Effect of the structure of ethylene oxide-propylene oxide block copolymers on their interaction with biological membranes

Partition coefficients of ethylene oxide-propylene oxide block copolymers between the lipid phase and water have been estimated via equilibrium dialysis. It has been shown that for the triblock copolymer (Pluronic L61), the partition coefficient is 45 ± 9, while for the diblock copolymer (REP), this parameter is as high as 78 ± 17. The effect of the copolymers on the permeation of the charged organic ion carboxyfluorescein across the lecithin bilayer membrane changes in the same direction. Even though the triblock copolymer binding is weaker, it shows a stronger effect on the rate of transbilayer migration of lipids and on the permeation of the uncharged substance (doxorubicin). The incorporation of cholesterol into the membrane decreases its sensitivity to the action of copolymers; however, the character of changes induced by both copolymers remains invariable. The experimental data of this study indicate that the triblock structure of amphiphilic macromolecules is responsible for their higher ability to disturb lipid bilayer membranes.