Orchestrating Directional Molecular Motions: Kinetically Controlled Supramolecular Pathways of a Helical Host on Rodlike Guests

International audience; An aromatic oligoamide sequence was designed to fold and self-assemble into a double helical host having a cylindrical cavity complementary to linear oligo–carbamates guests. Formation of helical pseudo–rotaxane complexes – foldaxanes – between the host and guests having binding stations of different affinities was evidenced by NMR and x-ray crystallography. Rod-like guests possessing two or three binding stations, long alkyl or oligoethylene glycol spacers or bulky barriers in-between the binding stations, and a single bulky stopper at one end, were synthesized. Kinetic investigations of the threading and translation of the double helix along multistation rods were monitored by 1 H NMR. Results show that multiple events may occur upon sliding of the host from the non-bulky end of the rod to reach the thermodynamically most stable state before unfolding-mediated dissociation has time to take place, including binding on intermediate stations and rapid sliding along non-binding spacers. Conversely, installing a kinetic barrier that blocks sliding allows for the deliberate integration of a helix dissociation re-association step in the supramolecular trajectory. Typical sliding processes can be monitored over the course of hours whereas steps involving unwinding/rewinding of the helix proceeded over the course of days. These results further demonstrate the interest of foldaxanes to design complex sequences of supramolecular events within networks of equilibria through the adjustment of the kinetics of the individual steps involved.