| Lipid bilayer structures are important to cellular function and it is potentially of great utility in the field of chemical sensing. The use of lipid bilayer structures in chemical sensing stems for its ability to house chemically selective transmembrane proteins in their active conformation(s). Mammalian plasma membranes have been studied extensively, with significant effort being invested in understanding how the organization and dynamics of bilayer structures mediates the conformation of transmembrane proteins. Mammalian plasma membranes contain approximately 100 or more different chemical species, therefore it is desirable to create a biomimetic bilayer structure that performs the required protein support function but with much less compositional complexity. The use of a limited number of bilayer components is desirable from an experimental point of view, but making the compositional and morphological connection between model bilayers and mammalian plasma membranes is not straightforward. The ultimate goal of this research program is to make this connection and the initial steps in that direction are contained in this dissertation.;We used different model bilayer compositions, preparation methods, and means of characterization to evaluate the relationship between compositional and physical challenges to the bilayer structure and the dynamical properties it exhibits. The model bilayer structures formed are sensitive to chemical challenges at the bilayer/water interface. The spectroscopic measurements used to interrogate model bilayer structures provide insight into their organization and dynamics.;The model bilayers used are composed of phosphocholine(s), sphingomyelin and cholesterol. The system is known to exhibit phase separation behavior depending on the identity and amount of each bilayer constituent and the media with which it is in contact. Modifying the heterogeneous planar lipid bilayer morphology can be accomplished through the introduction of short chain alcohols, such as ethanol and n-butanol, to an aqueous overlayer solution. The initial experiments performed was to determine whether and how the headgroup-bound rhodamine will interact with model bilayer structures and if the chromophore is sensitive to the organizational variations in the lipid bilayer. There were measurable interactions between the chromophore-tagged phospholipid and other lipid species present in the system and this interaction could be detected if sufficient tethered chromophore was present. It is possible to observe local heating effects in bilayer structures through the measurement of (tethered) chromophore reorientation dynamics. These data revealed local heating in the proximity of the chromophore, with the extent of heating depending on bilayer composition.;Studies of planar supported lipid bilayers on mica showed that the morphology and dynamics of the headgroup-bound rhodamine was sensitive to constituents in the aqueous overlayer. Changes as a function of ethanol concentration were found in cholesterol domain size and chromophore lifetime and anisotropy decay dynamics. Exposure of supported bilayers to n-butanol resulted in structural perturbation and disruption of the lipid bilayer, with consequent changes in the chromophore dynamics. These effects were more pronounced for n-butanol than for ethanol and were seen for lower alcohol concentrations. Taken collectively, these data point to the significant and molecule-specific influence that the composition of the solution overlayer has on bilayer organization. These findings point the way toward control over the organization and dynamics of supported lipid bilayer structures. |
