Where Are Sodium Ions in AOT Reverse Micelles? Fluoride Anion Probes Nanoconfined Ions by 19F Nuclear Magnetic Resonance Spectroscopy,Langmuir

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Where Are Sodium Ions in AOT Reverse Micelles? Fluoride Anion Probes Nanoconfined Ions by 19F Nuclear Magnetic Resonance Spectroscopy
Langmuir ( IF 3.7 ) Pub Date : 2023-05-23 , DOI: 10.1021/acs.langmuir.3c00649
Samantha L Miller ₁ , Ernestas Gaidamauskas ₁ , Ataf Ali Altaf _{1,

2} , Debbie C Crans _{1,

3} , Nancy E Levinger _{1,

4}

Affiliation

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 in ¹⁹F 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, the ¹⁹F 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.

中文翻译：

AOT 反胶束中的钠离子在哪里？用 19F 核磁共振光谱法探测氟化物阴离子纳米限制离子

将水限制在纳米空间内创造了一个独特的环境，可以改变水的结构和动态特性。当离子存在于这些纳米级空间中时，与散装水溶液中假设的均匀分布相比，有限数量的水分子和较短的筛选长度会显着影响离子的分布方式。在这里，我们证明了在氟化物阴离子 F ^–的¹⁹ F NMR 光谱中观察到的化学位移探测了钠离子 Na ⁺的位置，限制在由 AOT（二辛基磺基琥珀酸钠）表面活性剂制备的反胶束中。我们的测量表明，反胶束的纳米限制环境可导致极高的表观离子浓度和离子强度，超出本体水溶液的极限。最值得注意的是，我们在反胶束中观察到的¹⁹ F NMR 化学位移趋势表明 AOT 钠抗衡离子保留在表面活性剂和水之间的内部界面处或附近，从而为这一假设提供了第一个实验支持^。

更新日期：2023-05-23

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