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31.
Highly enantiomerically enriched N-protected α-amino acids can be easily prepared from optically pure N-(tert-butanesulfinyl)imines by a four-step sequence involving: diastereoselective addition of a triorganozincate to the imine, removal of the sulfinyl group, benzoylation of the nitrogen atom of the obtained primary amine and oxidation of one of the substituents on the carbon atom α to the nitrogen. Using the same configuration in the sulfinyl chiral auxiliary, amino acids with the (R) or the (S) configuration can be prepared by choosing the proper combination of imine and organozincate. α,α-Disubstituted α-amino esters with high optical purity can also be prepared by the diastereoselective addition of trialkylzincates to α-imino esters. 相似文献
32.
Raquel Fernndez Borja Fernndez dArlas Patricia A. Oyanguren Iaki Mondragon 《Thermochimica Acta》2009,493(1-2):6-13
Novel fluorescent materials were satisfactorily synthesized. With this aim, an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) was reacted with a laser dye, rhodamine B (RB), to achieve an epoxy-based prepolymer. Then, a diamine, m-xylylenediamine (MXDA), was used as hardener with the purpose of obtaining a crosslinked polymer. The curing conditions strongly influence the intended final properties and the optimization of the curing requires a reliable kinetic model. For that reason, this work presents the kinetic study of the polymerization of the epoxy resin by differential scanning calorimetry (DSC) in isothermal mode as well as by Fourier transform infrared spectroscopy (FTIR). DSC data were fitted using a Kamal autocatalytic equation. Conversion as a function of reaction time curves obtained by means of both techniques agreed well. In addition, the synthesized epoxy-based materials were characterized by proton nuclear magnetic resonance spectroscopy (1H NMR) and their fluorescent properties were also analysed. 相似文献
33.
Craig Aalseth Erica Andreotti Dirk Arnold Joan-Albert Sanchez Cabeza Detlev Degering Andrea Giuliani Raquel Gonzales de Orduña Rodolfo Gurriaran Mikael Hult Martin Keillor Matthias Laubenstein Gilbert le Petit Romul Mircea Margineanu Murray Matthews Harry Miley Iolanda Osvath Monica Pellicciari Wolfango Plastino Hardy Simgen Marc Weber Robert Werzi 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):731-735
Aerosol samples collected on filter media were analyzed using HPGe detectors employing varying background-reduction techniques in order to experimentally evaluate the opportunity to apply ultra-low background measurement methods to samples collected, for instance, by the Comprehensive Test Ban Treaty International Monitoring System (IMS). In this way, realistic estimates of the impact of low-background methodology on the sensitivity obtained in systems such as the IMS were assessed. The current detectability requirement of stations in the IMS is 30 μBq/m3 of air for 140Ba, which would imply ~106 fissions per daily sample. Importantly, this is for a fresh aerosol filter. One week of decay reduces the intrinsic background from radon daughters in the sample allowing much higher sensitivity measurement of relevant isotopes, including 131I. An experiment was conducted in which decayed filter samples were measured at a variety of underground locations using Ultra-Low Background (ULB) gamma spectroscopy technology. The impacts of the decay and ULB are discussed. 相似文献
34.
Joubert Trovati Roberto C. Giordano Raquel L. C. Giordano 《Applied biochemistry and biotechnology》2009,156(1-3):76-90
In a previous work, a continuous simultaneous saccharification and fermentation process to produce ethanol from cassava starch was studied, using a set of fixed-bed reactors. The biocatalyst consisted of glucoamylase immobilized in silica particles and co-immobilized with S. cerevisiae in pectin gel. Using 3.8 U mL?1 reactor and 0.05 gwet yeast mL?1 reactor at start-up, starch hydrolysis was the rate-limiting step. Maximum ethanol productivity was 5.8 gethanol L?1 h?1, with 94.0% conversion of total reducing sugars (TRS) and 83.0% of the ethanol theoretical yield. In this work, the molar mass of the substrate and the biocatalyst particle size were reduced in an attempt to improve the bioreactor performance. The diameters of silica and pectin gel particles were reduced from 100 μm and 3–4 mm, respectively, to 60 μm and 1–1.5 mm, and the degree of substrate prehydrolysis by α-amylase was increased. The bioreactor performance was assessed for different loads of immobilized glucoamylase (2.1, 2.8, and 3.8 U mL?1 reactor), for the same initial cell concentration (0.05 gwet yeast.mL?1 reactor). Feeding with 154.0 g L?1 of TRS and using 3.8 U mL?1 reactor, fermentation became the rate-limiting step. Productivity reached 11.7 g L?1 h?1, with 97.0% of TRS conversion and 92.0% of the ethanol theoretical yield. The reactor was operated during 275 h without any indication of destabilization. 相似文献
35.
Numerical Algorithms - A method for solving least squares problems (A ? Bi)x = b whose coefficient matrices have generalized Kronecker product structure is presented. It is based on the... 相似文献
36.
