Osmotic properties and water permeability of phospholipid liquid crystals

Abstract

A smectic mesophase (myelin-like structure, layer-latticed liquid crystal) of charged phospholipid behaves as an almost perfect osmometer when alkali metal salts, glucose, sucrose or mannitol are used as solutes. Other solutes show graded permeabilities (ethylurea, methylurea, ethylene glycol, ammonium acetate, propionamide, glycerol > urea > malonamide > erythritol). Osmotically driven swelling and shrinkage were followed by means of the changes in optical extinction; the validity of this was confirmed by determination of the volumes and interstitial spaces of centrifuged pellets. The rapid volume changes, determined optically, combined with the measured total external surface areas of the phospholipid dispersions, were used to calculate osmotic water permeability coefficients (0.8–16 μsec −1). The complementary effects of surface charge and electrolyte concentration on the equilibrium volumes of smectic mesophases were examined optically and by centrifugation. The volume of the particles decreased with increasing concentration of the electrolyte solution in which they formed. The intramellar spacings were not consistent with a single Hamaker constant over the range of electrolyte concentration and area-charge ratio studied. The constant was high (10- 11 ergs) with low electrolyte concentrations and lower by a factor of about 100 with a high electrolyte concentration.