Artículos y presentaciones en Congresos
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Examinando Artículos y presentaciones en Congresos por Autor "Arce, Valeria Beatriz"
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Acceso Abierto Combined Experimental and Computational Investigation of the Fluorescence Quenching of Riboflavin by Cinnamic Alcohol Chemisorbed on Silica Nanoparticles(Royal Society of Chemistry, 2014) Arce, Valeria Beatriz; Scotto, Juliana; Allegretti, Patricia E.; Melo, Mauricio; Airoldi, Claudio; Salum, María Laura; Erra-Balsells, Rosa; Pis Diez,Reinaldo; Mártire, Daniel O.Riboflavin (vitamin B2) is usually present in water courses, lakes, and seas and acts as a photosensitizer in the photo-oxidation of a range of contaminants. However, little is known about the interaction of this compound with aromatics sorbed on silica sediments or on suspended silica particles. This article describes the modification and characterization of silica nanoparticles by condensation of the silanol groups of the particles with E-cinnamic alcohol. The reaction was confirmed by Fourier transform infrared spectroscopy (FTIR), solid-state 13C and 29Si crosspolarization magic angle spinning (CPMAS) NMR, reduction of the specific surface area measured by BET, thermal analysis, and fluorescence spectroscopy. Toxicity to the marine bacteria Vibrio fischeri of the modified particles was also measured. Riboflavin fluorescence was quenched in aqueous medium in the presence of dissolved E-cinnamic alcohol or in suspensions of the modified particles. The results are interpreted in terms of formation of 1:1 complexes between the ground states of riboflavin and the free or adsorbed cinnamic alcohol. Density functional theory (DFT) calculations in aqueous medium support the existence of the complex and explain the observed quenching of riboflavin fluorescence upon addition of cinnamic alcohol without affecting the emission maximum of riboflavin. - Artículo
Acceso Abierto Photodegradation routes of the herbicide bromoxynil in solution and sorbed on silica nanoparticles(Royal Society of Chemistry, 2014) Escalada, Juan P.; Arce, Valeria Beatriz; Carlos, Luciano; Porcal, Gabriela; Biasutti, M. Alicia; Criado, Susana; García, Norman; Mártire, Daniel OsvaldoSome organic contaminants dissolved in natural waters tend to adsorb on suspended particles and sediments. In order to mimic the photodegradation routes in natural waters of bromoxynil (BXN) adsorbed on silica, we here prepare and characterize silica nanoparticles modified with BXN (NP-BXN). We measure the direct photolysis quantum yield of aqueous BXN at 307 nm (0.064 0.001) and detect the formation of bromide ions as a reaction product. Under similar conditions the photolysis quantum yield of BXN bonded to NP-BXN is much lower (0.0021 0.0004) and does not lead to formation of bromide ions. The rate constant of the reaction of NP-BXN with the excited triplet states of riboflavin, a molecule employed as a proxy of chromophore dissolved organic matter (DOM) was measured in laser flash-photolysis experiments. The rate constants for the overall (kt) and chemical interaction (kr) of singlet oxygen with NP-BXN were also measured. Kinetic computer simulations show that the relevance of the direct and indirect (through reactions with reactive species generated in photoinduced processes) photodegradation routes of BXN is very much affected by sorption on silica. Immobilization of the herbicide on the particles, on one hand, affects the photolysis mechanism and lowers its photolysis quantum yield. On the other hand, the results obtained in aqueous suspensions indicate that immobilization also lowers the rate of collisional encounter, which affects the quenching rate constants of excited triplet states and singlet oxygen with the herbicide.