Cooling at 4 Degrees

S.Ravichandran ravi at CMB2.SAHA.ERNET.IN
Fri Nov 19 23:48:26 EST 1999



Hi,


> Has anyone who has one of these had any problems using capillaries at 4 
> degrees? Please could you let me know of any tips regarding build-up of 
> condensation around the crystal.

	Well, we don't have an Xtream cooler (but the very old Oxford
cryosystems -cryostream cooler is there). Infact, we tried to collect data
at 4 degree C with this cryostat by mounting a protein crystal using
capillaries. As because the cooling rate and heat transfer was not faster,
the temperature gradients (or moisture) started to develop along the walls
of the capillary tube. The end result was water accumulation around the
crystal, as was also said in the literature -> Machin et al., 1984, where
in such a case, the possibility of background X-ray scattering will be
more!. 

	Some interesting studies (by Marsh & Petsko, 1973 and also in
McRee, 1993) tells that, when you combine the capillary mounting method
with some specially designed equipments, you may avoid (or rather
minimize) condensation effect, but possibly only upto a certain
temperature (say 277 K). The use of 'oil plugs' was well demonstrated very
recently by Lim et al. (1999) (check:
http://journals.iucr.org/j/issues/1999/01/00/wb0064/index.html). 

	Anyway, happy cooling.

Cheers,
Ravi.

REF:-
---
Lim, D., Ye, Q., Jia, Z. (1999). J. Appl. Cryst. 32, 134-135.
Machin, KJ, Begg, GS & Issac, NW (1984). J. Appl. Cryst. 17, 358-359.
Marsh, DJ & Petsko, GA (1973). J. Appl. Cryst. 6, 76-80.
McRee, DE (1993). Practical Protein Crystallography. San Diego: Academic Press.


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|S. Ravichandran                             ||                          |
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