Artificial molecular rotary motors

Artificial Molecular Rotary Motors Based on Rotaxanes... 

Molecular rotary motors are systems capable of undergoing unidirectional and repetitive rotations under the action of external energy inputs. The construction of molecular rotary motors poses several challenges, particularly because it is difficult to satisfy the unidirectional rotation requirement. Artificial rotary motors driven by light have been obtained by exploiting a-C=C-isomerization reaction in carefully designed overcrowded chiral alkenes. 

A molecular machine, a machine at the molecular level, is defined as a discrete number of molecular components that perform mechanical-like movements (output) in response to specific stimuli (input). Molecular machines include both naturally occurring devices found in biological systems and artificial molecular machines. There are many molecular machines in biological systems. Among the most prominent examples of molecular machines in living organisms are the muscle linear and ATPase rotary motors. In order to develop artificial machinery, scientists have constructed a variety of molecular and supramolecular systems with differences in shape, switching processes, or movements... 

For highest versatility, operating under diverse conditions, artificial molecular motors should have the following properties, in the authors opinion. Artificial motors should be rotary, and operate unidirectionally. 

Furthermore, just as photochemistry is a clean way to cause a reaction, it may offer a clean way to cause a movement in a macroscopic object. As a matter of fact, this is an issue rarely adopted by natme, where direct conversion of light into mechanical energy is limited to a few cases in bacteria [16]. This does not preclude adopting this principle for artificial system. As an example, one may think of controlling and directing the Brownian motion of molecules in solution and to induce directional translational and rotary motion of molecules or of nano-objects. In other words, rotary and translational motors may be devised and used to power future nanodevices. For example, rotary molecular motors allow the transmission of motion in multicomponent systems as well as reaching out-of-equilibrium assemblies (see Fig. 11.5) [18]. 

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