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 phosphatidyletha nolamine (TPE) was investigated by the steady-state fluorescence of 2- dimethylamino-(6-lauroyl)-naphtalene (laurdan) and (4-trimethylaminoph enyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The parameter generalised p olarisation (GP), calculated by exciting laurdan at 340 and 410 nm, re vealed 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 a lpha to H-II phase transition was not detected in TPE/N-OEA system, pr obably 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 gene ralised 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 simil arity in dynamic characteristics and hydration levels of phospholipid headgroups in the bilayer and cubic phases.