Objectives: The growth of macromolecular crystal structure determination and the increasing number of experiments performed at synchrotron facilities require that more efficient use is made of these infrastructures. Obtaining the phases of the structure factors is a limitation in structure determination second only to obtaining crystals. The multiple-wavelength anomalous dispersion (MAD) and optimised single isomorphous replacement with anomalous signal (SIRAS) techniques offer a general method of overcoming this problem. It is therefore desirable to perform diffraction experiments at energies close to the absorption edges of a wide variety of elements.
The objectives of the proposal are:
-to make available to the European crystallographic user community the ability to use xenon (Xe) and other elements for MAD or optimised SIRAS experiments at Kand L absorption edges;
-to make available standard devices for pressurising crystals under high pressures of Xe and other gases;
-to produce a two-dimensional detector appropriate for the recording of diffraction patterns produced with high energy (~40 keV) X-rays. The pixel detector will be based on the use of selenium as a photoconductor;
-to develop computer methods and software by which the experimental data measured at these energy extremes can be correctly and optimally processed;
-to develop computational methodologies to optimise the quality of the phase information obtained;
-to establish whether at high Xe pressures solvent contrast experiments can be carried out that can lead to phases for low angle reflections.
Results: The majority of the activities planned for the reporting period have been accomplished, and some are even ahead of the schedule, in particular the development of the prototype detector. Especially work on the low noise-high efficiency version of the prototype detector was planned to start only in the second year of the Project, while work has already started. Additionally, EMBL and Lure can already offer to the external users the possibility to use pressure cells at the beam-lines. This is well ahead of schedule, in which pressure cells available on the beam-lines for external users are planned only for the second half of the contract. The implementation of the kappa-goniometer at Elettra beam-line is by now proceeding according to the schedule. Even so it can be foreseen that the final implementation will delay in part due to long delivery times of Huber as well as on account of the complexity of installation. The installation of the new premirror on the EMBL Hamburg wiggler beam-lines is progressing a bit slower than planned, since the design of the mirror housing and arranging a time schedule require extensive discussions with staff at HASYLAB. In the interim it has been possible to investigate the use of the undulator beamline on the PETRA for diffraction experiments at both 25keV and 35keV. The tests of the Elettra beam-line showed that it is available for diffraction experiments in the wavelengths range 0.8 and 3.0 Å with no modifications to the beam-line optics.
Kristina Djinovic Carugo, Experimental Division, ss 14, Km. 163,5 in Area Science Park Basovizza, Trieste 34012, Italy