Novel Supramolecular Nanoparticles Derived from Cucurbit[7]uril and Zwitterionic Surfactants

Binding constants, log K ≈ 6.6 M^-1, and NMR characterization of the complexes formed by sulfobetaines and cucurbit[7]uril (CB7) support the electrostatic interaction as the major driving force. This very strong binding motif is cross-linked by additional CB7 molecules, resulting in the formation of supramolecular nanoparticles (SNPs) with an average diameter of 172 nm and a negative surface potential. The time course evolution of the particle size and the surface potential suggests the very fast formation of an amorphous aggregate that absorbs an additional amount of sulfobetaine. These aggregates afford very stable (more than 2 weeks) nanoparticles in an aqueous dispersion. The reversibility of the sulfobetaine/CB7 host/guest complexes allows SNP disaggregation by adding a competitive guest as shown by treatment with tetraethylammonium chloride. The addition of this competitive cation triggers a SNP-to-micelle transition. The potential application of these nanoparticles as drug delivery vehicles was investigated by using carboxyfluorescein. These experiments revealed that upon externally induced disruption of the SNPs (by tetraethylammonium chloride) the fluorescent dye was trapped in micellar aggregates that can be further disrupted by cyclodextrin addition.