Carboxylate Metal-organic Frameworks Research Articles

A nano-oxygen generator for enhanced light-controlled elimination of anaerobic bacteria in periodontal infections

Using nanomaterials with photodynamic therapy (PDT) to combat bacterial infections including periodontal infections has attracted the attention of researchers because of their high efficiency, simplicity and low susceptibility to drug resistance. However, the therapeutic effectiveness is threatened by the endogenous accumulation of hydrogen peroxide and insufficient amounts of the substrate oxygen. Here, we report a microporous Zr porphyrin carboxylate metal-organic framework (MOF) PCN-222 doped with platinum nanozymes, Pt@PCN-222, to reshape the microenvironment that is not conducive to the recovery of infected tissue and further promote recovery after periodontal tissue infection. This MOFdoped with platinum nanozymes can remove excessive endogenous hydrogen peroxide and produce dissolved oxygen simultaneously. This framework can effectively alleviate anaerobic bacterial infection in periodontal tissue, including efficiently killing the bacteria and reducing the level of inflammation in tissue. This work provides a new strategy to solve the long-term clinical challenge of anaerobic bacterial infections in periodontal tissue and proposes an innovative approach to improve treatment.

Advanced Characterization Methodology to Unravel the Biodegradability of Metal-Organic Framework Nanoparticles in Extremely Diluted Conditions.

Porous iron(III) carboxylate metal-organic frameworks (MIL-100; MIL stands for Material of Institute Lavoisier) of submicronic size (nanoMOFs) have attracted a growing interest in the field of drug delivery due to their high drug payloads, excellent entrapment efficiencies, biodegradable character, and poor toxicity. However, only a few studies have dealt with the nanoMOF degradation mechanism, which is key to their biological applications. Complementary methods have been used here to investigate the degradation mechanism of Fe-based nanoMOFs under neutral or acidic conditions and in the presence of albumin. High-resolution STEM-HAADF coupled with energy-dispersive X-ray spectroscopy enabled the monitoring of the crystalline organization and elemental distribution during degradation. NanoMOFs were also deposited onto silicon substrates by dip-coating, forming stable thin films of high optical quality. The mean film thickness and structural changes were further monitored by IR ellipsometry, approaching the "sink conditions" occurring in vivo. This approach is essential for the successful design of biocompatible nano-vectors under extreme diluted conditions. It was revealed that while the presence of a protein coating layer did not impede the degradation process, the pH of the medium in contact with the nanoMOFs played a major role. The degradation of nanoMOFs occurred to a larger extent under neutral conditions, rapidly and homogeneously within the crystalline matrices, and was associated with the departure of their constitutive organic ligand. Remarkably, the nanoMOFs' particles maintained their global morphology during degradation.

Melt-quenched glass formation of a family of metal-carboxylate frameworks

Metal-organic framework (MOF) glasses are an emerging class of glasses which complement traditional inorganic, organic and metallic counterparts due to their hybrid nature. Although a few zeolitic imidazolate frameworks have been made into glasses, how to melt and quench the largest subclass of MOFs, metal carboxylate frameworks, into glasses remains challenging. Here, we develop a strategy by grafting the zwitterions on the carboxylate ligands and incorporating organic acids in the framework channels to enable the glass formation. The charge delocalization of zwitterion-acid subsystem and the densely filled channels facilitate the coordination bonding mismatch and thus reduce the melting temperature. Following melt-quenching realizes the glass formation of a family of carboxylate MOFs (UiO-67, UiO-68 and DUT-5), which are usually believed to be un-meltable. Our work opens up an avenue for melt-quenching porous molecular solids into glasses.

Melt-quenched carboxylate metal–organic framework glasses

Although carboxylate-based frameworks are commonly used architectures in metal-organic frameworks (MOFs), liquid/glass MOFs have thus far mainly been obtained from azole- or weakly coordinating ligand-based frameworks. This is because strong coordination bonds of carboxylate ligands to metals block the thermal vitrification pathways of carboxylate-based MOFs. In this study, we present the example of carboxylate-based melt-quenched MOF glasses comprising Mg2+ or Mn2+ with an aliphatic carboxylate ligand, adipate. These MOFs have a low melting temperature (Tm) of 284 °C and 238 °C, respectively, compared to zeolitic-imidazolate framework (ZIF) glasses, and superior mechanical properties in terms of hardness and elastic modulus. The low Tm may be attributed to the flexibility and low symmetry of the aliphatic carboxylate ligand, which raises the entropy of fusion (ΔSfus), and the lack of crystal field stabilization energy on metal ions, reducing enthalpy of fusion (ΔHfus). This research will serve as a cornerstone for the integration of numerous carboxylate-based MOFs into MOF glasses.

