Libertador Experimental Pedagogical University
Rubio, Venezuela

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Murillo Pulgarin J.A.,University of Castilla - La Mancha | Garcia Bermejo L.F.,University of Castilla - La Mancha | Carrasquero Duran A.,Libertador Experimental Pedagogical University
Analytical Letters | Year: 2017

This study reports a simple and rapid method for the determination of the antioxidant activity of the phenolics present in plants of the Hibiscus genus. The protocol is based on the ability of the phenolic compounds to inhibit luminol chemiluminescence through the inactivation of free radicals in a flow injection system. Using the optimized operational conditions, the antioxidant activities of several phenolics were measured. The results were explained on the basis of structure–reactivity relationships. The antioxidant activities of dried flowers of Hibiscus rosa-sinensis and Hibiscus sabdariffa were evaluated. The protocol was validated by the 2,2-diphenyl-1-picrylhydrazyl-hydrate free radical assay. The differences in the antiradical activities were explained based on the concentrations of total polyphenol and flavonoid concentrations determined by spectrophotometric methods. It was concluded that the chemiluminescence method was complementary for the evaluation of hydrophilic antioxidants in plants. © 2017 Taylor & Francis.

The morphological features of the relief and its quantitative morphometric quantification are essential elements in interpreting its influence on the hydrogeomorphological dynamics of watersheds in mountainous environments. This is particularly important when studying small spatial units (micro watersheds) and torrential regimes, as this influences the sudden and aggressive hydrological responses of these systems and the likelihood of activation of mass removal processes. In the study region (Vargas State, Venezuela) the most important debris flow recorded in Venezuela's history occurred on December 14, 15 and 16, 1999, as a consequence of extremely heavy rainfall in those dates associated with a very particular weather. For the above reasons, this research conducted a quantitative analysis of the relief features in watersheds of “El Ávila” massive northern hillside and their impact on the local hydrogeomorphological dynamics, aimed at identifying the main attributes influencing these dynamics. The study area is located in the northern-central region of Venezuela, in the central part of Vargas state, delimited by 10°32’25”-10°37’35”N and 66°40’08”- 66°59’12”W, and comprises thirteen micro watersheds of mountainous environment. The methodology consisted of (a) the geomorphological characterization of the area, from the review and interpretation of digitized base maps at scales 1:5 000 and 1:25 000, the digital elevation model (DEM), aerial photographs at scale 1:5 000, orthophotomaps at scale 1:25 000, satellite images, Google Earth and Google Maps images, and geomorphological maps (landforms and geomorphological processes) at scale 1:25 000; (b) measurements and calculations of basic morphometric parameters of watershed relief on digital mapping using the ArcGIS 9.2 and their Spatial Analysis and ArcHydro modules, and the mathematical equations that define the other parameters using MS Excel; (c) descriptive statistical analysis (DSA) of morphometric parameters in Excel spreadsheets, based on the following statistics: maximum value, minimum value, mean, mode, median, variance, standard deviation, skewness, kurtosis, coefficient of variation, first quartile, second quartile and third quartile; (d) linear correlation analysis (LCA) between morphometric parameters, based on the application and estimation of the Pearson product-moment correlation using the MS Excel XLSTAT add-on software; and (e) principal component analysis (PCA) of morphometric parameters based on correlations, run with SPSS Statistics v. 17.0. The results show that the watersheds in the study area are conceived as exorheic hydrogeomorphological systems. Three relief units characteristic of these mountain environments systems were distinguished: catchment area, main drain channel and cone or alluvial fan, each with its own morphological features (landforms) and distinctive geomorphological processes. Landforms were grouped into two major groups: on the one hand, those that result from the depositional activity of the main creeks and rivers, prevailing in valleys of the main drain channels and in foothills (alluvial fans); on the other, those that have been shaped by the erosive action associated with drainage networks, being observed mainly on hillsides. Creeks and rivers are waterways running along very short distances from headwaters to outputs on the mountain front, exhibiting pronounced changes in slope, usually steep. These are typical of torrential systems in mountainous environments with abrupt relief, favoring sudden hydrological responses. As regards the morphometric parameters of watershed relief and drainage networks, these were defined as topographically very rugged areas with steep slopes and steep altitudinal slopes. These morphometric parameters are typically represented by the slopes along the longitudinal profiles of the main creeks and rivers, and by the pronounced mountainous relief (massivity coefficient, orographic coefficient and Melton's ruggedness number). The LCA between morphometric parameters of relief revealed a few cases with good-to-high correlation, mainly due to the mathematical and geometric relationships between them. The PCA allowed reducing the number of morphometric parameters of relief, defining as new variables to the four created components. The main relief components in the first PCA axis were mean slope, maximum altitude, maximum relief, mainstream longitudinal profile concavity and headwater altitude, identified as those that exert the greatest influence on the hydrogeomorphological dynamics of the watersheds studied. © 2016 Universidad Nacional Autonóma de México

