O biodiesel vem se consolidando como combustível alternativo devido às suas vantagens e importância econômica. Conforme seu percentual no diesel comercial cresce, o monitoramento da qualidade se torna cada vez mais importante para uma comercialização segura. No entanto, a estabilidade oxidativa do biodiesel é inferior à do diesel fóssil, assim antioxidantes sintéticos, tais como BHA, BHT, PG e TBHQ, são adicionados para prevenir a degradação do mesmo, evitando danos ao sistema de combustão automotivo. Os métodos para avaliar a estabilidade oxidativa e a quantidade de antioxidantes são em geral demorados, requerem preparação amostral ou equipamentos de alto custo. Com o objetivo de contornar tais problemas, neste trabalho foi aplicada uma metodologia para análise direta de antioxidantes em amostras de biodiesel por meio de voltametria de pulso diferencial. Conjuntamente, foi estudada a viabilidade da associação dessa metodologia com técnicas quimiométricas para a determinação simultânea desses antioxidantes em misturas de antioxidantes em biodiesel. Para permitir uma análise direta, sem extração e pré-concentração dos analitos, o biodiesel foi diluído em meio etanólico. Medidas de voltametria de pulso diferencial para cada antioxidante individualmente mostraram relação linear entre as concentrações dos antioxidantes e a corrente de oxidação. Os limites de detecção individuais obtidos foram de 20,5 mg L-1 para BHA, 32,4 mg L-1 para BHT, 35,5 mg L-1 para PG e 26,5 mg L-1 para TBHQ. A modelagem quimiométrica foi aplicada por meio das ferramentas Mínimos Quadrados Clássico (CLS), Mínimos Quadrados Parciais (PLS), Redes Neuronais Artificiais (ANN), Componentes Principais-Redes Neuronais Artificiais (PC-ANN) e Árvore de Decisão-Redes Neuronais Artificiais (DT-ANN). O modelo construído por PLS se mostrou melhor quando comparado à modelagem por CLS. O modelo construído por ANN’s sem seleção de dados de entrada apresentou erros semelhantes ao PLS. Quando a redução da quantidade de dados de entrada foi aplicada em conjunto com ANN’s através de Análise por Componentes Principais (PCA) e DT, a aplicação de PCA levou a aumento de 10,2% no erro de predição, enquanto que na seleção por DT os erros de predição foram reduzidos em 8,5%. A determinação simultânea dos quatro compostos pelo modelo DT-ANN apresentou precisão satisfatória, com recuperação de 98% para BHA, 97% para BHT, 103% para PG e 100% para TBHQ, o que indica que a técnica analítica e a modelagem quimiométrica são viáveis e promissoras para aplicação no controle de qualidade do biodiesel, bem como em análises de monitoramento nas plantas industriais. / Biodiesel is becoming established as an alternative fuel because its advantages and economic importance. As the levels of biodiesel in commercial diesel grows, quality monitoring becomes increasingly important for safe marketing. However, the oxidative stability of biodiesel is smaller than that of fossil diesel and synthetic antioxidants such as BHA, BHT, PG and TBHQ are added to it in order to prevent its degradation, avoiding damage to the automotive combustion system. Methods for evaluating oxidative stability and the amount of antioxidants are usually time-consuming, require sample preparation or expensive equipment. In order to overcome such problems, in this work a methodology was applied for direct analysis of antioxidants in biodiesel samples by means of differential pulse voltammetry. The viability of associating this methodology with chemometric techniques was studied for the simultaneous determination of these antioxidants in biodiesel. To allow a direct analysis, without extraction and preconcentration of analytes, biodiesel was diluted in ethanolic medium. Differential pulse voltammetric measurements for each antioxidant individually showed a linear relationship between antioxidant concentrations and oxidation current. The individual detection limits were 20,5 mg L-1 for BHA, 32,4 mg L-1 for BHT, 35,5 mg L-1 for PG and 26,5 mg L-1 for TBHQ. The chemometric modeling was applied using the Classical Least Squares (CLS), Partial Least Squares (PLS), Artificial Neural Networks (ANN), Principal Component-Artificial Neural Networks (PC-ANN) and Decision Tree-Artificial Neural Networks (DT-ANN) techniques. The model constructed by PLS was better than that obtained with CLS. The model constructed by ANN’s without input selection presented similar deviations in comparison to PLS. When amount of input data reduction was applied together with ANNs through Principal Component Analysis (PCA) and DT, the PCA application led to a 10.2% increase in prediction error, whereas in the selection by DT prediction errors were reduced by 8,5%. The simultaneous determination of the four compounds by the DT-ANN model presented satisfactory accuracy with 98% recovery for BHA, 97% for BHT, 103% for PG and 100% for TBHQ, indicating that the analytical technique and the chemometric modeling are feasible and promising for application in biodiesel quality control, as well as in monitoring analyzes in the industrial plants.

