Ecevit Yilmaz

New configurations and applications of molecularly imprinted polymers.

Molecularly imprinted polymers (MIPs) are applicable in a variety of different configurations. For example, bulk polymers imprinted with beta-lactam antibiotics are presented to be used as stationary phases for the chromatographic separation of beta-lactam antibiotics with both aqueous and organic mobile phases. However, in some analytical applications, monosized spherical beads are preferred over the currently used ground bulk polymers. A precipitation polymerization technique allows preparation of monosized spherical imprinted beads with diameters down to 200 nm having excellent recognition properties for different target molecules. Nevertheless, with current imprinting protocols a substantial amount of template has to be used to prepare the polymer. This can be problematic if the template is poorly soluble, expensive or difficult to obtain. It is shown that for analytical applications, the functional monomer:template ratio can be drastically increased without jeopardizing the polymers recognition properties. Furthermore, a substantial reduction of the degree of crosslinking is demonstrated, resulting in much more flexible polymers that are useful for example the preparation of thin imprinted films and membranes for sensors. Apart from analysis, MIPs also are applicable in chemical or enzymatic synthesis. For example, MIPs using the product of an enzyme reaction as template are utilized for assisting the synthetic reaction by continuously removing the product from the bulk solution by complexation. This results in an equilibrium shift towards product formation.

A facile method for preparing molecularly imprinted polymer spheres using spherical silica templates

A novel and facile preparation method for spherical molecularly imprinted polymer (MIP) beads is presented. Two types of beads were synthesized and investigated: (i) silica–MIP composites were obtained by filling spherical, porous C4-coated silica beads with print molecule and monomers followed by polymerisation; (ii) spherical molecularly imprinted polymer beads were acquired mirroring the silica particles in size, shape and pore structure by removing the silica matrix from the silica–MIP composites. With regard to their chromatographic properties and yield of the materials both types of particle were more advantageous compared to irregularly shaped traditional MIPs. Also the work-up time to obtain imprinted spherical particles is greatly reduced compared to traditional methods using polymer monoliths, which have to be ground, sieved and sedimented. Generally, the described method may open new possibilities for synthesis of novel types of imprinted polymer formats such as membranes, bulk polymers, films or in-situ columns using appropriate support or sacrificial materials.

An enzyme-linked molecularly imprinted sorbent assay

Based on a molecularly imprinted polymer, a competitive binding assay analogous to competitive enzyme immunoassay has been developed. The assay is specific for the herbicide 2,4-dichlorophenoxyacetic acid and uses, for the first time, an enzyme-labelled conjugate as a tracer. The label tobacco peroxidase allowed for colorimetric and chemiluminescence detection. The molecularly imprinted polymer was synthesised in the form of microspheres by precipitation polymerisation. The polymer efficiently and selectively bound the analyte in aqueous solution. Calibration curves were obtained corresponding to analyte concentrations ranging from 40–600 μg mL−1 for the colorimetric assay, and from 1–200 μg mL−1 for chemiluminescence assay.

Selective determination of acidic pharmaceuticals in wastewater using molecularly imprinted solid-phase extraction.

The determination of acidic pharmaceuticals, such as non-steroidal anti-inflammatory drugs NSAIDs and clofibric acid (metabolite of clofibrate), at low ngL(-1) levels in wastewater requires highly selective and sensitive analytical procedures. The removal of matrix components during sample preparation results in significant benefits towards reducing the matrix effects during LC-MS analysis. Therefore this work describes a simple method to enrich and clean up NSAIDs and clofibric acid from sewage water using molecularly imprinted solid-phase extraction (MISPE). Final analysis was performed by liquid chromatography-tandem mass spectrometry. The performance of this method has been evaluated in fortified tap and sewage water in terms of recovery, precision, linearity, and method quantification limit. Recovery for all compounds ranged in all matrices between 84 and 116% with intra-day R.S.D. values below 11.5%. Matrix effect evaluation demonstrated that even complex sample matrixes, such as pond or sewage water did not showed significant ion suppression/enhancement compared to tap water. The performance of the method was further emphasized by the study of pond water, which receives treated water from a sewage treatment plant in south Sweden. Raw sewage and treated water were also tested. In those samples, all acidic pharmaceuticals were detected in concentration above method quantification limits ranging from 5.1 to 5153.0ngL(-1).

Towards the use of molecularly imprinted polymers containing imidazoles and bivalent metal complexes for the detection and degradation of organophosphotriester pesticides

Abstract For the preparation of an enzyme mimic for phosphotriester hydrolysis, we have introduced catalytic groups in a polymer, mimicking the structure of the catalytic center of the enzyme phosphotriesterase. The polymers containing Co 2+ –imidazole complexes show a hydrolyric activity which was 20 times higher than polymers containing only imidazole or a solution containing only cobalt ions. Additionally, a molecularly imprinted polymer that was synthesized using a paraoxon analogue as template showed higher paraoxon hydrolysis activity than a control polymer prepared in the same way but without the template molecule.

