@misc{MondalBehrensMatthesetal.2014, author = {Mondal, Suvendu Sekhar and Behrens, Karsten and Matthes, Philipp R. and Sch{\"o}nfeld, Fabian and Nitsch, J{\"o}rn and Steffen, Andreas and Primus, Philipp-Alexander and Kumke, Michael Uwe and M{\"u}ller-Buschbaum, Klaus and Holdt, Hans-J{\"u}rgen}, title = {White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-79953}, pages = {4623 -- 4631}, year = {2014}, abstract = {Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a-d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+.}, language = {en} } @misc{MondalBhuniaKellingetal.2014, author = {Mondal, Suvendu Sekhar and Bhunia, Asamanjoy and Kelling, Alexandra and Schilde, Uwe and Janiak, Christoph and Holdt, Hans-J{\"u}rgen}, title = {A supramolecular Co(II)₁₄-metal-organic cube in a hydrogen-bonded network and a Co(II)-organic framework with a flexible methoxy substituent}, number = {169}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74098}, pages = {5441 -- 5443}, year = {2014}, abstract = {The reaction of 4,5-dicyano-2-methoxyimidazole (L1) with Co(NO3)2·6H2O under solvothermal conditions in DMF, a MOF, IFP-8 and a hydrogen-bonded network consisting of tetradecanuclear Co(II)14-metal organic cube (1) are achieved. 1 shows the bcu net with 14 cobalt atoms.}, language = {en} } @misc{XieHuangTitiricietal.2014, author = {Xie, Zai-Lai and Huang, Xing and Titirici, Maria-Magdalena and Taubert, Andreas}, title = {Mesoporous graphite nanoflakes via ionothermal carbonization of fructose and their use in dye removal}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-99427}, year = {2014}, abstract = {The large-scale green synthesis of graphene-type two-dimensional materials is still challenging. Herein, we describe the ionothermal synthesis of carbon-based composites from fructose in the iron-containing ionic liquid 1-butyl-3-methylimidazolium tetrachloridoferrate(III), [Bmim][FeCl4] serving as solvent, catalyst, and template for product formation. The resulting composites consist of oligo-layer graphite nanoflakes and iron carbide particles. The mesoporosity, strong magnetic moment, and high specific surface area of the composites make them attractive for water purification with facile magnetic separation. Moreover, Fe3Cfree graphite can be obtained via acid etching, providing access to fairly large amounts of graphite material. The current approach is versatile and scalable, and thus opens the door to ionothermal synthesis towards the larger-scale synthesis of materials that are, although not made via a sustainable process, useful for water treatment such as the removal of organic molecules.}, language = {en} } @misc{EhlertUngerSaalfrank2014, author = {Ehlert, Christopher and Unger, Wolfgang E. S. and Saalfrank, Peter}, title = {C K-edge NEXAFS spectra of graphene with physical and chemical defects}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74429}, pages = {14083 -- 14095}, year = {2014}, abstract = {Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.}, language = {en} } @misc{WirthNeumannAntoniettietal.2014, author = {Wirth, Jonas and Neumann, Rainer and Antonietti, Markus and Saalfrank, Peter}, title = {Adsorption and photocatalytic splitting of water on graphitic carbon nitride}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74391}, pages = {15917 -- 15926}, year = {2014}, abstract = {Graphitic carbon nitride, g-C₃N₄, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C₃N₄ by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H⁺ reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H₂ production O₂ evolution is only possible in the presence of oxidation cocatalysts.}, language = {en} } @misc{ViouxTaubert2014, author = {Vioux, Andr{\´e} and Taubert, Andreas}, title = {Ionic liquids 2014 and selected papers from ILMAT 2013}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1055}, issn = {1866-8372}, doi = {10.25932/publishup-47506}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475062}, pages = {6}, year = {2014}, language = {en} } @misc{ErmeydanCabaneHassetal.2014, author = {Ermeydan, Mahmut Ali and Cabane, Etienne and Hass, Philipp and Koetz, Joachim and Burgert, Ingo}, title = {Fully biodegradable modification of wood for improvement of dimensional stability and water absorption properties by poly(ε-caprolactone) grafting into the cell walls}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-97265}, pages = {3313 -- 3321}, year = {2014}, abstract = {Materials derived from renewable resources are highly desirable in view of more sustainable manufacturing. Among the available natural materials, wood is one of the key candidates, because of its excellent mechanical properties. However, wood and wood-based materials in engineering applications suffer from various restraints, such as dimensional instability upon humidity changes. Several wood modification treatments increase water repellence, but the insertion of hydrophobic polymers can result in a composite material which cannot be considered as renewable anymore. In this study, we report on the grafting of the fully biodegradable poly(ε-caprolactone) (PCL) inside the wood cell walls by Sn(Oct)2 catalysed ring-opening polymerization (ROP). The presence of polyester chains within the wood cell wall structure is monitored by confocal Raman imaging and spectroscopy as well as scanning electron microscopy. Physical tests reveal that the modified wood is more hydrophobic due to the bulking of the cell wall structure with the polyester chains, which results in a novel fully biodegradable wood material with improved dimensional stability.}, language = {en} } @misc{ErmeydanCabaneGierlingeretal.2014, author = {Ermeydan, Mahmut Ali and Cabane, Etienne and Gierlinger, Notburga and Koetz, Joachim and Burgert, Ingo}, title = {Improvement of wood material properties via in situ polymerization of styrene into tosylated cell walls}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98736}, pages = {8}, year = {2014}, abstract = {As an engineering material derived from renewable resources, wood possesses excellent mechanical properties in view of its light weight but also has some disadvantages such as low dimensional stability upon moisture changes and low durability against biological attack. Polymerization of hydrophobic monomers in the cell wall is one of the potential approaches to improve the dimensional stability of wood. A major challenge is to insert hydrophobic monomers into the hydrophilic environment of the cell walls, without increasing the bulk density of the material due to lumen filling. Here, we report on an innovative and simple method to insert styrene monomers into tosylated cell walls (i.e. -OH groups from natural wood polymers are reacted with tosyl chloride) and carry out free radical polymerization under relatively mild conditions, generating low wood weight gains. In-depth SEM and confocal Raman microscopy analysis are applied to reveal the distribution of the polystyrene in the cell walls and the lumen. The embedding of polystyrene in wood results in reduced water uptake by the wood cell walls, a significant increase in dimensional stability, as well as slightly improved mechanical properties measured by nanoindentation.}, language = {en} } @misc{SarauliXuDietzeletal.2014, author = {Sarauli, David and Xu, Chenggang and Dietzel, Birgit and Schulz, Burkhard and Lisdat, Fred}, title = {A multilayered sulfonated polyaniline network with entrapped pyrroloquinoline quinone-dependent glucose dehydrogenase}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98744}, year = {2014}, abstract = {A feasible approach to construct multilayer films of sulfonated polyanilines - PMSA1 and PABMSA1 - containing different ratios of aniline, 2-methoxyaniline-5-sulfonic acid (MAS) and 3-aminobenzoic acid (AB), with the entrapped redox enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) on Au and ITO electrode surfaces, is described. The formation of layers has been followed and confirmed by electrochemical impedance spectroscopy (EIS), which demonstrates that the multilayer assembly can be achieved in a progressive and uniform manner. The gold and ITO electrodes subsequently modified with PMSA1:PQQ-GDH and PABMSA1 films are studied by cyclic voltammetry (CV) and UV-Vis spectroscopy which show a significant direct bioelectrocatalytical response to the oxidation of the substrate glucose without any additional mediator. This response correlates linearly with the number of deposited layers. Furthermore, the constructed polymer/enzyme multilayer system exhibits a rather good long-term stability, since the catalytic current response is maintained for more than 60\% of the initial value even after two weeks of storage. This verifies that a productive interaction of the enzyme embedded in the film of substituted polyaniline can be used as a basis for the construction of bioelectronic units, which are useful as indicators for processes liberating glucose and allowing optical and electrochemical transduction.