Navegando por Palavras-chave "Voltammetry"

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    Avaliação do efeito da interação entre o íon metálico Cu (II) e o pesticida malathion em amostras de solo
    (Universidade Federal de São Paulo, 2021-12-17) Lima, Ana Layla Carvalho de [UNIFESP]; Akamatu, Eliana Maíra Agostini Valle [UNIFESP]; http://lattes.cnpq.br/1501926375630837; http://lattes.cnpq.br/0527284336985558
    Com a utilização sem fiscalizaçao de diversos pesticidas no meio ambiente devido a sua eficiência no tratamento de pestes em pequena e larga escala, estas substâncias acabam se tornando um grande motivo de preocupação ao solo e água. Sabe-se que suas moléculas apresentam grupos funcionais que podem interagir com íons metálicos, formando novos compostos no meio ambiente e alterando suas características, propriedades e biodisponibilidade no ambiente. Dessa forma, o intuito deste trabalho foi estudar a interação entre o pesticida malathion e o íon metálico cobre (II) em amostras de solo. Para este fim, foram utilizados técnicas eletroanalíticas e espectroscópicas.Inicialmente foi realizado um estudo do comportamento eletroquímico das espécies por meio da técnica de voltametria, onde foi observada a interação entre as duas espécies através do deslocamento de seus potenciais de oxidação e redução, confirmada pela técnica de espectroscopia UV-Vis. Posteriormente o efeito dessa complexação foi avaliado em amostras de solo, que foram digeridas por digestão ácida sob refluxo, seguida da determinação do teor de cobre total nas amostras com e sem a adição do pesticida por espectrometria de absorção atômica com chama. Com esta metodologia empregada, não foi possível verificar a interação entre as espécies, indicando que o cobre pode não estar disponível para interagir com o pesticida no meio, uma vez que pode estar complexado com a matéria orgânica do solo, formando uma espécie altamente estável nas condições do meio.
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    Determinação eletroanalítica em plantas medicinais e fitoterápicos: uma revisão
    (Universidade Federal de São Paulo, 2023) Neves, Rebecca Coelho Jordão das Neves [UNIFESP]; Oliveira, Lucia Codognoto de [UNIFESP]; http://lattes.cnpq.br/3696430664952773
    As plantas medicinais reúnem muitas substâncias que podem agir em conjunto, sendo um dos motivos que tornam muito complexa a padronização e o controle de qualidade destes fitoterápicos. As técnicas eletroanalíticas aparecem com uma alternativa para a determinação de compostos orgânicos de interesse, pois além de simples e de baixo custo oferecem a possibilidade de determinar a concentração de compostos diretamente na amostra e sem pré-tratamentos laboriosos. No entanto, no que diz respeito ao estudo eletroanalítico de plantas medicinais e fitoterápicos, poucos trabalhos são encontrados na literatura. Desta forma o objetivo deste trabalho foi fazer uma revisão da literatura e uma avaliação crítica (qualitativa e quantitativa) sobre a determinação eletroanalítica do princípio ativo de plantas medicinais e fitoterápicos como a Passiflora (maracujá), Mikania Glomerata (Guaco) e a Valeriana Officinalis (Valeriana selvagem). A partir dessa revisão bibliográfica foi possível observar que a determinação eletroanalítica provou ser uma abordagem valiosa no estudo de plantas medicinais e fitoterápicos. Técnicas de voltametria têm sido utilizadas como alternativa para determinação de compostos ativos, fornecendo informações importantes sobre a composição química dessas plantas e a quantificação de seus princípios ativos. Esses avanços contribuem para o desenvolvimento de medicamentos fitoterápicos seguros e de qualidade para uso na medicina tradicional e complementar. Portanto, as técnicas voltamétricas mostraram-se uma alternativa para determinação dos princípios ativos selecionados por apresentarem alta sensibilidade e repetibilidade de resultados, além de ser uma técnica barata e simples.
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    Estudo do comportamento voltamétrico de nitro-heterocíclicos
    (Universidade Federal de São Paulo, 2018-06-29) Chiavassa, Luisa Donatto [UNIFESP]; Scalea, Mauro Aquiles La [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Nitrocompounds exhibit a broad spectrum of biological action and the knowledge of their reduction mechanism can contribute to better understand their biological action. The reduction of nitrofurazone, nitrofurantoin, chloramphenicol, ornidazole and metronidazole was studied by cyclic voltammetry (CV) using a carbon fiber microelectrode as working electrode. The observed behavior demonstrated that the reduction mechanism for all compounds is similar in acidic medium, involving the same number of electrons, having as main product the formation of hydroxylamine derivative. The electrochemical reduction of nitrofurazone (NF), nitrofurantoin (NT) and furazolidone (FZ) was studied by square wave voltammetry (SWV) in aqueous medium. A single cathodic peak in acidic medium was recorded, confirming the same behavior recorded by CV. In the alkaline medium, the original peak was unfolded in two peaks, being the former reversible and pH-independent, corresponding to the nitro radical anion generation confirmed by the electrons number calculation for each compound, and the latter, irreversible and pH-dependent, corresponding to the hydroxylamine formation. The ratio between the direct and reverse current components and the amplitude variation analysis can indicate the existence of an EC mechanism, in which there is a disproportionation reaction after the charge transfer process. From the theoretical models and considering the disproportionation of the product formed, the kinetic constant value could be estimated. The reduction of NF was also studied by CV and SWV in nonaqueous medium using four different ionic liquids (ILs): BMImTf2N, EMImTf2N, BMImBF4 and BMMImTf2N. The NF showed similar reduction behavior in the four ILs, having a single reversible cathodic peak recorded in BMImBF4 and BMImTf2N. On the other hand, in BMMImTf2N and EMImTf2N, two reversible cathodic peaks were recorded. The reversibility of the former could also be observed by CV, since a reversible redox pair was recorded for this reduction. From the frequency variation, the systems reversibility with product and reagent adsorptions on the electrode surface was confirmed. The electrons number calculation involved in this reduction indicated the nitro radical anion formation followed by its respective dianion. For the first reduction, the EC mechanism was also considered for the systems in non-aqueous medium, in which there was a dimerization reaction after the charge transfer process, being the kinetic constants calculated following the Olmstead and Nicholson model.
