What is the mosaicity of the unfrozen crystal? Jim
-----Original Message----- From: Mary Fitzgerald <[EMAIL PROTECTED]> Date: Mon, 9 Jul 2007 18:05:10 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
