Diltiazem-imprinted porphyrinic covalent organic frameworks as solid-phase extractants and fluorescent sensors

Conjugated hypercrosslinked polymers for in situ imprinting, selective sorption, and fluorescent turn-on sensing of oxalic acid

Hypercrosslinked polymer (HCP) is a subclass of porous organic polymer possessing abundant microporosity, tailor-made functionality, and excellent stability. It features low-cost and easily direct knitting synthesis, facilitating the construction of π-conjugated frameworks with fluorescent properties by properly selecting building blocks (BBs) and linkers. Simultaneous imprinting of target molecules into the conjugated HCPs will create selective sorbents and sensors. We prepared several BBs to be polymerized with a terephthaloyl chloride (TCL) linker through Friedel-Crafts acylation in the presence of some imprinting molecules to clarify the best collocation for the advancement of imprinted polymer. With the highest increase in fluorescence intensity (F), the conjugated HCP comprised of dibenzofuran (DBF) and TCL was selected as contact with oxalic acid (OA). The OA-imprinted DBF-TCL (MICHP) was characterized by FTIR-approved structures, amorphous SEM images, TGA degradation at 390 °C, blue-shift emission, prolonged lifetime, and aggregation-caused quenching. The increase in F was proportional to OA concentration (0.17-20.0 μM, RSD = 1.6%, LOD = 0.03 μM) in THF/H2O (pH 7.0) containing MICHP (0.2 mg/3 mL) and 6.0 min equilibrium. The F increase arose from inhibiting the quenching of photo-induced electron transfer because of protonation and association of OA with imprinted cavities. Langmuir-Freundlich isotherm precisely modeled the imprinted cavity affinity for OA with binding sites of 114.5 μmol/g and heterogeneity of 0.939. The cavities distinctly recognized OA and malonic acid interferant, presenting imprinting factor (4.76 vs. 1.35), specific sorption ratio (79.0% vs. 25.7%), and relative selectivity coefficient (3.935 vs. 0.779), which sustained the precise measurements of OA in tomato, taro, and urine. This study approved a cheap and easy strategy to implant fluorescent and imprinting functions in HCPs using as sorbent and sensor through Friedel-Crafts acylation of electrophilic crosslinker and nucleophilic BB, especially those with heterocyclics.

Advances in covalent organic frameworks for sample preparation

Sample preparation is crucial in analytical chemistry, impacting result accuracy, sensitivity, and reliability. Solid-phase separation media, especially adsorbents, are vital for preparing of liquid and gas samples, commonly analyzed by most analytical instruments. With the advancements in materials science, covalent organic frameworks (COFs) constructed through strong covalent bonds, have been increasingly employed in sample preparation in recent years. COFs have outstanding selectivity and/or excellent adsorption capacity for a single target or can selectively adsorb multiple targets from complex matrix, due to their large specific surface area, adjustable pore size, easy modification, and stable chemical properties. In this review, we summarize the classification of COFs, such as pristine COFs, COF composite particles, and COFs-based substrates. We aim to provide a comprehensive understanding of the different classifications of COFs in sample preparation within the last three years. The challenges and development trends of COFs in sample preparation are also presented.

Construction of a Biomimetic Receptor Based on Hydrophilic Multifunctional Monomer Covalent Organic Framework Molecularly Imprinted Polymers for Molecular Recognition of Cyanidin-3-O-Glucoside

Anthocyanins (AOCs) are phenols that are readily soluble in water and are commonly present in plants. The chemical instability of AOC, however, causes it to be severely limited in terms of extraction and purification. Hence, in order to obtain efficient and stable extraction of AOC, we designed hydrophilic multifunctional monomer covalent organic framework molecularly imprinted polymers (HMCMIPs) as adsorbents. The functional reagent, p-aminobenzenesulfonic acid (ASA), was added to this material during synthesis to facilitate the sulfonation modification of covalent organic frameworks (COFs), which enhanced its affinity for hydrophilic guests (cyanidin-3-O-glucoside, the representative nutritional and functional ingredient in AOC). With ASA serving as a terminator, overextension of the material to form micron-level cross-linked structures is prevented, thereby increasing its surface area and mass transfer efficiency. The biomimetic receptors were then created by integrating MIPs into sulfonated COFs in order to create multiple binding sites specific for C3G recognition. HMCMIPs exhibited excellent adsorption capacity (1566 mg/g) and superior selectivity (selectivity coefficient >12) for C3G. It has been demonstrated that high purity (93.72%) C3G can be obtained rapidly and efficiently by utilizing HMCMIPs. There may be a potential benefit to the synthesis strategy of HMCMIPs for the extraction of specific active ingredients in the future.

