Rhodium(II)‐Catalyzed Enantioselective Synthesis of Troponoids

We report a rhodium(II)‐catalyzed highly enantioselective 1,3‐dipolar cycloaddition reaction between the carbonyl moiety of tropone and carbonyl ylides to afford troponoids in good to high yields with excellent enantioselectivity. We demonstrate that α‐diazoketone‐derived carbonyl ylides, in contrast to carbonyl ylides derived from diazodiketoesters, undergo [6+3] cycloaddition reactions with tropone to yield the corresponding bridged heterocycles with excellent stereoselectivity.     

Formation of Integral Asymmetric Membranes of AB Diblock and ABC Triblock Copolymers by Phase Inversion

The formation of integral asymmetric membranes from ABC triblock terpolymers by non‐solvent‐induced phase separation is shown. They are compared with the AB diblock copolymer precursors. Triblock terpolymers of polystyrene‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐b‐P2VP‐b‐PEO) with two compositions are investigated. The third block supports the formation of a membrane in a case, where the corresponding diblock copolymer does not form a good membrane. In addition, the hydrophilicity is increased by the third block and due to the hydroxyl group the possibility of post‐functionalization is given. The morphologies are imaged by scanning electron microscopy. The influence of the PEO on the membrane properties is analyzed by water flux, retention, and dynamic contact angle measurements.

     

Raman spectroscopic detection of Nickel impact on single Streptomyces cells – possible bioindicators for heavy metal contamination

Heavy metal contamination of soil has an immense impact on the surrounding environment, such as the ground water, and hence, has become an important issue within bioremediation. Therefore, heavy metal contamination has to be determined preferably cost‐efficiently, rapidly, and reliably. Here, soil bacteria of the genus Streptomyces are used as bioindicators for heavy metal contamination investigated via micro‐Raman spectroscopy. A single cell approach is studied to avoid time‐consuming culturing and plate counting. Bacteria of Streptomyces galilaeus were incubated in Ni²⁺ enriched media and single cell spectra were recorded. Supervised statistics linear discriminant analysis was used to evaluate the influence of the culture age and the anion on bacterial cells, which has been determined to be minor compared with the spectral impact of Ni²⁺. The identification of the Raman spectra according to different Ni²⁺ concentration ranges is accomplished with a prediction accuracy of about 88%. Therefore, we conclude that Streptomyces can be used as a bioindicator to predict Ni²⁺ concentrations in the micromolar range. Copyright © 2011 John Wiley & Sons, Ltd.     

The Role of the Nucleotides in the Insertion of the bis-Molybdopterin Guanine Dinucleotide Cofactor into apo-Molybdoenzymes

The role of the GMP nucleotides of the bis-molybdopterin guanine dinucleotide (bis-MGD) cofactor of the DMSO reductase family has long been a subject of discussion. The recent characterization of the bis-molybdopterin (bis-Mo-MPT) cofactor present in the E. coli YdhV protein, which differs from bis-MGD solely by the absence of the nucleotides, now enables studying the role of the nucleotides of bis-MGD and bis-MPT cofactors in Moco insertion and the activity of molybdoenzymes in direct comparison. Using the well-known E. coli TMAO reductase TorA as a model enzyme for cofactor insertion, we were able to show that the GMP nucleotides of bis-MGD are crucial for the insertion of the bis-MGD cofactor into apo-TorA.     

Statischer Starkeffekt von Cadmium I und Cadmium II

Stark-effect patterns of neutral and singly ionized Cadmium emitted from an obstructed and constricted glow-discharge have been recorded. For hydrogen-like terms experiments agree with calculations obtained by perturbation theory.     

Magnon-polaritons and magnetic reststrahlen-bands of uniaxial antiferromagnetic crystals

The magnitudinal and directional dispersion of the two kinds of magnon-polaritons (magnitons) in uniaxial antiferromagnetic crystals is studied. In particular a proof is given for the existence of a purely longitudinal magnon propagating perpendicular to the optic axis. Furthermore, the corresponding magnetic reststrahlenbands for crystal cuts are discussed.     

PHOTOPHYSICAL PARAMETERS OF CHLOROPHYLLS a AND b·FLUORESCENCE AND LASER-INDUCED OPTOACOUSTIC MEASUREMENTS

Abstract— The quantum yields of internal conversion (energy loss) of the photoexcited chlorophylls a and b in ethanol at 24°C have been determined by measuring the quantum yields of the competing radiative (fluorescence) and non-radiative (intersystem crossing) deactivation processes (which lead to energy storing species) by means of emission and laser-induced optoacoustic spectroscopy, respectively. The values for internal conversion of chlorophyll a are 10% and 14% in the presence and absence of molecular oxygen, respectively. The corresponding yields for chlorophyll b are negligibly small. The internal conversion in chlorophyll a is attributed to vibronic coupling with the substituents of the porphin system, since internal conversion was found to be substantially reduced for unsubstituted Mg-porphin in ethanol and for chlorophyll a when dissolved in a viscous medium.     

Color Centers in Alkali Borate Glasses Containing Cobalt,Nickel, or Copper

The absorption spectra and the magnetic moments of Co²⁺, Ni²⁺, and Cu²⁺ in alkali borate glasses of various compositions and in halide-containing glasses have been explained from the point of view of the ligand field theory. Spectra and magnetic moments are highly dependent on the composition of the base glass; this must be ascribed to the change in the coordination of the transition-metal ions. There are far-reaching analogies with corresponding complexes in solution or in the crystalline state.     

Water CI+, a new selective and highly sensitive method for the detection of environmental components using ion trap mass spectrometers

A new method for mass spectrometric trace analysis using an ion trap detector is presented based on chemical ionization with water as a reactant. The technique has advantages over the methods commonly used with regard to selectivity and detection limit and it facilitates the detection of unstable organic compounds. Specific applications in the trace analysis of polyaromatic hydrocarbons, trinitroaromatics as well as glycols and their derivatives are described.