On the structure of molecularly imprinted polymers by modifying charge on functional groups through molecular dynamics simulations

Molecularly imprinted polymers (MIPs) have been widely applied in many fields owing to their advantages. The recognition mechanism between target molecules and MIPs and the influence of dominant factor on the recognition process are still poorly understood. In this paper, a cubic methacrylate-based MIP model was constructed, and the charge on carboxyl group atoms was changed artificially to investigate the recognition process. It is found that the diffusion coefficients of the target molecules (cholesterol) are not affected by polymer network structure. The recognition process is mainly determined by the mesh sizes of the polymer network. In addition, the structure of modified MIP systems was also discussed from the viewpoints of radial distribution function and hydrogen bonds system. These results suggest that the polymer matrix structure would be enhanced with an increase in charge. Thus, it influences the structure of the water molecules in the system a little.     

Comparison of monofunctional and multifunctional monomers in phosphate binding molecularly imprinted polymers

In this study, molecularly imprinted polymers (MIPs) prepared using a multifunctional and a monofunctional monomer were compared with respect to their affinities, selectivities, and imprinting efficiencies for organophosphates. This is of interest because multifunctional monomers have higher affinities than traditional monofunctional monomers for their target analytes and thus should yield MIPs with higher affinities and selectivities. However, polymers containing multifunctional monomer may also have a higher number of unselective, non-templated binding sites. This increase in background binding sites could lead to a decrease in the magnitude of the imprinting effect and in the selectivity of the MIP. Therefore, phosphate selective imprinted and non-imprinted polymers (NIPs) were prepared using a novel multifunctional triurea monomer. The binding properties of these polymers were compared with polymers prepared using a monofunctional monourea monomer. The binding affinities and selectivities of the monomers, imprinted polymers, and NIPs were characterized by NMR titration, binding uptake studies, and binding isotherms. MIPs prepared with the triurea monomer showed higher binding affinity and selectivity for the diphenylphosphate anion in organic solvents than the MIPs prepared with the monofunctional monomer. Surprisingly, the binding properties of the NIPs revealed that the polymers prepared using the multifunctional and monofunctional monomers were very similar in affinity and selectivity. Thus, the multifunctional monomers increase not only the affinity of the MIP but also enhance the imprinting effect.     

Incorporation of styrene enhances recognition of ribonuclease A by molecularly imprinted polymers

Ribonuclease A (RNase A) is an RNA-cleaving enzyme characterized by its high conformational stability and strong catalytic activity. This enzyme is ubiquitous in living organisms and is difficult to inactivate. In polymerase chain reaction (PCR) RNase activity is removed by adding inhibitors. Molecularly imprinted polymers (MIPs) with high selectivity, high stability, low cost and facile synthesis could prove useful in extraction of target molecules, such as RNase A, from reaction mixtures. In this investigation, MIPs were synthesized from the monomers styrene and polyethyleneglycol 400 dimethacrylate (PEG400DMA) in several different ratios. Styrene as a functional monomer gave MIPs with a higher affinity for RNase A than other functional monomers tested, according to both enzyme-linked immnuosorbent assay (ELISA) and isothermal titration calorimetry (ITC). The optimum volume ratio of styrene/PEG400DMA was 20/100 at 25 degrees C, and this ratio maximized the rebinding efficiency of RNase A to MIPs. Isothermal titration calorimetry was also used, and could be useful to design the composition of molecularly imprinted polymers for various target molecules.     

Separation and screening of compounds of biological origin using molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) represent a new class of materials possessing high selectivity and affinity for the target molecule. Since their discovery in 1972, molecularly imprinted polymers have attracted considerable interest from bio- and chemical laboratories to pharmaceutical institutes. They have been utilized as sensors, catalysts, sorbents for solid-phase extraction, stationary phase for liquid chromatography, mimics of enzymes, receptors and antibodies. Among which, the application of molecularly imprinted polymers for molecular recognition-based separation and screening of compounds has undergone rapid extension and received much attention in recent years. This article mainly focuses on the separation and screening of certain pharmacophoric compounds of interests from biological origin using molecular imprinting technology. Examples of extraction and recognition of active components as anti-tumors or anti-Hepatitis C virus inhibitors from Chinese traditional herbs using molecularly imprinting technology are particularized in this article. Comparison between the screening effect based on MIPs and that based on antibodies is also represented. Consequently the merits and demerits of these two technologies are highlighted.     

