Mechanistic and molecular modeling studies of several capillary electrophoretic separation techniques employing cyclodextrin additives

Important historical and theoretical concepts of capillary electrophoretic separations are presented as a basis for understanding the three capillary electrophoretic techniques described. The influence of several fundamental parameters on separation performance in each of the techniques is discussed. In most cases, efficiency, selectivity, and system retention are found to be most important in defining separation mechanisms. Molecular modeling is used to study interactions between solutes and cyclodextrin separation buffer additives to gain further information regarding separation mechanisms. The resolving power of combinations of cyclodextrins and surfactants is demonstrated by cyclodextrin-modified micellar electrophoretic capillary separations of highly hydrophobic polycyclic aromatic hydrocarbons. These separations are optimized by altering the type and concentration of cyclodextrin, surfactant and organic modifier. Correlations are drawn between the elution order of several substituted benzopyrene isomers and computationally derived interaction energies. Enantiomers of several dansyl amino acids and binaphthyl compounds are resolved in separate studies using cyclodextrin-modified capillary electrophoresis. Once again, correlations are found between separation behavior and molecular modeling data. Furthermore, it is shown that there is a unique optimum cyclodextrin concentration that leads to maximum resolution of each pair of enantiomers. A new technique, cyclodextrin distribution capillary electrochromatography, that involves the use of combinations of neutral and charged cyclodextrins is presented. Polycyclic aromatic hydrocarbons are the solutes used to evaluate the fundamental characteristics of the technique. Unique selectivities afforded by this technique lead to speculation of future capillary electrophoretic studies employing cyclodextrin additives.