Influence of pH and chain length on the phase transition of phosphatidic acid

Phosphatidic acids (PA) are normally minor components in natural membranes but there is increasing evidence that these components play a key role in aggregation, fusion and transport processes in cellular membranes. The aim of this research was to investigate the influences of pH on the transition temperatures and enthalpies of various aqueous PA dispersions. The phase transition temperatures (Tt) and enthalpies (Ht) were measured using differential scanning calorimetry. The Tt vs pH diagrams of the four phosphatidic acids are quite similar, the transition temperatures decrease with increasing pH from 4 to 10. The Ht vs pH diagrams have similar shape. Our experimental data are compared with measurements of different authors. The chain length dependence of Tt and Ht at different pH values were established too. The diagrams are compared to that of phosphatidylcholines and phosphatidylethanolamines.