Tetrahedron complex Chain

The structures of silicates and related compounds contain anionic tetrahedron complexes of different configuration (single tetrahedra, pyrogroups, rings, chains, layers, frameworks etc.). Their comparative analysis considerably contributes to the sdentiiic ideas on the structures of crystalline materials in general. The interest in... 

If one takes into account the most specific features of a Si,0 tetrahedron complex, such as the number of tetrahedra in the chain period, or the types of rings which can be recognized in different layers, it is possible to estimate the total number of anionic tetrahedron complexes in the silicates as one hundred. 

ANIONIC TETRAHEDRON COMPLEXES IN THE FORM OF RINGS AND CHAINS... 

Several new types of anionic tetrahedron complexes were discovered during the last years an Isolated complex, built of 48 Sl,0 tetrahedra, pyrogroups [P2O7] In a phosphate mineral, a 18-membered [SiOs] rings, a [PO3] chain with 16 tetrahedra In the period, an interrupted [81205] framework, etc. The new scientific ideas on the structures of the siiicates and their analogues stimulate their appiications in different technologies (ex. shape selective catalysis with zeolites). 

Another zinc-utilizing enzyme is carbonate/dehydratase C (Kannan et al., 1972). Here, the zinc is firmly bound by three histidyl side chains and a water molecule or a hydroxyl ion (Fig. 27). The coordination is that of a distorted tetrahedron. Metals such as Cu(II), Co(Il), and Mn(ll) bind at the same site as zinc. Hg(II) also binds near, but not precisely at, this site (Kannan et al., 1972). Horse liver alcohol dehydrogenase (Schneider et al., 1983) contains two zinc sites, one catalytic and one noncatalytic. X-Ray studies showed that the catalytic Zn(II), bound tetrahedrally to two cysteines, one histidine, and water (or hydroxyl), can be replaced by Co(II) and that the tetrahedral geometry is maintained. This is also true with Ni(Il). Insulin also binds zinc (Adams etai, 1969 Bordas etal., 1983) and forms rhombohedral 2Zn insulin crystals. The coordination of the zinc consists of three symmetry-related histidines (from BIO) and three symmetry-related water molecules. These give an octahedral complex... 

Ogawa, T, Sugimoto, M, Kitajima, T, Sadozai, K K, Nukada, T, Synthetic studies on cell surface glycans. 51. Total synthesis of an undecasaccharide. A t)fpical carbohydrate sequence for the complex type of glycan chains of a glycoprotein. Tetrahedron Lett., 27, 5739-5742, 1986. 

Ionic surfactants with only one alkyl chain are generally extremely hydrophilic so that strongly curved and thus almost empty micelles are formed in ternary water-oil-ionic surfactant mixtures. The addition of an electrolyte to these mixtures results in a decrease of the mean curvature of the amphiphilic film. However, this electrolyte addition does not suffice to drive the system through the phase inversion. Thus, a rather hydrophobic cosurfactant has to be added to invert the structure from oil-in-water to water-in-oil [7, 66]. In order to study these complex quinary mixtures of water/electrolyte (brine)-oil-ionic surfactant-non-ionic co-surfactant, brine is considered as one component. As was the case for the quaternary sugar surfactant microemulsions (see Fig. 1.9(a)) the phase behaviour of the pseudo-quaternary ionic system can now be represented in a phase tetrahedron if one keeps temperature and pressure constant. 

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