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1
Grice, I. Darren, i n/a. "Some New Aspects of Radical Trapping Using an Aminoxyl Radical Trap". Griffith University. School of Science, 1993. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20050915.150556.
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An investigation of the initiation mechanism in the free radical copolymerisation of acrylonitrile and vinyl acetate using the aminoxyl radical trapping technique, employing 1,1 ,3,3-tetramethyl-2,3-dihydro- 1 Hisoindol-2-yloxyl is reported. Based upon the experimental results, the mechanism of initiation is suggested as proceeding via the 'free monomer' mechanism. Additionally, the effect of Lewis acids on the initiation mechanism is reported. A study of the addition of phosphorus-centred radicals to alkenes and phenylacetylene, utilising the aminoxyl radical trapping technique is reported. The results indicate a decreased rate of addition by both diphenylphosphinyl and dimethoxyphosphinyl radicals to cyclic versus acyclic alkenes. In contrast to cyclic alkenes, both these phosphorus-centred radicals add readily to the triple bond of phenylacetylene. The stereochemistry of the addition of diphenyiphosphinyl and dimethoxyphosphinyl radicals and of the aminoxyl trap is discussed. The stereochemistry of the addition of benzoyloxyl radicals to a conformationally rigid alkene, trans-a2-octalin is reported. Attempts to examine the initiation mechanism in the free radical copolymerisation of styrene/maleic anhydride and of styrene/tetracyanoethylene utilising the aminoxyl radical trapping technique are described. Also described are attempts to synthesise some new phosphorus radical initiators.
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Grice, I. Darren. "Some New Aspects of Radical Trapping Using an Aminoxyl Radical Trap". Thesis, Griffith University, 1993. http://hdl.handle.net/10072/365216.
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An investigation of the initiation mechanism in the free radical copolymerisation of acrylonitrile and vinyl acetate using the aminoxyl radical trapping technique, employing 1,1 ,3,3-tetramethyl-2,3-dihydro- 1 Hisoindol-2-yloxyl is reported. Based upon the experimental results, the mechanism of initiation is suggested as proceeding via the 'free monomer' mechanism. Additionally, the effect of Lewis acids on the initiation mechanism is reported. A study of the addition of phosphorus-centred radicals to alkenes and phenylacetylene, utilising the aminoxyl radical trapping technique is reported. The results indicate a decreased rate of addition by both diphenylphosphinyl and dimethoxyphosphinyl radicals to cyclic versus acyclic alkenes. In contrast to cyclic alkenes, both these phosphorus-centred radicals add readily to the triple bond of phenylacetylene. The stereochemistry of the addition of diphenyiphosphinyl and dimethoxyphosphinyl radicals and of the aminoxyl trap is discussed. The stereochemistry of the addition of benzoyloxyl radicals to a conformationally rigid alkene, trans-a2-octalin is reported. Attempts to examine the initiation mechanism in the free radical copolymerisation of styrene/maleic anhydride and of styrene/tetracyanoethylene utilising the aminoxyl radical trapping technique are described. Also described are attempts to synthesise some new phosphorus radical initiators.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Science
Science, Environment, Engineering and Technology
Full Text
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Franco, Pujante Carlos. "Organic free radicals for molecular electronics and spintronics". Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/399515.
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La presente tesis doctoral se centra en el campo de la electrónica molecular, en particular se ocupa del desarrollo de nuevos dispositivos moleculares y del estudio de los fenómenos de transferencias electrónica asociados a ellos. Las propiedad de los policloro trifenilmetil radicales (PTM) han sido utilizadas en este trabajo para investigar los diferentes mecanismos de transferencia de carga asociados a varios sistemas en los cuales los PTM están involucrados.
En la primera parte de la tesis se ha descrito el estudio de los procesos de transferencia de carga a través de dos diferentes familias de hilos moleculares, una de vinilo tiofene y la otra de oligo-p-fenilenos vinilenos fusionado conectados a dos moléculas de PTM las cuales actúan como dadores y aceptores de electrones en sistemas de valencia mixta D-B-A. Estos sistemas han sido completamente caracterizados por diferentes técnicas espectroscópicas en sus diferentes estados de oxidación: neutro, de valencia mixta y oxidada. Además, los mecanismos para la transferencia electrónica intermolecular a través de estos hilos moleculares han sido elucidados.
En la segunda parte de la tesis ha sido reportada la síntesis de una familia de derivados de PTM con grupos tiol conectados al PTM a través de un cadena alquílica de diferentes longitudes, capaces de formar monocapas auotensambladas (SAM) sobre substratos de oro. Asimismo, se ha estudiado los mecanismos de transferencia electrónica a través de las SAMs de PTM en sus diferentes estados de oxidación, contactadas estas por el electrodo de eutéctico galio-indio y por el microscopio de efecto túnel.
Para finalizar, en la última parte de la tesis, se ha reportado el estudio de las propiedades magnéticas y eléctricas de dos derivados de PTM en break-juction unimoleculares de oro y HOPG. Interesante fue el hecho de que en las break-juction unimoleculares de oro, se detectó un pico Kondo lo que indica que el momento magnético del radical PTM interactúa con los electrones de conducción.The present Doctoral Thesis is framed in the field of molecular electronics, specifically is focused on the development of new molecular electronic devices and on the study of the electron transfer phenomena associated to them. We exploit the properties of polychloro thriphenylmethyl radical (PTM) molecules to explore the charge transfer mechanisms involved in many different systems containing PTM derivatives. In the first part of the Thesis, we have described the study of the charge transfer process through two different families of molecular wires, oligo vinylene-thiophne (nTV) and fused oligo-p-phenylene vinylene (nCOPV), connecting two PTM moieties acting as electron donor/acceptor in mixed valence systems D-B-A. These systems were fully characterized by different spectroscopic techniques in their neutral, mixed valence and oxidized states. The mechanism for the intramolecular charge transfer through these wires was elucidated. In the second part of Thesis we have reported the synthesis of a family of PTM derivatives containing a thiol terminal group connected to the PTM through an alkyl chain with different length, able to form self-assembled monolayers (SAM) on gold substrates. We have studied the charge transport mechanisms through PTM SAMs contacted by eutectic gallium-indium electrode and scanning tunneling microcopy, in their different redox states. Finally, in last part of the thesis we have reported the study of the electric and magnetic properties of two PTM derivatives in gold and HOPG single molecule break-junctions. On gold PTM break-junctions, a Kondo peak was detected indicating that the localized magnetic moment of PTM radical interacts with conducting electrons.
4
Shergill, Raminder. "Radicals and radical pairs in chemical and biological systems". Thesis, University of Leicester, 2010. http://hdl.handle.net/2381/11008.
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Magnetic fields of different strengths can be applied to chemical and biological systems to study processes involving radicals or radical pairs. This work uses two such techniques, electron paramagnetic resonance (EPR) spectroscopy (≥ 150 mT) in addition to time resolved EPR spectroscopy and time resolved infrared (TRIR) spectroscopy (≤ 37 mT). The former are used to monitor metalloproteins, and the photochemistry of phosphorus oxides, while TRIR spectroscopy is used to record the magnetic field effects on the reaction kinetics of neutral radical pairs. The thesis begins with an introduction and an overview of the experimental techniques and developments. This is followed by an EPR study of the Fe(III) binding proteins, transferrin and lactoferrin and the effect thereon of catecholamine stress hormones. Catecholamines mediate bacterial growth by sequestering iron from the iron binding proteins. The mechanism of iron capture is unknown, however, the current work reveals Fe(III) binding by the catecholamine and supports subsequent reduction as the most likely route. Since catecholamines are also administered therapeutically, the validity of EPR as a diagnostic technique is examined and iron loss from human serum transferrin is observed. Also within this work, experiments are presented in which TRIR spectroscopy is used to investigate factors that affect the development of magnetic field effects for radical pairs in different solutions. This initially involves studies on acylphosphine oxides. In addition to the reported photoprocesses, alternative chemistry is uncovered, which occurs when bisacylphosphine oxide is in solutions where the solvent is sufficiently nucleophilic. The photochemistry is investigated using time resolved EPR and density functional theory calculations to suggest three possible structures that are responsible for the additional radicals observed. Furthermore, encapsulated organic radical pairs in reverse micelles are studied. These experiments, in combination with dynamic light scattering measurements provide insight into the magnitude of the observed magnetic field effects and the differing kinetics of the radical pair in the reverse micelles.
