Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Biotin-bestimmung in lebergewebe nach dem prinzip der isotopen-verdünnungsanalyse: RadioLigand assay for biotin in Liver tissues

Radioligand assay for biotin in liver tissuesA radioligand assay for biotin in liver tissue is described, ³H-biotin is used as tracer and avidin as binder. The biotin-loaded avidin is separated from free biotin on dextrancoated charcoal, which leaves the avidin—biotin complex in the supernatant liquid. Thus, the avidin—biotin complex can easily be utilized for determination of the radioactivity. Calibration with known additions of biotin in the range 0.25–8.0 ng per assay sample yields a linear logit-log plot. The biotin is extracted from liver tissues by enzymatic proteolysis with papain. This treatment is optimized to liberate the bound forms of the vitamin. Microbiological parallel assays with [Lactobacillus plantarum] were in good agreement with the radioligand assay giving a regression coefficient of 0.974 (n = 44). The coefficient of variation was found to be 4.2% in the range 500–1200 ng of biotin per g of liver tissue (n = 46). The method is simple and reliable and allows the simultaneous analysis of a considerable number of samples.     

Hydride as a leaving group in the reaction of pinacolborane with halides under ambient Grignard and Barbier conditions. One-pot synthesis of alkyl, aryl, heteroaryl, vinyl, and allyl pinacolboronic esters

Grignard reagents (aliphatic, aromatic, heteroaromatic, vinyl, or allylic) react with 1 equiv of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (pinacolborane, PinBH) at ambient temperature in tetrahydrofuran (THF) to afford the corresponding pinacolboronates. The initially formed dialkoxy alkylborohydride intermediate quickly eliminates hydridomagnesium bromide (HMgBr) and affords the product boronic ester in very good yield. Hydridomagnesium bromide (HMgBr) in turn disproportionates to a 1:1 mixture of magnesium hydride (MgH(2)) and magnesium bromide (MgBr(2)) on addition of pentane to the reaction mixture. DFT calculations (Gaussian09) at the B3LYP/6-31G(d) level of theory show that disproportionation of HMgBr to MgH(2) and MgBr(2) is viable in the coordinating ethereal solvents. This reaction also can be carried out under Barbier conditions, where the neat PinBH is added to the flask prior to the in situ formation of Grignard reagent from the corresponding organic halide and magnesium metal. Pinacolboronic ester synthesis under Barbier conditions does not give Wurtz coupling side products from reactive halides, such as benzylic and allylic halides. The reaction between PinBH and various Grignard reagents is an efficient, mild, and general method for the synthesis of pinacolboronates.     

Two-Dimensional Isotachophoresis for the Analysis of Homovanillic Acid and Vanillylmandelic Acid in Urine for Cancer Therapy Monitoring

Homovanillic acid (HVA) and vanillylmandelic acid (VMA) are routinely analyzed by HPLC with electrochemical detection after solid phase extraction for the diagnosis of neuroblastoma and phaechromocytoma. The aim of our study was to investigate whether these compounds can be determined without sample preparation using capillary isotachophoresis (ITP). For this purpose we used a commercially available instrument with two coupled capillary columns. HVA and VMA could be easily separated by ITP–ITP analysis at pH 3.4; the LODs were in the lower μmol · L⁻¹ range using conductivity detection. ITP calibration curves in spiked urine samples showed good linear correlation. However, although good correlation with HPLC analysis was also found, the ITP–ITP values were elevated compared to the HPLC values due to underlying matrix compounds in the respective zones.     

Substrate-Enabled Room-Temperature Electrochemical Deposition of Crystalline ZnMnO3

Mixed transition metal oxides have emerged as promising electrode materials for electrochemical energy storage and conversion. To optimize the functional electrode properties, synthesis approaches allowing for a systematic tailoring of the materials’ composition, crystal structure and morphology are urgently needed. Here we report on the room-temperature electrodeposition of a ternary oxide based on earth-abundant metals, specifically, the defective cubic spinel ZnMnO₃. In this unprecedented approach, ZnO surfaces act as (i) electron source for the interfacial reduction of MnO₄⁻ in aqueous solution, (ii) as substrate for epitaxial growth of the deposit and (iii) as Zn precursor for the formation of ZnMnO₃. Epitaxial growth of ZnMnO₃ on the lateral facets of ZnO nanowires assures effective electronic communication between the electroactive material and the conducting scaffold and gives rise to a pronounced 2-dimensional morphology of the electrodeposit forming – after partial delamination from the substrate – twisted nanosheets. The synthesis strategy shows promise for the direct growth of different mixed transition metal oxides as electroactive phase onto conductive substrates and thus for the fabrication of binder-free nanocomposite electrodes.     

Active frequency stabilization of an ultra-high Q whispering-gallery-mode microresonator

We report on active frequency stabilization of a whispering-gallery-mode microresonator with an ultra-high quality factor exceeding 2×10⁸ to an atomic transition using the Pound–Drever–Hall technique. The critically coupled resonator is stabilized to 5.4% of its linewidth, or 206 kHz. Thermal bistability and mode-splitting are also observed and have a significant effect on the error signal.     

Conformal Coverage of ZnO Nanowire Arrays by ZnMnO3: Room-temperature Photodeposition from Aqueous Solution

Compositionally and structurally complex semiconductor oxide nanostructures gain importance in many energy-related applications. Simple and robust synthesis routes ideally complying with the principles of modern green chemistry are therefore urgently needed. Here we report on the one-step, room-temperature synthesis of a crystalline–amorphous biphasic ternary metal oxide at the ZnO surface using aqueous precursor solutions. More specifically, conformal and porous ZnMnO₃ shells are photodeposited from KMnO₄ solution onto immobilized ZnO nanowires acting not only as the substrate but also as the Zn precursor. This water-based, low temperature process yields ZnMnO₃/ZnO composite electrodes featuring in 1 M Na₂SO₄ aqueous solution capacitance values of 80–160 F g⁻¹ (as referred to the total mass of the porous film i. e. the electroactive ZnMnO₃ phase and the ZnO nanowire array). Our results highlight the suitability of photodeposition as a simple and green route towards complex functional materials.