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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Modeling and analysis of chemiluminescence sensing for syngas, methane and jet-A combustion

Nori, Venkata Narasimham 17 June 2008 (has links)
Flame chemiluminescence has received increasing attention for its potential sensor and diagnostic applications in combustors. A number of studies have used flame chemiluminescence to monitor flame status, and combustor performance. While most of these studies have been empirical in nature, chemiluminescence modeling has the potential to provide a better understanding of the chemiluminescence processes and their dependence on various combustion operating conditions. The primary objective of this research was to identify and validate the important chemiluminescence reaction mechanisms for OH*, CH* and CO2*. To this end, measurements were performed at various operating conditions, primarily in laminar, premixed flames, fueled with methane, syngas (H2/CO) and Jet-A. The results are compared to 1-d laminar flame simulations employing the chemiluminescence mechanisms. The secondary objective was to use the experiments and validated chemiluminescence reaction mechanisms to evaluate the usefulness of flame chemiluminescence as a combustion diagnostic, particularly for heat release rate and equivalence ratio. The validation studies were able to identify specific mechanisms for OH*, CH* and CO2* that produced excellent agreement with the experimental data in most cases. The mechanisms were able to predict the variation of the chemiluminescence signals with equivalence ratio but not with pressure and reactant preheat. The possible reasons causing this disagreement could be due to the inaccuracies in the basic chemical mechanism used in the simulations, lack of accurate quenching data (for CH*), thermal excitation (for OH*) and radiative trapping (for OH* and CO2*) and interference from the emissions of other species (such as HCO and H2O), for CO2*. Regarding the utility of chemiluminescence for sensing, a number of observations can be made. In syngas-air flames, CO2* is a reasonable heat release rate marker, at least for very lean conditions. OH* shows some advantage in atmospheric-pressure methane and Jet-A flames in general, while CH* is advantageous at high pressure and very lean conditions at atmospheric pressure. The CO2*/OH* intensity ratio is not useful for sensing equivalence ratio in syngas flames, except maybe at very lean conditions. However, the CH*/OH* signal ratio is a promising approach for sensing equivalence ratio at low or very high pressure conditions in hydrocarbon flames. Thermal excitation and self-absorption processes for OH* chemiluminescence can become important for combustors operating at high pressure, high preheat and near stoichiometric conditions. Background subtracted chemiluminescence signals are recommended for sensing purposes.
42

Studies on a novel type of electrogenerated chemiluminescence and electroanalysis of biomolecules at fluorosurfactant-modifiedelectrodes

Chen, Zuofeng., 陳作鋒. January 2009 (has links)
published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy
43

Contribuição ao estudo de dioxetanos e de seu envolvimento em fotobioquímica no escuro / Contribution to the study of dioxetanes and their role in photobiochemistry in the dark

