Ring-opening polymerization with synergistic co-monomers: access to a boronate-functionalized polymeric monolith for the specific capture of cis-diol-containing biomolecules under neutral conditions

Synthesis and Characterization of Boronate Affinity Three-Dimensionally Ordered Macroporous Materials

Sample pretreatment is a key step for qualitative and quantitative analysis of trace substances in complex samples. Cis-dihydroxyl (cis-diol) group-containing substances exist widely in biological samples and can be selectively bound by boronate affinity adsorbents. Based on this, in this article, we proposed a simple method for the preparation of novel spherical three-dimensionally ordered macropore (3DOM) materials based on a combination of the boronate affinity technique and colloidal crystal template method. The prepared 3DOM materials were characterized using Fourier transform-infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and thermo-gravimetric analysis, and results showed that they possessed the characteristics of a high specific surface area, high porosity, and more boronic acid recognition sites. The adsorption performance evaluation results showed that the maximum adsorption capacity of the boron affinity 3DOMs on ovalbumin (OVA) could reach to 438.79 mg/g. Kinetic and isothermal adsorption experiments indicated that the boronate affinity 3DOM material exhibited a high affinity and selectivity towards OVA and adenosine. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the proteins in egg whites was conducted and proved that the glycoprotein in the egg whites could be separated and enriched with a good performance. Therefore, a novel boronate affinity 3DOM material a with highly ordered and interconnected pore structure was prepared and could be applied in the separation and enrichment of molecules with cis-diol groups from complex samples with a good selectivity, efficiency, and high throughput.

Oriented docking of the template for improved imprinting efficiency toward peptide with modifications

Molecular imprinting polymers (MIPs) are synthetic receptors as biomimetic materials for various applications ranging from sensing to separation and catalysis. However, currently existing MIPs are stuck to some of the issues including the longer preparation steps and poor performance. In this report, a facile and one-pot strategy by integrating the in-situ growth of magnetic nanoparticles and reversed phase microemulsion oriented molecularly imprinting strategy to develop magnetic molecular imprinted nanocomposites was proposed. Through self-assembling of the template, it brought up highly ordered and uniform arrangement of the imprinting structure, which offered faster adsorption kinetic as adsorption equilibrium was achived within 15 min, higher adsorption capacity (Qmax = 48.78 ± 1.54 μmol/g) and high affinity (Kd = 127.63 ± 9.66 μM) toward paradigm molecule-adenosine monophosphate (AMP) compared to the conventional bulk imprinting. The developed MIPs offered better affinity and superior specificity which allowed the specific enrichment toward targeted phosphorylated peptides from complex samples containing 100-fold more abundant interfering peptides. Interestingly, different types of MIPs can be developed which could targetly enrich the specific phosphorylated peptides for mass spectrometry analysis by simply switching the templates, and this strategy also successfully achieved imprinting of macromolecular peptides. Collectively, the approach showed broad applicability to target specific enrichment from metabolites to phosphorylated peptides and providing an alternative choice for selective recognition and analysis from complex biological systems.

Veni, Vidi, Vici: Immobilized Peptide-Based Conjugates as Tools for Capture, Analysis, and Transformation

Analysis of peptide biomarkers of pathological states of the organism is often a serious challenge, due to a very complex composition of the cell and insufficient sensitivity of the current analytical methods (including mass spectrometry). One of the possible ways to overcome this problem is sample enrichment by capturing the selected components using a specific solid support. Another option is increasing the detectability of the desired compound by its selective tagging. Appropriately modified and immobilized peptides can be used for these purposes. In addition, they find application in studying the specificity and activity of proteolytic enzymes. Immobilized heterocyclic peptide conjugates may serve as metal ligands, to form complexes used as catalysts or analytical markers. In this review, we describe various applications of immobilized peptides, including selective capturing of cysteine-containing peptides, tagging of the carbonyl compounds to increase the sensitivity of their detection, enrichment of biological samples in deoxyfructosylated peptides, and fishing out of tyrosine–containing peptides by the formation of azo bond. Moreover, the use of the one-bead-one-compound peptide library for the analysis of substrate specificity and activity of caspases is described. Furthermore, the evolution of immobilization from the solid support used in peptide synthesis to nanocarriers is presented. Taken together, the examples presented here demonstrate immobilized peptides as a multifunctional tool, which can be successfully used to solve multiple analytical problems.

