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Interplay between Slow Chirality Inversion and Slow Guest Uptake in a Triple-Helical Closed-Cage Metallocryptand
Sk Asif Ikbal1, Masahiro Ehara2, Shigehisa Akine1,3
1Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
Journal of the American Chemical Society
|June 29, 2026
Summary
Researchers developed a novel closed-cage cobalt(III) metallocryptand that slows guest uptake, enabling the study of guest-induced chirality inversion. This molecular cage allows for controlled manipulation of stereodynamic equilibria in responsive materials.
Area of Science:
- Supramolecular Chemistry
- Materials Science
- Stereochemistry
Background:
- Intelligent responsive materials are crucial for molecular machines and memory devices.
- The mechanism of guest-induced chirality inversion is poorly understood due to rapid guest binding kinetics.
- A system with slow, comparable timescales for chirality inversion and guest uptake is needed.
Purpose of the Study:
- To develop a molecular system that slows down guest uptake and chirality inversion.
- To investigate the mechanism of guest-induced chirality inversion.
- To explore the influence of cage architecture on stereodynamic processes.
Main Methods:
- Synthesis of a triple-helical closed-cage cobalt(III) metallocryptand using 1,7-heptanediamine (hpda) ligands.
- X-ray crystallography to determine the diastereomeric structure and helical handedness.
- Solution-state NMR spectroscopy to monitor dynamic equilibrium and interconversion rates.
- Kinetic analysis using a four-species reversible model to study guest uptake and chirality changes.
Main Results:
- A closed-cage cobalt(III) metallocryptand with a right-handed triple-helical structure ((P,R6) diastereomer) was synthesized.
- Slow interconversion between (P,R6) and (M,R6) diastereomers (t1/2(app) = 20 min) was observed in solution.
- Addition of CsCl induced slow chirality inversion (P to M) over hours, coupled with Cs+ uptake.
- Cs+ preferentially binds to the M-form, driving P→M isomerization and subsequent uptake.
- Addition of Cl- shifted the equilibrium towards the P-form, demonstrating opposite stereodynamic effects.
Conclusions:
- Closed-cage architecture significantly slows guest uptake and chirality inversion, enabling kinetic studies.
- Guest-induced chirality inversion pathway is modulated by cage closure, controlling timing and sequence.
- The study provides a kinetic platform for probing guest effects on stereodynamic equilibria.
- Strategies can be applied to design other smart molecular architectures.
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