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41.
42.
Badham NF Mendelson WL Allen A Diederich AM Eggleston DS Filan JJ Freyer AJ Killmer LB Kowalski CJ Liu L Novack VJ Vogt FG Webb KS Yang J 《The Journal of organic chemistry》2002,67(15):5440-5443
A convenient two-step homologation of both aliphatic and aromatic ketones to the corresponding carboxylic acid has been developed. First ketones were converted to epoxynitriles with the Darzens reaction. Second, a Lewis acid mediated rearrangement of these epoxynitriles with lithium bromide was achieved to give homologated secondary alkanoic acids (as well as aryl-alkanoic) in good yields. The mechanism and the scope of the rearrangement reaction were investigated. This strategy constitutes a two-step homologation of ketones to secondary carboxylic acids. 相似文献
43.
The activity of enzyme I (EI), the first protein in the bacterial PEP:sugar phosphotransferase system, is regulated by a monomer–dimer equilibrium where a Mg2+-dependent autophosphorylation by PEP requires the homodimer. Using inactive EI(H189A), in which alanine is substituted for the active-site His189, substrate binding effects can be separated from those of phosphorylation. Whereas 1 mM PEP (with 2 mM Mg2+) strongly promotes dimerization of EI(H189A) at pH 7.5 and 20 °C, 5 mM pyruvate (with 2 mM Mg2+) has the opposite effect. A correlation between the coupling of N- and C-terminal domain unfolding, measured by differential scanning calorimetry, and the dimerization constant for EI, determined by sedimentation equilibrium, is observed. That is, when the coupling between N- and C-terminal domain unfolding produced by 0.2 or 1.0 mM PEP and 2 mM Mg2+ is inhibited by 5 mM pyruvate, the dimerization constant for EI(H189A) decreases from >108 to <5 × 105 or 3 × 107 M−1, respectively. With 2 mM Mg2+ at 15–25 °C and pH 7.5, PEP has been found to bind to one site/monomer of EI(H189A) with KA′106 M−1 (ΔG′=−33.7±0.2 kJ mol−1 and ΔH=+16.3 kJ mol−1 at 20 °C with ΔCp=−1.4 kJ K−1 mol−1). The binding of PEP to EI(H189A) is synergistic with that of Mg2+. Thus, physiological concentrations of PEP and Mg2+ increase, whereas pyruvate and Mg2+ decrease the amount of dimeric, active, dephospho-enzyme I. 相似文献
44.
A collaborative study was conducted to compare the VIDAS Salmonella (SLM) with Rappaport-Vassiliadis (RV) method for detection of Salmonella in foods to the current standard method presented in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) and the culture method presented in AOAC's Official Methods of Analysis. The VIDAS SLM with RV method uses tetrathionate broth in combination with RV medium in place of selenite cystine broth for selective enrichment, thereby eliminating the hazardous waste issue for laboratories. Twenty five laboratories participated in the evaluation, each testing one or more of 8 test products: nonfat dry milk, dried egg, soy flour, lactic casein, milk chocolate, raw ground pork, raw ground turkey, and raw peeled shrimp. Results of the study showed no significant differences in the numbers of confirmed positive samples with the VIDAS SLM with RV procedure and the BAM/AOAC culture procedure. The VIDAS SLM with RV method was effective for rapid detection of Salmonella in foods. It is recommended that AOAC INTERNATIONAL modify the VIDAS Salmonella SLM procedure to include the RV method. 相似文献
45.
Lauren?B.?Brown Ann?M.?AndersonEmail author Mary?K.?Carroll 《Journal of Sol-Gel Science and Technology》2012,62(3):404-413
Titania (TiO2) and titania–silica (TiSi) aerogels are suitable for photocatalytic oxidation of volatile organic compounds for pollution mitigation; however, methods for fabricating these aerogels can be complex. In this work we describe the use of a rapid supercritical extraction (RSCE) technique to prepare TiO2 and TiSi aerogels in as little as 8 h. The RSCE technique uses a metal mold and a four-step hydraulic hot press procedure to bring the solvents in the sol–gel pores to a supercritical state and control the supercritical fluid release process. Resulting TiO2 aerogels were powdery with BET surface areas of 130–180 m2/g, pore volumes ~0.5 cm3/g and skeletal densities of 3.6 g/mL. Monolithic TiSi aerogels were made using two different methods. An impregnation process, in which titania precursor was added to a silica sol–gel, took 4–8 days to complete with a 7-h RSCE and resulted in translucent aerogels with high surface area (560–650 m2/g) and pore volume (2.0–2.6 cm3/g), bulk densities ranging from 0.1 to 0.4 g/mL and skeletal densities of 2.3 g/mL. A co-precursor method for preparing TiSi aerogels took 8 h to complete. The precursor chemical mixture was poured directly into the mold and processed in a 7-h RSCE process. The resulting aerogels were opaque, with high surface areas (510–580 m2/g), low bulk density (0.03 g/mL), skeletal densities of 2 g/mL and pore volumes of 2.6–3.5 cm3/g. Preliminary solar simulator studies show that TiO2 and TiSi aerogels are capable of photocatalytic degradation of methylene blue in aqueous solution. 相似文献
46.
