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151.
In this study, the synthesis, structural characterisation and mesomorphic and optical properties of seven new bent-shaped and polycatenar bent-shaped compounds derived from chalcone and cyanopyridine are reported. The mesomorphic behaviour was investigated by differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (XRD) and correlated with the molecular structure. Two bent-core hexacatenars molecules (Ic and IIc) presented liquid crystalline properties, showing a hexagonal columnar (Colh) phases at room temperature, being each disc constituted by two mesogens. Optical studies were also performed for the final molecules, being conducted by ultraviolet-visible and fluorescence spectrometry. The cyanopyridine derivatives show moderate luminescence quantum yields, ranging between 18% and 27%, with emission maxima around 371 nm. It is also shown that while the chalcone central unit favours a calamitic liquid crystalline behaviour in molecules with lower number of aliphatic chains, a polycatenar structure with cyanopyridine as the central unit favours a Colh arrangement, also providing luminescence properties to the molecule. 相似文献
152.
Daniela Belli Dell’Amico Luca Labella Fabio Marchetti Simona Samaritani 《Coordination chemistry reviews》2010,254(5-6):635-645
In this review we summarize some recent literature data concerning synthetic procedures, properties, structure, reactivity and applications of halo-carbonyl complexes of palladium, platinum and gold, taking into consideration that the organometallic chemistry of these metals, with a particular attention to the halo-carbonyls, has been reviewed 20 years ago [F. Calderazzo, J. Organomet. Chem. 400 (1990) 303]. A brief overview of the early studies is provided. 相似文献
153.
Oana Carp Luminita Patron Daniela C. Culita Petru Budrugeac Marcel Feder Lucian Diamandescu 《Journal of Thermal Analysis and Calorimetry》2010,101(1):181-187
The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000
(Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air
and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but
atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower
initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the
magnetite surface decomposes in air through a strong sharp exothermic process up to ~450 °C while in argon atmosphere two
endothermic stages are identified, one in the temperature range 160–450 °C and the other at 530–800 °C. 相似文献
154.
Dos Santos VA Dos Santos DP Castro-Gamboa I Zanoni MV Furlan M 《Molecules (Basel, Switzerland)》2010,15(10):6956-6973
This work describes the isolation of the secondary metabolites identified as the quinonemethides maytenin (1) and pristimerin (2) from Maytenus ilicifolia extracts obtained from root barks of adult plants and roots of seedlings and their quantification by high performance liquid chromatography coupled to a diode array detector. The electrochemical profiles obtained from cyclic voltammetry and a coulometric detector coupled to high-performance liquid chromatography contributed to the evaluation of their antioxidant capacity. The antioxidant properties of individual components and the crude extracts of the root barks of Maytenus ilicifolia were compared and the possible synergistic associations of quinonemethide triterpenes and phenolic substances were investigated by using rutin as a model phenolic compound. 相似文献
155.
Gomes de Melo J de Sousa Araújo TA Thijan Nobre de Almeida e Castro V Lyra de Vasconcelos Cabral D do Desterro Rodrigues M Carneiro do Nascimento S Cavalcanti de Amorim EL de Albuquerque UP 《Molecules (Basel, Switzerland)》2010,15(12):8534-8542
The objective of this study was to evaluate antiproliferative activity, antioxidant capacity and tannin content in plants from semi-arid northeastern Brazil (Caatinga). For this study, we selected 14 species and we assayed the methanol extracts for antiproliferative activity against the HEp-2 (laryngeal cancer) and NCI-H292 (lung cancer) cell lines using the (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazole) (MTT) method. In addition, the antioxidant activity was evaluated with the DPPH (2,2-diphenyl-2-picrylhydrazyl) assay, and the tannin content was determined by the radial diffusion method. Plants with better antioxidant activity (expressed in a dose able to decrease the initial DPPH concentration by 50%, or IC50) and with higher levels of tannins were: Poincianella pyramidalis (42.95±1.77 μg/mL IC50 and 8.17±0.64 tannin content), Jatropha mollissima (54.09±4.36μg/mL IC50 and 2.35±0.08 tannin content) and Anadenanthera colubrina (73.24±1.47 μg/mL IC50 and 4.41±0.47 tannin content). Plants with enhanced antiproliferative activity (% living cells) were Annona muricata (24.94±0.74 in NCI-H292), Lantana camara (25.8±0.19 in NCI-H292), Handroanthus impetiginosus (41.8±0.47 in NCI-H292) and Mentzelia aspera (45.61±1.94 in HEp-2). For species with better antioxidant and antiproliferative activities, we suggest future in vitro and in vivo comparative studies with other pharmacological models, and to start a process of purification and identification of the possible molecule(s) responsible for the observed pharmacological activity. We believe that the flora of Brazilian semi-arid areas can be a valuable source of plants rich in tannins, cytotoxic compounds and antioxidant agents. 相似文献
156.
