title: ITC and NMR Analysis of the Encapsulation of Fatty Acids within a Water-Soluble Cavitand and its Dimeric Capsule.
abstract: We report here NMR and ITC studies of the binding of ionizable guests (carboxylate acids) to a deep-cavity cavitand. These studies reveal that the shortest guests favored 1:1 complex formation, but the longer the alkyl chain the more the 2:1 host-guest capsule is favored. 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 favored, whereas as the pH is raised deprotonation of the guest favors the 1:1 complex. Interestingly, for one host-guest pair the energy required to de-cap the 2:1 capsular complex and form the 1:1 complex is sufficient to shift the pKaof the guest by ~ 3-4 orders of magnitude (4.1-5.4 kcal mol-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 de-capping of the capsule.
authors.affiliation: Department of Chemistry Tulane University New Orleans, LA 70118, USA.
authors.forename: Kaiya
authors.initials: K
authors.lastname: Wang
authors.affiliation: Department of Chemistry Tulane University New Orleans, LA 70118, USA.
authors.forename: Punidha
authors.initials: P
authors.lastname: Sokkalingam
authors.affiliation: Department of Chemistry Tulane University New Orleans, LA 70118, USA.
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Gibb