Analysis of Crystals

To analyze the spectra of crystals, it is necessary to carry out a site group or factor group analysis, as described in the following subsection. 

I4c2 P4/nbm 142m P4lnnc I42d P4lmbm P4lmnc P4lnmm 

The vibrational spectra of calcite and aragonite crystals are markedly different, although both have the same composition (Sec. 2.4). This result can be explained if we consider the difference in site symmetry of the COl ion between these crystals. According to X-ray analysis, the space group of calcite is and Z is 2 Appendix X 

There is no change in the selection rule in going from the free ion to 

25g=2Cs, Sl=i, 3C2, and 3a (glide plane). These elements are exactly the same as those of the point group Ds, although the last element is a glide plane rather than a plane of symmetry in a single molecule. 

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Ichimiya A, Ohno Y and Horio Y 1997 Structural analysis of crystal surfaces by reflection high energy electron diffraction Surf. Rev. Left 4 501-11... 

Most investigators have focused their attention on a differential segment of the zone between the feed injection and the crystal melter. Analysis of crystal formation and growth in the recoveiy section has received scant attention. Table 22-4 summarizes the scope of the literature treatment for center-fed columns for both solid-solution and eutectic forming systems. 

Prediction and analysis of crystallizer performance is achieved by constructing models based on conservation equations and rate expressions respectively, as follows. In general form, the conservation equation is given by... 

In the analysis of crystal growth, one is mainly interested in macroscopic features like crystal morphology and growth rate. Therefore, the time scale in question is rather slower than the time scale of phonon frequencies, and the deviation of atomic positions from the average crystalline lattice position can be neglected. A lattice model gives a sufiicient description for the crystal shapes and growth [3,34,35]. 

W. H. Bragg (University College, London) and W. L. Bragg (Manchester) analysis of crystal structure by means of X-rays. 

In addition to the occurrence in PE at high temperature and pressure, the hexagonal phase is frequently found in paraffin substances under various circumstances. The analysis of crystal structure and order of these hexagonal phases is not only interesting, but also important for the understanding of their origins. The circumstances in which hexagonal phases arise in paraffin substances can be summarized as follows ... 

Prabu-Jeyabalan M, Nalivaika E, Schiffer CA (2002) Substrate shape determines specificity of recognition for HIV-1 protease analysis of crystal structures of six substrate complexes. Structure 10 369-381... 

Once the pore is open, K+ ions appear to move outward in single file. Analysis of crystals shows four K+ ions interacting with the backbone carbonyl groups of the amino acid residues that form the ion selectivity filter (Fig. 6-8B). It is thought that two K+ ions occupy sites 1 and 3 (Fig. 6-8B, orange) and then switch to sites 2 and 4 (gray). The K+ ion in site 4 would dissociate into the extracellular space, the K+ ion in site 2 would move to site 3 and another... 

Devaux, C., Adrian, M., Berthet-Colominas, C., Cusack, S., andjacrot, B. (1990). Structure of adenovirus fibre. I. Analysis of crystals of fibre from adenovirus serotype 2 and 5 by electron microscopy and X-ray crystallography./ Mol. Biol. 215, 567-588. 

The X-ray analysis of crystals is by far the best experimental method in modem structural chemistry, as judged by the vast amount... 

Since the X-ray structural analysis of crystallized proteins yields the most direct information on the tertiary structure, many attempts have been made in the last decade to crystallize individual ribosomal proteins. However, it was many years before any progress in this field was made. The N- and C-terminal fragments of the . coU protein L7/L12 have been crystallized, and the crystals diffract to 4 and 2.6 A, respectively (Liljas et ai, 1978). According to the X-ray analysis, the C-terminal fragment (positions 53-120) has a compact, plum-shaped tertiary structure with three a helices and three p sheets (Leijonmarck et ai, 1980). 

The precision structure analysis of crystals and quantitative reconstruction of ESP requires the maximum possible set of structure amplitudes, which would provide a precise scaling factor, information on the thermal atomic motion and the high resolution of the ESP with good statistical accuracy being at least 1-2%. Such an experimental data set can be collected by an electron diffractometer which was designed on the basis of EMR-102 [3] (Fig. 3). 

Table VI. X-ray Structural Analysis of Crystals of N,N-dimethylamino-2-phenylpyridazin-3-one (LAB 2-chloro-5-13 338).

Kurki-Suonio, K., Analysis of Crystal Atoms on the Basis of X-ray Diffraction, Proceedings Italian Crystallographic Association Meeting, Bari, Italy (1971). 

NMR analysis (1r and 31p) of the reaction media and elemental analysis of crystals isolated from the reaction medium revealed the unique capacity of the phosphine oxide to form a hydrogen-bond (bridge) and behave as a cationic species ... 

Several models have been proposed for the active center of iron and sulphur in Clostridial ferredoxin in which the cysteine residues in the peptide chain participate in the sulphur bridging. Fig 9 166). Unfortunately X-ray analysis of crystals of these proteins has not been completed. It is difficult to confirm that all the irons are clustered in a single linear array 167, 168). X-ray studies of another non-heme iron protein, the high potential iron protein, hipip, from chromatium, carried out by J. Kraut (personal communication), indicate that the four irons of this molecule may be clustered in a tetrahedral array. 

X-Ray analysis of crystals of 2-methyl-5-phenyltriazolo[4,5-, triazole 38, obtained by diffusion from methane/ethanol (PI space group), indicates there are two molecules per asymmetric unit. The first is essentially planar, with a mean deviation (non-H-atoms) of 0.03A and a maximum absolute torsion angle, C(2)-C(l)-N(5 )-N(4 ), of 3.4°. The second molecule has a more pronounced twist with C(2A)-C(1A)-N(5 A)-N(4 A) being 9.6° <1993ZK133>. 

Applications discussed in this section are those that have traditionally been considered fields of crystallography, namely the determination and analysis of crystal structures. 

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