Bosch, Juergen wrote:
Hi Dirk,
I remember a neat paper don't recall who wrote it. I think it was in Acta D
where the
authors made a tiny probe the size of an elongated crystal glued to a
[/Advertisement on]
Hampton loop [/Advertisement off]. The probe was a temperature sensor and they
recorded
the cooling rate under different methods. The winner as far as I recall was
freezing in
liquid propane for the lack of the missing gas layer, but the second best
method was LN2.
Propane for whatever reason has gone extinct in certain areas of the world :-)
. I'll try
to find that reference but perhaps somebody else on this highly educated board
knows which
paper I'm referring to. I want to say it was published around 2004-2006.
Not highly educated, but I remember hearing Haken Hope talk about
this experiment at a workshop at SSRL- cooling a thermocouple or
thermister in the cold stream vs in LN2.
Maybe described here:
Cryocrystallography of biological macromolecules: a generally applicable method.
Hope H. Acta Crystallogr B. 1988 Feb 1;44 ( Pt 1):22-6.
BTW I don't thing the greater cooling rate with ethane/propane is due
to greater heat capacity so much as the fact that LN2 is used at
it's boiling point: heat capacity is irrelevant since it can't absorb
any more heat as a liquid, latent heat of vaporization is the reelevant
parameter, but once it is vaporized the gas has low heat capacity and
thermal conductivity.
The liquid hydrocarbons are prepared by chilling to around their
freezing point (hydrocarbon slush) so can absorb a lot of heat before any gas
forms.
Jürgen
On Feb 7, 2012, at 11:12 AM, Dirk Kostrewa wrote:
Dear Jürgen,
Am 07.02.12 16:58, schrieb Bosch, Juergen:
<snip>
Then one last remark, LN2 versus cryo-stream freeze. Dipping in LN2
leads to a quicker freeze of your material.
</snip>
Are you sure? There was a publication by Warkentin et al. [1] about a
cold gas layer above liquid nitrogen that reduces the expected cooling
rate a lot!
My very personal experience is, that cryo-cooling in the N2-stream
worked better for me than in LN2 in a variety of projects - but the
reason could just be me ;-)
Best regards,
Dirk.
[1] Matthew Warkentin, Viatcheslav Berejnov, Naji S Husseini, and Robert
E Thorne: "Hyperquenching for protein cryocrystallography", J. Appl.
Crystallogr., 39, 805-811 (2006)
--
*******************************************************
Dirk Kostrewa
Gene Center Munich
Department of Biochemistry
Ludwig-Maximilians-Universität München
Feodor-Lynen-Str. 25
D-81377 Munich
Germany
Phone: +49-89-2180-76845
Fax: +49-89-2180-76999
E-mail:kostr...@genzentrum.lmu.de <mailto:kostr...@genzentrum.lmu.de>
WWW:www.genzentrum.lmu.de
*******************************************************
......................
Jürgen Bosch
Johns Hopkins University
Bloomberg School of Public Health
Department of Biochemistry & Molecular Biology
Johns Hopkins Malaria Research Institute
615 North Wolfe Street, W8708
Baltimore, MD 21205
Office: +1-410-614-4742
Lab: +1-410-614-4894
Fax: +1-410-955-2926
http://web.mac.com/bosch_lab/