Msimelelo P. Siswana Kenneth Ikechukwu Ozoemena Daniela A. Geraldo Tebello Nyokong 《Journal of Solid State Electrochemistry》2010,14(8):1351-1358
This work reports for the first time that nanostructured nickel (II) phthalocyanine/multiwalled carbon nanotubes composite supported on a basal plane pyrolytic electrode (NiPcNP/MWCNT-BPPGE) could potentially serve as a viable platform for the sensitive electrocatalytic detection of asulam pesticide at phosphate-buffered solution (pH 7.0 conditions). Comparative electron transfer dynamics, using ferrocyanide/ferricyanide as outer sphere redox probe, were examined and interpreted using the Davies–Compton theoretical framework dealing with voltammetry at spatially heterogeneous electrodes. The NiPcNP/MWCNT-BPPGE exhibits fast electron transport and excellent electrocatalytic behavior toward asulam, with an onset potential of about 150 mV lower than observed for the electrode without MWCNTs or bare BPPGE. Also, NiPcNP/MWCNT-BPPGE displayed good analytical performance for asulam, with a detection limit of 0.285 µM, a linear concentration range of 91–412 µM, and a sensitivity of 44.6 µA mM?1. 相似文献
157.
Marli Roehsig Daniela Mendes Louzada de Paula Sidnei Moura Edna Maria de Albuquerque Diniz Mauricio Yonamine 《Journal of separation science》2010,33(14):2115-2122
A number of fatty acid ethyl esters (FAEEs) have recently been detected in meconium samples. Several of these FAEEs have been evaluated as possible biomarkers for in utero ethanol exposure. In the present study, a method was optimized and validated for the simultaneous determination of eight FAEEs (ethyl laurate, ethyl myristate, ethyl palmitate, ethyl palmitoleate, ethyl stearate, ethyl oleate, ethyl linoleate and ethyl arachidonate) in meconium samples. FAEEs were extracted by headspace solid‐phase microextraction. Analyte detection and quantification were carried out using GC‐MS operated in chemical ionization mode. The corresponding D5‐ethyl esters were synthesized and used as internal standards. The LOQ and LOD for each analyte were <150 and <100 ng/g, respectively. The method showed good linearity (r2>0.98) in the concentration range studied (LOQ – 2000 ng/g). The intra‐ and interday imprecision, given by the RSD of the method, was lower than 15% for all FAEEs studied. The validated method was applied to 63 authentic specimens. FAEEs could be detected in alcohol‐exposed newborns (>600 ng/g cumulative concentration). Interestingly, FAEEs could also be detected in some non‐exposed newborns, although the concentrations were much lower than those measured in exposed cases. 相似文献
158.
159.
Daniela Carta Maria F. Casula Salvatore Bullita Andrea Falqui Anna Corrias 《Journal of nanoparticle research》2011,13(8):3489-3501
A series of novel nanocomposites constituted of FeCo nanoparticles dispersed in an ordered cubic Im3m mesoporous silica matrix (SBA-16) have been successfully synthesized using the wet impregnation method. SBA-16, prepared
using the non-ionic Pluronic 127 triblock copolymer as a structure-directing agent, is an excellent support for catalytic
nanoparticles because of its peculiar three-dimensional cage-like structure, high surface area, thick walls, and high thermal
stability. Low-angle X-ray diffraction, N2 physisorption, and transmission electron microscopy analyses show that after metal loading, calcination at 500 °C, and reduction
in H2 flux at 800 °C, the nanocomposites retain the well-ordered structure of the matrix with cubic symmetry of pores. FeCo alloy
nanoparticles with spherical shape and narrow size distribution (4–8 nm) are homogeneoulsy distributed throughout the matrix
and they seem in a large extent to be allocated inside the pores. 相似文献
160.
Daniela Schiavo 《光谱学快报》2013,46(7):354-360
ABSTRACT The effects caused by concomitants [Na(I), K(I), Ca(II), and Mg(II)] on the atomization of cobalt and manganese by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) were here studied. The main concomitants were chosen according to typical major elements found in foods and beverages. Severe interference effects were caused by all concomitants. The interferences varied from ?101.0% to +360.0% and ?117.5% to +175.5% for Co and Mn, respectively. These data demonstrated a frequently paradoxical situation in spectrochemical analysis, that is, efforts are directed toward the introduction of a higher amount of sample, however, when this condition is attained, there is the manifestation of severe processes of interferences. These interference processes require the application of either previous separation steps or special strategies of calibration. 相似文献