Recognition of Sialic Acid Using Molecularly Imprinted Polymer

Elucidation of the Binding Orientation in α2,3- and α2,6-Linked Neu5Ac-Gal Epitopes toward a Hydrophilic Molecularly Imprinted Monolith

N-Acetylneuraminic acid and its α2,3/α2,6-glycosidic linkages with galactose (Neu5Ac-Gal) are major carbohydrate antigen epitopes expressed in various pathological processes, such as cancer, influenza, and SARS-CoV-2. We here report a strategy for the synthesis and binding investigation of molecularly imprinted polymers (MIPs) toward α2,3 and α2,6 conformations of Neu5Ac-Gal antigens. Hydrophilic imprinted monoliths were synthesized from melamine monomer in the presence of four different templates, namely, N-acetylneuraminic acid (Neu5Ac), N-acetylneuraminic acid methyl ester (Neu5Ac-M), 3'-sialyllactose (3SL), and 6'-sialyllactose (6SL), in a tertiary solvent mixture at temperatures varying from -20 to +80 °C. The MIPs prepared at cryotemperatures showed a preferential affinity for the α2,6 linkage sequence of 6SL, with an imprinting factor of 2.21, whereas the α2,3 linkage sequence of 3SL resulted in nonspecific binding to the polymer scaffold. The preferable affinity for the α2,6 conformation of Neu5Ac-Gal was evident also when challenged by a mixture of other mono- and disaccharides in an aqueous test mixture. The use of saturation transfer difference nuclear magnetic resonance (STD-NMR) on suspensions of crushed monoliths allowed for directional interactions between the α2,3/α2,6 linkage sequences on their corresponding MIPs to be revealed. The Neu5Ac epitope, containing acetyl and polyalcohol moieties, was the major contributor to the sequence recognition for Neu5Ac(α2,6)Gal(β1,4)Glc, whereas contributions from the Gal and Glc segments were substantially lower.

Sialyl-Tn Antigen-Imprinted Dual Fluorescent Core-Shell Nanoparticles for Ratiometric Sialyl-Tn Antigen Detection and Dual-Color Labeling of Cancer Cells

Sialyl-Tn (STn or sialyl-Thomsen-nouveau) is a carbohydrate antigen expressed by more than 80% of human carcinomas. We here report a strategy for ratiometric STn detection and dual-color cancer cell labeling, particularly, by molecularly imprinted polymers (MIPs). Imprinting was based on spectroscopic studies of a urea-containing green-fluorescent monomer 1 and STn-Thr-Na (sodium salt of Neu5Acα2-6GalNAcα-O-Thr). A few-nanometer-thin green-fluorescent polymer shell, in which STn-Thr-Na was imprinted with 1, other comonomers, and a cross-linker, was synthesized from the surface of red-emissive carbon nanodot (R-CND)-doped silica nanoparticles, resulting in dual fluorescent STn-MIPs. Dual-color labeling of cancer cells was achieved since both red and green emissions were detected in two separate channels of the microscope and an improved accuracy was obtained in comparison with single-signal MIPs. The flow cytometric cell analysis showed that the binding of STn-MIPs was significantly higher (p < 0.001) than that of non-imprinted polymer (NIP) control particles within the same cell line, allowing to distinguish populations. Based on the modularity of the luminescent core-fluorescent MIP shell architecture, the concept can be transferred in a straightforward manner to other target analytes.

Understanding the Molecular Structure of the Sialic Acid-Phenylboronic Acid Complex by using a Combined NMR Spectroscopy and DFT Study: Toward Sialic Acid Detection at Cell Membranes

The origin of the unusually high stability of the sialic acid (SA) and phenylboronic acid (PBA) complex was investigated by a combined nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) study. SA is a glycan-terminating monosaccharide, and its importance as a clinical target has long been recognized. Inspired by the fact that the binding properties of SA-PBA complexation are anomalously high relative to those of typical monosaccharides, great effort has been made to build a clinical platform with the use of PBA as a SA-selective receptor. Although a number of applications have been reported in recent years, the ability of PBA to recognize SA-terminating surface glycans selectively is still unclear, because high-affinity SA-PBA complexation might not occur in a physiological environment. In particular, different forms of SA (α- and β-pyranose) were not considered in detail. To answer this question, the combined NMR spectroscopy/DFT study revealed that the advantageous binding properties of the SA-PBA complex arise from ester bonding involving the α-carboxylate moieties (C1 and C2) of β-SA but not α-SA. Moreover, the facts that the C2 atom is blocked by a glycoside bond in a physiological environment and that α-SA basically exists on membrane-bound glycans in a physiological environment lead to the conclusion that PBA cannot selectively recognize the SA unit to discriminate specific types of cells. Our results have a significant impact on the field of SA-based cell recognition.

