enhanced stability and biocompatibility of HIPEs stabilized by cyclodextrin-metal organic frameworks with inclusion of resveratrol and soy protein isolate for β-carotene delivery

High internal phase Pickering emulsions (HIPEs) constitute a significant research domain within colloid interface chemistry, addressing the demand for robust emulsion systems across various applications. An innovative nanoparticle, synthesized from a cyclodextrin metal-organic framework encapsulated with a composite of resveratrol and soy isolate protein (RCS), was employed to fortify a high internal phase emulsion. The emulsion's three-dimensional printing capabilities, alongside the encapsulated delivery efficacy for β-carotene, were thoroughly examined. Cyclodextrin metal-organic frameworks (CD-MOFs), facilitated by cellulose nanofibrils, were synthesized to yield particles at the nanoscale, maintaining a remarkable 97.67 % cellular viability at an elevated concentration of 1000 μg/ml. The RCS nanoparticles demonstrated thermal stability and antioxidant capacities surpassing those of CD-MOF. The integration of soybean isolate protein augmented both the hydrophobicity (from 21.95 ± 0.64° to 59.15 ± 0.78°) and the interfacial tension (from 14.36 ± 0.46 mN/m to 5.34 ± 0.81 mN/m) of the CD-MOF encapsulated with resveratrol, thereby enhancing the RCS nanoparticles' adsorption at the oil-water interface with greater stability. The durability of the RCS-stabilized high internal phase emulsions was contingent upon the RCS concentration. Emulsions stabilized with 5 wt%-RCS exhibited optimal physical and chemical robustness, demonstrating superior performance in emulsion 3D printing and β-carotene encapsulation delivery. This investigation furnishes a novel perspective on the amalgamation of food customization and precision nutrition.

Constructing Photocatalytic Covalent Organic Frameworks with Aliphatic Linkers

Photocatalytic covalent organic frameworks (COFs) are typically constructed with rigid aromatic linkers for crystallinity and extended π-conjugation. However, the essential hydrophobicity of the aromatic backbone can limit their performances in water-based photocatalytic reactions. Here, we for the first time report the synthesis of hydrophilic COFs with aliphatic linkers [tartaric acid dihydrazide (TAH) and butanedioic acid dihydrazide] that can function as efficient photocatalysts for H2O2 and H2 evolution. In these hydrophilic aliphatic linkers, the specific multiple hydrogen bonding networks not only enhance crystallization but also ensure an ideal compatibility of crystallinity, hydrophilicity, and light harvesting. The resulting aliphatic linker COFs adopt an unusual ABC stacking, giving rise to approximately 0.6 nm nanopores with an improved interaction with water guests. Remarkably, both aliphatic linker-based COFs show strong visible light absorption, along with a narrow optical band gap of ∼1.9 eV. The H2O2 evolution rate for TAH-COF reaches up to 6003 μmol h-1 g-1, in the absence of sacrificial agents, surpassing the performance of all previously reported COF-based photocatalysts. Theoretical calculations reveal that the TAH linker can enhance the indirect two-electron oxygen reduction reaction for H2O2 production by improving the O2 adsorption and stabilizing the *OOH intermediate. This study opens a new avenue for constructing semiconducting COFs using nonaromatic linkers.

CD-MOF-1 Growth on Polysaccharide Gels through Only C2-OH/C3-OH or C5-O/C6-OH Group Formed Four-Coordinated K+ Ions for Developing Porous Biogels

The γ-cyclodextrin (γ-CD) metal-organic frameworks (CD-MOF-1) consist of γ-CD and potassium (K+) ions through coordinating an eight-coordinated K+ ion with two C5-linked oxygen and C6-linked hydroxyl (C5-O/C6-OH) groups in the primary faces of adjacent γ-CD units and two C2- and C3-linked hydroxyl (C2-OH/C3-OH) groups in the secondary faces. Herein, we found polysaccharide gels with only C2-OH/C3-OH or C5-O/C6-OH groups in pyranoid rings can form four-coordinated K+ ions and then coordinate γ-CD in a KOH solution for CD-MOF-1 growth. Exposure of C2-OH/C3-OH or C5-O/C6-OH groups in polysaccharide gels is important to form active four-coordinated K+ ions. Mechanism supporting this work is that four-coordinated K+ ion sites are first formed after coordinating C2-OH/C3-OH groups in pectin and then coordinating C5-O/C6-OH groups in the primary faces of γ-CD units. Alternatively, four-coordinated K+ ions with C5-O/C6-OH groups in chitosan can coordinate the C2-OH/C3-OH groups in the secondary faces of γ-CD units. Mechanism of CD-MOF-1 growing on pectin and chitosan gels through the proposed four-coordinated K+ ions is also universally applicable to other polysaccharide gels with similar C2-OH/C3-OH or C5-O/C6-OH groups such as alginate gel. Based on this mechanism, we developed pectin and chitosan gel-based CD-MOF-1 composites and exemplified applications of them in antibacterial and organic dye removal. To help future research and applications of this mechanism, we share our theoretical assumption for further investigations that any matrices with an ortho-hydroxyl carbon chain or ortho-hydroxyl ether structures may form four-coordinated K+ ions for CD-MOF-1 growth. The proposed mechanism will broaden the development of novel CD-MOF-1 composites in various fields.

