Influence of bivalent cations on the temperature of the phase transition in lipid membranes

A theory is developed explaining the temperature shift of the phase transition of the bilayer ΔT_c, a consequence of the interaction of the charged polar heads of lipid molecules. It is shown that adsorption on a heavily charged membrane of monovalent cations raises the temperature of the transition by about 15 °C, this value not depending on the ionic strength and dielectric constant ε of the medium. On adsorption of bivalent cations the shift of the temperature of the transition is greater. The value ΔT_c depends on ε of the medium in which the polar heads are present. If the membrane is in an electrolyte solution then ΔT_c ≈ 19 °C; with the appearance between the membranes of dehydrated contact with low dielectric constant the temperature of the transition in this zone must, rise by about 160 °C which agrees with the experimental findings of Papahadjopoulos et al.