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991.
Francisco Pérez-García José G. Alvarado-Rodríguez Carlos Andrés Galán-Vidal M. Elena Páez-Hernández Noemí Andrade-López Rafael Moreno-Esparza 《Structural chemistry》2010,21(1):191-196
Treatment of KS2P(OC6H4)2 (1) with five n-alkyl halides afforded the stable n-alkyldithiophosphate compounds RS2P(OC6H4)2 (2–6). Single crystal X-ray analysis revealed that the PS2 fragment in 1 displays an isobidentate coordination pattern; compounds 2–4 display a monodentate binding pattern. The crystal packing of title compounds is stabilized by cation-π, weak hydrogen bonding
C–H---O, as well as aromatic non-bonded interactions. 相似文献
992.
Eva Mª Barea Dr. Rubén Caballero Francisco Fabregat‐Santiago Dr. Pilar De La Cruz Dr. Fernando Langa Prof. Juan Bisquert Prof. 《Chemphyschem》2010,11(1):245-250
Five new sensitizers for dye sensitized solar cells have been designed consisting of conjugated thienylenevinylene units threaded with alkyl chains to improve solubility and cyanoacetic acid as anchoring group. The conjugation length was increased from 2 to 6 thienylenevinylene units, which resulted in a red‐shift of the optical absorption of the dyes from 550 to 750 nm, improving the spectral overlap with the solar spectrum. The photovoltaic performance of these dyes as sensitizers in mesoporous TiO2 solar cells shows a clear correlation of increasing photocurrent with the extension of the conjugation up to an optimal length. Further extension of the conjugation increases the absorption but additional effects like self‐quenching or recombination processes reduce the photocurrent and photovoltages and consequently the overall efficiency of the DSC. 相似文献
993.
Multiresidue determination of organochlorines in fish oil by GC-MS: A new strategy in the sample preparation 总被引:1,自引:0,他引:1
Juan José Berzas Nevado Francisco Javier Guzmán Bernardo Nuria Rodríguez Fariñas José Antonio Castro Osma 《Talanta》2010,81(3):887-289
A rapid, economic and environmentally friendly analytical methodology has been implemented for the determination of α-, β-, γ- and δ-HCH, p,p′-DDT, p,p′-DDD and p,p′-DDE, PCBs congeners #28, #52, #101, #153, #138 and #180 and Hexachlorobenzene in fish oil. 1,2,3,4-Tetrachloronaphtalene was used as internal standard. The sample preparation, consisting of a single step of clean-up and fractionation, took place in a column filled with different layers of neutral and sulphuric acid modified silica. The analytes were eluted by vacuum with of hexane. Significant reduction in terms of solvents, sorbents, and analysis time was achieved in comparison with literature.Gas chromatography coupled to mass spectrometry was used for the separation and determination of the analytes. The instrumental limits of detection were from 0.1 to 1.3 ng mL−1 and the response of the detector was linear up to 200 ng mL−1. The separation proved to be precise (RSD < 3.7% in peak area) and robust in terms of peak area, peak efficacy and resolution. The methodology was validated with two certified reference materials of cod liver oil, BCR 598 and BCR 349, obtaining no statistically significant differences between the concentrations found and certified. For the analytes that were not certified, aliquots of the reference materials were spiked and the recoveries obtained were satisfactory. These results were consistent with those found previously for DDTs by gas chromatography with an electron-capture detector.The methodology was applied to the analysis of three fish oil pills sold in Spain as a dietary supplement of vitamins and omega-3 fatty acids. The sum of the analytes studied was from 64 to 80 ng g−1. The most abundant compounds are PCBs, followed by DDTs in all samples. 相似文献
994.
995.
996.
Enriqueta Casal Rosa Lebrón‐Aguilar Francisco Javier Moreno Nieves Corzo Jesús Eduardo Quintanilla‐López 《Rapid communications in mass spectrometry : RCM》2010,24(7):885-893
Sialylated O‐linked oligosaccharides are involved in many biological processes, such as cell‐cell interactions, cell‐substance adhesion, and virus‐host interactions. These activities depend on their structure, which is frequently determined by tandem mass spectrometry. However, these spectra are frequently analyzer‐dependent, which makes it difficult to develop widely applicable analytical methods. In order to deepen the origin of this behavior, two couples of isomers of sialylated O‐linked oligosaccharides, NeuAcα2‐3Galβ1‐3GalNAc‐ol/Galβ1‐3(NeuAcα2‐6)GalNAc‐ol and NeuGcα2‐3Galβ1‐3GalNAc‐ol/Galβ1‐3(NeuGcα2‐6)GalNAc‐ol, were analyzed by liquid chromatography/negative electrospray ionization ion trap tandem mass spectrometry (LC/ESI(?)‐MSn) using both an ion trap and a triple quadrupole mass spectrometer. Results clearly showed that while ions obtained in the triple quadrupole instrument fitted very well with the standard fragmentation routes, in the ion trap several intense ions could not be explained by these rules, specially a fragment at m/z 597. Furthermore, this ion was observed in the mass spectrum of those isomers that sialic acid binds to GalNAc by an α2‐6 linkage. From the MS3 spectrum of this ion an unexpected structure was deduced, and it led to propose alternative fragmentation pathways. Molecular mechanics calculations suggested that the found atypical route could be promoted by a hydrogen bond located only in α2‐6‐linked oligosaccharides. It has also been demonstrated that this process follows a slow kinetic, explaining why it cannot be observed using an ion beam‐type mass analyzer. In conclusion, ion traps seem to be more appropriate than triple quadrupoles to develop a reliable analytical method to distinguish between isomeric O‐linked glycans. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
997.
Francisco Periago 《International Journal of Mathematical Education in Science & Technology》2013,44(4):549-559
In this paper, a didactical proposal is presented to introduce the variational methods for solving boundary value problems to engineering students. Starting from a couple of simple models arising in linear elasticity and heat diffusion, the concept of weak solution for these models is motivated and the existence, uniqueness and continuous dependence on the initial data for these solutions are proved. Finally, the solutions of the above mentioned problems are numerically evaluated by the finite element method. 相似文献
998.
Francisco M. Fernández 《Central European Journal of Physics》2013,11(4):470-473
We obtain accurate eigenvalues for two recently derived SUSY partner Hamiltonians. We improve the Rayleigh-Ritz variational method proposed by the authors and show how to apply the Riccati-Padé method to those particular partner potentials. 相似文献
999.
Conditions for pointwise Fourier inversion using spherical Cesàromeans of a given degree are established on rank 1 noncompactsymmetric spaces. 相似文献
1000.
A sufficient condition for the complementability of subspaces generated by disjoint function systems in rearrangement invariant
spaces is given. Orthogonal projections in L
p
-spaces are extended to certain rearrangement invariant spaces. Applications to Lorentz spaces are given. 相似文献