5
Johnson, Jamie. "Continued Radicals". TopSCHOLAR®, 2005. http://digitalcommons.wku.edu/theses/240.
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If a1, a2, . . . , an are nonnegative real numbers and fj(x) = paj + x, then f1o f2o· · · fn(0) is a nested radical with terms a1, . . . , an. If it exists, the limit as n ! 1 of such an expression is a continued radical. We consider the set of real numbers S(M) representable as an infinite nested radical whose terms a1, a2, . . . are all from a finite set M. We give conditions on the set M for S(M) to be (a) an interval, and (b) homeomorphic to the Cantor set.
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Fabbri, Claudia. "Mechanistic aspects of lignin degradation. Role of radicals and radical ions". Doctoral thesis, La Sapienza, 2005. http://hdl.handle.net/11573/917334.
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Qureshi, Tariq. "Spin chemistry". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365292.
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Herbert, Nicola M. A. "Alkyl ketene radicals". Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262948.
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Addison-Jones, Brenda. "Muon spin resonance studies of fullerenyl radicals and associated organic radicals". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0011/NQ61618.pdf.
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Mendonça, Tedra Madeiral. "Estudos de danos em biomoléculas promovidos pelo ácido indol-3-acético". Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/46/46131/tde-10092018-162828/.
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O ácido 3-indol acético (IAA), um conhecido hormônio de planta, e seu metabólito indol-3-carboxialdeído (ICA) têm sido envolvidos em várias patologias humanas como fenilcetonúria e doenças renais. A formação de espécies reativas de oxigênio e de estados eletronicamente excitados, como o oxigênio singlete (1O2) e a carbonila triplete (R2-C=O*), durante a oxidação aeróbica do IAA catalisada por peroxidase de raiz forte (HRP) têm sido relacionada com efeitos citotóxicos do IAA. Nossos resultados indicam aumento na formação de 8-oxo-7,8-dihidro-2\'desoxiguanosina (8-oxodGuo) após o tratamento da base com o sistema IAA/HRP/O2 in vitro, medido por um detector eletroquímico acoplado a um sistema de cromatografia líquida de alta performance (HPLC-EC). O tratamento de células de mamíferos (CV1-P e neutrófilos) com este sistema induziu o aumento na formação de 8-oxodGuo no DNA, assim como o aumento no nível de lipoperoxidação das células CV1-P quando comparadas ao controle. Detectamos a presença do adulo 1,N2-etenodesoxiguanosina em DNA de neutrófilos submetidos ao IAA. Portanto, neste estudo, apresentamos evidências de danos em biomoléculas promovidos pelo sistema IAA/HRP/O2.Indole-3-acetic acid (IAA), a2 plant hormone, and its metabolite indole-3-carboxialdehyde (ICA) has been involved in several human pathologies as phenylketonuria and renal diseases. Formation of reactive oxygen species and electronically excited states as singlet oxygen (1O2) and triplet carbonyl (R2-C=O*), during the aerobic oxidation catalyzed by horseradish peroxidase (HRP) has been reported to be involved in the IAA cytotoxic effects. Our results show an increase in the formation of 8-oxo-7,8-dihydro-2\'deoxiguanosine (8-oxoxdGuo) after IAA/HRP/O2 system treatment in vitro as inferred from high performance liquid chromatography-electrochemical detection (HPLC-EC) measurements. Treatment of mammalian cells (CV1-P and neutrophils) with the system induces 8-oxoxdGuo formation in DNA as well increased levels of lipid peroxidation CV1-P cells when compared to controls. The 1,N2-etenodeoxyguanosine was detected in neutrophils DNA. Therefore, in this study, we presented evidence of biomolecule damage by IAA/HRP/O2 system.
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Ishaq, Ahtsham. "The development and use of novel green radical methodology". Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=158370.
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Over the last forty years the steady use of radical reactions as the key steps in syntheses has increased. The most commonly used radical reagent is tributyl tinhydride. However such tin based radical reagents are toxic and often contaminate the product as they are difficult to remove. As an alternative to these tin reagents, a novel NaBH4/U.V. system was developed. This system was successfully used to effect the radical reduction of various aromatic halides. In light of these results it was thought that other useful transformations such as C-C bond formation could be achieved. Radical cyclisation onto unsaturated bonds, halogen atom transfers radical cyclisation (HATRC) and 1-5 hydrogen atom translocations were explored. This, 1-5 hydrogen atom translocations, methodology has been successfully applied to the synthesis of the spirocyclic natural products (±) horsfiline and coerulescine. With this success the use of the NaBH4/U.V. system on pyridine substrates was explored. Unfortunately this was not achieved with our current understanding of this reaction. However the use of tributylgernamium hydride, which is considered a ‘green’ radical reagent when compared to tin based reagents, proved successful. The novel application of this reagent in the 1-5 hydrogen atom transfer reaction on pyridine substrates was successfully demonstrated. Its use was successfully employed in the synthesis of a pyridine based bioisostere derivative of horsfiline.
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Zhu, Hai. "Construction of carbo- and oxacycles using radical relay cyclizations initiated by alkoxy radicals". Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44759.
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An investigation of a versatile radical relay cyclization methodology for the rapid construction of carbo- and heterocycles from simple linear precursors has been presented in this thesis. This thesis mainly focuses on 1,5-hydrogen atom translocation and subsequent cyclization reactions (radical relay cyclization reactions). In Chapter 1, an up-to-date literature review of this concept (radical relay cyclization) is presented including 1,5-hydrogen translocation reactions initiated by carbon radicals as well as oxygen and nitrogen radicals. In Chapter 2, the formation of cyclopentane and cyclohexane derivatives utilizing radical relay cyclization reactions initiated by alkoxy radicals has been described. The diastereoselectivity of final carbocycles is discussed. In Chapter 3, the formation of 1,2-disubstituted tetrahydrofuran and tetrahydropyran derivatives utilizing radical relay cyclization reactions has been described. With the incorporation of an oxygen atom into the precursors, the diastereoselectivity has been increased dramatically compared to carbon analogs. In Chapter 4, the formation of 2,3,5-trisubstituted tetrahydrofuran derivatives utilizing radical relay cyclization reactions has been described. With the strategic incorporation of an oxygen atom into cyclization precursors, 1,5-hydrogen atom translocation and subsequent cyclization reactions are able to compete over direct cyclization reactions and β-fragmentation reactions through the dative control. Furthermore, the incorporation of an oxygen atom into precursors enables 1,6-hydrogen atom translocation reactions to outcompete 1,5-hydrogen atom translocation reactions. In Chapter 5, the application of this radical relay cyclization methodology for the synthesis of the tetrahydrofuran fragment within (–)-amphidinolide K has been demonstrated. The final fragment in (–)-amphidinolide K can be achieved in 60% yield with a >95:5 ratio of cis to trans isomers.
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Wickström, David. "Dawn of the radicals : The connection between economic growth and political radicalism". Thesis, Linnéuniversitetet, Institutionen för nationalekonomi och statistik (NS), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-47340.
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This thesis explores how economic performance, measured as real GDP-growth per capita, affects the vote share of parties which relies on radical ideological platforms. Using a fixed effect model with panel data, based on real electoral outcomes of 18 western European democracies, the result reveals an ambiguous reality. The overall conclusion implies that low growth rates benefit the electoral success of radical-right parties and holds for robustness checks. No solid evidence of the relationship is found on the radical-left side.The result further reveals that the individuals decision to vote radical is relative more affected by the ongoing business cycle trend between the elections rather than sudden changes close to the election day. The relationship also appears to be stronger among nations of southern Europe.
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Shah, Hitesh. "Studies of aminyl radicals". Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/26945.
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This section contains a brief overview of alkyl radicals in synthesis and methods for their generation. The aminyl radical section gives a brief description of the nature of the radical and then proceeds with general techniques used, or now abandoned, for aminyl radical formation. It also reviews amidyl, aminium cation and Lewis acid metal complexed aminyl radicals describing their superiority over neutral aminyl radicals. Various methodologies are also described using aminyl radicals in the synthesis of heterocyclic and natural products.
