27 Works

Paleo-soraphens: chemical total syntheses and biological studies

Hai-Hua Lu, Bettina Hinkelmann, Thomas Tautz, Jun Li, Florenz Sasse, Raimo Franke & Markus Kalesse
The soraphens are natural products that exhibit a molecular structure different from what would have been expected by following its polyketidal assembly line. The most significant differences are the presence of a hemiketal instead of a trisubstituted double bond and a double bond at C9 and C10 where a saturated carbon chain was expected. We were interested in the biological activity of the soraphens with architectures as described by the polyketide synthase since we hypothesized...

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...

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...

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...

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...

Weg mit Hartz IV! : Die Montagsdemonstrationen in Leipzig zwischen 30. August und 4. Oktober 2004

Axel Philipps
Der Beitrag untersucht das Protestmaterial von sechs Leipziger Montagsdemonstrationen zwischen dem 30. August und dem 4. Oktober 2004. Das Material wurde inhaltlich als auch hinsichtlich der Gestaltung analysiert und interpretiert.

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...

A new CO2-resistant Ruddlesden-Popper oxide with superior oxygen transport: A-site deficient (Pr0.9La0.1)1.9(Ni0.74Cu0.21Ga0.05)O4+δ

Jian Xue, Qing Liao, Wei Chen, Henny J. M. Bouwmeester, Haihui Wang & Armin Feldhoff
A-site deficient (Pr0.9La0.1)1.9Ni0.74Cu0.21Ga0.05O4+δ ((PL)1.9NCG), with the K2NiF4 structure, is found to exhibit higher oxygen transport rates compared with its cation-stoichiometric parent phase. A stable oxygen permeation flux of 4.6 × 10−7 mol cm−2 s−1 at 900 °C at a membrane thickness of 0.6 mm is measured, using either helium or pure CO2 as sweep gas at a flow rate of 30 mL min−1. The oxygen flux is more than two times higher than that observed...

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...

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...

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...

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...

Charge carrier dynamics and photocatalytic behavior of TiO2 nanopowders submitted to hydrothermal or conventional heat treatment

Antonio Otavio T. Patrocinio, J. Schneider, M.D. Franca, Lidiaine M. Santos, B.P. Caixeta, Antonio Eduardo H. Machado & Detlef W. Bahnemann
The sol–gel technique followed by conventional (TiO2-1) and hydrothermal (TiO2-2) thermal treatment was employed to prepare TiO2-based photocatalysts with distinct particle sizes and crystalline structures. The as prepared metal oxides were evaluated as photocatalysts for gaseous HCHO degradation, methanol, and dye oxidation reactions. Additionally, metallic platinum was deposited on the TiO2 surfaces and H2 evolution measurements were performed. The photocatalytic activities were rationalized in terms of morphologic parameters along with the electron/hole dynamics obtained from...

Long-term investigation of the photocatalytic hydrogen production on platinized TiO2: an isotopic study

Tarek A. Kandiel, Irina Ivanova & Detlef W. Bahnemann
Long-term investigations of the photocatalytic hydrogen production on platinized TiO2 photocatalysts have been carried out employing different solutions of (deuterated) water and (deuterated) methanol. The results indicate that methanol acts as a sacrificial reagent, i.e., as an “electron donor” and that the amount of evolved molecular hydrogen is equivalent to the amount of H2 expected from the complete reforming of methanol or even less depending on the used photocatalyst. No evidence for photocatalytic water splitting...

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...

Six-fold-symmetry internal rotation in toluenes: the low barrier challenge of 2,6-and 3,5-difluorotoluene

K. P. Rajappan Nair, Michaela K. Jahn, Alberto Lesarri, Vadim V. Ilyushin & Jens-Uwe Grabow
Pure six-fold symmetry (V6) internal rotation poses significant challenges to experimental and theoretical determination, as the very low torsional barriers result in huge tunneling splittings difficult to identify and to model. Here we resolved the methyl group internal rotation dynamics of 2,6- and 3,5-difluorotoluene using a newly developed computer code especially adapted to V6 problems. The jet-cooled rotational spectra of the title molecules in the 5–25 GHz region revealed internal rotation tunneling doublings of up...

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.

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...

[Rez. o.T. zu: Ziesche, Rudolf: Der Manuskriptnachlaß Gerhart Hauptmanns. Teil 3. GH Hs 471-780. Anhang 1-80 u. Teil 4. Register]

Bernhard Tempel
Rezension des Katalogs zum Manuskriptnachlaß Gerhart Hauptmanns mit Hinweisen auf weitere Verzeichnisse des Hauptmann-Nachlasses (Briefnachlaß, Dokumente, Sammlung, Bibliothek) und von Nachlässen im Umfeld Hauptmanns (vor allem seiner zweiten Frau Margarete Hauptmann).

Zivilprozess in Zahlen : zum 70. Deutscher Juristentag in Hannover

Christian Wolf
Die prozessrechtliche Abteilung des 70. Deutschen Juristentags beschäftigt sich mit der Frage, ob ZPO und GVG noch zeitgemäß sind, um den gewandelten Anforderungen an den Zivilprozess Genüge tun zu können. Die Fragestellung ist für unser Rechtssystem hoch bedeutend. Der gleiche Zugang zu Gericht, die Chancengleichheit und Fairness vor Gericht sowie die Schnelligkeit und Effizienz der Gerichtsverfahren sind für den Rechtsstaat schlicht konstitutiv.

Phononenspektroskopie im Quanten-Hall-Effekt-Regime

Fritz Schulze Wischeler
In dieser Arbeit wurde der Quanten-Hall-Effekt mit Hilfe von Phononen untersucht. Ziel der Arbeit war es, die thermodynamischen Eigenschaften von zweidimensionalen Elektronensystemen und Größe der Energielücken im fraktionalen Quanten-Hall-Effekt präzise zu vermessen. So gelang es, die Composite-Fermion-Masse und Landé g-Faktoren zu bestimmen. Darüberhinaus konnte die spezifische Wärme eines zweidimensionalen Elektronensystemens für diverse Füllfaktoren gemessen werden, einer thermodynamischen Größe, für die bisher keine experimentelle Technik zur Verfügung stand.

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...

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...

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