Catalani, Luiz Henrique 02 October 1984 (has links)
Do interesse em espécies eletronicamente excitadas geradas por sistemas luminescentes químicos e biológicos, nasceu o interesse dos químicos pelos dioxetanos, seu comportamento e suas propriedades. Propostos como intermediários de tais reações, estes compostos (peróxidos cíclicos de anel tetratômico) sofrem clivagem térmica unimolecular com produção de dois fragmentos carbonílicos, um deles no estado eletronicamente excitado. Em geral, dioxetanos substituídos por grupos alquílicos e arílicos levam a altos rendimentos de estados triplete. Propôs-se, então, reinvestigar a termólise do tetrametildioxetano (TMD) em meio aquoso e utilizar esta fonte de acetona triplete como modelo químico, para o sistema enzimático de produção de acetona triplete (oxidação aeróbica do isobutanal (IBAL)/peroxidase (HRP)), em estudos de supressão e transferência de energia. O TMD tem sido preparado e cristalizado rotineiramente em nosso laboratório, pelo método de Kopecky. Os parâmetros de ativação de termólise (estabilidade térmica e rendimentos de quimiexcitação dos produtos) foram reestudados em solventes aromáticos (benzeno e tolueno), cicloalifáticos (ciclohexano e decalina), próticos (água) e apróticos (acetonitrila e CCl4).Concluiu-se que: (i) a estabilidade do TMD não é afetada pela natureza do solvente (Ea ~ 27,0 kcal mol-1); (ii) a eficiência global de transferência de energia triplete (acetona) → singlete (9,10-dibromoantraceno) nos solventes não aromáticos é praticamente constante (ΦTS ~ 10 %); (iii) em solventes aromáticos onde o doador excitado é na verdade um \"exciplex\" acetona-solvente, ΦTS ~ 30 %. A relação entre os rendimentos de quimiexcitação de triplete e singlete (3Φ /1Φ) em água foi determinada como sendo da ordem de 1x103, que concorda com valores determinados em tolueno e benzeno (7x102 e 8x102, respectivamente). Nos estudos em meio aquoso, o DBAS e o DPAS foram utilizados para monitorar a presença de acetona triplete e singlete, formada química, fotofísica ou enzimaticamente. Ambos foram sintetizados em nosso laboratório e suas propriedades fotofísicas, determinadas em água deionizada a 20°C. Através da medida de fluorescência do DBAS excitado por transferência de energia a partir de acetona triplete, determinou-se a vida média de acetona triplete em meio aquoso aerado e deaerado (τaer ~ 2 µs e τN2 ~ 10 a 20 µs). Seis classes de interceptadores de acetona triplete, gerada na termólise de TMD, foram investigadas em tampão aquoso a 35°C: dienos (ácido sórbico e acrilonitrila), pigmentos xantênicos, riboflavina, tirosina e derivados 3,5-dihalogenados, indol e derivados indólicos, e uma série de quinonas. Em geral, os valores das constantes de supressão de acetona triplete produzida diretamente no seio da solução, a partir de TMD, estão pelo menos uma ordem de grandeza abaixo dos valores correspondentes para acetona triplete produzida enzimaticamente. Estes resultados são consistentes com a hipótese de que acetona triplete gerada dentro da enzima tem vida média mais longa, pois se encontraria parcialmente \"protegida\" da ação supressora de O2. Outros argumentos podem, entretanto, ser igualmente satisfatórios. Parece claro que os supressares indólicos (IP ~ 8 eV) e ácido sórbico exercem sua ação através da formação de complexos de transferência de carga, tirosina e corantes xantênicos (IP ~ 7 eV) por um mecanismo de transferência de elétrons e riboflavina por mecanismo tipo Förster. As quinonas, cuja afinidade eletrônica é bastante alta (IP ~ 10-11 eV), suprimem acetona triplete por um mecanismo controlado por difusão; com estes compostos, o limite superior do esperado para um processo puramente colisional seria atingido (kq ~ 1 a 2x1010 M-1s- 1, em água a 35°C). De fato, derivados metilados de p-benzoquinona e naftoquinona suprimem acetona triplete com velocidade mais baixa, enquanto que em solvente mais viscoso (decalina, em relação a n-hexano), kq também é mais lenta. Por outro lado, observou-se um marcante \"efeito de átomo pesado\" na eficiência de transferência de energia triplete (acetona) → singlete (corante xantênico): ΦTS para fluoresceína, eosina e Rose Bengala na proporção 1:15:320. A oxidação da clorpromazina (CPZ) por reação com o TMD foi estudada em meio aquoso e meio tamponado e verificou-se que esta independe da formação de espécies excitadas, apesar da CPZ apresentar-se como eficiente supressor de acetona triplete. Espectros de RMN1H mostraram que a reaçao entre CPZ e TMD gera a clorpromazina-5-óxido (sulfóxido; CPZO) e o óxido de tetrametiletileno (o epóxido correspondente ao TMD). Estudos de espectroscopia U.V. e de cromatografia gasosa indicam que a estequiometria da reação TMD/CPZ é 1:1 e que a presença de competidores de supressão de acetona triplete não altera a velocidade da reação nem a estequiometria da mesma. Em vista destes resultados, reestudou-se a oxidação de CPZ pelo sistema do IBAL/HRP/O2, estudo feito inicialmente por DURÁN e colaboradores, no qual os autores propõem que a oxidação de CPZ é resultante de transferência de energia de excitação da acetona triplete gerada enzimaticarnente. Usando métodos inexplorados até então, verificamos a possibilidade de esta oxidação ocorrer por reação direta entre CPZ e os radicais de HRP formados durante a oxidação do isobutanal, sem a intervenção da acetona triplete. Outro estudo parelelo a este, foi feito visando determinar parâmetros cinéticos e termodinâmicos em dioxetanos com diferentes tipos de hidrogênios em posição γ do anel. Este estudo visava determinar de que maneira a interação oxigênio do anel-hidrogênio gama influia em tais parâmetros. Sintetizou-se uma série de 3-metil-3-alquildioxetanos (alquil = n-propil, n-butil e neopentil) e determinamos os seus parâmetros de ativação de termólise (Ea, ΔS≠, 3Φ e 1Φ). Constatamos que não há diferença significativa entre estes dioxetanos, sendo