Ammonia electro-oxidation on Pt–Ir alloys has been studied applying cyclic voltammetry and differential electrochemical mass spectrometry (DEMS), and the results were compared with pure Pt. ...Bimetallic alloys were prepared by electrodeposition and characterized using X-ray diffractometry (XRD) and Auger spectroscopy, before and after oxidation of ammonia. Pt/Ir atomic composition was 70:30 obtained from 1:1 solutions. Substitution alloys were established where Ir atoms replace Pt positions in the face-centered cubic structure. Preferential crystal orientations were detected in the electrodeposits with the development of a crystallographic texture. DEMS showed that N
2
is the main product during ammonia oxidation for both Pt and Pt–Ir, but the formation of nitrogen oxides is observed for
E
> 0.8 V
RHE
. The yield of N
2
is higher for the alloy, which also displays lower poisoning of the surface when increasing ammonia concentration. These results confirm Pt–Ir alloys as alternatives to Pt electrodes concerning ammonia oxidation. Finally, it was observed that XRD patterns, as well as texture coefficient values, change after using the electrodeposits for ammonia oxidation, with the less compact planes the more affected ones.
The carotenoid composition of butternut squash (Cucurbita moschata) cultivated in the province of Santiago del Estero, Argentina, was determined. The main carotenoids isolated were identified as ...beta-carotene (beta,beta-carotene), alpha-carotene (beta,epsilon-carotene), and lutein (beta,epsilon-carotene-3,3'-diol) and the minor carotenoids, as phytofluene (7,8,11,12,7',8'-hexahydro-psi,psi-carotene), zeta-carotene (7,8,7',8'-tetrahydro-psi,psi-carotene), neurosporene (7,8-dihydro-psi,psi-carotene), violaxanthin (5,6,5',6'- diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene-3,3'-diol) and neoxanthin (5,6-epoxy-6,7-didehydro-5,6,5',6'-tetrahydro-beta,beta- carotene-3,5,3'-triol). In some samples, 5,6,5',6'-beta-carotene diepoxide, (5,6,5',6'-diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene) and flavoxanthin (5,8-epoxy-5,8-dihydro-beta,epsilon-carotene-3,3'-diol) were detected. The presence of cis-isomers of beta,beta-carotene was also detected by HPLC. The vitamin A value obtained was 432 micrograms RE/100 g fresh sample, which indicates that this vegetable is an important source of provitamin A.
Metallic deposits of platinum-ruthenium were produced on a gold substrate by electrodeposition from salts in platinum and ruthenium solutions. These deposits were characterized by X-ray diffraction, ...Auger electron spectroscopy and X-ray photoelectron spectroscopy. The XRD studies showed a crystalline alloy whose structure was cubic centered on the face; that is, an alloy of one phase as a substitutional solid solution where the platinum atoms were replaced by ruthenium atoms. Some deposits grew with the crystals oriented according to a preferential direction and developed a crystallographic texture. The XPS analysis revealed that, in principle, there are no compounds with oxidation states different from metal ruthenium and metal platinum. Good correlations were obtained between the values of the ratios in atomic composition of Pt–Ru for the different samples calculated for XPS and Auger spectroscopy. The catalytic activity of the electrodeposits was measured in methanol solutions. From the XRD studies, the network parameters and the crystallographic texture were compared before and after using them in electrochemical methanol oxidation. The distribution of the observed relative integrated intensities of the diffraction patterns of the deposits showed a variation which is more evident when the deposit has a preferential grain orientation. The reflective power of planes (111) decreases after methanol oxidation.
The reduction-oxidation processes and conducting properties of manganese dioxide films prepared by electrochemical deposition on Pt substrate were studied in borate/boric acid solutions using ...electrochemical impedance spectroscopy (EIS). The characteristic parameters of the film can be determined as a function of the manganese oxide deposition routine as well as film thickness by application of transfer function analysis using non-linear fit routines. A model developed for thin layer intercalation electrodes, which is based on the insertion of protons and electrons, was used and the diffusion coefficients of protons were calculated for different manganese oxide thicknesses. The reversible behaviour of the manganese oxides during discharge-charge processes as a function of deposition routines was analyzed. Data obtained under a wide variety of experimental conditions show that the film generated on Pt substrate behaves as a
n-type semiconductor.
