Mesophase behaviour of 2,5-dibenzoyloxy-p-benzoquinone derivatives and tetrahydrobenzene tetraesters

The synthesis of 2,5-dibenzoyloxy-p-benzoquinone derivatives, their products after reduction and tetraesters from tetrahydroxybenzene prepared from those products is described. Their phase behaviour was investigated by differential scanning calorimetry and polarizing microscopy and is discussed in terms of their detailed structure.     

Über Hexagonale Perowskite mit Kationenfehlstellen. I. Verbindungen vom Typ Ba2B□2/3ReVIIO6

On Hexagonal Perovskites with Cationic Vacancies. I. Compounds of the Type Ba₂B □_2/3Re^VIIO₆ Compounds of Type Ba₂B□_2/3Re^VIIO₆ are formed with B^III = Sm? Gd Ho? Lu, Y, Sc, In (yellow); Tb (black-brown); Dy (yellow-orange). They crystallize with B^III = Sm? Lu, Y and Sc in a rhombohedral layer structure of 12 L-type (space group R3 m; sequence: cchhcchhcchh) with 6 formula units in the unit cell.     

Über Perowskitphasen in den Systemen AO-SE2O3-UO2,x mit A = Erdalkali und SE = Seltene Erden,La sowie Y. VI. IR-spektroskopische Untersuchungen an den Verbindungen Ba2SE0,67UO6 und Ba2SE0,67UO5,5

On Perovskite Phases in the Systems AO? SE₂O₃? UO_2,x with A=Alkaline Earth Metal and SE = Rare Earths, La and Y. VI. I.R. spectroscopical Investigations at the Compounds Ba₂SE_0,67UO₆ and Ba₂SE_0,67UO_5,5 According to the results of the i.r. spectroscopic investigations longer and shorter U? O-distances can be distinguished. The HT- and LT-modifications of Ba₂SE_0,67UO₆ contain UO-groups like other ternary uranium oxides. In the O-modifications these groups are only incompletely formed. On the contrary the perovskites Ba₂SE_0,67UO_5,5 with U(V) show two different longer U? O-bonds only.     

Über Ba2Ce0,75SbO6 – den ersten Vertreter einer weiteren Perowskitvariante

On Ba₂Ce_0,75SbO₆ – the First Representant of a Further Perovskite Variant The ochre coloured Ba₂Ce_0,75SbO₆ represents a perovskite variant with vacancies in the cationic lattice. The tetragonal cell dimensions are: a = 2×5,97₇ Å and c = 2×8,50₀ Å.     

Chemoenzymatic synthesis of both enantiomers of cispentacin

Based on the lipase-catalysed kinetic resolution of the silyloxyalcohol (1RS,2SR)-5 by transesterification with vinyl acetate in the presence of lipase from Pseudomonas cepacia a synthesis of both enantiomers of the β-amino acid cispentacin (1R,2S)-1 and (1S,2R)-1 using simple functional group interconversions is described.     

Über Sauerstoffperowskite des fünfwertigen Rutheniums ABIIIRuVO6 mit AII = Ba,Sr

On Oxygen Perovskites with Pentavalent Ruthenium A B^IIIRu^VO₆ with A^II = Ba, Sr The perovskites Ba₂B^IIIRu^VO₆ with B^III = La, Nd, Sm, Eu, Gd, Dy, Y, are cubic (B^III = La: a = 8,54₄ Å; Y: a = 8,33₇ Å); with a partial order for B^III and Ru^V. The Sc compound, Ba₂ScRuO₆, has a hexagonal 6 L structure (a = 5.79₅ Å; c = 14.22₉ Å; sequence (hcc)₂)₂. The lattice of the Sr perovskites, Sr₂B^IIIRu^VO₆, with B^III = Eu, Gd, Dy, Y is rhombic distorted. The IR and FRI spectra are discussed.     

