ABSTRACT A kinetic study of the cobalt electrodeposition onto a carbon fiber ultramicroelectrode of 11 μm of diameter was conducted in overpotential conditions from an aqueous solution containing 0.01 M CoCl2 + 0.1 M NH4Cl. From the voltamperometric and chronoamperometric studies, it was found that the value of the diffusion coefficient is 1.2x10−5 cm2 s−1. The analysis of the current density transients suggests that cobalt electrodeposition onto a carbon fiber electrode follows an instantaneous nucleation process controlled by spherical diffusion mass transport. Also, the number of active nucleation sites increases as the applied potential decreases.

ABSTRACT: Over the last few decades, electron microscopy (EM) and scanning probe microscopy (SPM) techniques have had a great contribution to the study of nanomaterials in many research fields, providing morphological, structural, interfacial, electric and magnetic information, among many others. Recent technological advances of these techniques have helped to achieve unprecedent spatial resolution limits unimaginable 25 years ago, being the last reported values of tenths of picometers (10-12 m). In addition, these techniques have grown in analytical capabilities in the nanoscience and nanotechnology fields, resulting in new independent, or even complimentary, techniques that have improved the understanding of interaction phenomena and physicochemical properties at the atomic and molecular scale. In this paper, an analysis of the actual importance of these techniques as well as some of their recent characterization and analytical achievements are discussed. Finally, in view of its enormous progress and large potential in the study and understanding of physical and chemical processes at the nanoscale, future challenges and perspectives are underlined.

RESUMEN: En las últimas décadas, las técnicas de microscopía electrónica (EM) y microscopía de barrido por sonda (SPM) han contribuido enormemente al estudio de nanomateriales en muchos campos de investigación, dando información de propiedades morfológicas, estructurales, de superficie, eléctricas y magnéticas, entre muchas otras. Los avances tecnológicos recientes asociados con estas técnicas han permitido alcanzar límites de resolución espacial que hace 25 años era inimaginables, siendo los últimos valores reportados de decenas de picómetros (10-12 m). Adicionalmente, estas técnicas han crecido en sus capacidades de análisis en el campo de las nanociencias y nanotecnología, dando lugar a otras microscopías independientes, o incluso complementarias, que han contribuido al entendimiento de fenómenos de interacción y propiedades fisicoquímicas a escalas atómicas y moleculares. En este articulo, se hace un análisis de la trascendencia actual que tienen las técnicas de microscopía electrónica y de microscopia de barrido por sonda, y se mencionan brevemente algunos de sus alcances actuales como métodos de caracterización y análisis. Finalmente, se señalan algunas retos, así como perspectivas, en cuanto a su enorme potencial para impulsar el estudio y entendimiento de procesos físicos y químicos a nanoescala.

Se utilizó Microscopía de Fuerza Atómica (AFM) para observar por etapas el crecimiento de capas búfer y películas de YBa- Cu-O sobre tres sustratos diferentes: Si (100) y MgO (100) como sustratos cristalinos y cuarzo como sustrato amorfo. Para comparar los beneficios de la capa búfer, se depositó YSZ sobre los tres sustratos mencionados y fueron caracterizados por topografía AFM en cada etapa del crecimiento: Sustratos, capa búfer de YSZ sobre el sustrato, películas de Y-Ba-Cu-O sobre YSZ en cada sustrato y películas de Y-Ba-Cu-O sobre cada uno de los sustratos. Las capas búfer de YSZ y las películas de Y-Ba-Cu-O se depositaron por medio de Rocío Pirolítico Ultrasónico. Las películas crecidas sobre las capas búfer presentan una superficie menos rugosa que aquellas crecidas sobre los sustratos sin capa búfer.

Atomic Force Microscopy (AFM) was used to observe the growth stages of both buffer layers and Y-Ba-Cu-O films on three different substrates: Si (100) and MgO (100) for crystalline ones and fused silica for the amorphous type. In order to compare the benefits of buffer layers, YSZ was grown on the three different substrates and AFM topographies were made at each stage of growth: Bare substrate, YSZ films on bare substrates, Y-Ba-Cu-O/YSZ films and Y-Ba-Cu-O on bare substrates. An Ultrasonic Spray Pyrolysis system was used to deposit all the films and layers. Films grown on buffer layers present smoother surfaces than those grown on bare substrates.

