Aqueous self-assembly of SDS@2b-CD complexes: lamellae and vesicles

Cyclodextrin (CD)/surfactant complexes were usually believed to be quite soluble in water and unable to form aggregates because of the hydrophilic outer surface. However, in this work, SDS@2b-CD complex is found to be able to self-assemble into well-defined lamellar structures in concentrated aqueous solution. The lamellae possess unprecedented in-plane solid-crystalline order in addition to classical lamellar liquid-crystalline order. Such a combination in orderliness makes the lamellar phase an intermediate phase between a solid and a liquid crystal. Upon dilution, the lamellae transform to microtubes and then to vesicles. The three classes of SDS@2b-CD aggregates share a consistent building block, the channel-type crystalline bilayer membrane. Moreover, since the outer surface of SDS@2b-CD is hydrophilic, its self-assembly behavior, unlike traditional amphiphilic assembly, does not rely on the hydrophobic effect. Therefore, the present nonamphiphilic self-assembly of SDS@2b-CD is envisioned to open new possibilities for self-assembly chemistry.