Über Geordnete Perowskite mit Kationenfehlstellen. II. Der Ersatz von UVI durch NbV in Ba2Gd0,67□0,33UO6

On Ordered Perovskites with Cationic Vacancies. II. The Incorporation of Nb^V in Ba₂Gd_0,67□_0,33UO₆ In Ba₂Gd_0.67□_0.33UO₆ a complete substitution of U^VI by Nb^V is possible by filling the cationic vacancies (x-phase: Ba₂Gd_0.67+0.33xU_1?xNb_xO₆). For the y-Phase (Ba₂Gd_0.67U_1?yNb_yO_6?0.5y) solid solutions are formed only for y ? 0.5. The properties of both phases are studied by x-ray and spectroscopic methods. In Ba₂GdNbO₆ – in contrary to the complete ordered Ba₂GdTaO₆ – the order of gadolinium and niobium id partial.     

Über das System BaFe1−xRuxO3−y

In the system BaFe_1?xRu_xO_3?y three phases, separated by immiscibility gaps, are present: an Fe-rich phase (x = 0-0.75) with hexagonal BaTiO₃ structure (6H; sequence (hcc)₂), a Ru-rich phase (x = 0.9) of hexagonal 4H type (sequence (hc)₂), and the pure Ru compound BaRuO₃ with rhombohedral 9R structure (sequence (hhc)₃). By vibrational spectroscopic investigations in the 6H phase a transition from n-type semiconduction (Fe-rich oxygen-deficient compounds) to good, metal-like conduction (Ru-rich compounds with complete oxygen lattice) can be detected. The 4H and 9R stacking polytypes are good, metal-like conductors.     

Über Perowskite ABBWVIO6

On Perovskites A B B W^VIO₆ Compounds of type ABBW^VIO₆ can be obtained with A^II ? Ba; B^I ? Li, Na and B^III ? La, Nd, Sm, Gd, Y, In, Sc just as with A^II ? Sr, B^I ? Li and B^III ? La, Nd, Sm, Gd, Y, In (all cubic ordered perovskites). For the cubic perovskites Sr₂Na_0,5La_0,5WO₆ and Sr₂Na_0,5Nd_0,5WO₆ additional superlattice reflections are observed (a ∽ 16.4 Å). The compounds Sr₂Na_0,5BWO₆ crystallize with B^III ? Sm, Gd in a monoclinic and with B^III ? Y, In in a rhombic distorted perovskite lattice. For the perovskites with A = Sr — dependent on ionic radii of the B ions — two different lattice types are present.     

Carbon and nitrogen isotope analysis of atrazine and desethylatrazine at sub-microgram per liter concentrations in groundwater

Environmental degradation of organic micropollutants is difficult to monitor due to their diffuse and ubiquitous input. Current approaches—concentration measurements over time, or daughter-to-parent compound ratios—may fall short, because they do not consider dilution, compound-specific sorption characteristics or alternative degradation pathways. Compound-specific isotope analysis (CSIA) offers an alternative approach based on evidence from isotope values. Until now, however, the relatively high limits for precise isotope analysis by gas chromatography—isotope ratio mass spectrometry (GC-IRMS) have impeded CSIA of sub-microgram-per-liter scale micropollutant concentrations in field samples. This study presents the first measurements of C and N isotope ratios of the herbicide atrazine and its metabolite desethylatrazine at concentrations of 100 to 1,000 ng/L in natural groundwater samples. Solid-phase extraction and preparative HPLC were tested and validated for preconcentration and cleanup of groundwater samples of up to 10 L without bias by isotope effects. Matrix interferences after solid-phase extraction could be greatly reduced by a preparative HPLC cleanup step prior to GC-IRMS analysis. Sensitivity was increased by a factor of 6 to 8 by changing the injection method from large-volume to cold-on-column injection on the GC-IRMS system. Carbon and nitrogen isotope values of field samples showed no obvious correlation with concentrations or desethylatrazine-to-atrazine ratios. Contrary to expectations, however, δ ¹³ C values of desethylatrazine were consistently less negative than those of atrazine from the same sites. Potentially, this line of evidence may contain information about further desethylatrazine degradation. In such a case, the common practice of using desethylatrazine-to-atrazine ratios would underestimate natural atrazine degradation.