Toluene as a novel carrier of xanthates—preparation,use and surrogate of S-tri- and di-chloromethyl xanthates

Toluene has been identified as a novel carrier of xanthates. Their corresponding fragmentative precursors proved to behave efficiently in radical group transfer reactions. As examples, unprecedented S-tri/di-chloromethyl xanthates could be prepared, isolated and further used in radical additions to olefins. Their precursors (de-aromatized toluene upon which is grafted, at one end, a tri/di-chloromethyl-group and, at the other end, a dithiocarbonyl group) can also be used directly in the transfer of both groups to olefins. The re-aromatizing loss of toluene by radical initiated fragmentation of the precursors brings thus new opportunities to the chemistry of xanthates, exemplified here in the intermolecular additions to olefins of new S-tri/di-chloromethyl xanthates.     

Synthesis and biological evaluation of 3-aryltyramines as fragments binding to BACE-1 and BACE-2

3-Aryltyramines were prepared in one single step from tyramine and various arenediazonium salts by radical arylation. Binding as well as enzyme inhibition data of the 14 compounds do not prove true interaction with BACE-1. In contrast, with BACE-2 inhibition and binding could be confirmed indicating that 3-aryltyramines are potential starting points for a drug discovery effort.     

Tris[2‐(1,3‐thiazol‐2‐yl‐κN)‐1H‐benzimidazole‐κN3]zinc(II) dinitrate ethanol hemisolvate monohydrate at 100 K

The Zn^II center in the dicationic complex of the title compound, [Zn(C₁₀H₇N₃S)₃](NO₃)₂·0.5C₂H₅OH·H₂O, is in a distorted octahedral environment with imperfect noncrystallographic C₃ symmetry. Each 2‐(1,3‐thiazol‐2‐yl)‐1H‐benzimidazole ligand coordinates in a bidentate manner, with the Zn—N(imidazole) bond lengths approximately 0.14 Å shorter than the Zn—N(thiazole) bond lengths. Charge‐assisted hydrogen bonds connect cations, anions and water molecules. A lattice void is occupied by an ethanol solvent molecule disordered about a crystallographic inversion center and π‐stacking is observed between one type of symmetry‐related benzene rings.     

Quantitative HPLC-MS analysis of nucleotide sugars in plant cells following off-line SPE sample preparation

An analytical workflow was developed for the absolute quantification of uridine diphosphate (UDP)-sugars in plant material in order to compare their metabolism both in wild-type Arabidopsis thaliana and mutated plants (ugd2,3) possessing genetic alterations within the UDP-glucose dehydrogenase genes involved in UDP-sugar metabolism. UDP-sugars were extracted from fresh plant material by chloroform-methanol-water extraction and further purified by solid-phase extraction with a porous graphitic carbon adsorbent with extraction efficiencies between 80?±?5 % and 90?±?5 %. Quantitative determination of the UDP-sugars was accomplished through HPLC separation with a porous graphitic carbon column (Hypercarb^TM) which was interfaced to electrospray ionization Orbitrap mass spectrometry. The problem of instable retention times due to redox processes on the stationary phase were circumvented by grounding of the column effluent and incorporation of a column regeneration procedure using acetonitrile-water containing 0.10 % trifluoroacetic acid. The method was calibrated using external calibration and UDP as internal standard. Calibration functions were approximated by first- or second-order regression analysis for concentrations spanning three orders of magnitude. Upon injecting sample volumes of 2.65 μL, the limits of detection for the UDP-sugars were in the 70 nmol L^?1 range. Six different UDP-sugars, including UDP-glucose, UDP-galactose, UDP-arabinose, UDP-xylose, UDP-glucuronic acid, and UDP-galacturonic acid were found in concentrations of 0.4 to 38 μg/g plant material. Data evaluation by analysis of variance (ANOVA) revealed statistically significant differences in UDP-sugar concentrations between wild-type and mutant plants, which were found to conclusively mirror the impaired metabolic pathways in the mutant plants.

Wavelength-agile H2O absorption spectrometer for thermometry of general combustion gases

Using a novel Fourier-domain mode-locking (FDML) laser scanning 1330-1380 nm, we have developed a gas thermometer based on absorption spectroscopy that is appropriate for combustion gases at essentially arbitrary conditions. The path-integrated measurements are particularly useful in homogeneous environments, and here we present measurements in a controlled piston engine and a shock tube. Engine measurements demonstrate a RMS temperature precision of ±3% at 1500 K and 200 kHz bandwidth; the precision is improved dramatically by averaging. Initial shock tube measurements place the absolute accuracy of the thermometer within ∼2% to 1000 K. The sensor performs best when significant H₂O vapor is present, but requires only at 300 K, at 1000 K, or at 3000 K for 2% accurate thermometry, assuming a 4 kHz measurement bandwidth (200 kHz scans with 50 averages). The sensor also provides H₂O mole fraction and shows potential for monitoring gas pressure based on the broadening of spectral features. To aid in designing other sensors based on high-temperature, high-pressure H₂O absorption spectroscopy, a database of measured spectra is included.     

Excellent passivation of thin silicon wafers by HF‐free hydrogen plasma etching using an industrial ICPECVD tool

In this work, hydrogen plasma etching of surface oxides was successfully accomplished on thin (～100 µm) planar n‐type Czochralski silicon wafers prior to intrinsic hydrogenated amorphous silicon [a‐Si:H(i)] deposition for heterojunction solar cells, using an industrial inductively coupled plasma‐enhanced chemical vapour deposition (ICPECVD) platform. The plasma etching process is intended as a dry alternative to the conventional wet‐chemical hydrofluoric acid (HF) dip for solar cell processing. After symmetrical deposition of an a‐Si:H(i) passivation layer, high effective carrier lifetimes of up to 3.7 ms are obtained, which are equivalent to effective surface recombination velocities of 1.3 cm s^–1 and an implied open‐circuit voltage (V_oc) of 741 mV. The passivation quality is excellent and comparable to other high quality a‐Si:H(i) passivation. High‐resolution transmission electron microscopy shows evidence of plasma‐silicon interactions and a sub‐nanometre interfacial layer. Using electron energy‐loss spectroscopy, this layer is further investigated and confirmed to be hydrogenated suboxide layers. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Composition of oxygen precipitates in Czochralski silicon wafers investigated by STEM with EDX/EELS and FTIR spectroscopy

In this work, we investigated the stoichiometry of oxygen precipitates in Czochralski silicon wafers. The thickness dependence of the Cliff–Lorimer sensitivity factor for the silicon/oxygen system was determined and applied for the investigation of the stoichiometry of oxygen precipitates by EDX. The results show that both plate‐like oxygen precipitates and a transitional form between plate‐like and octahedral precipi‐ tates consist of SiO₂. This was confirmed by EELS low loss spectra where the typical spectrum for amorphous SiO₂ was observed. Moreover, the absorption band of plate‐like precipitates at 1227 cm^–1 was found in the low temperature FTIR spectrum. It was demonstrated that this band can only be simulated by the dielectric constants of amorphous SiO₂. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)