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121.
P.M.A. de Farias B.S. Santos F.D. Menezes A.G. Brasil Jr. R. Ferreira M.A. Motta A.G. Castro-Neto A.A.S. Vieira D.C.N. Silva A. Fontes C.L. Cesar 《Applied Physics A: Materials Science & Processing》2007,89(4):957-961
Fluorescent semiconductor nanocrystals in quantum confinement regime (quantum dots) present several well-known features which
make them very useful tools for biological labeling purposes. Low photobleaching rates, high chemical stability and active
surface allowing conjugation to living cells explain the success of this labeling procedure over the commonly used fluorescent
dyes. In this paper we report the results obtained with highly fluorescent core–shell CdTe–CdS (diameter=3–7 nm) colloidal
nanocrystals synthesized in aqueous medium and conjugated to glucose molecules. The conjugated nanocrystals were incubated
with living yeast cells, in order to investigate their glucose up-take activity in real time, by confocal microscopy analysis.
PACS 87.83.+a; 61.46.Hk; 81.07.Ta 相似文献
122.
Magda B. Fontes Sergey L. Bud'ko Mucio A. Continentino Elisa M. Baggio-Saitovitch 《Physica B: Condensed Matter》1999,270(3-4)
In this work we present a magnetoresistance study on the CeRu2Ge2 compound. We analyze the ρ(T) curves for several applied magnetic fields using the electron–magnon scattering model for a ferromagnetic spin arrangement. From this analysis, the field dependence of the energy gap of the magnon spectrum is obtained. The magnetoresistance ρ(H) at various temperatures arises from a normal metal contribution with an additional scattering mechanism due to electron–magnon interaction. 相似文献
123.
Andr Augusto Gomes Faraco Jos Dias De Souza Filho Maria Auxiliadra Fontes Prado Ricardo Jos Alves Renata Fontes Prado Norma Beatriz D'Accorso 《Journal of heterocyclic chemistry》1999,36(5):1129-1133
The tetrazoles 5-(6′-acetamido-6′-deoxy-1′,2′:3′,4′-di-O-isopropylidene-D-glycero-α-D-galactohexopyranos-6′-yl)tetrazole ( 1 ) and 5-(6′-acetamido-6′-deoxy-1′,2′:3′,4′–di-O-isopropylidene-L-glycero-α-D-galacto-hexopyranos-6′-yl)-tetrazole ( 2 ) were synthesized by the 1,3-dipolar cycloaddition reaction of the epimeric α-acetamidonitriles 5 and 6 , respectively, with sodium azide. Reaction of tetrazole 1 with acetic anhydride in the presence of pyridine afforded the N-acetyl-1,3,4-oxadiazole derivative 3 and the N-acetylacetamido-1,3,4-oxadiazole derivative 7 . The N-acetylacetamido-1,3,4-oxadiazole derivative ( 8 ) was isolated when the tetrazole 2 was allowed to react under the same conditions. The physical and spectroscopic data of the five new compounds 1, 2, 3, 7 and 8 are presented. 相似文献
124.
Magnus Fontes 《偏微分方程通讯》2013,38(3-4):681-702
125.
126.
Fontes M Verdaguer X Solà L Pericàs MA Riera A 《The Journal of organic chemistry》2004,69(7):2532-2543
Here we report the use of 2-piperidino-1,2,2-triphenylethanol (5) as an outstanding catalyst for the ligand-catalyzed arylation of aldehydes. The use of 5 and a 2/1 mixture of Et(2)Zn/Ph(2)Zn provided the corresponding chiral diarylcarbinols with enantiomeric excess of up to 99% ee. The effect of temperature on the reaction enantioselectivity was studied and the inversion temperature (T(inv)) was determined to be 10 degrees C for reaction with p-tolylaldehyde. Most remarkably, lowering the amount of catalyst (5) to 0.5 mol % still afforded excellent levels of enantiocontrol (93.7% ee). Kinetics of the catalyzed and uncatalyzed arylation of aldehydes was studied by means of in situ FT-IR. The background uncatalyzed addition rates to p-tolylaldehyde when using pure Ph(2)Zn and Et(2)Zn/Ph(2)Zn (2/1) suggest that in the latter case a mixed zinc species forms (EtPhZn) minimizing the undesired nonselective addition. Formation of EtPhZn was modeled at the DFT calculation level. A four-center TS (TS-V) corresponding to the Et/Ph scrambling was localized along with two dimers (D-IV and D-VI). The model supports the hypothesis that Et/Ph exchange is a kinetically facile process. Gas evolution experiments during the formation of the active catalyst showed that the formation of an active site with a ONZn-Et (10) moiety is kinetically favored over ONZn-Ph (11). Finally, the phenyl transfer to benzaldehyde was modeled at the PM3(tm) level through anti and syn 5/4/4 tricyclic TS structures for both 10 and 11. The model could correctly predict the sense and selectivity of the overall process and predicted that 11 should be more selective than 10. 相似文献
127.
