MOF System Research Articles

Application of capsaicin and calcium phosphate-loaded MOF system for tumor therapy involving calcium overload

Calcium overload therapy refers to the condition of intracellular Ca2+ overload, which causes mitochondrial damage and leads to the uncontrolled release of apoptotic factors into the cytoplasm through the open mitochondrial permeability pore. Based on this, it is playing an increasingly important role in the field of oncology due to its good efficacy and small side effects. However, the regulation of calcium homeostasis by cancer cells themselves, insufficient calcium ions (Ca2+) in tumor sites and low efficiency of calcium entering tumor have limited its efficacy, resulting in unsatisfactory therapeutic effect. Therefore, a novel CAP/BSA@TCP-ZIF-8 nanoparticle drug carrier system was constructed that can provide Ca2+ from exogenous sources for pH-controlled degradation and drug release at the same time. Both in vivo and in vitro experiments have proved that the nanomaterial can activate TRPV1 channels and provide exogenous Ca2+ to cause Ca2+ overload and apoptosis, thus achieving anti-tumor effects.

Ultrasensitive Aptasensing Platform for the Detection of β-Amyloid-42 Peptide Based on MOF Containing Bimetallic Porphyrin Graphene Oxide and Gold Nanoparticles.

The prompt detection of diseases hinges on the accessibility and the capability to identify relevant biomarkers. The integration of aptamers and the incorporation of nanomaterials into signal transducers have not only expedited but also enhanced the development of nanoaptasensors, enabling heightened sensitivity and selectivity. Here, the bimetallic nickel-cobalt-porphyrin metal-organic framework ((Ni + Cu)TPyP MOF) is regarded as an electron mediator, immobilization platform for an Alzheimer aptamer and to increase the electrochemical signal for the detection of the main biomarker of Alzheimer's disease (AD), amyloid β (Aβ-42). Furthermore, the ((Ni + Cu)TPyP MOF) was combined with reduced graphene oxide (rGO) and gold nanoparticles (AuNPs), on a gold electrode (GE) to provide an efficient interface for immobilizing aptamer strands. Concurrently, the incorporation of rGO and AuNPs imparts enhanced electrical conductivity and efficacious catalytic activity, establishing them as adept electrochemical indicators. Owing to the superior excellent electrical conductivity of rGO and AuNPs, coupled with the presence of ample mesoporous channels and numerous Ni and Cu metal sites within (Ni + Cu)TPyP MOF, this nanostructure with abundant functional groups is proficient in immobilizing a substantial quantity of aptamer. These interactions are achieved through robust π-π stacking and electrostatic interactions, alongside the high affinity between the thiol group of the aptamer and AuNPs concurrently. The as-prepared ternary (Au@(Ni + Cu)TPyP MOF/rGO) nanostructure electrode exhibited an enhancement in its electrochemically active surface area of about 7 times, compared with the bare electrode and the Aβ-42 redox process is highly accelerated, so the peak currents are significantly higher than those obtained with bare GE substrate. Under the optimized conditions, the designed aptasensor had the quantitative detection of Aβ-42 with a low detection limit of 48.6 fg mL-1 within the linear range of 0.05 pg mL-1 to 5 ng mL-1 by differential pulse voltammetry (DPV), accompanied by precise reproducibility, satisfactory stability (95.6% of the initial activity after 10 days), and minimal impact of interfering agents. Recorded results in human blood plasma demonstrated the high efficacy of porphyrin MOF system sensing even in the clinical matrix. The great performance of this aptasensor indicates that our new design of Au@(Ni + Cu)TPyP MOF/rGO nanostructure provides more opportunities for the detection of chemical signals in early diagnosis of Alzheimer's disease.