Orientadores: Anne Helene Fostier, Susanne Rath / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-06T03:46:22Z (GMT). No. of bitstreams: 1 Pereira_MariadoSocorroSilva_D.pdf: 916851 bytes, checksum: 669cced4ecf66125f019f5d502b3de80 (MD5) Previous issue date: 2005 / Doutorado / Quimica Analitica / Doutor em Ciências

Submitted by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2016-05-04T18:05:02Z No. of bitstreams: 1 Dissertação - Robson Dantas Ferreira.pdf: 2998812 bytes, checksum: c551f20b9cce8eee052bd58fe5cf262d (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2016-05-04T18:05:41Z (GMT) No. of bitstreams: 1 Dissertação - Robson Dantas Ferreira.pdf: 2998812 bytes, checksum: c551f20b9cce8eee052bd58fe5cf262d (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2016-05-04T18:06:29Z (GMT) No. of bitstreams: 1 Dissertação - Robson Dantas Ferreira.pdf: 2998812 bytes, checksum: c551f20b9cce8eee052bd58fe5cf262d (MD5) / Made available in DSpace on 2016-05-04T18:06:29Z (GMT). No. of bitstreams: 1 Dissertação - Robson Dantas Ferreira.pdf: 2998812 bytes, checksum: c551f20b9cce8eee052bd58fe5cf262d (MD5) Previous issue date: 2016-01-28 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The discharge of potentially toxic metals in water bodies has promoted significant changes in behavior harmful physical, chemical and biological receptor body. The detection of these contaminants with adequate selectivity, sensitivity, and reprodutibility is essential for reliable methods and required to determine these metal ions. The voltammetry of stripping are important electrochemical techniques in trace metals analysis. There is no study of the adsorptive anodic stripping voltammetry (AdASV) technical for in the current literature the determination of metal ions, using the Boron Doped Diamond Electrode (BDD). This study aimed to carry out a study on the determination of metals in aqueous medium using the BDD electrode with AdASV technique the supporting electrolyte selected was Britton - Robinson buffer 0,04 M, pH (1-11), and EDTA as chelating agent. For the Study of adsorptive process on the electrode surface DDB, voltammetric behavior of the complexes Fe-EDTA, Cu-EDTA and Zn-EDTA were analyzed and being possible to observe the oxidation processes related to Fe2+, Cu2+ and Zn2+, the methodology Technical AdASV was optimized by varying the following parameters: Deposition time (Td), deposition potential (Ed), frequency (f) and amplitude (a). Calibration curves were prepared for certain metals and found values for the detection limits LD and limits of quantification LQ. As LD: 0,005 ppm for Fe2+, Cu2+ 0,002 ppm and 0,02 ppm for Zn2+. LQ: 0,019 ppm for Fe2+, Cu2+ to 0,007 and 0,07 to Zn2+. After optimization of technical parameters, triplicate tests were carried out with real samples of the stream of forty in Manaus-AM, Brazil, the concentrations found through the methodology proposed for certain metals were: 0,09 ppm for Fe2+, 0,24 ppm Cu2+ and 0,06 ppm Zn2+. The results obtained with the optimization of the parameters of the voltammetric technique and detection in real sample showed that it is possible to use the BDD electrode for detecting metals in aqueous solution by the technique AdASV / A descarga de metais potencialmente tóxicos em corpos aquáticos tem promovido alterações prejudiciais significativas nos comportamentos físicos, químicos e biológicos do corpo receptor. A detecção destes contaminantes com seletividade adequada, sensibilidade e reprodutibilidade é essencial para que sejam impostas metodologias confiáveis na determinação desses íons metálicos. As voltametrias de redissoluções são técnicas eletroquímicas importantes na análise de metais-traço. Não há na literatura trabalhos que realizem um estudo da Técnica Voltametria Adsortiva de Redissolução Anódica (AdASV) na determinação de íons metálicos, empregando o Eletrodo de Diamante Dopado com Boro (DDB). Este trabalho teve como objetivo