Cyclic daisy chain

When supramolecular polymers are treated with bulky stopper groups, they may form poly[2]rotaxane daisy chains [45-53]. Harada et al. [31] treated 6-p-aminoCiO-a-CD (40 mM) with 2M excess 2,4,6-trinitrobenzenesulfonic acid sodium salt (TNBS) as bulky stoppers in aqueous solutions. The resulting precipitate was found to be mainly a cyclic trimer by H NMR and TOF mass spectra. After purification of the crude product, the 2D ROESY spectrum of the cyclic trimer shows cross-peaks between phenyl protons close to an amino group and secondary hydroxyl groups (0(2)H). A trinitrophenyl group is found at the secondary hydroxyl group side. A proposed structure of a cyclic trimer (cyclic daisy chain) is shown in Fig. 3.12. Kaneda et al. [38] reported the preparation of cyclic di[2]rota-xane fashion constructed tail-to-tail by azobenzene derivatives of permethylated a-CDs and showed its computer-generated supramolecular structures (Fig. 3.13). Easton et al. [39] also reported the preparation of cyclic di[2]rotaxane constructed by stilbene-appended a-CDs in tail-to-tail fashion (Fig. 3.14). Kaneda et al. [40] 

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When supramolecular polymers are treated with bulky stopper groups, they may form poly[2]rotaxane daisy chains [32,60-68]. Cyclic tri[2]rotaxanes (daisy chain necklace) containing cyclodextrins have been prepared from the mixture of 6-(4-aminocinnamoyl)-Q -CD and 2,4,6-trinitrobenzene sulfonic acid sodium salt [50,59] in an agueous solution (Fig. 21). If the molecule changes its conformation (or co-conformation), the ring may expand or shrink by external conditions (temperature, solvents, photochemically, elec-trochemically). These compounds are important because the cycle can be used as a chemical valve as seen in ion channels in biological membranes. 

Fig.21 Harada s daisy chain necklace cyclic tri[2]rotaxane containing a-CD [41]...

A catenane is a molecule in which two or more rings are interlocked, in a manner resembling a daisy-chain. Chemists have speculated about the possibility of the synthesis of such motifs for a long time. The two arrangements of the interlinked cyclic molecules... 

An atypical rotaxane structure is that involving a thread covalently attached to the CyD ring. Such a system acts as both host and guest and it has to be specially designed so that the thread is induded spontaneously in a cavity other than the one bearing it intermolecular inclusion), whereas intramolecular indusion is prevented. The resulting assembly, named a daisy chain by J.F. Stoddart, is either an acyclic supramolecular polymer 8 or a cyclic supramolecular oligomer 9 [50] (Fig. 12.4). Acyclic cyclodextrin polymers were first observed in the solid state in... 

Fig. 12.4. Daisy-chain supramolecular polymer 8 and cyclic supramolecular dimer 9.

Cyclic dimers, also named [c2]daisy chains, are a special kind of mechanically interlocked molecule. Cyclic dimers have heen widely studied because of their characteristic topological structures and potential applieations in nanotechnology, materials science, and medicine. " ... 

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