assim, a interação hidrogênio gama-oxigênio do anel é inexpressiva. Porém, quando comparados com outros dioxetanos da mesma série, onde alquil = etil, isopropil e terc-butil (estudo em conjunto com outros pesquisadores) nota-se urna expressiva mudança na Ea a medida que aumenta o número de grupos rnetila na posição α, indicando um efeito estérico do tipo 3,3. / The interest in eletronically excited species generated by chemical and biological systems give rise to at interest in dioxetanes, their behavior and their properties. These coumpounds (cyclic four-membered ring), which have been proposed as intermediates in such reactions, undergo unimolecular thermal cleavage yielding two carbonyl fragments, one of which is tipically formed electronically excited. In general, alkyl and aryl substitued dioxetanes give high yields of triplet states. In the present work, the thermolyses of tetramethyldioxetane (TMD) was reinvestigated in agueous medium. This source of triplet acetone was then employed in quenching and energy transfer studies as a chemical model for the enzymatic systems which produces triplet acetone I aerobic oxidations of isobutanal (IBAL) catalysed by horseradish peroxidase (HRP) I. TMD was prepared and crystalised normally in our laboratory using Kopecky\'s method. Thermal activation parameters (thermal stability and chemiexcitation quantum yields) have been determined in several types of solvents, including aromatics (benzene and toluene), cycloaliphatics (cyclohexene and decalin), protic (water) and aprotic (acetonitrile and carbon tetrachloride) .We conclude that: (i) TMD stability is not affected by the nature of the solvente (Ea ~ 27,0 kcal/mol), (ii) the overall energy transfer efficiency 3Ac* → 1DBAS* is practically constant (ΦTS ~ 10%) in non-aromatic solventsi (iii) in aromatic solvents, where the excited donor is an acetone-solvent \"exciplex\", ΦTS ~ 30%. The ratio of triplet and singlet chemiexcitation yields (3Φ /1Φ) in water was deterrnined to be 1x103. This value is in good agreement with these determined in toluene and benzene (7x102 and 8x102, respectivelly). In studies in aqueous medium, DBAS and DPAS were used as probes to monitor the production of triplet and singlet acetone formed chemically, photophysically or enzymatically. Both probes were prepared in our laboratory and their photophysical properties deterrnined in deionized water at 20°C. The lifetime of triplet acetone in aerated and deaerated aqueous media was deterrnined on the basis of the cherniluminescence intensity of DBAS excited by energy transfer (τaer ~ 2 µs e τN2 ~ 10 a 20 µs). Six classes of quenchers were investigated in aqueous buffer at 35°C: dienes (sorbic acid and acrylonitrile), xanthene dyes, tyrosine and its 3,5-dihalogenoderivatives, indole and indolic derivatives, riboflavin and a serie of quinones. In general, rate constants for quenching of triplet acetone produced free in solution via TMD thermolyses are one order of magnitude lower than those for quenching of enzymatically generated triplet acetone. These results are in line with the hypothesis of a longer lifetime of the triplet acetone generated within the enzyme due a parcial \"protection\" for O2 quenching. It seerns clear that the indolic coumpounds (IP ~ 8 eV) and sorbic acid quench triplet acetone through the forrnation of a charge-transfer complex, tyrosine ans xanthene dyes (IP ~ 7 eV) by an electron-transfer mechanism and riboflavin by a Förster type mechanism. The quinones, which have high electronic affinities (IP ~ 10- 11 eV) , quench triplet acetone by a diffusion controlled process (kq ˜ 1 to 2x1010 M-1s-1 in water at 35°C). Methyl derivatives of p-benzoquinone and naphtoquinone quench triplet acetone at a slower rate; kq is also lower in a more viscous solvent (decalin versus n-hexane). On the other hand, the results indicate a strong \"heavy atom effect\" on the energy transfer efficiency from triplet acetone to singlet xanthene dye: ΦTS for fluorescein, eosin and Rose Bengal in the ratio 1:15:320. The chlorpromazine (CPZ) oxidation by reaction with TMD was studied in aqueous and buffered media. This reaction does not depend on the production of excited species, even though CPZ proved to be an efficient trip1et acetone quencher. The NMR1H spectra showed that chlorpromazine-5-oxide and tetrarnethylene oxide are the products of the reaction between CPZ and TMD. UV spectroscopic and gas chromatographic studies indicated a 1:1 stoichiometry for the TMD/CPZ reaction and no competition between this reaction and triplet acetone quenching by indole or sorbate. In view of these results, we reinvestigated the oxidation of CPZ by the IBAL/HRP/02 system, a reaction which has been suggested to occur via energy transfer from triplet acetone to CPZ in an earlier study. Using methods developed since the earlier study, we verified that this reaction in fact occurs via direct reaction between CPZ and HRP radicals produced during IBAL oxidation, without the intervention of triplet acetone. In another parallel study, we determined kinetic and thermodinamic parameters of a series of dioxetanes with different types of γ hydrogens in order to examine how the interaction between oxygen and the γ hydrogens might influence these parameters. Thus, a series of 3-methyl-3-alkyldioxetanes (alkyl = n-propyl, n-butyl and neopentyl) was sintesized and their thermal activation parameters (Ea, ΔS≠, 3Φ and 1Φ) determined. The results indicated that there are no significant differences among these dioxetanes; consequently the oxygen-γ hydrogen interaction is relativelly unimportant. However, when compared with other dioxetanes of similar structure (alkyl=ethyl, isopropyl and terc-butyl; joint study done with other researchers), there is a significant change in Ea upon increasing the number of rnethyl groups at the α position, pointing to a steric effect of the 3,3 type.
44