Preparation of molecularly imprinted polymers using nitroxide-mediated living radical polymerization

The use of molecularly imprinted polymers (MIPs) in chemical and bioanalytical applications has been gaining in interest in recent years. Compared to their biological receptor counterparts, MIPs are easy to prepare, have long shelf stability and can be used under a variety of harsh conditions. The majority of MIPs currently used are produced by traditional free radical polymerization. One drawback with the use of standard free radical initiators is that little control can be exerted over the chemical processes that form the final imprinted cavities. In this study we set out to investigate the application of controlled (living) free radical polymerization to the preparation of MIPs. This was exemplified by the synthesis of cholesterol-imprinted bulk polymers by nitroxide-mediated polymerization (NMP). A sacrificial covalent bond was employed to maintain imprinting fidelity at elevated temperature. Selective uptake of cholesterol from solutions in hexane was studied with imprinted polymers prepared under different conditions. The imprinted hydrolyzed MIP prepared by NMP displayed higher selective cholesterol binding than that prepared by a traditional radical polymerization.     

The microcontact imprinting of proteins: the effect of cross-linking monomers for lysozyme, ribonuclease A and myoglobin

The performance of molecularly imprinted polymers (MIPs) is of interest to researchers in the field of analytical chemistry, and in the pharmaceutical and food industries. Because the choice of the functional monomer(s) plays a key role in the selectivity of a MIP, the synthesis of an effective, tight-binding MIP can be difficult and time-consuming, involving the evaluation of the binding performance of MIPs of many different compositions. In this study, we report an express method combining molecular imprinting and microcontact printing techniques to prepare a polymer thin film as an artificial antibody. In addition to the microcontact printing technique, isothermal titration of monomers to proteins stamps was investigated to screen the functional monomer for MIPs. Finally, the importance of the choice of cross-linking monomers in MIPs was studied, and these studies suggest that monomers containing an optimal length PEG spacer give higher imprinting effectiveness. Several model antigens (lysozyme, ribonuclease A and myoglobin) were adsorbed on a cover glasses that were pretreated with hexamethyldisilazane (HMDS). These protein stamps were then contacted with different monomer solutions (cross-linking monomers) on a glass slide substrate. Photopolymerization yielded the molecularly imprinted polymer. This technique, analogous to microcontact printing, allows for the rapid, parallel synthesis of MIPs of different compositions, and requires very small volumes of monomers (ca. 4 microL). The technique also avoids potential solubility problems with the molecular targets. Of several cross-linking monomers screened, tetraethyleneglycol dimethacrylate (TEGDMA) gave the most selective lysozyme binding, while polyethyleneglycol 400 dimethacrylate (PEG400DMA) were most selective for ribonuclease A and myoglobin.     

HPLC-based bioseparations using molecularly imprinted polymers

HPLC-based separations of amino acids and peptides, nucleotide bases, drugs, sugars and steroids using molecularly imprinted polymers (MIPs) have been reviewed in this article. The molecular recognition mechanisms of the template molecules on the MIPs in organic and aqueous eluents were discussed. Furthermore, new polymerization methods suitable for preparations of HPLC columns and packing materials using molecular imprinting techniques, and their applications to HPLC-based separations are also dealt with.     

Application of molecularly imprinted polymers to solid-phase extraction of analytes from real samples

A review is presented of recent developments in the use of molecularly imprinted polymers (MIPs) as selective materials for solid-phase extraction. Compared with traditional sorbents, MIPs can not only concentrate but also selectively separate the target analytes from real samples, which is crucial for the quantitatively determination of analytes in complex samples. Consequently, as one of the most effective sorbents, MIPs have been successfully applied to the pretreatment of analytes in foods, drugs, and biological and environmental samples in the past five years.     

