Theresa,
Several suggestions that have been given are excellent advice:
Li salts suggested by Tommi Kajander is what I would use
in particular:
80% saturated lithium sulfate.
This should work. I would be very surprised if it does not.
Malonate as suggested by Sean Seaver is another great idea, but difficult
to prepare
see ccp4bb by Doug Ohlendorf :
> Malonic acid is dissolved in water and then pH adjusted to the desired
> value with NaOH. Caution: dissolving malonic acid is highly exothermic.
> Do it slowly, in a hood.
In general terms what needs to be considered is that
when one introduces a cryoprotectant it is important to
match the precipitating power of the precipitant.
If you just add glycerol, as suggested by some, you will tend to dissolve
your
crystals with respect to 2M ammonium sulfate.
"Ideally in a balanced cryoprotectant the mild solubility
enhancing effect of the glycols should be counteracted by
the addition of MPD or DMSO that can act as precipitants.
Therefore, an approach using a complex mixture of
glycols and cryoprecipitants should yield improved
results."
I have assembled a kit initially for my own personal use
that creates mixtures respecting these principles.
CEA Saclay has licenced it to Molecular Dimensions.
The details of the components, the mixtures and their use
are freely available:
http://www.moleculardimensions.com/applications/upload/CryoProtX.pdf - for
the product flyer and:
http://www.moleculardimensions.com/shopdisplayproducts.asp?id=201&cat=CryoKits
- to get more info and order the product.
What I prefer about Lithium sulfate compared with malonate is that I just
transfer the crystals in the 80% saturated Li2SO4
without bothering about the pH (no buffer) and it works. You may want to
transfer with a capillary rather than a loop to avoid
shocking the crystals, but for the rest it should give good results.
Enrico.
On Sun, 05 Feb 2012 23:49:25 +0100, Theresa H. Hsu <[log in to unmask]>
wrote:
> Hi all
>
> Is there a list of conditions to be tried *first* for cryoprotectant? My
> crystals diffract at room temperature capillary but no in 30% PEG 400.
> Crystals are from 2 M ammonium sulfate.
>
> Thank you.
>
> Theresa
--
Enrico A. Stura D.Phil. (Oxon) , Tel: 33 (0)1 69 08 4302 Office
Room 19, Bat.152, Tel: 33 (0)1 69 08 9449 Lab
LTMB, SIMOPRO, IBiTec-S, CE Saclay, 91191 Gif-sur-Yvette, FRANCE
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http://www.chem.gla.ac.uk/protein/mirror/stura/index2.html
e-mail: [log in to unmask] Fax: 33 (0)1 69 08 90 71
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