[1,n]-Rhodium Migrations for Directional Translational Motion

Abstract

The controlled translational motion displayed by nature’s enzymes underpins a wealth of processes
integral to life from DNA replication to muscle contraction, facilitated by DNA polymerase and Myosin,
respectively. These enzymes can either fully or partially enclose a biopolymeric substrate or remain
associated to the biopolymeric substrate via complex large interaction surfaces, upon which they
perform work. Sophisticated mechanisms ensure that the enzyme remains associated with the
biopolymeric substrate upon which it moves. This crucial property, the property that ensures that the
moving component remains associated with the linear substrate, is termed “processivity”.
Herin, we present [1,n]-rhodium migrations as a new approach to mimicking the dynamic association
that underpins directional translational molecular level motion displayed by biological systems.Current
artificial systems which display translational motion are mainly rotaxanes or molecular walkers.
Advanced rotaxane systems exploit mechanical bonds and ratcheting mechanisms to achieve
autonomous directional movement. However, the stepwise intervention of an experimentalist is
required to achieve directional translation within the bipedal walker systems. The system developed
within this thesis represents the first example of directional translational motion at the molecular level
in a fully synthetic system that operates autonomously and does not rely on mechanical bonds.
Upon a polyaromatic track, a rhodium centre is translated unidirectionally through repeating cycles of
the following three step process: incorporation of the strained hydrocarbon fuel norbornene (X=Y),
followed by an alkyl-to-aryl rhodium migration, then an aryl-to-aryl rhodium migration.
Through various experiments, we have shown the developed system displays complete processivity and
the incorporation of large norbornene groups onto tracks with varying structure and electronic
properties ratchet the system and drive the directional translation of a rhodium centre over extended
distances without the requirement of a mechanical bond. The prevalence of metal migrations, and the
processivity inherent to their mechanisms, alongside the breadth of possible fuels (X=Y), suggests that
the approach outlined here has the potential to become a general strategy for controlling motion at the
molecular level. By utilising this new approach to translational motion, the limitations of systems
displaying translational motion mediated by mechanical bonds may be circumvented, such as
translating along branched tracks.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Beatrice Collins (Supervisor)