Les zéolites, aluminosilicates cristallisés microporeux, sont largement utilisés en raffinage, en pétrochimie et en conversion de la biomasse. En raison du faible diamètre des micropores, limitations diffusionnelles et effets de confinement peuvent favoriser la formation de sous-Produits non désirés. L'introduction de mésopores par désalumination et/ou désilication ("zéolites hiérarchisées") peut diminuer ces phénomènes. Cependant, les mécanismes ces réactions restent méconnus à l'échelle moléculaire. Par calculs quantiques périodiques, au niveau de la théorie de la fonctionnelle de la densité (DFT) et selon une approche hybride QM/QM, nous avons pu mettre en évidence l'importance de l'attaque de la molécule d'eau sur l'atome d'aluminium, qui se fait en anti par rapport au site acide de Brønsted. Des structures d'Al penta ou tetra coordinées ont aussi été suggérées expérimentalement comme précurseurs de la désalumination. Malgré une forte hétérogénéité structurale des sites T, l'élucidation des chemins réactionnels et les énergies d’activation des étapes d’hydrolyse des liaisons Al-O (70-100 kJ/mol) dans les systèmes zéolitiques investigués (MOR, FAU, MFI, CHA) nous a permis d'établir des corrélations du type Brønsted-Evans-Polanyi. Ces corrélations permettent d'estimer et prédire des énergies d'activation par le biais de la thermodynamique, donne ainsi une prédiction aisée des sites T sensibles à la désalumination. Un autre facteur clé pour la compréhension de la désalumination est l'effet de confinement sur l'espèce aluminique extra-Réseau générée (EFAL), exercé par les cavités. Finalement nous avons pu montrer que le chemin réactionnel de désalumination et désilication, consécutif ou simultané, , est thermodynamiquement plus favorable qu'une simple désalumination ce qui est en accord avec les propositions mécanistiques de la littérature sur la genèse de mésopores par démétallation. / Zeolites are crystalline microporous aluminosilicates widely used in refining, petrochemistry and biomass conversion. However, diffusion limitation and confinement effect can promote the formation of undesired products. The introduction of mesopores by dealumination and/or desilication ("hierarchical zeolites") is a possible solution widely used experimentally. Nevertheless, the mechanisms of these demetallation reactions are poorly described at the molecular scale. We determine the mechanisms of the formation of extraframework Al species (EFAL) for zeotypes MOR, FAU, MFI and CHA occurring during the dealumination process, possibly associated with desilication. First-Principles periodic density functional theory (DFT) and hybrid QM/QM calculations have been employed in order to analyze full reaction paths leading to extraframework species and to quantify the activation energies of the determining steps. It has been demonstrated that the initiation of an Al-O(H) bond break takes place via water adsorption on the Al atom in anti-Position to the Brønsted acid site, via a penta- or tetra-Coordinated Al species. Such species are shown to be at the initiation of the Al dislodgement from the zeolitic framework. Despite a strong structural heterogeneity of T sites, we determined Brønsted-Evans-Polanyi (BEP) relationships for the entire dealumination pathway. Moreover, it is shown that not only the initiation and propagation mechanisms are primordial for the understanding of an Al extraction, but also the confinement effect on EFAL species within the zeolites cavities. Finally, from the energy profile of combined dealumination/desilication pathways, we show that it is thermodynamically favoured to extract extraframework Si species (EFSI) in the course of dealumination.

Human tissue transglutaminase (TG2) is a calcium-dependent multifunctional enzyme that natively catalyzes the post-translational modification of proteins, namely by the formation of isopeptide bonds between protein- or peptide-bound glutamine and lysine residues. This ubiquitously expressed enzyme plays important roles in cellular differentiation, extracellular matrix stabilization, and apoptosis, to name a few. However, its unregulated activity has been associated with many pathologies such as fibrosis, cancer, neurodegenerative disorders and celiac disease. Most of these disorders are associated with unregulated acyl-transferase activity. As such, the Keillor group has directed its efforts towards the development of TG2 inhibitors. Over the years, the Keillor group has synthesized large libraries of targeted covalent inhibitors against TG2. These compounds have undergone pharmacodynamic testing in order to examine their kinetic parameters of inhibition. Having gained knowledge of their enzyme kinetics, the logical next step was to consider their pharmacokinetic profiles. In the context of this thesis, we considered two important pharmacokinetic properties: membrane permeability and off-target reactivity. Firstly, we aimed to evaluate our inhibitors for their ability to permeate the cell membrane. In efforts to do so, we were able to adapt, optimize, and validate a parallel artificial membrane permeability assay (PAMPA) utilizing hexadecane as our artificial membrane. We were able to test a few of our own inhibitors and found that compounds NC9, VA4 and AA9 possess Log Pe values of -5.26 ± 0.01, -4.66 ± 0.04 and -6.5 ± 0.5 respectively. Secondly, we sought to investigate the susceptibility of our inhibitors to glutathione addition reactions under physiological conditions. We adapted and optimized a colorimetric assay using Ellman’s reagent (DTNB) and found that our inhibitors are minimally reactive with glutathione. The methods developed over the course of this work provide protocols that can be adopted for the characterization of future inhibitors in the Keillor group, along the process of developing TG2 inhibitors into drug candidates.

