Templates, imprinting Molecularly imprinted polymer

The aim of this chapter is to give a brief overview of the molecularly imprinted catalysts reported up to approximately the turn of the millennium, followed by a more concise review of the literature thereafter. In addition to catalysis, that is cases in which a reaction TSA or intermediate are used as the template, imprinted polymers capable of aiding chemical transformations will also be discussed. In these cases the reaction substrate or product are often used as the template in order to control the regio- or stereochemistry of the reaction. 

An important question in molecular imprinting has been addressed using covalent binding by two boronic acids to what extent can imprinted polymers also bind substances other than the template. For example, are racemates of other substances resolvable In the first experiments on glyceric acid esters 5 with a certain ester as template, imprinted polymers were shown to resolve a whole series of racemates even when the alcohol group in the racemate is varied (methyl, ethyl, benzyl, or 4-nitrophenyl) [39]. Aromatic amino acids were shown to behave similarly. Here, the aromatic group in the racemates can vary. A racemate resolution is possible provided that the rest of the structure remains the same [40]. 

It is known that molecularly imprinted [3-CD polymer may be used as optical receptor for detection of organic compounds. The molecularly imprinted [3-CD polymer was prepared from [3-CD, using TDI as a crosslinking agent in this procedure A-phenyl-l-naphthylamine (35) served as a template. The molecularly inprinted polymer was fluorometrically characterized using a fibre optic cable attached to a flow-cell. The above sensor was investigated for analytical determination of 35 [82]. 

Molecularly imprinted polymers (MIPs) can be prepared according to a number of approaches that are different in the way the template is linked to the functional monomer and subsequently to the polymeric binding sites (Fig. 6-1). Thus, the template can be linked and subsequently recognized by virtually any combination of cleavable covalent bonds, metal ion co-ordination or noncovalent bonds. The first example of molecular imprinting of organic network polymers introduced by Wulff was based on a covalent attachment strategy i.e. covalent monomer-template, covalent polymer-template [12]. 

Molecularly imprinted polymers (MIPs) are of growing interest for their potential biotechnological applications. Recently, the templating processes with living yeast cells were reported107 for the preparation of ordered and... 

The concept is extendable to templated sensors made of protein templated xerogels in which a luminescent reporter group is further added in close proximity to the template site so as to effectively transduce the protein-molecularly imprinted polymer binding event (Figure 6.12).11... 

Fig. 1. Concept of molecular imprinting - the non-covalent approach. 1. Self-assembly of template with functional monomers. 2. Polymerization in the presence of a cross-linker. 3. Extraction of the template from the imprinted polymer network. 4. Selective recognition of the template molecule...

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... 

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). 

EUwanger A, Berggren C, Bayoudh S, Crecnzi C, Karlsson L, Owens PK, Ensing K, Cormack P, Sherrington D, Sellergren B. Evaluation of methods aimed at complete removal of template from molecularly imprinted polymers. Analyst 2001 126 784-792. 

Rosengren AM, Karlsson JG, Andersson PO, Nicholls lA. Chemometric models of template— molecularly imprinted polymer binding. Anal Chem 2005 77 5700-5705. 

Wang HJ, Zhou WH, Yin XF, Zhuang ZX, Yang HH, Wang XR. Template synthesized molecularly imprinted polymer nanotube membranes for chemical separations. J Am Chem Soc 2006 128 15954-15955. 

Figure 20-23 (a) Surface plasmon resonance spectrum of sensor coated with molecularly imprinted polymer that selectively binds NAD+. (b) Response of sensor to four similar molecules shows largest response to NAD+, which was the template for polymerization. [From O. A. Raitman. V. I. Chegel, a B. Kharitonov. M. Zayats. E. Katz, and I. Winner. Analysis of NAD(P) and NAD(P)H Cofactors by Means of Imprinted Polymers Associated with Au Surfaces A Surface Plasmon Resonance Study. Anal. CNm. Ada 2004,504. 101.]... 

A molecularly imprinted polymer is one that is polymerized in the presence of a template molecule to which components of the polymer have some affinity. When the template is removed, the... 

Application of MIP chemosensors imprinted with two different templates can also improve detectability. For instance, polycyclic aromatic hydrocarbons (PAHs) have been determined using polymers molecularly imprinted with two different PAH templates [155]. Compared with MIPs of a single-template imprint, the detection signal of the resonant frequency change was enhanced by a factor of five and LOD for pyrene was as low as 60 pg L 1. This two-template largely improved detectability can be attributed to easier accessibility of the recognition sites through different diffusion pathways. 

Abstract Most analytical applications of molecularly imprinted polymers are based on their selective adsorption properties towards the template or its analogs. In chromatography, solid phase extraction and electrochromatography this adsorption is a dynamic process. The dynamic process combined with the nonlinear adsorption isotherm of the polymers and other factors results in complications which have limited the success of imprinted polymers. This chapter explains these problems and shows many examples of successful applications overcoming or avoiding the problems. 

Wei ST, Jakusch M, Mizaikoff B (2006) Capturing molecules with templated materials -analysis and rational design of molecularly imprinted polymers. Anal Chim Acta 578(1) ... 

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