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Published on: November 1, 2024
Guest rotations within a capsuleplex probed by NMR and EPR techniques
Revathy Kulasekharan1, Nithyanandhan Jayaraj, Mintu Porel
1Department of Chemistry, University of Miami, Coral Gables, Florida 33124, USA.
Guest molecules encapsulated in octa acid cavitands exhibit restricted rotation. Dynamics vary based on guest structure and temperature, with distinct behaviors observed on NMR and EPR timescales.
Area of Science:
- Supramolecular Chemistry
- Physical Chemistry
- Molecular Dynamics
Background:
- Octa acid is a water-soluble cavitand forming closed capsules with guest molecules.
- Understanding guest dynamics within host-guest complexes is crucial for molecular recognition and encapsulation studies.
Purpose of the Study:
- To investigate the rotational dynamics of guest molecules encapsulated within octa acid cavitands.
- To compare dynamics across different timescales using Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopy.
Main Methods:
- Utilized proton Nuclear Magnetic Resonance ((1)H NMR) spectroscopy to study diverse neutral organic guests.
- Employed Electron Paramagnetic Resonance (EPR) spectroscopy with paramagnetic nitroxide guests.
- Investigated dynamics at room temperature and elevated temperatures (55°C).
Main Results:
- Guest molecules exhibit free rotation along their long axis (x-axis) on the NMR timescale.
- Rotation is significantly slower on the EPR timescale compared to free rotation in water.
- Rotational mobility along other axes (y and z) is highly dependent on guest structure and temperature, leading to three distinct dynamic groups.
Conclusions:
- Encapsulation within octa acid significantly alters guest molecule dynamics.
- Guest structure plays a critical role in determining rotational mobility within the closed capsule.
- Even minor structural variations can lead to substantial changes in rotational dynamics.
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