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71.
72.
Ericka Santacruz Gabriela Huelgas Sandra K. Angulo Virginia M. Mastranzo Simón Hernández-Ortega Judit A. Aviña Eusebio Juaristi Cecilia Anaya de Parrodi Patrick J. Walsh 《Tetrahedron: Asymmetry》2009,20(24):2788-2794
New chiral thioureas 1–8 containing 1,2-ethylendiamine or trans-1,2-diaminocyclohexane as the carbon skeleton, and containing an (S)-α-phenylethyl group have been prepared (79–98% yield). Thioureas 1–8 were used as ligands for the zinc-based catalyzed asymmetric hydrosilylation of acetophenone with polymethylhydrosiloxane (PMHS). The best result was achieved with monothiourea 1 (up to 75% ee), in toluene and a catalyst load of 5 mol %. 相似文献
73.
Pseudo‐first‐order rate constants (kobs) for tertiary amine (DABCO and Me3N) buffer‐catalyzed cyclization of N′‐morpholino‐N‐(2′‐methoxyphenyl)phthalamide ( 1 ) to N‐(2′‐methoxyphenyl)phthalimide ( 2 ) reveal saturation (nonlinear) plots of kobs versus [Buf]T (total tertiary amine buffer concentration) at a constant pH. Such plots at different pH have been attributed to the presence of a reactive intermediate (T?) formed by tertiary amine buffer‐catalyzed intramolecular nucleophilic addition of the secondary amide nitrogen to the carbonyl carbon of the tertiary amide group of 1 . © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 263–272, 2010 相似文献
74.
A. M. Gazaliev S. D. Fazylov É. P. Sim M. Zh. Zhurinov 《Chemistry of Natural Compounds》1989,25(4):447-450
The electrooxidation of the alkaloid ephedrine at solid electrodes in a wide range of concentrations and pH values of solutions
has been studied by the methods of potentiodynamic voltammetric curves, preparative electrolysis, and quantum-chemical calculations
by the SCF MO LCAO method in the MINDO/3 approximation. A quantitative basis has been given for the sequence of stages in
the electrooxidation of ephedrine proposed previously by the authors of one of the cited papers. Good agreement has been established
between the values found theoretically and experimentally.
Institute of Organic Synthesis and Colloid Chemistry, Kazakh SSR Academy of Sciences, Karaganda. Translated from Khimiya Prirodnykh
Soedinenii, No. 4, pp. 523–526, July–August, 1989. 相似文献
75.
Y. K. Hong C. Y. Lee C. K. Jeong J. H. Sim K. Kim J. Joo M. S. Kim J. Y. Lee S. H. Jeong S. W. Byun 《Current Applied Physics》2001,1(6):3492
Through the chemical coating of polypyrrole (PPy) doped with naphthalene sulfonic acid (NSA) on electrically insulating poly (ethylene terephthalate) (PET) woven fabric, PPy–NSA/PET complexes were synthesized. By using the electrochemical coating of PPy doped anthraquinone-2-sulfonic acid (AQSA) on PPy–NSA/PET complexes, PPy–AQSA/PPy–NSA/PET complexes were synthesized. The silver (Ag) was thermally vacuum evaporated on the surface of PPy–AQSA/PPy–NSA/PET complexes (Ag|PPy–AQSA/PPy–NSA/PET). Electromagnetic interference (EMI) shielding efficiency (SE) and dc conductivity (σdc) of fabric complexes were measured for EMI shielding characteristics and theoretical simulation. The measurement of EMI SE in the frequency range from 50 MHz to 1.5 GHz was performed by using ASTM D4935-99 method. The EMI shielding characteristics such as transmittance, reflectance and absorbance were obtained from the S (scattering)-parameter analysis. We control the contribution of the absorbance or the reflectance to total EMI SE through the coating of conductive PPy and the evaporation Ag. 相似文献
76.
77.
Young Hee Lee Mayavan Viji Eunhwa Lee Hyeju Jo Kyung Yoo Jaeuk Sim Sunhwan Lee Kiho Lee Heesoon Lee Jae-Kyung Jung 《Tetrahedron letters》2017,58(26):2614-2617
During the process development for multistep synthesis of Rosuvastatin calcium several impurities were obtained along with the final Rosuvastatin calcium. Out of this; synthesis of impurity A (acetone adduct) a minor impurity of Rosuvastatin calcium (3R,5S,6E)-7-[4-(4-fluorophenyl)-2-[[(2-hydroxy-2-methylpropyl)sulfonyl(methyl)amino]-6-(1-methylethyl)-pyrimidin-5-yl]-3,5-dihydroxyheptenoicacid hemicalcium salt, is described. The synthesis of impurity A has been accomplished in 6 steps; starting from formation of β-hydroxy sulfonamide as the key intermediate and followed by using convenient routes with overall yield of 13.5%. The target compound can be used as the reference substance of impurity of the Rosuvastatin calcium. 相似文献
78.
