The phase behavior of partially hydrated 1,2-dioleoylphosphatidylethanolamine (DOPE) has been studied using differential scanning calorimetry and X-ray diffraction methods together with water sorption isotherms. DOPE liposomes were dehydrated in the H(II) phase at 29°C and in the L(α) phase at 0°C by vapor phase equilibration over saturated salt solutions. Other samples were prepared by hydration of dried DOPE by vapor phase equilibration at 29°C and 0°C. Five lipid phases (lamellar liquid crystalline, L(α); lamellar gel, L(β); inverted hexagonal, H(II); inverted ribbon, P(δ); and lamellar crystalline, L(c)) and the ice phase were observed depending on the water content and temperature. The ice phase did not form in DOPE suspensions containing <9 wt% water. The L(c) phase was observed in samples with a water content of 2-6 wt% that were annealed at 0°C for 2 or more days. The L(c) phase melted at 5-20°C producing the H(II) phase. The P(δ) phase was observed at water contents of <0.5 wt%. The phase diagram, which includes five lipid phases and two water phases (ice and liquid water), has been constructed. The freeze-induced dehydration of DOPE has been described with the aid of the phase diagram. Copyright (C) 1999 Elsevier Science B.V.
Shalaev, E. Y., & Steponkus, P. L. (1999). Phase diagram of 1,2-dioleoylphosphatidylethanolamine (DOPE): Water system at subzero temperatures and at low water contents. Biochimica et Biophysica Acta - Biomembranes, 1419(2), 229–247. https://doi.org/10.1016/S0005-2736(99)00068-1