The potentiodynamic behaviour of colloidal manganese hydroxide–oxide films obtained by chemical precipitation on a conducting substrate in alkaline solutions is described. The voltammetric response ...of cycled electrodes shows a main redox couple which is associated with the Mn(III)/Mn(IV) reaction occurring in solid state. The observed dependence of peak currents and peak potentials on sweep rate, charge and solution pH is similar to that reported for manganese and iridium oxides obtained by cycling the base metal. The optical response of cycled hydrous manganese oxide films is studied by
in-situ ellipsometry. Data can be explained using an anisotropic single layer model. The optical anisotropy is related to the morphology of the hydrous oxide layer. The electroreduction process produces a decrease of the refractive indices and a pronounced diminution of the extinction coefficients yielding a practically transparent film.
The proto-oncogene c-Kit, a transmembrane receptor tyrosine kinase, is an important regulator of cell growth whose constitutively active oncogenic counterpart, v-kit, induces sarcomas in cats. ...Mutations in murine c-kit that reduce the receptor tyrosine kinase activity cause deficiencies in the migration and proliferation of melanoblasts, hematopoietic stem cells, and primordial germ cells. We therefore investigated whether c-Kit regulates normal human melanocyte proliferation and plays a role in melanomas. We show that normal human melanocytes respond to mast cell growth factor (MGF), the Kit-ligand that stimulates phosphorylation of tyrosyl residues in c-Kit and induces sequential phosphorylation of tyrosyl residues in several other proteins. One of the phosphorylated intermediates in the signal transduction pathway was identified as an early response kinase (mitogen-activated protein MAP kinase). Dephosphorylation of a prominent 180-kDa protein suggests that MGF also activates a phosphotyrosine phosphatase. In contrast, MGF did not induce proliferation, the cascade of protein phosphorylations, or MAP kinase activation in the majority of cells cultured from primary nodular and metastatic melanomas that grow independently of exogenous factors. In the five out of eight human melanoma lines expressing c-kit mRNAs, c-Kit was not constitutively activated. Therefore, although c-Kit-kinase is a potent growth regulator of normal human melanocytes, its activity is not positively associated with malignant transformation.
There are no national dietary surveys regarding nutrient intake of Argentine population. On the other hand, nutrient content of foods in Argentina, as in other Latin American countries, is unknown ...because there are no data on food composition. Therefore, nutrient intakes must be calculated using foreign composition tables. In relation to vitamin A nutritional status, high prevalence of low vitamin A intake and low plasma retinol levels have been found in the eighties in several groups of university students. In this report, results of a 7-day dietary survey of students attending the course of Nutrition in the Universities of Buenos Aires, Luján and Tucumán are presented. Information was processed in a PC Computer (VAN Program, Lujan University, Argentina) to obtain the mean daily intake of carotenes with and without provitamin A activity, according to the German Food Composition Tables. The results showed that provitamin A carotenes provided between 40 and 82% of the vitamin A recommended allowances and that about 20% of the population had total carotene intake lower than 4 mg/day. These results are in agreement with other dietary surveys carried out in students in previous years and are a consequence of some characteristic feeding habits of the Argentine population. In order to obtain more reasonable results regarding actual intakes in our population, study of the composition of national foods would be imperative.
The galvanostatic electrodeposition of manganese dioxide films in the thickness range from 0 to 1000 nm was investigated by in situ ellipsometry. The results obtained can be fit into the whole ...thickness range in terms of the uniaxial anisotropy of the film. The optical indices and thicknesses were calculated. The anisotropic properties may be related to a preferential orientation of the deposits.
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