I've used a home-made guillotine type contraption to accelerate crystals through the gas layer and into the liquid N2. A bit disconcerting when you watch your crystal plunge rapidly into your cryo-dish but it works well.
Alternatively plunging into liquid ethane works better for flash freezing as it has a higher boiling point than N2 so you don't get films of ice on the crystal (the ethane forms larger bubbles that do not stick to the crystal). Simon -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of James Stroud Sent: 01 February 2007 11:06 To: [email protected] Subject: Re: [ccp4bb] Removal of cold gas layer for cryocooling I propose a simple contraption to minimize the vapor layer in cryocrystallography, using freezing in the liquid phase. This idea is based on the findings in the citation below. It is modified from designs used in the pet feeding industry. The novel aspect is that liquid nitrogen is used rather than water or nutritional liquids and that this particular contraption can be used for the freezing of crystals rather than the satiation of animals. The idea is to invert a dewar over a dish. The dewar sits on a block to raise its opening while the block has a gap to allow liquid N2 to escape from the dewar. The block is adjusted so that the opening to the dewar is just below the brim of the dish, minimizing the vapor head space. The cold vapor should either rise or fall depending on its density relative to the atmosphere, minimizing the thickness of the trapped vapor phase. The dish should be deep enough to allow one to plunge a crystal in the liquid N2 without easily hitting the bottom of the dish. I call this invention "James's Petfeeder Contraption for Cryocrystallography". A diagram is at: http://www.jamesstroud.com/Contraptions/Petfeeder.pdf James On Feb 1, 2007, at 12:52 AM, Florian Brückner wrote: > Dear everyone, > > has anyone tried removing the cold gas layer above liquid nitrogen > (or propane) by blowing or sucking to improve cooling rates in the > cryocooling of crystals. I would like to try and I would be happy > if someone could share some experience. > > Florian. > > P.S.: there is an interesting paper: J. Appl. Cryst. (2006). 39, > 805-811. > > -- > ---------------------------------------------------------------------- > --------------- > > Florian Brueckner > AG Cramer > Gene Center > Feodor-Lynen-Str. 25 > D-81377 Muenchen > Germany > > Fon: +49 89 2180-76955 > Fax: +49 89 2180-76999
