Post-synthetic Modification Research Articles

Reversible Acylation of RNA Enables Activatable Biosensing.

There is a high demand to develop chemical tools to control the property and function of RNA. Current methods mainly rely on ultraviolet light-based caging strategies, which may cause phototoxicity in live cell-based experiments. We herein report an endogenous stimulus-responsive RNA acylation approach by introducing boronate ester (BE) groups to 2'-hydroxyls through postsynthetic modification. Treatment with hydrogen peroxide (H2O2) yields a phenol derivative which undergoes a 1,6-eliminaton for the traceless release of 2'-hydroxyl. We demonstrated that the acylation of crRNA enabled conditional regulation of CRISPR/Cas13a activity for activatable detection of target RNA. We also showed that the highly specific acylation of the single RNA in 8-17 DNAzyme allowed reversible control of the catalytic activity of DNAzyme, which was further applied to the cell-selective imaging of metal ions in cancer cells. Thus, our strategy provides a simple, general, and cell-selective method to control RNA activity, affording great potential in the construction of activatable RNA sensors and pre-RNA medicines.

Enhancing methyl orange adsorption capacity via functionalizing ZIF-8 with amphiphilic cetylpyridinium bromide

BackgroundThe precise design or functionalization of metal organic frameworks (MOFs) based on the properties of organic dyes is a promising direction in environment remediation. MethodsHerein, using methyl orange (MO) as the target dye, cetylpyridinium bromide (CPB) functionalized ZIF-8 (CPB@ZIF-8) was fabricated by the post-synthetic modification strategy. Significant findingsThe surface area and the pore volume of CPB@ZIF-8 are greatly reduced compared with pure ZIF-8. However, the introduction of amphiphilic CPB molecules into ZIF-8 can significantly enhance the adsorption performance of MO. This enhanced MO adsorption capacity can be attributed to the incorporation of more positively charged sites, hydrophobic sites and aromatic rings in the CPB-modified ZIF-8 frameworks, which provides the electrostatic attractions, the hydrophobic and π-π interactions that mainly govern the adsorption of MO on CPB@ZIF-8. The pseudo-second-order kinetic model and the Langmuir isotherm model can well represent the adsorption process of MO. The maximum adsorption capacity (195.54 mg/g) has been obtained at 30 °C, outperforming pristine ZIF-8 and various reported absorbents. The prepared CPB@ZIF-8 composite is a superior example of the tunable adsorption affinity of MOFs for anionic dyes.

Post-synthetic thiol modification of covalent organic frameworks for mercury(II) removal from water.

Various materials have been developed for environmental remediation of mercury ion pollution. Among these materials, covalent organic frameworks (COFs) can efficiently adsorb Hg(II) from water. Herein, two thiol-modified COFs (COF-S-SH and COF-OH-SH) were prepared, through the reaction between 2,5-divinylterephthalaldehyde and 1,3,5-tris-(4-aminophenyl)benzene, followed by post-synthetic modification using bis(2-mercaptoethyl) sulfide and dithiothreitol, respectively. The modified COFs showed excellent Hg(II) adsorption abilities with maximum adsorption capacities of 586.3 and 535.5mgg-1 for COF-S-SH and COF-OH-SH, respectively. The prepared materials showed excellent selective absorbability for Hg(II) against multiple cationic metals in water. Unexpectedly, the experimental data showed that both co-existing toxic anionic diclofenac sodium (DCF) and Hg(II) performed positive effect for capturing another pollutant by these two modified COFs. Thus, a synergistic adsorption mechanism between Hg(II) and DCF on COFs was proposed. Moreover, density functional theory calculations revealed that synergistic adsorption occurred between Hg(II) and DCF, which resulted in a significant reduction in the adsorption system's energy. This work highlights a new direction for application of COFs to simultaneous removal of heavy metals and co-existing organic pollutants from water.

Cooperative Proton and Li-ion Conduction in a 2D-layered MOF via Mechanical Insertion of Lithium Halides.

