Massenspektrometrische Untersuchungen der Gasphase über As2O5

Mass Spectrometric Investigations of the Gaseous Phase above As₂O₅ The gaseous phase above solid As₂O₅ has been investigated in the temperature range between 862 and 939 K by mass spectrometric methods. The presence of gaseous As₄O_x-molecules (6 ≤ × ≤ 10) and O₂ was proved. Using the partial pressures, heats of formation (Δ_fH°(900), kJ · mol^?1; 2nd law calculations) were calculated (As₄O_7,g: -1209,5; As₄O_8,g: -1361,9; As₄O_9,g: -1495,4; As₄O_10,g: -1618,8). The enthalpy of formation of solid As₂O₅ was determined to be Δ_fH°(298) = ?1007,9 kJ · mol^?1. The thermochemical data of the As₄O_x-molecules are discussed in context with possibilities for the synthesis of solid As₄O₁₀.     

Electron microscopy, spectroscopy, and first-principles calculations of Cs2O

Oxides of cesium play a key role in ameliorating the photoelectron emission of various opto-electronic devices. However, due to their extreme reactivity, their electronic and optical properties have hardly been touched upon. With the objective of better understanding the electronic and optical properties of Cs₂O in relationship to its structure, an experimental and theoretical study of this compound was undertaken. First-principles density functional theory calculations were performed. The preferred structural motif for this compound was found to be anti-CdCl₂. Here three Cs-O-Cs molecular layers are stacked together through relatively weak van-der-Waals forces. The energy bands were also calculated. The lowest transition at 1.45 eV, was found to be between the K point in the valence band to the Γ point in the conduction band. A direct transition at 2 eV was found in the center (Γ) of the Brillouin zone. X-ray powder diffraction, transmission electron microscopy and selected area electron diffraction were used to analyze the synthesized material. These measurements showed good agreement with the calculated structure of this compound. Absorption measurements at 4.2 K indicated two optical transitions with somewhat higher energy (indirect one at 1.65 and a direct transition at 2.2 eV, respectively). Photoluminescence measurements also showed similar transitions, suggesting that the lower indirect transition is enhanced by three nearby minima at 1.5 eV in the Brillouin zone.     

The Crystal Structure of Disodium Phosphonate,Na2HPO3

Anhydrous disodium phosphonate, Na₂HPO₃, was prepared by dehydration of its pentahydrate. The crystal structure of Na₂HPO₃ was solved from high resolution X‐ray powder diffraction data (P2₁/n; Z = 4; a = 9.6987(1), b = 6.9795(1), c = 5.0561(1) Å, β = 92.37(1)°; V = 341.97(1) ų). The crystal structure consists of two types of sodium‐oxygen polyhedra, which are connected via common edges and vertices forming layers perpendicular to [100]. These Na(1)‐ and Na(2)‐layers are interlinked via common edges, forming in a 3D‐framework. The resulting topology is providing oxygen arrangements that please the coordinative requirement of phosphorus(III).     

Beiträge zum 121Sb-Mößbauer-Effekt. VI. 121Sb-Mößbauer-Spektrum und Schwingungsspektrum von Sb2O5

Contributions to the ¹²¹Sb-Mössbauer Effect. VI. ¹²¹Sb-Mössbauer Spectrum and Vibrational Spectrum of Sb₂O₅ The results of ¹²¹Sb-Mössbauer spectroscopy at 4.2 K on pure Sb₂O₅, obtained by hydrothermal synthesis, are reported. The vibrational spectrum (i.r., raman) is correlated with the expectations of factor group analysis. The findings are compared to measurements carried out on samples hitherto regarded as Sb₂O₅.     

Über die Ammonolyse von Organometallen. XII. Die Ammonolyse von Dimethyl-diphenyl- und Dimethyl-dibenzyl-silan

Dimethyl-diphenyl and dimethyl-dibenzyl-silane react in liqu. NH₃ in the presence of KKH₂ giving rise to the formation of H₂N? Si(Me₂)? NH? Si(Me₃)? NHK (III); exclusively C₆H₅ and C₆H₅CH₂ are split off and substituted by NH₂. Reaction of the potassium compound III with the equivalent amount of NH₄Cl brings about a mixture of octamethylcyclotetrasilazane and hexamethylcyclotrisilazane.     

Dimeric Sandwich‐like Ion Pairs in the Crystal Structure of Tetrabutylammonium Ozonide Ammoniate

The novel ionic ozonide {[N(C₄H₉)₄](O₃)}₄·4.75NH₃ was synthesized by ion‐exchange reaction in liquid ammonia. The crystal structure was determined by single crystal diffraction at 100 K (monoclinic space group P2₁, a = 15.014(11) Å, b = 13.696(10) Å, c = 19.890(15) Å, β = 105.407(12)°, V = 3943(5) ų, Z = 2). The structure consists of a packing of sandwich‐like dimeric ion pairs in which two ozonide anions are interspersed between two tetrabutylammonium cations. Ammonia molecules from the solvent are localized in cavities in the structure. They are involved in hydrogen bonding with the ozonide ions. The desolvated tetrabutylammonium ozonide forms stable solutions in dichloromethane which may open up novel possibilities of tapping into the synthetic potential of the ozonide ion.     

RNA integrity as a quality indicator during the first steps of RNP purifications : A comparison of yeast lysis methods

Background  

The completion of several genome-sequencing projects has increased our need to assign functions to newly identified genes. The presence of a specific protein domain has been used as the determinant for suggesting a function for these new genes. In the case of proteins that are predicted to interact with mRNA, most RNAs bound by these proteins are still unknown. In yeast, several protocols for the identification of protein-protein interactions in high-throughput analyses have been developed during the last years leading to an increased understanding of cellular proteomics. If any of these protocols or similar approaches shall be used for the identification of mRNA-protein complexes, the integrity of mRNA is a critical factor.     

Ligand requirements for glmS ribozyme self-cleavage

Natural RNA catalysts (ribozymes) perform essential reactions in biological RNA processing and protein synthesis, whereby catalysis is intrinsic to RNA structure alone or in combination with metal ion cofactors. The recently discovered glmS ribozyme is unique in that it functions as a glucosamine-6-phosphate (GlcN6P)-dependent catalyst believed to enable "riboswitch" regulation of amino-sugar biosynthesis in certain prokaryotes. However, it is unclear whether GlcN6P functions as an effector or coenzyme to promote ribozyme self-cleavage. Herein, we demonstrate that ligand is absolutely requisite for glmS ribozyme self-cleavage activity. Furthermore, catalysis both requires and is dependent upon the acid dissociation constant (pKa) of the amine functionality of GlcN6P and related compounds. The data demonstrate that ligand is integral to catalysis, consistent with a coenzyme role for GlcN6P and illustrating an expanded capacity for biological RNA catalysis.     

Li2H4I2O10, das erste Tetrahydrogendimesoperiodat

Li₂H₄I₂O₁₀, the First Tetrahydrogendimesoperiodate Li₂H₄I₂O₁₀ has been obtained as an intermediate during the dehydration of LiH₄IO₆ · H₂O to LiIO₄, for the first time. According to the results of an X-ray structure determination (monoclinic, P2₁/n, a = 533.98(4), b = 471.85(4), c = 1431.48(10) pm, β = 91.614(7)°, Z = 2, 726 diffractometer data, R = 0.056), Li₂H₄I₂O₁₀ contains the previously unknown tetrahydrogendimesoperiodate ion H₄I₂O₁₀^2?, consisting of two edge-shared IO₆ octahedra. They are connected with LiO₆ octahedra via common edges and vertices. The crystals are non-merohedrally twinned along (100).