Direct Methods in Organic Electron Crystallography

道格拉斯·多塞特由化学部理论和计算化学项目和材料研究部聚合物项目共同资助，继续他对电子结晶学直接方法的研究。该研究计划的总体主旨是继续将直接相变方法应用于电子结晶学。当前项目的具体目标是：1)改进收集更准确的电子衍射强度数据的方法；2)优化使用直接方法处理欠采样互易晶格；以及3)开发绕过与多次散射问题相关的困难的改进程序。尽管该建议主要集中在方法学的开发上，但也建议在小的有机体系，如三苯、TCNQ、芘、四烯和乙二烯，以及聚合物体系，如对氧苯甲酸酯的晶须晶体、蜘蛛拉线丝绸和聚四氟乙烯的取向膜上，提出各种应用。X射线衍射对化学和材料科学领域产生了巨大的影响。它提供了原子级分子结构的直接实验探针。然而，对于许多重要的有机化合物，只能生长出不适合用X射线衍射进行研究的小晶体。电子结晶学为研究这类化合物提供了一种强有力的替代方法，前提是可以克服一些技术困难。多塞特在这一领域的工作旨在将这种替代传统X射线结晶学的方法改进到精确和相对容易使用的程度。

Douglas Dorset is jointly supported by a grant from the Theoretical and Computational Chemistry Program in the Chemistry Division and the Polymers Program in Division of Materials Research to continue his studies of direct methods for electron crystallography. The overall thrust of the research program is to continue the application of direct phasing methods to electron crystallography. Specific goals of the current project are: 1) to improve methods for collecting more accurate electron diffraction intensity data; 2) to optimize the use of direct methods for handling undersampled reciprocal lattices; and 3) to develop refinement procedures which circumvent the difficulties associated with multiple scattering problems. Although the proposal is primarily focused on methodology development, various applications are also proposed on small organic systems such as triphenylene, TCNQ, pyrene, quaterrylene and anthanthrene, and polymeric systems such as whisker crystals of p-oxybenzoate, spider drag line silk, and oriented films of poly(tetrafluoroethylene). X-ray diffraction has had a tremendous impact on the fields of Chemistry and Material Science. It provides a direct experimental probe of molecular structure at the atomistic level. However, for many important organic compounds, only small crystals can be grown that are unsuitable for investigation by X-ray diffraction. Electron crystallography presents a powerful alternative for studying such compounds providing that a number of technical difficulties can be overcome. Dorset's work in this area is directed at improving this alternative to conventional X-ray crystallography to the point where it is precise and relatively easy to use.