Temperature-dependent morphological and phase behavior of sphingomyelin.

Aqueous dispersions of bovine brain sphingomyelin were studied as a function of temperature. 31P-NMR, X-ray diffraction, and negative-stain and freeze-fracture electron microscopy were used to determine the morphology and phase structure at several temperatures. 31P-NMR indicated a change in phase structure with an increase in temperature. Evidence was found only for the lamellar phase at all temperatures studied with X-ray diffraction. Electron microscopy unexpectedly revealed the spontaneous development of small unilamellar vesicles at elevated temperatures, consistent with the 31P-NMR data, in the absence of any outside disturbances.