Rm. Epand et al., ROLE OF THE POSITION OF UNSATURATION ON THE PHASE-BEHAVIOR AND INTRINSIC CURVATURE OF PHOSPHATIDYLETHANOLAMINES, Biophysical journal, 71(4), 1996, pp. 1806-1810
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. T
hus 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 transit
ion temperature in other lipids. Factors that may contribute to the de
pendence of T-H on double bond position were studied by x-ray diffract
ion of the hexagonal phases in the presence and absence of added alkan
e: with or without the osmotic stress of polyethylene glycol, and over
a wide temperature range, The lattice dimensions show that the intrin
sic radius of lipid monolayer curvature increases as the double bond i
s 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 v
alues for the other two, Consideration of the bilayer-to-hexagonal tra
nsition in terms of bending and interstitial energies provides a ratio
nale for the relative values of T-H.