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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