Hi Todd,
I believe the blue colour is caused by free electrons produced on irradiation (the size and shape is presumably v. similar to the beam and the colour will not spread beyond 1 um if at 100K) and these will be produced both in the crystals and the cryo solutions. I thought that it was described somewhere in the literature but I cannot find a reference, perhaps someone else knows? Best wishes, Matt.

Todd Geders wrote:

[log in to unmask]" type="cite">Greetings,

On a recent synchrotron trip, certain frozen samples were turning a blue upon exposure to the beam. Attached is a representative image from the crystal-centering camera. If you take snapshots down the crystal, you can make blue dots. Note that it also colors the frozen solution in addition to the crystal.

Details on conditions:

20 micron beam, unattenuated beam, 12.000 keV, GM/CA at APS
Protein solution: 20mM HEPES-KOH pH 7.5, 100mM KCl, 0.1mM EDTA, 2mM DTT
Crystallization solution: 39% w/v PEG 6000, 0.1M HEPES-KOH pH 7.6, 0.2M Ammonium sulfate
Cryo protection: Added 7% v/v glycerol as cryoprotectant

Anyone have any ideas on what is causing the color change?

Todd Geders
University of Minnesota
Dept. of Medicinal Chemistry
308 Harvard St. SE, #8-101WDH
Minneapolis, MN 55455
Office 2-163 WDH / Lab 2-160 WDH
Phone: 612-624-2448

-- 
Matthew Bowler
Structural Biology Group
European Synchrotron Radiation Facility
B.P. 220, 6 rue Jules Horowitz
F-38043 GRENOBLE CEDEX
FRANCE
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