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941.
Fatma Meddeb-Mouelhi Jessica Kelly Moisan Jodrey Bergeron Benoit Daoust Marc Beauregard 《Applied biochemistry and biotechnology》2016,178(7):1286-1302
The Microbacteriaceae family, such as Microbacterium, is well known for its ability to produce carotenoid-type pigments, but little has been published on the structure of such pigments. Here, we isolated the yellow pigment that is responsible for the yellowish color of a Microbacterium oxydans strain isolated from a decomposing stump of a resinous tree. The pigment, which is synthesized when the bacterium is grown under light, was purified and characterized using several spectroscopic analyses, such as ultraviolet-visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (1H NMR, 13C NMR), and high-resolution mass spectrometry (HRMS). From these analysis, a molecular formula (C27H42O2) and a chemical structure (8-hydroxymethyl-2,4,12-trimethyl-14-(2,6,6-trimethyl-cyclohex-2-enyl)-teradeca-3,7,9,11,13-pentan-2-ol) were deduced. The chemical properties of the pigment, such as aqueous stability at different pH, stability in different organic solvents, and antioxidant capacity, are also reported. Together, these data and previous studies have resulted in the identification of a new antioxidant pigment produced by M. oxydans. To the best of our knowledge, this is the first thorough investigation of this carotenoid-like pigment in the Microbacterium genera. 相似文献
942.
Nicoleta Doriana Banu Ionut Banu Banu Marios S. Katsiotis Anjana Tharalekshmy Samuel Stephen Jamie Whelan Gisha Elizabeth Luckachan Radu Vladea Saeed M. Alhassan 《Chemical Papers》2016,70(11):1503-1511
Open cell 3D titanium carbide/silicon carbide (TiC/SiC) composite was oxidised to titanium oxide/silicon carbide (TiO2/SiC) following different temperature profiles in a thermal gravimetric analysis (TGA) instrument in continuous air-flow and static air (oven) environments. The TiC oxidation to anatase, starting at temperatures over 450°C, was confirmed by Raman spectroscopy and X-Ray diffraction (XRD). By increasing the temperature, the mass fraction of anatase diminished, while the mass fraction of rutile increased. SiC oxidation started at 650°C when a mixture of TiO2/SiO2/SiC could be observed by Raman, XRD and HRTEM. 相似文献
943.
Claudio E. Grünenfelder Dr. Jessica K. Kisunzu Prof. Dr. Helma Wennemers 《Angewandte Chemie (International ed. in English)》2016,55(30):8571-8574
The tripeptide H‐d Pro‐Pro‐Asn‐NH2 is presented as a catalyst for asymmetric conjugate addition reactions of aldehydes to maleimide. The peptidic catalyst promotes the reaction between various aldehydes and unprotected maleimide with high stereoselectivities and yields. The obtained products were readily derivatized to the corresponding pyrrolidines, lactams, lactones, and peptide‐like compounds. 1H NMR spectroscopic, crystallographic, and computational investigations provided insight into the conformational properties of H‐d Pro‐Pro‐Asn‐NH2 and revealed the importance of hydrogen bonding between the peptide and maleimide for catalyzing the stereoselective C?C bond formation. 相似文献
944.
Electrocatalytic Nanostructured Ferric Tannates: Characterization and Application of a Polyphenol Nanosensor
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Dr. Massimiliano Magro Dr. Emanuela Bonaiuto Dr. Davide Baratella Dr. Jessica de Almeida Roger Dr. Petr Jakubec Vittorino Corraducci Dr. Jiri Tuček Dr. Ondrej Malina Prof. Radek Zbořil Prof. Fabio Vianello 《Chemphyschem》2016,17(20):3196-3203
A novel core–shell hybrid nanomaterial composed of peculiar maghemite nanoparticles (surface‐active maghemite nanoparticles (SAMNs)) as the core and tannic acid (TA) as the shell was developed by self‐assembly of ferric tannates onto the surface of SAMNs by simple incubation in water. The hybrid nanomaterial (SAMN@TA) was characterized by using UV/Vis, FTIR, and Mössbauer spectroscopies, magnetization measurements, and X‐ray powder diffraction, which provide evidence of a drastic reorganization of the iron oxide surface upon reaction with TA and the formation of an outer shell that consists of a cross‐linked network of ferric tannates. According to a Langmuir isotherm analysis, SAMN@TA offers one of most stable iron complexes of TA reported in the literature to date. Moreover, SAMN@TA was characterized by using electrical impedance spectroscopy, voltammetry, and chronoamperometry. The nanostructured ferric tannate interface showed improved conductivity and selective electrocatalytic activity toward the oxidation of polyphenols. Finally, a carbon‐paste electrode modified with SAMN@TA was used for the determination of polyphenols in blueberry extracts by square‐wave voltammetry. 相似文献
945.
