Boronate affinity materials for separation and molecular recognition: structure, properties and applications

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.

Boronic acid-functionalized spherical polymer brushes for efficient and selective enrichment of glycoproteins

Glycoproteins are related to many biological activities and diseases, and thereby their efficient capture and enrichment for diagnostics and proteomics have emerged to exhibit great significance. However, the lack of materials with high binding capacity and selectivity is still a big obstacle for further application. Herein, we reported a facile and eco-friendly approach to fabricate spherical polymer brushes with multiple boronic acid groups. Specifically, the whole process can be divided into three steps, the polystyrene (PS) core was obtained by traditional emulsion polymerization, followed by immobilization of a home-made photoinitiator. Subsequently, boronic acid-functionalized polymer chains (PBA) were chemically grafted via photo-emulsion polymerization, leading to spherical polymer brushes (PS-PBA) with boronate affinity. The particle size, morphology, and composition of as-prepared spherical polymer brushes were systematically characterized. The characteristics of glycoproteins binding to the spherical polymer brushes under different conditions, including pH values and ionic strength, were also investigated. PS-PBA brushes possess fast binding speed (30 min) and high binding capacity for glycoprotein ovalbumin (OVA) (377.0 mg g^-1) under physiological pH conditions at 25 °C, because the low steric hindrance of flexible polymeric PBA chains facilitates the interaction between boronic acid groups and glycoproteins. Moreover, the binding capacity of PS-PBA brushes for glycoprotein OVA was ∼6.7 times higher than that for non-glycoprotein bovine serum albumin (BSA), indicating the excellent selective adsorption. This study provided a facile and efficient approach for the fabrication of boronic acid-functionalized materials that will be useful in the enrichment and separation of glycoproteins for the diagnosis of diseases.

Cryogel Monoliths for Analyte Enrichment by Capture and Release

A platform based on cryogel monoliths in small capillaries, which allows very strong enrichment of an analyte through a capture and release process, is described. For their preparation, a photoreactive copolymer solution containing capture molecules of interest is filled into a capillary, frozen in, and then photochemically transformed into cryogel monoliths through C,H-insertion cross-linking reactions. As a test example, the platform is used for the preconcentration of dopamine from bovine serum albumin and urine samples through capture and release processes. During capture from a large volume and release into a smaller volume, the platform shows recovery rates up to 97% and allows up to a roughly 630-fold enrichment of the concentration of the analyte. The presented platform could be used as a disposable device for the purification and enrichment of a variety of cis-diol-containing samples.

Recent Advances in Micro/Nanomaterial-Based Aptamer Selection Strategies

Aptamers are artificial nucleic acid ligands that have been employed in various fundamental studies and applications, such as biological analyses, disease diagnostics, targeted therapeutics, and environmental pollutant detection. This review focuses on the recent advances in aptamer discovery strategies that have been used to detect various chemicals and biomolecules. Recent examples of the strategies discussed here are based on the classification of these micro/nanomaterial-mediated systematic evolution of ligands by exponential enrichment (SELEX) platforms into three categories: bead-mediated, carbon-based nanomaterial-mediated, and other nanoparticle-mediated strategies. In addition to describing the advantages and limitations of the aforementioned strategies, this review discusses potential strategies to develop high-performance aptamers.

Peptide and protein assays using customizable bio-affinity arrays combined with ambient ionization mass spectrometry

High-throughput identification and quantification of protein/peptide biomarkers from biofluids in a label-free manner is achieved by interfacing bio-affinity arrays (BAAs) with nano-electrospray desorption electrospray ionization mass spectrometry (nano-DESI-MS). A wide spectrum of proteins and peptides ranging from phosphopeptides to cis-diol biomolecules as well as thrombin can be rapidly extracted via arbitrarily predefined affinity interactions including coordination chemistry, covalent bonding, and biological recognition. An integrated MS platform allows continuous interrogation. Profiling and quantitation of dysregulated phosphopeptides from small-volume (∼5 μL) serum samples has been successfully demonstrated. As a front-end device adapted to any mass spectrometer, this MS platform might hold much promise in protein/peptide analysis in point-of-care (POC) diagnostics and clinical applications.

Customizable bio-affinity arrays were interfaced with ambient ionization mass spectrometry for high-throughput assays of protein/peptide biomarkers in biofluids.

