Estudos eletroanalíticos, eletrodegradativos e interação de agroquímicos sintéticos e naturais com o DNA

Abstract

The present work describes the electrochemical studies of the synthetic herbicides, Metribuzin (MTZ) and Sulfentrazone (STZ), along with the natural insecticide, Safrole (SAF), and its nitro derivative, Nitro-safrole (NSAF). On MTZ analysis, a quantification method by “anodic stripping” was developed, using glassy carbon (GC), carbon paste and carbon paste/castor oil electrodes. The best result was obtained with the last one, with the limit of detection (LOD) of 1.248x10-6 mol L-1. GC and carbon nanotubes-modified GC (GC/CNT) electrodes were used in STZ analysis. The sensor GC/CNT showed the best results (LOD = 2.70x10-6 mol L-1). Electroanalysis of SAF and NSAF were performed with GC, GC/CNT and GC/CNT/β-Cyclodextrin (β-CD) electrodes, in which, in the case of SAF, GC/CNT showed the best performance with LOD = 0.869 x10-7 mol L-1; whereas for NSAF, GC/CNT/β-CD was the best, with LOD = 0.23x10-6 mol L-1. Due to SAF and NSAF results using GC/CNT/β-CD sensor, interaction studies with β-CD were carried out, in which the formation constants were measured, for SAF and NSAF, as 4.14x104 L mol-1 and 5.12x104 L mol-1, respectively. The electrolysis of MTZ and STZ were carried out in controlled potential and analyzed by gas chromatography/mass spectrometry (GC-MS). Deaminometribuzin, diketometribuzin and deaminodiketometribuzin were obtained after MTZ electrolysis similarly to the results of microbiological degradation. The electrooxidation process of STZ occurs mainly on the heterocyclic ring and leads to the release of difluorocarbene, that is followed by hydration reaction or oxidation of the methyl group on the heterocycle, and ring opening of the triazole function. The mineralization studies of MTZ and STZ were performed by electro-fenton and analyzed by TOC. For MTZ, TOC was rapidly removed after 30 min, reaching 80% in 120 min. However, in STZ analysis, a decrease about 55% in TOC was observed after 5 min, showing a good performance of this method. The electrochemical analysis with dsDNA biosensor showed no interaction of the macromolecule with those chemicals. However, analyses employing ssDNA, on a GC electrode, have shown positive interaction with STZ, SAF and NSAF and only slight interaction with MTZ.