Different properties of H2O- and D2O-containing phospholipid-based reverse micelles near a critical temperature.
Different properties of H2O- and D2O-containing phospholipid-based reverse micelles near a critical temperature.
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临界温度附近含 H2O 和 D2O 的磷脂基反胶束的不同特性。
DOI：
10.1021/la060396d
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
J. Liquier
中科院分区：
文献类型：
--
作者：
J. Milhaud;E. Hantz;J. Liquier
研究发现，当 DPPC 与水的体积分数在 28 或 26 摄氏度（取决于水是 H2O 还是 D2O）在 0.78-0.89 范围内时，二棕榈酰磷脂酰胆碱 (DPPC)/水/吡啶反胶束会从透明液体转变为玻璃状。他们通过 SANS、FT-IR 和 1H NMR 对这种组合物进行的研究表明，水的同位素性质对其结构和动态特性具有显着影响。通过 SANS，在 38 至 43.5 摄氏度之间，胶束表现为柔性聚合物状圆柱体或短棒，具体取决于水是 H2O 还是 D2O。基于这个双重方面，胶束被可视化为支化圆柱体，其准球形分支点很容易组装成短棒。此外，当水中含有超过 40% 的 D2O 时，SANS 光谱上 0.12 A(-1) 处会出现布拉格反射，证明了胶束的组织。此外，FT-IR 光谱表明，仅当水为 D2O 时，DPPC 磷酸基团才以 D 键合。因此，我们假设倾向于组织含有 D2O 的胶束的力是相邻胶束之间在其分支点水平上的 D 键合水桥。事实上，从头计算表明，当桥原子为 D 而不是 H 时，水二聚体更稳定。形成这些水桥的原因是，当水为 D2O 时，分支点能够沿着胶束滑动，比水为 H2O 时保持闭合的时间更长。事实上，实验表明，在第一种情况下，任何层中磷脂分子的横向扩散都较慢。这种桥的形成引发了胶束之间的氘核迁移，这一点可以通过 1H NMR 在 43 摄氏度下测量的含 D2O 胶束中水的氘核弛豫率来证明。
Dipalmitoylphosphatidylcholine (DPPC)/water/pyridine reverse micelles have been found to transform from a clear liquid into a glass when the DPPC-to-water volume fraction is in the 0.78-0.89 range at 28 or 26 degrees C depending on whether water is H2O or D2O. Their study by SANS, FT-IR, and 1H NMR for this composition has shown remarkable effects of the isotopic nature of water on their structural and dynamic properties. By SANS, between 38 and 43.5 degrees C, micelles appear as either flexible polymer-like cylinders or short rods depending on whether water is H2O or D2O. On the basis of this dual aspect, micelles have been visualized as branched cylinders whose quasi-spherical branching points would be prone to assemble into short rods. In addition, when water contains more than 40% of D2O, a Bragg reflection emerges at 0.12 A(-1) on SANS spectra, evidencing an organization of micelles. In addition, FT-IR spectra show that DPPC phosphate groups are D bonded only when water is D2O. Consequently, we assumed that forces prone to organize the D2O-containing micelles are D-bonded water bridges between neighboring micelles at the level of their branching points. In fact, ab initio calculations have shown that water dimers are more stable when the bridging atom is D rather than H. These water bridges could be formed due to the fact that branching points, able to slide along micelles, keep close for a longer time when water is D2O than when it is H2O. Indeed, it has been shown experimentally that the lateral diffusion of phospholipid molecules in any layer is slower in the first case. Formation of such bridges triggers a deuteron migration between micelles evidenced by the 1/T1 relaxation rate of deuterons of water in D2O-containing micelles measured at 43 degrees C by 1H NMR.