A molecularly imprinted polymer for the determination of neopterin

A molecularly imprinted polymer (MIP) for the specific retention of neopterin has been developed. A set of 6 polymers was prepared by radical polymerization under different experimental condition using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as crosslinker, with the aim to understand their influence on the efficiency of the MIP. The performance of each MIP was tested in batch experiments via their binding capacity. The MIP prepared in the presence of nickel ions in dimethylsulfoxide-acetonitrile mixture (P4) exhibited the highest binding capacity for neopterin (260 μmol per gram of polymer). A selectivity study with two other pteridines demonstrated the polymer P4 also to possess the best selectivity.

Preparation of monodisperse curcumin-imprinted polymer by precipitation polymerization and its application for the extraction of curcuminoids from Curcuma longa L.

A monodisperse molecularly imprinted polymer (MIP) for curcumin was first prepared by precipitation polymerization using methacrylamide (MAM) and 4-vinylpyridine as functional co-monomers, divinylbenzene as a crosslinker, and a mixture of acetonitrile and toluene as a porogen. The use of MAM as the co-monomer resulted in the formation of a monodisperse MIP and non-imprinted polymer (NIP). MIP and NIP, respectively, were monodispersed with a narrow particle size distribution (3.3?±?0.09 and 3.5?±?0.10 μm). In addition to shape recognition, hydrophobic and hydrogen-bonding interactions affected the retention and molecular-recognition of curcumin on the MIP. The MIP for curcumin could extract curcuminoids (curcumin, demethoxycurcumin, and bisdemethoxycurcumin) in Curcuma longa L.

Hydrophilic molecularly imprinted polymers for bisphenol A prepared in aqueous solution

We have prepared a hydrophilic molecularly imprinted polymer (MIP) for the hydrophobic compound bisphenol A (BPA) in aqueous solution using 3-acrylamido-N,N,N-trimethylpropan-1-aminium chloride (AMTC) as the functional monomer. Under redox-polymerization conditions, BPA forms an ion-pair with AMTC, which was confirmed by ¹H-NMR titration. The imprinting effect in aqueous solution was evaluated by comparison of this material with the corresponding non-imprinted polymer (NIP) and with a control polymer (CP) bearing no AMTC. The MIP showed the highest activity among the three polymers, and the imprinting factors as calculated from the amount of BPA bound to the MIP divided by the amounts bound to NIP and CP, respectively, are 1.8 and 6.0. The MIP was selective for BPA in aqueous solution, while structurally related compounds are not recognized. Such a selectivity for a hydrophobic compound is rarely observed in aqueous medium because non-specific binding of BPA inevitably leads to hydrophobic interaction.

Molecularly imprinted dispersive solid-phase microextraction for determination of sulfamethazine by capillary electrophoresis

We have developed a rapid, selective and efficient method for dispersive solid-phase microextraction (DSPME) using microbeads of a molecularly imprinted polymer (MIP). It enables the pre-concentration of sulfamethazine and sample clean-up prior to capillary electrophoresis with UV detection. The microbeads were synthesized via precipitation polymerization using sulfamethazine, methacrylic acid and ethylene glycol dimethacrylate (EGDMA) as the template molecule, the functional monomer and the cross-linking monomer, respectively. Characterization by SEM displayed the high uniformity and dispersibility of the MIP microbeads. The adsorption and desorption of sulfamethazine and the parameters for CE were optimized to result in a limit of detection of 1.1?μg?L^?1, which is 373-fold lower than that of direct CE detection. The equilibration time of extraction was reduced to 5?min, and the selectivity of the microbeads was significantly improved compared to the non-imprinted polymer. The method was successfully applied to the determination of trace sulfamethazine in several milk samples, with recoveries in the range of 89?% to 110?%.

