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:[log in to unmask]] On Behalf Of
>> Paul Paukstelis
>> Sent: Tuesday, June 03, 2008 11:59 PM
>> To: [log in to unmask]
>> 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
>>>> http://in.promos.yahoo.com/groups/citygroups/
>>>>
>>>
>>>
>>
>>
>>
>> .
>>
>
--
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
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