Almost assuredly you are getting zinc hydroxide precipitate. Zn(OH)2
will readily precipitate from solutions of alkaline Zn(II). Your problem
is compounded by the fact that HEPES is a non-coordinating buffer, so it
does not help solubilize the zinc ion. You might find a weakly
coordinating buffer, like Tris, will help solubilize Zn(II) at a
sufficiently low concentration. Or you could lower the pH slightly to
lower the hydroxide ion concentration and increase the solubility of
Zn(II). You could also add a chelator like EDTA, tartrate, etc. to the
solution to solubilize Zn(II) under alkaline conditions, but then you
have the problem of hoping that your protein has a higher affinity for
the metal ion than the chelator.
Cheers,
_______________________________________
Roger S. Rowlett
Gordon & Dorothy Kline Professor
Department of Chemistry
Colgate University
13 Oak Drive
Hamilton, NY 13346
tel: (315)-228-7245
ofc: (315)-228-7395
fax: (315)-228-7935
email: rrowl...@colgate.edu
On 5/11/2012 12:26 PM, Rajesh Kumar wrote:
Dear All,
This question sounds simple but I dont know the answer.
I was preparing a 24 well crystal screen. When I try to use 10 mM
ZnSO4 with HEPES (pH 7.6) buffer it precipitates. I tried both ZnCl2
and Zn acetate the effect is same.
I dont know why this Zn in not compatible with HEPES.
Could you please tell me why is this?
I appreciate your help.
Thanks
Rajesh
