RESUMEN El tiofeno es un compuesto azufrado que se encuentra principalmente en la gasolina y es uno de los responsables de la contaminación atmosférica. En este trabajo se hizo la implementación de una metodología analítica para la cuantificación de tiofeno a lo largo de un proceso de desulfurización fotocatalítica, usando Voltamperometría Diferencial de Pulsos (VDP). La degradación fotocatalítica de tiofeno se hizo con radiación UV utilizando TiO2 modificado con Ag como semiconductor. El seguimiento electroquímico del tiofeno se realizó mediante dos metodologías. En la primera se tomaron alicuotas de la mezcla oléica cada 30 minutos y se midió la concentración de tiofeno a lo largo de 7 horas de degradación mediante Voltamperometría Diferencial de Pulsos (VDP). La concentración de tiofeno disminuyó en un 37.94%. En la segunda metodología se hizo la determinación electroquímica del tiofeno in situ, para lo cual, la mezcla de reacción se modificó por la adición de acetonitrilo y de una sal de amonio cuaternaria como electrolito soporte. En este medio se redujo la concentración de tiofeno en un 43.88% luego de 4 horas de degradación fotocatalítica.

ABSTRACT Thiophene is a sulfur compound found mostly in gasoline and contributor to air pollution. This paper analyzes UV light photocatalytic desulfurization of model oil using Ag/TiO2. Thiophene concentration in the oil phase was determined by the electrochemical analyzer using Differential Pulse Voltammetry (DPV). The electrochemical experimental works were performed by two methodologies. First, aliquots of the oleic mixture were taken every 30 minutes and the thiophene concentration was measured over 7 hours of degradation. The concentration of thiophene decreased by 37.94%. In the second methodology, the in situ thiophene concentration was determined by DPV, where the reaction mixture was altered by the addition of acetonitrile and a quaternary ammonium salt as solvent-supporting electrolyte system. In this medium, the thiophene concentration was reduced by 43.88% after 4 hours of photocatalytic degradation.

RESUMEN En esta investigación se llevó a cabo la degradación de hidrocarburos totales en mezclas sintéticas de agua y en muestras obtenidas del flujo de entrada de un skimmer (agua de producción), por medio de fotocatálisis heterogénea. Se usó dióxido de titanio (TiO2) modificado con óxido de hierro (III) como fotocatalizador, soportado en láminas de polimetilmetacrilato, dispuestas en dos reactores con capacidades volumétricas de 15,0 ml y 1,0 l. El proceso de degradación fue estudiado mediante dos métodos de análisis: Detección fotométrica y partición gravimétrica. Se obtuvieron porcentajes de degradación de 91.2% y 98% en muestras de campo y mezclas sintéticas respectivamente, en tiempos de 4 h; los cuales permiten evaluar el impacto de esta técnica en el tratamiento de agua de producción de la industria petrolera, buscando ser una alternativa a los métodos de tratamiento de aguas contaminadas con hidrocarburos.

ABSTRACT This research work focused on the degradation of total hydrocarbons in synthetic water mixtures and in samples obtained from the inflow of a skimmer (production water) by means of heterogeneous photocatalysis. Titanium dioxide (TiO2) was used, modified with iron oxide (III) as photocatalyst, supported on polymethyl methacrylate plates, arranged in two reactors with volumetric capacities of 15.0 ml and 1.0 l. The degradation process was studied using two analysis methods: Photometric detection and gravimetric partition. Degradation percentages of 91.2% and 98% were obtained in field samples and synthetic mixtures respectively, with 4 h times; this allows for assessment of this technique's impact on the treatment of produced water in the oil industry, seeking for an alternative to the methods for treating water contaminated with hydrocarbons.

Steroids from Solanum nudum (SNs) have demonstrated antiplasmodial activity against erythrocytic stages of the Plasmodium falciparum strain FCB-2. It is well known that steroids can alter the membrane function of erythrocytes. Thus, we assessed alterations in the membranes of uninfected red blood cells, the parasite invasiveness and the solute-induced lysis of parasitised red blood cells (pRBCs). induced by SNs. We found that most merozoites were unable to invade SN-treated erythrocytes. However, transmission electron microscopy revealed no effect on the morphology of uninfected erythrocytes treated with either SN2 or diosgenone and neither SN induced haemolysis of uninfected erythrocytes. SN2 and SN4 inhibited isosmotic sorbitol and alanine-induced haemolysis of pRBCs. In contrast, diosgenone and SN1 did not inhibit solute-induced haemolysis. The inhibition of solute-induced lysis of parasitised erythrocytes by SN2 and SN4 suggest an action of these SNs on new permeability pathways of pRBCs.

Bacillus thuringiensis produces d-endotoxins that require proteolytic processing to become active. The activation of the B. thuringiensis subsp. medellin 28 kDa (Cyt1Ab1) cytolytic toxin by trypsin, chymotrypsin and gut extract from Culex quinquefasciatus larvae was analyzed. The Cyt1Ab1 toxin of B. thuringiensis subsp. medellin was processed by all proteases tested to fragments between 23 and 25 kDa, while processing of the Cyt1Aa1 toxin produce fragments between 22.5 and 24.5 kDa. The Cyt1Ab1 toxin was preferentially processed at the alkaline pH of 12. The in vitro proteolytic processing of the Cyt1Ab1 toxin by C. quinquefasciatus larvae midgut extract showed a 25 kDa fragment; a similar result was observed when the activation was performed in the in vivo experiments. The solubilized Cyt1Ab1 toxin and the protease resistant cores generated by in vitro processing showed hemolytic activity but not mosquitocidal activity. Amino terminal sequence of the C. quinquefasciatus gut extract resistant fragment indicated that the cutting site was located between Lys31 and Asp32, with a sequence DDPNEKNNHNS; while for the trypsin-resistant fragment the cutting site was determined between Leu29 and Arg30, and for the chymotrypsin-resistant fragment between Arg30 and Lys31.