Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials

In a comparative study of the electrocatalytic CO₂ reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO₂ becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO₂. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.     

Identification of PET radiometabolites by cytochrome P450, UHPLC/Q-ToF-MS and fast radio-LC: applied to the PET radioligands [11C]flumazenil, [18F]FE-PE2I, and [11C]PBR28

A general method is presented for the identification of radiometabolites in plasma of human and monkey subjects after administration of positron emission tomography (PET) radioligands. The radiometabolites are first produced in vitro, using liver microsomes, subsequently separated using fast radio-liquid chromatography (radio-LC), and individually collected and identified by ultra high-performance liquid chromatography/quadrupole-time of flight-mass spectrometry in MS and MS^E mode. Fast radio-LC provided superior resolution compared to conventional radio-LC, resulting in separation of a greater number of metabolites. The radiometabolites produced in vivo are then compared to and identified based on the in vitro results. This approach was applied to three PET radioligands, [¹¹C]flumazenil, [¹⁸F]FE-PE2I, and [¹¹C]PBR28, resulting in the identification of five, two, and one radiometabolites, respectively. This procedure can easily be adopted to identify the radiometabolites produced in vivo from a variety of PET radioligands.     

Control of diabatic versus adiabatic field dissociation in a heavy Rydberg system

A novel phenomenon is observed in the dynamics of laser-prepared coherent wave packets, bound by the Coulombic 1/r potential of an ion-pair system. After exciting weakly bound (approximately 3 meV) H(+)(-) wave packets in a Stark field, and permitting them to evolve in time, control of field dissociation via adiabatic and diabatic routes is demonstrated by applying delayed pulsed-electric fields, involving a zero-field crossing. Control manifests itself through the production of ions from each pathway at a different instant in time. This phenomenon is applied to map the oscillatory behavior of an angular momentum wave packet in a heavy Rydberg system. The characteristic frequencies of the observed Stark oscillations verify predicted mass-scaling laws for heavy Rydberg systems.     

Direct catalytic azidation of allylic alcohols

A direct catalytic azidation of primary, secondary, and tertiary allylic alcohols has been developed. This new azidation reaction affords the corresponding allylic azides in high to excellent yields and regioselectivities. The reaction provides straightforward access to allylic azides that are valuable intermediates in organic synthesis, including the preparation of primary amines or 1,2,3-triazole derivatives.     

The effect of Fenton chemistry on the properties of microfibrillated cellulose

A fully bleached birch kraft pulp was treated with acidic hydrogen peroxide in the presence of ferrous ions (Fenton’s reagent) and thereafter treated mechanically in a colloid mill to produce a product containing microfibrillated cellulose (MFC). The produced MFC products were chemically and morphologically characterized and compared with MFC products produced without pretreatment as well as with enzymatic hydrolysis. Fenton treatment resulted in an increase in total charge and number of carbonyl groups while the intrinsic viscosity decreased. The Fenton treated pulps were easier to process mechanically i.e. they reached a higher specific surface area at a given mechanical treatment time and the MFC produced had a stable water-fibre suspension for at least 8 weeks compared to enzymatic pretreated pulps and pulps not subjected to any pretreatment.     

Methyl 3‐O‐β‐l‐fucopyranosyl α‐d‐glucopyranoside trihydrate

The water content of the title compound, C₁₃H₂₄O₁₀·3H₂O, creates an extensive hydrogen‐bonding pattern, with all the hydroxyl groups of the disaccharide acting as hydrogen‐bond donors and acceptors. The water molecules are arranged in columns along the crystallographic b axis and form, together with one of the hydroxyl groups, infinite hydrogen‐bonded chains. The conformation of the disaccharide is described by glycosidic torsion angles of −38 and 18°.     

C–F Bond Cleavage Reactions with Beryllium,Magnesium, Gallium,Hafnium, and Thorium Halides

The work describes unexpected stoichiometric C–F bond cleavage reactions of beryllium, magnesium, gallium, hafnium and thorium halides with α,α,α-trifluorotoluene. The reaction of BeBr₂ / GaBr₃ or MgBr₂ / GaBr₃ mixtures as well as neat GaI₃ with α,α,α-trifluorotoluene in the presence of (OSi₂Me₄)₂ ( I ) yields the carbenium ion containing compounds [Ph-C(O₂Si₂Me₄)][GaX₄] (X = Br: 1 , X = I/F: 2 ). Both compounds were successfully characterized and a defluorination type reaction under incorporation of a siloxy unit was observed. Compound 1 was also characterized by single-crystal X-ray diffraction analysis. The conversion of α,α,α-trifluorotoluene with BeI₂, HfI₄ or ThI₄ turned out to be a halodefluorination-type reaction with formation of α,α,α-triiodotoluene ( 3 ). An adequate NMR spectroscopic and the X-ray crystallographic characterization of 3 were performed for the first time.     

Aktive Kreiselsysteme

übersicht Aktive Elemente in Kreiselsystemen k?nnen sich in verschiedenartigen Effekten auswirken. Allgemeine Bewegungsgleichungen werden abgeleitet. Mit ihrer Hilfe lassen sich globale Aussagen zum Stabilit?tsverhalten von Kreiselsystemen mit Rotorantrieb gewinnen: 1) Konservative Systeme bleiben auch dann quasi-konservativ, wenn eine ideal wirkende Antriebsregelung vorhanden ist, die die relativen Geschwindigkeiten zwischen den Rotoren und ihren Geh?usen konstant h?lt. 2) Eigenstabile Asynchron-Antriebe machen ein grenzstabiles Kreiselsystem asymptotisch stabil bezüglich der Geschwindigkeiten. 3) Entsprechendes gilt für eigenged?mpfte Synchron-Antriebe; hier gilt die asymptotische Stabilit?t auch für die Rotorwinkel selbst. Am Beispiel einer motorangetriebenen Zentrifuge werden diese Ergebnisse durch Untersuchen der Eigenwerte pr?zisiert. Zugleich wird gezeigt, da? bezüglich der Lagewinkel Instabilit?t infolge kinetischer Auswanderung auftreten kann.

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Summary Due to active elements in gyroscopic systems various effects may occur. For their examination quite general equations of motion are derived, which allow some globale statements concerning the stability of gyro-systems with motor-driven rotors: 1) Conservative systems will behave quasi-conservative, if ideal working controllers are installed, which keep the relative rotational velocities of the rotors constant. 2) Asynchronous driving motors, which are stable for themselves, turn a marginal stable system into a system, asymptotically stable with respect to the velocities. 3) The same is valid for systems, in which the rotors are driven by damped synchronous motors; here asymptotic stability exists for the rotor-angles as well. As an example a motor-driven centrifuge is examined. The general results are proved and extended by calculating the eigenvalues. Furthermore it is shown that unstable behaviour with respect to the attitude angles is possible due to effects of kinetic drift.

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Hans Ziegler zum 70. Geburtstag gewidmet