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Re: [ccp4bb]: octyhedral ion M(X)6 <====> message 2
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Dear Weijun Huang,
from your buffer information and your M(X)6 with ~1.9 A metal-to-ligand
distance I think you've got most likely a central Mg2+ ion, surrounded
by oxygen atoms. The observed range of Mg-O distances is 2.00-.215 A
with a mean value of 2.08 A (Harding (1999), Acta Cryst. D55, 1432-1443)
whereas the minimum distance for Na-O is 2.25 A (Glusker (1991),
Advances in Prot. Chem., 42, 1-76), with an average expected value of
~2.4 A, which I simply calculate from the difference in cation radii
(Mg2+=0.65 A, Na+=0.95 A). Both metal ions show a strong preference for
oxygen ligands. You will hardly find a nitrogen or even sulphur in a
magnesium ligand sphere.
Good luck,
Dirk.
Weijun Huang wrote:
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> *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html ***
>
> Dear all,
>
> Thanks a lot for those who replied to the M(X)6 puzzle.
> Here is some info...
>
> In my Xtallization buffer, I have:
>
> Sodium Cacodylate
> Magnesium Chloride
> PEG
> DTT
> Ethylene glycol
>
> I also made a model of the ion M(X)6, the distances
> are estimated to be:
>
> M <---> X = 1.9 angstroms
> X <---> O (in ASP and C=O) = 3.0 angstroms
>
> Thanks,
> Weijun
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