Study of the nature of recognition in molecularly imprinted polymers, II

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.

Origin of macromolecular crowding: Analysis of recognition mechanism of dual-template molecularly imprinted polymers by in silico prediction

Multi-template imprinting is one of the challenge for molecular imprinting since the selectivity and binding affinity for each analyte decrease significantly compared with the corresponding molecularly imprinting polymers (MIPs) against single template. In this work, molecular crowding effect was tried to remedy the problem of imprinting reduction caused by the competition of two templates. Methacrylic acid (ACR) was used as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and polystyrene (PS) as macromolecular crowding agent. With levofloxacin (S-OFX) as the first template, a number of compounds with varied chemical structure were chosen as the second template to investigate the imprinting effect of dual-template. When S-OFX and naproxen (S-NAP) was used as the dual-template, the imprinting factor (IF) of the resulting MIP for S-OFX was 20.1 and IF for S-NAP was 10.9. In contrast, for the single-template MIPs, IF for S-OFX was 22.4, and IF for S-NAP was 11.9. As a comparison, the IF of the DT-MIP prepared in absence of PS was only 2.3 for S-OFX and 1.0 for S-NAP. To analyze recognition mechanism of the molecular crowding-based imprinting system, molecular dynamics simulations to the chain structure of PS and binding modes between template and functional monomers was conducted by NAMD software. All the results displayed that molecular crowding is a promising method to improve the affinity of the dual-template imprinted polymer.

Solid-Phase Extraction of Active Compounds from Natural Products by Molecularly Imprinted Polymers: Synthesis and Extraction Parameters

Molecularly imprinted polymers (MIPs) are synthetic polymers with a predetermined selectivity for a particular analyte or group of structurally related compounds, making them ideal materials for separation processes. Hence, in sample preparation, MIPs are chosen as an excellent material to provide selectivity. Moreover, its use in solid-phase extraction, also referred to as molecular imprinted solid phase extraction (MISPE), is well regarded. In recent years, many papers have been published addressing the utilization of MIPs or MISPE as sorbents in natural product applications, such as synthesis. This review describes the synthesis and characterization of MIPs as a tool in natural product applications.

Magnetic-molecularly imprinted polymers in electrochemical sensors and biosensors

Magnetic particles, as well as molecularly imprinted polymers, have revolutionized separation and bioanalytical methodologies in the 1980s due to their wide range of applications. Today, biologically modified magnetic particles are used in many scientific and technological applications and are integrated in more than 50,000 diagnostic instruments for the detection of a huge range of analytes. However, the main drawback of this material is their stability and high cost. In this work, we review recent advances in the synthesis and characterization of hybrid molecularly imprinted polymers with magnetic properties, as a cheaper and robust alternative for the well-known biologically modified magnetic particles. The main advantages of these materials are, besides the magnetic properties, the possibility to be stored at room temperature without any loss in the activity. Among all the applications, this work reviews the direct detection of electroactive analytes based on the preconcentration by using magnetic-MIP integrated on magneto-actuated electrodes, including food safety, environmental monitoring, and clinical and pharmaceutical analysis. The main features of these electrochemical sensors, including their analytical performance, are summarized. This simple and rapid method will open the way to incorporate this material in different magneto-actuated devices with no need for extensive sample pretreatment and sophisticated instruments.

Evaluation of acrylamide-based molecularly imprinted polymer thin-sheets for specific protein capture-a myoglobin model

We evaluate a series of thin-sheet hydrogel molecularly imprinted polymers (MIPs), using a family of acrylamide-based monomers, selective for the target protein myoglobin (Mb). The simple production of the thin-sheet MIP offers an alternative biorecognition surface that is robust, stable and uniform, and has the potential to be adapted for biosensor applications. The MIP containing the functional monomer N-hydroxymethylacrylamide (NHMAm), produced optimal specific rebinding of the target protein (Mb) with 84.9% (± 0.7) rebinding and imprinting and selectivity factors of 1.41 and 1.55, respectively. The least optimal performing MIP contained the functional monomer N,N-dimethylacrylamide (DMAm) with 67.5% (± 0.7) rebinding and imprinting and selectivity factors of 1.11 and 1.32, respectively. Hydrogen bonding effects, within a protein-MIP complex, were investigated using computational methods and Fourier transform infrared (FTIR) spectroscopy. The quantum mechanical calculations predictions of a red shift of the monomer carbonyl peak is borne-out within FTIR spectra, with three of the MIPs, acrylamide, N-(hydroxymethyl) acrylamide, and N-(hydroxyethyl) acrylamide, showing peak downshifts of 4, 11, and 8 cm⁻¹, respectively.

