A Combined Solid-State NMR and Synchrotron X-ray Diffraction Powder Study on the Structure of the Antioxidant (+)-Catechin 4.5-hydrate
A Combined Solid-State NMR and Synchrotron X-ray Diffraction Powder Study on the Structure of the Antioxidant (+)-Catechin 4.5-hydrate
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DOI：
10.1021/ja907671p
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发表时间：
2010-03-10
影响因子：
15
通讯作者：
Von Dreele, Robert B.
中科院分区：
文献类型：
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作者：
Harper, James K.;Doebbler, Jennifer A.;Von Dreele, Robert B.
结合x射线粉末衍射（XRD）和固态核磁共振（SSNMR）数据的分析现在可以提供传统方法无法获得的具有挑战性的粉末的晶体结构。类黄酮儿茶素是这些方法的理想候选者，因为尽管进行了广泛的研究，但它仍无法进行晶体学表征。儿茶素第一次被描述是在近两个世纪前，它的粉末表现出不同程度的水合作用。在这里，同步加速器XRD数据提供了(+)-儿茶素4.5水合物的所有重原子位置，并建立了空间基团为C2。SSNMR数据（C-13张量和H-1/C-13相关性）通过提供儿茶素的五个OH氢取向来完成构象。自1903年以来，该相被错误地识别为4.0水合物，但XRD和密度数据证实，这种差异是由于位于单元胞中Wyckoff特殊位置的水分子容易损失。在x射线衍射扭角保持不变的情况下，对键长和价角进行几何优化，最终改善了重原子的位置。计算的C-13张量与实验数据的拟合显著改善，证实了最终结构的结构增强。
Analyses combining X-ray powder diffraction (XRD) and solid-state NMR (SSNMR) data can now provide crystal structures in challenging powders that are inaccessible by traditional methods. The flavonoid catechin is an ideal candidate for these methods, as it has eluded crystallographic characterization despite extensive study. Catechin was first described nearly two centuries ago, and its powders exhibit numerous levels of hydration. Here, synchrotron XRD data provide all heavy-atom positions in (+)-catechin 4.5-hydrate and establish the space group as C2. SSNMR data (C-13 tensor and H-1/C-13 correlation) complete the conformation by providing catechin's five OH hydrogen orientations. Since 1903, this phase has been erroneously identified as a 4.0 hydrate, but XRD and density data establish that this discrepancy is due to the facile loss of the water molecule located at a Wyckoff special position in the unit cell. A final improvement to heavy-atom positions is provided by a geometry optimization of bond lengths and valence angles with XRD torsion angles held constant. The structural enhancement in this final structure is confirmed by the significantly improved fit of computed C-13 tensors to experimental data.