Observed intensities, crystal structur

In all cases, broad diffuse reflections are observed in the high interface distance range of X-ray powder diffraction patterns. The presence of such diffuse reflection is related to a high-order distortion in the crystal structure. The intensity of the diffuse reflections drops, the closer the valencies of the cations contained in the compound are. Such compounds characterizing by similar type of crystal structure also have approximately the same type of IR absorption spectra [261]. Compounds with rock-salt-type structures with disordered ion distributions display a practically continuous absorption in the range of 900-400 cm 1 (see Fig. 44, curves 1 - 4). However, the transition into a tetragonal phase or cubic modification, characterized by the entry of the ions into certain positions in the compound, generates discrete bands in the IR absorption spectra (see Fig. 44, curves 5 - 8). 

Now the gradual decline in intensity for h — 4, 8,12 (Table I) requires that uy = -J-, and hence % = -J-. This puts the two sets of metal atoms in the same place, and is hence ruled out. It may also be mentioned that structure 1 would place eight metal atoms on a cube diagonal, giving a maximum metal-metal distance of 2.03 A, which is considerably smaller than metal-metal distances observed in other crystals. Structure 2, dependent on one parameter u, has structure factors... 

P2j Z = 2 Dx = 1.428 R = 0.033 for 932 intensities. This is a hydrolysis product92 of fortimicin B. The inositol derivative has an almost ideal, chair conformation with Q = 56 pm, and the methylamino and methoxyl groups are axial this is similar to the conformation observed for the parent molecyle. The small differences that are noted are related to the intramolecular hydrogen-bond present in the crystal structure of fortimicin B. 

P2j Z = 4 Dx = 1.32 R = 0.04 for 3,503 intensities. There are two symmetry-independent molecules in the crystal structure, with almost exactly the same conformations. The pyranoside conformations are 2S0, with Q = 75, 75 pm 6 = 92, 91°

[Pg.261]

Recent developments and prospects of these methods have been discussed in a chapter by Schneider et al. (2001). It was underlined that these methods are widely applied for the characterization of crystalline materials (phase identification, quantitative analysis, determination of structure imperfections, crystal structure determination and analysis of 3D microstructural properties). Phase identification was traditionally based on a comparison of observed data with interplanar spacings and relative intensities (d and T) listed for crystalline materials. More recent search-match procedures, based on digitized patterns, and Powder Diffraction File (International Centre for Diffraction Data, USA.) containing powder data for hundreds of thousands substances may result in a fast efficient qualitative analysis. The determination of the amounts of different phases present in a multi-component sample (quantitative analysis) is based on the so-called Rietveld method. Procedures for pattern indexing, structure solution and refinement of structure model are based on the same method. 

Fig. 5 The crystal structure of the antibody-octapeptide complex, with STD-NMR intensities mapped onto the bound peptide. Residues of the antibody combining site are shown in purple, with selected residues labeled, and the direction of the backbone indicated in ribbon representation. Residues of the peptide are labeled in italics. Heavy atoms of the peptide are shown in gray, while the default color for hydrogen atoms is white. Observed STD-NMR intensities are mapped onto hydrogen atoms of the peptide by color, with red indicating 50-100% enhancement, orange 30-50% enhancement, a.nd yellow < 30% enhancement. Protons that are definitely not enhanced are shown in black those for which no enhancement could be determined (due to interference by other resonances, or not observable in the ID spectrum) remain white. Reproduced with permission from [100]. 2004 Elsevier Science...

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