@article{MondalMarquardtJaniaketal.2016, author = {Mondal, Suvendu Sekhar and Marquardt, Dorothea and Janiak, Christoph and Holdt, Hans-J{\"u}rgen}, title = {Use of a 4,5-dicyanoimidazolate anion based ionic liquid for the synthesis of iron and silver nanoparticles}, series = {Dalton transactions : an international journal of inorganic chemistry}, journal = {Dalton transactions : an international journal of inorganic chemistry}, number = {45}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1477-9226}, doi = {10.1039/C6DT00225K}, pages = {5476 -- 5483}, year = {2016}, abstract = {Sixteen new ionic liquids (ILs) with tetraethylammonium, 1-butyl-3-methylimidazolium, 3-methyl-1-octylimidazolium and tetrabutylphosphonium cations paired with 2-substituted 4,5-dicyanoimidazolate anions (substituent at C2 = methyl, trifluoromethyl, pentafluoroethyl, N,N′-dimethyl amino and nitro) have been synthesized and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA). The effects of cation and anion type and structure of the resulting ILs, including several room temperature ionic liquids (RTILs), are reflected in the crystallization, melting points and thermal decomposition of the ILs. ILs exhibited large liquid and crystallization ranges and formed glasses on cooling with glass transition temperatures in the range of -22 to -71 °C. We selected one of the newly designed ILs due to its bigger size, compared to the common conventional IL anion and high electron-withdrawing nitrile group leads to an overall stabilization anion that may stabilize the metal nanoparticles. Stable and better separated iron and silver nanoparticles are obtained by the decomposition of corresponding Fe2(CO)9 and AgPF6, respectively, under N2-atmosphere in newly designed nitrile functionalized 4,5-dicyanoimidazolate anion based IL. Very small and uniform size for Fe-nanoparticles of about 1.8 ± 0.6 nm were achieved without any additional stabilizers or capping molecules. Comparatively bigger size of Ag-nanoparticles was obtained through the reduction of AgPF6 by hydrogen gas. Additionally, the AgPF6 precursor was decomposed under microwave irradiation (MWI), fabricating nut-in-shell-like, that is, core-separated-from-shell Ag-nano-structures.}, language = {en} } @article{KlaperWessigLinker2015, author = {Klaper, M. and Wessig, Pablo and Linker, Torsten}, title = {Base catalysed decomposition of anthracene endoperoxide}, series = {Chemical communications : ChemComm}, journal = {Chemical communications : ChemComm}, number = {52}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1364-548X}, doi = {10.1039/C5CC08606J}, pages = {1210 -- 1213}, year = {2015}, abstract = {Catalytic amounts of a weak base are sufficient to induce the decomposition of anthracene endoperoxides to anthraquinone. The mechanism has been elucidated by isolation of intermediates in combination with DFT calculations. The whole process is suitable for the convenient generation of hydrogen peroxide under very mild conditions.}, language = {en} } @article{MatisSchoenbornSaalfrank2015, author = {Matis, Jochen Ren{\´e} and Sch{\"o}nborn, Jan Boyke and Saalfrank, Peter}, title = {A multi-reference study of the byproduct formation for a ring-closed dithienylethene photoswitch}, series = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, journal = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, number = {17}, publisher = {The Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/C5CP00987A}, pages = {14088 -- 14095}, year = {2015}, abstract = {Photodriven molecular switches are sometimes hindered in their performance by forming byproducts which act as dead ends in sequences of switching cycles, leading to rapid fatigue effects. Understanding the reaction pathways to unwanted byproducts is a prerequisite for preventing them. This article presents a study of the photochemical reaction pathways for byproduct formation in the photochromic switch 1,2-bis-(3-thienyl)-ethene. Specifically, using single- and multi-reference methods the post-deexcitation reaction towards the byproduct in the electronic ground state S0 when starting from the S1-S0 conical intersection (CoIn), is considered in detail. We find an unusual low-energy pathway, which offers the possibility for the formation of a dyotropic byproduct. Several high-energy pathways can be excluded with high probability.