Sacrificial-Hydroxamate-Enabled Sizable Crystallization of Scandium Carboxylate Metal-Organic Frameworks.

Starting from labile hydroxamic acid ligands that are strong chelators, here, we implemented a sacrificial modulating strategy to prepare a series of scandium carboxylate metal-organic frameworks. Overcoming conventional syntheses that use excessive carboxylate modulators, the present strategy greatly reduces the organics required and produces large single crystals of several Sc-MOFs for X-ray crystallography.

Fabrication of a Cu(i)-carboxylate metal–organic framework by reduction of metal nodes for an azide–alkyne “click” reaction

A stable Cu(i)-carboxylate MOF is fabricated by ascorbic acid reduction, which breaks HSAB theory and achieves in situ phase transitions. The resultant Cu2H2DOBDC acting as a CuAAC catalyst exhibited superior catalytic performance.

A gold nanocluster/MIL-100(Fe) bimodal nanovector for the therapy of inflammatory disease through attenuation of Toll-like receptor signaling.

A better understanding of the molecular and cellular events involved in the inflammation process has opened novel perspectives in the treatment of inflammatory diseases, particularly through the development of well-designed nanomedicines. Here we describe the design of a novel class of anti-inflammatory nanomedicine (denoted as Au@MIL) synthesized through a one-pot, cost-effective and green approach by coupling a benchmark mesoporous iron(III) carboxylate metal organic framework (MOF) (i.e. MIL-100(Fe)) and glutathionate protected gold nanoclusters (i.e. Au25SG18 NCs). This nano-carrier exhibits low toxicity and excellent colloidal stability combined with the high loading capacity of the glucocorticoid dexamethasone phosphate (DexP) whose pH-dependent delivery was observed. The drug loaded Au@MIL nanocarrier shows high anti-inflammatory activity due to its capacity to specifically hinder inflammatory cell growth, scavenge intracellular reactive oxygen species (ROS) and downregulate pro-inflammatory cytokine secretion. In addition, this formulation has the capacity to inhibit the Toll-like receptor (TLR) signaling cascade namely the nuclear factor kappa B (NF-κB) and the interferon regulatory factor (IRF) pathways. This not only provides a new avenue for the nanotherapy of inflammatory diseases but also enhances our fundamental knowledge of the role of nanoMOF based nanomedicine in the regulation of innate immune signaling.

Metal-organic framework decorated with glycyrrhetinic acid conjugated chitosan as a pH-responsive nanocarrier for targeted drug delivery

Stimulus-responsive nanomaterials have become a hot spot in controllable drug delivery systems researches owing to their spatiotemporal controllable properties based on the differences between tumor microenvironment and normal tissue. Herein, iron (III) carboxylate metal-organic framework nanoparticles coated with glycyrrhetinic acid-chitosan conjugate (MIL-101/GA-CS) were successfully fabricated and acted as the pH-responsive and target-selective system to deliver doxorubicin (DOX) for hepatocellular carcinoma (HCC) therapy. The prepared nanocarrier possess the advantages of uniform size, comparable drug loading efficiency (28.89%), and superior pH-dependent controlled drug release (DOX release of 2.74% and 89.18% within 72 h at pH 7.4 and 5.5, respectively). In vitro cytotoxicity assays showed that the drug-loaded nanocarriers exhibited excellent inhibitory effects on HepG2 cells due to the sustained release of DOX, while the nanocarriers showed no significant toxicity. Furthermore, cell uptake experiments demonstrated that MIL-101-DOX/GA-CS could target HepG2 cells based on receptor-dependent internalization of glycyrrhetinic acid receptors mediated. In vitro 3D hepatoma cell microspheres experiments showed that MIL-101-DOX/GA-CS had excellent penetration and tumor killing ability. Therefore, MIL-101-DOX/GA-CS nanoparticles have a prospective application in cancer therapy as a pH-responsive controlled drug delivery system.

