Orientador: Nelson Ramos Stradiotto / Banca: Denis Ricardo Martins de Godoi / Banca: Marcelo Firmino de Oliveira / Resumo: A atual expansão do setor de aviação tem aumentado à dependência das companhias aéreas ao querosene de aviação e a outros derivados fósseis. A dependência desse setor para com esses combustíveis se reflete em grandes índices de poluição atmosférica devido à emissão do CO2 proveniente da queima dessas substâncias. Tendo em vista a necessidade de reduzir esse poluente, têm-se desenvolvido novas tecnologias para a produção de querosenes alternativos de aviação (bioquerosenes de aviação). Uma das formas de obtenção do bioquerosene de aviação é a partir da fermentação de açúcares. O biocombustível obtido através dessa rota tecnológica é composto basicamente pelo farnesano e possui como principal contaminante o hexahidrofarnesol. A preocupação com a presença do hexahidrofarnesol no bioquerosene de aviação se deve principalmente a sua solubilidade em água e a degradação dos componentes do sistema de combustível. Diante disso, se fazem necessárias metodologias analíticas simples, sensíveis, seletivas e de baixo custo para determinar esse contaminante no bioquerosene de aviação. Uma vez que essas características são encontradas nos sensores eletroquímicos, o objetivo deste trabalho consiste no desenvolvimento de um sensor eletroquímico baseado em polímero molecularmente impresso para a determinação de hexahidrofarnesol em bioquerosene de aviação. O sensor proposto foi preparado pela eletropolimerização da o-fenilenodiamina sobre um eletrodo de carbono vítreo na presença da molécula de hexahidrofarnesol pela técnica de voltametria cíclica. O eletrodo modificado foi caracterizado por várias técnicas, tais como voltametria cíclica, espectroscopia de impedância eletroquímica, microscopia eletrônica de varredura, espectroscopia RAMAN e microscopia de força atômica. Os parâmetros que influenciam o desempenho do sensor impresso, como a razão... / Abstract: Current expansion of the aviation sector has increased the dependence of airlines to aviation kerosene and other fossil derivatives. Dependence of this sector to such fuels is reflected in high rates of air pollution due to the emission of CO2 originated from burning of these substances. In view of the need for lower emissions these pollutants, new technologies have been developed for the production of alternative aviation kerosene (aviation biokerosene). One of the ways of get the aviation biokerosene is from the fermentation of sugars. The biofuel obtained through this technological route is basically composed of farnesane, and it has as main contaminant the hexahydrofarnesol. The concern with the presence of hexahydrofarnesol in aviation biokerosene is mainly due to its solubility in water and the degradation of fuel system components. Thus, the developments of simple, sensitive, selective and low cost analytical methodologies to determine such contaminant in the aviation biokerosene are necessary. Once these characteristics are found in the electrochemical sensors, the objective of this work consists in the development of an electrochemical sensor based on molecularly imprinted polymer for the determination of hexahydrofarnesol in aviation biokerosene. The proposed sensor was prepared by electropolymerization of the o-phenylenediamine on a glassy carbon electrode in the presence of the hexahydrofarnesol molecule by the cyclic voltammetry technique. The modified electrode was characterized by several techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, RAMAN spectroscopy, and atomic force microscopy. Parameters that influence the performance of the imprinted sensor, such as the molar ratio between the functional monomer and the template molecule, the number of cycles used in the electropolymerization, the pH of the solution used during the... / Mestre

