Theoretical vibrational sum-frequency generation spectroscopy of water near lipid and surfactant monolayer interfaces.
Theoretical vibrational sum-frequency generation spectroscopy of water near lipid and surfactant monolayer interfaces.
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DOI：
10.1063/1.4895546
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发表时间：
2014-09
期刊：
影响因子：
--
通讯作者：
Santanu Roy;S. Gruenbaum;J. L. Skinner
中科院分区：
文献类型：
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作者：
Santanu Roy;S. Gruenbaum;J. L. Skinner
了解细胞膜附近水的结构对于表征水介导的事件（如分子运输）至关重要。为了获得膜附近水的结构信息，有必要采用一种只探测界面水分子的表面选择技术。其中一项技术是振动和频率产生（VSFG）光谱学。作为研究膜头群/水相互作用的模型系统，本文考虑了水的脂质和表面活性剂单层。我们采用分子动力学模拟和相敏VSFG相结合的理论方法来研究这些界面附近的水结构。我们的模拟光谱在定性上与实验一致，并揭示了界面水分子在阳离子、阴离子和两性离子界面附近的取向顺序。水分子的OH键指向阴离子界面导致正的VSFG峰，而水氢原子指向远离阳离子界面导致负的VSFG峰。在水与阳离子和阴离子脂质混合物的界面附近，观察到这两种界面水的共存，在它们的VSFG光谱中同时存在负峰和正峰。在两性离子界面中，OH取向平均朝向界面，导致VSFG峰为正。
Understanding the structure of water near cell membranes is crucial for characterizing water-mediated events such as molecular transport. To obtain structural information of water near a membrane, it is useful to have a surface-selective technique that can probe only interfacial water molecules. One such technique is vibrational sum-frequency generation (VSFG) spectroscopy. As model systems for studying membrane headgroup/water interactions, in this paper we consider lipid and surfactant monolayers on water. We adopt a theoretical approach combining molecular dynamics simulations and phase-sensitive VSFG to investigate water structure near these interfaces. Our simulated spectra are in qualitative agreement with experiments and reveal orientational ordering of interfacial water molecules near cationic, anionic, and zwitterionic interfaces. OH bonds of water molecules point toward an anionic interface leading to a positive VSFG peak, whereas the water hydrogen atoms point away from a cationic interface leading to a negative VSFG peak. Coexistence of these two interfacial water species is observed near interfaces between water and mixtures of cationic and anionic lipids, as indicated by the presence of both negative and positive peaks in their VSFG spectra. In the case of a zwitterionic interface, OH orientation is toward the interface on the average, resulting in a positive VSFG peak.