Boronic acid with high oxidative stability and utility in biological contexts

Despite their desirable attributes, boronic acids have had a minimal impact in biological contexts. A significant problem has been their oxidative instability. At physiological pH, phenylboronic acid and its boronate esters are oxidized by reactive oxygen species at rates comparable to those of thiols. After considering the mechanism and kinetics of the oxidation reaction, we reasoned that diminishing electron density on boron could enhance oxidative stability. We found that a boralactone, in which a carboxyl group serves as an intramolecular ligand for the boron, increases stability by 10⁴-fold. Computational analyses revealed that the resistance to oxidation arises from diminished stabilization of the p orbital of boron that develops in the rate-limiting transition state of the oxidation reaction. Like simple boronic acids and boronate esters, a boralactone binds covalently and reversibly to 1,2-diols such as those in saccharides. The kinetic stability of its complexes is, however, at least 20-fold greater. A boralactone also binds covalently to a serine side chain in a protein. These attributes confer unprecedented utility upon boralactones in the realms of chemical biology and medicinal chemistry.

The molecular imprinting of magnetic nanoparticles with boric acid affinity for the selective recognition and isolation of glycoproteins

A strategy was designed for the molecular imprinting of magnetic nanoparticles with boric acid affinity (MNPs@MIP) which were then used for the selective recognition and isolation of glycoproteins. Fe₃O₄ nanoparticles were prepared by a solvothermal method and direct silanization by the condensation polymerization of aminopropyltriethoxysilane (APTES). Subsequently, phenylboric acid was functionalized by reductive amination between 2,3-difluoro-4-formyl phenylboric acid (DFFPBA) and the amido group. The resultant Fe₃O₄@SiO₂–DFFPBA was then used for the selective adsorption of a glycoprotein template. Finally, a molecularly imprinted layer was covered on the surface nanoparticles by the condensation polymerization of tetraethyl orthosilicate (TEOS). The adsorption capacities of the resultant MNPs@MIP–HRP and MNPs@MIP–OVA to horseradish peroxidase (HRP) or ovalbumin (OVA) were significantly higher than non-imprinted particles (MNPs@NIP). Moreover, the adsorption capacities of MNPs@MIP–HRP and MNPs@MIP–OVA on non-template protein and non-glycoprotein bovine serum albumin (BSA) were significantly lower than those of their respective template proteins, thus indicating that both of the prepared MNPs@MIP exhibited excellent selectivity.

A strategy was designed for the preparation of molecular imprinting of magnetic nanoparticles with boric acid affinity (MNPs@MIP), and the resultant MNPs@MIP exhibited excellent selectivity for template glycoproteins.

[Large-scale enrichment and identification of human urinary N-glycoproteins/N-glycopeptides]

N-Glycosylation of proteins, an important post-translational modification in eukaryotic cells, plays an essential role in the regulation of cell adhesion, migration, signal transduction, and apoptosis. Abnormal changes in protein glycosylation are closely related to the occurrence of many critical diseases, including diabetes, tumors, and neurological, kidney, and inflammatory diseases. A non-invasive type of liquid biopsy, urine sampling has the advantage of reducing the complexity of proteomic analysis. This facilitates the design of large-scale and continuous or multi-time point sampling strategies. However, the dynamic range of urinary protein abundance is relatively large, owing to individual differences and physiological conditions. Currently, there is a lack of specialized research on individual differences, physiological fluctuations, and physiological abundance ranges of urinary N-glycoproteins in large healthy populations. Therefore, it is difficult to accurately distinguish individual differences and normal physiological fluctuations from changes caused by disease; this poses a great challenge in disease marker research. Liquid chromatography-mass spectrometry (LC-MS) is an analytical technique widely used for the large-scale profiling of proteomes in biological systems, and the enrichment of N-glycopeptides is a prerequisite for their detection by MS.In this study, we established an approach based on hydrophilic interaction chromatography (HILIC) by optimizing the activation, cleaning, and elution processes of the enrichment method, for instance through the optimization of particle size and solvent composition, and investigated the identification number, selectivity, and stability of N-glycoprotein/N-glycopeptide enrichment under different experimental conditions. We found that N-glycoproteins and N-glycopeptides were highly enriched in a trifluoroacetic acid system with 5-μm filling particles in the HILIC column. On this basis, we analyzed the levels of N-glycoproteins/N-glycopeptides in urine samples. The consistency of N-glycoprotein/N-glycopeptide levels in urine samples taken from the same healthy person for five consecutive days was investigated by correlation analysis. This analysis revealed that the urinary N-glycoproteome of the same healthy person was relatively stable over a short period of time. Next, urinary samples from 20 healthy male volunteers and 20 healthy female volunteers were enriched for N-glycoproteins/N-glycopeptides, which were profiled by MS through qualitative and quantitative analyses. Screening and functional analysis of differential proteins were then carried out. A total of 1016 N-glycoproteins and 2192 N-glycopeptides were identified in the mid-morning urine samples of the 40 healthy volunteers. A label-free quantitation strategy was used to investigate the fluctuation range of the physiologically abundant urinary N-glycopeptides. The abundance of urinary N-glycopeptides spanned across approximately five orders of magnitude. Subsequently, gender differences in the N-glycosylation levels of urinary proteins were also explored in healthy people. Functional analysis of the N-glycoproteins that exhibited gender differences in abundance was performed. Based on multivariate statistical analysis, 206 differentially expressed proteins (p<0.05, fold change (FC)> 4) were identified. In females, we found 175 significantly down-regulated N-glycoproteins and 31 significantly up-regulated N-glycoproteins with respect to males. The expression levels of N-glycopeptides between the two groups suggested a clear gender difference. To investigate the biological processes and functions of these proteins, gene ontology (GO) analysis was performed on the N-glycoproteins/N-glycopeptides differentially expressed between males and females. Metabolic pathway analysis was also carried out based on the kyoto encyclopedia of genes and genomes (KEGG). Differentially expressed N-glycoproteins were mostly associated with platelet degranulation, extracellular region, and ossification. The top three relevant pathways were glycan biosynthesis and metabolism, metabolism of cofactors and vitamins, and lipid metabolism. Overall, sex may be an important factor for urinary N-glycoproteome differences among normal individuals and should be considered in clinical applications. This study provides relevant information regarding the function and mechanisms of the urinary glycoproteome and the screening of clinical biomarkers.

