Solute convection during the whole process of protein crystal growth

We numerically simulated sedimentation flow and buoyancy-driven convection during protein crystal growth in which the crystal size changes from 0.1 to 100 mum and clarified how gravitational fields affect the various stages o f crystal growth. When the crystal size is below a few mum, most crystals a re suspended in solution and solute transport near the crystal is mainly li mited by diffusive transport. When the crystal size is above a few mum, sed imentation flow dominates near the crystal, but solute transport is still m ainly limited to diffusive transport. When crystals grow to several mum, mo st of them settle to the bottom and continue to grow there. When the size i s above several 10 mum, buoyancy-driven convection dominates solute transpo rt near growing crystals at the bottom, and the contribution from buoyancy induced convection to crystal interfacial growth rate appears on Earth in c omparison with that under zero-gravity condition and increases with increas ing crystal size. During the whole crystal growth process, the crystal inte rface growth rate shows the tendency to decrease as the crystal grows under both normal and zero-gravity conditions. Moreover, our simulations of crys tal sedimentation are consistent with experimental observations of lysozyme crystallization that most crystals settle to the bottom when their size re aches several mum. (C) 2000 Elsevier Science B.V. All rights reserved.