Fourty years of molecular imprinting in synthetic polymers: origin, features and perspectives

Molecularly imprinted synthetic polymers were discovered 40 years back. They are prepared in the presence of interacting monomers around a molecule that acts as a template. Following polymerization of the monomers together with a large amount of a crosslinker and after removal of the template, an imprint is obtained whose shape and arrangement of functional groups are complementary to the structure of the template (often an analyte). Usually, selective binding of the analyte is observed. These highly cross-linked polymers are also well suitable to engineer enzyme-like activity and specificity. The first part of this review is a personal retrospective description of the first steps into this field. The second part describes recent efforts to develop enzyme models, e.g. for carboxypeptidase A, through the concept of transition state stabilization. It is shown that the introduction of special catalytic moieties such as metal ions leads to a defined orientation of groups inside the active site and, with this, to highly active catalysts. Their activity, efficiency, and proficiency clearly surpass those of other imprinted catalysts and even those of the corresponding catalytic antibodies. A further improvement was accomplished by placing the enzyme-analogue active site inside soluble nanoparticles. A special concept, referred to as post dilution polymerization method results in soluble, highly cross-linked, single molecule nanoparticles of controlled molecular weight (similar to 39 kDa) having one catalytically active site per particle on average.