Preparation of poly(caffeic acid)-coated epitope molecularly imprinted polymers and investigation of adsorption performance toward ovalbumin.

Food allergy can lead to severe allergic reactions that are potentially fatal for human, hence the detection of food allergens such as ovalbumin (OVA) is important. In this study, a poly(caffeic acid)-coated epitope molecularly imprinted polymer (EMIP) was prepared by chelation and autoxidation of caffeic acid with hexamethylenediamine. EMIP has not only imprinted cavities highly matched with OVA in size and spatial structure, but also externally abundant hydrophilic groups, resulting in few non-specific binding and good hydrophilicity. With high specificity, significant paramagnetism, and great reusability, EMIP can distinguish OVA from other proteins and selectively enrich OVA in egg white samples, which opens up a promising route to the determination of allergens in food products.

Design of reversibly charge-changeable rhodamine B modified magnetic nanoparticles to enrich phosphopeptides.

In the present study, by employing ethylenediaminetetraacetic acid (EDTA), tetraethylene pentaamine (TEPA), and rhodamine B (Rb), we designed and synthesized a magnetic adsorbent (Fe3O4@EDTA@TEPA@Rb) on the basis of reversible charge change of Rb and applied to capture phosphopeptides. Rb existing in open planarized zwitterion form when stimulated by acidic loading buffer adsorbs negative phosphopeptides via electrostatic interaction. Under the stimulation of alkalic eluent, ring-closed structure of Rb is formed to elute the enriched phosphopeptides. TEPA containing rich amino groups is used as a crosslinking agent, which is also protonated in acidic loading buffer to bond phosphopeptides. Then phosphopeptides are eluted when TEPA deprotonates in alkalic eluent. Coupled with matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) detection, phosphopeptide signals originated from 0.4 fmol/µL ß-casein digests were successfully detected. In addition, Fe3O4@EDTA@TEPA@Rb can also efficiently enrich phosphopeptides from skimmed milk, human serum and saliva samples (26, 4, 39 phosphopeptides, respectively), opening a new gallery for phosphopeptides-related analysis. In general, the developed adsorbent has the great potential for further application in the near future.

Design of a hydrophilic mercaptosuccinic acid-functionalized ß-cyclodextrin polymer via host-guest interaction: toward highly efficient glycopeptide enrichment.

A hydrophilic interaction chromatography (HILIC) strategy is considered as an efficient strategy for efficient glycopeptide enrichment. Here, a novel hydrophilic material (denoted as magCDP@Ada-MSA) was constructed through host-guest interaction between crosslinked ß-cyclodextrin (ß-CD) polymers and mercaptosuccinic acid (MSA) derived adamantane. On the one hand, crosslinked ß-CD polymers have great hydrophilicity due to their abundant hydrophilic hydroxyl groups. On the other hand, the hydrophilic functional molecule MSA was introduced into crosslinked ß-CD polymers through host-guest interaction for further hydrophilic modification of the material. Hydroxyl groups in crosslinked ß-CD polymers and carboxyl groups in MSA together endow the material with excellent hydrophilicity and good affinity toward glycopeptides. The prepared hydrophilic material demonstrated rapid magnetic separation (within 5 s) and reusability (at least 10 cycles). Thanks to the above advantages, magCDP@Ada-MSA showed satisfactory performance for the specific enrichment of glycopeptides (selectivity, 1 : 500 molar ratios of HRP/BSA and sensitivity, 0.1 fmol µL-1). Moreover, magCDP@Ada-MSA was successfully applied for selective glycopeptide enrichment from complex biological samples (human serum and saliva).

Tailoring a multifunctional magnetic cationic metal-organic framework composite for synchronous enrichment of phosphopeptides/glycopeptides.

