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41.
Linda K. Bell Wolfgang A. Herrmann Gangolf W. Kriechbaum 《Journal of organometallic chemistry》1982,240(4):381-393
An unexpected novel coordination mode of diazoalkanes has been verified via addition of 2-diazopropane to the metal—metal triple bond of bis[dicarbonyl(η5-pentamethylcyclopentadienyl)molybdenum] (MoMo). The dinuclear 1:1 addition product isolated in nearly quantitative yield is structurally characterized by a bent, 4-electron type η1:η2-diazoalkane ligand, with the terminal nitrogen atom symmetrically bridging the metal-metal “single bond” (d(MoMo) 305.0(2) pm; d(Mo---N(1)) 212.0(12) and 212.6(10) pm, respectively) and the second nitrogen atom being bonded to one molybdenum atom only (d(Mo---N(2)) 213.4(13) pm). 相似文献
42.
Johnston AM Scrimgeour CM Kennedy H Handley LL 《Rapid communications in mass spectrometry : RCM》2003,17(11):1099-1106
The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil. 相似文献
43.
Takeshita N Paradis LA Oner D McCarthy TJ Chen W 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8131-8136
Wettability was controlled in a rational manner by individually and simultaneously manipulating surface topography and surface chemical structure. The first stage of this research involved the adsorption of charged submicrometer polystyrene latex particles to oppositely charged poly(ethylene terephthalate) (PET) film samples to form surfaces with different topographies/roughness; adsorption time, solution pH, solution ionic strength, latex particle size, and substrate charge density are external variables that were controlled. The introduction of discrete functional groups to smooth and rough surfaces through organic transformations was carried out in the second stage. Amine groups (-NH(2)) and alcohol groups (-OH) were introduced onto smooth PET surfaces by amidation with poly(allylamine) and adsorption with poly(vinyl alcohol) (PVOH), respectively. On latex particle adsorbed surfaces, a thin layer of gold was evaporated first to prevent particle redistribution before chemical transformation. Reactions with functionalized thiols and adsorption with PVOH on patterned gold surfaces successfully enhanced surface hydrophobicity and hydrophilicity. Particle size and biomodal particle size distribution affect both hydrophobicity and hydrophilicity. A very hydrophobic surface exhibiting water contact angles of 150 degrees /126 degrees (theta(A)/theta(R)) prepared by adsorption of 1-octadecanethiol and a hydrophilic surface with water contact angles of 18 degrees /8 degrees (theta(A)/theta(R)) prepared by adsorption of PVOH were prepared on gold-coated surfaces containing both 0.35 and 0.1 microm latex particles. The combination of surface topography and surface-chemical functionality permits wettability control over a wide range. 相似文献
44.
Enright PM Tosin M Nieuwenhuyzen M Cronin L Murphy PV 《The Journal of organic chemistry》2002,67(11):3733-3741
The work described deals with the isolation and characterization of epoxides from 6-deoxyhex-5-enopyranosides and preliminary exploration of their synthetic potential. Prolonged epoxidation reaction times led to their hydrolysis in situ and gave novel protected D-hexos-5-ulose derivatives (sugar 1,5-dicarbonyls). Some reactions of the hexos-5-uloses were studied, and in some cases septanoside (seven-membered-ring saccharide) derivatives were isolated. Novel routes to D-xylo-hexos-5-ulose and D-lyxo-hexos-5-ulose, of interest as intermediates in the synthesis and biosynthesis of inositols and aza sugars, are also described. The structures of the epoxides and novel hexos-5-uloses were established by NMR and X-ray crystallographic methods. 相似文献
45.
We consider a Calabi-Yau compactification paradigm with three light generations and anR-symmetry. From a special form of the Tian-Yau manifold, we also construct a new three-generation model with markedly different phenomenology. Thecomplete spectrum of all light matter fields is obtained in a universal way and moreover in a physically suitable basis, allowing a straightforward analysis of all their couplings. Here we discuss all the renormalizable Yukawa couplings. This computation can equally well be repeated for all compactification models based on Calabi-Yau complete intersections in products of homogeneous spaces. 相似文献
46.
47.
