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Granada Crystallisation Box (GCB) is a new crystallisation device designed to perform counter-diffusion experiments. Here we describe the device and its use for protein crystallisation purposes. GCB allows one to explore and exploit the coupling between crystallisation and diffusion. The role of viscous fluids, gels and/or microgravity can be enhanced by using capillary volumes, creating a perfect diffusive mass transport scenario. The use of capillaries also reduces the consumption of macromolecules and avoids the handling of crystals for X-ray diffraction data collection.

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Mach-Zehnder interferometry is applied to quantitatively characterize growth of lysozyme crystals in microgravity. Experiments were performed by the Free Interface Diffusion technique into APCF FID reactors using large seeds. Tracking of the experiments using interferometry allowed to monitor the onset of supersaturation and the seed growth. A large and stable concentration depletion zone around the growing crystal developed, whose time evolution was analyzed. The interferograms were analyzed taking into account finite thickness of the cell by integrating the concentration over the straight lines through the optical path. It was concluded that there may be a quasi-steady state growth mode at the stage when the spacial concentration distribution did not change but its absolute value over all the cell was slowly diminishing. From this portion of the data, an estimate was made of the dimensionless parameter βR/D where β is the face kinetic coefficient, R is the effective crystal size and D is the lysozyme diffusivity in solution, as followed from the steady state model. For the assumed quasi steady state data portion, the parameter varies between 0.7 and 0.9 suggesting mixed diffusion-interface kinetic controlled growth.
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