| 1. |
- Courtois, Julien, et al.
(author)
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A study of surface modification and anchoring techniques used in the preparation of monolithic microcolumns in fused silica capillaries.
- 2006
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In: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 29:1, s. 14-24
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Journal article (peer-reviewed)abstract
- Based on a survey of the literature on pretreatment of fused silica capillaries, 3 etching procedures and 11 silanization protocols based on the vinylic silane 3-((trimethoxysilyl)propyl) methacrylate (gamma-MAPS) were found to be most representative as a means of ensuring attachment of in situ prepared vinylic polymers. These techniques were applied to fused silica capillaries and the success in establishing the intended surface modification was assessed. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state of the surface, providing information regarding presence of the reagent bound to the capillary. Wetting angles were measured and correlated with the XPS results. An adherence test was done by photopolymerization of a 2 mm long plug of 1,6-butanediol dimethacrylate in the prepared capillaries and evaluation of its ability to withstand applied hydraulic pressure. SEM was also performed in cases where the plug was released or other irregularities were observed. Finally, the roughness of the etched surface, considered to be of importance, was assessed by atomic force microscopy. Alkaline etching at elevated temperature provided a surface roughness promoting adhesion. The commonly used silanization protocols involving water in the silanization or washing steps gave inadequate surface treatment. The best silanization procedure was based on toluene as a solvent.
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| 2. |
- Courtois, Julien, et al.
(author)
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Assessing the macroporous structure of monolithic columns by transmission electron microscopy
- 2007
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In: Analytical Chemistry. - Columbus, OH : American Chemical Society. - 0003-2700 .- 1520-6882. ; 79:1, s. 335-344
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Journal article (peer-reviewed)abstract
- A set of monolithic stationary phases representing a broad span of monomers and porogens have been characterized directly in their capillary chromatographic format by computational assessment of their pore structure from transmission electron micrographs obtained after in situ embedment of the monoliths in contrast resin, followed by dissolution of the fused-silica tubing, further encasement of the resin-embedded monolith, and microtomy. This technique has been compared to mercury intrusion, a more conventional technique for macroporosity estimation. Supplementing the embedding resin by lead methacrylate gave a negative staining, and the resulting micrographs showed a good contrast between the polymeric monoliths and the embedding resin that allowed studies on the pore formation and polymer development. The technique was also applied to a commercial monolithic silica column.
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| 3. |
- Courtois, Julien, et al.
(author)
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Interactions of bupivacaine with a molecularly imprinted polymer in a monolithic format studied by NMR
- 2006
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In: Analytical Chemistry. - Columbus, OH : American Chemical Society. - 0003-2700 .- 1520-6882. ; 78:2, s. 580-584
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Journal article (peer-reviewed)abstract
- A trimethylolpropane trimethacrylate-based monolith of dimensions carefully chosen to fit exactly in a standard 4-mm solid-state CP/MAS NMR rotor was photopolymerized and subsequently molecularly imprinted with bupivacaine using a grafting protocol with methacrylic acid and ethylene dimethacrylate as monomers. As no crushing or grinding of the monolith was necessary, additional unspecific surface area was not created. This procedure ascertains that differences observed between imprinted and nonimprinted polymers are due only to graft imprinted surfaces and give therefore better results in NMR spectroscopy due to less unspecific interactions between analyte and monolith. This improves the comparability to chromatographic evaluations where uncrushed monolithic columns are also used. To track interactions between analyte and stationary phase, the saturation transfer difference (STD) technique was applied on the polymer in the suspended state using the same solvent as in the chromatographic evaluation. This relatively new NMR method has to our knowledge not been used on chromatographic materials before. By using STD NMR on pristine monoliths, it was possible to measure large differences between the imprinted or nonimprinted polymers and the analyte indicating significant differences in the interaction mechanisms. These could be directly correlated with retention differences observed in chromatographic evaluations.
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| 4. |
- Courtois, Julien, et al.
(author)
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Molecularly imprinted polymers grafted to flow through poly(trimethylolpropane trimethacrylate) monoliths for capillary-based solid-phase extraction
- 2006
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In: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673 .- 1873-3778. ; 1109:1, s. 92-99
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Journal article (peer-reviewed)abstract
- Monolithic previous termmolecularly imprinted polymersnext term (mMIPs) have been synthesized in a novel way using a trimethylolpropane trimethacrylate core material photo-polymerized in situ in a 100 μm I.D. UV-transparent capillary and further photo-previous termgraftednext term to create specific cavities in the previous termgraftednext term layer. This polymerization technique allows the imprints to be directly created on the surface of the material using a minimum amount of template. Three different anaesthetics of similar structures (bupivacaine, mepivacaine and S-ropivacaine) were used as model target molecules to synthesize sample enrichment media. Hence, various mMIPs have been prepared and evaluated on a micro-system against each analyte in order to test the retention properties and cross-selectivities of the materials. The retention factors were determined and compared with the non-previous termimprintednext term reference column (mNIP), yielding high imprinting factors together with good selectivity factors between the three analytes. A study with a pure enantiomeric target was carried out to assess the degree of stereo-specific imprinting for injection of racemic mixtures. Finally, one column was previous termimprintednext term with an equimolar mixture of all three anaesthetics to provide further comprehension of the retention mechanism and accredit the possibility of using the material as a sample enrichment entity. Scanning electron microscopy (SEM), nitrogen absorption/desorption (BET) and mercury intrusion porosimetry were used to characterize the monolith and the mMIPs properties. Nuclear magnetic resonance (NMR) has been used to assess the similarities between the mMIP and mNIP.