[pt] O presente trabalho apresenta a comparação da reatividade ao CO2 de Carvões Minerais, de Biomassas e Coques. Os ensaios realizados foram feitos empregando pastilhas de forma cilíndrica, tanto para materiais sem desvolatilização e desvolatilizados e sob uma temperatura de 1100 graus Celsius. É apresentado um breve histórico das matérias primas carbonosas e seus comportamentos com respeito à reatividade. Os experimentos de reatividade foram realizados em Forno elétrico tubular e em Termobalança, enquanto que as análises da porosidade foram realizadas no MEV. Os resultados mostraram que o material carbonoso que apresentou menor reatividade foi o Coque Verde de Petróleo (CVP), 65,89 por cento e 46,77 por cento, para amostras sem desvolatilização e desvolatilizadas, respectivamente. Por outro lado o Carvão Vegetal apresentou a maior reatividade, 98,05 por cento e 95,96 por cento, também para amostras sem desvolatilização e desvolatilizadas, respectivamente. No caso da nova biomassa empregada, o Carvão de Capim Elefante, a reatividade foi superior ao CVP, similar ao Coque Metalúrgico, mas muito distante do Carvão Vegetal. Com relação à porosidade, os materiais depois de reagirem com o CO2, tornaram-se mais porosos que as amostras virgens. Observou-se também em aumentos de 1800x, alguns materiais apresentaram a tendência de se aglomera formando pequenas esferas sobre a superfície das partículas. Na análise TGA, mediu-se para o Carvão Vegetal, a maior perda de peso em presença do CO2 (maior reatividade) e ainda, que Coque Verde de Petróleo sofreu a menor perda de peso (menor reatividade). O modelo cinético empregado, modelo de reação contínua, teve boa correlação, perto de 99 por cento, para os diferentes tipos de materiais. As energias de ativação aparente das biomassas foram menores que as determinadas para os carvões e coques. / [en] This work presents comparisons between the reactivity with CO2, measured at 1100 Celsius degrees, for Coals, Biomass and Cokes, shaped as cylindrical pellets, tested without volatilization and devolatilized. A brief historical review is presented for these carbonaceous materials together with their reactivity behavior. The experimental runs for the materials were made in a Tubular Furnace, Thermogravimetric Balance and the characterizations, as porosity, using a SEM, following the experimental procedure and parameters suggested in the bibliography. The obtained results showed that the carbonaceous material with the lowest reactivity was the Green Petroleum Coke, 65.89 per cent and 46.77 per cent , for samples without devolatilization and devolatilizated, respectively. The Charcoal, on the other hand rated 98.05 per cent and 95.96 per cent, also for samples without devolatilization and devolatilizated, respectively. In the case of new biomass used, Elephant Grass, its reactivity was superior to that of the Green Petroleum Coke, similar to the Metallurgical Coke but far greater than the Charcoal. As for the porosity, the devolatilized materials, after the reaction with CO2 became more porous than the virgin material, presenting also residues that tended to clump together forming small beads on the material’s surface, these were observed with increases at 1800x. The analyses TGA confirmed that Charcoal, submitted to CO2, lost more weight than the other tested carbonaceous materials and the GPC lost the least. The kinetic model, continuous reaction, showed good correlation, about 99 per cent , for every material. The apparent activation energies for the biomasses showed lower values than for the coals and cokes.

