Complexation between a triptycene-derived oxacalixarene and π-extended viologens: linker-length-dependent orientation of the macrocycles in pseudo[3]rotaxanes

With an expanded electron-rich cavity and a fixed conformation, macrocycle H was found to encapsulate π-extended viologens G1-G4 to form the first case of pseudo[3]rotaxanes based on oxacalixarenes. The complexation was investigated in detail both in solution and in the solid state using NMR spectroscopy and X-ray crystallography. Due to the three-dimensional nonsymmetric structure of H, three orientational isomers of the pseudorotaxanes could be expected theoretically. However, as the crystal structure analysis revealed, only one of the three isomers was obtained with either G1 or G3. Moreover, with regard to the different lengths of the linkers in the guest molecules, completely opposite orientations of the macrocycles on the axles were observed, which could be explained by different complexation modes between the components in the pseudo[3]rotaxanes. Additionally, the complexation between the host and the guest could be reversibly switched on and off using a suitable acid and base. These results will provide us with the opportunity to design and elaborately regulate high-order molecular devices.

Copper(i)-induced amplification of a [2]catenane in a virtual dynamic library of macrocyclic alkenes

The interlocked virtual component 1 of a well-behaved dynamic library of cyclic olefins is resuscitated by means of the template effect.

New structural insights into mechanically interlocked polymers revealed by ion mobility mass spectrometry

Mechanically interlocked polymers can possess significant additional physical properties, in comparison to those associated with their constituent parts. Their unique properties make them attractive for a range of potential applications, such as as biomaterials and molecular machines. Their efficient and reproducible synthesis is therefore of much interest. Both their synthesis and subsequent characterization are intriguing yet demanding. The properties of mechanically interlocked polymeric systems depend not only on the properties of their individual components but also on the topology of the subsequent product. Here traveling wave ion mobility mass spectrometry has been used to investigate the structural properties of a polyrotaxane system. Ion mobility studies reveal that this system remains linear in form with increase in size. Both ion mobility studies and tandem mass spectrometry studies indicate that the macrocycle preferentially remains associated with the ammonium moiety of the polymeric repeat unit and is impeded from moving freely along the axle. This is consistent with NMR observations of the average structure. Analysis of mechanically interlocked polymers by ion mobility mass spectrometry provides additional structural insights into these systems relating to dynamics, heterogeneity, and topology. This molecule-specific information is vital in order to understand the origin of a system's functional properties.