The distribution of α-tocopherol in mixed aqueous dispersions of phosphatidylcholine and phosphatidylethanolamine

Abstract

The effect of α-tocopherol on the structure and phase behaviour of mixed aqueous dispersions of phosphatidylcholine and phosphatidylethanolamine has been examined by synchrotron X-ray diffraction. Equimolar mixtures of dioleoylphosphatidylethanolamine:dioleoylphosphatidylcholine and dimyristoylphosphatidylcholine:dioleoylphosphatidylethanolamine did not show evidence of phase separation of an inverted hexagonal structure typical of α-tocopherol and phosphatidylethanolamine from lamellar phase. Mixed dispersions of dioleoyl derivatives of phosphatidylethanolamine:phosphatidylcholine (3:1) form a typical miscible gel phase at low temperatures but which phase separates into lamellar liquid–crystal and inverted hexagonal phases at temperatures greater than 65°C. The presence of 1, 2 or 5 mol% α-tocopherol caused a decrease in the temperature at which the inverted hexagonal phase appears. Phase separation of non-lamellar phase from lamellar gel phase can be detected in the presence of 7.5 and 10 mol% α-tocopherol, indicating a limited capacity of the phosphatidylcholine to incorporate α-tocopherol into the lamellar domain. A partial phase diagram of the ternary mixture has been constructed from the X-ray scattering data. It was concluded that there is no preferential interaction of α-tocopherol with phosphatidylethanolamine in mixed aqueous dispersions containing phosphatidylcholines.