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151.
Wieland LC Vieira EM Snapper ML Hoveyda AH 《Journal of the American Chemical Society》2009,131(2):570-576
An efficient diastereo- and enantioselective Ag-catalyzed method for additions of a commercially available siloxyfuran to alpha-ketoimine esters is disclosed. Catalytic transformations require an inexpensive metal salt (AgOAc) and an air stable chiral ligand that is prepared in three steps from commercially available materials in 42% overall yield. Aryl- as well as heterocyclic substituted ketoimines can be used effectively in the Ag-catalyzed process. Additionally, two examples regarding reactions of alkyl-substituted ketoimines are presented. An electronically modified N-aryl group is introduced that is responsible for high reaction efficiency (>98% conversion, 72-95% yields after purification) as well as diastereo- (up to >98:2 dr) and enantioselectivity (up to 97:3 er or 94% ee). The new N-aryl unit is crucial for conversion of the asymmetric vinylogous Mannich (AVM) products to the unprotected amines in high yields. Spectroscopic and X-ray data are among the physical evidence provided that shed light on the identity of the Ag-based chiral catalysts and some of the mechanistic subtleties of this class of enantioselective C-C bond forming processes. 相似文献
152.
Vieira EF Cestari AR de Santos EB Rezende CX 《Journal of colloid and interface science》2006,298(1):74-78
Isothermal calorimetry was used to determine enthalpy changes for interaction of divalent cobalt, nickel, copper, and zinc chlorides with silica gel functionalized with vanillin, Sil-Van. The thermal effect, Q(int), and the corresponding amount of cation that interacts, n(int), were obtained in the same experiment. Langmuir expressions for adsorption isotherms were applied to determine the maximum adsorption capacity to form a monolayer, N(mon), and the energy of interaction for a saturated monolayer per gram of Sil-Van, Q(mon). From knowledge of N(mon) and Q(mon), the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of Sil-Van, Delta(mon)H(m), was determined. Interactions between the Lewis-acidic cations and the donor atom attached to silica are reflected by Delta(mon)Hm values in the order Ni2+ > Cu2+ > Zn2+ congruent with Co2+. 相似文献
153.
Determination of parathion in biological fluids by means of direct solid-phase microextraction 总被引:1,自引:0,他引:1
Gallardo E Barroso M Margalho C Cruz A Vieira DN López-Rivadulla M 《Analytical and bioanalytical chemistry》2006,386(6):1717-1726
A new and simple procedure for the determination of parathion in human whole blood and urine using direct immersion (DI) solid-phase
microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) is presented. This technique was developed using only
100 μL of sample, and ethion was used as internal standard (IS). A 65-μm Carbowax/divinylbenzene (CW/DVB) SPME fibre was selected
for sampling, and the main parameters affecting the SPME process such as extraction temperature, adsorption and desorption
time, salt addition, agitation and pH effect were optimized to enhance the sensitivity of the method. This optimization was
also performed to allow the qualitative determination of parathion’s main metabolite, paraoxon, in blood. The limits of detection
and quantitation for parathion were 3 and 10 ng/mL for urine and 25 and 50 ng/mL for blood, respectively. For paraoxon, the
limit of detection was 50 ng/mL in blood. The method showed linearity between the LOQ and 50 μg/mL for both matrices, with
correlation coefficients ranging from 0.9954 to 0.9999. Precision and accuracy were in conformity with the criteria normally
accepted in bioanalytical method validation. The mean absolute recoveries were 35.1% for urine and 6.7% for blood. Other parameters
such as dilution of sample and stability were also validated. Its simplicity and the fact that only 100 μL of sample is required
to accomplish the analysis make this method useful in forensic toxicology laboratories to determine this compound in intoxications,
and it can be considered an alternative to other methods normally used for the determination of this compound in biological
media. 相似文献
154.
I. T. Vieira R. C. H. Cheng P. R. Harper V. de Senna 《Annals of Operations Research》2010,178(1):173-200
It has long been recognised that the structure of social networks plays an important role in the dynamics of disease propagation.
The spread of HIV results from a complex network of social interactions and other factors related to culture, sexual behaviour,
demography, geography and disease characteristics, as well as the availability, accessibility and delivery of healthcare.
