Spectral assignment and orientational analysis in a vibrational sum frequency generation study of DPPC monolayers at the air/water interface
Spectral assignment and orientational analysis in a vibrational sum frequency generation study of DPPC monolayers at the air/water interface
复制标题
空气/水界面处 DPPC 单层振动和频率生成研究中的光谱分配和方向分析
DOI：
10.1063/1.4972564
复制
发表时间：
2016-12-28
影响因子：
4.4
通讯作者：
Guo, Yuan
中科院分区：
文献类型：
--
作者：
Feng, Rong-Juan;Li, Xia;Guo, Yuan
利用表面选择性振动和频产生光谱（VSFG）研究了两性离子磷脂分子二棕榈酰磷脂酰胆碱（DPPC）的界面行为。然而，仍然是缺乏协议之间的各种取向测量的磷脂单分子层在空气/水界面，主要是因为难以分配拥挤的VSFG功能。在这项研究中，偏振相关的VSFG测量揭示了DPPC烷基尾中末端甲基的面内和面外反对称伸缩模式之间的频移，有利于C-s局部对称性模型，而不是先前假设的C-3v对称性。同位素标记的DPPC的进一步VSFG实验成功地捕获了甘油主链的振动特征。利用新推导的C-s对称性VSFG极化选择规则和更新的光谱归属，可以确定DPPC分子的烷基尾基、胆碱头基和甘油骨架的平均倾斜角，显示了VSFG光谱的强大能力揭示界面的结构细节。在这项工作中开发的Cs对称性的VSFG偏振依赖规则和取向分析程序适用于其他庞大的分子中的甲基不能自由旋转，因此，他们在未来的VSFG研究的一般应用。出版社：AIP Publishing
The interfacial behavior of the benchmark zwitterionic phospholipid molecule dipalmitoylphosphatidylcholine (DPPC) has been extensively investigated by surface-selective vibrational sum frequency generation spectroscopy (VSFG). However, there is still a lack of agreement between various orientational measurements of phospholipid monolayers at the air/water interface, mainly because of the difficulty in assigning congested VSFG features. In this study, polarization-dependent VSFG measurements reveal a frequency shift between the in-plane and out-of-plane antisymmetric stretching modes of the terminal methyl groups in the DPPC alkyl tails, favoring the model of C-s local symmetry rather than the previously assumed C-3v symmetry. Further VSFG experiments of isotopically labeled DPPC successfully capture the vibrational signatures of the glycerol backbone. With the newly derived VSFG polarization selection rules for C-s symmetry and the refreshed spectral assignments, the average tilt angles of the alkyl tail groups, choline headgroup, and glycerol backbone of DPPC molecules can all be determined, showing the powerful capability of VSFG spectroscopy in revealing the structural details at interfaces. The VSFG polarization dependence rules and the orientational analysis procedures developed for Cs symmetry in this work are applicable to other bulky molecules in which the methyl group cannot freely rotate, and they therefore have general applications in future VSFG studies. Published by AIP Publishing.