Oriented immobilization of antibodies onto sensing platforms - A critical review

The immunosensor has been proven a versatile tool to detect various analytes, such as food contaminants, pathogenic bacteria, antibiotics and biomarkers related to cancer. To fabricate robust and reproducible immunosensors with high sensitivity, the covalent immobilization of immunoglobulins (IgGs) in a site-specific manner contributes to better performance. Instead of the random IgG orientations result from the direct yet non-selective immobilization techniques, this review for the first time introduces the advances of stepwise yet site-selective conjugation strategies to give better biosensing efficiency. Noncovalently adsorbing IgGs is the first but decisive step to interact specifically with the Fc fragment, then following covalent conjugate can fix this uniform and antigens-favorable orientation irreversibly. In this review, we first categorized this stepwise strategy into two parts based on the different noncovalent interactions, namely adhesive layer-mediated interaction onto homofunctional support and layer-free interaction onto heterofunctional support (which displays several different functionalities on its surface that are capable to interact with IgGs). Further, the influence of ligands characteristics (synthesis strategies, spacer requirements and matrices selection) on the heterofunctional support has also been discussed. Finally, conclusions and future perspectives for the real-world application of stepwise covalent conjugation are discussed. This review provides more insights into the fabrication of high-efficiency immunosensor, and special attention has been devoted to the well-orientation of full-length IgGs onto the sensing platform.

Phenylboronic acid-functionalized cross-linked chitosan magnetic adsorbents for the magnetic solid-phase extraction of benzoylurea pesticides

In this study, a 4-formylphenylboronic acid-modified cross-linked chitosan magnetic nanoparticle (FPBA@CCHS@Fe₃ O₄ ) was fabricated. The synthesized material was utilized as the magnetic solid-phase extraction adsorbent for the enrichment of six benzoylurea pesticides. In addition to B-N coordination, FPBA@CCHS@Fe₃ O₄ interacts with benzoylureas through hydrogen bonds and π-π stacking interaction on account of rich active groups (amino and hydroxyl) and aromatic rings in structure. Compared to traditional extraction methods, less adsorbent (20 mg) and reduced extraction time (3 min) were achieved. The adsorbent also exhibited good reusability (no less than 10 times). Coupled with a high-performance liquid chromatography-diode array detector, satisfactory recoveries (89.1-103.9%) and an acceptable limit of detection (0.2-0.7 μg/L) were obtained. Under optimized conditions, the established method was successfully applied to the tea infusion samples from six major tea categories with acceptable recoveries ranging from 76.8 to 110%, indicating its application potential for the quantitative detection of pesticides in complex matrices.

Tug-of-War between Covalent Binding and Electrostatic Interaction Effectively Killing E. coli without Detectable Resistance

Antimicrobial resistance in Gram-negative bacteria has become one of the leading causes of morbidity and mortality and a serious worldwide public health concern due to the fact that Gram-negative bacteria have an additional outer membrane protecting them from an unwanted compound invading. It is still very difficult for antimicrobials to reach intracellular targets and very challenging to treat Gram-negative bacteria with the current strategies. Here, we found that (o-(bromomethyl)phenyl)boronic acid was incorporated into poly((2-N,N-diethyl)aminoethyl acrylate) (PDEA), forming a copolymer (poly(o-B_n-DEA)) having both phenylboronic acid (B) and ((2-N,N-diethyl)amino) (DEA) units. Poly(o-B_n-DEA) exhibits very strong intramolecular B-N coordination, which could highly promote the covalent binding of phenylboronic acid with lipopolysaccharide (LPS) on the outer membrane of E. coli and lodge poly(o-B_n-DEA) on the LPS layer on the surface of E. coli. Meanwhile, the strong electrostatic interaction between poly(o-B_n-DEA) and the negatively charged lipid preferred tugging the poly(o-B_n-DEA) into the lipid bilayer of E. coli. The combating interactions between covalent binding and electrostatic interaction form a tug-of-war action, which could trigger the lysis of the outer membrane, thereby killing Gram-negative E. coli effectively without detectable resistance.

A novel aggregation-induced enhanced emission aromatic molecule: 2-aminophenylboronic acid dimer

Aggregation-induced enhanced emission (AIEE) molecules have significant applications in optoelectronics, biomedical probes and chemical sensors, and large amounts of AIEE molecules have been reported since the concept of AIEE was proposed. Most aromatic AIEE molecules have complex structures consisting of multiple aromatic rings and/or polycyclic skeletons. In this study, we find that 2-aminophenylboronic acid (2-APBA) with a simple structure is highly emissive in the solid state. Further studies reveal that 2-APBA exists in a dimeric form, and the 2-APBA dimer is a novel AIEE molecule. The underlying AIEE mechanism is that the 2-APBA dimeric units aggregate through intermolecular interactions to produce highly ordered molecular packing without the presence of π–π stacking interactions that would lead to aggregation-caused quenching. Furthermore, the 2-APBA dimer aggregates could reversibly transform into its non-fluorescent monomer form driven by new kinds of dynamic covalent B–N and B–O bonds, illustrating its good potential in molecular recognition, nanogating, chemo/bio-sensing and controlled drug release.