Many devastating problems face South Africa’s young children that can hamper their emotional and social development. The Emotional Literacy and Persona Doll programme (Buchanan, 2007) attempts to intervene in the young child’s emotional development. Persona Dolls are used to encourage emotional expression and management in young children. Previous research has indicated the positive effects of the Persona Dolls and Emotional Literacy programmes with children. However, the development in the trainees and practitioners who use these dolls has yet to be researched. This research study assessed the development of empathy, and the personal experiences of trainees who underwent the emotional literacy and Persona Doll training programme in South Africa. Participants included social workers, psychologists, and preschool and foundation phase teachers. Participants’ empathy was assessed before the first training session, and at the end of the training through Davis Interpersonal Reactivity Index (1980). Participants also documented their feelings, experiences, and thoughts while undergoing the training, in a journal. Process notes of persona doll sessions and evaluation forms were also used in the study. Although the quantitative results did not show any significant results in terms of an improvement in empathy for the trainees, the qualitative results demonstrated that the participants found that they were more able to think and talk about their own emotions, and the emotions of others. This is a crucial aspect of emotional literacy, where one is able to identify and think about one’s own emotions. Furthermore, the group of participants learnt important reflection and containment skills, which they believe they can and are using in their work with others, and with their families. While there is no statistically grounded argument for the improvement of empathy, and in extension emotional literacy, the participants in the training seemed to have developed their own emotional literacy skills, and found that they are better able to work with children and adults in the realm of emotional work. Implications and suggestions for further research are discussed.

School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa 26 February 2016 / Many reports in the open literature have focused on Fischer-Tropsch (FT) kinetics, yet none of them appear to be able to explain FTS completely. Few of the FT models consider the production of olefins and paraffins separately. To study whether the selectivity to olefins and paraffins follows similar trends and if kinetics alone suffices to explain FT phenomena, a series of FT experiments were conducted in a fixed bed reactor loaded with 10% Co/TiO2. FT feeds were periodically switched from syngas to syngas + N2 by adjusting the total reactor pressure so that the reactant partial pressures (PCO and PH2) remained constant. During the initial deactivation (the first 1200 hours), it was found that the formation rates of olefins remained fairly constant (in some cases they increased) while those of paraffins decreased. This indicates the deactivation is mainly caused by the decrease in the paraffin formation rate. Currently, none of the published kinetic models can explain the phenomenon that the decay of the reaction rates of olefins and paraffins were not the same during the deactivation. At steady state (1055 to 2700 hours, overall reaction rate fairly constant), adding extra N2 decreased the selectivity to the light hydrocarbons. These results suggest that by feeding the extra N2 there could be an increase in selectivity and formation rates to long chain hydrocarbons (C5+). Plotting molar ratios of paraffin to olefin (P/O) with carbon number n+1 versus the ratio with carbon number n revealed linear relationships which are independent of feed gases, catalyst activity and reaction temperature. These results imply that product distributions might be determined by some sort of equilibrium. Another plot of normalised mole fractions of CnH2n, Cn+1H2n+2, and CnH2n+2 in ternary diagrams showed that after disturbances these product distributions tended to stable points. It is suggested that this could be due to slow changes in the liquid composition after the disturbances. Although not all the results are explained, the researcher emphasises that normal kinetics alone cannot explain these results completely. There might be factors, iii including vapour-liquid equilibrium or reactive distillation, which are worthy of consideration to explain FTS. / MT2016

