A glassy carbon electrode was modified by drop-coating technique using 1,4,10,13-Tetraoxa-7,16-diazaciclooctadecano (diaza-18 -crown-6 or DA18C6) and Nafion (NF) for the determination of Pb (II) by square wave anodic stripping voltammetric (SWASV). The new electrode exhibits an increase in due to major pre-concentration of aza crown ether and ionic exchange of NF with metal cations. Optimal conditions were: 3 mmol L-1 DA18C6, 3 wt % NF, 10 mmol L-1 HCl as supporting electrolyte, a frequency of 15 Hz, an accumulation time of 300 s and an accumulation potential of -0.80 V. The detection limit was 0.09 μg L-1 and linear range was 10-50 μg L-1. Interference from metal ions such us Fe (II), Pb (II), Cd (II) and Cu (II) was also studied. The method is sensitive, selective and simple with a relative standard deviation of 11%.

Background: Mortality rate is dramatically high in high grade brain tumors. The presence of multiple drug resistance transporters in glioblastoma multiforme, has contributed largely to the poor effcacy of targeted therapy against cancer in the central nervous system. Aim: To analyze the percentage of survival and mortality of patients with glioblastoma multiforme in a cohort of patients in Chile and to co-rrelate the chemo-resistance of these cells with the expression level of multiple drug resistance transporters. Materials and Methods: Eighteen biopsies of glioblastoma multiforme were obtained from patients at the Institute of Neurosurgery Dr. Asenjo (INCA). The tumor cells were obtained from primary cultures and the expression and activity of multiple drug resistance transporters was assessed by RT-PCR and immunohistochemistry. Population-based study was performed using the databases of the Department of Neurosurgery of INCA. Results: The number of patients with glioblastoma multiforme increased between 2007 and 2009, from 3.5% to 7.9% of total brain tumors. Mortality of these tumors is 90 % at three years. A high expression and activity of the multiple drugs resistance associated protein 1 (Mrp1) transporter was observed in primary cultures of biopsies. Conclusions: We propose that Mrp1 activity is responsible for the chemo-resistance of the glioblastoma multiforme and inhibition of this transporter could represent a plausible strategy for the treatment.

Multiwall Carbon Nanotubes (MWCNTs) were synthesized by Chemical Vapor Deposition (CVD). Two different procedures were used to grow MWCNT films roughly, aligned in the direction normal to the SiO2/Si(111) substrate. Inverse Photoemission Spectroscopy measurements, on these samples, show the existence of resonances which could be traced back to a flat graphene sheet. The unoccupied valence band is fairly similar to that shown by graphite except by an additional intensity in the vicinity of the Fermi level. This resonance could be interpreted both as tubes tips end effects or van Hove singularities in the density of states.

In this work metallic colloidal dispersions were obtained by simultaneous cocondensation of nickel atoms with organic solvents at 77 K. The atoms were produced by resistive heating and were reacted with 2-propanol, 2-methoxyethanol, 2-ethoxyethanol and acetone to produce colloids. The kinetic stability of colloid dispersions was related to the solvation effect of organic molecules, e.g. low stability for ketones and higher stability for 2-propanol colloids. The colloidal particles were characterized by UV-Vis measurements showing an absorption band around 212 nm. The electrophoretic measurements reveal that particles are weakly positively charged. The transmission electron microscopy studies reveal an average particles size distribution ranging from 4 to 23 nm depending on the solvent. Most of the colloids exhibit a spherical shape with some degree of agglomeration

En este trabajo se preparan dispersiones coloidales por condensación simultánea de átomos de níquel con solventes orgánicos a 77K. Los átomos fueron producidos por calentamiento resistivo y se hacen reaccionar con 2.propanol, 2- metoxietanol, 2-etoxietanol y acetona para producir coloides de níquel. La estabilidad cinética de las dispersiones coloidales fueron relacionadas con el efecto de solvatación de moléculas orgánicas, p. Ej., una baja estabilidad para cetonas y mayor estabilidad para los coloides de 2-propanol. Las partículas coloidales fueron caracterizadas mediante medidas de UV-Vis mostrando una banda de absorción alrededor de 212 nm. Las medidas de electroforesis revelan que las partículas están débilmente cargadas positivamente. La microscopía electrónica de transmisión revela una distribución de tamaño promedio de partículas en el rango de 4 a 23 nm dependiendo del solvente. La mayoría de los coloides muestran una forma esférica con algún grado de aglomeración