THE EFFECTS OF LANTHANIDE IONS AND THEIR COMPLEXES ON THE PHASE-TRANSITION PROPERTY OF DIPALMITOYLPHOSPHATIDYLETHANOLAMINE LIPOSOMES

The effects of metal ions and lanthanide complexes on the gel-to-liqui d crystal phase transition temperature T-m of dipalmitoylphosphatidyle thanolamine liposomes have been studied by differential scanning calor imetry (DSC) method. The results show that the addition of metal ions to the dipalmitoylphosphatidylethanolamine (DPPE) liposomes dispersion s 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 enhancemen t of Pr3+ is larger than that of La3+. Remarkable differences were obs erved between La-citrate and La-lactate complexes at different pH solu tions. At pH 7.0, La-citrate complex has no effect on the T-m, La-lact ate complex, however, increases the T-m value, and the increase is lar ger than that of free lanthanide ions at the same concentration. The d ecrease of pH of complexes solutions lowers the phase transition tempe rature. We have preliminarily discussed the mechanism of the enhanceme nts 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.