Estudo mecanístico do sistema peróxi-oxalato / Mechanistic study of peroxyoxalate system

Cassius Vinicius Stevani 12 September 1997 (has links)
Ao contrário das reações bioluminescentes, que apresentam rendimentos quânticos de emissão de luz por volta de 90%, as reações quimiluminescentes, geralmente, apresentam rendimentos abaixo de 1%. Entretanto, existe um sistema quimiluminescente cujo rendimento está na faixa de 30%, o denominado sistema peróxi-oxalato, descoberto na década de 60 e muito utilizado hoje em dia como ferramenta analítica. O sistema peróxi-oxalato consiste na reação de ésteres fenólicos do ácido oxálico com H2O2, catalisada por uma base e em presença de compostos poliaromáticos fluorescentes com baixos potenciais de oxidação (ACT). Um dos principais motivos para que este sistema seja tão pesquisado há trinta anos deve-se ao seu alto rendimento quântico de emissão e à dificuldade em se obter informações sobre o mecanismo de geração de estados excitados. Na verdade, até hoje não se sabe com certeza qual é o intermediário de alta energia (IAE) que transfere a \"energia química\" para o ACT, levando este último para o estado excitado que, pelo decaimento, emite luz. Uma controvérsia ainda maior existe sobre o mecanismo de quimi-excitação. Enquanto a maior parte dos pesquisadores da área aceitam o mecanismo \"Chemically lnitiated Electron Exchange Luminescence\" (CIEEL) como operante no sistema peróxi-oxalato e em muitos outros sistemas quimiluminescentes, alguns pesquisadores argumentam em contrário a este mecanismo, mostrando as suas deficiências e a falta de evidências claras para a comprovação da seqüência de eventos proposta. Os estudos mecanísticos desenvolvidos até o presente momento sobre o sistema peróxi-oxalato permitiram propor (I) diversas moléculas como lAE, responsáveis pela excitação do ACT (I - IV). Neste trabalho é relatado um estudo mecanístico do sistema peróxi-oxalato, o único com alta eficiência comprovada que pode envolver o mecanismo CIEEL, com o objetivo de contribuir para um melhor entendimento do passo de quimi-excitação. Foi sintetizado um derivado do intermediário do tipo 11, o 4-clorofenil O,O-hidrogênio monoperoxalato (1), caracterizado por RMN 13C (INVGATE), infi-avermelho e espectrometria de massa. O resultado mais significativo deste trabalho é o fato de 1, em presença de um ACT (i.e. rubreno, DPA, perileno), não emitir luz, o que exclui, definitivamente, intermediários do tipo fi como intermediários de alta energia. 1 somente emite em presença de um ACT e de bases com pKa adequado (pKa > 6). Tal fato sugere que deve ocorrer uma reação química anterior à emissão, provavelmente uma ciclização, que dá origem ao intermediário de alta energia. Foram feitos estudos cinéticos da reação de 1 com diversas bases [i.e. imidazol, p-clorofenolato e t-butóxido de potássio e 1,8-bis(dimetilamino)naftaleno], observando-se a emissão de luz em presença de DP A ou a absorção do p-clorofenol liberado em 292 orn. Destes estudos puderam ser propostos esquemas mecanísticos dos processos que antecedem a etapa de quimiexcitação e foram obtidas evidências indiretas para a ocorrência da 1,2-dioxetanodiona (I) como lAE. Visando obter informações sobre a etapa de quimio-excitação foram medidos os rendimentos quânticos de quimiluminescência da reação de 1 com imidazol, em presença de sete ativadores, com diferentes potenciais de oxidação. Destes estudos foram obtidas informações indiretas a respeito da velocidade de transferência de elétron. Com estes dados pode-se verificar a validade do mecanismo CIEEL, propondo um mecanismo condizente com os resultados experimentais. Para finalizar, tentou-se verificar a natureza volátil do lAE e de seqüestrar o lAE, possivelmente a 1,2-dioxetanodiona (I), utilizando-se trifenilantimônio. Apesar de várias tentativas, utilizando diversas condições experimentais, os resultados foram pouco conclusivos. / Contrarily to bioluminescent reactions which present quantum yields of around 90%, chemiluminescent reactions generally present quantum efficiencies of around 1%. However, there is a chemiluminescent system discovered in the 60\'s and widely used nowadays as analytical tool, which quantum yields can reach up to 30%, the so called peroxyoxalate system. This system consists in the reaction of aromatic oxalyl esteres with H2O2 catalyzed by a base in the presence of polyaromatic, highIy fluorescent compounds with low oxidation potentials (ACT). The main reason for the studies of the peroxyoxalate system during 30 years is its highIy chemiluminescence quantum yield and difficulties to obtain informations about the mechanism of the excited states generation. In fact, there is no strong evidence till now about the high energy intermediate (HEI) responsible for the transformation of the \"chemical energy\" into the ACTs electronically excitation, which leads to light emission. There exists a still greater controversy with respect to the chemiexcitation mechanism. While the most chemiluminescence researchers accept the \"Chemically Initiated Electron Exchange Luminescence\" (CIEEL) mechanism to explain the chemiexcitation process in the peroxyoxalate and many others chemiluminescent systems, some researchers contest it, exposing the lack of clear evidences for the sequence of events proposed. The mechanistic research developed till now about the peroxyoxalate system allowed the proposal of several structures as (I) HEI, as the most probable to excite the ACT (I-IV). In this work is reported a mechanistic study on the peroxyoxalate system, the only one with proven high efficiency supposed to involve the CIEEL mechanism, aiming to contribute to a better knowledge of the chemiexcitation pathway. A type n intermediate derivative, 4-chIorophenyl O,O-hydrogen monoperoxalate (1), was synthesized and characterized by l3C NMR (INVGATE) inftared and mass spectrometry. Perhaps the most significant result in this work is the fact that 1, in the presence of a suitable ACT (i.e. rubrene, DPA, perylene) does not lead to light emission. What excludes definitively type n structures as high energy intermediates in the peroxyoxalate system. Moreover, as 1 only lead to light emission in the presence ofbases with suitable pKa (pKa > 6) and an ACT, it suggests that a chemical reaction has to take place before emission, probably a cyclization leading to the high energy intermediate. Kinetic investigations on the reaction of 1 with several bases [i.e. imidazole, potassiump-chlorophenolate and t-butoxide and 1,8-bis(dimethylamino)naphthaleneJ were performed. The reaction was followed either by light emission in the presence of DPA or by changes in absorption at 292 nm due to p-chlorophenol released. These investigations allow the proposal of mechanistic schemes for the processes that occur before chemiexcitation and indirect evidences for the occurrence of 1,2-dioxetanedione (I) as the HEI could be obtained. The chemiluminescent quantum yields of the reaction of 1 with imidazole in the presence of seven ACTs with different oxidation potentials were measured with the aim to obtain informations about the chemiexcitation pathway. Indirect informations on the electron transfer rate constant could be obtained. The validity of the CIEEL mechanism could be verified with these data and a mechanism proposed which is in agreement with the experimental results. Finally, trapping of the HEI, probably 1,2-dioxetanedione (I), using triphenylantimony was attempted. Several attempts to trap the HEI, although using various experimental conditions, were not successful. The results were not conclusive.
45