Ronald C. Crouch Ann O. Davis Timothy D. Spitzer Gary E. Martin Maged M. H. Sharaf Paul L. Schiff Charles H. Phoebe Albert N. Tackie 《Journal of heterocyclic chemistry》1995,32(3):1077-1080
Elucidation of minor natural product structures has been significantly augmented by inverse-detection; further improvement has been afforded by the development of micro inverse-detection probes. We report here the elucidation of the structure of a new alkaloid, quindolinone (5H, 10H-indolo[3,2-b]quinolin-11-one), from the West African plant Cryptolepis sanguinolenta. All nmr data for this minor, preparative hplc-isolated alkaloid, including 1H-15N one? bond heteronuclear shift correlation (HMQC) data, were recorded on an 800 μg sample of the alkaloid dissolved in 140 μl of 100% d6-DMSO using a 400 MHz spectrometer. 相似文献
47.
Simultaneous determination of nitrite and nitrate in human plasma by on-capillary preconcentration with field-amplified sample stacking 总被引:1,自引:0,他引:1
A simple method for the determination of nitrite and nitrate in human plasma has been developed using CZE with minimal sample preparation. Field‐amplified sample stacking (FASS) was used to achieve submicromolar detection by dilution of the plasma sample with deionized water. In CZE, the separation of nitrite and nitrate was achieved within 10 min without adding EOF modifier. The optimal condition was achieved with 50 mM phosphate buffer at pH 9.3. The ninefold diluted plasma samples were injected hydrodynamically for 40 s into a 60 cm×75 μm id uncoated fused‐silica capillary. The separation voltage was 20 kV (negative potential) and UV detection was performed at 214 nm. The linearity curves for nitrite and nitrate were obtained by the standard addition method. The estimated LODs for nitrite and nitrate in ninefold diluted plasma sample were 0.05 and 0.07 μM, respectively. The LODs for nitrite and nitrate in original plasma samples were 0.45 and 0.63 μM. The intra‐ and inter‐day precisions for both analytes were <2.6% and the recovery ranged between 92.3 and 113.3%. It was found that nitrite was more stable than nitrate in the plasma after the sample preparation. This proposed method was applied to a number of human plasma samples and the measured nitrite and nitrate concentrations in human plasma were consistent with the literature ranges. 相似文献
48.
Fadi HatoumJana Engler Christina ZelmerJohannes Wißen Cherie Ann MottiJohann Lex Michael Oelgemöller 《Tetrahedron letters》2012,53(42):5573-5577
A series of 3-(alkyl and aryl)methyleneisoindolin-1-one derivatives were synthesized in a simple two-step procedure using a recently established photodecarboxylative addition of carboxylates to phthalimides as the key-step. Subsequent acid-catalyzed dehydration and deprotection furnished the desired target compounds with high E-selectivity. The reaction sequence was applied to the synthesis of the known bioactive phenylethylene derivative, AKS-186. Different analogues, including heteroatom-containing isosteres were also synthesized using this approach. 相似文献
49.
Manage DP Lauzon J Atrazhev A Morrissey YC Edwards AL Stickel AJ Crabtree HJ Pabbaraju K Zahariadis G Yanow SK Pilarski LM 《Lab on a chip》2012,12(9):1664-1671
Herpes simplex virus (HSV) is one of the most prevalent viruses, with acute and recurrent infections in humans. The current gold standard for the diagnosis of HSV is viral culture which takes 2-14 days and has low sensitivity. In contrast, DNA amplification by polymerase chain reaction (PCR) can be performed within 1-2 h. We here describe a multiparameter PCR assay to simultaneously detect HSV-1 and HSV-2 DNA templates, together with integrated positive and negative controls, with product detection by melting curve analysis (MCA), in an array of semi-solid polyacrylamide gel posts. Each gel post is 0.67 μL in volume, and polymerized with all the components required for PCR. Both PCR and MCA can currently be performed in one hour and 20 min. Unprocessed genital swabs collected in universal transport medium were directly added to the reagents before or after polymerization, diffusing from atop the gel posts. The gel post platform detects HSV templates in as little as 2.5 nL of raw sample. In this study, 45 genital swab specimens were tested blindly as a preliminary validation of this platform. The concordance of PCR on gel posts with conventional PCR was 91%. The primer sequestration method introduced here (wherein different primers are placed in different sets of posts) enables the simultaneous detection of multiple pathogens for the same sample, together with positive and negative controls, on a single chip. This platform accepts unprocessed samples and is readily adaptable to detection of multiple different pathogens or biomarkers for point-of-care diagnostics. 相似文献
50.
Ann M. Tickner G. Kris Huang Kerry Gombatz Robert J. Mills Vance Novack Kevin S. Webb 《合成通讯》2013,43(16):2497-2505
Two efficient syntheses of methyl 4-mercaptobenzoate are described, one utilizing the dianion of 4-bromothiophenol, the other a SNAr reaction starting with 4-fluorobenzonitrile. 相似文献