The oxygen defect perovskites Ba3La3Cu6O14+y: a progressive transition from semi-conductive to semi-metallic properties. I. Structural Aspects and energy levels

Sites potential calculations for the oxygen defect perovskites Ba₃La₃Cu₆O_14+y have been made in order to explain the electron transport properties of these compounds for(0.5?y?0.43). This study has allowed the Cu³⁺ ions to be located and a choice to be made between the three possible positions available for the additional oxygen, corresponding to y>0. A schematic energy levels diagram has been proposed.     

Electric-field-induced phase transitions in co-doped Pb(Zr1−xTix)O3 at the morphotropic phase boundary

The strain- and polarization-electric field behavior was characterized at room temperature for Pb_0.98Ba_0.01(Zr_1−xTi_x)_0.98Nb_0.02O₃, 0.40 ⩽ x ⩽ 0.60. The investigated compositions were located in the vicinity of the morphotropic phase boundary, giving insight into the influence of crystal structure on the hysteretic ferroelectric behavior. The remanent strain of particular compositions is shown to be larger than theoretically allowed by ferroelectric switching alone, indicating the presence of additional remanent strain mechanisms. A phenomenological free energy analysis was used to simulate the effect of an applied electric field on the initial equilibrium phase. It is shown that electric-field-induced phase transitions in polycrystalline ferroelectrics can account for the experimental observations. The experimental and simulation results are contrasted to neutron diffraction measurements performed on representative compositions in the virgin and remanent states.     

The effect of prednisolone and a protein-deficient diet on plasma albumin and fibrinogen in a turpentine-induced acute-phase reaction in rats

The acute-phase reaction (APR) that follows inflammation is characterized by profound metabolic changes such as hypoalbuminemia, which is frequently aggravated by malnutrition; and hyperfibrinogenemia. Because some of these changes are mediated by cytokines, corticosteroids that are known to suppress cytokine production might be expected to alleviate the course of the APR. In the present study, for 3 weeks rats were fed (1) a standard diet (25%) protein), (2) a protein-deficient diet (5% protein), or (3) a standard diet supplemented by treatment with intraperitoneal prednisolone (7.5 mg twice daily starting 3 days before and throughout the experiment). Changes in plasma albumin, fibrinogen, and total protein levels were measured 0, 1, 3, and 8 days after turpentine was injected subcutaneously. Albumin and fibrinogen were immunohistochemically stained in the liver 0, 3, and 8 days after injection. Plasma albumin decreased by roughly 50% in all three groups, and reached a nadir on day 3. Fibrinogen peaked by day 1 in all animals and fell gradually thereafter. The total protein concentration, which was higher with prednisolone, remained unchanged in all three groups. The level of immunostainable liver albumin was initially reduced in malnourished rats. If further diminished in the majority of hepatocytes after administration of turpentine in all groups. Although few hepatocytes stained positive for fibrinogen before the onset of inflammation, uniform increase in immunostaining occurred by day 3 in all rats regardless of treatment. Neither prednisolone nor malnutrition substantially altered the decrease in plasma albumin and the simultaneous increase in fibrinogen in a turpentine-induced APR.(ABSTRACT TRUNCATED AT 250 WORDS)     

A retrospective study of combined fixed-removable reconstructions with their analysis of failures

The survival rate and the reasons for failures of 130 combined fixed-removable reconstructions (CFR), incorporated in 112 patients, were assessed. Each CFR reconstruction was classified depending on its attachments: 76 reconstructions were attached with rigid, precise attachments, and constituted the rigid group; 54 reconstructions were attached with either semi-precision or individual attachments and were defined as the semi-rigid group. Of the 130 reconstructions, 41 were determined as complete successes, 39 as partial successes and 50 as failures, leading to 37 major repairs and to 13 new reconstructions. Three reconstructions failed due to technical reasons, 36 due to biological reasons and for 11 reconstructions, both categories of reasons were responsible for their failure. In total, technical reasons were counted 15 times in comparison to 73 biological reasons for those 50 failed reconstruction, with 29 fractured abutment teeth as the most common biological reason. Within the rigid group, 45 failed reconstructions were observed, whereas within the semi rigid group only 5 failures occurred, leading to an 8-year survival estimate (+/- SD) of 30.1% (+/- 6.9%) for the rigid group and 93.1% (+/- 3.9%) for the semi rigid group. Beside the attachment type, the anatomy of the partially edentulous tooth arch in form of the free-end situation and the dentate opposing jaw were identified as risk factors.     

