UNIDIRECTIONAL ROTATION IN A MECHANICALLY INTERLOCKED MOLECULAR ROTOR

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UNIDIRECTIONAL ROTATION IN A MECHANICALLY
INTERLOCKED MOLECULAR ROTOR
NATURE - VOL 424 - 10 JULY 2003 David A. Leigh,
Jenny K. Y. Wong, Francois Dehez Fraceso
Zerbetto
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2CATENANE BASED MOLECULAR ROTOR

• 2Catenane in which one ring moves sequentially
  between three different binding sites.
• An ability required to switch two of the sites
  between on and off positions.
• Small ring moves to the binding site that is
  thermodynamically most stable.

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2CATENANE MOLECULAR ROTOR SYNTHESIS
Large Ring Ring Closing Metathesis (RCM) using
Grubbs Reagent
A
D
B
C
Small Ring Base induced amide bond formation (In
presence of large macrocycle)
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CHANGE IN BINDING AFFINITIES
Initial condition is that A gt B C.
Step 1. Site A ? A Photoisomerism of alkene
double bond leads to reduction in binding
affinity.
2? AMIDE FUMARAMIDE
Now B gt A C
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CHANGE IN BINDING AFFINITIES
Step 2. Site B - Photoisomerisation of alkene
double bond leads to reduction of binding affinity
3 AMIDE FUMARAMIDE Binds less strongly due to
extra bulk of Me groups
Now C gt A B
SUCINNIC AMIDE ESTER Binds less strongly due to
increased flexibility of group and fact that one
group is an ester
Step 3. Heating at 100 C for 48 h returns both
A and B return to A and B but as return to A
can occur in either direction, making this rotor
not truly unidirectional.
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3CATENANE BASED MOLECULAR ROTOR

• Addition of a secondary ring allows a true
  unidirectionality.
• In this case presence of the second ring
  occupying the second strongest binding site means
  that the upon photoisomerism ring moves the
  opposite direction.
• One cycle of diastereomer interconversions E,E ?
  E,E leads to the two rings swopping posistions
  relative to one another.
• Two cycles of diasteromer interconversions leads
  to both rings going through 360.