Ultrasound-Driven Secondary Self-Assembly of Amphiphilic β-Cyclodextrin Dimers

The controlled secondary self-assembly of amphiphilic molecules in solution is theoretically and practically significant in amphiphilic molecular applications. An amphiphilic beta-cyclodextrin (beta-CD) dimer, namely LA-(CD)(2), has been synthesized, wherein one lithocholic acid (LA) unit is hydrophobic and two beta-CD units are hydrophilic. In an aqueous solution at room temperature, LA-(CD)(2) self-assembles into spherical micelles without ultrasonication. The primary micelles dissociates and then secondarily form self-assemblies with branched structures under ultrasonication. The branched aggregates revert to primary micelles at high temperature. The ultrasound-driven secondary self-assembly is confirmed by transmission electron microscopy, dynamic light scattering, H-1 NMR spectroscopy, and Cu2+-responsive experiments. Furthermore, 2D NOESY NMR and UV/Vis spectroscopy results indicate that the formation of the primary micelles is driven by hydrophilic-hydrophobic interactions, whereas host-guest interactions promote the formation of the secondary assemblies. Additionally, ultrasonication is shown to be able to effectively destroy the primary hydrophilic-hydrophobic balances while enhancing the hostguest interaction between the LA and b-CD moieties at room temperature.