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Browsing by Author "Sousa, Camila Pinheiro"

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  • Evaluation of degradation mechanism of chlorhexidine by means of Density Functional Theory calculations
    Publication . Salvador, Michele Aparecida; Sousa, Camila Pinheiro; Morais, Simone; Lima-Neto, Pedro de; Correia, Adriana Nunes; Homem-de-Mello, Paula
    Chlorhexidine (CHD), a germicidal drug, has degradation products that can be hemotoxic and carcinogenic. However, there is no consensus in literature about the degradation pathway. In order to shed light on that mechanism, we have employed Density Functional Theory to study reactants, in different protonation states, products and intermediates involved in the different pathways. Based on free energy values comparison and frontier molecular orbital analysis, we have obtained the most stable structures in each protonation state. CHD in saturated form has HOMO localized in one p-chloroaniline, and, due to molecule's symmetry, HOMO-1 has contributions from the other side of the molecule, but mainly from the biguanide portion of the molecule, instead of from the p-chloroaniline. For the saturated form, we have studied two possible degradation pathways, starting from the monoprotonated structure, and three pathways starting from the neutral structure. We found out that the mechanisms proposed in literature, whose pathways lead to p-chloroaniline (PCA) formation in a smaller number of steps, are more likely than the mechanisms with more intermediate steps or pathways that do not predict PCA formation. Also, based on free energy results, we have found that the formation of another sub-product (PBG-AU) is favorable as well.
    2017Journal article Open access Show more
  • Sensing of formetanate pesticide in fruits with a boron-doped diamond electrode
    Publication . Ribeiro, Francisco Wirley Paulino; Sousa, Camila Pinheiro; Morais, Simone; Lima-Neto, Pedro de; Correia, Adriana Nunes
    This study describes the development of a simple and accurate methodology for carbamate pesticide formetanate (FMT) analysis in fruits based on the use of a boron-diamond doped electrode (BDDE) cathodically pretreated and on the forward component of the current of square-wave voltammetry (SWV). FMT exhibits a well-defined irreversible oxidation process, which reaction mechanism is diffusion-controlled, involves the participation of one electron and is influenced by the electrolyte pH. However, protonation does not participate in the rate-determining step in the redox process. The optimum experimental and voltammetric conditions were pH 7.0 (0.04 mol L−1 Britton-Robinson buffer), pulse potential frequency of 20 s−1, amplitude of the pulse of 25 mV, and height of the potential step of 3 mV. Under the optimum conditions, calibration curve was linear from 4.98 × 10−7 to 1.70 × 10−5 mol L−1 FMT with a limit of detection of 3.7 × 10−7 mol L−1. FMT sensing was performed in different fruits (mango and grape). Recoveries ranged from 95.2 ± 2.8 to 104.0 ± 3.5% for mango and 96.5 ± 2.5 to 105.2 ± 3.5% for grape proving the accuracy and precision of the electroanalytical methodology. The attained data validated the applicability of the developed approach for FMT quantification in fruits.
    2018Journal article Open access Show more