Extended Data Fig. 5: A two-dimensional position map describing the movement of two CBPQT^4+/2(+•) rings around the loop.

The x and y axes represent the positions of the CBPQT^4+/2(+•) rings on the loop. The green, black, blue and magenta lines represent the positions of the IPP, BPM, PY⁺ and T units, respectively. The hypothetical paths involving switching of the [3]catenane [3]CMM during the redox cycles are illustrated in blue (oxidation) with purple (reduction) arrows, which are periodic on account of the cyclic nature of the loop. The trajectories indicate that, for unidirectional motion, there is a Coulombic barrier (PY⁺) and a steric barrier (IPP) under reducing and oxidizing conditions, respectively. The dashed red diagonal line represents a barrier that cannot be crossed physically for the simple reason that two CBPQT^4+/2(+•) rings would end up occupying the same space.