Ionic conduction in highly designable and porous metal-organic frameworks has been explored through the introduction of various ionic species (H+, OH-, Li+, etc.) using post-synthetic modification such as acid, salt, or ionic liquid incorporation. Here, we report on high ionic conductivity (σ > 10-2 S cm-1) in a two-dimensionally (2D)-layered Ti-dobdc (Ti2(Hdobdc)2(H2dobdc), H4dobdc: 2,5-dihydroxyterephthalic acid) via LiX (X= Cl, Br, I) intercalation using mechanical mixing. The anionic species in lithium halide strongly affect the ionic conductivity and durability of conductivity. Solid-state pulsed-field gradient nuclear magnetic resonance (PFG-NMR)verified the high mobility of H+ and Li+ ions in the temperature range of 300-400 K. In particular, the insertion of Li salts improved the H+ mobility above 373 K owing to strong binding with H2O. Furthermore, the continuous increase in Li+ mobility with temperature contributed to the retention of the overall high ionic conductivity at high temperatures.

Metal-Organic Framework Supported Copper Photoredox Catalysts for Iminyl Radical-Mediated Reactions.

Visible-light copper photocatalysis has recently emerged as a viable technology for building sustainable synthetic processes. To broaden the applications of phosphine-ligated copper(I) complexes, we describe herein an effective metal-organic framework (MOF)-supported copper(I) photocatalyst for multiple iminyl radical-mediated reactions. Due to site isolation, the heterogenized copper photosensitizer has a significantly higher catalytic activity than its homogeneous counterpart. Using a hydroxamic acid linker to immobilize copper species on MOF supports affords the heterogeneous catalysts with high recyclability. The post-synthetic modification sequence on MOF surfaces allows for the preparation of previously unavailable monomeric copper species. Our findings highlight the potential of using MOF-based heterogeneous catalytic systems to address fundamental challenges in the development of synthetic methodologies and mechanistic investigations of transition-metal photoredox catalysis.

Ni(II)-Pyrazolate Framework Bearing a Metalated Schiff-Base Moiety for Electrocatalytic Hydrogen Evolution.

A robust and porous Ni-based metal-organic framework (MOF), NiL1, was assembled from Ni(II) ions and a dipyrazolate linker (L12-). A Ni(II)-anchored MOF catalyst Ni@NiL1-Sal has been successfully prepared by post-synthetic modification (PSM) condensation between NiL1 with salicylaldehyde, followed by chelation of Ni(II) ions by salicylaldimine as a secondary active site. Ni@NiL1-Sal with carbon black was found to exhibit enhanced electrocatalytic hydrogen evolution reaction (HER) performance (the smallest overpotential, 384 mV, and Tafel slope, 87 mV dec-1) when compared with primitive NiL1 and NiL1-Sal. Such improvement in HER highlights the creation of unambiguous secondary active sites as an avenue to the rational design of a functional MOF-based electrocatalyst.

Ethylene Dimerization Performance of NiBTCs Synthesized Using Different Solvents

MOFs have attracted widespread attention in the field of catalytic ethylene dimerization. Compared with post-synthetic modification, ion exchange and other methods to introduce external active centers, the direct use of MOF materials as catalysts is still the most convenient and prospective. Herein, the NiBTCs are synthesized using a one-pot method in two kinds of solvent and characterized by XRD, FT–IR, ICP–OES, XPS, TGA and N2 physical adsorption. After treatment at 150 °C, the catalytic activities of both materials in ethylene dimerization are up to 470.9, and 647.0 gpro./(gcat.·h) and the selectivity of 1-butene in all products could reach 83.2% and 81.7%, respectively. Stability testing of the catalysts demonstrated that they do not decompose during the reaction, but their reuse performance is degraded. In addition, a probable Cossee–Arlman–type mechanism is proposed. The NiBTCs are shown to have superior catalytic performance in ethylene dimerization compared to employing Ni(pyz)2Cl2 or α–Ni(im)2 as catalysts.