The 2-APBA dimer tending to aggregate into a highly ordered structure is discovered to be AIEE active. Through alternate treatment with CO₂ and N₂, 2-APBA can switch between monomer and dimer aggregates driven by dynamic covalent B–N and B–O bonds.

Task specific monolith for magnetic field-reinforced in-tube solid phase microextraction of mercury species in waters prior to online HPLC quantification

In this study, a novel sorbent based on task specific monolith doped with Fe₃O₄ was in situ fabricated in capillary and acted as the extraction medium of magnetic field-reinforced in-tube solid phase microextraction (MFR/IT-SPME) to trap and preconcentrate mercury species which were coordinated with dithizone to form chelates. Various characterization technologies evidenced that the obtained monolithic adsorbent presented porous and super paramagnetic properties, and possessed abundant functional groups. Results evidenced that the implementation of magnetic field during extraction stages enhanced the extraction efficiency of studied Hg chelates from 48.5% to 75.3% to 69.9-94.4%. Under the optimized extraction parameters, the introduced MFR/IT-SPME was online coupled to HPLC/DAD to quantify mercury species at ultra-trace levels in various water samples. Limits of detection varied from 0.0067 μg/L to 0.016 μg/L, and the RSDs for precision were below 7.5%. Additionally, related extraction mechanism was deduced and revealed multiple forces co-contributed to the enrichment. The reliability and accuracy of suggested online approach for speciation analysis of mercury was well proved by confirmatory experiments.

6-Aminopyridine-3-boronic acid functionalized magnetic nanoparticles for highly efficient enrichment of cis-diol-containing biomolecules

Boronate affinity materials, as efficient sorbents for extraction, separation and enrichment of cis-diol-containing biomolecules, have attracted more and more attention in recent years. However, conventional boronate affinity materials require a basic binding pH (usually 8.5), which gives rise to not only inconvenience in operation but also the risk of degradation of labile compounds, and suffer from low binding affinity, which make the extraction of cis-diol-containing compounds of low concentration difficult or impossible. In order to reduce the binding pH to neutral or acidic conditions and improve binding affinity, we present a type of material, 6-aminopyridine-3-boronic acid functionalized magnetic nanoparticles, with affinity towards cis-diol-containing biomolecules. 6-Aminopyridine-3-boronic acid, exhibiting low binding pH, high affinity and excellent water solubility toward cis-diol-containing compounds, was first employed as an affinity ligand. The result indicated that the boronate affinity MNPs exhibited low binding pH (5.0) and high binding affinity toward cis-diol-containing biomolecules. Such a property enabled the selective extraction of cis-diol-containing biomolecules with low concentration under neutral or acidic conditions. This feature greatly favored the selective enrichment of cis-diol-containing biomolecules with low concentration from real samples. The feasibility for practical applications was demonstrated with the selective enrichment of cis-diol-containing biomolecules with low concentration in a human urine sample.

One-step preparation of cyclen-containing hydrophilic polymeric monolithic materials via epoxy-amine ring-opening reaction and their application in enrichment of N-glycopeptides

Considering the special structure of 1,4,7,10-tetraazacyclododecane (cyclen) which is easy to form complexes with ions, it is beneficial to achieve particular selectivity. Cyclen was selected as a precursor to react with triglycidyl isocyanurate (TGIC), and a novel kind of hydrophilic polymeric monolithic material was facilely prepared via epoxy-amine ring-opening reaction in the presence of a binary porogenic system of acetonitrile (ACN) and polyethylene glycol. The resulting poly (TGIC-co-cyclen) monolithic column was used to separate both nonpolar alkylbenzenes using mobile phase of ACN/H₂O (35/65, v/v) and polar phenolic compounds and anilines under the mobile phase of ACN/H₂O (60/40, v/v) in reversed-phase capillary liquid chromatography (cLC). It should be pointed that the monolith was further used for separation of a mixture of toluene, DMF, acrylamide and thiourea under the mobile phase of ACN/H₂O (95/5, v/v) by hydrophilic interaction chromatography (HILIC). These results indicated that the poly (TGIC-co-cyclen) column exhibited mixed-mode retention mechanism. As a result, the prepared monolithic material was employed for enrichment of glycosylated peptides from the tryptic digest of human immunoglobulin G (IgG) and serum protein tryptic digests. A total of 531 N-glycopeptides and 329 N-glycosylation sites, mapped to 166 glycoproteins, were identified from 2 μL human serum digest. The results indicated the prepared monolith had ability for enriching N-glycopeptides from complex biological samples.

