Hi Andre,
a very effective method is the use of a humidity control device. It has
the great advantage that you can characterize changes that occur and
also move straight to data collection. There are several HC1 devices in
Europe (developed here at the EMBL and available at Diamond, BESSY and
MaxLab) and at least 1 in the USA - there is also the FMS. You can of
course also do this in the lab but the disadvantage is that any change
induced cannot be observed. The relative humidity (RH) that is in
equilibrium with your mother liquor is 99%, you could think about slowly
replacing the reservoir solution with increasing salt solutions so as to
dehydrate in the drop - this avoids handling the crystal - equations to
convert between PEG concentrations and salt concentrations for RH
matching can be found here:
http://www.esrf.eu/UsersAndScience/Experiments/MX/How_to_use_our_beamlines/forms/equation-4
Below are some links that might help, best wishes, Matt.
Website for HC1 experiments at the ESRF:
http://www.esrf.eu/UsersAndScience/Experiments/MX/About_our_beamlines/ID14-2/HC1b
Calculation website for mother liquor RH equilibria: http://go.esrf.eu/RH
On 29/10/2013 16:18, Andre Godoy wrote:
Dear all
I'm trying to solve a beautiful large crystal that, unfortunately,
doesn't go further than 5 A resolution. I believe that in this case,
the lack of resolution is due the high solvent content (about 66%).
Therefore, my next strategy should be the dehydratation. Yet, I never
(sucessfully) did that. I read different approachs, were people
equilibrate crystals in dehydratation solution for days, or do more
than 20 steps, or add solvents. Since i never had sucess in my trials,
I was thinking that someone can suggest a protocol (should I remove
all salt?, should I keep the additive concentration?, how much
precipitant should I add? how many steps?).
crystal condition: 23% PEG 3350, 0.2M NaCl, 0.1M Tris pH 8.5, 3%
galactose (orthorhombic crystals, with about 0.6 x 0.6 mm)
all the best,
Andre Godoy
--
Matthew Bowler
Synchrotron Science Group
European Molecular Biology Laboratory
BP 181, 6 rue Jules Horowitz
38042 Grenoble Cedex 9
France
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