Konkurrenz um Harnstoff: Die Translationsisomerie eines neutralen [2]Rotaxans lässt sich in Lösung durch Zugeben und Entfernen von Acetationen steuern. In Abwesenheit von Acetationen erkennt der makrocyclische Wirt ein Diphenylharnstoff‐Derivat; bei Erkennung von Acetationen durch die Harnstoff‐Einheit wird der Makrocyclus zu einer anderen Bindungsstelle verschoben (siehe Bild).

Vying for urea: The translational isomerism of a neutral [2]rotaxane can be controlled in solution through the addition and removal of acetate anions. In the absence of acetate ions, the macrocyclic host recognizes a diphenylurea derivative; recognition of acetate ions by the urea‐based station causes relocation of the macrocycle to another binding site (see picture).

The mild and efficient reaction between triethyl phosphite and benzylic azides allows us not only to construct rotaxanes in high yield from dibenzo[24]crown-8 (DB24C8) and dibenzylammonium (DBA(+))-derived threads but also to incorporate di(p-toluidine)[24]crown-8, which binds DBA(+) ions much more weakly than does DB24C8, into a corresponding [2]rotaxane.

We report a new host molecule in which one diethylene glycol chain (i.e., a loop possessing only three oxygen atoms) incorporated along with two phenolic aromatic rings is linked by a xylene spacer into a macroring. The design of the molecular structure of this macrocycle "amplifies" any potential [cation...pi], [N+-H...pi], and [N+C-H...pi] interactions between the dibenzylammonium (DBA+) ion and the phenolic rings of the macrocycle; as such, these species display a very strong binding affinity in CD3NO2 (Ka = 15,000 M(-1)). The macroring also coordinates to bipyridinium ions in a [2]pseudorotaxane fashion, which makes it the smallest macrocycle (i.e., a 25-membered ring) known to complex both DBA+ and bipyridinium ions in solution. To confirm unambiguously that these pseudorotaxanes exist in solution, we synthesized their corresponding interlocked molecules, namely rotaxanes and catenanes.