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81.
Ana Filipa L.O.M. Santos André R. Monteiro Jorge M. Gonçalves William E. Acree Maria D.M.C. Ribeiro da Silva 《The Journal of chemical thermodynamics》2011,43(7):1044-1049
In this paper, the first, second and mean (N?O) bond dissociation enthalpies (BDEs) were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, , at T = 298.15 K, of 2,2′-dipyridil N-oxide and 2,2′-dipyridil N,N′-dioxide. These values were calculated from experimental thermodynamic parameters, namely from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, , at T = 298.15 K, obtained from the standard molar enthalpies of combustion, , measured by static bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from Knudsen mass-loss effusion method. 相似文献
82.
J. Pires M. Brotas de Carvalho F. R. Ribeiro E. G. Derouane 《Reaction Kinetics and Catalysis Letters》1991,43(2):313-319
The silicoaluminophosphate SAPO-37 as well as ZSM-20 zeolite have a faujaside-like structure and are potentially useful as catalysts. We report in this work different procedures to decompose the organic template occluded in SAPO-37. The texture of the final products was analyzed by means of nitrogen adsorption. The acid properties of SAPO-37 and ZSM-20 were also compared by IR measurements of adsorbed pyridine and related to the acidic properties of the presently commonly used cracking catalyst zeolite Y.
-37, ZSM-20 . , -37. . -37 ZSM-20 - . , .相似文献
83.
André A. S. T. Ribeiro Ricardo B. de Alencastro 《Journal of computational chemistry》2012,33(8):901-905
A mixed Monte Carlo/Molecular Dynamics method using the trial moves for peptide backbone sampling known as Concerted Rotations with Angles was implemented. The algorithm was used to study polyalanine systems. Equivalent results to conventional Molecular Dynamics were obtained for simulations of Ala6 in implicit solvent. To test the efficiency of the implemented method, several 150 ns simulations of Ala12 in explicit water were performed. The results show that the present method yields significantly faster formation of secondary structure than the conventional Molecular Dynamics simulations. This opens the possibility to selectively sample alanine‐rich regions of larger peptides or proteins. It remains to be established whether hydrophilic amino acid residues can be successfully treated with the present methodology. © 2012 Wiley Periodicals, Inc. 相似文献
84.
D. C. Oliveira Y. Messaddeq K. Dahmouche S. J. L. Ribeiro R. R. Gonçalves A. Vesperini D. Gindre J.-M. Nunzi 《Journal of Sol-Gel Science and Technology》2006,40(2-3):359-363
Organic-inorganic hybrid materials were prepared from an ureasil precursor (ureapropyltriethoxysilane designated as UPTES)
and acrylic acid modified zirconium (IV) n-propoxide. Thin films containing rhodamine 6G (Rh6G) were prepared by spin-coating on glass substrates with different Zr:Si molar ratios (Zr:Si = 75:25, 50:50 and 25:75). Refractive
index, thickness, number of propagating modes and attenuation coefficient were measured at 543.5, 632.8 and 1550 nm wavelengths
by the prism coupling technique. Distributed feedback (DFB) laser effect was observed and studied as a function of films thickness
and refractive index. 相似文献
85.
H. S. Barud R. M. N. Assunção M. A. U. Martines J. Dexpert-Ghys R. F. C. Marques Y. Messaddeq S. J. L. Ribeiro 《Journal of Sol-Gel Science and Technology》2008,46(3):363-367
Bacterial cellulose (BC) hydrated membranes present nanometric reticulated structure that can be used as a template in the
preparation of new organic–inorganic hybrids. BC–silica hybrids were prepared from BC membranes and tetraethoxysilane, (TEOS)
at neutral pH conditions at room temperature. Macroscopically homogeneous membranes were obtained containing up to 66 wt.%
of silica spheres, 20–30 nm diameter. Scanning electron micrographs clearly show the silica spheres attached to cellulose
microfibrils. By removing the cellulose, the silica spheres can be easily recovered. The new hybrids are stable up to 300 °C
and display a broad emission band under UV excitation assigned to oxygen-related defects at the silica particles surface.
Emission color can be tuned by changing the excitation wavelength. 相似文献
86.
