Host–guest complexations of local anaesthetics by cucurbit[7]uril in aqueous solution?

Organic & Biomolecular Chemistry Pub Date: 2009-11-06 DOI: 10.1039/B915694A

Abstract

The cucurbit[7]uril (CB[7]) host molecule forms very stable host–guest complexes with the local anaesthetics procaine (KCB[7] = (3.5 ± 0.7) × 104 dm3 mol?1), tetracaine (KCB[7] = (1.5 ± 0.4) × 104 dm3 mol?1), procainamide (KCB[7] = (7.8 ± 1.6) × 104 dm3 mol?1), dibucaine (KCB[7] = (1.8 ± 0.4) × 105 dm3 mol?1) and prilocaine (KCB[7] = (2.6 ± 0.6) × 104 dm3 mol?1) in aqueous solution (pD = 4.75). The stability constants are 2–3 orders of magnitude greater than the values reported for binding by the comparably sized β-cyclodextrin host molecule. The inclusion by CB[7] raises the first pKa values of the anaesthetics by 0.5–1.9 pK units, as the protonated forms are bound more strongly in acidic solution. The complexation-induced chemical shift changes in the guest proton resonances provide an indication of the site(s) of binding and the effects of protonation on the location of the binding sites.

Graphical abstract: Host–guest complexations of local anaesthetics by cucurbit[7]uril in aqueous solution
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