Pokorna Sarka, Jurkiewicz Piotr, Vazdar Mario, Cwiklik Lukasz, Jungwirth Pavel, Hof Martin
J. Heyrovský Institute of Physical Chemistry of the Academy of Sciences of the Czech Republic v.v.i., Dolejskova 3, 18223 Prague 8, Czech Republic.
Division of Organic Chemistry and Biochemistry, Rudjer Bošković Institute, P.O.B. 180, HR-10002 Zagreb, Croatia.
J Chem Phys. 2014 Dec 14;141(22):22D516. doi: 10.1063/1.4898798.
Time-dependent fluorescence shift (TDFS) of Laurdan embedded in phospholipid bilayers reports on hydration and mobility of the phospholipid acylgroups. Exchange of H2O with D2O prolongs the lifetime of lipid-water and lipid-water-lipid interactions, which is reflected in a significantly slower TDFS kinetics. Combining TDFS measurements in H2O and D2O hydrated bilayers with atomistic molecular dynamics (MD) simulations provides a unique tool for characterization of the hydrogen bonding at the acylgroup level of lipid bilayers. In this work, we use this approach to study the influence of fluoride anions on the properties of cationic bilayers composed of trimethylammonium-propane (DOTAP). The results obtained for DOTAP are confronted with those for neutral phosphatidylcholine (DOPC) bilayers. Both in DOTAP and DOPC H2O/D2O exchange prolongs hydrogen-bonding lifetime and does not disturb bilayer structure. These results are confirmed by MD simulations. TDFS experiments show, however, that for DOTAP this effect is cancelled in the presence of fluoride ions. We interpret these results as evidence that strongly hydrated fluoride is able to steal water molecules that bridge lipid carbonyls. Consequently, when attracted to DOTAP bilayer, fluoride disrupts the local hydrogen-bonding network, and the differences in TDFS kinetics between H2O and D2O hydrated bilayers are no longer observed. A distinct behavior of fluoride is also evidenced by MD simulations, which show different lipid-ion binding for Cl(-) and F(-).
嵌入磷脂双分子层中的劳丹的时间依赖性荧光位移（TDFS）反映了磷脂酰基的水合作用和流动性。H₂O与D₂O的交换延长了脂质-水和脂质-水-脂质相互作用的寿命，这在明显更慢的TDFS动力学中得到体现。将H₂O和D₂O水合双分子层中的TDFS测量与原子分子动力学（MD）模拟相结合，为表征脂质双分子层酰基水平的氢键提供了一种独特的工具。在这项工作中，我们使用这种方法来研究氟阴离子对由三甲基铵丙烷（DOTAP）组成的阳离子双分子层性质的影响。将DOTAP得到的结果与中性磷脂酰胆碱（DOPC）双分子层的结果进行对比。在DOTAP和DOPC中，H₂O/D₂O交换都延长了氢键寿命，并且不会扰乱双分子层结构。这些结果通过MD模拟得到证实。然而，TDFS实验表明，对于DOTAP，在氟离子存在的情况下这种效应被抵消了。我们将这些结果解释为证据，即高度水合的氟能够夺取桥接脂质羰基的水分子。因此，当氟被吸引到DOTAP双分子层时，它会破坏局部氢键网络，并且不再观察到H₂O和D₂O水合双分子层之间TDFS动力学的差异。MD模拟也证明了氟的独特行为，其显示出Cl⁻和F⁻与脂质的结合不同。
