Study on the mechanism of chiral recognition with molecularly imprinted polymers Original Research Article

This study aimed at elucidating the chiral recognition mechanism with molecularly imprinted polymers (MIPs) in aqueous environment. The system used ethylene glycol dimethacrylate (EGDMA), methacrylic acid (MAA), and 4-l-phenylalanylamino-pyridine (4-l-PheNHPy) as the cross-linking monomer, functional monomer and template, respectively, to assemble the imprinted polymer. A self-assembly mechanism, which includes the pre-organizing functional monomers around template before polymerization process, was proposed. This mechanism was supported by 1H NMR titration test. Interactions between functional monomer and template were observed using UV-Vis spectroscopy of solutions of these components as well. These studies indicated a 1:2 molecular complex dominantly formed between 4-l-PheNHPy and MAA. Association constant was estimated to be 97,000 M−2. Based on these results, a model mainly involving two-spot interaction was proposed evolving from our reported concept of exact placement of functional group. Ionic interaction between the primary amino group of 4-l-PheNHPy and carboxylic acid group inside the microcavity on MIPs was believed to play a predominate role in the enantioselectivity as supported by the observation of the relationship between the retention factor of 4-l-PheNHPy and the pH of mobile phase. While thermodynamic study at different pH revealed that, the interaction between the pyridyl group of 4-l-PheNHPy and the carboxylic acid group on the MIPs is also strong, implying that it also plays a profound role in determining the highly chiral selectivity of MIPs.