Tuning Cellular Biological Functions Through the Controlled Release of NO from a Porous Ti-MOF

Materials for the controlled release of nitric oxide (NO) are of interest for therapeutic applications. However, to date, many suffer from toxicity and stability issues, as well as poor performance. Herein, we propose a new NO adsorption/release mechanism through the formation of nitrites on the skeleton of a titanium-based metal–organic framework (MOF) that we named MIP-177, featuring a suitable set of properties for such an application: (i) high NO storage capacity (3 μmol mg⁻¹_solid), (ii) excellent biocompatibility at therapeutic relevant concentrations (no cytotoxicity at 90 μg mL⁻¹ for wound healing) due to its high stability in biological media (<9 % degradation in 72 hours) and (iii) slow NO release in biological media (≈2 hours for 90 % release). The prospective application of MIP-177 is demonstrated through NO-driven control of mitochondrial respiration in cells and stimulation of cell migration, paving the way for the design of new NO delivery systems for wound healing therapy.     

Formation of a Single‐Crystal Aluminum‐Based MOF Nanowire with Graphene Oxide Nanoscrolls as Structure‐Directing Agents

An innovative strategy is proposed to synthesize single‐crystal nanowires (NWs) of the Al³⁺ dicarboxylate MIL‐69(Al) MOF by using graphene oxide nanoscrolls as structure‐directing agents. MIL‐69(Al) NWs with an average diameter of 70±20 nm and lengths up to 2 μm were found to preferentially grow along the [001] crystallographic direction. Advanced characterization methods (electron diffraction, TEM, STEM‐HAADF, SEM, XPS) and molecular modeling revealed the mechanism of formation of MIL‐69(Al) NWs involving size‐confinement and templating effects. The formation of MIL‐69(Al) seeds and the self‐scroll of GO sheets followed by the anisotropic growth of MIL‐69(Al) crystals are mediated by specific GO sheets/MOF interactions. This study delivers an unprecedented approach to control the design of 1D MOF nanostructures and superstructures.     

Multivariate Modulation of the Zr MOF UiO‐66 for Defect‐Controlled Combination Anticancer Drug Delivery

Metal–organic frameworks (MOFs) are emerging as leading candidates for nanoscale drug delivery, as a consequence of their high drug capacities, ease of functionality, and the ability to carefully engineer key physical properties. Despite many anticancer treatment regimens consisting of a cocktail of different drugs, examples of delivery of multiple drugs from one MOF are rare, potentially hampered by difficulties in postsynthetic loading of more than one cargo molecule. Herein, we report a new strategy, multivariate modulation, which allows incorporation of up to three drugs in the Zr MOF UiO‐66 by defect‐loading. The drugs are added to one‐pot solvothermal synthesis and are distributed throughout the MOF at defect sites by coordination to the metal clusters. This tight binding comes with retention of crystallinity and porosity, allowing a fourth drug to be postsynthetically loaded into the MOFs to yield nanoparticles loaded with cocktails of drugs that show enhancements in selective anticancer cytotoxicity against MCF‐7 breast cancer cells in vitro. We believe that multivariate modulation is a significant advance in the application of MOFs in biomedicine, and anticipate the protocol will also be adopted in other areas of MOF chemistry, to easily produce defective MOFs with arrays of highly functionalised pores for potential application in gas separations and catalysis.     

BioMOFs: Metal–Organic Frameworks for Biological and Medical Applications

The class of highly porous materials called metal–organic frameworks offer many opportunities for applications across biology and medicine. Their wide range of chemical composition makes toxicologically acceptable formulation possible, and their high level of functionality enables possible applications as imaging agents and as delivery vehicles for therapeutic agents. The challenges in the area encompass not only the development of new solids but also improvements in the formulation and processing of the materials, including tailoring the morphology and surface chemistry of the frameworks to fit the proposed applications.     

