“We built three controllable molecular shuttles into the three legs of a rig-like component and then fused three rings onto a platform,” Fraser Stoddart of UCLA told nanotechweb.org. “Using chemicals in the form of acid and base, we can make the platform move up and down with respect to the rig.”

To create the elevator, Stoddart and colleagues built on earlier work on molecular shuttles based on rotaxane molecules. The resulting device, which was about 2.5 nm high and roughly 3.5 nm in diameter, was able to develop forces of up to 200 pN.

Each leg of the elevator contained two notches (or recognition sites), at different levels. The top-level notches incorporated dialkylammonium (-NH2+) centres, while the bottom-level notches contained bipyridinium (BIPY2+) units. An acid-base reaction provided the energy for the platform to move between these two levels, a distance of about 0.7 nm. That’s because introducing basic conditions caused deprotonation of the -NH2+ centres, destroying the hydrogen bonding between the platform rings and the centres so that the platform moved down to the BIPY2+ units. Adding an acid restored the -NH2+ centres and moved the platform back up to the higher level.

“Previously, we had demonstrated relative movements between pairs of single components,” added Stoddart. “In this molecule, we have multiple (triple) components in each case. It was a big challenge learning how to bring multiple components together in a self-complementary manner.”

Stoddart believes the molecular elevator could find near-term application in a controlled, slow-release drug delivery system and “in a sophisticated separation system for other molecular compounds, using the elevator’s potential to host guest molecules in its inner cavity.”

Now, the scientists say they will try to put the molecular elevator down on nano-porous, meso-structured silica surfaces in order to demonstrate the controlled release of molecules trapped in the pores of the glass.

The researchers reported their work in Science.