X-ray studies on phospholipid bilayers. II. Polymorphic forms of dipalmitoyl phosphatidylethanolamine.

Oriented films and powder samples of the phospholipid L-alpha-dipalmitoyl phosphatidylethanolamine (DPPE) were studied by X-ray fiber diffraction techniques. The specimens were photographed under a complete range of hydration at room temperature. Two polymorphic forms were found. One of them was present in oriented films. It showed a close packing of DPPE molecules lying parallel to the normal to the bilayer plane. The other form, observed in the powder samples, had the molecules tilted by about 25 degrees. Both forms were characterized by their unit cell dimensions, space groups, molecular conformations and packing arrangements.