Application of Pattern Recognition Methods for the investigation of chemical homogeneity of solids

Summary Two Pattern Recognition Methods, the Multivariate Variance and Discriminance Analysis (MVDA) and the Point Density Analysis (PDA), were applied to problems of chemical homogeneity of solid samples. The results obtained with three examples, representative for different types of inhomogeneities, show that these methods are advantageously applicable for characterizing homogeneity independent from the local frequency of the concentration fluctuation.

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Anwendung von Pattern-Recognition-Methoden zur Untersuchung der chemischen Homogenität von Festkörpern

Zusammenfassung Zwei Pattern-Recognition-Methoden, die mehrdimensionale Varianzund Diskriminanzanalyse (MVDA) und die Punktdichteanalyse (PDA) wurden zur Homogenitätscharakterisierung von Festkörpern eingesetzt. Die Anwendung auf Proben mit unterschiedlichem Charakter der Konzentrationsverteilung zeigt, daß sich diese Methoden vorteilhaft zur Homogenitätscharakterisierung eignen und weitgehend unabhängig von der Ortsfrequenz der Konzentrationsschwankungen sind.

     

Darstellung von Calcium- und Strontiumwolframat durch tribochemische Reaktion

Stoichiometric powder mixtures CaO/WO₃ and SrO/WO₃ react tribochemically on grinding in a vibrating mill to CaWO₄ and SrWO₄, respectively. IR spectra, X-raydiffraction, DTA and solubilities indicate at least 70–80% CaWO₄ are formed after periods of drinding of 50 hours, and 100% SrWO₄ after periods of 15 hours. Observations on the behaviour of the ground samples on subsequent annealing contribute to the general solid-state reaction MO + WO₃ → MWO₄.     

Kristallstrukturen von Säurehydraten und Oxoniumsalzen. VIII. Dihydrat und primäres Ammoniumsalz der Trimetaphosphimsäure

Crystal Structures of Acid Hydrates and Oxonium Salts. VIII. Dihydrate and Primary Ammonium Salt of Trimetaphosphimic Acid The dihydrate of the crystal structure of trimetaphosphimic acid, H₃(PO₂NH)₃ · 2H₂O, crystallizes in the monoclinic space group P2₁/c with four formula units in the unit cell (a = 7.022(1), b = 14.008(1), c = 9.353(2) Å, β = 93.34(2)°). The primary ammonium salt includes one molecule of methanol in its crystal structure, the orthorhombic space group Pbca contains eight formula units NH₄H₂(PO₂NH)₃ · CH₃OH in the unit cell (a = 15.025(3), b = 7.264(1), c = 19.252(1) Å). The crystal structures have been determined from three-dimensional X-ray diffraction data collected with an automatic single crystal diffractometer. Both rings of phosphorus and nitrogen atoms show boat conformation with the nitrogen atoms in the imido form. A similar pattern of bond lengths in both molecules and the disorder of one water-oxygen atom in the dihydrate indicate a partial proton transfer from the acid molecule to the water structure. In both structures the anion is linked to other anions by three hydrogen bonds N–H ?O, with an approximate length of 2.9 Å and two very short hydrogen bonds O–H ?O of approximate length 2.5 Å.     

Highly regioselective synthesis of amino-functionalized dendritic polyglycerols by a one-pot hydroformylation/reductive amination sequence

[reaction: see text] Dendritic architectures with neutral core structures and amines groups in the shell are a synthetic challenge, and there is a need for an efficient access. In this paper, highly selective Rh-catalysts are used for sequential hydroformylation/reductive amination of dendritic perallylated polyglycerols 1 with various amines in a one-pot procedure to give dendritic polyamines 3a-e in high yields (73-99%). In all cases, complete conversion of the allyl ether and aldehyde intermediate has been observed. Furthermore, the use of protected amines provides reactive core-shell-type architectures after deprotection. These soluble but membrane filterable multifunctional dendritic polyamines are of high interest as reagents in synthesis or as supports in homogeneous catalysis as well as nonviral vectors for DNA-transfection.     

Amperometric biosensors based on nafion coated screen-printed electrodes for the determination of cholinesterase inhibitors

Screen-printed electrodes coated with the nafion layer have been investigated for cholinesterase biosensor design. The butyrylcholinesterase (ChE) from horse serum was immobilised onto the nafion layer by cross-linking with glutaraldehyde vapours. The biosensors obtained showed better long-term stability and lower working potential in comparison to those obtained with no nafion coating. The sensitivity of a biosensor toward organophosphate pesticides is not affected by the nafion coating. The detection limits were found to be 3.5x10(-7) M for trichlorfon and 1.5x10(-7) M for coumaphos.     

Synthesis and Structure of YbCuGe and YbIrGe

The equiatomic ytterbium–transition metal–germanides YbCuGe and YbIrGe were synthesized in single crystalline form from CuGe and IrGe master alloys and ytterbium via the Bridgman technique and they were characterized through their X-ray powder patterns. The structures were refined from X-ray single crystal diffractometer data: NdPtSb type, P6₃mc, a=421.36(8), c=703.9(1) pm, wR2=0.0234, 210 F² values, 11 variable parameters, BASF=0.35(9) for YbCuGe and TiNiSi type, Pnma, a=671.09(6), b=421.55(5), c=757.16(7) pm, wR2=0.0782, 519 F² values, 20 variable parameters for YbIrGe. The copper (iridium) and germanium atoms build up [CuGe] and [IrGe] networks. In YbCuGe the two-dimensional [CuGe] network consists of puckered layers of Cu₃Ge₃ hexagons (247pm Cu–Ge) that are charge balanced and separated by the ytterbium atoms. In contrast, the ordered Ir₃Ge₃ hexagons show a strong orthorhombic distortion and the [IrGe] network is three-dimensional with a distorted tetrahedral germanium coordination around iridium with almost equal Ir–Ge distances (252–259pm). The ytterbium atoms fill cages within this network. The cell volumes of YbCuGe and YbIrGe are indicative for purely trivalent ytterbium.     

Upper critical magnetic fields of the heavy fermion superconductors CeCu2Si2, UPt3, and UBe13: Comparison between experiment and theory

We report measurements of the upper critical magnetic field,B _c2 (T), on single crystal and polycrystalline samples of the heavy-fermion superconductors CeCu₂Si₂, UPt₃ and UBe₁₃. Comparison is made with experimental results for a conventional superconductor (CeRu₃Si₂) and with results of the weak-coupling theory applied to both ans-wave superconductor in the dirty-limit and ap-wave superconductor. New anomalies are discovered to add to the unusualB _c2 (T) behavior.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday