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

Abstract

An aromatic oligoamide sequence was designed to fold and self-assemble into a double helical host having a cylindrical cavity complementary to linear oligocarbamate guests. Formation of helical pseudorotaxane complexes, foldaxanes, between the host and guests having binding stations of different affinities was evidenced by NMR and X-ray crystallography. Rodlike 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 H NMR. Results show that multiple events may occur upon sliding of the host from the nonbulky 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 nonbinding spacers. Conversely, installing a kinetic barrier that blocks sliding allows for the deliberate integration of a helix dissociation reassociation 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 in foldaxanes to design complex sequences of supramolecular events within networks of equilibria through the adjustment of the kinetics of the individual steps involved.

The Diverse World of Foldamers: Endless Possibilities of Self-Assembly

“…A related heteroundecamer host with two additional quinoline units, Piv-PDCA 3 -(7-amino-8-fluoro-2-quinolinecarboxylic acid) 8 -Boc, was also used with rationally designed rod-like guests with a very bulky stopper at only one extremity [ 159 ]. These experiments followed the first experiences with foldaxanes made of the same double-helical foldamer threading on mono-station (dicarbamates) or double-station (two dicarbamate anchoring stations) rod-like guests, for which no end-capping was used.…”

Directional Threading and Sliding of a Dissymmetrical Foldamer Helix on Dissymmetrical Axles

“…Helices based on 7‐amino‐8‐fluoro‐2‐quinolinecarboxylic acid oligoamides such as 1 possess a tubular cavity that can accommodate α,ω‐alkanediamine‐derived dicarbamate guests and slide along them. Threading and sliding of these helices along guests are much faster than their direct unwinding and rewinding, allowing for the design of kinetically favored supramolecular pathways depending on whether bulk too large to pass through the helix cavity is on the way or not . Solution and solid state data demonstrated that helix‐rod association is mainly driven by hydrogen bonds between carbamate carbonyl groups on the rods and 2,6‐pyridinedicarboxamide protons on the helix carbamate cleft (CC in Figure b).…”

A pyrene-functionalized foldamer: structural impact and recognition properties supported by donor–acceptor interactions

“…This positive curvature and the saturation observed at two equivalents indicates that quenching is not purely due to collisional or dynamic quenching and reveals a static quenching process attributed to the formation of the donor-acceptor association 1•7. [14][15][16]…”

“…These elegant structures have already allowed outstanding achievements in research fields as different as HIV treatment, 9 drug delivery, 10 catalysis 11,12 or molecular machinery. [13][14][15][16] All these discoveries lie on the rich supramolecular chemistry of foldamers and, more particularly, helical foldamers. The latter are very appealing chemical entities since the modification of their primary structure allows for i) tuning the number of loops 17 and their hybridization ability (foldamers can form double, triple or quadruple helices), [18][19][20] ii) inducing a desired handedness, 21,22 and iii) modulating the volume, the shape and the surface potential of the cavity formed upon folding.…”