Facile stabilization of a cyclodextrin metal-organic framework under humid environment via hydrogen sulfide treatment

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.

Glutathione-responsive CD-MOFs co-loading honokiol and indocyanine green biomimetic active targeting to enhance photochemotherapy for breast cancer

Breast cancer has now replaced lung cancer as the most prevalent malignant tumor worldwide, posing a serious health risk to women. We have recently designed a promising option strategy for the treatment of breast cancer. In this work, cyclodextrin metal-organic frameworks with high drug-carrying properties were endo-crosslinked by 3,3'dithiodipropionyl chloride to form cubic phase gel nanoparticles, which were drug-loaded and then coated by MCF-7 cell membranes. After intravenous injection, this multifunctional nanomedicine achieved dramatically homologous targeting co-delivery of honokiol and indocyanine green to the breast tumor. Further, the disulfide bonds in the nanostructures achieved glutathione-responsive drug release, induced tumor cells to produce reactive oxygen species and promoted apoptosis, resulting in tumor necrosis, and at the same time, inhibited Ki67 protein expression, which enhanced photochemotherapy, and resulted in a 94.08 % in vivo tumor suppression rate in transplanted tumor-bearing mice. Thereby, this nanomimetic co-delivery system may have a place in breast cancer therapy due to its simple fabrication process, excellent biocompatibility, efficient targeted delivery of insoluble drugs, and enhanced photochemotherapy.

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.

Ethanol-mediated synthesis of γ-cyclodextrin-based metal-organic framework as edible microcarrier: performance and mechanism

Here, an ethanol-mediated method was introduced to fabricate γ-cyclodextrin-based metal-organic frameworks (γ-CD-MOFs) as microcarriers for epigallocatechin-3-gallate (EGCG). Through adjusting ethanol gas diffusion temperature and ethanol liquid feed speed, we achieved control of crystallization efficiency and crystals size without extra surfactants. Under the sequential regulatory by ethanol in two phases, the obtained γ-CD-MOFs with cubic shape exhibited excellent crystallinity, high surface area, and uniform size distribution. Through the interplay of hydrogen bonding, hydrophobic interactions and π stacking, EGCG molecules could be stored efficiently within cavities and tunnels of the γ-CD-MOFs with high load capability of 334 mg g^-1. More importantly, the incorporation of EGCG within frameworks wouldn't disintegrate the unique body-centered cubic structure of γ-CD-MOFs, in turn, would improve the thermostability and antioxidative activity of EGCG. Significantly, all food-grade materials ensured the γ-CD-MOFs high acceptance and applicability for food and biomedical applications.

Tracking the Dissolution Surface Kinetics of a Single Fluorescent Cyclodextrin Metal-Organic Framework by Confocal Laser Scanning Microscopy

The understanding of the dissolution processes of solids is important for the design and synthesis of solids in a controlled and precise manner and for predicting their fate in the aquatic environment. We report herein single-particle-based confocal laser scanning microscopy (CLSM) for tracking the dissolution surface kinetics of a single fluorescent cyclodextrin metal-organic framework (CD-MOF). As a proof of concept, CD-MOF containing fluorescein, named as CD-MOF⊃FL, was synthesized by encapsulating fluorescein into the interior of CD-MOF via a vapor diffusion method and used as a single-particle dissolution model because of its high FL efficiency and unique structure. The morphology of CD-MOF⊃FL and the distribution of fluorescein within CD-MOF⊃FL were characterized. The growth and dissolution processes of CD-MOF⊃FL at the single-particle level were visualized and quantified for the first time by recording the change of the fluorescence emission. Three processes, including nucleation, germination growth, and saturation stage, were found in the growth of CD-MOF⊃FL, and the growth kinetics followed Avrami's model. The dissolution rate at the face of a single CD-MOF⊃FL crystal was slower than that of its arris, and the dissolution rate of the CD-MOF⊃FL crystal was increased with the increase of the water amount in methanol solution. The dissolution process of the CD-MOF⊃FL crystal was a competitive process of erosion and diffusion in different methanol aqueous solutions, and the dissolution kinetics followed the Korsmeyer-Peppas model. These results offer new insights into the nature of dissolution kinetics of CD-MOF⊃FL and provide new venues for the quantitative analysis of solid dissolution and growth at the single-particle level.

Organo-macrocycle-containing hierarchical metal-organic frameworks and cages: design, structures, and applications

Developing hierarchical ordered systems is challenging. Using organo-macrocycles to construct metal-organic frameworks (MOFs) and porous coordination cages (PCCs) provides an efficient way to obtain hierarchical assemblies. Macrocycles, such as crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, can be incorporated within MOFs/PCCs and they also endow the resultant composites with enhanced properties and functionalities. This review summarizes recent developments of organo-macrocycle-containing hierarchical MOFs/PCCs, emphasizing applications and structure-property relationships of these hierarchically porous materials. This review provides insights for future research on hierarchical self-assembly using macrocycles as building blocks and functional ligands to extend the applications of the composites.

