Understanding bile salt micelle formation and bile salt micelles' chiral recognition processes using MEKC and NMR
Kyle W. Eckenroad, Timothy G. Strein, Christine M. Hebling, Laura E. Thompson, Gregory A. Manley, and David Rovnyak. Bucknell University, Lewisburg, PA
Using deoxycholate and cholate in bile salt mediated micellar electrokinetic capillary chromatography (MEKC) for chiral separations has been well-documented. However, despite the numerous reports of bile salts being used for chiral recognition in both chromatography and capillary electrophoresis, the molecular-level interactions between the isomers and the micelles are not well characterized. Even the mechanisms of micelle formation from surfactant monomers are not fully understood. This work attempts to infer such information through systematic characterization of both the MEKC behavior of model-drug analytes and nuclear magnetic resonance (NMR) signals obtained from MEKC solutions. Using the model analytes 1,1'-binaphthyl-2,2'diyl hydrogenphosphate and 1,1'-binaphthyl as probes, we are able to examine the interactions between micelles and chiral isomers and have begun to characterize the micelle-analyte interactions. We have used similar analysis to understand the micelle formation mechanisms. Using the mobility of the analyte and the micelle we have been able to determine the critical micelle concentration (CMC) and the possible existence of a secondary CMC as well as several chromatographic constants which provide further insight into this MEKC system. The NMR examination of these aqueous MEKC systems has included 1H and 31P chemical shift analysis as well as relaxation time experiments and, very recently, 2D Nuclear Overhauser Effect Spectroscopy (NOESY), and these data are correlated with MEKC results. We will present recent results from both MEKC and NMR that aid our understanding of the complicated interactions between individual bile salt monomers, bile salt micelles and the analyte molecules.