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51.
The development of a FIA system for the determination of total choline content in several types of milk is described. The samples were submitted to hydrochloric acid digestion before injection into the system and passed through an enzymatic reactor containing choline oxidase immobilised on glass beads. This enzymatic reaction releases hydrogen peroxide which then reacts with a solution of iodide. The decrease in the concentration of iodide ion is quantified using an iodide ion selective tubular electrode based on a homogeneous crystalline membrane. Validation of the results obtained with this system was performed by comparison with results from a method described in the literature and applied to the determination of total choline in milks. The relative deviation was always < 5%. The repeatability of the method developed was assessed by calculation of the relative standard deviation (RSD) for 12 consecutive injections of one sample. The RSD obtained was < 0.6%. 相似文献
52.
Joseína Moutinho Tavares de Souza Maria do Carmo Rangel 《Reaction Kinetics and Catalysis Letters》2002,77(1):29-34
The replacement of chromium by aluminium in high temperature shift catalysts was investigated. It was found that aluminium-doped hematite is a convenient candidate as an environmental friendly catalyst. 相似文献
53.
54.
Muhammad Rafiq Muhammad Khalid Muhammad Nawaz Tahir Muhammad Umair Ahmad Muhammad Usman Khan Muhammad Moazzam Naseer Ataualpa Albert Carmo Braga Shabbir Muhammad Zahid Shafiq 《应用有机金属化学》2019,33(11)
Present study advocates the joint experimental and computational studies of two potent benzoimidazole‐based hydrazones with chemical formula C23H18F2N4O ( 5a ) and C25H22FN5O3 ( 5b ). Both 5a and 5b were synthesized and resolved into their crystal structures using SC‐XRD for the assessment of bond lengths, bond angles, unit cells and space groups. The structures of 5a and 5b were chemically characterized using infrared (FT‐IR), UV–Visible, nuclear magnetic resonance (1H‐NMR and 13C‐NMR), EIMS and elemental analysis. DFT at M06‐2X/6‐31G(d,p) level of theory was performed to get optimized structures and countercheck the experimental findings. Overall, DFT findings show excellent concurrence with the experimental data which confirms the purity of both compounds. FMO, NBO analysis, MEP surfaces and nonlinear optical (NLO) properties were explored at same level of theory. UV–Vis analysis at TDDFT/M06‐2X/6‐31G(d,p) level of theory showed that 5b is red shifted with λmax 331.69 nm as compared to 5a with λmax 240.25 nm. Global reactivity parameters were estimated using energy of FMOs indicated the greater harness value than the softness values of 5a and 5b . NBO analysis confirmed that the presence of non‐covalent interactions, hydrogen bonding and hyper conjugative interactions are pivotal cause for the existence of 5a and 5b in the solid‐state. NLO results of 5a and 5b were observed better than standard molecule recommended the NLO activity of said molecules for optoelectronic applications. 相似文献
55.
Ivone Peres Sandra Rocha Joana A. Loureiro Maria do Carmo Pereira Galya Ivanova Manuel Coelho 《Journal of nanoparticle research》2012,14(9):1-11
We report a simple and effective supercritical fluid route to uniformly load ultrafine metal nanoparticles on the hydrophobic surfaces of graphene sheets. In the presence of supercritical carbon dioxide, PtRu alloy nanoparticles are decorated evenly on functionalized graphene sheets (FGSs) upon the reduction of organic platinum (II) and ruthenium (III) precursors, and its application as an electrocatalyst for methanol oxidation is studied. Transmission electron microscopy observation shows that highly dispersed PtRu metallic nanoparticles with an average size of about 3.11?nm are uniformly and densely distributed on the hydrophobic surface of FGSs. X-ray diffraction patterns demonstrate that the particles had a face-centered cubic crystal structure, and X-ray photoelectron spectroscopy analysis indicates the existence of zero-valence metals. Compared with the widely used Vulcan XC-72 carbon black, the PtRu/FGS composites exhibit superior catalytic activity and stability for methanol oxidation. The huge surface area of graphene and uniform distribution of nanosized metal particles are two critical factors for the significantly enhanced electrocatalytic efficiency. The findings suggest that the supercritical fluid method is highly efficient in preparing graphene-supported metallic catalysts, and FGSs serve as a favorable electrocatalytic carrier for direct methanol fuel cells. 相似文献
56.
