PHASE-DIAGRAMS OF PSEUDO-BINARY PHOSPHOLIPID SYSTEMS .3. INFLUENCE OF THE HEAD GROUP METHYLATION ON THE MISCIBILITY BEHAVIOR OF N-METHYLATED PHOSPHATIDYLETHANOLAMINE MIXTURES IN AQUEOUS DISPERSIONS

Five phase diagrams of pseudo-binary phospholipid systems consisting of N-methylated phosphatidylethanolamines with different numbers of methyl groups were investigated and compared. Four of the five phase diagrams showed phase separation in the gel phase. The width and the concentration ranges of the miscibility gaps were changing systematically with increasing degree of methylation of the head group. The influence of the number of CH3-grous on the miscibility properties of the different phospholipids is connected with different possibilities of the phosphatidylethanolamines to form H-bridges. According with the model proposed by Elder et al. (M. Elder P. Hitchcock, F.R.S. Mason and G.G. Shipley (1977) Proc. R. Soc. London, Ser. A 354, 157-165) it is obvious that each phospholipid molecule can only form two H-bridges over the N-atom of the head group to the adjacent molecule of the same layer. Consequently the substitution of the H-atom on the N-atom by CH3-groups reduce the possibility to form H-bridges. This phenomenon is connected with systematical changes in the miscibility properties of the different N-methylated phosphatidylethanolamines from the system with complete miscibility to systems with miscibility gaps. © 1990.