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161.
Valle MS Saraiva MF Retailleau P de Almeida MV Dodd RH 《The Journal of organic chemistry》2012,77(13):5592-5599
4-Hydroxymethylbutenolide 4 was transformed into its sulfamoyl derivative 5, which upon treatment with iodosobenzene diacetate and magnesium oxide in the presence of a rhodium catalyst afforded the product of intramolecular aziridination 6. Reaction of 6 with primary or secondary amines in DMA led to regioselective opening of the aziridine ring at C2 to give the corresponding bicyclic derivatives 7a-7g in good to excellent yields. Methanolysis of the lactone ring of the N-benzyl-N-methyl derivative 7c followed by protection of the resulting secondary hydroxy group and treatment of the product with Boc anhydride provided the activated cyclic sulfamates 13 and 14. The latter then reacted with a second nucleophile (azide or thiophenol) to give the corresponding difunctionalized α,β-diamino methyl esters 15-18, 20. 相似文献
162.
The cationic halochromism of phenolate betaines was reproduced with the aid of a simple theoretical model, by calculation of the longest wavelength transition energies of supermolecules obtained by positioning a cation Mn+ at a variable distance from the oxygen atom of the dye. The theoretical results were compared with experimental data for three systems, Reichardt’s betaine 1, Brooker’s merocyanine 2 and the N-methyl-8-oxyquinolinium dye 3. The model was validated by molecular dynamics simulations of solutions of dye 3, in methanol and DMSO, in the presence of variable concentrations of Na+. 相似文献
163.
B. N. Sismanoglu K. G. Grigorov R. Caetano M. V.O. Rezende Y. D. Hoyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,60(3):505-516
This paper is dedicated to the study of the electrical and optical
characteristics of direct current microhollow cathode discharges (MHCD) in
argon flow. Experiments have been carried out in order to determine the
so-called Paschen’s curves in a static open MHCD. Current-voltage
characteristics were obtained as a function of the pressure and hole
diameter. MHCD enable stable direct current discharge operation, which could
be ignited for pressures ranging from 12 to 800 Torr, in a very wide range of
current densities and electrodes materials. Optical emission spectroscopy
and analysis of the spectral line broadening of plasma line emissions were
performed in order to measure parameters such as electron number density (2–4 × 1014 cm-3)^{-3}), gas
temperature (460–640 K), excitation
temperature (~ 7000 K) and electron temperature (~ 8500 K), for
current ranging from 7 to 15 mA. Lower gas temperature was measured compared
to the static MHCD ones. 相似文献
164.
Tânia Maria Monteiro Janaína Marques Rodrigues Eliane Cristina Pires do Rego Werickson Fortunato de Carvalho Rocha Juliana Swensson de Mattos Fernanda Figueiredo Nunes Valnei Smarçaro da Cunha Marcus Henrique Campino de la Cruz Vanderléa de Souza 《Accreditation and quality assurance》2013,18(3):197-206
Cachaça is the typical and genuine denomination for the sugar cane beverage produced in Brazil. It has an alcoholic content between 38 and 48 % by volume, at 20 °C, and is obtained from the distillation of fermented sugar cane juice with the possible addition of up to 6 g/L of sugar, expressed by sucrose. This paper aims to outline the approach taken for the certification of the mass fraction of individual alcohols and their associated uncertainties in a cachaça certified reference material (CRM) produced by the Organic Analysis Laboratory of the Chemical Metrology Division of Inmetro. The requirements of ISO Guide 31, ISO Guide 34 and ISO Guide 35 were followed for the certification. This included the assessment of the degree of homogeneity of the material, the short-term stability study to determine the transport conditions, the long-term stability study to establish the shelf life and storage conditions of the CRM and the characterization process. The certified values were determined by two analytical techniques: gas chromatography coupled to mass spectrometry and gas chromatography with flame ionization detection. In order to support the routine testing of cachaça, in helping analytical laboratories validate and standardize their methods, the certified reference material (CRM 02.1/10.003b) was developed and certified for the mass fractions of methanol (9.18 mg/100 g ± 0.82 mg/100 g), 2-butanol (4.15 mg/100 g ± 0.40 mg/100 g), 1-butanol (1.30 mg/100 g ± 0.18 mg/100 g), isobutanol (24.0 mg/100 g ± 1.0 mg/100 g) and 1-propanol (29.4 mg/100 g ± 1.3 mg/100 g) in a spiked cachaça. 相似文献
165.
Gabriele H. Greco Maria Pia Moschen Eliane Quelho Frota Rezende 《Annali dell'Universita di Ferrara》1998,44(1):27-39
Kaleva [9] has studied the relationships between the metric convergencesH andD of fuzzy convex sets on Euclidean spaces. The distanceH between two fuzzy set is given by Hausdorff distance of their sendographs, whileD is the supremum of the Hausdorff distances of the level sets corresponding to the fuzzy sets. The aim of this paper is to
compareH andD with the variational convergence, called γ-convergence (see De Giorgi and Franzoni [3]). Our analysis which is carried out
in the setting of metric spaces (not necessarily locally compact or vector spaces), improves Kaleva's results.
Sunto Kaleva ha investigato in [9] le relazioni esistenti tra due convergenze metriche, detteH eD, di sottoinsiemi fuzzy di spazi euclidei finito-dimensionali. In questo articolo le convergenzeH eD (la loro definizione dipende dalla distanza di Hausdorff tra insiemi compatti) sono confrontate con la convergenza variazionale, detta γ-convergenza, introdotta da De Giorgi and Franzoni in [3] nel contesto degli spazi topologici. Tale confronto con la γ-convergenza (vedi Teorema 3.7), svolto nell'ambito degli spazi metrici (non necessariamente, localmente compatti o lineari) migliora ed estende i precedenti risultati di Kaleva.相似文献
166.
