DETERMINATION OF ASSOCIATION CONSTANTS IN CYCLODEXTRIN OR VANCOMYCIN-MODIFIED MICELLAR CAPILLARY ELECTROPHORESIS

The estimation of association constants of chiral analytes to chiral s electors is often useful in determining the nature and extent of inter actions that exist between them. These determinations also provide ins ight into the mechanisms that are involved in the enantiorecognition o f these analytes. Simple models have been developed previously to esti mate association constants of analytes binding through a 1:1 stoichiom etry with a ligand. These models have also been extrapolated to explai n the binding behavior of analytes in systems containing two ligands. In the present study, the binding behavior of some chiral analytes was studied in micellar capillary electrophoresis (CE) systems modified w ith hydroxypropyl-beta-cyclodextrin (HPBCD) or vancomycin as the chira l selectors. The pseudophase or three phase model was used as the basi s for the determination of the absolute binding constants of the solut es to the selector and to the micellar phases. However, these systems are complicated due to the interactions that exist not only between th e analyte and the chiral selector/micellar phase but also between the ligands themselves. in the case of the hydroxypropyl-beta-cyclodextrin /sodium dodecyl sulfate (SDS) system the SDS monomers are included in the cyclodextrin cavity. Similarly, in the vancomycin/SDS system, vanc omycin partitions itself into micelles. The limitations associated wit h the use of ideal mathematical models in these complex systems, are a lso discussed.