Silvia Reyna

Degradation of 1-hydroxy-2,4-dinitrobenzene from aqueous solutions by electrochemical oxidation: role of anodic material.

Electrochemical oxidation (ECOx) of 1-hydroxy-2,4-dinitrobenzene (or 2,4-dinitrophenol: 2,4-DNP) in aqueous solutions by electrolysis under galvanostatic control was studied at Pb/PbO2, Ti/SnO2, Ti/IrxRuySnO2 and Si/BDD anodes as a function of current density applied. Oxidative degradation of 2,4-DNP has clearly shown that electrode material and the current density applied were important parameters to optimize the oxidation process. It was observed that 2,4-DNP was oxidized at few substrates to CO2 with different results, obtaining good removal efficiencies at Pb/PbO2, Ti/SnO2 and Si/BDD anodes. Trends in degradation way depend on the production of hydroxyl radicals (OH) on these anodic materials, as confirmed in this study. Furthermore, HPLC results suggested that two kinds of intermediates were generated, polyhydroxylated intermediates and carboxylic acids. The formation of these polyhydroxylated intermediates seems to be associated with the denitration step and substitution by OH radicals on aromatic rings, this being the first proposed step in the reaction mechanism. These compounds were successively oxidized, followed by the opening of aromatic rings and the formation of a series of carboxylic acids which were at the end oxidized into CO2 and H2O. On the basis of these information, a reaction scheme was proposed for each type of anode used for 2,4-D oxidation.

Electrochemical oxidation of oxalic acid in the presence of halides at boron doped diamond electrode

Aim of this work is to discuss the electrochemical oxidation of oxalic acid (OA), analyzing the influence of NaCl and NaBr. Experiments were carried out at boron-doped diamond (BDD) electrodes, in alkaline media. BDD electrodes have a poor superficial adsorptivity so their great stability toward oxidation allows the reaction to take place with reactants and intermediates in a non-adsorbed state. The process is significantly accelerated by the presence of a halogen salt in solution; interestingly, the mediated process does not depend on applied current density. Based on the results, bromide was selected as a suitable mediator during OA oxidation at BDD. Br- primarily acts in the volume of the solution, with the formation of strong oxidants; while Cl- action has shown lower improvements in the OA oxidation rate at BDD respect to the results reported using Pt electrode. Finally, the parameters of removal efficiency and energy consumption for the electrochemical incineration of OA were calculated.

Diketopiperazines from cultures of the fungus Colletotrichum gloesporoides

Abstract Five diketopiperazines, cyclo-(L-prolyl-L-glycine), cyclo-(L-prolyl-L-valine), cyclo-(L-leucyl-L-proline), cyclo-(L-alanyl-L-proline) and cyclo-(L-phenylalanyl-L-proline), were isolated from the phytopathogenic fungus Colletotrichum gloesporoides.

Macrophominol, a diketopiperazine from cultures of Macrophomina phaseolina

A diketopiperazine named macrophominol was isolated from the phytopathogenic fungus Macrophomina phaseolina.

THREE DIKETOPIPERAZINES FROM THE CULTIVATED FUNGUS Fusarium oxysporum

Abstract Three bioactive diketopiperazines, cyclo-(L-prolyl-L-glycine), cyclo-(L-prolyl-L-valine) and cyclo-(L-leucyl-L-proline) were isolated from the phytopathogen fungus Fusarium oxysporum.

Diketopiperazines from Cultures of Fungus Pestalotia palmarum

Abstract Tyrosol and five bioactive diketopiperazines, cyclo-(L-prolyl-L-glycine), cyclo-(L-prolyl-L-valine), cyclo-(L-leucyl-L-proline), cyclo-(L-tirosil-L-proline) and cyclo-(L-alanil-L-proline) were isolated from the phytopathogenic fungus Pestalotia palmarum.