Synthesis of Nanosized γ-Cyclodextrin Metal-Organic Frameworks as Carriers of Limonene for Fresh-Cut Fruit Preservation Based on Polycaprolactone Nanofibers

To address the issue of bacterial growth on fresh-cut fruits, this paper reports the synthesis of nanosized γ-cyclodextrin metal-organic frameworks (CD-MOFs) using an ultrasound-assisted method and their application as carriers of limonene for antibacterial active packaging. The effects of the processing parameters on the morphology and crystallinity of the CD-MOFs are investigated, and the results prove that the addition of methanol is the key to producing nanosized CD-MOFs. The limonene loading content of the nanosized CD-MOFs can reach approximately 170 mg g-1. The sustained-release behaviors of limonene in the CD-MOFs are evaluated. Molecular docking simulations reveal the distribution and binding sites of limonene in the CD-MOFs. CD-MOFs are deposited on the surfaces of polycaprolactone (PCL) nanofibers via an immersion method, and limonene-loaded CD-MOF@PCL nanofibers are prepared. The morphology, crystallinity, thermal stability, mechanical properties, and antibacterial activity of the nanofibers are also studied. The nanofiber film effectively inhibits bacterial growth and prolongs the shelf life of fresh-cut apples. This study provides a novel strategy for developing antibacterial active packaging materials based on CD-MOFs and PCL nanofibers.

Multilayer Ti3C2-CNTs-Au Loaded with Cyclodextrin-MOF for Enhanced Selective Detection of Rutin

In this work, multi-layer Ti3C2 - carbon nanotubes - gold nanoparticles (Ti3C2-CNTs-Au) and cyclodextrin metal-organic framework - carbon nanotubes (CD-MOF-CNTs) have been prepared by in situ growth method and used to construct the ultra-sensitive rutin electrochemical sensor for the first time. Among them, the large number of metal active sites of Ti3C2, the high electron transfer efficiency of CNTS, and the good catalytic properties of AuNPs significantly enhance the electrochemical properties of the composite carbon nanomaterials. Interestingly, CD-MOF has a unique host-guest recognition and a large number of cavities, molecular gaps, and surface reactive groups, which gives the composite outstanding accumulation properties and selectivity for rutin. Under the optimized conditions, the constructed novel sensor has satisfactory detection performance for rutin in the range of 2 × 10-9 to 8 × 10-7 M with a limit of detection of 6.5 × 10-10 M. In addition, the sensor exhibits amazing anti-interference performance against rutin in some flavonoid compounds and can be used to test natural plant samples (buckwheat, Cymbopogon distans, and flos sophorae immaturus). This work has promising applications in the field of environmental and food analysis, and exploring new directions for the application of Mxene-based composites.

Controlled release of vitamin A palmitate from crosslinked cyclodextrin organic framework for dry eye disease therapy

Controlled release drug delivery systems of eye drops are a promising ophthalmic therapy with advantages of good patient compliance and low irritation. However, the lack of a suitable drug carrier for ophthalmic use limits the development of the aforementioned system. Herein, the crosslinked cyclodextrin organic framework (COF) with a cubic porous structure and a uniform particle size was synthesized and applied to solidify vitamin A palmitate (VAP) by using the solvent-free method. The VAP@COF suspension eye drops were formulated by screening co-solvents, suspending agents, and stabilizing agents to achieve a homogeneous state and improve stability. According to the in vitro release study, the VAP@COF suspension exhibited a controlled release of VAP within 12 h. Both the ex vivo corneal contact angle and in vivo fluorescence tracking indicated that the VAP@COF suspension prolonged the VAP residence time on the ocular surface. This suspension accelerated the recovery of the dry eye disease (DED) model in New Zealand rabbits. Furthermore, the suspension was non-cytotoxic to human corneal epithelial cells and non-irritation to rabbit eyes. In summary, the particulate COF is an eye-acceptable novel carrier that sustains release and prolongs the VAP residence time on the ocular surface for DED treatment.

Encapsulation of apigenin into β-cyclodextrin metal-organic frameworks with high embedment efficiency and stability

In an effort to improve the application performance of apigenin, β-cyclodextrin metal-organic frameworks (BCDMOFs) known as porous materials were used to encapsulate apigenin via an innovative pH-adjusted method. The embedment efficiency had a significant positive pH dependence, reaching a maximum of 79.2 % ± 1.2 % at pH12. Scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis demonstrated formation of apigenin/BCDMOFs composites, and exposure of BCDMOFs pores facilitated high embedment efficiency. Storage stability experiment and kinetic analysis showed degradation of apigenin/BCDMOFs composites was less than that of apigenin alone. Apigenin stability was increased by approximately 18 % after 7 days. BCDMOFs effectively encapsulated and controlled the release of apigenin, and the composites exhibited improved application performance in vitro.

