Adsorption of ions on model phospholipid membranes

Abstract Calcium and cerium chlorides, as well as cerium nitrate and cerium ammonium nitrate were examined in model lipid membranes of hydrated L ‑α‑dipalmitoylphosphatidylcholine (DPPC) by means of differential scanning calorimetry (DSC). The shift of main transition temperature of DPPC membrane (Δ T m ) was chosen as a measure of the ion-membrane effects resulting from ions adsorption on the membrane surface. A model DPPC membrane (50% hydrated) was prepared using 0.45 M water solution of CaCl 2 , CeCl 3 , Ce(NO 3 ) 3 ·6H 2 O and Ce(NH 4 ) 2 (NO 3 ) 6 . Comparative studies have been carried out of ion effects on DPPC membranes. It was established that both Ce 3+ and Ca 2+ caused sufficient positive Δ T m , but the effect per unit concentration for cerium was an order of magnitude higher than that for calcium. It was also observed that cerium nitrate and cerium ammonium nitrate, as distinct from cerium chloride, caused membrane disruption, which was apparently related to their redox activity. A model of ion effects on lipid membranes was proposed, which described, іn particular, linear relation between Δ T m and the cationic radius.