Control of the rate of evaporation in protein crystallization by the 'microbatch under oil' method

Microbatch crystallization under oil is a powerful procedure for obtaining protein crystals. Using this method, aqueous protein solutions are dispensed under liquid oil, and water evaporates through the layer of oil, with a concomitant increase in the concentrations of both protein and precipitant until the nucleation point is reached. A technique is presented for regulating the rate of water evaporation, which permits fine tuning of the crystallization conditions as well as preventing complete desiccation of the drops in the microbatch crystallization trays.