Molecular pseudorotaxane

Molecular movements in pseudorotaxanes,rotaxanes,andcatenanes with macroheterocyclic fragments 98ACR405. 

The synthesis of [3]- (figuratively shown as 7) and a [5]rotaxane (8) with one central and two terminal porphyrins in the open configuration has been reported <96AG(E)906> also a rotaxane with two Ru(terpy>2 stoppers has appeared <96CC1915>. A pseudorotaxane comprised of a macroring of 2,9-diphenyl-1,10-phenanthroline unit and a molecular string... 

Fig. 5. [3]Pseudorotaxane dendrimers from complexation of the dendrophanes and molecular rod with rigid oligo(phenylacetylene) spacers and terminal steroid units... 

Fig. 7. [4] Pseudorotaxane dendrimers from dendrons with a macroq cle at the focal point and a triply branched molecular rod...

In particular, rotaxane dendrimers capable of reversible binding of ring and rod components, such as Type II, pseudorotaxane-terminated dendrimers, can be reversibly controlled by external stimuli, such as the solvent composition, temperature, and pH, to change their structure and properties. This has profound implications in diverse applications, for instance in the controlled drug release. A trapped guest molecule within a closed dendrimeric host system can be unleashed in a controlled manner by manipulating these external factors. In the type III-B rotaxane dendrimers, external stimuli can result in perturbations of the interlocked mechanical bonds. This behavior can be gainfully exploited to construct controlled molecular machines. 

Keywords Molecular Devices a Molecular Machines a Molecular Wires a Antenna Systems a Molecular Switches a Plug/socket Systems a Pseudorotaxanes a Rotaxanes a Catenanes a Supramolecuiar Chemistry a Photochemistry a Electrochemistry a Luminescence... 

Rationale and efficient synthetic approaches for the preparation of complicated (supra)molecular systems like pseudorotaxanes, rotaxanes and catenanes have been devised only recently.1171 The strategies chosen by Stoddart and coworkers1181 are based... 

Dethreading/rethreading of the wire and ring components of a pseudorotaxane reminds the movement of a piston in a cylinder. We have shown that, in suitably designed systems, the movement of such a rudimentary molecular machine can be driven by chemical energy or electrical energy and, most importantly, by light... 

The first attempt at designing1221 a photochemically driven molecular-level machine of a pseudorotaxane type was based (Figure 6a) on the use of an... 

P. R. Ashton, R. Ballardini, V. Balzani, E. C. Constable, A. Credi, O. Kocian, S. J. Langford, J. A. Preece, L. Prodi, E. R. Schofield, N. Spencer, J. E Stoddart, S. Wenger, Ru(II)-Polypyridine Complexes Covalently Linked to Electron Acceptors as Wires for Light-Driven Pseudorotaxane-Type Molecular Machines , Chem. Eur. J. 1998, 4, 2411-2422. 

Pseudorotaxanes have the general form of a rotaxane but the molecular-strand component is without bulky end groups. 

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. 

Product 129 containing a cyclopentene-based photochromic fragment was proposed as an axis of pseudorotaxane structures, which has potential for use in the construction of a prototype of molecular machines active as a functional stopper (08DP294). 

Formation of molecular necklaces [n]MN (n=4-7) has taken on a new 2+2 approach in which pseudorotaxanes containing two molecular beads, e.g. cucurbituril, are treated with the connective metal centers to afford the desired 25<99ACIE638>. 

A pseudorotaxane is the supramolecular product of the self-assembly of two components (i.e., a [2]pseudorotaxane), a molecular ring (macrocycle) and a molecular wire (thread) threaded into it. The occurrence of specific interactions between the two components lowers the free energy of the assembled system with respect to the separate components and drives the self-assembly of the pseudorotaxane (threading process). Threading occurs generally in solution and, upon changes of solvent... 

Nakashima et al. [49] have self-assembled (Figure 32) a Tight-driven molecular shuttle by relying upon the threading of one a-cyclodextrin (99) on to an acyclic guest, followed by the covalent attachment of two stoppers at both its ends. The azobenzene-based guest 104 is bound by a-cyclodextrin 99 with a pseudorotaxane... 

Scheme 11.10 Pseudorotaxane-based, chemically driven chromophoric molecular switch.

Fig. 10 Principle behind electrochemically induced molecular motion in a copper(l) complex pseudorotaxane. The stable, four-coordinate, monovalent complex is oxidized to an intermediate tetrahedral, divalent species. This compound undergoes a rearram gementto afford the stable, five-coordinate...

The XNOR logic gate combines the NOT and XOR operations (Figure 12), both of which have molecular scale counterparts. Nevertheless, only one example of this type of behavior is known, and it comes from the same stable as the case in Section 11.8. Again it involves pseudorotaxane chemistry (see Chapters 7 and 8), produced this time from components 27 and 28. 71 ... 

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