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31.
Lúcia Codognoto Eduardo Winter Keity Margareth Doretto Gabriel Bezzan Monteiro Susanne Rath 《Mikrochimica acta》2010,169(3-4):345-351
Monolayers of 2-mercapto-5-methylbenzimidazole (MMB) were prepared on a polycrystalline gold electrode via a self-assembly process to produce a self-assembled monolayer. The resulting electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy, and applied to the determination of chloramphenicol (CAP) in a pharmaceutical formulation using flow injection analysis along with amperometric detection. The amperometric cell was operated at ?0.75 V (vs Ag/AgCl) at a flow rate of 3 mL min?1. The method was applied to the determination of CAP in ophthalmic solutions, and its performance was compared to a previously validated HPLC method. The response to CAP is linear in the range from 0.050 to 1.000 µmol L?1 (r?=?0.9990), and the limit of detection is 44 µmol L?1. 相似文献
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Vanessa de Freitas Cunha Lins Laureanny MadeiraJose Mario Carneiro Vilela Margareth Spangler AndradeVicente Tadeu Lopes Buono Juliana Porto GuimarãesEvandro de Azevedo Alvarenga 《Applied Surface Science》2011,257(13):5871-5878
Hot galvanized steels have been extensively used in the automotive industry. Selective oxidation on the steel surface affects the wettability of zinc on steel and the grain orientation of inhibition layer (Fe-Al-Zn alloy) and reduces the iron diffusion to the zinc layer. The aim of this work is to identify and quantify selective oxidation on the surface of a dual phase steel, and an experimental steel with a lower content of manganese, annealed at different dew points. The techniques employed were atomic force microscopy, X-ray photoelectron spectroscopy, and glow discharge optical emission spectroscopy. External selective oxidation was observed for phosphorus on steel surface annealed at 0 °C dp, and for manganese, silicon, and aluminum at a lower dew point. The concentration of manganese was higher on the dual phase steel surface than on the surface of the experimental steel. The concentration of molybdenum on the surface of both steels increased as the depth increased. 相似文献
33.
Sylvia C.S. Teixeira Maria Margareth Moreira Aline P. Lima Luciene S. Santos Bianca M. da Rocha Edson S. de Lima Raphael A.A.F. da Costa Ana Lúcia N. da Silva Marisa C.G. Rocha Fernanda M.B. Coutinho 《Polymer Testing》2005,24(8):983-987
Calcium carbonate (CaCO3)/high density polyethylene (HDPE) composites were prepared in a HAAKE twin screw extruder. The influence of the CaCO3 particle size and content and the processing conditions were investigated by using a factorial experimental design. The dependent variables studied were tensile properties, such as Young's modulus, stress at break and toughness, and the rheological property, zero-shear viscosity, η0. Preliminary results have shown that the most significant processing variables were content and mineral filler type. Mathematical modeling has given us a more efficient evaluation of the results obtained and has become an important tool in the development of this work. 相似文献
34.
Małgorzata Brzostowska Jacek Gawroński 《Monatshefte für Chemie / Chemical Monthly》1984,115(11):1373-1376
The enantiomeric excess of the product of conjugate addition of a thioacid to 2-cyclohexenone can be increased by proper choice of the thioacid structure, concentration and modification of the structure of the chiral catalyst.
Die asymmetrische Induktion beeinflussende Faktoren bei der Addition von Thiocarbonsäuren an 2-Cyclohexen (Kurz Mitteilung)
Zusammenfassung Es konnte der enantiomere Überschuß in den Produkten aus der Addition von Thiocarbonsäuren an 2-Cyclohexen durch die Auswahl geeigneter Thiocarbonsäuren, deren Konzentration und durch Modifikation am chiralen Katalysator gesteigert werden.相似文献
35.
