I would like to point out that flash-cooling in liquid propane has the
added complication that the liquid propane can have a range of temperature
and still be liquid. If you use propane you may not know which
temperature you are actually using. The temperature in the exposed layer
of the propane will be warmer (could be 231 K) than the bottom layer
unless you stir the propane. Luger's group has published their work on
flash-cooling in propane. [Raji, who posts here often must be away from
the internet :) ] See Edayathumangalam and Luger (2005) Acta Cryst D 51,
891-898.
As an alternative to propane and ethane, one might consider carbon
tetrafluoride instead. It is a liquid between about 88 K and 145 K, so
not quite the range of propane, but if you see liquid, you know you are
are below 145 K. And it's non-flammable. Note that the CRC has the wrong
boiling point for this cryogenic gas which I believe is why CF4 is not
used as much.
For more tips on cryo-cooling, see also the PDF linked at
http://www.rigaku.com/cryo/ and the references therein.
Jim
On Fri, 6 Jun 2008, R.M. Garavito wrote:
Tommi,
The question has been asked and answered not by protein crystallography, but
by cyroelectron microscopy and EM freeze etch research. Even as far back as
the early 1960's, people noticed that liq. N2 was really slow at cooling.
Read the cyroEM work on the bacteriorhodopsin photocycle and check out the
wicked guillotine device for freezing.
The slower freezing in liq. N2 is partly due to nitrogen's low heat capacity,
which can be seen in the fact that there is only about a 13 degree difference
between the freezing and boiling points of N2 (~64K vs. ~77K). In contrast,
difference between the freezing and boiling points for propane is almost 148
degrees (~83K vs. ~231K). Thus, it makes sense to freeze in liq. propane,
but then shift to liq. N2 for storage and shipping. Making propane popsicles
for storage, shipping, and mounting is not necessary.
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]
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On Jun 5, 2008, at 5:11 PM, Tommi Kajander wrote:
according to literature,see below and references
http://www.px.nsls.bnl.gov/courses/papers/ZD_EG_papers.html,
it is not clear that liq. propane plunged item would cool
faster. (whilst i havent tested this)...
Would anyone have actual experimental data with protein crystals
on the hyperquenching suggested by
Warkentin, V. Berejnov, and R. E. Thorne, J. Appl. Cryst. (2006) 39,
805-811. (no diffraction data in the paper). in particular with
small samples.
thanks,
Tommi
Quoting Petr Leiman <[EMAIL PROTECTED]>:
yes you are right, but I assumed if people see a cloud of condensed
fog over their LN2 bath they should remove that by
a) filling up the bowl completely e.g. some LN2 drips out of the bowl
b) blow the fog away before you dip
I think the original poster meant the relatively low heat conduction of
liquid N2, which causes boiling around the crystal immediately after
plunging.
The best way to freeze things is to put a small container of liquid
ethane
or propane into a liquid N2 bowl, and plunge into the ethane/propane
(this
methods was suggested earlier).
Petr
--
Tommi Kajander, Ph.D.
Macromolecular X-ray Crystallography
Research Program in Structural Biology and Biophysics
Institute of Biotechnology
P.O. Box 65 (Street address: Viikinkaari 1, 4th floor)
University of Helsinki
FIN-00014 Helsinki, Finland
Tel. +358-9-191 58903
Fax +358-9-191 59940
