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91.
Philippe Zinck Andreia Valente Fanny Bonnet Ana Violante André Mortreux Marc Visseaux Simona Ilinca Rob Duchateau Pascal Roussel 《Journal of polymer science. Part A, Polymer chemistry》2010,48(4):802-814
The ability of various rare earth borohydride and chloride complexes/n‐butylethylmagnesium systems to operate styrene chain transfer polymerization in mild conditions has been assessed. Thirteen precatalysts have been considered: the rare earth trisborohydrides Ln(BH4)3(THF)x (x = 3, Ln = Nd (1), La (2), Sm (3), x = 2, Ln = Y (4), Sc (5)), the rare earth chlorides LnCl3(THF)x (x = 3, Ln = Nd (6), La (7), Sm (8), Y (9), x = 2, Ln = Sc (10)), the mixed La(BH4)2Cl(THF)2.6 (11) and the half‐lanthanidocenes Cp*Ln(BH4)2(THF)2 (Ln = Nd (12), La (13)). Six systems were found to be active precatalysts for the polymerization of styrene. 1 , 2 , and 11 led to an efficient transmetalation of the growing polystyrene chain with the simultaneous occurrence of βH elimination, whereas 7 , 12 , and 13 led to catalyzed chain growth behavior. It is noteworthy that the catalyzed chain growth obtained with 12 and 13 occurs with significant stereoselectivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 802–814, 2010 相似文献
92.
A series of supports functionalized with different alkyl chains and covered with magnetite were synthesized, characterized and applied in the sample pre-concentration of four non-steroidal anti-inflammatory drugs (acetaminophen, naproxen, diclofenac and ibuprofen) contained in wastewater samples. The general methodology involved magnetic solid phase dispersion followed by the analysis by high-performance liquid chromatography with ultraviolet detection. The magnetic supports were initially dispersed in the samples with the aid of Triton X-100, then supports were magnetically isolated and the analytes were eluted with methanol. Finally the extract was injected into the HPLC system. The highest recovery percentage (>90%) was obtained with the support containing octyl chains (C8) at pH 3. The lowest limits of detection achieved ranged within 1-2 μg L−1 with repeatability (expressed as RSD) below 5% in all cases. The method was applied in the analysis of wastewater samples. 相似文献
93.
Ana M.G. Silva Andreia Leite Paula Gameiro Vítor Felix Maria Rangel 《Tetrahedron》2010,66(44):8544-8550
Two novel 3-hydroxy-4-pyridinone/naphthalene conjugates (L1 and L2) with different distances between the chelating and the fluorescent moieties were synthesized using conventional heating and microwave irradiation achieving a shorter reaction time. The structure of both compounds was confirmed by X-ray crystallography, revealing that these compounds were isolated as hydrochloride salts in dihydroxypyridinium forms. In solution and in the presence of a base, the tautomeric keto forms may be obtained as it was elucidated by NMR analysis. The dihydroxypyridinium form of L1 exhibits fluorescence at 450 nm, both in ACN and DMSO, whereas the corresponding keto form exhibits fluorescence at 365 nm. In contrast, the dihydroxypyridinium form of L2 only fluoresces in DMSO, exhibiting a band at 340 nm, while the keto form is non-fluorescent. These distinct fluorescent behaviors reveal that the tautomeric form in which the ligands are isolated and the distance between the chelating and fluorescent functions strongly influences their fluorescence properties. Ligand L1 exhibits better fluorescence properties and its fluorescence intensity is quenched in the presence of variable concentration of Cu2+, Zn2+, and Fe3+, thus making it suitable to be used as ion sensor. 相似文献
94.
The combined effects of an in-growth direction applied electric field and hydrostatic pressure on the exciton binding energy and photoluminescence energy transitions are reported in this work for triple vertically coupled quantum dots. The calculations have been carried out within the effective mass approximation, and using a variational procedure. The results show that the exciton binding energy and the photoluminescence energy transitions are functions of external probes like the hydrostatic pressure and the applied electric field. 相似文献
95.
A problem of decision making under uncertainty in which the choice must be made between two sets of alternatives instead of two single ones is considered. A number of choice rules are proposed and their main properties are investigated, focusing particularly on the generalizations of stochastic dominance and statistical preference. The particular cases where imprecision is present in the utilities or in the beliefs associated to two alternatives are considered. 相似文献
96.
V. Rodríguez-Lugo L. Ortiz-Velázquez J. Miranda M. Ortiz-Rojas V. M. Castaño 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(2):561-569
The characterization of samples of painted plasters obtained from the archaeological site of Xochicalco, in Central Mexico,
is presented. Elemental concentrations of the painted layers were obtained by using proton induced X-ray emission (PIXE).
The main crystalline structures of the samples are identified with the help of X-ray diffraction (XRD), while the microstructure
is studied by scanning electron microscopy (SEM). The information resulting from the application of these three techniques
is used to achieve more accurate values for the elemental concentrations. Additional data regarding organic components of
the paintings was obtained through Fourier transform infrared spectrometry (FTIR). Although the latter results only provided
reliable data on inorganic components, they help to clarify the results from XRD and confirm those of SEM. 相似文献
97.
M. Agostinha R. Matos Margarida S. Miranda Victor M. F. Morais Joel F. Liebman 《Molecular physics》2013,111(2-3):221-228
The standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous phase at a temperature of 298.15?K have been experimentally determined for saccharin and for benzenesulfonamide. These compounds were also studied theoretically using density functional theory, the B3LYP functional and extended basis sets. 相似文献
98.
99.
A cohomological method for computing the set of similarity classes of endomorphisms locally similar to a given endomorphism is presented and several calculations are made. 相似文献
100.
Robson Miranda da Gama Tatiana Santana Balogh Simone França Tânia Cristina Sá Dias Valcinir Bedin André Rolim Baby Jivaldo do Rosário Matos Maria Valéria Robles Velasco 《Journal of Thermal Analysis and Calorimetry》2011,106(2):399-405
This research aimed the effect on Caucasian hair tresses treated with oxidative hair dye, either incorporated or not with
conditioners agents, analyzed by Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TG). The formulations
of hair dyes were emulsions oil-in-water with light blond color containing or not the conditioners agents: silanetriol and
panthenol; PEG-12 dimethicone; hydrolyzed silk, hydrolyzed milk protein, and lactose. Each dye (1.5 g) was applied in the
hair tress (2.0 g/20.0 cm of length of Caucasian light-brown), previously treated, more 1.5 g of hydrogen peroxide 20 vol
during 40 min. Evaluation of mass loss of the different hair sample demonstrates that these chemical hair treatments impair
the hair fibers, reduced their moisture content with respect to the untreated hair. The incorporation of conditioners agents
(silanetriol and panthenol; PEG-12 dimethicone; hydrolyzed silk, hydrolyzed milk protein, and lactose) in oxidative hair dyes
types did not decrease the damage caused on the tresses by the coloring process quantified by TG/DTG. However, the DSC curves
demonstrated those conditioners agents (silanetriol and panthenol; PEG-12 dimethicone) dislocated the beginning of the third
event in 20 °C and they inhibited the presence of the fourth event, having characterized thermal protection to the hair. 相似文献