[ReCl2(NS)(NSCl)(Pyridin)2], ein Thionitrosyl-chlorthio-nitrenkomplex des Rheniums

[ReCl₂(NS)(NSCl)(Pyridine)₂], a Thionitrosyl-chlorothionitrene Complex of Rhenium The title compound was obtained by the reaction of pyridine with either [ReCl₃(NSCl)₂POCl₃] or [ReCl₃(NSCl)₂]₂ · (μ-N₂S₂) under the reducing action of dichloromethane. It is slightly soluble in CH₂Cl₂, from which it can be obtained in form of black crystals. The IR spectrum is reported. The crystal structure of [ReCl₂(NS)(NSCl)(Pyridine)₂] was determined by X-ray diffraction (R = 0.027 for 2105 observed reflexions). Crystal data: a = 1551.6, b = 694.9, c = 1513.2 pm, β = 96.50°, space group P2₁/c, Z = 4. In the monomer molecules, each rhenium atom has a distorted octahedral coordination of two cis-chlorine atoms, two cis-nitrogen atoms of the pyridine ligands and two cis-nitrogen atoms of the thionitrosyl and chloro thionitrene ligands. One of the pyridine groups is in trans position to the nearly linear thionitrosyl group (angle ReNS 176°) with distances ReN of 177 pm and NS of 152 pm. However, in the trans position of the chlorothionitrene group (angle ReNS 159°, distances ReN 189 pm, NS 149 pm) a chlorine atom is found.     

High turnover number and rapid, room-temperature amination of chloroarenes using saturated carbene ligands

[equation--see text] A catalytic system for the mild amination of aryl chlorides is described. This system consists of a Pd(0) precursor and a dihydroimidazoline carbene ligand, which is generated in situ from its protonated tetrafluoroborate salt (2). Using this catalyst, aryl and heteroaryl chlorides react with secondary amines and anilines within hours at room temperature. Turnover numbers as high as 5000 are obtained at elevated temperatures for reaction of morpholine with an unactivated aryl chloride.     

Maniplating the phenolic acid content and digestibility of italian ryegrass (Lolium multiflorum)b y vacuolar-targeted epession of a fungal ferulic acid esterase

In grass cell walls, ferulic acid esters linked to arabinosyl residues in arabinoxylans play a key role in crosslinking hemicellulose. Although such crosslinks have a number of important roles in the cell wall, they also hinder the rate and extent of cell wall degradation by ruminant microbes and by fungal glycohydrolyase enzymes. Ferulic acid esterase (FAE) can release both monomeric and dimeric ferulic acids from arabinoxylans making the cell wall more susceptible to further enzymatic attack. Transgenic plants of Lolium multiflorum expressing a ferulic acid esterase gene from Aspergillus niger, targeted to the vacuole under a constitutive rice actin promoter, have been produced following microprojectile bombardment of embryogenic cell cultures. The level of FAE activity was found to vary with leaf age and was highest in young leaves. FAE expression resulted in the release of monomeric and dimeric ferulic acids from cell walls on cell death and this was enhanced severalfold by the addition of exogenous β-1,4-endoxylanase. We also show that a number of plants expressing FAE had reduced levels of cell wall esterified monomeric and dimeric ferulates and increased in vitro dry-matter digestibility compared with nontransformed plants.     

Ultrathin-layer chromatography

The development of ultrathin-layer silica gel plates with a monolithic structure opens up a new dimension in thin-layer chromatography (TLC). The very small layer thickness of approximately 10 microm and the absence of any kind of binder in combination with the framework of this stationary phase lead to new and improved properties of these ultrathin-layer chromatographic (UTLC) silica-gel plates compared with conventional TLC and high-performance TLC (HPTLC) precoated layers. First of all, the advantages of the UTLC plates are the very short migration distances and, in combination with this, the short development times as well as the very low consumption of solvents as the mobile phase in connection with high sensitivity. The separations of amino acids, pesticides, pharmaceutically active ingredients, phenols, and plasticizers effectively demonstrate the possibilities of the new ultrathin-layer silica-gel plates. Furthermore, a comparison of UTLC, HPTLC, and TLC concerning retention behavior, efficiency, detection limits, migration times, and solvent consumption is performed effectively by the separation of caffeine and paracetamol.     

Practical aspects of birdcage coils.

Numerical modeling and experimental results are presented for a variety of birdcages for high-field MRI microscopy. The data include the first published numerical calculations and experimental measurements of magnetic filling factors of birdcages or other MRI coils. Fast, 3D calculations for shielded coils are demonstrated using the Biot-Savart law along with energy minimization. It is shown that the near-field, higher-order inhomogeneity effects remaining after a first-order, asymmetry correction may easily exceed 20% in situations where it is desirable to maximize filling factor. It is also found that an order-of-magnitude improvement in the accuracy of predicted capacitor values may be achieved by using a more detailed circuit model of the birdcage resonator.     

Ground‐state structures of polymers

Two‐ and three‐dimensional structures A_xB_y can be characterized by the numbers T₁ and T₂ of nearest and next‐nearest neighbors of the same kind. A small number of structures at the border of the T₁, T₂ structure map is stabilized by enthalpy compared to an increased number of entropy stabilized structures. About 60 three‐dimensional structures with T₁=2 nearest neighbors of all A atoms are suitable for infinite chains of polymers like (CH)_∞, (CHCH₂)_∞, or (CH₂)_∞. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1944–1955, 2001     

Ultra-Thin Layer Chromatography (UTLC) — A New Dimension in Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Miniaturization is general trend in modern analytical methods, with the main targets of increasing sensitivity, shortening analysis...     

A Conservative,Entropic Multispecies BGK Model

We derive a conservative multispecies BGK model that follows the spirit of the original, single species BGK model by making the specific choice to conserve species masses, total momentum, and total kinetic energy and to satisfy Boltzmann’s \(\mathcal {H}\)-Theorem. The derivation emphasizes the connection to the Boltzmann operator which allows for direct inclusion of information from higher-fidelity collision physics models. We also develop a complete hydrodynamic closure via the Chapman-Enskog expansion, including a general procedure to generate symmetric diffusion coefficients based on this model. We numerically investigate velocity and temperature relaxation in dense plasmas and compare the model with previous multispecies BGK models and discuss the trade-offs that are made in defining and using them. In particular, we demonstrate that the BGK model in the NRL plasma formulary does not conserve momentum or energy in general.     

Oxygen nonstoichiometry and electrical conductivity of the solid solutions La2−xSrxNiOy (0≤x≤0.5)

Oxygen nonstoichiometry and electrical resistance of a series La_2−xSr_xNiO_y solid solutions, where x=0.0, 0.2 and 0.5 in argon flows at oxygen partial pressures 1.5, 10.2, 49.2, 100 and 286 Pa within the temperature range of 20–1050°C were studied. Nickelate oxygen desorption/sorption spectra when heating–cooling at constant rate demonstrated strong dependence of cation composition of the samples. Unlike La_1.5Sr_0.5NiO_y compounds those of La₂NiO_y and La_1.8Sr_0.2NiO_y have weakly bonded oxygen, capable to exchange reversibly with the gas phase at the temperatures higher than 250°C. The equilibrium values of oxygen nonstoichiometry and specific resistance for the these nickelates were determined at 300–1050°C and p_O2=1.5–286 Pa as a functions of temperature versus oxygen partial pressure. All nickelate studied appear to be p-type conductors with metal electric conductivity at equilibrium states.