The Crystal Structure of 5-Aminouracil and the Ambiguity of Alternative Polymorphs,Israel Journal of Chemistry

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The Crystal Structure of 5-Aminouracil and the Ambiguity of Alternative Polymorphs
Israel Journal of Chemistry ( IF 2.3 ) Pub Date : 2021-09-04 , DOI: 10.1002/ijch.202100062
Taylor A. Watts ₁ , Louise S. Price ₂ , Sarah L. Price ₂ , Sara M. Niederberger ₁ , Jeffery A. Bertke ₁ , Jennifer A. Swift ₁

Affiliation

The nucleobase derivative 5-aminouracil (AUr, C₄H₅N₃O₂) is of interest for its biological activity, yet the solid state structure of this compound has remained elusive owing to its propensity to crystallize as aggregates of microcrystalline particles. Here we report the first single-crystal structure of AUr determined from synchrotron x-ray diffraction data. An early crystal structure prediction effort, which assumed that AUr was rigid in the isolated molecule optimized conformation, provided several poor matches to the simulated PXRD pattern. Revisiting these crystal structures, by periodic electronic level modelling (PBE-TS optimization) gave more realistic relative lattice energies, but a good match to the experimental powder pattern required using the experimental cell parameters. PXRD and Raman spectroscopy suggest that phase impurities may be present in the bulk crystallization product, though the identity of alternative polymorphs could not be confirmed on the basis of the data available.

中文翻译：

5-氨基尿嘧啶的晶体结构和替代多晶型的模糊性

核碱基衍生物 5-氨基尿嘧啶 (AUr, C ₄ H ₅ N ₃ O ₂) 因其生物活性而受到关注，但由于其倾向于结晶为微晶颗粒的聚集体，因此该化合物的固态结构仍然难以捉摸。在这里，我们报告了从同步加速器 X 射线衍射数据确定的第一个 AUr 单晶结构。早期的晶体结构预测工作假设 AUr 在分离的分子优化构象中是刚性的，但与模拟的 PXRD 图案的匹配性较差。通过周期性电子水平建模（PBE-TS 优化）重新审视这些晶体结构，提供了更真实的相对晶格能量，但与使用实验电池参数所需的实验粉末图案良好匹配。PXRD 和拉曼光谱表明，大块结晶产物中可能存在相杂质，

更新日期：2021-10-25

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