Estudo mecanístico do sistema peróxi-oxalato / Mechanistic study of peroxyoxalate system

Stevani, Cassius Vinicius 12 September 1997 (has links)
Ao contrário das reações bioluminescentes, que apresentam rendimentos quânticos de emissão de luz por volta de 90%, as reações quimiluminescentes, geralmente, apresentam rendimentos abaixo de 1%. Entretanto, existe um sistema quimiluminescente cujo rendimento está na faixa de 30%, o denominado sistema peróxi-oxalato, descoberto na década de 60 e muito utilizado hoje em dia como ferramenta analítica. O sistema peróxi-oxalato consiste na reação de ésteres fenólicos do ácido oxálico com H2O2, catalisada por uma base e em presença de compostos poliaromáticos fluorescentes com baixos potenciais de oxidação (ACT). Um dos principais motivos para que este sistema seja tão pesquisado há trinta anos deve-se ao seu alto rendimento quântico de emissão e à dificuldade em se obter informações sobre o mecanismo de geração de estados excitados. Na verdade, até hoje não se sabe com certeza qual é o intermediário de alta energia (IAE) que transfere a \"energia química\" para o ACT, levando este último para o estado excitado que, pelo decaimento, emite luz. Uma controvérsia ainda maior existe sobre o mecanismo de quimi-excitação. Enquanto a maior parte dos pesquisadores da área aceitam o mecanismo \"Chemically lnitiated Electron Exchange Luminescence\" (CIEEL) como operante no sistema peróxi-oxalato e em muitos outros sistemas quimiluminescentes, alguns pesquisadores argumentam em contrário a este mecanismo, mostrando as suas deficiências e a falta de evidências claras para a comprovação da seqüência de eventos proposta. Os estudos mecanísticos desenvolvidos até o presente momento sobre o sistema peróxi-oxalato permitiram propor (I) diversas moléculas como lAE, responsáveis pela excitação do ACT (I - IV). Neste trabalho é relatado um estudo mecanístico do sistema peróxi-oxalato, o único com alta eficiência comprovada que pode envolver o mecanismo CIEEL, com o objetivo de contribuir para um melhor entendimento do passo de quimi-excitação. Foi sintetizado um derivado do intermediário do tipo 11, o 4-clorofenil O,O-hidrogênio monoperoxalato (1), caracterizado por RMN 13C (INVGATE), infi-avermelho e espectrometria de massa. O resultado mais significativo deste trabalho é o fato de 1, em presença de um ACT (i.e. rubreno, DPA, perileno), não emitir luz, o que exclui, definitivamente, intermediários do tipo fi como intermediários de alta energia. 1 somente emite em presença de um ACT e de bases com pKa adequado (pKa > 6). Tal fato sugere que deve ocorrer uma reação química anterior à emissão, provavelmente uma ciclização, que dá origem ao intermediário de alta energia. Foram feitos estudos cinéticos da reação de 1 com diversas bases [i.e. imidazol, p-clorofenolato e t-butóxido de potássio e 1,8-bis(dimetilamino)naftaleno], observando-se a emissão de luz em presença de DP A ou a absorção do p-clorofenol liberado em 292 orn. Destes estudos puderam ser propostos esquemas mecanísticos dos processos que antecedem a etapa de quimiexcitação e foram obtidas evidências indiretas para a ocorrência da 1,2-dioxetanodiona (I) como lAE. Visando obter informações sobre a etapa de quimio-excitação foram medidos os rendimentos quânticos de quimiluminescência da reação de 1 com imidazol, em presença de sete ativadores, com diferentes potenciais de oxidação. Destes estudos foram obtidas informações indiretas a respeito da velocidade de transferência de elétron. Com estes dados pode-se verificar a validade do mecanismo CIEEL, propondo um mecanismo condizente com os resultados experimentais. Para finalizar, tentou-se verificar a natureza volátil do lAE e de seqüestrar o lAE, possivelmente a 1,2-dioxetanodiona (I), utilizando-se trifenilantimônio. Apesar de