Lutein Loaded in β-Cyclodextrin Metal-Organic Frameworks for Stability and Solubility Enhancements

Lutein (Lut) is a recognized nutritional supplement known for its antioxidative and anti-inflammatory properties, crucial in mitigating ocular disease. However, enhancements to Lut stability and solubility remain challenges to be addressed in the healthcare industry. Herein, we fabricated and evaluated a food-grade highly porous β-cyclodextrin metal-organic framework (β-CD-MOF) for its ability to encapsulate Lut. Lut stability considerably improved when loaded into β-CD-MOF to form a Lut@β-CD-MOF complex, which exhibited better stability than Lut loaded into the γ-cyclodextrin metal-organic framework (Lut@γ-CD-MOF), Lut@β-CD, and commercial product (Blackmores™) at 40°C, 60°C, and 70°C, respectively. The solubility of Lut@β-CD-MOF in water increased by 26.8-fold compared to raw Lut at 37°C. Lut@β-CD-MOF exhibited greater hydrophilicity, as determined by measuring the water contact angle. Molecular docking and other characterizations of Fourier transform infrared spectroscopy and powder X-ray diffraction confirmed that Lut was successfully encapsulated in the chamber formed by the three cyclodextrins in β-CD-MOF. Thermogravimetric analysis and Raman spectroscopy demonstrated that Lut distributed in the β-CD-MOF cavity deeply improved Lut stability and solubility. In conclusion, our findings underscored the function of β-CD-MOF in enhancing Lut stability and solubility for formulation applications.

β-Cyclodextrin metal-organic framework as a green carrier to improve the dissolution, bioavailability, and liver protective effect of luteolin

The incidence of acetaminophen-induced liver injury has increased, but effective prevention methods are limited. Although luteolin has hepatoprotective activity, its low solubility and bioavailability limit its applications. Cyclodextrin metal-organic frameworks (CD-MOFs) possess 3D-network structures and large inner cavities, which make them excellent carriers of poorly soluble drugs. In this study, we used CD-MOFs as carriers to improve the dissolution of luteolin and assessed their antioxidant activity, bioavailability, and hepatoprotective effects. Luteolin was loaded into β-CD-MOF, γ-CD-MOF, β-CD, and γ-CD, and characterized by powder X-ray diffractometry (PXRD) and thermogravimetric analysis (TGA). Our results showed that luteolin-β-CD-MOF was the most stable. The main driving forces were hydrogen bonds and van der Waals forces, as determined by molecular simulation. The loading capacity of luteolin-β-CD-MOF was 14.67 wt%. Compared to raw luteolin, luteolin-β-CD-MOF exhibited a 4.50-fold increase in dissolution and increased antioxidant activity in vitro. Luteolin-β-CD-MOF increased the bioavailability of luteolin by approximately 4.04- and 11.07-fold in healthy rats and liver injured rats induced by acetaminophen in vivo, respectively. As determined by biochemical analysis, luteolin-β-CD-MOF exhibited a better hepatoprotective effect than raw luteolin in rats with acetaminophen-induced liver injury. This study provides a new approach for preventing acetaminophen-mediated liver damage.

Building respirable powder architectures: utilizing polysaccharides for precise control of particle morphology for enhanced pulmonary drug delivery

INTRODUCTION

Dry powder inhaler (DPI) formulations are gaining attention as universal formulations with applications in a diverse range of drug formulations. The practical application of DPIs to pulmonary drugs requires enhancing their delivery efficiency to the target sites for various treatment modalities. Previous reviews have not explored the relation between particle morphology and delivery to different pulmonary regions. This review introduces new approaches to improve targeted DPI delivery using novel particle design such as supraparticles and metal-organic frameworks based on cyclodextrin.

AREAS COVERED

This review focuses on the design of DPI formulations using polysaccharides, promising excipients not yet approved by regulatory agencies. These excipients can be used to design various particle morphologies by controlling their physicochemical properties and manufacturing methods.

EXPERT OPINION

Challenges associated with DPI formulations include poor access to the lungs and low delivery efficiency to target sites in the lung. The restricted applicability of typical excipients contributes to their limited use. However, new formulations based on polysaccharides are expected to establish a technological foundation for the development of DPIs capable of delivering modalities specific to different lung target sites, thereby enhancing drug delivery.

Enhanced Stability and Solidification of Volatile Eugenol by Cyclodextrin-Metal Organic Framework for Nasal Powder Delivery

Eugenol (Eug) holds potential as a treatment for bacterial rhinosinusitis by nasal powder drug delivery. To stabilization and solidification of volatile Eug, herein, nasal inhalable γ-cyclodextrin metal-organic framework (γ-CD-MOF) was investigated as a carrier by gas-solid adsorption method. The results showed that the particle size of Eug loaded by γ-CD-MOF (Eug@γ-CD-MOF) distributed in the range of 10-150 μm well. In comparison to γ-CD and β-CD-MOF, γ-CD-MOF has higher thermal stability to Eug. And the intermolecular interactions between Eug and the carriers were verified by characterizations and molecular docking. Based on the bionic human nasal cavity model, Eug@γ-CD-MOF had a high deposition distribution (90.07 ± 1.58%). Compared with free Eug, the retention time Eug@γ-CD-MOF in the nasal cavity was prolonged from 5 min to 60 min. In addition, the cell viability showed that Eug@γ-CD-MOF (Eug content range 3.125-200 µg/mL) was non-cytotoxic. And the encapsulation of γ-CD-MOF could not reduce the bacteriostatic effect of Eug. Therefore, the biocompatible γ-CD-MOF could be a potential and valuable carrier for nasal drug delivery to realize solidification and nasal therapeutic effects of volatile oils.