Ratio fluorescence/colorimetric dual mode aptasensor and smartphones-assisted miniaturized device for early diagnosis of prostate cancer

Prostate specific antigen (PSA) is the most common tumor biomarker for prostate cancer (PCa), and its precise determination is essential to improving survival rate and reducing treatment cost of cancer patient. Here, we have proposed a novel ratio fluorescence/colorimetric dual mode aptasensor based on CdTe-apt + B-CDs + ZrFe MOF system for PSA determination. Specifically, as-prepared ZrFe MOF with good peroxidase like activity can quench the fluorescence of B-CDs + CdTe-apt system via inner filter effect (IFE), while the existence of PSA can restore fluorescence of CdTe-apt but virtually unchanged fluorescence of B-CDs due to specific identification between PSA and aptamer. Similarly, the addition of PSA can recover the peroxidase like activity of ZrFe MOF which is significantly suppressed by PSA aptamer. Based on this, the proposed ratio fluorescence/colorimetric dual mode aptasensor has achieved satisfactory results in PSA analysis of serum specimens. Valuably, an inexpensive, portable but credible smartphones-assisted miniaturized device is expected to be exploited for the early diagnosis of PCa, inspiring the design and construction of advanced portable devices for self-monitoring and home screening of various cancers.

Intertwining of Localized (d) and Delocalized (π) Spins in Magnetically Frustrated Two-Dimensional Metal-Organic Frameworks.

Two-dimensional metal-organic frameworks (2D MOFs) are emerging as a new class of multifunctional materials for diversified applications, although magnetic properties have not been widely explored. The metal ions and organic ligands in some of the 2D MOFs are arranged in the well-known Kagome lattice, leading to geometric spin frustration. Hence, such systems could be the potential candidates to exhibit an exotic quantum spin liquid (QSL) state, as was observed in Cu3(HHTP)2 (HHTP = hexahydroxytriphenylene), with no magnetic transition down to 38 mK. Hereto, we have investigated the spin intertwining in a bimetallic 2D MOF system, M3(HHTP)2 (M = Cu/Zn), arising from the localized (d-electron) and delocalized (π-electron) S = 1/2 spins from the Cu(II) ions and the HHTP radicals, respectively. The origin of the spin frustration (down to 5K) was critically examined by varying the metal composition in bimetallic systems, CuxZn3-x(HHTP)2 (x = 1, 1.5, 2), containing both S = 1/2 and S = 0 spins. Additionally, to gain a deeper understanding, we studied the spin interaction in the pristine Zn3(HHTP)2 system containing only S = 0 Zn(II) ions. In view of the quantitative estimate of the localized and delocalized spins, the d-π spin correlation appears essential in understanding the unusual magnetic and/or other physical properties of such hybrid organic-inorganic 2D crystalline solids.

A bis-aromatic MOF system constructed with a copper iodine cluster and porphyrinic ligand for enhancing near-infrared photothermal conversion

An organic–inorganic bis-aromatic system achieves an NIR-II photothermal efficiency of up to 63.77%.

Controllable amorphization and morphology engineering on mixed-valence MOFs for ultra-fast and high-stability near-pseudocapacitance Li+ storage.

Coulombic efficiency (CE) and rate capability are crucial parameters for advanced secondary batteries. Herein, for the first time, we report controllable amorphization and morphology engineering on mixed-valence Fe(II,III)-MOFs from the crystalline to amorphous state and micro-clustered to hollow nano-spherical geometry through valence manipulation by a dissolved oxygen-mediated pathway. The disordered structure and the hollow nanostructure can endow the MOFs with the highest initial CE (>80%) to date for MOF electrodes, and ultrafast and super-stable near-pseudocapacitance lithium storage. These findings can provide new ideas for the engineering of MOF systems for application in LIBs.

Manipulating AIE ligands into layers of pillar-layered MOFs for enhanced emission.

Four pillar-layered AIEgen-based MOFs exhibit higher thermal stability, tunable emission colors and improved QYs compared with that of non-pillar-layered AIEgen-based MOFs by confining the AIE ligands into layers. These results reveal that rationally manipulating AIE ligands into layers of pillar-layered MOFs is an effective strategy for the design and construction of tunable luminescent MOF systems.