Numerical Recognition System and Ultrasensitive Fluorescence Sensing Platform for Al3+ and UO22+ Based on Ln (III)-Functionalized MOF-808 via Thiodiglycolic Acid Intermediates

Continuous accumulation of Al3+ in the human body and unintended leakage of UO22+ have posed a great threat to human health and the global environment; thus searching an efficient probe for the detection of Al3+ and UO22+ is of great importance. Herein, we designed and synthesized two hydrolytically stable Eu3+- and Tb3+-functionalized MOF materials Eu@MOF-808-TDA and Tb@MOF-808-TDA via thiodiglycolic acid (TDA) intermediates by the postsynthetic modification method. Among them, Tb@MOF-808-TDA was applied to construct numerical recognition systems of multiples of three and four by the combination of fluorescent signals, hierarchical cluster analysis, and logical gates. In addition, Tb@MOF-808-TDA exhibits good selectivity and sensitivity for the detection of Al3+ and UO22+. The detection limit is calculated to be 0.085 ppm for Al3+ and 0.082 ppm for UO22+ in aqueous solutions, which is lower than or close to that of latest reported Ln-MOFs. Moreover, the probe shows excellent hydrolytic stability and luminescence stability in the pH range of 4-11, further providing solid evidence for the practical application of Tb@MOF-808-TDA. More importantly, a mixed matrix hydrogel PVA-Tb@MOF-808-TDA was prepared to achieve the visual detection of Al3+, which broadens the potential in real-world sensing applications.

Cp*Co(III)-Catalyzed C(8)-Nucleophilic Cascade Cyclization of Quinoline N-Oxide with 1,6-Enyne

The C(8)-selective nucleophilic cascade cyclization of quinoline N-oxide with easily derived 1,6-enyne from phenol derivatives is demonstrated. A variety of quinoline N-oxide and alkynes are discovered to be suitable for producing a library of quinoline N-oxide tethered cis-hydrobenzofurans with high yields and excellent functional group tolerance. The utility of the protocol has been accomplished by post-synthetic modification of the cyclized product. The mechanistic studies indicate a base-assisted internal electrophilic-type substitution (BIES)-type pathway for C-H bond activation, and electrospray ionization mass spectrometry (ESI-MS) analysis of the stoichiometric reaction confirmed the formation of a key five-membered cobaltacycle.

In Situ Nanoarchitectonics of a MOF Hydrogel: A Self-Adhesive and pH-Responsive Smart Platform for Phototherapeutic Delivery.

Metal-organic frameworks (MOFs) have dramatically changed the fundamentals of drug delivery, catalysis, and gas storage as a result of their porous geometry, controlled architecture, and ease of postsynthetic modification. However, the biomedical applications of MOFs still remain a less explored area due to the constraints associated with handling, utilizing, and site-specific delivery. The major drawbacks associated with the synthesis of nano-MOFs are related to the lack of control over particle size and inhomogeneous dispersion during doping. Therefore, a smart strategy for the in situ growth of a nano-metal-organic framework (nMOF) has been devised to incorporate it into a biocompatible polyacrylamide/starch hydrogel (PSH) composite for therapeutic applications. In this study, the post-treatment of zinc metal ion cross-linked PSH with the ligand solution generated the nZIF-8@PAM/starch composites (nZIF-8, nano-zeolitic imidazolate framework-8). The ZIF-8 nanocrystals thus formed have been found to be evenly dispersed throughout the composites. This newly designed nanoarchitectonics of an MOF hydrogel was found to be self-adhesive, which also exhibited improved mechanical strength, a viscoelastic nature, and a pH-responsive behavior. Taking advantage of these properties, it has been utilized as a sustained-release drug delivery platform for a potential photosensitizer drug (Rose Bengal). The drug was initially diffused into the in situ hydrogel, and then the entire scaffold was analyzed for its potential in photodynamic therapy against bacterial strains such as E. coli and B. megaterium. The Rose Bengal loaded nano-MOF hydrogel composite exhibited remarkable IC50 values within the range of 7.37 ± 0.04 and 0.51 ± 0.05 μg/mL for E. coli and B. megaterium. Further, reactive oxygen species (ROS) directed antimicrobial potential was validated using a fluorescence-based assay. This smart in situ nanoarchitectonics hydrogel platform can also serve as a potential biomaterial for topical treatment including wound healing, lesions, and melanoma.

