Studies of lipid interactions in mixed Langmuir monolayers

The mixed monolayers of dipalmitoyl phosphatidylcholine (DPPC) with 3-monopalmitoyl glycerol (PG) and palmitic acid 4-methylumbelliferyl ester (4-MU) were compared. Relevant thermodynamic parameters such as excess area (ΔAE) and excess free energy of mixing (ΔGmixE) were derived from the surface pressure data obtained from compression measurements performed in a Langmuir trough. Generally, DPPC formed more condensed monolayers with PG and greater negative values of ΔAE and ΔGmixE were observed for DPPC/PG system than for DPPC/4-MU one. The positive values of the excess free entropy of mixing (ΔSmixE) were calculated for DPPC/4-MU system at lower temperatures and for DPPC/PG system at higher temperatures.