Conquering Metal–Organic Frameworks by Raman Scattering Techniques

AbstractMetal–organic frameworks (MOFs) have emerged as a versatile class of materials. Understanding the structural and chemical properties of MOFs is essential for tailoring their performance to suit specific applications. In recent years, Raman spectroscopy, a non‐destructive vibrational spectroscopic technique, has evolved into a powerful tool for characterizing MOFs. Beyond spontaneous Raman scattering, numerous advanced Raman techniques have been developed to amplify the inherently weak Raman signal. These innovations have significantly enhanced the spatial resolution, frame rate, and sensitivity of Raman imaging, thereby opening up new possibilities for applications, such as label‐free sensing. This tutorial work is designed to demystify the fundamental theory and instrumentation of Raman spectroscopy, elucidating the differences between commonly used Raman techniques. Particular emphasis is placed on their advantages and limitations when applied to MOF materials. Furthermore, this work showcases how Raman techniques are employed in studying MOF systems to address societal needs and explore future directions. Ultimately, this review emphasizes the crucial role of Raman spectroscopy and the development of novel Raman‐based in situ techniques to conquer the field of MOFs.

Experimental Investigation of Thermodynamic Stabilization in Boron Imidazolate Frameworks (BIFs) Synthesized by Mechanochemistry.

This study experimentally explores the energetics for the formation of boron-imidazolate frameworks (BIFs), which are synthesized by mechanochemistry. The topologically similar frameworks employ the same tetratopic linker based on tetrakis(imidazolyl)boric acid but differ in the monovalent cation metal nodes. This permits assessment of the stabilizing effect of metal nodes in frameworks with sodalite (SOD) and diamondoid (dia) topologies. The enthalpy of formation from endmembers (metal oxide and linker), which define thermodynamic stability of the structures, has been determined by use of acid solution calorimetry. The results show that heavier metal atoms in the node promote greater energetic stabilization of denser structures. Overall, in BIFs the relation between cation descriptors (ionic radius and electronegativity) and thermodynamic stability depends on framework topology. Thermodynamic stability increases with the metallic character of the cation employed as the metal node, independent of the framework topology. The results suggest unifying aspects for thermodynamic stabilization across MOF systems.

A Stable Triphenylamine-Based Zn(II)-MOF for Photocatalytic H2 Evolution and Photooxidative Carbon–Carbon Coupling Reaction

Efficient charge transfer has always been a challenge in heterogeneous MOF-based photoredox catalysis due to the poor electrical conductivity of the MOF photocatalyst, the toilless electron-hole recombination, and the uncontrollable host-guest interactions. Herein, a propeller-like tris(3'-carboxybiphenyl)amine (H3TCBA) ligand was synthesized to fabricate a 3D Zn3O cluster-based Zn(II)-MOF photocatalyst, Zn3(TCBA)2(μ3-H2O)H2O (Zn-TCBA), which was applied to efficient photoreductive H2 evolution and photooxidative aerobic cross-dehydrogenation coupling reactions of N-aryl-tetrahydroisoquinolines and nitromethane. In Zn-TCBA, the ingenious introduction of the meta-position benzene carboxylates on the triphenylamine motif not only promotes Zn-TCBA to exhibit a broad visible-light absorption with a maximum absorption edge of 480 nm but also causes special phenyl plane twists with dihedral angles of 27.8-45.8° through the coordination to Zn nodes. The semiconductor-like Zn clusters and the twisted TCBA3- antenna with multidimensional π interaction sites facilitate photoinduced electron transfer to render Zn-TCBA a good photocatalytic H2 evolution efficiency of 27.104 mmol·g-1·h-1 in the presence of [Co(bpy)3]Cl2 under visible-light illumination, surpassing many non-noble-metal MOF systems. Moreover, the positive enough excited-state potential of 2.03 V and the semiconductor-like characteristics of Zn-TCBA endow Zn-TCBA with double oxygen activation ability for photocatalytic oxidation of N-aryl-tetrahydroisoquinoline substrates with a yield up to 98.7% over 6 h. The durability of Zn-TCBA and the possible catalytic mechanisms were also investigated by a series of experiments including PXRD, IR, EPR, and fluorescence analyses.