15
Barbiero, Gennaro. "Chemistry of biphenoxy radicals". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0026/NQ29884.pdf.
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Sherburn, Michael S. "Radicals and reactive rings". Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277935.
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Critchley, Andrew Duncan James. "Structure of free radicals". Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327188.
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Lu, Zhou. "Mesomorphic organic stable radicals". Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/8702/.
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Araujo, Deborah de Arantes e. Oliveira Valim 1972. "Avaliação da gastroproteção do óleo essencial do Protium heptaphyllum March (Burceraceae) bem como os possíveis mecanismos de ação envolvidos em modelos de úlcera gástrica em ratos : Evaluation of gastroprotection essential oil Protium heptaphyllum March (Burceraceae) and the possible mechanisms involved on experimental gastric ulcer models in rats". [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/313745.
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Orientadores: Alba Regina Monteiro Souza Brito, Anderson Luiz FerreiraDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas
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Resumo: Protium heptaphyllum March (Burseraceae), conhecido como almécega ou breu branco, é uma planta medicinal abundante na região Amazônica. Seu exudato resinoso in natura é um conceituado remédio popular com ação anti-inflamatória, antiulcerogênica, analgésica e cicatrizante. O gênero Protium compreende cerca de 135 espécies, estima-se que a maioria das espécies da família Burseraceae pertençam a este gênero, tendo como principal característica sua capacidade em exsudar resinas aromáticas voláteis, usadas como curativo de feridas, tratamento de dor de dente, antisséptico, analgésico e distúrbios gastrointestinais. O objetivo deste trabalho, foi avaliar o potencial gastroprotetor do óleo essencial comercial do Protium heptaphyllum March (Burseraceae) (BB), bem como os possíveis mecanismos de ação envolvidos, através de modelos de úlcera gástrica em ratos Unib:WH. A análise de cromatografia gasosa-espectrometria de massa (CG-EM) do BB indicou a presença de três monoterpenos majoritários: ?-pineno (40%), p-mentha-1.4(8)-dieno (12%) e ?-phellandreno (10%). Foram realizados diferentes modelos experimentais de úlcera gástrica que, com base em suas respectivas especificações, foram incluídos dois grupos controles, sendo um positivo (Lansoprazol 30 mg/kg, Carbenoxolona 200 mg/kg ou Cimetidina 100 mg/kg) e um negativo (Veículo - Tween 80® 12%, 10 mL/Kg). Após cada experimento, foi realizada eutanásia por deslocamento cervical, os estômagos removidos, abertos na região da maior curvatura e fotografados para quantificação da área de lesão ulcerativa (ALU) por meio do programa AVSoft®. O BB, na dose de 100 mg/Kg (dose mais efetiva), apresentou atividade antiulcerogênica contra lesões gástricas induzidas por etanol absoluto (96%) e por Drogas ant-inflamatórias não esteroidais (DAINEs) (97%). Para avaliar os mecanismos de ação envolvidos a atividade antissecretória, muco, prostaglandina, atividade antioxidante e envolvimento dos Grupamentos Sulfidrila (G-SH), foram analisados. Além disto, o modelo de úlcera gástrica induzida por ácido acético e análise por Western blotting da expressão de COX-2 e EGF foram utilizadas para avaliar a capacidade cicatrizante do BB. Foi verificado que este óleo essencial não interfere na secreção ácida na mucosa gástrica; porém, sua gastroproteção depende de compostos com G-SH. A atividade gastroprotetora do BB não ocorre devido ao aumento na produção de muco induzido pelos níveis gástricos de PGE2. Como o BB não atuou nos mecanismos citoprotetor e antissecretório, objetivou-se verificar o envolvimento do mecanismo antioxidante na atividade gastroprotetora. Existem evidências de que espécies reativas de oxigênio participem na etiologia da úlcera gástrica e muitos óleos essenciais foram recentemente qualificados como antioxidantes naturais. A capacidade do BB de reduzir ou prevenir estresse oxidativo foi avaliada in vivo, a partir de modelos de úlcera induzida por etanol absoluto. O BB apresentou atividade antioxidante modulando enzimas antioxidantes como Superóxido Dismutase (SOD), Glutationa Peroxidase (GSH-Px) e Glutationa Redutase (GSH-Rd), desta forma, diminuindo a peroxidação lipídica (LPO) e atividade da Mieloperoxidase (MPO). BB demonstrou também potente capacidade de cicatrização, com 95% de redução da ALU, aumentando a expressão de COX-2 (55%) e EGF (100%) na mucosa gástrica. Em adição, nenhum sinal de toxicidade foi observado durante os 14 dias de tratamento, considerando os parâmetros analisados. Portanto o BB é composto essencialmente por terpenos, não apresenta atividade antissecretora nem citoprotetora, apresenta atividade antioxidante e cicatrizante
Abstract: Protium heptaphyllum March (Burseraceae), known as "Almécega" or "Breu Branco", a medicinal plant is abundant in the Amazon region, its resinous exudates in nature, is a renowned folk remedy with anti-inflammatory, antiulcer, analgesic and healing. Protium genus comprises about 135 species, it is estimated that most species of Burseraceae, belong to this genus, the main feature, its ability to exude volatile aromatic resins, used for various purposes such as dressing for wounds, pain tooth, antiseptic, analgesic, treatment of stomach, among others. Based on the popular indications of this plant for the treatment of gastrointestinal disturbances, the present work aimed on evaluating the gastroprotective potential of the commercial essential oil of Protium heptaphyllum March (Burseraceae) (BB), as well as its possible mechanisms of action involved, through models of gastric ulcer in rats Unib: WH. Gas chromatography-mass spectrometry (GC-MS) analysis of BB indicated the presence of three majority monoterpenes as major compounds: ?-pinene (40%), p-mentha-1.4(8)-diene (12%) and, ?-phellandreno (10%). We performed different experimental models of gastric ulcer, based on your specifications included two control groups, a positive (Lansoprazole 30 mg/kg, Cimetidine 100 mg/kg or Carbenoxolone 200 mg/kg) and a negative (Vehicle - Tween 80, 12%, 10 mL/Kg). After each experiment, rats were killed by cervical dislocation, their stomachs removed and opened in the region of greater curvature and photographed for quantification of lesion area ulcerative through the AVSoft program. BB at a dose of 100 mg / kg (effective dose) showed antiulcer activity against gastric lesions induced by absolute ethanol (96%) and nonsteroidal ant-inflammatory drugs (NSAIDs) (97%). To evaluate the mechanisms involved in the BB aniulcerogenic activity, the antisecretory action, mucus, prostaglandins, antioxidant activity and involvement of sulfhydryl group (G-SH) were analyzed. The acetic acid-induced gastric ulcer model and western blotting assay COX-2 and EGF were also used to evaluate the BB healing capacity. This essential oil does not interfere with acid secretion in the gastric mucosa, but their gastroproteção depends on G-SH compounds. The gastroprotective activity of the BB is not due to increased production of gastric mucus induced by PGE2 levels. As the BB did not act in cytoprotective mechanisms and antissecretório, aimed to verify the involvement of the antioxidant mechanism in gastroprotective activity. There is evidence that reactive oxygen species involved in the etiology of gastric ulcer and many essential oils have recently been classified as natural antioxidants. The role of the essential oil in reducing or preventing the oxidative stress was evaluated in vivo, from absolute ethanol-induced gastric ulcer model. The BB showed antioxidant activity by modulating antioxidant enzymes like Superoxide Dismutase (SOD), glutathione peroxidase (GSH-Px) and glutathione reductase (GSH-Rd), thereby decreasing lipid peroxidation (LPO) and activity Myeloperoxidase (MPO). The BB has demonstraded potent healing capacity, with 95% reduction of the ulcerative lesion area due to increased expression of COX-2 (55%) and EGF (100%) in the gastric mucosa. In addition, no signs of toxicity were observed during the 14 days of treatment, considering the analyzed parameters. So BB is composed mainly of terpenes, shows no activity antissecretora or cytoprotective, exhibits antioxidant activity and healing
Mestrado
Farmacologia
Mestre em Farmacologia
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Guarienti, Cíntia. "Potencial antioxidante da microalga spirulina frente a condições de estresse oxidativo". reponame:Repositório Institucional da FURG, 2009. http://repositorio.furg.br/handle/1/2918.