Facile and large-scale synthesis of trifluoromethyl-grafted covalent organic framework for efficient microextraction and ultrasensitive determination of benzoylurea insecticides

Owing to the excessive usage of benzoylurea insecticide (BUs), ecological and environmental problem has been attractedincreasingpublic attention. Herein, a novel trifluoromethyl-grafted covalent organic framework (COF), named COF-(CF3)2, was synthetized through Suzuki-Miyaura cross-coupling reaction based on post-synthetic modification (PSM) strategy under mild condition. The synthesized operation was simplified to make it suitable for large-scale production and application. Characterization methods, such as fourier transform-infrared spectrum, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, were implemented to confirm the successful synthesis of COF-(CF3)2. Considering the enhanced electrostatic interaction and fluorine–fluorine interactions, COF-(CF3)2 was applied as solid phase microextraction (SPME) coating. An analytical method coupling direct immersion (DI)-SPME with ultra-high performance liquid chromatography-tandem mass spectrometrywas established for effective enrichment and ultrasensitive determination of seven BUs in environmental water. Satisfactory analytical parameters for target BUs were obtained, including wide linearity of 1–1000 ng L−1 with correlation coefficient (R2) of 0.9991–0.9999, low limits of detection (LOD) of 0.06–0.50 ng L−1, high enrichment factors (EFs) of 44–105 and satisfactory precision with relative standard deviations (RSD) ≤ 10.2%. The excellent performance of the proposed method was validated by the recovery test in real water samples with recoveries of 76.2–107.6% and RSD ≤ 11.1%. Furthermore, multiple interactions between COF-(CF3)2 and BUs molecules were analyzed combined with theoretical simulations to explain the adsorption mechanism. It illustrated that exceptional BUs adsorption performance of COF-(CF3)2 might be attributed tosynergistic effect of mesoporous structure and trifluoromethyl modification. This work represents a rational design of functional materials through a novel and versatile PSM approach for the effective enrichment and ultrasensitive analysis of BUs in environmental water, and provides a multiscale understanding of high-performance adsorbent.

The Journey from Porous Materials to Metal-organic Frameworks and their Catalytic Applications: A Review.

Metal-Organic Frameworks (MOFs), a class of inorganic-organic hybrid materials, have been at the center of material science for the past three decades. They are synthesized by metal ions and organic linker precursors and have become very potential materials for different applications ranging from sensing, separation, catalytic behaviour to biomedical applications and drug delivery, owing to their structural flexibility, porosity and functionality. They are also very promising in heterogeneous catalysis for various industrial applications. These catalysts can be easily synthesized with extremely high surface areas, tunable pore sizes, and incorporation of catalytic centers via post-synthetic modification (PSM) or exchange of their components as compared to traditional heterogeneous catalysts, which is the preliminary requirement of a better catalyst. Here, in this review, we have presented the history of MOFs, different synthesis procedures, and MOFcatalysed reactions; for instance, coupling reactions, condensation reactions, Friedel-Crafts reaction, oxidation, etc. Special attention has been given to MOFs containing different catalytic centers, including open metal sites, incorporation of catalytic centers through PSM, and bifunctional acidbase sites. The important role of catalytic centers present in MOFs and reaction mechanisms have also been outlined with examples.

Preparation of heterogeneous catalysts by the post-synthetic modification of mesoporous metal-organic framework MIL-101

Preparation of heterogeneous catalysts by the post-synthetic modification of mesoporous metal-organic framework MIL-101

Tailor-Made Pdn L2n Metal-Organic Cages through Covalent Post-Synthetic Modification.

Post-synthetic modification (PSM) is an effective approach for the tailored functionalization of metal-organic architectures, but its generalizability remains challenging. Herein we report a general covalent PSM strategy to functionalize Pdn L2n metal-organic cages (MOCs, n=2, 12) through an efficient Diels-Alder cycloaddition between peripheral anthracene substituents and various functional motifs bearing a maleimide group. As expected, the solubility of functionalized Pd12 L24 in common solvents can be greatly improved. Interestingly, concentration-dependent circular dichroism and aggregation-induced emission are achieved with chiral binaphthol (BINOL)- and tetraphenylethylene-modified Pd12 L24 , respectively. Furthermore, Pd12 L24 can be introduced with two different functional groups (e.g., chiral BINOL and achiral pyrene) through a step-by-step PSM route to obtain chirality-induced circularly polarized luminescence. Moreover, similar results are readily observed with a smaller Pd2 L4 system.

