MOLECULAR-ORGANIZATION OF HYDRATED DISPERSIONS OF N-ACYLETHANOLAMINE PHOSPHOLIPIDS AND MIXTURES WITH PHOSPHATIDYLCHOLINE

The physical properties of aqueous dispersions of N-acylphosphatidylet hanolamine (N-acylPE) of natural origin with a long N-acyl chain have been studied and compared with those of phosphatidylcholine (PC). Satu rated N-acylPEs form lamellar structures with a restricted head-group rotational mobility and with the same motional freedom in the hydropho bic area as PC. However, the presence of unsaturations in N-acylPE inc reases the mobility of the head group in the gel phase compared to tha t of the synthetic saturated analogue The presence of an additional hy drocarbon chain and the suggested formation of hydrogen bonds between amide groups produces a significant increase in the thermodynamic para meters (transition temperature and enthalpy) of the main calorimetric transition. Another stabilizing factor could be related to the increas e in the degree of hydration of the interfacial and head-group molecul ar regions of N-acylPE with respect to those of PC. Analysis of mixtur es of N-acylPE and PC reveals that both phospholipids were miscible ov er the entire range of composition assayed. When increasing the PC con tent of N-acylPE bilayers, decreases in the transition temperature, tr ansition enthalpy and cooperativity of the main transition occur. Alth ough the mixing of the components is clearly nonideal, no lateral phas e separation of the components occurs in the bilayer of the binary sys tem. The polymorphic behaviour of the binary systems observed by P-31- NMR reveals a hydrated lamellar phase spectrum composite of the two sp ectral line shapes corresponding to both phospholipids with the same c hemical shift anisotropy of the monocomponent systems.