Interactions between L-α-phosphatidylglycerol sodium salts and water molecules were examined primarily with a differential scanning calorimeter (DSC) and surface pressure meter. With an increase in alkyl chain length of L-α-phosphatidylglycerol sodium salts, stability of the coagel phase relative to that of the gel phase increased due to decrease in the dissociation of counterions (sodium ions). Monolayers of L-α-phosphatidylglycerol sodium salts (PG-Na) were readily converted to expanded monolayers with NaCl, and the temperature at which only expanded monolayers formed was in good agreement with a gel-lamella crystalline transition temperature (Tc). The molecular orientation of the PG-Na monolayer was shown in some causes to differ with that of its bilayer.