Manfredo P. do Carmo Qiaoling Wang Changyu Xia 《Annali di Matematica Pura ed Applicata》2010,189(4):643-660
In this paper, we study eigenvalues of elliptic operators in divergence form on compact Riemannian manifolds with boundary
(possibly empty) and obtain a general inequality for them. By using this inequality, we prove universal inequalities for eigenvalues
of elliptic operators in divergence form on compact domains of complete submanifolds in a Euclidean space, and of complete
manifolds admitting special functions which include the Hadamard manifolds with Ricci curvature bounded below, a class of
warped product manifolds, the product of Euclidean spaces with any complete manifold and manifolds admitting eigenmaps to
a sphere. 相似文献
57.
58.
Sandra Rocha Rumen Krastev Andreas F Thünemann M Carmo Pereira Helmuth M?hwald Gerald Brezesinski 《Chemphyschem》2005,6(12):2527-2534
The adsorption of amyloid beta-peptide at hydrophilic and hydrophobic modified silicon-liquid interfaces was characterized by neutron reflectometry. Distinct polymeric films were used to obtain noncharged (Formvar), negatively (sodium poly(styrene sulfonate)) and positively charged (poly(allylamine hydrochloride)) hydrophilic as well as hydrophobic surfaces (polystyrene and a polysiloxane-dodecanoic acid complex). Amyloid beta-peptide was found to adsorb at positively charged hydrophilic and hydrophobic surfaces, whereas no adsorbed layer was detected on hydrophilic noncharged and negatively charged films. The peptide adsorbed at the positively charged film as patches, which were dispersed on the surface, whereas a uniform layer was observed at hydrophobic surfaces. The thickness of the adsorbed peptide layer was estimated to be approximately 20 A. The peptide formed a tightly packed layer, which did not contain water. These studies provide information about the affinity of the amyloid beta-peptide to different substrates in aqueous solution and suggest that the amyloid fibril formation may be driven by interactions with surfaces. 相似文献
59.
The stability constants of the 1:1 and 1:2 complexes of nickel and copper(II) with beta-ethylthioethylenethioglycollic acid have been determined at 25 degrees at ionic strength 1.0 (NaClO(4)). The values for the nickel complexes are K(1) = 1.11 +/- 0.06 x 10(2) (spectrophotometrically) or 1.25 +/- 0.11 x 10(2) (potentiometrically) and K(2) = 3.04 +/- 0.24 x 10(2) (potentiometrically). The corresponding values for the copper complexes are K(1) = 1.27 +/- 0.02 x 10(3) or 1.28 +/- 0.03 x 10(3) and K(2) = 7.29 +/- 0.30 x 10(2). 相似文献
60.
M. Carmo Freitas 《Journal of Radioanalytical and Nuclear Chemistry》1995,192(2):171-181
k0-Based instrumental neutron activation analysis (k0 INAA) was used to determine the concentrations of Cr, Fe, Co, Zn, Se, Sb and Hg in the vascular plantsCistus salvifolius andInula viscosa and in the lichenParmelia sulcata. The samples were collected in the neighbourhood of industrial complexes. The elemental accumulation in the vascular plants and the lichen are compared to optimize the choice of the bioaccumulator. It is concluded thatP. sulcata seems to be the best accumulator of the three species for the elements studied;Cistus salvifolius is sensitive to the contents of Zn, Fe, Cr and Sb in the air;Inula viscosa seems to accumulate Fe, Sb, Co, Cr and Zn. Nevertheless, it is concluded that lichen is a good air pollution indicator, while the vascular plants are not due to the large seasonal variations found in the elemental concentrations. 相似文献