Hi James, I would first ask you what is your crystallization condition? You mentioned MPD at 70%. Very high concentration (and this is very high) of organic non volatile alcohols like MPD or polymers like PEGs will promote phase separation if there is some salt around. The higher the polymer concentration the less salt you need to observe this and the more likely this is going to happen . This is particularly true with ammonium sulfate for example in my own experience.
You can try to use glycerol as a co-solvent and try to lower the MPD crystallization. I would try also all propane-diol compounds (1,2 and 1,3) and ethylene glycol. Do you know if those crystals are protein crystals? because phase separation in drops also promotes crystallization of salts. Very often you prepare the reservoirs at room temperature and after a couple of days at 4C the phase separation also happens in the wells. It may sound like a naive question but have you checked for this? If you see the phase separation in your well, have you looked for crystals in the well too. It is however possible to get good protein crystals in phase separations. This has been reported in many cases. If you know they are protein crystals then I would try to lower the polymer concentration and increase salt concentration to try to get out of this region of the phase diagram. Hope this helps -- Pascal F. Egea, PhD Assistant Professor UCLA, David Geffen School of Medicine Department of Biological Chemistry 314 Biomedical Sciences Research Building office (310)-983-3515 lab (310)-983-3516 email pe...@mednet.ucla.edu
