空气-水界面处自由OH水基团的定义,Journal of Chemical Theory and Computation

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空气-水界面处自由OH水基团的定义
Journal of Chemical Theory and Computation ( IF 5.7 ) Pub Date : 2017-12-04 00:00:00 , DOI: 10.1021/acs.jctc.7b00566
Fujie Tang _{1,

2} , Tatsuhiko Ohto ₃ , Taisuke Hasegawa _{2,

4} , Wen Jun Xie _{2,

5} , Limei Xu _{1,

6} , Mischa Bonn ₂ , Yuki Nagata _{2,

7}

Affiliation

通常在水-疏水介质界面处发现游离的OH基团，例如，水与疏水性蛋白质残留物接触，或在水-空气界面处。在使用和频生成（SFG）光谱的表面特定振动光谱研究中，在O–H拉伸区域中通过3700 cm ^–1的尖锐峰对自由的O–H基团进行了实验性表征。尽管这些自由的O–H基团通常被定义为不与其他水分子氢键连接的O–H基团，但这种非氢键的O–H基团与3700 cm ^–1 SFG反应之间存在直接关系一直缺乏。我们的数据表明，常用的氢键定义不能充分捕获对3700 cm ^–1贡献的游离O-H基团顶峰。因此，我们通过分子间距离和水二聚体形成的角度，通过比较〜3700 cm ^–1 SFG响应和选择的自由基团的响应，为捕获表面自由的O–H基团的亚群制定了新的定义。HOD-空中接口处的O–H组。使用这些优化的游离OH基团定义，我们可以推断出具有28％游离OH基团，游离OH组的振动寿命为1.3 ps的界面水分子以及游离O形成的夹角-H组，水-空气界面的表面法线为67°。我们期望这种改进的游离OH基团定义有助于探索界面水的结构和动力学。

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Definition of Free O–H Groups of Water at the Air–Water Interface

Free O–H groups of water are often found at the water-hydrophobic medium interface, e.g. for water contact with hydrophobic protein residues, or at the water–air interface. In surface-specific vibrational spectroscopic studies using sum-frequency generation (SFG) spectroscopy, free O–H groups are experimentally well characterized in the O–H stretch region by a sharp 3700 cm^–1 peak. Although these free O–H groups are often defined as the O–H groups which are not hydrogen-bonded to other water molecules, a direct correlation between such non-hydrogen-bonded O–H groups and the 3700 cm^–1 SFG response has been lacking. Our data show that commonly used hydrogen bond definitions do not adequately capture the free O–H groups contributing to the 3700 cm^–1 peak. We thus formulate a new definition for capturing the subensemble of the surface free O–H groups using the intermolecular distance and the angle formed by the water dimer, through the comparison of the ∼3700 cm^–1 SFG response and the responses from the selected free O–H groups at the HOD–air interface. Using these optimized free O–H group definitions, we infer the fraction of interfacial water molecules with free O–H groups of 28%, a vibrational lifetime of the free O–H groups of 1.3 ps, and the angle formed by the free O–H groups and the surface normal of 67° at the water–air interface. We expect that this improved free O–H group definition can be helpful in exploring the structure and dynamics of the interfacial water.

更新日期：2017-12-04

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