Recognition and enantioselection of drugs and biochemicals using molecularly imprinted polymer technology

Determination of methimazole based on electropolymerized-molecularly imprinted polypyrrole modified pencil graphite sensor

Preparation of a molecularly imprinted polymer (MIP) film and its recognition property for methimazole (MMZ) was investigated. The polypyrrole (PPy) film was prepared by the cyclic voltammetric deposition of pyrrole in the presence of a supporting electrolyte (NaClO₄·H₂O) with and without MMZ through on a pencil graphite electrode (PGE). A computational study based on density functional theory was developed to evaluate the template-monomer geometry and interaction energy in the prepolymerization mixture. The performance of MIP sensor and non-imprinted polymer (NIP) film was evaluated by differential pulse voltammetry (DPV). The most important parameters controlling the performance of sensor were investigated and optimized. The prepared electrode was used for MMZ measurement by a three-step procedure, including analyte extraction in the electrode, electrode washing and electrochemical measurement of MMZ. The molecularly imprinted film exhibited a high selectivity and sensitivity toward methimazole in the experimental conditions. The calibration curve demonstrated linearity over a concentration range of 0.007-6mM with a correlation coefficient (r²) of 0.9808. The accuracy of the method was studied through spiking blank samples showed recovery of 98% with precision of 4%. Limit of detection based on S/N=3 was obtained 3×10^-6M. The proposed sensor was applied successfully to determine MMZ in biological model samples and pharmaceuticals.

Molecularly imprinted beads by surface imprinting

Molecular imprinting is a state-of-the-art technique for imparting molecular recognition properties to a synthetic polymeric matrix. Conventionally, the technique is easily carried out using bulk imprinting, where molecularly imprinted polymers (MIPs) are prepared in large chunks and post-treatment processes like grinding and sieving are then required. However, this strategy tends to produce sharp-edged, irregular MIP bits with a limited scope of direct application. In addition, due to the creation of binding sites within the polymeric bulk, the issue of the hindrance of adsorbate diffusion (especially in the case of macromolecules) during template rebinding makes the MIPs prepared through this approach unsuitable for practical applications. Thus over the years, many efforts to address the limitations of conventional molecular imprinting techniques have resulted in new imprinting methodologies. Systems like suspension and precipitation polymerization, where MIPs with tunable morphologies can be prepared, have been developed. Additionally, strategies like surface imprinting have also been employed. Ultimately, both of these approaches have been combined to prepare regularly shaped surface-imprinted MIP beads. Such an approach incorporates the advantages of both methodologies at the same time. Given their desirable physical morphologies and favorable adsorption kinetics, MIPs prepared in this manner show significant promise for industrial applications. Therefore, they will be the main focus of this review.

Surface imprinting strategies for the detection of trypsin

Self-organized receptor layers are synthesized by molecular imprinting methods directly on pre-coated 10 MHz quartz-crystal microbalances (QCMs). The surface-imprinting is performed by three methods using amorphous, crystalline and solubilized trypsin, respectively, as templates. These attempts allowed us to compare imprinting results obtained with templating proteins in the dry state as well as in aqueous solution. All methods are generally applicable for surface imprinting of thin films. The biomimetic sensor layers allow selective enzyme enrichment on the imprinted electrode with detection limits as low as 100 ng ml(-1) and response times of a few minutes. Solution-based polymer imprinting with native trypsin as template resulted in the highest specific enzyme recognition, which even allowed us to distinguish denatured trypsin from the native form.

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.

Imprinted polymers for chiral resolution of (+/-)-ephedrine: understanding the pre-polymerisation equilibrium and the action of different mobile phase modifiers

A thorough study has been made of the ephedrine-methacrylic acid (MAA) system for molecular imprinting, involving NMR studies of the pre-polymerisation equilibria, modelling and HPLC enantioseparations with different mobile phases. When dimerisation of MAA is accounted for, NMR titrations demonstrate there is a very strong ('stoichiometric', K approximately 10000 M(-1)) interaction between ephedrine and a single MAA monomer. Polymers prepared with a 1:1 monomer:template ratio are capable of enantioseparation, indicating, in combination with the NMR results, that the 1:1 interaction probably involves the carboxylic acid acting as a chelating monomer, forming hydrogen bonds to both the template amine and hydroxyl moieties. Higher monomer:template ratios cause further changes in the NMR signals, suggesting at least one further MAA can interact with the amine group, with a weaker association constant (K approximately 80 M(-1)). Polymers prepared with a 4:1 monomer:template ratio are thus proposed to contain a mixture of 1-monomer binding sites and 2-monomer binding sites, the latter being of enhanced acidity. In HPLC, better results are obtained with the 4:1 polymer using acetic acid as a modifier, while better results are obtained for the 1:1 polymer using butylamine as a modifier. We propose a model whereby acetic acid exerts its effect by reducing binding to the 1-monomer sites, while butylamine works largely through blocking the most acidic, 2-monomer sites. For preparative chromatography we suggest the 1:1 polymer, with a larger population of weaker but more uniform binding sites, is most promising.