Borate-driven ionic rectifiers based on sugar-bearing single nanochannels

Recently, much scientific effort has been centered on the control of the ionic transport properties of solid state nanochannels and the rational design and integration of chemical systems to induce changes in the ionic transport by means of interactions with selected target molecules. Here, we report the fabrication of a novel nanofluidic device based on solid-state nanochannels, which combines silane chemistry with both track-etched and atomic layer deposition (ALD) technologies. Nanodevice construction involves the coating of bullet-shaped single-pore nanochannels with silica (SiO₂) by ALD and subsequent surface modification by reaction between silanol groups exposed on pore walls and N-(3-triethoxysilylpropyl)-gluconamide, in order to create a gluconamide-decorated nanochannel surface. The formation of a boroester derivative resulting from the selective reaction of borate with the appended saccharides leads to important changes in the surface charge density and, concomitantly, in the iontronic properties of the nanochannel. Furthermore, we propose a binding model to rationalize the specific interaction saccharide-borate in the surface. Besides, this unique nanodevice exhibits a highly selective and reversible response towards borate/fructose exposure. On the basis of the surface charge variation resulting from borate binding, the nanochannel can reversibly switch between "ON" and "OFF" states in the presence of borate and fructose, respectively. In addition, this work describes the first report of the functionalization of PET/SiO₂ nanochannels by the ALD technique. We believe that this work provides a promising framework for the development of new nanochannel-based platforms suitable for multiple applications, such as water quality monitoring or directed molecular transport and separation.

[Preparation of branched polyethyleneimine-assisted boric acid-functionalized magnetic nanoparticles and its application to selective enrichment of ginsenoside Re]

为了实现更高效的人参皂苷富集,以硼亲和色谱为核心,结合支链聚乙烯亚胺放大硼酸配基数量,合成了支链聚乙烯亚胺辅助硼酸功能化磁性纳米粒(PEI-BA-MNPs),用于实际样品中人参皂苷的选择性富集,结合高效液相色谱,建立了一种分析实际样品中的人参皂苷的方法。以人参皂苷Re为代表,在优化的磁性固相萃取的条件下,该方法在50~800 μg/L的范围内呈现良好的线性,线性相关系数(R²)为0.9681。添加水平在0.1~10 mg/L时,回收率为91.5%~117.3%,相对标准偏差为7.2%~13.4%。由于所得材料对于人参皂苷的高亲和力,经所建立的方法富集过后,人参皂苷Re的灵敏度提高了约50倍。同时,所得材料重复使用5次以后还可以保持至少72%的原始吸附量。最后,将该方法用于启脾口服液中人参皂苷Re的含量分析,并与2015版《中国药典》的标准方法做对比。结果显示,所建立的方法检测出的人参皂苷Re含量为0.27%,虽然与标准方法测得的含量(0.31%)有些微差距,但该法极大地节约了实际操作中样品前处理的步骤和时间。结果表明,所制得的PEI-BA-MNPs可以用作磁性固相萃取吸附剂实现实际样品中人参皂苷的选择性富集。该方法亲和力强,选择性好,灵敏度高,操作快速简便且准确度高,具有很大的应用价值和发展前景。

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Molecular Imprinting: Green Perspectives and Strategies