Herein, for the first time, a multifunctional magnetic cationic MOF composite (Fe3O4@ILI-01@Ti4+) was successfully prepared for the synchronous enrichment of phosphopeptides/glycopeptides. The as-prepared Fe3O4@ILI-01@Ti4+ bears attractive properties like abundant surface positive charge and excellent hydrophilicity, ensuring that phosphopeptides/glycopeptides can be well captured based on electrostatic attraction and hydrophilic interaction. By integrating Fe3O4@ILI-01@Ti4+ and mass spectrometry (MS) determination, high sensitivity (0.5 fmol for ß-casein and 0.1 fmol for HRP), excellent selectivity (1 : 5000 for ß-casein : BSA and 1 : 500 for HRP : BSA, mass ratio), and high recyclability (5 cycles) were achieved. In addition, Fe3O4@ILI-01@Ti4+ exhibits superior enrichment performance on synchronous enrichment of phosphopeptides/glycopeptides from ß-casein/HRP tryptic digests. Further applying it to actual samples like human serum and saliva, phosphopeptides and glycopeptides with high intensity were identified, indicating that Fe3O4@ILI-01@Ti4+ possesses great practical application value in synchronous enrichment of phosphopeptides/glycopeptides. This work offers a new channel for the application of MOFs in phosphoproteomics/glycoproteomics.

Glutathione-functionalized magnetic thioether-COFs for the simultaneous capture of urinary exosomes and enrichment of exosomal glycosylated and phosphorylated peptides.

Exosomes play an irreplaceable role in physiological and pathological processes, and the study of proteomics (especially protein post-translational modifications, PTMs) in exosomes can reveal the pathogenesis of diseases and screen therapeutic disease targets. The separation and enrichment process is an essential step in mass spectroscopy-based exosomal PTMs studies to reduce sample complexity and ionization-suppression effects. Herein, we designed a novel magnetic zwitterionic material, namely glutathione-functionalized thioether covalent organic frameworks (Fe3O4@Thio-COF@Au@GSH), possessing fast magnetic responsiveness, regular porosity, and a suitable surface area. Thanks to the hydrophilicity and charge-switchable feature of GSH, for the first time, both the capture of exosomes from biological fluids and enrichment of the inherent glycoproteins/phosphoproteins in the exosomes were achieved with the same material. Furthermore, the high enrichment capacity was validated by theoretical calculations. The low detection limits (0.2/0.4 fmol for HRP/ß-casein), high selectivity (1 : 1000 for HRP/ß-casein : BSA molar ratio), and high exosomal glycoproteomics/phosphoproteomics profiling capability proved the feasibility of the developed method. This work provides a new heuristic strategy to solve the problems of exosomal capture and glycoproteins/phosphoproteins pretreatment in exosomal proteomics.

Design of a Spiropyran-Based Smart Adsorbent with Dual Response: Focusing on Highly Efficient Enrichment of Phosphopeptides.

Smart responsive materials have attractive application prospects due to their tunable behaviors. In this work, we design novel spiropyran (SP)-based magnetic nanoparticles (MNP-SP) with dual response to ultraviolet light and pH and apply them to the enrichment of phosphopeptides. SP is modified on the surface of magnetic nanoparticles through a simple esterification reaction, based on which an MNP-SP-MS phosphopeptide identification platform is established. The capture and release of phosphopeptides are facilely adjusted by changing external light and the pH of the solution. The smart responsive MNP-SP has fast magnetic response performance, high sensitivity (detection limit of 0.4 fmol), and good reusability (6 cycles). In addition, MNP-SP is used for the enrichment of phosphopeptides in skimmed milk, human saliva, and human serum samples, indicating that it is an ideal adsorbent for enriching low-abundance phosphopeptides in complex biological environments.

[Recent developments of pesticide adsorbents based on cyclodextrins].

