Hi Theresa, Try glycerol at 10 % with 5 % increments up to 30 % v/v. You may also be able to attain protection by increasing the ammonium sulfate concentration along with incremental glycerol approach.
Crystallization of RNA/protein complexes by Garber and colleagues (Acta Cryst. (2002). D58, 1664-1669) reported using 25% - 30% (w/v) of glucose for cryoprotection with ethanol, MPD, PEG, ethylene glycol, sucrose not being found suitable with concentrated ammonium sulphate. May also want to consider sodium malonate and DMSO along with the already suggested Paratone-N/Paraffin Oil blends. DMSO: http://www.bio.brandeis.edu/publications/bi035849h.pdf Sodium malonate: http://journals.iucr.org/d/issues/2003/12/00/fw5004/fw5004.pdf Take Care, Sean Seaver P212121 http://store.p212121.com/