Injectable Biodegradable Polymeric Complex for Glucose-Responsive Insulin Delivery

Insulin therapy is the central component of treatment for type 1 and advanced type 2 diabetes; however, its narrow therapeutic window is associated with a risk of severe hypoglycemia. A glucose-responsive carrier that demonstrates consistent and slow basal insulin release under a normoglycemic condition and accelerated insulin release in response to hyperglycemia in real-time could offer effective blood glucose regulation with reduced risk of hypoglycemia. Here, we describe a poly(l-lysine)-derived biodegradable glucose-responsive cationic polymer for constructing polymer-insulin complexes for glucose-stimulated insulin delivery. The effects of the modification degree of arylboronic acid in the synthesized cationic polymer and polymer-to-insulin ratio on the glucose-dependent equilibrated free insulin level and the associated insulin release kinetics have been studied. In addition, the blood glucose regulation ability of these complexes and the associated glucose challenge-triggered insulin release are evaluated in type 1 diabetic mice.

Morphology Control and Metallization of Porous Polymers Synthesized by Michael Addition Reactions of a Multi-Functional Acrylamide with a Diamine

Porous polymers have been synthesized by an aza-Michael addition reaction of a multi-functional acrylamide, N,N',N″,N‴-tetraacryloyltriethylenetetramine (AM4), and hexamethylene diamine (HDA) in H2O without catalyst. Reaction conditions, such as monomer concentration and reaction temperature, affected the morphology of the resulting porous structures. Connected spheres, co-continuous monolithic structures and/or isolated holes were observed on the surface of the porous polymers. These structures were formed by polymerization-induced phase separation via spinodal decomposition or highly internal phase separation. The obtained porous polymers were soft and flexible and not breakable by compression. The porous polymers adsorbed various solvents. An AM4-HDA porous polymer could be plated by Ni using an electroless plating process via catalyzation by palladium (II) acetylacetonate following reduction of Ni ions in a plating solution. The intermediate Pd-catalyzed porous polymer promoted the Suzuki-Miyaura cross coupling reaction of 4-bromoanisole and phenylboronic acid.

Simultaneous analysis of two urinary biomarkers of oxidative damage to DNA and RNA based on packed-fiber solid phase extraction coupled with high-performance liquid chromatography

The determination of the concentrations of urinary biomarkers of oxidative damage to DNA and RNA is difficult due to the low content of targets and the complex matrix of urine. A method using polystyrene/polypyrrole (PS/PPY) electronspun nanofibers as the adsorbent was introduced to the routine urinary treatment and determination of 8-OHdG and 8-oxoG for the first time. And 2-aminoethyl diphenylborate (DPBA) solution was creatively used in the loading and rinsing steps in order to promote the retention of the analytes as well as remove impurities. Under optimal conditions, 8-OHdG, 8-oxoG and IS were separated very well and exhibited a good linearity in the range of 0.5-50 ng mL^-1, with correlation coefficients of R² > 0.996. Limits of detection (LOD) were 0.058 ng mL^-1 and 0.093 ng mL^-1, and limits of quantification (LOQ) were 0.195 ng mL^-1 and 0.309 ng mL^-1, respectively. The recoveries were 88.8-104.9%. The proposed method was so simple and economical that it had the potential to be applied to batch quantitative analysis of 8-OHdG and 8-oxoG in urine. And it was successfully applied to real urine samples of cancer patients.

A novel Wulff-type boronate acid-functionalized magnetic metal-organic framework imprinted polymer for specific recognition of glycoproteins under physiological pH

Boronate affinity molecularly imprinted materials have been widely used for the separation of glycoproteins under alkaline conditions that is not conducive to the structural stability of the protein. In this work, a kind of novel molecularly imprinted polymer (MIP/TBA/MOF@Fe₃ O₄ ) was prepared via grafting self-assembled molecular team of boronic acids on the surface of the magnetic metal-organic framework core. The teamed boronate affinity was formed by 2-mercaptoethylamine and 4-mercaptophenylboronic acid for specific separation of glycoproteins under physiological pH (pH 7.4). The obtained nanoparticles show high binding capacities (337.8 mg/g), fast adsorption equilibrium time (20 min), and good specificity (imprinting factor, 4.52) for glycoproteins under physiological pH. Furthermore, the prepared imprinted polymer still shows good adsorption capacity for glycoprotein after five times of repeated use, and its adsorption capacity only dropped by 4.7%. More importantly, the prepared nanoparticles have good potential to adsorb glycoproteins from real biological samples.

Boronate affinity material-based sensors for recognition and detection of glycoproteins

This review comprehensively presents the current overview and development potential of BAMs-based sensors for glycoprotein recognition and detection.