várias tentativas, utilizando diversas condições experimentais, os resultados foram pouco conclusivos. / Contrarily to bioluminescent reactions which present quantum yields of around 90%, chemiluminescent reactions generally present quantum efficiencies of around 1%. However, there is a chemiluminescent system discovered in the 60\'s and widely used nowadays as analytical tool, which quantum yields can reach up to 30%, the so called peroxyoxalate system. This system consists in the reaction of aromatic oxalyl esteres with H2O2 catalyzed by a base in the presence of polyaromatic, highIy fluorescent compounds with low oxidation potentials (ACT). The main reason for the studies of the peroxyoxalate system during 30 years is its highIy chemiluminescence quantum yield and difficulties to obtain informations about the mechanism of the excited states generation. In fact, there is no strong evidence till now about the high energy intermediate (HEI) responsible for the transformation of the \"chemical energy\" into the ACTs electronically excitation, which leads to light emission. There exists a still greater controversy with respect to the chemiexcitation mechanism. While the most chemiluminescence researchers accept the \"Chemically Initiated Electron Exchange Luminescence\" (CIEEL) mechanism to explain the chemiexcitation process in the peroxyoxalate and many others chemiluminescent systems, some researchers contest it, exposing the lack of clear evidences for the sequence of events proposed. The mechanistic research developed till now about the peroxyoxalate system allowed the proposal of several structures as (I) HEI, as the most probable to excite the ACT (I-IV). In this work is reported a mechanistic study on the peroxyoxalate system, the only one with proven high efficiency supposed to involve the CIEEL mechanism, aiming to contribute to a better knowledge of the chemiexcitation pathway. A type n intermediate derivative, 4-chIorophenyl O,O-hydrogen monoperoxalate (1), was synthesized and characterized by l3C NMR (INVGATE) inftared and mass spectrometry. Perhaps the most significant result in this work is the fact that 1, in the presence of a suitable ACT (i.e. rubrene, DPA, perylene) does not lead to light emission. What excludes definitively type n structures as high energy intermediates in the peroxyoxalate system. Moreover, as 1 only lead to light emission in the presence ofbases with suitable pKa (pKa > 6) and an ACT, it suggests that a chemical reaction has to take place before emission, probably a cyclization leading to the high energy intermediate. Kinetic investigations on the reaction of 1 with several bases [i.e. imidazole, potassiump-chlorophenolate and t-butoxide and 1,8-bis(dimethylamino)naphthaleneJ were performed. The reaction was followed either by light emission in the presence of DPA or by changes in absorption at 292 nm due to p-chlorophenol released. These investigations allow the proposal of mechanistic schemes for the processes that occur before chemiexcitation and indirect evidences for the occurrence of 1,2-dioxetanedione (I) as the HEI could be obtained. The chemiluminescent quantum yields of the reaction of 1 with imidazole in the presence of seven ACTs with different oxidation potentials were measured with the aim to obtain informations about the chemiexcitation pathway. Indirect informations on the electron transfer rate constant could be obtained. The validity of the CIEEL mechanism could be verified with these data and a mechanism proposed which is in agreement with the experimental results. Finally, trapping of the HEI, probably 1,2-dioxetanedione (I), using triphenylantimony was attempted. Several attempts to trap the HEI, although using various experimental conditions, were not successful. The results were not conclusive.
46

