Structure of cerebrosides. II. Small angle X-ray diffraction study of cerasine

Cerasine having a molecular weight of 800 differs chemically from phrenosine only in the hydroxyl group attached to the fatty acid tail which is replaced by a hydrogen atom. Nevertheless, remarkable differences between both cerebrosides are detected in the lamellae periodicities. In the range of 23--66 degrees C just one single (instead of two) structure with a similar subcell to the triclinic one component of phrenosine detected. Between 66 and 87 degrees C three new components (instead of one in phrenosine) appear. Two of the structures are similar to the two phrenosine-components at low temperature and the tilt angles of their chains with respect to the basal planes can explain the stabilizing capacity of the 201 and 301 netplanes of the paraffin-like subcells respectively. These lattice planes are parallely aligned to the surfaces of the lamellae. The long period of 58 A of component II cannot be explained in such a way. This period persists up to 105 degrees C and coexists from 87 degrees C with a new component showing a 40 A-periodicity, which cannot either be explained in the above manner. Paracrystalline distortions of the arrangement of the bilayers can be justified by orientational disorder of the galactose heads.