[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [ccp4bb]: octyhedral ion M(X)6 <====> message 2



***  For details on how to be removed from this list visit the  ***
***    CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html    ***

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:

> ***  For details on how to be removed from this list visit the  ***
> ***    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

--

*********************************************************
* Dirk Kostrewa          |                              *
* Paul Scherrer Institut | e-mail: dirk.kostrewa@psi.ch *
* Life Sciences          |  phone: +41-56-310-4722      *
* OSRA/007               |    fax: +41-56-310-4556      *
* CH-5232 Villigen PSI   |    WWW: www.sb.psi.ch        *
* Switzerland            |                              *
*********************************************************