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Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Engenharia e Ciência de Alimentos, Escola de Química e Alimentos, 2009.Submitted by Caroline Silva (krol_bilhar@hotmail.com) on 2012-08-27T19:37:20Z No. of bitstreams: 1 dissertao cintia_defesa.pdf: 808863 bytes, checksum: d9ab57cfdbf88e2f2fc31318462a352c (MD5)
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As propriedades nutricionais da microalga Spirulina têm sido relacionadas com possíveis propriedades antioxidantes, caracterizando-a no âmbito dos alimentos funcionais. Os antioxidantes são compostos que atuam inibindo e/ou diminuindo efeitos desencadeados pelo estresse oxidativo, conservando a harmonia entre a produção fisiológica de radicais livres e sua detoxificação. Objetivou-se avaliar o potencial antioxidante da microalga Spirulina e seu principal pigmento, a ficocianina, em situações de estresse oxidativo induzido. Foram realizados estudos com células da levedura Saccharomyces cerevisiae, submetidas a estresse oxidativo pela adição de 1,1´-dimetil-4,4´-bipiridilo (paraquat) nas concentrações 0, 10 e 15 mM, avaliando o potencial antioxidante da Spirulina através da sobrevivência celular (plaqueamento) e da lipoperoxidação (índice de substâncias reativas ao ácido tiobarbitúrico, TBA). Também foi avaliado o efeito protetor da Spirulina e/ou da ficocianina em córtex cerebral de ratos submetidos a estresse oxidativo por administração de glutamato monossódico ou por situação de pânico. No córtex dos animais foram avaliados os índices de TBA e a atividade específica das enzimas superóxido dismutase (SOD) e catalase (CAT). O uso do herbicida paraquat nas concentrações 10 mM e 15mM, diminuiu a sobrevivência celular da levedura em relação ao controle (39,4 % e 17,1%, respectivamente) e aumentou significativamente a lipoperoxidação (p≤0,05). O agente estressor glutamato monossódico provocou aumento significativo (p≤0,05) da lipoperoxidação e diminuição significativa (p≤0,05) das atividades específicas das enzimas SOD e CAT no córtex cerebral dos ratos. O estresse por situação de pânico também provocou alterações significativas (p≤0,05) no córtex dos ratos, aumentando a peroxidação lipídica e a atividade da enzima SOD e diminuindo a atividade da enzima CAT. O uso da Spirulina, bem como da ficocianina, atenuaram os efeitos deletérios decorrentes do estresse oxidativo induzido em células de leveduras e em córtex de ratos, mantendo os parâmetros dos grupos tratados com estressor e antioxidante estatisticamente iguais aos do grupo controle. Estes resultados contribuem com a caracterização da microalga no âmbito dos alimentos funcionais antioxidantes.
The nutritional properties of the microalgae Spirulina have been related with possible therapeutical properties, characterizing it in the scope of functional and nutraceutical foods mainly had its antioxidant potential. The antioxidant substances are composites that act inhibiting and/or decreasing the effect unchained of oxidative stress, conserving the balance between physiological production of free radicals and its detoxification. It was objectified to evaluatethe antioxidant potential of the microalgae Spirulina and its main pigment, the phycocyanin, in situation of oxidative stress induced. studies whit cells of Saccharomyces cerevisiae yeast had been carried, submitted oxidative stress for the addition of 1,1´-dimetil-4,4´-bipiridilo (paraquat) in concentrations 0, 10 and 15 mM, evaluating the antioxidant potential of the Spirulina throught the cellular survival and reactives substances index to the tiobarbituric acid (TBA). Also was evaluated the protective effect of the Spirulina and phycocyanin, in cerebral cortex of rats submitted to oxidative stress induced for glutamate monosodic administration or panic situation. In the cortex of animals the TBA index, and activity of enzymes superoxide dismutase (SOD) and catalase (CAT) had been evaluated. The use of paraquat in concentrations 10 mM and 15mM, decreased yeast cellular survival in relation to the control (39.4% and 17.1%, respectively) and increased the lipoperoxidation significantly (p≤0,05). The estressor agent glutamate monossodic provoked significant increase (p≤0,05) in lipoperoxidation and significant reduction (p≤0,05) of enzymes SOD and CAT in the cerebral cortex of the rats. The oxidative stress for panic situation also provoked significant alterations (p≤0,05) in the cortex of the rats, increasing the lipidic peroxidation and the activity of enzyme SOD and diminishing the activity of enzyme CAT. The use of the Spirulina, as well as phycocyanin, had attenuated the decurrent deleterious effect of oxidative stress induced in cells of yeast and in cortex of rats, keeping the parameters of the groups dealt with statistical equal stressor and antioxidant substance to the ones of the group has controlled. These results contribute with the characterization of the microalgae in the scope of antioxidant functional foods.
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Ryzhakov, Dmytro. "Désaromatisation radicalaire d'indoles pour la synthèse de spiroindolines trifluorométhylées ou phosphorées". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS366.
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Les spirooxindoles se retrouvent fréquemment dans les produits naturels et les composés biologiquement actifs. Certains principes actifs pharmaceutiques contenant un motif spirooxindole ont également été décrits, stimulant un grand intérêt pour la construction et la modification de ce squelette. Cependant, peu de travaux ont été réalisés pour remplacer le carbonyle en position 2 par un autre groupe fonctionnel d’intérêt. Basées sur l’expertise reconnue de notre équipe en désaromatisation d’indoles par umpolung et l’importance des fonctions CF₃ et PO(OR)₂ nous avons entrepris la synthèse de 3,3-spiroindolines substitueés en position 2 par un trifluoromethyl ou un phosphonate. Nous avons ainsi généré des radicaux trifluoromethyl ou phosphonyl par oxydation respective de trifluoromethyl sulfinate de sodium et de phosphites. Les espèces radicalaires obtenues peuvent ensuite s’additionner sur la position 2 des indoles et effectuer la désaromatisation d’indolesSpirooxindoles are frequently found in natural products and biologically active compounds. Certain pharmaceutical active ingredients containing a spirooxindole motif have also been described, stimulating great interest in the construction and modification of this structures. However, not a lot of work has been done to replace the carbonyl in position 2 with another functional group of interest. Based on the recognized expertise of our team in deflation of indoles by umpolung and the importance of CF₃ and PO(OR)₂ functions, we have undertaken the synthesis of 3,3-spiroindolines substituted in position 2 by a trifluoromethyl or a phosphonate . We have thus generated trifluoromethyl or phosphonyl radicals by respective oxidation of sodium trifluoromethyl sulfinate and phosphites. The radical species obtained can then be added to the position 2 of the indoles and perform the dearomatization of indoles
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Blasi, Davide. "Molecular and supramolecular strategies for highly luminescent trityl radicals and their sensing applications". Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/405307.
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Dentro del campo de la óptica y de la optoelectrónica, los radicales orgánicos se están convirtiendo en prometedores materiales gracias a su configuración de capa abierta. En este marco, el objetivo de esta tesis ha sido el desarrollo de radicales tritilo fotoestables y altamente luminiscentes.
En el capítulo I, tras una introducción sobre la luminiscencia, se describirán las propiedades ópticas de los radicales libres de carbono central, centrándose en las capacidades y perspectivas que ofrecen estas moléculas en la microscopía de fluorescencia y en dispositivos electroluminiscentes.
En el capítulo II, se presentarán las propiedades ópticas de los radicales tris(2,4,6-triclorofenil)metilo (TTM) y perclorotrifenilmetilo (PTM) cuando se emplean como especies emisoras en nanopartículas orgánicas (ONPs) y en películas poliméricas. Además, a pesar de que existe un amplio conocimiento sobre las propiedades luminiscentes de estos radicales en solución, no hay estudios acerca del efecto del confinamiento de estos radicales en matrices rígidas orgánicas. Como sistemas huéspedes, se han escogido el tris(2,4,6 triclorofenil)metano (TTM-αH) y el poli(metilmetacrilato) para nanopartículas orgánicas y películas, respectivamente. De especial interés resulta el caso del TTM dopado con nanopartículas orgánicas (TTMd-ONPs) en el que se observa, por primera vez, la formación de excímeros en radicales libres de carbono central. Ambos sistemas resultan de gran interés ya que, por primera vez, se observan emisiones de excímeros desde radicales libres de carbono central debido a la formación de pares de radicales supramoleculares estables y persistentes. Gracias a su emisión en la zona NIR-roja (650-800 nm), estos materiales basados en excímeros de radicales libres se han convertido en materiales moleculares muy prometedores para la bioimagen y en aplicaciones optoelectrónicas.
