Where Are Sodium Ions in AOT Reverse Micelles? Fluoride Anion Probes Nanoconfined Ions by 19F Nuclear Magnetic Resonance Spectroscopy
Where Are Sodium Ions in AOT Reverse Micelles? Fluoride Anion Probes Nanoconfined Ions by 19F Nuclear Magnetic Resonance Spectroscopy
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DOI：
10.1021/acs.langmuir.3c00649
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发表时间：
2023-05-23
期刊：
影响因子：
3.9
通讯作者：
Levinger，Nancy E.
中科院分区：
文献类型：
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作者：
Miller，Samantha L.;Gaidamauskas，Ernestas;Levinger，Nancy E.
将水限制在纳米级空间中创造了一个独特的环境，可以改变水的结构和动力学特性。当离子存在于这些纳米级空间中时，与本体水溶液中假定的均匀分布相比，水分子的有限数量和短的屏蔽长度可以显著影响离子的分布方式。在这里，我们证明了氟阴离子，F-，探针的位置，钠离子，Na+，限制在反胶束制备的AOT（琥珀酸二辛酯磺酸钠）表面活性剂的化学位移in 19 F NMR光谱。我们的测量表明，反胶束的纳米限制环境可以导致极高的表观离子浓度和离子强度，超出了在本体水溶液中的极限。最值得注意的是，19 F NMR化学位移趋势，我们观察到的F-在反胶束表明，AOT钠抗衡离子保持在或接近表面活性剂和水之间的内部界面，从而为这一假设提供了第一个实验支持。
Confining water to nanosized spaces creates a unique environment that can change water’s structural and dynamic properties. When ions are present in these nanoscopic spaces, the limited number of water molecules and short screening length can dramatically affect how ions are distributed compared to the homogeneous distribution assumed in bulk aqueous solution. Here, we demonstrate that the chemical shift observed in19F NMR spectroscopy of fluoride anion, F–, probes the location of sodium ions, Na+, confined in reverse micelles prepared from AOT (sodium dioctyl sulfosuccinate) surfactants. Our measurements show that the nanoconfined environment of reverse micelles can lead to extremely high apparent ion concentrations and ionic strength, beyond the limit in bulk aqueous solutions. Most notably, the19F NMR chemical shift trends we observe for F–in the reverse micelles indicate that the AOT sodium counterions remain at or near the interior interface between surfactant and water, thus providing the first experimental support for this hypothesis.