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.

γ-Cyclodextrin modulates the chemical reactivity by multiple complexation.

Multiple complexation by γ-CD has been studied by self-diffusion coefficients (DOSY) and chemical kinetics experiments in which 4-methoxybenzenesulfonyl chloride (MBSC) solvolysis was used as a chemical probe. The addition of a surfactant as a third component to the reaction mixture induced a very complex reactivity pattern that was explained on the basis of multiple complexation phenomena and surfactant self-assembly to form micelles. A cooperative effect that yielded a ternary complex formed by cyclodextrin-surfactant-MBSC was observed. The larger cavity of γ-CD in comparison with ß-CD is responsible for the change from the competitive complexation mechanism predominant with ß-CD to a cooperative/competitive mixed mechanism operating for the larger derivative. The cavity size in γ-CD is large enough to bind two surfactant alkyl chains with a cooperative effect. Water molecules released by the formation of 1:1 host-guest complexes made the cavity more hydrophobic and promoted further inclusion. A reduction in the available volume of the cavity should be considered on binding a second guest.