Abstract
Cucurbit[7]uril inclusion complexes with guests bearing dimethylamino groups show the expected upward pK (a) shifts, whereas their diethylamino counterparts display a decrease in pK (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.