Made available in DSpace on 2014-11-10T11:09:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-06-06Bitstream added on 2014-11-10T11:57:27Z : No. of bitstreams: 1 000790893.pdf: 3580842 bytes, checksum: 8e21b24ec71bb11cfd19592e7dce78a6 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O intuito desta pesquisa foi caracterizar eletrodos quimicamente modificados (EQM) pela formação de monocamadas auto-organizadas (SAM) com os tióis (11- mercaptoundecil)-N’,N’’,N’’’-trimetilamônio e 6-(ferrocenil)hexanotiol sobre a superfície do eletrodo de ouro. E, ainda, verificar seu comportamento de transferência eletrônica com solução de hexacianoferrato(II) e (III) e sua aplicação como biossensor para glicose. As monocamadas auto-organizadas vêm sendo comumente usadas devido ao seu comportamento homogêneo, o que confere ao eletrodo maior sensibilidade e reprodutibilidade, tornando-se possível desenvolver eletrodos para vários fins e aplicações. Neste trabalho, foram estudadas as monocamadas formadas a partir dos tióis (11-mercaptoundecil)-N’,N’’,N’’’- trimetilamônio e 6-(ferrocenil)hexanotiol. A caracterização eletroquímica e morfológica das monocamadas auto-organizadas foi realizada através da voltametria cíclica e microscopia eletrônica de varredura, respectivamente. Foi notado que as monocamadas mistas na proporção (1:2) apresentaram maior efeito catalítico, uma vez que se obtiveram maiores sinais analíticos, através do incremento das correntes anódicas e catódicas. A viabilidade da molécula de hexacianoferrato (III) foi verificada através da troca iônica destas moléculas eletroativas com as monocamadas auto-organizadas. Para a aplicação dos eletrodos modificados com monocamadas como biossensor para glicose, optou-se pela modificação na proporção (1:2) de (11-mercaptoundecil)-N’,N’’,N’’’-trimetilamônio e 6- (ferrocenil)hexanotiol, respectivamente, assim como a utilização do mediador hexacianoferrato pré-concentrado por troca iônica durante 2 horas, em virtude que, neste tempo ocorreu uma maior concentração de espécies eletroativas sobre a superfície do ouro, tendo como favorecido o processo de transferência eletrônica. A construção do biossensor .. / The purpose of this research was to characterize chemically modified electrodes (CME) by the formation of self-assembled monolayers (SAMs) with thiols (11- mercaptoundecyl)-N’,N’’,N’’’trimethylammonium and 6-(ferrocenyl)hexanethiol on the surface of gold electrode. And also verify their behavior of electron transfer in solution with hexacyanoferrate (II) and (III) and its application as a biosensor for glucose. The self-assembled monolayers have been commonly used due to its homogenous, which gives the electrode higher sensitivity and reproducibility, becoming possible to develop electrodes for various purposes and applications. In this research, it was studied the monolayers formed from the thiols (11-mercaptoundecyl)- N’,N’’,N’’’trimethylammonium and 6-(ferrocenyl)hexanethiol. Electrochemical and morphological characterization of self-assembled monolayers were performed using cyclic voltammetry and scanning electron microscopy, respectively. The electrochemical characterization of the different SAMs under study occurred in a solution of 0.10 mol L-1 hexacyanoferrate(II) and (III) potassium, verifying the electronic transfer mechanisms involved. It was noted that the self assembled monolayers in proportion (1:2) showed higher catalytic effect, since obtained higher analytical signals by increasing the anodic and cathodic currents. The viability of the hexacyanoferrate (III) molecule was verified by ion exchange these electroactive molecules with self-assembled monolayers. For the application of electrodes modified with monolayers as a biosensor for glucose, we opted for the change in the ratio (1:2) of (11-mercaptoundecyl)-N’,N’’,N’’’trimethylammonium and 6- (ferrocenyl)hexanethiol, respectively, as well as the use of pre-concentrated by ion exchange mediator hexacyanoferrate for 2 hours, because that, this time there was a greater concentration of electroactive species on the surface of gold having favore / FAPESP: 12/21703-7

Electrochemical methods were researched for the analysis of metals, proteins and the identification of metal binding proteins. Adsorptive cathodic stripping voltamrnetry for metal analysis combines the inherent sensitivity of electrochemical techniques with the specificity of ligands for the nonfaradaic preconcentration of analytes at the electrode. The utility of catechol, resorcinol, 4-methylcatechol and 4-t-butylcatechol as ligands was explored for the sensitive analysis of copper, bismuth, cadmium and lead on a mercury film glassy carbon electrode. Metal complexes of lead, copper and bismuth with resorcinol showed the largest increase in current with increase in metal concentration, whereas complexes of these metals with 4-t-butylcatechol showed the lowest current response. Cadmium showed the highest current responses with 4-methylcatechol. The four metals could be determined simultaneously in the presence of resorcinol, although considerable interference was observed between bismuth and copper. The electroanalysis of cysteine and cysteine containing proteins at carbon electrodes are impaired by slow electron transfer rates at carbon electrodes, exhibiting high overpotentials, greater than 1 V vs Ag! Agel. Metallophthalocyanines have been shown to promote the electrocatalysis of cysteine at lowered potentials. Chemical modification of electrodes with appropriate modifiers is a means of incorporating specificity into electroanalysis, with applications in electrocatalysis. A glassy carbon electrode was modified by electrodeposition of cobalt (II) tetrasulphophthalocyanine [Co(II)TSPct to produce a chemically modified glassy carbon electrode (CMGCE). The CoTSPc-CMGCE catalysed the oxidation of cysteine in the pH range 1 to 10. The significance of this electrode is an application for analysis of proteins at biological pH's. A biscyanoruthenium(II) phthalocyanine CMGCE catalysed the oxidation of cysteine at 0.43 V vs Ag/AgCl a significant lowering in the overpotential for the oxidation of cysteine. Metallothionein, a metal binding protein, is believed to be involved in metal homeostasis and detoxification in the peripheral organs of living systems. A method for the quantitative determination of this protein utilising its high cysteine content was presented. At pH 8.4 Tris-HCl buffer, and using a CoTSPc-CMGCE modified by electrodeposition of the modifier, the anodic peaks for the oxidation of metallothionein was observed at 0. 90 V vs Ag/ AgCI. Ferredoxin is a simple iron-sulphur protein. One tenth of its residues are cysteine. Ferredoxin is involved in simple electron transfer processes during photosynthesis and respiration. Electrochemical studies of spinach ferredoxin were conducted at a CoTSPc-CMGCE. Anodic currents for the oxidation of the cysteine fragment of ferredoxin was observed at 0.85 V vs Ag/AgCl in HEPES buffer at pH 7.4, representing a new method for analysis of this protein. Voltammetric studies of its ferric/ferrous transition have shown quasi-reversible waves atE~ -0.62 V vs Ag/AgCl only in the presence of promoters. At a CoTSPc-CMGCE, a cathodic wave attributed to the reduction of Fe(III)/Fe(II) was observed at Epc -0.34 V vs Ag/AgCl. This represents an alternative method for voltammetric studies of the ferric/ferrous transition at significantly lowered potentials. Melatonin, a pineal gland hormone functions m setting and entraining circadian rhythms and in neuroprotection as a free radical scavenger and general antioxidant. Using adsorptive cathodic stripping voltammetry, the binding affinities of melatonin, serotonin and tryptophan for metals, were measured. The results showed that the following metal complexes were formed: aluminium with melatonin, serotonin and tryptophan; cadmium with melatonin and tryptophan; copper with melatonin and serotonin; iron (III) with melatonin and serotonin; lead with melatonin, tryptophan and serotonin, zinc with melatonin and tryptophan and iron (II) with tryptophan. The studies suggest a further role for melatonin in the reduction of free radical generation and in metal detoxification and may explain the accumulation of aluminium in Alzheimer's disease.

