Ice Formation in Model Biological Membranes in the Presence of Cryoprotectors

Ice formation in model biological membranes is studied by SAXS and WAXS in the presence of cryoprotectors: dimethyl sulfoxide and glycerol. Three types of phospholipid membranes: DPPC, DMPC, DSPC are chosen for the investigation as well-studied model biological membranes. A special cryostat is used for sample cooling from 14.1C to -55.4C. The ice formation is only detected by WAXS in binary phospholipid/water and ternary phospholipid/cryoprotector/water systems in the condition of excess solvent. Ice formation in a binary phospholipid/water system creates an abrupt decrease of the membrane repeat distance by delta-d, so-called ice-induced dehydration of intermembrane space. The value of delta-d decreases as the cryoprotector concentration increases. The formation of ice does not influence the membrane structure (delta-d = 0) for cryoprotector mole fractions higher than 0.05.