Chiral-recognition polymer prepared by surface molecular imprinting technique

Abstract

A highly enantioselective polymer was prepared by the surface molecular imprinting technique for the separation of optically active tryptophan methyl ester. A synthetic host molecule (phenyl phosphonic acid monododecyl ester) was proved to be effective for recognizing the chirality of amino acid esters. The l- or d-tryptophan methyl ester (TrpOMe)-imprinted polymer containing the functional host molecules revealed high enantioselectivity toward the corresponding imprinted isomer. While, the racemic-TrpOMe-imprinted and unimprinted polymers did not show the enantioselectivity at all. These results mean that the complementary binding sites such as ‘template-fit pockets’, in which the position and the alignment of the functional group in the functional host molecule are optimally adjusted for binding the corresponding imprinted isomer, are a principal factor to recognize the target molecule. These enantioselectivities were quantitatively supported by high binding constants for the corresponding imprinted isomer. To verify the recognition mechanism of the imprinted polymer, FT-IR and 1H-NMR measurement and computational modeling were conducted. Based on the results obtained, it was concluded that the enantiomeric selectivity is endowed by the electrostatic and hydrogen bonding interactions between the functional molecule and the target tryptophan methyl ester along with the chiral space formed on the polymer surface.