Murillo Pulgarin J.A.,University of Castilla - La Mancha | Garcia Bermejo L.F.,University of Castilla - La Mancha | Carrasquero Duran A.,Libertador Experimental Pedagogical University
International Journal of Environmental Science and Technology | Year: 2017

A luminol chemiluminescence (CL) detection/flow injection analysis technique coupled with ion chromatography (IC) has been employed for the determination of low levels of Cu(II) and Co(II) in drinking water samples. The detection system was the CL of luminol/perborate or luminol/percarbonate in alkaline medium catalyzed by these transition metals. Oxalic acid in a solution of KOH and N(CH3)4OH was used as an eluent in the IC to improve the column selectivity (Dionex CS5A). Concentration and pH of the eluent affected simultaneously the CL intensity and the retention times (tR). Under the elution conditions used here, the retention times of both metal ions were much greater when the concentration of oxalic acid was decreased. Thus, Rt(Cu) = 2.15 min and tR(Co) = 4.50 min were measured at 80 mM oxalic acid concentration, while tR raised to 4.12 and 18 min for Cu(II) and Co(II), respectively, using a 10-mM concentration, but on the other hand, the CL signals showed substantially higher values when the concentration of oxalic acid was lesser in the eluent. An optimum oxalic acid concentration of 20 mM and an eluent pH = 4.7 were selected in order to have reproducible signals with a total analysis time of 10 min. The optimum flow rate for the mobile phase was 1.5 mL min−1. The concentration and pH of the postcolumn reagents also affected the CL signal, obtaining optimum concentrations of 5 mM for both oxidants (perborate or percarbonate) and luminol, this last dissolved in a 0.1-M borate buffer at pH 12. The optimum flow rate for the postcolumn reagents was 1 mL min−1. Linear calibrations for both transition metal ions were established, with calculated detection limits of 0.15 ng mL−1 for Co(II) and 0.20 μg mL−1 for Cu(II). Others ions commonly present in natural waters showed little or no interference. The method was successfully applied to water samples spiked with Cu(II) and Co(II), obtaining recoveries in the range of 85–128%, depending on the metal concentrations. © 2016, Islamic Azad University (IAU).

Stansell N.D.,University of Pittsburgh | Abbott M.B.,University of Pittsburgh | Rull V.,CSIC Botanic Institute of Barcelona | Rodbell D.T.,Union College at Schenectady | And 2 more authors.
Earth and Planetary Science Letters | Year: 2010

A radiocarbon dated sediment record from Laguna de Los Anteojos, a cirque lake in the Mérida Andes of Venezuela, indicates that warmer and wetter atmospheric conditions occurred in the northern tropics at the onset of the Bølling (~. 14,600. cal. yr BP), and abruptly colder and drier conditions around the time of the Younger Dryas (YD). Geochemical and clastic sediment analyses from Los Anteojos show that glaciers advanced at ~. 12,850. cal. yr BP, reached their YD maximum extent at ~. 12,650. cal. yr BP, and then retreated until complete deglaciation of the watershed at ~. 11,750. cal. yr BP. The onset of warmer conditions that ended the coldest phase of the YD occurred several hundred years earlier at Los Anteojos than in the high latitudes of the Northern Hemisphere. During the peak YD glacial advance, glacier equilibrium-line altitudes in the region were ~. 360 to 480. m lower, and temperature was ~. 2.2 to 2.9 °C colder than modern. Independent palynological evidence from the Los Anteojos sediment core indicates that the northern Andes were more arid and at least 2.3 °C colder during the YD. The direction and timing of glacial fluctuations in Venezuela are consistent with observations of marine sediment records from the Cariaco Basin that suggest abrupt cooling occurred at ~. 12,850. cal. yr BP, followed by a shift to higher temperature after ~. 12,300. cal. yr BP. The timing and pattern of climatic changes in northern South America are also consistent with paleoclimate records from the southern Tropical Andes that suggest a southward shift in the position of the Intertropical Convergence Zone occurred at the start of the cooling event, followed by a return to wetter conditions in northern South America during the late stages of the YD. The early warming of the tropical atmosphere and invigoration of the hydrologic cycle likely contributed to the shift to increased temperature in the higher latitudes of the Northern Hemisphere at the end of the late Glacial stage. © 2010 Elsevier B.V.

Microbial crust develops on the surface of the soil due to colonization of microorganisms as cyanobacteria and macro organisms such as bryophytes and lichens. Initial support is a physical crust that dominates in arid and semi-arid areas such as the de Quíbor, state Lara, Venezuela. The objective of this study is to show the interaction of the crust organ microbial mineral through different structures anchoring morphological and organic excretions microorganisms contribute to the onset of the formation of micro aggregates and soil retention. The morphological diversity of microbiological structures of the crust was studied by Scanning Electron Microscopy (SEM). The results show different sizes of micro aggregates, which show the effect of rhizoids and rhizines, and also cyanobacteria into entanglement of soil aggregates. Aggregation occurs by the action of the same organisms, as the entanglement of bryophytes and rhizines rhizoids along fungal hyphae, facilitates stabilizing micro aggregates entrapment. Secretions of polysaccharides and / or cyanobacteria gummy exudate and lichens generate an adhesive effect of the mineral particles remain bound, which provides the initiation and formation of micro aggregates, improving the structure and thus protects the soil from hidric erosion.

