Valle, E.M.A. (Eliana M.A.)
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- Picloram and Thiram: 2 pesticides acting as heavy metals carriers portrayed by DPASV(ISE, 2008-09-07) Santamaria-Elola, C. (Carolina); Valle, E.M.A. (Eliana M.A.); Machado, S.A.S. (Sergio A.S.); Fernandez-Alvarez, J.M. (José María)Comunicación presentada en el Program of the 59th Annual Meeting of the International Society of Electrochemistry, Seville, 2008, S10-P085:Page 141. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxilic acid) is a herbicide widely used, alone or in combination with other herbicides to control of weeds in crops of sugar cane, rice, pasture and wheat1. It can stay active for long time, depending on the type of soil, moisture and temperature. Thiram (N,N-dimethildithiocabamate) is a fungicide used for a control of a variety diseases in the crops of fruits, vegetables and ornamentals2. From an electrochemical point of view, the study of the redox behaviour of both pesticides on modified electrodes has been reported recently3. However, few works reported the interactions between metallic ions and pesticides and their properties in the environment, although these molecules usually present functional groups that can act as ligands. In this work, we studied the interaction between heavy metals (Zn, Cu, Pb and Cd) and the pesticides (picloram and thiram) using the Differential Pulse Anodic Stripping Voltammetry technique on Hg electrode (DPASV) which has shown efficient in the evaluation of the formation of complexes in natural samples4 through the competing role of Hg for metals with respect to ligands. Electrochemical measurements provided a simple means to evaluate the stoichiometry of the complexes, and Scatchard and Langmuir algorithms allowed the calculation of the conditional complexation constants for both systems in an acetate pH 4 buffered solutions. Studies carried out for both Zn and Cu with Picloram have shown that 1:1 complexes were formed in all instances. Calculated conditional stability constants are quite close (log K’ ~ 6) for both metallic species, Cu consistently yielding highest values.
- Thiram: un fungicida atrapador de metales. Caracterización electroquímica(Universidad de Navarra, 2008-05-30) Santamaria-Elola, C. (Carolina); Valle, E.M.A. (Eliana M.A.); Fernandez-Alvarez, J.M. (José María)El thiram es un fungicida, de la familia de los ditiocarbamatos, muy utilizado en los cultivos de frutas y verduras, tanto para proteger las cosechas en el campo como para prevenir su deterioro durante los periodos de almacenamiento y transporte. En su estructura hay grupos funcionales que son capaces de formar enlaces con iones metálicos como el cobre, plomo y cadmio que están presentes en el medio ambiente libres o formando complejos con diversas moléculas orgánicas. La unión de estos metales con el thiram puede modificar las características contaminantes del fungicida, por lo que se considera de elevado interés conseguir una metodología capaz de cuantificar algunas de las propiedades de estos complejos. En el presente trabajo, se pretende evaluar esta interacción metal-fungicida, utilizando una técnica electroquímica como es la voltametría de redisolución anódica por pulso diferencial y la espectroscopía ultravioleta/visible. El empleo de estas dos técnicas permitirá confirmar la formación de complejos entre ciertos metales y thiram, así como cuantificar la fuerza de esta unión a través de las constantes condicionales de formación respectivas. El thiram presenta un comportamiento electroquímico que se ve alterado cuando se estudia en presencia de alguno de los metales anteriormente mencionados, lo que permite verificar la formación de un complejo entre ambas especies. Del mismo modo esta diferencia es visible por espectroscopía, donde después de la adición del metal se registran bandas adicionales a las observadas sólo para el thiram, que también sugieren la formación del complejo.
- Thiram and picloram as entrapping agents for lead depicted by electrochemical methods(Sociedade Brasileira de Química, 2010-05-01) Santamaria-Elola, C. (Carolina); Valle, E.M.A. (Eliana M.A.); Machado, S.A.S. (Sergio A.S.); Fernandez-Alvarez, J.M. (José María)The affinity of two widely used pesticides of diverse specificities, i.e., the fungicide Thiram and the herbicide Picloram, for lead ions has been studied by an electrochemical approach. The anodic stripping voltammetric profile of the studied metallic ion was significantly affected by the chemical nature of pesticide (ligand) used and new light has been shed on the nature, strength and possible stoichiometry of formed complexes. Thiram caused a pronounced effect on the stripping signals of Pb. Linearization algorithms of titration data with the metal allowed the conditional stability constant to be calculated for Thiram (log K' = 6.8) and Picloram (log K' = 6.0). It was found that both pesticides contribute to the formation of the respective 1:1 complexes with Pb in a high percentage (ca. 83%).