H1 H2Fig. 1. Structure of the title compound displaying mean-square displacement ellipsoids at 90% probability.
AbstractThe structure of H8Si8012 has been determined by neutron diffraction at 29 K and compared with X-ray determinations at 9.5 and 100K. There are only small geometrical differences, but it can be concluded that the deviation from the ideal molecular symmetry, Oh (m-3m), increases with decreasing temperature and that the large vibration amplitudes for the O atoms observed in the X-ray analyses are also present in the neutron structure. Static disorder of the O atoms is excluded. The molecular deformation is caused by the rigid HSiO3 tetrahedra performing a cooperative torsional movement inducing vibrational deformations of the flexible Si--O--Si angles.
Deoxyuridine triphosphate nucleotidohydrolase (dUTPase), an enzyme in the nucleotide metabolism that is a pyrophosphatase hydrolyzing dUTP, has been crystallized. The crystals belong to the trigonal space group R3 and diffract beyond 2 A. The native dUTPase crystals and a mercury derivative are stable in the X-ray beam and are suitable for a high resolution X-ray structure analysis.
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