Biogenic carbonates were studied as catalysts in this work for the direct synthesis of amides under solvent-free conditions. Solids were synthesized by microbial coprecipitation of CaCl 2 and Ni salts and Cu and Fe salts. The catalysts were characterized by thermogravimetric analysis, nitrogen physisorption measurements, X-ray diffraction, and X-ray photoelectron spectroscopy. The polymorphism, hydrophilicity, and textural properties depended on the metal oxides type incorporated on CaCO 3 . N-Arylsuccinimides synthesis was employed as test reaction, obtaining remarkable selectivity and conversion in the reaction of succinic acid with p-toluidine and aniline, respectively. Optimized conditions were subsequently extended to the solvent-free synthesis of diverse amides in good yields using CuO−CaCO 3 as the catalyst in air. The direct amidation protocol was amenable to the use of different primary amines and nonactivated carboxylic acids.
RESUMENEl método voltametría de onda cuadrada (OSWV) fue validado para la cuantificación de Cd 2+ y Pb 2+ en aguas superficiales. El estudio fue realizado usando solución BrittonRobinson como electrolito de soporte a pH 4,8, carbón vítreo como electrodo de trabajo, Ag/AgCl como electrodo de referencia y platino como electrodo auxiliar. La técnica presenta un límite de detección 211 µg/L para Pb y 268 µg/L para Cd. La aplicación de la técnica voltamétrica OSWV fue realizada en aguas de la quebrada Las Torres del sector Parque Industrial en Sogamoso (Colombia), hallando una concentración de: Pb 2 + 0,750±0,067 mg/L y Cd 2 + 0,570±0,071 mg/L, los cuales sobrepasan los límites máximos establecidos por las normas nacionales (Decreto 4728/2010) e internacionales vigentes para aguas residuales. Los resultados fueron contrastados por el método de referencia espectrofotometría de absorción atómica aceptado como referencia, permitiendo deducir que el método electroquímico genera resultados con un nivel de confianza del 95%.
PALABRAS CLAVEVoltametría, carbón vítreo, metales pesados, voltagrama.
ELECTROCHEMICAL DETERMINATION OF LEAD AND CADMIUM IN SURFACE WATER ABSTRACTThe square wave electrochemical voltammetry method (OSWV) to quantification of cadmium and lead in surface waters was validated. It used a Britton-Robinson buffer as solution supporting electrolyte to pH 4.8, working electrode glassy carbon, Ag/AgCl as reference electrode and platinum as counter electrode. The limit of detection determined was 211 µg/L for Pb and 268 µg/L for Cd. The application of voltammetric technique OSWV was performed in waters of the creek Towers Industrial Park Sector in Sogamoso (Colombia). The ions concentration in the samples analyzed was 0.750±0.067 mg/L for Pb 2 + and 0.570±0.071 mg/L for Cd 2 +, exceeding the national and international standards limits for wastewater. The results obtained by voltammetry were compared with atomic absorption method spectrophotometer traditionally accepted, allowing deducing that the voltammetric method generates results with a confidence level of 95%.
KEY WORDSVoltammetry, vitreous carbon, heavy metals, voltammogram.
Whey in large quantities can cause environmental problems when discarded, because it reduces dissolved oxygen and aquatic life. Nonetheless, it could be used as an easily available and economical alternative to reduce culture medium costs in microbially induced calcium carbonate precipitation (MICP). In this work, a native Sporosarcina pasteurii was isolated and then cultured by using different proportions of whey (W) in nutrient broth (NB). The solids were characterized by XRD, FT-IR, TGA, and SEM. The potential applications in bioconsolidation were also studied. Whey concentration was directly related to CaCO3 production. Higher whey concentrations reduced calcium carbonate purity to nearly 80%. All experiments showed calcite and vaterite fractions, where a whey increment in the media increased calcite content and decreased vaterite content, causing a decrease in crystal size. MICP improved compressive strength (CS) in sand and fly ash. The best CS results were obtained by fly ash treated with 25 W-75 NB (37.2 kPa) and sand with 75 W-25 NB (32.1 kPa). Whey changed crystal polymorphism in biogenic CaCO3 production. Material bioconsolidation depends on the CaCO3 polymorph, thus fly ash was effectively bioconsolidated by crystallization of vaterite and sand by crystallization of calcite.
El desarrollo de sensores basados en nanoestructuras de polidiacétileno (PDA) se atribuye a sus propiedades cromáticas, actuando como transductor colorimétrico. Este material único permite un acercamiento de primer nivel de investigadores de ciencias básicas y aplicadas e ingeniería de biomiméticos cromáticos en el país, hacia la síntesis, características y propiedades de bloques nanométricos denominados liposomas para la construcción de sensores basados en polidiacétileno. En el presente estudio, se evaluó el periodo de fotopolimerización y el efecto de estímulos como temperatura, pH, interacción covalente y reconocimiento biomolecular sobre las propiedades cromáticas de los liposomas, su caracterización física se llevó a cabo mediante dispersión de luz dinámica, microscopía electrónica de barrido, y espectroscopia UV-Vis y Fluorescencia. Para efectos de comparación, el indicador denominado respuesta colorimétrica (RC%) se calculó a partir de los espectros de absorción UV-Vis. Una población dispersa de liposomas de tamaño nanométrico se utilizó para todos los experimentos. El valor de RC% más intenso (37,3%) se alcanzó cuando se adicionó una solución básica a los liposomas. En contraste, un RC% moderado de 14,0% y 12,0%, se obtuvo en los ensayos con liposomas funcionalizados con N-hidroxisuccinimida o Tripsina para reconocimiento de Albúmina de Suero Bovino (BSA). Los resultados muestran que los liposomas en solución son estables y facilitan el desarrollo de aplicaciones analíticas colorimétricas sencillas.
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