Application of a molecularly imprinted polymer for the effective recognition of different anti-epidermal growth factor receptor inhibitors

A molecularly imprinted polymer (MIP) was prepared using (E)-piceatannol, a natural potential anti-epidermal growth factor receptor (EGFR) inhibitor, as the template and 4-vinylpyridine as the functional monomer. The template was isolated from a Chinese traditional Tibetan medicinal herb, Caragana jubata, by a solid-phase extraction procedure. The crude extract of this herb was loaded on the MIP column for the binding test, and two different compounds besides the template itself were specifically recognized by the polymer, which were identified to be butein and quercetin possessing potent anti-EGFR tyrosine kinase activities with IC(50) values of 10 and 15 microM, respectively. Affinity and selectivity for these inhibitors and another three compounds coexisting with the template in this herb were evaluated in the chromatographic mode. For the first time, the affinity of a molecularly imprinted polymer was investigated to be correlative to the bioactivities of the analytes. The chromatographic behavior of the analytes was consistent with their activity values: the more active inhibitor was retained longer on the MIP. This research work afforded us a new approach for the effective recognition of novel anti-EGFR inhibitors from herbs by using the MIP as the receptor mimic to assay the bioactivities of reserved components, which will be very helpful in the direct separation of lead candidates for anticancer drugs.

Effect of solvents on the selectivity of terbutylazine imprinted polymer sorbents used in solid-phase extraction

A solid-phase extraction sample preparation method using a molecularly imprinted polymer (MIP) selective for the triazine type pesticide terbutylazine has been developed. The method involves preconcentration from large volumes of water samples on a C18 disk coupled to selective clean-up on the MIP. The method has been optimised by studying the recovery and retention of terbutylazine and some other structurally related triazine derivates as a function of the selective washing solvent used. The effect of the water content of the selective washing solvent was also investigated on the recovery of the MIP. River water samples were analysed with the coupled technique, and efficient clean-up of the samples was observed.

The use of high pressure for separation and production of bioactive molecules

Due to its action on the forces governing inter- and intramolecular interactions, the application of high pressure to biopurification or bio-elaboration of a product are of interest. The two closely thermodynamically related parameters, pressure and temperature, render processes based on their action clean, as no chemical reagents have to be added (and thus further removed) when they are applied. The use of high pressure in the development of desorption methods for the purification of bioactive molecules, particularly in the immunoaffinity field, is reviewed and discussed. Also mentioned is the application of the pressure parameter during the synthesis of a bioreagent. Finally, integrated processes relative to the synthesis and purification of these compounds are proposed.

Bioimprinting of polymers and sol-gel phases. Selective detection of yeasts with imprinted polymers

Coated quartz crystal microbalances were modified with a surface-imprinting process using whole yeast cells. These molded polymer and sol-gel surfaces show honeycomb-like structures as shown by atomic force microscopy. Reinclusion of cells allows a selective on-line monitoring of these microorganism concentrations in water over 5 orders of magnitude. The sensitivity to cells holds up in growth media up to 21 g/L. Even cell fragments can be detected in flowing conditions. The highly robust polymers on the sensor devices are suitable for biotechnological applications.

Selective solid-phase extraction sorbent for caffeine made by molecular imprinting

A molecularly imprinted polymer (MIP) was prepared with caffeine as the template molecule. Thermal polymerisation (60 degrees C) was optimised, varying ratios of monomer, cross linker and template. The polymer was used as a solid-phase extraction (SPE) sorbent, for selective trapping and pre-concentration of caffeine. Caffeine was loaded on the MIP-SPE cartridge using different loading conditions (solvents, pH value). Washing and elution of the caffeine bound to the MIP was studied utilising different protocols. The extraction protocol was successfully applied to the direct extraction of caffeine from beverages and spiked human plasma.

Target specific sample preparation from aqueous extracts with molecular imprinted polymers

In this paper we report a method for the synthesis of molecular imprinted polymers for use in sample preparation with aqueous biological materials. Highly cross-linked bulk polymers were synthesized in the presence of the template molecule, 2,6-pyridinedicarboxylic acid (DPA) using acrylamide (ACD) and 4-vinylpyridine (VP) as functional monomers. Conditions are described for the optimization of the template complex with temperature, copolymer mixture and crosslinker type. Selective binding of the template molecule is demonstrated in comparison to structural isomers and analogs for molecular imprinted polymers (MIPs) synthesized with three different crosslinkers, ethyleneglycol dimethacrylate (EGDMA), bisacrylamide and N,N'-1,3-phenylene bismethacrylamide (PBMA). The chromatographic capacity factors and selectivities for a series of structural analogs were compared. Molecular imprinted polymers prepared with equimolar ratios of ACD and VP and either PBMA or bisacrylamide resulted in highly selective binding for the template versus analogs with similar structure and chemistry. Multiple molecular dissociation constants were measured with the maximum binding capacities for EGDMA, PBMA and bisacrylamide measuring 17, 27 and 90 micromol/g, respectively.

