Batch and column separation characteristics of copper-imprinted porous polymer micro-beads synthesized by a direct imprinting method

Copper (II) ion-imprinted porous polymethacrylate micro-particles were prepared. Two functional monomers, methacrylic acid and vinyl pyridine, formed a complex with the template copper ion through ionic interactions. The self-assembled copper/monomer complex was polymerized in the presence of an ethylene glycol dimethacrylate cross-linker by a suspension method. After the imprinting sites were provided through removal of the template, the micro-porous particles, of approximate size 200 μm, were obtained for batch and column separation applications. The chemical structure and morphology of the Cu(II)-imprinted micro-porous particles were analyzed using FTIR, SEM, and BET. The adsorption capacity and adsorption kinetics of the imprinted beads for the template Cu(II) ion were significantly affected by particle size, copper ion concentration, pH, and flow rate of the feed solution. The imprinted particles showed high selectivity for the copper ion over other metal ions such as Ni and Zn. The selectivity of the present imprinted polymers for the copper ion was at least 10 times as high as those from commercial sources.     

Quartz crystal microbalance sensor for organic vapor detection based on molecularly imprinted polymers

Molecularly imprinted polymers on quartz crystal microbalances (QCM) are examined for their ability to detect vapors of small organic molecules with greater sensitivity and selectivity than the traditional amorphous polymer coatings. Hydroquinone and phenol serve as noncovalently bound templates that generate shape-selective cavities in a poly(acrylic) or poly(methacrylic) polymer matrix. The imprinted polymers are immobilized on the piezoelectric crystal surface via a precoated poly(isobutylene) layer. The behavior of the imprinted polymer films is characterized by the dynamic and steady-state response of the QCM frequency to pulses of organic vapors in dry air. The apparent partition coefficients are determined for imprinted and nonimprinted polymers prepared by two synthetic methods and for varying mole ratios of template to monomer. The hydroquinone-imprinted polymers and, to a lesser extent, the phenol-imprinted polymers exhibit greater sensitivity and higher selectivity than the nonimprinted polymers toward organic vapors that are structurally related to the templates. These results indicate that molecularly imprinted polymers are promising for the development of selective piezoelectric sensors for organic vapor detection.     

Probing the recognition of molecularly imprinted polymer beads

A facile, robust and cost-effective suspension polymerisation methodology for the generation of ibuprofen molecularly imprinted polymers in bead formats was evaluated. Mineral oil was employed as the continuous phase whereby microdroplets of the pre-polymerisation mixture were formed through vigorous agitation, followed by photo-polymerisation resulting in formation of imprinted beads. For comparison purposes, irregular particles were also prepared from monolith polymers. Physical characteristics of the imprinted polymers were investigated using scanning electron microscope, particle size distribution, nitrogen sorption porosimetry and solvent swelling ratios, with subsequent correlation of these parameters to analyte rebinding performance. Overall, an increase in affinity was observed with decreasing the degree of cross-linking, however, specific rebinding was compromised. An inverse relationship between polymer affinity for the template and surface area was identified, while solvent swelling ratios were directly related to polymer affinity. Correlation between pre-polymerisation studies and polymer binding performance highlighted the significance of employing the polymerisation solvent in template rebinding in order to achieve superior recognition capabilities. Additionally, shape selectivity of binding sites was demonstrated by the decreased binding performance of template structural analogues to the imprinted polymer.     

Extraction and purification of penicillin G from fermentation broth by water-compatible molecularly imprinted polymers

Highly selective molecularly imprinted polymer (MIP) was synthesized by using methacrylic acid as functional monomer, trimethylolpropane trimethacrylate as cross-linker, chloroform as porogen and penicillin G potassium as template molecule. These imprinted polymers were used as solid-phase extraction sorbent for the selective extraction of penicillin G from the fermentation broth samples. Various parameters affecting the extraction efficiency of the MIP particles such as; effects of pH, wash and eluent solutions were evaluated. Molecular recognition properties and selectivity of these MIPs were estimated and the obtained results revealed high affinity for the target antibiotic. Equilibrium binding experiments were done to assess the performance of the MIP relative to non imprinted polymer (NIP). After optimizing the extraction parameters in molecularly imprinted solid-phase extraction (MISPE), successful imprinting was confirmed by comparison of the recoveries from the fermentation broth, ranging between 24–26% (RSD 4.1–4.5%, n = 4) for the NIPs and 83–88% (RSD 3.1–3.4%, n = 4) for the MIPs.     

