Chemistry Reference
In-Depth Information
Scheme 15.4 Molecular imprinting of the tripeptide Lys-Trp-Asp using both covalent and non-
covalent interactions. Adapted from Klein et al. (1999). Copyright 1999 Wiley InterScience.
process is particularly sensitive to changes in polymerization conditions because of
the instability and reversible nature of noncovalent monomer-template complexes.
Generally, conditions that favor the formation of the noncovalent monomer-template
complex yield MIPs with higher capacities and selectivities. For example, lower
temperatures, higher monomer and template concentrations, and less polar solvents
enhance the fidelity of the imprinting process. The polymerization conditions can
also control material properties such as the porosity, surface area, and rigidity of
the polymer matrix. Some of the more important variables and their influences on
the imprinting process are discussed here.
Polymerization Methods.
The majority of MIPs have been prepared via free-
radial polymerization of vinyl monomers. Radical polymerization conditions are
favored because they are mild, can utilize a large pool of commercially available
monomers, and are compatible with most functional groups. This last attribute
enables the use of monomers containing polar, aromatic, acidic, basic, and charged
recognition groups. Polymerizations are carried out with 1-5% of a radical initiator
such as AIBN, benzophones, or a-dialkoxy-aceto-phenones. Both thermal and UV
irradiation polymerization conditions have been used. The thermal irradiation con-
ditions are more general and can be applied to a broader array of monomers, cross-
linkers, and templates and yield more uniform polymers. UV irradiation conditions
can be carried out at lower temperatures that are more favorable for noncovalent
imprinting conditions. MIPs have also been prepared using other polymerization
methods. The largest and most successful of these are the imprinted sol gels
(Katz and Davis 2000; Chang et al. 2002). MIPs have also been prepared using
