Ultrathin Monolayer Lipid Membranes from a New Family of Crown Ether-Based Bola-Amphiphiles

Article abstract of DOI:10.1021/ja00058a014

Twelve novel α,Ω-bis(N-azacrown ether) compounds have been prepared, characterized, and converted into a previously unknown type of niosome.Four are bis(15-crown-5) derivatives having the following spacer chains: (CH2)12 (1), (CH2)16 (2), CO(CH2)20CO (3), and (CH2)22 (4).The eight bis(aza-18-crown-6) derivatives have the following spacers: (CH2)10 (5), CO(CH2)10CO (6), (CH2)12 (7), CO(CH2)14CO (8), (CH2)16 (9), (CH2)22 (10), (CH2)12O(CH2)12 (11), and CO(CH2)11S(CH2)12S(CH2)11CO (12).Aggregation studies of 1 and 7, employing transmission electron microscopy as well as dynamic and static light scattering, demonstrate that these compounds form a novel class of spherical monolayer lipid membrane vesicles when dispersed in water.Debye light-scattering profiles obtained from a suspension of large (ca. 200 nm diameter) vesicles indicate a relative refractive index near 1.Dynamic turbidimetry in acidic media on a suspension of bola-amphisomes formed from 1, suggested that the contribution of micelle-vesicle equilibria to the bolyte aggregation state is negligible.In neutral or slightly alkaline pH at 35 deg C, the vesicles grew irreversibly to yield large, probably multilamellar, aggregates.In acidic media at pH 2, the bola-amphisomes do not coalesce, even at 65 deg C.On the basis of the observations presented here, bola-amphiphiles having a hydrocarbon span of 10-12 carbon atoms aggregate in aqueous media into vesicles.When the aliphatic backbone incorporates 16 or more carbon atoms, micelles are formed.