Screening: studies comparing microbatch with vapor diffusion

The table below summarizes the results of several studies where microbatch was compared to vapor diffusion in screening experiments (i.e. searching for initial crystallization conditions).  All the studies that we know of have been included.

All of these studies except the first used only a "Modified Microbatch" method.  This refers to microbatch modified by using a 50:50 mixture of silicone oil and paraffin oil to cover the drops ("Al's Oil").  The silicone is slightly permeable to water, and allows slow evaporation.  This gives a scanning effect (similar to vapor diffusion with salt, but not PEG) where gradually increasing concentrations of protein and precipitants are sampled.  This method has been shown to find more hits than using pure paraffin and is now generally used for regular microbatch screening experiments.

More recently, D'Arcy and colleagues (2003) have shown that more hits can be found by using pure silicone oil to cover the drops in place of the silicone / paraffin mixture.  The hits also appear much more rapidly - taking about 9 days instead of up to 70 using the mixture.  The disadvantage of using pure silicone is that crystals do not last for long, so this method is particularly suitable for use with automatic imaging systems.

References:

P.F.M. Baldock, V. Mills, P.D. Shaw Stewart. A comparison of microbatch and vapour diffusion for initial screening of crystallization conditions. Journal of Crystal Growth. 168 (1996), pp 170-174 or: http://www.douglas.co.uk/rep2.htm

A. D’Arcy, G.E. Dale, M. Stihle, B. D’Arcy.  Results reported at the 8th International Conference on the Crystallization of Biological Macromolecules, May 18, 2000 .

N. Noordeen and S. Cowan-Jacob.  Novartis Pharma AG. https://www.hamptonresearch.com/documents/ramc/P6.ppt

Misuaki Sugahara, Riken Harima Institute, SPring8.  Personal communication.