Design and Synthesis of Non-Equilibrium Systems

The direction of net motion of a large object on a on a one-dimensional track depends solely on the direction of an applied force. This concept from the macroscopic world, however, does not translate to the molecular level because of the continuous rapid, random motion of molecules. If one imagines a single molecule confined to an imaginary one-dimensional track, and defines one direction as forward and the other as backward, then the simple placement of an obstacle behind the molecule would block its movement backward; as a result, the molecule can only move in a forward direction. If the same process is repeated, the result would be a forward ratcheting of the molecule as viewed by and external observer. In this proposal we aim to demonstrate how this type of control could be applied to a system consisting of a small ring (a macrocycle) on a track (a rotaxane), resulting in directed motion on the molecular-scale. In practical terms, the proposed work will entail the laboratory synthesis of a variety of compounds so as to permit self-assembly of a molecular ratchet. The required synthetic components include (i) a variety of elongated molecular threads (one-dimensional tracks), (ii) a variety of macrocyclic rings (the moving component), (iii) a variety of slippage stoppers (allowing threading of the ring under select conditions) and electrostatic stoppers (charged pyridinium units to prevent backward motion of the ring). A combinatorial approach will be used to match up the various components in many combinations so as to select the best performing ratchet assemblies.