Calorimetric studies on saturated mixed-chain lecithin-water systems. Nonequivalence of acyl chains in the thermotropic phase transition.

Aqueous dispersions of synthetic lecithins with different fatty acids in positions 1 and 2 of the glycerol molecule were studied by calorimetry. The data show that variation of the acyl chains in different positions of the glycerol backbone either have no influence upon or contribute 0.5 kcal/mol per CH2 segment to the phase transition enthalpy. Different molecular ordering of the mixed acyl chain lecithins in the bilayer is discussed in light of the results.