Energetic Origin of Proton Affinity to the Air/Water Interface
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- 作者：Hideaki Takahashi ; Kunihiro Maruyama ; Yasuhito Karino ; Akihiro Morita ; Masayoshi Nakano ; Pavel Jungwirth ; Nobuyuki Matubayasi
- 刊名：Journal of Physical Chemistry B
- 出版年：2011
- 出版时间：April 28, 2011
- 年：2011
- 卷：115
- 期：16
- 页码：4745-4751
- 全文大小：863K
- 年卷期：v.115,no.16(April 28, 2011)
- ISSN：1520-5207
文摘
Recent experimental and theoretical studies showed the preference of the hydronium ion for the vapor/water interface. To investigate the mechanism responsible for the surface propensity of this ion, we performed a series of novel quantum chemical simulations combined with the theory of solutions. The solvation free energy of the H3O+ solute placed at the interface was obtained as 鈭?7.9 kcal/mol, being more stable by 3.6 kcal/mol than that of the solute embedded in the bulk. Further, we decomposed the solvation free energies into contributions from the water molecules residing in the oxygen and the hydrogen sides of the solute to clarify the origin of the surface preference. When the solute was displaced from the bulk to the interface, it was shown that the free energy contribution from the oxygen side is destabilized by 10 kcal/mol because of a reduction of the number of surrounding solvent water molecules. It was observed, however, that the free energy contribution due to the hydrogen side of the solute is unexpectedly stabilizing and surpasses the destabilization in the opposite side. We found that the stabilization in the hydrogen side originates from the solute鈭抯olvent interaction in the medium range beyond the nearest neighbor. It was also revealed that the free energy contribution due to the solute鈥檚 electronic polarization amounts to about the half of the total free energy change associated with the solute displacement from the bulk to the interface.