En el capítulo III, se estudiarán los procesos de asociación y disociación de los excímeros de TTM (estructura molecular, naturaleza del receptor, efectos térmicos). En particular, se ha encontrado que el TTMd-ONPs ofrece la posibilidad de ser utilizado como nanotermómetro rentable y radiométrico. En este marco, se ha estudiado la salida ratiométrica de la suspensión acuosa de TTMd-ONPs al 20% en diferentes condiciones de polaridad, fuerza iónica y pHs, con el objetivo de probar su posible aplicación como biosensor térmico.
Finalmente, en el capítulo IV, se presentará la síntesis del primero ejemplo de polibromotrifenilmetil radical. Esta nuevo radical constituye un componente prometedor para la síntesis de radicales tritilo altamente luminiscentes y fotoestables. De hecho, gracias a la triple funcionalización de bromo en las posiciones para, este nuevo radical permite fácilmente superar la poca versatilidad sintética de los radicales policlorotrifenilmetilo. Además, en comparación con su especie análoga clorada, el radical tris (2,4,6 tribromofenil)metilo (TTBrM) presenta una absorción y emisión desplazados hacia el rojo , alta fotoestabilidad, y es capaz de formar excímeros NIR cuando se dispersa en nanopartículas orgánicas, transformándose en un radical muy prometedor para aplicaciones en bioimagen.Organic radicals are emerging as promising materials in optics and optoelectronics thanks to their open-shell configuration. In this framework, the aim of this Thesis is the development of highly luminescent and photostable trityl radicals. In Chapter I, after an overview on luminescence, the unique optical properties of carbon-centred free-radicals will be introduced, focusing on the strengths and perspectives offered by these molecules in fluorescence microscopy and electroluminescence devices. In Chapter II, a study on the optical properties of the tris(2,4,6-trichlorophenyl)methyl radical (TTM) and perchlorotriphenylmethyl radical (PTM) when used as emitting specie in organic nanoparticles (ONPs) and polymeric films will be presented. Indeed, despite the good knowledge about the luminescence properties of trityl radicals in solution, no systematic studies are reported about the effect of the confinement of radicals in organic rigid matrices. As host systems the optically neutral tris(2,4,6-trichlorophenyl)methane (TTM-αH) and poly(methylmethacrylate) for ONPs and films respectively, have been chosen. Particularly interesting is the case of TTM doped ONPs (TTMd-ONPs) in which, for the first time for a carbon-centred free-radical, it has been observed the formation of excimers. Both systems become particularly interesting because for the first time, excimeric emissions from carbon centered free-radicals will be observed due to the formation of stable and persistent supramolecular radical-pairs. Thanks to their emission in the red-NIR region (650-800 nm), these free-radical excimer-forming materials become promising molecular materials for bioimaging and optoelectronics applications In Chapter III, the processes which explain the association and dissociation of TTM excimers (molecular structure, nature of the host, thermal effects) will be studied. In particular, it will be found that TTMd-ONPs offer the possibility to be employed as cost-effective, ratiometric nanothermometer. In this framework, the ratiometric output of 20% TTMd-ONPs water suspension has been studied in different conditions of polarity, ionic strength and pHs, in order to test its possible applicability as bio thermal sensor. Finally, in Chapter IV it will be presented the synthesis of a new class of radicals, i.e. polybromotriphenylmethyl radicals. This new molecule constitutes the perfect building block for the synthesis of highly luminescent and photostable trityl radicals. In fact, thanks to its three para bromine functionalizations, this new radical allows to easily overcome the poor synthetic versatility of polychlorotriphenylmethyl radicals. Moreover, compared to the analogous chlorinated specie, the tris(2,4,6-tribromophenyl)methyl radical (TTBrM) exhibits a red-shifted absorption and emission, a higher photostability, and it is able to form NIR-excimers when dispersed in ONPs, constituting a promising radical for bio-imaging applications.
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Clark, Thomas Tyler. "Continued Radicals and Cantor Sets". TopSCHOLAR®, 2012. http://digitalcommons.wku.edu/theses/1145.
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We examine the formation of sets homeomorphic to the ternary Cantor set by continued radicals. We determine properties of bridges and gaps and calculate the thickness of the Cantor set. From this we apply information from continued fractions to continued radicals to obtain new results. We also consider the measure of several Cantor sets.
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Rudderham, John Andrew. "Tandem reactions of oxiranylcarbinyl radicals". Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/27150.
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The work described in this thesis is an investigation into the reactivity and possible synthetic applications of oxiranylcarbinyl radicals. These radicals rapidly rearrange via β-cleavage, which can proceed by breakage of either the C-O or the C-C bond. Cleavage of the latter only occurs when the molecule has a vinyl or phenyl stabilising group attached to the epoxide ring.
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Derbyshire, David Wyn. "LIF studies of simple radicals". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328636.
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Doherty, Sean. "Apoplastic proteins, enzymes and radicals". Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4376/.
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The soluble and readily extractable part of the plant extracellular matrix has been termed, the apoplast and contains a wide range of components such as, complex carbohydrates, structural proteins, enzymes and radicals that are known to be responsive to stress and developmental pressures. This thesis describes the development of a technique for the selective enrichment of apoplastic components for a range of subsequent analyses. Using this technique a number of apoplastic proteins were N-terminally sequenced and revealed 2 cell wall related enzymes, an antifungal protein and 3 auxin-binding/germin-like proteins. This technique also provided a novel approach to the further study of auxin-binding proteins via the use of affinity chromatography at their putative site of action, the apoplast. Three potential auxin-binding protiens were identified. Many attempts were made to subject the material extracted from the apoplast to the highly resolving technique of 2-dimensional electrophoresis, and during the process two unusual 2D systems were developed. These systems could be run in a small format that permitted very rapid analysis and/or using an in-gel loading strategy to subject up to 500µg of protein to 2D separation therefore permitting N-terminal sequencing from single 2D gels. Unfortunately 2D separation of apoplastic proteins was never fully achieved within the time frame of this study due to the vast degree of heterogenity present in the sample material. It did however demonstrate the very complex nature of apoplastic components. A series of experiments revealed that the tobacco leaf apoplast contained compartment specific antioxidant enzymes, some of which share physical characteristics with similar enzymes from other species. The activity of these enzymes altered in response to stress and according to the developmental age of the tissue. The reduced activity of these enzymes directly correlated to the degree of oxidative modification of apoplastic proteins illustrating that these enzymes are important in the detoxification of apoplastic radicals. Follow on experiments following the apoplastic generation of the superoxide anion and nitric oxide from impact stressed potato tuber tissue showed that radicals play important roles in the responses of plant tissue to stress, and show the first involvement of nitric oxide in plants in response to abiotic stress.
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Breen, Anthony O. "Vinyl epoxides, radicals and DNA". Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336204.
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Fiumana, Andrea. "Indole radicals in organic synthesis". Thesis, Kingston University, 2002. http://eprints.kingston.ac.uk/20697/.
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The generation and subsequent reactions of radicals formed from aryl halides is now well documented and several natural product syntheses based on aryl radical cyclisation have been reported. However, little work has been published on the generation of radicals in heteroaromatic systems such as indole. Radical reactions, particularly those involving aryl and indole radicals are reviewed. The generation of 2-indolyl radicals and their addition to a variety of radical acceptors to prepare 2-substituted indoles is presented. The addition to aromatic solvent is also reported as an alternative route to the palladium catalysed cross-coupling method for the synthesis of 2-arylindoles. Annulation of indole via indole radicals is also explored. A short synthesis of fused [1,2-a]indoles via radical addition to the benzene ring followed by rearomatisation is described. One example undergoes an unusual radical translocation/addition reaction. The mitomycin skeleton and the mode of biological action of mitomycin are briefly discussed. A new synthetic strategy is described involving a translocation/cyclisation of N-substituted 2-indolyl radicals. An attempted asymmetric synthesis of aziridinomitosenes is described. An investigation of indole C2-C3 radical cyclisation as a route to cyc1opentano[b ]indole alkaloids is described. The effects of substituents on the radical acceptor are explored. Full experimental and spectroscopy data is given for all new and key intermediary compounds.