Effect of the Molecularly Imprinted Polymer Component Ratio on Analytical Performance

Molecular imprinting technology is a new analytical method that is highly selective and specific for certain analytes in artificial receptor design. The renewal possibilities of this technology make it an ideal material for sundry application fields. Molecularly imprinted polymers (MIPs) are polymeric matrices that have molecules printed on their surfaces; these surfaces can chemically interact with molecules or follow the pattern of the available template cavities obtained using imprinting technology. A MIP is useful for separating and analysing complex samples, such as biological fluids and environmental samples, because it is a strong analytical recognition element that can mimick natural recognition entities like biological receptors and antibodies. The MIP components consist of the target template, functional monomer, crosslinker, polymerisation initiator, and porogen. The effectiveness and selectivity of a MIP are greatly influenced by variations in the components. This review will provide an overview of the effect of MIP component ratio on analytical performance to each target analyte; it will also provide a strategy to obtain the best MIP performance. For every MIP, each template : monomer : crosslinker ratio shows a distinct performance for a specific analyte. The effects of the template : monomer : crosslinker ratio on a MIP's analytical performances-measured by the imprinting factor, sorbent binding capacity, and sorbent selectivity-are briefly outlined.

Bioengineered Polymer/Composites as Advanced Biological Detection of Sorbitol: An Application in Healthcare Sector

Bioengineered polymers and nanomaterials have emerged as promising and advanced materials for the fabrication and development of novel biosensors. Nanotechnology-enabled biosensor methods have high sensitivity, selectivity and more rapid detection of an analyte. Biosensor based methods are more rapid and simple with higher sensitivity and selectivity and can be developed for point-of-care diagnostic testing. Development of a simple, sensitive and rapid method for sorbitol detection is of considerable significance to efficient monitoring of diabetes-associated disorders like cataract, neuropathy, and nephropathy at initial stages. This issue encourages us to write a review that highlights recent advancements in the field of sorbitol detection as no such reports have been published till the date. The first section of this review will be dedicated to the conventional approaches or methods that had been playing a role in detection. The second part focused on the emerging field i.e. biosensors with optical, electrochemical, piezoelectric, etc. approaches for sorbitol detection and the importance of its detection in healthcare application. It is expected that this review will be very helpful for readers to know the different conventional and recent detection techniques for sorbitol at a glance.

Effect of Formulation on the Binding Efficiency and Selectivity of Precipitation Molecularly Imprinted Polymers

This study investigated the effect of feed formulation: the template:functional monomer (T:fM) and functional monomer:crosslinker (fM:X) ratios as well as the initiator concentration, on the binding performance and selectivity of caffeine (CAF) and theophylline (THP) imprinted polymers obtained by precipitation polymerisation in acetonitrile at 60 °C using methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as functional monomer and crosslinker, respectively. Template incorporation, monitored by quantitative ¹H-NMR spectroscopy, ranged from 8 to 77% and was found to be more favourable at both high and low T:fM ratios, low fM:X ratio and high initiator concentration. The resulting T:fM ratio in most MIPs were found to be lower than their feed ratios. Incorporation of THP into the polymers was observed to be consistently higher than CAF and, for most MIPs, the observed binding capacities represent less than 10% of the incorporated template. Improved imprinting factors were obtained from molecularly imprinted polymers (MIPs) with high crosslinker content, i.e., fM:X ratio of 1:10, and high initiator concentration, i.e., initiator:total monomer (I:tM) ratio of 1:5, while T:fM ratio (1:2 to 1:8) was found not to influence binding capacities and imprinting factors (IF). The NIPs showed no preference for either CAF or THP in competitive selectivity studies while MIPs were observed to bind preferentially to their template with THP displaying higher selectivity (72⁻94%) than CAF (63⁻84%). Template selectivity was observed to increase with increasing initiator concentration, with MIPs from I:tM ratio of 1:5 shown to be the most selective towards CAF (84%) and THP (93%). The fM:X ratio only showed minimal effect on MIP selectivity. Overall, for the MIP systems under study, template incorporation, binding capacity, imprinting factor and selectivity are enhanced at a faster rate of polymerisation using an I:tM ratio of 1:5. Polymer particles obtained were between 66 to 140 nm, with MIPs generally smaller than their NIP counterparts, and have been observed to decrease with increasing T:fM and fM:X ratios and increase with increasing initiator concentration.

