Every small molecule dataset I collected as a graduate student in
chemistry back in the mid to late 1980's was at 100K. I never had to
worry about crystal slippage during collection, organic solvent
evaporation, air oxidation of the sample (organometallic metal
clusters) or secondary radiation damage.
When I switched to protein crystallography, I was absolutely amazed
when told that "you can not cool a protein crystal below 4 degrees C
for data collection."
How times have changed,
Diana
On Jun 19, 2008, at 9:03 AM, Ian Tickle wrote:
I would go along with Harry & friends, I used crystal cooling when I
was
at Aafje Vos' Struktuurchemie lab in Groningen in 1972, when the
technique had already been in routine use there for at least 10 years,
in order to study compounds that are liquid at ambient temp (of course
it was custom-built kit using a collection of liq N2 Dewar vessel &
tubes, nothing as fancy as a Cryostream!). The Groningen group really
pioneered the use of low temp for small molecule structures and I
don't
recall increased mosaicity ever being an issue. Occasionally you
would
get a compound with a phase transition on the way down and the crystal
would literally explode in a puff of powder before your eyes! The
motive for using low temp was of course to reduce the thermal motion
and
libration effects, and thus greatly improve the accuracy of the
molecular geometry, and low temp is pretty well essential if you're
into
valence density deformation maps, again in order the minimise the
contribution from thermal motion.
-- Ian
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of harry powell
Sent: 19 June 2008 14:05
To: Remy Loris
Cc: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] is it Ok to freeze
Hi
Without wishing to start an argument, I've been checking with
some of my colleagues who are chemical crystallographers -
the reply I get is that, for routine structural analysis,
"pretty well all datasets are collected at 100K unless the
crystals fall apart at low T, or if the cryostream is broken".
I should point out that the first production Cryostream that
I came across (serial number 2, which I think may have been
the first one sold!) was in the Cambridge Department of
Chemistry in about 1985. They didn't become common until the
mid-1990's in PX labs, when they were already
well-established as a bit of pretty well essential kit for
small molecule work.
So although what Remy says is true, the practice is to
cryocool most of the time.
On 19 Jun 2008, at 12:08, Remy Loris wrote:
Typically crystals of small organic compounds do not
require freezing as there are no solvent channels. They do in
general not suffer from radiation damage at room temperature
the way protein crystals do. Occasionally they are mounted in
a capillary instead of simply glueing them to a goniometer if
they are air sensitive. In principle freezing should not
damage the crystals, but one still may have to be carefull if
the crystals are large. I think you risk increasing
mosiacity, and any manipulation that is not needed will on
average only reduce the quality of the specimen rather than improve
it
Remy Loris
Vrije Univesiteit Brussel
Jayashankar wrote:
Dear Scientists and Friends,
I am not sure, whether organic crystals need
to be in cryo stream necessarily during data collection from
an in house
xray machine .
How most of the organic crystals have been
solved mostly?
--
S.Jayashankar
(A bit confused new generation researcher).
Research Student
Institute for Biophysical Chemistry
Hannover Medical School
Germany
Harry
--
Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC
Centre, Hills Road, Cambridge, CB2 2QH
Disclaimer
This communication is confidential and may contain privileged
information intended solely for the named addressee(s). It may not
be used or disclosed except for the purpose for which it has been
sent. If you are not the intended recipient you must not review,
use, disclose, copy, distribute or take any action in reliance upon
it. If you have received this communication in error, please notify
Astex Therapeutics Ltd by emailing [EMAIL PROTECTED]
and destroy all copies of the message and any attached documents.
Astex Therapeutics Ltd monitors, controls and protects all its
messaging traffic in compliance with its corporate email policy. The
Company accepts no liability or responsibility for any onward
transmission or use of emails and attachments having left the Astex
Therapeutics domain. Unless expressly stated, opinions in this
message are those of the individual sender and not of Astex
Therapeutics Ltd. The recipient should check this email and any
attachments for the presence of computer viruses. Astex Therapeutics
Ltd accepts no liability for damage caused by any virus transmitted
by this email. E-mail is susceptible to data corruption,
interception, unauthorized amendment, and tampering, Astex
Therapeutics Ltd only send and receive e-mails on the basis that the
Company is not liable for any such alteration or any consequences
thereof.
Astex Therapeutics Ltd., Registered in England at 436 Cambridge
Science Park, Cambridge CB4 0QA under number 3751674
* * * * * * * * * * * * * * * * * * * * * * * * * * * *
Diana R. Tomchick
Associate Professor
University of Texas Southwestern Medical Center
Department of Biochemistry
5323 Harry Hines Blvd.
Rm. ND10.214B
Dallas, TX 75390-8816, U.S.A.
Email: [EMAIL PROTECTED]
214-645-6383 (phone)
214-645-6353 (fax)
