ENANTIOMERIC SEPARATION OF A TETRAPEPTIDE WITH CYCLODEXTRIN - EXTENSION OF THE MODEL FOR CHIRAL CAPILLARY ELECTROPHORESIS BY COMPLEX-FORMATION OF ONE ENANTIOMER MOLECULE WITH MORE THAN ONE CHIRAL SELECTOR MOLECULES

In this paper the enantiomeric separation by capillary electrophoresis (CE) of the tetrapeptide LEF553 (Tyr-D-Arg-Phe-Phe-HN2) and its diast ereoisomers is presented. The run buffer consisted of 10 mmol l(-1) he ptakis(2,6-di-O-methyl)-beta-cyclodextrin in 0.1 mol l(-1) phosphoric acid adjusted to pH 3.0 with triethanolamine. Large differences were f ound between the different steric conformations of the peptide. The re lationships between the apparent mobility differences of the enantiome rs versus the cyclodextrin concentration were investigated. For some o f the conformations of the peptide, the curve forms that were obtained could not be explained by Wren's model, which assumes a 1:1 interacti on between enantiomer and chiral selector. A possible explanation coul d be that each peptide molecule could interact with two or three cyclo dextrin molecules. An extended model in which the enantiomer complexes with more than one chiral selector molecule is presented. Using this extended model, curves for the mobility difference versus the chiral s elector concentration can be obtained that have the same shape as the experimental curves. (C) 1997 Elsevier Science B.V.