Taking Supramolecular Assembly to the Next Level: Assembly of Flexible Molecules with Complex Internal Structure and Chemistry

芝加哥大学的卡尔·弗里德（Karl Freed）获得了化学学部化学理论、模型和计算方法项目的奖励，他研究了分子的平衡自组装成非共价键有序的超分子结构。这种现象在化学、材料科学和生物学中普遍存在，其控制在工业和医学中有许多应用。早期的研究基于忽略分子内部结构细节的模型阐明了这种自发和可逆组织的一般基本原理。目前的工作正在扩展这些理论进展，以解释组装单元的化学结构、几何形状和相互（通常是定向的）相互作用对它们的强烈而微妙的影响。先前发展的晶格簇理论形式被推广到包括(i)强和/或吸引相互作用和（ii）柔性/可变形分子。目标是描述结构化单元的五种定性不同类型的自组装，包括组装成链和网络结构。分子内和分子间结构和热力学的贡献是非相加的，增加了计算挑战，但也与现实的化学关联有关。这一类新的自组装理论使我们能够检验普遍存在的焓-熵补偿现象，在这种现象中，由于预期会产生（反应的）焓的巨大变化而对系统进行的修改，在很大程度上被相应的熵的变化所补偿（反之亦然）。当溶液中的分子聚集在一起并自发组织时，用于工业和医学应用的材料的自下而上制造成为可能。弗里德和他的团队正在开发计算工具，描述在平衡自组装过程中相邻分子的化学联系，他们的工作使这种情况变得更加清晰。不同的结构可能产生，例如链和网络结构，结果可能受到单个分子的形状、振动和旋转行为的影响。这项工作的目标是了解不同分子如何产生不同的结果，并利用这些知识来控制自组装，以便在自下而上的材料设计中充分利用它。

Karl Freed of the University of Chicago is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to investigate equilibrium self-assembly of molecules into non-covalently bonded ordered supramolecular structures. This phenomenon is pervasive in chemistry, materials science, and biology, and its control has numerous applications in industry and medicine. Earlier studies elucidated general underlying principles of this spontaneous and reversible organization based on models that ignored details of the internal structure of the molecules. The current work is extending those theoretical advances to account for the strong and often subtle influence of the chemical structure of the assembling units, their geometrical shapes, and their mutual (often directional) interactions. The Lattice Cluster Theory formalism developed earlier is being generalized to include (i) strong and/or attractive interactions and (ii) flexible/deformable molecules. The goal is to describe five qualitatively different types of self-assembly of structured units, including assembly into chains and network structures. The intramolecular and intermolecular structure and thermodynamics contributions are nonadditive, adding computational challenge but also relevance to realistic chemical association. This new class of self-assembly theories enables examination of the ubiquitous enthalpy-entropy compensation phenomenon, where modification of a system by what is anticipated to produces large changes in the enthalpy (of a reaction) is largely compensated by a corresponding change in the entropy (and vice versa).The bottom-up manufacture of materials for applications in industry and medicine is made possible when molecules in solution come together and organize spontaneously. The circumstances under which this occurs have become clearer from the work of Freed and his group, who are developing computational tools describing the chemical association of neighboring molecules in this process of equilibrium self-assembly. Different structures may result, for example, chains and network structures, and the outcomes can be influenced by the shapes and vibrating and rotating behavior of the individual molecules. The goals of the work are to understand how different outcomes occur for different molecules and to use this knowledge to control self-assembly so that it can be fully exploited in bottom-up material design.