title: Cucurbit[6]uril pseudorotaxanes: distinctive gas-phase dissociation and reactivity.
abstract: Cucurbit[6]uril forms a doubly charged complex with 1,4-butanediammonium cation that is observed using electrospray ionization Fourier transform mass spectrometry. Such 1:1 complexes are not observed for the smaller cucurbit[5]uril, which forms a 2:1 ammonium:cucurbituril complex instead. The 1:1 complex with cucurbit[6]uril is difficult to fragment via collisional activation; when it does fragment, both breakup of the cucurbituril cage and loss of the amine are observed. Further, the complex reacts with tert-butylamine via slow adduction. In contrast, nonrotaxane analogues (such as doubly charged 2:1 complexes of either protonated 1,4-butanediamine or protonated ethylenediamine with cucurbit[6]uril) fragment via easy loss of the intact amine upon collisional activation and react with tert-butylamine via rapid displacement of the original amine. On the basis of stoichiometry, fragmentation behavior, and reactivity, we conclude that the doubly charged complex of cucurbit[6]uril with 1,4-butanediammonium is a gas-phase pseudorotaxane.
authors.affiliation: Brigham Young University, Department of Chemistry and Biochemistry, C100 BNSN, Provo, Utah 84602-5700, USA.
authors.forename: Haizhen
authors.initials: H
authors.lastname: Zhang
authors.forename: Eric S
authors.initials: ES
authors.lastname: Paulsen
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Walker
authors.forename: Krzysztof E
authors.initials: KE
authors.lastname: Krakowiak
authors.forename: David V
authors.initials: DV
authors.lastname: Dearden