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排序方式: 共有166条查询结果,搜索用时 234 毫秒
31.
M.A. Continentino J.C. Fernandes R.B. Guimar aes H.A. Borges A. Sulpice J.-L. Tholence J.L. Siqueira J.B.M. da Cunha C.A. dos Santos 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):613-618
The system Cu2FeO2BO3 is an oxyborate belonging to the family of the ludwigites. In this paper we present AC susceptibility, magnetization measurements
and M?ssbauer spectroscopy on this material which allows for a complete characterization of its complex magnetic behavior.
We find an hierarchy of interactions which clearly defines three regimes with decreasing temperature. These are associated
with, the freezing of the Fe moments, the antiferromagnetic ordering of the Cu sub-lattice and finally the coupling between
both systems.
Received 25 September 1998 相似文献
32.
Graziela Teixeira de Oliveira Jaqueline Maria Siqueira Ferreira William Gustavo Lima Lucas Ferreira Alves Joaquim Maurício Duarte-Almeida 《Natural product research》2018,32(6):723-731
Ethanol extract and fractions obtained from fresh and dry aerial parts of Lippia alba were examined in order to determine their phytochemical composition, antioxidant capacity and antibacterial activities. The ethanol extracts and fractions exhibited an antioxidant effect by the DPPH assay, especially samples of fresh plant. HPLC analysis of the ethyl acetate fractions identified the presence of phenolic acids and flavonoids. The ethanol extract and fractions showed activity against reference and multidrug-resistant strains of Staphylococcus aureus and Enterococcus faecalis (MIC range 2000–250 μg/mL). The hexane and dichloromethane fractions of fresh plant showed better activity against reference strains of Escherichia coli (MIC of 250 and 125 μg/mL, respectively), but all extracts and fractions were less active against multidrug-resistant strains of all the Gram-negative species evaluated. The results showed that the extract and fractions of L alba aerial parts showed antibacterial activity, even against multidrug-resistant Gram-positive bacteria, and antioxidant effect (DPPH assay). 相似文献
33.
Costa B. A. Nunes W. D. G. Bembo L. H. Siqueira A. B. Caires F. Leles M. I. G. Ionashiro E. Y. 《Journal of Thermal Analysis and Calorimetry》2018,134(2):1205-1210
Journal of Thermal Analysis and Calorimetry - Coordination compounds of heavier lanthanides with terephthalate ligand have been synthesized and characterized employing simultaneous thermogravimetry... 相似文献
34.
Mrcia R. Siqueira Liange de Oliveira Diehl Robert A. Burrow 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(2):m67-m69
In the centrosymmetric title compound, [Co2(C12H10O2P)4(C5H5N)4(H2O)2], each approximately octahedral Co atom features two trans‐coordinated pyridine molecules, one water molecule, a terminally coordinated monodentate diphenylphosphinate ligand, and two bidentate diphenylphosphinate ligands that bridge the two Co atoms across a centre of inversion to form a dimeric binuclear complex. The discrete molecules are linked by double hydrogen bonds between the terminally coordinated diphenylphosphinate ligand and the water molecule to form a continuous chain along the crystallographic b axis. 相似文献
35.
36.
This work deals with the displacement of end-anchored copolymers by the addition of solvent displacer. The adsorption behavior of functionalized polystyrene-block-polybutadiene diblock copolymers from dilute solution in toluene using silicon wafers as solid substrates is investigated by means of null-ellipsometry. The desorption phenomena are observed by adding displacers of low molecular weight to the mixture. The displacers used are tetrahydrofuran (THF) and acetone. The critical composition of the binary solvent mixture at which the desorption is complete, is determined experimentally. 相似文献
37.
Fernanda A. Siqueira 《Tetrahedron letters》2010,51(16):2102-10631
In this Letter, we report, for the first time, the development of an efficient method for the intramolecular Heck reaction of arenediazonium salts in the synthesis of benzofuran and indole derivatives. In addition, this methodology allowed the synthesis of a series of dihydrobenzofuran acetic acid derivatives via a domino Heck-Matsuda coupling-carbonylation reaction. 相似文献
38.
Liniquer Andr Fontana Josili Demetrio Siqueira Joice Ceolin Bernardo Almeida Iglesias Paulo Cesar Piquini Ademir Neves Davi Fernando Back 《应用有机金属化学》2019,33(7)
New mixed‐valence cobalt complexes with ligands derived from pyridoxal were synthesized and characterized, and their application as mimetics of the peroxidase enzyme was investigated. Single‐crystal X‐ray diffraction was used to analyze all complex structures in the solid state and their electrochemical behavior was investigated. A reactivity pattern was observed in the complex synthesis regarding the cobalt compounds from which analogous zwitterionic derivatives were obtained. The importance of these compounds lies in understanding their behavior in an oxidizing environment and evaluating whether they can activate hydrogen peroxide to oxidize phenolic compounds. In nature, enzymes called peroxidases, which efficiently oxidize phenolic compounds, trigger many reactions involving the activation of hydrogen peroxide to oxidize organic substrates. However, these enzymes present several disadvantages, including denaturation and elevated costs. Therefore, these limitations can be overcome by expanding research into the study of synthetic catalysts for the oxidation of phenolic compounds using hydrogen peroxide, which is a highly relevant field of bioinorganic chemistry. 相似文献
39.
40.
Carlos Bruno Barreto Luna Danilo Diniz Siqueira Edcleide Maria Araújo Emanuel Pereira do Nascimento Joo Baptista da Costa Agra de Melo 《先进技术聚合物》2022,33(1):111-124
Polypropylene (PP) blends with acrylonitrile-butadiene-styrene (ABS) were prepared using the styrene-ethylene-butylene-styrene copolymer (SEBS) as a compatibilizing agent. The blends were prepared in a co-rotational twin-screw extruder and injection molded. Torque rheometry, Izod impact strength, tensile strength, heat deflection temperature (HDT), differential scanning calorimetry, thermogravimetry, and scanning electron microscopy properties were investigated. The results showed that there was an increase in the torque of PA6/ABS blends with SEBS addition. The PP/ABS/SEBS (60/25/15%) blend showed significant improvement in impact strength, elongation at break, thermal stability, and HDT compared with neat PP. The elastic modulus and tensile strength have not been significantly reduced. The degree of crystallinity and the crystalline melting temperature increased, indicating a nucleating effect of ABS. The PP/ABS blends compatibilized with 12.5% and 15% SEBS presented morphology with well-distributed fine ABS particles with good interfacial adhesion. As a result, thermal stability has been improved over pure PP and the mechanical properties have been increased, especially impact strength. In general, the addition of the SEBS copolymer as the PP/ABS blend compatibilizer has the advantage of refining the blend's morphology, increasing its toughness and thermal stability, without jeopardizing other PP properties. 相似文献