Template-monomer assemblies

Fig. 6-5. Model of the binding site for L-PA based on spectroscopic and chromatographic characterization of the prepolymerization monomer-template assemblies.

Fig. 6-8. Factors affecting the recognition properties of MIPs related to the monomer template assemblies.

Fig. 6-11. Stabilization of monomer template assemblies by thermodynamie eonsiderations.

An important part of the optimization process is the stabilization of the monomer-template assemblies by thermodynamic considerations (Fig. 6-11). The enthalpic and entropic contributions to the association will determine how the association will respond to changes in the polymerization temperature [18]. The change in free volume of interaction will determine how the association will respond to changes in polymerization pressure [82]. Finally, the solvent s interaction with the monomer-template assemblies relative to the free species indicates how well it will stabilize the monomer-template assemblies in solution [16]. Here each system must be optimized individually. Another option is simply to increase the concentration of the monomer or the template. In the former case, a problem is that the crosslinking as well as the potentially nonselective binding will increase simultaneously. In the... 

Some limitations of this molecular imprinting technique are obvious the template must be available in preparative amounts, it must be soluble in the monomer mixture and it must be stable and unreactive under the conditions of the polymerization. The solvent must be chosen considering the stability of the monomer-template assemblies and it should result in the porous structure necessary for rapid kinetics of the template interaction with the binding sites. If these criteria are satisfied, a robust material capable of selectively rebinding the template can be easily prepared and evaluated in a short period of time. 

Also of considerable importance is the mechanism of site formation. At what stage in the polymerisation are the high energy sites formed and stabilised Does the solution structure of the monomer-template assemblies reflect the disposition of functional groups at the binding sites [24] (See Chapter 5 for a further discussion.) Attempts to correlate the association constants determined for the monomer-template interactions in homogeneous solution with the rebinding association... 

It is of obvious importance that the functional monomers strongly interact with the template prior to polymerisation, since the solution structure of the resulting assemblies presumably defines the subsequently formed binding sites. By stabilising the monomer-template assemblies it is possible to increase the number of imprinted sites. At the same time the number of non-specific binding sites will be minimised, since there will be a reduction in the amount of free, non-associated functional monomer. For any particular template, the following factors that are likely to affect the recognition properties of the site have been identified (Fig. 5.14). 

An important part of the optimisation process is the stabilisation of the monomer-template assemblies by thermodynamic considerations (Fig. 5.17). The... 

Fig. 5.17. Stabilisation of monomer template assemblies by thermodynamic considerations.

To what extent do the solution complexes formed between the monomer and the template in solution reflect the architecture of the polymeric binding sites This question is important, since a thorough characterisation of the monomer-template assemblies may assist in deducing the structure of the binding sites in the polymer and thus have a predictive value. 

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