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Hydrated excess proton at water-hydrophobic interfaces
Satoru Iuchi1, Hanning Chen, Francesco Paesani
1Department of Chemistry and Center for Biophysical Modeling and Simulation, University of Utah, Salt Lake City, 84112-0850, USA.
The Journal of Physical Chemistry. B
|September 30, 2008
Summary
The hydrated excess proton prefers interfaces, driven by its amphiphilic nature. Molecular dynamics simulations reveal energetic stabilization at water-vapor and water-hydrophobic interfaces.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Surface Science
Background:
- The behavior of hydrated ions at interfaces is crucial for understanding chemical reactions and biological processes.
- Previous studies suggested surface preference for excess protons at the water-vapor interface.
Purpose of the Study:
- To investigate the behavior of the hydrated excess proton at various interfaces (water-vapor, water-hydrophobic wall, water-carbon tetrachloride).
- To analyze the structural, delocalization, and thermodynamic driving forces behind the proton's interfacial preference.
Main Methods:
- Molecular dynamics simulations using the multistate empirical valence bond model (MS-EVB3).
- Free energy profile decomposition into internal energy and entropic contributions.
- Analysis of hydrated proton structures and charge defect delocalization.
Main Results:
- Confirmed surface preference of the excess proton at the water-vapor interface.
- Demonstrated for the first time the preference for other water-hydrophobic interfaces.
- Identified energetic stabilization of "rigid" hydrated proton structures due to amphiphilicity as the driving force.
Conclusions:
- The hydrated excess proton exhibits interfacial concentration enhancement at both water-vapor and water-hydrophobic interfaces.
- Energetic factors, not entropic ones, dominate the surface preference.
- The amphiphilic nature of the hydrated proton is key to its interfacial behavior.
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