Supramolecular Structure of the β-Cyclodextrin Metal-Organic Framework Optimizes Iodine Stability and Its Co-delivery with l-Menthol for Antibacterial Applications

The spread of upper respiratory tract (URT) infections harms people's health and causes social burdens. Developing targeted treatment strategies for URT infections that exhibit good biocompatibility, stability, and strong antimicrobial effects remains challenging. The dual antimicrobial and antiviral effects of iodine (I2) in combination with the cooling sensation of l-menthol in the respiratory tract can simultaneously alleviate URT inflammation symptoms. However, as both I2 and l-menthol are volatile, addressing stability issues is crucial. In this study, a potassium iodide β-cyclodextrin metal-organic framework [β-CD-POF(I)] with appropriate particle size was used to coload and deliver I2 and l-menthol. Primarily, β-CD-POF(I) was employed as the most efficient carrier to significantly enhance the stability of I2, surpassing any other known protection strategies in the pharmaceutical field (CD complexations, PVP conjugations, and cadexomer iodine). The mechanism underlying the improvement in stability of I2 by β-CD-POF(I) was investigated through scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and molecular docking. The results revealed that the key processes involved in improving stability were the inclusion of I2 by β-CD cavities in β-CD-POF(I) and the formation of polyiodide anion between iodine ions and I2. Furthermore, the potential of β-CD-POF(I) to load and deliver drugs was validated, and coloading of l-menthol and I2 demonstrated reliable stability. β-CD-POF(I) achieved a rate of URT deposition ≥95% in vitro, and the combined antibacterial effects of coloaded I2 and l-menthol was better than I2 or PVP-I alone, with no irritation noted following URT administration in rabbits. Therefore, the stable coloading of drugs by β-CD-POF(I), leading to enhanced antimicrobial effects, provides a new strategy for treating URT infections.

Synergistic applications of cyclodextrin-based systems and metal-organic frameworks in transdermal drug delivery for skin cancer therapy

This review article explores the innovative field of eco-friendly cyclodextrin-based coordination polymers and metal-organic frameworks (MOFs) for transdermal drug delivery in the case of skin cancer therapy. We critically examine the significant advancements in developing these nanocarriers, with a focus on their unique properties such as biocompatibility, targeted drug release, and enhanced skin permeability. These attributes are instrumental in addressing the limitations inherent in traditional skin cancer treatments and represent a paradigm shift towards more effective and patient-friendly therapeutic approaches. Furthermore, we discuss the challenges faced in optimizing the synthesis process for large-scale production while ensuring environmental sustainability. The review also emphasizes the immense potential for clinical applications of these nanocarriers in skin cancer therapy, highlighting their role in facilitating targeted, controlled drug release which minimizes systemic side effects. Future clinical applications could see these nanocarriers being customized to individual patient profiles, potentially revolutionizing personalized medicine in oncology. With further research and clinical trials, these nanocarriers hold the promise of transforming the landscape of skin cancer treatment. With this study, we aim to provide a comprehensive overview of the current state of research in this field and outline future directions for advancing the development and clinical application of these innovative nanocarriers.

Metal-Assisted Carbohydrate Assembly

The sequence-controlled assembly of nucleic acids and amino acids into well-defined superstructures constitutes one of the most revolutionary technologies in modern science. The elaboration of such superstructures from carbohydrates, however, remains elusive and largely unexplored on account of their intrinsic constitutional and configurational complexity, not to mention their inherent conformational flexibility. Here, we report the bottom-up assembly of two classes of hierarchical superstructures that are formed from a highly flexible cyclo-oligosaccharide─namely, cyclofructan-6 (CF-6). The formation of coordinative bonds between the oxygen atoms of CF-6 and alkali metal cations (i) locks a myriad of flexible conformations of CF-6 into a few rigid conformations, (ii) bridges adjacent CF-6 ligands, and (iii) gives rise to the multiple-level assembly of three extended frameworks. The hierarchical superstructures present in these frameworks have been shown to modulate their nanomechanical properties. This research highlights the unique opportunities of constructing convoluted superstructures from carbohydrates and should encourage future endeavors in this underinvestigated field of science.

A Hydrogen-Bonded Organic Framework Equipped with a Molecular Nanovalve

The concept of a molecular nanovalve is applied to a synthesized biocompatible hydrogen-bonded organic framework (HOF), termed RSS-140, to load, trap, and subsequently release an antioxidant on command. Specifically, we exploit the pore windows of RSS-140 (i.e., β-CD cavities) to first load and trap the antioxidant, Trolox, within the internal pores of the HOF (Trolox⊂RSS-140) and, to prevent it from leaching, utilize supramolecular chemistry to complex azobenzene (Azo) with β-CD (Trolox⊂Azo@RSS-140). The molecular nanovalve is fully realized upon exposing Trolox⊂Azo@RSS-140 to UV light with a specific wavelength, which induces Azo isomerization, Azo decomplexation from β-CD, and subsequent release of Trolox from the pores of RSS-140. The biocompatibility and nontoxicity of Trolox⊂Azo@RSS-140, together with the absolute control over the nanovalve opening, were established to yield a system that safely and slowly releases Trolox for longer-lasting antioxidant efficacy. As the field of supramolecular chemistry is rich with similar systems and many such systems can be used as building blocks to construct HOFs or other extended framework materials, we envision the molecular nanovalve concept to be applied widely for controllably delivering molecular cargo for diverse applications.

