Polymorphism of ceramide 6: a vibrational spectroscopic and X-ray powder diffraction investigation of the diastereomers of N-(α-hydroxyoctadecanoyl)-phytosphingosine

A preparative chromatographic method was developed for the quantitative isolation of the diastereomers of synthetic N-(α-hydroxyoctadecanoyl)-phytosphingosine (dl-CER6). The l- and the d-compound were studied each by means X-ray powder diffraction, FT-Raman and FT-IR spectroscopy. The diastereomers exhibit different thermotropic polymorphism. Three lamellar crystalline and a lamellar liquid crystalline phase were found for l-CER6. The natural occurring d-CER6 forms an Lα phase with a larger repeating distance than the l-CER6. The two lamellar crystalline phases of the d-compound have a significant larger dimension than those of the l-compound. The addition of water lowers the phase transition temperatures but does not induce structural changes such as incorporation into the lamellar sheets.