Synthesis and properties of porous polymers synthesized by Michael addition reactions of multi-functional acrylate, diamine, and dithiol compounds

Porous polymers have been synthesized by Michael addition reactions of multi-functional acrylate and diamine or dithiol compounds. Aza-Michael addition reaction of multi-functional acrylate, trimethylolpropane propoxylate triacrylate (TPT) and hexamethylene diamine (HDA) in dimethyl sulfoxide (DMSO) successfully yielded the porous polymer. The porous structure was characterized by connected globules or co-continuous structure, and could be controlled by the reaction conditions. Mechanical properties of the porous polymers were investigated by compression test. The porous polymers with co-continuous structure showed higher Young's modulus than those with connected globules. The porous polymer absorbed some organic solvents, especially CHCl₃. The porous polymer as prepared in DMSO state showed coloring induced by Christiansen filter effect depending on the reaction time and observation temperature. The thio-Michael addition reaction of TPT and 1,6-hexanedithiol (HDT) in DMSO using different base catalysts also yielded the porous polymer. The porous structure could be controlled by the catalysts amount when the reaction was initiated by a photo-base generator as the base catalyst. The present reaction systems make it possible to synthesize the porous polymers with simple process without phase separator.

Thermoregulated extraction of luteolin under neutral conditions using oligo(ethylene glycol)-based magnetic nanoparticles with Wulff-type boronate affinity

Oligo(ethylene glycol)-based thermoresponsive polymers with Wulff-type boronate affinity were anchored on magnetic nanoparticles. The resultant magnetic nanoparticles were used as sorbents for extracting luteolin, a cis-diol-containing model analyte. By exploiting the thermoresponsive properties and Wulff-type boronate affinity of the sorbents, target adsorption at room temperature (25 °C) and target release at high temperature (40 °C) were achieved under neutral conditions without pH alteration. The proposed thermoregulated extraction method was favorable for automated boronate affinity extraction, preventing degradation of the target and avoiding acidic elution for breaking Wulff-type boronate sites. Compared to reported sorbents for extracting luteolin, the sorbents possessed higher maximum adsorption capacity (98.7 mg g^-1) with acceptable sensitivity, simplified operation procedure, and mild extraction condition. Furthermore, the sorbents were applied in thermoregulated extraction of luteolin from honey samples. Satisfactory recoveries in the range of 83.2% - 89.1% with RSD ranging from 2.2% to 4.6% were achieved. The results demonstrated that this work provided a new research direction to design and synthesize efficient thermoresponsive materials for recognition and release of cis-diol compounds under neutral conditions.

Boronic acid-functionalized agarose affinity chromatography for isolation of tropomyosin in fishes

BACKGROUND

Tropomyosin is now receiving increasing attention because of its significant allergenic activity in various fishery products but its simple and effective isolation still remains a challenging task.

RESULTS

An agarose-based boronate affinity chromatography was produced for the first time to isolate tropomyosin in various fishery products using 3,5-difluoro-4-formyl-phenylboronic acid as the functional monomer, tris(2-aminoethyl)amine as the multi-branched ligand, and agarose gel particles as supporting materials. The agarose concentration, binding pH, and the concentration of elution buffers demonstrated significant effects on separation performance. Under optimized conditions, the purity of the isolated tropomyosin was higher than 90%, with the column adsorption capacity over 1.85 mg mL^-1 and the enrichment efficiency over 65%. Such efficiency was also validated with different fish samples including Paralichthys olivaceus, Thunnusthynnus, Oreochromis spp., and Lophius litulon.

CONCLUSION

In comparison with conventional methods, the established affinity chromatography demonstrated excellent biocompatibility (without involving any organic solvent), better speed (from at least 1-2 days to 3-4 h), and simplicity (from at least five steps to three steps). This suggests that it is a novel and promising technique for the isolation of tropomyosin and other glycoproteins (including most allergens) in foodstuffs. © 2019 Society of Chemical Industry.

Charge-switchable polymeric complex for glucose-responsive insulin delivery in mice and pigs

Glucose-responsive insulin delivery systems with robust responsiveness that has been validated in animal models, especially in large animal models, remain elusive. Here, we exploit a new strategy to form a micro-sized complex between a charge-switchable polymer with a glucose-sensing moiety and insulin driven by electrostatic interaction. Both high insulin loading efficiency (95%) and loading capacity (49%) can be achieved. In the presence of a hyperglycemic state, the glucose-responsive phenylboronic acid (PBA) binds glucose instantly and converts the charge of the polymeric moiety from positive to negative, thereby enabling the release of insulin from the complex. Adjusting the ratio of the positively charged group to PBA achieves inhibited insulin release from the complex under normoglycemic conditions and promoted release under hyperglycemic conditions. Through chemically induced type 1 diabetic mouse and swine models, in vivo hyperglycemia-triggered insulin release with fast response is demonstrated after the complex is administrated by either subcutaneous injection or transdermal microneedle array patch.

