p-Nitrophenol (pNP) is a widely used compound for analytical determinations of several esterases (EC. 3.1.1.X), including lipases (E.C. 3.1.1.3). Most enzymatic measurements employ pNP derivatives such as esters, which are broken down by enzymatic hydrolysis, releasing pNP that is quantified by its absorbance at 410 nm. Although this type of methods was developed a few decades ago, the spectrophotometric analysis of pNP requires analytical measurements of pH and temperature to achieve reliable determinations. The aim of this paper is to offer a graphical update of how pH and temperature affect the p-nitrophenol absorbance at different wavelengths in lipase emulsified media, due to its relevance for the quantitative determination of lipase activity using spectrophotometric methods. To highlight the importance of each variable involved in this analysis, we dissolved pNP in emulsified media (for lipase activity quantification) at several pH values from 4.00 to 11.00, and measured its absorbance in a range of 270 nm – 500 nm and at several temperatures from 25°C to 50°C. The absorption patterns of pNP under the established conditions were graphed in 3D plots. The constructed 3D plots showed that, regardless of the temperature, below pH 6.00, pNP predominantly absorbs at 317 nm, due to the greater abundance of its protonated form, which is completely predominant at pH 3.50 and below. On the other hand, at pH 10.0 and above, the major absorption occurs at about 401 nm, confirming that the equilibrium is completely shifted to the pNP anionic form. These results also indicate that close to neutral pH value pNP, it displays a temperature dependence effect, increasing absorbance to 410 nm at higher temperatures. Due to many analytical determinations of enzymatic activities, the release of pNP is carried around pH 7.00. It is necessary to consider the determinant role of both pH and temperature over these measurements, how these variables must be strictly controlled, and how the calibration curves and blanks should take the reaction media pH and temperature into account.
Daniel Esquivel-Alvarado y otros Artículo protegido por licencia Creative Commons: BY-NC-ND / Protected by Creative Commons: BY-NC-ND Revista de acceso y publicación gratuita/ Access and publication in Uniciencia is totally no fee. Estudio de la actividad antibacteriana de los extractos orgánicos liquénicos obtenidos de Lobaria subdissecta y Parmotrema latissimum Study of the antibacterial activity of the organic extracts from lichen Lobaria subdisecta and Parmotrema latissimum
Con el fin de evaluar las principales propiedades antioxidantes y antibióticas del exocarpio del fruto de Santol (Sandoricum koetjape), se realizó una bioprospección sobre este, así como una caracterización del contenido de polifenoles totales y proantocianidinas. Para lo anterior, al material seco y molido del exocarpio se le realizaron diferentes pruebas cuantitativas y fraccionamientos cromatográficos con diversas resinas, con el propósito de obtener metabolitos puros o mezclas de ellos más concentrados. Las fracciones y extractos fueron analizados empleando el método de Folin-Ciocalteu (polifenoles totales), DMAC (proantocianidinas totales) y DPPH (actividad antioxidante), utilizando siempre un patrón tradicional y uno propio de la muestra. Los resultados obtenidos con este último fueron hasta un 80 % más alto en comparación con los patrones tradicionales; además, se determinó cómo las fracciones con un mayor contenido de proantocianidinas presentan una mayor actividad antibiótica, con un 73 ± 4 % sobre la batería S. Aureus y un 42 ± 2 % sobre Bacilus spp., ambos análisis realizados por el método de Kirby-Bauer.
Se determinó la concentración de seis aldehídos en muestras de aire, durante abril-junio de 2015, en la Reserva Biológica Monteverde (RBM) y en Heredia, Costa Rica. El formaldehído, el acetaldehído, el propanal, el butanal, el hexanal y el heptanal se tomaron con cartuchos de adsorción recubiertos con una disolución de la 2,4-dinitrofenilhidrazina (2,4-DNFH) y se analizaron por HPLC con un detector ultravioleta visible. Las concentraciones promedio de cada aldehído en Heredia se encontraron entre 12,78 µg/m3 y 72,57 µg/m3 durante la época seca y entre 7,95 µg/m3y 62,30 µg/m3 durante la transición a la época lluviosa; mientras que en la RBM las concentraciones encontradas estuvieron entre 1,93 µg/m3 y 22,62 µg/m3 durante la época seca y entre 0,26 µg/m3 y 4,68 µg/m3 durante la transición a la época lluviosa. La concentración total de los carbonilos en Heredia fue de 241,08 µg/m3 en la época seca y de 172,95 µg/m3 en la transición a la época lluviosa; esto, debido al efecto de dilución de contaminantes que hacen las lluvias y que la actividad fotoquímica es mayor en la época seca que en la transición a la época lluviosa. La concentración total de los carbonilos en la RBM fue de 42,07 µg/m3 en la época seca y de 13,47 µg/m3 en la transición a la época lluviosa.
Secondary metabolites from Hibiscus sabdariffa have been used to prevent different diseases. Roselle Hibiscus is known for being rich in phenolic bioactive compounds. The extraction conditions are directly related to the chemical composition and then to the overall bioactivity of the extract. In this study, a Box-Behnken experimental design has been used to optimize the antioxidant activity, considering four variables: ethanol:water ratio, temperature, extraction time, and solvent:solid ratio. The experiment comprises 27 experiments and 3 repetitions at the central point. The results are described by surface response analysis and a second-degree polynomial equation. The model explains 87% of the variation in the response. The maximum antioxidant activity is yielded when 1% solids are extracted in 35.5% ethanol at 60 °C for 33 min. Finally, a nutritional functional supplement of 495 µmol Trolox Equivalent (TE) antioxidant capacity was prepared with the optimized extract.
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