Surface tension of an artificial bileaflet membrane in comparison to parent lipid solution - water interfacial tension

Bileaflet membranes were produced between 0.1 N NaCl solutions from a solution of 4% cholesterol and 5.5% egg-lecithin in methyl oleate. The surface tension of these membranes was calculated from the measured change in capacitance in response to a change in pressure difference across the membrane. The change in capacitance was assumed to reflect change in bulging of membrane. A surface tension of 0.49 ±s.d. 0.15 dyn/cm (n = 15) was found. The surface tension increased with membrane aging. The water-parent lipid solution interfacial tension was 0.72 dyn/cm. It is concluded that the difference between the free energy of formation of two interfacial surfaces and that of a bileaflet membrane is more than 1 erg/cm². Only a negligible fraction if this difference could be accounted for by the interaction between water molecules across the ultrathin membrane.