Exploring binding microenvironments in organized media: I. Spectroscopic studies of novel bile salt phases. II. Lifetime-resolved fluorescence-detected circular dichroism: A new technique for resolving chirality in complex systems

Applications of organized media in chemical analysis has been of significant interest in analytical chemistry in recent years. Most work has been focused on the use of conventional detergent media and cyclodextrins in areas including luminescence analysis and separation sciences. We have been investigating biological bile salts as an alternative to the conventional detergents as chemical reagents. Our fluorescence probe studies have shown that bile salt micelles provide a uniform microenvironment which suppresses unfavorable probe interactions that are commonly experienced in the conventional detergent micelles.; This work focuses on understanding the types of microenvironments provided by individual bile salt micelles and mixed micelles formed between bile salts and cationic detergents. Fluorescence studies of polycyclic aromatic hydrocarbon probes supply information about the solublization sites in the organized media. Measurements of spectra, spectral band intensity ratios, lifetimes, and anisotropy are used to study microviscosity, rigidity, polarity, and accessibility of probe binding site. Additionally, scattered light intensity measurements provide complementary details about the bulk properties of the bile salt phases.; A particularly interesting property of some bile salt phases is their ability to perform chiral chromatographic separations. This suggests that the bile salts interact selectively with chiral solutes, either as monomers or micelles. These interactions in bile salt phases were studied by molecular chirality as determined by chiroptical techniques, including circular dichroism spectroscopy, CD, and fluorescence-detected circular dichroism spectroscopy, FDCD. However, both techniques are limited to only supplying the overall, average chirality of a system. We recently introduced a new technique, lifetime-resolved fluorescence-detected circular dichroism, LRFDCD, which combines the chiral selectivity of FDCD and the resolving power of dynamic lifetime measurements. LRFDCD is a powerful tool for studying molecular interactions and conformations in complex systems. This is accomplished by resolving the overall FDCD signal, chiral or achiral contributions, into the individual contributions for each lifetime component. New instrumental and experimental approaches to FDCD and LRFDCD will be discussed. Studies of simple mixtures of chiral and achiral components were performed to evaluate the performance of the instrument. The potential of the LRFDCD technique for the study of heterogeneous environments is demonstrated in the study of inclusion complexes formed between benzo(a)pyrene and {dollar}gamma{dollar}-cyclodextrin.