This thesis presents the results and discussion of the investigation of the effects of Brönsted bases on the kinetics and thermodynamics of two proton-coupled electron transfer processes: the mediated oxidation of glutathione and the electrochemical oxidation of hydroquinone. Proton-coupled electron transfer (PCET) is the name given to reactions that involve the transfer of electron(s) accompanied by the exchange of proton(s). PCETs are found in many chemical and biological processes, some of current technological relevance such as the oxygen reduction reaction in fuel cells, which involves the transfer of four electrons and four protons (4e-, 4H+); or the splitting of water into protons (4H+), electrons (4e-) and oxygen (O2) efficiently achieved in photosynthesis. The study of PCET mechanisms is imperative to understanding biological processes as well as to developing more efficient technological applications. However, there are still many unanswered questions regarding the kinetic and thermodynamic performance of PCETs, and especially about the effect of different proton acceptors on the rate and mechanism of PCET reactions. This study aimed to investigate the effect of Brönsted bases as proton acceptors on the kinetics and thermodynamics of two model PCET processes, the oxidation of glutathione and hydroquinone. The analysis presented in this thesis provides insight into the influence of different proton acceptors on the mechanism of PCET and it does so by studying these reactions from a different angle, that one of the acid-base catalysis theory which has been successfully applied to the investigation of numerous chemical reactions coupled to proton transfer. We hope future research of PCETs can benefit from the knowledge of acid-base catalysis to better understand these reactions at a molecular level.

In this study the possibilities of utilization of boron-doped diamond (BDD) electrodes for electrochemical reduction of organic compounds and their determination in aqueous media were investigated. For this purpose BDD electrodes have several advantages (relative wide potential window in cathodic region, low sensitivity towards oxygen evolution) but are not frequently used. For the study were selected biologically active organic compounds with typical reducible groups. Vanillin (natural essential oil, synthetic aroma; reducible aromatic aldehyde) is not reducible at BDD electrode. Azidothymidine (antiviral drug; reducible azido group) shows voltammetric signal in Britton -Robinson buffer at pH 6.0 - 8.0, but its analytical utilization is difficult due to the close positioning to the decomposition of the supporting electrolyte. The height and potential of the reduction signal of 5-nitroquinoline (environmental pollutant; reducible nitro group on the aromatic nucleus and at higher potentials reducible heterocycle) is significantly influenced by the boron concentration in BDD film. Reduction of quinoline skeleton is visible in the range of pH6.0 - 11.0 in BR buffer. For differential pulse and DC voltammetry (reduction of nitro group) in BR buffer pH 5.0 limits of detection 0.2 µmol.l-1 and 2.7...

Anilazine (4,6-dichloro-N-(2-chlorophenyl)-1,3,5-triazin-2-amine) is a fungicide from a group of triazine pesticides. These have been very widely used but for their toxicity for water environment they are being cancelled. Use of anilazine is not allowed anymore in the European Union. However, traces of its residues are able to find in environmental samples. The diploma thesis deals with determination of anilazine using silver solid amalgam electrode modified by mercury meniscus (m-AgSAE). Differential pulse voltammetry was used. For the determination, an acidic solution is necessary. In the work Britton-Roninson buffer pH = 2 was used. This is because of electrochemical reduction of anilazine (and other triazines) which is started by protonization of heterocycle ring. Anilazine exhibits one single well-defined peak, the potential of the peak was about Ep = -827 mV (vs. 3 mol l-1 argentochloride electrode). The limit of quantification achieved in surface water was 2 µmol.l-1. Other two possibilities of getting lower limit of quantification were examined - Adsorptive Stripping Voltammetry (AdSV) and preconcentration by Solid Phase Extraction (SPE). Using AdSV the limit of quantification LQ = 0,5 µmol.l-1. Conditions of adsorption were as following: Eacc = -100 mV, tacc = 60 s. For SPE, 200-mg columns...

