Solid Solutions of Grimm–Sommerfeld Analogous Nitride Semiconductors II-IV-N2 (II=Mg,Mn, Zn; IV=Si,Ge): Ammonothermal Synthesis and DFT Calculations

Grimm–Sommerfeld analogous II-IV-N₂ nitrides such as ZnSiN₂, ZnGeN₂, and MgGeN₂ are promising semiconductor materials for substitution of commonly used (Al,Ga,In)N. Herein, the ammonothermal synthesis of solid solutions of II-IV-N₂ compounds (II=Mg, Mn, Zn; IV=Si, Ge) having the general formula (II^a_1−xII^b_x)-IV-N₂ with x≈0.5 and ab initio DFT calculations of their electronic and optical properties are presented. The ammonothermal reactions were conducted in custom-built, high-temperature, high-pressure autoclaves by using the corresponding elements as starting materials. NaNH₂ and KNH₂ act as ammonobasic mineralizers that increase the solubility of the reactants in supercritical ammonia. Temperatures between 870 and 1070 K and pressures up to 200 MPa were chosen as reaction conditions. All solid solutions crystallize in wurtzite-type superstructures with space group Pna2₁ (no. 33), confirmed by powder XRD. The chemical compositions were analyzed by energy-dispersive X-ray spectroscopy. Diffuse reflectance spectroscopy was used for estimation of optical bandgaps of all compounds, which ranged from 2.6 to 3.5 eV (Ge compounds) and from 3.6 to 4.4 eV (Si compounds), and thus demonstrated bandgap tunability between the respective boundary phases. Experimental findings were corroborated by DFT calculations of the electronic structure of pseudorelaxed mixed-occupancy structures by using the KKR+CPA approach.     

Final-state-interaction and SU(3)-breaking effects in

Based on the quark-diagram scheme and the recent measurement of D⁰→π⁰π⁰, we analyze the decays D⁰→π⁺π⁻, π⁰π⁰, K⁺K⁻, and . To fit the data, we find that there must be both final-state-interaction and SU(3)-breaking effects: of the former, nonzero elastic phase shifts in both π and are determined and no inelasticity in phase shifts is required; the SU(3) breaking effects are at the maximal level of 30% and of particular interest are those in the spectator W-emission and the non-spectator W-exchange diagrams.     

Recent developments in speciation and determination of organometallic compounds in environmental samples

Summary Recent developments in the techniques of speciation and determination of organometallic compounds in the environment are reviewed. There is an increasing trend in the use of high performance liquid chromatography as separation tool, and in the use of plasma-excited atomic emission spectrometry as detector. New techniques have been reported to overcome the historically difficult interface of HPLC to furnace AAS. There are also new techniques in the derivatization of ionic organometallic species for gas chromatography. Tandem analytical systems are getting more and more sophisticated, so are the sensitivity and specificity.     

Taxol biosynthesis: Molecular cloning and characterization of a cytochrome P450 taxoid 7 beta-hydroxylase

Biosynthesis of the anticancer drug Taxol in yew species involves eight cytochrome P450-mediated oxygenations and four coenzyme A-dependent acylations of the diterpenoid core. A family of cytochrome P450 genes, obtained from a yew cell cDNA library, were functionally expressed and screened with taxusin (taxa-4(20),11(12)-dien-5 alpha,9 alpha,10 beta,13 alpha-tetraol tetraacetate) as a surrogate substrate. One clone converted this substrate to an oxygenated derivative that was identified as 7 beta-hydroxytaxusin. The structure and properties of this 7 beta-hydroxylase are similar to those of other taxoid hydroxylases. Kinetic and binding assays indicated selectivity of the 7 beta-hydroxylase for polyoxygenated and acylated taxoid substrates, an observation consistent with the operation of this enzyme in the central portion of the Taxol biosynthetic pathway. Although the 7 beta-hydroxyl of Taxol is not essential for antimitotic activity, this functional group provides a convenient means for preparing taxoid derivatives.     

Novel routes to chiral 2-alkoxy-5-/6- methoxycarbonylmethylidenepyrrolidines/-piperidines

We report the results of a study aimed at the diastereoselective synthesis of chiral 2-alkoxy-5-/6-methoxycarbonylmethylidenepyrrolidines/-piperidines by condensation of chiral amines onto omega-oxo alkynoates and omega-oxo beta-keto esters.     

Extension of the voltammetric theory to inert,permeable thin-film coated rotating disc electrodes: Part II. Behaviour of ferrocene-ferricinium ion and quinone-hydroquinone systems on polymer-coated electrodes

The voltammetric behaviour of ferrocene-ferricinium ion and quinone-hydroquinone systems is investigated on electrochemically thin film polymer coated electrodes. Ferrocene oxidation is studied in 0.1 M NBu₄ ClO₄-nitromethane on rotating disc platinum electrodes coated with poly(2-hydroxymethyl-1,4-phenylene) oxide (I), poly-(2,6-dimethyl-1,4-phenylene) oxide (II), and poly[4-(2-aminoethyl)-1,2-phenylene] oxide (III) films. The quinone-hydroquinone system is investigated in aqueous medium (1 M HClO₄) with (I), (II) and poly-(2-cyano-1,4-phenylene) oxide films. Experimental results are in good agreement with the previously calculated voltammetric curves in steady-state mass transfer conditions. The charge transfer and diffusion parameters on these polymer-coated electrodes are calculated The quinone-hydroquinone system is rendered reversible by coating a platinum electrode with I.     

Observation of new neutron rich nuclei29F,35,36Mg,38,39Al,40,41Si,43,44P,45–47S,46–49Cl,and49–51Ar from the interactions of 55 MeV/U48Ca+Ta

After magnetic separation, identification through time of flight and δE×E measurements has allowed the observation of the new nuclei,²⁹F,^35,36Mg,^38,39Al,^40,41Si,^43,44P,^45,46,47S;^46,47,48,49Cl;^49,50,51Ar from the interaction of a⁴⁸Ca beam of 55 MeV/u with tantalum targets.     

Studies on the adsorption and migration of radium in natural minerals

The aim of this paper is to consider using effective natural minerals in studying the retardation and migration of radium under the influence of groundwater in the far-field of a radioactive waste repository. The properties of adsorbing radium by minerals are studied by adopting the static and dynamic adsorption method. Preliminary experimental results give confidence in the validity of using Maifanshih and barite to adsorb radium in water and to serve as effective retarding materials in radioactive waste repositories, their Kd values being 3815 and 2955, respectively. The study on a certain number of conditions of adsorbing radium by the promissing material Maifanshih is reported for the first time. The mechanism of radium adsorption has been discussed and modeling of migration of radium in the minerals has been presented to establish a rational basis for the longterm prediction required for safety assessment of underground disposal of radioactive waste.