One-Molecule Car Drives on Electron Fuel

[n2doc]

By John Timmer, Wired UK

Utopian visions of the nanotechnology revolution suggest that one day we’ll be able to put tiny machines inside our body to perform routine screening and maintenance. But we’re a long way off from that future, as most of the nanoscale “machinery” we’ve created requires extensive intervention or carefully prepared conditions in order to do anything. But a report in today’s Nature describes an impressive feat of molecule-scale engineering: a four-wheel-drive “car” that can run across any conductive surface, powered by electrons.

The whole thing is a single molecule. Its core is formed by two hubs that have a five-ringed structure at their core. The hubs are connected by a rigid rod formed from carbon atoms, held together by triple bonds. Each hub is flanked by two “wheels,” each consisting of a three-ringed structure. The bulk of the molecule is a carbon backbone, with a small number of nitrogen and sulfur molecules thrown in.

The key to the system is the bond between the wheel and its hub, which is a double bond formed between two carbon atoms. Electrons can cause this double bond to rotate, which places part of the wheel in close proximity to a bulky side-molecule attached to the hub. This bulky piece acts a bit like a ratchet; the wheel requires some vibrational energy to get past it. Once it does, it’s positioned so that another dose of electrons can cause it to rotate again.

By repeating this cycle, the wheel will turn indefinitely in a single direction relative to the rest of the molecule. It’s worth noting that the wheel analogy is pretty inexact. The part of the molecule that rotates is actually much closer to a large, flat plate. If you could actually go for a ride with wheels like this one, it would be an extremely bumpy one, as the plate would lift the vehicle and then hurtle it forward as it went flat again.

Still, it’s so small that the only thing it could take for a ride is another molecule, so the authors are unlikely to hear any complaints.

more
http://www.wired.com/wiredscience/2011/11/molecular-nanocar-electrons/

[MineralMan]

1. Most cool! I love this molecular engineering stuff.

I wonder what unexpected applications it will be put to.

[DetlefK]

2. How to get this car to drive all by itself:

They make it drive by getting a STM-tip (scanning tunneling microscope) really close (I estimate ~1-2 nm) and giving a voltage-pulse.

AND: They need the surface to be a noble metal, like copper. I strongly doubt, that it would work on iron.

The following scenario would be interesting: Let's look at the molecule with real-time STM-scans (tricky, but feasible) and then let's slowly ramp the temperature (it's 7K, remember). Vibrational degrees of freedom should be activated first, but I don't think they are relevant.
At slightly higher temperatures, rotational degrees of freedom will be activated. And I guess, at this point the vehicle will start to drive by itself, without applying electrical energy.