Machine learning of spectra-property relationship for imperfect and small chemistry data

Machine learning (ML) is causing profound changes to chemical research through its powerful statistical and mathematical methodological capabilities. However, the nature of chemistry experiments often sets very high hurdles to collect high-quality data that are deficiency free, contradicting the need of ML to learn from big data. Even worse, the black-box nature of most ML methods requires more abundant data to ensure good transferability. Herein, we combine physics-based spectral descriptors with a symbolic regression method to establish interpretable spectra-property relationship. Using the machine-learned mathematical formulas, we have predicted the adsorption energy and charge transfer of the CO-adsorbed Cu-based MOF systems from their infrared and Raman spectra. The explicit prediction models are robust, allowing them to be transferrable to small and low-quality dataset containing partial errors. Surprisingly, they can be used to identify and clean error data, which are common data scenarios in real experiments. Such robust learning protocol will significantly enhance the applicability of machine-learned spectroscopy for chemical science.

Magnetoelectricity-Mediated Tunable Absorption and Release of Peroxide Dianions

Peroxide dianion (O22-) has strong oxidizing activity and ease of proton abstraction and is extremely unstable. Direct and controllable adsorption and release of O22- has large application implication and is a large challenge so far. Here, we use a unique metal (Ni)-organic (diphenylalanine, DPA) framework (MOF), Ni(DPA)2, as adsorbents for absorption and release of O22-. This MOF structure has room-temperature magnetoelectricity via distortion of the Ni-centered octahedron {NiN2O4} and thus possesses a tunable ferroelectric polarization under applied electric/magnetic fields. Controllable adsorption and release of O22- are realized in such a MOF system via electrochemical redox measurements. Structural/spectroscopic characterization and calculations reveal that a number of NH active sites in the nanopores of MOF can effectively adsorb O22- by hydrogen bonds and then tunable ferroelectric polarization induces controllable release of O22- under applied magnetic fields. This work presents a constructive way for controllable adsorption and release of reactive oxygen species.

Redox‐Active Mixed‐Linker Metal–Organic Frameworks with Switchable Semiconductive Characteristics for Tailorable Chemiresistive Sensing

AbstractMetal–organic frameworks (MOFs), with diverse metal nodes and designable organic linkers, offer unique opportunities for the rational engineering of semiconducting properties. In this work, we report a mixed‐linker conductive MOF system with both tetrathiafulvalene and Ni‐bis(dithiolene) moieties, which allows the fine‐tuning of electronic structures and semiconductive characteristics. By continuously increasing the molar ratio between tetrathiafulvalene and Ni‐bis(dithiolene), the switching of the semiconducting behaviors from n‐type to p‐type was observed along with an increase in electrical conductivity by 3 orders of magnitude (from 2.88×10−7 S m−1 to 9.26×10−5 S m−1). Furthermore, mixed‐linker MOFs were applied for the chemiresistive detection of volatile organic compounds (VOCs), where the sensing performance was modulated by the corresponding linker ratios, showing synergistic and nonlinear modulation effects.

An electrochemiluminescence aptasensor based on highly luminescent silver-based MOF and biotin-streptavidin system for mercury ion detection.

