Actually, in our hands, we have gotten a mixture of clear drops and precipitate when scaling from teeny drops to larger ones. Teeny drops equilibrate faster, and have more pronounced surface and edge effects than larger ones. We have also found that it is easier to crystallize salt in teeny drops (and harder to scale salt crystals up).
One of our usual tricks is to dilute the precipitant relative to the reservoir (2 protein + [1-1.5 precipitant + 0.5-1 water]) , so that as vapor diffusion progresses, the protein concentrates even more. On scale-up, we test all permutations of this. It's obvious but maddening: for proteins that are moderately easy to crystallize (5-10% crystalline hits), it is very easy to translate hits from teeny scale to large scale. The crystal quality may not be good, but there will be crystals to test. When there is less than 1% hit rate, it gets harder. Also, crystals that arise from the muck of the precipitate are very hard to translate (and repeat). However, these are to be preferred to the protein that crystallizes in >40% of the experiments (but gives uniformly low quality crystals). I hate it when we have to chase down more than 15 widely different conditions. Lisa BTW "teeny" is the highly technical term for drops smaller than 50nl total volume. -- Lisa A. Nagy, Ph.D. University of Alabama-Birmingham [EMAIL PROTECTED] From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Oganesyan, Vaheh Sent: Thursday, January 17, 2008 8:41 AM To: [email protected] Subject: Re: [ccp4bb] crystallisation robot Mark, What was the state of the larger drops when tiny counterparts had crystals? My guess - they all precipitated. I'm trying to understand why some proteins or some conditions require change in protein concentration while others do not when migrating from smaller drops to larger ones. If it is protein dependent then I'm afraid there might be no one answer; if it is not then there should be a trend and explanation of phenomena. Vaheh
