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You might to consider that PEG 3350 has phosphate contamination, so playing around with small amounts of phosphate (or removing it) might be worthwhile. Cheers, tom From: Regina Kettering [mailto:[log in to unmask]] Sent: Thursday, August 25, 2011 04:46 AM To: [log in to unmask] <[log in to unmask]> Subject: Re: [ccp4bb] spherulites and PEG3350 Something to consider is the quality of the PEG 3350. We have found that different qualities of PEG 3350 can give different results, depending on the type and amount of contaminants. What used to be the Fluka PEG 3350 is now the pharm grade of PEG 3350 (aka Miralax). We use high quality PEG 3350 for normal screening, but switch to the highest quality grade we can get for optimizing. Regina ________________________________ From: Jan van Agthoven <[log in to unmask]> To: [log in to unmask] Sent: Wednesday, August 24, 2011 2:05 PM Subject: [ccp4bb] spherulites and PEG3350 Dear all, I recently obtained some spherulites while trying to crystallize my protein. The spherulites are manually reproducible, but changing pH, protein concentration, and salt concentration does not result in crystal formation. Microseeding with crushed spherulites isn't a solution either as it only yields new spherulites. Next stepp is the use of an optimization kit but I have a limited amount of material, and I start doubting that these are protein spherulites, as the spherulites are not particularly soft. The condition contains 15% PEG 3350 and 200 mM NaCl. Does anyone know if PEG 3350 forms easily spherulites around that concentration? Thanks,