title: Bistable cucurbituril rotaxanes without stoppers.
abstract: Bistable rotaxanes are important design elements of molecular devices for a broad range of applications, such as controlled drug release, molecular rotary motors, and chemical sensors. The host-guest complexes of cucurbit[6]uril and 1,4-bis(alkylaminomethyl)benzene were found to exhibit two stable binding modes with an unexpectedly high barrier between them. Their structural and dynamic properties, kinetic and thermodynamic parameters, as well as different chemical reactivity towards the azide-alkyne [3+2] cycloaddition reaction (click chemistry), were discovered by NMR spectroscopy, X-ray crystallography, and isothermal titration microcalorimetry. The highly stable 2:1 complex, which is formed at room temperature, was found to be a kinetic product, which may be converted to the thermodynamic 1:1 complex upon prolonged heating to 100 °C. The latter is a very stable rotaxane despite the fact that it lacks bulky end groups.
authors.affiliation: Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa, Israel.
authors.forename: Mantosh K
authors.initials: MK
authors.lastname: Sinha
authors.forename: Ofer
authors.initials: O
authors.lastname: Reany
authors.forename: Maayan
authors.initials: M
authors.lastname: Yefet
authors.forename: Mark
authors.initials: M
authors.lastname: Botoshansky
authors.forename: Ehud
authors.initials: E
authors.lastname: Keinan
mesh_terms: D001665:Binding Sites; D057930:Click Chemistry; D018360:Crystallography, X-Ray; D047028:Macrocyclic Compounds / Q000737:chemistry*; D008958:Models, Molecular; D043862:Rotaxanes / Q000737:chemistry*; D013816:Thermodynamics; D000099246:Cucurbit(n)urils
chemical_list: D047028:Macrocyclic Compounds; D043862:Rotaxanes; D000099246:Cucurbit(n)urils