Weakly Hydrogen-Bonded Water Inside Charged Lipid Monolayer Observed with Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy
Weakly Hydrogen-Bonded Water Inside Charged Lipid Monolayer Observed with Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy
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DOI：
10.1021/acs.jpcc.6b09229
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发表时间：
2017-02-02
影响因子：
3.7
通讯作者：
Yamaguchi, Shoichi
中科院分区：
文献类型：
--
作者：
Nojima, Yuki;Suzuki, Yudai;Yamaguchi, Shoichi
许多生物学过程如光合作用和信号转导都在脂/水界面进行。虽然脂质膜内的水分子被认为在这些过程中具有关键作用，但很难在实验上观察到具有高选择性的水分子。本文采用单通道外差探测和频产生光谱法测量了水分子在阴离子脂质（1，2-dipalmitoyl-sn-glycero-3-phosphoglycerol，DPPG）和阳离子脂质（1，2-dipalmitoyl-3-trimethylammonium-propane，DPTAP）界面上的Im chi（（2））（二阶非线性光学极化率的虚部）光谱，并研究了水分子在脂质界面上的结构。位于脂质头基上方的弱氢键水分子的存在被清楚地确定。Im χ（2）光谱表明，头基上方的水分子与头基下方的水分子方向相反，它们与脂质的羰基和甘油基团形成氢键。很可能脂质单层内的水分子可以自由翻转而不终止弱氢键。
Many biological processes such as photosynthesis and signal transduction proceed at lipid/water interfaces. Although water molecules inside lipid membranes are considered to have a critical role in these processes, it has been difficult to experimentally observe those water molecules with high selectivity. Here, we measure the Im chi((2)) (imaginary part of second-order nonlinear optical susceptibility) spectra of water at anionic lipid (1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol, DPPG) and cationic lipid (1,2-dipalmitoyl-3trimethylammonium-propane, DPTAP) interfaces with single-channel heterodyne-detected sum frequency generation spectroscopy and investigate the structure of water molecules at the lipid interfaces. The presence of weakly hydrogen-bonded water molecules located above the lipid head group is clearly identified. The Im chi((2)) spectra indicate that water molecules above the head group are oriented oppositely to those below the head group and they donate hydrogen bonds to the carbonyl and glycerol groups of the lipids. It is likely that water molecules inside the lipid monolayers can freely flip without terminating the weak hydrogen bonds.