realizar um estudo acerca da determinação de metais em meio aquoso utilizando o eletrodo DDB com a técnica AdASV. Foi selecionado como eletrólito suporte o Tampão Britton – Robinson 0,04M, pH (1-11), e o EDTA como agente quelante. Para o Estudo do processo adsortivo na Superfície do Eletrodo DDB, foram analisados os comportamentos voltamétricos dos seguintes complexos: Fe-EDTA, Cu-EDTA e Zn-EDTA, sendo possível observar processos de oxidação referentes aos íons Fe2+, Cu2+ e Zn2+, a metodologia da Técnica AdASV foi otimizada variando os seguintes parâmetros: Tempo de Deposição (Td), Potencial de Deposição (Ed), Frequência (f) e amplitude (a). Foram elaboradas curvas analíticas para os determinados metais e encontrados valores referentes aos Limites de detecção LD e Limites de Quantificação LQ. Sendo LD: 0,005 ppm para o Fe2+, 0,002 ppm para Cu2+ e 0,02 ppm para o Zn2+. LQ: 0,019 ppm para o Fe2+, 0,007 para o Cu2+ e 0,07 para o Zn2+. Após a otimização dos parâmetros da técnica, foram realizados ensaios triplicatas com amostras reais coletadas do igarapé do quarenta em Manaus-AM-Brasil, as concentrações encontradas através da metodologia proposta para os determinados metais foram: 0,09 ppm para Fe2+, 0,24 ppm Cu2+ e 0,06 ppm para Zn2+. Os Resultados obtidos com a otimização dos parâmetros voltamétricos da Técnica e a detecção em amostra real demonstraram que é possível utilizar o Eletrodo DDB para detecção de metais em solução aquosa através da Técnica AdASV

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Neste trabalho à apresentada a investigaÃÃo do processo de deposiÃÃo voltamÃtrica do telureto de cÃdmio sobre substrato de platina em meio Ãcido sulfÃrico a temperatura ambiente (24ÂC). Para este efeito, recorreu-se a tÃcnica de voltametria de varredura linear de potencial, a fim de estabelecer os valores de potencial de deposiÃÃo. Os potenciais de deposiÃÃo variaram entre -167 e -444mV. Os dados extraÃdos dos ensaios sugerem que etapas quÃmicas e eletroquÃmicas estÃo envolvidas no processo. A formaÃÃo de pico catÃdico com a subseqÃente formaÃÃo de patamar de corrente aponta a existÃncia de controle misto na deposiÃÃo do CdTe; enquanto o pico anÃdico indica que a dissoluÃÃo do material à completa. O filme depositado apresenta cor cinza escura e a tonalidade varia com o potencial de deposiÃÃo. Os filmes foram caracterizados por microscopia eletrÃnica de varredura (MEV) e difraÃÃo de raios-X (DRX). Foi verificado que os filmes depositados nos diferentes potenciais apresentam aspectos morfolÃgicos semelhantes, em forma de grÃos, uniformes e compactos. O tamanho dos cristalitos à influenciado pelo potencial de deposiÃÃo. Os difratogramas dos filmes depositados mostraram picos de difraÃÃo associados aos planos (200), (220), (311), (421) e (422). / This work presents the investigation on the voltammetrc deposition of cadmium telluride (CdTe) onto platinum substrate from sulfuric acid-based electrolyte, at room temperature (24 ÂC). For this purpose, the linear sweep voltammetry technique was used in order to establish the values of deposition potential (-167 up to -444mV). The data extracted from the voltammetric essays suggest that different chemical and electrochemical steps are involved. The formation of cathodic peak with subsequent formation of the current plateau indicates the existence of mixed control of the CdTe deposition, while the anodic peak points out that the anodic dissolution of the material is complete. The deposited film presents dark gray color and its tonality depends on the potential. The films were characterized by scanning electron microscopy (SEM) and X-rays diffraction (XRD) techniques. It was found that the films deposited at different potentials have similar morphology, as like grains, are uniform and compact. The crystallite size is influenced by the potential. The XRD patterns of deposited films show peaks associated with the (200), (220), (311), (421) and (422) planes.

