Dear Dean (and Andrew),
I am certainly no radiation damage guru, but at the RD8 Workshop in
Hamburg 3 weeks ago (http://www.rd-eight.org/RD8-01/) I heard a talk by
Pernille Harris about the photoreduction by X-rays of Cu(II) to Cu(I) in a
Cu-insulin crystal.
Tim's description couldn't be more appropriate: Cu(II) likes e.g.
square-planar or square-bipyramidal coordination, while Cu(I) likes
tetrahedral coordination; so a Cu(II) atom photoreduced to a Cu(I) might
find itself acutely uncomfortable in its previous surroundings and want to
rearrange its ligands. If its presence in the protein is the outcome of an
evolutionary choice to enable it to carry out e.g. some electron transport
function, a rearrangement upon a change of oxidation state can be expected
to be be well choreographed, and the ligand rearrangement quite orderly.
However if the catalytic role of that metal is predicated on a fixed
oxidation state, the environment of the photoreduced metal atom could become
highly disordered: that atom and the surrounding ones would then end up with
very high B-factors and would look as if they had "disappeared".
Do get in touch with the real gurus, though, as listed on the RD8 page
indicated above.
With best wishes,
Gerard.
--
On Wed, Apr 30, 2014 at 01:08:59PM +0100, Andrew Leslie wrote:
> Can the radiation damage gurus comment on this ? I know there is a problem
with radiation damage changing the valence state of metals, but I don't
remember hearing about the metal actually being lost due to radiation
damage. Is this really common ?
>
> Thanks,
>
> Andrew
>
> On 30 Apr 2014, at 11:46, Tim Gruene <t...@shelx.uni-ac.gwdg.de> wrote:
>
> > -----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>
> >>
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> >
> > - --
> > - --
> > Dr Tim Gruene
> > Institut fuer anorganische Chemie
> > Tammannstr. 4
> > D-37077 Goettingen
> >
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> >
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> > xZgDCvIlf5YEWHLTDLiKcRc=
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> > -----END PGP SIGNATURE-----
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