Lourenço JM Ribeiro PA Botelho do Rego AM Braz Fernandes FM Moutinho AM Raposo M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8103-8109
The amount of counterions in layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) has been determined with X-ray photoelectron spectroscopy (XPS) for films prepared from solutions with various NaCl concentrations. Sodium and chloride counterions are present in LBL films produced from salt solutions, which are located at the surface and in the bulk of the films. The percentage of bulk counterions increases with the ionic strength of the polyelectrolyte before reaching a constant value. The bulk sodium/sulfur percentage ratios tend to 0.8 for samples washed with pure water and for samples washed with NaCl aqueous solutions, while the bulk chlorine/nitrogen percentage ratios tend to 0.5 for the same samples. The ratio between the percentages of polyelectrolyte ionic groups lies close to unity for all samples, indicating that counterions do not contribute to charge compensation in the polyelectrolyte during the adsorption process. The presence of counterions in LBL films is explained by Manning condensation near the polyelectrolyte ionic groups, leading to inter-polyelectrolyte ionic bondings via ionic networks. It is believed that condensation leads to the formation of NaCl crystallites in these LBL films, which was confirmed by X-ray diffraction measurements. 相似文献
87.
Novel extracellular polymeric substances produced by Cupriavidus necator IPT 027 grown on glucose and crude glycerol originated from biodiesel 下载免费PDF全文
The aim of this study was to evaluate the production and properties of novel extracellular polymeric substances (EPS) from glucose (EPS 1) and crude glycerol (CG) from castor beans oil (EPS 2). Cupriavidus necator IPT 027 cultivated with glucose and CG (35 °C, 150 rpm, 72 hr, pH 7, shaker) produced approximately 1.60 ± 0.01 and 2.83 ± 0.02 g l?1 EPS, respectively, with high‐molecular weight (3.89 × 105 and 1.89 × 107 Da) and constituted of different functional groups such as uronic acid, monosaccharides (glucose, mannose, arabinose, and fucose) and primary amine group. The composition of the fermentable substrate influenced the melting temperature (221.11 and 230.18 °C), crystallinity (34.36% and 37.11%), degradation temperature (255.06 and 296.62 °C) and morphology. EPS showed pseudoplastic non‐Newtonian fluid behavior in the aqueous solutions, presenting potential applicability biotechnological and industrial mainly in food industry as emulsifiers and biosurfactants. This is the first study on the production and characterization of EPS obtained by C. necator IPT 027 in culture with glucose and CG. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
88.
89.
Margarida M. Antunes Andreia F. Silva Carolina D. Bernardino Auguste Fernandes Filipa Ribeiro Anabela A. Valente 《Molecules (Basel, Switzerland)》2021,26(23)
Heterogeneous catalysis, which has served well the petrochemical industry, may valuably contribute towards a bio-based economy by sustainably enabling selective reactions to renewable chemicals. Carbohydrate-containing matter may be obtained from various widespread sources and selectively converted to furanic platform chemicals: furfural (Fur) and 5-(hydroxymethyl)furfural (Hmf). Valuable bioproducts may be obtained from these aldehydes via catalytic transfer hydrogenation (CTH) using alcohols as H-donors under relatively moderate reaction conditions. Hafnium-containing TUD-1 type catalysts were the first of ordered mesoporous silicates explored for the conversion of Fur and Hmf via CTH/alcohol strategies. The materials promoted CTH and acid reactions leading to the furanic ethers. The bioproducts spectrum was broader for the reaction of Fur than of Hmf. A Fur reaction mechanism based on literature data was discussed and supported by kinetic modelling. The influence of the Hf loading and reaction conditions (catalyst load, type of alcohol H-donor, temperature, initial substrate concentration) on the reaction kinetics was studied. The reaction conditions were optimized to maximize the yields of 2-(alkoxymethyl)furan ethers formed from Fur; up to 63% yield was reached at 88% Fur conversion, 4 h/150 °C, using Hf-TUD-1(75), which was a stable catalyst. The Hf-TUD-1(x) catalysts promoted the selective conversion of Hmf to bis(2-alkoxymethyl)furan; e.g., 96% selectivity at 98% Hmf conversion, 3 h/170 °C for Hf-TUD-1(50). 相似文献
90.
M. C. Morán T. Laranjeira A. Ribeiro M. G. Miguel B. Lindman 《Journal of Dispersion Science and Technology》2013,34(10):1494-1499
Novel DNA-chitosan particles were prepared based on associative phase separation and interfacial diffusion. These particles formed at water/water emulsion type interfaces were characterized with respect to several properties including stability, DNA conformational state, and entrapment and release of DNA. In particular it was found that the chitosan molecular weight is a good controlling parameter. 相似文献