Mechanistic aspects of chiral discrimination on a molecular imprinted polymer phase

The mechanism of chiral selectivity of a difunctional polymer imprinted with dansyl-L-phenylalanine was investigated using the polymer as an HPLC stationary phase. Temperature studies revealed that the mass transfer of the imprinted enantiomer with the polymer was sluggish at low temperatures, leading to a nonequilibrium migration down the column. Conversely, retention of the non-imprinted enantiomer was controlled by a thermodynamic equilibrium over the entire temperature range of the study. Variation of the structure of the analyte indicated a single leading interaction between both enantiomers of dansyl-phenylalanine and the polymer phase; a hydrogen bonding interaction between the carboxylic acid group of dansyl-phenylalanine and pyridinyl sites on the polymer. Secondary processes contributing to enantioselectivity were also deduced; a hydrogen bonding interaction occurring between the imprinted enantiomer and carboxyl sites on the polymer and a precise steric fit of the amino acid side chain into the imprinted sites. Studies varying the mobile phase hydrogen bond competitor agree with the results obtained by the structural studies.