Pardo L C, McLain S E
Universitat Poltècnica de Catalunya, Grup de Caracteritzacio de Materials (UPC), Avda Eduard Maristany, Spain.
Phys Chem Chem Phys. 2018 Jan 17;20(3):2116-2119. doi: 10.1039/c7cp06072f.
In his comment on a recent publication by us, G. Graziano claims that solubility differences of indole in methanol and water can be rationalized by the reversible work needed to create a cavity in the solvent of the size of the solute, in this case indole. This quantity, he argues, is closely related to the solvent accessible surface area, which is greater for methanol compared with water, thus making indole more soluble in the former solvent. G. Graziano asserts that it is this property which is responsible for the large difference between the solubilities of indole in methanol and water. Further, G. Graziano claims that the differences in excess entropies and in distance distribution functions of indole in methanol and water and in methanol and water as a cosolvent found in our original work (Henao, et al., Phys. Chem. Chem. Phys., 2016, 18, 23006) are too "small" to be able to account for the differences in solubility of the indole molecule. We show in this work that the differences found by us are not small, by displaying some selected distance distribution functions in an alternative way to that described in our original paper. In fact we conclude that the differences in these functions are quantitatively greater than those found by Graziano in his comment. Secondly, we show in this reply that although the increase of the solvent accessible surface area may rationalize the differences in the indole-methanol and indole-water binary systems, and thus the work required for cavity creation, it is insufficient to fully account for the increase of indole solubility in water by the addition of very small quantities of methanol in the ternary system indole-methanol-water. In other words, as stated in our original paper, methanol is actively changing the solvation shell and not just passively increasing the solvent accessible surface area around indole. As a result of these additional analyses, we conclude that our work on the solvation differences of indole in water and methanol successfully captures differences in the solvation shells of both solvents around indole in both binary and ternary systems. Finally, while we do agree that Graziano's calculations are able to capture the role of cavity creation to explain differences in solubility, we think that our results concerning the quantification of changes in molecular interaction should be added to the calculations suggested by him to lead to a full description of the solubility.
在对我们最近发表的一篇文章的评论中，G. Graziano声称，吲哚在甲醇和水中的溶解度差异可以通过在溶剂中形成与溶质（即吲哚）大小相同的空穴所需的可逆功来解释。他认为，这个量与溶剂可及表面积密切相关，甲醇的溶剂可及表面积比水大，因此吲哚在前者溶剂中的溶解度更高。G. Graziano断言，正是这一性质导致了吲哚在甲醇和水中溶解度的巨大差异。此外，G. Graziano声称，我们原始研究（Henao等人，《物理化学化学物理》，2016年，18卷，23006页）中发现的吲哚在甲醇和水中以及在甲醇和水作为共溶剂体系中的过量熵和距离分布函数的差异过于“微小”，无法解释吲哚分子溶解度的差异。在这项工作中，我们通过以与原始论文中不同的方式展示一些选定的距离分布函数，表明我们发现的差异并非微小。事实上，我们得出结论，这些函数的差异在数量上大于Graziano在其评论中发现的差异。其次，我们在本回复中表明，尽管溶剂可及表面积的增加可以解释吲哚 - 甲醇和吲哚 - 水二元体系中的差异，进而解释形成空穴所需的功，但它不足以完全解释在吲哚 - 甲醇 - 水三元体系中加入极少量甲醇后吲哚在水中溶解度的增加。换句话说，正如我们在原始论文中所述，甲醇正在积极改变溶剂化层，而不仅仅是被动地增加吲哚周围的溶剂可及表面积。经过这些额外分析，我们得出结论，我们关于吲哚在水和甲醇中溶剂化差异的研究成功捕捉了二元和三元体系中两种溶剂围绕吲哚的溶剂化层差异。最后，虽然我们确实同意Graziano的计算能够捕捉形成空穴对溶解度差异的解释作用，但我们认为，应该将我们关于分子相互作用变化量化的结果加入到他提出的计算中，以全面描述溶解度。
