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Diffusion Coefficients, Electrophoretic Mobilities, and Morphologies of Charged Phospholipid Vesicles by Pulsed Field Gradient NMR and Electron Microscopy

Abstract Charged phospholipid vesicles were characterized at low ionic strengths by means of pulsed field gradient NMR and scanning electron microscopy for use as model systems for electrokinetic studies. Vesicles containing dioleoylphosphatidylglycerol (DOPG) and 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) in a molar ratio of 1:4 with 250 m M sucrose and neutral pH but no added salt were found to be unstable and to have diffusion coefficients unrelated to the 0.1- or 0.2-μm filter pore sizes used in their preparation. Scanning electron microscopy showed giant multilamellar structures and aggregates for this vesicle system. In contrast, neutral vesicles containing only POPC exhibited average sizes comparable to the filter pore sizes and electron micrographs with mainly normal unilamellar structures. It was also found that charged vesicles prepared with dilauroylphosphatidylglycerol (DLPG) and either dilauroylphosphatidylcholine (DLPC) or egg phosphatidylcholine (EPC) at 1:4 molar ratio were well behaved and stable. Why the short-chained DLPG (saturated C 12 chains, 12:0) enhances stability compared with DOPG is not clear. The distribution of electrophoretic mobilities for unilamellar, 0.1 μm DLPG/ EPC (1:4) vesicles was determined by electrophoretic NMR.