Phase properties of the aqueous dispersions of n-octadecylphosphocholine

Properties of the aqueous dispersions of n-octadecylphosphocholine are examined by differential scanning calorimetry, fluorescence depolarization, light scattering, 31P-NMR, pig pancreatic phospholipase A2 binding, and X-ray diffraction. On heating, these dispersions exhibit a sharp lamellar to micelle transition at 20.5 degrees C. The lamellar phase consists of frozen (gel-state) alkyl chains which do not bind phospholipase A2. The kinetics of the transition are asymmetric: the micelle to lamellar transition is very slow and the lamellar to micelle transition is fast. It is suggested that the lamellar phase is a frozen chain bilayer in which the chains interdigitate.