Drastically enhancing the cycle stability of copper-dicarboxylate as an anode material for lithium-ion batteries by rational fluorination

Metal-organic frameworks (MOFs) are extensively investigated in lithium-ion batteries because of their large specific surface area, adjustable chemical properties, porous structure, and rich reaction sites. However, the severe capacity attenuation of MOF electrodes has been one of the hardest obstacles hindering the further application of MOFs, due to the embedding and de-embedding of lithium ions during the cycles leading to the structural disintegration and volume fluctuation. Inspired by the wide application of fluorinated additives in commercial electrolytes, a typical carboxylate MOF, copper 1,4-benzenedicarboxylate is fluorinated molecularly to improve its cycle stability. Without enough fluorine source for a robust SEI film, the performance of fluorine-free copper 1,4-benzenedicarboxylate degrades rapidly to 99.5 mAh/g in the initial 21 cycles at a current density of 100 mA g−1, while its fluorinated counterpart, copper tetrafluoroterephthalate, delivers drastically enhanced cycle stability and maintains a reversible specific capacity of 575.5 mAh/g after 500 cycles, due to the SEI-promoting effect of fluorine in the framework. The present fluorination strategy is proved effective and can be extended in much wider applications of MOF materials.

Ag@MOF-199 metal organic framework for selective detection of nickel ions in aqueous media

Monitoring heavy metal ions (HMIs) in water is always a challenging and vital issue due to their hazardous effects on the environment and human health. Therefore, it is necessary to detect heavy metals in the water. Herein, we first-time report the use of silver nanoparticles (Ag NPs) incorporated copper benzene carboxylate (MOF-199) metal organic framework (Ag@MOF-199) for detection of heavy metal ions in water. A glassy carbon electrode-modified Ag@MOF-199 electrochemical sensor probe was fabricated and showed a selective and sensitive response towards nickel (Ni(II)) ions only by cyclic voltammetry. The Ag@MOF-199-based sensor did not offer any cyclic voltammetric sensing response towards cadmium (Cd(II)), lead (Pb(III)), chromium (Cr(III)), and ferric (Fe(III)) ions (1 μM/L) at pH values ranging from 3 to 10. The Ag@MOF-199 sensor displayed high sensitivity of 1.48 μA/nM on the exponential scale for Ni(II) ions at pH 7 and a lower detection limit of 6.06 nM/L with good reproducibility below US EPA suggested maximum contamination limit. The synthesized Ag@MOF-199 was characterized by spectroscopic (viz. UV–visible spectroscopy, Raman spectroscopy and mapping, energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy), surface area (viz. Brunauer–Emmett-Teller surface area analysis), electrochemical activity (viz. cyclic voltammetry, electrochemical impedance spectroscopy), morphological (viz. field emission scanning electron microscopy (FE-SEM)), structural (viz. X-ray diffraction (XRD)), and thermogravimetric analysis.

Energetic Systematics of Metal-Organic Frameworks: A Case Study of Al(III)-Trimesate MOF Isomers.