}, language = {en} } @misc{CommingesFrascaSuetterlinetal.2014, author = {Comminges, Cl{\´e}ment and Frasca, Stefano and S{\"u}tterlin, Martin and Wischerhoff, Erik and Laschewsky, Andr{\´e} and Wollenberger, Ursula}, title = {Surface modification with thermoresponsive polymer brushes for a switchable electrochemical sensor}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-99471}, year = {2014}, abstract = {Elaboration of switchable surfaces represents an interesting way for the development of a new generation of electrochemical sensors. In this paper, a method for growing thermoresponsive polymer brushes from a gold surface pre-modified with polyethyleneimine (PEI), subsequent layer-by-layer polyelectrolyte assembly and adsorption of a charged macroinitiator is described. We propose an easy method for monitoring the coil-to-globule phase transition of the polymer brush using an electrochemical quartz crystal microbalance with dissipation (E-QCM-D). The surface of these polymer modified electrodes shows reversible switching from the swollen to the collapsed state with temperature. As demonstrated from E-QCM-D measurements using an original signal processing method, the switch is operating in three reversible steps related to different interfacial viscosities. Moreover, it is shown that the one electron oxidation of ferrocene carboxylic acid is dramatically affected by the change from the swollen to the collapsed state of the polymer brush, showing a spectacular 86\% decrease of the charge transfer resistance between the two states.}, language = {en} } @misc{BaldKopyraKeller2014, author = {Bald, Ilko and Kopyra, Janina and Keller, Adrian}, title = {On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-73412}, pages = {6825 -- 6829}, year = {2014}, abstract = {Gemcitabine (2′,2′-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (<10 eV) electrons are produced that can directly induce chemical bond breakage in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2′-deoxycytidine, 2′-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavage. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA.}, language = {en} } @misc{PieperWeheBornhorstetal.2014, author = {Pieper, Imke and Wehe, Christoph A. and Bornhorst, Julia and Ebert, Franziska and Leffers, Larissa and Holtkamp, Michael and H{\"o}seler, Pia and Weber, Till and Mangerich, Aswin and B{\"u}rkle, Alexander and Karst, Uwe and Schwerdtle, Tanja}, title = {Mechanisms of Hg species induced toxicity in cultured human astrocytes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74379}, pages = {662 -- 671}, year = {2014}, abstract = {The toxicologically most relevant mercury (Hg) species for human exposure is methylmercury (MeHg). Thiomersal is a common preservative used in some vaccine formulations. The aim of this study is to get further mechanistic insight into the yet not fully understood neurotoxic modes of action of organic Hg species. Mercury species investigated include MeHgCl and thiomersal. Additionally HgCl2 was studied, since in the brain mercuric Hg can be formed by dealkylation of the organic species. As a cellular system astrocytes were used. In vivo astrocytes provide the environment necessary for neuronal function. In the present study, cytotoxic effects of the respective mercuricals increased with rising alkylation level and correlated with their cellular bioavailability. Further experiments revealed for all species at subcytotoxic concentrations no induction of DNA strand breaks, whereas all species massively increased H2O2-induced DNA strand breaks. This co- genotoxic effect is likely due to a disturbance of the cellular DNA damage response. Thus, at nanomolar, sub-cytotoxic concentrations, all three mercury species strongly disturbed poly(ADP-ribosyl)ation, a signalling reaction induced by DNA strand breaks. Interestingly, the molecular mechanism behind this inhibition seems to be different for the species. Since chronic PARP-1 inhibition is also discussed to sacrifice neurogenesis and learning abilities, further experiments on neurons and in vivo studies could be helpful to clarify whether the inhibition of poly(ADP-ribosyl) ation contributes to organic Hg induced neurotoxicity.}, language = {en} }