Monovalent structures derivatives

As a last example of a 1 1 structure derived from a cubic close-packed anion sublattice we mention that of the mineral sulvanite CU3VS4. Here, the copper atoms occupy three of the four positions of one set of tetrahedral holes, while the vanadium atom is located at one position of the other set. Thus, the anion is no longer tetrahedrally coordinated but has all four cation neighbours on the same side. In C113VS4 vanadium may be replaced by Nb and Ta and the sulphur by Se and Te (178). These compounds all are diamagnetic semiconductors containing monovalent copper and a pentavalent transition element, as does CuTaS3 (179) where Ta, however, is octahedrally coordinated. 

Behavior of Carbethoxynitrene toward Polyisoprene Structures. After studying the reaction of a number of divalent carbon derivatives with polyenes (17, 18), attention was directed to monovalent nitrogen derivatives. Of these, carbethoxynitrene, N—C02Et, gives addition reactions with olefins (12, 13). It can be produced either by photolysis of ethyl azidoformate (12), or by a-elimination (13) (Figure 5). 

Figure 1 Structure of a G-tetrad showing complexation around a monovalent cation (Na or ), and five possible G-quadruplex structures derived from intramolecular folding (a) basket, (b) propeller and (c) mixed hybrid structure ...

Several of the structure types found for the halides are observed for other important monovalent anion systems such as the trihydroxides and trihydrides and derivatives of these structures are observed for a variety of ternary phases (Haschke, 1975c and 1976b). Other monovalent anions, Y, are accommodated in PuBt3- and UCh-type RX3 phases by replacement of the X layers. The resulting RX2Y compositions are structural derivatives of the parent trihalide structures. These observations and the phase equilibria and crystal growth habits of the ternary derivatives support the conclusion that several of the trihalide structures are accurately described by alternation of RXj and X layers, but additional work is clearly necessary. 

As far as bis(pyrazolyl)hydroborato derivatives of monovalent ions are concerned, only the structure of Tl[BpBut Me] has been determined by x-ray diffraction (19). The structure consists of a monomer in which... 

Lautite CuAsS is another mineral with a structure related to ZnS (174—176), but since the S positions in sphalerite are occupied here with S, As and Cu, the lautite structure is better described as derived from the diamond structure. The coordination immediately reveals the existence of monovalent copper. The neighbourhood is... 

Compounds of monovalent silicon are predominantly diatomic molecules, though exceptions such as SiNH and SiCC are known. Due to the formation of pupil bonds, the structural parameters of these molecules or radicals are much closer to those of the carbon analogues than is observed in stable Si derivatives. 

Much like the search for protein-binding compounds requires consideration of tertiary structure in addition to peptide sequence, thinking about selective nucleic acid binding solely in the context of primary sequence is often an oversimplification. In the context of DNA recognition, a particularly important example of this is the case of G-quadruplexes. As their name implies, these structures consist of stacked tetrads of guanosine bases, typically ordered around a monovalent cation. One representative structure, a quadruplex derived from human telomeric DNA, is shown in Fig. 5 many variants of this motif formed by either parallel or antiparallel DNA strands have been observed. 

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