Thermal stability and thermodynamic properties of aluminum(III)-1,3,5-benzenetricarboxylate (Al-BTC) metal-organic frameworks (MOFs), including MIL-96, MIL-100, and MIL-110, have been investigated through a suite of calorimetric and X-ray techniques. In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC) revealed that these MOFs undergo thermal amorphization prior to ligand combustion. Thermal stabilities of Al-BTC MOFs follow the increasing order MIL-110 < MIL-96 < MIL-100, based on estimated amorphization temperatures. Their thermodynamic stabilities were directly measured by high-temperature drop combustion calorimetry. Normalized (per mole of Al) enthalpies of formation (ΔH*f) of MIL-96, MIL-100, and MIL-110 from Al2O3, H3BTC, and H2O (only Al2O3 and H3BTC for MIL-100) were determined to be -56.9 ± 13.7, -36.2 ± 17.9, and 62.8 ± 11.6 kJ/mol·Al, respectively. Our results demonstrate that MIL-96 and MIL-100 are thermodynamically favorable, while MIL-110 is metastable, in agreement with thermal and hydrothermal stability trends. The enthalpic preferences of MIL-96 and MIL-100 may be attributed to their shared trinuclear μ3-oxo-bridged (Al3(μ3-O)) secondary building units (SBUs) promoting stabilization of Al polyhedra by the ligands within these frameworks, in comparison to the sterically strained Al8 octamer cluster cores formed in MIL-110. Furthermore, similar ΔH*f of MIL-96 and MIL-100 explain their concurrent formation as physical mixtures often encountered during synthesis, implying the importance of kinetic factors that may facilitate the formation of Al-BTC framework isomers. More importantly, the normalized formation enthalpies of Al-BTC MOF isomers follow a negative correlation with the ratio of charged coordinated substituents to linkers (normalized per mole of Al within the MOF formula unit), with enthalpic preference given to systems with smaller (O2- + OH-)/ligand ratios. This trend has been successfully extended to the previously measured ΔH*f of several Zn4O-based frameworks (e.g., MOF-5, MOF-5(DEF), MOF-177, UMCM-1), all of which have been found to be metastable with respect to their dense phases (ZnO, H2O, and ligands). The result suggests that carboxylate MOFs with higher metal coordination environments attain more enthalpic stabilization from the coordinated ligands. Thus, the formation of some lanthanide/actinide, transition metal, and main group carboxylate frameworks may be energetically more favored, which, however, requires further studies.

The Impact of Secondary Building Units in Metal–Organic Frameworks on Plasmonic Gold‐Sensitized Photocatalysis

AbstractEmbedding plasmonic metals in metal–organic frameworks (MOFs) can build an advanced visible‐light photocatalyst architecture utilizing the localized surface plasmon resonance (LSPR) effect, while the practical performances have been restricted by the sluggish charge transfer at metal–MOF interface and through the secondary building units (SBUs) of the adopted carboxylate MOFs currently. Herein, a pyrazolate Ni‐MOF (PFC‐9) featured with an 1D SBU chain is selected to be the host catalyst to immobilize Au nanoparticles as a novel and optimized construction for LSPR photocatalysis. Compared with the common 3D‐connected SBUs of carboxyl‐ZrOx and pyrazole‐NiOx configurations in the reference MOFs, the 1D (−Ni−NPz−NPz−)∞ chain in PFC‐9 creates abundant Au/MOF contacts, a short and low‐resistant pathway for Au‐to‐Ni2+ transport of hot electrons, and enables fluent electron utilization at the continuous active Ni sites. Consequently, the Au/PFC‐9 photocatalyst achieves the optimum activity for visible‐light‐driven H2 production. This work shows an example to promote the LSPR‐sensitized photocatalysis taking the advantage of MOFs’ structural tunability, providing significant guidance for the rational design of highly efficient photocatalysts.

Cover Feature: Formation of Iron (III) Trimesate Xerogel by Ultrasonic Irradiation (Eur. J. Inorg. Chem. 15/2022)

The Cover Feature shows the ultrasound-assisted formation of Fe-BTC gels, iron carboxylate metal-organic frameworks (MOFs) constructed from iron ions and 1,3,5 benzenetricarboxylic acid linkers. The gels were obtained by two different procedures: ultrasonic irradiation (US) of different water solutions containing the linker and iron nitrate, with or without the additive tetramethylammonium hydroxide. Gelation was observed regardless of the duration of the irradiation, the precursor concentration, the additive, or the US apparatus used. While drying, the wet gels underwent shrinking and cracked into tiny fractions of transparent solid xerogels consisting of interconnected spherical, thermally stable nanoparticles with a permanent microporous structure. The authors acknowledge Prof. Christoph Hartl for gently assisting with the cover′s graphic layout. More information can be found in the Research Article by G. Mannias, M. Pilloni and co-workers.

