Cheng Ji-Xin, Pautot Sophie, Weitz David A, Xie X Sunney
Department of Chemistry and Chemical Biology, Division of Engineering and Applied Sciences, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2003 Aug 19;100(17):9826-30. doi: 10.1073/pnas.1732202100. Epub 2003 Aug 6.
We demonstrate ordered orientation of the hydration water at the surface of phospholipid bilayers by use of coherent anti-Stokes Raman scattering (CARS) microscopy, a highly sensitive vibrational imaging method recently developed. We investigated negatively charged POPS (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine) and neutral POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) multilamellar onions dispersed in deuterated dodecane. The imaging contrast based on the CARS signal from the H2O stretching vibration shows a clear dependence on the excitation field polarization. Our results provide direct experimental evidence that water molecules close to the phospholipid bilayer surface are ordered with the symmetry axis along the direction normal to the bilayer. Moreover, the amount of ordered water molecules depends on the lipid polar group. The spectral profile for the inter-lamellar water shows that the water molecules bound to the bilayer surface are less hydrogen-bonded and exhibit a higher vibrational frequency than bulk water.
我们通过使用相干反斯托克斯拉曼散射（CARS）显微镜证明了磷脂双分子层表面水化水的有序取向，CARS显微镜是最近开发的一种高灵敏度振动成像方法。我们研究了分散在氘代十二烷中的带负电荷的POPS（1-棕榈酰-2-油酰-sn-甘油-3-磷酸-L-丝氨酸）和中性POPC（1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱）多层洋葱结构。基于来自H2O伸缩振动的CARS信号的成像对比度显示出对激发场偏振的明显依赖性。我们的结果提供了直接的实验证据，即靠近磷脂双分子层表面的水分子沿垂直于双分子层的方向以对称轴有序排列。此外，有序水分子的数量取决于脂质极性基团。层间水的光谱特征表明，与双分子层表面结合的水分子氢键较少，并且比本体水表现出更高的振动频率。
