Structural relationship

The XRD powder pattern of C-S-H gel (Fig. 5.6) suggests structural i similarities to 1.4-nm tobermorite and jennite. The band at 0.27-0.31 nm and the peak at 0.182nm could be derived from the sharper peaks in i corresponding parts of the patterns of either or both of those phases. The.I 

At one time, the relation between C-S-H gel and tobermorite was widely believed to be very close, and the name tobermorite gel was in common use. The Ca/Si ratio and poor crystallinity of C-S-H gel do not justify this name. Assuming the idealized formula CjSgHg for 1.4-nm tobermorite, removal of 

From their studies on C-S-H(di,poly) , Stade and Wicker (S45) concluded that Ca and OH ions could both be present in the interlayer region of a tobermorite-like structure. Stade (S46) suggested that in the products containing both dimeric and polymeric ions, one surface of each tobermorite-type layer was composed of dimeric, and the other of polymeric, ions, thus accounting for the observed near-constancy of dimer/ polymer ratio. In the purely dimeric material isolated at — IO C. both surfaces were composed of dimeric ions. 

A fist of atomic positions is often not very helpful when a variety of structures have to be compared. In this section two ways of looking at structures that facilitate comparisons are described. In the first of these, structures are described in terms of being built up by packing together spheres, and, in the other, in terms of polyhedra linked by comers and edges. 

The (100) face of an fee structure showing the relationship between the atomic radii and the length of the unit cell. 

This same diagonal would be along the [111] direction in the bcc structure. Therefore, for the bcc structure. 

The basis for the bcc system is (0,0,0) (1 /2,1 /2,1 /2) so there are eight comer atoms and one interior atom for a total of two atoms per unit cell. 

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Calculational methods. Associating the analysis, the knowledge of the property-structure relationships, and the calculation methods has made possible the replacement of costly and arduous test methods by quicker tests whose results are linked by calculations to the characteristic under study. Some examples are the cetane number, in some cases, the octane number, or the characteristics of LPG (refer to Chapter 3). 

Spectral features and their corresponding molecular descriptors are then applied to mathematical techniques of multivariate data analysis, such as principal component analysis (PCA) for exploratory data analysis or multivariate classification for the development of spectral classifiers [84-87]. Principal component analysis results in a scatter plot that exhibits spectra-structure relationships by clustering similarities in spectral and/or structural features [88, 89]. 

Saccharin was discovered at Johns Hopkins Uni versity in 1879 in the course of research on coal tar derivatives and is the oldest artificial sweetener In spite of Its name which comes from the Latin word for sugar saccharin bears no structural relationship to any sugar Nor is saccharin itself very soluble in wa ter The proton bonded to nitrogen however is fairly acidic and saccharin is normally marketed as its water soluble sodium or calcium salt Its earliest applications were not in weight control but as a... 

R. G. Bums and V. M. Bums, Structural Relationships Between Manganese(IW) Oxides in The Manganese Dioxide Symposium, Vol. 1,1. C. Sample Office, 1975. 

Table 4. Dimer Acid Feedstock—Structure Relationship...

We now describe two applications of comparative modeling in more detail (1) Modeling of substrate specificity aided by a high accuracy model and (2) confinning a remote structural relationship based on a low accuracy model. 

PE Leopold, M Montal, JN Onuchic. Protein folding funnels A kinetic approach to the sequence-structure relationship. Pi oc Natl Acad Sci USA 89 8721-8725, 1992. 

Figure 13.14 (a) Schematic diagram of the main chain and four almost invariant residues of the fourth WD repeat of Gp from transducin. The view is roughly perpendicular to the central tunnel and the plane of the sheet. The red stripes denote hydrogen bonds, (b) Schematic view of two WD repeats illustrating the structural relationships between two consecutive repeats. The first repeat is brown and the second repeat is orange. The positions of the four almost invariant residues in the first repeat are circled. (Adapted from J. Sondek et al., Nature 379 369-374, 1996.)... 

Despite the structural relationship between ginkgolide B and bilobalide, retrosynthetic analysis of the latter produced a totally different collection of sequences. A successful synthesis of bilobalide was implemented using a plan which depended on stereochemical and FG-based strategies. A process for enantioselective synthesis was based on an initial enantioselective Diels-Alder step in combination with a novel annulation method. 

P. Sakya, J. M. Seddon, R. H. Templer, R. J. Mirkin, G. J. T. Tiddy. Micellar cubic phases and their structural relationships the nonionic surfactant system Ci2EOi2/water. Langmuir 75 3706-3714, 1997. 

