Dear Jacob,
for NH4+, you would expect a (partial) tetrahedral coordination with
typical H-bond distances of ~2.9 A. For Na+, you would expect a
(partial) octahedral coordination with Metal-to-ligand distances of ~2.4
A (see Harding, Acta Cryst., D62, 678-682 (2006); Harding, Acta Cryst.,
D58, 872-874 (2002); Glusker, Advances in Protein Chemistry, 42, 1-76
(1991)).
But depending on your data resolution and quality, and on the
completeness of the coordination sphere, it might be difficult to
distinguish between them.
Best regards,
Dirk.
Am 16.11.11 19:20, schrieb Jacob Keller:
Dear Crystallographers,
I have crystals containing 666mM NH4 and 540mM Na, and there appears
to be a "water" which is only about 2.2 Ang from some polar atoms. It
is currently reasonably happy as a Na, but is there any reasonable way
to decide which cation is there?
JPK
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Dirk Kostrewa
Gene Center Munich, A5.07
Department of Biochemistry
Ludwig-Maximilians-Universität München
Feodor-Lynen-Str. 25
D-81377 Munich
Germany
Phone: +49-89-2180-76845
Fax: +49-89-2180-76999
E-mail: kostr...@genzentrum.lmu.de
WWW: www.genzentrum.lmu.de
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