Artigos

URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11800

Navegar

Resultados da Pesquisa

Agora exibindo 1 - 10 de 308
  • Imagem de Miniatura
    Item
    DLLME-GC/ECD Method for the Residual Analysis of Parathion-Methyl and its Application in the Study of the UV-Photodegradation Process
    (Journal of the Brazilian Chemical Society, 2017-11) Pimenta, Gustavo G.; Queiroz, Maria E. L. R. de; Victor, Raquel P. D.; Noronha, Luiz M.; Neves, Antônio A.; Oliveira, André F. de; Heleno, Fernanda F.
    A new method has been developed to determine trace levels of organophosphorus pesticide parathion-methyl in water samples by using dispersive liquid-liquid microextraction (DLLME), followed by gas chromatograph coupled with electron capture detector (GC/ECD) analysis. The optimized and validated method showed high extraction recovery (101.1%), high enrichment factor (57.3), low limits of detection and quantification, 0.083 and 0.250 µg L-1, respectively. The established DLLME-GC/ECD method has been successfully applied for the evaluation of the photodegradation of the parathion-methyl by UV254nm radiation in different conditions of pH and temperature. The parathion-methyl photodegradation at pH 3 and 35 °C achieved > 99.5% after 120 min of exposition. For this condition, it was observed the kinetic rate of 0.0515 min-1, the quantum yield of 1.22 × 10-5 mol Einstein-1 and a half-life time of 13.46 min. All experimental conditions tested proved to be strongly influenced by pH and temperature. The application of the optimized process in distilled and drinking water spiked with parathion-methyl provided residues of this pesticide at levels below the maximum permitted by Brazilian legislation, which is 9.0 µg L-1.
  • Imagem de Miniatura
    Item
    Multivariate calibration to determine phorbol esters in seeds of Jatropha curcas l. Using near infrared and ultraviolet spectroscopies
    (Journal of the Brazilian Chemical Society, 2017-08) Roque, Jussara V.; Dias, Luiz A. S.; Teófilo, Reinaldo F.
    The building of partial least squares (PLS) regression models using near infrared (NIR) and ultraviolet (UV) spectroscopies to estimate the concentrations of phorbol esters (PEs) in Jatropha curcas L. is presented. The models were built using two algorithms for variable selection, ordered predictors selection (OPS) and genetic algorithm (GA). Chromatographic analyses were performed to determine the concentrations of PEs. Spectral data were obtained from seeds and oil extract. The results of PLS models were performed by analyzing statistical parameters of quality such as root mean square error of prediction (RMSEP) and correlation coefficient of external predictions (Rp). The parameters obtained for NIR-PLS and UV-PLS models with OPS were respectively: RMSEP 0.48 and 0.22 mg g-1 and Rp 0.49 and 0.96. For GA were obtained, respectively: RMSEP 0.52 and 0.28 mg g-1 and Rp 0.12 and 0.95. The models built from seeds and oil extracts can be used respectively for screening and to accurately predict the PEs content. The OPS method provided simpler and more predictive models compared to those obtained by the selection of variables using the GA. Thus, the UV-PLS-OPS model can be used as an alternative method to quantification of PEs.
  • Imagem de Miniatura
    Item
    Removal of beta-lactams antibiotics through zero-valent copper nanoparticles
    (Journal of the Brazilian Chemical Society, 2018) Oliveira, Lucas M. F.; Nascimento, Mayra A.; Guimarães, Yuri M.; Oliveira, André F.; Silva, Antônio A.; Lopes, Renata P.
    The removal of the beta-lactam antibiotics (ceftriaxone and cefadroxil) through zero-valent copper nanoparticle (nZVC) was studied in this work. Excellent removal degrees (> 85%) were obtained for both analytes in only 20 min of reaction. Studies were performed in both oxic and anoxic conditions, and in the presence of t-butyl alcohol (TBA), an inhibitor of radicals. The results did not show significant changes. Therefore, the hydroxyl radicals are not the main species responsible for the removal. Total organic carbon cefadroxil analysis indicated a removal of 57% after 180 min of reaction. Studies involving Cu+ indicated that probably these are the principal species responsible for the removal of antibiotics. Kinetic studies have shown that two-phase reaction occurred in the antibiotics removal process and both phases followed pseudo-first order kinetic model. The first mechanism is related to the antibiotics degradation by Cu+ species and the second mechanism is related to the antibiotics adsorption by hydroxides/oxides of Cu2+ species.
  • Imagem de Miniatura
    Item
    Características físico-químicas de ácidos húmicos em diferentes etapas da vermicompostagem
    (Eclética Química, 2010) Reis, E. L.; Reis, C.; Brighenti, C. R. G.
