Effect of Gd³⁺ on the colloidal stability of liposomes

Lanthanide ions such as La³⁺ and Gd³⁺ are well known to have large effects on the structure of phospholipid membranes. Unilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) were prepared by sonication method and confirmed by transmission electron microscopy. The effects of concentration of gadolinium ions Gd³⁺ on DPPC unilamellar vesicles in aqueous media were studied by different techniques. As physical techniques, photon correlation spectroscopy, electrophoretic mobility, and differential scanning calorimetry were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersities values were observed as Gd³⁺ concentration increases, suggesting that this cation induces the aggregation of vesicles. Electrophoretic mobility measurements on unilamellar vesicles as a function of Gd³⁺ ion concentration show that the vesicles adsorb Gd³⁺ ions. Above Gd³⁺ concentrations of 0.1  mol  dm^–3, the potential and light scattering measurements indicate the beginning of aggregation process. For comparison with similar phospholipids, the zeta potential of phosphatidylcholine interacting with Gd³⁺ was measured, showing an analogous behavior. Differential scanning calorimetry has been used to determine the effect of Gd³⁺ on the transition temperature (T_c) and on the enthalpy (H_c) associated with the process.

©2006 The American Physical Society