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101.
F. Bredice F.O. Borges H. Sobral M. Villagran-Muniz H.O. Di Rocco G. Cristoforetti S. Legnaioli V. Palleschi A. Salvetti E. Tognoni 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
We present measurements of the Stark broadening of several Mn lines in the conditions of typical laser-induced plasmas. Single-and double-pulse Laser-Induced Breakdown spectroscopy (LIBS) configurations are studied on a series of Fe–Mn alloy samples with Mn concentration ranging from 6% to 30%. The effects of self-absorption on the measured line broadenings are discussed in detail. In particular, the experimental results evidence that self-absorption is much higher in laser-induced plasmas generated with double pulses, compared to the case of single pulse. After measurement of the electron density, the Stark coefficients of several neutral and ionic Mn lines are derived through the measure of the broadening in conditions of optically thin plasma. The results obtained for singly ionized Mn lines are compared with the theoretical and experimental data present in the literature. For the first time, experimental measurements of the Stark coefficient for several neutral Mn lines are also presented. 相似文献
102.
Martínez-Núñez E Vazquez SA Borges I Rocha AB Estévez CM Castillo JF Aoiz FJ 《The journal of physical chemistry. A》2005,109(12):2836-2839
The photodissociation of formic acid at 248 and 193 nm was investigated by classical trajectory and RRKM calculations using an interpolated potential energy surface, iteratively constructed using the B3LYP/aug-cc-pVDZ level of calculation. Several sampling schemes in the ground electronic state were employed to explore the possibility of conformational memory in formic acid. The CO/CO2 branching ratios obtained from trajectories initiated at the cis and at the trans conformers are almost identical to each other and in very good accordance with the RRKM results. In addition, when a specific initial excitation that simulates more rigorously the internal conversion process is used, the calculated branching ratio does not vary with respect to those obtained from cis and trans initializations. This result is at odds with the idea of conformational memory in the ground state proposed recently for the interpretation of the experimental results. It was also found that the calculated CO vibrational distributions after dissociation of the parent molecule at 248 nm are in agreement with the experimental available data. 相似文献
103.
Anderson Schwingel Ribeiro Daniel L. Gallindo Borges Mariana Antunes Vieira Adilson Jos Curtius 《Microchemical Journal》2007,85(2):341-346
The use of ultrasonic nebulization (USN) with desolvation system for sample introduction in flame atomic absorption spectrometry (F AAS) and flame furnace atomic absorption spectrometry (FF AAS) with a nickel tube is described. Polytetrafluorethylene (PTFE) adaptors were built to replace the pneumatic nebulizer for USN-F AAS measurements. For USN-FF AAS analysis, an alumina injector allowed the direct introduction of the dry aerosol into the nickel tube. The analytical performance of both systems is shown for Ag, Bi, Cd, Cr, Cu, Mn, Pb, Sb, Se, Tl and Zn. The results demonstrate that a sensitivity gain of up to 39 times can be achieved using USN-FF AAS, mainly due to the increase in residence time and to the absence of dilution of the analyte by the flame gases, as the atomization takes place inside the nickel tube. However, elements that require higher atomization temperatures, such as Cr and Mn, are more efficiently determined using USN-F AAS. To evaluate the accuracy of the proposed methods for the determination of trace elements, five certified reference samples were analyzed, and good agreement was, in general, achieved between certified and determined values at a 95% confidence level. The relative standard deviation was frequently below 5%, demonstrating good precision, particularly for USN-FF AAS. In this sense, coupling of USN with F AAS and especially with FF AAS has proved to be simple, safe, with high precision and good accuracy, also maintaining some of the most important features of F AAS, such as the high analytical frequency and the low running cost. 相似文献
104.
