Sulfido‐bridged rhenium–carbonyl complexes with planar and folded Re2S2 cores

The two sulfido‐bridged dirhenium complexes bis(μ‐4‐methoxy­phenyl­sulfido‐S)bis­(tetra­carbonyl­rhenium), [Re₂(C₇H₇­OS)₂­(CO)₈], and bis(μ‐naphthyl­sulfido‐S)bis[tricarbonyl(dicyclohexylphosphane)rhenium], [Re₂­(C₁₂­H₂₃P)₂(C₁₀H₇S)₂­(CO)₆], show different geometries of the common Re₂S₂ core. The 4‐methoxy­phenyl derivative has crystallographic symmetry and the naphthyl derivative has C² symmetry. This results from intramolecular repulsion due to different substitution patterns at the Re and S atoms.     

Oligonary Nitrides and Oxonitrides of Si,P, Al,and B in Combination with Rare Earth or Transition Metals as well as Molecular Precursor Compounds with Nitrido Bridges M‐N‐Si (M = Ti,Zr, Hf,W, Sn)

A novel synthetic approach is presented leading to hitherto unknown nitridosilicates, oxonitridosilicates, oxonitridoaluminosilicates, carbidonitridosilicates, as well as nitridoborates and oxonitridoborates of rare earth elements, alkali, and alkaline earth metals. Typically, the respective metals were reacted with silicon diimide, aluminum nitride, or poly(boron amide imide), respectively, under pure nitrogen atmosphere utilizing a radiofrequency furnace. Usually, the compounds are obtained within short reaction periods as coarsely crystalline products. Zink nitridophosphates of the sodalite structure type were obtained by the reaction of phosphorus nitride imide with zinc or zinc chalcogenides, respectively. Several molecular metal silylamides and imides containing nitridobridges between the metals and silicon were obtained by the reaction of differently chlorinated disilazanes with metal chlorides. During these investigations hitherto unknown bis(trimethylsilyl)ammonium salts have been discovered. Furthermore, we report about the synthesis of N‐silyl metal hydrazides.     

Reaction of Hexamethyldisilazane with Borane in Tetrahydrofuran

Hexamethyldisilazane 1 reacts with borane in tetrahydrofuran (THF? BH₃, 2 ) first by formation of an adduct (Me₃Si)₂NH? BH₃ ( 3 ), and then either to the N,N-bis-(trimethylsilyl)-μ-aminodiborane 5 or to the mixture of 5 and N-trimethylsilyl-μ-aminodiborane(6) 6 , depending on the reaction conditions. The compounds 5 and 6 can be quantitatively converted to the N,N′,N″-tris(trimethylsilyl)borazine 4 . Three intermediates can be identified, namely N,N-bis(trimethylsilyl)borane 7 , N,N-bis(trimethylsilyl)amino(N′-trimethylsilylamino)borane 8 and N-trimethylsilylaminoborane-trimer. All products and intermediates were characterized by multinuclear NMR spectroscopy, and coupling constant ¹J(²⁹Si, ¹⁵N) were measured from ²⁹Si NMR spectra by using the Hahn-echo-extended (HEED) INEPT pulse sequence.     

The path player game

We give an explicit PDE characterization for the solution of the problemof maximizing the utility of both terminal wealth and intertemporal consumption undermodel uncertainty. The underlying market model consists of a risky asset, whosevolatility and long-term trend are driven by an external stochastic factor process. Therobust utility functional is defined in terms of a HARA utility function with risk aversionparameter 0 < α < 1 and a dynamically consistent coherent risk measure, whichallows for model uncertainty in the distributions of both the asset price dynamics andthe factor process. Ourmethod combines recent results by Wittmüß (Robust optimizationof consumption with random endowment, 2006) on the duality theory of robustoptimization of consumption with a stochastic control approach to the dual problemof determining a ‘worst-case martingale measure’.     

Performance and limitations of the unsteady RANS approach

Turbulent flows in complex geometries often exhibit an oscillating behavior of large coherent structures, even in the case of steady state boundary conditions. Recently, numerous efforts have been made to resolve these oscillations by means of numerical simulations. Unfortunately, large-eddy simulations are often very time- and memory-consuming in the case of complex flows. Therefore, the unsteady RANS (URANS) approach is an attractive alternative, especially when numerical simulations are used as a design and optimization tool. Here, two complex flow situations are presented, the tundish flow and a jet in a crossflow. For these flows, relationships between the Strouhal number and important flow parameters are known from experiments. In the paper, URANS models are applied to resolve those relationships also numerically. The evaluation of the numerical results demonstrates the abilities and the limitations of the URANS approach when resolving the dynamics of large coherent structures in complex flows. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Antibacterial Activity and Synergistic Effect of Biosynthesized AgNPs with Antibiotics Against Multidrug-Resistant Biofilm-Forming Coagulase-Negative Staphylococci Isolated from Clinical Samples

Silver nanoparticles form promising template for designing antimicrobial agents against drug resistant pathogenic microorganisms. Thus, the development of a reliable green approach for the synthesis of nanoparticles is an important aspect of current nanotechnology research. In the present investigation, silver nanoparticles synthesized by a soil Bacillus sp. were characterized using UV–vis spectroscopy, FTIR, SEM, and EDS. The antibacterial potential of biosynthesized silver nanoparticles, standard antibiotics, and their conjugates were evaluated against multidrug-resistant biofilm-forming coagulase-negative S. epidermidis strains, S. aureus, Salmonella Typhi, Salmonella Paratyphi, and V. cholerae. Interestingly, silver nanoparticles (AgNPs) showed remarkable antibacterial activity against all the test strains with the highest activity against S. epidermidis strains 145 and 152. In addition, the highest synergistic effect of AgNPs was observed with chloramphenicol against Salmonella typhi. The results of the study clearly indicate the promising biomedical applications of biosynthesized AgNPs.     

A Highly K+‐Selective Phenylaza‐[18]crown‐6‐Lariat‐Ether‐Based Fluoroionophore and Its Application in the Sensing of K+ Ions with an Optical Sensor Film and in Cells

Herein, we report the synthesis of two phenylaza‐[18]crown‐6 lariat ethers with a coumarin fluorophore ( 1 and 2 ) and we reveal that compound 1 is an excellent probe for K⁺ ions under simulated physiological conditions. The presence of a 2‐methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat‐free phenylaza‐[18]crown‐6 ether analogues. Probe 1 shows a high K⁺/Na⁺ selectivity and a 2.5‐fold fluorescence enhancement was observed in the presence of 100 mM K⁺ ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8 % per 1 mM K⁺ within the range 1–10 mM K⁺. The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K⁺ ions on both the extracellular and intracellular levels.     

Generalization in large committee machines

We study generalization in large committee machines. For a model with nonoverlapping receptive fields a full replica calculation yields results qualitatively similar to those for single-layer machines. For a fully connected architecture, within the annealed approximation we find a transition from a symmetric state to one with specialized hidden units, accompanied by a discontinuous drop in the generalization error, for both binary and continuous weights. The poorly generalizing symmetric states are metastable for arbitrarily large training sets.