Two phase coexistence in ternary mixtures of saturated and polyunsaturated phosphatidylcholines with cholesterol

Combining 2H and 14N nuclear magnetic resonance measurements on ternary lipid/cholesterol mixtures it is possible to quantitate the phase separation into coexisting ℓo and ℓd domains using a single sample whose composition is within the two phase region. Mixtures of each of the unsaturated phospholipids dioleoyl phosphatidylcholine, dilinoleoyl phosphatidylcholine and dilinolenoyl phosphatidylcholine with the saturated dipalmitoyl phosphatidylcholine and cholesterol all exhibit ℓo and ℓd phase coexistence over a substantial range of compositions and temperatures. A higher degree of unsaturation broadens the temperature range of two phase coexistence and results in the ℓd phase domains actually being significantly more 'fluid' at lower temperatures than they are at higher temperatures.