Cyclodextrin metal-organic frameworks and derivatives: recent developments and applications

While there is a tremendous amount of scientific research on metal organic frameworks (MOFs) for gas storage/separation, catalysis and energy storage, the development and application of biocompatible MOFs still poses major challenges. In general, they can be synthesised from various biocompatible linkers and metal ions but particularly cyclodextrins (CDs) as cyclic oligosaccharides are an astute choice for the former. Although the field of CD-MOF materials is still in the early stages and their design and fabrication comes with many hurdles, the benefits coming from CDs built in a porous framework are exciting. Versatile host-guest complexation abilities, high encapsulation capacity and hydrophilicity are among the valuable properties inherent to CDs and offer extended and novel applications to MOFs. In this review, we provide an overview of the state-of-the-art synthesis, design, properties and applications of these materials. Initially, a rationale for the preparation of CD-based MOFs is provided, based on the chemical and structural properties of CDs and including their advantages and disadvantages. Further on, the review exhaustively surveys CD-MOF based materials by categorising them into three sub-classes, namely (i) CD-MOFs, (ii) CD-MOF hybrids, obtained via combination with external materials, and (iii) CD-MOF-derived materials prepared under pyrolytic conditions. Subsequently, CD-based MOFs in practical applications, such as drug delivery and cancer therapy, sensors, gas storage, (enantiomer) separations, electrical devices, food industry, and agriculture, are discussed. We conclude by summarizing the state of the art in the field and highlighting some promising future developments of CD-MOFs.

Polydimethylsiloxane Membranes Incorporating Metal-Organic Frameworks for the Sustained Release of Antibacterial Agents

Cyclodextrin metal-organic frameworks (CD-MOFs) possess great potential in environmental applications due to their high specific surface area and good biocompatibility properties. However, the hydrophilicity of the CD-MOF hinders its ability to maintain a sustained release in water as a carrier. In this study, we prepared a CD-MOF that has codelivery ability for both phytochemicals [caffeic acid (CA)] and silver nanoparticles (Ag NPs) and further incorporated this material (CA@Ag@CD-MOF) into the polydimethylsiloxane (PDMS) matrix to construct a hybrid membrane. This hybrid membrane could effectively maintain the release capacity of the CD-MOF in water, while endowing PDMS with swelling ability in water. The hybrid membrane can achieve a sustained release for up to 48 h in water. In addition, the elastic modulus of the hybrid membrane increases by nearly 100%, and the swelling degree of the hybrid membrane in water increases by 42% compared with that of the pure PDMS membrane, indicating better mechanical properties. The hybrid membrane exhibits excellent antibacterial effects on Escherichia coli O157:H7 (E. coli O157:H7) and Staphylococcus aureus (S. aureus). We expect that this work will be beneficial to the delivery research of the CD-MOF in more environmental scenarios, especially in water treatment.

Precision release systems of food bioactive compounds based on metal-organic frameworks: synthesis, mechanisms and recent applications

Controlled release (CR) systems have become a powerful platform for accurate and effective delivery of bioactive compounds (BCs). Metal-organic frameworks (MOFs) are one of the best BCs-loaded carriers for CR systems. In the review, the principles and methods of the design and synthesis of MOFs-CR systems are summarized in detail, the encapsulation of BCs by MOFs and CR mechanisms are explored, and their biological toxicity and biocompatibility are highlighted and applications in the food industry are discussed. In addition, current challenges in this field and possible future development directions are also presented. MOFs have been proven to encapsulate BCs effectively, including gaseous and solid molecules, and control the release of BCs through spontaneous diffusion or stimulus-response. The solubility, stability and biocompatibility of BCs encapsulated by MOFs are greatly improved, which expands their applications in foods. The effective CR of BCs by MOFs-CR systems is beneficial to assist in maintaining or even improving the quality and safety of food, reduce the BCs usage while increasing the bioavailability. Low- or non-biotoxic MOFs, especially bio-MOFs, show greater application prospects in the food industry.

Recent Advances of Porous Materials Based on Cyclodextrin

Porous materials have attracted significant attention because of their rising applications in many fields. Cyclodextrins (CDs) are suitable building units in the fabrication of porous materials owing to their intrinsic nanoporous structure, easy modification, and biocompatibility, which may result in the formation of CD-based organic frameworks (including cyclodextrin metal-organic frameworks (CD-MOFs) and cyclodextrin covalent organic frameworks (CD-COFs)), and CD-based polymer hybrid porous materials. This review focuses on the recent progress in the fabrication and applications of CD-based porous materials with novel structures and functionalities.

