Contrasting p K a Shifts in Cucurbit[7]uril Host-Guest Complexes Governed by an Interplay of Hydrophobic Effects and Electrostatic Interactions.

Cucurbit[7]uril inclusion complexes with guests bearing dimethylamino groups show the expected upward p K _a shifts, whereas their diethylamino counterparts display a decrease in p K _a due to the preferential stabilization of the unprotonated form. These results identify the diethylamino group as the substituent of choice to avoid receptor-assisted protonation of guest molecules and present new evidence for the role of the hydrophobic effect as a driving force in cucurbituril complexation.
Competing Interests: The authors declare no competing financial interest.