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Absorbed dose calculations for macromolecular crystals: improvements to RADDOSE
Karthik S Paithankar1, Robin Leslie Owen, Elspeth F Garman
1Laboratory of Molecular Biophysics, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
Journal of Synchrotron Radiation
|February 26, 2009
Summary
Accurate radiation dose calculations in macromolecular crystallography are improved by accounting for fluorescent photon escape. This refinement is crucial for understanding X-ray damage in protein and nucleic acid crystals.
Area of Science:
- Crystallography
- Structural Biology
- Biophysics
Background:
- Radiation damage is an inherent challenge in macromolecular crystallography.
- Quantifying X-ray-induced damage requires accurate absorbed dose measurements.
- The RADDOSE program is used for calculating absorbed dose in crystals.
Purpose of the Study:
- To present significant improvements to the RADDOSE program.
- To incorporate the probability of fluorescent photon escape into dose calculations.
- To assess the impact of this phenomenon on various crystal types.
Main Methods:
- Enhancement of the RADDOSE program to include fluorescent escape probability.
- Calculation of absorbed dose considering photoelectric absorption and subsequent de-excitation.
- Application of the improved model to crystals containing heavy atoms (iron, uranium, selenium) and nucleic acids.
Main Results:
- The refined RADDOSE program now accounts for energy loss via fluorescent photon escape.
- Fluorescence escape significantly impacts absorbed dose calculations, especially for heavier elements.
- Up to a 27% reduction in calculated absorbed dose was observed for selenomethionine protein crystals irradiated at the selenium K-edge.
Conclusions:
- The inclusion of fluorescent escape provides a more accurate measure of absorbed dose in macromolecular crystallography.
- This refinement is particularly important for crystals containing heavy atoms.
- Improved dose calculations aid in understanding and mitigating radiation damage during X-ray experiments.
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