Zur jodometrischen Analyse eines Gemenges von Sulfid; Sulfit und Thiosulfat

Ohne Zusammenfassung     

Die Kristallstruktur des SF5−-Anions

Crystal Structure of the SF₅^?-Anion The carbanion SF₅? C(CF₃)₂^? decomposes slowly forming SF₅^?, and (CF₃)₂C?C(CF₃)₂. The pentafluorosulfates(IV) grow in large crystals which are stable for prolonged times in presence of a SF₄ vapour pressure. Crystal structure analysis of Rb⁺SF₅^? (Pbnm, a = 776.1(14), b = 990.3(5), c = 614.1(3) pm, Z = 4) revealed the SF₅^? anion in the expected square pyramidal structure. The axial bond is 15.9 pm shorter than the average equatorial bonds. The sulfur atom is located below the equatorial fluorine atoms. Pure Cs⁺SF₅^?-crystals seem to be notoriously twinned. Accidentally we isolated a double salt (Cs⁺)₆(SF₅^?)₄ (HF₂^?)₂ (P4 b2, a = 1031.7(15), c = 627.6(9) pm, Z = 1). Herein the anion SF₅^? has the same structure as in Rb⁺SF₅^?.     

Ex-vivo determination of blood glucose by microdialysis in combination with infrared attenuated total reflection spectroscopy

Several biosensors have been developed for continuous monitoring of human blood glucose, which is desirable for insulin-dependent diabetic patients. Developments in the field of quantitative assays using infrared attenuated total reflection spectroscopy allow the determination of metabolites at low concentrations. The microdialysis technique can provide a continuous sampling of extracellular body fluids. As only compounds of low molecular weight are passed on, infrared spectrometric quantitation is eased considerably. Samples were obtained by microdialysis of human blood plasma and aqueous glucose solutions. Multivariate calibration by partial least-squares was evaluated for its analytical performance in ex-vivo blood glucose monitoring. Mean squared prediction errors obtained by cross validation were 5.4 mg/dL for dialysate samples from different patients and 1.3 mg/ dL for dialysates from glucose solutions. Further investigations were carried out to achieve miniaturization of the measuring and detection device.     

Relaxation of quantum hydrodynamic modes

In this article, we develop a series of hierarchical mode‐coupling equations for the momentum cumulants and moments of the density matrix for a mixed quantum system. Working in the Lagrange representation, we show how these can be used to compute quantum trajectories for dissipative and nondissipative systems. This approach is complementary to the de Broglie–Bohm approach in that the moments evolve along hydrodynamic/Lagrangian paths. In the limit of no dissipation, the paths are the Bohmian paths. However, the “quantum force” in our case is represented in terms of momentum fluctuations and an osmotic pressure. Representative calculations for the relaxation of a harmonic system are presented to illustrate the rapid convergence of the cumulant expansion in the presence of a dissipative environment. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Die Entwässerung von Zeolithgermanaten

Zusammenfassung Germanate des TypsM ₃HGe₇O₁₆·4H₂O (M=Alkali) bzw.M ₂Ge₇O₁₆·xH₂O (M=Ba, Pb) mit Zeolithcharakter wurden mittelsDTA, Thermogravimetrie und mit derGuinier-Lenné-Kamera im Temperaturbereich von 20 bis etwa 1000°C bei Atmosphärendruck untersucht.Die Elementarzelle der Germanate schrumpft beim Aufheizen infolge Wasserabgabe; erst nach weiterer Temperaturerhöhung macht sich eine Ausdehnung bemerkbar. Während der NH₄–Ge-Zeolith bereits bei 160°C instabil wird, bleibt das Gerüst des Rb–Ge-Zeoliths bis etwa 600°C bestehen. Die Li-und Na–Ge-Zeolithe verhalten sich wie der K–Ge-Zeolith. Si/Ge-Austausch im NH₄–Ge-Zeolith unterdrückt die Bildung der GeO₂-Cristobalit- und-Rutilform.Die bei höheren Temperaturen entstehenden wasserfreien Germanate lassen sich zum größten Teil identifizieren.

