I would think there is some chance of positively identifying Ga, if the f'' is significantly higher than the expected values for Fe and Ru.  Ru is also 18 electrons heavier so it may be identifiable based on the real scattering.  In any case, I agree that some more rigorous characterization is required in order to obtain a publishable result.


On Tue, Jul 1, 2014 at 9:17 AM, Tim Gruene <tg@shelx.uni-ac.gwdg.de> wrote:
Dear Aleks,

you won't be able to reliably distinguish between these metals unless you
measure anywhere above and below the absorption of the metal of interest. If you
want to proove that metal is not present in the entire crystal, you could do a
fluorescence scan, but I don't know if there are SAXS machines that work around
an Fe-edge.

Best,
Tim

On Tue, Jul 01, 2014 at 05:44:04PM +0200, Aleksandar Bijelic wrote:
> Dear phenix developers and users,
> I wanted to ask if there is a possibility to considerably distinguish
> betwenn two/three metals. I crystallized an iron-binding protein
> (transferrin in apo form) with a Ru- and Ga-compound. I see density in the
> metal-binding site which should come from the Ru/Ga metal since
> crystallization was done with the apo-form, but nevertheless I need to
> prove this. The wavelength of the X-ray was 1.02 Angstrom and the
> respective f''and f' values for the metals are +1.66e/+0.30e (Fe),
> +1.62/-0.5 (Ru) and +2.95/-0.76 (Ga). Is it possible to distinguish
> between Ru/Ga and Fe and thus to prove that Fe was not bound? The
> resolution is moderate with 3.1 angstrom and all metals are able to
> exhibit the same coordination geometry, thus you cannot distinguish
> according to the geometry. Unfortunately, I was also not able to measure
> the crystal with multiple wavelenghts because the crystals were very
> fragile. I hope you can help me and give me some advice. Thank you in
> advance.
>
> Best Regards,
>
> Aleks
>
>
> --
> Aleksandar Bijelic, MSc.
>
> Institut für Biophysikalische Chemie
> Universität Wien
>
> Althanstrasse 14
> 1090 Wien
>
> Tel: +43 1 4277 52536
>
> e-Mail:aleksandar.bijelic@univie.ac.at
>
>
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--
--
Dr Tim Gruene
Institut fuer anorganische Chemie
Tammannstr. 4
D-37077 Goettingen

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