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排序方式: 共有436条查询结果,搜索用时 31 毫秒
371.
Helen A. Goulart Dr. Daniela R. Araujo Lucas E. B. Iarocz Bruna R. Pizzi Prof. Thiago Barcellos Prof. Márcio S. Silva Prof. Gelson Perin 《European journal of organic chemistry》2023,26(14):e202300021
We report a protocol for the synthesis of new dialkyl(1-(organolthio)naphthalen-2-yl)phosphates and derivatives via a dehydrogenative phosphorylation reaction between functionalized naphthols and H-phosphonates. Diphenyl ditelluride was employed as an organocatalyst and sonochemistry as an alternative energy source. The reaction conditions were defined through a factorial design approach, and the best condition provided the synthesis of dialkyl(1-(organolthio)naphthalen-2-yl)phosphates in yields that varied from 51–98 % under ultrasound irradiation after 2 h of sonication. The synthetic protocol was also effective for phenol and thiophenol starting materials. All products were characterized by state-of-the-art spectroscopic and spectrometric techniques. 相似文献
372.
Marcelo J. B. Souza Antonio S. Araujo Anne M.G. Pedrosa Stevie H. Lima 《Reaction Kinetics and Catalysis Letters》2008,94(1):47-53
In this paper the application of a series of CoMo/AlMCM-41 catalysts with different Si/Al ratios was studied in the model
reaction of thiophene hydrodesulfurization. The results obtained showed good catalytic activity for the formation of H2S, isobutene, 1-butene, n-butane, 2-trans-butene-and 2-cis-butene. 相似文献
373.
Elsa E. Sileo Oscar E. Piro Graciela Rigotti Miguel A. Blesa Alexandre S. de Araujo Eduardo E. Castellano 《Structural chemistry》2008,19(4):651-657
The synthesis, an improved refined crystal and molecular structure re-determination, and the thermal decomposition behavior of two Zn(II) derivatives of isocinchomeronic acid (2,5-pyridinedicarboxylic acid or H22,5-pydc) are presented. [Zn(2,5-pydc)(H2O)3Zn(2,5-pydc)(H2O)2]2 (1) crystallizes in the triclinic P-1 space group with a = 7.106(2), b = 11.450(2), c = 11.869(1) Å, α = 107.29(1), β = 104.08(1), γ = 90.32(2)°, and Z = 2. [Zn(2,5-pydc)(H2O)2] · H2O (2) is orthorhombic (P212121 space group), with a = 7.342(1), b = 9.430(1), c = 13.834(2) Å, and Z = 4. The structures were refined to agreement R 1-factors of 0.0315 (1) and 0.0336 (2). Complex (1) is arranged as molecular Zn4(2,5-pydc)4(H2O)10 tetramers, the cages of which define channels that remain unblocked by anions. Compound (2) is polymeric with Zn(2,5-pydc)(H2O)2 and Zn(2,5-pydc)(H2O)3 units linked through bridging ligands. Both compounds were synthesized under mild conditions in aqueous media, without need to resort to hydrothermal media. Changing the pH from 4.51 to 5.75 suffices to direct the chemical processes toward the orthorhombic compound rather than to the triclinic one. 相似文献
374.
de Araujo AS Piro OE Castellano EE Danil de Namor AF 《The journal of physical chemistry. A》2008,112(46):11885-11894
We describe here a procedure to bridge the gap in the field of calixarene physicochemistry between solid-state atomic-resolution structural information and the liquid-state low-resolution thermodynamics and spectroscopic data. We use MD simulations to study the kinetics and energetics involved in the complexation of lower rim calix[4]arene derivatives (L), containing bidentate ester (1) and ketone (2) pendant groups, with acetonitrile molecule (MeCN) and Cd(2+) and Pb(2+) ions (M(2+)) in acetonitrile solution. On one hand, we found that the prior inclusion of MeCN into the calix to form a L(MeCN) adduct has only a weak effect in preorganizing the hydrophilic cavity toward metal ion binding. On the other hand, the strong ion-hydrophilic cavity interaction produces a wide open calix which enhances the binding of one MeCN molecule (allosteric effect) to stabilize the whole (M(2+)) L(MeCN) bifunctional complex. We reach two major conclusions: (i) the MD results for the (M(2+)) 1(MeCN) binding are in close agreement with the "endo", fully encapsulated, metal complex found by X-ray diffraction and in vacuo MD calculations, and (ii) the MD structure for the more flexible 2 ligand, however, differs from the also endo solid-state molecule. In fact, it shows strong solvation effects at the calixarene lower bore by competing MeCN molecules that share the metal coordination sphere with the four CO oxygens of an "exo" (M(2+)) 2(MeCN) complex. 相似文献
375.
