Dynamics in Diether Lipid Bilayers and Interdigitated Bilayer Structures Studied by Time-Resolved Emission Spectra, Decay Time and Anisotropy Profiles

We present a comparative fluorescence spectroscopic investigation of diacyl and diether phosphatidylcholine vesicles using different probes with well-defined localization within either the hydrophilic headgroup region or the hydrophobic part of the bilayer. Time-resolved emission spectra have been used to characterize the solvent relaxation behavior in both symmetric and asymmetric diether and diacyl phosphatidylcholines. It is shown that time-resolved emission spectra of Prodan (6-propionyl-2-(dimethylamino)-naphthalene) and its long-alkyl chain derivative Patman (6-palmitoyl-2-trimethylammoniumethyl]methylamino]-naphthalene chloride) are a sensitive tool for the detection of differences in the micropolarities and viscosities at the hydrophobic/hydrophilic membrane interface of diether and diacyl lipids, respectively. Moreover, a new approach for the detection of interdigitated bilayers is discussed. It relies on the construction of anisotropy and decay time profiles for the set of n-anthroyloxy fatty acids and is compared with an older fluorescence assay based on intensity measurements only. The shape of plots of the fluorescence steady-state anisotropy versus the position of the chromophore (anthracene-9-carboxylic acid) combined with fluorescence lifetime measurements can be used to differentiate among non-fully, and mixed interdigitated gel phase structures and to predict structures for new lipid species.