Christopher R. Benson, Christopher Maffeo, Elisabeth M. Fatila, Yun Liu,
Edward G. Sheetz, Aleksei Aksimentiev, Abhishek Singharoy, and Amar H. Flood.
Inchworm movement of two rings switching onto a thread by biased
Brownian diffusion represent a three-body problem.
Proceedings of the National Academy of Sciences, USA,
115:9391-9396, 2018.
(PMC: PMC6156619)
BENS2018-AA
The coordinated motion of many individual components underpins the
operation of all machines. However, despite generations of experience in
engineering, understanding the motion of three or more coupled
components remains a challenge, known since the time of Newton as the
“three-body problem.” Here, we describe, quantify, and simulate a molecular
three-body problem of threading two molecular rings onto a linear molecular
thread. Specifically, we use voltage-triggered reduction of a tetrazine-based
thread to capture two cyanostar macrocycles and form a [3]pseudorotaxane
product. As a consequence of the noncovalent coupling between the
cyanostar rings, we find the threading occurs by an unexpected and rare
inchworm-like motion where one ring follows the other. The mechanism was
derived from controls, analysis of cyclic voltammetry (CV) traces, and
Brownian dynamics simulations. CVs from two noncovalently interacting
rings match that of two covalently linked rings designed to thread via the
inchworm pathway, and they deviate considerably from the CV of a
macrocycle designed to thread via a stepwise pathway. Time-dependent
electrochemistry provides estimates of rate constants for threading.
Experimentally derived parameters (energy wells, barriers, diffusion
coefficients) helped determine likely pathways of motion with rate-kinetics
and Brownian dynamics simulations. Simulations verified intercomponent
coupling could be separated into ring–thread interactions for kinetics, and
ring–ring interactions for thermodynamics to reduce the three-body problem
to a two-body one. Our findings provide a basis for high-throughput design
of molecular machinery with multiple components undergoing coupled
motion.
Download Full Text
The manuscripts available on our site are provided for your personal
use only and may not be retransmitted or redistributed without written
permissions from the paper's publisher and author. You may not upload any
of this site's material to any public server, on-line service, network, or
bulletin board without prior written permission from the publisher and
author. You may not make copies for any commercial purpose. Reproduction
or storage of materials retrieved from this web site is subject to the
U.S. Copyright Act of 1976, Title 17 U.S.C.