Neste trabalho, 2 diferentes procedimentosforam utilizados para a extração de lignina a partir do licor negro, caracterizando-se quimicamente as amostras de lignina obtidas em relação a umalignina comercial, visando a aplicação no desenvolvimento de sensores voltamétricos. A análise elementar, espectroscopia na região do infravermelho, análise térmica e caracterização eletroquímica do material mostraram que, tanto a origem da lignina quanto a metodologia de obtenção da mesma, a partir do licor negro, podem fornecer materiais com propriedades químicas distintas, embora possuam comportamento eletroquímico similar. Observou-se, também, que a lignina só pode ser armazenada na forma sólida,devido à oxidação pelo oxigênio dissolvidodurante o tempo em que a solução mãe é armazenada.No entanto, a oxidação dalignina é necessária quando se tem por objetivo o desenvolvimento de sensores voltamétricos, devido a predominância de carbonos sp2na estrutura químicaoxidada, condição em que se obtém maior condutividade. Constatou-se também a necessidade de utilizar um transdutor metálico para o desenvolvimento de eletrodos qumicamente modificados com este material, visto que os eletrodos de carbono modificados com lignina oxidada ou não oxidada não apresentaram atividade eletroquímica. Devido à pequena porcentagem de enxofre existente na estrutura química, a lignina oxidada tende a se organizar pelos grupamentos SH quando na presença de ouro, expondo os grupamentos quinônicos eletroativos. A lignina oxidada ainda foi utilizada no preparo de eletrodo de pasta de carbono com nanopartículas de ouro, na qual a lignina oxidada impregnada no grafite atua como redutor \"in-situ\" do ouro, permitindo o preparo de um sensor voltamétrico versátil, capaz de realizar a determinação de ácido ascórbico, dopamina, nitrito e iodato. No que tange ao comportamento eletroquímico de fármacos e estudos de interação fármaco-DNA, eletrodos de carbono foram modificados com DNAdupla fita com a finalidade de monitorar a interação DNA-Gemcitabina.O fármaco não apresentou atividade eletroquímica tanto na região positiva quanto na região negativa de potencial. A interação do mesmo com o DNA promove a condensação/agregação das duplas fitas do DNA em uma primeiraetapa, seguida da clivagem do nucleosídeo guanosina, formando guanina livre. O comportamento eletroquímico de leflunomida e sulfasalazina, dois fármacos aplicados ao tratamento da artrite reumatóide, foi estudado e mecanismos de oxidação foram propostos para cada fármaco. / The chemical properties of samples of lignin, which were precipitated from black liquor using two different methodologies (precipitation with CO2 and H2SO4), were studied and the results compared to those obtained from a commercial lignin sample in order to prepare voltammetric sensors. The elementary analysis, infrared spectroscopy, thermal analysis and electrochemical characterization of the material demonstrated that both, the source of lignin and the precipitation method from the black liquor, can provide lignin samples with different chemical properties, although the electrochemical behavior of all samples has been the same. Lignin could only be stored in solid form as lignin in the black liquor is slowly and quantitatively oxidized by dissolved oxygen, preventing the extraction procedures. However, the lignin as extracted from black liquor cannot be used to modify solid electrodes due its high resistivity. The previous oxidation of the all material was necessary when the aim was its application on the sensors development. The electrical conductivity in the oxidized lignin was achieved, probably due to the predominance of sp2 hybridized carbon atoms, which improved orbital overlapping in the material. In addition, it was necessary to use a metallic transducer to produce electrodes modified with films of lignin with good electrochemical activity. The films drying time was also important parameter, which suggested a specific organization of lignin macromolecules over the electrode surface. Due to the small percentage of sulfur in the material, the oxidized lignin tended to be organized by the SH groups in the presence of metallic substrates, exposing its electroactive quinone groups. The oxidized lignin was further used to prepare carbon paste electrodes modified with gold nanoparticles, in which the impregnated oxidized lignin on graphite acted as an \"in situ\" reducing agent towards HAuCl4.The resulting composite allowed the preparation of a versatile voltammetric sensor, capable of detecting ascorbic acid, dopamine, nitrite and iodate. Regarding the electrochemical behavior and drug interaction studies DNA-molecule, carbon electrodes were modified with double strand DNA with the purpose of monitoring Gemcitabine-DNA interaction. The drug showed no electrochemical activity both, in the positive and the negative potential. The Gemcitabine-DNA interaction promoted condensation / aggregation of the double strand DNA in a first step, followed by cleavage of the nucleoside guanosine in the form of free guanine. In addition, the electrochemical behavior of sulfasalazine and leflunomide, two pharmacological compounds applied to the treatment of rheumathoid arthritis, were studied and their oxidation mechanisms were proposed.

