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Analytica Chimica Acta (v.542, #1)
Polymeric devices containing imprinted nanospheres: a novel approach to improve recognition in water for clinical uses by D. Silvestri; C. Borrelli; P. Giusti; C. Cristallini; G. Ciardelli (pp. 3-13).
Molecular imprinting permits to introduce in synthetic macromolecules molecular information through the polymerisation of a monomer in the presence of a stamp molecule (template): the solution polymerisation is receiving, in the last 5 years, increasing attention due to the effective selective behaviour of produced materials obtained in the shape of micro or nanoparticles. The frontier of this family of materials is the improvement of recognition performances in aqueous environment. Our work started from the idea to increase binding and selective behaviour of cross-linked poly(methylmethacrylate-co-methacrylic acid) nanospheres in aqueous media through an innovative approach: imprinted nanospheres are loaded in the bulk or on the surface of poly(methylmethacrylate-co-acrylic acid) membranes. In this way, enhanced recognition performances of acrylic membranes can be expected, taking advantage of recognition characteristics of imprinted nanospheres. Recognition and binding behaviour of free and supported particles was compared, showing an increased recognition factor for loaded particles. Imprinted particles were able to keep-on 1.72mg of theophylline and 4.12mg of caffeine/g of polymer in physiological solution and the recognition factors for each template resulted to be higher for supported particles, in particular in the case of theophylline (passing from 1.02 to 6.32), suggesting the creation of a preferred microenvironment for the rebinding of nanoparticles.
Keywords: Molecular imprinting; Recognition in water; Nanospheres; Selective membranes
Molecularly imprinted solid-phase extraction of cocaine metabolites from aqueous samples by A. Zurutuza; S. Bayoudh; P.A.G. Cormack; L. Dambies; J. Deere; R. Bischoff; D.C. Sherrington (pp. 14-19).
Cocaine is a well-known drug of abuse which, when ingested nasally or by smoking, undergoes a number of biotransformation and degradation reactions. In the present work, a synthetic analogue of the cocaine metabolite benzoylecgonine was prepared and used as a template molecule in the preparation of a series of molecularly imprinted polymers (MIPs). Molecularly imprinted solid-phase extraction (MISPE) conditions were established under which benzoylecgonine in aqueous samples could be selectively extracted and quantified at clinically relevant concentrations (μg/ml). Under optimised MISPE conditions, recoveries of analyte were high (>70%) and excellent discrimination between imprinted and non-imprinted materials observed.
Keywords: Molecularly imprinted polymers; Solid-phase extraction; Cocaine; Cocaine metabolites; Benzoylecgonine
C-reactive protein thin-film molecularly imprinted polymers formed using a micro-contact approach by Pei-Chen Chou; John Rick; Tse-Chuan Chou (pp. 20-25).
A method for micro-contact imprinting CRP has been developed. An analogue, O-(-4-nitrophenylphosphoryl)choline, of the templates natural ligand, phosphorylcholine, was used as the functional monomer. A series of non-imprinted polymers made without template, but with varying cross-linking agents, were made in order to produce a control polymer with minimal non-specific recognition.The affinity of the imprinted polymers for the competing proteins, lysozyme and albumin, was examined. Their respective relative affinities, with 1.04μg/cm2 of the template protein bound to the imprinted surface as reference, were CRP/albumin=4.0 and CRP/lysozyme=346. Measurement of the film thickness showed it to be approximately 10μm.A competitive binding experiment showed the CRP imprinted material to retain good selectivity for its template when jointly incubated with human serum albumin and CRP. Using the same method we were able to form a micro-contact imprint of human serum albumin which demonstrated relatively good recognition for its own template 2.66μg/cm2 compared with 0.27μg/cm2 for CRP.
Keywords: C-reactive protein; Thin film; Polymers; Micro-contact approach
Imprinting unique motifs formed from protein–protein associations by John Rick; Tse-Chuan Chou (pp. 26-31).
