Kay,
Go with LiCl as a reservoir solution (not necessarily in the protein
drop). It can generate a very low water vapor pressure. It will
suck the water out of almost anything. The CRC handbook has all the
information although buried deep within it. However, the DNA and
polysaccharide diffractionists used to bubble air through LiCl
solutions to get just the right humidity in the sample changer. They
had a nice chart to match LiCl concentration to humidity, but my 33
year old copy has crumbled into dust.
To keep microbatch plates hydrated a week or two longer, we put them
into chambers with ~0.5 M LiCl to match ~40% PEG4000 or ~1.5-2 M LiCl
to match ~60-70% ammonium sulfate (~2.4 - 3 M). The newer microbatch
plates do have little reservoir chambers just for this purpose. The
drawback with ammonium sulfate is that you have ammonia transfer and
the risk of pH changes.
Michael
****************************************************************
R. Michael Garavito, Ph.D.
Professor of Biochemistry & Molecular Biology
513 Biochemistry Bldg.
Michigan State University
East Lansing, MI 48824-1319
Office: (517) 355-9724 Lab: (517) 353-9125
FAX: (517) 353-9334 Email: [EMAIL PROTECTED]
****************************************************************
On 07/04/2008, at 15.46, Kay Diederichs wrote:
Dear all,
a protein which we work on is available in low quantity. The only
crystallization screen we set up is completely clear, no
precipitate, nothing.
Now we would like to modify the reservoirs of this screen, by
adding LiCl or Ammoniumsulfate or ... , with the goal of reducing
the vapour pressure, to at least get the protein concentration in
the drop into the range where "something happens".
Does anyone have advice as to which salt we should add (to the
reservoir only)? AmSO4 is only soluble to 4M, LiCl goes to 10M.
But vapour pressure reduction is not the same as molarity.
thanks for any insight,
Kay
--
Kay Diederichs http://strucbio.biologie.uni-
konstanz.de
email: [EMAIL PROTECTED] Tel +49 7531 88 4049 Fax
3183
Fachbereich Biologie, Universität Konstanz, Box M647, D-78457
Konstanz
