Michael, Chris and Nick, Thank you so much for your help. -Jerome Jerome Nwachukwu [email protected]<mailto:[email protected]>
On Jul 14, 2014, at 1:48 PM, R. M. Garavito <[email protected]<mailto:[email protected]>> wrote: Jerome, >> Does anyone know the best way to store crystallization >> screening blocks that contain PEG 3350? I would recommend storing them in a fridge or a clean coldroom (mold-free). Lower temperature and low light does help. >> Is it a good idea to freeze the PEG solutions >> at -80°C and thaw them before use? Good idea, if they were pre-aliquoted into useful volumes. We do that occasionally. However, -20°C is just as good. >> Would the freeze-thaw process considerably >> alter the PEG chain lengths? No, the real issue is the generation of oxygen reactive species that cause aldehyde and peroxide formation, which in turn can modify your protein. It also causes cross-linked polymer formation. Also avoid metal ion contamination. Like lipids, plain PEG solutions in water and most detergents with PEG head groups (C12E8, octyl-POE, Brij, Triton, Tween, etc.) should be stored under argon and at -20°C. So, if you are tempted to use the 5-year old bottle of Triton X-100 or old 50% stock of PEG on the bench top, caveat emptor. Take a look at an old paper by Fran Jurnak (J. Cryst, Growth, 76, 577-582, 1986) for the trials and tribulations of working with PEG from different manufacturers of PEG (as well as how the purify it if you really get worried). Regards, Michael **************************************************************** R. Michael Garavito, Ph.D. Professor of Biochemistry & Molecular Biology 603 Wilson Rd., Rm. 513 Michigan State University East Lansing, MI 48824-1319 Office: (517) 355-9724 Lab: (517) 353-9125 FAX: (517) 353-9334 Email: [email protected]<mailto:[email protected]> **************************************************************** I also used to store my PEG solutions in light, and my stocks do sit out on the bench. I can't say for sure whether light or temperature make a difference, but I like to heed what seem like superstitions in crystallography to eliminate variables. We purchase our screens from Qiagen, who suggests that blocks be stored in the fridge and warmed to RT before use. Best, Chris On 7/14/14, Nicholas Larsen <[email protected]<mailto:[email protected]>> wrote: I don't think storage matters. I doubt Hampton stores their PEG stock solutions at -80 before they ship out to customers. I've solved tons of structures leaving my PEGS and PEG screens at RT in the light. Nick On Jul 14, 2014, at 11:33 AM, Jerome Nwachukwu <[email protected]<mailto:[email protected]>> wrote: Dear all, I have 3 short questions about PEG solutions: Does anyone know the best way to store crystallization screening blocks that contain PEG 3350? Is it a good idea to freeze the PEG solutions at -80°C and thaw them before use? Would the freeze-thaw process considerably alter the PEG chain lengths? Thank you, -Jerome Jerome Nwachukwu
