Dear Theresa,
an interesting question, I think the answer is yes it does, very
much. Using Raoult's law we can calculate the equilibrium vapour
pressure above a 5M NaCl solution, it is a relative humidity of 82.6%.
This is much lower than say a solution of 20% PEG 4000, here we can
again use Raoult's law but add in a term to cope with large polymers and
we get a equilibrium relative humidity of 99.3%. So you can see that
you would be dehydrating your drop significantly. However, what you can
see is that for most PEG solutions used in initial screening (over
1000Da at a concentration of 10-30%) the relative humidity will be in
the 99% range - you could therefore use water in the reservoir for these
experiments.
I have made an online calculator using Raoult's law to calculate the
relative humidity equilibria for precipitant solutions which can be
accessed here: http://go.esrf.eu/RH
Cheers, Matt
On 13/11/2012 07:03, Theresa Hsu wrote:
Dear all
In *initial screening* using vapor diffusion crystallization, does it matter
whether the reservoir buffer is also the precipitant in the drop or just a high
salt solution like 5 M NaCl?
Thank you.
Theresa
--
Matthew Bowler
Synchrotron Science Group
European Molecular Biology Laboratory
BP 181, 6 rue Jules Horowitz
38042 Grenoble Cedex 9
France
===================================================
Tel: +33 (0) 4.76.20.76.37
Fax: +33 (0) 4.76.88.29.04
http://www.embl.fr/
===================================================
