Molecularly imprinted polymers monomer-template rigidity

Figure 6 The template theophylline (T) is allowed to interact with the functional monomer methacrylic acid (M) to form a self-assembly. The monomers will interact with theophylline and will form a self-assembly complex mainly based on hydrogen bonding. This self-assembly and the positions of the functional monomers are then frozen and held in place by copolymerization with cross-linker ethyleneglycol dimethacrylate (L). This leads to a rigid polymer scaffold that retains the spatial conformation and thus the specific binding cavity of the original template. After extraction of the template, a molecularly imprinted polymer (MIP) is obtained and the imprinted cavity is able to specifically rebind the template and other, even similar structures are excluded from the binding site cavity.

Molecular 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. The current technique makes use of noncovalent self-assembly of the template with functional monomers before polymerization, free radical polymerization with a cross-linking monomer, and then template extraction followed by rebinding by noncovalent interactions. The functional monomer is often methacrylic acid, the cross-linker is ethylene glycol dimethacrylate, the initiator is 2,2-azo-A,lV -to-isobutyronitrile. They are mixed with template and the mixture is reacted at elevated temperature. The resultant rigid polymer is ground into a sieved powder and the template enantiomer washed off. 

Scheme 1 Generalized depiction ofthe molecular imprinting technique 1—monomers a, b, and c form an attachment to complementary sites on the template. 2—The preassembled template-monomer complex is polymerized with a large excess of crosslinker. 3—The rigid polymer formed in this process retains an arrangement of functional elements complementary both in shape and spatial orientation to the template. 4—Removal of the template reveals a binding pocket or cavity, which can be used to recapture the template species.

---