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Advanced hybrid polybenzimidazole membrane enabled by a “linker” of metal-organic framework for high-performance vanadium flow battery

High current density vanadium flow batteries (VFBs) are important for the wide range of applications of renewable energy. The balance between proton conductivity and vanadium permeability of proton exchange membrane has been a huge challenge for the development of high-power density VFBs. Herein, a post-synthetic modification of Zr-MOFs (PSM) is introduced into PBI matrix to break the trade-off between vanadium permeability and ion selectivity, and remarkably improves the power density of VFBs. As a “linker” between the PBI backbone, the PSM creates more proton transport sites in the hybrid membrane, which significantly increases the proton conductivity. Meanwhile, the “acid-base” pairs are formed between PSM and PBI matrix, further promoting the proton transfer in the hybrid membrane. More importantly, the denser structure of hybrid membrane blocks the vanadium ion permeation based on the Donnan exclusion and size sieving effect, respectively. In consequence, the ion selectivity of the PBI/PSM hybrid membrane is substantially improved, almost four times that of the pure PBI membrane. Benefiting from such rational design, the VFB equipped with the PBI/PSM hybrid membrane exhibits an excellent energy efficiency of 75.4% at 500 mA cm−2, and at 300 mA cm−2, the energy efficiency can reach 81.2%, and the efficiency stability can maintain 600 cycles in charge and discharge. Consequently, the use of “linker” offers a very prospective strategy for the development of high-performance proton exchange membrane.

Ratio Fluorescent Detecting of Tryptophan and Its Metabolite 5-Hydroxyindole-3-acetic Acid Relevant with Depression via Tb(III) Modified HOFs Hybrids: Further Designing Recyclable Molecular Logic Gate Connected by Back Propagation Neural Network.

Exploring intelligent fluorescent materials with high reliability and precision to diagnose diseases is significant but remains a great challenge. Herein, based on coordination post-synthetic modification, a Tb3+ functionalized ME-PA (Tb@1) is prepared, which can emit brilliant green fluorescence through ligand-to-mental charge transfer-assisted energy transfer (LMCT-ET) process from ME-PA to Tb3+ ions. Tb@1 can simultaneously distinguish Tryptophan (Try) and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA), two effective indicators for depression, in ratio and colorimetric mode. And this sensor behaves the advantages of high efficiency and sensitivity, as well as excellent reusability and anti-interference. The PET process from ME to Try and 5-HIAA, and the competitive absorption between analytes and Tb@1 may be relevant to sensing mechanism. In realistic serum or urine environment, the detection limits of Tb@1 for Try and 5-HIAA are 0.0183 and 0.0149mg L-1 respectively. Moreover, in conjunction with back propagation neural network (BPNN), two dual-output molecular logic gates that can be calculated circularly are further designed, which realizes intelligent control of the electronic component to identify the existence of two biomarkers and judge their concentrations from fluorescence images. This work offers a novel approach to modulate logic circuits based on ML-assisted HOF fluorescent sensor, with promising application for a precise and pictorial depression diagnosis.

Surface Modification of UiO-66 on Hollow Fibre Membrane for Membrane Distillation.