Lysozyme and cytochrome c were imprinted in aqueous media, both as individual proteins and in combination, together with the functional monomer 3-aminophenylboronic acid (APBA) using ammonium persulphate as the initiator. The polymers were formed as films on the gold surfaces of quartz crystal microbalance (QCM) electrodes. It was shown that the lysozyme imprinted polymer was capable of selective template recognition. Micro-calorimetry measurements were used to determine the ratio of lysozyme and cytochrome c giving rise to the maximum enthalpy change when combined in the presence of the functional monomer. Using this procedure a maximum enthalpic change was found when the two proteins were present in an equimolar ratio. A polymer, formed by jointly imprinting the proteins in this ratio, exhibited minimal recognition for the individual template proteins, but was however able to recognise them in combination, suggesting that the proteins when imprinted together interact to form a ‘new’ imprintable motif.The introduction of a series of protein solutions, comprising the imprint proteins in various ratios, to the lysozyme/cytochrome c imprinted films, showed that the films exhibit maximum affinity towards the proteins when they are presented in approximately the same mole ratio (57% cytochrome c and 43% lysozyme) as was used to form the original imprint (equimolar ratio).Frequency response profiles of the QCM electrodes carrying the films, as a function of time, showed the establishment of a new stable baseline (−4.3Hz) after the electrode was challenged with template protein (1.39×10−9mol) in less than 3min.
Keywords: Protein; Imprinting; Thin film; Aminophenylboronic acid; Microcalorimetry; Receptor; Quartz crystal microbalance (QCM)
Molecularly imprinted polymers for chemical agent detection in multiple water matrices by Amanda L. Jenkins; Sue Y. Bae (pp. 32-37).
In the past few years concerns over the possibility of terrorist actions against domestic and military water supplies has become paramount. Antibodies, peptides, and enzymes have been used as molecular recognition elements in chemical sensors; however, such devices often have storage and operational stability issues that limits their success. Molecularly imprinted polymers (MIPs), have been successfully demonstrated an alternative in pesticide applications [A.L. Jenkins, R. Yin, J.J. Jensen, Analyst 126 (2001) 798–802]. The MIP materials possess selective molecular recognition properties that are complementary to the analyte in the shape and positioning of functional groups. These polymers have high selectivity and affinity constants while maintaining excellent thermal and mechanical stability. In this study, direct imprinting of chemical agents EA2192, VX, sarin, and soman (the “G� agents), was performed and the limits of detection calculated. The ability of these sensors to work in various water matrices including tap, deionized and reverse osmosis water with residual chlorine was also evaluated. Typical detection limits for these MIP sensors are approximately 50ppt with wide linear dynamic ranges (ppt–ppm). Sensor response time is approximately 15min.
Keywords: Molecularly imprinted polymers; Chemical agents; Luminescence; Detection
Synthesis and evaluation of new propazine-imprinted polymer formats for use as stationary phases in liquid chromatography by F.G. Tamayo; M.M. Titirici; A. Martin-Esteban; B. Sellergren (pp. 38-46).
Silica particles have been used as supports for the preparation of three different propazine-imprinted polymer formats. First format refers to grafting of thin films of molecularly imprinted polymers (MIPs) using an immobilised iniferter-type initiator (inif-MIP). The other two new formats were obtained by complete filling of the silica pores with the appropriate polymerisation mixture leading to a silica–MIP composite material (c-MIP) followed by the dissolution of the silica matrix resulting in spherical MIP beads (dis-MIP). These techniques offer a mean of fine-tuning the particle morphology of the resulting MIP particles leading to enhanced capacity in chromatographic applications. Porous silica (specific surface area S=380m2g−1, particle size ps=10μm, pore volume Vp=1.083mlg−1 and pore diameter dp=10.5nm), methacrylic acid and ethylenglycol dimethacrylate were used for the preparation of the materials. All the MIP formats imprinted with propazine have been characterised by elemental analysis, FT-IR spectroscopy, nitrogen adsorption and scanning electron microscopy. Further, the materials were assessed as stationary phases in HPLC. Capacity factors, imprinting factors and theoretical plate numbers were calculated for propazine and other related triazines in order to compare the chromatographic properties of the three different stationary phases. For the inif-MIPs the column efficiency depended strongly on the amount of grafted polymer. Thus, only the polymers grafted as thin films of ca. 1.3nm average thickness show imprinting effects and the highest column efficiency giving plate numbers ( N) of 1600m−1 for the imprinted propazine. The performance of the c-MIP stationary phase decreases as result of the complete pore filling after polymerisation and increases again after the removal of the silica matrix due to a better mass transfer in the porous mirror-image resulting polymer. From this study can be concluded that the inif-MIP shows the best efficiency for use as stationary phase in HPLC for the separation of triazinic herbicides.