The invention and application of pesticides have greatly increased the yield of crops, greatly contributing to ensuring people's basic livelihoods and gradually improving their livelihoods to a well-off level. However, foods, water sources, and soil, containing high levels of pesticide residues, result in increasingly serious pollution. Pesticide residues usually have the characteristics of micro toxicity, difficult biodegradation, and bioaccumulation, and thus pose serious threat to living organisms and ecosystems. In recent years, pesticide pollution has earned worldwide focus. Thus, methods for the efficient detection of trace pesticides and reduction of the harm caused by pesticide pollution are urgently required. Researchers have used catalysis, electrochemistry, membrane separation, adsorption, and other methods to enrich pesticides from complex matrices. Among these, adsorbents have attracted much attention owing to their advantages of simple operation steps, rapid treatment process, and low amounts of organic solvents required. Research on adsorption materials has always been a very active field, and is also the key to the success of separation and enrichment of pesticides from complex matrices. Development of adsorbents with the advantages of simple synthesis, environment-friendliness, high stability, and strong reusability is of great significance. There has been some progress in the field of pesticide adsorption using supramolecular compounds. Cyclodextrin is a macrocyclic compound with a cavity after crown ether, which can form inclusion complexes via host guest interactions as the main body. Cyclodextrin can also be modified by etherification, esterification, oxidation, and other chemical reactions to improve its adsorption performance. Pesticides can be classified into organic and inorganic substances. One of the most widely used inorganic fungicides is the Bordeaux solution, whose main component is Cu2+. Organic fungicides, insecticides, herbicides, and plant growth regulators are basically organic molecules, whose hydroxyl and carboxyl groups can form complexes with Cu2+. As a matrix, cyclodextrin not only increases the surface area of the materials, but also provides the binding sites of hydroxyl and carboxyl groups, which guarantees efficient enrichment of Cu2+. Organic pesticides with high polarity, high electron density, and strong hydrophobicity could be better adsorbed. In this paper, the application of cyclodextrin-based adsorbents in pesticide adsorption was reviewed, and on this basis, reference to future development directions and application prospects were provided. The adsorption capacity of individual pesticide adsorbents based on cyclodextrin, as reviewed in this paper, is not high enough. Therefore, improving the adsorption capacity is currently a major research target. Some of the above-mentioned adsorbents have unclear degradation mechanisms and can easily cause secondary pollution. Therefore, the development of environment-friendly pesticide adsorbents that are easy to regenerate is a promising research direction for the future. After adsorption, some detection methods are used to determine whether the pesticide residues are up to the standard; however, the detection instruments are expensive. Therefore, the development of a combined detection mechanism that can reduce workload and cost is a promising research direction. Finally, the development of smart cyclodextrin-based adsorbents is also an efficient and rapid method to reduce the cost of detecting residual pesticide concentrations and the risk of pesticide pollution. For example, intelligent materials, whose color changes can be observed by the naked eye, not only adsorb pesticides, but also respond according to the concentration of residual pesticides.

Engineering Magnetic Guanidyl-Functionalized Supramolecular Organic Framework for Efficient Enrichment of Global Phosphopeptides.

Comprehensive mass spectrometry-based proteomics analysis is currently available but remains challenging, especially for post-translational modifications of phosphorylated proteins. Herein, multifunctional magnetic pillar[5]arene supramolecular organic frameworks were fabricated and immobilized with arginine (mP5SOF-Arg) for highly effective enrichment of global phosphopeptides. The specific phosphate-P5/phosphate-guanidine affinities and large surface area with regular porosity contribute to the high enrichment capacity. By coupling with mass spectrometry, high detection sensitivity (0.1 fmol), excellent selectivity (1:5000 molar ratios of ß-casein/cytochrome c), and high recyclability (seven cycles) were achieved for phosphopeptide analysis. mP5SOF-Arg can efficiently enrich phosphopeptides from practical samples, including defatted milk, egg yolk, and human saliva. Notably, a total of 450 phosphopeptides were explored for highly selective identification from A594 cells and 1445 phosphopeptides were identified from mouse liver tissue samples. mP5SOF-Arg exhibited great potential to serve as the basis for peptidomic research to identify phosphopeptides and provided insight for biomarker discovery.

A turn-on fluorescence sensor for creatinine based on the quinoline-modified metal organic frameworks.

