Stepwise Motion in a Multivalent [2](3)Catenane

The
motions of biomolecular machines are usually multistep processes,
and are 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 the
multivalency nature of the catenane, the acid–base triggered
motion was performed by a stepwise manner. The coconformations of
the four related stable states have been directly identified and quantified
which confirmed the multistep process. In order to quantify the dynamics
with environmental acidity changes, the values of the three levels
of dissociation constant pKa 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.

生物分子机器的运动通常为多步骤过程，且伴随一系列构象变化。本文报道了一种新型三重互锁型[2](3)索烃（[2](3)­catenane），其由三冠醚主体eTC与带有三个二苄基铵（dibenzyl ammonium, DBA）结合位点及三个N-甲基三唑鎓（N-methyltriazolium, MTA）结合位点的环形双位点客体构成。由于该索烃的多价特性，其酸碱触发的运动以分步方式进行。四种相关稳定态的共构象已被直接鉴定并定量，证实了该多步骤过程。为定量分析环境酸度变化对动力学的影响，研究测定了三级解离常数pKa的数值。该[2](3)索烃独特的互锁拓扑结构，也使主体中每个冠醚环的运动对MTA位点表现出意外的选择性。本研究为理解复杂生物分子机器的潜在运动机制提供了思路，同时也为设计具备优异机械化学性能的人工分子机器提供了参考。