School of Chemistry, University of Southampton, Southampton, UK.
Department of Chemical Engineering and Analytical Science, The University of Manchester, Manchester, UK.
Nature. 2021 Feb;590(7845):275-278. doi: 10.1038/s41586-021-03194-y. Epub 2021 Feb 10.
Molecular self-assembly is the spontaneous association of simple molecules into larger and ordered structures. It is the basis of several natural processes, such as the formation of colloids, crystals, proteins, viruses and double-helical DNA. Molecular self-assembly has inspired strategies for the rational design of materials with specific chemical and physical properties, and is one of the most important concepts in supramolecular chemistry. Although molecular self-assembly has been extensively investigated, understanding the rules governing this phenomenon remains challenging. Here we report on a simple hydrochloride salt of fampridine that crystallizes as four different structures, two of which adopt unusual self-assemblies consisting of polyhedral clusters of chloride and pyridinium ions. These two structures represent Frank-Kasper (FK) phases of a small and rigid organic molecule. Although discovered in metal alloys more than 60 years ago, FK phases have recently been observed in several classes of supramolecular soft matter and in gold nanocrystal superlattices and remain the object of recent discoveries. In these systems, atoms or spherical assemblies of molecules are packed to form polyhedra with coordination numbers 12, 14, 15 or 16. The two FK structures reported here crystallize from a dense liquid phase and show a complexity that is generally not observed in small rigid organic molecules. Investigation of the precursor dense liquid phase by cryogenic electron microscopy reveals the presence of spherical aggregates with sizes ranging between 1.5 and 4.6 nanometres. These structures, together with the experimental procedure used for their preparation, invite interesting speculation about their formation and open different perspectives for the design of organic crystalline materials.
分子自组装是指简单分子自发地组装成较大的有序结构。它是胶体、晶体、蛋白质、病毒和双螺旋 DNA 等多种自然过程的基础。分子自组装激发了人们对具有特定化学和物理性质的材料进行合理设计的策略，是超分子化学中最重要的概念之一。尽管分子自组装已经得到了广泛的研究，但理解控制这一现象的规律仍然具有挑战性。在这里，我们报告了一种简单的福米吡啶盐酸盐，它可以结晶成四种不同的结构，其中两种采用了不寻常的自组装，由氯化物和吡啶离子的多面体簇组成。这两种结构代表了小而刚性有机分子的弗兰克-卡斯珀（Frank-Kasper，FK）相。尽管 FK 相在 60 多年前就在金属合金中被发现，但最近在几类超分子软物质和金纳米晶超晶格中也观察到了 FK 相，并且仍然是最近发现的对象。在这些系统中，原子或分子的球形组装体被包装成具有 12、14、15 或 16 配位数的多面体。这里报道的两种 FK 结构从密集的液相中结晶出来，表现出通常在小而刚性有机分子中观察不到的复杂性。通过低温电子显微镜对前体密集液相的研究揭示了存在尺寸在 1.5 到 4.6 纳米之间的球形聚集体。这些结构，以及用于制备它们的实验过程，引发了对它们形成的有趣推测，并为有机结晶材料的设计开辟了不同的视角。
