Molecular motors rotor

In the previous sections, our main focus was on mechanical molecular switches based on mechanically interlocked structures pseudorotaxanes, rotaxanes, and cate-nanes. Molecular motors, rotors, and propellers based on single rotor molecules, as important molecular machines, have also attracted great attention during the last two decades. Molecular motors can be defined as molecules that are able to convert any energy input into controlled motion. Inspired by the unidirectional rotary motion of Fi-ATPase, much effort has been focused on systems that allow controlled molecular rotation and translation. 

A unique feature of the F/V/A-ATPases is that they are rotary molecular motor enzymes. This has been shown by experiment for members of the F-and V-ATPase subfamilies and is generally assumed to be true for the closely related A-ATPases as well. The two enzymatic processes, ATP synthesis/hydrolysis and ion translocation, are coupled via a rotational motion of a central domain of the complex (the rotor) relative to a static domain (the stator). The A-, F-, and V-ATPases represent the smallest rotary motors found in the living cell so far. Most of what we know about the structure and mechanism of these microscopic energy converters comes from studies conducted with the F-ATPase. In the following review, current structural knowledge for all three members of the family of F-, V-,... 

Any macroscopic motor is divided into a static portion, the stator, and a portion that is moving with respect to the static portion, called the rotor. To understand the mechanical properties of the molecular motor, we have to look at the properties of the motor s rotor and stator and their interactions on a molecular level. In the case of the A/V/F-ATPases, deciding which portion to call the rotor and which the stator is based on the relative molecular masses of the two functional elements. In the E. coli F-ATPase, for example, the stator is composed of with a relative molecular... 

F-ATPase is a reversible enzyme that can work in the direction of proton gradient-driven ATP synthesis and in the direction of ATP hydrolysis-driven proton pumping. Reversibility has recently been shown by elegantly turning the rotor in the F-ATPase mechanically in the direction of ATP synthesis. When ADP and inorganic phosphate were present during the forced rotation, ATP was synthesized and released from the enzyme (Itoh et al, 2004). This means that the complex contains two molecular motors the F, which is an ATP hydrolysis-driven motor, and the F0, which is a... 

Fi-ATPase, a water-soluble portion of ATP synthase, has been predicted [1,2] and proved [3] to be an ATP-driven rotary molecular motor in which the central Y subunit rotates inside a hexameric cylinder made of alternately arranged three a and three P subunits [4]. When the rotor subunit y is rotated in reverse by the application of an external force, the motor turns into a generator and synthesizes ATP from ADP and inorganic phosphate (Pi) in the catalytic sites [5,6]. Fi is thus a reversible chemo-mechanical energy converter as its physiological role implies [7-11]. 

Fig. 8. Schematic of a molecular motor activated by intramolecular vibration energy relaxation of manifold A towards the rotor part of the motor. The rotor is positioned on an axis connected to reservoir 1 kept at a temperature T. Vibration manifold A is represented here by a simple molecular spring that can be excited by light or by the inelastic effect of a tunneling current passing through the molecular spring. Without such an excitation, manifold A is statistically populated by reservoir 1. A specific choice of a molecular structure equivalent to the spring may avoid its complete thermalization, for example by filtering the thermal noise giving rise to a unidirectional rotary motion...

Early in 1967, a molecular propeller-like compound was reported by Akkerman et al. In 1981, Mislow et al. synthesized a molecular gear system.In these systems, the two brakes or gears move cooperatively, and the relative movements of the two gears can be induced by the hit of solvent molecules. However, because the hit of the solvent molecules are aU spontaneous, these cannot be considered as molecular motors due to the random movements of the rotor in different directions. 

A molecular motor with unidirectional rotation driven by visible light has been described [311]. Hereby the rotor is donor-acceptor substituted by dimethylamino-and nitro-groups. 

Lubbe AS, Ruangsupapichat N, Caroli G, Feringa BL (2011) Control of rotor function in light-driven molecular motors. J Org Chem 76 8599-8610... 

Molecular weight, effect on centrifugal sizing, 159 Mollier charts, 27 Monitoring system, 356 Motor, 146 enclosure, 260 equations, 267 insulation, 257 locked rotor torque, 270 selection, 270 service factor, 262 starting characteristics, 270 starting time, 273, 274 synchronous vs induction, 265 variable frequency drives, 27/, 280 voltage, 258 Motors... 

Finally, the making of real motors at the molecular level remains a challenge. Not only will the motion have to be continuous, in the sense that cyclic processes, with a turnover, are required, but directionality will be essential. This is especially true for molecular ensembles aimed at mimicking the dynamic properties of ATP synthase. Although still relatively remote from continuous directional rotary motion, one interesting chemical system with behavior reminiscent of rotary motors has recently been proposed.11041 For a photochemical driven unindirectional rotor,11051 see Chapter 5. Other systems, based on related or different principles, will no doubt be reported in the future. 

In a macroscopic rotary machine, the turning part is called the rotor and the stationary part is called the stator. In the molecular world, any part of a rotary motor that is rigidly attached to the surface can be considered as the stator, while that which is not is called the rotor (or rotator). 

Surface-mounted molecular rotary motors are extremely interesting from a basic viewpoint.33 They could also find applications in a variety of molecular-sized devices and machines, for example, in the fields of nanoelectronics, nanophotonics, and nanofluidics.50 Two different types of surface-mounted molecular rotors can be... 

Light-driven unidirectional molecular rotary motors based on photoisomerization around a C=C bond51 have been successfully immobilized on nanoparticle gold surfaces by two thiol-functionalized legs to yield an azimuthal rotary motor (compound 1 in Fig. 17.2).52 Repetitive and unidirectional 360-degree rotary motion of the rotor moiety with respect to the surface-immobilized stator part was observed to occur on... 

Carbon-carbon double bonds (olefins) present significantly higher rotational barriers—typically 25-65 kcalmol 1—than single bonds, providing kinetic stability of both cis and trans isomers. This stability, together with the possibility of their interconversion by photoisomerization, have been exploited in the construction of a wide variety of rotors—and even directional molecular rotary motors—in which the rotor and base are connected via an olefin. 

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