Pretransitions in the hydrocarbon chains of phosphatidylethanolamines. A wide angle X-ray diffraction study

The hydrocarbon chain packing of fully hydrated phosphatidylethanolamine multilayers is investigated by X-ray diffraction. An analysis of the wide angle reflections (short spacings) as a function of temperature indicates that, apart from the well-known ordered-disordered lipid phase transition, a second transition takes place at lower temperatures. This transition, which is in the present paper referred to as the pretransition, is characterized by a transformation of the hydrocarbon chain packing. A first model for the chain lattice is presented, which gives rise to the expectation that similar pretransitions might be found with other phospholipids.