Molecular imprinting by noncovalent interactions. Enantioselectivity and binding capacity of polymers prepared under conditions favoring the formation of template complexes

Abstract

Abstract A molecular imprinting procedure based on electrostatic and hydrogen bonding interactions was developed, resulting in polymers of high selectivity for complexing of L ‐phenylalanine anilide. The polymerization conditions were chosen in such a way that the formation of solution complexes between methacrylic acid (MAA) and the template ( L ‐phenylalanine anilide) prior to polymerization would be favored. Thus, by increasing the ratio of MAA to the crosslinker (ethylene dimethacrylate, EDMA), polymers of a higher enantioselectivity and binding capacity were obtained. In the chromatographic mode, a high chiral separation factor ( a = 3,4) was observed even for polymers prepared in presence of nearly 50 mol‐% MAA in the monomer mixture. However, the use of polymers prepared by initiating at a lower temperature (40 instead of 60°C) and polymers prepared using porogens of lower polarity (benzene instead of acetonitrile) only resulted in higher capacity factors ( K' ). The association constant for the binding of L ‐phenylalanine anilide to the sites of an imprinted polymer as well as the number of accessible sites of the latter were estimated from a binding study using a batch and a chromatographic procedure.