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Abstract :
[en] Inspired by the many folded conformations of the molecular machineries responsible for chemical reactions and mechanical tasks in nature, such as enzyme catalysis and duplication in nucleic acids, chemists have been developing the syntheses of artificial folded molecular architectures, namely foldamers (Guichard and Huc, 2011). The investigation of these molecules using AFM-based Single Molecule Force Spectrosocopy (SMFS) allows the elucidation of both mechanochemical properties and conformational dynamics on the unimolecular scale in solution.
The stepwise synthesis of aromatic oligoamide-based foldamers was designed (Jiang et al., 2003; Huc, 2004) to produce well-defined helically-folded molecular architectures. A poly(ethylene oxide) PEO tether was coupled to one end of the foldamer. This tether design enables the coupling with the AFM tip and increases the number of potentially accessible physicochemical parameters through SMFS experiments.
SMFS pulling experiments on this system yielded specific and reproducible force-extension patterns characteristic of single foldamers. Those patterns were further analyzed to determine unfolding forces and dynamics as well as to propose mechanistics hypotheses of the unfolding process. Several helical foldamers presenting variable lengths were considered. Experiments in multiple solvents pointed out a variation in the foldamer stability, leading to different average forces values. This last study enabled us to modulate the intramolecular interactions responsible for the folding and to evaluate the mechanochemical properties of the helix. The force values measured for those foldamers are higher than those previously measured in natural biopolymers (Clausen-Schaumann et al., 2000; Janshoff et al., 2000), showing a high stability under a load and a propensity for the development of emergent properties. In addition, the increased stability of these aromatic oligoamide foldamers was confirmed by the observation of almost instantaneous reversibility of the unfolding under load.