Microfluidic droplet-based liquid-liquid extraction

We study microfluidic systems in which mass exchanges take place between moving water droplets, formed on-chip, and an external phase (octanol). Here, no chemical reaction takes place, and the mass exchanges are driven by a contrast in chemical potential between the dispersed and continuous phases. We analyze the case where the microfluidic droplets, occupying the entire width of the channel, extract a solute-fluorescein-from the external phase (extraction) and the opposite case, where droplets reject a solute-rhodamine-into the external phase (purification). Four flow configurations are investigated, based on straight or zigzag microchannels. Additionally to the experimental work, we performed two-dimensional numerical simulations. In the experiments, we analyze the influence of different parameters on the process (channel dimensions, fluid viscosities, flow rates, drop size, droplet spacing, ...). Several regimes are singled out. In agreement with the mass transfer theory of Young et al. (Young, W.; Pumir, A.; Pomeau, Y. Phys. Fluids A 1989, 1, 462), we find that, after a short transient, the amount of matter transferred across the droplet interface grows as the square root of time and the time it takes for the transfer process to be completed decreases as Pe-2/3, where Pe is the Peclet number based on droplet velocity and radius. The numerical simulation is found in excellent consistency with the experiment. In practice, the transfer time ranges between a fraction and a few seconds, which is much faster than conventional systems.     

Cinchona-modified platinum catalysts: from ligand acceleration to technical processes

This Account records work carried out in our laboratories during the last 2 decades in the field of enantioselective heterogeneous hydrogenation. Of particular interest was Orito's catalytic system, platinum catalysts modified with cinchona alkaloids for the hydrogenation of activated ketones. Described are the development of the optimal platinum catalyst and modifier and the expansion of the scope of the catalyst. Kinetic studies aimed at understanding the mode of action of the catalyst revealed that the cinchona modifier not only renders the catalyst enantioselective but strongly accelerates the hydrogenation. This was the first case of ligand acceleration with a heterogeneous catalytic system. Finally, a number of industrial processes are summarized with the enantioselective hydrogenation of various alpha-keto esters as a key step.     

Oxidative Heck Coupling of Allylic Amines with 2,2,6,6‐Tetramethylpiperidine‐N‐oxyl (TEMPO) as Oxidant for the Preparation of Tetrasubstituted Alkenes

The paper describes the oxidative Heck arylation of various allylic amines using arylboronic acids for the preparation of tetrasubstituted alkenes. As oxidant the commercially available 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) is used and coupling reactions occur under very mild conditions at room temperature. The densely substituted alkenes are formed in good to excellent yields with complete control of the diastereoselectivity. Substrate scope with respect to the allylic amine and the arylboronic acid is investigated.

     

Transition-metal-free oxidative coupling reactions for the formation of C-C and C-N bonds mediated by TEMPO and its derivatives

The application of nitroxides for the development of new synthetic methods and their implementation in polymer chemistry, material science and beyond is one of the major research topics in our laboratory in the institute of organic chemistry at the WWU Münster. This short review focuses on our recent progress towards nitroxide-based transition-metal-free oxidative coupling reactions. The demand for organic surrogates for transition metals in such transformations is in our eyes unquestionable, since environmental and economic issues have become progressively more important in recent years. For this purpose, the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) is shown to be a highly efficient oxidant for the homo- and cross-coupling of Grignard reagents. This powerful C-C bond forming strategy allows the generation of conjugated polymers from bifunctional Grignard reagents. Moreover, cross-coupling of alkynyl Grignard compounds and nitrones can be accomplished under aerobic atmosphere with catalytic amounts of TEMPO. It is also shown that TEMPO-derived N-oxoammonium salts can act as suitable oxidants for formation of C-N bonds between non-preactivated benzoxazoles and secondary amines under metal-free conditions.     

High-Temperature Phase Equilibria of Duplex Stainless Steels Assessed with a Novel <Emphasis Type="Italic">In-Situ</Emphasis> Neutron Scattering Approach

Duplex stainless steels are designed to solidify with ferrite as the parent phase, with subsequent austenite formation occurring in the solid state, implying that, thermodynamically, a fully ferritic range should exist at high temperatures. However, computational thermodynamic tools appear currently to overestimate the austenite stability of these systems, and contradictory data exist in the literature. In the present work, the high-temperature phase equilibria of four commercial duplex stainless steel grades, denoted 2304, 2101, 2507, and 3207, with varying alloying levels were assessed by measurements of the austenite-to-ferrite transformation at temperatures approaching 1673 K (1400 °C) using a novel in-situ neutron scattering approach. All grades became fully ferritic at some point during progressive heating. Higher austenite dissolution temperatures were measured for the higher alloyed grades, and for 3207, the temperature range for a single-phase ferritic structure approached zero. The influence of temperatures in the region of austenite dissolution was further evaluated by microstructural characterization using electron backscattered diffraction of isothermally heat-treated and quenched samples. The new experimental data are compared to thermodynamic calculations, and the precision of databases is discussed.