The study of the substituent effect on the voltammetric behaviour of newly synthesized N benzyl-salicylthioamides and the preparation and identification of products of their electrooxidation were the aims of this thesis. The voltametric characteristics were measured by DC voltammetry on a rotating disc electrode in a non-aqueous media. Using QSER, the effect of substituents on the anodic half wave potential was quantified, and statistically valid correlation equations were obtained. The influence of reaction media on the compounds electrooxidation was also studied. Using preparative electrolysis, the electrooxidation products of two selected N benzylsalicylthioamides were obtained. The one (structurally similar) product was identified in both cases. The following general scheme of electrochemical oxidation of N-benzylsalicylthioamides studied was proposed: the electrooxidation starts on sulphur atom by elimination of electrons, followed by translocation of charge on nitrogen atom, then hydrogen sulphite is eliminated, and a new ring is closed between two molecules of appropriate N-benzylsalicylthioamide.

Ce travail de thèse s’inscrit dans un projet plus large qui vise à développer avec le laboratoire Ampère et l’Etablissement Français du Sang un microsystème capable de réaliser un phénotypage plaquettaire pour le diagnostic de la thrombopénie néonatale. Ce microsystème doit permettre d’isoler les plaquettes du sang total et de détecter les antigènes plaquettaires présents à leur surface. L’isolation des plaquettes se fera grâce à un module de magnétophorèse et un module de diélectrophorèse. La détection sera électrochimique. Le cœur de ce travail de thèse a donc consisté à développer des nanoparticules magnétiques pour le module de magnétophorèse. Ces nanoparticules doivent permettre la capture spécifique des plaquettes et servir de marqueur pour la détection électrochimique. Pour ce faire, des nanoparticules magnétiques ont donc été doublement fonctionnalisées en une seule étape avec un anticorps anti-CD32 dirigé contre l’antigène CD32 présent à la surface des plaquettes et avec une molécule électroactive. Après optimisation des différents paramètres de greffage, les propriétés électrochimiques de ces particules ont été caractérisées. Leurs propriétés de bioreconnaissance ont été testées sur l’antigène purifié puis sur plaquettes entières. Enfin la faisabilité de la manipulation des structures nanoparticules/plaquettes par magnétophorèse avec des micro-aimants a été démontrée. / Fetal/neonatal alloimmune thrombocytopenia (F/NAIT) represents a great threat to new-borns or fetus. It occurs when a woman becomes alloimmunized against fetal platelet antigens. With the aim to improve fetal and neonatal survival, in collaboration with Ampere Laboratory and Etablissement Français du Sang, we plan at developing a Point-of-Care (POC) platform for platelet phenotyping. The final POC microsystem will be able to perform magnetophoresis and dielectrophoresis for platelets isolation from whole blood, and their selective electrochemical detection allowing for their phenotyping. The development of nanoparticles (NPs) with magnetic, electrochemical and bio-selection properties is a key issue. Herein, we have focused on the elaboration of magnetic NPs bearing 1) anti-CD32 antibody for specific interaction with CD32 antigen, which is present at the surface of platelets and 2) ferrocene carboxylic acid, an electroactive molecule for detection. To achieve this, the coupling reactions of this electroactive molecule and this antibody were optimized and a one-pot reaction for double functionalization was developed. The bioactivity of the immobilized antibody was tested at the molecular and cellular level. The dual-functionalized NPs voltammetric signals were also investigated. Finally the feasibility of platelets capture and actuation by magnetophoresis with micro-magnet array were demonstrated.

7 ABSTRACT (EN) This dissertation thesis is focused on the study of electrochemical properties of new types of carbon paste electrodes (CPE) and carbon fiber rod electrodes (CFRE), which were used for the development of new highly sensitive and selective voltammetric and amperometric methods for the determination of 5-amino-6-nitroquinoline and trans- and cis- isomers of resveratrol. The carbon paste electrodes were compared in terms of size of the microparticles of glassy carbon contained in the paste (diameters 0.4 - 12 µm; 10 - 20 µm; 20 - 50 µm) in comparison with carbon paste electrode consisting of crystalline graphite and solid glassy carbon electrode. The electrochemical properties were tested using potassium hexacyanoferrate in an aqueous supporting electrolyte and 5-amino-6-nitroquinoline (5A6NQ) in a mixed methanol-water supporting electrolyte. The carbon paste electrode was further used in an amperometric detector of a wall-jet type connected in series with a spectrophotometric detector for the development of a new HPLC method with electrochemical detection and spectrophotometric detection for the determination of trans-resveratrol and cis-resveratrol in samples of grains, hulls and leaves of common and tartary buckwheat. The method was optimized and used for the determination of resveratrol in...