Neste trabalho foi utilizada uma metodologia eletroanalítica para o estudo do comportamento dos pesticidas triazínicos, Atrazina e Ametrina em água e sedimentos do rio Mogi-Guaçu. Para isto utilizou-se a técnica de voltametria de onda quadrada (SWV) e o eletrodo de gota suspensa de mercúrio (HMDE). Inicialmente, os parâmetros experimentais (e voltamétricos) foram otimizados a fim de se obter a melhor resposta, em termos de intensidade de corrente de pico e definição do perfil voltamétrico. As melhores condições encontradas foram: eletrólito suporte CaCl2 0,01 mol L-1 em pH 3,0 e 2,3, para Ametrina e Atrazina, respectivamente, f = 100 s-1; a = 50 mV e DEs=2,0 e 10,0, para Ametrina e Atrazina respectivamente. Após a otimização, curvas de trabalho foram construídas para os dois pesticidas. Foram determinados os limites de detecção (LD) e quantificação (LQ), fatores de recuperação, repetibilidade, reprodutibilidade e sensibilidade da metodologia utilizada. Os resultados obtidos utilizando esta metodologia eletroanalítica foram comparados com os obtidos por HPLC-UV. Para Ametrina e Atrazina em eletrólito preparado com água do Milli-Q, os valores de LD encontrados foram de 2,12 ?g L-1 e 1,16 ?g L-1 e os de LQ foram de 7,06 ?g L-1 e 3,90 ?g L-1, respectivamente. Os valores de LD obtidos utilizando HPLC-UV para Ametrina e para a Atrazina foram de 2,69 ?g L-1 e 1,37 ?g L-1, enquanto aqueles para o LQ foram de 9,01 e 10,62 ?g L-1, respectivamente. Observou-se, desta maneira, que os resultados obtidos usando as duas técnicas são muito próximos e inferiores aos valores recomendados pela Comissão Nacional do Meio Ambiente (CONAMA) para águas residuais e efluentes industriais, 50 ?g L-1 para a Atrazina. Além disto, os valores reportados acima são tão baixos quanto os valores máximos aceitos pela Enviromental Protection Agency (EPA - USA) para águas potáveis, 3 ?g L-1 e pela Agência Nacional de Vigilância Sanitária (ANVISA), também para águas potáveis, 2 ?g L-1. A aplicação da mesma metodologia para águas naturais forneceu parâmetros importantes para verificar o comportamento destes pesticidas em águas, principalmente no que se refere à sua persistência. Foram determinados os limites de detecção (LD) e quantificação (LQ), assim como os fatores de recuperação para amostras de água do Rio Mogi-Guaçu, coletadas em três pontos diferentes, utilizando a técnica de SWV. Para Ametrina em eletrólito preparado com água do rio, os valores de LD variaram entre 15,41 e 29,54 ?g L-1 enquanto que os valores de LQ situaram-se entre 51,38 e 98,49 ?g L-1. Já para a Atrazina, os valores de LD variaram entre 4,90 e 6,19 ?g L-1 e os valores de LQ entre 16,36 e 20,65 ?g L-1 respectivamente. Os fatores de recuperação para Ametrina variaram entre 98,12 e 98,50% e para Atrazina entre 98,00 e 98,80%. As fotodegradações dos pesticidas foram estudadas com a exposição à radiação solar de soluções contendo os pesticidas e preparadas com água do Milli-Q, água de rio e água de rio contendo amostras de sedimentos. Os decaimentos da corrente de pico de redução da Ametrina e da Atrazina com o tempo de exposição à luz solar, variaram conforme o ponto de coleta da água do rio Mogi- Guaçu e a natureza do pesticida. Assim, para a Ametrina as porcentagens de decaimento de corrente após 32 horas de exposição foram de 19,10% (água do Milli-Q); 28,24% (ponto 1); 47,62% (ponto 2) e 30,92% (ponto 3). Já para a Atrazina, as respectivas porcentagens de decaimento das correntes de pico de redução foram de 37,50%; 45,90%; 46,10% e 36,53%. Para soluções contendo os sedimentos, a porcentagem de degradação ficou por volta de 30% para Ametrina enquanto que para a Atrazina a diferença foi marcante, ficando em torno de 86%. Os valores dos coeficientes das isotermas de adsorção de Freundlich obtidos indicaram uma dependência da adsorção com o teor de matéria orgânica e argila no sedimento para os três pontos de coleta do sedimento. De acordo com o critério adotado pelo IBAMA, os pesticidas Ametrina e Atrazina apresentam adsorção baixa, ficando pouco adsorvidos no sedimento. Os valores do 1/n da isoterma de Freundlich variaram entre 1,00 e 1,15 indicando uma característica de partição linear para todos os pontos. Os valores de matéria orgânica para os três pontos de coleta, variaram de 5,45 a 