L’oxyde de zirconium est un matériau prometteur pour le stockage des actinides en formation géologique profonde. Pour la sureté de stockage, la stabilité de ces matrices dans les milieux géologiques doit être examinée. Une connaissance approfondie de la solubilité des phases solides de confinement des déchets radioactifs s’avère donc nécessaire. La solubilité de ZrO2 est très faible aux pH neutres (<10-8M), et augmente aux pH acides et alcalins. Cependant, les valeurs de solubilités publiées varient de plus de 6 ordres de grandeurs. L’objectif de ces travaux de thèse est de comprendre les processus ayant lieu, à l’équilibre, à l’interface ZrO2/solution et d’étudier la réactivité de surface de ce matériau en contact avec des solutions aqueuses. La solubilité de ZrO2 monoclinique et cubique a été explorée en approchant l’équilibre depuis les conditions de sous-saturation. Un protocole expérimental robuste a été développé permettant de mesurer, au plus précis possible, les très faibles concentrations de zirconium en solution (limite de quantification [Zr] ~10-11M). Les phases solides ont été caractérisées par BET, XRD, SAXS,HR-TEM and STEM-HAADF avant et après l’atteinte de l’équilibre afin d’étudier la réactivité de surface des matériaux mis en contact avec les solutions aqueuses. En vue de comprendre les mécanismes se déroulant à l’interface aussi bien que la faible solubilité dans les milieux aqueux, l’hydrolyse des liaisons Zr-O-Zr par les molécules d’eau a été étudiée par la méthode DFT en utilisant le code VASP. Cette étude nous a permis de proposer un mécanisme de dissolution dont l’étape limitante, aux pH neutres, est la difficulté de former un complexe activé à l’interface ZrO2/solution. / Zirconium dioxide is a promising ceramic for the specific immobilization of actinides in a geological disposal vault. An appropriate knowledge of the solubility controlling solid phases confining radioactive waste is necessary if one wants to assess the stability of ZrO2 in a disposal environmental conditions. The solubility of zirconium oxide is very low at neutral pH (<10-8M), but increases at highly acidic and alkaline pH. Solubility values may differ by more than 6 orders of magnitude at a given pH, indicating high uncertainties. The objective of this work is to understand processes governing the equilibrium between zirconium oxide and water, and to study the surface reactivity of the material in contact with aqueous solutions. The solubility of monoclinic and of cubic ZrO2 in aqueous solutions were investigated, approaching equilibrium from under-saturated conditions.The low solubility of zirconia makes its measurement a challenging task. A reliable experimental procedure was developed to measure low concentrations of zirconium (limit of quantitation[Zr] ~10-11M). In order to examine the surface reactivity, solid phases were further characterized by BET, XRD, SAXS, HR-TEM and STEM-HAADFbefore and after reaching equilibrium. In order to understand the reaction mechanism taking place at the zirconia/water interface as well as the low solubility in aqueous phase, hydrolysis of Zr-O-Zr bonds by a single and multiple water molecule were studied using the periodic DFT code, with Vienna ab initio simulation package (VASP). This study led to the proposal of a dissolution mechanism whose limiting step, in the neutral pH range, is the difficulty of formation of an activated complex.

Neste estudo, investigaram-se mudanças nas propriedades coloidais de uma esmectita pilarizada com polihidroxicátion de alumínio. A solução pilarizante foi preparada mediante gotejamento de solução NaOH 0,4 mol L-1 em solução de AlCl3.6H2O 0,2 mol L-1, a qual foi adicionada à suspensão de argila de 1% m/m. Para avaliar mudanças nas propriedades das argilas, recorreu-se às técnicas de titulação potenciométrica descontínua, análise química total, DRX, FTIR, CTC e isotermas de adsorção/dessorção de N2. Além disso, foram realizados ensaios de adsorção de Cu2+ para avaliar a capacidade de remoção do metal de soluções aquosas pelas argilas pilarizadas e gerar informações relacionadas à interação entre adsorvente e adsorbato. Naturalmente, a argila apresentou espaçamento basal de 1,26 nm, ao passo que as pilarizadas apresentaram valores de 1,78 nm (500 oC) e 1,80 nm (350 oC). Dados da análise química total mostraram se tratar de uma montmorillonita com altos teores de Fe3+, e confirmou o aumento nos teores de Al3+ na estrutura da argila após pilarização. Os valores de área superficial específica e volume de microporos foram maiores para as argilas pilarizadas, enquanto que a CTC foi maior para a argila natural. A