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    Estudos voltamétrico e espectroscópico da interação dos íons metálicos cobre e chumbo com o pesticida paration metílico
    (Universidade Federal de São Paulo, 2017-12-07) Cardoso, Daisy Alves [UNIFESP]; Oliveira, Lucia Codognoto de [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The objective of this work was to analyze the interaction between the pesticide methyl parathion molecule and the copper and lead metal ions that may be present in soil and water. Initially, electrochemical studies were performed using cyclic voltammetry with a carbon electrode reused from the zinc cell for characterization of the species. Methyl parathion (PM) in 0.4 mol L-1 BR buffer had a cathode peak at approximately -0.57 V, corresponding to the reduction of the nitro group to hydroxylamine. This process was followed by a couple of peaks at -0.02 V and -0.04 V, corresponding to reversible oxidation of the hydroxylamine. In buffer BR 0.4 mol L-1 the copper metal ion showed a cathode peak at -0.09 V and an anode peak at -0.14 V corresponding to the reduction / oxidation of the copper ion and the lead ion in 0.1 mol L-1 KNO3 had a cathode peak at -0.65 V and an anode peak at - 0.44 V corresponding to the reduction / oxidation of the lead ion. Both presented a process controlled by the diffusion of the species on the surface of the electrode. The evaluation of the formation of the complex was performed by cyclic voltammetry and anodic redissolution voltammetry by differential pulse at pH 6.0. The studies of the evaluation of the interaction between PM and Cu(II) did not present satisfactory evidence on the formation of a new species in solution. A new peak at -0.60 V corresponding to the formation of a new species in solution with 1:2 stoichiometry (Pb: PM) was observed for the PM-Pb(II) studies. The stability constant for this new species was calculated (log K'=7.6) from the Langmuir linearization method. Comparative studies using UV-Vis indicated the formation of a new species in solution with increased absorbance of the band of the PM ligand in alkaline medium when in the presence of lead. In the interaction between the PM and Cu (II) by differential the changes in the peak potentials appear in close potential interval hindering an adequate definition of the formation of a new species in solution, already in the interaction between the PM and the Pb (II) was evidenced the formation of a new peak. The studies by voltammetry presented more satisfactory results compared to the technique by UV-Vis.
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    Redução voltamétrica de artemisinina e sua interação com grupo heme (hemina)
    (Divisão de Biblioteca e Documentação do Conjunto das Químicas da Universidade de São Paulo, 2007-09-01) La-Scalea, Mauro Aquiles [UNIFESP]; Silva, Hélio Santa Rosa Costa; Ferreira, Elizabeth Igne; Universidade Federal de São Paulo (UNIFESP); Universidade de São Paulo (USP)
    Malaria is the tropical disease most devastating of the world and this situation is worsened by the absence of effective treatment. However, the plasmodium resistance to artemisinin does not show clinical relevance. The drug mechanism of action is associated to the heme group, with free radical formation and endoperoxide moiety breakage. The voltammetric behavior of artemisinin was studied by cyclic and square-wave voltametries. This drug was irreversibly reduced on glassy carbon electrode and the peak potential values are pH independent, however the biggest value of current peak was observed at pH 6.0. The voltammetric behavior of artemisinin was significantly changed in the heme group presence, provoking an anticipation of about 600 mV on cathodic peak. By square-wave voltammetry it was observed that this new peak was sensitive to the hemin concentration, reaching a value around 10 times larger regarding the original cathodic peak of artemisinin, being the concentration of 20 mmol/L for the former and 50 mmol/L for the latter. In addition, results indicated that this electro-catalytic process depends on the Fe(II)-hemin formation on the electrode surface, indicating the possible electro-polymerization of hemin on the glassy carbon electrode. This adsorptive effect was evaluated from the superficial concentration (G) estimation of the hemin on the working electrode at pH 6.0. The modification of the glassy carbon electrode using hemin showed that the interaction between artemisinin and the heme group predominantly occurs on the electrode surface and not in solution. Therefore, clarifying artemisinin mechanism of action is important in order to contribute for the design and development of new antimalarial agents.