}, language = {en} } @article{PrestelMoeller2015, author = {Prestel, Andreas and M{\"o}ller, Heiko Michael}, title = {Spatio-temporal control of cellular uptake achieved by photoswitchable cell-penetrating peptides}, series = {Chemical communications : ChemComm}, journal = {Chemical communications : ChemComm}, number = {52}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1364-548X}, doi = {10.1039/C5CC06848G}, pages = {701 -- 704}, year = {2015}, abstract = {The selective uptake of compounds into specific cells of interest is a major objective in cell biology and drug delivery. By incorporation of a novel, thermostable azobenzene moiety we generated peptides that can be switched optically between an inactive state and an active, cell-penetrating state with excellent spatio-temporal control.}, language = {en} } @article{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+,Er3+-co-doped NaYF4 nanomaterials}, series = {Journal of materials chemistry C ; Materials for optical and electronic devices}, journal = {Journal of materials chemistry C ; Materials for optical and electronic devices}, number = {3}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2050-7526}, doi = {10.1039/C5TC02218E}, pages = {11228 -- 11238}, year = {2015}, abstract = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.}, language = {en} } @article{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale}, series = {RSC Advances : an international journal to further the chemical sciences}, journal = {RSC Advances : an international journal to further the chemical sciences}, number = {5}, publisher = {RSC Publishing}, address = {London}, issn = {2046-2069}, doi = {10.1039/C5RA11502G}, pages = {67149 -- 67156}, year = {2015}, abstract = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.}, language = {en} } @article{deCarvalhoMetzlerCherstvy2015, author = {de Carvalho, Sidney J. and Metzler, Ralf and Cherstvy, Andrey G.}, title = {Inverted critical adsorption of polyelectrolytes in confinement}, series = {Soft matter}, journal = {Soft matter}, number = {11}, publisher = {Royal Society of Chemistry}, address = {London}, issn = {1744-6848}, doi = {10.1039/C5SM00635J}, pages = {4430 -- 4443}, year = {2015}, abstract = {What are the fundamental laws for the adsorption of charged polymers onto oppositely charged surfaces, for convex, planar, and concave geometries? This question is at the heart of surface coating applications, various complex formation phenomena, as well as in the context of cellular and viral biophysics. It has been a long-standing challenge in theoretical polymer physics; for realistic systems the quantitative understanding is however often achievable only by computer simulations. In this study, we present the findings of such extensive Monte-Carlo in silico experiments for polymer-surface adsorption in confined domains. We study the inverted critical adsorption of finite-length polyelectrolytes in three fundamental geometries: planar slit, cylindrical pore, and spherical cavity. The scaling relations extracted from simulations for the critical surface charge density sc—defining the adsorption-desorption transition—are in excellent agreement with our analytical calculations based on the ground-state analysis of the Edwards equation. In particular, we confirm the magnitude and scaling of sc for the concave interfaces versus the Debye screening length 1/k and the extent of confinement a for these three interfaces for small ka values. For large ka the critical adsorption condition approaches the known planar limit. The transition between the two regimes takes place when the radius of surface curvature or half of the slit thickness a is of the order of 1/k. We also rationalize how sc(k) dependence gets modified for semi-flexible versus flexible chains under external confinement. We examine the implications of the chain length for critical adsorption—the effect often hard to tackle theoretically—putting an emphasis on polymers inside attractive spherical cavities. The applications of our findings to some biological systems are discussed, for instance the adsorption of nucleic acids onto the inner surfaces of cylindrical and spherical viral capsids.