Advances in revolutionary technologies pose new challenges for human life; in response to them, global responsibility is pushing modern technologies toward greener pathways. Molecular imprinting technology (MIT) is a multidisciplinary mimic technology simulating the specific binding principle of enzymes to substrates or antigens to antibodies; along with its rapid progress and wide applications, MIT faces the challenge of complying with green sustainable development requirements. With the identification of environmental risks associated with unsustainable MIT, a new aspect of MIT, termed green MIT, has emerged and developed. However, so far, no clear definition has been provided to appraise green MIT. Herein, the implementation process of green chemistry in MIT is demonstrated and a mnemonic device in the form of an acronym, GREENIFICATION, is proposed to present the green MIT principles. The entire greenificated imprinting process is surveyed, including element choice, polymerization implementation, energy input, imprinting strategies, waste treatment, and recovery, as well as the impacts of these processes on operator health and the environment. Moreover, assistance of upgraded instrumentation in deploying greener goals is considered. Finally, future perspectives are presented to provide a more complete picture of the greenificated MIT road map and to pave the way for further development.

Magnetic borate-modified Mxene: A highly affinity material for the extraction of catecholamines

A novel magnetic borate-modified MXene composite was prepared by in situ growth of Fe₃O₄ particles onto the surface of phenylboronic acid modified Ti₃C₂T_x nanosheets. The magnetic composite possesses highly selective recognition properties to catecholamines, and high adsorption capacity (up to 319.6 μmol g^-1) for dopamine. Besides, the adsorption of urinary catecholamines can be accomplished within 2.0 min. The excellent adsorption performance can be assigned to its unique 2D layered structures, which helps to shorten the diffusion path and facilitate molecular transport. In addition, the multilayer adsorption and the synergetic interactions of borate affinity, van der Waals forces, hydrogen bonding and π-π stacking also contribute to the adsorption. By coupling the magnetic boronate affinity composites with high-performance liquid chromatography-fluorescence detection, a sensitive method for the determination of catecholamines in urine samples was proposed. The validation results revealed it can offer good linearities (correlation coefficients higher than 99%). The method detection limits were 0.06, 0.16, 0.03 and 0.14 ng mL^-1 for norepinephrine, epinephrine, dopamine and isoprenaline, respectively, and relative recoveries for these catecholamines were in the range of 98.56-108.1%, 92.56-110.0%, 98.79-112.3% and 88.14-97.81%, respectively. The proposed method was successfully applied to analyze the catecholamines in the urine samples from 15 healthy volunteers and 16 patients with Alzheimer's disease. The results indicated that the magnetic borate-modified Mxene composite possesses superior extraction performance, and can be used as an outstanding candidate for the extraction of catecholamines in pre-clinical or clinical studies.

Hydrogels in Electrophoresis: Applications and Advances

A hydrogel is a solid form of polymer network absorbed in a substantial amount of aqueous solution. In electrophoresis, hydrogels play versatile roles including as support media, sieving matrixes, affinity scaffolds, and compositions of molecularly imprinting polymers. Recently, the study of hydrogels has been advancing with unprecedented speed, and the application of hydrogels in separation science has brought new opportunities and possible breakthroughs. A good understanding about the roles and effects of the material is essential for hydrogel applications. This review summarizes the hydrogels that has been described in various modes of electrophoretic separations, including isoelectric focusing gel electrophoresis (IEFGE), isotachophoresis (ITP), gel electrophoresis and affinity gel electrophoresis (AGE). As microchip electrophoresis (ME) is one of the future trends in electrophoresis, thought provoking studies related to hydrogels in ME are also introduced. Novel hydrogels and methods that improve separation performance, facilitate the experimental operation process, allow for rapid analysis, and promote the integration to microfluidic devices are highlighted.

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.

Selective recognition of tumor cells by molecularly imprinted polymers

Molecularly imprinted polymers, developed 50 years ago, have garnered enormous attention as receptor-like materials. Lately, molecularly imprinted polymers have been employed as a specific target tool in favor of cancer diagnosis and therapy by the selective recognition of tumor cells. Although the molecular imprinting technology has been well-innovated recently, the cell still remains the most challenging target for imprinting. In this review, we summarize the advances in the synthesis of molecularly imprinted polymers suitable for the selective recognition of tumor cells. Through a sustained effort, three strategies have been developed including peptide-imprinting, polysaccharide-imprinting, and whole-cell imprinting, which have resulted in inspiring applications in effective cancer diagnosis and therapy. The major challenges and perspectives on the further directions related to the synthesis of molecularly imprinted polymers were also outlined.

