Hi Charlie,
yes you are right, but I assumed if people see a cloud of condensed fog
over their LN2 bath they should remove that by
a) filling up the bowl completely e.g. some LN2 drips out of the bowl
b) blow the fog away before you dip
c) ask someone for advice
In general I have observed much better results with cryo-cooling
crystals by plunging them into LN2 versus mounting them on a blocked
cryostream and then unblock it. Some tend also just to swing the crysal
onto the goniometer head without worrying about the cryostream, so the
crystal is cooled while it is mounted. Unless you have a very good cryo,
this procedure will result in bad reproducibility and most likely very
often in badly frozen crystals.
Just my 3 eurocents,
Juergen
Charlie Bond wrote:
I seem to recall an explanation a few years ago that a problem with
dunking into liquid nitrogen is that a cushion of nitrogen gas
persists around the crystal/loop so that 'freezing' is not so
reproducible (hopefully an expert will elaborate on this). The same
problem doesn't exist with liquid propane, but it has other issues...
I generally default to using the cryostream unless I know by
experiment that dunking works.
Cheers,
Charlie
Ohren, Jeffrey wrote:
Could it be that evaporation on the way from the microscope to the cold
stream increases the effective cryo concentration as well as causing a
beneficial dehydration effect?
There are quite a few publications that have carefully evaluated
optimizing cryo cooling. Check out Elspeth Garman's many excellent
papers on the subject as well as J. Appl. Cryst. (2006). 39, 244-251;
Methods 34 (2004) 415-423 and Acta Cryst. (2002). D58, 459-471, to name
a few.
Jeff
-----Original Message-----
From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of
Paul Paukstelis
Sent: Tuesday, June 03, 2008 11:59 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] crystallisation and mosaicity
I have also observed this. In my cases I have also been able to get away
with using less cryoprotectant when freezing in the cryostream.
--paul
Daniel Pomeranz Krummel wrote:
Dear Sajid,
I have observed a consistent reduction in mosaicity (from approx. 0.95
to
0.45) for one case by freezing the crystals in a cryostream (N2
vapour) as
opposed to submerging in liquid nitrogen.
Have others observed this?
Daniel
Dear All
My protein size is ~30kD and crystallizes with
19%Peg3350, 0.2M Nacl, and 0.1M Na Cacodylate buffer.
Please refer the attached crystal image with this. The
crystal looks like good enough for home source. These
crystals appears in 4-5 days at room temp.
Sometimes I'm getting crystals like this, but very few
in 24 well tray. Most of the time, I found the drop
contains needles. If I reduce the precipitant little
bit, I wont find any change in the drop even after
long time. Changing pH (or temp)of the buffer does not
help me any better. The crystal appears only around
5.5pH.
The problem is mosaicity. This crystal diffracted in
home source upto 3.2A and the mosaicity is 2.5degree.
Almost all the good crystal like this having same
mosaicity.
Good cryo condition so far that I found was
10%Glycerol with mother liquor. Other conditions
weekens the diffraction quality or increase mosaicity.
In many crystal I could see some crack in the middle
of the crystal, it looks like twin crystal. Or the
crystal appears with some sattelite crystals.
Can anyone suggest me some good way to overcome these
problems.
Thankz
Sajid
From Chandigarh to Chennai - find friends all over India. Go to
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--
Jürgen Bosch
University of Washington
Dept. of Biochemistry, K-426
1705 NE Pacific Street
Seattle, WA 98195
Box 357742
Phone: +1-206-616-4510
FAX: +1-206-685-7002
Web: http://faculty.washington.edu/jbosch
