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Spontaneously Formed Monodisperse Biomimetic Unilamellar Vesicles: The Effect of Charge, Dilution, and Time

M.-P. Nieh ^*, T. A. Harroun ^*, V. A. Raghunathan , C. J. Glinka  and J. Katsaras ^*

^* National Research Council Canada, Steacie Institute for Molecular Sciences, Chalk River, Ontario K0J 1J0, Canada; Raman Research Institute, Bangalore-560 080, India; and Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 USA

Correspondence: Address reprint requests to John Katsaras, National Research Council Canada, Steacie Institute for Molecular Sciences, Chalk River, Ontario K0J 1J0, Canada. Tel.: 613-584-3311 ext. 3984; E-mail: john.katsaras{at}nrc.ca.

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 1 wt %), spontaneously forming unilamellar vesicles (ULVs) were found, and their polydispersity was determined to be 20%. 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_lp). However, doping the dimyristoyl/dihexanoyl system with both Ca²⁺ and DMPG resulted in ULVs whose R_o was found to be C_lp 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.