Tailor-made magnetic nanocomposite with pH and thermo-dual responsive copolymer brush for bacterial separation

Rapid detection of pathogenic bacteria particularly in food samples demands efficient separation and enrichment strategies. Here, hydrophilic temperature-responsive boronate affinity magnetic nanocomposites were established for selective enrichment of bacteria. The thermo-responsive polymer brushes were developed by surface-initiated atom transfer radical polymerization of N-isopropylacrylamide (NIPAm) and allyl glycidyl ether (AGE), followed by a reaction of epoxy groups, and incorporation of fluorophenylboronic acid. The physical and chemical characteristics of the magnetic nanocomposites were analyzed systematically. After optimization, S. aureus and Salmonella spp. showed high binding capacities of 32.14 × 10⁶ CFU/mg and 50.98 × 10⁶ CFU/mg in 0.01 M PBS (pH 7.4) without bacteria death. Bacterial bindings can be controlled by altering temperature and the application of competing monosaccharides. The nanocomposite was then utilized to enrich S. aureus and Salmonella spp. from the spiked tap water, 25% milk, and turbot extraction samples followed by multiplex polymerase chain reaction (mPCR), which resulted in high bacteria enrichment, and demonstrated great potential in separation of bacteria from food samples.

Electrically programmable adhesive hydrogels for climbing robots

Although there have been notable advances in adhesive materials, the ability to program attaching and detaching behavior in these materials remains a challenge. Here, we report a borate ester polymer hydrogel that can rapidly switch between adhesive and nonadhesive states in response to a mild electrical stimulus (voltages between 3.0 and 4.5 V). This behavior is achieved by controlling the exposure and shielding of the catechol group through water electrolysis-induced reversible cleavage and reformation of the borate ester moiety. By switching the electric field direction, the hydrogel can repeatedly attach to and detach from various surfaces with a response time as low as 1 s. This programmable attaching/detaching strategy provides an alternative approach for robot climbing. The hydrogel is simply pasted onto the moving parts of climbing robots without complicated engineering and morphological designs. Using our hydrogel as feet and wheels, the tethered walking robots and wheeled robots can climb on both vertical and inverted conductive substrates (i.e., moving upside down) such as stainless steel and copper. Our study establishes an effective route for the design of smart polymer adhesives that are applicable in intelligent devices and an electrochemical strategy to regulate the adhesion.

Advances in epitope molecularly imprinted polymers for protein detection: a review

Epitope molecularly imprinted polymers (EMIPs) are novel imprinted materials using short characteristic peptides as templates rather than entire proteins. To be specific, the amino acid sequence of the template peptide is the same as an exposed N- or C-terminus of a target protein, or its amino acid composition and sequence replicate a similar conformational arrangement as the same amino acid residues on the surface of the target protein. EMIPs have a good application prospect in protein research. Herein, we focus on classification of epitope imprinting techniques, methods of epitope immobilization on matrix materials including boronate affinity immobilization, covalent bonding immobilization, physical adsorption immobilization and metal ion chelation immobilization, and application of EMIPs in peptides, proteins, target imaging and target therapy fields. Finally, the main problems and future development are summarized.

Boronate Affinity-Based Oriented and Double-Shelled Surface Molecularly Imprinted Polymers on 96-Well Microplates for a High-Throughput Pharmacokinetic Study of Rutin and Its Metabolites

The boronate affinity-based oriented and double-shelled surface molecularly imprinted polymers on 96-well microplates (BDMIPs) were designed and applied to high-specific and high-throughput pharmacokinetic (PK) study of rutin and its metabolites from rat plasma without concentration and redissolution. It integrated the advantages of covalent effects-based boronate affinity, noncovalent effects of ethylene imine polymer (PEI) dendrimer, multiple cavities-based double-shelled layers, and multiparallel wells-based 96-well microplates. Furthermore, ultrahigh-performance liquid chromatography triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) was used to accurately quantify targets. It showed lower limits of detection (LODs) up to 100-fold than the conventional method. And PKs of rutin and trace isoquercetin (IQC) were first reported at the same time. The platform can provide a fast, simple, low-cost, high-selective, high-effective, and high-throughput methodological reference for analysis of large-scale samples in the fields of agriculture and food.

Functionalized polyoxometalate microspheres ensure selective adsorption of phosphoproteins and glycoproteins

Lacunary polyoxometalate (POM), [PW₉O₃₄]^9-, grafts with a boronic acid group attached via an organosilane bridge assemble into microspheres, PW₉-Si-APBA. The oxygen-rich and hydrophilic surface of POM facilitates the binding of phosphate groups in phosphoproteins and glycans in glycoproteins. While the metal-oxo in POM provides π-π interactions with the phosphate groups of phosphoproteins, the boronic acid group specifically binds to glycoproteins via the cis-diols of glycans. Therefore, these multi-driving forces ensure the selective adsorption of phosphoproteins and glycoproteins by PW₉-Si-APBA microspheres in biological sample matrixes, even in the presence of very high protein abundance, i.e., BSA, at mass ratio of β-ca/IgG/OVA/BSA = 1 : 1 : 1 : 200.