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Balke, Willem. "Calvin and the Anabaptist Radicals /". Ann Arbor [Mich.] : UMI-Books on demand, 1998. http://catalogue.bnf.fr/ark:/12148/cb37006352v.
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Linares, Edlaine. "Papel do peroxinitrito na atividade leishmanicida de macrófagos em modelos murinos". Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/46/46131/tde-06112008-143840/.
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Os mecanismos oxidativos pelos quais macrófagos exercem atividade microbicida permanecem em discussão, e estudos com hospedeiros animais serão essenciais para elucidar tal questão. Nesse trabalho, estudamos os mecanismos microbicidas de macrófagos in vivo comparando parâmetros de infecção nas lesões de camundongos resistentes (C57Bl/6) e suscetíveis (BALB/c) ao protozoário Leishmania amazonensis. A comparação mostrou que o controle da infecção pelos camundongos resistentes é dependente da ativação de macrófagos com expressão da enzima óxido nítrico sintase induzível, síntese de óxido nítrico e extensa nitração e hidroxilação das proteínas dos parasitas dentro dos fagolisossomos dos macrófagos. O principal agente tóxico aos parasitas parece ser derivado do peroxinitrito porque a nitração dos parasitas ocorreu na ausência virtual de células polimorfonucleares e foi acompanhada de hidroxilação. Além disso, tempol um inibidor de reações de nitração mediadas por peroxinitrito, inibiu a nitração de proteínas da lesão e aumentou o número de parasitas nelas presentes. Também, estudos com parasitas em cultura confirmaram que o peroxinitrito é citotóxico aos parasitas enquanto o óxido nítrico é citostático. O camundongo suscetível se mostrou capaz de sintetizar óxido nítrico mas o fez em estágios tardios da infecção e, provavelmente, em resposta a uma infecção secundária por bactérias. Tomados conjuntamente, os resultados indicam que o peroxinitrito e radicais dele derivados são os principais agentes leishmanicidas produzidos por macrófagos in vivo.Macrophage oxidative microbicidal mechanisms remain debatable and their elucidation is likely to depend on studies with mammalian hosts. To examine macrophage microbicidal mechanisms in vivo, we compared infection parameters in the lesions of resistant (C57Bl/6) and susceptible (BALB/c) mice to the protozoan Leishmania amazonensis. This comparison demonstrated that infection control by resistant mice relied on macrophage activation with inducible nitric oxide synthase expression, nitric oxide synthesis and extensive nitration and hydroxylation of the proteins of the parasites inside macrophage phagolysosomes. The toxic agent to the parasite is likely to be peroxynitrite-derived because parasite nitration occurred in the virtual absence of polymorphonuclear cells and was accompanied by parasite hydroxylation. In addition, tempol, an inhibitor of peroxynitrite-mediated nitrations, inhibited protein nitration of the lesions and increased the number of parasites in them. Also, studies with parasite cultures confmed that peroxynitrite is cytotoxic to the parasites whereas nitric oxide is cytostatic. The susceptible mice were also able to synthesize nitric oxide but only at late infection time and, most likely, in response to a secondary bacterial infection. Taken together, the results indicate that peroxynitrite and derived radicals are the main leishrnanicidal agents produced by macrophages in vivo.
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Krudopp, Heimke [Verfasser]. "Free lipid radicals and nitroxide radicals in dispersed systems studied by EPR spectroscopy / Heimke Krudopp". Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1173163212/34.
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Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation". Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1413.
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This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.
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Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation". University of Sydney, 2006. http://hdl.handle.net/2123/1413.
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Doctor of Philosophy (PhD)This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.
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Friedline, Robert Alan. "The Reaction Kinetics of Neutral Free Radicals and Radical Ions Studied by Laser Flash Photolysis". Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11157.
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t-Butoxyl radical has been used as a chemical model for hydrogen abstractions in many enzymatic and biological systems. However, the question has arisen as to how well this reactive intermediate mimics these systems. In addressing this concern, absolute rate constants and Arrhenius parameters for hydrogen abstraction by t-butoxyl radical were measured for a broad class of substrates including amines, hydrocarbons, and alcohols using laser flash photolysis. Initially, no obvious reactivity relationship between rate constant and substrate structure was observed for these homolytic reactions. However, by closely examining the Arrhenius parameters for hydrogen abstraction, a pattern was revealed. For substrates with C-H bond dissociation energy (BDE) > 92 kcal/mole, activation energy increases with increasing BDE (as expected). However, for substrates with a lower BDE, the activation energy levels out at approximately 2 kcal/mole, essentially independent of structure. Viscosity studies with various solvents were conducted, ruling out the possibility of diffusion-controlled reactions. Entropy rather than enthalpy appears to be the dominating factor at 25°C, contributing to the free energy barrier for these reactions.
Laser flash photolysis was also used to study radical anions. Using an indirect photoexcitation method, the properties of radical anions, generated from aryl ketones, were investigated. These radical anions, such as t-butyl phenyl ketone and cyclopropyl phenyl ketone, measured to have decay rate constants of 1.0 x 106 s-1, although they are known to be persistent when studied electrochemically. They also had measured activation energies around 6.0 kcal/mole and log A values close to 9.5. By extending the molecules's conjugation, the decay rate constants increased to greater than 107 s-1, decreased their activation energy by half, and lowered the log A values to 8.0. This trend was observed in aryl ketones such as trans-1-benzoyl-3-phenyl cyclopropane. It is believed that the generation of a benzyl radical during the decay that facilitates the enhancement of the unimolecular decays. These unimolecular decays were also observed with the previously studied hypersensitive SET probes, 5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one and 1,1,-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one. The decay rate constants for these radical anions were measured to be greater than 108 s-1, driven by the formation of an aromatic ring.Ph. D.
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Gonçalves, Maria Cecilia. "Estudo experimental da polimerização via radical livre controlada em presença de radicais nitroxido (NMRP)". [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266346.
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Orientador: Liliane Maria Ferrareso LonaDissertação (mestrado) - Universidade Estadual de Campinas. Faculdade de Engenharia Quimica
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Resumo: A polimerização via radical livre controlada mediante radicais nitróxido (NMRP) tem recebido cada vez mais atenção como uma técnica para produção de polímeros com estrutura altamente controlada. Distribuições de pesos moleculares estreitas são obtidas, com polidispersidades baixas. Neste trabalho, será estudado o processo NMRP, no qual ocorre a adição de um radical nitróxido estável, como o 2,2,6,6-tetrametil-l-piperidinoxil (TEMPO) para capturar o radical em crescimento. Embora o processo NMRP de ao polímero características controladas (polidipersidades baixas e pesos moleculares que aumentam linearmente com a conversão), ainda existe um desafio nos processos controlados, por apresentarem baixas velocidades de reação. O objetivo principal deste trabalho está focado num estudo experimental do processo NMRP visando aumentar a velocidade de reação sem perder as características principais do processo. O efeito de dois iniciadores BPO (peróxido de benzoíla) e TBEC (tert-butilperóxido-2-etilhexil carbonato) foi analisado. Observou-se que o TBEC (iniciador com constante de decomposição baixa) foi capaz de aumentar significativamente a taxa de polimerização do processo NMRP, quando comparado ao BPO, pois conversões mais altas foram obtidas, num mesmo tempo de reação, mantendo a característica controlada do sistema. O uso do TBEC apresenta uma vantagem frente ao BPO em processos controlados, não somente porque reduz o tempo de reação, mas também porque concentrações menores de iniciador e controlador foram usadas, obtendo uma taxa de reação ainda maior, o que reduz o custo operacional. Para as condições estudadas, comprovou-se experimentalmente que a taxa de reação é inversamente proporcional à concentração inicial de TEMPO, para uma mesma concentração de iniciador. A análise dos resultados através da aplicação da técnica de planejamento de experimento auxiliou numa melhor compreensão do sistema e na obtenção de condições ótimas de operação para se obter baixas polidispersidades e baixos tempos de polimerização
Abstract: NMRP process (Nitroxide Mediated Radical Polymerization) has received increasing attention as a technique for production polymers with highly controlled structures, narrow molecular weight distribution (MWD) and polydispersity index dose to 1.0. In this work 2,2,6,6-tetramethyl-l-piperidinoxyl (TEMPO) is used as the stable radical to reversibly terminate the growing polymer chain. Polymerizations were performed in ampoules, using TBEC (tert-butylperoxy-2-ethylhexyl carbonate) and BPO (benzoyl peroxide) as initiators. With the purpose of enhancing the reaction rate for NMRP process maintaining the controlled and living characteristics of the polymer synthesized (low polidispersity and molecular weights increasing linearly with conversion) an experimental study was done to evaluate the effect of two different initiators (BPO and TBEC). It was observed that TBEC (initiator with low decomposition rate) was able to enhance significant1y the polymerization rate compared to BPO, keeping the living and controlled characteristics of the system. The results show that TBEC seems to be a promising initiator that make the NMRP process more efficient, not only because it reduces the polymerization time, but also because it allows smaller amounts of controller and initiator to be used. For the operational conditions studied, experimental results with TBEC exposed that the polymerization rate in inversely proportional to the initial concentration of TEMPO, for the same amount of initiator. Using a statistical planning, it was possible to obtain a better understanding of the system and to search for operating conditions that bring low polydispersity and low reaction rates. Finally, the results are expected to have significant benefits for controlled polymerization on an industrial setting
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química
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Liu, Jinjun. "Laser-induced fluorescence spectroscopy of the alkoxy radicals". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1169752930.