OH* Chemiluminescence: Pressure Dependence of O + H + M = OH* + M

Donato, Nicole 2009 December 1900 (has links)
The measure of chemiluminescence from the transition of the hydroxyl radical from its electronically excited state (A^2 Sigma^positive) to its ground state (X^2 Pi) is used in many combustion applications for diagnostic purposes due to the non-intrusive nature of the chemiluminescence measurement. The presence of the ultraviolet emission at 307nm is often used as an indicator of the flame zone in practical combustion systems, and its intensity may be correlated to the temperature distribution or other parameters of interest. To date, the measurement of the excited state OH, OH*, is mostly qualitative. With the use of an accurate chemical kinetics model, however, it is possible to obtain quantitative measurements. Shock-tube experiments have been performed in highly diluted mixtures of H2/O2/Ar at a wide range of pressures to evaluate the pressure-dependent rate coefficient of the title reaction. In such mixtures the main contributing reaction to the formation of OH* is, O H M = OH* M. R1 Previous work has determined the reaction rate of R1 at atmospheric conditions and accurately predicts the amount of OH* experimentally produced. At elevated pressures up to 15 atm, which are of interest to the gas turbine community, the currently used reaction rate of R1 (i.e., without any pressure dependence) significantly over predicts the amount of OH* formed. This work provides the pressure dependence of R1. The new reaction rate is able to reproduce the experimental data over the range of conditions studied and enables quantitative measurements applicable to practical combustion environments.
47

Chemiluminescence and Ignition Delay Time Measurements of C9H20 Oxidation in O2-Ar Behind Reflected Shock Waves

Rotavera, Brandon 2009 December 1900 (has links)
Stemming from a continuing demand for fuel surrogates, composed of only a few species, combustion of high-molecular-weight hydrocarbons (>C5) is of scientific interest due to their abundance in petroleum-based fuels, which contain hundreds of different hydrocarbon species, used for military, aviation, and transportation applications. Fuel surrogate development involves the use of a few hydrocarbon species to replicate the physical, chemical, combustion, and ignition properties of multi-component petroleum-based fuels, enabling fundamental studies to be performed in a more controlled manner. Of particular interest are straight-chained, saturated hydrocarbons (n-alkanes) due to the high concentration of these species in diesel and jet fuels. Prior to integrating a particular hydrocarbon into a surrogate fuel formulation, its individual properties are to be precisely known. n-Nonane (n-C9H20) is found in diesel and aviation fuels, and its combustion properties have received only minimal consideration. The present work involves first measurements of n-C9H20 oxidation in oxygen (O2) and argon (Ar), which were performed under dilute conditions at three levels of equivalence ratio (phi = 0.5, 1.0, and 2.0) and fixed pressure near 1.5 atm using a shock tube. Utilizing shock waves, high-temperature, fixed-pressure conditions are created within which the fuel reacts, where temperature and pressure are calculated using 1D shock theory and measurement of shock velocity. Of interest were measurements of ignition times and species time-histories of the hydroxyl (OH*) radical intermediate. A salient pre-ignition feature was observed in fuel-lean, stoichiometric, and fuel-rich OH* species profiles. The feature at each equivalence ratio was observed above 1400 K with the time-of-initiation (post reflected-shock) showing dependence on phi as the initiation time shortened with increasing phi. Relative percentage calculations reveal that the fuel-rich condition produces the largest quantity of pre-ignition OH*. Ignition delay time measurements and corresponding activation energy calculations show that the phi = 1.0 mixture was the most reactive, while the phi = 0.5 condition was least reactive.
48

Flow Injection Chemiluminescence determination of sucrose based on the luminol-ferricyanide/ferrocyanide reaction system

Tseng, Shih-Wen 12 August 2003 (has links)
none
49

Electrochemistry and electrogenerated chemiluminescence of unique organic chromophores and organic nanoparticles