Boronoisophthalic acid as a novel affinity ligand for the selective capture and release of glycoproteins near physiological pH

Boronic acid-based affinity materials have gained tremendous attention for the selective separation and recognition of cis-diol containing biomolecules. But often, these boronate affinity materials are stuck to some serious issues like high binding pH and weak affinity, especially in the case of glycoproteins. Here in this study, we used 5-boronoisophthlic acid as a novel affinity ligand for the selective capture and release of glycoproteins. The pKa value of 5-boronoisophthalic acid is investigated to be 7.8 which is just closed to physiological pH and is ideally suitable for the fast binding and elution kinetics of glycoproteins to avoid their degradation and deactivation. The affinity ligand is attached to the surface of polymer support using branched polyethyleneimine (PEI) which enhances the binding strength as it has multiple amine groups available for the attachment of 5-boronoisophthalic for synergistic interactions. The resulting affinity material is characterized and packed in a micropipette-tip using hydrophilic melamine foam as a frit to make the separation process smooth, simple, reliable, and robust. This boronic acid-based affinity tip exhibits binding constants for model glycoproteins in the range of 10^-6-10^-7 M, binding capacities in the range of 0.662 μM/g, and selectivity up to 1:1000 (HRP to BSA) under optimized extraction conditions. Finally, the boronic-based affinity tip is successfully applied to selectively capture the glycoproteins from the human milk sample, especially lactoferrin which is highly important in dairy manufacture.

Boronic Acid Functionalized Nanosilica for Binding Guest Molecules

Dendritic fibrous nanosilica (DFNS) has very high surface area and well-defined nanochannels; therefore, it is very useful as supporting material for numerous applications including catalysis, sensing, and bioseparation. Due to the highly restricted space, addition of molecular ligands to DFNS is very challenging. This work studies how ligand conjugation in nanoscale pores in DFNS can be achieved through copper-catalyzed click reaction, using an optional, in situ synthesized, temperature-responsive polymer intermediate. A clickable boronic acid is used as a model to investigate the ligand immobilization and the molecular binding characteristics of the functionalized DFNS. The morphology, composition, nanoscale pores, and specific surface area of the boronic acid functionalized nanosilica were characterized by electron microscopy, thermogravimetric and elemental analysis, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption measurements. The numbers of boronic acid molecules on the modified DFNS with and without the polymer were determined to be 0.08 and 0.68 mmol of ligand/g of DFNS, respectively. We also studied the binding of small cis-diol molecules in the nanoscale pores of DFNS. The boronic acid modified DFNS with the polymer intermediate exhibits higher binding capacity for Alizarin Red S and nicotinamide adenine dinucleotide than the polymer-free DFNS. The two types of boronic acid modified DFNS can bind small cis-diol molecules in the presence of large glycoproteins, due in large part to the effect of size exclusion provided by the nanochannels in the DFNS.

Hollow MnFe2O4@C@APBA Nanospheres with Size Exclusion and pH Response for Efficient Enrichment of Endogenous Glycopeptides

Enrichment and detection of glycopeptides are an important clinical measure for the diagnosis of complex diseases. Enrichment materials play a key role in this process; they must have an effective sample-screening ability to eliminate the interference of nonglycopeptides. In this work, novel hollow MnFe₂O₄@C@APBA nanospheres (HMCAs) with magnetic and pH responsiveness were prepared for glycopeptide enrichment. The as-prepared composites have a suitable hollow structure and large specific surface area, and the boron hydroxyl group in their cavities can fix or disconnect the hydrophilic groups of the glycopeptides at different pH, so the glycopeptides can be adsorbed or desorbed in a controllable way. Enrichment results showed that the HMCAs exhibited an excellent enrichment performance: ultralow limit of detection (approximately 0.5 fmol μL^-1), perfect size-exclusion effect (HRP/BSA, 1:800, w/w), favorable universality (HRP, IgG, and RNase B), and high binding capacity (150 mg/g). In order to verify the application of materials in practice, the HMCAs were used for the analysis of complex samples and it was found that 474 glycopeptides were identified from 210 glycoproteins in three replicate analyses of 2 μL of human serum. The results showed that the HMCAs could be used as a promising enrichment material for glycopeptide characterization in MS-based glycoproteomics and related fields.

Metal-organic frameworks as advanced materials for sample preparation of bioactive peptides

Development of novel affinity materials and separation techniques is crucial for the progress of modern proteomics and peptidomics. Detection of peptides and proteins from complex matrices still remains a challenging task due to the highly complicated biological composition, low abundance of target molecules, and large dynamic range of proteins. As an emerging area of analytical science, metal-organic framework (MOF)-based separation of proteins and peptides is attracting growing interest. This minireview summarizes the recent advances in MOF-based affinity materials for the sample preparation of proteins and peptides. Some newly emerging MOF nanoreactors for the degradation of peptides and proteins are introduced. An update of MOF-based affinity materials for the isolation of glycopeptides, phosphopeptides and low-abundance endogenous peptides in the last two years is focused on. The separation mechanism is discussed along with the chemical structures of MOFs. Finally, the remaining challenges and future development of MOFs in analyzing peptides and proteins in complicated biological samples are discussed.

