Threading hydrogen-bonding based

Figure 10.63 Crown ether ammonium ion based rotaxane type hydrogen bonded complexes (a) [3] rotaxane, (b) three threads in one ring and (c) two threads linking two rings.

Figure 4. Hydrogen bond templated threading of a tetraamide ring in synthesis of amide-based catenanes and...

The threading of the dibenzylammonium cation into dibenzo[24]crown[8] has been exploited to assemble pseudorotaxanes at the surface of a nanocrystal96 and to induce and control formation of nanoparticle aggregates.97 However, the possibility of pH-triggered aggregation, related to the acid-base controlled dethreading of hydrogen-bonded pseudorotaxanes, was not explored. 

Fig. 7 Molecular-level plug/socket system for energy transfer based on the reversible acid-base driven threading-dethreading motions in the hydrogen bonded pseudorotaxane 4d5H+ (CH2C12 room temperature). The acid-driven threading of compound 6, incorporating a bulky benzyl group, through the macrocyclic cavity of 4 does not occur [57]...

Fig. 1.4. Anion-templated rotaxane synthesis. The axle center piece is threaded through the macrocycle s cavity by hydrogen bonding. Stopper attachment to both axle ends traps the wheel on the axle. Inset hydroquinone-based center piece which can also be used, but with lower efficiency.

Fluorescence spectroscopy was used also as a detection tool in case of a peptide based [2]rotaxane [72]. It was observed that in polar solvents like dimethyl sulfoxide (DMSO) fluorescence emission spectra were virtually same like those of the thread alone. Since fluorescence origins in this rotaxane from anthracene group, it was concluded that hydrogen bonds linking the macrocycle to the anthracene-based stopper were broken and the macrocycle resided on the alkyl side of the thread. When the solvent was hardly polar like 1,4-dioxane, the macrocycle rest bonded to the anthracene stopper and the spectrum broadened and red-shifted. By mean of time-resolved fluorescence spectroscopy, the authors demonstrated that it was... 

---