Paulo J. Amorim Madeira Ana Raquel Fernandes Sitoe Daniel Gonçalves Tiago Rodrigues Rita C. Guedes Francisca Lopes Rui Moreira M. Rosário Bronze 《Journal of the American Society for Mass Spectrometry》2014,25(9):1650-1661
The gas-phase behavior of 12 quinolon-4(1H)-imine derivatives with antiplasmodial activity was investigated using electrospray ionization tandem mass spectrometry together with collision induced dissociation and density functional theory (DFT) calculations. The most probable protonation site was predicted by calculating the proton affinity (PA) values for each possible protonation site and it was found to be the imine nitrogen for all compounds under study. Fragmentation pathways of the protonated molecules were proposed and the assignment of product ion structures was performed taking into account theoretical calculations. The nature of the quinoline substituent was found to influence the gas-phase behavior of the compounds under study. The data acquired allowed to bracket the proton affinity of the quinolin-4-imine scaffold, which can be a useful starting point to choose appropriate references for determining PA values of this scaffold. Figure
? 相似文献
37.
Carlyle T. B. Menezes Erilson C. Barros Raquel D. Rufino Juliana M. Luna Leonie A. Sarubbo 《Applied biochemistry and biotechnology》2011,163(4):540-546
Dissolved air flotation (DAF) is a well-established separation process employing micro bubbles as a carrier phase. The application
of this technique in the treatment of acid mine drainage, using three yeast biosurfactants as alternative collectors, is hereby
analyzed. Batch studies were carried out in a 50-cm high acrylic column with an external diameter of 2.5 cm. High percentages
(above 94%) of heavy metals Fe(III) and Mn(II) were removed by the biosurfactants isolated from Candida lipolytica and Candida sphaerica and the values were found to be similar to those obtained with the use of the synthetic sodium oleate surfactant. The DAF
operation with both surfactant and biosurfactants, achieved acceptable turbidity values, in accordance with Brazilian standard
limits. The best ones were obtained by the biosurfactant from C. lipolytica, which reached 4.8 NTU. The results obtained with a laboratory synthetic effluent were also satisfactory. The biosurfactants
removed almost the same percentages of iron, while the removal percentages of manganese were slightly higher compared with
those obtained in the acid mine drainage effluent. They showed that the use of low-cost biosurfactants as collectors in the
DAF process is a promising technology for the mining industries. 相似文献
38.
Raquel G. Soengas 《Tetrahedron letters》2010,51(1):105-574
Indium-mediated Reformatsky reactions of simple lactones and aldonolactones with ethyl α-bromoisobutyrate allow the synthesis of the corresponding ketals and ulosonic acid esters, respectively, in good yields. 相似文献
39.
Antonia Camacho Montserrat Montaña Isabel Vallés Ricard Devesa Raquel Céspedes-Sánchez Isabel Serrano 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(1):297-306
22 sludge samples were analyzed from three municipal wastewater treatment plants to assess both the occurrence and the temporal behavior of radioactivity during 8 sampling campaigns carried out over the period 2007–2009. As regards natural gamma emitters radionuclides from the natural 238U series (such as 234Th, 214Pb, 214Bi, 210Pb) and the 232Th series (such as 228Ac, 212Pb, 212Bi and 208Tl) and other natural gamma emitters such as 7Be, 210Pbu or 40K were measured. In the case of man-made radionuclides small amounts of 137Cs were found, while significant amounts of 131I were detected in some samples. Correlations were found between radionuclides with the same origin. No seasonal variation for the 238U and 232Th series was found in the studied period but 7Be and 210Pbu showed seasonal variation that was explained by the monthly rainfall. The internal and external hazard indices were calculated and the results indicate that the radiological characteristics of the sludge do not present a significant radiological risk and make them suitable for future applications. 相似文献
40.
Raquel da Silva Cabral Andre L. L. Aquino Alejandro C. Frery Osvaldo A. Rosso Jaime A. Ramírez 《Central European Journal of Physics》2013,11(12):1645-1652
Wireless sensor networks are an important technology for making distributed autonomous measures in hostile or inaccessible environments. Among the challenges they pose, the way data travel among them is a relevant issue since their structure is quite dynamic. The operational topology of such devices can often be described by complex networks. In this work, we assess the variation of measures commonly employed in the complex networks literature applied to wireless sensor networks. Four data communication strategies were considered: geometric, random, small-world, and scale-free models, along with the shortest path length measure. The sensitivity of this measure was analyzed with respect to the following perturbations: insertion and removal of nodes in the geometric strategy; and insertion, removal and rewiring of links in the other models. The assessment was performed using the normalized Kullback-Leibler divergence and Hellinger distance quantifiers, both deriving from the Information Theory framework. The results reveal that the shortest path length is sensitive to perturbations. 相似文献