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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.
A multi-reference study of the byproduct formation for a ring-closed dithienylethene photoswitch
(2015)
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.
Spatio-temporal control of cellular uptake achieved by photoswitchable cell-penetrating peptides
(2015)
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.
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.
Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale
(2015)
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.
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.
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.
Friedhelm Hufen ist geboren im letzten Kriegswinter in Winterberg, im Sauerland, aufgewachsen ist er in Leverkusen und Münster. Studiert hat er in Münster,
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 Verfahrensverständnis nachhaltig geprägt. Den
größten 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, realitätsbezogene und integrative Verfassungsverständnis 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 für sein Rechtsverständnis und seine Sicht auf die Wissenschaften vom Recht. Die Verfassung ist für ihn nicht allein eine
Rechtsnorm, sondern sie ist der Gesamtzustand eines politischen Gemeinwesens, das sich mit der Verfassung zugleich ein Gesetz dafür gegeben hat, wie das Zusammenleben der Menschen organisiert sein soll. Denken von der Verfassung her bedeutet für Friedhelm Hufen wiederum Denken von der Freiheit her. Freiheit
und Verantwortung sind für 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 möglichst große Gewähr für Freiheit und Pluralismus bieten: den Bundesstaat und alle Formen der Selbstverwaltung.
Das Buch befasst sich mit der Frage, ob und wie international tätige Unternehmen europäische Auslandsverluste bei der inländischen Besteuerung geltend machen können. Im Mittelpunkt der rechtlichen Auseinandersetzung steht die Rechtsprechungsentwicklung des EuGH seit der Rechtssache Marks & Spencer. Mit zunehmender Anzahl an Gerichtsentscheidungen wurde die grenzüberschreitende Verlustverrechnung im Rahmen der 'finalen Verluste' Gegenstand intensiver und kontroverser Rechtsdiskussion. Die vorliegende Arbeit nimmt eine kritische Bestandsaufnahme des nationalen Steuerrechts vor. Dabei untersucht der Autor, welche Folgen mit der EuGH-Rechtsprechung einhergehen und welche Lösungsansätze einen gangbaren Weg ebnen könnten, um dem Europäischen Gedanken eines gemeinsamen Binnenmarkts gerecht zu werden.