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Locking the Dynamic Axial Chirality of Biphenyl Crown Ethers through Threading
Tomoya Kimura1, Shinobu Miyagawa1, Hikaru Takaya2,3
1Department of Materials Science and Engineering, Faculty of Engineering, University of Fukui, Bunkyo, Fukui, 910-8507, Japan.
This study synthesizes rotaxanes with biphenyl crown ethers and ammonium ions. The 23-membered crown ether rotaxane locks axial chirality at room temperature, unlike the 26-membered version.
Area of Science:
- Supramolecular Chemistry
- Organic Synthesis
- Stereochemistry
Background:
- Rotaxanes are mechanically interlocked molecules with potential applications in molecular machines.
- Dynamic axial chirality in biphenyl moieties presents opportunities for developing chiral switches.
- Crown ethers and ammonium ions are common components in rotaxane construction.
Purpose of the Study:
- To synthesize [2]rotaxanes using biphenyl crown ethers and secondary ammonium ions.
- To investigate the locking of dynamic axial chirality in these rotaxane structures.
- To study the racemization kinetics of the rotaxanes and the influence of solvent polarity.
Main Methods:
- Synthesis of [2]rotaxanes with 23- and 26-membered biphenyl crown ethers.
- Chiral high-performance liquid chromatography (HPLC) for separation and analysis of enantiomers.
- Kinetic studies of racemization at different temperatures and in various solvents (DMSO, o-dichlorobenzene).
Main Results:
- Successful synthesis of rotaxanes incorporating 23- and 26-membered biphenyl crown ethers.
- The 26-membered crown ether rotaxane racemized at room temperature.
- The 23-membered crown ether rotaxane exhibited stability against racemization at room temperature for three days.
- Enantiomers of the 23-membered rotaxane showed faster stereoinversion in polar DMSO compared to nonpolar o-dichlorobenzene.
Conclusions:
- The size of the macrocyclic component (crown ether) influences the stability of the locked axial chirality in rotaxanes.
- Solvent polarity plays a significant role in the rate of stereoinversion, with polar solvents accelerating racemization.
- These findings contribute to the design of rotaxanes with controllable stereochemical properties for advanced applications.
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