A aplicação do processo de fotoeletrocatálise à eliminação de interferentes orgânicos em baixa concentração na eletroanálise de metais foi abordada tomando o quelato Cu(II)-EDTA como sistema modelo e o restabelecimento da onda voltamétrica do cobre como indicador de efetividade. Desenvolveram-se células eletroquímicas de camada delgada (espessura de 600 micrômetros) nas quais alguns microlitros de amostra são tratados sobre um eletrodo modificado com TiO2 (tipo P25, rico em anatase), cuja superfície é irradiada através de uma janela por um LED (370 nm). Foram construídos e avaliados os seguintes eletrodos: pasta de carbono, TiO2 e óleo parafínico (CPE-TiO2), compósitos de grafite, TiO2 e adesivo epóxi ou de silicone e ouro com oclusão de TiO2 por eletrodeposição. Estudo do efeito de parâmetros como potencial aplicado ao eletrodo, composição do eletrólito e concentração de EDTA sobre a fotocorrente permitiu selecionar condições de trabalho e estabelecer algumas correlações. Por exemplo, observou-se linearidade entre a fotocorrente e a concentração de EDTA até 1,0 mmol/L, aparente limite superior do controle difusional do processo para potência radiante aplicada, acima do qual, a cinética de oxidação passa a sobrepujar o transporte no controle da velocidade de reação. O restabelecimento pleno da onda de Cu(II) 1,0 mmol.L-1 foi observado após a irradiação por 10 min quando a concentração de EDTA não excedia 0,94 mmol.L-1. Descobriu-se um procedimento mais rápido que consiste na aplicação do tratamento fotoeletrocatalítico simultâneo ao registro de voltamogramas cíclicos repetitivos (eletrodo de Au-TiO2, 0,3 a 0,7 V vs. Ag/AgCl, 100 mV.s-1). Após o sexto ciclo, a altura do pico de redissolução anódica do Cu (reduzido durante a varredura no sentido negativo) estabiliza, permitindo a quantificação sem etapa prévia de abertura. / The photoelectrocatalysis process was investigated for the elimination of organic compounds interference on the electroanalysis of trace metals. Cu(II)-EDTA chelate was chosen as model system and the recovery of copper voltammetric peak, as effectiveness indicator. Thin layer cells (thickness of 600 micrometers) were designed for the treatment of some microliters of sample by irradiation (370 nm LED) of an electrode modified with TiO2 (P25, anatase rich). The following modified electrodes were prepared and evaluated: carbon paste with TiO2 and paraffin oil (CPE-TiO2), composites of graphite, TiO2 and epoxy or silicone binders and TiO2 occluded in electrodeposited gold on a gold substrate. The effect of parameters like potential bias, electrolyte composition and EDTA concentration on the photocurrent was evaluated to setup working conditions. Some correlations were observed, e.g., a linear dependence between photocurrent and EDTA concentration up to 1.0 mmol/L. For the irradiance applied, this concentration is possibly the upper limit of operation diffusion transport control, above which, the kinetics of the oxidation at the TiO2 modified electrode becomes the controlling process. For EDTA concentrations not exceeding 0.94 mmol.L-1, full recovery of 1.0 mmol.L-1 Cu(II) voltammetric peaks was observed after 10 min of irradiation. A faster procedure was discovered and consists in recording repetitive cyclic voltammograms (Au-TiO2 electrode, 0,3 to 0,7 V vs. Ag/AgCl scans, 100 mV.s-1) simultaneously with continuous irradiation. After the sixth cycle, the copper anodic stripping peak height stabilizes allowing quantification without previous sample pre-treatment step.