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Lahib, Ahmad. "Analytical Developments for Measuring Atmospheric Peroxy Radicals". Electronic Thesis or Diss., Ecole nationale supérieure Mines-Télécom Lille Douai, 2019. http://www.theses.fr/2019MTLD0022.
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Les radicaux peroxyles (HO2 et RO2) sont des espèces clés en chimie atmosphérique. Avec le radical hydroxyl (OH), ils sont impliqués dans les mécanismes d’oxydation conduisant à la formation de polluants secondaires tels que l’ozone et les aérosols organiques. Comparer les mesures ambiantes de ces espèces à très courte durée de vie aux concentrations issues de modèles de boîte permet d’évaluer la robustesse des mécanismes chimiques implémentés dans les modèles atmosphériques. Cependant, ces mesures ambiantes sont très difficiles à réaliser et quelques techniques seulement sont disponibles pour les mesures de terrain.L’objectif principal de ce travail est d’améliorer nos connaissances sur deux de ces techniques : l’Amplification Chimique (CA) et la Fluorescence Induite par Laser des ROx (ROxLIF). La technique CA, simple et bon marché, permet la mesure de la somme HO2+RO2 et constitue une bonne solution pour le terrain. La technique ROxLIF, plus complexe, permet de mesurer distinctement HO2 et la somme des RO2. Dans une première partie, un amplificateur à deux voies d’échantillonnage a été construit à l’IMT Lille Douai (France) et caractérisé pour deux chimies d’amplification :1) au monoxyde de carbone (PERCA, PEroxy Radical Chemical Amplifer) et 2) à l’éthane (ECHAMP, Ethane CHemical AMPlifier). Dans une seconde partie, la technique ROxLIF a été implémentée sur un instrument FAGE (Fluorescent Assay by Gas Expansion) à l’Université d’Indiana (USA). Les deux outils ont ensuite été testés lors de mesures ambiantes. Dans une dernière partie, PERCA et RoxLIF ainsi qu’une troisième technique basée sur la spectrométrie de masse à ionisation chimique ont été comparés lors d’une campagne intensive à la chambre de simulation atmosphérique HELIOS à Orléans (France). Plusieurs expériences ont été menées afin d’évaluer la robustesse des mesures de radicaux peroxylesPeroxy radicals (HO2 and RO2) are key species in atmospheric chemistry, which together with the hydroxyl radical (OH), are involved in oxidation processes leading to the formation of secondary pollutants such as ozone and organic aerosols. Monitoring these short-lived species during intensive field campaigns and comparing the measured concentrations to box model simulations allow assessing the reliability of chemical mechanisms implemented in atmospheric models. However, ambient measurements of peroxy radicals are still considered challenging and only a few techniques have been used for field measurements.The main objective of this work was to improve our knowledge on two measurement techniques: CA (Chemical Amplification) and ROxLIF (Rox Laser Induced Fluorescence). CA is a chemical technique for measuring the sum of peroxy radicals (HO2+RO2) whose simplicity and low cost makes it attactive for field measurements. ROxLIF is a laser-based technique allowing to speciate HO2 and the sum of RO2. In the first part of this thesis, a two-channel chemical amplifier was built at IMT Lille Douai (France) and characterized using 2 different amplification chemistries (PERCA, PEroxy Radical Chemical Amplifer, and ECHAMP, Ethane CHemical AMPlifier). In a second part, the ROxLIF technique was implemented on an existing FAGE (Fluorescent Assay by Gas Expansion) instrument at Indiana University (United States). Both the CA and ROxLIF were tested for ambient measurements. In a last part, the CA using the PERCA approach, ROxLIF and an additional technique based on chemical ionization mass spectrometry were intercompared at the HELIOS atmospeheric chamber in Orleans (France). Several experiments were conducted to investigate the reliability of peroxy radical measurments
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Gawas, Dnyaneshwar V. "Radicals from enamines and their reactions". [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983309086.
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Maj, Stanislaw Paul. "ESR studies of organo-halide radicals". Thesis, University of Leicester, 1985. http://hdl.handle.net/2381/33795.
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Exposure of a range of dilute solutions of halogenobenzenes in fluoro-trichloromethane to 60Co y-rays at 77 K gave the corresponding cations characterised by their ESR spectra. The approximate spin-densities on the halogens were greater than predicted by comparison with neutral x-bromo radicals and increased from ca, 8% for PhF+ to 23% for PhCl+, 30% for PhBr+ and 46% for PhI+ In accord with the fall in the ionization potential for this series of halogen. For PhBr+, replacement of para hydrogen by Br, OH and SH gave a steady fall in spin-density on Br reflecting increasing n delocallsation onto the para substituent. Evidence for dimer cation formation in concentrated solutions is presented. The major species obtained from benzyl chloride suggested a preferred conformation with the chlorine close to, but not in, the plane of the benzene ring, with a significant barrier for the in-plane site, in contrast with benzyl bromide with strong hyperfine coupling to bromine [Chapters 3, 4 and 9]. Exposure of dilute solutions of Me2C(Br)C(Br)Me2 In CD3OD and MeTHF to 60Co y-rays at 77 K gave the radical Me2CC(Br)Me2. From changes in the e.s.r. spectrum of this radical, it is deduced that the stable structure is asymmetric, but that the rate of migration of bromine between the two equivalent sites becomes fast on the e.s.r. time-scale at ca. 100-1 [Chapter 6]. Evidence is given for the 1,2-intramolecular proton shift in the interconversion of isobutyl to tert-butyl radicals. The parent material was dissolved in a variety of matrices and exposed to 60Co y-rays at 77 K. The reaction was observed using an in-cavity Proportional, Integral and Differential (PID) temperature control system [Chapter 5]. A single crystal of ethyl iodide was grown and irradiated at 77 K with a a 60Co y-ray source. The spectra were orientation dependent but it was not possible to determine the principal g-values and the elements of the hyperfine tensor [Chapter 7]. 1-Bromo adamantane was dissolved in a variety of deuterated matrices and exposed to 60Co y-rays at 77 K. No firm conclusions can be drawn regarding the single proton coupling of ca. 65 G to the bromine. Exposure of dilute solutions of m-dinitrobenzene or s-trinitrobenzene in methyltetrahydrofuran to 60Co y-rays at 77 K gave two species at 77 K. One, favoured at low doses, had features characteristic of mono-anions with the unpaired electron localized on one nitro-group. At high 7-ray doses a second species with triplet state characteristics grew at the expense of the first. The average separation between the two unpaired electrons was estimated to be 5-6 A.
