Structural chemistry rotaxane structure

A useful summary of the various and numerous types of rotaxanes, catenanes, and knots can be found in a review of template routes to interlocked molecular structures 468). Inorganic chemistry is centrally involved in the templating involved in self-assembly and in controlled synthesis of such species. 

Fig. 12 Examples of the use of color in depictions of various types of MIMs. Note how the colors and positions of constituent parts in the three-dimensional structures reflect those in the structural drawings to enhance clarity between representations of (a) a donor-acceptor [2]catenane [75] and (b) an ammonium-binding [2]rotaxane [76] from our group, (c) a transition metal-templated Solomon Knot from the Sauvage and Fujita groups [77], and (d) a benzylic amide [2]catenane from the Leigh group [78]. Reproduced with permission from [75] (copyright 1991 Royal Society of Chemistry), [76] (copyright 2000 Wiley-VCH), [77] (copyright 1999 Royal Society of Chemistry), [78] (copyright 1995 Wiley-VCH)...

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. 

The chemistry of rotaxanes has progressed well in accordance with the interest in their unique structures and the expectation of development as parts of molecular machines and molecular devices. It was in 1976 that Ogata et al. [69] reported the synthesis of the inclusion complex with polyamide. When /3-CD was stirred with aliphatic diamines in water, precipitates were... 

Because of their wheel and axle structure, much of the interest in rotaxane chemistry is focused on the mechanical movements of the ring around and along the dumbbell-shaped component. Of particularly interest is the possibility to control... 

CT interactions and electron transfer processes play a fundamental role in the chemistry of rotaxanes and catenanes. CT interactions are often responsible for the driving forces that lead to the syntheses of these compounds such interactions live on when the components have been interlocked, and therefore contribute to determine the actual structure of the resulting compound. Because of the presence of CT interactions, the electronic absorption and emission spectra, as well as the electrochemical behavior, of many rotaxanes and catenanes exhibit characteristic features, quite different from those exhibited by the separated components. 

Scheme 1 illustrates the simplest structures of rotaxane, catenane, and knot besides polyrotaxane and polycatenane. From the fact that the main chain-type polyrotaxane at the left side is the only interlocked polymer synthesized so far among the three polymers shown at the bottom of the scheme, progress in synthesis of interlocked polymers appears to be sluggish judging from the level of activity in synthetic polymer chemistry in the world. 

In this review, I describe our efforts to construct interlocked structures such as rotaxanes, polyrotaxanes and molecular necklaces incorporating cucurbituril as a molecular bead by utilizing the principles of self-assembly and coordination chemistry. A key to the success of this synthesis is the high affinity of cucurbituril toward alkyl diammonium ions, which allows formation of a stable pseudorotaxane... 

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