Keywords: Triazines; Molecular imprinting; Polymer grafting; Iniferter; Stationary phases; HPLC
Adaptation of the molecular imprinted polymers towards polar environment by Elena V. Piletska; Maria Romero-Guerra; Antonio R. Guerreiro; Kal Karim; Anthony P.F. Turner; Sergey A. Piletsky (pp. 47-51).
A new simple method for the post-polymerisation treatment of molecularly imprinted polymers was proposed. A layer of mineral oil was deposited onto the surface of the polymer in order to create a hydrophobic environment in the binding sites and to improve the recognition properties of the polymer in polar solvents. The testing of polymers performed in acetonitrile showed that the modified polymers possessed significantly increased selectivity as compared with non-treated ones. The three-fold improvement of recognition of the template (cocaine) was achieved; the same time, for non-specific molecule (morphine) the improvement was only 1.3 times. The investigation of the stability of mineral oil coating on the polymer surface suggested that the effect produced is stable over a long period of time. This approach could be used to broaden the range of experimental conditions where molecularly imprinted polymers can perform successfully.
Keywords: Molecular imprinting; Molecular modelling; Mineral oil; Cocaine; Chromatography
A comparative study of the potential of acrylic and sol–gel polymers for molecular imprinting by Wayne Cummins; Patrick Duggan; Peter McLoughlin (pp. 52-60).
The successful molecular imprinting of 2-aminopyridine (2-apy) in bulk polymerisations of acrylic and sol–gel based polymers has been achieved. Both polymeric systems reveal varying degrees of affinity in rebinding the original template as well as a number of structural analogues. Rebinding was conducted in chloroform, acetonitrile and methanol in order to assess the role of hydrogen bonding in imprinting. The acrylic imprinted polymer retained approximately 50% of the template in rebinding studies in chloroform compared to 100% for the sol–gel. However, this higher affinity for the sol–gel was accompanied by a higher degree of non-specific binding. While the acrylic polymer performed poorly in acetonitrile, the sol–gel maintained a high degree of discrimination.The acrylic polymer exhibited little discrimination between imprinted and reference polymers for 3-aminopyridine (3-apy) indicating the high selectivity of the MIP polymer for 2-apy relative to 3-apy. This selectivity was reduced in acetonitrile. Selectivity of the sol–gel for 2-apy in chloroform was poor as 3-apy was retained to a similar degree. Comparable results were obtained in acetonitrile. 4-Aminopyridine (4-apy) bound strongly to all polymers in all solvents and proved very difficult to remove due to the high degree of non-specific binding for both polymeric matrices.
Keywords: Molecular imprinting; Molecular recognition; 2-Aminopyridine; Sol–gel; Acrylic
Investigation of protein imprinting in hydrogel-based molecularly imprinted polymers (HydroMIPs) by Daniel M. Hawkins; Derek Stevenson; Subrayal M. Reddy (pp. 61-65).
We have developed a strategy to produce molecularly imprinted polymers based on polyacrylamide hydrogels for the selective imprinting of bovine haemoglobin (BHb). For the first time, we have explored in detail a variety of template removal strategies including varying ratios of sodium dodecylsulphate:acetic acid (SDS:AcOH) and also the use of a trypsin digest. The optimum ratio of SDS:AcOH was found to be a 10% (w/v):10% (v/v) for the most effective template removal. This resulted in >90% (imprinting efficiency) of re-loaded template (protein) molecule being selectively bound within the MIP. At 15%:15% of SDS:AcOH, although there was even more initial template removal, subsequent re-binding studies showed a decrease in imprinting efficiency (67.9%). Trypsin solutions were also used as a method of template removal. Up to 87.4% of template was reproducibly removed initially; however, the imprinting efficiency was only 20.4%. The high selectivity of the BHb HydroMIP to BHb compared with other structural analogues (namely cytochrome C and myoglobin) was successfully demonstrated.
