Rotaxanes redox control

The redox-controlled mechanical switching in SAMs of disulfide-functionalized bistable TTF-DMN rotaxanes consisting of cyclophane 124+ and a dumbbell-shaped component containing TTF and DMN stations was also extensively investigated.49... 

Figure 6.10 Palindromic rotaxane 118+ and redox-controlled switching between its contracted and extended forms.

Figure 16.11 (a) Redox-controlled rotaxane gate consisting of a DON-TTF derivatized axis and a... 

Figure 10.16. The redox-controlled switching of the [2]rotaxane 20 4PF6.

Figure 2.35. Diagram of the molecular motions in copper(I)-complexed [2]-rotaxane 101 controlled by the redox state dependence of the stereoelectronic requirements of Cu. Cu(I) and Cu(II) are represented by black and white circles, respectively. Chelating sites are represented by thick lines. Initially, the string coordinates Cu(I) together with the bidentate site of the macrocycle in a tetrahedral geometry, affording the state 101(4). Electrochemical oxidation of Cu(I) to Cu(II) produces the state 101+(4), which slowly converts into the state 101+(5) after rotation of the Cu(II)-complexed macrocycle. The cycle is completed by reduction of Cu(II), which produces the state 101(5), converting to the initial state by back motion of the Cu(I)-complexed macrocycle.

Figure 6.13 A pseudo-rotaxane capable of switching between two arrangements under redox control ...

Figure 38 Molecular motions in copper(l)-complexed [2]-rotaxane (114) controlled by the redox state of the metal. In the Cu(I) state (114) the macrocycle is held at the phenanthroline site of the dumbbell. In the Cu(II) state (115) the macrocycle is held at the terpyridine site of the dumbbell. Therefore oxidation of Cu(I) to Cu(II) has triggered a translational motion of the complexed macrocycle along the dumbbell [29].

Over the past decade, cycIo6w(paraquat-p-phenylene) has been the benchmark compound in the design of molecular switches, in 7t-7t-stacking, and related dynamic processes and this continues in redox-controllable amphiphilic [2]rotaxanes <04CEJ155>. 

Other interesting and recent contributions have shown (i) the utilization of self-complexing molecules as a Brownian ratchet, (ii) the use of reductive electrochemistry to turn on attractive axle-wheel interactions in a rotaxane, (iii) the use of CDs as wheels in redox-switchable rotaxanes,and (iv) redox control on the movements of two... 

The cellular unit that is active toward the contraction of skeletal muscles, known as the sarcomere, is comprised of alternatively stacked filaments of the proteins actin and myosin. During muscle contraction, the protein filaments slide past each other as a result of a rowing action of the surface myosin heads (Figure 6.92a). Hence, an effective biomimetic approach would entail the design of a linear architecture that features sliding components that will respond to a chemical stimulus. This approach has recently been demonstrated with the design of a rotaxane molecule that exhibits redox-controlled contraction and extension of the molecular architecture, in response to a chemical or electrochemical stimulus (Figure 6.92b). ... 

The pioneering papers by Stoddart and Sauvage have stimulated the design of a variety of movable rotaxanes and catenanes, whose controlled motion is promoted by a redox change. In all cases, the process of the redox-driven intramolecular motion can be described by a square scheme, as illustrated in Fig. 2.1. 

As discussed in Section 13.2.2, when a rotaxane contains two different recognition sites in its dumbbell component, it can behave as a controllable molecular shuttle, and, if appropriately designed by incorporating suitable redox units, it can perform its machine-like operation by exploiting electrochemical energy inputs. Of course, in such cases, electrons/holes, besides supplying the energy needed to make the machine work, can also be useful to read the state of the systems by means of the various electrochemical techniques. 

The electrochemical and chemical behavior of rotaxane 7 + was analyzed by CV and controlled potential electrolysis experiments.34,35 From the CV measurements at different scan rates (from 0.005 to 2 V/s) both on the copper(I) and on the copper(II) species, it could be inferred that the chemical steps (motions of the ring from the phenanthroline to the terpyridine and vice versa) are slow on the timescale of the experiments. As the two redox couples involved in these systems are separated by 0.7 V, the concentrations of the species in each environment (tetra- or pentacoor-dination) are directly deduced from the peak intensities of the redox signals. In Fig. 14.13 are displayed some voltammograms (curves a-e) obtained on different oxidation states of the rotaxane 7 and at different times. 

A Redox and Chemically Controllable Bistable Neutral [2]Rotaxane 8.4.3.1 Electrochemical Switching... 

Fig. 8 (a) Chemical and stylized representation of the strategy of redox-mediated molecular brake passing from sulhde to sulfoxide and sulfone (b) an example of oxygen-flipped rotary switch (c) its stylized representation (d) X-ray structure of a bisarylanthracene peroxide (H atoms were omitted for clarity) (e) control of the frequency of molecular motions in rotaxanes of which annulus (macrocycle) contains a photoisomerizable dianthrylethane group (see text for details)... 

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