Magnetic nanoparticles with an imprinted polymer coating for the selective extraction of uranyl ions

We have synthesized ferromagnetic nanoparticles with an imprinted polymer coating that is capable of adsorbing and extracting uranyl ions. The adsorbent was characterized using infrared spectroscopy, elemental analysis, X-ray powder diffraction analysis, and scanning electron microscopy. The effects of sample pH, sample volume, weight of the adsorbent, contact time and of other ions have been investigated in the batch extraction mode. The performance of the material was compared to that of particles coated with a non-imprinted polymer. The adsorbent containing the imprinted coating displays higher sorption capacity and better selectivity to uranyl ions. The method was successfully applied to the determination of uranyl ions in water samples.

Transferrin recognition based on a protein imprinted material prepared by hierarchical imprinting technique

A novel kind of transferrin imprinted polymer particles was synthesized by a hierarchical strategy. First, transferrin was immobilized on silica beads by non-covalent absorption. Then, a pre-polymerization mixture, composed of 1,4-bis(acryloyl)piperazine, methacrylamide, methacrylic acid, ammonium sulfate and polyoxyethylene sorbitan monolaurate, was irrigated into the pores of silica particles, and polymerized at 25 °C. Finally, the silica matrix was etched with ammonium hydrogen fluoride, not only to remove the template protein, but also to expose protein recognition sites on the surface of the imprinted polymer. The binding capacity of the transferrin-imprinted particles is 6.3 mg of protein per gram of material, and the time required to reach adsorption equilibrium was less than 10 min. The imprinting factor of transferrin is ca. 3.3 in the presence of ribonuclease B, cytochrome c and β-lactoglobulin. The results indicate that these imprinted polymer particles can recognize transferrin with good selectivity, high binding capacity and fast mass transfer. They may be applied as an artificial antibody to remove the high abundance proteins in plasma.

Towards a synthetic avidin mimic

A series of streptavidin-mimicking molecularly imprinted polymers has been developed and evaluated for their biotin binding characteristics. A combination of molecular dynamics and NMR spectroscopy was used to examine potential polymer systems, in particular with the functional monomers methacrylic acid and 2-acrylamidopyridine. The synthesis of copolymers of ethylene dimethacrylate and one or both of these functional monomers was performed. A combination of radioligand binding studies and surface area analyses demonstrated the presence of selectivity in polymers prepared using methacrylic acid as the functional monomer. This was predicted by the molecular dynamics studies showing the power of this methodology as a prognostic tool for predicting the behavior of molecularly imprinted polymers.

Flame photometric determination of cesium ion after its preconcentration with nanoparticles imprinted with the cesium-dibenzo-24-crown-8 complex

We report on the synthesis of cesium ion-imprinted polymer nanoparticles that were prepared by a precipitation polymerization strategy using dibenzo-24-crown-8 ether as a selective crown ether, methacrylic acid as the functional monomer, ethyleneglycol dimethacrylate as the crosslinker, and AIBN as the radical initiator. The prepared sorbents have a diameter of 50–90 nm and display highly selective binding capability for Cs(I) ion, with rapid adsorption and desorption. The maximum adsorption capacity is 50 mg g^?1, and the preconcentration factor is around 100 at pH 9.0. Cesium ion was then determined by flame photometry with a detection limit (3σ) of 0.7 ng mL^?1 and with a standard deviation of 0.9 %.

Monolithic molecularly imprinted solid-phase extraction for the selective determination of trace cytokinins in plant samples with liquid chromatography–electrospray tandem mass spectrometry

Cytokinins (CTKs) are a class of growth-regulating hormones involved in various physiological and developmental processes. More novel analytical methods for the accurate identification and quantitative determination of trace CTKs in plants have been desired to better elucidate the roles of CTKs. In this work, a novel method based on monolithic molecularly imprinted solid-phase extraction followed by liquid chromatography–electrospray tandem mass spectrometry (mMI-SPE-LC-MS/MS) was developed for accurate determination of four CTKs in plant samples. The molecularly imprinted polymer monolith was prepared by using kinetin as the template in syringes and exhibited specific recognition ability for the four CTKs in comparison with that of non-imprinted polymer monolith. Several factors affecting the extraction performance of mMI-SPE, including the pH of loading sample solution, the nature and volume of elution solvent, the flow rate of sample loading, and sample volume, were investigated, respectively. Under the optimized conditions, the proposed mMI-SPE-LC-MS/MS method was successfully applied in the selective extraction and determination of four CTKs in plant tissues, and it offers detection limits (S/N?=?3) of 104, 113, 130, and 89 pg/mL and mean recoveries of 85.9%, 79.3%, 73.5%, and 70.1% for kinetin, kinetin glucoside, trans-zeatin, and meta-topolin (mT), respectively, with the corresponding RSDs less than 15%.

