NMR Study of the Reversible Trapping of SF6 by Cucurbit[6]uril in Aqueous Solution

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• 作者：Luca Fusaro ; Emanuela Locci ; Adolfo Lai ; Michel Luhmer
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：November 27, 2008
• 年：2008
• 卷：112
• 期：47
• 页码：15014-15020
• 全文大小：233K
• 年卷期：v.112,no.47(November 27, 2008)
• ISSN：1520-5207

文摘

The complexation of sulfur hexafluoride (SF₆), a highly potent greenhouse gas, by cucurbit[6]uril (CB) was studied at various temperatures in Na₂SO₄ aqueous solutions by ¹⁹F and ¹H NMR. CB shows a remarkable affinity for SF₆, suggesting that it is a suitable molecular container for the design of materials tailored for SF₆ trapping. At 298 K, the equilibrium constant characterizing the inclusion of SF₆ by CB is 3.1 × 10⁴ M⁻¹ and the residence time of SF₆ within the CB cavity is estimated to be of the order of a few seconds. The enthalpic and entropic contributions to the free energy of encapsulation were determined and are discussed. This work also reports on the interest of SF₆ in the framework of the spin-spy methodology. The advantages and drawbacks of solution-state ¹⁹F NMR of SF₆ with respect to ¹²⁹Xe NMR are discussed. SF₆ comes forward as a versatile and informative spin-spy molecule for probing systems in solution because its detection limit by ¹⁹F NMR reaches the micromolar range with standard equipment and because quantitative integral measurements, relaxation time measurements, and demanding experiments, such as translational diffusion coefficient measurements, are easily carried out in addition to chemical shift measurements. Solution-state ¹⁹F NMR of SF₆ emerges as a promising alternative to ¹²⁹Xe NMR for probing cavities and for other applications relying on the encapsulation of an NMR active gaseous probe.