102 Works

Entgrenzung und Zusammenarbeit – die Notwendigkeit von Kooperationen im Lernraum

Anne May & Susanne Kannenberg
Die Hochschule ist ein Lernraum – dieser Satz ist für die meisten ein Allgemeinplatz. Dahinter verbirgt sich aber weit mehr – eine entwicklungsfähige Zukunftsaufgabe, bei der es um mehr als ein räumlich- infrastrukturelles Angebot für Studierende geht. Für einen vielseitigen, zukunftsfähigen Lernraum ist die Entgrenzung institutioneller Zuständigkeiten notwendige Voraussetzung. Diese Notwendigkeit ergibt sich sowohl für die Entwicklung und den Betrieb von räumlich-technischen Infrastrukturen als auch für die Weiterentwicklung von Beratungs- und Schulungsangeboten. Dienstleistungskooperation ist nötig...

Ergebnisbericht der ExplorAging-Befragung des Gasthörenden- und Seniorenstudiums an der Leibniz Universität Hannover

Thomas Bertram & Sabine Bertram
Abschlussbericht zu einer Fragebogenerhebung, die im Wintersemester 2006/2007 im Gasthörenden- und Seniorenstudium der Leibniz Universität im Rahmen des ExplorAging-Projekts durchgeführt wurde.

Origin of metallicity in atomic Ag wires on Si(557)

U. Krieg, T. Lichtenstein, C. Brand, Christoph Tegenkamp & Herbert Pfnür
We investigated the metallicity of Ag-root 3 ordered atomic wires close to one monolayer (ML) coverage, which are formed on Si(557) via self assembly. For this purpose we combined high resolution electron energy loss spectroscopy with tunneling microscopy. By extending the excess Ag coverage up to 0.6 ML on samples annealed at high temperatures where partial desorption occurs, we demonstrate that one-dimensional metallicity in the Ag-root 3 x root 3 R30 degrees ordered atomic wires...

Unraveling the internal dynamics of the benzene dimer: a combined theoretical and microwave spectroscopy study

Melanie Schnell, Undine Erlekam, P. R Bunker, Gert Von Helden, Jens-Uwe Grabow, Gerard Meijer & Ad Van Der Avoird
We report a combined theoretical and microwave spectroscopy study of the internal dynamics of the benzene dimer, a benchmark system for dispersion forces. Although the extensive ab initio calculations and experimental work on the equilibrium geometry of this dimer have converged to a tilted T-shaped structure, the rich internal dynamics due to low barriers for internal rotation have remained largely unexplored. We present new microwave spectroscopy data for both the normal (C6H6)(2) and partially deuterated...

Assessing Climate Change Induced Turnover in Bird Communities Using Climatically Analogous Regions

Janine Sybertz & Michael Reich
It is crucial to define and quantify possible impacts of climate change on wildlife in order to be able to pre-adapt management strategies for nature conservation. Thus, it is necessary to assess which species might be affected by climatic changes, especially at the regional scale. We present a novel approach to estimate possible climate change induced turnovers in bird communities and apply this method to Lüneburg Heath, a region in northern Germany. By comparing species...

Innovativer Eisenbahnbrückenbau : Langzeitverhalten der Längsverschieblichen Festen Fahrbahn unter klimatischen Einflüssen

Raul Enrique Beltrán Gutiérrez
Die Längsverschiebliche Feste Fahrbahn (LvFF) auf Brücken, als eine integrale Konstruktion, wird durch das Schwinden und die Temperaturschwankung aufgrund der Verformungsbehinderung beansprucht. So entstehen Zwangskräfte in Längsrichtung, die das Bauteil unter wechselnder Druck- und Zugbeanspruchung setzen. Das Tragverhalten der LvFF wird auf der Druckseite durch die viskoelastischen Stoffeigenschaften des Betons charakterisiert. Die Relaxation des Betons spielt dabei eine wichtige Rolle. Auf der Zugseite weist das Bauteil ein sprödes Verhalten auf. In diesem Fall stehen die...

