Physical studies of phospholipids. VI. Thermotropic and lyotropic mesomorphism of some 1,2-diacyl-phosphatidylcholines (lecithins)

Abstract The thermotropic and lyotropic mesomorphism of a series of saturated 1,2-diacyl-L-phosphatidylcholines (lecithins) has been studied by light microscopy, differential thermal analysis, X-ray diffraction, infrared and nuclear magnetic resonance spectroscopy. The phosphatidylcholines exhibit polymorphism and generally exist in the form of their monohydrates. Anhydrous phosphatidylcholines can be prepared by heating the monohydrates or, alternatively, by crystallisation from certain solvents. Three different liquid crystalline phases have been characterised; the higher homologues of the monohydrates exist in a cubic liquid crystalline phase within certain well defined temperatures. This cubic phase gives rise to a high resolution proton magnetic resonance spectrum showing peaks associated with the different proton groupings in the molecule. The structures of the lyotropic phases formed by the addition of water to the phosphatidylcholines have been determined. The phase diagram of the 1,2-dipalmitoyl-L-phosphatidylcholine/water system has been determined as a function of water concentration and temperature. Calorimetric techniques show that approximately ten molecules of water are bound to each molecule of phosphatidylcholine.