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621.
The pendant drop technique is one of the most accurate methods to measure surface tension of liquids. Recently, it has been found that the value of the surface/interfacial tension found using the pendant drop method might be drop-volume dependent. In this work, the surface tension of glycerol at a 25 °C and the surface tension of polypropylene at 240 °C were measured using the pendant drop method for different drop volumes. It was shown that the values of the surface tension depend on the drop size if no calibration to take into account the anisotropy in the optical enlargement is performed. However, when a calibration procedure for optical anisotropy correction is performed, the values of the surface tension obtained do not depend on the volume drop size and they corroborate the values in the literature. 相似文献
622.
Diana T. Patoilo Artur M.S. Silva Diana C.G.A. Pinto Clementina M.M. Santos Augusto C. Tomé José A.S. Cavaleiro 《Tetrahedron letters》2012,53(22):2722-2725
The Diels–Alder reaction of (E)-2-styrylchromones with a pyrimidine ortho-quinodimethane is reported for the first time. These cycloaddition reactions afford mixtures of two regioisomeric tetrahydroquinazoline-substituted chromones in moderate to excellent global yields. Irrespective of the substituents on the 2-styrylchromones, the 2-(7-aryl-4-methoxy-2-methyl-5,6,7,8-tetrahydroquinazolin-6-yl)chromone derivatives are always the major isomers. 相似文献
623.
Negreiros Marcos J. Maculan Nelson Batista Pablor L. Rodrigues Joo A. Palhano Augusto W. C. 《Annals of Operations Research》2022,316(2):1157-1185
Annals of Operations Research - This work studies Heterogeneous Capacitated Clustering Problems (HCCP) which are variations of the Capacitated Clustering Problem (CCP). They are applied to the... 相似文献
624.
Caroline Rita Venturi Srgio Augusto De Loreto Bordignon Samuel Paulo Cibulski Grace Gosmann 《Natural product research》2018,32(16):1960-1962
The chemical composition and antiviral activity of aqueous extract from Baccharis anomala was studied by bioactivity-guided fractionation. Ethanol precipitation and fractionation by molecular permeation allowed the separation of the anti-herpes simplex virus 1 (HSV-1) active fraction from aqueous extract (Fraction B). Natural Product Reagent A, FeCl3 and thin-layer chromatography indicated the presence of phenolic compounds in the aqueous extract. Fraction B showed pronounced antiviral activity when tested with HSV-1 strains VR733/ATCC and Acyclovir-resistant 29-R, displaying virucidal but not virustatic activity. 相似文献
625.
α‐Arylation/Heteroarylation of Chiral α‐Aminomethyltrifluoroborates by Synergistic Iridium Photoredox/Nickel Cross‐Coupling Catalysis
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Dr. Mirna El Khatib Dr. Ricardo Augusto Massarico Serafim Prof. Gary A. Molander 《Angewandte Chemie (International ed. in English)》2016,55(1):254-258
Direct access to complex, enantiopure benzylamine architectures using a synergistic iridium photoredox/nickel cross‐coupling dual catalysis strategy has been developed. New C(sp3)? C(sp2) bonds are forged starting from abundant and inexpensive natural amino acids. 相似文献
626.
Fast Quantitation of Target Analytes in Small Volumes of Complex Samples by Matrix‐Compatible Solid‐Phase Microextraction Devices
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Dr. Hamed Piri‐Moghadam Fardin Ahmadi MSc. German Augusto Gómez‐Ríos Dr. Ezel Boyacı MSc. Nathaly Reyes‐Garcés Dr. Ali Aghakhani Dr. Barbara Bojko Prof. Janusz Pawliszyn 《Angewandte Chemie (International ed. in English)》2016,55(26):7510-7514
Herein we report the development of solid‐phase microextraction (SPME) devices designed to perform fast extraction/enrichment of target analytes present in small volumes of complex matrices (i.e. V≤10 μL). Micro‐sampling was performed with the use of etched metal tips coated with a thin layer of biocompatible nano‐structured polypyrrole (PPy), or by using coated blade spray (CBS) devices. These devices can be coupled either to liquid chromatography (LC), or directly to mass spectrometry (MS) via dedicated interfaces. The reported results demonstrated that the whole analytical procedure can be carried out within a few minutes with high sensitivity and quantitation precision, and can be used to sample from various biological matrices such as blood, urine, or Allium cepa L single‐cells. 相似文献
627.
