Department of Chemistry, Gauhati University, Guwahati, India.
Magn Reson Chem. 2021 May;59(5):569-576. doi: 10.1002/mrc.4975. Epub 2020 Mar 25.
Determination of configurations and conformations is an important step in the structural characterization of small molecules. Apart from utilizing isotropic J-couplings and nuclear overhauser effect (NOEs) measured in isotropic solution, anisotropic Nuclear Magnetic resonance (NMR) data such as residual dipolar couplings and residual chemical shift anisotropies (RCSAs) were also used to elucidate complex small molecule structures. Measuring RCSA has always been historically difficult due to the isotropic shift effect accompanied by molecular alignment and therefore only occasionally applied in a few examples. Here, we present a robust measurement of carbon RCSAs using a smaller gel-stretching device to determine the structures of a few small molecules. A systematic study on how different density functional theory computed anisotropies of the chemical shift anisotropy tensors impact RCSA data interpretation has also been discussed. We also discuss the effect of utilizing various carbons as reference nuclei for RCSA data extraction as well as the orientation behavior of estrone in orthogonal alignment media.
确定构型和构象是小分子结构特征化的重要步骤。除了利用各向同性溶液中测量的各向同性 J 耦合和核 Overhauser 效应（NOE）外，还利用各向异性核磁共振（NMR）数据，如残差偶极耦合和残差化学位移各向异性（RCSA）来阐明复杂小分子结构。由于与分子取向相关的各向同性位移效应，测量 RCSA 一直具有挑战性，因此仅在少数情况下偶尔应用。在这里，我们使用较小的凝胶拉伸装置对碳 RCSA 进行了稳健的测量，以确定几个小分子的结构。还讨论了如何使用不同的密度泛函理论计算化学位移各向异性张量的各向异性对 RCSA 数据解释的影响的系统研究。我们还讨论了利用不同的碳作为 RCSA 数据提取的参考核以及甾酮在正交排列介质中的取向行为的影响。
