Structural differences in aqueous dispersions of alpha-tocopheryl acetate and phosphatidylcholine upon varying their molar fractions
Asai, Y.
Die Pharmazie 59(11): 849-853
2004
ISSN/ISBN: 0031-7144 PMID: 15587585 Document Number: 583652
The purpose of this study was to investigate the structure of dispersed particles composed of a-tocopheryl acetate (TA) and phospholipid. TA was dispersed with soybean phosphatidylcholine (PC) using sonication and the dispersal mechanism was evaluated by characterizing the dispersed particles using dynamic light scattering, fluorescence spectroscopy and surface layer techniques. The dispersions in the TA mole fraction range of 0.1-0.7 were stable at room temperature for 3 days. A limited amount of TA was incorporated into PC bilayer membranes (approximately 5 mol%). The excess TA separated from the PC bilayers was stabilized as emulsion particles by the PC surface monolayer. When the PC content was less than the solubility in TA (mole fraction of TA: more than 0.8), the PC monolayer did not completely cover the hydrophobic TA particle surfaces. In the case, the particle size increased drastically andseparation into oil and water occurred. The miscibility between TA and PC and the lipid composition were critically important for the stability of the dispersed particles (coexistence of emulsion particles (surface monolayer of PC + core of TA) with vesicular particles (bilayer)) of the lipid mixtures.