In this study, for the first time, a silver-based metal-organic framework (Ag-MOF) was synthesized and used as the electrochemiluminescence (ECL) emitter for building an ECL sensor. After modification with chitosan (CS) and gold nanoparticles (Au NPs), the ECL stability of Ag-MOF was improved. To detect mercury ions, a biosensor was constructed using the mercury ion aptamer and steric effect of streptavidin. First, the capture strand (cDNA) with terminal-modified sulfhydryl group was attached to the electrode surface by the Au-S bond. Then, the mercury-ion aptamer (Apt-Hg) modified with biotin was anchored to the electrode by complementary pairing with cDNA. Streptavidin (SA) could be fixed on the electrode by linking with biotin, thereby reducing the ECL signal. However, in the presence of mercury ions, the aptamer was removed and streptavidin could not be immobilized on the electrode. Hence, the ECL signal of the sensor increased with the concentration of mercury ions, which was linear in the range from 1 μM to 300 fM. The detection limit could reach 66 fM (S/N = 3). The sensor provided a new method for the detection of mercury ions.

Modeling the Effect of Defects and Disorder in Amorphous Metal-Organic Frameworks.

Amorphous metal–organic frameworks (aMOFs) are a class of disordered framework materials with a defined local order given by the connectivity between inorganic nodes and organic linkers, but absent long-range order. The rational development of function for aMOFs is hindered by our limited understanding of the underlying structure–property relationships in these systems, a consequence of the absence of long-range order, which makes experimental characterization particularly challenging. Here, we use a versatile modeling approach to generate in silico structural models for an aMOF based on Fe trimers and 1,3,5-benzenetricarboxylate (BTC) linkers, Fe-BTC. We build a phase space for this material that includes nine amorphous phases with different degrees of defects and local order. These models are analyzed through a combination of structural analysis, pore analysis, and pair distribution functions. Therefore, we are able to systematically explore the effects of the variation of each of these features, both in isolation and combined, for a disordered MOF system, something that would not be possible through experiment alone. We find that the degree of local order has a greater impact on structure and properties than the degree of defects. The approach presented here is versatile and allows for the study of different structural features and MOF chemistries, enabling the derivation of design rules for the rational development of aMOFs.

Theoretical Study on the Electrochemical Water Splitting of Two-Dimensional Metal–Organic Frameworks TM3C12O12 (TM = Mn, Fe, Co, Ni)

Recently, two-dimensional metal–organic frameworks have received increasing interest due to their flexible components with adjustable structures, abundant accessible active sites, and high conductivity. In this paper, the thermal stability and electronic structure of 2D transition metal–organic framework (TM-O MOF, TM = Mn, Fe, Co, Ni) single-layer structures are systematically explored using first-principles calculations. Theoretical results reveal that these TM-O MOF systems exhibit good thermal stability due to sufficient π-electron conjugation and effective interaction between the transition metal and the organic ligands. They all show metallic behavior with spin magnetism. The catalytic property of TM-O MOFs depends on the d-electron occupations in the TM atoms. Interestingly, the active sites of HER and OER are O atoms and TM atoms, respectively, enhancing the water splitting process. The Co-O MOF shows a good HER and OER catalysis performance with the Gibbs free energy of adsorbed hydrogen atoms ΔG*H = 0.02 eV and the over potential ηOER = 0.53 V. The insights confirm the stability and highlight the outstanding water splitting catalytic performance of 2D MOFs under normal reaction conditions.

Electrostatic Secondary‐Sphere Interactions That Facilitate Rapid and Selective Electrocatalytic CO2 Reduction in a Fe‐Porphyrin‐Based Metal–Organic Framework

AbstractMetal–organic frameworks (MOFs) are promising platforms for heterogeneous tethering of molecular CO2 reduction electrocatalysts. Yet, to further understand electrocatalytic MOF systems, one also needs to consider their capability to fine‐tune the immediate chemical environment of the active site, and thus affect its overall catalytic operation. Here, we show that electrostatic secondary‐sphere functionalities enable substantial improvement of CO2‐to‐CO conversion activity and selectivity. In situ Raman analysis reveal that immobilization of pendent positively‐charged groups adjacent to MOF‐residing Fe‐porphyrin catalysts, stabilize weakly‐bound CO intermediates, allowing their rapid release as catalytic products. Also, by varying the electrolyte's ionic strength, systematic regulation of electrostatic field magnitude was achieved, resulting in essentially 100 % CO selectivity. Thus, this concept provides a sensitive molecular‐handle that adjust heterogeneous electrocatalysis on demand.