Second-moment budgets in cloud topped boundary layers: A large-eddy simulation study

Rieke Heinze, Dmitrii Mironov & Siegfried Raasch
A detailed analysis of second-order moment budgets for cloud topped boundary layers (CTBLs) is performed using high-resolution large-eddy simulation (LES). Two CTBLs are simulated—one with trade wind shallow cumuli, and the other with nocturnal marine stratocumuli. Approximations to the ensemble-mean budgets of the Reynolds-stress components, of the fluxes of two quasi-conservative scalars, and of the scalar variances and covariance are computed by averaging the LES data over horizontal planes and over several hundred time steps....

sp(3)-sp(3) Coupling reactions in the synthesis of natural products and biologically active molecules

Egor Geist, Andreas Kirschning & Thomas Schmidt
This Highlight covers the current status of relatively unexplored sp(3)-sp(3) cross-coupling reactions with particular focus on natural product and related syntheses.

A mass spectrometric and quantum chemical study of the vaporisation of lead monoxide in a flow of gaseous arsenic and antimony trioxides

K. Kunkel, E. Milke & Michael Binnewies
Mass spectrometric studies of the vapours over solid lead oxide in a flow of gaseous arsenic and antimony trioxides were conducted. The following ions of the ternary oxides were detected: Pb3As2O6+, Pb3AsO4+, PbAs2O4+, PbAsO2+, PbSb2O4+, and PbSbO2+. The origin of these species produced by the ionisation and/or fragmentation of ternary gaseous oxides is discussed. The PbAs2O4 species was undoubtedly identified by the determination of the appearance energy. Presumably, the Pb3As2O6 and PbSb2O4 species also existed...

Pyrolysis of azetidinone derivatives: a versatile route towards electron-rich alkenes, C-1 allylation and/or homologation of aldehydes

Nouf S. Al-Hamdan, Osama M. Habib, Yehia A. Ibrahim, Nouria A. Al-Awadi & Osman M. E. El-Dusouqui
Pyrolysis of beta-lactams and beta-thiolactams led essentially to stereoselective synthesis of the high energy electron-rich Z-alkenes. Extension of this methodology to the pyrolysis of 3-allyloxy derivatives gave a simple direct route to the synthetically important 4-pentenal. These pyrolytic transformations convert aldehydes to aryloxyalkenes (a protected homologation) and 4-pentenal (a C-1 allylation and homologation). The starting 3-aryloxy and 3-allyloxy-beta-lactams were synthesized by the standard Staudinger ketene-imine [2 + 2] cycloaddition. The corresponding beta-thiolactams have readily been...

Continuous flow chemistry: a discovery tool for new chemical reactivity patterns

Jan Hartwig, Jan B. Metternich, Nikzad Nikbin, Andreas Kirschning & Steven V. Ley
Continuous flow chemistry as a process intensification tool is well known. However, its ability to enable chemists to perform reactions which are not possible in batch is less well studied or understood. Here we present an example, where a new reactivity pattern and extended reaction scope has been achieved by transferring a reaction from batch mode to flow. This new reactivity can be explained by suppressing back mixing and precise control of temperature in a...

A CO2-stable reduction-tolerant Nd-containing dual phase membrane for oxyfuel CO2 capture

Huixia Luo, Tobias Klande, Zhengwen Cao, Fangyi Liang, Haihui Wang & Jürgen Caro
We report a novel CO2-stable reduction-tolerant dual-phase oxygen transport membrane 40 wt% Nd0.6Sr0.4FeO3-delta-60 wt% Ce0.9Nd0.1O2-delta (40NSFO-60CNO), which was successfully developed by a facile one-pot EDTA-citric sol-gel method. The microstructure of the crystalline 40NSFO-60CNO phase was investigated by combined in situ X-ray diffraction (XRD), scanning electron microscopy (SEM), back scattered SEM (BSEM), and energy dispersive X-ray spectroscopy (EDXS) analyses. Oxygen permeation and long-time stability under CO2 and CH4 atmospheres were investigated. A stable oxygen flux of...

Uncovering the origin of Z-configured double bonds in polyketides: intermediate E-double bond formation during borrelidin biosynthesis

Nadine Kandziora, Jennifer N. Andexer, Steven J. Moss, Barrie Wilkinson, Peter F. Leadlay & Frank Hahn
Formation of Z-configured double bonds in reduced polyketides is uncommon and their origins have not been extensively studied. To investigate the origin of the Z-configured double bond in the macrolide borrelidin, the recombinant dehydratase domains BorDH2 and B0rDH3 were assayed with a synthetic analogue of the predicted tetraketide substrate. The configuration of the dehydrated products was determined to be E in both cases by comparison to synthetic standards. Detailed NMR spectroscopic analysis of the biosynthetic...

