Generally crystals require a much higher precipitant concentration for
nucleation than for growth and maybe even less for maintenance of their
crystalline state.
Therefore I would
a) try micro seeding into less Ammonium Sulpahte
b) reduce the ammonium sulfate concentration in the drop by adding
ammonium sulphate free mother liquor to the reservoir (not the drop
itself!) This would re-equilibrate the drop to lower a AS
concentration. You could remove one crytal and try to find the lowest
possible AS concentration with it separately.
Tim
--
Tim Gruene
Institut fuer anorganische Chemie
Tammannstr. 4
D-37077 Goettingen
GPG Key ID = A46BEE1A
On Tue, 4 Nov 2008, Sabine Schneider wrote:
Hi everyone,
We got crystals that grew in ~3.2M ammonium sulphate and some tris-buffer at
18dgC. Unfortunately the crystals take a while to grow (~4-5 weeks) and so
far we only have 4-5 xtals.
I tried to freeze the crystals, but as soon as I broke though the skin of the
drop the ammonium sulphate started to crystallise. I got the crystals out,
froze them using sort of an artifical mother liquor with sodium malonate as
cryo and tested the diffraction. The freezing seems to be OK and it is
definitely a protein crystal. The crystal suffered when the ammonium sulphate
in the drop started to crystallise, but didn't seem to deteriorate anymore in
the cryo. Well the corners had already more or less disappeared by the time I
got them out of the drop...
Since we only have a few xtals at the moment and I can't try out a lot of
things, I was wondering if anyone has experienced and solved a similar
problem? My freezing attempt so far was in an airconditioned room with 18dgC.
I thought about higher humidity and temperature in the room, and/or adding
the cryo directly to the drop.... Any ideas are very much appreciated!
Sabine
------------------------------------------
Dr. Sabine Schneider
Ludwig-Maximilians-University
Department of Chemistry and Pharmacy
Butenandtstrasse 5-13, Building F
81377 Munich
Germany
Phone: +49 (0)89 2180 77846
Fax: +49 (0)89 2180 77756
http://www.carellgroup.de/
