Zustandsdiagramme von Alkalibromid-Lanthanoid(III)-bromid-Mischungen

Phase Diagrams of Alkali Bromide - Lanthanoid(III) Bromide Mixtures The phase diagrams of the systems KBr? PrBr₃ (NdBr₃, SmBr₃, GdBr₃, DyBr₃, ErBr₃, YbBr₃), RbBr? NdBr₃ (SmBr₃, GdBr₃, DyBr₃, ErBr₃, YbBr₃) and CsBr? PrBr₃ (NdBr₃, SmBr₃, GdBr₃, ErBr₃, YbBr₃) were determined by differential thermal analysis and differential scanning calorimetry. The compound M₃LnBr₆, whose stability increases with increasing size of the alkali cation resp. decreasing of the Ln³⁺ ion, was found in all investigated systems. Additionaly congruently melting compounds of the type MLn₂Br₇ were found in the system from PrBr₃ to DyBr₃ which are, however, peritectic in systems with smaller alkali cations. Another peritectic compound has the composition M₂LnBr₅, in case that the quotient ^rMe^+rX^?/^rLn³⁺ exceeds 3 this composition shifts to M₃Ln₂Br₉. The compounds M₃LnBr₆ have a transition with a transition temperature, which is concentration dependent. This May indicate that at the composition ?M₃LnBr₆”? in fact two compounds exist with slightly different composition, of which one is stable at higher the other at lower temperatures.     

Incorporation of carbon originating from CO2 into different compounds of soil microbial biomass and soil organic matter

In general, soils without the vegetation growing on them are regarded as sources of CO2. However, there are indications that CO2 is also fixed by soil microorganisms. Although this process is not significant from a quantitative point of view, it may change the isotopic composition of soil organic matter. Therefore, we conducted an incubation study with soil and 13C-labeled CO2 to investigate this process. We found that the label was transferred from CO2 into organic compounds in soil. At the end of a 61-day incubation period, 1.3 micromol C g(-1) soil, corresponding to approximately 0.08% of the soil organic carbon, had been fixed. CO2 may, therefore, be an additional source of soil organic carbon. Compound-specific analysis of amino sugars, amino acids, and fatty acids indicated that the label is incorporated into microbial, mainly bacterial, biomass. All groups of microorganisms were involved in the assimilation of CO2, but the relatively high enrichment of mono-unsaturated and mid-chain branched fatty acids indicates that gram negative bacteria and actinomycetes may be slightly more important in this process than other groups of microorganisms.     

Highly regioselective Diels-Alder reactions toward oroidin alkaloids: use of a tosylvinyl moiety as a nitrogen masking group with adjustable electronics

[reaction: see text] The use of the p-toluenesulfonyl (Ts) and tosylvinyl (Tsv) groups as nitrogen masking groups imparted high regioselectivity in Diels-Alder reactions directed toward members of the oroidin-derived marine alkaloid family. The electron-withdrawing Tsv group was utilized as an electronically adjustable nitrogen-protecting group as subsequent hydrogenation provided the more electron-rich tosylethyl (Tse) group. This electronic adjustment strategy avoided a protecting group exchange and provided the required electronics for the key chlorination/ring-contraction sequence.     

Control of vertically coupled InGaAs/GaAs quantum dots with electric fields

Controllable interactions that couple quantum dots are a key requirement in the search for scalable solid state implementations for quantum information technology. From optical studies of excitons and corresponding calculations, we demonstrate that an electric field on vertically coupled pairs of In(0.6)Ga(0.4)As/GaAs quantum dots controls the mixing of the exciton states on the two dots and also provides controllable coupling between carriers in the dots.     

Control of interlayer exchange coupling in Fe/Cr/Fe trilayers by ion beam irradiation

The manipulation of the antiferromagnetic interlayer coupling in epitaxial Fe/Cr/Fe(001) trilayers by 5 keV He ion beam irradiation has been investigated. It is shown that even for irradiation with low fluences a drastic change in strength of the coupling appears. For thin Cr spacers (below 0.6-0.7 nm) it decreases with fluence, becoming ferromagnetic for fluences above 2x10(14) ions/cm(2). The effect is connected with the creation of magnetic bridges in the layered system due to atomic exchange events caused by the bombardment. For thicker Cr spacers an enhancement of the antiferromagnetic coupling strength is found. A possible explanation of the enhancement effect is given.     

Nonproteolytic cleavage of aspartyl proline bonds in the cellulosomal scaffoldin subunit from Clostridium thermocellum

Previous work from our group [Morag (Morgenstern), E., Bayer, E. A., and Lamed, R. (1991), Appl. Biochem. Biotechnol. 30, 129–136] has demonstrated an anomalous electrophoretic mobility pattern for scaffoldin, the 210-kDa cellulosome-integrating subunit of Clostridium thermocellum. Subsequent evidence [Morag, E., Bayer, E. A., and Lamed, R. (1992), Appl. Biochem. Biotechnol. 33, 205–217] indicated that the effect could be attributed to a nonproteolytic fragmentation of the subunit into a defined series of lowermolecular-weight bands. In the present work, a recombinant segment of the scaffoldin subunit was employed to determine the site(s) of bond breakage. An Asp-Pro sequence within the cohesin domain was identified to be the sensitive peptide bond. This sequence appears quite frequently in the large cellulosomal proteins, and the labile bond may be related to an as yet undescribed physiological role in the hydrolysis of cellulose by cellulosomes.     

Solvation and Solvent Relaxation in Swellable Copolymers as Studied by Time-Resolved Fluorescence Spectroscopy

The fluorescent probe dimethylaminonaphthylsulfonamide is covalently bound to the ends of the pol(ethylene glycol) chains of the swellable block copolymers poly(ethylene glycol)–polystyrene (PEG-PS) and poly(ethylene glycol)–poly(ethylene imine) (PEG-PEI) to investigate the molecular mobility inside the polymers, swollen by different liquids. Steady-state and time-resolved studies of the Stokes shift between absorption and fluorescence spectra reveal that the probe is solvated by both the polymer matrix and the liquid phase. The extent of solvation by the liquid and the mobility of the microenvironment of the probe depend on both the swelling volume of the polymer and the solubility of the probe in this liquid. Steady-state and time-resolved fluorescence depolarisation measurements show that the polymer matrix forms a very rigid solvent cage, which almost completely immobilizes the probe. Upon solvation of the probe by the liquid, the mobility of the probe increases. In PEG-PEI swollen by polar solvents, the mobilities of the probe itself and of its microenvironment, although not reaching the values observed in homogeneous solution, are significantly higher than in PEG-PS, due to the hydrophilic nature of the polymeric backbone in PEG-PEI.