Application of a 1H δ-resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes
Application of a 1H δ-resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes
复制标题
DOI：
10.1002/mrc.2387
复制
发表时间：
2009-04-01
影响因子：
2
通讯作者：
Merlet, Denis
中科院分区：
文献类型：
--
作者：
Giraud, Nicolas;Joos, Marc;Merlet, Denis
我们提出了一个二维宽带同质去耦质子核磁共振实验对映体的可视化应用。在手性环境中，非对映异构体分子间相互作用的存在可以产生-通常轻微-从一种对映异构体到另一种对映异构体的质子化学位移变化。我们表明，这种方法，它依赖于NMR样品的空间编码，是特别适合对映异构体混合物的分析，因为它允许，在一个单一的二维实验，检测对映异构体之间的微妙的化学位移差异，即使在存在几个耦合。这个序列，它使用半选择性射频（rf）脉冲组合到z场梯度脉冲，在样品的不同部分产生不同的选择性回波。所得到的均质去偶提供了沿着2D图的对角线沿着的原始δ分辨光谱，其中可以通过每个质子位点探测手性分化过程，其中所得到的化学位移的变化是可检测的。我们讨论了这种方法的优点和缺点，关于其他实验提供homodecoupled质子光谱。该方法适用于观察（1）（+/-）2-甲基-异冰片配位铕（III）三[3-（三氟甲基-羟基亚甲基）-（+）酒石酸盐]在各向同性溶液中的对映异构体，以及（2）（+/-）3-丁炔-2-醇溶解在手性液晶溶剂中，以显示该脉冲序列对各种手性样品的稳健性。版权所有（c）2009约翰威利父子有限公司。
We present the application of a 2D broadband homodecoupled proton NMR experiment to the visualization of enantiomers. In a chiral environment, the existence of diastereoisomeric intermolecular interactions can yield - generally slight - variations of proton chemical shifts from one enantiomer to another. We show that this approach, which relies on a spatial encoding of the NMR sample, is particularly well suited to the analysis of enantiomeric mixtures, since it allows, within one single 2D experiment, to detect subtle chemical shift differences between enantiomers, even in the presence of several couplings. This sequence, which uses semiselective radio-frequency (rf) pulses combined to a z-field gradient pulse, produces different selective echoes in various parts of the sample. The resulting homonuclear decoupling provides an original delta-resolved spectrum along the diagonal of the 2D map where it becomes possible to probe the chiral differentiation process through every proton site where the resulting variation in the chemical shift is detectable. We discuss the advantages and drawbacks of this approach, regarding other experiments which provide homodecoupled proton spectra. This methodology is applied to the observation of enantiomers of (1) (+/-)2-methyl-isoborneol coordinated to europium (III) tris[3-(trifluoromethyl-hydroxymethylene)-(+)camphorate] in isotropic solution, and (2) (+/-)3-butyn-2-ol dissolved in a chiral liquid-crystal solvent, in order to show the robustness of this pulse sequence for a wide range of chiral samples. Copyright (c) 2009 John Wiley & Sons, Ltd.