Active cellulose acetate/purple sweet potato anthocyanins@cyclodextrin metal-organic framework/eugenol colorimetric film for pork preservation

As a natural pH-sensing colorant, purple sweet potato anthocyanins (PSPAs) have demonstrated great potential in colorimetric film for freshness monitoring. However, the photothermal instability of PSPAs is still a challengeable issue. Herein, γ-cyclodextrin metal-organic framework (CD-MOF) loaded with PSPAs (PSPAs@CD-MOF, i.e., PM) and eugenol (EUG) were incorporated in cellulose acetate (CA) matrix for developing a smart active colorimetric film of CA/PM/EUG, where PM and EUG were hydrogen-bonded with CA. Attentions were focused on the photothermal colorimetric stability, colorimetric response, and antibacterial activity of the films. The presence of PM and EUG endowed the film outstanding UV-blocking performance and enhanced the barrier against water vapor and oxygen. Target film of CA/PM15/EUG10 had good photothermal colorimetric stability due to the protection of CD-MOF on PSPAs and the color changes with pH-stimuli were sensitive and reversible. In addition to antioxidant activity, CA/PM15/EUG10 had antibacterial activity against Escherichia coli and Staphylococcus aureus. The application trial results indicated that the CA/PM15/EUG10 was valid to indicate pork freshness and extended the shelf-life by 100 % at 25 °C, which has demonstrated a good perspective on smart active packaging for freshness monitoring and shelf-life extension.

Carboxymethyl potato starch hydrogels encapsulated cyclodextrin metal-organic frameworks for enantioselective loading of S-naproxen and its programmed release

A natural polysaccharide-based vehicle is facilely prepared for enantioselective loading of S-naproxen (S-NPX) and its programmed release. Cyclodextrin metal-organic frameworks (CD-MOF) are synthesized through the coordination of K+ with γ-cyclodextrin (γ-CD). Compared with R-NPX, the CD-MOF preferably combines with S-NPX, which can be confirmed by the thermodynamic calculations. The S-NPX loaded CD-MOF (CD-MOF-S-NPX) is grafted with disulfide bond (-S-S-) to improve its hydrophobicity, and the loaded S-NPX is further encapsulated in the chiral cavity of γ-CD by carboxymethyl potato starch (CPS) hydrogels. The intermolecular hydrogen bonding of the CPS hydrogels is prone to be destroyed in mildly basic media (∼pH 8.0), resulting in the swelling of the hydrogels; the -S-S- linkage in the vehicle can be cleaved in the presence of glutathione (GSH), leading to the collapse of the CD-MOF. Therefore, the programmed release of S-NPX can be achieved. Also in this work, the release kinetics is investigated, and the results indicate that the release of S-NPX is controlled by the Higuchi model.

Pore engineering of micro/mesoporous nanomaterials for encapsulation, controlled release and variegated applications of essential oils

Essential oils have become increasingly popular in fields of medical, food and agriculture, owing to their strongly antimicrobial, anti-inflammation and antioxidant effects, greatly meeting demand from consumers for healthy and safe natural products. However, the easy volatility and/or chemical instability of active ingredients of essential oils (EAIs) can result in the loss of activity before realizing their functions, which have greatly hindered the widely applications of EAIs. As an emerging trend, micro/mesoporous nanomaterials (MNs) have drawn great attention for encapsulation and controlled release of EAIs, owing to their tunable pore structural characteristics. In this review, we briefly discuss the recent advances of MNs that widely used in the controlled release of EAIs, including zeolites, metal-organic frameworks (MOFs), mesoporous silica nanomaterials (MSNs), and provide a comprehensive summary focusing on the pore engineering strategies of MNs that affect their controlled-release or triggered-release for EAIs, including tailorable pore structure properties (e.g., pore size, pore surface area, pore volume, pore geometry, and framework compositions) and surface properties (surface modification and surface functionalization). Finally, the variegated applications and potential challenges are also given for MNs based delivery strategies for EAIs in the fields of healthcare, food and agriculture. These will provide considerable instructions for the rational design of MNs for controlled release of EAIs.

Enhanced stability of anthocyanins by cyclodextrin-metal organic frameworks: Encapsulation mechanism and application as protecting agent for grape preservation

Anthocyanins are promising naturally occurring food preservatives for enhancing the quality of food products due to their excellent antioxidant properties. However, their low stability hinders their food packaging application. Here, we propose a facile strategy to achieve the improved stability of anthocyanins encapsulated in γ-cyclodextrin metal-organic frameworks (CD-MOFs) with an in-depth exploration of their structure-property relationships. The adsorbed anthocyanins in CD-MOFs are stabilized by multiple cooperative non-covalent interactions including hydrogen bonding and van der Waals (vdW) interactions as demonstrated by density functional theory (DFT) calculations and spectroscopy analysis. Particularly, by ion-exchange of acetate ions into the pores of CD-MOFs, the resulting CD-MOFs (CD-MOF_OAc) shows a higher anthocyanins adsorption rate with a maximum loading capacity of 83.7 % at 1 min. Besides, CD-MOF_OAc possesses the more effective protecting effect on anthocyanins with at least two-fold enhancement of stability in comparison of free anthocyanins under heating and light irradiation. The anthocyanins encapsulated CD-MOFs films for fruit freshness was validated by the Kyoho experiment. This novel encapsulation system provides a new possibility for the potential use of CD-MOFs as the encapsulating material for anthocyanins in fruit preservation.

