Untersuchungen im System Os/Cl/O,Chemischer Transport von Osmium

Studies in the System Os/Cl/O. Chemical Transport of Osmium The compounds OsCl₄, OsCl_3.5, OsO_0.5Cl₃, OsOCl₂, and OsOCl₄ have been prepared in ampoules. The Guinier diagrams, densities, magnetic behaviours, mass spectra and the behaviour on the thermobalance of these compounds have been investigated. Osmium has been transported via OsOCl_4,g into the zone of highest temperature (950°C) of an ampoule.     

Investigations on wine bouquet components by solid-phase microextration -capillary gas chromatography (SMPE-CGC) using different fibers

The extraction of wine bouquet components with solid-phase microextraction (SPME) using different fibers was studied. Polyacrylate fibers (PA-85) achieve the most complete bouquet profiles. About ninety substances were identified by capillary gas chromatography-MS and their retention factors were calculated to allow peak identification in capillary-GC-FID chromatograms. The terpene profiles of different wines were recorded by SPME (PA-85)-CGC-FID.     

Characterization of high purity gallium

Multi-step wet analytical procedures were tested on gallium samples of different purity grades. Results obtained were compared with those of spark source mass spectrometry (SSMS) and glow discharge mass spectrometry (GDMS). It was found that multi-step procedures, as applied, with preconcentration factors of 200 are suitable to determine most of the detectable elements in high purity gallium in the ng/g-range. The results thus obtained agree well with those obtained by mass spectrometry. The sensitivity of the multi-step and mass spectrometry methods is not sufficient to detect traces of the investigated elements in super purity gallium, i.e. better than 6 N. These qualities can be differentiated, however, by single crystal resistivity measurement.     

Confromational Studies on Peptides Containing Enantiometric α-Methyl α-Amino Acids. Part I. Differential conformational properties of (R)- and (S)-2-methylaspartic acid

The conformational properties of four model peptides of the general formula Ac-Tyr-Xaa-Yaa-Zaa-Ala-Lys-Glu-ala-Ala-Glu-Lys-Ala-Zaa-Yaa-Xaa-Lys-NH₂ (Xaa-Yaa-Zaa = Ala-Ala-(R)-Asp(2-Me), 1 ; Ala-Ala-(S)-Asp(2-Me), 2 ; Ala-Aib-Asp, 3 ; Ala-Ala-Asp, 4 ; Asp(2-Me) = 2-methylaspartic acid; Aib = 2-aminoisobutyric acid) were studied by CD spectroscopy in solution, to evaluate the helix-inducing potential of enantiomerically pure 2-methylaspartic acid as a function of its chirality at C(2). At neutral pH and 1°, all peptides exhibit significant helix formation in aqueous solution, the degree of helicity increasing in the order 4 3 ≈ 1 . Lowering the pH to 2 results in a dramatic increase in helicity for peptide 1 , while the diastereoisomeric peptide 2 now exists in a predominantly unordered conformation. Helix induction by protonated (R)-Asp(2-Me) exceeds Aib-induced helix formation in peptide 3 , and the helix content of 1 in aqueous solution at pH 2 is comparable to the degree of helicity in the strongly helix-inducing solvent 2,2,2-trifluoroethanol.     

Trace characterization of high-purity molybdenum and tungsten by electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry and total reflection X-ray fluorescence spectrometry involving analyte—matrix separation

A technique for the separation of 42 trace elements from up to 5 g of molybdenum and tungsten matrices was developed by means of the radiotracer technique. It is based on adsorption of the analyses on the cation exchanger Dowex 50 W x 9 from a 4% H₂O₂/0.01 mol 1⁻¹ HNO₃ solution followed by their elution with 15 ml of 4 mol I⁻¹ HNO₃ in the opposite flow direction. Both matrices were removed with a separation factor > 10⁴. The separation technique was applied to the analysis of these materials by electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry and total reflection X-ray fluorescence spetrometry. For all the determination methods used, the limits of detection are given and compared with those of other methods. With inductively coupled plasma mass spectrometry, for 22 of the 30 assayed elements, limits of detection at the sub-ng g⁻¹ level were achieved. The results are compared with those obtained by radiochemical neutron activation analysis in this work and by glow discharge mass spectrometry, secondary ion mass spectrometry, isotope dilution mass spectrometry and by solution spectrometric methods in other laboratories.     

