Thermodynamic characteristics of DSPC/DSPE-PEG2000 mixed monolayers on the water subphase at different temperatures

Abstract Distearoylphosphatidylcholine (DSPC) spread at the air/water interface is used as a model membrane and to study the lateral interaction between DSPC and distearoylphosphatidylethanolamine-polyethylene glycol 2000 (DSPE-PEG2000). DSPE-PEG2000 was found to be miscible with DSPC by our measurements of surface pressure–area per molecule (Π–A) isotherms at different temperatures. At different temperatures the nonideality and miscibility of mixed monolayer were determined by the analysis of excess area as a function of compositions, and the temperature effects on these deviations from ideality were evaluated. Furthermore, the interfacial thermodynamic characteristics of this mixed system including the change of entropies, the change of latent heats, and excess and mixing free energies during the compression process were calculated from the isotherms as a function of temperature in order to understand factors that affect the stability of mixed monolayer. It was found that increasing temperature and incorporation of DSPE-PEG2000 both may make the mixed monolayer more compressible.