γ-Cyclodextrin metal-organic frameworks as the promising carrier for pulmonary delivery of cyclosporine A

γ-Cyclodextrin metal-organic frameworks (CD-MOFs) are considered as a green and biocompatible material with great potential in drug delivery systems. Original CD-MOFs show the poor aerosol properties, which limit the application in pulmonary drug delivery. To improve the in vitro deposition properties, herein, we synthesized CD-MOFs by the vapor diffusion method using a series of modulators to achieve better pulmonary delivery of cyclosporine A (CsA). The results showed that blank CD-MOFs and drug loaded CD-MOFs prepared with different modulators all preserved the cubical shape, and exhibited the similar crystal form, structural characteristics, thermal behaviors and release properties. In addition, drug loaded CD-MOFs prepared with polyethylene glycol 10000 (PEG 10000) as a modulator exhibited better in vitro aerosol performance than those of synthesized using other modulators, and the in vivo pharmacokinetics data demonstrated that the bioavailability of CsA could be significantly enhanced by inhalation administration of drug loaded CD-MOFs compared with oral administration of Neoral®. The repeated dose inhalation toxicity also confirmed the fine biocompatibility of CD-MOFs as the carrier for pulmonary drug delivery. Therefore, the results demonstrated CD-MOFs as the promising carrier could be used for pulmonary drug delivery.

Recent advances in metal organic frameworks-based magnetic nanomaterials for waste water treatment

Magnetic nanoparticle-incorporated metal organic frameworks (MOF) are potential composites for various applications such as catalysis, water treatment, drug delivery, gas storage, chemical sensing, and heavy metal ion removal. MOFs exhibits high porosity and flexibility enabling guest species like heavy metal ions to diffuse into bulk structure. Additionally, shape and size of the pores contribute to selectivity of the guest materials. Incorporation of magnetic materials allows easy collection of adsorbent materials from solution system making the process simple and cost-effective. In view of the above advantages in the present review article, we are discussing recent advances of different magnetic material-incorporated MOF (Mg-MOF) composite for application in photocatalytic degradation of dyes and toxic chemicals, adsorption of organic compounds, adsorption of heavy metal ions, and adsorption of dyes. The review initially discusses on properties of Mg-MOF, different synthesis techniques such as mechanochemical, sonochemical (ultrasound) synthesis, slow evaporation and diffusion methods, solvo(hydro)-thermal and iono-thermal method, microwave-assisted method, microemulsion method post-synthetic modification template strategies and followed by application in waste water treatment.

Chitosan-graft-poly(lactic acid)/CD-MOFs degradable composite microspheres for sustained release of curcumin

The solubility of cyclodextrin metal-organic frameworks (CD-MOFs) in aqueous media making it not suitable as sustained-release drug carrier. Here, curcumin-loaded CD-MOFs (CD-MOFs-Cur) was embedded in chitosan-graft-poly(lactic acid) (CS-LA) via a solid-in-oil-in-oil (s/o/o) emulsifying solvent evaporation method forming the sustained-release composite microspheres. At CS-LA concentration of 20 mg/mL, the composite microspheres showed good sphericity. The average particle size of CS-LA/CD-MOFs-Cur (2:1), CS-LA/CD-MOFs-Cur (4:1) and CS-LA/CD-MOFs-Cur (6:1) composite microspheres was about 9.3, 12.3 and 13.5 μm, respectively. The above composite microspheres exhibited various degradation rates and curcumin release rates. Treating in HCl solution (pH 1.2) for 120 min, the average particle size of above microspheres reduced 28.19 %, 24.34 % and 6.19 %, and curcumin released 86.23 %, 78.37 % and 52.57 %, respectively. Treating in PBS (pH 7.4) for 12 h, the average particle size of above microspheres reduced 30.56 %, 26.56 % and 10.66 %, and curcumin released 68.54 %, 54.32 % and 31.25 %, respectively. Moreover, the composite microspheres had a favorable cytocompatibility, with cell viability of higher than 90 %. These composite microspheres open novel opportunity for sustained drug release of CD-MOFs.

Never-Ending Story: New Cyclodextrin-Based Metal-Organic Framework Crystal Structures Obtained Using Different Crystallization Methods

Six novel cyclodextrin (CD)-based metal-organic frameworks (MOFs) were synthesized using distinct crystallization methodologies. A modified vapor diffusion method is introduced for the first time, termed fast crystallization, which enables the rapid solid-state formation of MOF compounds. This innovative method yielded four of the newly synthesized MOFs. The crystal structures of five obtained frameworks were structurally characterized through single-crystal X-ray diffraction, while one, compound 5 (γ-CD-K-5), was additionally characterized as a bulk powder. Structural analysis revealed that two of the newly obtained MOFs, namely, compound 2 (α-CD-K-2) and compound 3 (α-CD-Rb-3), exhibited isostructural characteristics, forming a three-dimensional (3D) framework. Compound 1 (α-CD-K-1) shared the same space group as EVEGET (α-CD-K) and displayed the same framework type. Furthermore, the crystal packing of compound 4 (β-CD-K-4) closely resembled that of compound 1 and EVEGET, with the only distinction lying in the type of CD employed. Notably, compound 6 (γ-CD-K-6) incorporated an iodine ion with an occupancy of 0.2. To discern the intermolecular interactions within the obtained MOFs, the Hirshfeld surface was calculated using Crystal Explorer software.

