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1.
New Perspectives for Old Clusters: Anderson–Evans Anions as Building Blocks of Large Polyoxometalate Frameworks in a Series of Heterometallic 3 d–4 f Species 下载免费PDF全文
Dr. Beñat Artetxe Dr. Santiago Reinoso Dr. Leire San Felices Prof. Luis Lezama Prof. Juan M. Gutiérrez‐Zorrilla Dr. Cristian Vicent Fadi Haso Prof. Tianbo Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4616-4625
A series of nine [Sb7W36O133Ln3M2(OAc)(H2O)8]17? heterometallic anions ( Ln3M2 ; Ln=La–Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs‐type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW9O33} capping unit formed by a planar {MW6O24} fragment to which three {WO2} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ?‐Keggin cluster. It is shown, for the first time, that classical Anderson–Evans {MW6O24} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk‐shaped species is also revealed. The Ln3M2 anions possess chirality owing to a {Sb4O4} cluster being encapsulated in left‐ or right‐handed orientations. Their ability to self‐associate in blackberry‐type vesicles in solution has been assessed for the Ce3Co2 derivative. 相似文献
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Dr. Aleksandra Mitrović Stefan Wild Vicent Lloret Michael Fickert Dr. Mhamed Assebban Dr. Bence G. Márkus Prof. Ferenc Simon Dr. Frank Hauke Dr. Gonzalo Abellán Prof. Andreas Hirsch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3361-3366
Two-dimensional (2D) black phosphorus (BP) represents one of the most appealing 2D materials due to its electronic, optical, and chemical properties. Many strategies have been pursued to face its environmental instability, covalent functionalization being one of the most promising. However, the extremely low functionalization degrees and the limitations in proving the nature of the covalent functionalization still represent challenges in many of these sheet architectures reported to date. Here we shine light on the structural evolution of 2D-BP upon the addition of electrophilic diazonium salts. We demonstrated the absence of covalent functionalization in both the neutral and the reductive routes, observing in the latter case an unexpected interface conversion of BP to red phosphorus (RP), as characterized by Raman, 31P-MAS NMR, and X-ray photoelectron spectroscopies (XPS). Furthermore, thermogravimetric analysis coupled to gas chromatography and mass spectrometry (TG-GC-MS), as well as electron paramagnetic resonance (EPR) gave insights into the potential underlying radical mechanism, suggesting a Sandmeyer-like reaction. 相似文献
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Biomonitoring of both currently-used and banned-persistent pesticides is a very useful tool for assessing human exposure to these chemicals. In this review, we present current approaches and recent advances in the analytical methods for determining the biomarkers of exposure to pesticides in the most commonly used specimens, such as blood, urine, and breast milk, and in emerging non-invasive matrices such as hair and meconium. We critically discuss the main applications for sample treatment, and the instrumental techniques currently used to determine the most relevant pesticide biomarkers. We finally look at the future trends in this field. 相似文献
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Dr. Jose Ángel Pino‐Chamorro Dr. Artem L. Gushchin Prof. M. Jesús Fernández‐Trujillo Dr. Rita Hernández‐Molina Dr. Cristian Vicent Dr. Andrés G. Algarra Prof. Manuel G. Basallote 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):2835-2844
A study, involving kinetic measurements on the stopped‐flow and conventional UV/Vis timescales, ESI‐MS, NMR spectroscopy and DFT calculations, has been carried out to understand the mechanism of the reaction of [Mo3S4(acac)3(py)3][PF6] ([ 1 ]PF6; acac=acetylacetonate, py=pyridine) with two RC?CR alkynes (R=CH2OH (btd), COOH (adc)) in CH3CN. Both reactions show polyphasic kinetics, but experimental and computational data indicate that alkyne activation occurs in a single kinetic step through a concerted mechanism similar to that of organic [3+2] cycloaddition reactions, in this case through the interaction with one Mo(μ‐S)2 moiety of [ 1 ]+. The rate of this step is three orders of magnitude faster for adc than that for btd, and the products initially formed evolve in subsequent steps into compounds that result from substitution of py ligands or from reorganization to give species with different structures. Activation strain analysis of the [3+2] cycloaddition step reveals that the deformation of the two reactants has a small contribution to the difference in the computed activation barriers, which is mainly associated with the change in the extent of their interaction at the transition‐state structures. Subsequent frontier molecular orbital analysis shows that the carboxylic acid substituents on adc stabilize its HOMO and LUMO orbitals with respect to those on btd due to better electron‐withdrawing properties. As a result, the frontier molecular orbitals of the cluster and alkyne become closer in energy; this allows a stronger interaction. 相似文献
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Lipiao Bao Baolin Zhao Vicent Lloret Marcus Halik Frank Hauke Andreas Hirsch 《Angewandte Chemie (International ed. in English)》2020,59(17):6700-6705
Patterned functionalization can, on the one hand, open the band gap of graphene and, on the other hand, program demanding designs on graphene. The functionalization technique is essential for graphene‐based nanoarchitectures. A new and highly efficient method was applied to obtain patterned functionalization on graphene by mild fluorination with spatially arranged AgF arrays on the structured substrate. Scanning Raman spectroscopy (SRS) and scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy (SEM‐EDS) were used to characterize the functionalized materials. For the first time, chemical patterning on the bottom side of graphene was realized. The chemical nature of the patterned functionalization was determined to be the ditopic scenario with fluorine atoms occupying the bottom side and moieties, such as oxygen‐containing groups or hydrogen atoms, binding on the top side, which provides information about the mechanism of the fluorination process. Our strategy can be conceptually extended to pattern other functionalities by using other reactants. Bottom‐side patterned functionalization enables utilization of the top side of a material, thereby opening up the possibilities for applications in graphene‐based devices. 相似文献
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Vicent Aragó 《European Journal of Operational Research》2011,215(2):393-403
This paper analyzes the influence of sudden changes in the unconditional volatility on the estimation and forecast of volatility and its impact on futures hedging strategies. We employ several multivariate GARCH models to estimate the optimal hedge ratios for the Spanish stock market including in each one some well-known patterns that may affect volatility forecasts (asymmetry and sudden changes). The main empirical results show that more complex models including sudden changes in volatility outperform the simpler models in hedging effectiveness both with in-sample and out-of-sample analysis. However, the evidence is stronger when the loss distribution tail is used as a measure for the effectiveness (Value at Risk (VaR) and Expected Shortfall (ES)) suggesting that traditional measures based on the variance of the hedged portfolio should be used with caution. 相似文献
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Freezing Capture of Polymorphic Aggregates of Bolaamphiphilic L‐Valine‐Based Molecular Hydrogelators 下载免费PDF全文
Dr. Vicent J. Nebot Dr. Santiago Díaz‐Oltra Dr. Johan Smets Susana Fernández Prieto Dr. Juan F. Miravet Dr. Beatriu Escuder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5762-5767
Nanostructured xerogels have been prepared by the freeze‐drying of hydrogels and aggregates formed by bolaamphiphilic L ‐valine derivatives after aging under different environmental conditions. A wide variety of shapes and sizes has been achieved by a simple methodology. These nanostructures have been studied by SEM and WAXD and a dramatic influence of structural flexibility on the kinetics of aggregation has been observed. Such flexibility and a modulation of the hydrophobic effect have shown a profound influence in the packing of these compounds and revealed a high degree of polymorphism. 相似文献