Small-angle neutron-scattering studies of nonionic surfactant vesicles

Small-angle neutron-scattering (SANS) studies have been performed on potent ial drug delivery vesicles formed from 1,2-di-O-octadecyl- and 1,2-di-O-hex adecyl-rac-glycerol-3-(omega-methoxydodecaethylene glycol) (2C(18)E(12) and 2C(16)E(12), respectively). The 2C(18)E(12) vesicles. are shown to be deli mited by single bilayers 55 Angstrom thick, while the 2C(16)E(12) vesicles are more likely delimited by twin bilayers (with lamellae thicknesses of 10 4 Angstrom). For both types of surfactant the molecular interfacial areas o ccupied in the vesicle bilayers are calculated to be similar to 100 Angstro m(2). Through model fitting of the SANS data, approximating the vesicle lam ellae as infinite sheets, it is shown that the lamellae have undulating (ra ther than perfectly flat); surfaces, with a small proportion of the surfact ant's polyoxyethylene chains intermixed with the hydrocarbon chains, and a rather low level of headgroup hydration (of the order of 1 H2O per oxyethyl ene unit). In the presence of 0.15 M NaCl (used as a crude approximation to human blood plasma), the 2C(18)E(12) vesicle lamellae are completely unaff ected, while the 2C(16)E(12) vesicles have mean lamellae thicknesses that a re reduced by similar to 20%, possibly because the salt causes changes in t he relative proportions of unilamellar and bilamellar vesicles in the sampl es.