Spontaneously formed monodisperse biomimetic unilamellar vesicles: The effect of charge, dilution, and time

Using small-angle neutron scattering and dynamic light scattering, we have constructed partial structural phase diagrams of lipid mixtures composed of the phosphatidylcholines dimyristoyl and dihexanoyl doped with calcium ions (Ca2+) and/or the negatively charged lipid, dimyristoyl phosphatidylglycerol (DMPG). For dilute solutions (lipid concentration less than or equal to l wt %), spontaneously forming unilamellar vesicles (ULVs) were found, and their polydispersity was determined to be similar to20%. The stability of the Ca2+- or DMPG-doped ULVs was monitored over a period of 4 days and their structural parameters (e.g., average outer radius, (R-o)) were found to be insensitive to the lipid concentration (C-ip). However, doping the dimyristoyl/ dihexanoyl system with both Ca2+ and DMPG resulted in ULVs whose (R-o) was found to be C-ip dependent. The (R-o) of DMPG-doped ULVs remained unchanged over an extended period of time (at least 4 days), a good indication of their stability.