Rotaxane, structures

Squaraines 17b and 17c have terminal acetylene residues, which allowed to convert the squaraine dyes and tetralactam macrocycles into permanently interlocked rotaxane structures using copper-catalyzed and copper-free cycloaddition reactions with bulky stopper groups [58]. 

Polymers are generally not discussed in this book. However, a polymer with rotaxane structures involving cyclodextrins in side chains 408 [36], pseudorotaxane superstructures [37], doubly twisted polyrotaxane [38] as well as infinite polyrotaxane network (Figure 8.2.5) [39] can be mentioned here. 

Rotaxane 80e can even be dimerized by reaction with l,3,5-tris(4-methyl-phenyl)benzene (105) [42]. Considering the steric crowding, it is remarkable that the resulting wheel-tris[2]rotaxane ([4]rotaxane) 106 is formed in 35% yield (Figure 42). Extension of the strategy of coupling rotaxanes to multifunctional units should enable easy access to amide-linked dendritic rotaxane structures. 

In order to explain this increase in electron transfer rate and to elucidate which pathway was followed (intraligand or interligand), a rotaxane structure was elaborated171,721 (Figure 6). Here, the principle of construction of the architecture was again based on the 3-dimensional template effect of copper (i). 

The rotaxane is composed of a glycylglycine chain, a simple dipeptide, bearing two diphenylmethane blocking groups, which prevent the dethreading of the benzylic amide macrocycle. The synthesis of the rotaxane structure is based on... 

The rotaxane structure of 22 can be demonstrated by ESI-MS or MALDI-TOF-MS. It remains intact in TH F-d8, a solvent in which the tetra-urea dimers usually dissociate. However, an upfield shift of the NH-signals in 1 H NMR indicates that the... 

Synthesis of metal-free rotaxane Structure 28 (PF6 ) (Scheme 9.21)... 

The binding of ammonium ion, NH4+, by 18-crown-6 was demonstrated early in the history of macrocycle chemistry. The O-H-N in crowns or N-H-N interaction in azacrowns has been characterized by a variety of techniques, including NMR, calorimetry, and X-ray crystal structure analysis. Recent studies in this area have shown that both quaternary and secondary ammonium salts can form complexes with crowns. In the latter case, a rotaxane molecule was prepared by treatment of a dibenzylammonium salt with dibenzo-24-crown-8 and other macrocycles, including pyrido-24-crown-8. The solid-state structure of the pseudo-rotaxane structure obtained with pyrido-24-crown-8 is shown in the left panel of Figure 23. 

Rotaxanes-Threading Molecular Rings Rotaxanes are obtained by threading linear polymers through molecular rings such as cyclodextrins, crown ethers and cyclophanes. Molecular shuttles based on the rotaxane structure have been proposed. 

Researchers attempted to design and syntheze artificial rotaxane structures long before biological rotaxanes were discovered. A stepwise process involving the fixation of cyclic molecules, insertion of a linear molecule and then stopper fixation at both ends of this linear molecule, produced rotaxane structures in low yields, was reported in the 1960s. When supramolecular concepfs were... 

If the cyclodextrins in the rotaxane structure are linked covalently, then the cyclodextrin array is maintained even after the stoppers and the polymer chain have been removed (Fig. 3.19). Reacting the cyclodextrins with epichlorohydrin under weak alkali conditions induces crosslinking between facing hydroxyl groups. The stoppers are then removed under stronger alkali... 

An alternative approach for the preparation of CD-based polyrotaxane using photoreactions is described (Scheme 9). The authors prepared a-CD-based polyrotaxanes by capping ends of a-CD-PPG complexes, in a pseudo-poly-rotaxane structure, with covalently bound stoppers. A polyrotaxane containing a number of /3-CD molecules was prepared by photoreactions of a precursor complex between /3-CD with PPG having a triphenyhnethyl group at... 

On the basis of the hypothesis of the intertwining mechanism described above, the syntheses of the first amide-based rotaxanes (Structures 20a, 20b) were successful as well [21], Their (supramolecular template) syntheses were strikingly simple. The central part of the axle 13a is added to a tetralactam wheel and subsequently capped with triphenylmethane stoppers. The macromonocycle ( wheel ) provides the receptor cavity for the axle and the stoppers confirm the mechanical bond between wheel and axle . 

More detailed general structures of the representative polyrotaxanes and polycatenanes are shown in Scheme 2. Polyrotaxanes can be categorized into two types one is the polyrotaxanes consisting of the main chains of covalent type as shown in the top four examples (A-D), while the other involves the polyrotaxanes of which monomer linking units are constructed by the rotaxane structure as shown in the following two structures (E, F). The essen-... 

Hydrogen Bonding Interaction Used for Complexation to Rotaxane Structure... 

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