单一结合位点分子印迹聚合物的合成及性能

采用分子自组装印迹技术在光引发条件下制备了以(S)-布洛芬为模板分子,α-甲基丙烯酸为功能单体的分子印迹聚合物。通过红外对聚合物的结构进行了表征。透射电镜结果表明,交联剂用量对印迹聚合物的形貌特征具有显著的影响。同时结合Scatchard分析研究了印迹聚合物的吸附性能及选择性识别能力,表明印迹聚合物特异性吸附容量为41μmol/g,印迹指数为2.28,对(S)-布洛芬形成单一结合位点,且表现出明显的吸附选择性。     

Controlled fabrication of theophylline imprinted polymers on multiwalled carbon nanotubes via atom transfer radical polymerization

Theophylline imprinted polymers were synthesized on the surface of multiwalled carbon nanotubes via atom transfer radical polymerization using brominated multiwalled carbon nanotubes as an initiator. The nanotube-based initiator was prepared by directly reacting acyl chloride-modified multiwalled carbon nanotubes with 2-hydroxylethyl-2'-bromoisobutyrate. The grafting copolymerization of 2-hydroxyethyl-2-methyl-2-propenoate and ethylene glycol dimethacrylate in the presence of template theophylline led to thin molecularly imprinted polymer films coating multiwalled carbon nanotubes. The thickness of molecularly imprinted polymer films prepared in this study was about 5 nm as determined by transmission electron microscopy. Fourier-transform infrared spectroscopy was utilized to follow the introduction of initiator groups as well as polymers on the carbon nanotube surfaces. Thermogravimetric analysis indicated that the molecularly imprinted polymers were successfully grown from the carbon nanotube surfaces, with the final products having a polymer weight percentage of ca. 50 wt%. The adsorption properties, such as adsorption dynamics, special binding and selective recognition capacity, of the as-prepared molecularly imprinted polymer films were evaluated. The results demonstrated that the composite of molecularly imprinted polymers and multiwalled carbon nanotubes not only possessed a rapid dynamics but also exhibited a good selectivity toward theophylline, compared to caffeine.     

Exploiting β-cyclodextrin as functional monomer in molecular imprinting for achieving recognition in aqueous media

A series of molecularly imprinted polymers (MIPs) for 4,4′-(1,4-phenylenediisopropylidene)bisphenol (BPP) were prepared by using β-cyclodextrin (β-CD) as functional monomer, toluene 2,4-diisocyanate (TDI) or 4,4′-Diphenylmethane diisocyanate (DDI) as the cross-linker. The results of binding experiments showed that the MIPs can bind the template selectively in aqueous media. The binding specificity mechanism of the polymers was investigated in detail. The template molecule is too large and cannot be included in the cavity of one β-CD molecule. The mutual orientation of β-CD molecules in the imprinted polymers is regulated by molecular imprinting, so that they can cooperatively bind the template molecule. It is suggested that the major contribution to the recognition ability of the imprinted polymer was the stereo-shape effect inherent in the MIPs. The study indicated that hydrophobic effects play an important role in the recognition process.     

Molecularly imprinted polymeric fibers for solid-phase microextraction

Solid-phase microextraction (SPME) is widely used in analytical laboratories for the analysis of organic compounds, thanks to its simplicity and versatility. However, the current commercially available fibers are based on nonselective sorbents, making difficult in some cases the final determination of target compounds by chromatographic techniques. Molecularly imprinted polymers (MIPs) are stable polymers with selective molecular recognition abilities, provided by the template used during their synthesis. In the present work, a simple polymerization strategy allowing the obtainment of molecularly imprinted polymeric fibers to be used in SPME is proposed. Such a strategy is based on the direct synthesis of molecularly imprinted polymeric fibers (monoliths) using silica capillaries as molds, with silica being etched away after polymerization. The system propazine:methacrylic acid was used as a model for the preparation of molecularly imprinted fibers, and its ability to selectively rebind triazines was evaluated. Variables affecting polymer morphology (i.e., polymerization time, fiber thickness) and binding-elution of target analytes (i.e., solvents, time, temperature) were studied in detail. The imprinted fiber showing the best performance in terms of selectivity and affinity for triazines was successfully applied to the extraction of target analytes from environmental and food samples.     