Application of molecularly imprinted polymers to solid-phase extraction of analytes from real samples

A review is presented of recent developments in the use of molecularly imprinted polymers (MIPs) as selective materials for solid-phase extraction. Compared with traditional sorbents, MIPs can not only concentrate but also selectively separate the target analytes from real samples, which is crucial for the quantitatively determination of analytes in complex samples. Consequently, as one of the most effective sorbents, MIPs have been successfully applied to the pretreatment of analytes in foods, drugs, and biological and environmental samples in the past five years.     

Towards water compatible MIPs for sensing in aqueous media

When synthesizing molecularly imprinted polymers (MIPs), a few fundamental principles should be kept in mind. There is a strong correlation between porogen polarity, MIP microenvironment polarity and the imprinting effect itself. The combination of these parameters eventually determines the overall binding behavior of a MIP in a given solvent. In addition, it is shown that MIP binding is strongly influenced by the polarity of the rebinding solvent. Because the use of MIPs in biomedical environments is of considerable interest, it is important that these MIPs perform well in aqueous media. In this article, various approaches are explored towards a water compatible MIP for the target molecule l-nicotine. To this end, the imprinting effect together with the MIP matrix polarity is fine-tuned during MIP synthesis. The binding behavior of the resulting MIPs is evaluated by performing batch rebinding experiments that makes it possible to select the most suitable MIP/non-imprinted polymer couple for future application in aqueous environments. One method to achieve improved compatibility with water is referred to as porogen tuning, in which porogens of varying polarities are used. It is demonstrated that, especially when multiple porogens are mixed, this approach can lead to superior performance in aqueous environments. Another method involves the incorporation of polar or non-polar comonomers in the MIP matrix. It is shown that by carefully selecting these monomers, it is also possible to obtain MIPs, which can selectively bind their target in water.     

Evaluating the potential of thermal read‐out techniques combined with molecularly imprinted polymers for the sensing of low‐weight organic molecules

In recent years, there has been a tremendous increase in the papers published on synthetic recognition elements. Molecularly imprinted polymers (MIPs), also referred to as “man‐made mimics” of antibodies, are able to rebind their template molecules with high affinity. Advantages compared with those of natural receptors include their excellent thermal and chemical stability, low cost, and ease of the production process. However, their use in commercial biosensors is limited owing to the difficulty to incorporate MIPs into suitable sensing platforms and traditional detection techniques, such as chromatography, that require bulky and sophisticated equipment. In this review, we evaluate the potential to use MIPs combined with thermal read‐out for the detection of low‐weight organic molecules. We discuss thermal methods to study MIP‐template complexation and to determine neurotransmitters concentrations. In particular, we highlight the heat‐transfer method, a recent technique that is straightforward and low cost and requires minimal instrumentation. Until now, sample preparation involves a 2‐step process, making it time‐consuming, and measuring biological samples is difficult owing to the noise in the signal. Different sample preparation methods are discussed, and it will be demonstrated how this affects the thermal response. An outlook is given in novel methods that can simplify and speed up sample preparation. Finally, we show a novel thermal technique, which is based on the analysis of transport of thermal waves rather than evaluating the fixed heat‐transfer resistance. Through applying the concept of thermal waves, signal‐noise ratio is significantly increased, which results in lower detection limits and has potential for the study of biological samples.     

Molecular imprinting in sol-gel matrix

Molecular imprinting is a newly developed methodology which provides molecular assemblies of desired structures and properties and is being increasingly used for several applications such as in separation processes, microreactors, immunoassays and antibody mimics, catalysis, artificial enzymes, biosensor recognition elements and bio- and chemo-sensors. The ambient processing conditions and versatility of the sol-gel process makes sol-gel glassy matrix suitable for molecular imprinting. The progress of sol-gel based molecular imprinted polymers (MIPs) for various applications can be seen from the growing number of publications. The main focus of the review is molecular imprinting in sol-gel matrix and applications of molecular imprinted sol-gel derived materials for the development of sensors. Combining sol-gel process with molecular imprinting enables to procure the sensors with greater sensitivity and selectivity necessary for sensing applications. The merits, problems, challenges and factors affecting molecular imprinting in sol-gel matrix have been discussed. Considerable attention has been drawn on recent developments like use of organically modified silane precursors (ORMOSILS) for the synthesis of hybrid molecular imprinted polymers (HMIPs) and applying surface sol-gel process for molecular imprinting. The development of molecular imprinted sol-gel nanotubes for biochemical separation and bio-imprinting is a new advancement and is under progress. Templated xerogels and molecularly imprinted sol-gel films provide a good platform for various sensor applications.     

