Stabilization of the monoolein Pn3m cubic structure on trehalose glasses

Trehalose is known to protect some organisms from various stresses due to d rought and high temperature. To explore the molecular mechanism of the prot ective function, the mesomorphic properties of the monoolein-water system, dried in the presence of trehalose, were studied by X-ray diffraction. Whil e, in pure water, two bicontinuous inverse cubic structures (the Pn3m and I a3d phases) and a lamellar L alpha phase exist as a function of concentrati on, only the Pn3m cubic phase has been detected in concentrated trehalose s olutions or in trehalose glasses, even under extremely dry conditions. Depe nding on the sugar concentration, or after glass dehydration, the Pn3m cubi c unit cell decreases to very low values, much below the smaller one observ ed in pure water. However, as no phase transitions occur, a simple osmotic mechanism can be excluded. An additional stabilization of the lipid phase, arising from interfacial free energy changes due to trehalose-water-lipid d irect interactions, and large enough to affect the energetic balance betwee n the Pn3m and the Ia3d cubic phases, evidently occurs. Moreover, no differ ences in the Pn3m cubic structure were observed when the sugar platelets co nvert to the glassy state; no apparent structural modifications that can be related to mechanical pressure exerted on the lipid phase have been detect ed.