Cyclodextrin Metal-Organic Frameworks and Their Applications

Cyclodextrin-based metal-organic frameworks (CD-MOFs), derived from γ-cyclodextrin (γ-CD) and alkali metal cations, constitute a class of porous, renewable, and edible MOFs that can be synthesized from a naturally occurring carbohydrate on a large scale. γ-CD is a C₈-symmetrical cyclic oligosaccharide composed of eight asymmetric α-1,4-linked d-glucopyranosyl residues that possesses a bucket-shaped cavity with an inner diameter of ∼1 nm and a depth of ∼0.8 nm. Upon combination of 1 equiv of γ-CD with 8 equiv of potassium hydroxide in an aqueous solution, followed by vapor diffusion of MeOH (or EtOH) into this solution during several days, CD-MOF-1 is obtained as cubic crystals. This carbohydrate-based MOF, which was discovered serendipitously in 2010, was the first highly crystalline CD-MOF to be obtained. X-ray crystallography of a single crystal reveals that it adopts the space group I432 with unit cell dimensions of approximately 31 × 31 × 31 ų. Other CD-MOFs, namely, CD-MOF-2 and CD-MOF-3, can be obtained when potassium ions are replaced by rubidium and cesium ions, respectively. CD-MOFs comprise extended body-centered frameworks of (γ-CD)₆ cubic units, which contain spherical pores that reside at the center of the cubes, interconnected by alkali metal cations, forming both cylindrical and triangular channels.During the past decade, CD-MOFs have emerged as a useful class of multifunctional materials based on porous frameworks with extended structures displaying robust crystallinity, permanent porosity, and excellent biocompatibility. The family of CD-MOFs has been joined by a growing collection of metal nodes involving alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and γ-CD as well as its derivatives. As a result of the ability of their extended porous frameworks to absorb guest molecules, including gases, drugs, metal-based nanoclusters, and nanoparticles, CD-MOFs have potential applications in areas as disparate as templating syntheses of metal-based nanoparticles and gels, adsorption and separation, trapping highly reactive intermediates, catalyst supports, sensing, electrical memory, and drug delivery.In this Account, we tell the story of CD-MOFs, a scientific discovery made in our research laboratory at Northwestern University, and the opportunities to use these environmentally friendly porous materials across different fields of science and technology. The story includes representative synthetic protocols for the preparation of CD-MOFs, along with an overview of their structural features, functionalization, and chemical modification aimed at increasing their stabilities in aqueous environments, and finally, a summary of their applications. The examples we will discuss, however, are only illustrative, and there is a significant body of additional findings emanating from our laboratory and others, especially in the realm of developing new synthetic strategies, tuning the framework stabilities, and exploring the guest inclusion and emergent properties of CD-MOFs. We refer readers to the original communications, papers, and reviews cited herein. We hope that, in the telling of the story of CD-MOFs, this Account may promote new scientific discoveries and further development of CD-MOF-based technologies in the future.

Recent progress in the synthesis, structural diversity and emerging applications of cyclodextrin-based metal-organic frameworks

Inorganic-organic hybrid materials, especially metal-organic frameworks (MOFs) composed of metals and organic linkers, have emerged as a new class of versatile materials owing to their tunable structure and controllable functionality. As typical biocompatible MOFs, cyclic oligosaccharide cyclodextrin-based carbohydrate metal-organic frameworks (CD-MOFs) have recently attracted considerable attention due to their edible, renewable and biodegradable nature. Herein, we focus on the latest advances concerning these materials. First, the synthesis methods and structural diversity of CD-MOFs are introduced and summarized. Besides, the synthetic strategies of moisture-resistant CD-MOFs are also emphasized. Moreover, their applications, including gas adsorption, separation, sensing, memristor fabrication, as templates in nanoparticle synthesis, light emission and especially drug delivery, are systematically discussed and highlighted. Finally, to conclude the review, some insights and current challenges that need to be addressed for the further development of these materials are proposed. We anticipate that this review will result in a better understanding of CD-MOFs and will help maximize the potential functions of these materials.

Amino-Functionalized β-Cyclodextrin to Construct Green Metal-Organic Framework Materials for CO2 Capture

The adsorption of CO₂ by conventional liquid alkanolamine adsorbents does not meet the requirements for green-friendly development in industrial applications. In this work, we constructed NH₂-β-CD-MOF for the first time through the amino-functionalization of the lowest-priced, readily available, and biocompatible β-CD. Subsequently, the samples were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, elemental analysis, and N₂ adsorption/desorption. The CO₂ adsorption capacity of NH₂-β-CD-MOF was found to be 12.3 cm³/g, which is 10 times that of β-CD-MOF. In addition, NH₂-β-CD-MOF has outstanding selective adsorption of CO₂/N₂ (947.52) compared with the reported materials. The adsorption mechanism of CO₂ was analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Furthermore, we have found that NH₂-β-CD-MOF has better water stability relative to β-CD-MOF and γ-CD-MOF, and it can be recycled by an ultrasonic method.