Nachweis und Anwendung von Gaskomplexen beim Chemischen Transport

Evidence and Applications of Gaseous Complexes during the Chemical Transport By means of the chemical transport method the formation of gaseous complex compounds has been observed. Using Al₂Cl₆ as a transport agent, the chlorides FeCl₂, CoCl₂, NiCl₂, CuCl₂, PdCl₂, PtCl₂, MoCl₃, YCl₃, LaCl₃, ThCl₄ and UCl₄ are transported within a temperature gradient. Similary are transported by means of Ga₂Cl₆ the chlorides CoCl₂ and NiCl₂, by means of Fe₂Cl₆ the chlorides FeCl₂, CuCl₂ and YCl₃, by means of NbCl₅ the chlorides NaCl and CrCl₃. Examples concerning the practical application of gaseous complexes are refered.     

Direct determination of arsenic in acid digests of plant and peat samples using HG-AAS and ICP-SF-MS

A new analytical procedure for the reliable and direct determination of arsenic (As) in nitric acid digests of ombrotrophic peat samples in the low ng l⁻¹ range has been developed based on hydride generation-atomic absorption spectrometry (HG-AAS). The pre-reduction capabilities of KI/ascorbic acid and of l-cysteine in nitric acid digests of peat and plant samples for the conversion of As(V) to As(III) were tested systematically. Samples were digested with high purity nitric acid in a high-pressure microwave autoclave at 240 °C and subsequently measured using HG-AAS or ICP-SF-MS (inductively coupled plasma-sector field-mass spectrometry). Using KI/ascorbic acid as pre-reductant, the accuracy and precision were poor when digests of complex matrices, such as peat were analyzed for As by HG-AAS. However, 10 g l⁻¹ l-cysteine was successfully employed as pre-reductant in diluted nitric acid digests (3%, v/v) of peat samples prior to hydride generation of As with 0.5% (m/v) of NaBH₄ and 7 mol l⁻¹ HCl. The analytical procedure was critically evaluated by analyzing several certified plant reference materials, two in-house peat reference materials and by the determination of As in diluted digests of peat samples with ICP-SF-MS. The results for the determination of As in various peat and plant materials showed excellent agreement with the reference values. The method detection limits for the determination of As by the optimized HG-AAS procedure and by ICP-SF-MS were 23 ng g⁻¹ and 1.4 ng g⁻¹ in solid peat, respectively. The newly developed analytical procedure was applied to the determination of As in selected peat samples. Results for As in these peat samples obtained by the developed HG-AAS procedure and the optimized procedure for the determination of As with ICP-SF-MS were highly correlated (R² = 0.993, n = 12).     

Darstellung und Kristallstruktur von NaBi2AuO5

Synthesis and Crystal Structure of NaBi₂AuO₅ NaBi₂AuO₅ was obtained by hydrothermal reaction of ‘Bi₂O₅’, Au₂O₃ · 2H₂O and saturated aqueous NaOH solution at temperatures from 300 to 600°C and oxygen pressure from 3 × 10⁸ to 6 × 10⁸ Pa for the first time. The crystal structure (P4 b2; a = 1 220.02(6) pm; b = 386.68(3) pm; Z = 4; R_w = 0.022) consists of bisphenoidic distorted AuO₄ groups, which are stacked in c-direction. They are connected by square pyramidal BiO₅ units. Sodium is occupying holes within the Au/Bi/O framework thus formed.     

Loops on loops: generation of complex scaffolded peptides presenting multiple cyclic fragments

Scaffolded peptides presenting two different cyclic peptide fragments through a cyclic peptidomimetic scaffold in a site-selective fashion, were generated by stepwise solid phase synthesis and fragment condensation in parallel, demonstrating that either strategy is adequate to generate complex scaffolded peptides.     

Studies of complex reactions using modem hyphenated methods: alpha-pinene ozonolysis as a model reaction

Modern analytical equipment, in this case the combinations of gas chromatography (GC) with mass spectrometry (MS) and infrared spectroscopy (IR) and liquid chromatography (LC) with mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy and infrared spectroscopy, respectively, have been used to monitor complex reactions that do not only form one or two but a larger number of products. Additionally, side reactions of one primary product with a reactant form a second line of secondary products. To be able to propose formation pathways or even mechanistic interpretation of reactions like these, sophisticated analytical instrumentation is necessary to be able to observe all steps of such a reaction. In this case, the gas phase reaction of alpha-pinene with ozone has been used as a model reaction. A number of both volatile and low-volatile reaction products could be characterized and formation pathways for a reaction with ozone and OH radicals were proposed.     

Incorporation of bond-length constraints in Monte Carlo simulations of cyclic and linear molecules: Conformational sampling for cyclic alkanes as test systems

A simple method for incorporating bond-length constraints in Monte Carlo simulations of cyclic and linear molecules is described. As an example, the conformational behavior of five even-numbered cyclic alkanes is studied using Monte Carlo simulation and the MM2 force field. © 1994 by John Wiley & Sons, Inc.     

Sign change of the Soret coefficient of poly(ethylene oxide) in water/ethanol mixtures observed by thermal diffusion forced Rayleigh scattering

Soret coefficients of the ternary system of poly(ethylene oxide) in mixed water/ethanol solvent were measured over a wide solvent composition range by means of thermal diffusion forced Rayleigh scattering. The Soret coefficient S(T) of the polymer was found to change sign as the water content of the solvent increases with the sign change taking place at a water mass fraction of 0.83 at a temperature of 22 degrees C. For high water concentrations, the value of S(T) of poly(ethylene oxide) is positive, i.e., the polymer migrates to the cooler regions of the fluid, as is typical for polymers in good solvents. For low water content, on the other hand, the Soret coefficient of the polymer is negative, i.e., the polymer migrates to the warmer regions of the fluid. Measurements for two different polymer concentrations showed a larger magnitude of the Soret coefficient for the smaller polymer concentration. The temperature dependence of the Soret coefficient was investigated for water-rich polymer solutions and revealed a sign change from negative to positive as the temperature is increased. Thermodiffusion experiments were also performed on the binary mixture water/ethanol. For the binary mixtures, the Soret coefficient of water was observed to change sign at a water mass fraction of 0.71. This is in agreement with experimental results from the literature. Our results show that specific interactions (hydrogen bonds) between solvent molecules and between polymer and solvent molecules play an important role in thermodiffusion for this system.     

Einige Bemerkungen zu Einheiten in reinen kubischen Körpern

Ohne ZusammenfassungDiese Arbeit entstand im Rahmen eines durch das Land Nordrhein-Westfalen geförderten Forschungsvorhabens Explizite Theorie spezieller Typen algebraischer Zahlkörper.     

A Dimeric η1,η5‐Germole Dianion Bridged Titanium(III) Complex with a Multicenter Ti−Ge−Ge−Ti Bond

Dimeric germole dianion bridged Ti^III and Zr^IV complexes have been synthesized. In these complexes, the germole dianion adopts a formal η¹,η⁵ coordination to the two metal centers. The bonding situation in these bridged dimers is dominated by a covalent Ge?Ge interaction that results, for example, in a strong antiferromagnetic coupling of the d¹ Ti centers.     

The maximal normal -group

Let be a prime number and let be an abelian -group. Let be the maximal normal -subgroup of and the maximal -subgroup of its centre. Let be the torsion radical of . Then . The result is new for and 3, and the proof is new and valid for all primes .