Preparation and characterization of an imprinted monolith by atom transfer radical polymerization assisted by crowding agents

A method based on reverse atom transfer radical polymerization (R-ATRP) and molecular crowding has been used for design and synthesis of monolithic molecularly imprinted polymers (MIPs) capable of recognizing ibuprofen (IBU). 4-Vinylpyridine (4-VP) was used as the functional monomer, and ethylene glycol dimethacrylate (EDMA) was the crosslinking monomer. Azobisisobutyronitrile (AIBN)–CuCl₂–N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) was used as the initiating system. Compared with conventional radical polymerization-based IBU-MIPs, the imprinting effects of the obtained IBU-MIPs was enhanced, suggesting the merit of combination of reverse ATRP and molecular crowding. In addition, it was found that the polymerization time of the molecularly imprinted monolithic column, the amount of template, the degree of crosslinking, and the composition of mobile phase greatly affected retention of the template and the performance of molecular recognition .

Determination of t,t-muconic acid in urine samples using a molecular imprinted polymer combined with simultaneous ethyl chloroformate derivatization and pre-concentration by dispersive liquid–liquid microextraction

The present communication describes the preparation and evaluation of a molecularly imprinted polymer (MIP) as a solid-phase extraction (SPE) sorbent and simultaneous ethyl chloroformate (ECF) derivatization and pre-concentration by dispersive liquid–liquid microextraction (DLLME) for the analysis of t,t-muconic acid (t,t-MA) in urine samples using gas chromatography–mass spectrometry. The imprinting polymer was prepared using methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, 2,2-azobisisobutyronitrile as the initiator and t,t-MA as a template molecule. The imprinted polymer was evaluated for its use as a SPE sorbent by comparing both imprinted and non-imprinted polymers in terms of the recovery of t,t-MA from urine samples. Molecular modelling studies were performed in order to estimate the binding energy and efficiency of the MIP complex formed between the monomer and the t,t-MA. Various factors that can affect the extraction efficiency of MIP, such as the loading, washing and eluting conditions, were optimized; other factors that can affect the derivatization and DLLME pre-concentration were also optimized. MIP in combination with ECF derivatization and DLLME pre-concentration for t,t-MA exhibits good linearity, ranging from 0.125 to 2 μg?mL^?1 (R ²?=?0.9971), with limit of detection of 0.037 μg?mL^?1 and limit of quantification of 0.109 μg?mL^?1. Intra- and inter-day precision was found to be <6 %. The proposed method has been proven to be effective and sensitive for the selective pre-concentration and determination of t,t-MA in urine samples of cigarette smokers.

Chiral separation of racemic mandelic acids by use of an ionic liquid-mediated imprinted monolith with a metal ion as self-assembly pivot

A new chiral stationary phase based on molecularly imprinted polymers (MIP) was prepared in ionic liquid by use of the metal pivot concept. Imprinted monoliths were synthesized by use of a mixture of R-mandelic acid (template), 4-vinylpyridine, ethylene glycol dimethacrylate, and several metal ions as pivot between the template and functional monomer. A ternary mixture of dimethyl sulfoxide–dimethylformamide–[BMIM]BF₄ containing metal ions was used as the porogenic system. Separation of the enantiomers of rac-mandelic acid was successfully achieved on the MIP thus obtained, with resolution of 1.87, whereas no enantiomer separation was observed on the imprinted monolithic column in the absence of metal ions. The effects of polymerization conditions, including the nature of the metal ion and the ratios of template to metal ions and template to functional monomer, on the chiral separation of mandelic acid were investigated. The results reveal that use of metal ions as a pivot, in combination with ionic liquid, is an effective method for preparation of a highly efficient MIP stationary phase for chiral separation.