}, language = {en} } @article{HentrichJungingerBrunsetal.2015, author = {Hentrich, Doreen and Junginger, Mathias and Bruns, Michael and B{\"o}rner, Hans Gerhard and Brandt, Jessica and Brezesinski, Gerald and Taubert, Andreas}, title = {Interface-controlled calcium phosphate mineralization}, series = {CrystEngComm}, journal = {CrystEngComm}, number = {17}, publisher = {Royal Society of Chemistry}, address = {London}, issn = {1466-8033}, doi = {10.1039/C4CE02274B}, pages = {6901 -- 6913}, year = {2015}, abstract = {The phase behavior of an amphiphilic block copolymer based on a poly(aspartic acid) hydrophilic block and a poly(n-butyl acrylate) hydrophobic block was investigated at the air-water and air-buffer interface. The polymer forms stable monomolecular films on both subphases. At low pH, the isotherms exhibit a plateau. Compression-expansion experiments and infrared reflection absorption spectroscopy suggest that the plateau is likely due to the formation of polymer bi- or multilayers. At high pH the films remain intact upon compression and no multilayer formation is observed. Furthermore, the mineralization of calcium phosphate beneath the monolayer was studied at different pH. The pH of the subphase and thus the polymer charge strongly affects the phase behavior of the film and the mineral formation. After 4 h of mineralization at low pH, atomic force microscopy shows smooth mineral films with a low roughness. With increasing pH the mineral films become inhomogeneous and the roughness increases. Transmission electron microscopy confirms this: at low pH a few small but uniform particles form whereas particles grown at higher pH are larger and highly agglomerated. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirm the formation of calcium phosphate. The levels of mineralization are higher in samples grown at high pH.}, language = {en} } @incollection{Bickenbach2015, author = {Bickenbach, Christian}, title = {Wissenschaftsfreiheit zwischen Krieg und Frieden}, series = {Von der Kultur der Verfassung : Festschrift f{\"u}r Friedhelm Hufen zum 70. Geburtstag}, booktitle = {Von der Kultur der Verfassung : Festschrift f{\"u}r Friedhelm Hufen zum 70. Geburtstag}, editor = {Geis, Max-Emanuel and Winkler, Markus and Bickenbach, Christian}, publisher = {Beck}, address = {M{\"u}nchen}, publisher = {Universit{\"a}t Potsdam}, pages = {277 -- 287}, year = {2015}, language = {de} } @book{OPUS4-8951, title = {Von der Kultur der Verfassung}, editor = {Geis, Max-Emanuel and Winkler, Markus and Bickenbach, Christian}, publisher = {Beck}, address = {M{\"u}nchen}, isbn = {978-3-406-67481-5}, publisher = {Universit{\"a}t Potsdam}, year = {2015}, abstract = {Friedhelm Hufen ist geboren im letzten Kriegswinter in Winterberg, im Sauerland, aufgewachsen ist er in Leverkusen und M{\"u}nster. Studiert hat er in M{\"u}nster, Freiburg und Princeton. Insbesondere der Aufenthalt in den Vereinigten Staaten hat durch die damalige Rechtsprechung des Supreme Courts und die Erfahrung des melting pot sein Freiheits- und Verfahrensverst{\"a}ndnis nachhaltig gepr{\"a}gt. Den gr{\"o}ßten Einfluss auf Friedhelm Hufen aber hatten seine akademischen Lehrer: Hans-Peter Schneider, der seine Habilitation in Hannover betreut hat, sowie vor allem sein Freiburger Doktorvater Konrad Hesse. Das politische, realit{\"a}tsbezogene und integrative Verfassungsverst{\"a}ndnis hat hier seinen Ursprung und findet sich sowohl in der Dissertation zum Thema Gleichheitssatz und Bildungsplanung als auch in der Habilitationsschrift zur Freiheit der Kunst in staatlichen Institutionen. Friedhelm Hufen denkt nicht vom Staat, sondern von der Verfassung her. Das Grundgesetz hat elementare Bedeutung f{\"u}r sein Rechtsverst{\"a}ndnis und seine Sicht auf die Wissenschaften vom Recht. Die Verfassung ist f{\"u}r ihn nicht allein eine Rechtsnorm, sondern sie ist der Gesamtzustand eines politischen Gemeinwesens, das sich mit der Verfassung zugleich ein Gesetz daf{\"u}r gegeben hat, wie das Zusammenleben der Menschen organisiert sein soll. Denken von der Verfassung her bedeutet f{\"u}r Friedhelm Hufen wiederum Denken von der Freiheit her. Freiheit und Verantwortung sind f{\"u}r ihn zwei Seiten einer Medaille. Seine Abschiedsvorlesung in Mainz war dem Motto Selbst Denken; gewidmet. Das Kantsche Diktum "sapere aude" stand dabei Pate. Weil ihm Freiheit so wichtig ist, bevorzugt Friedhelm Hufen staatliche Organisationsstrukturen, die eine m{\"o}glichst große Gew{\"a}hr f{\"u}r Freiheit und Pluralismus bieten: den Bundesstaat und alle Formen der Selbstverwaltung.}, language = {de} }