Binding of Phosphates to Aminocyclodextrin Biomimetics

Aminocyclodextrins (ACDs) in which the primary face is perfacially substituted with amino pendant groups provide three potential biomimetic binding domains: the hydrophobic cavity, the cationic annulus, and the corona formed by the pendant tendrils. Binding of phosphate monoester dianions and diester monoanions by ACDs and native CDs is compared to that of neutral guest molecules. Binding to ACDs can be understood in terms of cooperativity between binding domains in which electrostatic and hydrophobic forces may be additive or compromised. Unexpectedly, slow chemical exchange is observed, in particular for dianionic aryl ester guest molecules. The substantial kinetic barriers for dissociation of these pseudorotaxane complexes are explained by the unfavorable passage of the anionic phosphate headgroup through the relatively hydrophobic ACD cavity.