Van der Waals nanocapsular complexes of amphiphilic calixarenes

The inclusion complexes of p-alkanoyl calix[ 4] arenes with alkanoyl chain lengths from C4 to C10 (C4OH-C10OH) and tetrahydrofuran, dioxane, and some halocarbons as guests were prepared and their structures were studied by single-crystal X-ray diffraction, TGA, DSC, and C-13 CP-MAS NMR. The complexes of C6OH are nanocapsules stabilized by van der Waals interactions between the calixarene cavity as extended by the alkanoyl chains and one or more guest molecules. The stability of the nanocapsule compounds depends strongly on the size and saturation vapor pressure of the guests, as well as on the presence of halogen atoms in the guest molecule. In the presence of the latter, the C6OH capsular complexes have markedly lower stability and easily eject the guests. C4OH calixarene prefers to form open-container type complexes, whereas it is possible to prepare quasicapsular complexes of C10OH with dioxane as a guest. In this case, two dioxane molecules are encapsulated by two molecules of calixarene and the third dioxane molecule provides interlayer stabilization of the crystal lattice by hydrogen bonding of dioxane oxygens with OH groups of the neighboring calixarenes. The general trends in the formation and stability of van der Waals capsular complexes of amphiphilic calixarenes are discussed, as well as how they relate to the formation of solid lipid nanoparticles.