Templating molecule shape

To prepare artificial enzymatic systems possessing molecular recognition ability for particular molecules, molecular imprinting methods that create template-shaped cavities with the memory of the template molecules in polymer matrices, have been developed [22, 30-35] and established in receptor, chromatographical separations, fine-chemical sensing, etc. in the past decade. The molecular... 

In addition to imprinted acid-base catalysts [49-55], attempts to imprint metal complexes have been reported and constitute the current state of the art [46, 47]. In most cases of metal-complex imprinting, ligands of the complexes are used as template molecules, which aims to create a cavity near the metal site. Molecular imprinting of metal complexes exhibits several notable features (i) attachment of metal complex on robust supports (ii) surrounding of the metal complex by polymer matrix and (iii) production of a shape selective cavity on the metal site. Metal complexes thus imprinted have been appHed to molecular recognition [56, 57], reactive complex stabilization [58, 59], Hgand exchange reaction [60] and catalysis [61-70]. 

Added along with the imprinting vinylpyridine are cross-linkers, spacers, or poro-gens. These cross-linkers or spacers should be miscible with the other ingredients, but have shapes that are dissimilar so that they do not become an integral part of the assembly around the template molecule. For naproxen, the cross-linker is ethylene glycol dimethylacrylate (EDMA). 

This chapter will introduce the field of sensors based on molecular imprinted polymers (MIPs). MIPs are highly cross-finked polymers that are formed with the presence of a template molecule (Haupt and Mosbach 2000 Wulff 2002). The removal of the template molecule from the polymer matrix creates a binding cavity that is complementary in size and shape to the template molecule and is fined with appropriately positioned recognition groups (Scheme 15.1). 

In the molecular imprinting technique, a cross-linked polymer matrix is formed around a target analyte (the template). The precursor mixture contains a functional monomer which can interact with the template molecule by covalent or non-covalent bonding. After the polymerisation process, the functional groups are held in position by the polymer backbone and the template molecule is removed. The residual binding sites are complementary to the target molecules in size and shape. 

A large number of organoalkoxysilanes can be purchased or synthesized to help impart selectivity to the matrix. These functional monomers can be selected to complement specific functional groups on the template molecule to provide the materials with chemical specificity in addition to shape selectivity. 

Molecularly imprinted polymers (MIPs) form when template molecules are surrounded by monomers which then react with cross-linkers to produce a porous polymer around the templating species. Once the template has been removed a porous polymer remains in which the pores are ideal binding sites for a target with the same molecular shape as the template as shown in Fig. 4.28. 

While dynamic light scattering revealed an average apparent hydrodynamic particle diameter of about 200 20 nm, transmission electron microscopy gave a more realistic image of the shape and the size distribution of the nanoMIPs. Figure 9 shows that spherical particles with a rather broad size distribution were formed. They had a diameter of 50 nm up to 300 nm with an average particle diameter around 110 nm and the absence or presence of the template molecule... 

Zeolites and related aluminosilicates constitute a vital family of microporous materials with immense applications in catalysis, sorption and separation processes [1-3]. The discovery of aluminophosphates is an important landmark in the science of these materials [4], All these materials are, in general, synthesized under hydrothermal conditions by making use of template molecules [2]. The template molecules are usually organic amines and they are involved in the formation of these framework structures in more ways than one. While it is difficult to pinpoint the exact manner in which the amines participate or direct the formation of these inorganic structures, it is generally believed that their size and shape are crucial in determining the pore structure. In recent years, a variety of open-framework structures formed by divalent metal phosphates... 

Molecular imprinting is a technique in which the shape of a template molecule (analyte) is imprinted in a polymer, e.g. described by Kriz et al. (1997), Reid et al. (1998), Yano (1999), Yan (2002). The imprinted polymer can be used as an antibody mimic for an immunoassay. 

This review will focus on the situation where a template molecule interacts either with a performed polymer or with the constituents of a polymerisable mixture. The interactions exploited have to be reversible and can either be of a well-defined nature, such as in the formation of a covalent bond, or rather ill-defined as in the case of hydrophobic interactions. The preformed polymer undergoes conformational changes in the presence of the template, whereas in the case of the polymerisable mixture an entirely new polymer is formed around the template. In both instances the template is incorporated into the polymer network and subsequently extracted. The template leaves behind spaces or cavities, which to varying extents are complementary to the shape and/or electronic features of the template. The properties of the polymers obtained and their potential applications depend on the characteristics of the template and its mode of interaction with the precursor polymer or polymerisable mixture, but also on the final polymer structure itself... 

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