It was carried out an electrochemical study of the cobalt electrodeposition onto HOPG electrode from an aqueous solution containing 10-2 M of CoSO4 + 1M (NH4)2SO4. Nucleation parameters such as nucleation rate, density of active nucleation sites, saturation nucleus and the rate constant of the proton reduction reaction (kPR) were determined from potentiostatic studies. An increase in kPR values with the decrease in the applied potential suggested a competition between H+ and Co2+ by the active sites on the surface. The ΔG energy calculated for the formation of stable nucleus was 8.21x10-21 J/nuclei. The AFM study indicated the formation of small clusters of 50-400 nm in diameter and 2-120 nm in height.

Introduction: Diverse natural products of the Annona genus has been used in the treatment of the cancer. Annona cherimola has diverse pure compounds of its seeds and stems that have demonstrated antitumor activity against nasopharyngeal carcinoma. Objective: To determine the cytotoxic effect of the Annona cherimola seed extract on the cell lines MCF-7 (Human breast adenocarcinoma), ME-180(epidermal carcinoma of the cervix), K562 (chronic myeloid leukemia) and 3T3 (normal mouse fibroblasts). Materials and methods: The lines MCF-7, ME-180, K 562 and 3T3, were exposed to four concentrations of the Annona cherimola seed ethanolic extract (0.125, 0.031, 0.008, 0.002mg/mL), also to different concentrations of 5-fluorouracil (5-FU) (0.01563, 0.00391, 0.00098, 0.00024mg/mL) and Cisplatin (0.00250, 0.00063, 0.00016, 0.00004mg/ mL) which were used as a positive controls. Percentage growth was assessed after 48 hours. The growth inhibitory concentration 50 (CI50) was determined using linear regression analysis; also we obtained the coefficients of determination r2 using Microsoft Office Excel 2007. Finally the Selectivity Index of each sample was determined. Results: The CI50 in μg/mL of the Annona cherimola seed ethanolic extracts were 9.4(r2 = 0.96) for MCF-7; 6.6(r2 = 0.99) for ME-180; 2.2 (r2 = 0.96) for K562 and 29.5(r2 = 0.98) for 3T3. The CI50 of 5-FU were 3.4(r2 = 0.95) for MCF-7; 3.8(r2 = 0.96) for K562 and 0.2(r2 =0.98) for 3T3 and the CI50 of Cisplatin were 12.1(r2 = 0.96) for MCF-7; 0.1(r2 = 0.96) for K562 and 0.3(r2 = 0.99) for 3T3. The dose-response relationship of the extract to the 3T3 cell line was -0.98 (p<0.05) and for the K562 tumor cell line was -0.98 (p<0.05). The extract selectivity index were 2.17, 6.07 and 2.39 for the MCF-7, K562 and ME-180 cell lines, respectively; On the contrary, the 5-FU and Cisplatin, only reached values of 0.07 and 0.06; 0.02 and 2.25 for the lines MCF-7 and K562 respectively. Conclusions: The cytotoxic profile of the Annona cherimola seed etanolic extract is very encouraging by its high citotoxicity against tumor cells and low citotoxicity against normal cells; surpassing, drugs widely known like 5-FU and Cisplatin in selectivity index.

