Introduction of Positive Charges into Zwitterionic Phospholipid Monolayers Disrupts Water Structure Whereas Negative Charges Enhances It
Introduction of Positive Charges into Zwitterionic Phospholipid Monolayers Disrupts Water Structure Whereas Negative Charges Enhances It
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DOI：
10.1021/acs.jpcb.8b08476
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发表时间：
2018-12-27
影响因子：
3.3
通讯作者：
Cremer, Paul S.
中科院分区：
文献类型：
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作者：
Pullanchery, Saranya;Yang, Tinglu;Cremer, Paul S.
研究了1，2-二油酰-sn-甘油-3-磷脂酰胆碱单分子膜在空气/水界面上的水结构和磷酸根水合作用。振动和频光谱（VSFS）和朗缪尔单层压缩测量。PC脂质主要通过其磷酸胆碱（P-N）偶极子和羰基部分定向水分子。在引入低浓度的1，2-二油酰基-3-三甲基铵丙烷（DOTAP），带正电荷的双链表面活性剂，TAP头基被吸引到相邻的PC脂质上的磷酸基团。这种吸引力导致单分子膜收缩，排出与磷酸基团形成氢键的水分子。此外，OH伸缩信号的幅度降低。在较高的DOTAP浓度，单层上的正电荷引起的面积增加，每个头基和水分子在近表面散装区域变得越来越一致。在这些后者的条件下，OH拉伸幅度是线性成比例的表面电位。相比之下，引入1，2-二油酰-sn-甘油-3-磷脂酰甘油（一种带负电荷的脂质）并没有改变每个脂质的面积或磷酸盐-水氢键网络。随着界面电位的增大，OH伸缩幅度不断增大。值得注意的是，在界面水光谱的变化是独立的化学用于创建正或负的界面电位。例如，Ca 2+和丁卡因（均带正电荷）破坏水结构类似于低DOTAP浓度，而SCN-和布洛芬（均带负电荷）增强水结构。这些结果表明，界面水结构，面积每脂质，和表面电荷密度之间的直接相关性。
The interfacial water structure and phosphate group hydration of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine monolayers were investigated at air/water interfaces. Both vibrational sum frequency spectroscopy (VSFS) and Langmuir monolayer compression measurements were made. The PC lipids oriented water molecules predominantly through their phosphate-choline (P-N) dipoles and carbonyl moieties. Upon the introduction of low concentrations of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), a positively charged double chain surfactant, the TAP headgroups were attracted to the phosphate moieties on adjacent PC lipids. This attraction caused the monolayers to contract, expelling water molecules that were hydrogen bonded to the phosphate groups. Moreover, amplitude of the OH stretch signal decreased. At higher DOTAP concentrations, the positive charge on the monolayer caused an increase in the area per headgroup and water molecules in the near-surface bulk region became increasingly aligned. Under these latter conditions, the OH stretch amplitude was linearly proportional to the surface potential. By contrast, introducing 1,2-dioleoyl-sn-glycero-3-phosphatidylglycerol, a negatively charged lipid, did not change the area per lipid or the phosphate-water hydrogen bonding network. As the interfacial potential grew more negative, the OH stretch amplitude increased continuously. Significantly, changes in the interfacial water spectrum were independent of the chemistry employed to create the positive or negative interfacial potential. For example, Ca2+ and tetracaine (both positively charged) disrupted the water structure similarly to low DOTAP concentrations, whereas SCN- and ibuprofen (both negatively charged) enhanced the water structure. These results suggest a direct correlation amongst the interfacial water structure, area per lipid, and surface charge density.