农药对硫磷分子印迹聚合物合成及亲和性评价

对硫磷为模板分子,甲基丙烯酸(MAA)为功能单体,乙二醇二甲基丙烯酸酯(EGDMA)为交联剂,偶氮二异丁腈(AIBN)为引发剂,热引发沉淀聚合法合成对硫磷分子印迹聚合物(MIP)。通过计算机模拟和紫外分析阐述模板与功能单体的分子间作用;通过电镜观察和平衡吸附试验讨论引发剂用量与聚合物性质关系;通过吸附试验Scatchard分析测得最大吸附量为3.92μmol/g,平衡解离常数为91.7μmol/L,且具有较好的吸附特异性。该分子印迹聚合物性能优良,有望应用于环境中对硫磷的富集和检测。     

Cr(III)-imprinted polymeric beads: Sorption and preconcentration studies

The purpose of this study is to prepare a novel molecular imprinted adsorbent to Cr(III) analysis with high selectivity. Initially, chromium (III)-methacryloylhistidine (MAH/Cr(III)) complex monomer was synthesized and then Cr(III) ion imprinted ethyleneglycoldimethacrylate-methacryloylhistidine (poly(EDMA-MAH/Cr(III))) was polymerized. Cr(III) ions were removed from the Cr(III)-imprinting polymer. Selective cavity for the chromium (III) ions was obtained in the (poly(EDMA-MAH/Cr(III))) beads. These Cr(III)-imprinted beads were used in the sorption-desorption process. The effect of initial concentration of metal, the sorption rate and the pH of the medium on sorption capacity of Cr(III)-imprinting sorbents were studied. Sorption equilibrium time was achieved in about 30min. The maximum sorption of Cr(III) ions onto imprinted beads was about 69.28mg/g. Sorption studies of Co(II), Ni(II), Cr(III) and Cr(VI) ions were also investigated using Cr(III)-imprinting polymers. The obtained results show that selectively adsorbed amount of Cr(III) ion on Cr(III)-imprinting polymers is higher than all other studied ions. When the beads were used repeatedly, their adsorption capacity was showed feasibility.     

On the synthesis and rebinding properties of [Co(C2H3O2)2(z-Histidine)] imprinted polymers prepared by precipitation polymerization

In the present study, the synthesis via free-radical precipitation polymerization of metal-complexing polymer microparticles capable of specific binding to [Co(C₂H₃O₂)₂(z-Histidine)] complex is reported. Initially, the functional monomer (i.e., 4-vinylpyridine, a vinyl monomer with metal chelate properties) is complexed together with the template [Co(C₂H₃O₂)₂(z-Histidine)] molecule via the mediation of cobalt ions. Evidence of the polymerizable complex formation is obtained through the compleximetric titration of the z-Histidine in the prepolymerization reaction mixture. Subsequent polymerization of the polymerizable complex with a bi-functional or tri-functional cross-linker results in the formation of imprinted polymer microparticles in the size range of 1–5 µm. The effects of agitation, cross-linker type, degree of cross-linking and molar ratio of the template to the functional monomer on the rebinding properties of the imprinted polymers are experimentally assessed. The synthesized imprinted polymers can potentially find application in the purification of his-tagged recombinant proteins.     

Surface-grafted molecularly imprinted polymers for protein recognition.

A technique for coating microplate wells with molecularly imprinted polymers (MIPs) specific for proteins is presented. 3-Aminophenylboronic acid was polymerized in the presence of the following templates: microperoxidase, horseradish peroxidase, lactoperoxidase, and hemoglobin, via oxidation of the monomer by ammonium persulfate. This process resulted in the grafting of a thin polymer layer to the polystyrene surface of the microplates. Imprinting resulted in an increased affinity of the polymer toward the corresponding templates. The influence of the washing procedure, template concentration, and buffer pH on the polymer affinity was analyzed. It was shown that the stabilizing function of the support and spatial orientation of the polymer chains and template functional groups are the major factors affecting the imprint formation and template recognition. Easy preparation of the MIPs, their high stability, and their ability to recognize small and large proteins, as well as to discriminate molecules with small variations in charge, make this approach attractive and broadly applicable in biotechnology, assays and sensors.     