15,16%. A matéria orgânica encontra-se revestindo grande parte das frações minerais do solo e sedimento. Estas frações minerais variam de 15,7 a 20,8%, sendo os teores de silte de 12,3 a 16,3%. / An electroanalytical methodology was employed aiming to study the behaviour of the triazinic pesticides Atrazine and Ametrine in water and sediment collected from the Mogi-Guaçu River. The square wave voltammetry (SWV) and the hanging mercury drop electrode (HMDE) were employed. In a first step, the experimental (and voltammetric) parameters were optimized in order to yield the highest current signals as well as the most well defined voltammetric profiles. The best conditions were achieved as: 0.01 mol L-1 CaCl2 as the support electrolyte at pH 3.0 and 2.3 for Ametrine and Atrazine respectively, f = 100 s-1, a = 50 mV and ?Es = 2.0 and 10.0 for Ametrine and Atrazine respectively. After this initial step, analytical curves were obtained for both pesticides. The corresponding detection (LD) and determination (LQ) limits were calculated, as well as the recovering factors, repeatability, reproducibility and sensibility for the analytical methodology, which was compared with those, obtained using the HPLC-UV. For Ametrine and Atrazine, in pure electrolyte the LD values were 2.12 and 1.16 ?g L-1, while the LQ ones were 7.06 and 3.90 ?g L-1, respectively. The same parameters, obtained with HPLC-UV yielded LD values of 2.69 and 1.37 ?g L-1 for Ametrine and Atrazine, respectively, while the LQ ones were 9.01 and 10.62 ?g L-1, respectively. In this way, it is apparent that the results obtained in this work were very close for both techniques and lower than the minimum limit allowed by the Conselho Nacional do Meio Ambiente (CONAMA) for waste water or industrial effluents, 50 ?g L-1. Moreover, they are close to the maximum allowed value for drinking water postulated by the Environmental Protection Agency (EPA – USA), 3 ?g L-1 and the Agência Nacional de Vigilância Sanitária (ANVISA), 2 ?g L-1. The application of the same methodology for natural water samples yielded important parameters to establish the behaviour of pesticides, mainly concerning with its persistency. It were determined the detection and quantification limits and recovering factors by the SWV technique, for river water samples collected in three different points. For Ametrine, the LD values for electrolytes prepared with river waters, varied between 15.41 and 29.54 ?g L-1, while the values for LQ were between 51.38 and 98.49 ?g L-1. The same values for Atrazine were determined between 4.90 and 6.19 for LD and 16.36 and 20.65 for LQ. The recovering factors for Ametrine were found to be between 91.12 and 98.50% and for Atrazine between 98 and 98.8%. The photodegradations of pesticide molecules were studied by exposition to daylight of solutions containing the pesticides prepared with Milli-Q water, river water and river water containing sediments. The peak current decaying for Ametrine and Atrazine with exposition time varied accordingly the water collection point in the Mogi-Guaçu River and the nature of the pesticide. In this way, for Ametrine the percentage of decaying after 32 hours of exposition were 19.10% for Milli-Q water, 28.24% point 1, 47.62% point 2 and 30.92% point 3. For Atrazine, the respective decaying percentages of peak currents were 37.5%, 45.90%, 46.10% and 36.53% respectively. For solutions containing sediments (also collected in points 1, 2 and 3) the degradation percentage was around 30% for Ametrine, while for Atrazine the difference, around 86%. The coefficients from Freundlich adsorption isotherms presented values depending on the organic matter and clay present in the sediment samples. The pesticides presented low adsorption characteristic on the sediments. The 1/n values from Freundlich isotherm varied between 1.00 and 1.15, indicating a linear partition coefficient characteristic in all points. In this way, it is possible to associate the Kf values with the partition coefficients (Kd). The organic matter content for the three collection points varied between 5.45 and 15.15. The organic matter is found to be covering the mineral fractions of soils and sediments. These mineral fractions varied from 15.7 to 20.8%, while silt content were among 12.3 and 16.3%.

