Numerous variations on the theme of molecular imprinting have been demonstrated. A particularly ingenious idea is to use the relatively strong hydrophobic effect to press template molecules into the surfaces of silica particles. By attaching a surfactant molecule to a template molecule, one ends up with what Bruce Paul Garber calls a "molecule-on-a-stick" (see figure). This process was recently used to increase accessibility to binding sites by pressing a transition state analogue into spherical silica nanoparticles with diameters of 400 - 600 nanometers. Because these nanoparticles are so small and numerous, their effective surface area is much greater than larger particles. During formation of the nanoparticles the templates-on-a-stick self-assemble around the silica spheres, thus pressing their shape into the surface. Upon removal of the templates (and the sticks), one is left with nanoparticles coated with binding sites specific for the template. In this case, a transition state analogue was used as the template, resulting in a novel catalyst that can hydrolyze amides in an enantioselective manner.
Reference: M. A. Markowitz, P. K. Kust, G. Deng, P. E. Schoen, J. S. Dordick, D. S. Clark, and B. P. Gaber, "Catalytic Silica Particles via Template-Directed Molecular Imprinting" (2000) Langmuir, 16, 1759-1765.
Acknowledgements: I'm grateful to Keith Brain, Chris Allender, Bruce Paul Garber, Jesper G. Karlsson, Ian A. Nicholls, the Society for Molecular Imprinting and MIPworkshop.org for their generous contributions both to this article and to the field of Molecular Imprinting.
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