Molecularly Imprinted Polymer Nanoparticles: An Emerging Versatile Platform for Cancer Therapy

Molecularly imprinted polymers (MIPs) are chemically synthesized affinity materials with tailor-made binding cavities complementary to the template molecules in shape, size, and functionality. Recently, engineering MIP-based nanomedicines to improve cancer therapy has become a rapidly growing field and future research direction. Because of the unique properties and functions of MIPs, MIP-based nanoparticles (nanoMIPs) are not only alternatives to current nanomaterials for cancer therapy, but also hold the potential to fill gaps associated with biological ligand-based nanomedicines, such as immunogenicity, stability, applicability, and economic viability. Here, we survey recent advances in the design and fabrication of nanoMIPs for cancer therapy and highlight their distinct features. In addition, how to use these features to achieve desired performance, including extended circulation, active targeting, controlled drug release and anti-tumor efficacy, is discussed and summarized. We expect that this minireview will inspire more advanced studies in MIP-based nanomedicines for cancer therapy.

Visual detection of hepatocellular carcinoma cells with cell imprinted substrate and pH-sensitive allochroic-graphene oxide

Herein, we integrate cell-imprinted substrate (CIS) and allochroic-graphene oxide (AGO) for specific visualization sorting of hepatocellular carcinoma cells. The state-of-the-art-of detection method relies on the enzyme linked immunosorbent assay (ELISA)-like sandwich strategy with hierarchical recognition. The target tumor cells are first selectively captured by the CIS based on cell imprinted recognition, and then specifically labeled with AGO by boronate affinity recognition between boronic acid on AGO and cis-diols on the surface of target cells. The selectively recognition of CIS for target template cells is verified by cell function experiments. It is also worth mentioning that the AGO can specifically recognize target tumor cells under physiological pH, and then perform signal amplification and output through pH-triggered allochroism. The CIS linked AGO for cell assay (CIS-AGO-CA) is successfully used for visualization detection of human hepatocarcinoma HLE cells from hepatocyte suspension. When the hepatocyte suspension is spiked with 1.0 × 10⁵ cells, the recoveries of CIS-AGO-CA are 80.67 ± 4.33% for target HLE cells, and only 12.00 ± 1.00% for non-target Hep3B cells. It is worth emphasizing that the CIS-AGO-CA process is antibody-free. Therefore, this novel ELISA-like sandwich strategy is high specificity, cost-efficient and easy-to-use, and exhibits great prospect in the visualization sorting of tumor subpopulation.

Synthesis of molecularly imprinted polymers based on boronate affinity for diol-containing macrolide antibiotics with hydrophobicity-balanced and pH-responsive cavities

In this research, in order to separate and purify diol-containing macrolide antibiotics, like tylosin, from complex biological samples, molecularly imprinted polymer (MIP) based on boronate affinity for tylosin was synthesized by using precipitation polymerization method with 4-vinylphenylboronic acid (VPBA) and dimethyl aminoethyl methacrylate (DMAEMA) as pH-responsive functional monomers, and N,N'-methylene bisacrylamide (MBAA)/ ethylene glycol dimethacrylate (EGDMA) as the co-crosslinkers that balance the hydrophobicity of the MIP. The synthesized tylosin-MIP had the advantages of high adsorption capacity (120 mg/g), fast pH-responsiveness responsible for the accessibility of imprinted cavities, and high selectivity coefficient towards tylosin versus its analogues (2.8 versus spiramycin, 7.3 versus desmycosin) in an aqueous environment. The mechanism of boronate affinity between tylosin and VPBA in the form of charged hydrogen bonding was analyzed via density functional theory (DFT). MIPs were used to successfully separate diol-containing macrolides through molecularly imprinted solid phase extraction (MISPE). The results show that MIPs prepared in this method have a good application prospect in the separation and purification of the diol-containing macrolide antibiotics.

Advances and applications of in-tube solid-phase microextraction for analysis of proteins

In-tube solid-phase microextraction (IT-SPME) with capillary column as extraction device is a well-established green extraction technique with a lot of applications in the fields of biomedicine, food and environment. This article reviews the research contributions of IT-SPME for analysis of proteins. The paper first briefly describes the history of IT-SPME. Then, the development and principle of IT-SPME for analysis of proteins are introduced, in which capillary column configurations of IT-SPME and instruments for quantitative analysis of proteins are summarized. Subsequently, the synthesis strategy and recognition principle of different recognition units, including antibodies, aptamers, molecularly imprinted polymers, and boronate affinity materials, are discussed in detail. This part also introduces several rare recognition units, including lectins, restricted access materials, lysine modified with β-cyclodextrin and cell membrane. The development trend and possible future direction of IT-SPME for analysis of proteins are mentioned.

