I would recommend any one of these things:
1. Increase the concentration of the chemicals present, i.e. add more
iso-propanol OR add more PEG, but use a low molecular weight, like PEG400.
Either one or both. You will need 5% glycerol to get a good (ice-free)
cryo-condition or 10% PEG400 or 10% ethylene glycol or 10% propylene glycol.
You can find these numbers in this reference: McFerrin & Snell, J. Appl.
Cryst. 35 (2002), 538-45.
Note that adding 30% glycerol is overkill, less may be better for your
mosaicity.
2. Try things "randomly". If you think carefully, it may make sense to give
preference to compounds similar to the ones in your mix - hoping that 'more of
the same' will not change your crystals much.
3. Add cryo-protectant, such as glycerol, to your growth conditions.
Particularly because you only need 5%, this may not matter at all for growing
crystals, but if it works you can harvest the crystals and freeze them
directly, no treatment or soak.
4. Mount and expose a crystal at room temperature (in a capillary, almost a
lost art from what I see around me). The advantage is that you can estimate the
mosaicity without freezing the crystal. If it is poor, then you know you must
grow better crystals. If it is good, then you know that you must improve your
freezing technique/recipe. It is nice to know that you are not barking up the
wrong tree.
Good luck.
Mark
-----Original Message-----
From: [EMAIL PROTECTED]
To: CCP4BB@JISCMAIL.AC.UK
Sent: Tue, 3 Apr 2007 3:11 AM
Subject: [ccp4bb] Question about cryoprotectant
Hi,
l have a crystal grow at condition screen l 40: 0.1M tri-sodium citrate
dihydrate pH5.6 isoproponal 20%PEG4k 20% and the crystal need a
cryoprotectant, we have used the 30% glycerol but it is not good, the mosaicity
of
the diffraction pattern is a little high, so anyone knows which is the best
cryoprotectant for this crystal?
Thanks!
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