Keywords: Hydrogel; HydroMIP; Molecular imprinting; Proteins; Polyacrylamide; Molecularly imprinted polymers; MIP
Synthesis and characterisation of molecularly imprinted catalytic microgels for carbonate hydrolysis by Pamela Pasetto; Stacey C. Maddock; Marina Resmini (pp. 66-75).
Novel molecularly imprinted microgels incorporating arginine and tyrosine side chains as functional monomers have been designed and synthesised with percentages of cross-linker ranging from 70 to 90%. Full chemico-physical characterisation including Mr, coil density and size particle determination concluded that all polymer preparations obtained can be classified as microgels. Molecular imprinting using a phosphate template was used to generate catalytic microgels for the hydrolysis of p-nitrophenyl carbonates. Kinetic characterisation of the catalytic activity of the different preparations indicated that values of critical monomer concentration ( CM) and percentage of cross-linker play an important role in determining the catalytic efficiency of the different preparations. Microgels containing 70% cross-linker were the only ones following the Michaelis–Menten saturation model and kinetic parameters were obtained using 4mg/ml of M397: Vmax=1.34×10−6Ms−1 (S.E. 1.28×10−7) and KM=2.38×10−3M (S.E. 3.1×10−4).
Keywords: Molecularly imprinted microgels; Phosphate; Catalytic polymers
Amperometric morphine sensing using a molecularly imprinted polymer-modified electrode by Wei-Ming Yeh; Kuo-Chuan Ho (pp. 76-82).
This study incorporates morphine into a molecularly imprinted polymer (MIP) for the amperometric detection of morphine. The polymer, poly(3,4-ethylenedioxythiophene), PEDOT, is an electroactive film that catalyzes morphine oxidation and lowers the oxidization potential on an indium tin oxide (ITO) electrode. The MIP-PEDOT modified electrode is prepared by electropolymerizing PEDOT onto an ITO electrode in a 0.1M LiClO4 solution with template addition (morphine). After template molecule extraction, the oxidizing current of the MIP-PEDOT modified electrode is measured in a 0.1M KCl solution (pH=5.3) at 0.75V (versus Ag/AgCl/sat’d KCl) with the morphine concentration varying in the 0.1–5mM range. A linear range, displaying the relationship between steady-state currents and morphine concentrations, from 0.1 to 1mM, is obtained. The proposed amperometric sensor could be used for morphine detection with a sensitivity of 91.86μA/cm2 per mM. A detection limit of 0.2mM at a signal-to-noise ratio of 3 is achieved. Moreover, the proposed method can discriminate between morphine and its analogs, such as codeine.
Keywords: Amperometric detection; Molecularly imprinted polymer (MIP); Morphine; PEDOT
Molecularly imprinted electrochemical sensor able to enantroselectivly recognized andl-tyrosine by Hui-Jing Liang; Tzong-Rong Ling; John F. Rick; Tse-Chuan Chou (pp. 83-89).
Electrochemical sensors were fabricated on nickel electrodes by molecularly imprintingd andl-tyrosine on polypyrrole films to form complementary cavities for subsequent template recognition. The performance of the imprinted films was evaluated by coulometry using an applied positive potential to induce adsorption of the target molecules. Using this procedure high enantioselectivities was found for each imprinted film. The individual selectivities forl andd-tyrosine on their respective imprinted films were estimated to bel/d=9.4/1 andd/l=27.2/1, determined by applying potential at a sweep rate of 0.1V/s from −0.1 to 0.5V (versus Ag/AgCl) with the two enantiomers being present at the same concentration (5mM). Several factors affecting rebinding, such as extraction time, film thickness, template concentration and sweep rate were investigated to achieve optimum recognition ability. The diffusion of target molecules in the polypyrrole films was also examined. A recognition mechanism for the interaction of the polypyrrole film for its template under the influence of an applied positive potential is proposed in this study.
Keywords: Molecular imprinting; Electrochemical sensor; Polypyrrole; Tyrosine
Amperometric detection of morphine based on poly(3,4-ethylenedioxythiophene) immobilized molecularly imprinted polymer particles prepared by precipitation polymerization by Kuo-Chuan Ho; Wei-Ming Yeh; Tsai-Shih Tung; Jung-Yu Liao (pp. 90-96).
