Improving the strategy and performance of molecularly imprinted polymers using cross-linking functional monomers

A new strategy for monomer design has been investigated that combines interactive monomer functionality with a cross-linking format, giving as a result noncovalent molecularly imprinted polymers (MIPs) with improved performance. This strategy was explored under the premise that more functionality could be introduced without suffering performance losses due to reduced cross-linking. While this proved to be correct, equally important contributions to selectivity enhancement at the molecular level by conformation control and diastereomeric complexation were also discovered. Monomers derived from l-serine and l-aspartic acid were synthesized and used to prepare MIPs, with the best performance obtained for the MIP formulated with the serine-based cross-linker (N,O-bis-methacryloyl l-serine, 3), versus the aspartic-acid-based cross-linkers and the traditional methacrylic acid/ethylene glycol dimethacrylate (MAA/EGDMA) formulation. Quantitative structure-selectivity relationship (QSSR) studies revealed that the improved performance of 3 was due to three key factors: (1) the cross-linking nature of this monomer; (2) control of conformational flexibility; (3) a strong influence of monomer chirality on enantioselectivity in MIPs.