    Amostras de materiais coletados em diferentes estádios de vermicompostagem foram submetidas a procedimentos de extração de ácidos húmicos. Técnicas de titulação potenciométrica, termogravimetria (DTG), difração de raios X e espectrofotometria no uv/visível e no infravermelho foram utilizadas no estudo desses materiais. Os dados de titulação foram submetidos ao ajuste por regressão não-linear, determinando-se, assim, cinco valores de pKa característicos de cinco classes de grupos tituláveis. Nas curvas DTG, foram observadas duas etapas, sendo a primeira característica da separação de estruturas alifáticas e, ou, alicíclicas e a segunda, a decomposição de estruturas aromáticas. A difratometria de raios X apresentou diferenças marcantes nos resultados, principalmente nos três primeiros picos onde parecem ocorrer reorganização estrutural e polimerização ao longo do processo de vermicompostagem. Os espectros do infravermelho não apresentaram diferenciação entre os espectros. Os valores da razão E4/E6 encontrados estão de acordo com os característicos dos ácidos húmicos, mas não fornecem informações que possam contribuir para a elucidação da estrutura e formação desses ácidos.
  • Imagem de Miniatura
    Item
    Evaluation of aerobic and anaerobic biodegradability and toxicity assessment of real pharmaceutical wastewater from industrial production of antibiotics
    (Brazilian Journal of Chemical Engineering, 2016-07) Marcelino, R. B. P.; Andrade, L. N.; Starling, M. C. V. M.; Amorim, C. C.; Barbosa, M. L. T.; Lopes, R. P.; Reis, B. G.; Leão, M. M. D.
    This study evaluates aerobic and anaerobic biodegradability and toxicity of a real pharmaceutical wastewater, which focuses on antibiotics production. Zahn-Wellens and Organization for Economic Cooperation and Development (OECD) methodologies were applied in order to verify the wastewater's biodegradability and Microtox® analysis was performed for toxicity tests. Tests achieved more than 89% and 63% of Total Organic Carbon reduction, showing 80% and 50% of antibiotic removal, for aerobic and anaerobic processes, respectively. Moreover, acute ecotoxicological tests revealed that both techniques decreased the toxic character of real pharmaceutical wastewater. Desorption tests showed that the antibiotic was not degraded, but, in fact, adsorbed onto the sludge. Since biological treatment is the most widely used method for industrial wastewater treatment, this study indicates that this kind of treatment is probably unable to mineralize antibiotics present in pharmaceutical wastewaters, which may induce the development of resistant pathogens. Therefore, efforts must be taken to elucidate the main mechanisms of biological antibiotic removal from wastewaters since the presence of antibiotics in the environment is considered to be an emerging environmental issue.
  • Imagem de Miniatura
    Item
    Synthesis and phytotoxicity of 4,5 functionalized tetrahydrofuran-2-ones
    (Journal of the Brazilian Chemical Society, 2012-12) Resende, Gabriela C.; Alvarenga, Elson S.; Galindo, Juan C. G.; Macias, Francisco A.
    In this work we report a versatile synthesis of fourteen γ-lactones all structurally related, nine of which are novel compounds, accomplished from the readily available furfural. The phytotoxic activity of the synthesized compounds was evaluated in vitro by the influence on the growth of wheat coleoptiles. The percentages of inhibition were mostly small and not statistically different from control after the third dilution (100 µmol L-1). In general, α,β-unsaturated lactones presented better activities than the saturated ones. The most active compounds presented 51, 68 and 76% of inhibition in 1000 µmol L-1. The results indicate that regardless of saturation, the presence of the γ-lactone moiety is important for the bioactivity, but their presence has no implications with potency.
  • Imagem de Miniatura
    Item
    Avaliação de bis(4-metilfenilditiocarbimato)zincato(II) de tetrabutilamônio como acelerador em composições de borracha natural
    (Polímeros, 2008) Mariano, Roberta M.; Visconte, Leila L. Y.; Oliveira, Marcelo R. L.; Rubinger, Mayura M. M.
    Neste trabalho a substância ZNIBU [bis(4-metilfenilditiocarbimato)zincato(II) de tetrabutilamônio] foi usada em formulações de borracha natural (NR) e o seu efeito como acelerador de vulcanização foi investigado. As composições, vulcanizadas com a substância em questão, foram submetidas a testes mecânicos e os resultados comparados com os de outras composições vulcanizadas com os aceleradores comerciais CBS (N-ciclohexil-2-benzotiazol-2-sulfenamida), TMTD (dissulfeto de tetrametiltiuram) e MBTS (dissulfeto de benzotiazol). Propriedades como dureza, resiliência e densidade foram avaliadas em presença ou não da carga negro de fumo.
