The main phase transition of mica-supported phosphatidylcholine membranes

The phase behavior of mica-supported bilayers has been studied with a diffe rential scanning calorimeter, owing to a significant increase of the substr ate area resulting from chopping a piece of mica into a large number of mic roscopic chips. We have found that then are two main phase transitions for supported phosphatidylcholine bilayers, separated by about 2 degrees C, and that the lower transition temperature is about 2 degrees C higher than the main phase transition temperature of lamellar bilayers. Therefore, support ed bilayers do have the essential feature of free-standing lipid bilayers. However, the double transitions and higher transition temperatures indicate that details of the main phase transition in lipid layers are highly sensi tive to their surrounding environment.