Neste trabalho foi realizada a funcionalização de grafite sem prévio tratamento em condições de Fridel-Crafts. Considerando que a grafite não possui hidrogênio em sua estrutura, não se observa uma reação de substituição eletrofílica. Por outro lado, o trabalho mostra o papel da umidade presente no grafite na reação de funcionalização. Dessa forma, foi proposto um mecanismo para a reação com a participação da água adsorvida na grafite estabilizando o carbocátion formado. O grafite funcionalizado obtido na reação foi utilizado como material eletródico. Para a reação de funcionalização, quatro moléculas foram utilizadas: ácido ferrocenomonocarboxílico, cloreto de 4-nitrobenzoíla, cloreto de 3,5-dinitrobenzoíla e ácido 3,4-dinitrobenzóico. Para o estudo das condições ótimas da reação, utilizou-se diferentes potências de radiação no reator de micro-ondas, sendo que a extensão da funcionalização mostrou-se sensível à variação deste parâmetro. Para a caracterização dos materiais, utilizou-se voltametria cíclica e análise térmica (TG e DTA). Resultados de infravermelho e Ramam são apresentados no Apêndice A. Os resultados eletroquímicos mostraram que os materiais funcionalizados em maiores potências apresentaram maior corrente Faradaica, mas ao mesmo tempo, o material obtido foi mais resistivo. A diferença de potencial relacionada ao processo redox do ferroceno aumentou conforme a extensão da funcionalização, uma vez que um sobrepotencial é necessário devido ao fluxo iônico (para a manutenção da eletroneutralidade) relativo ao número de espécies envolvidas. Os resultados eletroquímicos também indicaram que a funcionalização do grafite com os nitro compostos foi baixa. A análise térmica evidenciou que a reação de funcionalização do grafite com o ferroceno resultou em materiais com 15% a 20% (m/m) de material ligado ao grafite. Os materiais funcionalizados a maiores potências apresentaram maior massa ligada ao grafite. A funcionalização com os nitro compostos resultou em materiais com menos de 3% (m/m) de composto ligado ao grafite. Os resultados das duas técnicas mostraram coerência na análise da extensão da funcionalização. O material funcionalizado com o ácido ferrocenomonocarboxilico foi o que apresentou os melhores resultados e propõe-se uma explicação para tal baseado no mecanismo de reação sugerido. Com o objetivo de melhor elucidar o mecanismo da reação, foram realizadas algumas reações na ausência de alguns reagentes. Por exemplo, quando tenta-se funcionalizar o material sem a presença de cloreto de alumínio ou sem a umidade natural do grafite, a reação não ocorre. / In this work natural graphite functionalization in Fridel-Crafts conditions is performed using a one-step microwave assisted reaction. Since there is no hydrogen in graphite structure, it is not possible to observe electrophilic substitution. On the other hand this work shows the role of the moisture present on graphite in the functionalization reaction under this condition. Therefore, a reaction mechanism with the participation of the water naturally adsorbed on graphite stabilizing the formed carbocation has been suggested. After the reaction, the functionalized graphite was used as electrode material. Four molecules were used to functionalize graphite: Ferrocene monocarboxylic acid, 4-nitrobenzoyl chloride, 3,5-dinitrobenzoyl chloride and 3,4-dinitrobenzoic acid. To study the optimal conditions of the reaction, the microwave radiation power was varied and the extent of the functionalization on graphite was sensitive to this parameter. Two techniques were used to characterize the materials, cyclic voltammetry and thermal analysis (TG and DTA). IR and Raman data are shown in appendix A. Electrochemical results have shown that the materials functionalized at higher microwave radiation power have higher Faradaic current, but are more resistive. The potential difference between the peaks of the redox process of ferrocene increased with the extent of functionalization. This occurs because an overpotencial is needed to compensate the ionic flux (in order to maintain the electroneutrality) related to the number of species involved. The electrochemical results also indicated that the extent of functionalization of graphite with the nitro compounds was low. The thermal analysis have shown that the functionalization of graphite with ferrocene lead to values between 15% to 20% (m/m) of compound in the material. The materials functionalized at higher microwave radiation power presented higher relative mass in the material. The reaction with the nitro compounds lead to less than 3% (m/m) of compound in the final material. The results of both techniques were coherent about the extent of functionalization. The material functionalized with ferrocene monocarboxylic acid showed the best results, and an explanation for that based on the reaction mechanism is suggested. In order to elucidate the reaction mechanism, some experiments were realized in absent of some reagents. When the reaction were carried out without aluminum chloride or with dried graphite, the reaction has not occurred.

