Switches electrochemically controlled

Goldston. H.M.. Jr. Scribner. A.N. Trammell, S.A. Tender. L.M. A model recognition switch. Electrochemical control and transduction of imidazole binding by electrode-immobilized microperoxidase-11. Chem. Commun. 2002. 416-417. 

It has been reported that the electrical properties of single molecules incorporating redox groups (e.g. viologens [114, 119, 120, 123, 124], oligophenylene ethynylenes [122, 123], porphyrins [111, 126], oligo-anilines and thiophenes [116, 127], metal transition complexes [118,128-132], carotenes [133], ferrocenes [134,135],perylene tetracarboxylic bisimide [93, 136, 137] and redox-active proteins [138-143]), can be switched electrochemically. Such experiments, typically performed by STM on redox-active molecules tethered via Au-S bonds between a gold substrate and a tip under potential control, allow the possibility to examine directly the correlation between redox state and the conductance of individual molecules. 

An example of a system that can be switched reversibly in three different states through electrochemical control of the guest properties of one component is illustrated in Figure 10.1281 Tetrathia-fulvalene is stable in three different oxidation states, TTF(0), TTF+, and TTF2+. On oxidation, the electron-donor power of tetrathiafulvalene decreases with a... 

Figure 13.25 Stmcture formula of rotaxane 284+ and its electrochemically controlled switching process.

Electrochemically Controlled Switching of TTF/DNP-based [2]Rotaxanes 8.4.2.1 Solution-phase Switching... 

So far, several example of the chemically and electrochemically controlled switching of bistable linear molecular machines have been presented. The final section of this chapter will be dedicated to illustrating how such molecular switches and motors, when designed ingenuously, can also be powered by nature s most abundant and powerful energy source - light. 

The last example is a molecular shuttle with two different states between which one can switch electrochemically and chemically [25]. The more electron-rich part of the axle is the bisaniline moiety and, consequently, the electron-poor wheel tends to bind more strongly to this side (Scheme 6.5.9, center). On oxidation and/ or protonation charge repulsion moves the wheel to the bisphenol part of the axle. Thus, the switching between the two states can be controlled by two different... 

Ion transport, especially cation transport, was one of the early focal points in macrocyclic chemistry, revolving primarily around the crown ethers and cryptands. Later efforts have been to provide switches to control the rates of cation transport. Two examples of the types of switches that have been developed include photo switches using cryptands,and electrochemical switches using anthraquinone-derived lariat ethers. 

P.R. Ashton, R. Ballardini, V. Balzani, S.E. Boyd, A. Credi, M.T. Gandolfi, M. Gomez Lopez, S. Iqbal, D. Philp, J.A. Preece, L. Prodi, H.G. Ricketts, J.R Stoddart, M.S. Tolley, M. Venturi, A. J.R White, D.J. Williams, Simple Mechanical Molecular and Supramolec-ular Machines Photochemical and Electrochemical Control of Switching Processes , Chem. Eur. J., 3, 152 (1997)... 

Then x variable plays in Zeeman s model the role of length of a fibre of the cardiac muscle while the b variable corresponds to the electrochemical control (contraction of the cardiac muscle is triggered by a biochemically generated electric impulse). A stable stationary point E may occur near the point B which is infinitely sensitive to perturbations. To transfer the system from the stable stationary point E to B, a perturbation of the system is required if E is located close to B the perturbation can be small. The mechanism of switching the heart from the state of equilibrium E (lack of heartbeat) to the state of action involves removing the system from the state E to B by way of stimulation, for example by an electric impulse. On reaching the state B the model system imitates the heartbeat — this is the trajectory BB CC E. A subsequent cycle requires the repeated stimulation at the point E. 

The use of a disulfide in a macrocycle such as in (151) provides the possibility of reductive ring opening which can be important in cation transport. Shinkai et al. <85JA3950) investigated redox mechanisms and their application to membrane transport. They demonstrated that the rate of Cs" " transport was regulated by the interconversion of (151)ox to (151)red in the membrane phrase. Thus, electrochemically controlled processes may switch ion transport on or off. Ion transport may also... 

Furthermore, porous CPs (e.g., polypyrrole, polyanUine) films have been used as host matrices for polyelectrolyte capsules developed from composite material, which can combine electric conductivity of the polymer with controlled permeability of polyelectrolyte shell to form controllable micro- and nanocontainers. A recent example was reported by D.G. Schchukin and his co-workers [21]. They introduced a novel application of polyelectrolyte microcapsules as microcontainers with a electrochemically reversible flux of redox-active materials into and out of the capsule volume. Incorporation of the capsules inside a polypyrrole (PPy) film resulted in a new composite electrode. This electrode combined the electrocatalytic and conducting properties of the PPy with the storage and release properties of the capsules, and if loaded with electrochemical fuels, this film possessed electrochemically controlled switching between open and closed states of the capsule shell. This approach could also be of practical interest for chemically rechargeable batteries or fuel cells operating on an absolutely new concept. However, in this case, PPy was just utilized as support for the polyelectrolyte microcapsules. 

Recently, Stoddart et al. reported a novel push-button molecular switch (Figure 42) based on a single-station mechanically hetero[2]catenane. The [2]catenane could be easily switched by redox reactions between its two conformations, with a TTF unit inside or outside of the CBPQT" + cyclophane. This push-button molecular switch is an ideal candidate for introduction into solid-state electronic device settings owing to the unique combination of two discrete translational forms and the ability to toggle completely between these two electrochemically controllable states. ... 

The authors found that, under mild conditions, the reaction proceeds with simple aliphatic olefins, selectively and reversibly, to form 1 1 adducts. Upon reaction with olefins, the deep purple solution turns light yellow. The 1 1 adducts are formed when an olefin is in the oxidized form, and the bound olefin is released when it is reduced. Fast on-off switching from the higher to lower oxidation state by electrochemical control allows binding and then release of the olefin, thus enabling olefin separation from other components and its purification. The purification makes use of the rapid binding of an olefin by the electrochemically generated neutral dithiole species and the subsequent release of the olefin upon electrochemical reduction of the adduct. In this way, reversible olefin complexation to dithiolene complexes offers a novel approach to olefin separation and purification. 

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