In situ Synchrotron IR Microspectroscopy of CO2 Adsorption on Single Crystals of the Functionalized MOF Sc2(BDC‐NH2)3

Synchrotron radiation (SR) IR microspectroscopy has enabled determination of the thermodynamics, kinetics, and molecular orientation of CO₂ adsorbed in single microcrystals of a functionalized metal–organic framework (MOF) under conditions relevant to carbon capture from flue gases. Single crystals of the small‐pore MOF, Sc₂(BDC‐NH₂)₃, (BDC‐NH₂=2‐amino‐1,4‐benzenedicarboxylate), with well‐defined crystal form have been investigated during CO₂ uptake at partial pressures of 0.025‐0.2 bar at 298–373 K. The enthalpy and diffusivity of adsorption determined from individual single crystals are consistent with values obtained from measurements on bulk samples. The brilliant SR IR source permits rapid collection of polarized spectra. Strong variations in absorbance of the symmetric stretch of the NH₂ groups of the MOF and the asymmetric stretch of the adsorbed CO₂ at different orientations of the crystals relative to the polarized IR light show that CO₂ molecules align along channels in the MOF.     

Correlating Pressure‐Induced Emission Modulation with Linker Rotation in a Photoluminescent MOF

Conformational changes of linker units in metal‐organic frameworks (MOFs) are often responsible for gate‐opening phenomena in selective gas adsorption and stimuli‐responsive optical and electrical sensing behaviour. Herein, we show that pressure‐induced bathochromic shifts in both fluorescence emission and UV/Vis absorption spectra of a two‐fold interpenetrated Hf MOF, linked by 1,4‐phenylene‐bis(4‐ethynylbenzoate) ligands ( Hf‐peb ), are induced by rotation of the central phenyl ring of the linker, from a coplanar arrangement to a twisted, previously unseen conformer. Single‐crystal X‐ray diffraction, alongside in situ fluorescence and UV/Vis absorption spectroscopies, measured up to 2.1 GPa in a diamond anvil cell on single crystals, are in excellent agreement, correlating linker rotation with modulation of emission. Topologically isolating the 1,4‐phenylene‐bis(4‐ethynylbenzoate) units within a MOF facilitates concurrent structural and spectroscopic studies in the absence of intermolecular perturbation, allowing characterisation of the luminescence properties of a high‐energy, twisted conformation of the previously well‐studied chromophore. We expect the unique environment provided by network solids, and the capability of combining crystallographic and spectroscopic analysis, will greatly enhance understanding of luminescent molecules and lead to the development of novel sensors and adsorbents.     

Thermo‐Responsive MOF/Polymer Composites for Temperature‐Mediated Water Capture and Release

We report an in situ polymerization strategy to incorporate a thermo‐responsive polymer, poly(N‐isopropylacrylamide) (PNIPAM), with controlled loadings into the cavity of a mesoporous metal–organic framework (MOF), MIL‐101(Cr). The resulting MOF/polymer composites exhibit an unprecedented temperature‐triggered water capture and release behavior originating from the thermo‐responsive phase transition of the PNIPAM component. This result sheds light on the development of stimuli‐responsive porous adsorbent materials for water capture and heat transfer applications under relatively mild operating conditions.     

Direct Observation of Molecular‐Level Template Action Leading to Self‐Assembly of a Porous Framework

The molecular steps involved in the self‐assembly of Cu₃(BTC)₂ (BTC=1,3,5‐benzenetricarboxylic acid) metal–organic frameworks that enclose Keggin‐type H₃PW₁₂O₄₀ heteropolyacid molecules were unraveled by using solution ¹⁷O, ³¹P, and ¹⁸³W NMR spectroscopy, small‐angle X‐ray scattering, near‐IR spectroscopy, and dynamic light scattering. In aqueous solution, complexation of Cu²⁺ ions with Keggin‐type heteropolyacids was observed. Cu²⁺ ions are arranged around the Keggin structure so that linking through benzenetricarboxylate groups results in the formation of the Cu₃(BTC)₂ MOF structure HKUST‐1. This is a unique instance in which a templating mechanism that relies on specific molecular‐level matching and leads to explicit nanoscale building units can be observed in situ during formation of the synthetic nanoporous material.     

