[Relation of the birefringence of a bilayer lipid membrane to the ionic strength of the medium].

A direct method of measuring the optical phase difference arising in a bilayer lipid membrane at the expence of its birefringent properties is offered. A dependence of the value and sign of lipid bilayer birefringence on ionic concentration in the medium has been observed. For example, the birefringence value of the bilayer from egg lecithin with eta-decan changes from -0.005 to 0.01 with a change of NaCl concentration from 0 to 5 M, the sign changing at about 1 M. It is suggested that the polar region of the bilayer has negative birefringence, and that it is its infrastructure that changes with the ionic strength of the solution.