Thanks very much for the reference; I have always wondered about precisely
this relationship (how much salt = how much PEG). Interestingly, the authors
note that down to PEG 1500, the MW of the PEG does not change the
corresponding salt values very much. I wonder whether anybody did this for
MPD, which would definitely be more tricky as it is volatile. Probably for
more volatile alcohols, one would simply assume the alcohol diffusion is
very fast relative to water, so could be ignored. In the short term
(minutes?), the drop would get bigger owing to influx of alcohol, but in the
longer term would equilibrate to the salt concentration of the well.
Jacob
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: j-kell...@northwestern.edu
*******************************************
----- Original Message -----
From: "Imre Toeroe" <t...@embl.de>
To: <CCP4BB@JISCMAIL.AC.UK>
Sent: Wednesday, February 03, 2010 4:25 AM
Subject: Re: [ccp4bb] Vapor diffusion calculator
Hi,
this might be relevant here:
http://scripts.iucr.org/cgi-bin/paper?S0907444995000436
Imre
Clemens Grimm wrote:
regardless of what such a (kinetic) calculator will calculate at the end -
we will have to feed it with data of the type "vapour pressure vs.
concentration and temperature" of substance X. Even without a whole
simulation tool for the kinetics of a vapour diffusion experiment this
will already enable us to tell what the equilibrium state/endpoint of the
experiment will be.
As the substances we are interested in are typically stuff like PEGs and
at very high concentration (non-ideal behaviour!), we will need
experimental data. For some salts there are tables. But for PEGs etc. this
has to be generated. I feel that only having this kind of data at hand
would already be tremendously useful!
Clemens
Zitat von Jacob Keller <j-kell...@md.northwestern.edu>:
Dear Crystallographers,
Is anybody aware of a calculator for vapor diffusion experiments to plot
concentrations of various solvent components as a function of time? For a
simple example, what happens when I mix a protein solution containing 50mM
NaCl 1:1 with a reservoir containing 50% MPD but no salt? Where is the
vapor diffusion equilibrium, and how does the drop composition change as a
function of time? More complicated would be experiments involving volatile
components other than water, as I think, for example, ethanol would almost
instantly equilibrate, then the water diffusion would kick in over a
longer time scale. Even more complicated would be pH-dependent
volatilities such as acetate. I don't think this would be impossible to
figure out, but it would be nice if there were a pre-existing tool/server
to do such.
Regards,
Jacob Keller
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: j-kell...@northwestern.edu
*******************************************
--------------------------------------------------
Dr. Clemens Grimm
Institut für Biochemie
Biozentrum der Universität Würzburg
Am Hubland
D-97074 Würzburg
Germany
e-mail: clemens.gr...@biozentrum.uni-wuerzburg.de
phone : +49 0931 888 84031
-------------------------------------------------
