OPTICAL-PROPERTIES OF LIPID DISPERSIONS INDUCED BY PERMEANT MOLECULES

The effect of erythritol on the refractive index and light scattering of multilamellar liposomes and small unilamellar vesicles has been analyzed and compared with those occurring at the gel-liquid crystalline transition temperature. The results indicate that the decrease of the absorbance of the dispersion is related to the penetration of erythritol into the lipid bilayer. Simultaneously, the permeability barrier properties of the bilayer decreases as shown by the correlation between the absorbance decrease and the leakage of K+ ions. Neither the refractive index nor the permeability is affected by permeants in sonicated vesicles. Thus, the optical changes observed during swelling or shrinkage are related to the packing of the lipids in the membrane. The response of liposomes as osmometers implies variations in the free volume of the liposomes by the permeant and water penetration affecting the membrane fluidity or the tightening of the hydrogen belt which has been claimed to form the rate-limiting barrier for solutes penetrating the lipid membrane.