Rotaxane peptide-based

The templated syntheses of amide-based rotaxanes discussed until now have made use of the threading-followed-by-capping method. However there are also examples in which the clipping approach has been employed. Leigh, for example, has used a five-component clipping method to prepare [2]rotaxanes. Isophthalamide and peptide-based threads were shown to template the formation of benzylic amide macrocycles about them in non-polar solvents [69, 70]. When the peptide-based threads (49) contain bulky stoppers at their ends, the [2]rotaxanes (50) can be prepared in high yields (see Scheme 24) [71]. 

Wurpel, G. W. H., Brouwer, A. M., van Stokkum, I. H. M., Farran, A., Leigh, D. A., Enhanced hydrogen bonding induced by optical excitation Unexpected subnanosecond photoinduced dynamics in a peptide-based [2]rotaxane. J. Am. Chem. Soc. 2001, 123, 11327-11328. 

In a very recent work [117], the complex fluorescence behavior exhibited by a similar peptide-based [2]rotaxane bearing an anthracene unit as one of the stoppers has been interpreted in terms of a very fast (subnanosecond), short-amplitude translation of the macrocycle upon light excitation of the anthracene subunit. However, it seems that alternative explanations, such as the formation of intercomponent exciplexes [118], cannot be ruled out. 

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... 

One of the earliest rotaxane syntheses was based on statistical threading (Figure 2.6).3 Harrison and Harrison coupled the 30-membered macrocycle 1 bearing a pendent carboxylic group to a Merrifield s peptide resin, forming... 

In 2001, Leigh et al. reported a photoinduction of fast, reversible translational motion in a molecular shuttle (Figure 62) based on a peptide [2]rotaxane with two binding sites, a succinamide unit and a naphthalene imide unit. The molecular shuttle was realized by the photoexcitation of the naphthalene imide unit the corresponding radical anion ( 1 its previous photo-driven shnttles generally function... 

Figure 63 A photo-driven chiroptical molecular switch based on a peptide rotaxane.

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