Characterization of bicelle model membranes using multidimensional spectroscopy of fluorescent probes

Bilayered mixed micelles, or bicelles, are a new model membrane system consisting of spontaneously forming aggregates of long chain phospholipids and short chain detergent molecules that align in the presence of magnetic fields. This alignment process is a function various experimental parameters such as lipid composition, total lipid concentration and temperature.;This dissertation investigates bicelle morphology and phase behavior as a function of temperature using fluorescence spectroscopy. First, mixing of long and short chain lipids as a function of temperature was investigated using steady state fluorescence spectroscopy. The interactions of tagged probe lipids indicate a consistent mixing of lipids as a function of temperature. These results are inconsistent with the model of bicelle disk formation proceeding from homogeneous lipid aggregate structures leading to magnetic alignment at elevated temperatures. Bilayer fusion experiments indicate that bicelle aggregates are dynamic interacting structures, with the rate of interactions a function of temperature. The results of this work are consistent with bicelle aggregates forming disk structures which coalescence to form extended bilayer networks interrupted by pores at temperatures a few degrees higher than the gel to liquid-crystal phase transition temperature of the long chain lipids.;The bilayer phase transition in bicelles was investigated using multivariate analysis of multidimensional emission decay data of fluorescent probes. The photokinetics of aminonaphthalene probes, which are sensitive to the phase transition in vesicles, were characterized in isotropic solvents and small unilamellar vesicles. Multivariate analysis of multidimensional emission decay data revealed the sensitivity to bilayer phase transition in the emission profiles of these probes to be the result of specific excited state interactions of the probes with their environment. The emission decay data of the aminonaphthalene probes in bicelle samples was compared to data from small unilamellar vesicles. The phase transition of bicelle bilayers varies slightly from that of vesicles, with indications of an extended transition temperature range, possibly due to detergent molecule disruptions of the bilayer regions. (Abstract shortened by UMI.)...