Molecularly imprinted polymers print molecule

Fig. 4.5 Chromatogram representing print molecule (oxacillin) and two other /3-lactam antibiotics (penicillin G and V) on oxacillin MIP (a) compared with the control blank MIP (b). Reprinted from J. Chromatogr. A, 889, Briiggemann et al. New configurations and applications of molecularly imprinted polymers , 15-24 (2000), with permission...

Figure 7.8 A schematic representation of the preparation of molecularly imprinted polymers [19]. (a) Functional monomer MAA (1) is mixed with print molecule, here theophylline (2), and EDMA, the cross-linking monomer, in suitable solvent. MAA is selected for its ability to form hydrogen bonds with a variety of chemical functionalities of the print molecule. (6) The polymerization reaction is started by addition of initiator (2,2 -azobis(2-methylpropionitrile), AIBN). A rigid insoluble polymer is formed, Imprints , which are complementary to the print molecule in both shape and chemical functionality, are now present within the polymeric network, (c) The print molecule is removed by solvent extraction. The wavy line represents an idealized polymer structure but does not take into account the accessibility of the substrate to the recognition site,...

Figure 1 Representation of the general scheme of noncovalent molecular imprinting. For a template molecule (or target or print molecule), T appropriate functional monomers M are chosen and allowed to form a self-assembly construct. By co-polymerization with a cross-linking monomer L, a polymer network is formed in which the self-assembly is set. Thereby, the position and the spatial conformation of the monomers are constructed according to the template. The embedded template T can then be extracted from and rebind to the molecularly imprinted polymer (MIP).

The new strategy for chiral separation in chromatography and capillary electrophoresis is the development of molecularly imprinted polymers. First of all, Wulf et al. [141] presented the idea of a molecularly imprinted polymers technique. This involves the incorporation of a target molecule (an imprint molecule) into a polymer and the removal of the print molecule, to leave a substrate selective site or cavities. This may be achieved either by... 

Figure 7.5. A Chromatogram of a mixture containing the print molecule (oxacillin), two other P lactam-antibiotics (penicillin G and penicillin V) and a non-P-lactam-antibiotic (bacitracin) on an oxacillin imprinted MIP containing 4-vinylpyridine residues, cross-linked with TRIM. The analysis was performed in organic mobile phase (ACN/AcOH, 99 1), B same conditions but using the respective control polymer, C Structures of penicillin V, penicillin G and oxacillin. Reprinted with permission from Skudar K, Briiggemann O, Wittelsberger Aet al. Selective recognition andseparation ofp-lactam antibiotics using molecularly imprinted polymers. Anal Commun 1999 36 327-331.

An early attempt to make a real electrochemical sensor based on a molecularly imprinted methacrylate polymer utilised conductometric measurements on a field-effect capacitor [76]. A thin film of phenylalanine anilide-imprinted MAA-EDMA copolymer was deposited on the surface of semiconducting p-type silicon and covered with a perforated platinum electrode. An AC potential was applied between this electrode and an aluminium electrode on the back side of the semiconductor and the capacitance measured as a function of the potential when the device was exposed to the analyte in ethanol. The print molecule could be distinguished from phenylalanine but not from tyrosine anilide and the results were very variable between devices, which was attributed to difficulties in the film production. The mechanism by which analyte bound to the polymer might influence the capacitance is again rather unclear. 

Molecular imprinting technique was recently used to prepare highly selective tailor-made synthetic affinity media used mainly in chromatographic resolution of racemates or artiftcial antibodies [130-133]. A complex between the template molecule and the functional monomer is first formed in solution by covalent or non-covalent interactions (Figure 3.10). Subsequently, the three-dimensional architecture of these complexes is confined by polymerization with a high concentration of cross-linker. The template molecules are then extracted from the polymer leaving behind complementary sites (both in shape and functionahty) to the imprinted molecules. These sites can further rebind other print molecules. 

The molecularly imprinted copolymer of 2-hydroxyethyl methacrylate (HEMA) and p-CyD-coupled HEMA was synthesized in chloroform to study its interaction with a pair of steroids cholesterol and testosterone [42]. The molecularly imprinted copolymer was found to absorb the print molecule several times better than an imprinted poly HEMA. Asanuma et al. [44] concluded that cholesterol binding by the HEMA polymer was not due to CyD inclusion because no inclusion of CyD to cholesterol can form in chloroform. Another strategy developed for imprinting using CyD elements is the vinyl CyD (Table 1 and 10.3(A)), which has been successfully applied for imprinting antibodies, oligo-peptides [45], and vancomycin [46[. 

Molecular imprinting is a method for the synthesis of polymers with predeterminated selectivity for various compounds. This technique uses noncovalent prearrangement of functional monomers in the presence of the print molecules prior to the polymerization for the creation of highly specific binding sites. After polymerization the print molecules are washed out of the macroporous polymer matrix. The result is a polymer with recognition sites due to the shape of the print molecules. The proper arrangement of the functional groups in the polymer have the affinity for the print molecules. This fact leads to the restriction that the structure of the enantiomers, to be separated, must be very similar to these of the print molecules. 

Figure 7.12. Synthesis of Z-asparlame in the presence and absence of MIP imprinted with product curve 1 MIPi, Z-aspartameasprint molecule, curve 2 control polymer, no print molecule, curve 3 MIP2, Z-L-Asp and L-Phe-OMe as print molecules, curved the polymer-free enzymatic reaction. Reprinted with permission from Ye L, Mansson M-O, Mosbach K et al. A new apphcadon of molecularly imprinted materials. J Molec Recog 1998 11 75-78. 1998 John Wiley Sons, Ltd.

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