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 ...

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Ph.D. (Chemistry) / In this study, carbon based electrode materials such as glassy carbon, graphene, diamond and exfoliated graphite were explored as suitable electrode materials for electrochemical detection, electrochemical and photoelectrochemical degradation of organic water pollutants. Graphene modified glassy carbon electrode sensor was developed for bisphenol A. Cyclic voltammetry was used to study the electrochemical properties of the prepared graphene- modified glassy carbon electrode using potassium ferricyanide as a redox probe. The prepared graphene- modified glassy carbon electrode exhibited more facile electron kinetics and enhanced current of about 75% when compared to the unmodified glassy carbon electrode...

The complex Fe2(TIED)4+ (compound I) [see PDF] has a characteristic intense low energy electronic absorption band (λ = 874 nm, ε = 24,600 M-1cm-1). This band is assigned as a metal to ligand charge transfer, MLCT, and it exhibits a very large solvent dependence which is attributed to replacement of the axial ligands on the iron atoms by solvent. The complex has two reversible oxidation and two reversible reduction steps in the cyclic voltammogram in dry CH3CN. The oxidation involves the iron atoms while the reduction places electrons on the conjugated part of the ligand. The cyclic voltammogram shows a single, apparently, two-electron reduction process in DMF and in H2O. A mixed-valence FeII/FeIII (Fe2(TIED)5+) compound has been obtained by electrochemical oxidation of Fe2(TIED)4+. The mixed-valence compound has an intense near-infrared band (λ = 940 nm, ε = 28,000 M-1cm-1). Analysts of this band using the Hush equations for an intervalence transition indicates that the system is delocalized. The difference in oxidation potentials, ΔE1/2 = ΔE1/2 (FeIII/FeIII) - ΔE1/2 (FeII/FeIII), is 500 mV and this corresponds to a comproportionation constant of 2.8 x 108. This large value indicates the mixed-valence species is stabilized by delocalization. The Mössbauer spectrum of the mixed-valence compound consists of a single quadrupole-split doublet at 90 K and 4.2 K. This establishes that the iron atoms are equivalent of the Mössbauer time scale, and the mixed-valence compound is classified as valence-average, ((Fe2.5/Fe2.5).

The object of this research was to develop an arsenic(V) selective electrode. The electrode is based on a solid state membrane prepared by pressing a precipitate of silver arsenate-silver sulfide into a pellet. After the electrode was made, experiments were designed to check for three general characteristics of the electrodes: dependence of potential on pH for constant arsenic(V) concentration; dependence of potential on arsenic(V) concentrations at constant pH and extent of interference due to phosphate and arsenic(III) ions. From these measurements, it was found that Ag2HAs04 was formed originally in the membranes containing a small fraction of arsenic(V) and that this compound was converted to Ag3As04 on the electrode surface in alkaline solutions.

The problem taken for investigation was discovered when a cryostat needed for use in polarography in liquid ammonia (the original problem) was found broken. For experience it was decided to turn to another form of nonaqueous polarography while the parts were on order. Materials remaining from a previous diamine investigation by Foss (21) were found in the laboratory. After reading the dissertation in which they had been used, it was decided to reproduce some of the results that had been previously obtained. Following preparation of the chemicals and several polarographic runs, a previously unreported wave was persistently observed. Further perusal of the dissertation found no such wave reported and only one other similar wave had been noted by Robert Burrus (12), as was revealed in a thorough search of the literature. It was the study of this new wave that was taken for the problem to be investigated.

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