Quantitative characterization of weak interactions

托莱多大学的A. Alan Pinkerton教授和Elizabeth Zhurova博士将利用先进的、高分辨率的x射线晶体学技术，通过化学结构、动力学和机制项目资助的这一奖项，定量表征固态中原子或分子之间重要的弱相互作用。电子密度分布将由单晶散射的x射线的强度确定，并通过将原子中心多极膨胀的参数拟合到观测数据来量化。将研究先前从结构数据中确定的一系列分子内和分子间相互作用，其中许多具有明显低于范德华半径总和的“非键”距离。目前已经确定了20种不同固体分子中20种不同原子对之间的潜在相互作用。这项研究的信息将为材料设计/晶体工程和生物配体受体结合/细胞信号传导等广泛的科学领域提供新的见解。所有材料的性质都与原子和分子之间电子的分布密切相关。例如，金刚石和石墨完全由碳原子组成，但性质却截然不同，金刚石非常坚硬，而石墨是一种软润滑剂。这很容易理解，因为金刚石中的电子分布导致三维上的强共价键，而石墨在二维上是强键，在三维上是弱键。几代化学家已经认识到强化学键的重要性，通过理论和实验对其进行表征是教科书的材料。弱相互作用的重要性，除了氢键之外，迄今为止还没有使用x射线衍射技术系统地研究过，它代表了化学研究的一个新的方向。这一追求将使研究生和博士后获得低温学和高分辨率x射线晶体学方面的专业培训。低温数据收集和分析的新方法，以及随后培训其他人的讲习班，将推动实验可获得的极限。这个项目也将被整合到一个向高中生介绍晶体学科学的推广计划中。

Through this award, funded by the Chemical Structure, Dynamics, and Mechanisms Program of the Division of Chemistry, Prof. A. Alan Pinkerton and Dr. Elizabeth Zhurova from the University of Toledo, will quantitatively characterize important weak interactions between atoms or molecules in the solid state using advanced, high resolution, X-ray crystallographic techniques. The electron density distribution will be determined from the intensities of the X-rays scattered from single crystals, and quantified by fitting the parameters of an atom-centered multipole expansion to the observed data. A range of intra- and inter-molecular interactions that have been previously identified from structural data, many with "non-bonded" distances significantly below the sum of the Van der Waals radii, will be studied. Currently potential interactions between 20 different atom pairs have been identified for 20 different molecular solids. Information from this study will provide new insight into a wide spectrum of scientific areas such as materials design/crystal engineering and biological ligand-receptor binding/cell signaling. Properties of all materials are intimately related to the distribution of electrons between the atoms and molecules. For example, diamond and graphite are composed entirely of carbon atoms, but have vastly different properties, diamond being very hard, and graphite being a soft lubricant. This is easily understood as the distribution of electrons in diamond leads to strong covalent bonds in three dimensions, whereas graphite is strongly bonded in two dimensions, and weakly bonded in the third. The importance of strong chemical bonds has been recognized by generations of chemists, and their characterization by theory and experiment is the material for text books. The importance of weak interactions, with the exception of hydrogen bonds, has not been systematically studied using X-ray diffraction techniques until now, and represents a new investigative direction in chemistry. This pursuit will allow graduate students and postdoctoral fellows to acquire specialized training in cryogenics, and in high resolution X-ray crystallography. The new methods for cryogenic data collection and analysis, followed by workshops to train others, will push the limits of what is experimentally obtainable. This project will also be integrated into an outreach program to introduce high school students to the science of crystallography.