Rotaxanes

1. Rotaxanes
Shreya Ray. Rahi Reja. Mandar Kulkarni. Surabhi Jirapuri. Prarabdha Jagdhane
20101021

2. Definition
Supramolecular assemblies consisting of macrocyclic molecules physically
threaded by, but not chemically bonded to, a linear molecule chain or a
linear subchain of a molecule capped with bulky end-groups (referred to as
“stoppers”) which prevent dethreading of cyclic molecules are known as
"rotaxanes"
Ref - Terminology and Nomenclature for Macromolecular Rotaxanes and Pseudorotaxanes, 2011 . IUPAC

3. Statistical Synthesis
6.00 % yield

4. Template-Directed Syntheses
Noncovalent forces used in templated synthesis are
1 .  acceptor - donor
2. Metal Ligand Interaction
3. Hydrogen bonding
4. Hydrophobic Interactions / cyclodextrin based template
synthesis

Clipping – Linear Guest and partial Cyclic host
complex and then end portion is “clipped” by reacting
with another molecule .

5. Template-Directed Syntheses
Threading – Formation of
pseudorotaxane first, followed by
stoppering using end bulky groups .



Snapping – linear component with
bulky terminal groups dissociates in 2
fragments and one complexes with
cyclic component , then reconstitution
of another part .



Slippage – Heating of system causing
slippage of linear group with terminal
bulky groups through cyclic species .

∆

6. Metal-Template Synthesis
Wu, C.; Lecavalier, P.R.; Shen, Y.X.; Gibson, H.W. Chem. Mater. 1991, 3, 569-572

7. Click Chemistry
Org. Lett., Vol. 12, No. 17, 2010
C- C bond formation using
Click Chemistry

8. Polyrotaxane
Harada, A.; Li, J.; Kamachi, M. Nature (London, U. K.) 1992, 356,325.
“Molecular Neckace”

9. Switchable Rotaxanes
Binding constants between wheel and each station
should be in the order: A>B>A’
The two states must be reversible
The process should be controllable by external
stimuli
Applications:
Logic Gates
NanorecordingMemory Dots
The switch may be:
Chemically Driven (Acid-Base Reaction)
Photochemically Driven (Olefin Isomerization)
Electrochemically Driven (Reduction-Oxidation
Reaction)

10. Switchable Rotaxanes

11. Bright Rotaxanes
Photoisomerisation of thread
reversibly changes fluorescent
properties of molecule.


Fluoroscence enhancement or
quenching can be used to indicate
shuttling of conformations.


High sensitivity and specificity.
Chem. Soc. Rev., 2010, 39, 70–80

12. Nanovalves
A rotaxane shuttle can serve as a molecular device to switch on a surface.
Shuttling of the macrocycle closer to and away from the pore orifices of mesoporous
silica could close and open the silica nanopores, respectively.
The lengths of the linkers determines efficiency of nanovalves.
Chem. Soc. Rev., 2010, 39, 70–80

13. Dye Delivery
Bolamphiphilic
pseudorotaxane built from
hydrophobic stoppers and
hydrophilic macrocycle.
Slow spontaneous
dissociation of reverse vesicle
can be used to slowly release
dye
Langmuir 2012, 28, 14839−14844

14. Enhanced Reactivity
Interlocked components are
forced into close proximity

 One component may sterically
protect the other from chemical
attack

Alternatively, steric strain may be
introduced, enhancing reactivity

Macrocycle contraction is
obtained by substitution: amideNH
residues form stronger H-bonds

Stopper group crowding is
achieved by shortening thread
length
Org. Lett., Vol. 12, No. 21, 2010

15. Molecular Muscle
(1) Rotaxane-like Interlocked
components
(2) Fluoride-sensitive molecular
muscles: fluoride weakens N
+
H…O
H-bonding as compared to CH…O
H-bonding of pyridinium ions.
Org. Lett., Vol. 11, No. 2, 2009

16. Conclusion
Rotaxanes comprise of a Macrocycle and a dumbell-shaped molecule
Rotaxanes can be prepared using template-directed synthases like clipping,
threading, snapping and slippage
Switchable Rotaxanes have many applications like logic gates, memory
dots, nanovalves
Rotaxanes can be used to reduce or enhance reactivity
Rotaxanes can be used to built molecular muscles
Rotaxanes can be used to make amphiphiles that can self-assemble and
release dye slowly