Enantioselective 1,4-Addition of Aliphatic Grignard Reagents to Enones Catalyzed by Readily Available Copper(I) thiolates derived from TADDOL. Preliminary communication

Two simple thiols derived from the parent TADDOL, α,α,α′,α′ tetraphenyl-2,2-dimethyl-1,3-clioxolan-4,5-dimethanol, are used to prepare Cu¹ complexes C and D to catalyze (0.05 equiv.) 1,4-additions of Grignard reagents RMgCl to cyclic enones with enantioselectivities which are comparable to or better than previously reported (enantiomer ratios up to 92:8).     

A continuous flow instrument with flow regulation and automatic sensitivity range adaptation for the determination of atmospheric H2S

A set-up for continuous measurements of atmospheric H₂S concentrations in the range between 0.138 g/m³ and 17.5 g/m³ is described. All flows are regulated by flow sensors which are connected to the respective pump by a feed back circuit. The instrument is working in two sensitivity ranges. One is provided for low H₂S concentrations (lower than 1.75 g/m³) and the other for higher levels (higher than 1.75 g/m³). During continuous measurements the set-up enables an automatic adaptation of one of the sensitivity ranges to ambient H₂S concentrations. The critical step of absorption of gaseous H₂S into the liquid phase of the continuous flow system could be stabilised by the development of a new fluid level control system. After numerous test measurements under laboratory conditions the instrument was tested for the first time in June 1993 during field measurements in the tropics. These measurements took place in the environment of natural and industrial sources of H₂S in the vicinity of Salvador da Bahia in Brazil. Data are presented which prove the ability of the instrument.Dedicated to Professor D. Dieter Klockow on the occasion of his 60th birthday     

Modular Breath Analyzer (MBA): Introduction of a Breath Analyzer Platform Based on an Innovative and Unique,Modular eNose Concept for Breath Diagnostics and Utilization of Calibration Transfer Methods in Breath Analysis Studies

Exhaled breath analysis for early disease detection may provide a convenient method for painless and non-invasive diagnosis. In this work, a novel, compact and easy-to-use breath analyzer platform with a modular sensing chamber and direct breath sampling unit is presented. The developed analyzer system comprises a compact, low volume, temperature-controlled sensing chamber in three modules that can host any type of resistive gas sensor arrays. Furthermore, in this study three modular breath analyzers are explicitly tested for reproducibility in a real-life breath analysis experiment with several calibration transfer (CT) techniques using transfer samples from the experiment. The experiment consists of classifying breath samples from 15 subjects before and after eating a specific meal using three instruments. We investigate the possibility to transfer calibration models across instruments using transfer samples from the experiment under study, since representative samples of human breath at some conditions are difficult to simulate in a laboratory. For example, exhaled breath from subjects suffering from a disease for which the biomarkers are mostly unknown. Results show that many transfer samples of all the classes under study (in our case meal/no meal) are needed, although some CT methods present reasonably good results with only one class.     

Between Two Chairs: Combination of Theory and Experiment for the Determination of the Conformational Dynamics of Xylosides

The conformational properties of monosaccharides constitute fundamental features of oligosaccharides. While the energy landscape of monosaccharides can be altered by a specific biochemical environment or by chemical modifications, the analysis of resulting dynamic conformational equilibria is not feasible by experimental means alone. In this work, a series of β-d -xylopyranosides is used to outline how a combination of experimental NMR parameters and computed molecular properties can be used to determine conformers and quantify the composition of conformational equilibria. We demonstrate that identifying the most stable conformers using energy calculations is challenging and computing of NMR shieldings is typically not sensitive enough. On the other hand, computed spin-spin coupling constants for the xyloside ring can be used to unambiguously assign experimental NMR data of dynamic conformational equilibria and quantify the ratio of different conformers in the mixture. As a proof of principle, this procedure allowed to analyze a hitherto unknown dynamic equilibrium of a diamino-xyloside as a precursor of a molecular switch.     

Laser-based modification of wettablility for carbon fiber reinforced plastics

This paper presents a laser-based technique for surface preparation of carbon fiber reinforced plastics (CFRP) for bonded repair. Ablative and non-ablative treatment of the surface is produced by variation of laser power and the resulting surface energy determined by goniometric measurements. Wettability has been directly related to a calculated wetting envelope. The investigations show an additional major influence of the surface topography on the shear strength of the joint. The direction of the applied laser lines in relation to the fiber direction was identified as an essential influence for this roughness. A ns IR-laser demonstrates high potential for surface preparation as well as for selective ply removal. The laser prepared surfaces are examined through optical microscopy, scanning electron microscope (SEM), and contact angle measurements. The wettability studies show a significant increment in surface energy after laser treatment, in relation to non-treated as well as surface grinding samples.     

Improved analysis of ladderane lipids in biomass and sediments using high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

Ladderane lipids, containing three or five linearly concatenated cyclobutane moieties, are considered to be unique biomarkers for the process of anaerobic ammonium oxidation, an important link in the oceanic nitrogen cycle. Due to the thermal lability of the strained cyclobutane moieties, the ladderane lipids are difficult to analyze by gas chromatography. A method combining high-performance liquid chromatography coupled to positive ion atmospheric pressure chemical ionization tandem mass spectrometry (HPLC/APCI-MS/MS) was developed for the analysis of the most abundant ladderane lipids, occurring as fatty acids and ether-bound to glycerol. Detection was achieved by selective reaction monitoring of four specific fragmentations per ladderane lipid. Detection limits of 30-35 pg injected on-column and a linear response (r(2) > 0.99) over nearly 3 orders of magnitude were achieved for all compounds. Using this method, these unique ladderane lipids were for the first time identified in a surface sediment from the Gullmarsfjorden, in concentrations ranging from 1.1-5.5 ng/g for the ladderane fatty acids and of 0.7 ng/g for the monoether. It is foreseen that this method will allow the investigation of the occurrence of anaerobic ammonium oxidation in natural settings in much greater detail than before.     

Computer evaluation of gas chromatograms with wide dynamic range

Summary If the complete dynamic range of the flame ionisation detector (FID) amplifier signal is to be integrated during trace analysis, the computer used for this purpose must have an effective dynamic range of at least six decades. The detection limit for traces in the ppm range (parts per million), whilst the major component is simultaneosly integrated, is discussed using samples of pure styrene, propylene and vinyl chloride. The dynamic range can be increased by using minor components as internal markers, by a computer-controlled attenuator switch and by a splitter which produces an internal marker in the chromatogram. In this way, trace components around the ppm level can be determined with standard deviations of a few percent.