One-pot aqueous synthesis of highly strained CdTe/CdS/ZnS nanocrystals and their interactions with cells

Mehriban Ulusoy, Johanna-Gabriela Walter, Antonina Lavrentieva, Imme Kretschmer, Lydia Sandiford, Alix Le Marois, Rebecca Bongartz, Pooyan Aliuos, Klaus Suhling, Frank Stahl, Mark Green & Thomas Scheper
In this work, a very simple one-pot synthetic approach was developed to generate aqueous CdTe/CdS/ZnS type-II/type-I red-emitting nanocrystals (NCs). Strain-induced optical properties of CdTe/CdS particles having core((small))/shell((thick)) structure with a maximum quantum yield (QY(max)) similar to 57% were further improved with the overgrowth of a ZnS shell, resulting in a core((small))/shell((thick))/shell((small)) structure (QY(max) similar to 64%). The spectral properties were tuned further to the near-infrared region as the ZnS shell grew in thickness. X-ray powder...

Lithium conductivity in glasses of the Li2O-Al2O3-SiO2 system

Sebastian Ross, Anna-Maria Welsch & Harald Behrens
To improve the understanding of Li-dynamics in oxide glasses, i.e. the effect of [AlO4](-) tetrahedra and non-bridging oxygens on the potential landscape, electrical conductivity of seven fully polymerized and partly depolymerized lithium aluminosilicate glasses was investigated using impedance spectroscopy (IS). Lithium is the only mobile particle in these materials. Data derived from IS, i. e. activation energies, preexponential factors and diffusivities for lithium, are interpreted in light of Raman spectroscopic analyses of local structures in...

Electrochemical deposition of Fe2O3 in the presence of organic additives: a route to enhanced photoactivity

Dereje H. Taffa, Ines Hamm, Christian Dunkel, Ilya Sinev, Detlef W. Bahnemann & Michael Wark
The photoelectrochemical activity of hematite films prepared by electrochemical deposition (ED) in the presence of organic additives is discussed. The studies focus on the role of small organic additive molecules in the tuning of the morphology of the films and their influence on the photoelectrochemical oxidation of water. The organic additives, namely, coumarin 343 (C343), γ-glucuronic acid (GA) and sodium dodecyl sulfonate (Sds), possess functional moieties to interact with iron ions in the ED bath...

Mycotoxins: Producing Fungi and Mechanisms of Phytotoxicity

Ahmed A. Ismaiel & Jutta Papenbrock
Mycotoxins are secondary fungal metabolites, toxic to humans, animals and plants. Among the hundreds of known mycotoxins, aflatoxins, citrinin, patulin, penicillic acid, tenuazonic acid, ochratoxin A, cytochalasins, deoxynivalenol, fumonisins, fusarin C, fusaric acid, and zearalenone are considered the types that most contaminate cereal grain. The majority of the mycotoxins in these groups are produced by three fungal genera: Aspergillus, Penicillium and Fusarium. These metabolites primarily affect the seed quality, germination, viability, seedling vigour, growth of...

The angular overlap model extended for two-open-shell f and d electrons

Harry Ramanantoanina, Werner Urland, Fanica Cimpoesu & Claude Daul
We discuss the applicability of the Angular Overlap Model (AOM) to evaluate the electronic structure of lanthanide compounds, which are currently the subject of incredible interest in the field of luminescent materials. The functioning of phosphors is well established by the f–d transitions, which requires the investigation of both the ground 4fn and excited 4fn−15d1 electron configurations of the lanthanides. The computational approach to the problem is based on the effective Hamiltonian adjusted from ligand...

Ligand field density functional theory for the prediction of future domestic lighting

Harry Ramanantoanina, Werner Urland, Amador Garcia-Fuente, Fanica Cimpoesu & Claude Daul
We deal with the computational determination of the electronic structure and properties of lanthanide ions in complexes and extended structures having open-shell f and d configurations. Particularly, we present conceptual and methodological issues based on Density Functional Theory (DFT) enabling the reliable calculation and description of the f → d transitions in lanthanide doped phosphors. We consider here the optical properties of the Pr3+ ion embedded into various solid state fluoride host lattices, for the...

