Azacrown ethers as amphiphile headgroups: Formation of stable aggregates from two- and three-armed lariat ethers

Ten 18-membered ring lariat ether compounds have been prepared as one-, two-, and three-armed derivatives of aza-, diaza-, and triaza-18-crown-6. They include N-[[(3-cholestanyloxy)carbonyl]methyl]aza-18-crown-6, 1, N-tetradecylaza-18-crown-6, 2, N,N'-dibutyl-4,13-diaza-18-crown-6, 3, N,N'-dinonyl-4,13-diaza-18-crown-6, 4, N,N'-didodecyl-4,13-diaza-18-crown-6, 5, N,N'-ditetradecyl-4,13-diaza-18-crown-6, 6, N,N'-dioctadecyl-4,13-diaza-18-crown-6, 7, N,N'-bis[[(3-cholestanyloxy)carbonyl]methyl]-4,13-diaza-18-crown-6, 8, N,N'-bis[[(3-cholestanyloxy)carbonyl]decyl]4,13-diaza-18-crown-6, 9, and N,N'N ''-tri-n-hexyl-4,10,16-triaza-18-crown-6, 10. Compounds 2, 8, and 9 are previously unreported. Aqueous suspensions of these monomers were sonicated, and the first evidence for stable aggregates formed from diaza and triaza lariat ethers (3-10) was obtained. The formation of aggregates from 3 or 10 is especially notable since the side chains are butyl or hexyl, respectively. The aggregates were studied by a combination of laser light scattering, electron microscopy, and dye entrapment. All of the amphiphiles proved to form aggregates thought to be vesicles except 2, which formed micelles. The similarity in sizes of the vesicles, apparently irrespective of side chain, and the general indifference of aggregate size to the presence of cations suggest that headgroup organization determines overall size in this case. Protonation of one or more macroring nitrogen atoms could lead to a hydrogen-bond network that would stabilize the aggregates and have low affinity for added cations.