THE EFFECTS OF SOLUTES ON THE FREEZING PROPERTIES OF AND HYDRATION FORCES IN LIPID LAMELLAR PHASES

Quantitative deuterium nuclear magnetic resonance is used to study the freezing behavior of the water in phosphatidylcholine lamellar phases , and the effect upon it of dimethylsulfoxide (DMSO), sorbitol, sucros e, and trehalose, When sufficient solute is present, an isotropic phas e of concentrated aqueous solution may coexist with the lamellar phase at freezing temperatures. We determine the composition of both unfroz en phases as a function of temperature by using the intensity of the c alibrated free induction decay signal (FID), The presence of DMSO or s orbitol increases the hydration of the lamellar phase at all freezing temperatures studied, and the size of the increase in hydration is com parable to that expected from their purely osmotic effect. Sucrose and trehalose increase the hydration of the lamellar phase, but, at conce ntrations of several molar, the increase is less than that which their purely osmotic effect would be expected to produce. A possible explan ation is that very high volume fractions of sucrose and trehalose disr upt the water structure and thus reduce the repulsive hydration intera ction between membranes. Because of their osmotic effect, all of the s olutes studied reduced the intramembrane mechanical stresses produced in lamellar phases by freezing. Sucrose and trehalose at high concentr ations produce a greater reduction than do the other solutes.