Michael S. Roberts Nicholas S. Selvo Jessica K. Roberts Vinay M. Daryani Thandranese S. Owens K. Elaine Harstead 《液相色谱法及相关技术杂志》2016,39(16):745-751
A rapid and robust method for measuring methotrexate (MTX) and its two primary metabolites, 7-hydroxymethotrexate (7-OHMTX) and 2,4-diamino-N10-methylpteroic acid (DAMPA), was developed for use in pharmacokinetic studies of plasma and cerebrospinal fluid samples collected from infants with malignant brain tumors. Sample aliquots (100?µL) were prepared for bioanalysis of MTX and metabolites using a Waters Oasis HLB microelution solid-phase extraction (SPE) plate. Chromatography was performed using a Phenomenex Synergi Polar-RP 4 µ 75?×?2.0?mm ID column heated to 40°C. A rapid gradient elution on a Shimadzu HPLC system was used, with mobile phase A consisting of water/formic acid (100/0.1?v/v) and mobile phase B consisting of acetonitrile/formic acid (100/0.1?v/v). Column eluent was analyzed using AB Sciex QTRAP 5500 instrumentation in electrospray ionization mode. The ion transitions (m/z) monitored were 455.2?→?308.1, 471.1?→?324.1, and 326.2?→?175.1 for MTX, 7-OHMTX, and DAMPA, respectively. The method was linear over 0.0022–5.5?µM for MTX, 0.0085–21?µM for 7-OHMTX, and 0.0031–7.7?µM for DAMPA. The method was applied to the analysis of serial plasma samples obtained from infants diagnosed with malignant brain tumors receiving high-dose methotrexate and results were compared to MTX concentrations from an immunoassay based on fluorescence polarization. 相似文献
946.
Le Dung Pham Red O. Smith-Sweetser Briana Krupinsky Carolyn E. Dewey Prof. Dr. Jessica R. Lamb 《Angewandte Chemie (International ed. in English)》2023,62(48):e202314376
N-Heterocyclic carbenes (NHCs) are powerful organocatalysts, but practical applications often require in situ generation from stable precursors that “mask” the NHC reactivity via reversible binding. Previously established “masks” are often simple small molecules, such that the NHC structure is used to control both catalytic activity and activation temperature, leading to undesirable tradeoffs. Herein, we show that NHC-carbodiimide (CDI) adducts can be masked precursors for switchable organocatalysis and that the CDI substituents can control the reaction profile without changing the NHC structure. Large electronic variations on the CDI (e.g., alkyl versus aryl) drastically change the catalytically active temperature, whereas smaller perturbations (e.g., different para-substituted phenyls) tune the catalyst release within a narrower window. This control was demonstrated for three classic NHC-catalyzed reactions, each influencing the NHC-CDI equilibrium in different ways. Our results introduce a new paradigm for controlling NHC organocatalysis as well as present practical considerations for designing appropriate masks for various reactions. 相似文献
947.
A regioselective fluorocyclisation of β,γ-unsaturated oximes through I(I)/I(III) catalysis is disclosed to generate 5-fluoromethylated isoxazolines. The transformation leverages p-iodotoluene as an inexpensive catalyst, Selectfluor® as the terminal oxidant and an amine⋅HF complex (1 : 7.5) as both the fluoride and Brønsted acid source. The λ3-iodane p-TolIF2, which is generated in situ, engages the pendant alkene of the substrate to facilitate a cyclisation/fluorination sequence. A range of 5-fluoromethyl isoxazolines can be generated using this method, including aliphatic and aromatic systems (up to 56 % yield). Single crystal X-ray analysis of a representative example reveals a conformation that is consistent with the stereoelectronic gauche effect between the exocyclic C(sp3)−F bond and the C(sp3)−O of the isoxazoline (ϕOCCF=−62.0°). 相似文献
948.
949.
Dr. Daixuan Zhang Dr. Foad Vashahi Dr. Erfan Dashtimoghadam Dr. Xiaobo Hu Claire J. Wang Jessica Garcia Aleksandra V. Bystrova Dr. Mohammad Vatankhah-Varnoosfaderani Prof. Frank A. Leibfarth Prof. Sergei S. Sheiko 《Angewandte Chemie (International ed. in English)》2023,62(8):e202217941
The inability to re-process thermosets hinders their utility and sustainability. An ideal material should combine closed-loop recycling and upcycling capabilities. This trait is realized in polydimethylsiloxane bottlebrush networks using thermoreversible Diels–Alder cycloadditions to enable both reversible disassembly into a polymer melt and on-demand reconfiguration to an elastomer of either lower or higher stiffness. The crosslink density was tuned by loading the functionalized networks with a controlled fraction of dormant crosslinkers and crosslinker scavengers, such as furan-capped bis-maleimide and anthracene, respectively. The resulting modulus variations precisely followed the stoichiometry of activated furan and maleimide moieties, demonstrating the lack of side reactions during reprocessing. The presented circularity concept is independent from the backbone or side chain chemistry, making it potentially applicable to a wide range of brush-like polymers. 相似文献
950.
Liang Liang Quanchen Feng Xingli Wang Jessica Hübner Ulrich Gernert Marc Heggen Longfei Wu Tim Hellmann Prof. Jan P. Hofmann Prof. Peter Strasser 《Angewandte Chemie (International ed. in English)》2023,62(12):e202218039
The chemical selectivity and faradaic efficiency of high-index Cu facets for the CO2 reduction reaction (CO2RR) is investigated. More specifically, shape-controlled nanoparticles enclosed by Cu {hk0} facets are fabricated using Cu multilayer deposition at three distinct layer thicknesses on the surface facets of Au truncated ditetragonal nanoprisms (Au DTPs). Au DTPs are shapes enclosed by 12 high-index {310} facets. Facet angle analysis confirms DTP geometry. Elemental mapping analysis shows Cu surface layers are uniformly distributed on the Au {310} facets of the DTPs. The 7 nm Au@Cu DTPs high-index {hk0} facets exhibit a CH4 : CO product ratio of almost 10 : 1 compared to a 1 : 1 ratio for the reference 7 nm Au@Cu nanoparticles (NPs). Operando Fourier transform infrared spectroscopy spectra disclose reactive adsorbed *CO as the main intermediate, whereas CO stripping experiments reveal the high-index facets enhance the *CO formation followed by rapid desorption or hydrogenation. 相似文献