Abstract：
Inspired by the recently proposed cooperative mechanism of hydrotropy, where water molecules mediate the aggregation of hydrotrope around the solute, this work studies the impact of apolar volume and polar group position on the performance of hydrotropes. To do so, the ability of two different families of alkanediols (1,2-alkanediols and 1,n-alkanediols) to increase the aqueous solubility of syringic acid is initially investigated. Interestingly, it is observed that in the dilute region (low hydrotrope concentration), the relative position of the hydroxyl groups of the alkanediols does not impact their performance. Instead, their ability to increase the solubility of syringic acid correlates remarkably well with the size of their alkyl chains. However, this is not the case for larger hydrotrope concentrations, where 1,2-alkanediols are found to perform, in general, better than 1,n-alkanediols. These seemingly contradictory findings are reconciled using theoretical and experimental techniques, namely the cooperative model of hydrotropy and chemical environment probes (Kamlet-Taft and pyrene polarity scales). It is found that the number of hydrotropes aggregated around a solute molecule does not increase linearly with the apolar volume of the former, reaching a maximum instead. This maximum is discussed in terms of competing solute-hydrotrope and hydrotrope-hydrotrope interactions. The results suggest that hydrotrope self-aggregation is more prevalent in 1,n-alkanediols, which negatively impacts their performance as hydrotropes. The results reported in this work support the cooperative model of hydrotropy and, from an application perspective, show that hydrotropes should be designed taking into consideration not only their apolar volume but also their ability to stabilize their self-aggregation in water, which negatively impacts their performance as solubility enhancers.
摘要：
受最近提出的水溶协同机制的启发，水分子介导溶质周围水溶助长剂的聚集，这项工作研究了非极性体积和极性基团位置对水溶助长剂性能的影响。要做到这一点，初步研究了两种不同链烷二醇家族（1,2-链烷二醇和1,n-链烷二醇）增加丁香酸水溶性的能力。有趣的是,观察到在稀释区域(低水溶助长剂浓度)，链烷二醇的羟基的相对位置不影响它们的性能。相反，它们增加丁香酸溶解度的能力与其烷基链的大小密切相关。然而,对于更大的水溶助长剂浓度，情况并非如此，其中发现1,2-链烷二醇起作用，总的来说,优于1，正链烷二醇。这些看似矛盾的发现通过理论和实验技术得以调和，即水溶探针和化学环境探针（Kamlet-Taft和pyr极性尺度）的合作模型。发现在溶质分子周围聚集的水溶助长剂的数量不会随前者的非极性体积线性增加，达到最大值。这个最大值是根据竞争的溶质-水溶助长剂和水溶助长剂-水溶助长剂的相互作用来讨论的。结果表明，水溶助长剂自聚集在1，正链烷二醇中更为普遍，这对它们作为水溶助长剂的性能产生了负面影响。这项工作报告的结果支持水溶的合作模型，从应用的角度来看，表明水溶助长剂的设计不仅要考虑它们的非极性体积，还要考虑它们在水中稳定自聚集的能力，这对它们作为溶解度增强剂的性能产生了负面影响。
