Small unilamellar vesicles can be formed by changing the pH: is this one aspect of a more general phenomenon?

Abstract

The formation of small (100 nm) unilamellar vesicles induced by increasing the pH of dispersions of phosphatidic acid and mixtures of this with other phospholipids has been described [22]. Here it is shown that this method of vesiculation also produces small unilamellar vesicles from mixtures of phosphatidic acid with phosphatidylcholine and cholesterol, with monoolein and with monomyristin. Further, the proposal [32] that lipids that show, so called, unlimited swelling form unilameltar vesicles in excess water is confirmed. The disruption of the formation of multilamellar vesicles from egg phosphatidylcholine by the inclusion of charged amphiphiles (cholic acid, dodecyltrimethylammonium bromide and chlorpromazine) in the bilayers was followed by the decrease in light scattering and the increase in vesicles not sedimented by centrifugation. Both these changes correlate with the formation of unilamellar vesicles that can be demonstrated by electron microscopy.