Imprinting, three-dimensional

Molecular imprinted polymers MIPs exhibit predetermined enan-tioselectivity for a specific chiral molecnle, which is nsed as the chiral template dnring the imprinting process. Most MIPs are obtained by copolymerization from a mixture consisting of a fnnctional mono-nnsatn-rated (vinylic, acrylic, methacrylic) monomer, a di- or tri-nnsatnrated cross-linker (vinylic, acrylic, methacrylic), a chiral template (print molecnle) and a porogenic solvent to create a three-dimensional network. When removing the print molecnle, chiral cavities are released within the polymer network. The MIP will memorize the steric and functional binding featnres of the template molecnle. Therefore, inclusion of the enantiomers into the asymmetric cavities of this network can be assumed as... 

One direct approach to the separation of chiral compounds is called molecular imprint polymers (MIPs) that involves the formation of a three-dimensional cavity with the shape and electronic features that are complementary to the imprinted or target molecule. 

Fig. 3 Application of the Doehlert experimental design to optimize a MIP for propranolol with respect to the type of cross-linker (EDMA or TRIM) and the degree of cross-linking, (a) Three-dimensional representation of response surfaces for the percentage of bound [3H]propanolol to the molecularly imprinted polymer (MIP) and the corresponding non-imprinted control polymer (NIP), (b) Contour plot of the function describing binding of [3H]propanolol to MIPs relative to the degree and the kind (bi or trifunctional) cross-linking. The values were corrected for non-specific binding to the non-imprinted control polymer. Adapted from [31] with kind permission from Springer Science + Business Media...

It should be noted that the presence of cross-links results in the partial or complete loss of control over the size of the polymer molecules, even if the living character of the polymerization can sometimes be preserved. Incidently, one of the characteristics of MIPs is that they are cross-linked polymers. This cross-linking is necessary in order to maintain the conformation of the three-dimensional binding sites obtained through the molecular imprinting process, and thus the ability of the polymer to recognize specifically and selectively its target molecule. Nevertheless, even with cross-linked polymers, the use of CRP methods may be beneficial, as it can, up to a certain point, improve the structure of the polymer matrix. Indeed, all of the above CRP methods have been applied to MIPs. 

Molecular imprinting allows the generation of specific three-dimensional cavities in polymer matrices by using a template molecule around which functional monomers and cross-linker are self-assembled in a pre-polymerisation state. Following polymerisation and template removal, the polymer matrix is left with the free three-dimensional cavities capable of rebinding the molecule, or others structurally very similar, used for the imprinting. 

The multilayer nanocomposite films containing layers of quasi-spherical Fe nanoparticles (d — 5.8 nm) separated by dielectric layers from boron nitride (BN) are synthesized by the repeated alternating deposition of BN and Fe onto a silicon substrate [54]. In this work the authors managed to realize the correlation in the arrangement of Fe nanoparticles between the layers the thin BN layer deposited on the Fe layer has a wave-like relief, on which the disposition of Fe nanoparticles is imprinted as a result, the next Fe layer deposited onto BN reproduces the structure of the previous Fe layer. Thus, a three-dimensional ordered system of the nanoparticles has been formed on the basis of the initial ordered Fe nanoparticle layer deposited on silicon substrate [54]. The analogous three-dimensional structure composed of the Co nanoparticles layers, which alternate the layers of amorphous A1203, has been obtained by the PVD method [55]. 

Molecular imprinting in synthetic polymers was reported for the first time in 1972 [1--4]. The initial idea was to obtain in the polymer highly specific binding clefts with a predetermined size, shape and three-dimensional arrangement of functional groups. Later on, further experiments demonstrated that such functionalised cavities could be tailored to mimic the active sites of enzymes ( enzyme analogue built polymer ). 

Molecular imprinting approaches using inorganic matrices 8.3. THREE-DIMENSIONAL MATRICES... 

In addition to the one-dimensional templated structure of the MCM-41 materials, two- and three-dimensional systems have also been prepared. A number of papers have used the lamellar structures of amphiphile assemblies to prepare flat, striated metal oxide materials [72,73]. These materials often exhibit enhanced properties over materials that have uncontrolled three-dimensional growth. Vesicles have also been used to engineer spherical imprints into silicates [74,75]. Even more elaborate supramolecular surfactant systems, that yield toroidal and other unusually shaped metal oxides, have also been reported [76,77]. 

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. 

Fig. 6.1 (a) Three-dimensional and (b) two-dimensional imprinting polymerization, (courtesy of VTT)38... 

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