title: Host-guest chemistry of a water-soluble pillar[5]arene: evidence for an ionic-exchange recognition process and different complexation modes.
abstract: The complexation of an anionic guest by a cationic water-soluble pillararene is reported. Isothermal titration calorimetry (ITC), (1)H NMR, (1)H and (19)F DOSY, and STD NMR experiments were performed to characterize the complex formed under aqueous neutral conditions. The results of ITC and (1)H NMR analyses showed the inclusion of the guest inside the cavity of the pillar[5]arene, with the binding constant and thermodynamic parameters influenced by the counter ion of the macrocycle. NMR diffusion experiments showed that although a fraction of the counter ions are expelled from the host cavity by exchange with the guest, a complex with both counter ions and the guest inside the pillararene is formed. The results also showed that at higher concentrations of guest in solution, in addition to the inclusion of one guest molecule in the cavity, the pillararene can also form an external complex with a second guest molecule.
authors.affiliation: Departamento de Química Física, Centro de Investigación en Química Biológica y Materiales Moleculares (CIQUS), Universidad de Santiago, 15782 Santiago (Spain), Fax: (+34) 981595012.
authors.forename: Borja
authors.initials: B
authors.lastname: Gómez
authors.forename: Vitor
authors.initials: V
authors.lastname: Francisco
authors.forename: Fernando
authors.initials: F
authors.lastname: Fernández-Nieto
authors.forename: Luis
authors.initials: L
authors.lastname: Garcia-Rio
authors.forename: M
authors.initials: M
authors.lastname: Martín-Pastor
authors.forename: M Rita
authors.initials: MR
authors.lastname: Paleo
authors.forename: F Javier
authors.initials: FJ
authors.lastname: Sardina
mesh_terms: D047250:Calixarenes; D007474:Ion Exchange; D008958:Models, Molecular; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000644:Quaternary Ammonium Compounds; C570642:pillar(5)arene; D014867:Water; D047250:Calixarenes
keywords: NMR spectroscopy; calorimetry; host-guest systems; ion exchange; molecular recognition; supramolecular chemistry