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  • 1
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    Zn3 and Ga3 Triangles as Building Units in Sr2Au6Zn3 and Sr2Au6Ga3 (2013)
    Wiley
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    Publication Date: 2013-09-07
    Description: The intermetallic compounds Sr 2 Au 6.52 Zn 2.48 , Sr 2 Au 6 Zn 3 , and Sr 2 Au 6 Ga 3 were obtained by induction melting of the elements in sealed tantalum tubes. Their structures were studied by X-ray diffraction on powders and refined from single crystal diffraction data: R c , a = 844.5(2), c = 2187.7(5) pm, wR 2 = 0.0411, 936 F 2 values and 20 variables for Sr 2 Au 6.52 Zn 2.48 ; a = 841.6(2), c = 2191.5(7) pm, wR 2 = 0.0126, 587 F 2 values and 19 variables for Sr 2 Au 6 Zn 3 ; and a = 841.9(2), c = 2191.1(7) pm, wR 2 = 0.0199, 660 F 2 values and 19 variables for Sr 2 Au 6 Ga 3 . The gold substructures of Sr 2 Au 6 Zn 3 and Sr 2 Au 6 Ga 3 can be considered as diamond polytypes with 6R stacking sequences (287–304 pm Au–Au in Sr 2 Au 6 Zn 3 ). The cavities formed by this network are filled in an ordered manner by strontium atoms and Zn 3 (281 pm Zn–Zn), respectively Ga 3 (286 pm Ga–Ga) triangles in a 2:1 ratio. Consequently one can describe the Sr 2 Au 6 Zn 3 and Sr 2 Au 6 Ga 3 structures as ordered substitution variants of the Zintl phase CaIn 2 . This structural relationship is discussed on the basis of a group-subgroup Scheme. Sr 2 Au 6.52 Zn 2.48 shows Zn/Au mixing on the triangle.
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
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  • 2
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    Dissection of Different Donor Abilities Within Bis(pyrazolyl)­pyridinylmethane Transition Metal Complexes (2013)
    Wiley
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    Publication Date: 2013-04-10
    Description: Using the bis(pyrazolyl)pyridinylmethane ligand α,α,α-bis(1-pyrazolyl)(2-pyridinyl)toluene {(ph)C(pz) 2 (py)} for bioinorganic inspired coordination chemistry studies, we synthesised and structurally characterised three monofacial complexes [{(ph)C(pz) 2 (py)}CoCl 2 ] ( C1 ), [{(ph)C(pz) 2 (py)}CuCl 2 ] ( C2 ), [{(ph)C(pz) 2 (py)}ZnCl 2 ] ( C3 ) and the binuclear halogenido-bridged complexes [{(ph)C(pz) 2 (py)} 2 (μ-Cl) 2 Fe 2 Cl 2 ] ( C4 ) and [{(ph)C(pz) 2 (py)} 2 (μ-Br) 2 Cu 2 Br 2 ] ( C5 ). In four of these complexes, severe disorders between pyrazolyl and pyridinyl donor groups are observed such that bis(pyrazolyl) and (pyrazolyl)(pyridinyl) coordination modes are concomitantly found. The donor competition is dissected by DFT calculation of the energy differences between the two coordination modes and NBO analysis of the donor situation. The pyrazolyl units provide with more donor strength although pyridine is considerably more basic.
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
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  • 3
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    Constraints on the major sources of dissolved organic carbon in Alpine ice cores from Radiocarbon analysis over the bomb peak period (2013)
    Wiley
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    Publication Date: 2013-03-30
    Description: [1]  Radiocarbon ( 14 C) has proven to be a powerful tool in distinguishing modern and fossil fuel sources contributing to organic aerosols. By applying this concept to ice core records of the dissolved organic carbon (DOC) fraction, we developed a setup dedicated to the extraction of DOC from Alpine ice core samples for 14 C micro-analysis. With respect to the difficulties and limitations of this analytical method, it is shown that a total process blank mass of (6 ± 3) μgC with a 14 C signature of (0.71 ± 0.17) can be obtained, corresponding to a minimum sample size between 200 g for industrial and 600 g for pre-industrial ice. Radiocarbon analyses of eight DOC ice core samples from the high accumulation glacier Col du Dôme (European Alps) were mainly performed over the bomb peak period. These data, being associated with snow deposition over the summer half-years, show an overall mean fossil contribution of (25 ± 9) %. Adaptation of the DO 14 C values to the atmospheric 14 CO 2 record revealed that the biogenic input to ice core DOC is associated with a fast recycling biospheric component, likely linked to a turnover time of less than three years.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Crystal Structure of Apo- and Metalated Thiolate containing RNase S as Structural Basis for the Design of Artificial Metalloenzymes by Peptide-Protein Complementation (2013)
    Wiley
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    Publication Date: 2013-10-23
    Description: Ribonuclease S (RNase S) is a versatile model system to introduce non-canonical amino acids into a protein scaffold by self-assembly of the protein complex from S-protein and S-peptide. We have introduced two cysteines into the S-peptide replacing lysine-7 and glutamine-11 of the α-helical region of this peptide. The crystal structure of this variant was determined in the apo state and in complex with Hg II ions. These structures serve as a template for the construction of artificial hybrid catalysts based on RNase S, e.g. for phosphanyl amino acids complexing transition metal ions for organometallic catalysis.
