The effects of metal ions and lanthanide complexes on the gel-to-liquid crystal phase transition temperature T~m of dipalmitoylphosphatidylethanolamine liposomes have been studied by differential scanning calorimetry (DSC) method. The results show that the addition of metal ions to the dipalmitoylphosphatidylethanolamine (DPPE) liposomes dispersions increases the main phase transition temperature T~m in the order of monovalent＜divalent＜trivalent cations. The enhancement of T~m is not large as increasing the lanthanide ions concentration. The enhancement of Pr^3^+ is larger than that of La^3^+. Remarkable differences were observed between La-citrate and La-lactate complexes at different pH solutions. At pH 7.0, La-citrate complex has no effect on the T~m, La-lactate complex, however, increases the T~m value, and the increase is larger than that of free lanthanide ions at the same concentration. The decrease of pH of complexes solutions lowers the phase transition temperature. We have preliminarily discussed the mechanism of the enhancements of lanthanide ions and the synergism of lanthanide ion and lactate ligand follow the ion induced dehydration of lipid and the potential effects of ion-lipid interaction.

Key words: PHASE TRANSFORMATION, RARE EARTH METAL COMPLEX, DIFFERENTIAL SCANNING CALORIMETRY, METAL ION