Heloiza Ferreira Alves-Prado Fabiana Carina Pavezzi Rodrigo Simões Ribeiro Leite Valéria Maia de Oliveira Lara Durães Sette Roberto DaSilva 《Applied biochemistry and biotechnology》2010,161(1-8):333-346
Hemicelluloses are polysaccharides of low molecular weight containing 100 to 200 glycosidic residues. In plants, the xylans or the hemicelluloses are situated between the lignin and the collection of cellulose fibers underneath. The xylan is the most common hemicellulosic polysaccharide in cell walls of land plants, comprising a backbone of xylose residues linked by β-1,4-glycosidic bonds. So, xylanolytic enzymes from microorganism have attracted a great deal of attention in the last decade, particularly because of their biotechnological characteristics in various industrial processes, related to food, feed, ethanol, pulp, and paper industries. A microbial screening of xylanase producer was carried out in Brazilian Cerrado area in Selviria city, Mato Grosso do Sul State, Brazil. About 50 bacterial strains and 15 fungal strains were isolated from soil sample at 35 °C. Between these isolated microorganisms, a bacterium Lysinibacillus sp. and a fungus Neosartorya spinosa as good xylanase producers were identified. Based on identification processes, Lysinibacillus sp. is a new species and the xylanase production by this bacterial genus was not reported yet. Similarly, it has not reported about xylanase production from N. spinosa. The bacterial strain P5B1 identified as Lysinibacillus sp. was cultivated on submerged fermentation using as substrate xylan, wheat bran, corn straw, corncob, and sugar cane bagasse. Corn straw and wheat bran show a good xylanase activity after 72 h of fermentation. A fungus identified as N. spinosa (strain P2D16) was cultivated on solid-state fermentation using as substrate source wheat bran, wheat bran plus sawdust, corn straw, corncob, cassava bran, and sugar cane bagasse. Wheat bran and corncobs show the better xylanase production after 72 h of fermentation. Both crude xylanases were characterized and a bacterial xylanase shows optimum pH for enzyme activity at 6.0, whereas a fungal xylanase has optimum pH at 5.0–5.5. They were stable in the pH range 5.0–10.0 and 5.5–8.5 for bacterial and fungal xylanase, respectively. The optimum temperatures were 55C and 60 °C for bacterial and fungal xylanase, respectively, and they were thermally stable up to 50 °C. 相似文献
79.
Bhaskar Godugu Pedatsur Neta Yamil Simón-Manso Stephen E. Stein 《Journal of the American Society for Mass Spectrometry》2010,21(7):1169-1176
A prominent dissociation path for electrospray generated tryptic peptide ions is the dissociation of the peptide bond linking
the second and third residues from the ammo-terminus. The formation of the resulting b2 and y
n−2 fragments has been rationalized by specific facile mechanisms. An examination of spectral libraries shows that this path
predominates in diprotonated peptides composed of 12 or fewer residues, with the notable exception of peptides containing
glutamine or glutamic acid at the N-terminus. To elucidate the mechanism by which these amino acids affect peptide fragmentation,
we synthesized peptides of varying size and composition and examined their MS/MS spectra as a function of collision voltage
in a triple quadrupole mass spectrometer. Loss of water from N-terminal glutamic acid and glutamine is observed at a lower
voltage than any other fragmentation, leading to cyclization of the terminal residue. This cyclization results in the conversion
of the terminal amine group to an imide, which has a lower proton affinity. As a result, the second proton is not localized
at the N-terminus but is readily transferred to other sites, leading to fragmentation near the center of the peptide. Further
confirmation was obtained by examining peptides with N-terminal pyroglutamic acid and N-acetyl peptides. Peptides with N-terminal
proline maintain the trend of forming b2 and y
n−2 because their ring contains an imine rather than imide and has sufficient proton affinity to retain the proton at the N-terminus. 相似文献
80.
Myjavcová R Marhol P Křen V Simánek V Ulrichová J Palíková I Papoušková B Lemr K Bednář P 《Journal of chromatography. A》2010,1217(51):7932-7941
Anthocyanins from the fruit Lonicera caerulea L. var. kamtschatica (blueberry honeysuckle, Caprifoliaceae) were studied via (semi)preparative chromatographic fractionation followed by MS and μLC/MS analysis. The extraction procedure was optimized with respect to analytical purposes as well as its potential use for the preparation of nutraceuticals. The highest yield of anthocyanins was obtained using acidified methanol as the extraction medium. A comparable total anthocyanin content was obtained using a mixture of methanol and acetone. However, when Lonicera anthocyanins were in contact with acetone, a condensation reaction occurred to a large extent and related 5-methylpyranoanthocyanins were found. The effect of other extraction media, including ethanol as a "green" solvent, is also discussed. The potential of two fractionation procedures for extract purification differing in their chromatographic selectivity and scale was studied (i.e. using a Sephadex LH-20 gel column and a reversed phase). Fractions obtained by both procedures were used for a detailed analysis. MS and μLC/MS(2) methods were used for monitoring anthocyanin and 5-methylpyranoderivatives content as well as identifying less common and more complex dyes (dimer of cyanidin-3-hexoside, cyanidin-ethyl-catechin-hexosides, etc.). These more complex dyes are most likely formed during fruit treatment. 相似文献