__MAIN_TEXT__
feature-image

Page 15

PSI Scientific Report 2008

PSI-XFEL  13

Protein structure from 2D-crystals Protein structure determines the function of the building blocks of life, and its knowledge permits the intelligent design of drugs to treat genetic diseases. Many clinically relevant proteins are membrane bound. Their 3D crystallization is difficult and requires tedious optimization to yield well-diffracting crystals. With the PSI-XFEL, it should be possible to extract high-resolution structural data from diffraction experiments on two-dimensional crystals (see Figure 4), complementing the techniques of electron diffraction/microscopy [4]. Although each XFEL shot will locally destroy the sample, with a focus spot size of 100 nm and the 100 Hz repetition rate of the PSIXFEL, it will be possible to reposition the sample between Figure 2: Predicted magnetic behaviour [2] at the centre of a Co-nanodisk, illustrating how a magnetic field pulse can change

shots.

the direction of a vortex core from up (red) to down (green).

will be possible to take “snapshots” of the instantaneous magnetization distribution in thin-film nanostructures, and hence to follow this process in detail.

Unstable intermediates in surface catalysis Surface catalytic reactions play a central role in many industrial chemical processes, in clean energy production and in eliminating environmental pollutants. A typical reaction is shown schematically in Figure 3. In the presence of a heated

Figure 4: A high-intensity XFEL pulse scatters on a 2D-membrane protein crystal. Sufficient scattered photons are collected to

substrate, reactant species go through a series of short-lived

allow a structural solution before the pulse locally destroys the

intermediate states, finally emerging as the desired product.

sample [5].

Figure 3 illustrates a possible “THz pump / X-ray absorption spectroscopy probe” XFEL measurement, which will elucidate the chemical nature of intermediate states on a ps-ns time-

References

scale [3].

[1] http://fel.web.psi.ch [2] R. Hertel, S. Gliga, M. Fähnle, C.M. Schneider, Phys. Rev. Lett. 98 117201 (2007); J. Raabe et al., ibid 94 217204 (2005). [3] H. Ogasawara, et al., Proc. 27th FEL Conf. (2005); A. Wokaun and I. Czekaj, private communication. [4] M. van Heel et al., Quarterly Rev. Biophys. 33 307 (2000). [5] C. Kewish, P. Thibault, O. Bunk, F. Pfeiffer, submitted (2009).

Figure 3: The “Haber-Bosch” catalytic process for synthesizing ammonia. At the PSI-XFEL, such a reaction may be initiated with a THz pulse and probed at time τ later with soft X-ray spectroscopy [3].

Profile for Paul Scherrer Institut

Scientific Report 2008  

The whole range of PSI's research in more than 100 pages – this is what the new Scientific Report has to offer. Examples of the latest scien...

Scientific Report 2008  

The whole range of PSI's research in more than 100 pages – this is what the new Scientific Report has to offer. Examples of the latest scien...