Phasenumwandlungserscheinungen in Lecithin/Wasser-Systemen

1. By means of differential-scanning-calorimetry the phase transition temperatures and -enthalpies were determined and evaluated for the three following lecithin/water systems: 1,2-dimyristoyl-lecithin/water; 1,2-dipalmitoyl-lecithin/water; 1,2-distearoyllecithin/water.
2. The preparation of the lecithin/water mixtures was made by adsorption of water from the gaseous phase. The adsorption isotherms were evaluated by the BET equation.
3. Four phase transitions were found for the monohydrates of the lecithins. The parameters depend systematically on the length of the alkyl residues.
4. In the heterogeneous two phase region the main-transition and the pre-transition occurred. The thermodynamical parameters of both transitions depend on the alkyl chain length.
5. Whole the results refer to the conclusion that the lecithin head group hydration is a stepwise process. The hydration of the first shell is finished if 5 to 6 molecules water per molecule lecithin are present, while the second hydration shell is complete when about 13 water molecules are adsorbed