Dual regulations on texture and water mobility of shrimp surimi gel with sustained-release epigallocatechin-3-gallate in γ-cyclodextrin metal organic frameworks: Insights into functionality and mechanisms

Epigallocatechin-3-gallate (EGCG) could demonstrate crosslinking effects on myofibrillar proteins, yet its proneness to self-aggregation could bring excessive crosslinking and water loss within gels, hindering its application as an additive during thermal gelation process. Here, encapsulation with the γ-cyclodextrin metal organic framework (γ-CD-MOF) before the use of EGCG was found to play a dual role: alleviating over-crosslinking of proteins and elevating water retention within gels. Results showed that EGCG got a sustainable release throughout the thermal process due to the gradual fracture of O-K coordinate bounds and structural collapse of γ-CD-MOF. Mechanism insights revealed that the use of EGCG loaded γ-CD-MOF (EGCG@γ-CD-MOF) could regulate formation efficiency on disulfide bounds and promote protonation transition of the amino groups in proteins. Moreover, EGCG@γ-CD-MOF brought a higher retention of phenols within gels through preventing oxidative transformation of phenols towards quinones, which were verified to display a higher affinity towards myosin via molecular calculations.

New opportunities for cyclodextrins in supramolecular assembly: metal organic frameworks, crystalline self-assembly, and catalyzed assembly

Cyclodextrins (CDs) are widely used macrocycles in supramolecular assembly due to their easy availability, versatile functionality and excellent biocompatibility. Although they are well-known for forming host-guest complexes with a wide range of guests and this host-guest chemistry has long been utilized in industry and academia, new opportunities have arisen in recent years, particularly in supramolecular assembly. In the present review, we will first provide a basic introduction to CDs and then summarize their emerging roles in the fields of supramolecular chemistry and materials. This includes their involvement in hybrid frameworks with inorganic components such as metal ions and polyoxometalates, crystalline self-assembly with amphiphilic molecules, and their new possibility of "catassembly" and induced chiral supramolecular structures that have previously been overlooked. Finally, we will comment on the future perspectives of CDs to inspire more ideas and efforts, with the aim of promoting diverse applications of CDs in supramolecular materials.

From 3D to 2D: Directional Morphological Evolution of a Three-Dimensional Covalent Organic Framework

The morphology of materials has a huge impact on their properties and functions; however, the precise control and direct evolution toward specific morphologies remains challenging. Herein, we outline a novel strategy for the morphology modulation of covalent organic frameworks based on COF-300 with the diamond structure, which usually exhibits a three-dimensional shuttle morphology. A monofunctional structural regulator has been designed to break the continuity of the three-dimensional structure. As the proportion of the monofunctional structural regulator increases, the morphology of COF-300 shows a directional evolution from a shuttle morphology to a two-dimensional nanosheet, while still retaining the consistency of the crystal structure. Our study reports the first two-dimensional nanosheet based on a three-dimensional structured COF to date and will inspire future research into the traced morphological evolution in materials by predesign.

A selenoureido-iminoglycolipid transported by zeolitic-imidazolate framework nanoparticles: a novel antioxidant therapeutic approach

A selenium-containing metal-organic framework with remarkable antioxidant capacity and ROS-scavenging activity was constructed by a controlled de novo encapsulation approach of a glycoconjugate mimetic, specifically a sp2-iminoglycolipid bearing a selenoureido fragment (DSeU), within a zeolitic-imidazolate framework exoskeleton. Biocompatible and homogeneous nanosized particles of ∼70 nm (DSeU@ZIF8) were obtained, which could be efficiently internalized in cells, overcoming the poor solubility in biological media and limited bioavailability of glycolipids. The ZIF-particle served as nanocarrier for the intracellular delivery of the selenocompound to cells, promoted by the acidic pH inside endosomes/lysosomes. As demonstrated by in vitro studies, the designed DSeU@ZIF8 nanoparticles displayed a high antioxidant activity at low doses; lower intracellular ROS levels were observed upon the uptake of DSeU@ZIF8 by human endothelial cells. Even more interesting was the finding that these DSeU@ZIF8 particles were able to reverse to a certain level the oxidative stress induced in cells by pre-treatment with an oxidizing agent. This possibility of modulating the oxidative stress in living cells may have important implications in the treatment of diverse pathological complications that are generally accompanied with elevated ROS levels.

Efficient oral delivery of resveratrol-loaded cyclodextrin-metal organic framework for alleviation of ulcerative colitis

Developing innovative strategies for the oral administration of phytochemicals presents a promising approach to addressing intestinal diseases. However, numerous challenges persist, including limited therapeutic efficacy, poor bioavailability, and inadequate biocompatibility. In this study, we employed a cross-linked cyclodextrin-metal organic framework (CDF) to encapsulate resveratrol (Res), generating Res-CDF, which was subsequently incorporated into natural polysaccharide hydrogel microspheres (Res-CDF in MPs) for targeted oral delivery to alleviate ulcerative colitis (UC). The underlying adsorption mechanism of Res by γ-CD elucidated by molecular dynamics simulations. Importantly, the Res-CDF in MPs formulation protected against gastric acid degradation while preserving the bioactivity of Res. Moreover, the design enabled specific release of Res-CDF in response to the mildly alkaline environment of the intestinal tract, followed by sustained Res release. In UC mice model, Res-CDF in MPs demonstrated potent anti-inflammatory effects by attenuating pro-inflammatory cytokine production and exhibited antioxidant properties. Additionally, Res-CDF in MPs enhanced the expression of tight junction proteins ZO-1, Occludin, and mucin-2 (Muc-2), thereby maintaining normal intestinal barrier function. This innovative oral delivery strategy capitalizes on the advantageous properties of polysaccharide hydrogel and CDF to augment bioavailability of phytochemicals, laying the groundwork for developing novel oral interventions employing natural phytochemicals to address intestinal-related diseases.

