Light-Operated Machines Based on Threaded Molecular Structures

Abstract

Rotaxanes and related species represent the most common implementation of the concept of artificial molecular machines, because the supramolecular nature of the interactions between the components and their interlocked architecture allow a precise control on the position and movement of the molecular units. The use of light to power artificial molecular machines is particularly valuable because it can play the dual role of "writing" and "reading" the system. Moreover, light-driven machines can operate without accumulation of waste products, and photons are the ideal inputs to enable autonomous operation mechanisms. In appropriately designed molecular machines, light can be used to control not only the stability of the system, which affects the relative position of the molecular components but also the kinetics of the mechanical processes, thereby enabling control on the direction of the movements. This step forward is necessary in order to make a leap from molecular machines to molecular motors.

Directional threading of a chiral porphyrin cage compound onto viologen guests

“…Unidirectional threading and motion has been studied in great detail in the literature. [14][15][16][17] The threading and binding process of H 2 1 was followed by 1 H-NMR and fluorescence spectroscopy. In the latter case the fluorescence of the porphyrin of H 2 1 is quenched as soon as the cage compound binds to the viologen trap.…”

Structural and organisational conditions for being a machine

“…This third characteristic is a key difference between artificial nano-devices and biomolecular machines, because synthetic nanomachines have not so far been incorporated into artificial biochemical networks. Consequently, whereas the energy input of biomolecular motors is constantly provided by the biochemical network in such a way that biological machines regenerate, synthetic nano-machines cannot do this, and therefore need an opposite input to reset (Balzani et al 2005;Credi et al 2014).…”

Dynamics of individual molecular shuttles under mechanical force

“…Here, we exploit the properties of optical tweezers to quantify the real-time operation of individual synthetic molecular shuttles. In molecular shuttles, a macrocycle trapped onto a linear component (axle) can be moved reversibly between two or more portions of the axle (stations), in response to external stimuli 15 – 17 . These architectures are the basis for some of the most advanced examples of synthetic molecular machines 18 – 22 .…”