THERMODYNAMIC PROPERTIES OF SHORT-CHAIN PHOSPHATIDYLCHOLINE ISOMERS - MICELLIZATION AND ADSORPTION AT AN AIR-WATER-INTERFACE

Surface tensions of aqueous solutions of phosphatidylcholines (diheptanoyl-, 1-lauroyl-2-acetyl-, and 1-decanoyl-2-butyrylphosphatidylcholine) with 14 carbons total in the two fatty acyl chains have been measured as a function of temperature from 10 to 40-degrees-C. These data were used to extract critical micelle concentrations, thermodynamic parameters for micellization and surface adsorption, and limiting surface areas for the three phosphatidylcholines. The process of micellization is entropy-controlled at lower temperature but enthalpy-controlled at higher temperature. The process of adsorption, however, is predominantly an entropy-controlled process. An analysis of the decrease of surface tension at lipid concentrations above the critical micelle concentrations of the asymmetric phosphatidylcholines was used to determine their micelle aggregation numbers.