I typically collect data at -50C on all small molecule samples. I've had quite a few cases where there are phase transitions, and you can damage the crystals, especially when the molecules are packed in a pi-pi stacking motif, or I'm dealing with alloy systems.
I've also collected data at 16K, so it all depends on your sample. Instead of finding out if there is a phase transition, -50C seems to be a good choice of a temperature to reduce the displacement amplitudes, radiation damage, and solvent loss. Bernie Santarsiero On Thu, June 19, 2008 9:40 am, Diana Tomchick wrote: > 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). 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