Cluster structural features

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]. 

The individual structural features of the high-tem-perature superconductors are found in other substances. A substance with alternating metal-salt layers is Ag2F, with sequence FAgAgFAgAgF . Resonance between a covalent bond and a no-bond is found in B (l =3,Z. 6) and in metals and organometallic clusters. Hyperelectronic-hypoelectronic electron transfer occurs... 

The definitions of the cluster ligands of the [3Fe-4S] cluster and of the related structural features are quite useful to predict cluster types in other Fds of known sequence, as well as to determine the nature of the cluster coordinating atoms (and variability) and their control on the type and performances of the metal sites, in particular in terms of cluster stability, cluster interconversion capability, and acceptance of other metals at the cluster. 

The structural features of most niobium oxychlorides known to-date are summarized in Table 6.1. The use of a combination of chloride and oxide hgands leads to compounds with unique structure types [41], characterized by a remarkable variety of cluster frameworks, ranging from discrete cluster units to chains, layers, and three-dimensional nets, some topologies of which are unprecedented in compounds containing octahedral clusters. Most of the niobium oxychlorides known to date have anisotropic structures (the exceptions are Cs2LuNb,5Cli70 and PbLusNbsClisOg). 

We plan to make studies on palladium-copper, iridium-copper, and platinum-copper catalysts to extend our investigation of the effect of varying miscibility of the components on the structural features of the bimetallic clusters present. With these additional systems, the whole range from complete immiscibility to total miscibility of copper with the Group VIII metal will be encompassed. 

The results of the EXAFS studies on supported bimetallic catalysts have provided excellent confirmation of earlier conclusions (21-24) regarding the existence of bimetallic clusters in these catalysts. Moreover, major structural features of bimetallic clusters deduced from chemisorption and catalytic data (21-24), or anticipated from considerations of the miscibility or surface energies of the components (13-15), received additional support from the EXAFS data. From another point of view, it can also be said that the bimetallic catalyst systems provided a critical test of the EXAFS method for investigations of catalyst structure (17). The application of EXAFS in conjunction with studies employing ( mical probes and other types of physical probes was an important feature of the work (25). 

Most of the G-protein-coupled receptors are homologous with rhodopsin however, other quantitatively minor families as well as some individual receptors do not share any of the structural features common to the rhodopsin family (Figure 2.3). The most dominant of these are the glucagon/VIP/caldtonin receptor family, or family B (which has approximately 65 members), and the metabotropic glutamate receptor family, or family C (which has approximately 15 members), as well as the frizzled/smoothened family of receptors. Thus, the only structural feature that all G-protein-coupled receptors have in common is the seven-transmembrane helical bundle. Nevertheless, most non-rhodopsin-like receptors do have certain minor structural features in common with the rhodopsin-like receptors — for example, a disulfide bridge between the top of TM-III and the middle of extracellular loop-3, and a cluster of basic residues located just below TM-VI. 

The cluster 15, which crystallizes in the rhombohedral space group R3, has a remarkably different structure with respect to the structural features of 3a, 5a, and 10 (see Section II,D). Although a dode-cameric aggregate is present, as is the case for 5a (21), the cluster framework in 15 does not adopt a globular shape (39). The structure is built up of 24 Cu atoms surrounded by 12 triorganosilylphos-phanediyl moieties. The 24-metal-atom cluster consists of three planar Cu6 rings and two peripheral Cu3 cycles that all lie parallel to one another (Fig. 17). 

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