Understanding Intermolecular Interactions using Metastable Clusters and Assemblies

分子粘在一起就形成了固体。 然而，对于两个分子的所有取向，吸引力的强度并不相同，因为分子的某些部分比其他部分更粘。 因此，即使是简单的分子也具有复杂的相互作用，使得难以基于单个分子的化学结构来预测晶体的结构。在化学系大分子、超分子和纳米化学项目的支持下，S。圣母大学的亚历克斯·坎德尔正在探索分子是如何从溶液中结晶出来的。从该项目中获得的见解正在推进我们对材料科学的理解，并对制药业产生深远的商业影响。 该项目包括培养研究生，以及让大学生和高中生参与科学研究。通过将含有小有机分子的微升大小的溶液液滴注入真空中，形成分子簇和晶体。随着溶剂蒸发，形成固体结构，沉积在干净的基底上，并使用扫描隧道显微镜（STM）进行表征。 沉积方法捕获了一系列的几何形状和分子构型，而不仅仅是热力学最小自由能状态附近的结构。表征多个亚稳态结构的能力提供了对由两个或更多个分子上的几个相互作用的官能团所产生的复杂势面的详细了解。 实验方法比较了一系列化学相似的系统，以确定对于给定的分子，每个特定的官能团如何有助于分子间的相互作用，最终控制簇和更大结构的形成。 还将分子尺度STM图像与使用电喷雾电离质谱法对气相离子团簇进行的测量进行比较，并根据团簇几何形状的理论计算来检查两者的结果。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Solids are formed when molecules stick together. The strength of the attraction is not the same for all orientations of two molecules, however, as some parts of a molecule are stickier than others. Thus, even simple molecules have complex interactions that make it difficult to predict the structure of a crystal based on the chemical structure of the individual molecules. With support from the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professor S. Alex Kandel of the University of Notre Dame is exploring how molecules crystallize from solution. The insights gained from the project are advancing our understanding of materials science, as well as have far-reaching commercial implications in the manufacture of pharmaceuticals. The project includes training of graduate students, and involvement of undergraduate and high-school students in scientific research.Molecular clusters and crystals are formed by injecting microliter-sized droplets of solutions containing small organic molecules into vacuum. As the solvent evaporates, solid structures are formed, deposited onto clean substrates, and characterized using scanning tunneling microscopy (STM). The deposition method captures a range of geometries and molecular configurations, not just the structures near the thermodynamic minimum-free-energy state. The ability to characterize multiple metastable structures provides detailed insight into the complex potential surface created by several interacting functional groups on two or more molecules. The experimental approach compares a range of chemically similar systems to determine how, for a given molecule, each specific functional group contributes to the intermolecular interactions that ultimately control the formation of clusters and larger structures. Molecular-scale STM images are also compared with measurements made on gas-phase ionic clusters using electrospray-ionization mass spectrometry, and the results of both are examined in the light of theoretical calculations of cluster geometries.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.