Templates imprinting

FIGURE 1.49 Principle of molecular imprinting.169 1 = functional monomers 2 = cross-linking monomer 3 = molecule whose imprint is desired (molecular template). In (A), 1 and 2 form a complex with 3 and hold it in position in (B), polymerization involving 1 2 occurs and the template (imprint molecule) is held in the polymeric structure in (C) and (D) the imprint molecule is removed leaving a cavity complementary to its size and shape into which a target analyte of similar dimensions can fit. (Reproduced with permission from Taylor Francis.)... 

Lauceri, R., Raudino, A., Scolaro, L. M Mical, N., and Purrello, R. (2002). From achiral porphyrins to template-imprinted chiral aggregates and further self-replication of chiral memory from scratch. / Am. Chem. Soc., 124, 894-5. 

Isosorbide 2,5-dimethacrylate was used for preparation of template-imprinted vinyl and acrylic polymers.266... 

Similar features may be achieved with organic polymeric materials. Template imprinting of complementary cavities containing appropriate functional groups yields models of enzyme active sites [7.34, 7.35, 7.75]. They perform the synthesis of amino acids with enantioselectivity [7.76] or the esterolysis of activated esters by TSA imprinting [7.77]. 

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. 

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. 

Dauksher W, Le N, Ainley E, Nordquist K, Gehoski K, Young S, Baker J, Convey D, Mangat P. Nano-imprint lithography templates, imprinting and wafer pattern transfer. Microelectronic Engineering 2006, 83, 929-932. 

Bellacchio E, Lauceri R, Gurrieri S et al (1998) Template-imprinted chiral porphyrin aggregates. J Am Chem Soc 120 12353-12354... 

Fig. 11.4. Laser confocal and SEM of the materials prepared according to the process depicted in Fig. 11.3. Photographs show individual stages in the cell-mediated lithography of polymer surfaces using Listeria monocytogenes (left column a, c, e, g) and Staphylococcus aureus (right column b, d, f, h) as templates. Imprinted microcapsules (a, b) and solid polymer beads before (c, d) and after (e, f) the removal of template cells, (g, h) Show the imprint sites after reacting the beads with fluorescent-labelled Concanavalin A.

Islands of bonded molecules. The method of molecular templates (imprints)... 

It was observed that a high proportion of template (10%) can be introduced without losing the mesomorphic order [ 199]. Moreover after template extraction, the polymorphism was quite different from that of the non-imprinted material, the variations depending on the structure of the template used and on its concentration [200]. The last point is the manifestation of a significant memory effect of the template, imprinted inside the mesomorphic structure. It arises from the interactions between template and the other parts of the network which can induce conformational constraints inside the networks during cross-linking. It occurs even though the amount of crosslinker is low (5%). Moreover, this point constitutes a means for the direct study of the imprint left in the network by the template. 

The metal template (Cu(I)) was selectively extruded by reacting the [2]ro-taxane complex40 + with KCN (50 equiv.) [68]. This decomplexation reaction liberated the free [2]rotaxane 41+ quantitatively. As studied by NMR spectroscopy, and depicted in Fig. 16, the template imprint (a bis-dpp, tetrahedral coordination sphere) has completely vanished through rearrangement of the threaded macrocycle around its axle [78]. Recomplexation of 41+ with Ag+ or Li+ by reaction with AgBF4 or LiBF4 restored the template imprint and afforded the Ag+- and Li+-[2]rotaxane complexes 42 + and 43 + quantitatively. 

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]. 

Shi, H.Q. Tsai, W.B. Garrison, M.D. Ferrari, S. Ratner, B.D. Template-imprinted nanostructured surfaces for protein recognition. Nature 1999, 398, 593-597. 

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