Über Pentaiodoplatinate M2PtI5 · 2 H2O (M  K,Rb, NH4). Gemischtvalente Verbindungen mit linear kettenförmigen,iodverbrückten Anionen

On Pentaiodoplatinates(II, IV) M₂PtI₅ · 2 H₂O (M ? K, Rb, NH₄). Mixed-valence Compounds with Linear Chain Iodobridged Anions Pentaiodoplatinates M₂PtI₅ · 2 H₂O (M ? K, Rb, NH₄) are obtainable by crystallization from aqueous solutions formed by dissolving of tetrachloroplatinates(II) in highly concentrated solutions of alkali iodides MI. The structural parameters were determinated from single crystal data. The compounds are classed with the group of linear chain mixed-valence platinum complexes from Wolffram's Salt type. In the crystal structures PtI₄-units are connected by asymnetric I-bridges to [PtI₄I_2/2] chains. There was no evidence of the existence of crystalline tetraiodoplatinates(II) M₂PtI₄.     

Die Kristallstruktur des Lithiumdigermanats Li2Ge2O5

The compound Li₂Ge₂O₅ has been prepared by annealing a glassy melt (500° C). The lattice parameters have been determined from single crystal photographs:a=5,99,b=15,19,c=4,97 Å and β=90,0°, space group C _S ⁴ :?Cc. Li₂Ge₂O₅ has a layer structure and is isostructural with Li₂Si₂O₅.     

Die Kristallstruktur von Rb6Si10O23

Zusammenfassung Die Kristallstruktur der Verbindung Rb₆Si₁₀O₂₃ (bisher als Rb₂Si₄O₉ beschrieben) wurde mit Hilfe dreidimensionaler Röntgendaten bestimmt und bis zu einemR-Wert von 0,078 verfeinert. Die Gitterparameter der rhombischen Elementarzelle (C2mm-C _2v ¹⁴ ) betragen:a=9,348,b=16,290 undc=8,055 Å. Die Struktur besitzt ein dreidimensionales Gerüst aus [SiO₄]-Tetraedern, die sowohl über 4 als auch über 3 Ecken vernetzt vorliegen. Die Anordnung der Tetraeder kann aus der Tridymitstruktur abgeleitet werden und zeigt noch deutlich pseudohexagonale Symmetrie. Bei 500 °C geht die Verbindung in eine Hochtemperaturform mit hexagonaler Symmetrie über (a=9,48 undc=8,16 Å bei 500 °C).

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The crystal structure of Rb₆Si₁₀O₂₃

The crystal structure of the compound Rb₆Si₁₀O₂₃ (identical with Rb₂Si₄O₉) has been determined by means of three-dimensional X-ray data resulting anR-value of 0.078. The lattice parameters of the orthorhombic unit cell (C2mm-C _2v ¹⁴ ) are:a=9.348,b=16.290 andc=8.055 Å. The structure consists of a three-dimensional framework built up by [SiO₄] tetrahedra sharing 4 as well as 3 corners. The arrangement of tetrahedra can be derived from tridymite structure and exhibits pseudohexagonal symmetry. The compound transforms to a high-temperature modification with hexagonal symmetry at 500 °C (a=9.48 andc=8.16 Å).

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Mit 3 Abbildungen     

Die Verbindungen 2SiO2·P2O5 und 2GeO2·P2O5

Zusammenfassung Bei röntgenographischen Untersuchungen im System GeO₂-P₂O₅ wird eine Verbindung der Zusammensetzung 2 GeO₂·P₂O₅ aufgefunden. Einkristallaufnahmen ergeben eine hexagonale (trigonale) Elementarzelle mita=7,99₈ undc=24,8₆ Å. Die schon beschriebene Verbindung 2 SiO₂·P₂O₅ erweist sich als isotyp:a=7,86₂ undc=24,1₃ Å.     

Structural Comparison of Oligoribonucleotides and Their 2′-Deoxy-2′-fluoro Analogs by heteronuclear NMR spectroscopy

1-(2′-Deoxy-2′-fluororibofuranosyl)pyrimidines were synthesized and incorporated into an RNA oligonucleotide to give 5′-r[C_fGC_f(U_fU_fC_fG)GC_fG]-3′ (C_f: short form of C = 2′-deoxy-2′-fluorocytidine; U_f: short form of U = 2′-deoxy-2′-fluorouridine). The oligomer was investigated by means of UV, CD, and NMR spectroscopy to address the question of how F-labels can substitute ¹³C-labels in the ribose ring. Through-space (NOE) and through-bond (scalar couplings) experiments were performed that make use of the ameliorated chemical-shift dispersion induced by ¹⁹F as an alternative heteronucleus. A comparison of the structures of fluorinated vs. unmodified oligomer is given. It turns out that the fluorinated oligonucleotide exists in a 14:3 equilibrium between a hairpin and a duplex conformation, in contrast to the unmodified oligonucleotide which predominantly adopts the hairpin conformation. Furthermore, the fluorinated hairpin structure adopts two distinct conformations that differ in the sugar conformation of the U and C nucleoside units, as detected by the ¹⁹F-NMR chemical shifts. The role of the 2′-OH group as stabilizing element in RNA secondary structure is discussed.     

Minimal kernels of Dirac operators along maps

Let M be a closed spin manifold and let N be a closed manifold. For maps and Riemannian metrics g on M and h on N, we consider the Dirac operator of the twisted Dirac bundle . To this Dirac operator one can associate an index in . If M is 2‐dimensional, one gets a lower bound for the dimension of the kernel of out of this index. We investigate the question whether this lower bound is obtained for generic tupels .     

Simultaneous Determination of Hydrogen Peroxide and Organic Hydroperoxides in Water

The kinetics of the reactions of H 2 O 2 and of methyl, ethyl, tert -butyl, and cumene hydroperoxides with I m were investigated in the presence and absence of molybdate as catalyst. These results were utilized to develop an analytical method for the simultaneous determination of H 2 O 2 and organic hydroperoxides in aqueous solutions. The total amount of H 2 O 2 and organic hydroperoxides can be determined by the spectrophotometric measurement of $ {\rm I}_3^ - $ formed quantitatively during 30 min of heating at 60°C. Catalase selectively decomposes H 2 O 2 in solutions containing organic hydroperoxides. The total amount of the latter can therefore be determined iodometrically after H 2 O 2 decomposition. In the oxidation of leuco crystal violet to crystal violet by H 2 O 2 and organic hydroperoxides, horseradish peroxidase exerts similar activities in the reactions involving methyl and ethyl hydroperoxides and H 2 O 2 , but its activity is much lower with tert -butyl and cumene hydroperoxide. It was observed that acetate buffer is unsuitable for pH adjustment in this type of hydroperoxide determination in consequence of the slow oxidation of the dye in the blank solution.     

Epitaxy of helical polyolefins

The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices.