A water-stable metal-organic framework: serving as a chemical sensor of PO43– and a catalyst for CO2 conversion

A pH-Stable TbIII-Based Metal-Organic Framework as a Turn-On and Blue-Shift Fluorescence Sensor toward Benzaldehyde and Salicylaldehyde in Aqueous Solution

A new polydentate tetracarboxylic acid with a benzothiadiazole unit (4',4'''-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid), H₄BTDBA) has been used to prepare a pH-stable three-dimensional Tb^III-based metal-organic framework (MOF) with the formula {[(CH₃)₂NH₂]_0.7[Tb₂(BTDBA)_1.5(lac)_0.7(H₂O)₂]·solvents}_n (Hlac = lactic acid, JXUST-19). JXUST-19 exhibits a new (4,4,12)-connected topology based on tetranuclear [Tb₄] clusters. JXUST-19 can remain stable when soaked in water for at least 1 week and in aqueous solutions with various pH values (2-12) for 24 h. Fluorescence study indicates JXUST-19 can be employed as a rare turn-on and blue-shift MOF sensor toward benzaldehyde (BZ) and salicylaldehyde (SA). To date, JXUST-19 represents the first Tb^III-based turn-on MOF sensor toward salicylaldehyde in aqueous solution, and the fluorescence enhancement and naked-eye detection of BZ have been rarely reported. In addition, JXUST-19 based fluorescent test papers, light-emitting diode lamp beads, and portable composite films were developed to realize naked-eye detection of BZ and SA, which has great potential in practical applications.

Effective enhancement of capacitive performance by the facile exfoliation of bulk metal-organic frameworks into 2D-functionalized nanosheets

Recently, much attention has been paid to two-dimensional MOF nanosheets (MONs) due to their widespread application in many specific areas. In this work, a simple and efficient congenerous-exfoliation strategy was developed to prepare vast and uniform few-layered Ni²⁺@Ce-MOF (Ce-MOF: {[Ce(HPIA)(PIA)(H₂O)₂]·H₂O}_n) nanosheets with a thickness of ca. 10 nm. In the exfoliation process, the synergistic action of Ni²⁺ and methanol solvents under ultrasonication plays a major role in restraining the interactions between the layers. Importantly, supercapacitor applications indicate that the exfoliated Ni²⁺@Ce-MOF nanosheet shows a remarkable improvement in the specific capacitance (921.05%) in comparison with that of the bulk Ce-MOF sample before modification.

A Novel Drug Delivery System: the Encapsulation of Naringenin in Metal-Organic Frameworks into Liposomes

Poorly water-soluble naringenin (NAR) was selected as a model drug and loaded into the porous MOFs for the construction of NAR@ZIF-8 inclusion complex. By film dispersion method, NAR@ZIF-8 was further encapsulated into liposomes to fabricate a novel drug delivery system. Liposomes and a novel drug delivery system were established. Subsequently, the lipid-drug ratio, phospholipid-cholesterol ratio, and hydration temperature were investigated using the Box-Behnken design based the single factor experiment. The prepared liposomes system showed spherical or quasi-spherical shape, uniform particle size distribution, and complete structure. More specifically, the average particle size was 113.2 ± 1.4 nm, and zeta potential was - 7.536 ± 0.264 mV. Moreover, the drug release behaviors of NAR, NAR@ZIF-8, and NAR@ZIF-8 liposomes were explored in vitro. Compared with free NAR and NAR@ZIF-8 which exhibited a burst drug release, NAR@ZIF-8 liposomes showed a more sustained release behavior with 79.86% drug release in 72 h. In vitro cytotoxicity experiments showed that, compared with free NAR and NAR@ZIF-8, NAR@ZIF-8 liposomes exhibited higher inhibition efficiency on lung adenocarcinoma A549 cells and gastric cancer SGC-7901 cells in a concentration-dependent manner.