Polissar P.J.,Lamont Doherty Earth Observatory | Abbott M.B.,University of Pittsburgh | Wolfe A.P.,University of Alberta | Vuille M.,Albany State University | Bezada M.,Libertador Experimental Pedagogical University
Proceedings of the National Academy of Sciences of the United States of America | Year: 2013

Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, seasurface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Paci fic sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate.

On the floor of Quíbor, grows discontinuously a crust formed by lichens, bryophytes and cyanobacteria. The purpose of this research is to identify variations in the behaviours of some soil properties by comparing soil samples with and without crust. This is a field research developed in three phases: The first, called field, in order to collect samples of soil, with support in the random digits table and from two longitudinal transects, they are used on every ten meters a quadrat square 25 × 25 cm; the second phase, laboratory, in which soil properties determined: a) physical as % moisture; b) chemicals such as salinity, pH, Electrical Conductivity (EC) and organic carbon (OC); and c) biochemical, including organic matter (OM) and carbon dioxide (CO2) given off; the third phase, statistical analysis, "t" test was used in order to identify significant changes between the two sample groups. We conclude that the presence of the crust on the soil surface increases metabolic activity, the OC and OM. As for pH, EC, salinity and% H there were no significant changes.

Murillo Pulgarin J.A.,University of Castilla - La Mancha | Bermejo L.F.G.,University of Castilla - La Mancha | Duran A.C.,Libertador Experimental Pedagogical University
European Journal of Lipid Science and Technology | Year: 2010

A flow injection analysis (FIA) methodology has been developed for the estimation of the radical scavenging activity (RSA) of edible oils as a measure of their antioxidant activity. The RSA determination was based on the inhibition of the luminol chemiluminescence (CL) induced by the Fenton's reagent in a microemuslion (n-hexane in water). At the optimum operational conditions, the RSA of gallic acid and buthylhydroxylanisol, usually employed as antioxidant in vegetable oils, as well as corn, sunflower, olive, soybean and sesame oils, were measured in terms of the IC50 (the concentration required to reduce in 50% the CL emission measured in the absence of antioxidants in the organic phase). For this purpose, the percentage of the CL inhibition (%Inh) against the sample concentration was plotting. Virgin oils of sesame and olive showed the greatest RSA, which was associated to their elevated concentration of natural antioxidants, such as phenols, tocopherols and lignans. The refined soybean oil also has an important antioxidant activity due to the addition of synthetic antioxidants after the refining process, while the lower RSA activities were found in the refined corn and sunflower oils. The results of the proposed method showed good agreement with those obtained by the DPPH test, which suggests that it could be used as a complementary method for the evaluation of hydrophobic substances with antioxidant properties. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pulgarin J.A.M.,University of Castilla - La Mancha | Bermejo L.F.G.,University of Castilla - La Mancha | Duran A.C.,Libertador Experimental Pedagogical University
Food Analytical Methods | Year: 2012

This study establishes a simple and fast flow injection analysis methodology for the determination of the antioxidant activity in wines, tea infusions, and grape seeds, based on the inhibition effect of their natural antioxidants on the Co(II)/EDTA-induced luminol-perborate chemiluminescence. At the optimum operational conditions, the antioxidant activity was measured by plotting the inhibition percentage vs logarithm of sample mass to calculate the IC 50 (mass of sample needed to reduce in 50% the chemiluminescence in absence of the antioxidant). The method was examined with pure phenolic compounds for the purpose of relating the molecular structure with the response of the method, and then with the composition of tea infusions, wines, and grape seeds on the antioxidant activity. The results revealed that the white and green tea samples and the red wine had a stronger antioxidant activity because these showed smaller IC 50. Results showed good agreement with the total biophenolic content determined by the Folin-Ciocalteu method. © 2011 Springer Science+Business Media, LLC.

Pulgarin J.A.M.,University of Castilla - La Mancha | Bermejo L.F.G.,University of Castilla - La Mancha | Duran A.C.,Libertador Experimental Pedagogical University
Environmental Monitoring and Assessment | Year: 2013

A flow injection analysis method based on ion chromatography and luminol chemiluminescence detection was used for the simultaneous determination of copper (II) and cobalt (II) trace levels in soils and sediments following microwave-assisted acid digestion. Detection was based on chemiluminescence (CL) of the luminol-perborate system in an alkaline medium, which is catalyzed by both transition metals. The concentration and pH of the eluent (oxalic acid) was found to affect CL intensities and retention times, both of which were inversely proportional to the oxalic acid concentration. The calibration curves for both metal ions were linear and allowed a limit of detection of 0.003 μg l-1 for cobalt (II) and 0.014 μg l-1 for cooper (II) to be calculated. The proposed method was successfully used to determine both metal ions in certified reference materials of stream and river sediments and soil samples. Based on the results, the determination is free of interferences from the usual concomitant ions. © 2012 Springer Science+Business Media B.V.

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