Molecular imprinting is a novel technique used for chiral separation, artificial antibodies, sensors, and assays. Typically, molecular imprinted polymers (MIPs) are monoliths with irregular shapes. However, microspherical shapes with more uniform size can be obtained by the method of precipitation polymerization, which offers a higher active surface area by manipulating its compositions. In this study, MIP particles for the target molecule, morphine, were synthesized using a precipitation polymerization method that is more facile than the previous one that produced a thermally polymerized bulk. The conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), was utilized to immobilize the MIP particles onto the indium tin oxide (ITO) glass as a MIP/PEDOT-modified electrode. The sensitivity for the MIP/PEDOT-modified electrode with MIP particles was 41.63μA/cm2mM, which is more sensitive than that with non-MIP particles or that of a single PEDOT film with no incorporated particles in detecting morphine ranging from 0.1 to 2mM. The detection limit was 0.3mM (S/N=3). In addition, we presented that the modified electrode can discriminate codeine that plays an interfering species.
Keywords: Amperometric detection; Molecular imprinted polymer (MIP); Morphine; PEDOT; Precipitation polymerization
The use of molecularly imprinted polymers for extraction of sulfonylurea herbicides by J. Bastide; J.-P. Cambon; F. Breton; S.A. Piletsky; R. Rouillon (pp. 97-103).
Molecularly imprinted polymers (MIPs) possessing a good binding ability for the family of sulfonylurea herbicides were prepared using 4- or 2-vinyl pyridine as functional monomers and ethylene glycol dimethylacrylate as a crosslinker. Metsulfuron methyl was used as a template. It was found that MIP prepared in a polar organic solvent (acetonitrile) showed good recognition of the template and five other sulfonylurea herbicides (thifensulfuron methyl, chlorsulfuron, prosulfuron, chlorimuron ethyl, triflusulfuron methyl). The binding capacity was 0.08–0.1mgg−1 of the polymer. It was found that the polymer could be used for quantitative enrichment (>75%) of five sulfonylurea herbicides from water.
Keywords: Molecularly imprinted polymer; Sulfonylurea; Metsulfuron methyl; Solid phase extraction (SPE)
Comparison of particle size and flow rate optimization for chromatography using one-monomer molecularly imprinted polymers versus traditional non-covalent molecularly imprinted polymers by Ryan Simon; Stephen Houck; David A. Spivak (pp. 104-110).
The dependence of enantio-selective chromatographic performance on particle size, as measured by separation factor, was investigated for one-monomer molecularly imprinted polymers (OMNiMIPs) compared to traditionally formed EGDMA/MAA molecularly imprinted polymers (MIPs). Five particle size ranges were compared (<20μm, 20–25μm, 25–38μm, 38–45μm, and 45–63μm), revealing that the particle sizes above 25μm provided the highest separation factor, and thus the best enantiomer separation, for both imprinted polymers. Other chromatographic parameters such as the number of theoretical plates and resolution exhibited only minor changes for the OMNiMIPs as the particle size changed, except for particles 20μm and below. However, the number of theoretical plates and resolution for EGDMA/MAA are higher for particles in the 20–25μm range. Thus, chromatographic factors for the EGDMA/MAA polymers are better in this range, despite better enantioselectivity for particle sizes above 25μm. In contrast, OMNiMIPs generally show the most favorable performance for particle sizes in the 38–45μm range. It was also found that decreasing flow rate resulted in improved enantioselectivity for both MIPs for all particle sizes.
Keywords: OMNiMIP; NOBE; Particle size; Flow rate; Performance
Towards the development of multisensor for drugs of abuse based on molecular imprinted polymers by Elena V. Piletska; Maria Romero-Guerra; Iva Chianella; Kal Karim; Anthony P.F. Turner; Sergey A. Piletsky (pp. 111-117).
