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/
>>>
>>
>
>
> .
>
--
Charlie Bond
Professorial Fellow
University of Western Australia
School of Biomedical, Biomolecular and Chemical Sciences
M310
35 Stirling Highway
Crawley WA 6009
Australia
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+61 8 6488 4406
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