Preparation of highly fluorinated and boron-rich adsorbent for magnetic solid-phase extraction of fluoroquinolones in water and milk samples

Effective extraction is an indispensable procedure for the sensitive analysis of fluoroquinolones (FQs) in complex samples. According to the molecular properties of FQs, a new highly fluorinated and boron-rich adsorbent (FBA) was synthesized and employed as the extraction phase of magnetic solid-phase extraction (MSPE). Results revealed that the prepared FBA displayed satisfactory extraction capability for FQs through fluorophilic and B-N coordination interactions. Besides, the synthesized FBA also exhibited strong magnetic responsiveness and good life-span. Under the most favorable conditions, the FBA/MSPE was combined with high-performance liquid chromatography with diode array detection (HPLC-DAD) to sensitively quantify trace levels of FQs in environmental water and milk samples. The developed approach showed good linearity within the studied concentration range, satisfactory precision and low limits of detection (0.0049-0.016 μg/L for water sample and 0.010-0.046 μg/kg for milk sample). In the analysis of target FQs in real samples, the recoveries of different fortified concentrations were in the ranges of 80.1-120% and 78.9-119% for water and milk samples, respectively. The relative standard deviations for reproducibility were all below 11%. The results well evidence that the introduced FBA/MSPE is a promising extraction technology for FQs, and the established FBA/MSPE-HPLC/DAD approach is suitable to measure low concentrations of FQs in water and milk samples.

Dual functional monomers modified magnetic adsorbent for the enrichment of non-steroidal anti-inflammatory drugs in water and urine samples

According to the molecular properties of non-steroidal anti-inflammatory drugs (NSADs), a new adsorbent for magnetic solid phase extraction (MSPE) was designed and synthesized. Triethyl-(4-vinylbenzyl)aminium chloride and 4-vinylbenzeneboronic acid were utilized as dual functional monomers to copolymerize with divinylbenzene on the surface of pre-modified Fe₃O₄ nanoparticles. The prepared magnetic adsorbent (Fe₃O₄@TCVA) was characterized by elemental analysis, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometer. Due to the abundant boronic acid, quaternary amine and phenyl groups, the Fe₃O₄@TCVA displayed satisfactory extraction performance for target NSADs (diclofenac acid, ibuprofen and mefenamic acid) by means of B-N coordination, anion-exchange, π-π and hydrophobic interactions. Under the optimized conditions, the Fe₃O₄@TCVA/MSPE was combined with high-performance liquid chromatography with diode array detection (HPLC-DAD) to sensitively analyze NSADs in water and human urine samples. Results indicated that the limits of detection for water and urine samples were in the ranges of 0.014-0.031 μg/L and 0.029-0.11 μg/L, respectively. The relative standard deviations for the intra-day and inter-day assay variability were below 10%. The applicability of the proposed Fe₃O₄@TCVA/MSPE-HPLC-DAD method was demonstrated by the successful extraction and quantification of trace levels of NSADs in real water and human urine samples. Satisfactory spiked recovery and reproducibility were achieved.

Recent advances in mixed-mode chromatographic stationary phases

Mixed-mode phases have become very popular in the last decade, and the number of new mixed/multi-mode sorbents is growing fast. Unlike single-mode stationary phases, perfectly suited for the separation of the analytes possessing similar physicochemical properties, for instance reversed-phase chromatography for hydrophobic solutes, mixed-mode sorbents providing multimodal interactions can render better separation selectivity for complex mixtures of solutes differing significantly in their physicochemical characteristics. The most frequent modern mixed-mode stationary phases are di/tri-mode sorbents embracing the following interactions, hydrophobic, electrostatic (coulombic), and hydrophilic. According to their structures, it is possible to distinguish silica-based, polymer-based, hybrid, and monolithic mixed-mode stationary phases. Herewith, newly synthesized mixed-mode sorbents developed within the last two and half years are categorized, discussed, and summarized. The main attention is devoted to the description of the synthetic routes and characterization methods applied for the new stationary phases.

Phenylboronic acid functionalized C3N4 facultative hydrophilic materials for enhanced enrichment of glycopeptides

It is challenging to capture N-glycopeptides with high recovery and high specificity from complicated biosystems. Herein, we present a facile and economical procedure to generate a novel self-assembling 4-Mercaptobenzene boronic acid functionalized and Au-doped Straticulate C₃N₄ (MASC), with enhanced affinity capability towards glycopeptides. The materials possess low pH value adaptation, high hydrophilicity and stability, good repeatability and recyclability, and provided high selectivity (1:100), low limit of detection (0.33 fmol/μL), high enrichment efficiency (~ 80%) and high recovery rate (~ 90%) towards glycopeptides. The materials can capture glycopeptides unbiasedly, as demonstrated by the identification of 37 glycopeptides from IgG and 21 glycopeptides from horseradish peroxidase (HRP). The performance of MASC on human urine and serum glycoproteome analysis was also tested. An average of 1465 glycopeptides from 839 glycoproteins and 1553 glycopeptides from 884 glycoproteins were identified from female and male urine samples in a single mass spectrometry analysis. O-glycopeptides from human urine were also significantly enriched. Additionally, 463 glycopeptides assigned to 209 glycoproteins were identified from 5 μL of human serum. All of these results indicate that MASC presents a good performance and applicability in the field of glycoproteomic research.

