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Exploiting excited-state aromaticity for the design of efficient molecular motors : A quantum chemical studyEngberg, André January 2019 (has links)
In this work, a study of a recent approach in the design of light-driven molecular motors is presented. The approach involves enabling part of the motor to obtain aromatic-like properties through photoexcitation, and is found to significantly facilitate the rotary motion by reducing the barriers normally present in the excited-state potential energy surfaces of rotary motors.
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DetecÃÃo EletroanalÃtica e Estudo do Mecanismo de OxidaÃÃo do Pesticida Dimetomorfe / Electroanalytical Detection and Oxidation Mechanism Study of Dimethomorph Pesticide.Francisco Willian de Souza Lucas 17 July 2012 (has links)
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O Dimetomorfe (DIM) pertence à classe dos fungicidas morfolÃnicos, tem aÃÃo sistÃmica, à persistente nas matrizes alimentÃcias e em solos de plantio onde foi aplicado e à um possÃvel interferente endÃcrino, o que justifica o desenvolvimento de metodologias para detecÃÃo e quantificaÃÃo desse composto. No estudo eletroquÃmico pode-se observar que DIM apresentou processo eletroquÃmico controlado por difusÃo e caracterizado como quasi-reversÃvel, com potencial de eletrodo em torno de 1,28 V vs. eletrodo de Ag/AgCl/Cl-(KCl sat.), referente à transferÃncia de dois elÃtrons. No desenvolvimento da metodologia eletroanalÃtica utilizando voltametria de onda quadrada e o eletrodo de diamante dopado com boro, constatou-se que as melhores condiÃÃes experimentais e voltamÃtricas foram obtidas em tampÃo Britton-Robinson pH 3, como eletrÃlito de suporte, frequÃncia de aplicaÃÃo dos pulsos de potencial de 30 s-1, amplitude dos pulsos de potencial de 50 mV e incremento de potencial de 2 mV. Partindo dessas condiÃÃes foi possÃvel desenvolver uma metodologia analÃtica com faixa linear de 4,57x10-6 a 3,78x10-4 mol L-1, limite de detecÃÃo de 3,11x10-7 mol L-1, limite de quantificaÃÃo de 1,04x10-6 mol L-1, repetibilidade de 0,13% (n = 10) e reprodutibilidade de 0,92% (n = 5). A avaliaÃÃo da interferÃncia das espÃcies iÃnicas presentes no eletrÃlito de suporte e do Mancozebe (MZB), presente em coformulaÃÃes de DIM, na exatidÃo e na precisÃo da metodologia mostrou que essas espÃcies exercem pouca influÃncia. A recuperaÃÃo em eletrÃlito foi de 97,25  0,70 %, com confianÃa de 95%, e BIAS de 2,74 %. O percentual de interferÃncia do MZB, em diferentes concentraÃÃes, foi menor que |10%|. A aplicaÃÃo da metodologia proposta na determinaÃÃo do DIM em uva in natura e em vinho tinto apresentou percentual de recuperaÃÃo de 101,0  12,1% e 105,1  10,8% com confianÃa de 95%, respectivamente, e BIAS menor que 6%. Baseando-se nas informaÃÃes quÃmico-computacionais, pode-se inferir que o sÃtio de oxidaÃÃo do DIM à na dupla ligaÃÃo nÃo aromÃtica. Os dados obtidos por cromatografia gasosa acoplada a um espectrÃmetro de massa levaram à conclusÃo que a natureza do substrato eletrÃdico nÃo interfere no mecanismo global da reaÃÃo de eletrooxidaÃÃo do DIM, sendo formado o (4-clorofenil)-(3,4-dimetoxifenil)metanona como produto majoritÃrio. / Dimethomorph (DIM) belongs to the class of morpholinic fungicides, it has systemic action, it is persistent in food matrices and in planting soils where was applied and a possible endocrine interferent, justifying the development of methodologies for detection and quantification of this compound. In the electrochemical study can be seen that the DIM had electrochemical process diffusion-controlled and characterized as quasi-reversible, with electrode potential of approximately 1.28 V vs. Ag/AgCl/Cl-(KCl sat.) electrode and involving two electrons transfer. In the development of electroanalytical methods using the square-wave voltammetry and the boron-doped diamond electrode, it was found that the best experimental and voltammetric conditions were obtained in Britton-Robinson buffer pH 3, as supporting electrolyte, pulse potential frequency of 30 s-1, square-wave amplitude of 50 mV and potential step increment of 2 mV. From these conditions it was possible to develop an analytical method with a linear range from 4.57x10-6 to 3.78x10-4 mol L-1, detection limit of 3.11x10-7 mol L-1, quantification limit of 1.04x10-6 mol L-1, 0.13% of repeatability (n = 10) and 0.92% of reproducibility (n = 5). The evaluation of the interference of the ionic compounds present in the supporting electrolyte and the Mancozebe (MZB), present in DIM co-formulations, in the accuracy and precision of the methodology showed that these species have little influence. The recovery in electrolyte was of 97.25  0.70%, with 95% confidence, and BIAS of 2.74%. The percentage of MZB interference, in different concentrations, was less than |10%|. The application of the proposed methodology for determining of the DIM in fresh grapes and red wine showed a percent recovery equal to 101.0  12.1% and 105.1  10.8% with 95% confidence, respectively, and BIAS less than 6 %. Based on the quantum-chemicals information, we can infer that the site of oxidation of DIM is the non-aromatic double bond. The data obtained by gas chromatography-mass spectrometry led to the conclusion that the electrodic substrate nature does not interfere in the overall mechanism of the DIM electrooxidation reaction, in which is formed the (4-chlorophenyl)-(3,4-dimethoxyphenyl)methanone as major product.
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