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: [log in to unmask]
>> [mailto:[log in to unmask]] On Behalf Of harry powell
>> Sent: 19 June 2008 14:05
>> To: Remy Loris
>> Cc: [log in to unmask]
>> 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
>>
>>
>>
>>
>>
>
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Diana R. Tomchick
Associate Professor
University of Texas Southwestern Medical Center
Department of Biochemistry
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