School of Engineering, The University of Edinburgh, The King's Buildings, Sanderson Building, Mayfield Road, Edinburgh EH9 3JL, United Kingdom.
J Phys Chem B. 2022 Nov 3;126(43):8882-8891. doi: 10.1021/acs.jpcb.2c04489. Epub 2022 Oct 25.
The importance of the formation of giant clusters in solution, in nature and industry, is increasingly recognized. However, relatively little attention has been paid to the formation of giant clusters in solutions of small, relatively soluble but nonamphiphilic molecules. In this work, we present a general methodology based on molecular dynamics that can be used to investigate such systems. As a case study, we focus on the formation of apparently stable clusters of pentaethylenehexamine (PEHA) in water. These clusters have been used as templates for the construction of bioinspired silica nanoparticles. To better understand clustering in this system, we study the effect of PEHA protonation state (neutral, +1, and +2) and counterion type (chloride or acetate) on PEHA clustering in dilute aqueous solutions (200 and 400 mM) using large-scale classical molecular dynamics. We find that large stable clusters are formed by singly charged PEHA with chloride or acetate as the counterion, although it is not clear for the case with acetate whether bulk phase separation, that might lead to precipitation, would eventually occur. Large clusters also appear to be stable for doubly charged PEHA with acetate, the less soluble counterion. We attribute this behavior to a form of complex coacervation, observed here for relatively small and highly soluble molecules (PEHA + counterion) rather than the large polyions usually found to form such coacervates. We discuss whether this behavior might also be described by an effective SALR (short-range attraction, long-range repulsion) interaction. This work might help future studies of additives for the design of novel bioinspired templated nanomaterials and of giant clustering in small-molecule solutions more generally.
巨型团簇在溶液中的形成，无论是在自然界还是工业领域，其重要性都日益受到人们的认可。然而，人们相对较少关注于在小而具有一定可溶性但非两亲性分子的溶液中形成巨型团簇。在本工作中，我们提出了一种基于分子动力学的通用方法，可用于研究此类体系。作为案例研究，我们专注于在水中形成五亚乙基六胺（PEHA）的显然稳定的团簇。这些团簇已被用作仿生二氧化硅纳米颗粒构建的模板。为了更好地理解该体系中的聚集现象，我们研究了 PEHA 质子化状态（中性、+1 和+2）和抗衡离子类型（氯化物或乙酸盐）对在稀水溶液（200 和 400mM）中 PEHA 聚集的影响，使用了大规模经典分子动力学。我们发现，带一个电荷的 PEHA 与氯化物或乙酸盐作为抗衡离子可以形成大而稳定的团簇，尽管对于乙酸盐的情况，是否会发生可能导致沉淀的体相分离尚不清楚。带两个电荷的 PEHA 与乙酸盐（溶解度较低的抗衡离子）也似乎形成大的团簇。我们将这种行为归因于一种复杂凝聚的形式，在此观察到相对较小且高度可溶性的分子（PEHA+抗衡离子），而不是通常用于形成这种凝聚物的大聚离子。我们讨论了这种行为是否也可以用有效 SALR（短程吸引，长程排斥）相互作用来描述。这项工作可能有助于未来对用于设计新型仿生模板纳米材料的添加剂的研究以及对小分子溶液中巨型团簇的研究。
