College Park, Maryland      June 6 - 10 , 2004

MP21: Highly Stable Phospholipid Unilamellar Vesicles from Spontaneous Vesiculation: A DLS and SANS Study

B. Yue, C-Y. Huang (Chemical Engineering Dept. NJIT), M-P. Nieh (National Research Council, Chalk River, Ontario, Canada), C. J. Glinka (National Institute of Standards and Technology), J. Katsaras (National Research Council, Chalk River, Ontario, Canada)

Spontaneously formed unilamellar vesicles (ULVs) composed of short- and long-chain phospholipids, dihexanoyl (DHPC) and dimyristoyl phosphorylcholine (DMPC) mixtures doped with negatively charged dimyristoyl phosphorylglycerol (DMPG) were studied by small angle neutron scattering (SANS) and dynamic light scattering (DLS). Vesicle formation was found to follow a quick bicelle-to-vesicle transition mechanism. The SANS and DLS data showed that ULVs with narrow size distribution were highly stable at low lipid concentrations, Clp<0.50 wt.%, and salt concentrations (Cs). ULV size was found independent of both Clp and Cs, when they were below 0.33 wt.% and 0.5 wt.% respectively. Surface charge is found to be an important factor for stabilizing ULVs with a constant size. This observation is not in total agreement with most previous experimental results and cannot be completely explained with previous theoretical predications based on equilibrium calculations for catanionic surfactant mixtures. The size of ULVs was almost constant over a wide temperature range below and above the phase transition temperature of DMPC, TM, for months, even after sonication.

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