Frank AT Farina NS Sawwan N Wauchope OR Qi M Brzostowska EM Chan W Grasso FW Haberfield P Greer A 《Molecular diversity》2007,11(3-4):115-118
This paper examines ring size patterns of natural product macrocycles. Evidence is presented that natural macrocycles containing
14-, 16-, and 18-membered rings are of frequent occurrence based on a data mining study. The results raise a question about
the limited diversity of macrocycle ring sizes and the nature of the constraints that may cause them. The data suggest that
the preference bears no relationship to the odd–even frequency in natural fatty acids. The trends reported here, along with
those reported previously (Wessjohann et al. (2005) Mol Divers 9:171), may be generalized to better understand the possible
structure preferences of natural macrocycles. 相似文献
36.
Aebisher D Brzostowska EM Mahendran A Greer A 《The Journal of organic chemistry》2007,72(8):2951-2955
A mechanism is proposed for the formation of cyclic 5,6,7,8,9-pentathiabenzocycloheptene-1,2-diol, 4, from the reaction of o-benzoquinone with reduced elemental sulfur, H2Sx. 1,6-conjugate addition to the quinone is favored over 1,4-conjugate addition. Hydrogen bonding to the quinone oxygen enhances the nucleophilicity of H2Sx by facilitating the removal of the S-H proton. We propose that initially formed 3-polysulfidobenzene-diol intermediates are oxidized to their corresponding quinones and closure of the polysulfur ring subsequently takes place at the C3-C4 bond leading to 4. A possible mechanism for the formation of the pentasulfur linkage in 4 is discussed, which is the key moiety found in a number of natural products. 相似文献
37.
Xavier Francisco J. S. Lira Andressa B. Verissimo Gabriel C. de S. Saraiva Fernanda S. de Oliveira Filho Abrahão A. de Souza-Fagundes Elaine M. de F. F. M. Diniz Margareth Gomes Maria A. Castro Aleff C. Silva Fábio P. L. Lima-Junior Claudio G. Vasconcellos Mário L. A. A. 《Molecular diversity》2022,26(4):1969-1982
Molecular Diversity - Giardiasis is a neglected disease, and there is a need for new molecules with less side effects and better activity against resistant strains. This work describes the... 相似文献
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39.
Xiao-Shu He Dragana Tadi Malgorzata Brzostowska Arnold Brossi Maureen Bell Cyrus Creveling 《Helvetica chimica acta》1991,74(7):1399-1411
O-Methylation of the optically active 3′-hydroxycoclaurines 3a and 3b and of the N-methylated analogs 5a,b with S-adenosyl-L -[methyl-14C]methionine in presence of mammalian COMT was investigated in vitro. The N-unsubstituted (1S)- and (1R )-isomers 3a and 3b , respectively, afforded almost equal amounts of the corresponding N-norreticuline 4 and N-nororientaline 19 , besides two unknown by-products (see Fig. and Table 1). The N-methylated (1S)-isoquinoline 5a , on the other hand, afforded largely (S)-orientaline ((S)- 19 ), while an almost equal mixture of (R)-reticuline ( 6b ) and (R)-orientaline ((R)- 19 ) was obtained from the (1R)-enantiomer 5b . The isoquinolines 3a,b and 5a,b were prepared by a Bischler-Napieralski cyclization yielding O-benzyl-protected isoquinoline 10 (Scheme 1). The optical resolution of 10 was accomplished with 2′-bromotartranilic acid. The N-methylated isoquinolines were prepared by N-formylation of 10a,b and reduction of the formamides 13a,b with diborane (→ 14a,b ). Deblocking of the benzyl-ether moieties of 10a,b and 14a,b was accomplished by catalytic hydrogenation in presence of HCl, affording directly 3a,b ·HCl and 5a,b ·HCl, respectively. 相似文献
40.
This work investigated the chemiluminescent reaction of free chlorine with bis(2,4,6-(trichlorophenyl)oxalate) (TCPO) in the presence of 9,10-diphenylanthracene in acetonitrile/water medium, with analytical application for free chlorine in tap water. In the absence of free chlorine, the background signal increased with the pH and the chemiluminescence emission showed strong dependence with the sample acidity. A flow injection analysis system, for free chlorine determination, was developed. The linear range for free chlorine was (0.2-3.0)×10−5 mol l−1. Chloramine 1.0×10−5 mol l−1 and chlorite 1.0×10−6 mol l−1 also enhanced the chemiluminescence intensity. 相似文献