Isolation of sinapic acid from broccoli using molecularly imprinted polymers

A molecularly imprinted polymer was synthesized for the purpose of sinapic acid isolation from Egyptian nutraceutical Botrytis italica, L. (broccoli) due to its prominent medicinal and wide pharmacological activities. A computational study was first developed to determine the optimal template to functional monomer molar ratio. Based on the computational results, five polymers were synthesized using a bulk polymerization method with sinapic acid as the template molecule. Evaluation of the synthesized polymers binding performance was carried out using batch rebinding assay, which revealed that the molecularly imprinted polymer of molar ratio (1:4:20), template to functional monomer (4-vinyl pyridine) to crosslinker (ethylene glycol dimethacrylate) was of optimum performance, thus, this polymer was applied for sinapic acid isolation from closely related analogues. This represents a more practical approach to isolate sinapic acid from different natural extracts selectively.

Rational design of molecularly imprinted polymers

Molecular imprinting is the process whereby a polymer matrix is cross-linked in the presence of molecules with surface sites that can bind selectively to certain ligands on the polymer. The cross-linking process endows the polymer matrix with a chemical 'memory', such that the target molecules can subsequently be recognized by the matrix. We present a simple model that accounts for the key features of this molecular recognition. Using a combination of analytical calculations and Monte Carlo simulations, we show that the model can account for the binding of rigid particles to an imprinted polymer matrix with valence-limited interactions. We show how the binding multivalency and the polymer material properties affect the efficiency and selectivity of molecular imprinting. Our calculations allow us to formulate design criteria for optimal molecular imprinting.

Characterization of the Binding Properties of Molecularly Imprinted Polymers

The defining characteristic of the binding sites of any particular molecularly imprinted material is heterogeneity: that is, they are not all identical. Nonetheless, it is useful to study their fundamental binding properties, and to obtain average properties. In particular, it has been instructive to compare the binding properties of imprinted and non-imprinted materials. This chapter begins by considering the origins of this site heterogeneity. Next, the properties of interest of imprinted binding sites are described in brief: affinity, selectivity, and kinetics. The binding/adsorption isotherm, the graph of concentration of analyte bound to a MIP versus concentration of free analyte at equilibrium, over a range of total concentrations, is described in some detail. Following this, the techniques for studying the imprinted sites are described (batch-binding assays, radioligand binding assays, zonal chromatography, frontal chromatography, calorimetry, and others). Thereafter, the parameters that influence affinity, selectivity and kinetics are discussed (solvent, modifiers of organic solvents, pH of aqueous solvents, temperature). Finally, mathematical attempts to fit the adsorption isotherms for imprinted materials, so as to obtain information about the range of binding affinities characterizing the imprinted sites, are summarized.

Preparation of metallic pivot-based imprinted monoliths with a hydrophilic macromonomer

The hydrophilic macromonomer oligo(ethyleneglycol) methyl ether methacrylate (OEG) was introduced into a metal ion-mediated MIP matrix to achieve good selectivity and less hydrophobic character.

Water-compatible molecularly imprinted polymers prepared using metal–organic gel as porogen

A novel water-compatible approach suitable for molecular imprinting was described by using metal–organic gel (MOG) as the porogenic solvent.

Synthesis of imprinted monolithic column with high content of monomers in ionic liquid

A MIP monolith with good permeability was successfully achieved using a strategy involving a high content of monomers in a [BMIM][BF₄]-based green solvent.

Molecularly Imprinted Hydrogels for Affinity-controlled and Stimuli-responsive Drug Delivery

The performance of smart or intelligent hydrogels as drug-delivery systems (DDSs) can be notably improved if the network is endowed with high-affinity receptors for the therapeutic molecule. Conventional molecular imprinting technology aims to create tailored binding pockets (artificial receptors) in the structure of rigid polymers by means of a template polymerization, in which the target molecules themselves induce a specific arrangement of the functional monomers during polymer synthesis. Adaptation of this technology to hydrogel synthesis implicates the optimization of the imprinting pocket to be able to recover the high-affinity conformation when distorted by swelling or after the action of a stimulus. This chapter analyzes the implementation of the molecular imprinting technology to the synthesis of both non-responsive and responsive loosely cross-linked hydrogels, and provides recent examples of the suitability of the imprinted networks to attain affinity-controlled, activation-controlled or stimuli-triggered drug and protein release.