A method was developed for the determination of As, Cd, Pb and Tl by electrothermal vaporization inductively coupled plasma
mass spectrometry (ETV-ICP-MS) with slurry sample introduction using certified reference coal samples. The 75As, 111Cd, 208Pb and 205Tl isotopes were monitored, considering the lower probabilities of these isotopes in suffering interferences. The carrier
and modifier effect of Ru added in solution was evaluated, demonstrating that sensitivity for all elements is considerably
improved by the addition of 15 μg of Ru to each individual measurement. This confirms its ability to act as a physical carrier
particularly for the analytes in aqueous solution. Pyrolysis and vaporization temperatures of 500 and 2500 °C, respectively,
were selected after optimization for aqueous solutions and for coal slurries. Similarly, the carrier gas flow rate was optimized
as 1.1 L min−1. After optimization of the operational parameters, the determination of the four elements in six certified reference coal
samples was carried out by external calibration against aqueous standards in 5% v/v HNO3, resulting in good agreement between the certified or given values and the determined ones. For Tl, due to the absence of
certified values, a comparison was established considering previously published data using solid sampling high-resolution
continuum source graphite furnace atomic absorption spectrometry. Detection limits (μg g−1) of 0.1, 0.004, 0.045 and 0.001 were achieved for As, Cd, Pb and Tl, respectively, and the precision was typically better
than 10%. 相似文献
105.
Ionics - Detection and quantification of cocaine is a key tool in fields such as police apprehensions and the fight against drug trafficking. Thus, a simple, fast and inexpensive electroanalytical... 相似文献
106.
107.
Ligand and Metal Effects on the Stability and Adsorption Properties of an Isoreticular Series of MOFs Based on T‐Shaped Ligands and Paddle‐Wheel Secondary Building Units
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Ying Xiong Yan‐Zhong Fan Dr. Daiane Damasceno Borges Cheng‐Xia Chen Zhang‐Wen Wei Hai‐Ping Wang Dr. Mei Pan Dr. Ji‐Jun Jiang Prof. Guillaume Maurin Prof. Cheng‐Yong Su 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(45):16147-16156
The synthesis of stable porous materials with appropriate pore size and shape for desired applications remains challenging. In this work a combined experimental/computational approach has been undertaken to tune the stability under various conditions and the adsorption behavior of a series of MOFs by subtle control of both the nature of the metal center (Co2+, Cu2+, and Zn2+) and the pore surface by the functionalization of the organic linkers with amido and N‐oxide groups. In this context, six isoreticular MOFs based on T‐shaped ligands and paddle‐wheel units with ScD0.33 topology have been synthesized. Their stabilities have been systematically investigated along with their ability to adsorb a wide range of gases (N2, CO2, CH4, CO, H2, light hydrocarbons (C1–C4)) and vapors (alcohols and water). This study has revealed that the MOF frameworks based on Cu2+ are more stable than their Co2+ and Zn2+ analogues, and that the N‐oxide ligand endows the MOFs with a higher affinity for CO2 leading to excellent selectivity for this gas over other species. 相似文献
108.
M. H. Godinho J. P. Borges J. C. Bordado M. T. Cidade A. F. Martins 《Liquid crystals》2013,40(3):653-659
Abstract A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) of Mw = 60000 g mol?1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone and N,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase. 相似文献
109.
Raquel G. Jacob Márcio S. Silva Samuel R. Mendes Elton L. Borges Eder J. Lenardão 《合成通讯》2013,43(15):2747-2762
Here we present a simple, solvent-free, one-pot, hetero-Diels–Alder reaction of (R)-citronellal or 3-(phenylthio)-citronellal with arylamines using solid-supported catalyst (SiO2/ZnCl2). This general, efficient, and improved method is selective, affording preferentially new trans-fused 3-(phenylthio)-octahydroacridines (S-OHAs) in good yields. The use of microwave irradiation facilitates the procedure and accelerates the reaction. 相似文献
110.
Keyller Bastos Borges Warley de Souza Borges Rosa Durán-Patrón Mônica Tallarico Pupo Pierina Sueli Bonato Isidro González Collado 《Tetrahedron: Asymmetry》2009,20(4):385-397
The development of novel biocatalytic methods is a continuously growing area of chemistry, microbiology, and genetic engineering due to the fact that biocatalysts are selective, easy-to-handle, and environmentally friendly. A wide range of reactions are catalyzed by microorganisms. Fungi can be considered as a promising source of new biocatalysts, mainly for chiral reactions. Chemo-, regio-, and stereoselective processes are very important in the synthesis of many chemical, pharmaceutical, and agrochemical intermediates; active pharmaceuticals; and food ingredients. This report reviews stereoselective reactions mediated by fungi, such as stereoselective hydroxylation, sulfoxidation, epoxidation, Baeyer–Villiger oxidation, deracemization, and stereo- and enantioselective reduction of ketones, published between 2000 and 2007. 相似文献