Ph.D. (Chemistry) / Materials that are to be used as reference samples are frequently analysed using costly and sophisticated instrumentation, itself calibrated with similar certified standards. Analytical programmes using such instrumentation are only as accurate as the initial calibrations, and their poor results have led to the adoption by the United States National Bureau of Standards of definitive methods of analysis for the determination cf trace elements ...

>Magister Scientiae - MSc / Architecturally enhanced electrode materials for lithium ion batteries (LIB) with permeable morphologies have received broad research interests over the past years for their promising properties. However, literature based on modified porous nanoparticles of lithium manganese phosphate (LiMnPO₄) is meagre. The goal of this project is to explore lithium manganese phosphate (LiMnPO₄) nanoparticles and enhance its energy and power density through surface treatment with transition metal nanoparticles. Nanostructured materials offer advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. The material can store lithium ions but have large structure change and volume expansion during charge/discharge processes, which can cause mechanical failure. LiMnPO₄ is a promising, low cost and high energy density (700 Wh/kg) cathode material with high theoretical capacity and high operating voltage of 4.1 V vs. Ag/AgCl which falls within the electrochemical stability window of conventional electrolyte solutions. LiMnPO₄ has safety features due to the presence of a strong P–O covalent bond. The LiMnPO₄ nanoparticles were synthesized via a sol-gel method followed by coating with gold nanoparticles to enhance conductivity. A magnesium oxide (MgO) nanowire was then coated onto the LiMnPO₄/Au, in order to form a support for gold nanoparticles which will then form a thin film on top of LiMnPO₄ nanoparticles crystals. The formed products will be LiMnPO₄/Mg-Au composite. MgO has good electrical and thermal conductivity with improved corrosion resistance. Thus the electronic and optical properties of MgO nanowires were sufficient for the increase in the lithium ion diffusion. The pristine LiMnPO₄ and LiMnPO₄/Mg-Au composite were examined using a combination of spectroscopic and microscopic techniques along with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Microscopic results revealed that the LiMnPO₄/Mg-Au composite contains well crystallized particles and regular morphological structures with narrow size distributions. The composite cathode exhibits better reversibility and kinetics than the pristine LiMnPO₄ due to the presence of the conductive additives in the LiMnPO₄/Mg-Au composite. This is demonstrated in the values of the diffusion coefficient (D) and the values of charge and discharge capacities determined through cyclic voltammetry. For the composite cathode, D= 2.0 x 10⁻⁹ cm²/s while for pristine LiMnPO₄ D = 4.81 x 10⁻¹⁰ cm2/s. The charge capacity and the discharge capacity for LiMnPO₄/Mg-Au composite were 259.9 mAh/g and 157.6 mAh/g, respectively, at 10 mV/s. The corresponding values for pristine LiMnPO₄ were 115 mAh/g and 44.75 mAh/g, respectively. A similar trend was observed in the results obtained from EIS measurements. These results indicate that LiMnPO₄/Mg-Au composite has better conductivity and will facilitate faster electron transfer and therefore better electrochemical performance than pristine LiMnPO₄. The composite cathode material (LiMnPO₄/Mg-Au) with improved electronic conductivity holds great promise for enhancing electrochemical performances, discharge capacity, cycle performance and the suppression of the reductive decomposition of the electrolyte solution on the LiMnPO₄ surface. This study proposes an easy to scale-up and cost-effective technique for producing novel high-performance nanostructured LiMnPO₄ nanopowder cathode material.