Electrode reactions of palladium(II) in chloride solution at carbon paste electrodes modified with derivatives of N-benzoylthiourea

The study of the electrode reactions of palladium(II) at non-modified carbon paste electrodes (CPEs) in chloride solution has revealed the existence of a chloropalladate(II) complex at the electrode surface. The complex is formed during the application of anodic potentials after preceding palladium deposition. In the present paper the electrode reactions of Pd^II at CPEs modified with some N′,N′-disubstituted derivatives of N-benzoylthiourea [as selective ligands for palladium(II)] are studied in chloride solution by cyclic voltammetry. Two reduction peaks are observed in the cathodic scans recorded after deposition of palladium and anodization of the electrode. From the results it is concluded that [in addition to the chloropalladate(II) complex, observed at the non-modified electrode] a second palladium complex is formed at positive potentials. The formation of the palladium(II) complex of the N-benzoylthiourea derivatives by ligand exchange at the electrode surface is assumed. The ligand exchange itself occurs without charge transfer across the electrode|solution interface; therefore, it cannot be detected electrochemically. After palladium deposition and anodic treatment a pronounced "inverse" peak (i.e., an anodic peak in the cathodic scan) with peak currents up to 100 μA is observed at about +0.8 V. Its peak current increases with the amount of deposited palladium and the number of cycles. The reactions at the electrode surface are discussed. The results of the study reveal the existence of two different surface complexes of palladium(II) at ligand-modified CPEs, but the surface reactions could not be elucidated in detail. Electronic Publication     

Polysulfonylamine. LXXIII [1]. Metall(II)-dimesylamid-Tetrahydrate: Das Dimesylamid-Anion als einzähniger O-Ligand und tetrafunktioneller Wasserstoffbrücken-Akzeptor in den isotypen Komplexen [M(H2O)4 {(CH3SO2)2N}2] mit M = Magnesium,Nickel, Kupfer und Zink

Polysulfonyl Amines. LXXIII. Metal(II) Dimesylamide Tetrahydrates: The Dimesylamide Anion as a Monodentate O-Ligand and a Tetrafunctional Hydrogen Bond Acceptor in the Isotypic Complexes [M(H₂O)₄{(CH₃SO₂)₂N}₂], where M = Magnesium, Nickel, Copper, or Zinc By treating aqueous HN(SO₂CH₃)₂ solutions with the appropriate metal hydroxides, oxides, or carbonates, the crystalline tetrahydrates M[(CH₃SO₂)₂N]₂ · 4 H₂O (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Cd) were obtained and analytically characterized. The crystal structures of the Mg, Ni, Cu and Zn compounds, as determined by single-crystal X-ray diffraction at low temperatures, reveal an isotypic series (triclinic, space group P1 , Z = 1). The structures consist of centrosymmetric trans-octahedral [M(H₂O)₄{(CH₃SO₂)₂N}₂] molecules in which the anionic ligand acts as a monodentate O-donor. For the Mg, Ni and Zn complexes, the M? OH₂ and M? O(anion) distances lie in the ranges 203–206 pm and 209–214 pm, respectively. The copper compound features a marked Jahn-Teller distortion with Cu? OH₂ = 195.8 and 197.7 pm and Cu? O(anion) = 232.5 pm. The cis-angles O? M? O of the four molecules do not deviate appreciably from 90°. The complex units are associated through a highly organized three-dimensional hydrogen bond network in which all the water protons act as donors and the non-coordinating oxygen atoms and the nitrogen atom of the anionic ligand are involved as acceptors. The H-bond pattern is subjected to a graph-theoretical analysis at the first and second levels.     

A non-empirical SCF and CI study of the electronic spectrum of pyrrole

Various electronically excited states of pyrrole have been studied by ab initio SCF and CI calculations including π → π^* and π → Rydberg excitations. Optically allowed valence type transitions are found at energies higher than 6.5 eV whereas all the lower singlet states are of Rydberg type. In addition to the experimentally known triplet states at 4.23 and 5.10 eV, several new triplet transitions with energies from 5.71 to 7.10 eV are predicted. In most cases good agreement with experimental data is found.