Zheng Meng, Ying Han, Li-Na Wang, Jun-Feng Xiang,* Sheng-Gui He* and Chuan-Feng Chen*

The motions of biomolecular machines are usually multistep processes and involved in a series of conformational changes. In this paper, a novel triply interlocked [2](3)catenane composed of a tris(crown ether) host eTC and a circular ditopic guest with three dibenzyl ammonium (DBA) sites and three N-methyltriazolium (MTA) sites was reported. Due to multivalency nature of the catenane, the acid-base triggered motion was performed by a stepwise manner. The co-conformations of the four related stable states have been directly identified and quantified which confirmed the multistep process. In order to quantify its dynamics with environmental acidity change, the values of the three level of dissociation constant pK_a have been determined. The special interlocked topology of the [2](3)catenane also endows the motion of each crown ether ring in the host with unexpected selectivity for the MTA sites. This study provides clues to comprehend the underlying motion mechanism of intricate biological molecular machines, and further design artificial molecular machine with excellent mechanochemistry properties.

This work has been published in J. Am. Chem. Soc., 2015, 137, 9739-9745.