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91.
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93.
Rachid S Krug D Kunze B Kochems I Scharfe M Zabriskie TM Blöcker H Müller R 《Chemistry & biology》2006,13(6):667-681
The jaspamide/chondramide family of depsipeptides are mixed PKS/NRPS natural products isolated from marine sponges and a terrestrial myxobacterium that potently affect the function of the actin cytoskeleton. As a first step to improve production in heterologous host cells and permit genetic approaches to novel analogs, we have cloned and characterized the chondramide biosynthetic genes from the myxobacterium Chondromyces crocatus Cm c5. In addition to the expected PKS and NRPS genes, the cluster encodes a rare tyrosine aminomutase for beta-tyrosine formation and a previously unknown tryptophan-2-halogenase. Conditions for gene transfer into C. crocatus Cm c5 were developed, and inactivation of several genes corroborated their proposed function and served to define the boundaries of the cluster. Biochemical characterization of the final NRPS adenylation domain confirmed the direct activation of beta-tyrosine, and fluorinated chondramides were produced through precursor-directed biosynthesis. 相似文献
94.
Chen Z Jiao H Seifert G Horn AH Yu D Clark T Thiel W von Ragué Schleyer P 《Journal of computational chemistry》2003,24(8):948-953
Structural studies of fullerene-like Si(60) and Ge(60) cages using ab initio methods were augmented by density functional tight-binding molecular dynamics (DFTB-MD) simulations of finite temperature effects. Neither the perfect I(h) symmetry nor the distorted T(h) structures are true minima. The energies of both are high relative to distorted, lower symmetry minima, C(i) and T, respectively, which still preserve C(60)-type connectivity. Both Si(60) and Ge(60) favor C(i) symmetry cages in which Si and Ge vertexes exhibit either near-trigonal or pyramidal geometries. These structural variations imply significant reactivity differences between different positions. The small magnetic shielding effects (NICS) indicate that aromaticity is not important in these systems. The inorganic fullerene cages have lower stabilities compared with their carbon analogs. Si(60) is stable towards spontaneous disintegration up to 700 K according to DFTB-MD simulations, and thus has potential for experimental observation. In contrast, Ge(60) preserves its cage structure only up to 200 K. 相似文献
95.
The photopolymerization of a commercial sheet material as used in the dental laboratory was investigated by using the photocalorimeter DSC7/DPA7 (Perkin-Elmer). Using normal reaction conditions (light wavelength 400 nm, light intensity 1 mW cm–2 and sample thickness 2.5 mm), the curing was completed within few min. The reaction rate was nearly independent on the light wavelength in the range between =300 and 380 nm, but decreased distinctively at longer wavelengths. After desmearing the DSC curves, the dependence of the reaction rate on light intensity and sample thickness could be described in very good approximation by an equation derived by Tryson [1]. Comparable with pure acrylates or methacrylates, a pronounced dark reaction was found after interruption of the illumination.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
96.
Hsi WC Kunde GJ Pochodzalla J Lynch WG Tsang MB Begemann-Blaich ML Bowman DR Charity RJ Cosmo F Ferrero A Gelbke CK Glasmacher T Hofmann T Imme G Iori I Hubele J Kempter J Kreutz P Kunze WD Lindenstruth V Lisa MA Lynen U Mang M Moroni A Müller WF Neumann M Ocker B Ogilvie CA Peaslee GF Raciti G Rosenberger F Sann H Scardaoni R Schüttauf A Schwarz C Seidel W Serfling V Sobotka LG Stuttge L Tomasevic S Trautmann W Tucholski A Williams C Wörner A Zwieglinski B 《Physical review letters》1994,73(25):3367-3370
97.
From the enthalpy of solution of MoOBr3 in NaOH/H2O2 the enthalpy of formation ΔH°(MoOBr3,f,298) = ?109,5(±0,4) kcal/mol was derived. The sublimation of MoOBr3 is connected with simultaneous decomposition (see “Inhaltsübersicht”). From the temperature function of the saturated vapor pressure the values ΔH°(subl., MoOBr3, 298) = 36(±1,5) kcal/mol and ΔS°(subl., MoOBr3, 298) = 56(±3) cl are calculated. 相似文献
98.
The Crystal Structure of Trimethyltin Methanesulfinate, (CH3)3SnO2SCH3 Trimethyltin methanesulfinate, (CH3)3SnO2SCH3 crystallizes orthorhombie in the space group A2122. The lattice constants are: a = 7.98 ± 0.01, b = 12.59 ± 0.02 and c = 17.83 ± 0.02 Å Within the crystal structure the Sn atoms are linked together via bridging RSO2 groups to form a helical chain along [l00]. Each Sn atom is surrounded by three C and two 0 atoms in a trigonal bipyramidal arrangement. The Sn? C distances are in the range from 2.09 to 2.18 Å the Sn? 0 distance amounts to 2.23 Å. 相似文献
99.
The nitate-selective membrane electrode based on tributyloctadecylphosphonium nitrate can be used to quantify perrhenate and perchlorate after appropriate conditioning of the membrane. Near-Nernstian responses are obtained for 10?3–10?6 M perrhenate and 10?2–4 × 10?6 M perchlorate. Iron(II), copper(II) and chloride do not interfere in moderate amounts; other interferences are discussed. Rhenium leaches are analysed after suitable sample preparation. The electrode is useful in following the potentiometric titration of perrhenate with nitron. 相似文献
100.
M. Feist R. Kunze D. Neubert K. Witke E. Kemnitz 《Journal of Thermal Analysis and Calorimetry》1997,49(2):635-647
(trienH2)[CoCl4], which contains tetrahedral chlorocobaltate(II) anions, decomposes under argon in two stages via a stepwise deprotonation of the cation. The decomposition starts at 310°C with the liberation of HCl, followed at 400°C by the simultaneous release of a further mole of HCl and triene and/or its cracking products. The second decomposition stage is strongly influenced by the atmosphere. In the lower temperature region (<400°C), increasing oxygen contents of the carrier gas lead to decreasing mass losses. Therefore, the solid residues contain various amounts of C,N-containing products as well as coke. The thermal decomposition of the iron(III) compound, which contains μ-oxalato-bridged FeCl4 units, begins with the dehydratation followed by the decay of the complex anion to produce CO, CO2, and HCl. Instead of a binuclear, monooxobridged chloroferrate(III) complex, a [FeCl4]? — containing compound is proposed as one of the final products. The third decomposition stage, partially overlaying the preceding one, is the degradation of the organic cation as found for the cobalt compound. The results of thein situ-TA-MS measurements are compared with those obtained from usual TA techniques as well as from the residue characterization by X-ray diffraction, Raman spectroscopy, and chemical analysis. 相似文献