Auchère F Raleiras P Benson L Venyaminov SY Tavares P Moura JJ Moura I Rusnak F 《Inorganic chemistry》2003,42(4):938-940
Superoxide reductases catalyze the monovalent reduction of superoxide anion to hydrogen peroxide. Spectroscopic evidence for the formation of a dinuclear cyano-bridged adduct after K(3)Fe(CN)(6) oxidation of the superoxide reductases neelaredoxin from Treponema pallidum and desulfoferrodoxin from Desulfovibrio vulgaris was reported. Oxidation with K(3)Fe(CN)(6) reveals a band in the near-IR with lambda(max) at 1020 nm, coupled with an increase of the iron content by almost 2-fold. Fourier transform infrared spectroscopy provided additional evidence with CN-stretching vibrations at 2095, 2025-2030, and 2047 cm(-)(1), assigned to a ferrocyanide adduct of the enzyme. Interestingly, the low-temperature electronic paramagnetic resonance (EPR) spectra of oxidized TpNlr reveal at least three different species indicating structural heterogeneity in the coordination environment of the active site Fe ion. Given the likely 6-coordinate geometry of the active site Fe(3+) ion in the ferrocyanide adduct, we propose that the rhombic EPR species can serve as a model of a hexacoordinate form of the active site. 相似文献
48.
The relative effectiveness of the SimPlate Yeast and Mold-Color Indicator method (Y&M-CI) was compared to the U.S. Food and Drug Administration's (FDA) Bacteriological Analytical Manual (BAM) method and the proposed International Organization for Standardization (ISO) method, ISO/CD 21527, for enumerating yeasts and molds in foods. Test portions were prepared and incubated according to the conditions stated in both the BAM and ISO methods. Six food types were analyzed: frozen corn dogs, nut meats, frozen fruits, cake mix, cereal, and fresh cheese. Nut meats, frozen fruits, and fresh cheese were naturally contaminated. All other foods were artificially contaminated with either a yeast or mold. Seventeen laboratories throughout North America and Europe participated in the study. Three method comparisons were conducted. In general, there was <0.3 mean log count difference in recovery between the SimPlate method and the 2 corresponding reference methods. Moreover, mean log counts between the 2 reference methods were also very similar. The repeatability (Sr) and reproducibility (SR) standard deviations were comparable between the 3 method comparisons. These results indicate that the BAM method and the SimPlate method are equivalent for enumerating yeast and mold populations in foods. Similarly, the SimPlate method is comparable to the proposed ISO method when test portions are prepared and incubated as defined in the proposed ISO method. 相似文献
49.
Abstract Micelles formed by sodium taurocholate (NaTC) and mixed micelles formed by NaTC with detergents (SDS, reduced Triton X-100 and CTAC) were studied with fluorescent probes. Pyrene was used as an indicator of the polarity of the micellar binding site by comparison of the fluorescence spectra and vibronic band intensity ratios of pyrene in the different systems. Perylene was used as a fluorescence polarization probe to study the rigidity of the NaTC and mixed micelles. The fluorescence lifetime of perylene in the different systems was also measured. Results of the studies were compared with measurements of the probes in cyclohexane, ethanol and aqueous beta-cyclodextrin. Perylene was found to be more rigidly bound in the NaTC micelles than in the detergent micelles. Insertion of small amounts of reduced Triton X-100 into the NaTC micelles appears to increase the rigidity. The binding sites of NaTC and CTAC have similar polarities, and are more polar than those of SDS and reduced Triton X-100. Insertion of any of the detergents into the NaTC micelle decreases the polarity of the binding site, possibly by reducing the penetration of water into the micelle. 相似文献
50.
Stefaan J. H. Soenen Linda Desender 《International journal of environmental analytical chemistry》2013,93(10-11):783-796
The complex of diethylenetriaminepentaacetate (DTPA) with the paramagnetic gadolinium ion [Gd(III)] is a well-known blood pool contrast agent for magnetic resonance imaging (MRI). To obtain MRI pictures from other anatomical structures, for instance from tissues containing cells with phagocytic activity, larger colloidal complexes have to be constructed. Therefore, in view of modifying the physiological behaviour, the DTPA chelate was first hydrophobized by covalently linking it to phosphatidylethanolamine (PE), and the resulting conjugate was then incorporated into nanometre-sized, sonicated phospholipid vesicles. Qualitative information on the affinity of the PE–DTPA derivative for Gd(III) ions was derived from competition experiments using the dye Arsenazo. Furthermore, it was found that only the membranotropic adducts residing in the outer shell of the vesicle bilayer are accessible to the lanthanide ion. The vesicular particulate was also used as a vehicle to transport PE–DTPA into the coating of so-called magnetoliposomes which consist of nanometre-sized iron oxide cores onto which a phospholipid bilayer is strongly chemisorbed. After loading the resulting structures with Gd(III), this new type of magnetoliposome may offer unique potentialities as a novel bi-label MRI contrast medium. 相似文献