Abstract
Interactions between L-α-phosphatidylcholines and water molecules were examined primarily by a differential scanning calorimeter (DSC) and a surface pressure meter. With increasing temperature, only a gel-lamella liquid crytstalline transition (Tc) occured in a lower moisture region, while a coagel-gel transition (Tgel) was noted at a temperature less than Tc, in a moisture region higher than 20wt%. With increase in alkyl chain length of L-α-phosphatidylcholine molecules, the transition enthalpy at Tc increased, while that of Tgel remained essentially constant. L-α-phosphatidylcholine monolayer had a form of condensed-film in a lower temperature region and that of an expanded-film in a higher temperature region. Their limiting molelcular areas suddenly increased steeply at Tc-temperature. Tc for L-α-phosphatidylcholine as determined from surface pressure was in good agreement with that found by DSC measurement. This may be due to the fact that the Tc transition results from the horizontal intermolecular interaction.