Dynamic Metal-Iodide Bonds in a Tetracoordinated Cadmium-Based Metal-Organic Framework Boosting Efficient CO2 Cycloaddition under Solvent- and Cocatalyst-Free Conditions.

Due to the inherent thermodynamic stability and kinetic inertness of CO2, heterogeneous catalytic conversion of CO2 to cyclic carbonates often requires harsh operating conditions, high temperature and high pressure, and the addition of cocatalysts. Therefore, the development of efficient heterogeneous catalysts under cocatalyst-free and mild conditions for CO2 conversion has always been a challenge. Herein, an infrequent tetracoordinated Cd-MOF was synthesized and used to catalyze CO2 cycloaddition reactions efficiently without the addition of any cocatalyst, and its catalytic mechanism was systematically investigated through a series of experiments, including fluorescence analysis, X-ray photoelectron spectroscopy, microcalorimetry, and density functional theory (DFT) calculation. Cd-MOF features a 3D supermolecule structure with 1D 11.6 × 7.7 Å2 channels, and the abundant Lewis acid/base and I- sites located in the confined channel boost efficient CO2 conversion with a maximum yield of 98.2% and a turnover number value of 1080.11 at 60 °C and 0.5 MPa, far surpassing most pristine MOF-based catalytic systems. A combined experimental and DFT calculation demonstrates that the exposed Cd(II) Lewis acid sites rapidly participate in coordination to activate the epoxides, and the resulting large steric hindrance facilitates leaving of the coordinated iodide ions in a reversibly dynamic fashion convenient for the rate-determining step ring-opening as a strong nucleophile. Such a pristine MOF catalyst with self-independent catalytic ring-opening overcomes the complicated operation limitation of the traditional cocatalyst-free MOF systems based on encapsulating/postmodifying cocatalysts, providing a whole new strategy for the development of simple, green, and efficient heterogeneous catalysts for CO2 cycloaddition.

Ethylene oxide functionalization enhances the ionic conductivity of a MOF

A synergistic approach, combining methods known to enhance solid-state conductivity, is applied here resulting in a true solid-state lithium conducting MOF system with ionic conductivity similar to reported MOF/Li salt/solvent electrolytes.

Selective and Sensitive Fluorescence Turn-On Detection of Cyanide Ions in Water by Post Metallization of a MOF.

Owing to detrimental impact of cyanide ion (CN- ) towards the entire living system as well as its availability in drinking water, it has become very important developing potential sensory materials for the selective and sensitive recognition of CN- ions in water. In the domain of sensory materials, luminescent metal-organic frameworks (LMOFs) have been considered as a promising candidate owing to their unique host-guest interaction, where MOFs can serve as an ideal scaffold for encapsulating relevant guest molecules rendering specific functionality. In this study, a post-synthetically modified MOF (viz., CuCl2 @MOF-867) was applied to recognize cyanide (CN- ) ions in water via "turn-on" response. The bipyridyl functionalities in MOF-867 were used to perform post-synthetic metalation to infiltrate CuCl2 inside porous architecture of the MOF. Moreover, a CuCl2 @MOF-867 based probe demonstrated highly selective and sensitive aqueous phase recognition of CN- ions even in the presence of other interfering anions such as Br- , NO3- , I- , SO42- , OAc- , SCN- , NO2- , etc. The selective binding of CN- ions to the copper-metal center has led to the generation of stable Cu(CN)2 species. This phenomenon has further resulted in a fluorescence turn-on response. The aqueous phase cyanide detection by the rationally modified MOF system exhibited very low limit of detection (0.19 μM), which meets the standardized limit stated by World Health Organization (WHO) that is 1.9 μM.