Berlin 2005 – scientific programme

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AKB: Biologische Physik

AKB 200: Poster Session II

AKB 200.55: Poster

Tuesday, March 8, 2005, 17:00–19:00, Poster TU C

Theoretical investigations of radiation damage in protein crystals produced by X-rays — •Melanie Zehnder, Ivan Vartaniants, and Edgar Weckert — HASYLAB at DESY, Notkestrasse 85, 22607 Hamburg

The data quality and the achievable resolution in X-ray crystal-structure analysis of protein crystals is limited by radiation damage in many cases. The aim of the investigation is a better quantitative understanding of the damage caused by the absorbed photon and the subsequent processes in proteins by Monte-Carlo simulations.

The dominating inelastic interaction for X-ray photons of usual energies with an atom in the protein is the photo-effect, in which photo-electrons with nearly the incoming photon energy and low energy Auger-electrons are created. At higher energies the Compton scattering becomes more and more dominant. In this case an electron of few keV is produced and most of the energy is kept by the photon. For normal protein crystal sizes of around 0.3 mm this photon interacts in general just once. In contrast, the produced electrons have a high inelastic cross-section, so that the resulting electron cascade has a high damage-potential.

By means of a Monte-Carlo approach the electron cascade and the spatial distribution of ions and excited atoms produced by inelastic interactions are analyzed in order to obtain more quantitative information of the damage. Furthermore, the average time for a cascade produced by each photon is evaluated. One of the aims of these investigations is to find the optimum data collection energy dependent on a given chemical composition.