Selective extraction of triazine herbicides based on a combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction

A selective extraction technique based on the combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction for triazine herbicides in food samples was developed. Simazine, atrazine, prometon, terbumeton, terbuthylazine and prometryn were extracted from aqueous food samples into a hydrophobic polypropylene membrane bag containing 1000μL of toluene as the acceptor phase along with 100mg of MIP particles. In the acceptor phase, the compounds were re-extracted onto MIP particles. The extraction technique was optimised for the type of organic acceptor solvent, amount of molecularly imprinted polymers particles in the organic acceptor phase, extraction time and addition of salt. Toluene as the acceptor phase was found to give higher triazine binding onto MIP particles compared to hexane and cyclohexane. Extraction time of 120min and 100mg of MIP were found to be optimum parameters. Addition of salt increased the extraction efficiency for more polar triazines. The selectivity of the technique was demonstrated by extracting spiked cow pea and corn extracts where clean chromatograms were obtained compared to only membrane assisted solvent extraction or only molecularly imprinted solid phase extraction. The study revealed that this combination may be a simple way of selectively extracting compounds in complex samples.

Analysis of permethrin isomers in composite diet samples by molecularly imprinted solid-phase extraction and isotope dilution gas chromatography-ion trap mass spectrometry.

Determination of an individuals aggregate dietary ingestion of pesticides entails analysis of a difficult sample matrix. Permethrin-specific molecularly imprinted polymer (MIP) solid-phase extraction cartridges were developed for use as a sample preparation technique for a composite food matrix. Vortexing with acetonitrile and centrifugation were found to provide optimal extraction of the permethrin isomers from the composite foods. The acetonitrile (with 1% acetic acid) was mostly evaporated and the analytes reconstituted in 90:10 water/acetonitrile in preparation for molecularly imprinted solid-phase extraction. Permethrin elution was accomplished with acetonitrile and sample extracts were analyzed by isotope dilution gas chromatography-ion trap mass spectrometry. Quantitation of product ions provided definitive identification of the pesticide isomers. The final method parameters were tested with fortified composite food samples of varying fat content (1%, 5%, and 10%) and recoveries ranged from 99.3% to 126%. Vegetable samples with incurred pesticide levels were also analyzed with the given method and recoveries were acceptable (81.0-95.7%). Method detection limits were demonstrated in the low ppb range. Finally, the applicability of the MIP stationary phase to extract other pyrethroids, specifically cyfluthrin and cypermethrin, was also investigated.

Fast identification of selective resins for removal of genotoxic aminopyridine impurities via screening of molecularly imprinted polymer libraries

This study describes the identification and evaluation of molecularly imprinted polymers (MIPs) for the selective removal of potentially genotoxic aminopyridine impurities from pharmaceuticals. Screening experiments were performed using existing MIP resin libraries to identify resins selective towards those impurities in the presence of model pharmaceutical compounds. A hit resin with a considerable imprinting effect was found in the screening and upon further investigation, the resin was found to show a broad selectivity towards five different aminopyridines in the presence of the two model active pharmaceutical ingredients (APIs) piroxicam and tenoxicam.

Studies towards enantioselective surface imprinted polymers

Molecularly imprinted polymers (MIPs) are tailor-made materials that can specifically rebind desired target molecules. Usually, the template is in solution with monomers that form a specific polymeric cavity around the template. Here, a model system with an amino acid (Fmoc-L-Histidine) is presented. This new approach entails the imprinting of templates that are bound to support materials. It is shown that the new approach leads to materials that exhibit symmetric peak shapes for both enantiomers under isocratic conditions.

Molecularly imprinted polymers synthesized via template immobilization on fumed silica nanoparticles for the enrichment of phosphopeptides

Phosphorylation is a protein post‐translational modification (PTM) that plays an important role in cell signaling, cell differentiation, and metabolism. The hyper phosphorylated forms of certain proteins have been appointed as biomarkers for neurodegenerative diseases, and phosphorylation‐related mutations are important for detecting cancer pathways. Due to the low abundance of phosphorylated proteins in biological fluids, sample enrichment is beneficial prior to detection. Thus, a need to find new strategies for enriching phosphopeptides has emerged. Molecularly imprinted polymers (MIPs) are synthetic polymeric materials manufactured to exhibit affinity for a target molecule. In this study, MIPs have been synthesized using a new approach based on the use of fumed silica as sacrificial support acting as solid porogen with the template (phosphotyrosine) immobilized on its surface. Phosphotyrosine MIPs were tested against a mixture of peptides and phosphopeptides by performing micro‐solid phase extraction using MIPs (μMISPE) packed in a pipette tip. First, the capability of the materials to preferentially enrich phosphopeptides was evaluated. In a next step, the enrichment of phosphopeptides from a whole‐cell lysate of human embryonic kidney (HEK) 293T cells was performed. The eluates were analyzed using MALDI‐MS in the first case and with nano‐HPLC‐ESI‐MS/MS in the second case. The results showed that the MIPs provided affinity for phosphopeptides, binding preferentially to multi‐site phosphorylated peptides. The MIPs could enrich phosphopeptides in over 10‐fold compared with the number of phosphopeptides found in a cell lysate without enrichment.