2. MOLECULAR MIMICS
Some molecules have similar properties and they may be useful as
molecular machines in nanotechnology.
A Molecular level machine can be defined as an assembly of a
distinct number of molecular components that are designed to
perform machine like movements as a result of some input
Molecular mimicry is structural, functional, or immunological
similarities shared between macromolecules found on
infectious pathogens and in host tissue.
3. In common with their macroscopic counterparts, a molecular machine is
characterised by several criteria such as:
The type of energy
needed to make it
work
The nature of the
movement during
which work is done
or energy is trans-
formed
The way it can be
controlled
The ability to repeat
its operation
The time needed for
a useful action
6. ROTAXANES
This are long, fairly linear molecules
Dumbbell shaped molecule
threadend through a macrocyclic ring .
The name is derived from a latin for wheel (rota) and axle(axis).
Same as catenanes ,rotaxanes also cannot decompose into ring and chain without breaking chemical
bonds.
Hence,the bulky groups terminate the linear ,chain part of the molecule and it is too large to fit
through the cyclic fragment.
Rotaxanes without such physical barriers ,in which the thread can leave the
needle,are called pseudorotaxanes.
Pseudorotaxanes are necessary precursours for both rotaxanes and catenanes.
7.
8. MOLECULAR SWITCHES
• The principle behind using rotaxanes as molecular
switches is the ability to move the collar under
some external influence. If the collar can be
switched back and forth from each site ‘S’ then it
acts as a switch
MS
• The number of sites at which the collar can stop
can be increased so that there are a number of
stations where it may decide to stop.
• These structures then become molecular railway
lines and the collar is in effect a train.
MS
9. The structure of rotaxanes and
catenanes
Mechanism of rotaxane shuttling
polycatenanes
Blocking group
shuttling
polymerisation
11. ELECTRON DRIVEN MOLECUALR SHUTTLE SWITCH
(EDMSS)
•If part of the rotaxane can be made to redox reaction.
•This is an electrically driven nanomachine because
electrons are needed to move the shuttle. A typical
electron driven molecular shuttle switch works because
of charge transfer interactions between a cyclic
bipyridinium unit, which forms the collar and the axle
•An oxidisable benzidine unit forms one station (station 1)
and a biphenol group forms the other station (station 2)
on a rotaxane rod.
EDMSS
•molecule are electron rich (unoxidised) state the train
shuttle resides mainly on the benzidine station. On
removal of an electron (oxidation) from the benzidine
station, the train shuttle moves along the rotaxane rod to
reside over the biphenol station. The process is
reversible.
•This structure is not unique.
•A number of other molecules can be used for oxidation
and reduction.
EDMSS
12. • The rotaxane has been prepared by
interlocking these dumbbell-shaped
compounds with a bipyridinium-
based tetracationic cyclophane collar.
EDMSS
• The central 9,10 or a 2,6-
dioxyanthracene units and a 1,4-
dioxybenzenestructure are the train
stations.
• The cyclophane can be displaced
from the dioxyanthracene to the 1,4-
dioxybenzene station by
electrochemical removal of electrons.
EDMSS
14. PH DRIVEN MOLECULAR SHUTTLE SWITCH
(PHDMSS)
The benzidine biphenol device can also be driven by a change in pH
because the nitrogens can be protonated.
In alkaline solution, such as pyridine, the shuttle resides mainly on the
benzidine station but when an acid is added (TFA, trifluoroacetic acid)
the shuttle moves along the rotaxane rod to reside over the biphenol
station
This molecular switch could be very sensitive in detecting molecular
acidity imbalances
15. LIGHT DRIVEN MOLECULAR SHUTTLE SWITCH
(LDMSS)
Some double bond structures will transpose from
trans to cis and cis to trans stereochemistry under
the influence of light, sometimes in the visible
range. Others change structure in the presence of
ultraviolet light.
The light driven molecular switch structure
consists of an azobenzene molecule connected to
dipyridyl units with methylene spacers and 2,4–
dinitrobenzene moieties as end caps with a
cyclodextrin sheath around the outside
A cyclodextrin is a polymeric carbohydrate
molecule that has the shape of a fat washer and
hence makes an excellent collar.
Like other molecular shuttles, light driven cis-
trans shuttles are not unique.
LDMSS
16. Ruthenium polypyridine complex as one of its stoppers . A p-terphenyl type ring system is used
as a rigid spacer and two 4,4’-bipyridinium units are used as π electron accepting stations.
A tetraarylmethane group is used as the second stopper
Temperature controlled (-140 to 50˚C) molecular shuttles based on rotaxanes
It should therefore be possible in principle to produce a rotaxane that responds to at least
three different stimuli: light, heat and pH.
17. LDMSS
• Azobenzene light driven molecular switch,
• The active unit is a π-electron-donating macrocycle polyether, namely
bis-p- phenylene-34-crown ether, and a dumbbell shaped component
that contains a ruthenium polypyridine complex as one of its stoppers.
