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741.
Kämmer E Dörfer T Csáki A Schumacher W Da Costa Filho PA Tarcea N Fritzsche W Rösch P Schmitt M Popp J 《The journal of physical chemistry. C, Nanomaterials and interfaces》2012,116(10):6083-6091
UV-SERS measurements offer a great potential for environmental or food (detection of food contaminats) analytics. Here, the UV-SERS enhancement potential of various kinds of metal colloids, such as Pd, Pt, Au, Ag, Au-Ag core-shell, and Ag-Au core-shell with different shapes and sizes, were studied using melamine as a test molecule. The influence of different activation (KF, KCl, KBr, K(2)SO(4)) agents onto the SERS activity of the nanomaterials was investigated, showing that the combination of a particular nanoparticle with a special activation agent is extremely crucial for the observed SERS enhancement. In particular, the size dependence of spherical nanoparticles of one particular metal on the activator has been exploited. By doing so, it could be shown that the SERS enhancement increases or decreases for increasing or decreasing size of a nanoparticle, respectively. Overall, the presented results demonstrate the necessity to adjust the nanoparticle size and the activation agent for different experiments in order to achieve the best possible UV-SERS results. 相似文献
742.
Juliano C.R. Freitas Túlio R. Couto Antônio A.S. Paulino João R. de Freitas Filho Ivani Malvestiti Roberta A. Oliveira Paulo H. Menezes 《Tetrahedron》2012,68(41):8645-8654
Catalytic amounts of tellurium(IV) tetrachloride were used to promote the O-glycosylation of 3,4,6-tri-O-acetyl-d-glucal to give the corresponding 2,3-unsaturated-O-glycosides. With simple alcohols, the desired compounds were obtained in good yields and excellent anomeric selectivity in a short reaction time using only 2 mol % of the catalyst. The application of the method in the synthesis of a small set of glycopyranosides with rigid or flexible linkers gave the corresponding α anomers as products in good yields. Further applications of some of the synthesized compounds in allylation reaction of aldehydes gave the corresponding homoallylic alcohols in good yields. 相似文献
743.
In this work, a hydrophilic clay, Na-montmorillonite from Wyoming, USA, was rendered organophilic by exchanging the inorganic interlayer cations for hexadecyltrimethylammonium ions (HDTA), with the formulae of [(CH3)3N(C16H33)]+ ion. Based on fact that organo-clay has high affinities for non-ionic organic molecules, 1,3,4-thiadiazole-2,5-dithiol was loaded on the HDTA-montmorillonite surface, resulting in the 1,3,4-thiadiazole-2,5-dithiol-HDTA-montmorillonite complex (TDD-organo-clay).The following properties of TDD-organo-clay are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II).The main point of this paper is the construction of a selective sensor, a carbon paste electrode modified with TDD-organo-clay, its properties and its application to the determination of mercury(II) ions, as this element belongs to the most toxic metals. The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. 相似文献
744.
Sanchez-Carrera RS Coropceanu V da Silva Filho DA Friedlein R Osikowicz W Murdey R Suess C Salaneck WR Brédas JL 《The journal of physical chemistry. B》2006,110(38):18904-18911
The vibrational coupling in the ground and excited states of positively charged naphthalene, anthracene, tetracene, and pentacene molecules is studied on the basis of a joint experimental and theoretical study of ionization spectra using high-resolution gas-phase photoelectron spectroscopy and first-principles correlated quantum-mechanical calculations. Our theoretical and experimental results reveal that, while the main contribution to relaxation energy in the ground state of oligoacene systems comes from high-energy vibrations, the excited-state relaxation energies show a significant redistribution toward lower-frequency vibrations. A direct correlation is found between the nature of the vibronic interaction and the pattern of the electronic state structure. 相似文献
745.
A simple and rapid method based on solid-phase micro extraction (SPME) technique followed by gas chromatography-mass spectrometry with selected ion monitoring (GC-MS, SIM) was developed by the simultaneous determination of 16 pesticides of seven different chemical groups [Six organophosphorus (trichlorfon, diazinon, methyl parathion, malathion, fenthion and ethyon), three pyrethroids (bifenhin, permethrin, cypermethrin), two imidazoles (imazalil and prochloraz), two strobilurins (azoxystrobin and pyraclostrobin), one carbamate (carbofuran), one tetrazine (clofentezine), and one triazole (difenoconazole)] in water. The pesticides extraction was done with direct immersion mode (DI-SPME) of the polyacrilate fiber (PA 85 µm). The extraction temperature was adjusted to 50 °C during 30 min, while stirring at 250 rpm was applied. After extraction, the fiber was introduced in the GC injector for thermal desorption for 5 min. at 280 °C. The method was validated using ultra pure water samples fortified with pesticides at different concentration levels and shows good linearity in the concentrations between 0.05 and 250.00 ng mL− 1. The LOD and LOQ ranged, from 0.02 to 0.30 ng mL− 1 and 0.05 to 1.00 ng mL− 1, respectively. Intra-day and inter-day precisions were determined in two concentration levels (5.00 and 50.00 ng mL− 1). Intra-day relative standard deviation (%R.S.D.) ranged between 3.6 and 13.6%, and inter-day (%R.S.D.) ranged between 6.3 and 18.5%. Relative recovery tests were carried out spiking the ultra pure sample with standards in three different concentration levels 0.20, 5.00 and 50.00 ng mL− 1. The recovery at 0.20 ng mL− 1 level varied from 86.4 ± 9.4% to 108.5 ± 10.5%, at 5.00 ng mL− 1 level varied from 77.5 ± 10.8% to 104.6 ± 9.6% and at 50.00 ng mL− 1 level varied from 70.2 ± 4.6% to 98.4 ± 8.5%. The proposed SPME method was applied in twenty-six water samples collected in the “Platô de Neópolis”, State of Sergipe, Brazil. Methyl parathion was detected in five samples with an average concentration of 0.17 ng mL− 1 and bifenthrin, pyraclostrobin and azoxystrobin residues were found in three samples with average concentrations of 2.28, 3.12 and 0.15 ng mL− 1, respectively. 相似文献
746.