MOF Scaffold for a High‐Performance Mixed‐Matrix Membrane

A novel composite membrane consisting of an interconnected MOF scaffold coated with cross‐linked poly(ethylene glycol) (PEG) has been developed. As a result of its unique structure, the membrane shows an exceptional 18‐fold permeability enhancement as compared to pristine PEG membranes, without compromising the selectivity. This performance is unattainable with current mixed‐matrix membranes (MMMs). Our optimized membrane has a permeability of 2700 Barrer with a CO₂/N₂ selectivity of 35, which surpasses the latest Robeson upper bound.     

Iron Metal–Organic Frameworks MIL‐88B and NH2‐MIL‐88B for the Loading and Delivery of the Gasotransmitter Carbon Monoxide

Crystals of MIL‐88B‐Fe and NH₂‐MIL‐88B‐Fe were prepared by a new rapid microwave‐assisted solvothermal method. High‐purity, spindle‐shaped crystals of MIL‐88B‐Fe with a length of about 2 μm and a diameter of 1 μm and needle‐shaped crystals of NH₂‐MIL‐88B‐Fe with a length of about 1.5 μm and a diameter of 300 nm were produced with uniform size and excellent crystallinity. The possibility to reduce the as‐prepared frameworks and the chemical capture of carbon monoxide in these materials was studied by in situ ultrahigh vacuum Fourier‐transform infrared (UHV‐FTIR) spectroscopy and Mössbauer spectroscopy. CO binding occurs to unsaturated coordination sites (CUS). The release of CO from the as‐prepared materials was studied by a myoglobin assay in physiological buffer. The release of CO from crystals of MIL‐88B‐Fe with t_1/2=38 min and from crystals of NH₂‐MIL‐88B‐Fe with t_1/2=76 min were found to be controlled by the degradation of the MIL materials under physiological conditions. These MIL‐88B‐Fe and NH₂‐MIL‐88B‐Fe materials show good biocompatibility and have the potential to be used in pharmacological and therapeutic applications as carriers and delivery vehicles for the gasotransmitter carbon monoxide.     

Tuning Proton Conductivity by Interstitial Guest Change in Size‐Adjustable Nanopores of a CuI‐MOF: A Potential Platform for Versatile Proton Carriers

By exploiting the breathing behavior of nanopores, we have studied for the first time the dependency of the guest‐induced proton conductivity of an interpenetrated Cu^I metal–organic framework (Cu^I‐MOF, [ 1 ]) on various guest molecules. Proton conductivities of over 10^?3 S cm^?1 under humid conditions were induced by a series of guest molecules, namely N,N‐dimethylformamide, dimethyl sulfoxide, diethylamine, 1,4‐dinitrobenzene, nitrobenzene, pyridine, and 1H‐1,2,4‐triazole. A detailed investigation of the guest‐incorporated complexes revealed that low‐energy proton conduction occurs under humid conditions through the Grotthuss mechanism in [ 1 ?NB] and through the vehicle mechanism in the rest of the complexes. Single‐point energy computations revealed considerable stabilization upon guest encapsulation. To the best of our knowledge, [ 1 ] represents the first example in which considerably high protonic conductivity is triggered upon the facile incorporation of small molecules of such a variety. The investigation portrayed herein may be a stepping stone towards the rational design of proton‐conducting materials for practical applications.     

Incorporating Polyoxometalates into a Porous MOF Greatly Improves Its Selective Adsorption of Cationic Dyes

