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I would like to point out that flash-cooling in liquid propane has the added complication that the liquid propane can have a range of temperature and still be liquid. If you use propane you may not know which temperature you are actually using. The temperature in the exposed layer of the propane will be warmer (could be 231 K) than the bottom layer unless you stir the propane. Luger's group has published their work on flash-cooling in propane. [Raji, who posts here often must be away from the internet :) ] See Edayathumangalam and Luger (2005) Acta Cryst D 51, 891-898. As an alternative to propane and ethane, one might consider carbon tetrafluoride instead. It is a liquid between about 88 K and 145 K, so not quite the range of propane, but if you see liquid, you know you are are below 145 K. And it's non-flammable. Note that the CRC has the wrong boiling point for this cryogenic gas which I believe is why CF4 is not used as much. For more tips on cryo-cooling, see also the PDF linked at http://www.rigaku.com/cryo/ and the references therein. Jim On Fri, 6 Jun 2008, R.M. Garavito wrote: > Tommi, > > The question has been asked and answered not by protein crystallography, but > by cyroelectron microscopy and EM freeze etch research. Even as far back as > the early 1960's, people noticed that liq. N2 was really slow at cooling. > Read the cyroEM work on the bacteriorhodopsin photocycle and check out the > wicked guillotine device for freezing. > > The slower freezing in liq. N2 is partly due to nitrogen's low heat capacity, > which can be seen in the fact that there is only about a 13 degree difference > between the freezing and boiling points of N2 (~64K vs. ~77K). In contrast, > difference between the freezing and boiling points for propane is almost 148 > degrees (~83K vs. ~231K). Thus, it makes sense to freeze in liq. propane, > but then shift to liq. N2 for storage and shipping. Making propane popsicles > for storage, shipping, and mounting is not necessary. > > Michael > > **************************************************************** > R. Michael Garavito, Ph.D. > Professor of Biochemistry & Molecular Biology > 513 Biochemistry Bldg. > Michigan State University > East Lansing, MI 48824-1319 > Office: (517) 355-9724 Lab: (517) 353-9125 > FAX: (517) 353-9334 Email: [log in to unmask] > **************************************************************** > > > On Jun 5, 2008, at 5:11 PM, Tommi Kajander wrote: > >> according to literature,see below and references >> http://www.px.nsls.bnl.gov/courses/papers/ZD_EG_papers.html, >> it is not clear that liq. propane plunged item would cool >> faster. (whilst i havent tested this)... >> >> Would anyone have actual experimental data with protein crystals >> on the hyperquenching suggested by >> Warkentin, V. Berejnov, and R. E. Thorne, J. Appl. Cryst. (2006) 39, >> 805-811. (no diffraction data in the paper). in particular with >> small samples. >> >> thanks, >> Tommi >> >> Quoting Petr Leiman <[log in to unmask]>: >> >>>>> 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 >>> >>> I think the original poster meant the relatively low heat conduction of >>> liquid N2, which causes boiling around the crystal immediately after >>> plunging. >>> >>> The best way to freeze things is to put a small container of liquid >>> ethane >>> or propane into a liquid N2 bowl, and plunge into the ethane/propane >>> (this >>> methods was suggested earlier). >>> >>> Petr >>> >>> >> >> >> -- >> Tommi Kajander, Ph.D. >> Macromolecular X-ray Crystallography >> Research Program in Structural Biology and Biophysics >> Institute of Biotechnology >> P.O. Box 65 (Street address: Viikinkaari 1, 4th floor) >> University of Helsinki >> FIN-00014 Helsinki, Finland >> Tel. +358-9-191 58903 >> Fax +358-9-191 59940 >> >