titulação potenciométrica mostrou modificação nas curvas de titulação com o processo de pilarização, em que nas argilas pilarizadas surgiram novos sítios de reação. Dentre as equações de adsorção aplicadas, Langmuir, Freundlich e Temkin, a primeira apresentou valores de r2 das equações linearizadas maior para todas as argilas e menor desvio médio (?g%) para argila natural, ao passo que a equação de Temkin mostrou valores de ?g(%) menores para as argilas pilarizadas. Parâmetros termodinâmicos confirmaram que a reação de adsorção de Cu2+ é espontânea para todas as argilas, principalmente para as argilas pilarizadas. Além disso, cálculos baseados em equações de Dubinin-Radushkevich evidenciam que a ligação é fraca entre metal e argila, caracterizando reações de fisissorção. / In this study, an Al-pillared smectite was synthesized and changes in its colloidal properties were investigated. The pillaring solution was prepared adding dropwise adequate volume of NaOH 0,4M to AlCl3.6H2O 0,2M solution. Then, the pillaring solution was added to a 1% w/w clay slurry with constant stirring. Potentiometric titration, chemical analysis, XRD, FTIR, CEC and N2 sorption/dessoption isotherms analysis were done to characterize the changes in clay properties. Moreover, adsorption experiments were carried out in order to evaluate the capacity of the pillared clays to remove Cu2+ from aqueous solution and to characterize the interaction between adsorbent and adsorbate. The natural clay has a basal spacing of 1.26 nm whereas the pillared clays reached 1.78 nm (500 oC) and 1.80 nm (350 oC) after calcination. Chemical analysis revealed that the montmorillonite used has high content of Fe3+ and the increase in the Al3+ amount in the structure of the pillared clays after pillaring process. The surface area and micropore volume were higher for the pillared clays and the CEC was higher for the natural clay. The pillaring process changed the potentiometric titration curves, wherein the pillared clays exhibited new reactive site. Experimental data were fit to Langmuir, Freundlich and Temkin adsorption equations, being the the first one the best (highest r2 value) for all the clays and lower standard deviation (?g%) for the natural clay. On the other hand, Temkin equation exhibited ?g% value lower for the pillared clays. Thermodynamics parameters demonstrate that the Cu2+ adsorption process is spontaneous for all the clays, but with higher values for the pillared materials. In addition, application of the Dubinin-Radushkevich equation revealed that the bond between the metal and the clay are weak, characterizing a physisorption.

Avaliou-se a participação do óxido nítrico (NO), do fator hiperpolarizante derivado do endotélio (EDHF), dos produtos da ciclooxigenase (COX), das espécies reativas de oxigênio (EROs) e o efeito do tratamento com metformina (Met) nas alterações vasculares em ratos com obesidade induzida por glutamato monossódico (MSG). O tratamento com Met corrigiu alterações metabólicas em ratos MSG, reduzindo o acúmulo de gordura visceral, corrigindo a resistência à insulina, a hiperinsulinemia e a dislipidemia. Ratos MSG apresentaram aumentada resposta contrátil e diminuída sensibilidade à Ach, associadas a alterações na via do NO, do EDHF, dos produtos da COX e das EROs. Ratos MSG com 16 semamas apresentaram hiperresponsividade ao nitroprussiato de sódio, que foi mantida nos ratos tratados com Met. A Met corrige as alterações da resposta vascular atuando sobre o NO e o EDHF, reduzindo a geração de EROs e interferindo na resposta do músculo liso vascular, mantendo a hiperresponsividade ao NO. / The role of the nitric oxide (NO), the endothelium derived hyperpolarizing factor (EDHF), the ciclooxygenase (COX) products and the reactive oxygen species (ROS), as well as the effect of metformin (Met) treatment on the vascular alterations in rat model of obesity induced by monosodium glutamate (MSG) were evaluated. Met treatment corrected metabolic alterations in MSG, reducing fat accumulation, correcting dyslipidemia, insulin resistance and hyperinsulinemia. MSG rats had an increased response to norepinephrine and decreased sensitivity to acetilcholine, which were associated with alterations in NO, COX products and ROS. Sixteen-week-old MSG rats presented hyperresponsiveness to sodium nitroprusside, which was preserved in Met-treated group. Met corrects the alterations of the vascular reactivity acting on NO and EDHF, and decreasing the ROS generation, besides its effect on the vascular smooth muscle response, preserving the hyperresponsiveness to NO.

