Effect of ethanol on the main phase transition of distearoylphosphatidylcholine

A highly sensitive scanning microcalorimeter and a low scanning rate (0.1 K/min) has been used to determine the thermodynamic properties of the main phase transition of distearoylphosphatidylcholine (DSPC) in presence of ethanol in the 0–0.20 ethanol mole fraction (x2) range. These measurements revealed previously unreported features of DSPC/water/ethanol phase behavior and visualized distinct changes in the main phase transition mechanism induced by addition of ethanol. It is found that the well known interdigitated phase in DSPC induced by ethanol above x2 =0.01 abruptly disappears at x2 =0.12. The abrupt change in the DSPC phase behavior at x2 = 0.12 shows some analogies with the observed one relative to the conformation response of DNA molecule to solvent condition altered by varying amounts of ethanol. As inferred from previous adiabatic compressibility and IR data in water/ethanol mixtures, a correlation between changes in properties of the solvent, and the effect of ethanol on both the conformational properties of DNA and the main phase transition of DSPC clearly appears from the data. © 2002 Elsevier Science B.V. All rights reserved.