Introducción: Diversos productos naturales del género Annona han sido utilizados en el tratamiento del cáncer. Annona cherimola posee diversos compuestos puros de sus semillas y tallos que han demostrado actividad antitumoral frente a células de carcinoma nasofaríngeo. Objetivo: Determinar el efecto citotóxico del extracto etanólico de semillas de Annona cherimola en las líneas celulares MCF-7(adenocarcinoma de mama humano), ME-180(carcinoma epidermoide de cervix), K562 (leucemia mieloide crónica) y 3T3 (fibroblastos normales de ratón). Materiales y métodos: Las líneas MCF-7, ME-180, K562 y 3T3, fueron expuestas a cuatro concentraciones del extracto etanólico de semillas de Annona cherimola (0,125, 0,031, 0,008, 0,002mg/mL), asimismo a diferentes concentraciones de 5-fluorouracilo (5-FU) (0,01563, 0,00391, 0,00098, 0,00024mg/mL) y Cisplatino (0,00250, 0,00063, 0,00016, 0,00004mg/mL) como controles positivos. Se hallaron los porcentajes de crecimiento en 48 horas. Luego se determinó la concentración inhibitoria de crecimiento 50 (CI50) mediante correlación lineal, asimismo se obtuvieron los coeficientes de determinación r2 utilizando Microsoft Office Excel 2007. Finalmente se precisó el Índice de Selectividad de cada muestra. Resultados: Los CI50 en μg/mL del extracto etanσlico de semillas de Annona cherimola fueron 9,4(r2 =0,96) para MCF-7; 6,6(r2 =0.99) para ME-180; 2,2(r2 =0,96) para K562 y 29,5(r2 =0,98) para 3T3. Los CI50 de 5-FU fueron 3,4(r2 =0,95) para MCF-7; 3,8(r2 =0,96) para K562 y 0,2(r2 =0,98) para 3T3 y los CI50 del Cisplatino fueron 12,1(r2 =0,96) para MCF-7; 0.1(r2 =0,96) para K562 y 0,3(r2 =0,99) para 3T3. La relación dosis respuesta del extracto para la línea celular 3T3 fue de -0,98 (p<0.05) y para una línea celular tumoral K562 fue de -0,98 (p<0,05). Los índices de selectividad del extracto fueron de 2,17, 6,07 y 2,39 para las líneas celulares MCF-7, K562 y ME-180 respectivamente. Por el contrario, el 5-FU y Cisplatino, solo alcanzaron valores índices de 0,07 y 0,06; 0,02 y 2,25 para las líneas MCF-7 y K562 respectivamente. Conclusiones: El perfil citotóxico del extracto etanólico de las semillas de Annona cherimola es muy alentador por su alta citotoxicidad para células tumorales y su baja toxicidad para las células normales; superando en cuanto a índice de selectividad a los fármacos ampliamente conocidos como el 5-FU y el cisplatino.

Filmes finos foram crescidos sobre a superfície de elétrodos de grafito pirolizado altamente orientado a partir de precursores p-doadores utilizando a técnica cíclica de voltametria cíclica e eletroquímica-microscopia de força atômica. Os resultados indicam que é possível a formação de novos compostos chamados materiais moleculares, estes são formados pelo acoplamento de espécies N-trifluormetanosulfonil-1-aza-hexa-1,3,5-trieno eletro-oxidadas e o anion [Cr(C2O4)3]3- . Diferentes técnicas foram empregadas para caracterizar a morfologia e composição dos filmes formados. Os resultados indicam que os materiais novos exibiram uma resposta eletroquímica particular e uma textura diferente dependendo da composição química dos materiais de partida.

Thin films have been created on the surface of highly oriented pyrolytic graphite electrodes from chemically synthesized pi-donor species by using the cyclic voltammetry technique and in situ electrochemistry-atomic force microscopy. Results indicate that it is possible to form new compounds called molecular materials from the coupling of electro-oxidized N-trifluoromethanesulfonyl-1-azahexa-1,3,5-triene species and a [Cr(C2O4)3]3- anion. Different techniques such as AFM, SEM and EDS were employed to characterize the films morphology and composition. Results indicate that the new materials exhibited a particular electrochemical response and a different film texture depending on the chemical composition of the starting compounds.

Filmes finos foram crescidos sobre a superfície de elétrodos de grafito pirolizado altamente orientado a partir de precursores p-doadores utilizando a técnica cíclica de voltametria cíclica e eletroquímica-microscopia de força atômica. Os resultados indicam que é possível a formação de novos compostos chamados materiais moleculares, estes são formados pelo acoplamento de espécies N-trifluormetanosulfonil-1-aza-hexa-1,3,5-trieno eletro-oxidadas e o anion [Cr(C2O4)3]3-. Diferentes técnicas foram empregadas para caracterizar a morfologia e composição dos filmes formados. Os resultados indicam que os materiais novos exibiram uma resposta eletroquímica particular e uma textura diferente dependendo da composição química dos materiais de partida.

Thin films have been created on the surface of highly oriented pyrolytic graphite electrodes from chemically synthesized π-donor species by using the cyclic voltammetry technique and in situ electrochemistry-atomic force microscopy. Results indicate that it is possible to form new compounds called molecular materials from the coupling of electro-oxidized N-trifluoro-methanesulfonyl-1-azahexa-1,3,5-triene species and a [Cr(C2O4)3]3- anion. Different techniques such as AFM, SEM and EDS were employed to characterize the films morphology and composition. Results indicate that the new materials exhibited a particular electrochemical response and a different film texture depending on the chemical composition of the starting compounds.