Mechanistic analysis of the oxygen reduction reaction at (La,Sr)MnO3 cathodes in solid oxide fuel cells

The primary aim of this work was to establish the mechanism of the oxygen reduction reaction (ORR) at (La(0.8)Sr(0.2))0.98MnO3 (LSM)-based cathodes in solid oxide fuel cells. Rate equations, based on the Butler-Volmer equation and employing either Langmuir or Temkin adsorption conditions for reactant and intermediate species, were derived, yielding predicted reaction orders and transfer coefficients. Experimental data were collected using half-cell cyclic voltammetry in a variable pO2 atmosphere (0.03 to 1 atm) at 600 to 900 degrees C, using both dense and porous LSM-based cathodes, employed to establish the impact of the accessibility of the active site on cathode activity. The rate of the ORR at dense LSM has been found to be limited by the dissociation of O(2ads)- at low currents and by the first electron-transfer step, reducing O(2ads) to O(2ads)-, at high currents. However, at porous LSM cathodes, the reaction mechanism is more difficult to deduce because the electrode morphology impacts significantly on the measured kinetic and mechanistic parameters, giving anomalous transfer coefficients of <0.5.     

Metastable 11 K Superconductor Na(1-y)Fe(2-x)As(2)

The topochemical deintercalation of Na(+) ions from solid NaFeAs at room temperature in THF with iodine yields the superconducting phase Na(1-y)Fe(2-x)As(2) (T(c) ≈ 11 K). This metastable iron arsenide decomposes at 120 °C and is not accessible by high-temperature solid-state synthesis. X-ray powder diffraction confirms the ThCr(2)Si(2)-type structure, but reveals very small coherently scattering domains with a mean composition Na(0.9(2))Fe(1.7(1))As(2). HRTEM investigations show crystalline as well as strongly distorted areas with planar defects. The latter are probably due to sodium loss and disorder which is also detected by (23)Na solid state NMR. The (57)Fe-M?ssbauer spectrum of Na(1-y)Fe(2-x)As(2) shows one type of iron atoms in tetrahedral coordination. All results point to one crystallographic phase with very small domains due to fluctuations of the chemical composition. From electronic reasons we suggest the superconducting phase is presumably NaFe(2)As(2) in the ordered fractions of the sample.     

D-optimal design of an untargeted HS-SPME-GC-TOF metabolite profiling method

In recent times we have seen the development of many "-omics" technologies. One of the youngest is undoubtedly metabolomics, which aims to define the whole chemical fingerprint unique to each specific organism. The development and optimisation of an untargeted high-throughput method capable of investigating the volatile fraction of a biological system represents a crucial step for the success of such holistic approaches, and specific optimisation criteria must be developed in connection with suitable experimental designs. In this paper experimental designs (D-optimal) were applied for the first time as an automatic optimisation tool to an untargeted HS-SPME-GC-TOF method. In this case, optimal conditions correspond to a maximal number of detected features, in order to provide a fingerprint that is as complete as possible. The system under study is the grape berry. Four variables were considered: the type of fibre, extraction time, equilibration time and temperature. The results show that the D-optimal design methodology provides an easily interpretable assessment of experimental settings. This and other specific properties of the D-optimal design, such as the possibility to explicitly exclude certain experimental conditions, make it an extremely suitable strategy for method optimisation in untargeted metabolomics.     

Microwave‐assisted synthesis of α‐hydroxy‐benzylphosphonates and ‐benzylphosphine oxides

A series of α‐hydroxy‐benzylphosph‐ onates and ‐benzylphosphine oxides was synthesized by the Na₂CO₃‐catalyzed microwave‐assisted addition of dialkyl phosphites and dipenylphosphine oxide to P‐substituted benzaldehydes. The solventless reaction provided the products in short reaction times and in 71–88% yield. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:15–17, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20649     

Synthesis of hexaazacryptands containing furan and benzene groups in the bridging arms

Two new hexaazacryptands were prepared. One contains two propylene groups and a 2,5-furandimethylene unit between the nitrogen atoms of each bridge. The other has two propylene groups and a p-phenylene unit between the nitrogen atoms of each bridge.     

Pion condensation in heavy ion collisions

We calculate the pion spectrum in dense nuclear matter for finite temperatures. The critical temperatureT _c(ρ) that marks the beginning of a second order phase transition due to pion condensation is given in a phase diagram. We show that in heavy ion collisions, pion condensation should occur, leading to an enhancement in the formation of nuclear shock waves.     

Zinc, copper and aluminium in the corpuscular components of peripheral blood in patients with pre-terminal and terminal renal failure

Summary Trace elements play an essential role in the activation and regulation of metabolic processes. By using the flameless graphite furnace-AAS, accurate results can be obtained. In order to verify blood cells as more representative than plasma to reflect the whole body content of trace elements at uremic state, two patient groups, one with preterminal renal failure (n=40) and the second with chronic renal failure undergoing hemodialysis (n=20) were examined. The concentration levels of zinc, copper and aluminium were measured in different matrices, i.e. whole blood, plasma and corpuscular blood components. The analytical technique is eligible to isolate mono- and polymorphnuclear leucocytes for the determination of intracellular contents. In agreement with other reports, zinc and copper were decreased and aluminium was increased in the plasma of both patient groups. Different results could be found for intracellular contents with mean zinc concentration of erythrocytes, thrombocytes and leucocytes between mean and higher levels, though staying within normal values. Copper was decreased in erythrocytes and increased in thrombocytes, but not detectable in leucocytes. The results of this study point out the differences between the plasmatic and intracellular alteration of trace element contents in uremic patients. However, the concentration levels of all cellular compartments show high standard deviation, which shows the necessity of measuring additional matrices, e.g. plasma. Uremic symptoms relate to the disorders of the trace element homeostasis. Regarding the increased fragility of erythrocytes with shortened life duration, decreased copper contents could play an essential role. Increased aluminium concentration levels might also be one of the interfering factors in the uremic thrombocytopathy. Yet the measurement of the plasma content is inevitable to diagnose and reflect the whole body content of trace elements at uremic state. By keeping analysis control, important information about progression and influence of therapy can be obtained.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday