Molecular elevator. Molecular model of the two levels of an acid-base molecular lift. Each leg of the elevator (grey carbon atoms) contains two notches (or recognition sites), at different levels. The top-level notches incorporate dialkylammonium (NH2+, blue) centres, while the bottom-level notches contain bipyridinium (BIPY2+, blue) units. An acid-base reaction provides the energy for the platform (pink carbon atoms) to move between these two levels, a distance of about 0.7 nanometres. The 2016 Nobel Prize in Chemistry was awarded to the chemists Jean-Pierre Sauvage, J. Fraser Stoddart, and Bernard Feringa for their work on the design and synthesis of molecular machines.