O mel de abelhas é um produto biológico muito complexo, cuja composição varia notavelmente em função da flora visitada pelas abelhas e das condições climáticas e edáficas da região onde foi produzido. Este trabalho teve como objetivos confrontar os resultados das análises físico-químicas entre as amostras de méis produzidos em diferentes localidades do Brasil por Apis mellifera e por Meliponíneos e investigar se o mel produzido por essas abelhas nas suas diferentes regiões de origem apresenta níveis toleráveis de contaminantes inorgânicos. Para tanto, foram avaliadas 56 amostras de méis de A. mellifera e 56 amostras de méis de Meliponíneos dos Estados da Bahia, Minas Gerais, Mato Grosso do Sul, Paraíba, Piauí, Paraná, Santa Catarina e São Paulo, em relação aos seguintes parâmetros: umidade, atividade de água, viscosidade, pH, acidez livre, índice de formol, açúcares redutores, sacarose aparente, teor de cinzas, cor, condutividade elétrica, hidroximetilfurfural, atividade diastásica e metais (Hg+2, Zn+2, Cd+2, Pb+2 e Cu+2). Foi utilizada a técnica de Voltametria de Redissolução Anódica de Pulso Diferencial (DPASV) para quantificar os metais, e métodos convencionais e próprios para mel nas demais análises. Os resultados mostraram que a legislação atual, referente ao mel de A. mellifera, não é adequada para os parâmetros açúcares redutores, umidade e atividade diastásica de algumas espécies de Meliponíneos. Pôdese concluir que as espécies A. mellifera, Tetragonisca angustula, Melipona quadrifasciata, M. scutellaris, M. mandacaia, M. fasciculata, M. subnitida produzem méis com características físico-químicas diferentes e próprias de cada uma delas. Para todas as espécies avaliadas, os níveis de contaminantes inorgânicos encontrados nos méis foram toleráveis à saúde humana. Os méis produzidos por A. mellifera apresentaram variações nas características físico-químicas: atividade de água, viscosidade, acidez livre, índice de formol, açúcares redutores, condutividade elétrica, hidroximetilfurfural, atividade diastásica e o mineral zinco, em função dos diferentes locais onde foram produzidos. / The honeybee is a very complex biological product, whose composition varies markedly depending on the plant visited by the bees and the weather and soil conditions in the region where it was produced. This study aimed to compare the results of physicochemical analysis between the samples of honey produced in different locations in Brazil by Apis mellifera and Meliponid and to investigate whether honey produced by these bees, in different regions of origin, has tolerable levels of inorganic contaminants. To this end, we evaluated 56 samples of honey from A. mellifera and 56 samples of honey from Meliponid from the states of Bahia, Minas Gerais, Mato Grosso do Sul, Paraíba, Piauí, Paraná, Santa Catarina and São Paulo, for the following parameters: moisture content, water activity, viscosity, pH, free acidity, formol index, reducing sugars, apparent sucrose, ash content, color, electrical conductivity, hydroxymethylfurfural, diastase activity and metals (Hg+2, Zn+2, Cd+2, Pb+2 and Cu+2). Differential Pulse Anodic Stripping Voltammetry (DPASV) technique was used to quantify the metals, and, to the other analysis, conventional and suitable methods for honey were used. The results showed that the current legislation, referring to the honey of A. mellifera, is not appropriate for the parameters reducing sugars, moisture content and diastase activity of some species of Meliponid. It was concluded that the species A. mellifera, Tetragonisca angustula, Melipona quadrifasciata, M. scutellaris, M. mandacaia, M. fasciculata, M. subnitida produce honeys with different and specific physico-chemical characteristics. For all species studied, levels of inorganic contaminants found in honey were tolerable to human health. The honey produced by A. mellifera showed variations in physicochemical water activity, viscosity, free acidity, formol index, reducing sugars, electrical conductivity, hydroxymethylfurfural, diastase activity and the mineral zinc, depending on the different locations where they were produced.

