Crystallographic techniques synchrotron radiation

The x-ray crystallographic analysis of protein structures is a remarkably successful technique. Since the publication of the first protein structure, that of myoglobin in 1958, many other protein structures have been determined. The resulting structural details often approaching atomic level have led to great insights into enzyme catalysis, hormone function, the organisation of the immune system, the molecular architecture of virus particles and protein synthesis. Why then should such an apparently successful technique need synchrotron radiation ... 

We have said as manybody, before to become synchrotron radiation users, that nothing was better that single crystal X-ray diffraction crystallographic structure. Our story tells that when order and disorder problems are involved, this settlement should be tempered and that SRO techniques have an irreplaceable interest. Indeed, instead of opposing SRO and LRO pictures, we show that it is the comparison of both views which is fruitful in low-dimensional materials, where anisotropy makes the problem easier to solve. We guess that a more systematic combined LRO and SRO... 

In our work, we have used one of these photoisomers, [Ru(S02)(NH3)4(H20)j. [tosylate]2, as a test material in the development of photo-induced X-ray crystallographic techniques at the synchrotron radiation source (SRS) at Daresbury UK. Cop-pens and coworkers had shown previously that the tj -S02 group photo-isomerised to the metastable 17 -802 species upon application of light at 355 nm, with the crystal held at 100K [10, 11], During our tests, we first reproduced this result, and then varied several key experimental parameters to observe and to understand better their effect on the resultant refinement of the light-activated crystal stiucture. 

The main focus of Block s interests was the behavior of surfaces in strong electric fields, which he explored using field emission phenomena, especially field-ion microscopy and field-ion mass spectrometry. Field desorption permitted inferences regarding the electronic properties of surfaces and surface adsorbates, and the atomic scale resolution of the technique allowed very precise local analysis of crystallographically well-defined surfaces. However, it required that the substrate be manufacturable in the appropriate form, i.e. thin, sharp needles. Also, since the photoexcitation of field-ion formation using light, synchrotron radiation or laser pulses (photofield emission) evinced no penetrating power, it was treated as... 

A major recent innovation has been to use substrates that are unreactive but may be activated by, for example, photolysis (see Chapter 6). This has necessitated the introduction of crystallographic procedures that can gather data in fractions of a second, rather than the minutes or hours conventionally used. Conventional protein crystallography uses a beam of monochromatic x-rays. An older technique that has been reintroduced is that of von Laue, which uses a spectrum of polychromatic radiation. An intense beam from a synchrotron, spanning wavelengths from 0.25 to 2.5 A, enables data for the Laue method to be taken over a fraction of a second.46,47... 

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