Abstract The binary phase diagrams of Sulfanilamide-Urea (SN-U) and Sulfacetamide-Urea (SC-U) were measured using differential scanning calorimetry technique (DSC). Both examined mixtures were found to form simple binary eutectics. The limited miscibility in the solid state observed by DSC, proving inability of co-crystallization in new multi-molecular form, was also confirmed using PXRD and FTIR-ATR measurements of solid dispersions obtained via liquid assisted co-grinding. The lack of intermolecular complex formation in the crystals does not imply the lack of interactions in the liquid state. Detailed characteristics of potential homo- and hetero-molecular pairs were offered using ab initio and the first principle quantum chemistry computations. The obtained results happened to be strongly dependent on the applied level of theory. The importance of including the zero point energy contributions and electron correlation corrections was emphasized. It was found that the mole fraction of hetero-complexes with urea is the highest among all other constituents of studied systems at their eutectic points. Finally, the importance of intermolecular interaction leading to complexes formation in the liquid state at saturated position was documented by computed values of solvation Gibbs free energy. Based on computed trends it was inferred that the eutectic mixtures can be interpreted as such equilibria for which mutual solvation of all components is maximized.

中文翻译：

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尿素二元混合物与磺胺和磺胺乙酰胺的固液平衡和分子间相互作用的研究

摘要 使用差示扫描量热技术(DSC) 测量了磺胺-尿素(SN-U) 和磺胺-尿素(SC-U) 的二元相图。发现两种检查的混合物形成简单的二元共晶。通过 DSC 观察到的固态混合性有限，证明无法以新的多分子形式共结晶，使用 PXRD 和 FTIR-ATR 测量通过液体辅助共研磨获得的固体分散体也证实了这一点。晶体中缺乏分子间复合物的形成并不意味着在液态下缺乏相互作用。使用 ab initio 和第一原理量子化学计算提供了潜在的同质和异质分子对的详细特征。所获得的结果恰好强烈依赖于理论的应用水平。强调了包括零点能量贡献和电子相关校正的重要性。发现与尿素的杂络合物的摩尔分数在所研究系统的所有其他成分中在其共晶点处最高。最后，通过溶剂化吉布斯自由能的计算值证明了分子间相互作用导致饱和位置液态络合物形成的重要性。根据计算的趋势推断，共晶混合物可以解释为所有组分的相互溶剂化最大化的平衡。发现与尿素的杂络合物的摩尔分数在所研究系统的所有其他成分中在其共晶点处最高。最后，通过溶剂化吉布斯自由能的计算值证明了分子间相互作用导致饱和位置液态络合物形成的重要性。根据计算的趋势推断，共晶混合物可以解释为所有组分的相互溶剂化最大化的平衡。发现与尿素的杂络合物的摩尔分数在所研究系统的所有其他成分中在其共晶点处最高。最后，通过溶剂化吉布斯自由能的计算值证明了分子间相互作用导致饱和位置液态络合物形成的重要性。根据计算的趋势推断，共晶混合物可以解释为所有组分的相互溶剂化最大化的平衡。