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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
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A Regulable Internal Cavity inside a Resorcinarene-Based Hemicarcerand.

Kentaro Harada1, Ryo Sekiya1, Takeharu Haino1

  • 1Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|February 4, 2020
PubMed
Summary

Researchers developed a flexible covalent organic capsule with a tunable cavity size. Metal-coordination controls guest recognition, enabling stimuli-responsive uptake, transport, and release of chemicals for advanced supramolecular systems.

Keywords:
hemicarcerandshost-guest systemsmolecular recognitionresorcinarenessupramolecular chemistry

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Area of Science:

  • Supramolecular Chemistry
  • Materials Science

Background:

  • Covalent organic capsules like carcerands and hemicarcerands are molecular hosts with fixed cavity sizes, limiting their applications.
  • Developing adaptable host molecules is crucial for advanced chemical sensing and delivery systems.

Purpose of the Study:

  • To engineer a covalent organic capsule with an adjustable internal cavity size.
  • To investigate the impact of cavity size modulation on molecular recognition and guest encapsulation.
  • To demonstrate stimuli-responsive control over guest binding and release.

Main Methods:

  • Synthesis of a resorcinarene-based cavitand with bipyridyl arms.
  • Metal-directed dimerization and subsequent olefin metathesis to form the capsule.
  • Demetalation to induce cavity expansion and structural changes.
  • Guest encapsulation studies using different sized molecules (4,4'-diacetoxybiphenyl and a longer analogue).
  • Molecular mechanics calculations to predict cavity conformation changes.
  • Guest competition experiments to assess binding preferences.

Main Results:

  • A covalently linked capsule was synthesized with a cavity that can be expanded upon demetalation.
  • The metal-coordinated capsule selectively binds a smaller guest, while the metal-free form encapsulates a significantly longer guest.
  • Molecular modeling confirmed that cavity expansion occurs by unfolding alkyl chains.
  • Metalation and demetalation successfully switched the preferred guest, demonstrating external-stimuli-responsive behavior.

Conclusions:

  • The developed covalent organic capsule exhibits a flexible and regulable cavity, overcoming limitations of fixed-size hosts.
  • The ability to control cavity size and guest selectivity via metalation/demetalation opens avenues for smart supramolecular systems.
  • This work provides a foundation for designing functional materials for controlled chemical uptake, transport, and release.