Modulation of the electron transfer processes in Au-ZnO nanostructures

Matias E. Aguirre, A. Armanelli, Gonzalo Perelstein, Armin Feldhoff, Alfredo J. Tolley & Maria A. Grela
Plasmonic nanostructures comprising Au and ZnO nanoparticles synthesized by the spontaneous reduction of HAuCl4 in ethylene glycol were used to assess the possibility of modulating the direction of the electron transfer processes at the interface. One electron UV reduction and visible oxidation of the reversible couple TEMPOL/TEMPOL-H was confirmed by EPR spectroscopy. The apparent quantum yield for TEMPOL-H conversion under continuous wave visible excitation depends on the irradiation wavelength, being 0.57% and 0.27% at 450...

Lessons from the Synthetic Chemist Nature

Gerrit Juerjens, Andreas Kirschning & David A. Candito
This conceptual review examines the ideal multistep synthesis from the perspective of nature. We suggest that besides step- and redox economies, one other key to efficiency is steady state processing with intermediates that are immediately transformed to the next intermediate when formed. We discuss four of nature's strategies (multicatalysis, domino reactions, iteration and compartmentation) that commonly proceed via short-lived intermediates and show that these strategies are also part of the chemist's portfolio. We particularly focus...

Synthesis of new carolacton derivatives and their activity against biofilms of oral bacteria

Nico Stumpp, P. Premnath, T. Schmidt, J. Ammermann, Gerald Draeger, M. Reck, R. Jansen, Meike Stiesch, Irene Wagner-Döbler & Andreas Kirschning
Carolacton, a secondary metabolite isolated from the extracts of Sorangium cellulosum, causes membrane damage and cell death in biofilms of the caries- and endocarditis-associated bacterium Streptococcus mutans. Here, we report the total synthesis of several derivatives of carolacton. All new structural modifications introduced abolished its biological activity, including subtle ones, such as inversion of configuration at C9. However, a bicyclic bislactone derivative as well as the methyl ester of carolacton resulted in compounds with prodrug...

Conformational steering in dicarboxy acids: the native structure of succinic acid

Michaela K. Jahn, Estibaliz Mendez, K. P. Rajappan Nair, Peter D. Godfrey, Don McNaughton, Patricia Ecija, Francisco J. Basterretxea, Emilio J. Cocinero & Jens-Uwe Grabow
Succinic acid, a dicarboxylic acid molecule, has been investigated spectroscopically with computational support to elucidate the complex aspects of its conformational composition. Due to the torsional freedom of the carbon backbone and hydroxy groups, a large number of potentially plausible conformers can be generated with an indication that the gauche conformer is favored over the trans form. The microwave and millimeter wave spectra have been analyzed and accurate spectroscopic constants have been derived that correlate...

Enhanced stability of Zr-doped Ba(CeTb)O3−δ-Ni cermet membrane for hydrogen separation

Yanying Wei, Jian Xue, Wei Fang, Yan Chen, Haihui Wang & Jürgen Caro
A mixed protonic and electronic conductor material BaCe0.85Tb0.05Zr0.1O3−δ (BCTZ) is prepared and a Ni-BCTZ cermet membrane is synthesized for hydrogen separation. Stable hydrogen permeation fluxes can be obtained for over 100 h through the Ni-BCTZ membrane in both dry and humid conditions, which exhibits an excellent stability compared with Ni-BaCe0.95Tb0.05O3−δ membrane due to the Zr doping.

Polypyrrole nanoparticles for tunable, pH-sensitive and sustained drug release

Devleena Samanta, Jana L. Meiser & Richard N. Zare
We report the development of a generalized pH-sensitive drug delivery system that can release any charged drug preferentially at the pH range of interest. Our system is based on polypyrrole nanoparticles (PPy NPs), synthesized via a simple one-step microemulsion technique. These nanoparticles are highly monodisperse, stable in solution over the period of a month, and have good drug loading capacity (∼15 wt%). We show that PPy NPs can be tuned to release drugs at both...

Registration Year

  • 2015
    102

Resource Types

  • Collection
    102

Data Centers

  • Leibniz Universität Hannover
    102