The hydrophobicity of metal-organic frameworks (MOFs) is critical in enhancing the separation process in membrane distillation. Herein, a new superhydrophobic University of Oslo 66 (UiO-66) MOFs was successfully constructed on the top of alumina hollow fibre (AHF) membrane for desalination purposes. The fabrication methodology of the membrane involved in situ growth of pure crystalline UiO-66 on top of AHF and post-synthetic modification by fluorosilane grafting. The resultant membrane was characterised to study the physicochemical properties of the pristine and modified membrane. A superhydrophobic UiO-66 with a contact angle of 163.6° and high liquid entry pressure was obtained by introducing a highly branched fluorocarbon chain while maintaining its crystallinity. As a result, the modified membrane achieved 14.95 L/m2∙h water flux and 99.9% NaCl rejection with low energy consumption in the direct contact membrane distillation process. Furthermore, the high surface energy contributed by UiO-66 is maximised to produce the maximum number of accessible sites for the grafting process. The synergistic effect of surface hydrophobicity and porous UiO-66 membrane in trapping water vapour shows great potential for desalination application.

A post-synthetic modified NH2-MIL-125 (Ti) catalyst for boosting photochemical Cr (VI) reduction

MOFs-based composites with visible light response have gradually attracted wide researchers’ attention to water environmental remediation. Herein, a series of post-synthesis modified (PSM) NH2-MIL-125 (Ti) (R-BA-MIL-125 (Ti)) with phenyl-Schiff base-phenyl conjugate systems were successfully synthesized by a simple post-synthetic modification method. Under the optimization of catalyst structure designing, the photocatalytic reduction of Cr (VI) follows the order: –OH > -CH3 > -H > -Cl > -NO2-BA-MIL-125 (Ti) > NH2-MIL-125 (Ti). Among them, 4-hydroxybenzaldehyde-modified NH2-MIL-125 (Ti) (OH-BA-MIL-125 (Ti)) exhibited the highest photocatalytic removal efficiency of hexavalent chromium (Cr (VI)) at visible light conditions and the removal rate for Cr (VI) reached 98.3% under 90 min with only 5 mg photocatalyst, which displayed 2.07 times that of NH2-MIL-125 (Ti). The introduction of para-substituted benzaldehydes not only extended the conjugated chain length, but also subtly reduced the band-gap energy (Eg) of NH2-MIL-125 (Ti). Benefitting from broadening the range of photo-response and enhancing the ability of photoelectron generation, it could significantly enhance the ability of NH2-MIL-125 (Ti) to remove Cr (VI). ESR analyses indicate that e- and •O2- are the main active species. In addition, OH-BA-MIL-125 (Ti) exhibited good reusability and stability over 5 cycles. Therefore, this work will provide new insights into the fabrication of highly active catalysts by PSM for the remediation of chromium-containing wastewater.

CO2-Switchable Hierarchically Porous Zirconium-Based MOF-Stabilized Pickering Emulsions for Recyclable Efficient Interfacial Catalysis.

Stimuli-responsive Pickering emulsions are recently being progressively utilized as advanced catalyzed systems for green and sustainable chemical conversion. Hierarchically porous metal-organic frameworks (H-MOFs) are regarded as promising candidates for the fabrication of Pickering emulsions because of the features of tunable porosity, high specific surface area and structure diversity. However, CO2-switchable Pickering emulsions formed by hierarchically porous zirconium-based MOFs have never been seen. In this work, a novel kind of the amine-functionalized hierarchically porous UiO-66-(OH)2 (H-UiO-66-(OH)2) has been developed using a post-synthetic modification of H-UiO-66-(OH)2 by (3-aminopropyl)trimethoxysilane (APTMS), 3-(2-aminoethylamino)propyltrimethoxysilane (AEAPTMS) and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEAEAPTMS), and employed as emulsifiers for the construction of Pickering emulsions. It was found that the functionalized H-UiO-66-(OH)2 could stabilize a mixture of toluene and water to give an emulsion even at 0.25 wt % content. Interestingly, the formed Pickering emulsions could be reversibly transformed between demulsification and re-emulsification with alternate addition or removal of CO2. Spectral investigation indicated that the mechanism of the switching is attributed to the reaction of CO2 with amino silane on the MOF and the generation of hydrophilic salts, leading to a reduction in MOF wettability. Based on this strategy, a highly efficient and controlled Knoevenagel condensation reaction has been gained by using the emulsion as a mini-reactor and the emulsifier as a catalyst, and the coupling of catalysis reaction, product isolation and MOF recyclability has become accessible for a sustainable chemical process.