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Water inside a hydrophobic cavitand molecule
Jeffrey Ewell1, Bruce C Gibb, Steven W Rick
1Department of Chemistry, University of New Orleans, New Orleans, LA 70148, USA.
The Journal of Physical Chemistry. B
|July 30, 2008
Summary
Water molecules inside a bowl-shaped cavitand exhibit unique dynamics and reduced hydrogen bonding. Dewetting, or water expulsion, is triggered by hydrophobic guests, stabilizing the empty cavitand.
Area of Science:
- Supramolecular Chemistry
- Computational Chemistry
- Physical Chemistry
Background:
- Cavitands are host molecules with hydrophobic interiors capable of encapsulating guests.
- Understanding water's behavior within confined hydrophobic environments is crucial for host-guest chemistry.
Purpose of the Study:
- To investigate the structure, dynamics, and energetics of water confined within a water-soluble cavitand.
- To explore the influence of hydrophobic guests on water occupancy and stability within the cavitand.
Main Methods:
- Molecular dynamics (MD) computer simulations were employed to model water-cavitand interactions.
- Analysis of water molecule number, hydrogen bonding, translational and rotational motion, and energetic transitions.
Main Results:
- An average of 4.5 water molecules were found inside the cavitand, with fluctuations between empty and full states on nanosecond timescales.
- Inside water molecules displayed fewer hydrogen bonds and weaker interactions compared to bulk water, with reduced translational entropy.
- Hydrophobic guests, positioned above the cavitand entrance, induced dewetting by displacing stabilizing water molecules.
Conclusions:
- The cavitand's hydrophobic interior influences water structure and dynamics, leading to energetically favorable but entropically unfavorable filling.
- Dewetting is a key process driven by guest binding, altering the stability of the filled versus empty cavitand states.
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