MOFs-based nanoagent enables dual mitochondrial damage in synergistic antitumor therapy via oxidative stress and calcium overload

Targeting subcellular organelle with multilevel damage has shown great promise for antitumor therapy. Here, we report a core-shell type of nanoagent with iron (III) carboxylate metal-organic frameworks (MOFs) as shell while upconversion nanoparticles (UCNPs) as core, which enables near-infrared (NIR) light-triggered synergistically reinforced oxidative stress and calcium overload to mitochondria. The folate decoration on MOFs shells enables efficient cellular uptake of nanoagents. Based on the upconversion ability of UCNPs, NIR light mediates Fe3+-to-Fe2+ reduction and simultaneously activates the photoacid generator (pHP) encapsulated in MOFs cavities, which enables release of free Fe2+ and acidification of intracellular microenvironment, respectively. The overexpressed H2O2 in mitochondria, highly reactive Fe2+ and acidic milieu synergistically reinforce Fenton reactions for producing lethal hydroxyl radicals (•OH) while plasma photoacidification inducing calcium influx, leading to mitochondria calcium overload. The dual-mitochondria-damage-based therapeutic potency of the nanoagent has been unequivocally confirmed in cell- and patient-derived tumor xenograft models in vivo.

Controlled Demolition and Reconstruction of Imidazolate and Carboxylate Metal–Organic Frameworks by Acid Gas Exposure and Linker Treatment

The metal-linker coordination bond in metal–organic frameworks (MOFs) can be unstable in humid and acid gas environments, leading to loss of crystallinity and porosity. This degradation is not necessarily irreversible; solvent-assisted crystal redemption (“SACRed”) has been shown to recover the physical and chemical properties of ZIF-8 exposed to humid SO2. This approach can also be useful in creating mixed-linker materials that might be challenging to produce via de novo synthesis. Here, we expand more generally the concept of controlled degradation of a MOF with acid gas, followed by treatment with a fresh linker solution, to the use of different template MOFs (ZIFs, UiO-66, and UiO-67) and acid gases (SO2 and NO2 in dry and humid conditions). Significant losses in porosity and crystallinity along with structural changes (acid gas-linker complexes and linker functionalizations) are observed in the acid gas-exposed MOF templates, and SACRed is shown to reconstruct these partially demolished MOFs with a high degree of structural recovery. Detailed structural and spectroscopic characterizations of the controlled degradation and subsequent recovery are presented and analyzed. These findings indicate the generality of controlled degradation and reconstruction as a means for linker replacement in a wider variety of MOFs and also create the potential for linker substitutions (with non-native linkers) to obtain new hybrid MOFs.

Convenient synthesis of zwitterionic calcium(II)-carboxylate metal organic frameworks with efficient activities for the treatment of osteoporosis

Calcium supplementation is effective in alleviating the process of osteoporosis and the occurrence of osteoporotic fractures for people with long-term calcium deficiency. Herein, five water-stable calcium carboxylate compounds, that is, mononuclear coordination compound [Ca(Cbdcp)(H2O)6]·0.5H2O (1, H3CbdcpBr = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium bromide), and metal organic frameworks (MOFs) {[Ca3(Dcbdcp)2(H2O)12]·2H2O}n (2, H4DcbdcpBr = N-(3,5-dicarboxybenzyl)-(3,5-dicarboxyl)pyridinium bromide), {[Ca(Cmdcp)(H2O)4]·3H2O}n (3, H3CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide), {[Ca(Cdcbp)]·2H2O}n (4, H3CdcbpBr = 3-carboxyl-(3,5-dicarboxybenzyl)-pyridinium bromide) and {[Ca0.5(Cmcp)]·2H2O}n (5, H2CmcpBr = N-carboxymethyl-(3-carboxyl)pyridinium bromide), were synthesized from the reaction of CaCl2 with five different kinds of zwitterionic carboxylate ligands in the presence of NaOH, respectively. Compounds 1–5 were characterized by Fourier-transform infrared (FTIR) spectroscopy, elemental analyses, single-crystal X-ray crystallography, and inductively coupled plasma mass spectrometry (ICP-MS). Compound 1 features a mononuclear structure and MOF 2 with a one-dimensional (1D) structure while MOFs 3 and 5 with 2D layer structures and MOF 4 showing a 3D structure. Compounds 1–5 exhibited good water stability and possessed considerable biocompatibility with primary mice osteoblasts. The in vitro ability of compounds 1–5 in regulating osteoblastic differentiation was studied via alkaline phosphatase (ALP) staining, alizarin red S (ARS) staining, and quantitative real-time polymerase chain reaction (qPCR). Among these 5 compounds, MOF 4 showed the overall best in vitro osteogenic effects. Then, we administrated MOF 4 intragastrically to bilaterally ovariectomized mice for 8 weeks and found that bone loss caused by ovariectomy (OVX) was significantly alleviated. Besides, MOF 4 administration showed no toxic effects in the main organs of the mice. Altogether, zwitterionic carboxylate ligands-based calcium compounds provide a new strategy for calcium agents development.

