Small-Angle Neutron-Scattering Studies of Nonionic Surfactant Vesicles

Small-angle neutron-scattering (SANS) studies have been performed on potential drug delivery vesicles formed from 1,2-di-O-octadecyl- and 1,2-di-O-hexadecyl-rac-glycerol-3-(ω-methoxydodecaethylene glycol) (2C18E12 and 2C16E12, respectively). The 2C18E12 vesicles are shown to be delimited by single bilayers 55 A thick, while the 2C16E12 vesicles are more likely delimited by twin bilayers (with lamellae thicknesses of 104 A). For both types of surfactant the molecular interfacial areas occupied in the vesicle bilayers are calculated to be ∼100 A2. Through model fitting of the SANS data, approximating the vesicle lamellae as infinite sheets, it is shown that the lamellae have undulating (rather than perfectly flat) surfaces, with a small proportion of the surfactant's polyoxyethylene chains intermixed with the hydrocarbon chains, and a rather low level of headgroup hydration (of the order of 1 H2O per oxyethylene unit). In the presence of 0.15 M NaCl (used as a crude approximation to human blood plasma), the...