Cl. Copper et al., SEPARATIONS OF DERIVATIZED AMINO-ACID ENANTIOMERS BY CYCLODEXTRIN-MODIFIED CAPILLARY ELECTROPHORESIS - MECHANISTIC AND MOLECULAR MODELING STUDIES, Electrophoresis, 15(6), 1994, pp. 785-792
The enantiomers of 5-dimethylamino-1-naphthalene sulfonyl (DNS)-deriva
tives of selected amino acids were successfully separated using capill
ary electrophoresis (CE) employing cyclodextrins (CD) as enantio-selec
tive running buffer additives. A previously described model for retent
ion and chiral recognition in CD-modified CE is shown to adapt well in
this application. Resolution of the isomers is strongly influenced by
the type and concentration of cyclodextrin employed, as predicted by
the model. Although data indicates differences in the electrophoretic
mobilities for some of the completely complexed enantiomer pairs, sele
ctivity generally requires exploiting differences in the amino acid-CD
complexation constants for enantiomer pairs. In this work, the D-enan
tiomers exhibit larger formation constants and are complexed to a grea
ter degree (elute first) at moderate CD concentration. When mixtures o
f amino acids are analyzed, the effects of separation conditions on ge
neral elution behavior must be considered or separated enantiomer pair
s will co-elute with other enantiomers. Preliminary results aimed at p
redicting the strength of DNS-amino acid enantiomer-CD interactions ba
sed on molecular modeling studies are presented. A statistical mechani
cal approach to treating computationally derived enantiomer-CD interac
tion energies is shown to provide reasonable correlation with separati
on performance.