University of California, Irvine, California 92617, USA.
J Am Chem Soc. 2010 May 12;132(18):6434-42. doi: 10.1021/ja100508n.
The sum-frequency generation (SFG) spectrum from the water/[1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine] (DMPC) interface in the OH stretching mode region of water is simulated and shows three spectral peaks which are assigned to different environments. The weak 3590 cm(-1) peak is attributed to a few water molecules coupled to the glycerol backbone of DMCP. The 3470 cm(-1) feature comes from the top water layer adjacent to the hydrophilic headgroup of DMPC. The 3290 cm(-1) peak arises from the near-bulk water nonadjacent to DMPC. The stretching mode corresponding to the 3290 cm(-1) peak is strongly coupled to the neighboring water molecules. In contrast, the 3470 cm(-1) mode is decoupled from the surrounding water molecules, and the orientation of water is governed by DMPC. This decoupling explains the slow relaxation dynamics of water measured in the time-resolved SFG experiment. Despite the similarity of the SFG spectra, the peak origins of water/lipid and water/vapor interfaces are different.
水中/[1,2-二肉豆蔻酰-sn-甘油-3-磷酸胆碱](DMPC)界面在水中 OH 伸缩模式区域的和频产生(SFG)光谱被模拟,显示出三个光谱峰,它们被分配到不同的环境中。较弱的 3590 cm(-1) 峰归因于与 DMPC 的甘油骨架偶联的少数水分子。3470 cm(-1) 特征来自与 DMPC 的亲水头基相邻的顶层水层。3290 cm(-1) 峰来自与 DMPC 不相邻的近体相水。与 3290 cm(-1) 峰对应的伸缩模式与相邻的水分子强烈耦合。相比之下,3470 cm(-1) 模式与周围水分子解耦,水的取向由 DMPC 控制。这种解耦解释了在时间分辨 SFG 实验中测量到的水的慢弛豫动力学。尽管 SFG 光谱相似,但水/脂质和水/蒸气界面的峰起源不同。