128.
Soares Fontes Ana Paula Guerra Wendell Cavalieri Machado Flávia de Almeida Mauro Vieira Andrade Alves Wendel da Costa Ferreira Ana Maria Paduan-Filho Armando 《Transition Metal Chemistry》2004,29(4):382-387
Two new copper(II) complexes, [Cu2(L1)4(H2O)2](SO4)4· 2H2O and [Cu(L2)2(H2O)2]SO4, were isolated containing 2-furoic hydrazide and 5-nitro-2-furoic hydrazide ligands, respectively. The complexes were characterized by thermal, magnetic and spectroscopic techniques, showing a distorted tetragonal environment around the metal ion. Compound (1), containing 2-furoic hydrazide as the ligand, appears to be dimeric in the solid state, with substituted hydrazine acting as a bidentate bridging ligand. On the contrary, a monomeric species was observed with the 5-nitro-2-furoic hydrazide ligand, probably in the cis configuration, for compound (2). Magnetic measurements for the binuclear copper(II) complex (1) were carried out at low temperatures, in the 2–300 K range, and a magnetic field of 500 G, indicating that besides an intramolecular ferromagnetic interaction between the two Cu(II) centers, for which J/k = 1.07 K, further weak antiferromagnetic interactions between adjacent dimers, with Jz/k =–0.95 K, should be taken into account. However, in MeOH/H2O solution, evidence of equilibria involving the dimer (1) and the corresponding mononuclear cis and trans species was obtained from e.p.r. spectra. 相似文献
129.
Paulo A. Pereira Fernando A. C. C. Fontes Dalila B. M. M. Fontes 《Mathematical Programming》1976,10(1):409-412
Notice
Mathematical programming study 4Computational Practice in Mathematical Programming 相似文献130.
Sirlane G. da Silva Eric H. Fontes Mônica H.M.T. Assumpção Marcelo Linardi Estevam Spinacé Júlio César M. Silva Almir O. Neto 《Ionics》2017,23(9):2367-2376
Ethanol electro-oxidation reaction was investigated considering conventional electrochemical experiments in alkaline media, direct ethanol fuel cell (DEFC), and in situ ATR-FTIR. The working electrode/anodes were composed of monometallic Pt/C, Au/C, Ir/C, and trimetallic PtAuIr/C nanoparticles with atomic Pt/Au/Ir ratios of 40:50:10, 50:40:10, 60:30:10, 70:20:10, and 80:10:10. X-ray diffraction (XRD) suggests PtAuIr/C alloy formation, and according to transmission electron micrographs, the mean particle sizes are from 4 to 6 nm for all catalyst compositions. PtAuIr/C 40:50:10 showed the highest catalytic activity for ethanol electro-oxidation in the electrochemical experiments; using this material, the peak current density from ethanol electro-oxidation on cyclic voltammetry experiment was 50 mA per g of Pt, 3.5 times higher than that observed with Pt/C. The fuel cell performance was superior using all PtAuIr/C compositions than using Pt/C. Au/C and Ir/C presented very poor catalytic activity toward ethanol electro-oxidation. The improved results obtained using PtAuIr/C might be related to the OHads species formed at low overpotential on Ir and to the decrease on adsorption energy of poisoning intermediates on Pt sites, promoted by Au. 相似文献