Charlie, The insulating gas cushion is due to the Leidenfrost effect ( http://en.wikipedia.org/wiki/Leidenfrost_effect). We discussed this somewhat in:
J. Appl. Cryst. (2005). 38, 945-950 -Lokesh On Wed, Jun 4, 2008 at 8:11 PM, Charlie Bond <[EMAIL PROTECTED]> 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: [email protected] >> 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 > [EMAIL PROTECTED] > +61 8 6488 4406 >
