Wholly synthetic molecules involving both mechanical bonds and a folded secondary structure are one of the most promising architectures for the design of functional molecular machines with unprecedented properties. Here, we report dynamic single-molecule force spectroscopy experiments that explore the energetic details of donor–acceptor oligorotaxane foldamers, a class of molecular switches. The mechanical breaking of the donor–acceptor interactions responsible for the folded structure shows a high constant rupture force over a broad range of loading rates, covering three orders of magnitude. In comparison with dynamic force spectroscopy performed during the past 20 y on various (bio)molecules, the near-equilibrium regime of oligorotaxanes persists at much higher loading rates, at which biomolecules have reached their kinetic regime, illustrating the very fast dynamics and remarkable rebinding capabilities of the intramolecular donor–acceptor interactions. We focused on one single interaction at a time and probed the stochastic rupture and rebinding paths. Using the Crooks fluctuation theorem, we measured the mechanical work produced during the breaking and rebinding to determine a free-energy difference, ΔG, of 6 kcal·mol⁻¹ between the two local conformations around a single bond.

涉及机械键和折叠二级结构的全合成分子是设计具有前所未有性能的功能分子机器的最有前途的体系结构之一。在这里，我们报告了动态单分子力光谱实验，该实验探索了供体-受体低聚轮烷折叠剂（一类分子开关）的能量细节。供体-受体相互作用的机械破坏导致折叠结构显示出在较宽的加载速率范围内的高恒定断裂力，覆盖了三个数量级。与过去20年来对各种（生物）分子进行的动态力谱分析相比，低聚轮烷的近平衡态以更高的负载率持续存在，此时生物分子已达到其动力学态，说明了分子内供体-受体相互作用的快速动力学和非凡的重新结合能力。我们一次只关注一个单一的交互，并探讨了随机破裂和重新绑定的路径。使用克鲁克斯涨落定理，我们测量了断裂和重新结合过程中产生的机械功，以确定自由能差Δ在单个键周围的两个局部构象之间的G k为6 kcal·mol ^-1。