The small world phenomenon has recently been used for representing social network interactions. It states that, given some
random connections, the degrees of separation between any two individuals within a population can be very small. In this paper
we present a discrete event simulation model which uses a variant of the small world network model to represent social interactions
and the sexual transmission of HIV within a population. We use the model to demonstrate the importance of the choice of topology
and initial distribution of infection, and capture the direct and non-linear relationship between the probability of a casual
partnership (small world randomness parameter) and the spread of HIV. Finally, we illustrate the use of our model for the
evaluation of interventions such as the promotion of safer sex and introduction of a vaccine. 相似文献
155.
Ricardo Elgul Samad Lilia Coronato Courrol Ademar Benévolo Lugão Anderson Zanardi de Freitas Nilson Dias Vieira 《Radiation Physics and Chemistry》2010,79(3):355-357
We report here the creation of color centers in commercial, transparent PMMA samples by ultrashort pulses from a Ti:Sapphire laser emitting at 800 nm, with spatial control. Although the 800 nm photon energy is not sufficient to ionize the polymer, the centers are created following a multiphotonic absorption that causes the ionization. We propose that the free electrons quivering motion on the pulse electric field displaces atoms from its equilibrium positions, creating free radicals and double bonds that coalesce into color centers. The absorption and emission spectra of the centers were measured, but a dose-like curve could not be built due to the presence of damages created along with the centers that scatter the excitation and emission lights due to the commercial sample's poor optical quality. 相似文献
156.
Soliu O. Ganiyu Elisama Vieira dos Santos Carlos A. Martínez-Huitle Siegfried R. Waldvogel 《Current Opinion in Electrochemistry》2022
Thin-film boron-doped diamond (BDD) electrochemistry has made a tremendous progress in electrochemical synthesis/recovery of high-added value products from aqueous and gaseous waste streams. The distinguished electrochemical characteristic of this electrode has made this material emerging and successfully used in electrosynthetic transformations, besides its destructive and powerful performance in disinfection and detoxification of wastewaters. Organic electrosynthesis is achieved by the oxyl radical oxidation formed at BDD, peroxo compounds electrosynthesis is attained by oxidation of corresponding anions at the BDD surface, whereas electrochemical conversion of SO2, CO2, NO3?, and NH3 to value-added products occurs by BDD cathodic reduction process. There are still some challenges needed to address for seamless scale-up and translation into application of this future technology. 相似文献
157.
Rubanik V. V. Bahrets D. A. Vieira D. E. L. Salak A. N. 《Russian Journal of Electrochemistry》2020,56(12):989-996
Russian Journal of Electrochemistry - Titanium nitride (TiN) coatings which were fabricated by ion-plasma deposition on medical alloys—titanium nickelide (TiNi) and stainless steel were the... 相似文献
158.
159.
Boron-doped nanocrystalline silicon thin films for solar cells 总被引:1,自引:0,他引:1
This article reports on the structural, electronic, and optical properties of boron-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The films were deposited by plasma-enhanced chemical vapour deposition (PECVD) at a substrate temperature of 150 °C. Crystalline volume fraction and dark conductivity of the films were determined as a function of trimethylboron-to-silane flow ratio. Optical constants of doped and undoped nc-Si:H were obtained from transmission and reflection spectra. By employing p+ nc-Si:H as a window layer combined with a p′ a-SiC buffer layer, a-Si:H-based p-p′-i-n solar cells on ZnO:Al-coated glass substrates were fabricated. Device characteristics were obtained from current-voltage and spectral-response measurements. 相似文献
160.
Analysis of a system related to a model for phase transitions in dissipative isochoric thermoviscoelastic materials 下载免费PDF全文
Welington Vieira Assunção José Luiz Boldrini 《Mathematical Methods in the Applied Sciences》2017,40(10):3504-3527
We analyze a highly nonlinear system of partial differential equations related to a model solidification and/or melting of thermoviscoelastic isochoric materials with the possibility of motion of the material during the process. This system consists of an internal energy balance equation governing the evolution of temperature, coupled with an evolution equation for a phase field whose values describe the state of material and a balance equation for the linear moments governing the material displacements. For this system, under suitable dissipation conditions, we prove global existence and uniqueness of weak solutions. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献