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p K a shift‐associated effects in enantioseparations by cyclodextrin‐mediated capillary zone electrophoresis
Author(s) -
Rizzi Andreas M.,
Kremser Leopold
Publication year - 1999
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/(sici)1522-2683(19990901)20:13<2715::aid-elps2715>3.0.co;2-e
Subject(s) - isoelectric focusing , capillary electrophoresis , chemistry , enantiomer , isoelectric point , cyclodextrin , amino acid , electrophoresis , chromatography , pi , enantioselective synthesis , analyte , stereochemistry , enzyme , organic chemistry , biochemistry , catalysis
Enantioselective migration of dansylated (Dns) amino acids in the presence of hydroxypropylated‒β‒cyclodextrin under acidic conditions near the p I value of the analytes was investigated by means of capillary zone electrophoresis. Based on the migration data, the pH dependence of the complexation constants was evaluated, as well as the variation of the complex mobilities with pH. As a result of these data, the migration behavior in the pH region near the p I could be understood, which, in some instances, includes the reversal of migration order upon variation of selector concentration. The enantioselective p K a shifts upon complexation could be quantitated for the carboxylic and the amino group separately. p K a shifts were found in the order of 0.8 p I units, the differences between the enantiomers being up to 0.25 pH units. These data were in agreement with the p I shifts reported from isoelectric focusing experiments. The accurate determination of the p I values of the Dns amino acids makes it possible to calibrate the p I scale in isoelectric focusing in the presence of chiral selectors.