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
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  • 5
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    Diurnal variations of mid-latitude NLC parameters observed by daylight-capable lidar, and their relation to ambient parameters (2013)
    Wiley
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    Publication Date: 2013-11-30
    Description: [1]  Noctilucent Clouds (NLCs) are an important phenomenon of the summer mesopause region. While relatively common in high latitudes, NLCs are sparse (≤ 10% occurrence rate) below 60 ∘ latitude. We present the first study of diurnal variations ofmid-latitude NLCs based on lidar observations with full diurnal coverage at Kühlungsborn since 2010 independent from solar elevation. Overall, ∼100 hours of NLCs with a backscatter coefficient of β max ,532 nm  〉 0.5 ⋅ 10 − 10 m − 1 sr − 1 are observed within ∼1800 hours. Occurrence rates decrease regularly from 12% at 5 local solar time (LST) to ∼2% at 19 LST. The mean NLC brightness varies between ∼1 and ∼ 3 ⋅ 10 − 10 m − 1 sr − 1 with maxima at 4 and 18 LST. The simultaneously observed temperatures show a systematic (tidal) variation, but we do not find a direct relation to NLC rates. Comparing NLCs and ambient winds, we find strong indications for the meridional wind (advection) being the main driver for NLC occurrence above our site.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    REGULATION OF AMYLASE, CELLULASE AND CHITINASE SECRETION IN THE DIGESTIVE TRACT OF THE TWO-SPOTTED FIELD CRICKET, Gryllus bimaculatus (2013)
    Wiley
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    Publication Date: 2013-04-13
    Description: The secretion of amylase and cellulase in Gryllus bimaculatus is determined by increased food intake, whereby shortly after molting food consumption increases. About half of the standing amylase concentration (activity) in the endothelial cells can be secreted within 30 min. The peak of amylase and cellulase secretion that occurs in the photophase is related to the feeding peak in the previous scotophase. The secretion of chitinase on the other hand is primarily controlled by the molting cycle. Only amylase secretion was affected by calcium in the incubation medium, suggesting an apocrine release mechanism. Refeeding experiments (after 5 days without food) suggest that the release of amylase in response to a nutrient in the lumen (glucose) is not due to simple stimulation of exocytosis, but rather a stimulation of synthesis.
    Print ISSN: 0739-4462
    Electronic ISSN: 1520-6327
    Topics: Biology
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  • 7
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    Carbon burial in soil sediments from holocene agricultural erosion, central europe (2013)
    Wiley
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    Publication Date: 2013-07-26
    Description: [1]  Natural and human-induced erosion supplies high amounts of soil organic carbon (OC) to terrestrial drainage networks. Yet OC fluxes in rivers were considered in global budgets only recently. Modern estimates of annual carbon burial in inland river sediments of 0.6 Gt C, or 22% of C transferred from terrestrial ecosystems to river channels, consider only lakes and reservoirs and disregard any long-term carbon burial in hillslope or floodplain sediments. Here we present the first assessment of sediment-bound OC storage in central Europe from a synthesis of ~1,500 Holocene hillslope and floodplain sedimentary archives. We show that sediment storage increases with drainage-basin size due to more extensive floodplains in larger river basins. However, hillslopes retain hitherto unrecognised high amounts of eroded soils at the scale of large river basins such that average agricultural erosion rates during the Holocene would have been at least twice as high as reported previously. This anthropogenic hillslope sediment storage exceeds floodplain storage in drainage basins 〈10 5  km 2 , challenging the notion that floodplains are the dominant sedimentary sinks. In terms of carbon burial, OC concentrations in floodplains exceed those on hillslopes, and net OC accumulation rates in floodplains (0.7 ± 0.2 g C m -2 a -1 ) surpass those on hillslopes (0.4 ± 0.1 g C m -2 a -1 ) over the last 7,500 years. We conclude that carbon burial in floodplains and on hillslopes in Central Europe exceed terrestrial carbon storage in lakes and reservoirs by at least two orders of magnitude, and should thus be considered in continental carbon budgets.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 8
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    Infinite Linear Zinc Chains in AAu4Zn2 (A = Ca, Ce, Pr, Nd) with YbAl4Mo2 Type Structure (2013)
    Wiley
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    Publication Date: 2013-07-05
