THE EFFECT OF N-ACYL ETHANOLAMINES ON PHOSPHATIDYLETHANOLAMINE PHASE-TRANSITIONS STUDIED BY LAURDAN GENERALIZED POLARIZATION

The effect of N-lauroylethanolamine (N-LEA) and N-oleoylethanolamine (N-OEA) on the thermal behaviour of fully hydrated egg phosphatidylethanolamine (TPE) was investigated by the steady-state fluorescence of 2-dimethylamino-(6-lauroyl)-naphtalene (laurdan) and 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The parameter generalised polarisation (GP), calculated by exciting laurdan at 340 and 410 nm, revealed the gel to liquid crystalline lamellar (L alpha) as well as the L alpha to inverse hexagonal (H-II) phase transitions of TPE. The L alpha to H-II phase transition was not detected in TPE/N-OEA system, probably because of the formation of an intermediate Q(224) cubic phase. The formation of Q(224) phase in TPE/N-OEA and TPE/N-LEA systems was previously demonstrated by X-ray diffraction, but neither laurdan generalised polarisation nor TMA-DPH steady-state fluorescence anisotropy measurements revealed the presence of this phase. It is suggested that the lack of detection of the cubic phase is probably due to the similarity in dynamic characteristics and hydration levels of phospholipid headgroups in the bilayer and cubic phases.