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Building on Cram's legacy: stimulated gating in hemicarcerands
Fang Liu1, Roger C Helgeson, K N Houk
1Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
Accounts of Chemical Research
|May 8, 2014
Summary
Researchers designed "gated" container molecules that can switch between carcerand and hemicarcerand states. This gating controls guest release, offering new possibilities for molecular encapsulation and release applications.
Area of Science:
- Supramolecular Chemistry
- Organic Chemistry
- Molecular Recognition
Background:
- Donald Cram's Nobel Prize-winning work established host-guest chemistry and container molecules like carcerands and hemicarcerands.
- Carcerands form stable complexes (carceplexes) with guests, requiring bond breaking for release due to high constrictive binding.
- Hemicarcerands exhibit lower constrictive binding, allowing guest release at elevated temperatures without covalent bond cleavage.
Purpose of the Study:
- To design and synthesize novel container molecules capable of switching between carcerand and hemicarcerand states via a mechanism termed 'gating'.
- To investigate stimuli-responsive gating mechanisms, including thermal, redox, and photochemical control, for dynamic modulation of guest accessibility.
- To explore the potential applications of these gated hemicarceplexes in controlled molecular encapsulation and release.
Main Methods:
- Computational studies to identify and understand the conformational changes in hemicarceplex portals leading to guest release (thermally controlled gating).
- Design and synthesis of hemicarcerands equipped with gates responsive to redox or photochemical stimuli.
- Experimental and computational investigations to characterize the behavior of gated hemicarceplexes under various conditions.
Main Results:
- Demonstrated thermally controlled gating where portal structures change conformation, enlarging the opening and releasing guests, analogous to enzyme peptide loops.
- Successfully synthesized redox- and photo-controlled gated hemicarceplexes, enabling switching between closed (carceplex-like) and open (hemicarcerand-like) states.
- Showcased that closed gates lead to high constrictive binding, while opened gates dramatically reduce it, facilitating facile guest exchange.
Conclusions:
- Gating provides a mechanism to dynamically control guest access in container molecules, transitioning between high and low constrictive binding states.
- Stimuli-responsive gating (thermal, redox, photochemical) offers precise control over molecular encapsulation and release.
- Gated hemicarceplexes present promising platforms for advanced applications in molecular storage, delivery, and sensing.