Phenylboronic Acid Functionalized Adsorbents for Selective and Reversible Adsorption of Lactulose from Syrup Mixtures

Boronate affinity materials have been widely used for enrichment of cis-diol molecules. In this work, phenylboronic acid functionalized adsorbents were prepared via a simple and efficient procedure grafting phenylboronic acid groups onto amino macroporous resins. Elemental analysis has confirmed the successful functionalization of AR-1M and AR-2M with approximately 2.17% and 0.73% weight percentage of boron. Comparatively, AR-1M possessed higher lactulose adsorption capacity ( q_e-Lu, 84.78 ± 0.95 mg/g dry resin) under neutral conditions (pH = 7), while the introduced glutaraldehyde spacer arms on AR-2M resulted in excellent adsorption selectivity (α ≈ 23), high adsorption efficiency (π ≈ 22%), and fast adsorption/desorption rate. The purity of lactulose (Pu_D^Lu) through pH-driven adsorption (pH 7-8) and desorption (pH 1.5) can be effectively improved depending on the ratio of lactulose to lactose. When lactulose/lactose ≥ 1:1, Pu_D^Lu ≈ 95% was achieved. No significant drop in q_e-Lu (>90%) was observed after ten-consecutive repeats. Results demonstrated that the newly developed method may achieve satisfactory performance in lactulose purification.

Amorphous titania modified with boric acid for selective capture of glycoproteins

Amorphous titania was modified with boric acid, and the resulting material was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction and X-ray photoelectron spectrometry. The new material, in contrast to conventional boronate affinity materials containing boronic acid ligands, bears boric acid groups. It is shown to exhibit high specificity for glycoproteins, and this was applied to design a method for solid phase extraction of glycoproteins as shown for ribonuclease B, horse radish peroxidase and ovalbumin. Glycoproteins were captured under slightly alkaline environment and released in acidic solutions. The glycoproteins extracted were detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The binding capacities for ribonuclease B, horse radish peroxidase and ovalbumin typically are 9.3, 26.0 and 53.0 mg ∙ g^-1, respectively. The method was successfully applied to the selective enrichment of ovalbumin from egg white. Graphical abstract Schematic presentation of the capture of glycoproteins by amorphous titania modified with boric acid.

Specific enrichment combined with highly efficient solid-phase tagging for the sensitive detection of heparin based on boronic acid-functionalized mesoporous silica nanospheres

A combined specific enrichment and highly efficient solid-phase tagging approach is presented for heparin detection using boronic acid-functionalized mesoporous silica nanospheres as extraction sorbents and nanoscale reactors. It exhibits a faster reaction time (only 6 min), higher tagging-product purity and lower applicable sample concentration compared with liquid-phase tagging.

An inorganic boronate affinity in-needle monolithic device for specific capture of cis-diol containing compounds

In this work, inorganic boronate affinity monolith was prepared by in situ synthesis in 0.33mm i.d. stainless steel needle through sol-gel process using tetraethoxysilane and tetrabutyl orthotitanate as the co-precursors. The morphology, structure and composition of the monolith were characterized. In contrast to conventional boronate affinity materials, inorganic boric acid was used as affinity ligand. Different compounds were used for the evaluation of the boronate affinity of this inorganic monolithic material. The monolith exhibited good selectivity towards cis-diol containing compounds. Recovery of greater than 90% was achieved for in-needle extraction of catechol under neutral conditions. Owing to the hydrophilic property of the monolith, the procedure of affinity chromatography could be performed in aqueous solution. This monolithic in-needle device will be useful for boronate affinity extraction of small-volume samples.

Molecularly Imprinted Porous Monolithic Materials from Melamine-Formaldehyde for Selective Trapping of Phosphopeptides

