Direct Methods in Organic Electron Crystallography

布法罗医学基金会的道格拉斯多塞特博士得到了 从理论和计算化学计划在授予 化学部门和材料部门的聚合物计划 研究继续他的研究在发展直接的方法 用于有机化合物和聚合物的电子晶体学。 他正在与赫伯·豪普特曼（Herb Hauptman，1985年诺贝尔奖获得者）合作。 化学与杰罗姆卡勒的相关工作），以制定一个直接定相 电子晶体学数据的从头计算方法 未知的晶体结构。 正在采取若干步骤， 提高技术的可靠性，包括：1）提高数字 自动化程序的优点是更能抵抗动态 散射; 2）开发更可靠的定相程序; 3） 合并多切片计算以改进细化; 4） 更好地理解晶体学的局限性 相位确定;以及5）增加更高电压源的使用 以确保数据更接近单次散射极限。 应用 包括：1）聚（亚乙基）取向膜; 2）小 分子如C60和C70、铜酞菁和铜 全氟邻苯二甲酸酯，和3）被酯取代的烷烃链， 醚、胺和酮基。 到目前为止，最广泛使用的结构工具是X射线晶体学。 它被广泛使用的原因之一是技术 已经被开发用于自动地解决相位问题， 系统. 尽管如此，X射线还是有局限性的。 晶体学主要是由于难以获得 合适大小的晶体。 电子晶体学应该提供一个 补充替代X射线衍射的情况下， 技术有问题。 多塞特的工作是试图 改进电子晶体学技术， 将像现在的X射线晶体学一样自动化和简单易用。

Dr. Douglas Dorset, Medical Foundation of Buffalo, is supported by a grant from the Theoretical and Computational Chemistry Program in the Chemistry Division and the Polymers Program in the Division of Materials Research to continue his research in the development of direct methods for use in electron crystallography of organic compounds and polymers. He is working with Herb Hauptman (who shared the 1985 Nobel Prize in Chemistry with Jerome Karle for related work) to develop a direct phasing method for electron crystallographic data for the ab initio determination of unknown crystal structures. A number of steps are being taken to improve the reliability of the technique including: 1) improving a figure of merit for automated procedures that are more resistant to dynamical scattering; 2) developing more reliable phasing procedures; 3) incorporating a multislice calculation to improve refinement; 4) developing a better understanding of the limitations of crystallographic phase determination; and 5) increasing the use of higher voltage sources to ensure data closer to the single scattering limit. Applications include: 1) oriented films of poly (tetrafluorotheylene) ; 2) small molecules such as C60 and C70, copper phthalocyanine and copper perfluorophthalocyanine, and 3) alkane chains substituted with ester, ether, amine and keto groups. By far the most widely used structural tool is X-ray crystallography. One of the reasons for it's widespread use is the fact that techniques have been developed for automatically solving the phase problem for many systems. In spite of this, there are limitations to X-ray crystallography arising primarily from the difficulty of obtaining crystals of suitable size. Electron crystallography should provide a complementary alternative to X-ray diffraction for cases where the latter technique is problematic. Dorset's work is directed at attempting to improve the electron crystallographic technique to the point where it will be as automated and as easy to use as X-ray crystallography now is.