Various polyoxometalates (POMs) were successfully immobilized to the mesoporous coordination polymer MIL‐101 resulting in a series of POM–MOF composite materials POM@MIL‐101 (POM=K₄PW₁₁VO₄₀, H₃PW₁₂O₄₀, K₄SiW₁₂O₄₀). These materials were synthesized by a simple one‐pot reaction of Keggin POMs, tetramethylammonium hydroxide (TMAH), terephthalic acid (H₂bdc), and Cr³⁺ ions. XRD, FTIR, thermogravimetric analyses (TG), inductively coupled plasma (ICP) spectrometry, and energy‐dispersive X‐ray spectroscopy (EDX) collectively confirmed the successful combination of POMs and the porous framework. Further, these composites POM@MIL‐101 with different loading of POMs were achieved by variation of the POM dosage. Notably, the uptake capacity of MIL‐101 towards organic pollutants in aqueous solution was significantly improved by immobilization of hydrophilic POMs into cages of MIL‐101. An uptake capacity of 371 mg g^?1, comparable to that of the graphene oxide sponges, and much higher than that of the commercial activated carbon, was achieved at room temperature in 5 min when dipping 20 mg PW₁₁V@MIL‐101 in the methylene blue (MB) solution (100 mL of 100 mg L^?1 MB solution). Further study revealed that the POM@MIL‐101 composite materials not only exhibited a fast adsorption rate towards dye molecules, but also possessed of selective adsorption ability of the cationic dyes in wastewater. For example, the adsorption efficiency of PW₁₁V@MIL‐101 (10 mg) towards MB (100 mL of 10 mg L^?1) could reach 98 % in the initial 5 min, and it could capture MB dye molecules from the binary mixture of the MB and MO with similar size. Also, the POM@MIL‐101 materials could be readily recycled and reused, and no POM leached in the dye adsorption process.     

Assembly of MOF Microcapsules with Size‐Selective Permeability on Cell Walls

The assembly of metal–organic frameworks (MOFs) into microcapsules has attracted great interest because of their unique properties. However, it remains a challenge to obtain MOF microcapsules with size selectivity at the molecular scale. In this report, we used cell walls from natural biomaterials as non‐toxic, stable, and inexpensive support materials to assemble MOF/cell wall (CW) microcapsules with size‐selective permeability. By making use of the hollow structure, small pores, and high density of heterogeneous nucleation sites of the cell walls, uniform and continuous MOF layers could be easily obtained by inside/outside interfacial crystallization. The prepared MOF/CW microcapsules have excellent stability and enable the steady, slow, and size‐selective release of small molecules. Moreover, the size selectivity of the microcapsules can be adjusted by changing the type of deposited MOF.     

Adsorptive Separation of Acetylene from Light Hydrocarbons by Mesoporous Iron Trimesate MIL‐100(Fe)

A reducible metal–organic framework (MOF), iron(III) trimesate, denoted as MIL‐100(Fe), was investigated for the separation and purification of methane/ethane/ethylene/acetylene and an acetylene/CO₂ mixtures by using sorption isotherms, breakthrough experiments, ideal adsorbed solution theory (IAST) calculations, and IR spectroscopic analysis. The MIL‐100(Fe) showed high adsorption selectivity not only for acetylene and ethylene over methane and ethane, but also for acetylene over CO₂. The separation and purification of acetylene over ethylene was also possible for MIL‐100(Fe) activated at 423 K. According to the data obtained from operando IR spectroscopy, the unsaturated Fe^III sites and surface OH groups are mainly responsible for the successful separation of the acetylene/ethylene mixture, whereas the unsaturated Fe^II sites have a detrimental effect on both separation and purification. The potential of MIL‐100(Fe) for the separation of a mixture of C₂H₂/CO₂ was also examined by using the IAST calculations and transient breakthrough simulations. Comparing the IAST selectivity calculations of C₂H₂/CO₂ for four MOFs selected from the literature, the selectivity with MIL‐100(Fe) was higher than those of CuBTC, ZJU‐60a, and PCP‐33, but lower than that of HOF‐3.     

Probing the Structural Stability of and Enhanced CO2 Storage in MOF MIL‐68(In) under High Pressures by FTIR Spectroscopy

The unique structural topology of metal–organic framework (MOF) MIL‐68, featuring two types of channels with distinct pore sizes, makes it a promising candidate for application in gas storage and separation. In this study, the behavior of as‐made and activated MIL‐68(In) was investigated in a diamond‐anvil cell under high pressure by in situ IR spectroscopy. The framework exhibits high stability under compression up to 9 GPa, whereas the bridging OH groups appear to be very sensitive to compression. Pressure‐induced structural modifications were found to be completely reversible for as‐made MIL‐68(In) but irreversible for the activated framework. Moreover, the addition of Nujol as pressure‐transmitting medium makes the framework more resilient to pressure. Finally, when loaded with CO₂, the framework exhibited interesting differential binding affinities with CO₂ in the hexagonal and triangular pores at different pressures. The pressure‐enhanced CO₂ storage behavior and the guest–host interaction mechanism between CO₂ and the MOF framework were explored with the aid of Monte Carlo simulations. These studies demonstrated great potential for MIL‐68(In) in gas‐storage applications that require extreme loading pressures.     