Conjugated hypercrosslinked polymers imprinted with 3,5-dinitrosalicylic acid for the fluorescent determination of α-amylase activity

The discovery of a series of coupling reactions between various building blocks has driven the development of porous organic polymers, but the common usage of expensive and air-sensitive organometallic catalysts and complex procedures in harsh syntheses has limited their expansion. A microporous hypercrosslinked polymer (HCP) was synthesized by polymerizing a naphthalene monomer and a 1,4-dimethoxybenzene crosslinker using Friedel-Crafts alkylation over an FeCl₃ catalyst and imprinted with 3,5-dinitrosalicylic acid (DNS). The DNS-molecularly-imprinted HCPs (MIHCPs) were characterized as having IUPAC Type I mesoporosity, a specific surface area of 1134 m² g^-1, a monolayer adsorption capacity of 116 cm² g^-1, pore sizes ranging from 5 to 8.5 Å, amorphous frameworks, and distinctive absorption and emission bands by N₂ adsorption/desorption analyses, scanning and transmission electron microscopies, and FTIR, UV-Vis, and fluorescence spectrometries. The π-conjugated imprinted framework endowed the MIHCPs with 405-nm fluorescent emission at a 330-nm excitation and dynamic quenching, which was confirmed by changes in fluorescence lifetime and followed a linear Stern-Volmer plot against 1.0-200 μM DNS template molecules under optimized conditions of a pH 7.0 buffer, an MIHCP concentration of 125 μg mL^-1, and a 3.0-min equilibration time. The MIHCPs exhibited a high imprinted factor of 8.7 against nonimprinted HCP and a selectivity of 8.63 against reduced DNS, which enabled fluorometric detection of DNS molecules produced by the hydrolysis of starch with microbial, salivary, and pancreatic α-amylases and the subsequent redox incubation with the DNS oxidant. The fluorometric measurement of α-amylase activity was higher in accuracy and precision (RSD: 2.6-2.8% vs. 3.9-4.0%) than conventional UV-Vis spectrometry because the excellent fluorescent sensitivity and imprinting selectivity of the MIHCP probes enabled the use of higher dilution factors with weaker matrix effects.

Fluorescence determination of tannic acid imprinted in conjugated hypercrosslinked polymers by Friedel-Crafts acylation

A molecularly imprinted hypercrosslinked polymer (HCP) was synthesized from the polymerization of mesitylene monomer, terephthaloyl chloride crosslinker, and tannic acid (TA) template through FeCl₃-catalyzed Friedel-Crafts acylation. The TA-imprinted HCP (TAHCP) was capable of IUPAC Type I mesoporosity, with specific surface area of 1258 m² g^-1, monolayer adsorption capacity of 289 cm² g^-1, pore sizes ranging from 4.4 to 12.6 Å, amorphous morphology, and characteristic absorption and emission bands. The extended π-conjugation framework of TAHCP was endowed with 385-nm fluorescent emission at 310-nm excitation. The fluorescence intensity of TAHCP could be dynamically quenched by TA and was linearly correlated with 20-1000 nM TA concentrations on the Stern-Volmer plot in the optimized conditions of pH 5.5 buffer, 100 μg mL^-1 TAHCP, and 3.5 min equilibrium. The relative standard deviation (RSD) for 50 nM TA was 3.4% (n = 5), and the limit of detection was 6.2 nM based on the 3σ of the TA blanks). For 50nM TA, the imprinted factor was calculated to be 7.8, and the selectivity for 250 nM interferents, including ions, organic acids, saccharides, amino acids, and caffeine, which are commonly found in beverages, was 7.5-9.5, except for gallic acid (1.2). The recoveries of TA spiked in tea and juice beverages at three levels (10-150 nM) were 93.6-101.9% (RSD = 3.6-4.3%).

An imine-linked covalent organic framework for renewable and sensitive determination of antibiotic

Lanthanide-functionalized porous organic materials have been the promising candidates in the chemical and biological sensing. Considering the superior thermal and solvent stability of covalent organic frameworks (COFs), the development of lanthanide ions-functionalized COFs based sensing platform is meaningful, while remains to be a challenge. In this work, a new imine-linked COF which provides suitable coordination sites for Tb³⁺ was constructed via the Schiff base reaction between P-phenylenediamine (Pda) and 2,6-Diformylpyridine (Dfp). Benefiting from its high signal-to-noise, the COF@Tb shows excellent ability to determinate ciprofloxacin (CIP) with a detection limit of 3.01 nM. The measurement can maintain good stability in the presence of potential interference or in actual sample. Being washed with ethanol after each measurement, COF@Tb can be recycled for five times. This work provides a novel alternative strategy for efficient construction of lanthanide-grafted COFs and may promote the development of porous organic materials based chemical sensing.

Construction of LZU1@WO3 heterojunction photocatalysts: enhanced photocatalytic performance and mechanism insight

Our well-designed nano-WO3@LZU1 composite photocatalysts were fully characterized. Under simulated sunlight, the hybrid materials showed much higher photocatalytic activity for BBR degradation and MB degradation than WO3 or LZU1, and improved hydrogen production capacity.