Complex structural arrangements of ceramide lipids is produced by asymmetric molecular shape

Full text: Ceramide is an important class of sphingolipids, which can be found in minor amounts in cell membranes but participating in transmembrane signaling and in larger amounts in skin and epithelia, providing structural support. Sphingolipids endow a large chemical variability both in head group and in acyl chains, which give rise to a rich mesomorfic behavior. In this project we are studying the effect of the length of the fatty acid chain that is N-bonded to sphingosin in ceramides on the structure and thermodynamic properties of fully hydrated dispersions by means of X-ray techniques, infrared spectroscopy and differential scanning calorimetry. Our previous results showed that a short chain, asymmetric C10:0 ceramide form an inverted HII phase with ordered chains, the latter been not previously reported before [1]. Now we are investigating longer and shorter N-acyl chains lipids, which also show non-bilayer structures provided molecular asymmetry is maintained. Symmetrical shaped ceramides with intermediate chain length prefer to adopt flat bilayer like structures. WAXS shows several small peaks beyond the characteristic peak of hexagonal acyl chain packing. The grazing incidence X-Ray diffraction pattern from Langmuir monolayers at the air/water interface appears comparatively simple. Thickness of the Langmuir mono- and sub-layers is measured by Bragg rod at the Bragg peaks and grazing Incidence X-Ray Off Specular Scattering and compared to the ones measured by light reflectivity. (author)