Noncovalent imprinting

Scheme 15.3 Noncovalent imprinting of L-phenylalanine anilide in a methacrylic acid (MAA)/ethylene glycol dimethylcrylate (EGDMA) polymer matrix. Adapted from Sellergren et al. (1998). Copyright 1988 American Chemical Society.

Hybrid MIPs. More recently, hybrid imprinting strategies have been developed that combine the advantages of both the covalent and noncovalent imprinting strategies (Whitcombe et al. 1995 Lubke et al. 2000). A recent example by Whitcombe s group is presented in Scheme 15.4 (Klein et al. 1999). The monomer-template prepolymerization complex is formed via a combination of covalent amide bonds and... 

TABLE 15.2 Structural and Functional Building Blocks in Molecular Imprinting Monomers Used in Noncovalent Imprinting... 

The recognition and material properties of MIPs are strongly dependent on the polymerization conditions. Variation of the polymerization temperature solvent, template, and monomer concentrations and cross-linker percentage attenuates the fidelity of the imprinting process by changing the structure and stability of the prepolymerization complex as well as the templated binding sites. The noncovalent imprinting... 

Another possible way of overcoming the limitations posed by the presence of water in the suspension polymerisation process is to substitute the continuous water phase with alternative solvents that could still act as dispersing medium for the monomer mixture but better preserve noncovalent interactions in the template-monomer assembly. For example, liquid fluorocarbons are chemically inert and do not affect interactions which are used in noncovalent imprinting. Use of such solvents for the preparation of MIP microbeads has been demonstrated already in 1996 by Mayes and Mosbach [16,17]. A range of MIPs were prepared using Boc-l-phenylalanin as the template, MAA as the functional monomer and different kinds and amounts of crosslinkers and porogenic solvents. The resulting MIP microbeads... 

There are two processes by which the bulk imprinted polymers are formed covalent imprinting and noncovalent imprinting. In the former, the template molecule is first covalently functionalized with the monomer, and then copolymerized with the pure monomer. After that the covalent bond is broken and the template molecule is removed by extraction. In order to facilitate the extraction step, a so-called porogenic solvent is used. It effectively swells the polymer matrix. 

A simple drawing of the sol-gel noncovalent imprinting scheme described by us many years ago is shown in Figure 20.5.64,65 In this work, we were interested in making a thin film that was selective for dopamine over other common... 

Figure 20.5 Simplified drawing depicting the noncovalent imprinting of dopamine in hybrid silica thin film.

Fig. 23.9 Noncovalent imprinting synthesis of sitica functionalized with a catalytic triad. The catalytic hydrolysis of BAPNA is also shown [28]...

Fig. 23.10 An example of a covalent/noncovalent imprinting approach [29]. Imprint and monomers are polymerized, followed by cleavage of the imprint to leave imidazole and hydroxyl groups bound to the polymer. The catalytic hydrolysis of N-Boc,0-Nitrobenzyl-phenylalanine (BocPheONP) is shown...

Other variables in the imprinting process are stoichiometry and temperature, which are particularly important in the cases of noncovalent imprinted polymers. Lower temperatures and higher functional monomer to template ratios stabilize noncovalent prepolymerization complexes, resulting in noncovalent MIPs with higher capacities and selectivities. The imprinting process can be carried out at lower temperatures by either UV initiated radical polymerizations or by using azo-based radical initiators. 

Fig. 1 Common functional monomers (top) and cross-linking agents utilized in noncovalent imprinting.

Piletsky SA, Panasyuk TL, Piletskaya EV, El skaya AV, Levi R, Karube I, Wulff G (1998) Imprinted membranes for sensor technology opposite behavior of covalently and noncovalently imprinted membranes. Macromolecules 31(7) 2137—2140... 

FIGURE 5.12 Schematic illustration of (a) covalent and (b) noncovalent imprinting procedures. 

Thus, combining the ideas from these two lines of research, led us to the concept of noncovalent imprinting. The first successful MlPs that utilized noncovalent... 

Table 2 A Selection of Substance Classes Used as Templates in Molecular Imprinting Protocols Via Noncovalent Imprinting Techniques (Reviews by Mosbach and Ramstrom [50] and Sellergren [62])...

---