Separation of dipeptide and tripeptide enantiomers in capillary electrophoresis by the cationic cyclodextrin derivative 2-hydroxypropyltrimethyl-ammonium-β-cyclodextrin and by neutral β-cyclodextrin derivatives at alkaline pH

The enantioseparation of dipeptides and tripeptides by the cationic CD derivative 2-hydroxy-3-trimethylammoniumpropyl-beta-cyclodextrin (TMA-beta-CD) was studied under acidic and alkaline conditions. Enantioresolutions could be achieved at pH 3.5 when the peptides were partially positively charged, at pH 5.3 close to the isoelectric point of the peptides when the compounds are uncharged, and at pH 9.5 where the peptides exist as anions. Although not as effective as under acidic run conditions, native P-CD and neutral CD derivatives were able to resolve the enantiomers of several peptides at pH 9.5. Analysis of the complexation constants and the mobilities of the analyte-CD complexes at pH 9.5 in the presence of TMA-beta-CD and beta-CD revealed identical chiral recognition of both CDs towards Ala-Phe, Ala-Tyr, and Asp-PheOMe. Despite identical enantiomer migration order compared to the other peptides, TMA-beta-CD displayed opposite chiral recognition towards the enantiomers of Ala-Trp. In contrast to the other investigated peptides, the. enantiomer migration order of Ala-Trp was determined by the mobility of the CD-peptide complex which was higher in the case of the stronger complexed enantiomer.