Novel modified electrodes bearing dispersed Pd and Pt particles have been prepared from poly (allyl ether of the p-benzenesulfonic acid) films with incorporated nickel particles making use of galvanic displacement reactions. The SEM analysis of the new modified electrodes revealed efficient deposition of Pd but weak up-take of Pt. Electrocatalytic hydrogenation of several classes of organic substrates were carried out using the MEs Ni, Ni/Pd and Ni/Pt. The Ni/Pd ME showed to be the best of them for the hydrogenation of double, triple and carbonyl bonds. The complete hydrogenation of the aromatic rings for the well-adsorbed substrates acetophenone and benzophenone is noteworthy.

Este trabalho apresenta dois novos eletrodos de grafite modificados que foram preparados via polimerização da função fenólica, previamente funcionalizada por grupos azo (bipiridina e 2-metoxipiridina), que atuam como estruturas chaves para a ancoragem de ligantes de interesse. As sínteses dos monômeros BAP (4-([2,2’]bipiridinil-4-ilazo)-fenol) e PAPmetóxi (5-(4-hidroxifenilazo)piridin-2-metóxi) foram simples, deram bons rendimentos e os monômeros foram facilmente eletropolimerizados, levando à formação de eletrodos modificados (EM) química e mecanicamente estáveis. Em solução aquosa e em circuito aberto, o EM PAP-metóxi formou complexos estáveis com Cd, Cu e Pb, produzindo picos redox bem definidos, demonstrando o grande potencial deste eletrodo para futuras aplicações analíticas. O monômero BAP foi utilizado para produzir um complexo de rutênio (BAP-Ru) que foi eletropolimerizado entre +0.50 e +0.75V (vs. Ag/AgCl), permitindo que o rutênio permanecesse disponível para atuar como catalisador. O EM BAP-Ru oxidou seletivamente uma variedade de substratos orgânicos dando produtos com rendimentos próximos ou melhores que aqueles obtidos por catálise homogênea com complexos de rutênio similares, ou quando este tipo de catalisador é impregnado em pasta de carbono.

This work presents two new modified carbon electrodes which were prepared via the polymerization of a phenolic moiety previously functionalized with azo groups (bipyridine and 2-methoxypyridine) as key structures to anchor the desired ligands. The syntheses of BAP (4-([2,2’]-bipyridinyl-4-ylazo)-phenol) and PAPmethoxy (5-(4-hidroxyphenylazo) pyridin-2-methoxy) were simple to perform, gave good yields and the monomers were easily electropolymerized resulting in chemically and mechanically stable modified electrodes. The PAP-methoxy ME formed stable complexes with Cd, Cu and Pb in aqueous media at open circuit and produced well defined redox peaks, showing good potential for future analytical applications. The BAP monomer was used to produce a ruthenium complex (BAP-Ru) which was electropolymerized from +0.50 to +0.75V (vs. Ag/AgCl) to leave the ruthenium available to act as a catalyst. The BAP-Ru ME was able to oxidize a variety of organic substrates with good selectivity. The yields obtained were either similar to, or better than, those obtained by homogeneous catalysis using a similar ruthenium catalyst or when this type of catalyst is supported in a carbon paste electrode.

Este trabajo tuvo como objetivo clasificar 838 introducciones de ajonjolí, Sesamum indicum L., de la colección de germoplasma de Venezuela sobre la base de 17 variables de naturaleza cualitativa utilizando técnicas de análisis multivariado. La descripción se realizó a partir de 42 caracteres morfo-agronómicos utilizando los descriptores de sésamo. Las siembras de evaluación fueron efectuadas en Maracay, estado Aragua. Los grupos de individuos fueron determinados por clasificación jerárquica ascendente (CJA), cuya representación gráfica se realizó por diagrama de árbol con escala transformada. La separación de individuos se basó en coeficientes de distancia ultramétrica con valores £ 0,05. Las variables tomadas en cuenta para los análisis fueron: número días al 50% de emergencia, floración, y cosecha, nudos a primera flor, número flores y cápsulas/axila, desarrollo de nectários, posición de las cápsulas, longitud vellosidad de cápsulas, posición de las hojas, forma y pubescencia del tallo, hábito ramificación, ramas totales, color a madurez, forma y peso de 1 000 semillas. Estas variables, tanto las cualitativas como las cuantitativas, fueron estandarizadas en una escala de 2 ó 3 estados para generar la matriz de datos cualitativos. La CJA de las 17 variables mostró la creación de 20 clases con rango desde 12 hasta 92 entradas. La mayor variabilidad fue encontrada para las variables: pubescencia de tallos y cápsulas, color a madurez, ciclo, ramificación, número de flores y cápsulas/axila y desarrollo de nectarios. Las accesiones de la colección no mostraron una clara diferenciación por caracteres agro-morfológicos. Fueron identificados posibles duplicados de accesiones para las características estudiadas.

This study was conducted to classify 838 accessions of the Venezuelan sesame genbank according to 17 qualitative characters using multivariate analysis. Descriptions were performed for 42 agronomic and morphological characters using sesame descriptors. The collection was sown in Maracay, Aragua state, Venezuela. Groups of accessions were determined by hierarchical classification. The graphical representation was made by hierarchical dendrogram in a transformed scale. The hierarchical classification of 17 qualitative traits showed 20 classes. The grouping of accessions was based on ultrametric distance coefficients £ 0,05. The traits used for analysis were: number of days when 50% of plants reached emergence, flowering and harvest, number of nodes to first flower, number of flowers per axil, number of capsules per axil, extra-floral nectary development, capsule position in stem, length of capsule hair, leaves, stem shape and stem hairiness, branching habit, number of branches, mature plant color, seed shape and 1000 seed weight. These variables, quantitative as well as qualitative, were standardized in a categorized scale of 2 or 3 stages, to obtain qualitative data for analysis. The hierarchical classification of 17 qualitative variables explains 20 groups, consisting on 12 to 92 accessions. A higher variability was shown for: stem and capsules hairiness, color on mature plants, cycle, branching habit, number of flowers per axil, number of capsules per axil and extra-floral nectary development. Accessions did not show a clear differentiation among them. Duplications of accessions were identified for the traits taken into account.

Nickel, palladium and platinum micro-crystals were dispersed in films covering a vitreous carbon plate electrode by ion exchange followed by electroreduction of their ions. These modified electrodes were used in the electrocatalytic hydrogenation of several substrates of different classes and their efficiency is reported. A comparison among them was performed based on the structural characteristics of the metals. A modified electrode containing platinum showed to be more efficient than a palladium modified electrode and the one of nickel was the less efficient.

This paper presents some results on the employ of recycled graphite electrode obtained from used common 1.5 V batteries in the preparation of modified electrode and the electrocatalytical hydrogenation of benzaldehyde and of n-valeraldehyde. This inexpensive and easy to obtain electrode was prepared by coating it with a 1:1 mixed film of poly-(allylfenil ether): poly-[allyl p-(2-ethylammonium) benzene ether] and introduction of dispersed platinum particles by ion exchange and reduction of PtCl4-2. Electroreduction of H+ from aqueous H2SO4 using the proposed electrode hydrogenated the substrates in a way comparable with that of vitreous carbon electrode.