L-Alanyl-L-glutamine (Ala–Gln) is a dipeptide which is widely used in medical and nutritional fields. Two new crystalline forms (form III and form IV) and a DMSO solvate form (S_DMSO) of Ala–Gln were discovered in this study, which were distinguished from the known forms by Raman spectroscopy and powder X-ray diffraction (PXRD). Single crystal structures of the three new solid forms were obtained. Moreover, the crystal structure data of known forms: form II, dihydrate form (2H) and ethanol solvate form (S_EtOH), which have not been reported to the best of our knowledge, were solved. The results showed that there were four kinds of molecular arrangements and frameworks in the Ala–Gln solid forms. The comparison of the molecular arrangements and cell parameters indicated that the forms III, 2H and S_EtOH were isomorphic. The hydrogen bonding network of the DMSO solvate was different from those of forms II, III and IV. By comparing the bulk density, lattice energy and thermal analysis results of the three polymorphs of Ala–Gln, the order of bulk density and lattice energy was consistent with the decomposition enthalpy. Besides that, it was found that the crystal shape of the solvates can be retained after solvent removal.

中文翻译：

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二肽新固体形式的发现和探索：L-丙氨酰-L-谷氨酰胺

L-丙氨酰-L-谷氨酰胺（Ala-Gln）是一种广泛应用于医疗和营养领域的二肽。本研究发现了Ala-Gln的两种新晶型（晶型III和晶型IV）和DMSO溶剂化物晶型（S _DMSO），通过拉曼光谱和粉末X射线衍射（PXRD）将其与已知晶型进行了区分。获得了三种新固体形式的单晶结构。此外，还解决了据我们所知尚未报道的已知形式的晶体结构数据：形式II、二水合物形式(2H)和乙醇溶剂化物形式(S _{EtOH )。}结果表明，Ala-Gln固体形式存在四种分子排列和骨架。分子排列和细胞参数的比较表明，III、2H和S _EtOH晶型是同构的。DMSO溶剂化物的氢键网络与晶型II、III和IV不同。通过比较Ala-Gln三种多晶型物的堆积密度、晶格能和热分析结果，堆积密度和晶格能的顺序与分解焓一致。除此之外，还发现溶剂化物的晶体形状在除去溶剂后可以保留。