Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States.
J Phys Chem B. 2021 Jun 24;125(24):6629-6638. doi: 10.1021/acs.jpcb.1c02962. Epub 2021 Jun 15.
Solution structure in liquid-liquid extraction affects the efficacy of separation; however, even for simplified organic phases, structural characterization and attribution of aggregation to intermolecular interactions are fundamental challenges. We investigate water uptake into organic phases for two malonamides commonly applied to actinide and lanthanide separations. Extracted water induces reorganization of the amphiphilic extractant molecules, although we find this rearrangement is not strongly manifested in small-angle X-ray scattering making it challenging to probe without methods such as atomistic simulation. Using a graph theoretic approach to define hydrogen bonded water/malonamide aggregates from molecular dynamics simulations, we find evidence of a characteristic aggregate size by water number that results from geometric accommodation of the surrounding malonamide molecules. This implies a degree of size selectivity inherent to these water-in-oil aggregates. Conversely, we find no evidence of a characteristic size of the aggregates with respect to their malonamide number. By defining a separate graphical representation of self-association of the amphiphilic malonamides, we quantify how water affects the local and nonlocal topology of the malonamide network, providing a basis for characterization of the structure and impact of polar solutes in increasingly complex organic phases.
液-液萃取中的溶液结构会影响分离效果；然而，即使对于简化的有机相，结构特征和聚集归因于分子间相互作用也是基本的挑战。我们研究了两种常用于锕系元素和镧系元素分离的丙二酰胺在有机相中的水合作用。萃取水会引起两亲性萃取剂分子的重新排列，尽管我们发现这种重排并没有在小角 X 射线散射中得到强烈表现，因此如果没有原子模拟等方法，就很难进行探测。我们使用图论方法从分子动力学模拟中定义氢键结合的水/丙二酰胺聚集体，发现了由周围丙二酰胺分子的几何适应性产生的特征聚集体大小的证据，这表明这些油包水聚集体具有一定的尺寸选择性。相反，我们没有发现聚集体的特征尺寸与丙二酰胺的数量有关。通过定义两亲丙二酰胺自组装的单独图形表示，我们量化了水如何影响丙二酰胺网络的局部和非局部拓扑结构，为越来越复杂的有机相中的极性溶质的结构和影响提供了基础。
