Synthese und Kristallstruktur des Nitridokomplexes [Na-15-Krone-5]2[MoNF4]2 · 2 CH3CN

Synthesis and Crystal Structure of the Nitrido Complex [Na-15-crown-5]₂[MoNF₄]₂ · 2 CH₃CN The title compound is synthesized by the reaction of [MoCl₄(NSCl)]₂ with excess NaF in boiling acetonitrile in the presence of the crown ether 15-crown-5. [Na-15-crown-5]₂[MoNF₄]₂ · 2 CH₃CN forms yellow crystals, which were characterized by an X-ray structure determination. Space group P1 , Z = 1. Lattice dimensions at ?90°C: a = 855.5, b = 1 069.9, C = 1 143.5 pm, α = 105.71°, β = 95.29°, γ = 102.25° (4 096 independent observed reflexions, R = 0.039). Short Na…?F contacts of 234 pm with the four axial fluoro ligands of the dimeric anion [MoNF₄]₂^2? allow formulation of a triple ion. The centrosymmetric anion is dimerized by bent fluoro bridges with Mo? F distances of 198 and 245 pm. The long Mo? F distances of the MoF₂Mo ring are in transposition to the nitrido ligands, the bond lengths of which (165 pm) correspond to triple bonds.     

Heavy alkaline earth metal pyrazolates: synthetic pathways, structural trends, and comparison with divalent lanthanoids

Two series of heavy alkaline earth metal pyrazolates, [M(Ph(2)pz)(2)(thf)(4)] 1 a-c (Ph(2)pz=3,5-diphenylpyrazolate, M=Ca, Sr, Ba; THF=tetrahydrofuran) and [M(Ph(2)pz)(2)(dme)(n)] (M=Ca, 2 a, Sr, 2 b, n=2; M=Ba, 2 c, n=3; DME=1,2-dimethoxyethane) have been prepared by redox transmetallation/ligand exchange utilizing Hg(C(6)F(5))(2). Compounds 1 a and 2 b were also obtained by redox transmetallation with Tl(Ph(2)pz). Alternatively, direct reaction of the alkaline earth metals with 3,5-diphenylpyrazole at elevated temperatures under solventless conditions yielded compounds 1 a-c and 2 a-c upon extraction with THF or DME. By contrast, [M(Me(2)pz)(2)(Me(2)pzH)(4)] 3 a-c (M=Ca, Sr, Ba; Me(2)pzH=3,5-dimethylpyrazole) were prepared by protolysis of [M[N(SiMe(3))(2)](2)(thf)(2)] (M=Ca, Sr, Ba) with Me(2)pzH in THF and by direct metallation with Me(2)pzH in liquid NH(3)/THF. Compounds 1 a-c and 2 a-c display eta(2)-bonded pyrazolate ligands, while 3 a,b exhibit eta(1)-coordination. Complexes 1 a-c have transoid Ph(2)pz ligands and an overall coordination number of eight with a switch from mutually coplanar Ph(2)pz ligands in 1 a,b to perpendicular in 1 c. In eight coordinate 2 a,b the pyrazolate ligands are cisoid, whilst 2 c has an additional DME ligand and a metal coordination number of ten. By contrast, 3 a,b have octahedral geometry with four eta(1)-Me(2)pzH donors, which are hydrogen-bonded to the uncoordinated nitrogen atoms of the two trans Me(2)pz ligands. The application of synthetic routes initially developed for the preparation of lanthanoid pyrazolates provides detailed insight into the similarities and differences between the two groups of metals and structures of their complexes.     

Observation of electrostatically released DNA from gold electrodes with controlled threshold voltages

DNA oligo-nucleotides, localized at Au metal electrodes in aqueous solution, are found to be released when applying a negative bias voltage to the electrode. The release was confirmed by monitoring the intensity of the fluorescence of cyanine dyes (Cy3) linked to the 5' end of the DNA. The threshold voltage of the release changes depending on the kind of linker added to the DNA 3'-terminal. The amount of released DNA depends on the duration of the voltage pulse. Using this technique, we can retain DNA at Au electrodes or Au needles, and release the desired amount of DNA at a precise location in a target. The results suggest that DNA injection into living cells is possible with this method.     

Development of quantitative vitellogenin-ELISAs for fish test species used in endocrine disruptor screening

The yolk protein precursor vitellogenin (Vtg) in plasma has proved to be a simple and sensitive biomarker for assessing exposure of fish to environmental estrogens. Within international bodies such as the Organization for Economic Cooperation and Development (OECD) work is ongoing to develop screening and testing programmes for endocrine disrupting effects of new chemicals, and in the focus of this development are the fish test species common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). In this study we have developed quantitative enzyme linked immunosorbent assays (ELISAs) for Vtg in common carp/fathead minnow, zebrafish and Japanese medaka. The assays were developed using a combination of monoclonal and polyclonal fish Vtg antibodies in a sandwich format, using stabilized Vtg from the test species as a standard. The carp Vtg ELISA has a working range of 1–63 ng/mL, a minimal detection limit of 0.6 ng/mL, and may also be used for quantification of Vtg in fathead minnow. In fathead minnow whole-body homogenate samples, the practical detection limit is 400 ng/mL due to the matrix effect. The zebrafish Vtg ELISA has a working range of 0.5–63 ng/mL, a minimal detection limit of 0.4 ng/mL, and a practical detection limit of 200 ng/mL in whole-body homogenate samples. The medaka Vtg ELISA has a working range of 0.25–16 ng/mL, a minimal detection limit of 0.1 ng/mL, and a practical detection limit of 125 ng/mL in whole-body homogenate samples. The intra- and inter-assay variations were below 20% for all assays. The assays were evaluated with sets of representative samples spanning the wide dynamic range of Vtg-levels found in fish exposed to environmental estrogens, and all three assays are currently undergoing international inter-laboratory validation.     