Suk, Jung Don 27 June 2012 (has links)
Electrogenerated chemiluminescence (ECL) studies were performed on several interesting compounds. A series of BODIPY derivatives was examined to understand the structural effects on the electrochemical, spectroscopic, and ECL behavior. Stable electrochemistry and high fluorescence in the green to the red regions were observed. PB, MCPB, DCPB and PM580 produced intense ECL, strong enough to be seen with the naked eye in a lighted room. Unlike MCPB and DCPB, PB produced the multiple ECL peaks. Totally blocked BODIPY compound showed the improvement of fluorescence and ECL quantum yield due to the stability of radicals. Strong signal of EPR data during the oxidative electrolysis was obtained by simultaneous electrochemical-electron paramagnetic resonance technique with home-made cell. Several new antrhacene derivatives such as a variety of 2- and 4-fold anthracene-functionalized tetraarylbimesityls and a series of 9-naphthylanthracene based dimer and trimer were studied. They showed one wave on the oxidation and reduction because of a sequence, two or more electron transfers during the annihilation of the radical ions. Depended on the structure, some of them exhibited excimer formation on ECL spectra. Azide-BTA compound which consists of two triphenylamine and 2,1,3-benzothiadiazole groups at the ends bridged by a fluorene moiety was synthesized and examined. The compound is a newly synthesized D-A-[pi]-A-D molecule which had reversibility upon electrochemical oxidation and reduction, and also showed intense red fluorescence and stable red ECL emission. Using a simple reprecipitation method, well-dispersed and spherical organic nanoparticles of Azide-BTA and 9-naphthylanthracene based dimer were prepared in an aqueous solution. Controlling the preparation condition, the size of nanoparticles can be minimized to 15 nm. Especially we prepared the organic nanoparticles of 9-naphthylanthracene based dimer dispersed in organic solvent, MeCN, one of the preferred solvents for electrochemical studies and ECL. / text
50

Study of methodologies for detecting bilirubin by electrochemical, UV,fluorescence and chemiluminescence techniques and their applicationfor CE determination of bilirubin and arsenic anions in biofluid

Mo, Shanlie., 莫善列. January 2012 (has links)
Capillary-based analytical methodologies were developed to meet the need for metabolite determination in two major areas. The first area is the determination of free bilirubin in sera for the management of jaundiced neonates under critical conditions. Three sensitive detection techniques were investigated, Quantum dots (QD) mediated fluorescence, Chemiluminescence (CL) and Microelectrode detection. Four different types of QDs were synthesized for the direct bilirubin determination. The CAH-capped CdTe QDs were selected as it shows the best performance compared to organic dyes and other QDs. Its optimized preparation conditions are: refluxing solution containing Cd/Te/CAH (1:0.5:2.4 w/w) for 4 hours at 100 °C. From Transmission Electron Microscope characterization, nano-size QDs with an uniform size distribution, high luminescence and good stability were obtained. The optimized detection conditions were: incubation of bilirubin with CAH-capped CdTe QDs (5 10-6 mol/L) in water at pH=5.6 and 20 oC for 8 min prior to spectrofluorometric determination (λex=473 nm and λem=580 nm). A linear working range from 0.043-0.86 μg/mL with 0.9943 correlation coefficient and 2 ng/mL detection limit (LOD, S/N=3) were achieved. Results from nFIA-CL indicate a quick response within seconds though a poorer LOD (S/N=3) of 15 μg/mL for the direct bilirubin determination. The third technique investigated used an enzyme microelectrode and it was found to be able to couple with capillary electrophoresis (CE) in frontal analysis (FA) for the determination of free bilirubin in serum samples. Making use of the micron size of the carbon-fiber electrode, a new MCNTs (Multi-wall Carbon Nanotubes) modified CFMEs (Carbon fiber microelectrodes) was fabricated within a microchip-CE device with three guided channels to enable electrodes alignment. Method to immobilize bilirubin oxidase (BOD) onto the CFMEs surface by the carbodiimide chemistry achieved the highest detection sensitivity. Under optimized conditions (sample introduced by hydrodynamic injection at △H (20 cm), and a running/detection buffer (10 mM phosphate) at pH 7.4, working potential for amperometric detection at +0.8 V), a linear working range between 1-40 μg/mL and a detection limit (S/N=3) at 0.15 μg/mL for free bilirubin was achieved. The second area for metabolite determination was developing a new analytical method for the management of APL (acute promyelocytic leukemia) patients under arsenic treatment, a drug required continued monitoring. The analytical requirements include a high detection sensitivity and the capability to provide timely results for multiple drug residues. Using a 20 mM phosphate as the running buffer and 0.05mM CTAH (Cetyl-trimethyl-ammonium hydroxide) as an additive for EOF reversal, co-EOF (co-electroosmotic flow) stacking was established to enhance up to 200 times of the detection limit for arsenite. Satisfactory baseline separation for arsenite, arsenate, MMA (Methylarsonic acid) and DMA (Dimethylarsinic acid) was achieved with linear working ranges (correlation coefficients > 0.999) from 1-50 μg/mL for arsenate and DMA, 0.5-50 μg/mL for MMA as well as 0.1-50 μg/mL for arsenite. Detection limits (S/N=3, n=3) achievable for arsenate, arsenite, MMA and DMA were found to be 0.41 μg/mL, 0.01 μg/mL, 0.04 μg/mL and 0.32 μg/mL respectively at levels meeting the requirement for APL patient urine monitoring. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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