Pseudorotaxane complex

The squaraine rotaxanes based on the macrocycle 16b exhibit intense NIR absorption and emission maxima, and it should be possible to develop them into molecular probes for many types of photonic and bioimaging applications. In contrast, the squaraine fluorescence intensity is greatly diminished when the dye is encapsulated with macrocycle 18. The fluorescence is restored when a suitable anionic guest is used to displace the squaraine dye from a pseudorotaxane complex, which indicates that the multicomponent system might be applicable as a fluorescent anion sensor. 

A variety of hydrophobic and hydrophilic squaraine rotaxane probes and labels such as 21a-21e c Rp and 22a-22e c Rp, containing reactive carboxylic functionalities and hydrophilic sulfo groups, are disclosed in a recent patent application [60]. It was shown that not only aniline-based squaraines 21a-21e but also heterocyclic squaraines 22a-22e can form stable pseudorotaxane complexes. The indo-lenine-based squaraine 22a forms rotaxane 22a C Rp. Importantly, also the sulfonated squaraine 22b could be successfully encapsulated in a Leigh-type, phenylene-based, tetralactam macrocycle to yield the water-soluble rotaxane 22b C Rp. Quatemized, indolenme-based squaraines do not form pseudorotaxanes probably because of sterical hindrance caused by /V-alkyl and 3,3 -dimethyl groups. On the other hand, quatemized benzothiazole (22c) and benzoselenazole (22d) squaraines could be embedded in a Leigh-type macrocycle to yield rotaxanes 22c C Rp and 22d C Rp, respectively. The hydrophilic, mono-reactive rotaxane 22e-NHS C Rp based on asymmetric squaraine, synthesized by a cross-reaction of squaric acid with the two different indolenines, was also obtained. 

The formation of pseudorotaxane complexes in aqueous solutions has also been exploited [10] to template the synthesis of cyclodextrin-containing rotaxanes. In the example illustrated in Figure 3-8, the diamine 29 is mixed [26, 27] with a methylated a-cyclodextrin derivative - either 30 or 31 - in aqueous solution. In both instances, a pseudorotaxane complex self-assembles spontaneously. The subsequent covalent attachment of bulky stoppers is achieved by reacting these complexes with sodium 2,4,6-trinitroben-zenesulfonate 32. The resulting [2]rotaxanes 33 and 34 can be isolated in yields of 42 and... 

Molecular motors or machines are inspired by biological molecules such as myosin which uses the chemical energy from hydrolysis of adenosine triphosphate to drive the linear push-pull motion of muscle. The different coordination demands of Cu and Cu are the basis of electro-chemically induced molecular motion in a pseudorotaxane complex of copper. As shown in Scheme 2, Cu 4, the stable, four-coordinate form is oxidized to unstable Cu°4, which rearranges to the stable five-coordinate form by sliding along the ligand. Reduction of the stable Cir s... 

Because of the redox responsiveness of the TTF hook guest, oxidation of these precipitates demonstrated the reversible nature of network formation as the amorphous precipitates could be dismpted and were observed to redissolve in solution. Reduction led again to the formation of NP precipitate and the chemical switching was demonstrated for several cycles. In addition, this property was further exploited as TTF is known to form much more stable pseudorotaxane complexes with blue box than with Np. A mixture of both TTF-AgNPs and Np-AuNPs with the blue box polymer 64 leads primarily to a silver-rich precipitate of AgNP aggregates as characterized by electron miaographs and electron dispersive analysis of the... 

Peculiar stereochemical features arise when a constitutionally asymmetric, directional axle is threaded by a three-dimensional nonsymmetrical, directional wheel. In fact, the threading of alkylbenzylammonium axles Sa-c" (Fig. 30.7) with a directional calix-wheel lb in principle would give rise to two diastereoisomeric pseudorotaxane complexes, one with an e/ido-cavity alkyl chain (endo-alkyl stereoisomer) and the other with an endo-cavity benzyl moiety (endo-benzyl stereoisomer) (Fig. 30.7) [17]. 

Another wide family of purely organic interlocked systems has been developed by Stoddart s group, based on hydrogen bonding and on donor-acceptor interactions. Suitably sized crown ethers can form pseudorotaxane complexes with appropriate secondary dialkylammonium ions which rely on N —H - 0 and C—H - 0 hydrogen bonds for stabiUzation. Similarly, a r-electron rich component, in interaction with a r-electron deficient moiety (traditionally cyclobis(paraquat-p-phenylene), CBPQ T, 21, ... 

The calix[6]arene wheel C (Scheme 7.1) forms fairly stable pseudorotaxane complexes with 4,4 -bipyridinium compounds in apolar solvents [28]. Therefore,... 

Pseudorotaxanes complexes can be rendered kinetically inert, i.e. transformed into rotaxanes, by attaching bulky groups at the extremities of the axle to prevent dethreading [1]. Therefore, the pseudorotaxane or rotaxane behavior of a given axle-macrocycle pair depends on the threading-dethreading rate constants, which in turn are determined by the intrinsic kinetic parameters of such processes— particularly, the energy barriers—and the experimental conditions [2, 3],... 

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