Extruded vesicles of dioctadecyldimethylammonium bromide and chloride investigated by light scattering and cryogenic transmission electron microscopy

Combined dynamic and static light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM) were used to investigate extruded cationic vesicles of dioctadecyldimethylammonium chloride and bromide (DODAX, X being Cl− or Br−). In salt-free dispersions the mean hydrodynamic diameter, DhDh, and the weight average molecular weight, MwMw, are larger for DODAB than for DODAC vesicles, and both DhDh and MwMw increase with the diameter (ϕ) of the extrusion filter. NaCl (NaBr) decreases (increases) the DODAB (DODAC) vesicle size, reflecting the general trend of DODAB to assemble as larger vesicles than DODAC. The polydispersity index is lower than 0.25, indicating the dispersions are rather polydisperse. Cryo-TEM micrographs show that the smaller vesicles are spherical while the larger ones are oblong or faceted, and the vesicle samples are fairly polydisperse in size and morphology. They also indicate that the vesicle size increases with ϕ and DODAB assembles as larger vesicles than DODAC. Lens-shaped vesicles were observed in the extruded preparations. Both light scattering and cryo-TEM indicate that the vesicle size is larger or smaller than ϕ when ϕ   is smaller or larger than the optimal ϕ∗≈200 nmϕ∗≈200 nm.

Cryo-TEM image of DODAB extruded vesicles.Figure optionsDownload as PowerPoint slide