title: Towards phasing using high X-ray intensity.
abstract: X-ray free-electron lasers (XFELs) show great promise for macromolecular structure determination from sub-micrometre-sized crystals, using the emerging method of serial femtosecond crystallography. The extreme brightness of the XFEL radiation can multiply ionize most, if not all, atoms in a protein, causing their scattering factors to change during the pulse, with a preferential 'bleaching' of heavy atoms. This paper investigates the effects of electronic damage on experimental data collected from a Gd derivative of lysozyme microcrystals at different X-ray intensities, and the degree of ionization of Gd atoms is quantified from phased difference Fourier maps. A pattern sorting scheme is proposed to maximize the ionization contrast and the way in which the local electronic damage can be used for a new experimental phasing method is discussed.
authors.affiliation: Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY , Notkestrasse 85, Hamburg, 22607, Germany ; Department of Physics, University of Hamburg , Luruper Chaussee 149, Hamburg, 22761, Germany.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Galli
authors.affiliation: Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY , Notkestrasse 85, Hamburg, 22607, Germany ; The Hamburg Centre for Ultrafast Imaging , Luruper Chaussee 149, Hamburg, 22761, Germany.
authors.forename: Sang-Kil
authors.initials: SK
authors.lastname: Son
authors.affiliation: Biomolecular Mechanisms, MPI for Medical Research , Jahnstrasse 29, Heidelberg, 69120, Germany.
authors.forename: Thomas R M
authors.initials: TR
authors.lastname: Barends
authors.affiliation: Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY , Notkestrasse 85, Hamburg, 22607, Germany.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: White
authors.affiliation: Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY , Notkestrasse 85, Hamburg, 22607, Germany.
authors.forename: Anton
authors.initials: A
authors.lastname: Barty
authors.affiliation: Max Planck Institute for Medical Research , Jahnstrasse 29, Heidelberg, 69120, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Botha
authors.affiliation: SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, 94025, USA.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Boutet
authors.affiliation: Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY , Notkestrasse 85, Hamburg, 22607, Germany ; Department of Physics and Astronomy, Uppsala University , Box 516, Uppsala, 75120, Sweden.
authors.forename: Carl
authors.initials: C
authors.lastname: Caleman
authors.affiliation: Max Planck Institute for Medical Research , Jahnstrasse 29, Heidelberg, 69120, Germany.
authors.forename: R Bruce
authors.initials: RB
authors.lastname: Doak
authors.affiliation: EMBL, Grenoble Outstation , Rue Jules Horowitz 6, Grenoble, 38042, France.
authors.forename: Max H
authors.initials: MH
authors.lastname: Nanao
authors.affiliation: Max Planck Institute for Medical Research , Jahnstrasse 29, Heidelberg, 69120, Germany.
authors.forename: Karol
authors.initials: K
authors.lastname: Nass
authors.affiliation: Max Planck Institute for Medical Research , Jahnstrasse 29, Heidelberg, 69120, Germany.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Shoeman
authors.affiliation: Department of Physics and Astronomy, Uppsala University , Box 516, Uppsala, 75120, Sweden ; Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University , Box 596, Uppsala, 75124, Sweden.
authors.forename: Nicusor
authors.initials: N
authors.lastname: Timneanu
authors.affiliation: Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY , Notkestrasse 85, Hamburg, 22607, Germany ; The Hamburg Centre for Ultrafast Imaging , Luruper Chaussee 149, Hamburg, 22761, Germany ; Department of Physics, University of Hamburg , Juniungstrasse 6, Hamburg, 20355, Germany.
authors.forename: Robin
authors.initials: R
authors.lastname: Santra
authors.affiliation: Max Planck Institute for Medical Research , Jahnstrasse 29, Heidelberg, 69120, Germany.
authors.forename: Ilme
authors.initials: I
authors.lastname: Schlichting
authors.affiliation: Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY , Notkestrasse 85, Hamburg, 22607, Germany ; Department of Physics, University of Hamburg , Luruper Chaussee 149, Hamburg, 22761, Germany ; The Hamburg Centre for Ultrafast Imaging , Luruper Chaussee 149, Hamburg, 22761, Germany.
authors.forename: Henry N
authors.initials: HN
authors.lastname: Chapman
keywords: X-ray free-electron lasers; electronic damage; high XFEL doses; high-intensity phasing; radiation damage; serial femtosecond crystallography