Molecular information ratchets
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Date
28/11/2012Author
Wilson, Adam Christopher
Metadata
Abstract
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.
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