The synthetic receptors for cocaine, deoxyephedrine, methadone and morphine were computationally designed and produced using molecular imprinting. The structure and energy of the molecular complexes were analysed by computational techniques. The possible structures of the binding sites in the synthetic receptors have been compared with those of corresponding natural receptors. The composition of imprinted polymers was optimised to allow adequate performance under the same experimental conditions. All selected molecular imprinting polymers (MIPs) demonstrated stronger affinity in comparison with corresponding blank polymers resulting in imprinted factors (I) equal to 1.2 (cocaine), 2.5 (deoxyephedrine), 3.5 (methadone) and 3 (morphine) which suggested that the specific binding site for each molecule was successfully created. The polymers studied possessed good selectivity and affinity towards their templates and could be recommended for the integration with sensor devices. From a practical point of view, especially for multisensor requirements, the synthetic receptors based on imprinted polymers could be superior to natural receptors due to their stability, robustness and compatibility with automation processes required for sensor fabrication.
Keywords: Cocaine; Deoxyephedrine; Methadone; Morphine; Molecular imprinting; Molecular modelling; HPLC; Sensor
Porogen formulations for obtaining molecularly imprinted polymers with optimized binding properties by Ronald H. Schmidt; Anne-Sophie Belmont; Karsten Haupt (pp. 118-124).
This paper examines the formulation of new porogenic mixtures used to prepare molecularly imprinted polymers (MIPs) in both thin film and bulk monolith formats. Films were cast by using spin coating to spread a pre-polymerization mixture onto a substrate, and rapid curing of the films was achieved with UV photolysis. The use of a low volatility solvent in combination with a linear polymer porogen resulted in a porous morphology and a 60-fold enhancement in the binding capacity, relative to a non-porous film prepared with a highly volatile solvent and in the absence of the polymer porogen. The opposite effect was seen in MIPs that were prepared in the traditional bulk monolith format, for which the binding efficiency of the MIP decreased monotonically with the concentration of the linear polymer porogen. Furthermore, bulk MIPs that were prepared in the presence of linear polymer porogens exhibited significantly decreased specific surface areas (from 620 to 8m2/g for samples prepared with pure solvent and 50% polymer porogen, respectively). Despite the change in binding capacity and morphology, the selectivity of the bulk MIPs remained unaffected by the presence of the polymer porogens (approximately 50% chiral selectivity for all bulk MIPs considered). This difference in behavior of the two systems was attributed to the large difference in the kinetics of polymerization.
Keywords: Molecularly imprinted polymers; Morphology; Porogen
Comparison of pyrimethanil-imprinted beads and bulk polymer as stationary phase by non-linear chromatography by Claudio Baggiani; Patrizia Baravalle; Laura Anfossi; Cinzia Tozzi (pp. 125-134).
A pyrimethanil-imprinted polymer (P1) was prepared by iniferter-mediated photografting a mixture of methacrylic acid and ethylene dimethacrylate onto homemade near-monodispersed chloromethylated polydivinylbenzene beads. The chromatographic behaviour of a column packed with these imprinted beads was compared with another column packed with irregular particles obtained by grinding a bulk pyrimethanil-imprinted polymer (P2). The comparison was made using the kinetic model of non-linear chromatography, studying the elution of the template and of two related substances, cyprodinil and mepanipyrim. Extension of the region of linearity, capacity factors for the template and the related substances, column selectivity, binding site heterogeneity, apparent affinity constant ( K) and lumped kinetic association ( ka) and dissociation rate constant ( kd) were studied during a large interval of solute concentration, ranging between 1 and 2000μg/ml. From the experimental results obtained, in the linearity region of solute concentration column selectivity and binding site heterogeneity remained essentially the same for the two columns, while column capacity (at 20μg/ml, P1=23.1, P2=11.5), K (at 20μg/ml, P1=8.3×106M−1, P2=2.5×106M−1) and ka (at 20μg/ml, P1=3.5μM−1s−1, P2=0.47μM−1s−1) significantly increased and kd (at 20μg/ml, P1=0.42s−1, P2=0.67s−1) decreased for the column packed with the imprinted beads. These results are consistent with an influence of the polymerisation method on the morphology of the resulting polymer and not on the molecular recognition properties due to the molecular imprinting process.
Keywords: Molecular imprinting; Pyrimethanil; Grafting; Non-linear chromatography; Affinity constant; Dissociation rate constant; Association rate constant; Selectivity
Erratum to “Molecularly imprinted polymer thin films on quartz crystal microbalance using a surface bound photo-radical initiator�
by Theeraphon Piacham; Åsa Josell; Hans Arwin; Virapong Prachayasittikul; Lei Ye (pp. 135-135).