Neste trabalho foram realizadas sínteses do nitrosilo complexo trinuclear de rutênio de fórmula [Ru3O(CH3COO)6(NO)(py)2]PF6 (py = piridina) seguindo duas rotas sintéticas diferentes (convencional (a) e uma nova (b) ) a fim de verificar e comparar a eficiência de ambas. Além disso, foi feito o mapeamento da rota sintética convencional para analisar a melhor forma de conduzi-la em cada etapa para que a síntese fosse bem sucedida. Com isso, foi possível afirmar na rota (a) que é preciso purificar dois precursores: o precursor 1 [Ru3O(CH3COO)6(S)3]+ e 3 [Ru3O(CH3COO)6(CO)(L)2], não sendo necessário a purificação do produto final. As modificações vistas necessárias para a otimização da síntese (a) foram a utilização de uma solução recém preparada de bromo e a substituição do metanol seco no frasco lavador por diclorometano seco. Não se descarta a possibilidade da nova rota sintética (b), somada às modificações apontadas neste trabalho, apresentar bons resultados. As caracterizações foram feitas utilizando técnicas de espectroscopia na região UV-visível, infravermelho e RMN. Os estudos de reatividade mostraram que, para ambos os complexos analisados ([RuIII,III,III3O(CH3COO)6(NO)(py)2]PF6 e [RuIII,III,III3O(CH3COO)6(4-acpy)2(NO)]PF6), sugere-se a formação da espécie [RuIII,III,II3O(CH3COO)6(NO2-)(L)2]- onde L = 4-acpy ou py - sendo esta reação dependente da concentração de íons hidroxila do meio. Estudos da reatividade e redução do [Ru3O(CH3COO)6(NO)(py)2]PF6 com o redutor de interesse biológico ácido ascórbico na presença de íons OH-, permitiram sugerir uma hipótese para o mecanismo de liberação de NO0 com estímulo redox, na ausência de luz. Propõe-se que primeiramente o ligante NO0 coordenado sofra um ataque nucleofílico dos íons hidroxila presentes no meio, concomitante a uma transferência eletrônica intra-molecular que gera a espécie [RuIII,III,II3O(CH3COO)6(NO2-)(py)2]-. Este último é reduzido pelo ácido ascórbico, restaurando o ligante NO0 que, agora coordenado à unidade metálica reduzida [RuIII,III,II3O], finalmente é labilizado, gerando o complexo [Ru3O(CH3COO)6(S)(py)2]0 / In this work, the synthesis of the trinuclear ruthenium complex [Ru3O(CH3COO)6(NO)(py)2]PF6 (py = pyridine) was performed following two different synthetic routes (conventional (a) and a new one (b)) in order to verify and to compare the efficiency of both. In addition, the mapping of the conventional synthetic route was done to analyze the best way to conduct it at each step for the synthesis to be successful. It was possible to state in route (a) that two precursors must be purified: precursor 1 [Ru3O(CH3COO)6(S)3]+ and 3 [Ru3O(CH3COO)6(CO)(L)2], no purification of the final product being necessary. The modifications required for the optimization of synthesis (a) were the use of a freshly prepared solution of bromine and the substitution of the dry methanol in the washing flask by dry dichloromethane. We can not rule out the possibility of the new synthetic route (b), added to the modifications pointed out in this work, to present good results. The characterizations were made using UV-visible, infrared and NMR spectroscopy techniques. Reactivity studies for both complexes analyzed ([RuIII,III,III3O(CH3COO)6(NO)(py)2]PF6 and [RuIII,III,III3O(CH3COO)6(4-acpy)NO)]PF6), suggested the formation of the species [RuIII,III,II3O(CH3COO)6(NO2-)(L)2]- - where L = 4-acpy or py - this reaction being dependent on the concentration of hydroxyl ions in the medium. Studies of the reactivity and reduction of compound [Ru3O(CH3COO)6(NO)(py)2]PF6 with the biological reductant ascorbic acid, in the presence of OH- ions, allowed to suggest a hypothesis for the NO0 release mechanism with redox stimulus, in the absence of light. It is proposed that the coordinated NO0 ligand undergoes a nucleophilic attack of the hydroxyl ions present in the medium, concomitant to an intra-molecular electron transfer that generates the species [RuIII,III,II3O(CH3COO)6(NO2-)(py)2]-. The latter is reduced by ascorbic acid, restoring the ligand NO0 which, now coordinated to the reduced metal unit [RuIII,III,II3O], is finally labilized, generating the complex [Ru3O(CH3COO)6(S)(py)2]0

O sistema quimiluminescente peróxi-oxalato vem sendo estudado por diversos grupos de pesquisa ao redor do mundo desde os anos 60. Esse interesse em especial se deve ao fato de que em comparação com a maioria dos sistemas quimiluminescentes, que apresentam rendimentos quânticos da ordem de 1%, esse sistema apresenta rendimentos quânticos de emissão consideravelmente maiores, cerca de 30%. O sistema peróxi-oxalato consiste na reação de ésteres fenólicos substituídos derivados do ácido oxálico com peróxido de hidrogênio, catalisada por uma base e em presença de compostos aromáticos policondensados fluorescentes com baixo potencial de oxidação, chamados de ativadores (ACT). O mecanismo desta reação, apesar de intensamente estudado, ainda não se encontra completamente esclarecido. Especificamente, a estrutura do intermediário