Atrazine-selective polymers prepared by molecular imprinting of trialkylmelamines as dummy template species of atrazine

Synthetic polymer receptors selective for atrazine have been prepared by molecular imprinting using trialkylmelamines as template molecules in place of atrazine. Trialkylmelamines were shown to be useful as templates for introducing affinity for atrazine into ethylene glycol dimethacrylate-methacrylic acid copolymers. The polymers showed the selective binding capacity for triazine herbicides including atrazine, whereas agrochemicals in other categories were not adsorbed to the imprinted polymers. The group selectivity demonstrated was comparable with that of the original atrazine imprinted polymers. Use of the nonagrochemical template molecules as a substitution to atrazine has made it possible to synthesize herbicide-receptor polymers free from troubles caused by analyte contaminants, which are desired for analytical applications.     

Fibers coated with molecularly imprinted polymers for solid-phase microextraction

The simplicity and flexibility of solid-phase microextraction have been combined with the selectivity of molecularly imprinted polymers (MIPs). Silica fibers were coated reproducible with a 75-microm layer of methacrylate polymer either nonimprinted or imprinted with clenbuterol to compare their extraction characteristics under various conditions. Although the template molecule could be removed effectively from the imprinted polymer, structural analogues of clenbuterol were used for evaluation. The influence of pH on the extractability of brombuterol was investigated. Extraction yields up to approximately 80% were obtained when both types of fibers were used to extract brombuterol from phosphate buffer (pH 7.0). In contrast, yields of about 75 and <5% were obtained when extraction was performed from acetonitrile with imprinted and nonimprinted polymers, respectively, which demonstrates the selectivity of the MIP-coated fiber. Time sorption profiles were measured for the extraction of brombuterol from buffer and acetonitrile at the 10 and 100 ng/mL level with both types of fibers in order to compare extraction characteristics. Equilibrium times of about 30 and 90 min were found for the extraction of brombuterol from acetonitrile and buffer, respectively. The MIP-coated fibers were capable of extracting five structural analogues of clenbuterol from both buffer and acetonitrile, which suggests that the amine alcohol part of these molecules is responsible for interaction with the imprinted polymer. To achieve selective extraction of brombuterol from human urine, MIP-coated fibers were washed with acetonitrile after the extraction. Clean extracts and yields of approximately 45% were obtained, demonstrating the suitability of MIP-coated fibers for the analysis of biological samples.     

Molecular imprinting under molecular crowding conditions: an aid to the synthesis of a high-capacity polymeric sorbent for triazine herbicides

Molecular crowding, an important feature of the molecular environments in biological cells, was applied to the synthesis of antibody-mimic polymers selective for a group of biologically active compounds, the triazine herbicides. Synthesis of these polymers was conducted using molecular imprinting under molecular crowding conditions, whereby atrazine (a template molecule) was complexed with methacrylic acid (a functional monomer) in the presence of a macromolecular crowding agent (either poly(methyl methacrylate) (PMMA) or polystyrene (PS)) followed by cross-linking with ethylene glycol dimethacrylate. After removal of atrazine from the polymer matrix, the retention properties and selectivity of the resultant polymers were assessed by chromatographic tests. The addition of a crowding-inducing agent resulted in polymers with superior retention properties and excellent selectivity for triazine herbicides, as compared to polymers prepared without addition of a crowding-inducing agent. An imprinted polymer prepared in the presence of PS as a crowding agent exhibited a retention factor for atrazine an order of magnitude larger than that of an imprinted polymer prepared in the absence of a crowding agent. NMR results suggest that the crowding agent is capable of promoting hydrogen bond formation between atrazine and methacrylic acid, which could account for the effect of crowding on molecular imprinting.     

Novel critical point drying (CPD) based preparation and transmission electron microscopy (TEM) imaging of protein specific molecularly imprinted polymers (HydroMIPs)

We report the transmission electron microscopy (TEM) imaging of a hydrogel based molecularly imprinted polymer (HydroMIP) specific to the template molecule bovine haemoglobin (BHb). A novel critical point drying based sample preparation technique was employed to prepare the molecularly imprinted polymer (MIP) samples in a manner that would facilitate the use of TEM to image the imprinted cavities, and provide an appropriate degree of both magnification and resolution to image polymer architecture in the <10 nm range. For the first time, polymer structure has been detailed that tentatively suggests molecularly imprinted cavities, ranging from 5 to 50 nm in size, that correlate (in terms of size) with the protein molecule employed as the imprinting template. The modified critical point drying sample preparation technique used may potentially play a key role in the imaging of all molecularly imprinted polymers, particularly those prepared in the aqueous phase.     

