"Smaller is better" is a hot automotive trend these days, but if you think your Mini is small, take a look at these one-molecule "nano-cars" than run on electron fuel:
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.
Link (Image: Randy Wind and Martin Roelfs)