title: Quinuclidine complex with alpha-cyclodextrin: a diffusion and 13C NMR relaxation study.
abstract: The stability of an inclusion complex of quinuclidine with alpha-cyclodextrin in solution was investigated by NMR measurements of the translational diffusion coefficient. A 1:1 stoichiometry model yielded an association constant of 35 +/- 3 M(-1). The guest molecules exchange rapidly between the host cavity and the bulk solution. The reorientational dynamics of the guest and host molecules was studied using carbon-13 NMR relaxation at two magnetic fields. The relaxation of the host nuclei showed very little dependence on the guest-host concentration ratio, while the 13C spins in quinuclidine were sensitive to the solution composition. Using mole-fraction data, it was possible to extract the relaxation parameters for the bound and free form of quinuclidine. Relaxation rates of the guest molecule, free in solution, were best described by an axially symmetric model, while the data of the complex species were analyzed using the Lipari-Szabo method. Applying the axially symmetric model to the complexed quinuclidine indicated that the anisotropy of its reorientation in the bound form was increased.
authors.affiliation: Department of Physical, Inorganic and Structural Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.
authors.forename: Sahar Nikkhou
authors.initials: SN
authors.lastname: Aski
authors.forename: Jozef
authors.initials: J
authors.lastname: Kowalewski
mesh_terms: D002247:Carbon Isotopes; D004058:Diffusion; D046911:Macromolecular Substances / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards*; D015394:Molecular Structure; D011522:Protons; D011812:Quinuclidines / Q000737:chemistry*; D013816:Thermodynamics; D047391:alpha-Cyclodextrins / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D046911:Macromolecular Substances; D011522:Protons; D011812:Quinuclidines; D047391:alpha-Cyclodextrins