Formation of CX Bonds in CO2 Chemical Fixation Catalyzed by Metal-Organic Frameworks

Transformation of CO₂ based on metal-organic framework (MOF) catalysts is becoming a hot research topic, not only because it will help to reduce greenhouse gas emission, but also because it will allow for the production of valuable chemicals. In addition, a large number of impressive products have been synthesized by utilizing CO₂ . In fact, it is the formation of new covalent bonds between CO₂ and substrate molecules that successfully result in CO₂ solidly inserting into the products, and only four types of new CX bonds, including CH, CC, CN, and CO bonds, are observed in this exploration. An overview of recent progress in constructing CX bonds for CO₂ conversion catalyzed by various MOF catalysts is provided. The catalytic mechanism of generating different CX bonds is further discussed according to both structural features of MOFs and the interactions among CO₂ , substrates, as well as MOFs. The future opportunities and challenges in this field are also tentatively covered.

Carbon Dioxide (CO2) Fixation: Linearly Bridged Zn2 Paddlewheel Nodes by CO2 in a Metal-Organic Framework

When the reaction of zinc nitrate with 4',4‴,4‴″,4‴‴'-(ethene-1,1,2,2-tetrayl)tetrakis[(1,1'-biphenyl-3-carboxylic acid)] (H₄tmpe) in dimethylformamide (DMF) under hydrothermal condition is performed in air or carbon dioxide (CO₂), [Zn₄(tmpe)₂(H₂O)₂(μ₂-CO₂)]·8DMF·18H₂O (1) crystallizes out. However, if it is in dioxygen, argon, or carbon monoxide, [Zn₂(tmpe)(DMF)]·2DMF·8H₂O (2) is the product. Both compounds are chemically stable coordination polymers. 1 contains zinc carboxylate paddlewheels as nodes linearly bridged by CO₂ into two interpenetrating lattices, and 2 has an infinite single framework formed by a tetranuclear node. 1 is the second example containing the linear CO₂-bridged paddlewheel node. Interestingly, CO₂ fixation in a μ₂-η²_O,O bridging mode is observed in 1, which is rarely characterized structurally and has been confirmed using IR and gas chromatography analysis. The stability of 1 is further verified by density functional theory calculations, which found an energy minimum with a Zn-O═C angle of 180°. Both compounds display strong emission around 490 nm and excited-state lifetimes around 2.4 ns.

New fluorescent chemosensors based on mononuclear copper complex for highly selective and sensitive detection of phosphate anion in aqueous solution and living cells

Three new probes, named, [Cu(L1)₂]Cl₂ (C1), [Cu(L2)₂]Cl₂ (C2) and [Cu(L3)₂]Cl₂ (C3) were synthesized and well characterized. The probes C1, C2 and C3 were successfully achieved for the efficient detection of PO₄^3- as turn-on fluorescence chemosensors in DMSO/H₂O (v:v = 2:8, Tris-HCl pH = 7.20). The limit of detection (LOD) of probes C1, C2 or C3 for PO₄^3- could be as low as 0.029 μM, 0.048 μM, 0.079 μM, respectively, which were effectively applied for the determination of the PO₄^3- concentration in environmental water of swimming pool. What's more, the binding constant between probes C1, C2, C3 and PO₄^3- are estimated to be 3.11 × 10⁷ M^-1 (R² = 0.9992), 1.84 × 10⁷ M^-1 (R² = 0.9956), 1.93 × 10⁷ M^-1 (R² = 0.9976), respectively. The proposed mechanism for the "on-off-on" fluorescence response was confirmed by ESI-MS and fluorescence spectrum. Moreover, the membrane-permeable probe C1 was successfully demonstrated in monitoring of PO₄^3- in cultured HepG2 cells.

A water-stable europium-MOF as a multifunctional luminescent sensor for some trivalent metal ions (Fe3+, Cr3+, Al3+), PO43− ions, and nitroaromatic explosives

Eu-MOF having a layered structure exhibits high sensitivity, selectivity, and recyclability towards sensing Fe³⁺, Cr³⁺, Al³⁺, and PO₄³⁻ ions and TNP.