Encapsulation of a \u3b2-carboline in cucurbit[7]uril

Inclusion of a biological photosensitizer and prototype of \u3b2-carbolines, norharmane (NHM), into the cavity of cucurbit[7]uril (CB[7]) has been investigated for the first time, by using 1H NMR and UV\u2013visible spectroscopy, and ab initio calculations. Protonated NHM forms a very stable host\u2013guest complex with CB[7] in aqueous solution, with a binding constant of (9.0 \ub1 0.5) 7 104 M 121. The encapsulation of NHM into CB[7] has driven the prototropic equilibrium of NHM to protonated NHM (NHMH+) at neutral pH. A pH titration for the host\u2013guest complex revealed a moderate shift of the acid\u2013base equilibrium in the ground-state (from 7.2 to 7.9), which may be caused by the low polarity microenvironment of the CB[7] cavity. The CB[7] provides a binding pocket for the hydrophobic molecule, and the polar, carbonyl-lined portals offering an anchoring site for the positive charge of the cationic species NHMH+.Peer reviewed: YesNRC publication: Ye