High resolution X-ray data

Multipole analysis with high-resolution X-ray data for [Ni(thmbtacn)]2+ was carried out to determine the electron configuration in the C3 symmetry-adapted orbitals of the Ni ion, confirming a higher occupancy of the crystal field-stabilized t2g orbitals relative to the destabilized eg orbitals. This is interpreted in terms of a predominantly ionic metal-ligand interaction.1424... 

Bacterial reaction centers crystallize readily, providing high-resolution X-ray data and stmctural information. Photoactivation of these crystals leads to structural changes that can be monitored in time-resolved X-ray experiments. In order to be able interpret these changes, it is important to know the actual extent and kinetics of photoactivation of the crystallized reaction center. It has been possible to measure polarized single crystal data in the near-IR region on crystals of the same size ( 200 J,m) and contained within the same 1 mm capillary tubes as were used in the X-ray experiments. 

Hemerythrin is the best studied example and high-resolution X-ray data are available for the deoxy (176), oxy (176), met (177), and azido-met (177) forms. Extensive spectroscopic studies have also been carried out on these forms and on the semi-met Fe" Fe form 178). The active site structure of hemerythrin is illustrated in Fig. 40. The two iron atoms are bridged by an oxygen donor (OH or 0 ) and by two carbox-ylates, one aspartate and one gluamate. The remaining protein donors are five histidine residues, three coordinated to one iron and two to the other. In the deoxy form one iron atom is five coordinate and this vacant site can be occupied by dioxygen in oxyhemerythrin or by other... 

Figure 2 Spacefill model of the Dickerson-Drew B-DNA dodecamer that illustrates the spine of hydration in the minor groove. The waters of minor groove hydration are shown in red (medium gray in black and white print), whereas the two DNA strands are shown in green (light gray in black and white print) and blue (dark gray in black and white print). The model was adapted from the high resolution X-ray data of Tereshko et al. (52).

Timehenko, A.A. Galzitskaya, O.V. Serdyuk, I.N. Roughness of the globular protein surface analysis of high resolution x-ray data. Proteins 1997, 28, 194-201. 

The advances of our capability in this area were aided by a number of remarkable new developments in analytical instrumentation. These new characterization tools include, among many, NMR, which provides information on the local environment of atoms in the structure (16-17), synchrotron XRD, which provides very high resolution x-ray data from powders (18-19), the application of Rietveld analysis of x-ray or neutron diffraction data to zeolite structure determination (20), and STEM, which provides atomic resolution of the crystal structure and its chemical composition (21), to name just a few. 

Of the neurohypophyseal hormones, oxytocin was first crystallized in 1952 (Pierce et ai, 1952) as the flavionate, but the crystals were unsuitable for X-ray analysis. The first of many syntheses of the hormone was carried out by du Vigneaud et ai (1953), and a variety of crystalline salts of oxytocin (Rudko et ai, 1971) and deaminooxytocin analogs (Low and Chen, 1966 Chiu et ai, 1969) have been crystallized. Crystals of deaminooxytocin (and probably also deamino-6-selenooxytocin) crystallize in P2j (two molecules in the asymmetric unit) with pseudo-C2 symmetry. High-resolution X-ray data ( 1 A resolution) on both these forms have been collected, and the structure analysis is being pursued by a combination of isomorphous replacement and vector superposition techniques and direct methods (S.P. Wood, I. J. Tickle, Y. Mascarenhas, T. L. Blundell, and V. Hruby, unpublished results, 1980). 

As a first approximation, the terms Vj j are taken here as the sum of monopole-monopole interactions of degenerate and non-degenerate singly excited states as recently suggested by Parson and Warshel (18). The atomic coordinates of the interacting molecules are based on the high resolution X-ray data of methylpheophorbide (20). 

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