Heterogeneous Structures of Ionic Liquids as Probed by CO Rotation with Nuclear Magnetic Resonance Relaxation Analysis and Molecular Dynamics Simulations.
Heterogeneous Structures of Ionic Liquids as Probed by CO Rotation with Nuclear Magnetic Resonance Relaxation Analysis and Molecular Dynamics Simulations.
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通过 CO 旋转、核磁共振弛豫分析和分子动力学模拟探测离子液体的异质结构。
DOI：
10.1021/acs.jpcb.0c08030
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Y. Kimura
中科院分区：
文献类型：
--
作者：
Takatsugu Endo;Hiroki Sumida;K. Fujii;Kenji Takahashi;Y. Kimura
通过核磁共振 (NMR) 弛豫测量和分子动力学 (MD) 模拟研究了离子液体 (IL) 中一氧化碳 (CO) 的旋转动力学。对 10 个离子液体（四种基于咪唑鎓阳离子的离子液体、四种基于鏻阳离子的离子液体和两种基于铵阳离子的离子液体，全部与双（三氟磺酰甲烷）亚胺阴离子配对）中的 17O 富集 CO 进行 NMR 自旋晶格弛豫时间测量。结合先前报告的五个 IL 数据和粘度数据，我们的结果表明，获得的旋转弛豫时间 (τ2R) 远小于使用 Stokes-Einstein-Debye (SED) 理论预测的值。对于相同的粘度/温度值，τ2R-1值随着阳离子中烷基碳原子数的增加而线性增加。与 SED 方程的偏差是由于 τ2R 对碳数不敏感，尽管较高的碳数通常会导致离子液体的粘度值较高。为了研究离子液体中 CO 的独特旋转特性，对含有 CO 溶质的五种代表性离子液体（两种咪唑鎓、两种鏻和一种铵）进行 MD 模拟。从旋转相关函数分析来看，CO旋转主要在1 ps内以类似自由旋转的方式发生，这解释了CO旋转对粘度的相对不敏感性。在随后的时间尺度（>1 ps）中，CO 旋转的次要成分在不同的 IL 之间被区分。强烈建议，因为CO优选位于阳离子中烷基的外部，所以缓慢的CO旋转与外部烷基动力学相关，其与整个阳离子旋转脱钩。
The rotational dynamics of carbon monoxide (CO) in ionic liquids (ILs) was investigated by nuclear magnetic resonance (NMR) relaxation measurements and molecular dynamics (MD) simulations. NMR spin-lattice relaxation time measurements were performed for 17O-enriched CO in 10 ILs (four imidazolium-cation-based, four phosphonium-cation-based, and two ammonium-cation-based ILs, all paired with the bis(trifluorosulfonylmethane)imide anion). In combination with previously reported data for five ILs and viscosity data, our results indicated that the obtained rotational relaxation times (τ2R) were much smaller than those predicted using the Stokes-Einstein-Debye (SED) theory. For the same viscosity/temperature values, the τ2R-1 value increased linearly with increasing carbon number of the alkyl group in the cation. The deviation from the SED equation was due to the insensitivity of τ2R to the carbon number, even though a higher carbon number generally leads to higher viscosity values for ILs. To investigate the unique rotational properties of CO in the ILs, MD simulations were performed on five representative ILs (two imidazolium, two phosphonium, and one ammonium) containing CO solutes. From rotational correlation function analyses, the CO rotation mainly occurred in a free rotation-like manner within 1 ps, which explained the relative insensitivity of CO rotation to viscosity. In the subsequent time scale (>1 ps), the minor component of the CO rotation was discriminated among different ILs. It was strongly suggested that, because CO preferably locates in the outer part of the alkyl groups in the cation, the slow CO rotation is correlated with the outer alkyl dynamics, which are decoupled from the whole cation rotation.
影响因子：
3
作者：
Kutzner, Carsten;Pall, Szilard;Grubmueller, Helmut
通讯作者：
Grubmueller, Helmut