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Guest-Induced Conformational Switching in "One Wall" Calix[4]pyrrole Cavitands Functionalized with an Inwardly
Mingkai Zhao1,2, Andrés F Sierra1, Gemma Aragay1
1Institute of Chemical Research of Catalonia (ICIQ-CERCA), The Barcelona Institute of Science and Technology (BIST), Av. Països Catalans, 16, 43007 Tarragona, Spain.
ACS Organic & Inorganic Au
|December 8, 2025
Summary
Two new molecular containers, aryl-extended calix[4]-pyrroles, exhibit guest-induced conformational switching. The quinoxaline-imidazole analogue switches geometry upon binding specific N-oxide guests, demonstrating responsive host behavior.
Area of Science:
- Supramolecular Chemistry
- Organic Synthesis
- Molecular Recognition
Background:
- Calix[4]-pyrroles are versatile molecular scaffolds for host-guest chemistry.
- Introverted acid motifs enable intramolecular interactions and guest binding.
- Controlling conformational dynamics in cavitands is crucial for designing responsive systems.
Purpose of the Study:
- To design and synthesize novel aryl-extended calix[4]-pyrrole (AE-C[4]-P) cavitands.
- To investigate guest-induced conformational switching in these AE-C[4]-P systems.
- To explore the structure-function relationships governing host behavior and guest recognition.
Main Methods:
- Synthesis of two AE-C[4]-P cavitands with specific bridging units.
- Binding studies using N-oxide guests with varying hydrogen bonding capabilities.
- Spectroscopic analysis and Density Functional Theory (DFT) calculations to determine conformations and interactions.
Main Results:
- One AE-C[4]-P cavitand (benzimidazole-based) showed high affinity but no conformational change.
- The other AE-C[4]-P cavitand (quinoxaline-imidazole) exhibited a solvent-dependent conformational switch from equatorial to axial.
- Ditopic guest binding and intramolecular CH···lone pair interactions stabilized the axial conformer.
Conclusions:
- The nature of the aromatic spacer critically influences host behavior and conformational dynamics.
- AE-C[4]-P cavitands can be designed for guest-responsive conformational switching.
- This work establishes a strategy for creating adaptable molecular containers.
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