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| 5. |
- Courtois, Julien, 1979-
(author)
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Monolithic separation media synthesized in capillaries and their applications for molecularly imprinted networks
- 2006
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Doctoral thesis (other academic/artistic)abstract
- The thesis describes the synthesis of chromatographic media using several different approaches, their characterizations and applications in liquid chromatography. The steps to achieve a separation column for a specific analyte are presented. The main focus of the study was the design of novel molecularly imprinted polymers. Attachment of monolithic polymeric substrates to the walls of fused silica capillaries was studied in Paper I. With a broad literature survey, a set of common methods were tested by four techniques and ranked by their ability to improve anchoring of polymers. The best procedure was thus used for all further studies. Synthesis of monoliths in capillary columns was studied in Paper II. With the goal of separating proteins without denaturation, various monoliths were polymerized in situ using a set of common monomers and cross-linkers mixed with poly(ethylene glycol) as porogen. The resulting network was expected to present “protein-friendly pores”. Chemometrics were used to find and describe a set of co-porogens added to the polymerization cocktails in order to get good porosity and flow-through properties. Assessment of the macroporous structure of a monolith was described in Paper III. An alternative method to mercury intrusion porosimetry was proposed. The capillaries were embedded in a stained resin and observed under transmission electron microscope. Images were then computed to determine the pore sizes. Synthesis of molecularly imprinted polymers grafted to a core mono-lith in a capillary was described in Paper IV. The resulting material, imprinted with local anaesthetics, was tested for its chromatographic performance. Similar imprinted polymers were characterized by microcalorimetry in Paper V. Finally, imprinted monoliths were also synthesized in a glass tube and further introduced in a NMR rotor to describe the interactions between stationary phase and template in Paper VI.
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| 6. |
- Courtois, Julien, et al.
(author)
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Novel monolithic materials using poly(ethylene glycol) as porogen for protein separation
- 2006
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In: Polymer. - Guildford, Surrey : Butterworth. - 0032-3861 .- 1873-2291. ; 47:8, s. 2603-2611
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Journal article (peer-reviewed)abstract
- Several recipes are described for the preparation of porous polymeric monoliths in the capillary format, using poly(ethylene glycol) (PEG) as porogen as well as constituent in the monomer mixture. Acrylic or methacrylic monomers with a variety of terminal groups, with and without ethylene glycol links of differing lengths in the side chains, have been used in combination with triethylene glycol dimethacrylate (TEGDMA) and trimethylol-propane trimethacrylate (TRIM) as cross-linkers. PEGs of 4–20 kDa molecular weight dissolved in 2-methoxy-ethanol were used as porogens to yield large, biocompatible pores. A number of common solvents have been used as co-porogens for the PEGs, and the surface areas, median pore diameters, and back pressures of the resulting monoliths have been correlated with a number of molecular descriptors by means of chemometrics to describe the results. Photopolymerizations induced by either continuous or pulsed UV light were furthermore compared. Pore size distribution and surface area characterization have been assessed by nitrogen adsorption–desorption and mercury intrusion porosimetry, and scanning electron microscopy (SEM) was used to evaluate the differences in macroporous morphology obtained with the different porogen solutions. Mixtures selected from screening syntheses carried out in vials have been implemented in 100 μm fused silica capillaries and the back pressures measured and cross-validated with the pore information. Some of these capillary columns were finally tested for the separation of proteins using micro-HPLC.
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| 7. |
- Emgenbroich, Marco, et al.
(author)
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A Phosphotyrosine-Imprinted Polymer Receptor for the Recognition of Tyrosine Phosphorylated Peptides
- 2008
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 14:31, s. 9516-29
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Journal article (peer-reviewed)abstract
- Hyperphosphorylation at tyrosine is commonly observed in tumor proteomes and, hence, specific phosphoproteins or phosphopeptides could serve as markers useful for cancer diagnostics and therapeutics. The analysis of such targets is, however, a challenging task, because of their commonly low abundance and the lack of robust and effective preconcentration techniques. As a robust alternative to the commonly used immunoaffinity techniques that rely on phosphotyrosine(pTyr)-specific antibodies, we have developed an epitope-imprinting strategy that leads to a synthetic pTyr-selective imprinted polymer receptor. The binding site incorporates two monourea ligands placed by preorganization around a pTyr dianion template. The tight binding site displayed good binding affinities for the pTyr template, in the range of that observed for corresponding antibodies, and a clear preference for pTyr over phosphoserine (pSer). In further analogy to the antibodies, the imprinted polymer was capable of capturing short tyrosine phosphorylated peptides in the presence of an excess of their non-phosphorylated counterparts or peptides phosphorylated at serine.
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| 8. |
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| 9. |
- Oxelbark, Joakim, et al.
(author)
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Chromatographic comparison of bupivacaine imprinted polymers prepared in crushed monolith, microsphere, silica-based composite and capillary monolith formats
- 2007
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In: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1160:1-2, s. 215-26
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Journal article (peer-reviewed)abstract
- A comprehensive comparison of five chromatographic stationary phases based on molecularly imprinted polymers is presented. Efficiency, imprinting factors, water compatibility and batch-to-batch reproducibility are discussed for crushed monolith, microspheres, two silica-based composites and capillary monoliths, all imprinted with the local anaesthetic bupivacaine. Synthesis protocol and chromatographic test conditions have been kept fixed within certain limits, in order to provide further insight into the strengths and weaknesses of the different formats. Excluding microparticles, all formats give satisfactory performance, especially in aqueous mobile phases. An assessment of batch-to-batch reproducibility in different mobile phases adds further value to this comparison study.
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