Extraction of tributyltin by magnetic molecularly imprinted polymers

We have prepared core-shell magnetic molecularly imprinted polymer nanoparticles for recognition and extraction of tributyl tin (TBT). The use of particles strongly improves the imprinting effect and leads to fast adsorption kinetics and high adsorption capacities. The functional monomer acrylamide was grafted to the surface of Fe₃O₄ nanospheres in two steps, and MIP layers were then formed on the surface by creating a MIP layer on the surface consisting of poly(ethyleneglycol dimethacrylate) with a TBT template. The particles were characterized in terms of morphological, magnetic, adsorption, and recognition properties. We then have developed a method for the extraction of TBT from spiked mussel (Mytilidae), and its determination by liquid chromatography-tandem mass spectrometry. The method has a limit of detection of 1.0 ng?g^?1 (n?=?5) of TBT, with a linear response between 5.0 and 1,000 ng?g^?1. The proposed method was successfully applied to the determination of trace TBT in marine food samples with recoveries in the range of 78.3–95.6 %.

Molecularly imprinted polystyrene–titania hybrids with both ionic and π–π interactions: a case study with pyrenebutyric acid

We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO₂) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO₂ and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO₂. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films.

A new ion imprinted polymer based on Ru(III)-thiobarbituric acid complex for solid phase extraction of ruthenium(III) prior to its determination by ETAAS

A new ruthenium ion imprinted polymer was prepared from the Ru(III) 2-thiobarbituric acid complex (the template), methacrylic acid or acrylamide (the functional monomers), and ethylene glycol dimethacrylate (the cross-linking agent) using 2,2′-azobisisobutyronitrile as the radical initiator. The ion imprinted polymer was characterized and used as a selective sorbent for the solid phase extraction of Ru(III) ions. The effects of type of functional monomer, sample volume, solution pH and flow rate on the extraction efficiency were studied in the dynamic mode. Ru(III) ion was quantitatively retained on the sorbents in the pH range from 3.5 to 10, and can be eluted with 4 mol L^?1 aqueous ammonia. The affinity of Ru(III) for the ion imprinted polymer based on the acrylamide monomer is weaker than that for the polymer based on the methacrylic acid monomer, which therefore was used in interference studies and in analytical applications. Following extraction of Ru(III) ions with the imprint and their subsequent elution from the polymer with aqueous ammonia, Ru(III) was detected by electrothermal atomic absorption spectrometry with a detection limit of 0.21 ng mL^?1. The method was successfully applied to the determination of trace amounts of Ru(III) in water, waste, road dust and platinum ore (CRM SARM 76) with a reproducibility (expressed as RSD) below 6.4 %.

A molecularly imprinted polymer for solid phase extraction of allantoin

We describe a molecularly imprinted polymer (MIP) for the solid-phase extraction of the skin protectant allantoin. The MIP was deposited on the surface of monodisperse silica microspheres possessing acroyl groups on the surface (MH-SiO₂). The resulting MIP microspheres (MH-SiO₂@MIP) showed a 3.4-fold higher adsorption capacity and a 1.9-fold better selectivity for allantoin than the respective non-imprinted polymer (MH-SiO₂@NIP). The monolayer adsorption capacities of the MH-SiO₂@MIP and the MH-SiO₂@NIP were calculated with the help of the Langmuir model and found to be 6.8 and 1.9 mg?g^?1, respectively. Adsorption kinetics fit a pseudo-second order rate mechanism, with an initial adsorption rate of 1.44 for the MH-SiO₂@MIP, and of 0.07 mg?g^?1?min^?1 for the MH-SiO₂@NIP. The material can be regenerated, and its adsorption capacity for allantoin remains stable for at least five regeneration cycles. It was successfully used as a sorbent for the selective solid-phase extraction of allantoin from Rhizoma dioscoreae.

