title: Examination of cucurbit[7]uril and its host-guest complexes by diffusion nuclear magnetic resonance.
abstract: The self-diffusion of cucurbit[7]uril (CB[7]) and its host-guest complexes in D2O has been examined using pulsed gradient spin-echo nuclear magnetic resonance spectroscopy. CB[7] diffuses freely at a concentration of 2 mM with a diffusion coefficient (D) of 3.07 x 10(-10) m(2) s(-1). At saturation (3.7 mM), CB[7] diffuses more slowly (D = 2.82 x 10(-10) m(2) s(-1)) indicating that it partially self-associates. At concentrations between 2 and 200 mM, CsCl has no effect on the diffusion coefficient of CB[7] (1 mM). Conversely, CB[7] (2 mM) significantly affects the diffusion of 133Cs+ (1 mM), decreasing its diffusion coefficient from 1.86 to 0.83 x 10(-9) m(2) s(-1). Similar changes in the rate of diffusion of other alkali earth metal cations are observed upon the addition of CB[7]. The diffusion coefficient of 23Na+ changes from 1.26 to 0.90 x 10(-9) m(2) s(-1) and 7Li+ changes from 3.40 to 3.07 x 10(-9) m(2) s(-1). In most cases, encapsulation of a variety of inorganic and organic guests within CB[7] decreases their rates of diffusion in D2O. For instance, the diffusion coefficient of the dinuclear platinum complex trans-[[PtCl(NH3)2}2mu-dpzm](2+) (where dpzm is 4,4'-dipyrazolylmethane) decreases from 4.88 to 2.95 x 10(-10) m(2) s(-1) upon encapsulation with an equimolar concentration of CB[7].
authors.affiliation: Nanoscale Organisation and Dynamics Group, School of Biomedical and Health Sciences, University of Western Sydney, Locked Bag 1797, Penrith South DC 1797, NSW, Australia.
authors.forename: Nial J
authors.initials: NJ
authors.lastname: Wheate
authors.forename: P G Anil
authors.initials: PG
authors.lastname: Kumar
authors.forename: Allan M
authors.initials: AM
authors.lastname: Torres
authors.forename: Janice R
authors.initials: JR
authors.lastname: Aldrich-Wright
authors.forename: William S
authors.initials: WS
authors.lastname: Price
mesh_terms: D001952:Bridged-Ring Compounds / Q000737:chemistry*; D017666:Deuterium Oxide / Q000737:chemistry; D004058:Diffusion; D007093:Imidazoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008672:Metals, Alkali / Q000737:chemistry; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D001952:Bridged-Ring Compounds; D017666:Deuterium Oxide; D007093:Imidazoles; D008672:Metals, Alkali; C456276:cucurbit(7)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils