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21.
A. Gustavo González M. Ángeles Herrador Agustín G. Asuero 《Accreditation and quality assurance》2005,10(7):386-391
The uncertainty evaluation of mass measurements when using “in-house” calibrated analytical balances is revisited according
to the Guide to the expression of Uncertainty Measurement (GUM). The calibration of analytical balances is discussed according
to the guidelines of several bodies such as ASTM, UKAS and DKD/PTB. The remainder components of uncertainty can be estimated
from the balance data sheet specifications. 相似文献
22.
Heider Nasser ákos Rédey Tatiana Yuzhakova Zsolt Németh Tóth Tamás Ollár 《Reaction Kinetics and Catalysis Letters》2007,92(2):329-335
CO adsorption at low temperature has been used to probe Lewis acid sites created upon dehydroxylation of γ-Al2O3 and reduction of Mo/Al2O3 catalysts, using Fourier Transform Infrared spectroscopy (FTIR).
Carbon-monoxide adsorption on γ-Al2O3 and Mo/Al2O3 catalysts dehydroxylated and reduced at different temperatures was studied at 78 K by IR spectroscopy. However, our results
indicate that there is an approximately linear correlation between the increase either of dehydroxylation or the extent of
reduction of the catalysts and the increasing absorbance of CO due to CO adsorption on Lewis acid sites created upon dehydroxylation
of γ-Al2O3 and reduction of Mo/Al2O3. 相似文献
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A Laplace Transform (LT) method is used to improve the results obtained in a quasi-elastic scattering (QELS) experiment. This is designed to determine the characteristic parameters of a bimodal solution of spherical and rod-like macromolecules. The theoretical study and the experimental simulation are carried out for low light levels and the results show that the LT technique provides a real alternative to the second order correlation function, g(2)(τ), in QELS measurements for these particularly difficult experimental conditions. 相似文献
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M. C. Villa-lojo E. Beceiro-GonzÁlez E. Alonso-Rodríguez D. Prada-Rodríguez 《International journal of environmental analytical chemistry》2013,93(3):377-389
Abstract The speciation of arsenic in the environment is among others controlled by reduction, methylation and oxidation processes and therefore influenced by the prevailing redox conditions. In this study we have analyzed sediments taken from La Coruña estuary in the north west of Spain. Inorganic (trivalent and pentavalent) and the organic (MMA and DMA) arsenic speciation is related to Eh, Fe and Mn load. The various of the arsenic species concentration and other parameters was analyzed at different depths in some of the sampling points. Low arsenic concentrations (1–10 μg·g–1) were found. In spite of oxidising conditions (Eh values between 31–96 mV), most of the samples showed a higher As(V) percentage than As (III). Principal component analysis was made to see a sample groups and the results showed that speciation depends on reducing conditions (Eh and Mn). 相似文献
28.
Unexpected reactivity of pyridinium salts toward alkynyl Fischer complexes to produce oxo‐heterocycles
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María Inés Flores‐Conde Fabiola N. de la Cruz Julio López J. Óscar C. Jiménez‐Halla Eduardo Peña‐Cabrera Marcos Flores‐Álamo Francisco Delgado Miguel A. Vázquez 《应用有机金属化学》2018,32(3)
The unprecedented reaction of ketone‐containing aromatic pyridinium salts 3a ‐ e and alkynyl Fischer complexes 1a ‐ f proceeds via a mild domino process to provide 4,6‐disubstituted pyran‐2‐ones 5a ‐ k and 2,3,5‐trisubstituted furans 6a ‐ h (45‐97%). According of the results of isotopic labeling experiments, a mechanism involving an initial Michael addition appears to be the key step, obtaining a mesomeric structure responsible for the formation of both products. 相似文献
29.
Dr. Lina M. Aguirre-Díaz Marcelo Echeverri Dr. Katherine Paredes-Gil Dr. Natalia Snejko Dr. Berta Gómez-Lor Prof. Dr. Enrique Gutiérrez-Puebla Prof. Dr. M. Ángeles Monge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(16):5298-5306
Three new cadmium-based coordination polymers, denoted [Cd(hfipbb)(4,4’-bipy)] ( CdPF-1 ), [Cd(hfipbb)(2,2’-bipy)] ( CdPF-2 ), and [Cd(hfipbb)(1,10-phen)] ( CdPF-3 ), have been hydrothermally synthesized by using the well-known V-shaped organic linker 4,4’-(hexafluoroisopropylidene)bis(benzoic acid) (H2hfipbb), together with different nitrogenated auxiliary linkers. Considering the d10 configuration of the transition metal selected, the luminescent properties for these CdPF-n materials were explored, finding that materials CdPF-2 and CdPF-3 act as excellent sensors in the detection of explosive nitro aromatic compounds. The photoluminescence properties of CdPF-2 and CdPF-3 revealed that significant and sensitive fluorescence quenching was observed toward NP (nitrophenol) for CdPF-2 and PA (picric acid) for CdPF-3 in MeOH suspensions. 相似文献
30.
János B. Czirok Ákos Tarcsay Pál D. Mezei András Simon László Balázs 《Supramolecular chemistry》2013,25(10-12):722-728
The size limit of substituents allowing O-through-the-annulus rotation of substituted calix[4]arenes was further extended to the propargyloxy group in 24-propargyloxy-25,26,27-tris(N,N-dimethylcarbamoylmethoxy)-p-tert-butylcalix[4]arene by demonstrating its free but slow motion affording equilibrium between the partial cone and 1,2-alternate conformers. The effect of solvent and upper rim substituents R1 on the conformational inversion was investigated by means of 1H NMR. The rotational isomerisation of the parent (R1 = H) analogue could not unambiguously be detected. The experimental results were supported by comprehensive density functional theory studies. 相似文献