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Dehydratation of zeolitic germanates

Germanates of typeM ₃HGe₇O₁₆·4H₂O (M=alkali metal ion) andM ₂Ge₇O₁₆·xH₂O (M=Ba, Pb) with zeolitic properties have been investigated by means ofDTA, thermogravimetry and theGuinier-Lenné-X-ray camera within the temperature range of 20 to approxim. 1000°C at atmospheric pressure.The germanates exhibit a comparatively narrow temperature region at which dehydratation occurs. Increase of temperature leads first to contraction due to the loss of water and later on to dilatation of the lattice parameters. Temperatures at which disintegration of the zeolite framework begins diverge considerably. Thus breakdown of the NH₄–Ge-zeolite lattice starts at 160°C whereas Rb–Ge-zeolite is stable up to 600°C. The observations made with Li- and Na–Ge-zeolites reveal similar properties as those of K–Ge-zeolite. Partial substitution of Ge by Si in NH₄–Ge-zeolite suppresses formation of the GeO₂-cristobalite- and rutile-modification.Identification of the dehydratated germanates originating at higher temperatures from the zeolites is possible in most cases.

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Mit 6 Abbildungen     

Frenkel exciton model of ultrafast excited state dynamics in AT DNA double helices

Recent ultrafast experiments have implicated intrachain base-stacking rather than base-pairing as the crucial factor in determining the fate and transport of photoexcited species in DNA chains. An important issue that has emerged concerns whether or not a Frenkel excitons is sufficient one needs charge-transfer states to fully account for the dynamics. Here we present an SU(2)  SU(2) lattice model which incorporates both intrachain and interchain electronic interactions to study the quantum mechanical evolution of an initial excitonic state placed on either the adenosine or thymidine side of a model B DNA poly(dA).poly(dT) duplex. Our calculations indicate that over several hundred femtoseconds, the adenosine exciton remains a cohesive excitonic wave packet on the adenosine side of the chain where as the thymidine exciton rapidly decomposes into mobile electron/hole pairs along the thymidine side of the chain. In both cases, the very little transfer to the other chain is seen over the time-scale of our calculations. We attribute the difference in these dynamics to the roughly 4:1 ratio of hole versus electron mobility along the thymidine chain. We also show that this difference is robust even when structural fluctuations are introduced in the form of static off-diagonal disorder.     

Time-convolutionless master equation for mesoscopic electron-phonon systems

The time-convolutionless master equation for the electronic populations is derived for a generic electron-phonon Hamiltonian. The equation can be used in the regimes where the golden rule approach is not applicable. The equation is applied to study the electronic relaxation in several models with the finite number of normal modes. For such mesoscopic systems the relaxation behavior differs substantially from the simple exponential relaxation. In particular, the equation shows the appearance of the recurrence phenomena on a time scale determined by the slowest mode of the system. The formal results are quite general and can be used for a wide range of physical systems. Numerical results are presented for a two level system coupled to Ohmic and super-Ohmic baths, as well as for a model of charge-transfer dynamics between semiconducting organic polymers.     

Hydrogen storage properties of metal nitroprussides M[Fe(CN)5NO], (M = Co, Ni)

The volumetric hydrogen adsorption isotherms of two isostructural dehydrated cubic metal nitroprussides M[Fe(CN)5NO] (M = Co2+, Ni2+) have been measured up to a pressure of 760 Torr at 77 and 87 K. These materials are among the most efficient H2 sorbents based on porous coordination polymers reported to date. The H2 uptake in both materials is approximately 1.6 wt % at 77 K and 760 torr. These H2 capacities match those reported recently in the structurally related M3[Co(CN)6]2 compounds and are approximately 25% higher than those reported for Zn4O(1,4-benzenedicarboxylate)3 under the same conditions of temperature and pressure. The isosteric heats of H2 adsorption calculated from the 77 and 87 K isotherms for both materials were found to vary from approximately 7.5 kJ/mol at 0.40 wt % coverage to approximately 5.5 kJ/mol at 1.2 wt % coverage. The N2 BET surface areas were determined to be 634 m2/g and 523 m2/g for M = Ni and M = Co, respectively.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.