Heteroatom fullerene-type clusters — The possibility of incorporation of hetero atoms into C clusters has excited the attention of both theoreticians and experimentalists since the earliest days of fullerene chemistry, particularly in view of the known stability and ubiquity of organic heterocycles. The structural relationship between Ceo and /3-rhombohedral boron has already been alluded to (p. 142). 

The structural relationships in Bi203 are more complex. At room temperature the stable fonn is monoclinic o -Bi203 which has a polymeric layer structure featuring distorted, 5-coordinate Bi in pseudo-octahedral iBiOs units. Above 717°C this transforms to the cubic -form which has a defect fluorite structure (Cap2, p. 118) with randomly distributed oxygen vacancies, i.e. [Bi203D]. The )3-form and several oxygen-rich forms (in which some of the vacant sites are filled... 

At least four series of periodates are known, interconnected in aqueous solutions by a complex series of equilibria involving deprotonation, dehydration and aggregation of the parent acid H5IO6 — cf. telluric acids (p. 782) and antimonic acids (p. 577) in the immediately preceding groups. Nomenclature is summarized in Table 17.24, though not all of the fully protonated acids have been isolated in the free state. The structural relationship between these acids, obtained mainly from X-ray studies on their salts, are shown in Fig. 17.24. H5IO6 itself (mp 128.5° decomp) consists of molecules of (HO)sIO linked into a three-dimensional array by O-H - O bonds (10 for each molecule, 260-278 pm). 

The present review covers the literature to the end of 1967 and all original sources have been consulted. Syntheses of each of the four ring systems are summarized separately, but physical, chemical, and biological properties are considered generally. Many pjTidopyri-midines were initially synthesized for a study of biological activity or physical properties because of the close structural relationship of these systems to the quinazolines (5) and pteridines (6). Recent reviews have discussed these related compounds. 

Buckles et al. suggested tentative structural assignments for 53a and 53b and their respective benzamido acids on the basis of ultraviolet spectral data and by comparison of physical properties with those of model compounds. They pointed out that it is not possible to establish structural relationships from configurations of the diastereomeric 2-benzamido-3-methoxy-3-phenylpropionic acids (54), each of which, on treatment with acetic anhydride, give mixtures of the azlactones. Similar observations have been made by others. ... 

The structural relationship of pivopril to the commercially important analogues captopril (51) and enalaprilat (52) is readily apparent. 

To clarify the relationship between intermediate 11 and its predecessor, intermediate 12, it is instructive to recognize the correspondence between the C-ll hydroxyl group and the C-6 carboxyl group in 11. Thus, even though the structural relationship between intermediates 11 and 12 may not appear to be close, subjection of... 

Functional insights based on structural relationships can only rise to the level of hypotheses, and these hypotheses must be tested by direct functional experiments. 

By 1945, Stacey speculated about the possibility of a structural relationship between Pneumococcus capsular polysaccharides and those produced by other organisms. With Miss Schliichterer, he had examined the capsular polysaccharide of Rhizobium radicicolum. This polysaccharide gave a precipitin reaction in high dilution, not only with Type III Pneumococcus antiserum, but also mixed with antisera from other Pneumococcus types. The chemical evidence indicated that the polysaccharide resembled the specific polysaccharides of Types I and II Pneumococcus. A decade later, the acidic capsular polysaccharide from Azoto-bacter chroococcum, a soil organism, was studied. It, too, produced serological cross-reactions with certain pneumococcal specific antisera. Although the molecular structure of the polysaccharide was not established, adequate evidence was accumulated to show a structural relationship to Type III Pneumococcus-specific polysaccharide. This was sufficiently close to account for the Type III serological cross-relationship. 

Fig. 33. Structure relationships and coordinations of lead chalcogenide halides a, Pb4SeBr, b, PbjSjI c, PbvSjBrio. (Redrawn from B. Krebs,. Z. Anorg. Allg. Chem. 396, 137 (1973), Figs. 1 2, and 3, pp. 141, 147, and 148.)...

NMR spectra have been reported for the Rieske-type ferredoxins from Xanthobacter strain Py2 (88) and of toluene 4-monooxygenase from Pseudomonas mendocina (T4MOC) (88a) as well as for the water-soluble Rieske fragment from the bci complex of Paracoccus deni-trificans (ISFpd) (89). The spectra of these proteins are similar, which is consistent with the close structural relationship between the three proteins. In the reduced (paramagnetic) state, all three proteins show several hyperfine-shifted resonances between +83 and -16 ppm at 400 MHz or between 110 and +25 ppm at 300 MHz (Table X). 

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