A molecularly imprinted polymer on indium tin oxide and silicon

Molecular imprinting is a technique for creating artificial receptor sites in a polymer. Molecularly imprinted polymers (MIPs) are produced by forming a polymer around a molecule that is used as the template. Upon removal of the template, molecular holes remain which are specific in shape and size to the target molecule. In this research, a MIP was formed for theophylline using a copolymer of methacrylic acid and ethylene glycol dimethacrylate. The theophylline MIP was formed on two platforms: indium tin oxide (ITO) and silicon, which were used as the working electrode for cyclic voltammetry measurements. The presence of theophylline was measured using cyclic voltammetry and corresponded to the peak current on the cyclic voltammograms. The results of this research agreed with previous results of MIPs immobilized on an ITO platform. The peak currents of the MIP in the presence and absence of theophylline were compared to the blank polymer for each platform. The ratio of peak currents on ITO increased by a factor of 9.5 for the MIP compared to the non-imprinted polymer. Similarly, the ratio of peak currents on silicon increased by a factor of 6 compared to the non-imprinted polymer. This research demonstrated a procedure for evaluating a MIP layer on two different platforms.     

Molecular imprinting and solid phase extraction of flavonoid compounds

Molecularly imprinted polymers (MIPs) for quercetin have been successfully prepared by a thermal polymerization method using 4-vinylpyridine (4-VP) and ethylene glycol dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. The obtained molecularly imprinted polymers were evaluated by HPLC using organic eluents, with respect to their selective recognition properties for quercetin and related compounds of the flavonoid class. Two equivalent control polymers, a blank polymer and a polymer imprinted with a structural analogous template, were synthesized, in order to confirm the obtained results. Furthermore, preliminary experiments confirm the applicability of the prepared MIPs for solid phase extraction (SPE), as rapid and facile clean-up of wine samples for HPLC analysis is an envisaged field of application. The successful preparation of molecularly imprinted polymers for flavones provides an innovative opportunity for the development of advanced separation materials, with applications in the field of wine and fermentation analysis.     

Molecularly imprinted polymers in pseudoimmunoassay

Immunoassays are a class of analytical techniques based on the selective affinity of a biological antibody for its antigen. Competitive binding assays, of which the radioimmunoassay (RIA) was the first example, are based on the competition between analyte and a labelled probe for a limited number of binding sites. Molecularly imprinted polymers (MIPs) have been shown to be suitable replacements for biological antibodies in such techniques. Molecularly imprinted sorbent assays (MIAs) similar to RIA have been developed for a range of analytes of clinical and environmental interest. Limits of detection and selectivities of such assays are often similar to those using biological antibodies. Some assays have been used for measurements directly in biological fluids. The field is reviewed and it is shown that some perceived disadvantages of MIPs do not hinder their application in competitive binding assays: many MIAs have been demonstrated in aqueous solvents, and it has been shown that the quantity of template required to prepare imprinted polymers can be drastically reduced, and that binding site heterogeneity is not a problem as long as the sites which bind the probe most strongly are selective. Finally, recent developments including assays in microtitre plates, the use of enzyme-labelled probes, flow-injection assays and a scintillation proximity MIA are discussed.     

Non-covalent molecular imprinting with emphasis on its application in separation and drug development

The molecular imprinting technique can be defined as the formation of specific nano-sized cavities by means of template-directed synthesis. The resulting molecularly imprinted polymers (MIPs), which often have an affinity and a selectivity approaching those of antibody-antigen systems, have thus been coined "artificial antibodies." MIPs are characterized by their high specificity, ease of preparation, and their thermal and chemical stability. They have been widely studied in connection with many potential applications, including their use for separation and isolation purposes, as antibody mimics (biomimetic assays and sensors), as enzyme mimics, in organic synthesis, and in drug delivery. The non-covalent imprinting approach, developed mainly in Lund, has proven to be more versatile than the alternative covalent approach because of its preparation being less complicated and of the broad selection of functional monomers and possible target molecules that are available. The paper presents a review of studies of this versatile technique in the areas of separation and drug development, with emphasis being placed on work carried out in our laboratory.     

