A molecular machine directs the synthesis of a catenane.

Precise mechanical manipulation of molecules is inherently difficult owing to random thermal motion. Although directed movement on the molecular scale has been achieved, using it to impose specific—especially energetically disfavored—shapes on molecules and construct mechanically interlocked structures remains a fundamental challenge. In this study, we report the synthesis of a catenane enabled by a molecular motor that winds molecular strands into discrete entangled structures, each defined by a specific number of mechanical crossings. Light energy drives unidirectional motor rotation, enabling path-dependent control over a sequence of thermodynamically disfavored yet mechanically distinct and kinetically stable winding states, which are covalently captured and subsequently released to yield a catenane. This machine-directed approach offers a general proof-of-concept strategy for the template-free construction of mechanically interlocked molecules. Editor's summary: A major difference between macroscopic and molecular machines is that on their relative scales, macroscopic machines tend to stay still when they are off. Atomic manipulation is instead a process of choreographing constant motion. Much of the recent focus has been on implementing rotors that spin in just one direction. Wachsmuth et al. have now put this type of rotor to work to produce linked rings (see the Perspective by Beves). Successive photochemical and thermal steps twist a cyclic backbone into a braid, and snipping ester connections then produces the catenane motif upon relaxation. —Jake S. Yeston [ABSTRACT FROM AUTHOR]