Evaluation of the electrochemical response of Saccharomyces cerevisiae using screen-printed carbon electrodes (SPCE) modified with oxidized multi-walled carbon nanotubes dispersed in water - Nafion®.

The evaluation of the electrochemical determination of Saccharomyces cerevisiae was carried out using a screen-printed carbon electrode (SPCE) modified with Nafion-dispersed oxidized multi-walled carbon nanotubes (OMWCNT). The morphology was studied using scanning electron microscopy (SEM), showing a complete modification of the surface with the nanotubes and yeast interaction with them instead of the graphite surface. The redox couple Fe(CN)6 4-/Fe(CN)6 3- was used to determine the electroactive area, the heterogeneous transfer constant, and the Nafion® effect. Results showed increases in electroactive area and heterogeneous transfer constant of 146% and 20.4%, respectively, due to the presence of nanotubes. Studies of the Nafion® effect showed that the polymeric membrane affects the electroactive area but not the heterogeneous transfer constant. Studies of the scan rate effect show that yeast oxidation is an irreversible mixed control process. As the concentration and scan rate increased, the anodic potential shifted toward more anodic values. The relationship between yeast concentration and the anodic current density (current/electroactive area) of yeast showed a linear range between 0.61 and 7.69 g L-1, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.17 g L-1, and 0.61 g L-1, respectively, and the sensibility obtained was 0.03 µA L g-1 mm-2. These results show that with the screen-printed carbon electrodes it is possible to improve the electrochemical determination of this microorganism, enhancing the analytical parameters and quantification, allowing greater portability and decreasing measurement times and associated waste.

Remediation effect of compost on soluble mercury transfer in a crop of Phaseolus vulgaris.

We studied the dynamics of mercury (Hg) transfer in Phaseolus vulgaris plants grown in soil with Hg-doped compost at the maximum levels permitted by Colombian law on organic amendments. Quantitative evaluation of transfer was made in different plant organs: roots, stem, leaves, pods and seeds. Matrix effect was determined in doped soil assays, using soil with and without addition of compost. Results showed that the use of organic matter reduced Hg transfer to the plant and the amount transferred was differentially distributed to the organs. We observed an inverse relationship between concentration and distance from the body to the root. It was evident that transfer was mediated by quantitative factors; the greater the presence of mercury in soil, the larger the amount that will be transferred. Results also indicate the remedial effect of compost and the presence of a barrier, at the root level, against mercury translocation to the plant aerial parts.

Hemisíntesis de un híbrido diosgenonaartesunato y su efecto antiplasmodial / Diosgenone-artesunate hybrid hemisynthesis and its antimalarial effect

Antecedentes: La malaria es una enfermedad causada por parásitos del género Plasmodium y transmitida por mosquitos de género Anopheles. Anualmente, se reportan alrededor de 220 millones de casos de malaria en el mundo, de los cuales mueren aproximadamente 650.000 personas, convirtiendo esta enfermedad en un problema de salud pública. En los últimos años se ha reportado resistencia de los parásitos a los antimaláricos: cloroquina, mefloquina y recientemente a los derivados de artemisininas, como artesunato. Objetivo: Obtener por hemisíntesis un híbrido de diosgenona-artesunato con un conector hidrolizable tipo éster, y valorar su actividad antiplasmodial y citotoxicidad in vitro. Métodos: Para la obtención del híbrido 4, se redujo el grupo carbonilo de la diosgenona en presencia de borohidruro de sodio, para generar un alcohol, el cual se usó para enlazarse con el artesunato, por medio de una reacción de esterificación promovida por el reactivo de Yamaguchi. La actividad antiplasmodial se determinó en la cepa 3D7 de P. falciparum sensible a cloroquina, la citotoxicidad se evaluó en la línea celular HepG2. Resultados: Mediante una reacción de esterificación con el reactivo de Yamaguchi, se obtuvo el primer híbrido diosgenona-artesunato 4 (IC50=0,0157 µM), el cual fue más activo que la molécula de partida diosgenona 1 (IC50=35,49 µM) y la diosgenona reducida 2 (IC50=46,33 µM) pero no más que el artesunato 3 (IC50=0,0020 µM). Conclusiones: Se obtuvo un nuevo híbrido de diosgenona-artesunato el cual presenta mejor actividad que la molécula natural; resultado de importancia para su uso potencial contra cepas resistentes al artesunato.