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My comments: Such observation is very uncommon for metals involved in catalysis by proteins. I have seen quite a few such structures involving Mg, Ca, Fe, Mn, Zn and most of the radiation damage was not at the catalytic metal. In case of Fe once I noticed slight shift in the position of the Fe ion upon exposure. The only metal ion that was significantly affected is Hg, and this was observed in multiple cases. We published results of radiation damage as a function of temperature going down up to 15K. There was some overall reduction of radiation damage, by about factor of 1.7; however, the most of the impact was away from the catalytic site. As a result, relative radiation damage was MORE concentrated at the catalytic site. Metals (Ca and Mn) were not particularly affected at any temperature. We observed that nitrate and iodine scavenge radicals help reduce specific radiation damage. However, increased X-ray absorption by iodine does makes overall situation worse and impact of nitrate was observed only at relatively low doses (up to 2 MGy). Kmetko at all. (2011) were negative about potential of using scavengers in general, including ascorbic acid. Data collection wavelength does not matter! It is an urban legend that shorter wavelength will help. I remember it being debunked two decades ago, and somehow it is still alive. Zbyszek Otwinowski > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Dear Dean, > > this is probably a very common observation: X-rays produce reducing > electrons and as you reduce a metal I imagine it does not like its > chemical environment as much as it did highly charged. > > Everything you can do to avoid radiation damage should help you > prevent the ion to disappear: > - - optimise your strategy to collect a minimal amount of data > - - add vitamin C > - - cool below 100K > - - collect at short wavelength > > When your ion is intended to be used for phasing there are of course > restraints limiting the choice. > > Regards, > Tim > > > On 04/30/2014 12:33 PM, Dean Derbyshire wrote: >> Hi all, Has anyone experienced catalytic metal ions disappearing >> during data collection ? If so, is there a way of preventing it? >> D. >> >> Dean Derbyshire Senior Research Scientist >> [cid:image001.jpg@01CF6470.5FA976D0] Box 1086 SE-141 22 Huddinge >> SWEDEN Visit: Lunastigen 7 Direct: +46 8 54683219 >> www.medivir.com<http://www.medivir.com> >> >> -------------------------------------------------------------------------- >> >> > This transmission is intended for the person to whom or the entity to > which it is addressed and may contain information that is privileged, > confidential and exempt from disclosure under applicable law. If you are > not the intended recipient, please be notified that any dissemination, > distribution or copying is strictly prohibited. If you have received > this transmission in error, please notify us immediately. >> Thank you for your cooperation. >> > > - -- > - -- > Dr Tim Gruene > Institut fuer anorganische Chemie > Tammannstr. 4 > D-37077 Goettingen > > GPG Key ID = A46BEE1A > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.12 (GNU/Linux) > Comment: Using GnuPG with Icedove - http://www.enigmail.net/ > > iD8DBQFTYNSPUxlJ7aRr7hoRAr7WAKCzC7FzqTkcVLILovmIL74OUQlsWQCgg2Yr > xZgDCvIlf5YEWHLTDLiKcRc= > =tp4F > -----END PGP SIGNATURE----- > Zbyszek Otwinowski UT Southwestern Medical Center at Dallas 5323 Harry Hines Blvd. Dallas, TX 75390-8816 Tel. 214-645-6385 Fax. 214-645-6353