Rotaxane

Report
Rotaxane
2010/06/02
Tobe Lab.
Furutani Hajime
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Contents
• What is Rotaxane?
• History
-First Synthesis
-Host-Guest Chemistry
-Improved Synthetic Method
• Applications of Rotaxane
-Rotaxane Specific Mobility
-Molecular Switch
-Molecular Machine
• My Project
-Chirality
-Rotaxane Specific Chirality
-My Project
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What is Rotaxane ?
A rotaxane is a supramolecule consisting of
a “dumbbell shaped axle” molecule and a “ring” molecule.
ring
Rotaxane
dumbbell
The dumbbell threads into cavity of the ring molecule.
There are no strong chemical bond
between the two components
The ring molecule is impossible to slip3 out.
History
-First Synthesisprobabilistic method
thread
Harrison, S. et al. J. Am. Chem. Soc. ,
1967, 89, 5723-5724
end-cap
rotaxane
Repetition of above thread-end-cap processes 70 times
afforded resulted rotaxanes in only 6% yield.
Holes of molecular rings is too small to be threaded.
The quite low probability makes rotaxane synthesis difficult.
How about using
“temporary covalent bonding” ?
History
-First Synthesis-
Schill, G. et al. 1967; Jus. Liebigs Ann. Chem. 1969, 53, 721
This synthesis needed many steps , and resulted in not good yield.
In general, rotaxanes were …
1. difficult to be synthesized.
2. interested only in their structure.
Progresses of “Host-Guest Chemistry” improved the situation dramatically.
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History
-Host-Guest ChemistryA molecule binds another molecule using weak interaction.
+
Host
Guest
Weak and Attractive
Interaction
Host-Guest
If a ring can bind an axle, a subsequent capping reaction gives a rotaxane.
+
Host-Ring
capping
Guest-Axle
Host-Guest
“Pseudo” rotaxane
Rotaxane
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History
-Improved Synthetic MethodCrown ethers are well-known as ring-shaped “host” molecules.
Crown ether
Lone pair
on oxgen
Electron
negativity
Crown ethers capture cations in their cavities.
If axles have cationic moieties, crownethers capture the axles very efficiently.
22% yield
D. H. Busch et al. J. Chem. Soc., Chem. Commun ,
1995, 89, 1289-1291
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Applications of Rotaxane
-Rotaxane Specific MobilityImprovements of rotaxane syntheses make advanced researches on rotaxane
specific properties easily.
One of the most important properties is “mobility”.
shuttling
In above scheme, the ring moves along the axle freely.
Because of this property, rotaxanes are expected to be prime candidate of
molecular switches, molecular memories and more advanced machines.
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Applications of Rotaxane
-Molecular Switch-
If a rotaxane consists of a ring and an axle having two cationic moieties,
the ring locates on one of the cationic units.
A position of a ring can be controlled by external stimuli.
J. F. Stoddart et al. J. Am. Chem. Soc. ,
1998, 120, 11932-11942
This positional control is elementary operation for “molecular switch”
and ”molecular memory”
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Applications of Rotaxane
-Molecular Machine-
Shuttling motion induced by UV light emittion
lifted a drop up .
The rotaxane worked as a transport machine.
D. A. Leigh et al. Nat. Mater ,
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2005, 4, 704-710
My Project
-ChiralityMolecules sometimes have right-handed or left-handed properties.
*
*
Central chirality
If a molecule in a mirror is not superimposable to an original molecule,
the molecule is ”chiral”.
Axial chirality
Planar chirality
Helicity
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My Project
-Rotaxane Specific Chirality-
Achiral ring
Achiral axle
A rotaxane consisting of an achiral ring and an achiral axle sometimes has chirality.
Chiral rotaxane
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My Project
I’ve been investigating in a rotaxane which can interconvert
between right and left handed-properties.
And the rotaxane can change the interconversion frequency
by photo or thermal stimuli.
Left-Handed
Right-Handed
I’ll talk in detail on presentation next semester.
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Summary
・A rotaxane is a supramolecule consisting of
a “dumbbell shaped axle” molecule and a “ring” molecule.
・Synthetic methods of supramolecules having threaded structure were
well improved accompanying with Host-Guest chemistry
・Rotaxanes have high flexibility of mobility.
・Rotaxanes are expected to be prime candidate for molecular
machines.
・Rotaxanes sometimes have rotaxane-specific chirality.
・I’ve been investigating in a rotaxane which interconverts between
enantiomers.
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