Role of the position of unsaturation on the phase behavior and intrinsic curvature of phosphatidylethanolamines

Biophys J. 1996 Oct;71(4):1806-10. doi: 10.1016/S0006-3495(96)79381-5.


The bilayer-to-hexagonal phase transition temperatures (T(H)) of di-18:1(C) phosphatidylethanolamine with double bonds at positions 6, 9, and 11 are 37 degrees C, 8 degrees C, and 28 degrees C, respectively, as measured by differential scanning calorimetry and x-ray diffraction. Thus T(H) exhibits a minimum when the C=C is around position 9, similar to what has been found for the gel-to-liquid crystalline phase transition temperature in other lipids. Factors that may contribute to the dependence of T(H) on double bond position were studied by x-ray diffraction of the hexagonal phases in the presence and absence of added alkane, with or without the osmotic stress of polyethylene glycol, and over a wide temperature range. The lattice dimensions show that the intrinsic radius of lipid monolayer curvature increases as the double bond is moved toward the tail ends. A measure of the bending moduli of these lipid monolayers shows a higher value for the 9 position, and lower values for the other two. Consideration of the bilayer-to-hexagonal transition in terms of bending and interstitial energies provides a rationale for the relative values of T(H).

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calorimetry, Differential Scanning
  • Gels
  • Lipid Bilayers*
  • Models, Structural
  • Molecular Conformation
  • Phosphatidylethanolamines / chemistry*
  • Structure-Activity Relationship
  • Thermodynamics
  • X-Ray Diffraction


  • Gels
  • Lipid Bilayers
  • Phosphatidylethanolamines