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Thermodynamic characterization of phospholipids dispersed in ethylammonium nitrate (a fused salt)

1992; Elsevier BV; Volume: 150; Issue: 1 Linguagem: Inglês

10.1016/0021-9797(92)90281-p

1095-7103

W. Tamura-Lis, L.J. Lis, Peter J. Quinn,

Protein Interaction Studies and Fluorescence Analysis

The phases and transition sequences and mechanisms for phospholipids dispersed in fused salt (ethylammonium nitrate, EAN) were examined via calorimetry, X-ray diffraction, and freeze-fracture electron microscopy. In most cases, complex and hysteretic phase behavior as a function of temperature was observed or inferred. Dilauroyl-, dimyristoyl-, and dipalmitoylphophatidylcholine; dipalmitoylphosphatidylethanolamine; and dipalmitoylphosphatadic acid were shown to produce nonlamellar phases above Tm when dispersed in 80% (vol/wt) EAN. However, the lipids distearoylphosphatidylcholine and dipalmitoylphosphatidylglycerol were found to produce lamellar phases over the temperature range studied, 0–80°C. In general, phospholipids dispersed in EAN were shown to favor curved surfaces, including the formation of the HII phase. There is some indication that the degree of curvature produced may be headgroup or acyl chain dependent. The complete characterization of these systems must involve studies of the influence of the complete thermal history (i.e., equilibration times and temperatures, rate of change of temperature with time) of the sample as well as composition and sample temperature.