formado durante a reação, que é responsável pela quimiexcitação do ativador, não é conhecida ainda. No presente trabalho, foram completados estudos previamente efetuados no nosso grupo com derivados perácidos, intermediários na reação peróxi-oxalato. Foram sintetizados e caracterizados dois novos derivados perácido, o O,Ohidrogênio monoperóxi-oxalato de 3-clorofenila e o O,O-hidrogênio monoperóxioxalato de 3-nitrofenila. Dos estudos cinéticos da reação destes perácidos com imidazol, na presença de 9,10-difenilantraceno como ativador, foram obtidos constantes de velocidade de ciclização e rendimentos quânticos singlete. As constantes de velocidade determinadas, junto com os dados obtidos anteriormente no grupo, mostram correlação linear de energia livre com as constantes de substituintes de Hammett, obtendo-se um valor de = 2,18 ± 0,16, o que indica a formação de alta densidade de carga negativa no estado de transição do passo lento. A correlação linear entre as constantes de velocidade e os valores de pKa dos grupos de partida fenólicos levou à determinação do valor de &#946;GP = -1,07 ± 0,08, indicando que a quebra da ligação para o grupo de partida é muito avançada no estado de transição no passo lento da reação. Os rendimentos quânticos singlete mostram dependência com as propriedades eletrônicas dos substituintes, aumentando inicialmente com o aumento das propriedades de atração de elétron do substituinte, porém, com substituintes mais atraentes que hidrogênio, observa-se uma leve diminuição no rendimento quântico. O conjunto de dados apresentados neste trabalho, junto com os resultados obtidos anteriormente pelo grupo, demonstra claramente que a reação de ciclização dos perácidos, catalisada por imidazol, deve ocorrer de maneira concertada, ou seja, a saída do grupo de partida fenólico ocorre em conjunto com o ataque nucleofílico do íon percarboxilato à função éster no passo lento da reação. Conseqüentemente, foram obtidas neste trabalho evidências experimentais fundamentadas para a ocorrência da 1,2- dioxetanodiona como intermediário de alta energia na reação peróxi-oxalato. / The peroxyoxalate chemiluminescence has been intensely studied since the sixties by several research groups all around the world. This interest is mainly due to the fact that the peroxyoxalate system is highly efficient, showing quantum yields of around 30 %, much higher than other well known chemiluminescence reactions which commonly show quantum yields of around 1% or less. The peroxyoxalate system consists in the base catalyzed reaction of activated oxalate esters with hydrogen peroxide in the presence of highly fluorescent polycondensed aromatic hydrocarbons with low oxidation potentials, called activators (ACT). Although intensely investigated, the mechanism of this complex transformation is still not yet completely clarified. This is true specifically for the structure of the high-energy intermediate, formed during the reaction sequence, which is responsible for chemiexcitation, not known at all up to now. In the present work, former studies of our group on peracid derivatives, intermediates in the peroxyoxalate reaction, were completed. Two new peracid derivatives, 3-chlorophenyl O,O-hydrogen monoperoxyoxalate and 3- nitrophenyl O,O-hydrogen monoperoxyoxalate were synthesized and characterized. Kinetic studies on the reaction of these peracid derivatives with imidazole, in the presence of 9,10-diphenylanthracene as activator, led to the determination of cyclization rate constants and singlet quantum yields. These rate constants, together with data formerly obtained by our group, show linear free-energy correlation with the Hammett substituent constants, resulting in a reaction constant of = 2,18 ± 0,16, that indicates the formation of a high negative charge density in the transition state of the rate-limiting step. Similarly, the linear correlation of the rate constants with the pKa values of the phenolic leaving groups leads to the determination of a value &#946;GP = -1,07 ± 0,08, indicating a high degree of leaving group bond cleavage in the transition state of the rate-limiting step. The singlet quantum yields also show dependence on the electronic properties of the substituents, initially increasing with the increase in the electron withdrawing nature of the substituent, however, a slight decrease in the quantum yields is observed with substituents more electron withdrawing than hydrogen. The data accumulated in this work, together with results earlier obtained in our group, clearly demonstrate that the cyclization reaction of the peracid derivatives, catalyzed by imidazole, proceeds in a concerted manner, i.e. the phenolic leaving group departure occurs together with the nucleophilic percarboxylate attach to the ester function in the rate-limiting reaction step. Consequently, it was possible to obtain in this work solid experimental evidence for the occurrence of 1,2-dioxetandione as the high-energy intermediate in the peroxyoxalate reaction.