In a new episode of Making-It-Move (previous one here) molecular walkers take the stage as reported by Haq et al. (DOI) . Walking or self-driving molecules have been around for some time. Unidirectional motion has not yet been achieved (the molecules stagger back and forth) and the new walker is not going to change that. New in the arena are especially designed fences for the walker to bounce back at.
Here are the details. The surface is copper. The walking event takes place at room-temperature. One type of porphyrin (Cobalt diphenylporphyrin) self-assembles into a fence measuring tens of nanometers thanks to interlinking copper atoms. The walker is 1,3-bis(imidazol-1-ylmethyl)benzene which when deposited on the copper surface adopts a horseshoe conformation. The imidazole feet can attach and detach from the surface because the N-Cu interaction is reversible. The spacer section allows the walker to take a leap when it detaches a foot. The walkers move perpendicular to the fences on copper tracks. Sure enough the Haq article has walkers moving between the fences in detailed STM images. With the fences really a short distance away the walkers are confined and can be accurately captured. With a larger distance between the fences the walkers can only be seen as a blur.