CHIRAL RECOGNITION MODELS OF ENANTIOMERIC SEPARATION ON CYCLODEXTRIN CHIRAL STATIONARY PHASES

The enantiomeric separation of several amino acid derivatives by reversed-phase liquid chromatography using two (R)- and (S)-naphthylethylcarbamate-beta-cyclodextrin(NEC-beta-CD) bonded stationary phases was studied to illustrate the chiral recognition model of the enantiomeric separation. The retention and enantioselectivity of the chiral separations with (R)- and (S)-NEC-beta-CD bonded phases were compared with similar separations with the native P-CD stationary phases. Especially, the enantioselectivity and elution orders between the derivatized amino acid enantiomers are carefully examined. These results can be illustrated by the chiral recognition models involving inclusion complexation, pi-pi interation, and/or hydrophobic interation. Inclusion complexation and hydrophobic interation of the naphthyl group of the NEC moiety seem to be major chiral recognition components in the enantiomeric separation of 2,4-dinitrophenyl amino acids and dabsyl amino acids on (R)- and (S)-NEC-beta-CD columns. For dansyl amino acids, only the inclusion complexation is the dominant factor. Three different chiral recognition models containing pi-pi interaction, inclusion complexation and hydrogen bonding were proposed for the separation of the 3,5-dinitrobenzoyl amino acid enantiomers, depending on the size and shape of amino acids.