Nanocar Ready To Roll!

The latest work from the laboratory of Professor James Tour, the creator of the NanoPutian, is a nano-sized, buckyball-wheeled vehicle named nanocar.
The nanocar’s “chassis” is built sturdily based on benzene rings and carbon-carbon triple bonds. The axles don’t stir, but it can rotate freely to let the fullerene wheels spin (Figure 1).

Nanocar

The size of a nanocar is only about 1/20,000 of a human hair, but the image of it running on gold surface has been observed using scanning tunneling microscopy. The research group has also been able to pull a nanocar directly with the tip of the microscope and show that it moves perpendicular to its axles but not parallel to it. This supports the idea that it moves by rolling, not by sliding on the surface. What’s more, they can control the direction of the nanocar’s movement by using electric fields, so the nanocar is much more than just a car-shaped molecule and can be called a legitimate “automobile.”
You can see that both the nanocar and the NanoPutian have the similar molecular framework based on benzene rings and carbon-carbon triple bonds. Perhaps the synthesis of the NanoPutian was a “practice” towards making the nanocar.

Fig.1 NanoPutian

A year later, the introduction of a new and improved model of nanocar was announced. Equipped with a light-powered motor, this one can run on its own.
The motor piece was originally developed by Professor Ben Feringa’s lab in the Netherlands, and the double bond in the central part of the molecule functions as a rotational axis (Figure 2). A double bond can’t rotate under normal circumstances, but light breaks one of the bonds to allow free rotation. To control the direction of rotation, the Feringa’s molecule uses a methyl group that works like ratchet (although the actual logic is a little more complicated than that).

Fig2 Feringa's Molecular Motor

The Tour group modified and incorporated the motor into the original nanocar’s chassis. When hit by light, the light green colored part in Figure 3 rotates and propels the machine in the direction shown by the arrow. The original nanocar used fullerene as wheels, but since it absorbs and quenches the light energy of the motor it was replaced by a structure called carborane (the yellow part in the figure).

Fig3 Nanoar with motor

I’ve always been impressed by the creative ideas and clever molecular designs by Professor Tour, whose group has also developed nanotruck and nano-pinwheel. Thinking about what can be added next to the nanocar by playing with a molecular model kit must be a really fun part of their research.
How can you attach things like, for example, accelerator, brake, transmission, or cargo loading/unloading function for further evolution? Could you make “nano-delivery” that transports a specific molecule to a specific location, or could “nano-F1”, a race among differently designed nanocars, be possible? Just by looking at the pictures in the Tour papers, fun ideas keep coming up endlessly. In my personal opinion, I think that this fun part is the privilege given to chemistry, the only genre in science that can create new “things.”

Note: The actual nanocars have long alkyl chains to increase solubility in organic solvent, but they aren’t shown for clarity purpose.