Dopamine (DA) is a key striatal neuromodulator central to normal functioning of the basal ganglia. Identifying and characterizing circuits governing striatal DA transmission is necessary for understanding DA involvement in adaptive behaviour and pathology. Properties of evoked striatal DA release can be examined using fast-scan cyclic voltammetry at carbon fibre microelectrodes, a technique enabling live monitoring of transmitter release events with sub-millisecond resolution. Experimental work presented in this thesis employed this approach to study regulation of striatal DA by acetylcholine (ACh) in health and disease in acute brain slices. Synchronous activity in a small population of striatal cholinergic interneurons (ChIs) was previously shown to directly drive striatal DA release. Here using optogenetic approach I explore physiological relevance of ChI-evoked drive of striatal DA by examining whether corticostriatal and thalamostriatal afferents to ChIs can trigger ACh-evoked DA events. Following floxed vector injections in motor cortex or caudal intralaminar thalamus of CaMK2a-Cre mice I examine the properties of evoked DA upon light activation of channelrhodopsin-2-transduced inputs to striatal ChIs. These experiments revealed that both cortical and thalamic afferents are capable of driving ACh-evoked DA release, but operate using a different complement of post-synaptic ionotropic glutamate receptors and display distinct release recovery profiles. I further explore if rebound excitation in a population of striatal ChIs could drive DA events by examining whether ACh-evoked DA release follows optical inhibition of striatal ChIs selectively expressing hyperpolarizing halorhodopsin 3.0 or archaerhodopsin 3.0 in ChAT-Cre mice. This work showed that hyperpolarizing ion pumps were not successful in triggering ChI-evoked DA release. I also investigate whether cholinergic brainstem innervation of striatum could contribute to or drive ACh-evoked striatal DA events in ChAT-Cre rat, concurrently showing that ChI-evoked DA release is not a species artefact, and is present in mouse and rat alike. Current results also suggest that cholinergic brainstem afferents do not drive or contribute to striatal ACh-evoked DA events. Close interaction between DA and ACh systems further indicates that ACh could impact dopaminergic dysfunction. To explore this I examined the state of ACh transmission in a mouse model of Parkinson’s disease overexpressing human wild type alpha–synuclein protein. These animals present with impaired striatal DA release from young age, but DA deficits could be mediated by changes in ACh tone. Here I show that impaired striatal DA release is the results of primary DA axon dysfunction, although in ventral striatum DA release deficits could be partially compensated by increased ACh tone at nicotinic receptors. I further show that the functional state of muscarinic ACh receptors in not altered following decreased DA transmission, although the data from aged animals suggest that alpha–synuclein-dependent changes in vesicle handling could contribute to impaired DA releasability. Finally, I show that vesicle handling may indeed be altered in this mouse model as impaired DA release is evident with short stimulation protocols, while with prolonged depolarization of DA axon terminals alpha–synuclein-overexpressor mice are better able to sustain evoked DA release. Overall, the main body of work presented in this thesis examined the processes regulating striatal DA transmission via ACh system. In particular, I show that ChI-evoked drive of striatal DA release can be recruited physiologically and further establish that changes in ACh transmission are not the primary drivers of impaired DA releasability in a mouse model of Parkinson’s disease overexpressing human alpha–synuclein protein.

Dopamine (DA) is a key neuromodulator in the striatum, and is important for action selection and reinforcement learning. Dysfunctions in striatal DA signalling contribute to numerous disorders including Parkinson’s disease (PD) and drug addiction. Midbrain DA neurons switch from low to high frequency firing in response to reward-related events, which is proposed to increase striatal DA release. However, in addition to DA neuron firing pattern, striatal DA signalling depends upon the short-term plasticity of DA release, which is controlled by presynaptic and local network factors. This thesis uses fast-scan cyclic voltammetry, in murine striatal slices, to detect subsecond changes in extracellular DA, and investigate the presynaptic control of striatal DA release and release plasticity. Acetylcholine from striatal cholinergic interneurons, acting at nicotinic receptors (nAChRs) on DA terminals, is one factor that strongly influences DA release. This thesis particularly explores how presynaptic factors interact with nAChRs to control DA release. Firstly, release probability, a key determinant of release plasticity at many synapses, was found to be only weakly related to DA release plasticity, and only when nAChRs are inactive. Secondly, a direct role of the DA uptake transporter (DAT) in controlling DA release plasticity was identified, when nAChRs are inactive. Thirdly, regional differences were identified in the role of the DAT in controlling DA release via control of D2 receptor activation, when nAChRs are active. Finally, mutant α-synuclein, which causes PD in humans, was found to only subtly affect striatal DA release. These data suggest that the control of striatal DA release differs substantially from other central transmitters. Release probability and α-synuclein play only minor roles, but nAChRs and the DAT significantly control DA release plasticity. These findings review our understanding of striatal DA release and may have implications for understanding the actions of drugs of abuse and early PD pathogenesis.