Hey David,
You can do Mn2+ identification by its anomalous diffraction using the Cu
Kalpha radiation. Mn is an anomalous scatterer at Cu Kalpha (1.5418 A),
despite being distant from its absorption edge (somewhere around 1.96 A
if I remember well). I did this for a double-manganese bound ConA, have
a look into THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 275, No. 26, Issue
of June 30, pp. 19778–19787, 2000 (you may need to use different
programs for making your anomalous difference Patterson and Fourier maps
these days).
Julie.
Kay Diederichs wrote:
David Briggs wrote:
Dear all.
I have recently solved a structure in-house, 2.8A, CuKa.
I have a metal ion bound very obvious hepta-valent co-ordination,
which would suggest either Ca or Mn.
Neither was present in the crystallisation setup, but there was some
Mg around, which has contaminants of both Ca & Mn.
At 2.8A, I don't really think I can reliably discriminate between
2.15A & 2.36A distances to coordinating atoms
(http://tanna.bch.ed.ac.uk/newtargs_06.html
<http://tanna.bch.ed.ac.uk/newtargs_06.html>).
The B factors for refined Ca are 18, and Mn 30. The B-factors of
coordinating atoms vary from... 18 > 30 - so no help there.
I have a nice clear 6sigma anomalous difference peak, but then,
according to http://skuld.bmsc.washington.edu/scatter/ both Ca (f"
~1.3) and Mn (f" ~2.8) scatter anomalously at that wavelength.
The obvious solution is go to a synchrotron and scan around the Mn
edge and see what happens, however, whilst waiting for beam time, is
there any way I could... oh I don't know, use the peak in my anomalous
difference Fourier to figure out what anomalous signal would be
required to generate a peak of that size - a sort of back-transform???
Is this do-able, and if so, how would one go about it?
Cheers,
Dave
Dave,
f" = 1.3 versus 2.8 sounds like quite a difference ... what is the anom
peak height of the sulfurs in your structure? The f" of sulfur at Cu Ka
wavelength is 0.55 . So I'd expect the ratio of peakheights of your
unknown metal divided by the average peakheight of sulfurs (of roughly
18-30 A**2 B-factor) to give you an idea of what you have. Of course
this is no proof ...
Are there any other anom scatterers in your structure?
best,
Kay
--
Julie Bouckaert, PhD [EMAIL PROTECTED]
VIB Project leader
VIB Department of Molecular and Cellular Interactions, Vrije
Universiteit Brussel
Tel. 32-2-629-1988 Fax 32-2-6291963
ULTR, Building E 4.18
Vrije Universiteit Brussel
Pleinlaan 2
1050 Brussel
Belgium
