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Title: Molecular information ratchets
Author: Wilson, Adam Christopher
ISNI:       0000 0004 2745 9364
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2012
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In the emerging aield of molecular machines, a molecular ratchet is a chemical system that allows the positional displacement of a submolecular component of be captured and directionally released. In information ratchets, the track over which a Brownian particle is to be transported is able to respond to the particle’s position. By raising energetic barriers to translation selectively behind the particle, it is possible to move the particle in a forward direction. This Thesis describes the development of a series of chemically-­‐driven information ratchets based on rotaxane architectures. Acylation of the rotaxane thread presents an impassible kinetic barrier to macrocycle shuttling. The incorporation of chiral centres into the thread allows the macrocycle’s position to have an effect on the kinetics of acylation in a chiral environment, with the result that the macrocycle is transported by successive acylation reactions in a direction speciaied by the handedness of a chiral. In Chapter One the physical principles of molecular motors are examined. It is shown that molecular motors are a subset of the much broader class of “triangular” reactions investigated by Onsager in 1931. Progress in the exciting aield of artiaicial chemical ratchets and motors is reviewed, and the deep connections between molecular motors and the cyclic reaction networks postulated to explain the origin of biological homochirality are explored. Chapter Two describes the synthesis and operation of a three-­‐compartment rotaxane information ratchet in which the macrocycle can be transported along a thread in either direction depending on the handedness of a chiral catalyst. Internal mechanisms of operation are elucidated by treating the system as a hidden Markov process. Chapter Three describes the synthesis and operation of a second-­‐generation three-­‐compartment information ratchet. A comparison between this system and that of the previous chapter sheds light on the complicated trade-­‐offs between kinetics and thermodynamics when these molecular ratchets are operated. In Chapter Four the ongoing efforts to construct extended information ratchets, incorporating many repeat units, are described. The synthesis of a aive-­‐ compartment information ratchet proved unexpectedly difaicult owing to problems of solubility. A four-­‐compartment rotaxane was easier to synthesise. Preliminary aindings suggest that an information ratchet mechanism is operating in this four-­‐compartment system.
Supervisor: Leigh, David; Cockroft, Scott Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: molecular machines ; ratchets ; dynamic kinetic resolution ; homochirality ; rotaxanes ; Markov chains