Ultrafast Synthesis of Graphene-Embedded Cyclodextrin-Metal-Organic Framework for Supramolecular Selective Absorbency and Supercapacitor Performance

Limited by preparation time and ligand solubility, synthetic protocols for cyclodextrin-based metal-organic framework (CD-MOF), as well as subsequent derived materials with improved stability and properties, still remains a challenge. Herein, an ultrafast, environmentally friendly, and cost-effective microwave method is proposed, which is induced by graphene oxide (GO) to design CD-MOF/GOs. This applicable technique can control the crystal size of CD-MOFs from macro- to nanocrystals. CD-MOF/GOs are investigated as a new type of supramolecular adsorbent. It can selectively adsorb the dye molecule methylene green (MG) owing to the synergistic effect between the hydrophobic nanocavity of CDs, and the abundant O-containing functional groups of GO in the composites. Following high temperature calcination, the resulting N, S co-doped porous carbons derived from CD-MOF/GOs exhibit a high capacitance of 501 F g-1 at 0.5 A g-1 , as well as stable cycling stability with 90.1% capacity retention after 5000 cycles. The porous carbon exhibits good electrochemical performance due to its porous surface containing numerous electrochemically active sites after dye adsorption and carbonization. The design strategy by supramolecular incorporating a variety of active molecules into CD-MOFs optimizes the properties of their derived materials, furthering development toward the fabrication of zeitgeisty and high-performance energy storage devices.

Cyclodextrin-based metal-organic framework materials: Classifications, synthesis strategies and applications in variegated delivery systems

Metal-organic frameworks (MOFs) are coordination compounds that possess an adjustable structure and controllable function. Despite their wide applications in various industries, the use of MOFs in the fields of food and biomedicine is limited mainly due to their potential biological toxicity. Researchers have thus focused on developing biocompatible MOFs to address this issue. Among them, cyclodextrin-based metal-organic frameworks (CD-MOFs) have emerged as a promising alternative. CD-MOFs are novel MOFs synthesized using naturally carbohydrate cyclodextrin and alkali metal cations, and possess renewable, non-toxic, and edible characteristics. Due to their high specific surface area, controllable porosity, great biocompatibility, CD-MOFs have been widely used in various delivery systems, such as encapsulation of nutraceuticals, flavors, and antibacterial agents. Although the field of CD-MOF materials is still in its early stages, they provide a promising direction for the development of MOF materials in the delivery field. This review describes classification and structural characteristics, followed by an introduction to formation mechanism and commonly used synthetic methods for CD-MOFs. Additionally, we discuss the status of the application of various delivery systems based on CD-MOFs. Finally, we address the challenges and prospects of CD-MOF materials, with the aim of providing new insights and ideas for their future development.

Applications of macrocycle-based solid-state host-guest chemistry

Macrocyclic molecules have been used in various fields owing to their guest binding properties. Macrocycle-based host-guest chemistry in solution can allow for precise control of complex formation. Although solution-phase host-guest complexes are easily prepared, their limited stability and processability prevent widespread application. Extending host-guest chemistry from solution to the solid state results in complexes that are generally more robust, enabling easier processing and broadened applications. Macrocyclic compounds in the solid state can encapsulate guests with larger affinities than their soluble counterparts. This is crucial for use in applications such as separation science and devices. In this Review, we summarize recent progress in macrocycle-based solid-state host-guest chemistry and discuss the basic physical chemistry of these complexes. Representative macrocycles and their solid-state complexes are explored, as well as potential applications. Finally, perspectives and challenges are discussed.

Porous Ionic Liquids Go Green

This Perspective points toward pathways to prepare porous ionic liquids using easily accessible materials, aiming for reduced environmental impact. We demonstrate that suspensions of porous solids are stable in eutectic mixtures, underscoring their potential for the preparation of porous ionic liquids. Porous ionic liquids retain the wide electrochemical window observed in their precursor pure ionic liquids, rendering them well-suited for green electrochemical reactions, particularly those involving gases whose solubility is enhanced in the porous suspensions. Moreover, their capacity as gas-rich media points to sustainable biomedical and pharmaceutical applications, provided nontoxic, biocompatible ionic liquids and porous solids are utilized.

Encapsulation Alleviates the Auto-browning of Epigallocatechin-3-gallate in Aqueous Solutions through Regulating Molecular Self-Aggregation Behavior

Catechins are widely recognized for superb antioxidant capability, but their application as food antioxidants is hindered by susceptibility to auto-browning under high-moisture conditions. Here, we proposed a strategy of ordered encapsulation with cyclodextrin-based metal-organic frameworks (CD-MOFs) to alleviate the auto-browning phenomenon of catechins while preserving their antioxidant capability and demonstrated the feasibility of this strategy via selecting epigallocatechin-3-gallate (EGCG) as a model. Even in aqueous solutions, EGCG@CD-MOFs still possessed delayed browning, in contrast with pristine EGCG, characterized by suppressed efficiencies on the generation of oxidative dimers (theasinensin A) and semiquinone radicals. Mechanism insights revealed that ordered encapsulation brought dual regulations on the self-aggregation behavior of EGCG: EGCG@CD-MOFs exhibited a gradual structural collapse from the framework toward irregular aggregates as O-K bonds broke progressively, which restricted molecular mobility of EGCG, and EGCG molecular conformations became constrained by the structure of EGCG@CD-MOFs as well as rich intermolecular forces, even after structural collapse.