Topography

ESF European synchrotron radiation news

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DCI

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Protein Crystallography

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The multireflexion diffractometer based on asp herical drift proportional chamber has been installed on the terminal station of beam line D1 of LURE-DCI with a channel-cut monochromonator (Si 220 or Ge 220); the available beam time was about 200 hours. First, alignment and various tests were performed, during which the wavelength was tuned from 1.20 to 1.85 A. As pointed out by Phillips (Ph.D. Thesis, 1978) and by A. Shaikevitch and Z. Kam (Acta Cryst., A37, (1981) 871), we have found for various protein crystals a very small mosaic spread (typically 0.3 mrad) which indicates a very good long range order; the software was accordingly modified to provide a continuous rotation of the sample during exposures instead of stationary pictures. Finally, partial three dimensional data sets were collected for a crystal ofa metallo-protein (cytochrome C3, a gift of R. Haser, Marseille) at 3 wavelengths around the iron Kedge at 1.74 A. The files are now being analysed and we hope to get useful structural information from such optimized anomalous scattering measurements. Even with the Ge monochromator, the count rate on the detector was less than 105, and focusing would be useful to speed up measurements. An interactive graphic display (Evans-Sutherland MPS system) has just been installed at LURE; the software for macromolecular crystallography FRODO is being implemented by A. Jones.

Topography M. SAUVAGE The second axis of the two-axis spectrometer is now equipped with a Eulerian cradle. The movements ofthe cradle ( 0 , X, ¢) together with the detector motion (2 0 ), are fully"computer controlled. Optical encoders allows for absolute positionning of the 0 circle (accuracy 1 sec of arc) and the 2 0 circle (accuracy 0.1°). In the field of white beam topography, a new compression stage for high temperature creep experiments under controlled atmosphere has been achieved by E. Freis and J. Castaing (Laboratoire de Physique de Mathriaux, CNRS-Bellevue). The first data were collected in October 1981.

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Fig 1 - Preliminary results from the RC 256 EC/I 7 array

Rapid Data Acquisition of Edge Spectra A.M. PLANK, A. FONTAINE, A. JUCHA, M. LEMONNIER, C. WILLIAMS Promising results have been obtained with photodiode arrays. These detectors have been used elsewhere to record dispersive EXAFS spectra produced with the continuous radiation of an X-ray tube operated at 14 kV and a current of 30 mA (Sand, Taniguchi, Yamatera, Chem. Let. (1980) 1285) and for S.A.S. experiments (Borso, Danyluk, Rev. Sci. Ins., December 1980, p. 1669). Very recently we have made a preliminary experiment to test the RC 256 EC/17 array(with one micron thick SiO2 window, manufactured by Reticon) for the synchrotron flux emerging from an almost fiat monochromator, positioned across the Ni-edge. Even with the highly modulated intensity of the incident beam, it has been possible to get the edge and the 9 eV split peaks (analogous to the Cu ones) using a very short