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Ciudad Guayana, Venezuela

Romano E.,National University of Tucuman | Castillo M.V.,National University of Tucuman | Marquez M.B.,National University of Tucuman | Gramajo M.B.,Laboratorio Of Fisicoquimica | Brandan S.A.,National University of Tucuman
Journal of Molecular Liquids | Year: 2014

Physicochemical properties of aqueous and physiological solutions of the antihypertensive agent 2-benzylimidazoline (BI), such as pH, refractive index, viscosity, density, conductivity and molar refractivity properties were studied at 25 and 37 °C in the concentration range 0.025-0.100 M. Equations which describe the relative viscosity of the solutions have also been given and viscosity B coefficients using the Jones-Dole equation have been calculated and interpreted in terms of ion-solvent interactions. The computed pKb values in both media varied between 5.0 and 8.58, and correlate well with the available experimental results found in the literature. The experimental properties of the studied species are shown and discussed. It is concluded that the interactions between solute and solute (BI+ and BI) or between solute and solvent could explain the different variations for 2-benzylimidazoline in both media. © 2014 Published by Elsevier B.V. Source

Mora A.,Laboratorio Of Fisicoquimica | Alfonso J.A.,Venezuelan Institute for Scientific Research | Baquero J.C.,Technical University of Madrid | Balza L.,Laboratorio Of Fisicoquimica | Pisapia D.,Laboratorio Of Fisicoquimica
Geochemistry, Geophysics, Geosystems | Year: 2010

This study describes the geochemistry of dissolved elements in the Caura River and gives information about weathering rates and associated CO2 consumption in an Orinoco River subbasin. Physicochemical variables (pH, conductivity, HCO3 -, dissolved O2, and temperature), dissolved elements (Na, K, Ca, Mg, Si, Al, Fe, Cu, Mn, Zn, and Cr), total suspended sediments (TSS), and dissolved organic carbon (DOC) concentrations were measured monthly from June 2007 to August 2008 in the Caura River. Major element concentrations (Na, Ca, Mg, and Si) showed an inverse correlation with discharge, whereas K showed high concentration values during the rising waters, probably due to biogenic sources. All these elements are provided mainly from weathering of plagioclases and K feldspars. The weathering rate (riverine flux of dissolved major cations and SiO2 derived from weathering per unit area) and the CO2 consumption rate in the Caura basin (15.4 tons km-2 yr-1 and 1.1 × 105 mol km-2 yr-1, respectively) were higher than those reported for the Orinoco basin and other black water river basins. This fact can be due to several factors such as lithology (volcanic rocks), high runoff, and the presence of organic acids, which can enhance the chemical weathering. The variability of the trace elements showed a different behavior than major elements. Fe and Al concentrations were correlated with DOC. Dissolved Mn content was correlated with pH, whereas the low concentrations of Cu and Cr are possibly associated with the low content of small size organic colloids. The high values of Zn observed during the decreasing stage suggest biogenic input of Zn to river waters. © 2010 by the American Geophysical Union. Source

Mora A.,Laboratorio Of Fisicoquimica | Mora A.,Technical University of Madrid | Baquero J.C.,Technical University of Madrid | Alfonso J.A.,Venezuelan Institute for Scientific Research | And 2 more authors.
Hydrological Processes | Year: 2010

The analysis of physicochemical variables and selected dissolved elements was performed on the Apure River waters for 15 months. The variables pH, alkalinity, dissolved O2, conductivity and Na, Ca, Mg and Cd concentrations showed maximum values during low water, whereas K, Si, Fe, Al, Mn, Zn, Cu, Cr and dissolved organic carbon (DOC) showed maximum concentrations during rising and high water. Five important factors were found to control the amount and temporal variability of the dissolved elements: lithology, hydrology, vegetation-floodplain processes, redox conditions and organic complexation. Weathering of silicates, carbonates and evaporites in the Andes provides most of the proportion of Na, Ca, Mg and HCO3- to waters. The temporal variability of these ions is controlled by a dilution process. Although Si can be taken up by the biomass, Si and K can be leached from the floodplain by weathering of clays. Microbial decay of the submerged plants in the floodplain during the inundation periods provides DOC and K to river waters and changes the redox conditions in water. The changing redox conditions control the solubility of Mn, Zn and Fe. Dissolved Mn is a function of pH-dependent redox process, whereas Zn solubility is controlled by scavenging of Zn during the oxidation of Mn2+ to MnO2. Positive relationships between Al, Fe, Cu, Cr and DOC suggest that these elements are complexed by organic colloids generated in the floodplain. Moreover, the binding capacity of Fe with DOC increases under reducing conditions. Although Cd seems to be provided by weathering in the Andes, several processes can affect the mobility of Cd during transport. © 2010 John Wiley & Sons, Ltd. Source

Salinas-Nolasco M.F.,Laboratorio Of Fisicoquimica | Mendez-Vivar J.,Laboratorio Of Fisicoquimica | Mendez-Vivar J.,Metropolitan Autonomous University
Langmuir | Year: 2010

Among several analysis techniques applied to the study of surface passivation using dicarboxylic acids, small angle X-ray scattering (SAXS) has proved to be relevant in the physicochemical interpretation of the surface association resulting between calcium carbonate and the molecular structure of malonic acid. It is possible to establish chemical affinity principles through bidimensional geometric analysis in terms of the fractal dimension obtained experimentally by SAXS. In this Article, we present results about the adsorption of malonic acid on calcite, using theoretical and mathematical principles of the fractal dimension. © 2010 American Chemical Society. Source

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