Trehalose maintains phase separation in an air-dried binary lipid mixture

Mixing and thermal behavior of hydrated and air-dried mixtures of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) and 1,2-distearoyl-d70-sn-glycero-3-phosphocholine (DSPCd-70) in the absence and presence of trehalose were investigated by Fourier transform infrared spectroscopy. Mixtures of DLPC:DSPCd-70 (1:1) that were air-dried at 25 degrees C show multiple phase transitions and mixed phases in the dry state. After annealing at high temperatures, however, only one transition is seen during cooling scans. When dried in the presence of trehalose, the DLPC component shows two phase transitions at -22 degrees C and 75 degrees C and is not fully solidified at -22 degrees C. The DSPCd-70 component, however, shows a single phase transition at 78 degrees C. The temperatures of these transitions are dramatically reduced after annealing at high temperatures with trehalose. The data suggest that the sugar has a fluidizing effect on the DLPC component during drying and that this effect becomes stronger for both components with heating. Examination of infrared bands arising from the lipid phosphate and sugar hydroxyl groups suggests that the strong effect of trehalose results from direct interactions between lipid headgroups and the sugar and that these interactions become stronger after heating. The findings are discussed in terms of the protective effect of trehalose on dry membranes.