Effect of lanthanide ions on the phase behavior of dipalmitoylphosphatidylcholine multilamellar liposomes

Abstract

The effect of lanthanide ions (Ln 3+) and their coordination compounds of diethylenetriamine pentaacetic acid (DTPA) on the phase behavior of dipalmitoylphosphatidycholine (DPPC) multilamellar liposomes has been studied by differential scanning calorimetry (DSC), Raman spectroscopy, and freeze-fracture electron microscopic techniques. The displacement of Ca 2+ binding on DPPC liposomes by lanthanide ions was also studied. The results show that the binding degree of four kinds of chloride salts with DPPC liposomes is: YbCl 3 > GdCl 3 > LaCl 3 > CaCl 3. Lanthanide ions increase the phase transition temperature of DPPC liposomes and decrease the membrane fluidity. Freeze-fracture electron microscopic results show that La 3+ enhances the order of DPPC membrane. The effect of coordination compounds of lanthanides with DTPA on the phase behavior of DPPC liposomes is smaller than that of their chlorides. La 3+, Gd 3+, and Yb 3+, can displace Ca 2+ binding on DPPC liposomes, but there coordination compounds of DTPA can hardly displace Ca 2+. Raman spectroscopic results show that a very slight effect in lateral packing order of DPPC liposomes was observed at various concentrations of lanthanides.