Crystallography electron

Figure Bl.17.11. Reconstructed density of an a,p-tiibulin protein dimer as obtained from electron crystallography (Nogales etal 1997). Note the appearance of the p-sheets ((a), marked B) and the a-helices ((b), marked H) in the density. In particular the right-handed a-helix H6 is very clear. Pictures by courtesy of E Nogales and Academic Press.

Nogales, E., Wolf, S., and Downing, K. H., 1998. Structure of die tnbnlin dimer by electron crystallography. Nature 391 199-203. 

Zeolite structure determination using electron crystallography... 

Electron crystallography offers an alternative approach in such cases, and here we describe a complete structure determination of the structure of polymorph B of zeolite beta [3] using this technique. The clear advantage of electron microscopy over X-ray powder diffraction for elucidating zeolite structures when they only occur in small domains is demonstrated. In order to test the limit of the structural complexity that can be addressed by electron crystallography, we decided to re-determine the structure of IM-5 using electron crystallography alone. IM-5 was selected for this purpose, because it has one of the most complex framework structures known. Its crystal structure was solved only recently after nine years of unsuccessful attempts [4],... 

Given the fact that structure determination by electron crystallography is general, success with these two zeolite structures also has implications for other materials, where... 

Kimura, Y., Vassylyev, D. G., Miyazawa, A. et al. Surface of bacteriorhodopsin revealed by high-resolution electron crystallography. Nature 389 206-211,1997. 

The electron crystallography method (21) has been used to characterize three-dimensional structures of siliceous mesoporous catalyst materials, and the three-dimensional structural solutions of MCM-48 (mentioned above) and of SBA-1, -6, and -16. The method gives a unique structural solution through the Fourier sum of the three-dimensional structure factors, both amplitude and phases, obtained from Fourier analysis of a set of HRTEM images. The topological nature of the siliceous walls that define the pore structure of MCM-48 is shown in Fig. 28. 

Abstract Electron crystallography is the quantitative use of different information by electron scattering to study perfect crystal structures as well as defects and interfaces. The development of electron crystallography is summarized. Electron crystallography is compared with X-ray crystallography. Examples of recent developments in electron crystallography are presented. 

Key words Electron diffraction, crystallographic image processing, 3D reconstruction. Structure factors, ultrafast electron crystallography, aberration corrected electron microscope, oversampling phasing method... 

Since 1990, more and more structures have been solved from HREM images and electron diffraction and more and more scientists have become interested in structure analysis by electron crystallography (Hovmoller 1992 Zou, 1995). This pushed electron crystallography a big step forward. The term electron crystallography was first introduced and soon been accepted. 

In HREM images of inorganic crystals, phase information of structure factors is preserved. However, because of the effects of the contrast transfer function (CTF), the quality of the amplitudes is not very high and the resolution is relatively low. Electron diffraction is not affected by the CTF and extends to much higher resolution (often better than lA), but on the other hand no phase information is available. Thus, the best way of determining structures by electron crystallography is to combine HREM images with electron diffraction data. This was applied by Unwin and Henderson (1975) to determine and then compensate for the CTF in the study of the purple membrane. 

ELECTRON CRYSTALLOGRAPHY HAVE SOME ADVANTAGES OVER X-RAY CRYSTALLOGRAPHY... 

X-ray crystallography is still the best technique for complete and accurate determination of crystal structures. However, electron crystallography has several important advantages over X-ray crystallography ... 

The mechanism by which electrons interact with crystals is different from that of X-rays. X-rays detect electron density distribution in crystals, while electrons detect electrostatic potential distribution in crystals. Electron crystallography may be used for studying some special problems related to potential distribution such as the oxidation states of atoms in the crystal. 

In conclusion, electron crystallography can be used to extend the range of samples amenable to structure analysis beyond those which can be studied by single crystal X-ray diffraction. Moreover, HREM images can supply some initial low resolution phases for X-ray diffraction which may aid in phase determination in X-ray crystallography. 

We have reconstructed the 3D structure of a complex quasicrystal approximant v-AlCrFe (P6 m, a = 40.687 and c = 12.546 A) (Zou et al, 2004). Due to the huge unit cell, it was necessary to combine crystallographic data from 13 projections to resolve the atoms. Electron microscopy images containing both amplitude and phase information were combined with amplitudes from electron diffraction patterns. 124 of the 129 unique atoms (1176 in the unit cell) were found in the remarkably clean calculated potential maps. This investigation demonstrates that inorganic crystals of any complexity can be solved by electron crystallography. 

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