Increasing the sensitivity of piezoelectric odour sensors based on molecularly imprinted polymers

The molecular imprinting technique has been used to create sensors with a predetermined selectivity for molecules in the gas phase. Based on previous results, piezoelectric quartz crystals were first coated with a layer of nylon, to provide increased sensitivity, and then a layer of a polymer imprinted with 2-methylisoborneol (MIB) was applied to endow the device with selectivity. The response of the 'imprinted' sensor was significantly higher than the response of the 'non-imprinted' sensor at MIB concentrations above 10 ppb. Our new sensor is thus 20 times more sensitive than our previous device. At concentrations greater than 10 ppb, the response of the 'non-imprinted' sensor to geosmin, another odorant often accompanying MIB, was significantly higher than the response of the 'imprinted' sensor. A number of other odorants were examined and, as in our previous work, the responses of the 'non-imprinted' sensors were found to be to greater than the responses of the 'imprinted' sensors.

Alternative methods providing enhanced sensitivity and selectivity in capillary electroseparation experiments

The study of alternative and novel techniques for altering selectivity and enhancing sensitivity as well as injection and detection protocols are important in the ongoing development of capillary electroseparation protocols. Some recent research from our laboratory in these fields is presented and discussed in this review. To improve sensitivity an off-line sample enrichment technique utilising solvent evaporation in a levitated drop or an on-line solid-phase extraction protocol was used. The selectivity was tuned by the use of protein gels or molecularly imprinted polymer mediated capillary electrochromatography. Furthermore, a picolitre droplet injection method is described as well as a detection protocol based on laser-induced fluorescence imaging.

A new application of molecularly imprinted materials

We have studied the possibility of shifting a thermodynamically unfavourable enzymatic equilibrium towards product formation via the addition of a highly specific adsorbent. The commercially interesting enzymatic condensation of Z-L-aspartic acid with L-phenylalanine methyl ester to the sweetener aspartame was chosen as the model system. Extremely stable and specific adsorbents for the product Z-L-Asp-L-Phe-OMe (Z-aspartame) were prepared using the emerging technique of molecular imprinting. A considerable increase (40%) in the yield of product was obtained when such adsorbents were present during the enzymatic reaction. The message of this investigation is that the use of such specific, sterilizable adsorbents should be considered for enzymatic processes to increase the yield. Finally, the direct isolation of a product formed by the retrieval of the adsorbents carrying the product can be envisaged, especially if the adsorbents are magnetic.

Novel chiral recognition elements for molecularly imprinted polymer preparation

The use of a novel chiral functional monomer system in molecular imprinting protocols is described. The monomer, dibenzyl (2R,3R)-O-monoacryloyl tartrate, possesses a hydroxyl moiety which can be used to direct template-functional monomer interactions during molecular imprinting polymerization. This system simultaneously positions benzyl ester-protected carboxyl groups in close proximity to the template, which upon deprotection yield recognition sites with stronger ligand-binding capacities. Furthermore, the inherent chirality of the monomer engenders the polymer with an inbuilt preference for a given stereoisomer. Application of the system to the molecular imprinting of the cinchonidine alkaloids (+)-cinchonine and (-)-cinchonidine yielded stereoselective polymers. The effect of imprinting (+)-cinchonine produced a polymer which more than reversed the inherent chiral selectivity of the chiral monomer residues present in the matrix.

Theophylline molecularly imprinted polymer dissociation kinetics: a novel sustained release drug dosage mechanism

The template release kinetics of theophylline molecularly imprinted polymers has been examined with a view to determining their potential as a controlled release drug dosage form. The basis for the ligand selectivity of these polymers has been shown through the demonstration of pre-polymerization template-monomer complexation and HPLC studies of the product polymer ligand selectivities. The release kinetics shows a dependence upon template loading and pH. Small differences in release characteristics between imprinted and non-imprinted (reference) polymers have been observed.

Imprinted polymers as tools for the recovery of secondary metabolites produced by fermentation

Imprinted polymers were synthesized using a mixture of pigments, N-glutamyl-rubropuctamine, and N-glutamyl-monascorubramine (I) as the template, and 2-methacrylamido-6-picoline or 4-aminostyrene as functional monomers, to obtain recognition materials capable of forming hydrogen bonds and charge interactions, respectively, with carboxyl groups of target I in the binding sites. The polymers were prepared thermally at a template loading of 5 mol% using ethylene-glycol dimethacrylate or trimethylolpropane trimethacrylate as crosslinkers and acetonitrile or tetrahydrofuran as porogens. The selective binding of I to both types of polymer was demonstrated, although aminostyrene-based materials showed higher overall adsorption and were studied in more detail. It was shown that the kinetics of binding of I from ethyl-acetate extracts of fermented Monascus sp. was very rapid and virtually all the pigment adsorbed can be released by washing the polymer with ethanol-water mixtures. The feasibility of reusing imprinted polymer in consecutive adsorption/desorption cycles was also demonstrated. Copyright 1999 John Wiley & Sons, Inc.