Electrostatic interaction is an important secondary force affecting the structure, stability, and function of lipid vesicles (liposomes). For this study, a negatively charged lipid with carboxylic acid was mixed with phospholipid to produce anionic vesicles. The electrostatics of the carboxylated anionic vesicle (ca. 200 nm diameter) was determined and correlated with entrapment capacity of the vesicles. Correlative analysis revealed the zeta potential of the vesicles as a factor quantitatively affecting the entrapment capacity for a water-soluble marker, in which the entrapment capacity reached its maximum level in less than -30 mV of zeta potential. Transmission electron microscopy (TEM) revealed that the vesicles with high entrapment capacity are composed of a unilamellar membrane. This finding is expected to be useful for efficient encapsulation of water-soluble pharmaceuticals within vesicles.
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