    Description: The intermetallic zinc compounds A Au 4 Zn 2 ( A = Ca, Ce, Pr, Nd) were obtained by induction melting of the elements in sealed tantalum tubes. The samples were studied by X-ray diffraction on powders. The structures of the calcium and the cerium compound were refined from single crystal diffraction data: YbAl 4 Mo 2 type, I 4/ mmm , a = 692.8(1), c = 527.6(1) pm, wR 2 = 0.0304, 244 F 2 values and 11 variables for CaAu 4.08 Zn 1.92 and a = 699.6(1), c = 531.2(1) pm, wR 2 = 0.1152, 186 F 2 values and 10 variables for CeAu 4 Zn 2 . The 4 d site of the calcium compound shows small mixed Zn/Au occupancy. The A Au 4 Zn 2 structures consist of three-dimensional gold networks (272–286 pm Au–Au in CeAu 4 Zn 2 ), which are penetrated by linear infinite zinc chains (266 pm Zn–Zn in CeAu 4 Zn 2 ) that extend along the c axis. The calcium or rare earth atoms fill Au 12 cavities within the networks. Temperature dependent magnetic susceptibility measurements reveal Pauli paramagnetism for CaAu 4 Zn 2 and Curie-Weiss paramagnetism for the cerium, praseodymium, and neodymium compound, respectively. No magnetic ordering was evident down to 2.5 K. The static intermediate-valent compound Ce 2 RuZn 4 crystallizes with a superstructure of CeAu 4 Zn 2 ( klassengleiche subgroup P 4/ nmm ) with a different but fully ordered substitution on the transition metal sites. This structural relationship is discussed on the basis of a group-subgroup scheme.
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    Topics: Chemistry and Pharmacology
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  • 9
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    Postglacial adjustment of steep, low-order drainage basins, Canadian Rocky Mountains (2013)
    Wiley
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    Publication Date: 2013-11-21
    Description: [1]  It is generally argued that the legacy of Pleistocene glaciation results in increased sediment flux in mountain systems. An important, but not well-constrained, aspect of Pleistocene glacial erosion is the geomorphic decoupling of cirque basins from main river systems. This study provides a quantitative link between glacier-induced basin morphology, postglacial erosion and sediment delivery for mountain headwaters (with basin area 〈10 km 2 ). We analyze the morphology of 57 headwater basins in the Canadian Rockies, and establish postglacial sediment budgets for select basins. Notable differences in headwater morphology suggest different degrees of erosion by cirque glaciers, which we classify into headwater basins with either cirque or non-cirque morphology. Despite steeper slope gradients in cirque basins, higher mean postglacial erosion rates in basins with non-cirque morphology (0.43-0.6 mm a -1 ) compared to those in cirques (0.19-0.39 mm a -1 ) suggest a more complex relationship between hillslope erosion and slope gradient in calcareous mountain environments than implied by the threshold hillslope concept. Higher values of channel profile concavity and lower channel gradients in cirques imply lower transport capacities and, thus, lower sediment delivery ratios (SDR). These results are supported by i) postglacial SDR values for cirques of 〈15 % with SDRs for non-cirque basins of 〉28 %; and ii) larger fan sizes at outlets of non-cirque basins (~15 % of basin area) compared to cirques (~5 %). Although small headwater basins represent the steepest part of mountain environments and erode significant postglacial sediment, the majority of sediment remains in storage under interglacial climatic conditions and does not affect large-scale mountain river systems.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    A global view of stratospheric gravity wave hotspots located with Atmospheric Infrared Sounder observations (2013)
    Wiley
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    Publication Date: 2013-01-26
    Description: [1]  The main aim of this study is to find and classify hotspots of stratospheric gravity waves on a global scale. The analysis is based on a 9 year record (2003 to 2011) of radiance measurements by the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite. We detect gravity waves based on 4.3 µm brightness temperature variances. Our method focuses on peak events, i.e., strong gravity wave events for which the local variance considerably exceeds background levels. We estimate the occurrence frequencies of these peak events for different seasons and time of day and use the results to find local maxima or “hotspots.” In addition, we use AIRS radiances at 8.1 µm to simultaneously detect convective events, including deep convection in the tropics and mesoscale convective systems at middle latitudes. We classify the gravity wave sources based on seasonal occurrence frequencies for convection, but also by means of time series analyses and topographic data. Our study reproduces well-known hotspots of gravity waves, e.g., the Andes and the Antarctic Peninsula. However, the high horizontal resolution of the AIRS observations also allows us to locate numerous mesoscale hotspots, which are partly unknown or poorly studied so far. Most of these mesoscale hotspots are found near orographic features like mountain ranges, coasts, lakes, deserts, or isolated islands. This study will help to select promising regions and seasons for future case studies of gravity waves.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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