Boron Isotope Tag-Assisted Ultrahigh-Performance Liquid Chromatography Coupled with High-Resolution Mass Spectrometry for Discovery and Annotation of cis-Diol-Containing Metabolites

cis-Diol-containing metabolites are widely distributed in living organisms, and they participate in the regulation of various important biological activities. The profiling of cis-diol-containing metabolites could help us in fully understanding their functions. In this work, based on the characteristic isotope pattern of boron, we employed a boronic acid reagent as the isotope tag to establish a sensitive and selective liquid chromatography-high-resolution mass spectrometry method for the screening and annotation of cis-diol-containing metabolites in biological samples. Boronic acid reagent 2-methyl-4-phenylaminomethylphenylboronic acid was used to label the cis-diol-containing metabolites in biological samples to improve the selectivity and MS sensitivity of cis-diol-containing metabolites. Based on the characteristic 0.996 Da mass difference of precursor ions and the peak intensity ratio of 1:4 originating from ¹⁰B and ¹¹B natural isotopes, the potential cis-diol-containing metabolites were rapidly screened from biological samples. Potential cis-diol-containing metabolites were annotated by database searching and analysis of fragmentation patterns obtained by multistage MS (MSⁿ) via collision-induced dissociation. Importantly, the cis-diol position could be readily resolved by the MS³ spectrum. With this method, a total of 45 cis-diol-containing metabolites were discovered in rice, including monoglycerides, polyhydroxy fatty acids, fatty alcohols, and so forth. Furthermore, the established method showed superiority in avoiding false-positive results in profiling cis-diol-containing metabolites.

Intermolecular B-N coordination and multi-interaction synergism induced selective glycoprotein adsorption by phenylboronic acid-functionalized magnetic composites under acidic and neutral conditions

Abnormal protein glycosylation is associated with many diseases including cardiovascular disease, diabetes, and cancer. Therefore, selective capturing of glycoproteins under physiological or weak acid conditions (tumor microenvironment) is vital for disease diagnosis and further comprehensive analysis. Here, we propose a strategy of intermolecular B-N bond-based phenylboronic acid affinity to capture glycoproteins under neutral and slightly acidic conditions. Surprisingly, the captured glycoproteins were released in alkaline solution. This is contrary to the traditional phenylboric acid affinity, and we studied this from the perspective of materials, proteins, and incubation conditions. We identified the synergistic effect of intermolecular B-N bond-based phenylboronic acid affinity, electrostatic interaction, and polymer brush structure-based glycoprotein adsorption under slightly acidic conditions. The electrostatic repulsion between Fe3O4@SiO2@poly (2-aminoethyl methacrylate hydrochloride)-4-carboxyphenylboronic acid (Fe3O4@SiO2@PAMA-CPBA) nanoparticles and transferrin (TRF) was far greater than the specific binding between phenylboric acid of CPBA and glycosylation residues of TRF resulting in the release of the captured glycoproteins in alkaline solution. Fe3O4@SiO2@PAMA-CPBA nanoparticles exhibited different selectivity capabilities toward different glycoproteins in multiprotein solutions due to protein interactions. These results may pave a new way for the design of phenylboric acid-based materials towards glycoprotein adsorption in a physiological environment.

Recent trends in sorbents for bioaffinity chromatography

Isolation or enrichment of biological molecules from complex biological samples is mostly a prerequisite in proteomics, genomics, and glycomics. Different techniques have been used to advance the efficiency of the purification of biological molecules. Bioaffinity chromatography is one of the most powerful technique that plays an important role in the isolation of target biological molecules by the specific interactions with ligands that are immobilized on different support materials. This review examines the recent developments in bioaffinity chromatography particularly over the past 5 years in the literature. Also properties of supports, immobilization techniques, types of binding agents, and methods used in bioaffinity chromatography applications are summarized.

Separation and purification of horseradish peroxidase from horseradish roots using a novel integrated method

The aim of the present work was to develop a novel method integrating two-step aqueous two-phase extraction and temperature-controlled affinity precipitation for the separation and purification of horseradish peroxidase (HRP) from horseradish roots.

Controllable regio- and stereo-selective coupling reactions of homoallenylboronates

Unprecedented palladium-catalysed regio- and stereo-selective coupling reactions of homoallenylboronates with (hetero)aryl iodides, allyl bromides and alkynyl bromides in aqueous solution were successfully developed.