Cyclodextrin-modified micellar electrokinetic capillary chromatography separations of benzopyrene isomers: correlation with computationally derived host-guest energies

General adjustment of system retention is often inadequate to resolve structurally similar compounds in micellar electrokinetic capillary chromatography (MECC). The use of cyclodextrins (CDs) as mobile-phase additives is described for separations of structural isomers. CDs are shown to provide dramatic and selective effects on the retention of benzopyrene isomers. Efficient separations of six methyl-substituted and three 1-position-substituted benzopyrene isomers are presented. Derivatized [gamma]-CD discriminates between substitutional isomers less than native [gamma]-CD. A comparison of sodium dodecylsulfate (SDS) and sodium cholate (NaC) surfactant systems indicates that SDS-CD mobile phases are more favorable for separation of benzopyrene isomers. Possible separation mechanisms are discussed and evaluated based on results of these studies. The computational procedures of a commercial molecular modeling system are modified and used to determine interaction energies for various host-guest (i.e., [gamma]-CD-benzopyrene) combinations. By use of the average of the five best energy values from interaction energy matrices, correct elution order is predicted for the 1-position-substituted and most of the methyl-substituted benzopyrene isomers. Consideration of different possible CD-benzopyrene orientations must be made to correctly predict elution order. Inspection of the interaction energy matrices revealed no obvious energy barriers that would inhibit inclusion complex formation. 28 refs., 4 figs., 2 tabs.