Thirty-five melamine-formaldehyde (MF) monolithic materials with bimodal pore distributions were synthesized in fused silica capillaries by catalyst-free polycondensation, starting with an aqueous MF precondensate, using acetonitrile as the macroporogen and a variety of aliphatic polyethers and triblock copolymeric surfactants as porogens and mesoporogens, respectively. By varying the prepolymer composition and the type and molecular weight of the polymeric porogen components, a library of porous monolithic materials was produced, covering a range of meso- and macroporous properties. A multivariate evaluation revealed that the amount of surfactant was the strongest contributor to specific surface area and pore volume and to the inversely related mesopore size, whereas the macropore dimensions were controlled mainly by the amount of aliphatic polyether porogen. One of these capillary monoliths, chosen based on the combination of meso- and macropores providing optimal percolative flow and accessible surface area, was synthesized in the presence of N-Fmoc and O-Et protected phosphoserine and phosphotyrosine to prepare molecularly imprinted monoliths with surface layers selective for phosphopeptides. These imprinted monoliths were characterized alongside nonimprinted monoliths by a variety of techniques and finally evaluated by liquid chromatography-mass spectrometry in the capillary format to assess their abilities to trap and release phosphorylated amino acids and peptides from partly aqueous media. Selective enrichment of phosphorylated targets was demonstrated, suggesting that these materials could be useful as trapping media in affinity-based phosphoproteomics.

Preparation of a silica stationary phase co-functionalized with Wulff-type phenylboronate and C12 for mixed-mode liquid chromatography

A silica stationary phase was designed and synthesized through the co-functionalization of silica with Wulff-type phenylboronate and C12 for mixed-mode liquid chromatography applications. The as-synthesized stationary phase was characterized by elemental analysis and Fourier Transform-InfraRed Spectroscopy (FT-IR). Retention mechanisms, including boronate affinity (BA), reversed-phase (RP) and anion-exchange (AE), were involved. Retention mechanism switching was easily realized by adjustment of the mobile phase constitution. Cis-diol compounds could be selectively captured under neutral conditions in BA mode and off-line separated in RP mode. Neutral, basic, acidic and amphiprotic compounds were chromatographed on the column in RP chromatography, while inorganic anions were chromatographed in AE chromatography to characterize the mixed-mode nature of the prepared stationary phase. In addition, the RP performance was compared with an octadecyl silica column in terms of column efficiency (N/m), asymmetry factor (A_f), retention factor (k) and resolution (Rs). The prepared stationary phase offered multiple interactions with analytes in addition to hydrophobic interactions under RP elution conditions. Based on the mixed-mode properties, off-line 2D-LC, for selective capture and separation of urinary nucleosides, was successfully realized on a single column, demonstrating its powerful application potential for complex samples.

Application of Porous Materials to Carbohydrate Chemistry and Glycoscience

There is a growing interest in using a range of porous materials to meet research needs in carbohydrate chemistry and glycoscience in general. Among the applications of porous materials reviewed in this chapter, enrichment of glycans from biological samples prior to separation and analysis by mass spectrometry is a major emphasis. Porous materials offer high surface area, adjustable pore sizes, and tunable surface chemistry for interacting with glycans, by boronate affinity, hydrophilic interactions, molecular imprinting, and polar interactions. Among the materials covered in this review are mesoporous silica and related materials, porous graphitic carbon, mesoporous carbon, porous polymers, and nanoporous gold. In some applications, glycans are enzymatically or chemically released from glycoproteins or glycopeptides, and the porous materials have the advantage of size selectivity admitting only the glycans into the pores and excluding proteins. Immobilization of lectins onto porous materials of suitable pore size allows for the use of lectin-carbohydrate interactions in capture or separation of glycoproteins. Porous material surfaces modified with carbohydrates can be used for the selective capture of lectins. Controlled release of therapeutics from porous materials mediated by glycans has been reported, and so has therapeutic targeting using carbohydrate-modified porous particles. Additional applications of porous materials in glycoscience include their use in the supported synthesis of oligosaccharides and in the development of biosensors for glycans.

Polydopamine assisted functionalization of boronic acid on magnetic nanoparticles for the selective extraction of ribosylated metabolites from urine

A novel strategy for the rapid and selective extraction of ribosylated metabolites by dopamine assisted functionalization of boronic acid on magnetic (Fe₃O₄@PDA-FPBA) nanoparticles has been demonstrated under optimized conditions.

Determination of Glycoproteins by a Self-Assembled 4-Mercaptophenylboronic Acid Film on a Quartz Crystal Microbalance

Glycosylation plays an important part in many biological processes. However, many glycoproteins are either of low abundance or covered by other components in biological samples. Hence, developing new methods to measure the glycoproteins with both high efficiency and low detection limit is important. In this work, a self-assembled 4-mercaptophenylboronic acid film was coated on a quartz crystal microbalance chip. By optimizing the reaction time and the concentration of 4-mercaptophenylboronic acid, a sensor that specifically responded to glycoproteins was created. Then, several parameters for the prepared sensor were investigated and the working curve for representative glycoprotein-transferrin was established. The linearity range was from 50 to 400 ng/mL and the detection limit was 21.0 ng/mL. The sensor was used to detect transferrin in artificial urine samples. This sensor has a low detection limit of glycoproteins requiring only a small amount of samples, and thus has potential applications in both pharmaceutical and medical areas.