The hydration properties of the interface between lipid bilayers and bulk water are important for determining membrane characteristics. Here, the emission properties of a solvent-sensitive fluorescence probe, 6-lauroyl-2-dimethylamino naphthalene (Laurdan), were evaluated in lipid bilayer systems composed of the sphingolipids D-erythro-N-palmitoyl-sphingosylphosphorylcholine (PSM) and D-erythro-N-palmitoyl-dihydrosphingomyelin (DHPSM). The glycerophospholipids 1-palmitoyl-2-palmitoyl-sn-glycero-3-phosphocholine and 1-oleoyl-2-oleoyl-sn-glycero-3-phosphocholine were used as controls. The fluorescence properties of Laurdan in sphingolipid bilayers indicated multiple excited states according to the results obtained from the emission spectra, fluorescence anisotropy, and the center-of-mass spectra during the decay time. Deconvolution of the Laurdan emission spectra into four components based on the solvent model enabled us to identify the varieties of hydration and the configurational states derived from intermolecular hydrogen bonding in sphingolipids. Sphingolipids showed specific, interfacial hydration properties stemming from their intra-and intermolecular hydrogen bonds. Particularly, the Laurdan in DHPSM revealed more hydrated properties compared to PSM, even though DHPSM has a higher T m than PSM. Because DHPSM forms hydrogen bonds with water molecules (in 2NH configurational functional groups), the interfacial region of the DHPSM bilayer was expected to be in a highly polar environment. The careful analysis of Laurdan emission spectra through the four-component deconvolution in this study provides important insights for understanding the multiple polarity in the lipid membrane.

The dynamic viscoelasticity and birefringence of well-characterized semiflexible polymer solutionscellulose tris­(phenyl carbamate)/tricresyl phosphate solutionswere investigated over a wide concentration region ranging from a dilute to a tightly entangled regime where the entanglement spacing is smaller than the Kuhn segment size. The stress optical rule did not hold true in the tightly entangled regime, indicating that the molecular origin of stress is not simply attributed to the orientation of segments but to the bending of chains, which does not contribute to birefringence significantly. At high frequencies, the power law behavior with the exponent 3/4 due to the tension stress was observed for the complex shear moduli at all the concentrations.