Phase diagrams of pseudo-binary phospholipid systems. II. Selected calorimetric studies on the influence of branching on the mixing properties of phosphatidylcholines.

The miscibility properties of branched phosphatidylcholines in mixtures of aqueous dispersions were studied by means of differential scanning calorimetry. The phase diagrams of four pseudo-binary systems from mixing type unbranched phosphatidylcholine/branched phosphatidylcholine/water (50 wt. % water) were investigated and discussed. The unbranched dipalmitoylphosphatidylcholine acts as a reference component of the mixtures. The phase diagrams of these four pseudo-binary phosphatidylcholine systems showed some connections between chain structure of the branched phosphatidylcholines and miscibility of the components. A change of the phase diagram type has been observed according to the branching and/or chain length differences of the phosphatidylcholines: complete miscibility and peritectic mixing behaviour. Generally we observed complete miscibility in the high-temperature phase (La-phase) and demixing in the low-temperature phases (gel phase). This is dependent on the branching and chain length differences of the mixing components.