High Frequency Access to Low Gravity Experimentation in Organic Crystal Growth from Solutions

Organic crystal growers now have access to a wide array of facilities and hardware on space shuttle missions and other international carriers. Agencies providing such access include governmental organizations (such as the NASA Marshall Space Flight Center and the European Space Agency), educational institutions (e.g., the Birmingham and Huntsville campuses of the University of Alabama, the University of Colorado-Boulder, Kansas State University, Massachusetts Institute of Technology, and the University of California-Riverside), and private companies (such as Instrumentation Technology Associates, Intospace GmbH, and Payload Systems Inc.). These organizations have published descriptions of the hardware they have designed for space flight, including hanging-drop vapor diffusion chambers, membrane-based solute diffusion and solvent-transport cells, sliding-block free diffusion cells, sliding film diffusion cells, batch mixing devices, and submerged crystal growth chambers. In recent years one or more of these facilities has been present on nearly every space shuttle mission, and, in most cases, a high level of automation makes this high frequency of experimentation possible. The total number of individual tests of organic crystallization using this array of devices now numbers into the thousands, making organic crystal growth the most frequently practiced low gravity research procedure in the history of space flight. The services of these facilities have been available for several years to corporate entities wishing to determine the structure of organic molecules having high commercial value. Current hardware can be used to perform any of the widely-utilized (and some of the newly-developed) techniques used for organic crystal growth. These techniques include vapor diffusion (hanging and sessile drop), batch growth (thermal gradient and isothermal), dialysis diffusion, osmotic dewatering, step osmotic dewatering, step dialysis diffusion, liquid-liquid (also known as interfacial or double) diffusion, step diffusion, and boundary-layer diffusion. Every one of these methods has resulted in the growth of diffraction-quality crystals in low gravity. In many cases crystals grown in low gravity have been of higher quality than those grown at 1 g. Some of the methods that have yielded superior crystals (e.g., liquid-liquid diffusion) cannot be practiced successfully at 1 g because of buoyancy-driven motions (convection and sedimentation). The practice of crystallization in low gravity, therefore, widens the variety of techniques available to researchers, and the high frequency of access to this microgravity environment allows researchers to continually improve and broaden their crystal growing capability.