Sicard D Cecioni S Iazykov M Chevolot Y Matthews SE Praly JP Souteyrand E Imberty A Vidal S Phaner-Goutorbe M 《Chemical communications (Cambridge, England)》2011,47(33):9483-9485
Atomic force microscopy reveals that Pseudomonas aeruginosa LecA (PA-IL) and a tetra-galactosylated 1,3-alternate calix[4]arene-based glycocluster self-assemble according to an aggregative chelate binding mode to create monodimensional filaments. Lectin oligomers are identified along the filaments and defects in chelate binding generate branches and bifurcations. A molecular model with alternate 90° orientation of LecA tetramers is proposed to describe the organisation of lectins and glycoclusters in the filaments. 相似文献
167.
Pieroni LG de Rezende FM Ximenes VF Dokkedal AL 《Molecules (Basel, Switzerland)》2011,16(11):9439-9450
Miconia is one of the largest genus of the Melastomataceae, with approximately 1,000 species. Studies aiming to describe the diverse biological activities of the Miconia species have shown promising results, such as analgesic, antimicrobial and trypanocidal properties. M. albicans leaves were dried, powdered and extracted to afford chloroformic and methanolic extracts. Total phenolic contents in the methanolic extract were determined according to modified Folin-Ciocalteu method. The antioxidant activity was measured using AAPH and DPPH radical assays. Chemical analysis was performed with the n-butanol fraction of the methanolic extract and the chloroformic extract, using different chromatographic techniques (CC, HPLC). The structural elucidation of compounds was performed using 500 MHz NMR and HPLC methods. The methanolic extract showed a high level of total phenolic contents; the results with antioxidant assays showed that the methanolic extract, the n-butanolic fraction and the isolated flavonoids from M. albicans had a significant scavenging capacity against AAPH and DPPH. Quercetin, quercetin-3-O-glucoside, rutin, 3-(E)-p-coumaroyl-α-amyrin was isolated from the n-butanolic fraction and α-amyrin, epi-betulinic acid, ursolic acid, epi-ursolic acid from the chloroformic extract. The results presented in this study demonstrate that M. albicans is a promising species in the search for biologically active compounds. 相似文献
168.
This present work reports the development and evaluation of a method for the direct determination of manganese in waters extracted during petroleum exploitation by Electrothermal Atomic Absorption Spectrometry (ET AAS) using Ir-W as permanent modifier. These waters, usually called produced waters, contain a wide range of organic and inorganic substances and are characterized by their high salinity. In order to achieve suitable experimental conditions for the method application, studies about the effect of operational variables (chemical modifier, pyrolysis and atomization temperatures) were performed, as well as the establishment of convenient calibration strategy. The best results were verified when the temperatures of pyrolysis and atomization were 1000 °C and 2300 °C, respectively, and using Ir-W as permanent modifier. The results showed that manganese can be determined by the standard addition method or employing external calibration with standard solutions prepared in the same salinity of the samples (with NaCl). Three real samples with salinities varying between 74 and 84‰ were successfully analyzed by the developed procedure. The limits of detection and quantification were 0.24 and 0.80 μg L−1, respectively, in purified water, and 0.34 and 1.1 μg L−1, respectively, in 0.4 mol L−1 NaCl medium (approximately 23‰ salinity). 相似文献
169.
Ferreira JG Reis AP Guimarães VM Falkoski DL Fialho Lda S de Rezende ST 《Applied biochemistry and biotechnology》2011,164(7):1111-1125
α-Galactosidases has the potential to hydrolyze α-1-6 linkages in raffinose family oligosaccharides (RFO). Aspergillus terreus cells cultivated on wheat bran produced three extracellular forms of α-galactosidases (E1, E2, and E3). E1 and E2 α-galactosidases
presented maximal activities at pH 5, while E3 α-galactosidase was more active at pH 5.5. The E1 and E2 enzymes showed stability
for 6 h at pH 4–7. Maximal activities were determined at 60, 55, and 50°C, for E1, E2, and E3 α-galactosidase, respectively.
E2 α-galactosidase retained 90% of its initial activity after 70 h at 50°C. The enzymes hydrolyzed ρNPGal, melibiose, raffinose
and stachyose, and E1 and E2 enzymes were able to hydrolyze guar gum and locust bean gum substrates. E1 and E3 α-galactosidases
were completely inhibited by Hg2+, Ag+, and Cu2+. The treatment of RFO present in soy milk with the enzymes showed that E1 α-galactosidase reduced the stachyose content to
zero after 12 h of reaction, while E2 promoted total hydrolysis of raffinose. The complete removal of the oligosaccharides
in soy milk could be reached by synergistic action of both enzymes 相似文献
170.
Long lasting phosphorescence in barium aluminates can be achieved by doping with rare earth ions in divalent charge states. The rare earth ions are initially in a trivalent charge state, but are reduced to a divalent charge state before being doped into the material. In this paper, the reduction of trivalent rare earth ions in the BaAl2O4 lattice is studied by computer simulation, with the energetics of the whole reduction and doping process being modelled by two methods, one based on single ion doping and one which allows dopant concentrations to be taken into account. A range of different reduction schemes are considered and the most energetically favourable schemes identified. 相似文献