Phase diagram of 1,2-dioleoylphosphatidylethanolamine (DOPE):water system at subzero temperatures and at low water contents

• Published in: Biochimica et biophysica acta Vol. 1419; no. 2; pp. 229 - 247
• Main Authors: Shalaev, Evgenyi Y., Steponkus, Peter L.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-07-1999
• Subjects: Calorimetry, Differential Scanning; Crystallization; Differential scanning calorimetry; Freezing; Ice melting; Lipid Bilayers - chemistry; Liposomes; Phase diagram; Phosphatidylethanolamine; Phosphatidylethanolamines - chemistry; Temperature; Thermodynamics; Water - analysis; Water - chemistry; Water sorption; X-Ray Diffraction; Ice melting; P δ, inverted ribbon phase; T c, the L c-to-H II phase transition temperature; T bh, the temperature of the monovariant L α→H II+L α→H II and invariant L α+water→H II+water phase transitions; Phase diagram; X-ray diffraction; DOPE, 1,2-dioleoyl- sn-glycero-3-phosphatidylethanolamine; Water sorption; T w i, the L α+ice→L α+water invariant phase transition temperature; L β, lamellar gel phase; DAPE, 1,2-diarachinoyl- sn-glycero-3-phosphoethanolamine; L c, lamellar crystalline phase; T m, the L β+water→L α+water invariant phase transition temperature in the supercooled samples; POPE, 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoethanolamine; DDPE, 1,2-didodecyl- rac-glycero-3-phosphoethanolamine; PC, phosphatidylcholine; Superscripts i and m refer to the invariant and monovariant phase transitions, respectively; Differential scanning calorimetry; Phosphatidylethanolamine; H II, inverted hexagonal phase; T w2 m, the L β+ice→L β monovariant phase transition temperature; PE, phosphatidylethanolamine; T m2 i, the L c+L β→L c+H II invariant phase transition temperature; T m m, the L β→L β+L α monovariant phase transition temperature; T w1 m, the L α+ice→L α monovariant phase transition temperature; L α, lamellar liquid crystalline phase; T m1 i, the L β+ice→L α+ice invariant phase transition temperature
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/S0005-2736(99)00068-1

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.