Creatinine (Cre) level is closely related to renal function of human. Therefore, it is of great significance to develop highly sensitive and selective tools for Cre determination. Herein, a turn-on fluorescence metal organic framework (MOF) sensor, which was synthesized by post-synthetic modification of 8-hydroxy-2-quinolinecarboxaldehyde (HQCA) and Al3+ toward UiO-66-NH2, was applied to detect Cre. The turn-on of fluorescence was attributed to the formation of Lewis acid-base complexes between Cre and Al3+, which led to the interruption of energy transfer and electron transfer from UiO-HQCA to Al3+. Thus, the fluorescence quenching of UiO-HQCA-Al caused by Al3+ was recovered. Results showed that the sensor exhibited wide linear range (0.05-200 µM), high sensitivity (detection limit = 4.7 nM), fast response time (1 min), and high selectivity toward Cre. The practicability of the sensor was verified by detecting Cre in human serum and urine samples. The present work was the first attempt that MOF material was used as a fluorescence sensor to detect Cre, which exhibited great application prospects in clinical diagnosis of related diseases.

Supramolecular adsorbents in extraction and separation techniques - A review.

Sample preparation procedure before the detection step is of great importance for successful realization of an analytical method. The extraction and preconcentration efficiency, sample throughput, and application potential of a sample preparation approach are greatly dependent on adsorbents. This review (with 172 references) reveals a critical view on the latest achievements of supramolecular materials in the field of adsorption. It covers the category of supramolecular compounds, their immobilization and applications in the adsorption of gases, inorganic ions, dyes, bisphenol A, herbicides/pesticides, plant growth regulators, and proteins. Finally, the challenges and future perspectives in relative research fields are discussed.

[Preparation of polyoxometalate-chitosan magnetic composite for the enrichment of phosphopeptides].

A method for the enrichment of phosphopeptides based on magnetic nanoparticles coated with polyoxometalate (POM) was developed. A layer-by-layer assembly technique was used to prepare magnetic nanoparticles (MNPs) coated with polyoxometalate and chitosan. The composites were used for phosphopeptide enrichment prior to analysis by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). The composites exhibited advantages of rapid magnetic separation, hydrophilicity, positive electricity, and a high selectivity for enrichment of phosphopeptides. ß-Casein was selected as a model phosphorylated protein to assess the performance of the enrichment technique. After the enrichment step, the limit of detection was determined to be 0.02 fmol. The prepared POM-based MNPs thus exhibit significant potential in the detection of low-abundance phosphoproteins.

A modulation approach for covalent organic frameworks: Application to solid phase microextraction of phthalate esters.

A modulation approach with 4-hydroxybenzhydrazide as the modulating agent was designed for constructing 2,4,6-triphenoxy-1,3,5-benzene-based covalent organic frameworks (COFs). The COFs materials were employed as solid phase microextraction (SPME) coatings for the extraction of phthalate esters (PAEs). Various experimental conditions including extraction temperature, extraction time, salt concentration, and desorption time were investigated and optimized. The introduction of modulating agent into the synthesis of fibers significantly enhanced the extraction efficiency towards PAEs. The linear range was 1-100 µg L‒1 and the detection limits in the range of 0.032-0.451 µg L‒1 were achieved with good linearity ranged from 0.9904 to 0.9970. Inter-batch and intra-batch relative standard deviations were in the ranges of 0.83-4.67% and 3.08-9.73%, respectively. Moreover, the developed coating fibers were used for the extraction of PAEs in water samples and satisfactory recoveries were achieved.

A triazine based organic framework with micropores and mesopores for use in headspace solid phase microextraction of phthalate esters.

A dual-pore covalent organic framework (COF) that contains micropores and mesopores was prepared from 2,4,6-triphenoxy-1,3,5-triazine (TPT). A building block is used in which double linking sites were introduced at each branch of a C3-symmetric skeleton. The COF is shown to be a viable coating for fibers for solid-phase microextraction of phthalic acid esters (PAEs). Its high specific surface, high hydrophobicity, and wide pore size distribution of a TPT-COF coated fiber result in extraordinarily powerful extraction of PAEs. The enrichment factor is up to 7790 under optimum conditions. The method has detection limits that range between 5 and 95 ng L-1. The inter-batch relative standard deviations are between 3.1 and 10.9%, and those for intra-batch assays are from 0.8 to 4.7%. The TPT-COF coated fibers were applied to the extraction of PAEs from (spiked) juice samples, and satisfactory recoveries were achieved. Graphical abstract TPT-COF coated SPME fiber was prepared for the preconcentration of phthalate esters coupled with GC-FID.

