Vesicle Formed by Amphiphilc Cucurbit[6]uril: Versatile, Noncovalent Modification of the Vesicle Surface, and Multivalent Binding of Sugar-Decorated Vesicles to Lectin

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Abstract
We report a novel vesicle formed by an amphiphilic CB[6] derivative, the surface of which can be easily modified via host−guest interactions by taking advantage of molecular cavities, readily accessible at the vesicle surface, and their strong affinity toward polyamines. Amphiphilic CB[6] derivative 1 synthesized by reaction between (allyloxy)12CB[6] and 2-[2-(2-methoxyethoxy)ethoxy]ethanethiol affords a vesicle that has been characterized by TEM, light scattering, and fluorescent dye entrapment experiments. Treatment of vesicle 1 with FITC (fluorescein isothiocyanate)−spermine conjugate ligand 2, in which spermine serves as a binding motif to CB[6] and FITC as a fluorescent tag, produced a surface-modified vesicle, which can be easily visualized by a confocal microscope. This result provides us with a new noncovalent, modular approach to the modification of vesicle surfaces. By treating the vesicle derived from the amphiphilic CB[6] with a tag-attached polyamine, we can easily decorate the surface of the vesicle with the tag. Sugar-decorated vesicles were prepared by this noncovalent method, and their interactions with concanavalin A (ConA) were studied. The binding constant of the vesicle decorated with mannose−spermidine conjugate 3 to ConA was measured to be ∼3 × 104 M-1, which is almost 3 orders of magnitude higher than that of free ligand 3 to ConA (K = ∼50 M-1). On the other hand, the binding constant of the vesicle coated with galactose−spermidine conjugate 4 to ConA was too small to be measured. These results illustrate the specific and multivalent interactions between the mannose-decorated vesicle and ConA. The ability for facile surface modification suggests many practical applications, including its use in targeted drug delivery and immunization.