628.
Luna AS da Costa AC Gonçalves MM de Almeida KY 《Applied biochemistry and biotechnology》2008,147(1-3):77-84
The effect of the surfactants polyoxyethylene monostearate (Tween 60), polyoxyethylene monooleate (Tween 80), cetyl trimethyl
ammonium bromide (CTAB), and sodium dodecyl sulfate (SDS) on the estimation of bacterial density (sulfate-reducing bacteria
[SRB] and general anaerobic bacteria [GAnB]) was examined in petroleum samples. Three different compositions of oil and water
were selected to be representative of the real samples. The first one contained a high content of oil, the second one contained
a medium content of oil, and the last one contained a low content of oil. The most probable number (MPN) was used to estimate
the bacterial density. The results showed that the addition of surfactants did not improve the SRB quantification for the
high or medium oil content in the petroleum samples. On other hand, Tween 60 and Tween 80 promoted a significant increase
on the GAnB quantification at 0.01% or 0.03% m/v concentrations, respectively. CTAB increased SRB and GAnB estimation for the sample with a low oil content at 0.00005% and
0.0001% m/v, respectively. 相似文献
629.
Pedroso MP de Godoy LA Ferreira EC Poppi RJ Augusto F 《Journal of chromatography. A》2008,1201(2):176-182
A method to detect potential adulteration of commercial gasoline (Type C gasoline, available in Brazil and containing 25% (v/v) ethanol) is presented here. Comprehensive two-dimensional gas chromatography with flame ionization detection (GCxGC-FID) data and multivariate calibration (multi-way partial least squares regression, N-PLS) were combined to obtain regression models correlating the concentration of gasoline on samples from chromatographic data. Blends of gasoline and white spirit, kerosene and paint thinner (adopted as model adulterants) were used for calibration; the regression models were evaluated using samples of Type C gasoline spiked with these solvents, as well as with ethanol. The method was also checked with real samples collected from gas stations and analyzed using the official method. The root mean square error of prediction (RMSEP) for gasoline concentrations on test samples calculated using the regression model ranged from 3.3% (v/v) to 8.2% (v/v), depending on the composition of the blends; in addition, the results for the real samples agree with the official method. These observations suggest that GCxGC-FID and N-PLS can be an alternative for routine monitoring of fuel adulteration, as well as to solve several other similar analytical problems where mixtures should be detected and quantified as single species in complex samples. 相似文献
630.
Ramos CI Santana-Marques MG Ferrer Correia AJ Tomé JP Alonso CM Tomé AC Neves MG Cavaleiro JA 《Journal of mass spectrometry : JMS》2008,43(6):806-813
The solutions of four meso-tetrakis(N-alkylpyridinium-4-yl)porphyrin salts and of the p-toluenesulfonate salt of meso-tetrakis(4-trimethylammoniumphenyl)porphyrin, in methanol, were studied by electrospray mass spectrometry, in order to investigate the influence of the type of counter ion, the length of the substituent N-alkyl groups of the four (N-alkylpyridinium-4-yl)porphyrins and the presence of an aromatic (alkylpyridinium) or aliphatic (trimethylammonium) nitrogen, in ion formation.In our experimental conditions, adducts with the counter ions were formed only for the meso-tetrakis(4-trimethylammoniumphenyl)porphyrin and were not observed for the other porphyrins, even when the counter ion was the same. In contrast, formation of reduced species, such as the [M(4+) + e(-)]3+, [M(4+) + 2e(-)]2+, [M(4+) + 4e(-) + 2H(+)]2+, and [M(4+) + 5e(-) + 2H(+)]+ ions was observed only for the (N-alkylpyridinium-4-yl)porphyrins and the appearance of these species is apparently solvent related and may occur via counter ion/solvent adducts. 相似文献