A síntese de filmes inorgânicos mesoporosos por métodos eletroquímicos pode ser viabilizada com o uso de agregados de surfactantes, os quais atuam como moldes durante o processo de eletrodeposição. Neste contexto, são apresentados estudos sobre a obtenção de filmes de óxidos de molibdênio em superfícies de carbono vítreo por meio de deposição eletroquímica de Mo(VI) em meio ácido na presença de surfactantes apropriados. Desta maneira, estudos dos processos catalíticos referentes à redução de ânions oxigenados na superfície modificada na presença de surfactante são mostrados e comparados com os resultados oriundos de filmes depositados em solução sem o surfactante. Um breve estudo comparativo variando a concentração de Mo(VI) e o pH da solução geradora foi executado com a finalidade de verificar o efeito destes parâmetros sobre as características eletrocatalíticas do filme. Em duas condições experimentais especiais foram obtidos filmes de óxidos de molibdênio com cores distintas (azul escuro e amarelo). Experimentos espectroscópicos demonstram que a diferença na cor se deve à presença de espécies de Mo em diferentes estados de oxidação. Em virtude da existência de diferentes espécies de Mo(VI) em função da concentração do íon metálico e do pH e que, em conseqüência deste fato, filmes com características eletrocatalíticas distintas frente à redução catódica do iodato são produzidos, desenvolveu-se um método empregando microeletrodos para a quantificação de H+ em soluções concentradas de surfactante. A metodologia se baseia na prévia determinação do coeficiente de difusão do próton e medição da corrente limite em experimentos voltamétricos no meio contendo o surfactante. Neste trabalho também são mostrados estudos voltamétricos em soluções micelares de CTAB com o uso de sondas eletroativas com alta afinidade pelo interior micelar. Com a análise dos dados obtidos foi possível avaliar o coeficiente de difusão micelar (1.7 x 10-6 cm2/s) e o raio hidrodinâmico (13 Å) destes agregados em solução de KCI 0,05M. Estudos sobre a influência da concentração de surfactante e da natureza e concentração de eletrólito suporte no coeficiente de difusão dos agregados micelares foram realizados e constatou-se que existe mudança na estrutura das micelas em soluções contendo KCI em concentrações superiores a 0,20 M. / In this work some studies involving the electrodeposition of molybdenum oxide thin films from solutions containing Mo(VI) are reported . The influence of the concentration of Mo(VI) and the pH on the characteristics of the obtained film were evaluated by spectroscopic techniques and by analysing the electrocatalytic effect of the modified electrode on the response for the cathodic reduction of iodate ions. Similar experiments were carried out at solutions containing surfactants such as Triton X-100 and Brij 56 as an attempt to generate mesoporous structures. However, no experimental evidence on the formation of such structures were obtained and the good response of the modified electrode prepared in surfactant medium was attributed to the formation of thin films which posses better performance towards the electrocatalytic reduction of iodate. Results were compared with those obtained f rom working solutions in the absence of surfactants. A methodology for acidity determination in solutions containing high concentrations of Triton X-100 was also developed. The procedure was based on the previous determination of the H+ diffusion coefficient in mixtures containing surfactant + water by using voltammetry with a platinum microelectrode. The results showed the influence of solution viscosity in the value of the diffusion coefficient of H+. Some results on the use of microelectrodes to measure the diffusion coefficient of ferrocene supported CTAB micelles were also performed. By using a classical theory that predicts the interaction between micelles as a function of the surfactant concentration, the diffusion coefficient of CTAB micelles at conditions of non-interaction (Dº) and the hydrodynamic radius (Rº) of the CTAB micelle at this experimental condition were found to be 1.7 x 10-6 cm2/s and 13 Å, respectively, at 0.05 M KCI solutions. The effect of different anions (bromide, chloride and fluoride) on the micellar diffusion coefficient was investigated and changes in the structure of spherical CTAB micelles at higher ionic strength values were postulated based on analysis of micellar interaction coefficient vs. CTAB concentration plots.