Effects of the presence of pyrite and carbonate minerals on the kinetics of the uranium release from a natural rock

Summary The influence of calcite, dolomite, pyrite and vaterite on the kinetics of uranium release from a natural rock under relevant, i.e., field conditions has been investigated. The time dependence of the U release has been studied in two different experimental procedures (open and closed systems) at laboratory temperature (21±2 °C). Performing batch experiments in tap water, the U release efficiency of a natural U-bearing rock was characterized in the presence of varying amounts of three different carbonate bearing minerals for experimental durations of up to 782 days. Another experiment was conducted for a period of 14 days in the presence of a pyrite mineral. The results demonstrate that the presence of carbonate minerals does not have any significant influence on U release in closed systems where the U concentration at saturation was ca. 54 mg/l. In contrast, in open systems, the U concentration was ca. 8 mg/l at saturation and the effects of all additives both on kinetics and saturation concentration of U were apparent.     

A METHOD FOR MEASURING PHYTOCHROME IN PLANTS GROWN IN WHITE LIGHT

Abstract— Quantitative spectrophotometric measurement of phytochrome in plants grown for relatively long periods of time in white light is not possible due to the presence of chlorophyll. A method is described that prevents the accumulation of chlorophyll permitting such direct spectrophotometric measurement in light-grown tissue. Oat seedlings grown in the presence of the herbicide San 9789† (Norflurazon) for 6 days in constant light have considerably less chlorophyll than etiolated seedlings exposed to 1 min of light. Phytochrome concentrations measured in vivo and in vitro in these herbicide-treated plants were found to be about 2% of the level in etiolated tissue.     

Reactions of Electron-Rich Olefins with Proton-Active Compounds

Proton-active substances react with certain electron-rich olefins with cleavage of the central C?C double bond to give compounds that can be formally regarded as insertion products of nucleophilic carbenes. If they satisfy certain structural conditions, they isomerize with β elimination to give open-chain compounds. Both CH-acidic compounds and compounds containing NH or OH groups can undergo this reaction. The mechanisms are discussed, and the importance of the intermediate products to biochemistry (thiamine, tetrahydrofolic acid) is indicated.     

Neue anorganische Ringsysteme. 34. Derivate eines Cyclo-1-thiaIV- und eines Cyclo-1-thiaIV- 3,4-disila-2,5-diazans

Novel Inorganic Ring Systems. 34. Derivatives of the Cyclo-1-thia^IV- and of the Cyclo-1-thia ^VI-3,4-disila-2,5-diazane Variations of fivemembered “hetero” cyclosilazanes of the type Si₂N₂El could be enlarged to the systems with El = SO and SO₂. They are obtained by the formation principles 4 + 1 and 2 + 3 respectively, according to the equation (1), (4) and (5). The prepared compound are described in their properties and confirmed in their structure (Tables 1–2).     

Synthesis of the ABC fragment of the pectenotoxins

[reaction: see text] A highly stereocontrolled synthesis of the C1-C16 ABC spiroacetal-containing fragment 5 of PTX7 (4) has been achieved. Appendage of the C ring to the AB fragment involved Wittig reaction of spiroacetal aldehyde 8 with a stabilized ylide 9 followed by displacement of allylic iodide 27 with a lithium acetylide to afford enyne 7. Fructose-derived chiral dioxirane and dihydroxylation were then used to introduce the correct functionality in the tetrahydrofuran C ring.     

Enantioconvergent Biocatalytic Redox Isomerization

Alcohol dehydrogenases can act as powerful catalysts in the preparation of optically pure γ‐hydroxy‐δ‐lactones by means of an enantioconvergent dynamic redox isomerization of readily available Achmatowicz‐type pyranones. Imitating the traditionally metal‐mediated “borrowing hydrogen” approach to shuffle hydrides across molecular architectures and interconvert functional groups, this chemoinspired and purely biocatalytic interpretation effectively expands the enzymatic toolbox and provides new opportunities in the assembly of multienzyme cascades and tailor‐made cellular factories.     

On vibrations in non-linear,forced, friction-excited systems

To accelerate the development of non-linear, friction-excited systems, i.e. automotive friction brakes, novel test procedures are being developed. These include the study of the system's forced vibrations. However, there is a lack of knowledge concerning feasible test procedures, the assessment of the gathered data, and the possible vibration phenomena. In this context, the contribution at hand discusses vibrations in non-linear, forced, friction-excited systems. In the pre-flutter regime proposed criteria for identification of parameter regions in which limit cycle oscillations can occur are challenged. In the post-flutter regime frequency spectra for different excitation conditions are studied. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of Heterocyclic Ring Systems for Heat-Resistant Plastics from Polyisocyanates

Investigations on space flight and rockets carried out in particular in the United States have aroused great interest in plastics with enhanced thermal stability. It has become possible to pass far beyond the expected limits of thermal stability with organic plastics, and to synthesize plastics and polymers that can be used at temperatures between about 200 and about 500 °C, a range that formerly appeared to be the exclusive province of inorganic materials.