A nanosized cadmium(II)-imprinted polymer for use in selective trace determination of cadmium in complex matrices

We describe a nanosized Cd(II)-imprinted polymer that was prepared from 4-vinyl pyridine (the functional monomer), ethyleneglycol dimethacrylate (the cross-linker), 2,2′-azobisisobutyronitrile (the radical initiator), neocuproine (the ligand), and Cd(II) (the template ion) by precipitation polymerization in acetonitrile as the solvent. The imprinted polymer was characterized by X-ray diffraction, thermogravimetric analysis, differential thermal analysis, and scanning electron microscopy. The maximum adsorption capacity of the nanosized sorbent was calculated to be 64 mg g^?1. Cadmium(II) was then quantified by FAAS. The relative standard deviation and limit of detection are 4.2 % and 0.2 μg L^?1, respectively. The imprinted polymer displays improve selectivity for Cd(II) ions over a range of competing metal ions with the same charge and similar ionic radius. This nanosized sorbent is an efficient solid phase for selective extraction and preconcentration of Cd(II) in complex matrices. The method was successfully applied to the trace determination of Cd(II) in food and water samples.

Thermal preparation of lysozyme-imprinted microspheres by using ionic liquid as a stabilizer

Thermal preparation of lysozyme-imprinted microspheres was firstly investigated by using biocompatible ionic liquid (IL) as a thermal stabilizer. The imprinted microspheres made with IL could obtain the good recognition ability to template protein, whereas the imprinted polymer synthesized in the absence of it had a similar adsorption capacity to the non-imprinted one. Furthermore, the preparation conditions of imprinted polymers (MIPs) including the content of IL, temperature of polymerization, and types of functional monomers and crosslinkers were systematically analyzed via circular dichroism spectrum and activity assay. The results illustrated that using hydroxyethyl acrylate as the functional monomer, ethylene glycol dimethacrylate as the crosslinker, 5 % IL as the stabilizer, and 75 °C as the reaction temperature could retain the structure of template protein as much as possible. The obtained MIPs showed excellent recognition ability to the template protein with the separation factor and selectivity factor value of 4.30 and 2.21, respectively. Consequently, it is an effective way to accurately imprint and separate template protein by cooperatively using circular dichroism spectroscopy and activity assay during the preparation of protein MIPs. The method of utilizing IL to stabilizing protein at high temperature would offer a good opportunity for various technologies to improve the development of macromolecules imprinting. Graphical Abstract

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Solid phase extraction of penicillins from milk by using sacrificial silica beads as a support for a molecular imprint

We have prepared molecularly imprinted beads with molecular recognition capability for target molecules containing the penicillanic acid substructure. They were prepared by (a) grafting mesoporous silica beads with 6-aminopenicillanic acid as the mimic template, (b) filling the pores with a polymerized mixture of methacrylic acid and trimethylolpropane trimethacrylate, and (c) removing the silica support with ammonium fluoride. The resulting imprinted beads showed good molecular recognition capability for various penicillanic species, while antibiotics such as cephalosporins or chloramphenicol were poorly recognized. The imprinted beads were used to extract penicillin V, nafcillin, oxacillin, cloxacillin and dicloxacillin from skimmed and deproteinized milk in the concentration range of 5–100 μg·L^?1. The extracts were then analyzed by micellar electrokinetic chromatography by applying reverse polarity staking as an in-capillary preconcentration step, and this resulted in a fast and affordable method within the MRL levels, characterized by minimal pretreatment steps and recoveries of 64–90 %.

Improving the synthesis of a molecularly imprinted sol-gel for serine using a Plackett-Burman design

We have studied the influence of the experimental conditions during synthesis on the properties of molecularly imprinted sol-gels for serine. The influence of hydrophobicity, presence of amino groups, additives, water/ethanol ratio and type of catalyst (basic or acid) were optimized using a Plackett-Burmann design in 12 blocks. Serine was selected as a target molecule for the imprinting process, and each imprinted and non-imprinted material was studied by competitive and non-competitive protocols. The results demonstrate the strong effect of 3-aminopropyltrimethoxysilane on the recognition capabilities of the materials in competitive assays. The mechanisms of interaction appear to be similar in acid-catalysed sol-gels, whereas sol-gels obtained under base catalysis tend to give interactions affecting the competitive experiments only.