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

Boronate affinity materials, as unique sorbents, have emerged as important media for the selective separation and molecular recognition of cis-diol-containing compounds. With the introduction of boronic acid functionality, boronate affinity materials exhibit several significant advantages, including broad-spectrum selectivity, reversible covalent binding, pH-controlled capture/release, fast association/desorption kinetics, and good compatibility with mass spectrometry. Because cis-diol-containing biomolecules, including nucleosides, saccharides, glycans, glycoproteins and so on, are the important targets in current research frontiers such as metabolomics, glycomics and proteomics, boronate affinity materials have gained rapid development and found increasing applications in the last decade. In this review, we critically survey recent advances in boronate affinity materials. We focus on fundamental considerations as well as important progress and new boronate affinity materials reported in the last decade. We particularly discuss on the effects of the structure of boronate ligands and supporting materials on the properties of boronate affinity materials, such as binding pH, affinity, selectivity, binding capacity, tolerance for interference and so on. A variety of promising applications, including affinity separation, proteomics, metabolomics, disease diagnostics and aptamer selection, are introduced with main emphasis on how boronate affinity materials can solve the issues in the applications and what merits boronate affinity materials can provide.

Boronate-Affinity Glycan-Oriented Surface Imprinting: A New Strategy to Mimic Lectins for the Recognition of an Intact Glycoprotein and Its Characteristic Fragments

Lectins possess unique binding properties and are of particular value in molecular recognition. However, lectins suffer from several disadvantages, such as being hard to prepare and showing poor storage stability. Boronate-affinity glycan-oriented surface imprinting was developed as a new strategy for the preparation of lectin-like molecularly imprinted polymers (MIPs). The prepared MIPs could specifically recognize an intact glycoprotein and its characteristic fragments, even within a complex sample matrix. Glycan-imprinted MIPs could thus prove to be powerful tools for important applications such as proteomics, glycomics, and diagnostics.

Surface-enhanced Raman scattering imaging of cancer cells and tissues via sialic acid-imprinted nanotags

Sialic acid-imprinted nanotags were designed and synthesized for surface-enhanced Raman scattering for imaging of cancer cells and tissues.

Photolithographic boronate affinity molecular imprinting: a general and facile approach for glycoprotein imprinting

Better than expected: With a regular boronic acid as the functional monomer, a general and facile approach for glycoprotein imprinting exhibited several highly favorable features that are beyond normal expectation, which make the prepared MIPs feasible for the recognition of trace glycoproteins in complicated real samples.

Glyco-macroligand microarray with controlled orientation and glycan density

We report a new type of glycan microarray, namely, oriented and density-controlled glyco-macroligand microarray based on end-point immobilization of glycopolymer that was accompanied with boronic acid (BA) ligands in different sizes as detachable "temporary molecular spacers". Briefly, an O-cyanate chain-end functionalized lactose-containing glycopolymer was pre-complexed with polyacrylamide-BA, lysozyme-BA, and bovine serum albumin (BSA)-BA conjugates as macromolecular spacers first and then immobilized onto an amine-functionalized glass slide via isourea bond formation both at pH 10.3, respectively. Subsequently, the macromolecular spacers were detached from the immobilized glycopolymers at pH 7.4 so as to afford the oriented and density controlled glycopolymer microarrays. The spaced glycopolymer microarray showed enhanced lectin (Arachis hypogaea) binding compared to a non-spaced one. Among them, the polyacrylamide-BA spaced glycopolymer showed the highest level of lectin binding compared to lysozyme-BA- and BSA-BA-spaced glycopolymers. Furthermore, SPR results confirmed the same trend of density-dependent lectin binding as the glycoarray. This glyco-macroligand microarray platform permits variations of glycan density in the polymer, glycopolymer density and its orientation on the microarray surface and thus will provide a versatile tool for profiling glycan recognition for both basic biological research and practical applications.

Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003

Over 1450 references to original papers, reviews and monographs have herein been collected to document the development of molecular imprinting science and technology from the serendipitous discovery of Polyakov in 1931 to recent attempts to implement and understand the principles underlying the technique and its use in a range of application areas. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by papers dealing with fundamental aspects of molecular imprinting and the development of novel polymer formats. Thereafter, literature describing attempts to apply these polymeric materials to a range of application areas is presented.

Molecular imprinting: a dynamic technique for diverse applications in analytical chemistry

Continuous advances in analyzing complex matrices, improving reliability and simplicity, and performing multiple simultaneous assays with extreme sensitivity are increasing. Several techniques have been developed for the quantitative assays of analytes at low concentrations (e.g., high-pressure liquid chromatography, gas chromatography, immunoassay and the polymerase chain reaction technique). To achieve highly specific and sensitive analysis, high affinity, stable, and specific recognition agents are needed. Although biological recognition agents are very specific and sensitive they are labile and/or have a low density of binding sites. During the past decade molecular imprinting has emerged as an attractive and highly accepted tool for the development of artificial recognition agents. Molecular imprinting is achieved by the interaction, either noncovalent or covalent, between complementary groups in a template molecule and functional monomer units through polymerization or polycondensation. These molecularly imprinted polymers have been widely employed for diverse applications (e.g., in chromatographic separation, drug screening, chemosensors, catalysis, immunoassays etc.) owing to their specificity towards the target molecules and high stability against physicochemical perturbations. In this review the advantages, applications, and recent developments in molecular imprinting technology are highlighted.

New synthetic ways for the preparation of high-performance liquid chromatography supports

The latest developments and in particular important synthetic aspects for the preparation of modern HPLC supports are reviewed. In this context, the chemistry of inorganic supports based on silica, zirconia, titania or aluminum oxide as well as of organic supports based on poly(styrene-divinylbenzene), acrylates, methacrylates and other, more specialized polymers is covered. Special consideration is given to modern approaches such as sol-gel technology, molecular imprinting, perfusion chromatography, the preparation of monolithic separation media as well as to organic HPLC supports prepared by new polymer technologies such as ring-opening metathesis polymerization. Synthetic particularities relevant for the corresponding applications are outlined.

Molecular imprinting: developments and applications in the analytical chemistry field

In analytical separation science, molecularly imprinted polymers have been applied in several analytical techniques, such as liquid chromatography, capillary electrochromatography and capillary electrophoresis, solid phase extraction, immunoassay, and as a selective sorbent in chemical sensors. A benefit of imprinted polymers is the possibility to prepare sorbents with selectivity pre-determined for a particular substance, or group of structural analogues. The application most close to a wider acceptance is probably that of solid phase extraction for clean-up of environmental and biological samples. The improved selectivity of imprinted polymers compared with conventional sorbents may lead to cleaner chromatographic traces in the subsequent analytical separation. Furthermore, the solid phase extraction application does not suffer from drawbacks generally associated with imprinted polymers in chromatography, such as peak broadening and tailing. Most liquid chromatographic studies have focused on using imprinted polymers as chiral stationary phases for enantiomer separations. Also, the use of imprinted polymers as selective sorbents in capillary electrochromatography has been presented. For this purpose, a protocol to prepare superporous, monolithic imprinted polymer-based capillary columns has been developed. Due to the high affinities and selectivities often achievable, imprinted polymers have been considered as alternative binding entities in biosensors and in immunoassay type protocols. Here, high stability, easy preparation and ability to be used for assay of both aqueous and organic solvent based samples are advantages of the polymers.

Separation and sensing based on molecular recognition using molecularly imprinted polymers

Molecular recognition-based separation and sensing systems have received much attention in various fields because of their high selectivity for target molecules. Molecular imprinting has been recognized as a promising technique for the development of such systems, where the molecule to be recognized is added to a reaction mixture of a cross-linker(s), a solvent(s), and a functional monomer(s) that possesses a functional groups(s) capable of interacting with the target molecule. Binding sites in the resultant polymers involve functional groups originating from the added functional monomer(s), which can be constructed according to the shape and chemical properties of the target molecules. After removal of the target molecules, these molecularly imprinted complementary binding sites exhibit high selectivity and affinity for the template molecule. In this article, recent developments in molecularly imprinted polymers are described with their applications as separation media in liquid chromatography, capillary electrophoresis, solid-phase extraction, and membranes. Examples of binding assays and sensing systems using molecularly imprinted polymers are also presented.