  • Imagem de Miniatura
    Item
    Remoção dos corantes Reactive Blue 21 e Direct Red 80 utilizando resíduos de sementes de Mabea fistulifera Mart. como biossorvente
    (Revista Ambiente & Água, 2012-01) Silveira Neta, Julieta de Jesus da; Silva, Carlos Juliano da; Moreira, Guilherme Costa; Reis, César; Reis, Efraim Lázaro
    Neste estudo empregou-se resíduos de Mabea fistulifera Mart. como bioadsorvente para a remoção dos corantes Reactive Blue 21 (RB 21) e Direct Red 80 (DR 80) em soluções aquosas e em amostras de efluentes reais fortificados com estes corantes. Foram investigados os ensaios da influência do pH, cinéticos e adsortivos para a remoção dos corantes por meio de uma série de experimentos de batelada. O bioadsorvente exibiu máxima adsorção em pH = 2,0 para ambos os corantes. O tempo de equilíbrio da adsorção foi estabelecido em 300 minutos para o DR 80 e 120 minutos para o RB 21. O modelo de Langmuir descreveu com maior fidelidade o comportamento do sistema sortivo, apresentando coeficiente de determinação (R 2 ) superior a 0,98. Por meio da Isoterma de Langmuir, foi possível obter a capacidade máxima de adsorção dos corantes Direct Red 80 e Reactive Blue 21 pelo bioadsorvente sendo encontrados os valores de 4,92 mg g-1 e 11,13 mg g-1 , respectivamente. O modelo cinético de pseudo-segunda ordem melhor descreveu o processo de adsorção do corante RB 21 sob o bioadsorvente, embora a difusão intra-partícula também esteja envolvida no mecanismo de adsorção. Já para o corante DR 80 o modelo de difusão de Morris e Weber sugeriu que a difusão intra-partícula é predominante em todo o processo de adsorção. Depois de otimizadas as condições adsortivas, o bioadsorvente foi empregado a amostras de efluentes têxteis reais fortificadas com soluções aquosas dos corantes, obtendo-se 85 % de remoção do RB 21 e 94 % de remoção do DR 80 na matriz do efluente.
  • Imagem de Miniatura
    Item
    Evaluation of anxiolytic-like effect of 7-epiclusianone isolated from Garcinia brasiliensis in mice
    (Revista Brasileira de Farmacognosia, 2018-05) Veloso, Clarice de Carvalho; Silva, Mayara Bueno da; Megda, Marianne de Oliveira; Santos, Marcelo Henrique dos; Giusti-Paiva, Alexandre; Vilela, Fabiana Cardoso
    Garcinia brasiliensis Mart., Clusiaceae, species became the target of studies for some years because it has several compounds including polyprenylated benzophenones, as 7-epiclusianone. This benzophenone has several properties, such as leishmanicidal, anti-inflammatory and antinociceptive effects, however still did not be studied anxiolytic activity. For this, the open field and elevated plus maze tests were used in order to evaluate the effect of administration of 7-epiclusianone (isolated from G. brasiliensis) on behav- ioral performance. Swiss male mice (n = 10 per group) were pre-treated with vegetable oil (10 ml/kg; i.p.) or 7-epiclusianone (1, 3 or 10 mg/kg, i.p.) or diazepam (0.2 mg/kg, i.p.). After 1 h, the animals were submitted to the open field and elevated plus maze tests. The administration of 7-epiclusianone exerted a possible anxiolytic effect in the open field, increased the number of central crossings and anti-tigmotactic effect. In pre-treated group with 7-epiclusianone (10 mg/kg) was also possible to determine a possible anxiolytic effect in the elevated plus maze due to increased permanence of animals in the open arms. The results suggest a possible anxiolytic-like effect presented by the 7-epiclusianone and suggest its potential for the treatment of anxiety.
  • Imagem de Miniatura
    Item
    Direct infusion esi-ms applied in the detection of byproducts due to reductive degradation of acetamiprid by zero-valent iron
    (Química Nova, 2015-09) Cruz, Jean C.; Reis, Marina F.; Salvador, Marília M.; Almeida, Marciano F.; Augusti, Rodinei; Lopes, Renata P.
    This study investigated the reductive degradation of acetamiprid (5 mg L-1) in aqueous medium (at pH 2.0) induced by zero-valent iron (50 mg). The process was monitored using high-performance liquid chromatography (HPLC) to determine the degradation rate as a function of reaction time, and direct infusion electrospray ionization mass spectrometry (DI-ESI-MS) to search for (and potentially characterize) any possible byproducts formed during degradation. The results obtained via HPLC showed that after 60 min, the degradation of the substrate reached nearly 100% in an acidic medium, whereas the mineralization rate (as determined by total organic carbon measurements) was as low as 3%. Data obtained by DI-ESI-MS showed that byproducts were formed mainly by insertions of hydrogen atoms into the nitrile, imine, and pyridine ring moieties, in addition to the observation of chlorine substitution by hydrogen replacement (hydrodechlorination) reactions.