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91.
Mauricio Osorio-olivares Bruce K. Cassels Silvia Sepúlveda-Boza Marcos Caroli Rezende 《合成通讯》2013,43(5):815-819
A novel route to 5,7-dimethoxy-6-hydroxyflavone is described, involving the cyclization of an intermediate phosphorane as the key step. 相似文献
92.
A Kinetic Investigation of Regioselective Solvation of a Solvatochromic Dye in Aqueous Alcohols
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Moisés Domínguez Vanderlei Gageiro Machado Leandro Guarezi Nandi Marcos Caroli Rezende Patricia Silva 《国际化学动力学杂志》2015,47(12):803-810
The kinetics of methylation of the solvatochromic dye 4‐[(2,4‐dinitrobenzyli‐dene)imino]‐2,6‐diphenylphenolate by dimethyl sulfate was investigated in three aqueous alcohols (1‐propanol, ethanol, and methanol), in the search of a sharp change in its reactivity in water‐rich media. The observed kinetic results paralleled previous observations of a sharp change in the solvatochromic behavior of the dye in the same media and was supported by a QM/MM simulation of the dye in two methanol–water mixtures, which rationalized the observed sharp change in the phenolate reactivity. 相似文献
93.
The synthesis of annofolin (1), an alkaloid isolated from Annona hayesii in small amounts, by a phase-transfer catalytic reduction-methylation of cleistopholin (2) is reported, together with the preparation of its derivatives (3) and (4) by the same method. 相似文献
94.
Bram Verbelen Lucas Cunha Dias Rezende Stijn Boodts Jeroen Jacobs Prof. Luc Van Meervelt Prof. Johan Hofkens Prof. Wim Dehaen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(36):12667-12675
A one‐step synthetic procedure for the radical C?H alkylation of BODIPY dyes has been developed. This new reaction generates alkyl radicals through the oxidation of boronic acids or potassium trifluoroborates and allows the synthesis of mono‐, di‐, tri‐, and tetraalkylated fluorophores in a good to excellent yield for a broad range of organoboron compounds. Using this protocol, multiple bulky alkyl groups can be introduced onto the BODIPY core thus creating solid‐state emissive BODIPY dyes. 相似文献
95.
The preparation of several amides and hydrazides from the reaction of the title compounds with different nitrogen nucleophiles is shown to be a general high-yield conversion of synthetic utility. 相似文献
96.
In this paper we prove, using the Poincaré-Hopf inequalities, that a minimal number of non-degenerate singularities can be computed in terms only of abstract homological boundary information. Furthermore, this minimal number can be realized on some manifold with non-empty boundary satisfying the abstract homological boundary information. In fact, we present all possible indices and types (connecting or disconnecting) of singularities realizing this minimal number. The Euler characteristics of all manifolds realizing this minimal number are obtained and the associated Lyapunov graphs of Morse type are described and shown to have the lowest topological complexity. 相似文献
97.
U.R. Lima M.C. Nasar R.S. Nasar M.C. Rezende J.H. Araújo 《Journal of magnetism and magnetic materials》2008
Nanoparticles of nickel–zinc ferrite have been prepared by using the citrate precursor method. According to scanning electron microscopy (SEM), the particle size is nanometric for the powder calcined at 350 °C/3.5 h. The phase formation has been studied by applying different calcining atmospheres, such as air and argon. Pure Ni–Zn ferrite has been observed when calcined in argon at the temperature of 350 °C. Hysteresis analyses have been done with magnetization of 53.01 emu/g at 350 °C and obtaining 84.62 emu/g at 1100 °C due to an optimization of domains formation at high temperature. Measures of reflectivity of Ni–Zn ferrite/epoxy composite have been obtained below 21% at 350 °C and above 96% at 1100 °C with a coercive field of 26.61 Oe. Low value of coercive field increased the mobilization of domains wall and increased the radiation absorption. 相似文献
98.
M C Rezende P Campodonico E Abuin J Kossanyi 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(6):1183-1190
The preparation and the solvatochromic behavior of two dyes, obtained by condensation of N,N'-dimethylbarbituric acid with dimethylaminobenzaldehyde and with 4,4'-bis(N,N-dimethylamino)benzophenone (Michler's ketone) are described. The latter dye is rather sensitive to the polarity of the medium, and in particular, to the hydrogen-bond-donor ability of protic solvents. The solvatochromism of both compounds is discussed in terms of the pi* and E(T)(30) solvent polarity scales and their differences in behavior interpreted with the aid of semiempirical calculations. 相似文献
99.
Thiago Augusto de Lima Burgo Camila Alves Rezende Sérgio Bertazzo André Galembeck Fernando Galembeck 《Journal of Electrostatics》2011,69(4):401-409
Electrostatic potential decay on corona-charged low-density polyethylene (LDPE) was recorded as a function of position and time, using a macroscopic scanning electrode and also Kelvin force microscopy. Potential decays independently in adjacent sample areas until reaching equilibrium at negative values (4.6 ± 0.7 V), irrespective of the initial potential signal. Other observations already described in literature were confirmed: negative potential decays slower than positive potential and the relative humidity has a large effect on the dissipation rates. These results are discussed considering ion exchange associated to adsorption and desorption of water clusters at the solid–gas interface. 相似文献
100.
Pedro J. de Rezende Flávio K. Miyazawa Anderson T. Sasaki 《Operations Research Letters》2013,41(5):552-555
We present PTASs for the disk cover problem: given geometric objects and a finite set of disk centers, minimize the total cost for covering those objects with disks under a polynomial cost function on the disks’ radii. We describe the first FPTAS for covering a line segment when the disk centers form a discrete set, and a PTAS for when a set of geometric objects, described by polynomial algebraic inequalities, must be covered. The latter result holds for any dimension. 相似文献