Structure of the L beta phases in a hydrated phosphatidylcholine multimembrane.

We report x-ray measurements on well aligned, freely suspended films of stacked bilayer membranes of the phospholipid dimyristoyl-phosphatidylcholine in a continuously variable humidity- and temperature-controlled environment. Remarkably, the most commonly observed L/sub ..beta..//sub '/ phase is in fact three distinct 2D phases where the phase transitions are driven by hydration forces and the phases are distinguished by the relation between the molecular tilt direction and the 2D bond direction.