Protein recognition via surface molecularly imprinted polymer nanowires

In this paper, we present a technique for the preparation of polymer nanowires with the protein molecule imprinted and binding sites at surface. These surface imprinting nanowires exhibit highly selective recognition for a variety of template proteins, including albumin, hemoglobin, and cytochrome c. This recognition may be through a multistep adsorption, with the specificity conferred by hydrogen bonding and shape selectivity. Due to the protein imprinted sites are located at, or close to, the surface; these imprinted nanowires have a good site accessibility toward the target protein molecules. Furthermore, the large surface area of the nanowires results in large protein molecule binding capacity of the imprinted nanowires.     

Molecular imprinted particles for lysozyme purification

Molecular recognition-based separation techniques have received much attention in chemistry and biology because of their high selectivity for target molecules. The aim of this study is to prepare lysozyme-imprinted polymers which can be used for the purification of lysozyme from aqueous solutions and egg white. N-methacryloyl-(l)-histidinemethylester (MAH) was chosen as the metal-complexing monomer. In the first step, Cu²⁺ was complexed with MAH and the lysozyme-imprinted poly(HEMA–MAH) [Lys-MIP] particles were synthesized by UV-initiated bulk polymerization. After that, the template (i.e., lysozyme) were removed using 0.1 M NaCl solution. The specific surface area of the Lys-MIP particles was found to be 22.9 m²/g with a size range of 20–63 μm in diameter and the swelling ratio was 57%. According to the elemental analysis results, the particles contained 421 μmol MAH/g polymer. The maximum lysozyme adsorption capacity was 12.1 mg/g polymer. The relative selectivity coefficients of imprinted particles for lysozyme/human serum albumin and lysozyme/cytochrome c were 3.6 and 4.1 times greater than NIP particles, respectively. Purification of lysozyme from egg-white was also monitored by determining the lysozyme activity using Micrococcus lysodeikticus as substrate. The purity of the desorbed lysozyme was about 89% with recovery about 84%. The Lys-MIP particles could be used many times without decreasing their adsorption capacities significantly.     

Preparation of molecularly imprinted polymers for the detection of aromatic hydrocarbons

In this study, the molecularly imprinted polymers (MIPs) are designed to improve their sensitivity and selectivity for specific aromatic hydrocarbons such as benzene, toluene, and xylene isomers. The MIPs based on methyl acrylate (MA) monomer are prepared using toluene and ethylene glycol dimetacrylate (EGDMA) as a template and a cross linking agent, respectively. The binding sites on the MIPs are characterized by using Fourier transform infrared spectrometry (FT-IR), nitrogen adsorption isotherms, and transmission electron microscopy (TEM). The selective behaviors of the MIPs are evaluated by their adsorption properties on a gravimetric apparatus. It is found that the performance is strongly influenced by the composition ratios of cross-linker, functional monomer, and template molecule. The molecular recognition ability can be assessed on the basis of an imprinting effect. The results indicate that the prepared MIPs can be used for the aromatic hydrocarbon sensor materials with high sensitivity and selectivity.     

Method for synthesis and screening of large groups of molecularly imprinted polymers

A technique for the synthesis of molecularly imprinted polymers (MIPs) in small scale (～55 mg) coupled with direct in situ processing and batch rebinding evaluation is reported. The primary assessment is based on quantification by HPLC or UV absorbance measurement of the amount of template released from the polymer in a given solvent. This method allows a rapid screening of the parameters of importance to reach a desired level of binding affinity capacity and selectivity for a given target molecule. This was demonstrated for the triazine herbicide terbutylazine, where an initial screening was performed for the type of functional monomer used in the MIP preparation. Thus among the six functional monomers tested, methyl methacrylate, 4-vinylpyridine, and N-vinyl-α-pyrrolidone led to rapid and quantitative extraction whereas methacrylic acid and (trifluoromethyl)acrylic acid led to polymers that retained the template the most. After having established useful functional monomers, a secondary screening for selectivity was performed. In this, nonimprinted blank polymers were prepared and a normal batch rebinding evaluation was performed. The polymer showing the highest selectivity was the one prepared using methacrylic acid as functional monomer. This polymer was shown to strongly retain chlorotriazines including atrazine when a normal-scale batch of the polymer was evaluated in chromatography.