NMR measurements and DFT studies of nuclear magnetic shielding in emodin and chuanxiongzine molecules

Emodin and chuanxiongzine are important active compounds of plants widely used in traditional Chinese medicine because of its well-known pharmacological and biological activity. In the present work the two compounds are studied using 1H, 13C and 14N NMR experiments and DFT calculations of nuclear magnetic shielding in the gaseous phase and in solution. The 1H and 13C experimental shielding values of emodin are directly compared with the appropriate results of calculations performed for an isolated molecule. It is shown that unknown inter- and intramolecular effects in shielding are significant and can be estimated within the range of ±6 ppm for carbons and ±3 ppm for hydrogen atoms. The similar comparison is also presented for the theoretical and experimental 1H and 13C chemical shifts of emodin. The 1H, 13C and 14N shieldings in chuanxiongzine molecule are analyzed by the same DFT calculations and NMR measurements as well. As shown the correlation between calculated and experimental shielding parameters is satisfactory especially when the PBE0/aug-cc-pVTZ approach is applied.