Targeted extraction of active compounds from natural products by molecularly imprinted polymers

One of the most promising separation techniques that have emerged during the last decade is based on the use of molecularly imprinted polymers (MIPs). MIPs are stable polymers that possess specific cavities designed for a template molecule, endowed with excellent selectivity compared to regular solid phase extraction techniques. Molecularly imprinted solid-phase extraction (MISPE) has already shown a high efficiency for the sample preparation from complex matrices. Natural products received huge attention in recent years. Indeed, the application of MISPE for the screening of natural products appears extremely interesting not only for the selective extraction of a target compound but also for the concomitant discovery of new drug candidates, promising sources of therapeutic benefits. In the present review, examples of recognition and separation of active components from natural extracts are emphasized. MIPs are very promising materials to mimic the recognition characteristics exhibited by enzymes or receptors although further developments are necessary to fully exploit their wide potential.

Molecularly imprinted nanoparticles prepared by miniemulsion polymerization as selective receptors and new carriers for the sustained release of carbamazepine

Water-compatible imprinted nanoparticles were prepared for carbamazepine as a template and used for the selective extraction and controlled release of carbamazepine. Assay materials and drug delivery carriers were typically used in aqueous environments, so it is generally preferable to prepare solvent-free molecularly imprinted nanoparticles in water using the miniemulsion polymerization method. The present work investigates a bio-analytical strategy generically applicable to imprinted materials for molecular recognition studies, including equilibrium and non-equilibrium binding, and release experiments, increasing the knowledge of the molecular interactions between the template molecules and imprinted nanoparticles. The results showed that the imprinted nanoparticles exhibited a higher binding level and slower release rate than non-imprinted nanoparticles. The selectivity of imprinted nanoparticles for carbamazepine studied in comparison with an analogue compound, oxcarbazepine, the main metabolite of carbamazepine. The recovery and selectivity of carbamazepine in human serum was determined to be 100%, 1.7 times that of oxcarbazepine. The results indicated that carbamazepine-imprinted nanoparticles are appropriate for serum level determination of the drug in therapeutic range. The template to functional monomer ratio as a key factor controlling the recognition and release kinetic mechanism of imprinted nanoparticles is discussed. The imprinted nanoparticles prepared at the appropriate template to functional monomer mole ratio (2:8) exhibited the best drug affinity (5.1 times higher) and a slower drug release rate due to the interaction of carbamazepine with the imprinted cavities within the nanoparticles. Loaded imprinted nanoparticles as drug reservoirs were able to prolong carbamazepine release, in 1% wt sodium dodecyl sulfate aqueous solution, for more than 8 days.

Preparation and evaluation of molecularly imprinted polymer liquid chromatography column for the separation of Cathine enantiomers

In this study molecular imprinting technology was employed to prepare a specific affinity sorbent for the resolution of Cathine, a chiral drug product. The molecularly imprinted polymer (MIP) was prepared by non-covalent molecular imprinting with either (+) or (-)-Cathine (threo-2-amino-1-hydroxy-1-phenyl propane; norpseudoephedrine) as the template. Methacrylic acid and ethylene glycol di-methacrylate were copolymerized in the presence of the template molecule. The bulk polymerization was carried out in chloroform with 2,2'-azobisisobutyronitrile as the initiator, at 5 °C and under UV radiation. The resulting MIP was ground into powders, which were slurry packed into analytical columns. After removal of template molecules, the MIP-packed columns were found to be effective for the resolution of (±)-Cathine racemates. The separation factor for the enantiomers ranged between 1.5 and 2.4 when the column was packed with MIP prepared with (+)-Cathine as the template. A separation factor ranging from 1.6 to 2.9 could be achieved from the column packed with MIP, prepared with (-)-Cathine as the template. Although the separation factor was higher with that previously obtained from reversed-phase column chromatography following derivatization with a chiral agent, elution peaks were broader due to the heterogeneity of binding sites on MIP particles and the possible non-specific interaction.