Hydration properties of N-(alpha-hydroxyacyl)-sphingosine: X-ray powder diffraction and FT-Raman spectroscopic studies

The thermotropic properties of N-(alpha-hydroxyacyl)-sphingosine (CERAS]) in dry and hydrated state were studied by means of X-ray powder diffraction and FT-Raman spectroscopy. The polymorphic states of the CERAS]/water mixture (lamellar crystalline, lamellar hexagonal gel, liquid crystalline) depend on the thermal pre-treatment of the sample. Only by heating the CERAS]/water mixture above the melting chain transition can the system be hydrated. At room temperature, both dry and hydrated states form lamellar structures, which differ in their repeat distance and packing of hydrocarbon chains. Above the melting chain transition, hydrated CERAS] forms a liquid crystalline hexagonal phase, whereas anhydrous CERAS] forms an isotropic liquid phase. The various phases of hydrated CERAS] are distinguished on the basis of the corresponding Raman spectra.