Recognition of G-1:C73 atomic groups by Escherichia coli histidyl-tRNA synthetase

This work focuses on the RNA-protein interactions necessary for efficient aminoacylation of tRNAHis by Escherichia coli histidyl-tRNA synthetase (HisRS). The E. coli tRNAHis acceptor stem is characterized by a unique "extra" G-1:C73 base pair. Previous in vivo and in vitro studies showed that G-1:C73 is a major recognition element for E. coli HisRS. To further probe the role of the G-1:C73 base pair in specific aminoacylation, we carried out atomic group "mutagenesis" studies. Systematic base analogue substitutions at the -1:73 position of chemically synthesized microhelixHis substrates suggest that the G-1 base serves to position the 5'-monophosphate, which is critical for aminoacylation. Additionally, the C73 and G-1 bases contain major groove exocyclic atomic groups that contribute to HisRS recognition.     

An improved method for the synthesis of cellulose membrane-bound peptides with free C termini is useful for PDZ domain binding studies

SPOT synthesis permits parallel synthesis and screening of thousands of cellulose membrane-bound peptides to study protein-protein interactions in a proteomic context. Recognition of C-terminal residues is one of the most common binding features of PDZ domains. Unfortunately, most solid support-bound peptide libraries lack a free C terminus due to C-terminal fixation on the solid support. To overcome this restriction, we developed a robust methodology based on our previous strategy for generating peptides with authentic C termini. To validate this improved method, we screened a human peptide library of 6223 C termini with the syntrophin PDZ domain. Furthermore, using the same library, new peptide ligands derived from membrane proteins and receptors were found for the ERBIN PDZ domain. Finally, we identified the protein kinase breakpoint cluster region, which is known as a negative regulator of cell proliferation and oncogenic transformation, as an ERBIN ligand.     

Simultaneous determination of fluoroquinolones,sulfonamides and tetracyclines in sewage sludge by pressurized liquid extraction and liquid chromatography electrospray ionization-mass spectrometry

A new scheme for the quantitative determination of traces of fluoroquinolones (FQs), tetracyclines (TCs) and sulfonamides (SAs) in sewage sludge was developed. The compounds were simultaneously extracted from sewage sludge by pressurized liquid extraction (PLE). A novel and effective method for PLE was developed. Solid-phase extraction was used for cleaning up the extracts. Identification and quantification of the compounds was done using high-performance liquid chromatography with electrospray ionization mass spectrometry in selected reaction monitoring mode. The best recovery of FQs and TCs was obtained by using hydrophilic–lipophilic balance cartridges, recoveries ranged 59% for norfloxacin to 82% for ofloxacin and 95% for doxycycline; for SAs strong cation-exchange cartridges were more efficient, recoveries were 96% for sulfamethoxazole and 43% for sulfadimethoxine. Limit of quantification ranged from 0.1 ng/g for SAs to 160 ng/g for tetracycline. Method precision for TCs was 5.06% and 1.12%, and for SAs 0.43% and 2.01%. FQs precision ranged from 0.77% to 1.89%.     

Comprehensive inter‐laboratory calibration of reference materials for δ18O versus VSMOW using various on‐line high‐temperature conversion techniques

Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high‐temperature conversion techniques (HTC) a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125‰, an artificially enriched reference water (δ¹⁸O of +78.91‰) and two barium sulfates (one depleted and one enriched in ¹⁸O) were prepared and calibrated relative to VSMOW2 b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded:

A straightforward method for analysing the grain-size distribution in tungsten carbide - cobalt hardmetals

Measurement of the grain-size distribution of sintered hardmetals is indispensable in research and production. In this study we present a method consisting of etching hardmetals in order to remove the cobalt binder and to analyse the remaining tungsten-cobalt (WC) crystallites on the basis of scanning electron microscopy images subjected to a PC-based image analysis by use of MATLAB®. Sample preparation is easy and quick to perform, i.e. it does not require metallographic polishing. It consists of either deep etching of the cobalt binder of cut and optionally hand-ground surfaces or etching of fracture surfaces. Two different computational routines and one combination thereof are described. Two hardmetal grades with average WC grain sizes slightly larger as well as smaller than 200 nm were investigated. The results of the computer algorithms are compared to data obtained by manual linear intercept analysis. The analysis has good potential to avoid time-consuming metallographic preparation and pre-treatment for grain-size analysis, which is especially true for hardmetals with extremely fine grain size.