Journal
SUPRAMOLECULAR CHEMISTRY
Volume 28, Issue 1-2, Pages 84-90Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/10610278.2015.1082563
Keywords
container molecule; water; self-assembly
Categories
Funding
- National Science Foundation [CHE 1244024]
- National Institutes of Health [GM098141]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1507344] Funding Source: National Science Foundation
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We report here NMR and Isothermal Titration Calorimetry studies of the binding of ionisable guests (carboxylate acids) to a deep-cavity cavitand. These studies reveal that the shortest guests favoured 1:1 complex formation, but the longer the alkyl chain the more the 2:1 host-guest capsule is favoured. For intermediate-sized guests, the equilibrium between these two states is controlled by pH; at low values the capsule containing the carboxylic acid guest is favoured, whereas as the pH is raised deprotonation of the guest favours the 1:1 complex. Interestingly, for one host-guest pair the energy required to decap the 2:1 capsular complex and form the 1:1 complex is sufficient to shift the pK(a) of the guest by 3-4 orders of magnitude (4.1-5.4kcalmol(-1)). The two largest guests examined form stable 2:1 capsules, with in both cases the guest adopting a relatively high energy J-shaped motif. Furthermore, these 2:1 complexes are sufficiently stable that at high pH guest deprotonation occurs without decapping of the capsule.
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