Supramolecular rotaxane polymer

CDs have been extensively used as rotors of rotaxanes and catenes [57-69]. If a [2]rotaxane containing a CD at one end of the axle and a guest at the other end is available, intermolecular complexes will be formed to give supramolecular poly- 

Many reports on the formation of supramolecular polymer in solution have been mentioned in this chapter. In particular, the interest in cydodextrin-based supra- 

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Fig. 3.34. STM image of the supramolecular [2]rotaxane polymer (a) and its schematic structure (b).

The pseudopolyrotaxane schematized in Fig. 3 has a supramolecular main-chain bond based on the dimerization of carboxyl groups. Philp and Stoddart had earlier suggested [27] that a molecular chain with appropriately spaced TT-rich rings could thread its way through several macrocycles containing n-acceptors (Fig. 9A) and subsequently be capped with large stoppers to form a permanent rotaxane polymer. The structure may be viewed as a molecular abacus with rotaxane units noncovalently linked to the molecular chain. Newer polyro-taxane polymers are described in this volume in Chapter 8. 

The importance of non - covalent interactions in biological systems has motivated much of the current interest in supramolecular assemblies [1]. A classical example of a supermolecule has been provided by the rotaxanes [2,3], in which a molecular rotor is threaded by a threaded by a linear axle . Another examples have been previously included as cyclic crown ethers threaded by polymers, paraquat -hydroquinone complexes [4] and cyclodextrin complexes [5,6],... 

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. 

Polymers involving CyD moieties can be either regular polymers or supramolecu-lar ones. The latter ones are novel and promising future applications while the former, more traditional ones have already found numerous applications. Since supramolecular oligomers and polymers seem to be more interesting they will be presented first. It should be stressed that most these systems have the rotaxane structure, which together with the structure of catenanes involving CyDs are discussed in Chapter 14. 

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]... 

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... 

Molecular Logic Gates, p. 893 Molecular Switches, p. 917 71 71 Interactions Theory and Scope, p. 1076 Rotaxanes and Pseudorotaxanes, p. 1194 Self-Assembling Capsules, p. 1231 Self-Assembling Catenanes, p. 1240 Self Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 Supramolecular Polymers, p. 1443... 

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