Crystallization in microgravity

The 46-residue protein crambin has been solved at 0.83 A resolution at 130 K.6 Some proteins have been crystallized in microgravity in space rockets where the convection-free conditions can produce larger and better crystals. RNase A crystals grown in microgravity diffracted x-rays to 1.06 A resolution, approximately 0.2 A higher resolution than previously observed in terrestrially grown RNase A crystals.7 At these very high resolutions, alternate conformations of some side chains may even be seen. 

F. Otalora, J. M. Garcia-Ruiz. Crystal growth studies in microgravity with the APCF. I. Computer simulation of transport dynamics. J Cryst Growth 752 141, 1997. 

Wang, Y. P., et al., Protein crystal growth in microgravity using a liquid/liquid diffusion method. Micrograv. Sci. Technol. 1996, 9 (4), 281-283. 

Miller, T. Y., He, X.M., Carter, D.C., A comparison between protein crystals grown with vapor diffusion methods in microgravity and protein crystals using a gel liquid liquid diffusion ground-based method. J. Cryst. Growth 1992, 122 (1-4), 306-309. 

Thomas, B. R., et al.. Distribution coefficients of protein impurities in ferritin and lysozyme crystals - Self-purification in microgravity. J. Cryst. Growth 2000,... 

Density gradients are established at several stages in the crystallization process (Fig. 5). As molecules attach to the growing crystal surface, the solution near the crystal is depleted of solute and becomes less dense than the bulk solution. Under the influence of gravity, such density differences result in convection currents. However, in microgravity, solutions with different densities are not subject to convection, so that solutions mix with less turbulence (Littke and John, 1984) and equilibration between solutions is much slower (DeLucas et al., 1986). 

Steiner, B. Dobbyn, R.C. Black, D. Burdette, H. Kuriyama, M. Spal, R. van den Berg, L. Fripp, A. Simcheck, R. Lai, R.B. Batra, A.K. Matthiesen, D. Ditchek, B. High resolution synchrotron X-radiation diffraction imaging of crystals grown in microgravity and closely related terrestrial crystals. J. Res. National Inst. Standards Technol. 1991, 96, 305. 

McPherson, A. Virus and protein crystal growth on earth and in microgravity. Appl. Phys. D 1993, 26, 104. 

Several elementary aspects of mass diffusion, heat transfer and fluid flow are considered in the context of the separation and control of mixtures of liquid metals and semiconductors by crystallization and float-zone refining. First, the effect of convection on mass transfer in several configurations is considered from the viewpoint of film theory. Then a nonlinear, simplified, model of a low Prandtl number floating zone in microgravity is discussed. It is shown that the nonlinear inertia terms of the momentum equations play an important role in determining surface deflection in thermocapillary flow, and that the deflection is small in the case considered, but it is intimately related to the pressure distribution which may exist in the zone. However, thermocapillary flows may be vigorous and can affect temperature and solute distributions profoundly in zone refining, and thus they affect the quality of the crystals produced. 

---