Relationships between miscibility behavior and chemical structure of phospholipids in pseudobinary systems

The influence of chain length differences of cephalines and the influence o f the head group methylation on the miscibility behavior of N-methylated ph osphatidylethanolamine (PE) mixtures in aqueous dispersions were tested. Ni ne different phase diagrams were studied by means of differential scanning calorimetry. The phase diagrams of the live pseudobinary cephaline/cephalin e/water systems (fatty acid chain length: C-n, n = 12-18) showed that in th e high temperature L-alpha phase all the homologous cephalines were complet ely miscible. In the low-temperature phase a distinct succession of the pha se diagram types was observed according to increasing chain length differen ces of the PEs: complete miscibilty (C-12/C-14; C-14/C-16), peritectic mixi ng behavior (G(12)/C-16; C-14/C-18), eutectic mixing behavior (C-12/C-18). Furthermore four phase diagrams of pseudobinary phospholipid systems consis ting of N-methylated PEs with different numbers of methyl groups and a cons tant length of fatty acid chains were investigated and compared. These four phase diagrams showed phase separations in the low-temperatures phase (gel phase), The width and the concentration range of the miscibility gaps chan ged systematically with increasing degree of methylation of the head group of the mixing components and are connected with different possibilities of PEs to form hydrogen bridges between the mixture components.