A base-free Chan–Lam reaction catalyzed by an easily assembled Cu(II)-carboxylate metal-organic framework

A new copper(II) metal-organic framework is constructed as a sustainable copper heterogeneous catalyst. Cu-DPTCA, with high catalytic activity, can effectively promote the Chan–Lam coupling reaction of arylboronic acids and amines without adding any base or additive.

Evaluating the Robustness of Metal-Organic Frameworks for Synthetic Chemistry.

Metal-organic frameworks (MOFs) are emerging as sustainable reagents and catalysts with promising applications in synthetic chemistry. Although the hydrothermal stabilities of MOFs have been well studied, their robustness toward various reagents, including acids, bases, nucleophiles, electrophiles, oxidants, and reductants, remains poorly characterized. As such, heterogeneous platforms for promising catalysts are generally identified on an ad hoc basis and have largely been limited to carboxylate frameworks to date. To address these limitations, here we systematically characterize the robustness of 17 representative carboxylate, salicylate, and azolate MOFs toward 30 conditions representing the scope of synthetic organic chemistry. Specifically, analysis of the full width at half-maximum of powder X-ray diffraction patterns, as well as infrared spectroscopy, 77 K N2 adsorption measurements, and scanning electron microscopy in select cases are employed to appraise framework degradation and dissolution under a range of representative conditions. Our studies demonstrate that azolate MOFs, such as Fe2(bdp)3 (bdp2- = 4,4'-(1,4-phenylene)bis(pyrazolate)), generally possess excellent chemical stabilities under myriad conditions. In addition, we find that carboxylate and salicylate frameworks possess complementary stabilities, with carboxylate MOFs possessing superior robustness toward acids, electrophiles, and oxidants, and salicylate MOFs demonstrating improved robustness toward bases, nucleophiles, and reductants. The guidelines provided herein should facilitate the rational design of robust frameworks for applications in synthetic chemistry and guide the development of new strategies for the postsynthetic modification of MOFs as well.

Degradation Mechanism of Porous Metal-Organic Frameworks by In Situ Atomic Force Microscopy.

In recent years, Metal-Organic Frameworks (MOFs) have attracted a growing interest for biomedical applications. The design of MOFs should take into consideration the subtle balance between stability and biodegradability. However, only few studies have focused on the MOFs’ stability in physiological media and their degradation mechanism. Here, we investigate the degradation of mesoporous iron (III) carboxylate MOFs, which are among the most employed MOFs for drug delivery, by a set of complementary methods. In situ AFM allowed monitoring with nanoscale resolution the morphological, dimensional, and mechanical properties of a series of MOFs in phosphate buffer saline and in real time. Depending on the synthetic route, the external surface presented either well-defined crystalline planes or initial defects, which influenced the degradation mechanism of the particles. Moreover, MOF stability was investigated under different pH conditions, from acidic to neutral. Interestingly, despite pronounced erosion, especially at neutral pH, the dimensions of the crystals were unchanged. It was revealed that the external surfaces of MOF crystals rapidly respond to in situ changes of the composition of the media they are in contact with. These observations are of a crucial importance for the design of nanosized MOFs for drug delivery applications.

C-AFM study on multi - resistive switching modes observed in metal–organic frameworks thin films

Abstract Metal-organic framework (MOF) materials have recently attracted much attention for use in resistive random-access memory due to the advantages of having high insulative properties, well-defined structures, a large specific surface area, and an adjustable pore size. In this study, the memory device based on zirconium (IV)-carboxylate MOF (UiO-66) nanoparticles exhibits the low operation voltage (V