13C NMR relaxation rates:: Separation of dipolar and chemical shift anisotropy effects
13C NMR relaxation rates:: Separation of dipolar and chemical shift anisotropy effects
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DOI：
10.1021/jp031300g
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发表时间：
2004-07-22
影响因子：
2.9
通讯作者：
Dölle, A
中科院分区：
文献类型：
--
作者：
Carper, WR;Wahlbeck, PG;Dölle, A
从C-13自旋-晶格弛豫数据获得分子再取向动力学的过程被简化为粘性溶液中的芳族碳。自旋-晶格弛豫时间（C-13）用于确定离子液体1-丁基-3-甲基咪唑六氟磷酸盐（[BMIM][PF 6]）的伪旋转相关时间。利用赝转动关联时间计算了修正后的最大核奥弗豪泽效应（NOE）因子。然后使用这些校正的最大NOE因子来确定咪唑环中每个C-13核的总弛豫速率的偶极弛豫速率部分。这种分析的结果是，最大NOE因子和总自旋-晶格弛豫时间的曲线图在相似的温度下具有最小值。咪唑鎓阳离子中芳香碳的化学位移各向异性值Δ Σ是温度依赖性的，最大Δ Σ值在约100 ℃。与自旋-晶格弛豫时间所观察到的温度相同。咪唑鎓环碳的平均Δ Σ值与液晶溶液中嘧啶的Δ Σ值相似。
The process of obtaining molecular reorientational dynamics from C-13 spin-lattice relaxation data is simplified for aromatic carbons in viscous solutions. Spin-lattice relaxation times (C-13) are used to determine pseudorotational correlation times for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The pseudorotational correlation times are used to calculate corrected maximum nuclear Overhauser effect (NOE) factors from a combined isotropic dipolar and NOE equation. These corrected maximum NOE factors are then used to determine the dipolar relaxation rate part of the total relaxation rate for each C-13 nucleus in the imidazolium ring. A consequence of this analysis is that a plot of the maximum NOE factors and the total spin-lattice relaxation times have minima at similar temperatures. Chemical shift anisotropy values, Deltasigma, for the aromatic carbons in the imidazolium cation are temperature dependent with maximum Deltasigma values at ca. the same temperature as observed for the spin-lattice relaxation times. The average Deltasigma values for the imidazolium ring carbons are similar to those of pyrimidine in liquid crystal solutions.