Development of Gd3+-immobilized glutathione-coated magnetic nanoparticles for highly selective enrichment of phosphopeptides.

In this study, we designed a gadolinium-based immobilized metal ion affinity chromatography material for the selective enrichment of phosphopeptides. Gadolinium ion was immobilized on the surface of glutathione-coated magnetic nanoparticles through a facile and effective synthetic route. The adsorbent integrated the advantages of superparamagnetism of Fe3O4 core, good biological compatibility of glutathione, and strong interaction between gadolinium ion and phosphopeptides. It was employed to enrich phosphopeptides from standard protein digests coupled with MALDI-TOF MS. Results demonstrated that the adsorbent possessed high selectivity for phosphopeptides, good reusability and reproducibility. Moreover, the material provided selective enrichment of phosphopeptides from real samples including non-fat milk digests and human serum. The developed method exhibited high sensitivity (detection limit of 10 fmol), showing great potential in the detection of low-abundance phosphopeptides in biological samples.

Peanut agglutinin and ß-cyclodextrin functionalized polymer monolith: Microextraction of IgG galactosylation coupled with online MS detection.

A facile online method coupling polymer monolithic microextraction (PMME) with mass spectrometry (MS) was developed for the detection of Immunoglobulin G (IgG) galactosylation glycopeptides. A peanut agglutinin-ß-cyclodextrin (PNA-ß-CD) functionalized poly(hydroxyethyl methylacrylate-ethyleneglycol dimethacrylate) monolith was designed via a click reaction. Thanking to the specificity of PNA-ß-CD for the targets, the material exhibited enhanced enrichment selectivity and extraction efficiency for IgG galactosylation glycopeptides. Under optimal conditions, the developed method gave a linear range of 0.005-5 pmol for IgG glycopeptides with the regression coefficient greater than 0.9990, and the detection limit of IgG galactosylation glycopeptides as low as 0.5 fmol was achieved. The PMME-MS method was applied to IgG galactosylation glycopeptides in real samples including human serum and acute myelogenous leukemia (AML) cell lysate. A series of unique IgG galactosylation glycopeptides were captured by the monolith in the complex samples, indicating satisfactory enrichment ability for IgG galactosylation glycopeptides. The quick and integrated online PMME-MS method exhibited high selectivity for IgG galactosylation, demonstrating its perspectives on the development and broad applications of MS in studying galactosylation proteins regulated biological processes.

Design of a ruthenium(III) immobilized affinity material based on a ß-cyclodextrin-functionalized poly(glycidyl methacrylate-ethylene dimethacrylate) monolith for the enrichment of hippuric acid.

Immobilized metal affinity chromatography has drawn great attention as a widespread separation and purification approach. In this work, ruthenium was firstly introduced into the preparation of immobilized metal affinity chromatography considering its affinity to N,O-donor ligands. A ß-cyclodextrin-functionalized poly(glycidyl methacrylate-ethylene dimethacrylate) monolith was designed and employed as the supporting material in immobilized metal affinity chromatography. Thiosemicarbazide was introduced into the synthesis process, which not only acted as a bridge between ß-cyclodextrin and glycidyl methacrylate, but also chelated with ruthenium because of its mixed hard-soft donor characteristics. The developed monolithic ruthenium(III)-immobilized metal affinity chromatography column was utilized for the adsorption and separation of hippuric acid, a biological indicator of toluene exposure. To achieve high extraction capacity, the parameters affecting the extraction efficiency were investigated with an orthogonal experiment design, L9 (34 ). Under the optimized conditions, the enrichment factor of hippuric acid was 16.7-fold. The method reproducibility was investigated in terms of intra- and interday precisions with relative standard deviations lower than 8.7 and 9.5%, respectively. In addition, ruthenium(III)-immobilized metal affinity chromatography material could be used for up to 80 extractions without an apparent change in extraction recovery.

Specific enrichment of glycoproteins with polymer monolith functionalized with glycocluster grafted ß-cyclodextrin.

