Great expectations: can artificial molecular machines deliver on their promise?

Abstract

The development and fabrication of mechanical devices powered by artificial molecular machines is one of the contemporary goals of nanoscience. Before this goal can be realized, however, we must learn how to control the coupling/uncoupling to the environment of individual switchable molecules, and also how to integrate these bistable molecules into organized, hierarchical assemblies that can perform significant work on their immediate environment at nano-, micro- and macroscopic levels. In this tutorial review, we seek to draw an all-important distinction between artificial molecular switches which are now ten a penny-or a dime a dozen-in the chemical literature and artificial molecular machines which are few and far between despite the ubiquitous presence of their naturally occurring counterparts in living systems. At the single molecule level, a prevailing perspective as to how machine-like characteristics may be achieved focuses on harnessing, rather than competing with, the ineluctable effects of thermal noise. At the macroscopic level, one of the major challenges inherent to the construction of machine-like assemblies lies in our ability to control the spatial ordering of switchable molecules-e.g., into linear chains and then into muscle-like bundles-and to influence the cross-talk between their switching kinetics. In this regard, situations where all the bistable molecules switch synchronously appear desirable for maximizing mechanical power generated. On the other hand, when the bistable molecules switch "out of phase," the assemblies could develop intricate spatial or spatiotemporal patterns. Assembling and controlling synergistically artificial molecular machines housed in highly interactive and robust architectural domains heralds a game-changer for chemical synthesis and a defining moment for nanofabrication.

N′-[1-(Pyrazin-2-yl)ethylidene]pyrazine-2-carbohydrazide

“…Its applications have focused on molecular switches (Coskun et al, 2012), sensors (Albelda et al, 2012) and single molecular magnets (SMMs) (Anwar et al, 2018). 2-Acetylpyrazine-based hydrazone ligands and their transition metal chemistry have also been reported (Hou et al, 2018;Li et al, 2015).…”

Mechanostereochemistry and the mechanical bond

“…The intriguing possibility of building synthetic molecular machines (Kay et al 2007;Coskun et al 2012) similar to biological ones has been raised to another level of sophistication by the development of molecular switches in the form of MIMs. A molecular switch Figure 15.…”

Single-atom fabrication with electron and ion beams: From surfaces and two-dimensional materials toward three-dimensional atom-by-atom assembly

“…17 This concept immediately captured the minds and imagination of broad swaths of the scientific community. 18,19 Experimentally, efforts toward light, 20,21 chemically 22 and electrochemically 23,24 activated molecular machines were undertaken, as recognized by the award of the 2016 Nobel Prize in Chemistry to J.-P. Sauvage, J. Fraser Stoddart, and B.L. Feringa.…”