Molecular imprinting imprinted pockets

Acid/base chemistry is also an obvious reaction path for selective detection of a variety of materials. For example, acid/base reaction can be made to occur within a molecularly imprinted pocket to assist in differentiating the molecule of choice before deprotonating it to produce an ion pair that then interacts with the evanescent field. This approach is currently being used to selectively detect TNT to levels in the low parts-per-trillion. 2,4,6-trinitrotoluene, a potent explosive, is also a weak acid having a p/sTa of approximately 14.5 [38]. A TNT derivative is synthesized with a tether to a silane. The silane is chosen so the group can be... 

The molecular imprinting approach, chosen to obtain enzyme mimics, has a lot in common with the generation of catalytic antibodies. The immunisation, in fact, allows generation of binding pocket in the catalytic antibodies as an immune response elicited from a hapten [7]. By following the same theoretical approach,... 

Molecularly imprinted polymers (MIPs) allow for predetermined selectivity of enantiomers. MIPs are prepared by polymerizing a mixture of functional mono-mer(s) and cross-linking monomer in the presence of a template molecule. The template molecule remains in a pocket by its interaction with a functional monomer through hydrogen bonding. This allows the MIP to be found at the surface of the polymer. When polymerization is complete and the template molecule is removed, the polymer remembers the template molecule. 

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.

Figure 22-34 A molecularly Imprinted polymer has a binding pocket for a specific template molecule.

Film devices are often developed based on polymer backbone or framework. For example, a poly-pyrrole film with borane in the backbone has been obtained by direct electropolymerisation. Boronic acid derivatised pyrroles have been employed to make molecular imprinted polymers (MIPs), for example for the detection of dopamine. Figure 8.8 shows the concept of polymer formation in the presence of analyte followed by extraction to provide highly selective pockets for dopamine to bind. The read-out in this case is based on the Fe(CN)/" redox probe. Poly-amino-boronic acid films without imprinting were employed for dopamine detection. Co-polymer sensor films based on poly(aniline-co-3-aminobenzeneboronic acid) and poly(acrylamidophenylboronic acid) have been reported. 

In homogeneous catalysis using chiral diamine 18 complexed with Rh, the acetophenone was reduced quantitatively with 55% ee, in 7 days. In the case of polymerized complex 36a, acetophenone reduction leads to 33% ee and with its templated analog 43% ee. With 36b, an increase of about 20% ee is observed between polymerized and templated ligand. These increases in ee were ascribed to a favourable molecular imprinting effect of the PM, ereating chiral pockets within the polymer network. 

Small molecule imprinting in sol-gel matrices has received considerable interest in recent years, undoubtedly due to the flexibility offered by the sol-gel process.5 Two different approaches have been utilized covalent assembly and noncovalent self-assembly.9 In the covalent assembly approach, the polymerizable functional group (i.e., the silicon alkoxide group) is covalently attached to the imprint molecule. The functionalized imprint molecule is then mixed with appropriate monomers (i.e., TMOS) to form the imprinted materials. After polymerization, the covalent bonds are cleaved to release the template and leave the molecular recognition pocket. Figure 20.4 shows a diagram of this process. 

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