The low abundance of glycoproteins in complex samples results in the prerequisite role of efficient and selective enrichment of them. In the present work, we designed a new kind of glycosylation poly(hydroxyethyl methacrylate-pentaerythritol triacrylate) monolith functionalized with glycocluster grafted ß-cyclodextrin for the enrichment of glycoproteins. The introduced modifiers endowed the monolithic material with enhanced hydrophilicity and surface area, which benefitted to improve the enrichment selectivity and extraction efficiency for glycopeptides. By combining with MALDI-MS detections, 22 glycopeptides from horseradish peroxidase digest were captured with the developed monolith while 4 glycopeptides were enriched by commercially available agarose matrix column. LOD of 6.6pmol was attained. When applied to the enrichment of glycopeptides from complex protein samples and human lymphoma (U937) cell line, the prepared monolith exhibited high selectivity for glycopeptides.

Highly selective enrichment of phosphopeptides by on-chip indium oxide functionalized magnetic nanoparticles coupled with MALDI-TOF MS.

Selective and efficient preconcentration is indispensable for low concentration of phosphopeptides in phosphorylated protein-related samples prior to MS-based analysis. Herein, an on-chip system coupled magnetic SPE with MALDI-TOF MS was designed. A metal oxide affinity chromatography material, indium oxide, was coated on the surface of Fe3 O4 magnetic nanoparticles to prepare the adsorbent, spatially confined with an applied magnetic field. The adsorbent exhibited high selectivity for phosphopeptides in tryptic digests of the mixture of ß-casein and BSA (1:1000) and the mixture of ß-casein, BSA, and ovalbumin (1:100:100). Thanking to the enrichment ability and specificity for phosphopeptides with the adsorbent, the on-chip magnetic SPE-MALDI-TOF MS approach showed high sensitivity with a low detection limit of 4 fmol. In addition, the developed approach was used to analyze phosphopetides in non-fat milk digests and human serum successfully.

Preparation of a polymer monolith modified with delaminated layered double hydroxides for the microextraction of ß-agonists.

In the present study, a novel poly(acrylamide-co-N-isopropylacrylamide-co-ethylene dimethacrylate) monolithic column modified with saline-modified delaminated layered double hydroxides was developed and exploited as the stationary phase in the polymer monolith microextraction of ß-agonists. Transmission electron microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis with derivative thermogravimetric determination were employed to characterize the monoliths. By coupling with high-performance liquid chromatography determinations, extraction parameters affecting the extraction efficiency, including sample volume, flow rate, sample pH, eluent volume, and eluent flow rate were investigated with an orthogonal experiment design, L16 (45 ). Results demonstrated that under the optimal experimental conditions, low limits of detection in the range of 0.025-0.280 ng/mL were obtained with relative standard deviations in the range of 4.3-7.6% (intraday) and 6.7-8.8% (interday). When the developed method was applied to the analysis of ß-agonists in pork samples, recovery values were obtained in the range of 80.5-108.6%.

Fabrication of cross-linked hydrazone covalent organic frameworks by click chemistry and application to solid phase microextraction.

Covalent organic frameworks (COFs) are an emerging class of porous organic frameworks with diverse promising applications. Herein, we presented the first example of cross-linked hydrazone COFs (cross-linked COFs) coating via thiol-ene click chemistry for solid phase microextraction (SPME). Strong covalent bonds and interlayer of the prepared networks ensured the adsorption capacity and durability of the novel SPME fiber. π-π conjugated structure existed because of abundant phenyl rings and -C=N groups in the cross-lined COFs. A series of characterizations indicated that the cross-linked COFs possessed large surface areas, high porosities and stabilities as well as hydrophobicities. The fiber was applied to SPME of pesticide residues coupled with gas chromatography with an electron capture detector (GC-ECD). Under the optimum experimental conditions, enhancement factors in the range of 2190-10,998 were obtained, illustrating that the cross-linked COFs possessed remarkable preconcentration ability. The low detection limits of 0.0003-0.0023ngkg-1 were achieved with relative standard deviations (RSDs) in the range of 3.4-7.6% (intra-batch) and 5.7-11.6% (inter-batch), respectively. Recovery values in the range of 78.2-107.0% were obtained when the SPME-GC method was applied to the analysis of pesticides in cucumber samples.