Space explorer, diffraction

The most unpredictable process in X-ray structure determination is the crystallization of the candidate protein into a form suitable for X-ray diffraction. Each protein requires a unique set of conditions to form crystals. Typically 100 mg of highly purified protein is required to determine the conditions that result in usable crystals of 0.1 to 0.3 mm size, although a size of 0.3 to 0.8 mm is preferred. The occurrence of crystals and the rate of crystallization are influenced by many factors such as protein purity, the solvent, concentration of added precipitants, pH, temperature, and the presence of ions and cofactors. The protein solution at a concentration of typically 5 to 20 mg/ml is allowed to slowly reach supersaturation by the removal of or by changing the composition of the solvent by liquid-liquid diffusion or vapor diffusion methods. Microscale methods have been developed to explore several crystallization conditions simultaneously using minimum amounts of the purified protein sample. Recently, use of the zero gravity atmosphere in space has been explored as a means of facilitating crystallization (Eisenberg and Hill, 1990 Branden and Tooze, 1991 Tomasselli et al, 1991). 

In 2002, Roimebro et alP explored the perovskite-related stmcture of Na3AlH6. These studies determined the positions of the hydrogen atoms from neutron diffraction data of a deuterated sample. It was found that the best fit data was for the monoclinic space group Pliln (no. 14). The structure was a distorted face-centered cubic (FCC) structure of [AlDg] units with sodium in all of the octahedral and tetrahedral sites. The complex anions were found to be distorted [AlFIg] octahedra. Selected interatomic distances and bond angles are reported in Table 14.2. The Al-D distances were 1.746,1.758, and 1.770 A,... 

XRD and neutron diffraction have been the most effective tool in exploring the rank of atomic, molecular group in three-dimensional space on solid material. XRD becomes an indispensable tool in the research of structure of solid material because of its intact theory. In particular, with the use of modern high-performance computer, it is even more surprising with its effectiveness and speed in material research. 

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