de Araujo AS Sonoda MT Piro OE Castellano EE 《The journal of physical chemistry. B》2007,111(9):2219-2224
We present new Lennard-Jones parameters for Cd2+ and Pb2+ ion-water interactions and describe a general methodology to obtain these parameters for any ion. Our strategy is based on the adjustment of ion parameters to reproduce simultaneously experimental absolute hydration free energy and structural properties, namely, g(r) and coordination numbers, obtained from X-ray liquid scattering and quantum mechanical/molecular mechanical (QM/MM) calculations. The validation of the obtained parameters is made by the calculation of dynamical properties and comparing them with experimental values and theoretical results from the literature. The transferability of parameters is checked by the calculation of thermodynamic, structural, and dynamical properties cited above with four different water models. The results obtained for Cd2+ and Pb2+ show an overall agreement with reference values. The absolute hydration free energy calculated with the TIP3P, SPC/E, SPC, and TIP4P water models presents, respectively, percent differences of 3.8, 3.0, 4.3, and 7.2% for lead(II) and 9.8, 8.4, 10.2, and 14.1% for cadmium(II) when compared with experimental values. Ion-water mean distance and coordination numbers for the first coordination shell are in good agreement with experimental and QM/MM results for both ions. Cd2+ shows a lesser diffusion coefficient compared to that of Pb2+ despite its smaller atomic radius, indicating a more persistent first coordination shell for the cadmium(II) ion, a result confirmed with calculations of the mean residence time of water molecules in the first coordination shell. 相似文献
376.
The local structure of Na-Al-P-O-F glasses, prepared by a novel sol-gel route, was extensively investigated by advanced solid-state NMR techniques. 27Al{19F} rotational echo double resonance (REDOR) results indicate that the F incorporated into aluminophosphate glass is preferentially bonded to octahedral Al units and results in a significant increase in the concentration of six-coordinated aluminum. The extent of Al-F and Al-O-P connectivities are quantified consistently by analyzing 27Al{31P} and 27Al{19F} REDOR NMR data. Two distinct types of fluorine species were identified and characterized by various 19F{27Al}, 19F{23Na}, and 19F{31P} double resonance experiments, which were able to support peak assignments to bridging (Al-F-Al, -140 ppm) and terminal (Al-F, -170 ppm) units. On the basis of the detailed quantitative dipole-dipole coupling information obtained, a comprehensive structural model for these glasses is presented, detailing the structural speciation as a function of composition. 相似文献
377.
378.
The Fokker-Planck equation is useful to describe stochastic processes. Depending on the force acting in the system, the solution of this equation becomes complicated and approximate or numerical solutions are needed. The relation with the Schrödinger equation allows building a method to obtain solutions of the Fokker-Planck equation. However, this approach has been limited to the study of confined potentials, restricting its applicability. In this work, we suggest a general treatment for non-confining potentials through the use of series of functions based on the solution of the Schrödinger equation, with part of discrete spectrum and part of continuum spectrum. Two examples, the Rosen-Morse potential and a limited harmonic potential, are analyzed using the suggested approach. 相似文献
379.
Marilia I. Frazão Barbosa Eliana M.A. Valle Salete L. Queiroz Javier Ellena Eduardo E. Castellano Valéria R.S. Malta Jackson R. de Sousa Oscar Piro Márcio P. de Araujo Alzir A. Batista 《Polyhedron》2010
The “Ru(P–P)” unit (P–P = diphosphine) is recognized to be an important core in catalytic species for hydrogenation of unsaturated organic substrates. Thus, in this study we synthesized six new complexes containing this core, including the binuclear complex [(dppb)(CO)Cl2Ru-pz-RuCl2(CO)(dppb)] (pz = pyrazine) which can be used as a precursor for the synthesis of cationic carbonyl species of general formula [RuCl(CO)(dppb)(N–N)]PF6 (N–N = diimine). Complexes with the formula [RuCl(py)(dppb)(N–N)]PF6 were synthesized by exhaustive electrolysis of these carbonyl compounds or from the precursors [RuCl2(dppb)(N–N)]. The new complexes were characterized by microanalysis, conductivity measurements, IR and 31P{1H} NMR spectroscopy, cyclic voltammetry and X-ray crystallography. 相似文献
380.
Bernhard Welz Lísia M.G. dos Santos Rennan G.O. Araujo Silvana do C. Jacob Maria Goreti R. Vale Michael Okruss Helmut Becker-Ross 《Spectrochimica Acta Part B: Atomic Spectroscopy》2010
The simultaneous determination of cadmium and iron in plant and soil samples has been investigated using high-resolution continuum source graphite furnace atomic absorption spectrometry. The primary cadmium resonance line at 228.802 nm and an adjacent secondary iron line at 228.726 nm, which is within the spectral interval covered by the charge-coupled device (CCD) array detector, have been used for the investigations. Due to the very high iron content in most of the soil samples the possibility has been investigated to reduce the sensitivity and extend the working range by using side pixels for measurement at the line wings instead of the line core. It has been found that the calibration curves measured at all the analytically useful pixels of this line consisted of two linear parts with distinctly different slopes. This effect has been independent of the positioning of the wavelength, i.e., if the Cd line or the Fe line was in the center of the CCD array. The most likely explanation for this unusual behavior is a significant difference between the instrument width ΔλInstr and the absorption line width ΔλAbs, which is quite pronounced in the case of Fe. Using both parts of the calibration curves and simultaneous measurement at the line center and at the wings made it possible to extend the working range for the iron determination to more than three orders of magnitude. 相似文献