X-ray and electron microscopic studies on the undulated phase in lipid/water systems

Using X-ray diffraction technique, the periods of undulation in the Pβ′ phase are determined as a function of temperature for dipalmitoyl phosphatidylcholine/water system at the weight ratio lipid/(lipid + water) of 0.75. The period is 156 Å at 38°C and shows a very small temperature dependence. The water rich lipid/water system is studied by freeze-fracture electron microscopy. The mode of undulation is quite different in 5 mM CaCl2 solution from the mode in pure water.