Biological Chitin–MOF Composites with Hierarchical Pore Systems for Air‐Filtration Applications

Metal–organic frameworks (MOFs) are promising materials for gas‐separation and air‐filtration applications. However, for these applications, MOF crystallites need to be incorporated in robust and manageable support materials. We used chitin‐based networks from a marine sponge as a non‐toxic, biodegradable, and low‐weight support material for MOF deposition. The structural properties of the material favor predominant nucleation of the MOF crystallites at the inside of the hollow fibers. This composite has a hierarchical pore system with surface areas up to 800 m² g⁻¹ and pore volumes of 3.6 cm³ g⁻¹, allowing good transport kinetics and a very high loading of the active material. Ammonia break‐through experiments highlight the accessibility of the MOF crystallites and the adsorption potential of the composite indicating their high potential for filtration applications for toxic industrial gases.     

Enzyme‐MOF Nanoreactor Activates Nontoxic Paracetamol for Cancer Therapy

Prodrug activation, by exogenously administered enzymes, for cancer therapy is an approach to achieve better selectivity and less systemic toxicity than conventional chemotherapy. However, the short half‐lives of the activating enzymes in the bloodstream has limited its success. Demonstrated here is that a tyrosinase‐MOF nanoreactor activates the prodrug paracetamol in cancer cells in a long‐lasting manner. By generating reactive oxygen species (ROS) and depleting glutathione (GSH), the product of the enzymatic conversion of paracetamol is toxic to drug‐resistant cancer cells. Tyrosinase‐MOF nanoreactors cause significant cell death in the presence of paracetamol for up to three days after being internalized by cells, while free enzymes totally lose activity in a few hours. Thus, enzyme‐MOF nanocomposites are envisioned to be novel persistent platforms for various biomedical applications.     

A Post‐Synthetically Modified MOF for Selective and Sensitive Aqueous‐Phase Detection of Highly Toxic Cyanide Ions

Selective and sensitive detection of toxic cyanide (CN^?) by a post‐synthetically altered metal–organic framework (MOF) has been achieved. A post‐synthetic modification was employed in the MOF to incorporate the specific recognition site with the CN^? ion over all other anions, such as Cl^?, Br^?, and SCN^?. The aqueous‐phase sensing and very low detection limit, the essential prerequisites for an effective sensory material, have been fulfilled by the MOF. Moreover, the present detection level meets the standard set by the World Health Organization (WHO) for the permissible limit of cyanide concentration in drinking water. The utilization of MOF‐based materials as the fluorometric probes for selective and sensitive detection of CN^? ions has not been explored till now.     

Unusual Transformation from a Solvent‐Stabilized 1D Coordination Polymer to a Metal–Organic Framework (MOF)‐Like Cross‐Linked 3D Coordination Polymer

An unusual 1D‐to‐3D transformation of a coordination polymer based on organic linkers containing highly polar push–pull π‐conjugated side chains is reported. The coordination polymers are synthesized from zinc nitrate and an organic linker, namely, 2,5‐bis{4‐[1‐(4‐nitrophenyl)pyrrolidin‐2‐yl]butoxy}terephthalic acid, which possesses highly polar (4‐nitrophenyl)pyrrolidine groups, with high dipole moments of about 7 D. The coordination polymers exhibit an unusual transformation from a soluble, solvent‐stabilized 1D coordination polymer into an insoluble, metal–organic framework (MOF)‐like 3D coordination polymer. The coordination polymer exhibits good film‐forming ability, and the MOF‐like films are insoluble in conventional organic solvents.