At the risk of sounding too commercial, here are some suggestions: 1. See if you can either place your crystallization tray in a cold room or crystallize it there. Mount your crystal in a capillary here so that at whatever lower temperature you use, the distillation of solvent will be reduced.
2. If capillaries are too hard to work with, even a quick diffraction image out of a loop, while the crystal is drying out, may give you some information. Alternately, I have saturated my stock solution with sugar from the coffee room and swished my crystal through this for getting a quick diffraction image. In a rare case, the crystal actually diffracted for several hours at room temperature. 3. Someone mentioned using Paratone oil. This is good, but a little thick and sticky. So, I use PerFluoroPolyEther (PFPE) as it is much less viscous and is colorless. I buy FOMBLIN Y VAC 14/6 from SigmaAldrich (Cat # 317934-100G). PFPE is mildly hydroscopic, so it is best to open the bottle infrequently (I withdraw ten 0.5 ml aliquots whenever I open the bottle). 4. The Free Mounting System (FMS) is ideal for RT screening. So long as you do not have a highly volatile component in solution, then you can use the standard FMS at temperatures in the range of 15 to 25 C. If you do have a volatile component, then Proteros bistructures GmbH (www.proteros.com) has the only FMS with the capability of adding solvents to the gas stream...and with some compensation, they will gladly help you with this. Kris ------------ Kris F. Tesh, Ph D Director, Macromolecular Products Rigaku Americas Corporation 9009 New Trails Drive The Woodlands, TX 77381 USA 001 281 362 2300 x 144 -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Benini, Stefano Sent: Wednesday, July 11, 2007 7:17 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Help with reducing crystal mosaicity Dear Mary, the problem encountered with cryoprotectans is the change in the solution surrounding your crystal as they may not be present in your crystallisation conditions or you need to increase their concentration to make them act as cryoprotectant. So I don't thik is the cryoprotectant itself as it is you mother liquor.. test it in a capillary so you could rule out that freezing is the problem of course you don't want to find new crystallisation conditions when you tried everything and I know what it means!! I would try to improve crystal quality using additives or ligand etc...., your long axis is very worrying as well!!! may be some magic additive could change the packing and givew better diffraction too I also had crystals growing from MPD, unfortunately there was a non-cleavable his-tag so I could not hope that metals would help..... and other additives did not make any difference then my contract finished and so did the project! I hope you still have a lot of time available to try different things but I would not waste time trying to change your cryo ciao Stefano Stefano Benini PhD AstraZeneca UK Structural Biology Mereside 50S38 Alderley Park -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] Behalf Of Patrick Shaw Stewart Sent: 11 July 2007 12:10 To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Help with reducing crystal mosaicity Just a thought, Mary - going back to your original question about MPD. I extracted the crystallization conditions from REMARK 280 of 3939 PDB entries a couple of years ago. The average concentration of the MPD used was high - 38.6%, while PEGs tended to be used at lower concs, e.g. PEG400 25.7%. You can see the data at www.douglas.co.uk/top14.htm I thought this information could be useful if you want to replace some of the MPD with another precipitant (or cryoprotectant). Best wishes Patrick Shaw Stewart -- [EMAIL PROTECTED] Douglas Instruments Ltd. DouglasHouse, EastGarston, Hungerford, Berkshire, RG177HD, UK Directors: Peter Baldock, Patrick Shaw Stewart, James Smith http://douglas.co.uk or http://www.douglasinstruments.com Tel: 44 (0) 148-864-9090 US toll-free 1-877-225-2034 Regd. England 2177994, VAT Reg. GB 480 7371 36 > -----Original Message----- > From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Mary > Fitzgerald > Sent: 09 July 2007 23:05 > To: CCP4BB@JISCMAIL.AC.UK > Subject: [ccp4bb] Help with reducing crystal mosaicity > > Help please! > > I'm looking for some new ideas. I have crystals that come out of a > sitting drop with a mixture of sodium cacodylate at pH 6.5, magnesium > acetate and MPD for the well solution. The MPD concentration is > sufficient to act as a cryoprotectant. Currently, I directly freeze > these crystals in liquid nitrogen. When I collect data, I typically > have high anisotropic mosaicity; it ranges from 0.8 to 1.2. This is > further complicated with a weakly diffracting crystal (4-5 A) that has > a long unit cell axis of ~500 and often twinning. > > It has been suggested to me that the cryoprotectent is a problem. I > haven't checked the diffraction at room temperature, yet. Please no > suggestions of finding a different crystal form as that's not a > consideration at the moment. I have my reasons. I did find one > crystal that has lower mosaicity (0.5 to 0.8) but had weaker > diffraction then the typical crystal. Attempts at flash cryoannealing > have not helped. > > So, what's a good way to change the cryoprotectant if the > cryoprotectant is the precipitant? I've considered trying dehydration > but wasn't certain if that would help with the mosaicity. > > Thanks for any ideas, > > Mary X. Fitzgerald > Postdoctoral Associate
