DIFFUSION-COEFFICIENTS, ELECTROPHORETIC MOBILITIES, AND MORPHOLOGIES OF CHARGED PHOSPHOLIPID-VESICLES BY PULSED-FIELD GRADIENT NMR AND ELECTRON-MICROSCOPY

Charged phospholipid vesicles were characterized at low ionic strength s by means of pulsed field gradient NMR and scanning electron microsco py for use as model systems for electrokinetic studies. Vesicles conta ining dioleoylphosphatidylglycerol (DOPG) and 1-palmitoyl-2-oleoyl pho sphatidylcholine (POPC) in a molar ratio of 1:4 with 250 mM sucrose an d neutral pH but no added salt were found to be unstable and to have d iffusion coefficients unrelated to the 0.1- or 0.2-mu m filter pore si zes used in their preparation. Scanning electron microscopy showed gia nt multilamellar structures and aggregates for this vesicle system, In contrast, neutral vesicles containing only POPC exhibited average siz es comparable to the filter pore sizes and electron micrographs with m ainly normal unilamellar structures. It was also found that charged ve sicles prepared with dilauroylphosphatidylglycerol (DLPG) and either d ilauroylphosphatidylcholine (DLPC) or egg phosphatidylcholine (EPC) at 1:4 molar ratio were well behaved and stable, Why the short-chained D LPG (saturated C-12 chains, 12:0) enhances stability compared with DOP G is not clear. The distribution of electrophoretic mobilities for uni lamellar, 0.1 mu m DLPG/EPC (1:4) vesicles was determined by electroph oretic NMR. (C) 1995 Academic Press, Inc.