X射线衍射和电子晶体学在解决复杂结构问题中的应用。

PubMed ID
发表日期 2017年11月

原始出处 化学研究记述
Accounts of chemical research
作者 Li  Jian  Sun  Junliang 

文献标题 X射线衍射和电子晶体学在解决复杂结构问题中的应用。
Application of X-ray Diffraction and Electron Crystallography for Solving Complex Structure Problems.

文献摘要

自然界中的所有晶体材料,无论是无机的、有机的还是生物的、宏观的还是微观的,都有其自身的化学和物理性质,这在很大程度上取决于它们的原子结构。因此,结构测定在化学、物理、材料科学等领域具有极其重要的意义。近几个世纪来,许多结构测定技术得到了发展。其中应用最广泛的是X射线晶体学(单晶X射线衍射(SCXRD)和粉末X射线衍射(PXRD)),它仍然是晶体材料结构测定中最重要的技术。尽管SCXRD和PXRD在许多情况下都是成功的,但由于许多原因限制了它们的应用,如纳米晶体的SCXRD、共生和缺陷的SCXRD以及复杂结构、多相样品、杂质、峰重叠等的PXRD。另一种最有价值的结构测定技术是电子晶体学(EC)。以电子为探针,单用EC也可用于结构测定,特别是对于太小而不能用SCXRD研究或太复杂而不能用PXRD研究的晶体。由于电子与物质的相互作用比X射线强得多,因此可以从纳米晶体中获得电子衍射(ED)图案和高分辨率透射电子显微镜(HRTEM)图像。然而,收集一套完整的ED模式或记录一个好的HRTEM图像需要相当多的电子显微镜和结晶学操作方面的专业知识。电子与材料之间的强相互作用也会导致动力学效应和束流损伤。这些困难使得从ED图像和HRTEM图像中确定结构变得不简单。近年来,人们发展了两种三维电子衍射技术:自动电子衍射层析成像(ADT)和旋转电子衍射(RED),它们以自动化的方式进行数据采集。尽管新发展的三维电子衍射技术(ADT,RED)中的动力学效应显著降低,但对于某些结构,由于光束损伤,在获得初始模型时仍然存在问题。X射线衍射法和EC法都是一种有效的方法,但都有其局限性。在许多复杂的情况下,单靠一种技术不足以解决晶体结构问题,而提供互补结构信息的不同技术必须相互支持才能完成结构的确定。本文综述了X射线衍射(PXRD和SCXRD)和EC(HRTEM和ED)在结构测定中的优缺点,综述了X射线衍射和EC在解决峰重叠、杂质、假对称和孪生等复杂结构问题中的应用,本文还简要介绍了结构测定的一些最新进展,即电致发光显示氢的位置,三维电子衍射显示蛋白质晶体结构溶液,X射线自由电子激光(XFEL)测定结构。


All crystalline materials in nature, whether inorganic, organic, or biological, macroscopic or microscopic, have their own chemical and physical properties, which strongly depend on their atomic structures. Therefore, structure determination is extremely important in chemistry, physics, materials science, etc. In the past centuries, many techniques have been developed for structure determination. The most widely used one is X-ray crystallography (single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD)), and it remains the most important technique for structure determination of crystalline materials. Although SCXRD and PXRD are successful in many cases, a number of reasons limit their applications, such as SCXRD for nanosized crystals, intergrowth, and defects and PXRD for complex structures, multiphasic samples, impurities, peak overlaps, etc. Another most valuable technique for structure determination is electron crystallography (EC). With the electron as a probe, EC alone can also be used for structure determination, especially for crystals that are too small to be studied by SCXRD or too complex for PXRD. As electrons interact much more strongly with matter than X-rays do, both electron diffraction (ED) patterns and high-resolution transmission electron microscopy (HRTEM) images can be obtained from nanosized crystals. However, collecting a complete set of ED patterns or recording a good HRTEM image requires considerable expertise on the operation of electron microscopes and crystallography. The strong interactions between electrons and materials can also lead to dynamical effects and beam damage. These difficulties make structure determination from ED patterns and HRTEM images not straightforward. Recently, two three-dimensional (3D) electron diffraction techniques, automated electron diffraction tomography (ADT) and rotation electron diffraction (RED), have been developed, which perform the data collection in an automated manner. Although the dynamical effects in the newly developed 3D electron diffraction techniques (ADT, RED) are reduced significantly, for some structures there are still problems with obtaining an initial model because of beam damage. The X-ray diffraction and EC methods discussed above are both powerful techniques but have their own limitations. In many complicated cases, one technique alone is not enough to solve the crystal structure, and different techniques that supply complementary structural information have to support each other for the complete structure determination. In this Account, we provide a summary of the advantages and disadvantages of X-ray diffraction (PXRD and SCXRD) and EC (HRTEM and ED) for structure determination and include a review of applications of X-ray diffraction and EC for solving complex structure problems such as peak overlap, impurities, pseudosymmetry and twinning, disordered frameworks, locating guests, aperiodic structures, etc. Some of the latest advances in structure determination are also presented briefly, namely, revealing hydrogen positions by ED, protein crystal structure solution by 3D electron diffraction, and structure determination using an X-ray free electron laser (XFEL).


获取全文 10.1021/acs.accounts.7b00366