Is [N+-H•••O] hydrogen bonding the most important noncovalent interaction in macrocycle-dibenzylammonium ion complexes?

[GRAPHICS] 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 center dot center dot center dot pi], [N+-H center dot center dot center dot pi], and [N+C-H center dot center dot center dot 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 (K-a = 15 000 M-1). The macroring also coordinates to bipyridinium ions in a [2]pseudorotaxane fashion, which makes it the smallest macrocycle (i.e., it 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.