Luiza Placidina da Luz Pedro José Sanches Filho Elina Bastos Caramão 《Microchemical Journal》2010,96(1):161-166
This paper describes the extraction and analysis of Polyaromatic Hydrocarbons (PAHs) in five points of the Patos Lagoon Estuary. These points were in the area named “colony Z3”, which is a craft fishermen community in Pelotas City (southern Brazil). Samples were collected in July of 2007, and the concentrations of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography coupled to a mass spectrometry detector (GC/MS). The PAH concentrations ranged from 4.7 to 112.5 µg kg− 1 dry weight. Sediment samples with the highest PAH concentrations appeared at point 2, which is a pier. The correlation between the total organic material (TOM) and the total PAH concentration suggests that TOM plays an important role in controlling the PAH levels in sediments. According to the observed ratios of individual PAHs, the contamination in the studied areas originated both from high-temperature pyrolytic processes and petrogenic sources. The levels of PAHs at the studied sites in the Z3 colony (Patos Lagoon) were low enough that they should not exert adverse biological effects. 相似文献
747.
Betânia H. Lunelli Rafael R. Andrade Daniel I. P. Atala Maria Regina Wolf Maciel Francisco Maugeri Filho Rubens Maciel Filho 《Applied biochemistry and biotechnology》2010,161(1-8):227-237
Lactic acid is an important product arising from the anaerobic fermentation of sugars. It is used in the pharmaceutical, cosmetic, chemical, and food industries as well as for biodegradable polymer and green solvent production. In this work, several bacterial strains were isolated from industrial ethanol fermentation, and the most efficient strain for lactic acid production was selected. The fermentation was conducted in a batch system under anaerobic conditions for 50 h at a temperature of 34 °C, a pH value of 5.0, and an initial sucrose concentration of 12 g/L using diluted sugarcane molasses. Throughout the process, pulses of molasses were added in order to avoid the cell growth inhibition due to high sugar concentration as well as increased lactic acid concentrations. At the end of the fermentation, about 90% of sucrose was consumed to produce lactic acid and cells. A kinetic model has been developed to simulate the batch lactic acid fermentation results. The data obtained from the fermentation were used for determining the kinetic parameters of the model. The developed model for lactic acid production, growth cell, and sugar consumption simulates the experimental data well. 相似文献
748.
Christine Bachoc Gabriele Nebe Fernando Mário de Oliveira Filho Frank Vallentin 《Geometric And Functional Analysis》2009,19(3):645-661
The Lovász theta function provides a lower bound for the chromatic number of finite graphs based on the solution of a semidefinite
program. In this paper we generalize it so that it gives a lower bound for the measurable chromatic number of distance graphs
on compact metric spaces.
In particular we consider distance graphs on the unit sphere. There we transform the original infinite semidefinite program
into an infinite linear program which then turns out to be an extremal question about Jacobi polynomials which we solve explicitly
in the limit. As an application we derive new lower bounds for the measurable chromatic number of the Euclidean space in dimensions
10, . . . , 24 and we give a new proof that it grows exponentially with the dimension. 相似文献
749.
Determination of the chemical oxygen demand (COD) using a copper electrode: a clean alternative method 总被引:1,自引:0,他引:1
Claudineia R. Silva Cleone D. C. Conceição Viviane G. Bonifácio Orlando Fatibello Filho Marcos F. S. Teixeira 《Journal of Solid State Electrochemistry》2009,13(5):665-669
A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as
an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater.
The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on
analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l−1 COD with detection limit of 20.3 mg l−1 COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The
results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate)
COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end
products do not contain toxic metals. 相似文献
750.
Soraya Alves de Morais Crislene Rodrigues da Silva Morais Petr?nio Filgueiras de Athayde Filho B. Freitas Lira Railda Shelsea Taveira Rocha do Nascimento 《Journal of Thermal Analysis and Calorimetry》2009,97(2):437-441
The mesoionic compounds are pentagonal heterocyclic betaines with their potential use mainly in the pharmacology field due
to the diversity of their biological activities. Their exceptional electric properties lead the compounds to be investigated
in the field such as the nonlinear optical devices. In this study, five mesoionic compounds of the 1,3-thiazole-5-thiolate
system had been synthesized from amino acids derived from glycine through 1,3-dipolar cycloaddition/cycloreversion reaction.
The compounds were characterized by the use of infrared spectrometry, thermogravimetry and differential scanning calorimetry
techniques. Thermal stability of each structure was determined and characterized by the kinetic study of the thermal decomposition
by non-isothermal thermogravimetry. The DSC curves for MI-1, MI-2, MI-3, MI-4, and MI-5 demonstrated their fusion and subsequent
decomposition with the exception of MI-3, which presented only decomposition stages. The kinetic models that better described
the thermal decomposition mechanism of the mesoionic compounds achieved by the non-isothermal methods were R1, R2 and R3 (based
on the geometric models). 相似文献