Institute of Organic Chemistry and Biochemistry, Flemingovo nám. 2, 16610 Prague, Czech Republic.
J Phys Chem A. 2012 Jan 12;116(1):680-8. doi: 10.1021/jp209408b. Epub 2011 Dec 29.
Selected guaianolide type sesquiterpene lactones were studied combining solution and solid-state NMR spectroscopy with theoretical calculations of the chemical shifts in both environments and with the X-ray data. The experimental (1)H and (13)C chemical shifts in solution were successfully reproduced by theoretical calculations (with the GIAO method and DFT B3LYP 6-31++G**) after geometry optimization (DFT B3LYP 6-31 G**) in vacuum. The GIPAW method was used for calculations of solid-state (13)C chemical shifts. The studied cases involved two polymorphs of helenalin, two pseudopolymorphs of 6α-hydroxydihydro-aromaticin and two cases of multiple asymmetric units in crystals: one in which the symmetry-independent molecules were connected by a series of hydrogen bonds (geigerinin) and the other in which the symmetry-independent molecules, deprived of any specific intermolecular interactions, differed in the conformation of the side chain (badkhysin). Geometrically different molecules present in the crystal lattices could be easily distinguished in the solid-state NMR spectra. Moreover, the experimental differences in the (13)C chemical shifts corresponding to nuclei in different polymorphs or in geometrically different molecules were nicely reproduced with the GIPAW calculations.
选择了几种愈创木烷型倍半萜内酯，结合溶液和固态 NMR 光谱学以及理论计算两种环境中的化学位移，并结合 X 射线数据进行了研究。经过真空状态下的几何优化（DFT B3LYP 6-31 G**），用 GIAO 方法和 DFT B3LYP 6-31++G**进行理论计算后，成功地再现了溶液中（1）H 和（13）C 化学位移的实验值。使用 GIPAW 方法计算了固态（13）C 化学位移。研究的情况涉及两种形式的白屈菜红碱、两种 6α-羟二氢芳香霉素的假多晶型物以及晶体中两种具有多个不对称单元的情况：一种是由一系列氢键连接的具有独立对称性的分子（印度黄莲辛），另一种是具有独立对称性的分子，没有任何特定的分子间相互作用，其侧链构象不同（苦玄参素）。在固态 NMR 光谱中，可以很容易地分辨出晶体晶格中存在的几何形状不同的分子。此外，用 GIPAW 计算很好地再现了对应于不同多晶型物或几何形状不同的分子中核的（13）C 化学位移的实验差异。