Fluorescent competitive flow-through assay for chloramphenicol using molecularly imprinted polymers

It is a fact that molecular imprinting techniques have reached tremendous importance in the research of new artificial recognition systems. These methods resemble the mechanism of natural recognition, generally based on non-covalent interactions, but improving their stability by means of a simple and inexpensive technique. Molecular imprinting polymers (MIPs) are easily obtained by copolymerisation of suitable functional monomers and crosslinkers in the presence of the print molecule. Removal of the template leaves a polymer that selectively recognises it. In this work, different imprinted polymers for chloramphenicol (CAP) obtained using different monomers and polymerisation conditions were tested in a HPLC system, in order to obtain a highly selective material for CAP. The optimised MIP was then used as recognition phase in a fluorescent competitive flow assay to determine chloramphenicol.     

Synthesis and evaluation of molecularly imprinted polymers for enalapril and lisinopril, two synthetic peptide anti-hypertensive drugs

Molecularly imprinted polymers (MIPs) for the recognition of enalapril and lisinopril were prepared using 4-vinylpyridine as the functional monomer. Following thermal polymerisation the resulting materials were crushed, ground and sieved. First generation MIPs were produced in protic polar porogenic solvents (mixture of methanol (MeOH) and acetonitrile (ACN)). These MIPs were used and validated as sorbents for solid phase extraction and binding assays. Second generation MIPs were produced with polar aprotic porogenic solvent (DMSO). These polymers were packed in HPLC columns in order to investigate their molecular recognition properties in a dynamic mode. The study of the mobile phase composition included two major parameters: organic modifier content and pH value. Retention factors illustrate selective binding of the template from the imprinted polymers, compared to structurally related compounds.     

Plastic antibody for the recognition of chemical warfare agent sulphur mustard

Molecularly imprinted polymers (MIPs) known as plastic antibodies (PAs) represent a new class of materials possessing high selectivity and affinity for the target molecule. Since their discovery, PAs have attracted considerable interest from bio- and chemical laboratories to pharmaceutical institutes. PAs are becoming an important class of synthetic materials mimicking molecular recognition by natural receptors. In addition, they have been utilized as catalysts, sorbents for solid-phase extraction, stationary phase for liquid chromatography and mimics of enzymes. In this paper, first time we report the preparation and characterization of a PA for the recognition of blistering chemical warfare agent sulphur mustard (SM). The SM imprinted PA exhibited more surface area when compared to the control non-imprinted polymer (NIP). In addition, SEM image showed an ordered nano-pattern for the PA of SM that is entirely different from the image of NIP. The imprinting also enhanced SM rebinding ability to the PA when compared to the NIP with an imprinting efficiency () of 1.3.     

Characterization of molecularly imprinted polymers using a new polar solvent titration method

A new method of characterizing molecularly imprinted polymers (MIPs) was developed and tested, which provides a more accurate means of identifying and measuring the molecular imprinting effect. In the new polar solvent titration method, a series of imprinted and non‐imprinted polymers were prepared in solutions containing increasing concentrations of a polar solvent. The polar solvent additives systematically disrupted the templation and monomer aggregation processes in the prepolymerization solutions, and the extent of disruption was captured by the polymerization process. The changes in binding capacity within each series of polymers were measured, providing a quantitative assessment of the templation and monomer aggregation processes in the imprinted and non‐imprinted polymers. The new method was tested using three different diphenyl phosphate imprinted polymers made using three different urea functional monomers. Each monomer had varying efficiencies of templation and monomer aggregation. The new MIP characterization method was found to have several advantages. To independently verify the new characterization method, the MIPs were also characterized using traditional binding isotherm analyses. The two methods appeared to give consistent conclusions. First, the polar solvent titration method is less susceptible to false positives in identifying the imprinting effect. Second, the method is able to differentiate and quantify changes in binding capacity, as measured at a fixed guest and polymer concentration, arising from templation or monomer aggregation processes in the prepolymerization solution. Third, the method was also easy to carry out, taking advantage of the ease of preparing MIPs. Copyright © 2014 John Wiley & Sons, Ltd.