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Rowland, Ian J. "Halogen 6* radicals : an ESR study". Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/33878.
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The main objective of the study was to characterise, by electron spin resonance (ESR) spectroscopy, novel halogen containing a* radicals. These species are formed by ?-irradiation in a variety of halogen containing systems at liquid nitrogen temperatures. In Chapter One, a brief description of the first halogen a* radical to be identified, the Vx centre in potassium chloride (C12.-), is given in order to illustrate the general magnetic properties of the species. The dependence of these properties on the host matrix is also described. Accepted radiation damage mechanisms are presented with particular reference to dihalogen a* radicals. Some theoretical aspects of the ESR experiment is discussed in Chapter Two which explains briefly some of the phenomena encountered in the study. Sample preparation and analysis are also mentioned. Chapter Three describes the characteristics of the simplest halogen containing a* radical: the hydrogen halide radical anion. Hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide radical anions isolated in a variety of host matrices are reported. The large matrix dependence of their magnetic parameters is explained in terms of intermolecular hydrogen bonding to the halogen. Attention is focused on nitrogen-halogen a* radicals in Chapter Four, where they are shown to be radiolytically formed in ammonium halides, mono, di and trialkylammonium iodides and monoalkylammonium bromides. Alkylamanium chloride radicals could not be identified. Chapter Five primarily explores the effect of the halide counter ion on the solid-state radiolysis of some tetraalkylammonium, trialkylsulphonium and trialkylsulphoxonium cations. During the course of the investigation, sulphur-halogen a* radicals are identified in the trialkylsulphonium salts after annealing. The last chapter investigates the factors which determine the type of species formed following electron capture by carbon halogen bonds. Both adducts and a* radicals are characterised and with particular reference to the specific example of iodoacetamide, consideration is given to the factors influencing their stability.
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梁韻詩 i Wan-sze Leung. "High resolution spectroscopy of free radicals". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31237319.
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Towle, Jonathan Peter. "The LMR spectra of free radicals". Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:7ac8e9e4-33e8-428b-962d-943bf07d5f94.
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Laser Magnetic Resonance (LMR) is a very sensitive, accurate and high resolution spectroscopic technique. Transitions of paramagnetic species are brought into coincidence with a fixed frequency laser using Zeeman tuning. Three different LMR spectrometers are described, two of which use the CO laser as a radiation source and the other used optically pumped far-infrared lasers. These LMR spectrometers have been used to study four radicals, germanium hydride (GeH), tellurium deuteride (TeD), iron hydride (FeH) and iron deuteride (FeD). Transitions in the fundamental and first hot bands of the GeH radical have been detected by CO LMR. The transitions occur within both 2Π1andfrasl;2 and 2Π3andfrasl;2 manifolds. These data have been fitted with previously published data for GeH and GeD to determine the parameters of a single model effective Hamiltonian which describes all naturally occurring isotopomers. Details of the Hamiltonian are given. The same Hamiltonian was used to model transitions in the fundamental and first two hot bands of the TeD radical that were also recorded using CO LMR. Resonances from the seven most abundant isotopomers, including the two with I = ½, have been identified. Seven transitions in the fundamental band of FeH have been observed using Faraday CO LMR. Due to the complicated electronic structure for FeH it is not possible to model these data using a single model effective Hamiltonian. It has been possible to fit the parameters of a second order Zeeman expression to these FeH data and so determine accurate zerofield transition wavenumbers for six of these transitions. Pure rotational transitions in the ground state of FeD have been observed using FIR LMR. As for FeH the parameters of second order Zeeman expressions can be fitted to these transitions and zero field wavenumbers determined.
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Gibson, Mandy. "Intramolecular trapping of aromatic #sigma#-radicals". Thesis, Queen's University Belfast, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266706.
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Mackay, David Bain. "Specific carbohydrate radicals and spin trapping". Thesis, University of Aberdeen, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277363.
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γ-irradiation of solid sugars produces a large number of radicals, detection of which is possible by e.s.r. However, unambiguous interpretation of these e.s.r. signals is extremely difficult either by direct measurement or by spin trapping/hplc methods. The present study set out to prepare specific sugar spin adducts and to compare their e.s.r. spectra with those obtained by spin trapping radicals present in γ-irradiated solid sugars. In this way unambigous identification of the spin adducts may be achieved. Most specific carbohydrate radicals have previously been prepared using tri-alkyl tin radicals and protected halo-sugars in organic solution. To impart water solubility to the tin radicals, the preparation of hexa(3-pyridyl-1'-oxide)ditin was attempted and resulted in the synthesis of a new tetra(3-pyridyl)tin. Model halogeno compounds on reaction with the carbon dioxide radical anion CO2.-, gave radicals which were trapped with 2-methy-2-nitrosopropane (MNP)) and the adducts identified by e.s.r. Both carboxylic acids, and ketones with an adjacent halogen, underwent reductive elimination to form on spin trapping, the dehalogenated spin adduct. Where the halogen, X = C1,Br is adjacent to a primary or secondary alcohol, oxidation occurred before dehalogenation. However, where X = I, oxidation did not occur and the corresponding deioinated radical was obtained. Iodo sugars were synthesised and selectively deiodinated using CO2.- to give specific carbohydrate radicals that were trapped with MNP and the adducts identified by e.s.r. New b N-t-butyl carbohydrate nitrones were prepared by reaction of the corresponding aldehyde and N-t-butylhydroxylamine. Derivatives were prepared by [2+3] cycloaddition reactions with styrene and dimethylacetylene dicarboxylate. Using these nitrones as spin traps, several simple radicals were trapped to give the corresponding spin adduct. The e.s.r. spectra obtained from the hydroxyl radical derived spin adducts showed small aH coupling constants in contrast to those already published for similar adducts. This is explained in terms of hydrogen bonding which fixes the conformations of these spin adducts.
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Simpson, Victoria Jane. "Spectra and kinetics of hydroxyalkyl radicals". Thesis, University of York, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329688.
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Robinson, Sean Wade. "Co-crystallisation with 1,2,3,5-dithiadiazolyl radicals". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20149.
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Ayuko, Washington O. "Free radicals as potential antitumour agents". Thesis, Aston University, 1991. http://publications.aston.ac.uk/12521/.
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The aim of this work was to use extremely low concentrations of free radical generating compounds as a 'catalyst' to trigger endogenous free radical chain reactions in the host and to selectively eliminate neoplastic cells in the host. To test the hypothesis, a number of free radical generating compounds were screened on several malignant cell lines in vitro to select model compounds that were used against tumour models in vivo. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and its derivatives were selected at the model compounds for in vivo experiments in view of their high cytotoxic potency against several malignant cell lines in vitro. The water soluble derivative, 2,2-diphcnyl-l-(2', 4'-dinitro-6'-sulphophenyl) hydrazyl (DDSH) given by subcutaneous injections demonstrated significant antitumour activities against the MAC 16 murine colon adcnocarcinoma implanted subcuta-ncously in male NMRI mice at nanomolar concentration range. 40-60% of long term survival of over 60 days was achieved (compared with control survival of 20 days) with total tumour elimination. This compound was also active against both P388 leukaemia in male BDF1 mice and TLX5 lymphoid tumour in male CBA/CA mice at a similar concentration range. However, some of these animals died suddenly after treatment with no evidence of disease present at post mortem. The cause of death was unknown but thought to be related to the treatment. There was significant increase in scrum level of malondialdchydc (MDA) following treatment, but did not correlate to the antitumour activities of these compounds. Induction of supcroxide dismutasc (SOD), and glutathione peroxidase (GPx) occurred around day 8 after the administration of DDSH. Histological sections of MAC16 tumours showed areas of extensive massive hacmorrhagic necrosis and vascular collapse associated with perivas-cular cell death following the administration of nanomolar concentration of DDSH which was probably compatible with the effects of free radicals. It was concluded that the antitumour activities of these compounds may be related to free radical and cytokinc production.
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Leung, Wan-sze. "High resolution spectroscopy of free radicals /". Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19737610.
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Gopalakrishnan, Sandhya. "Electronic spectroscopy of the alkoxy radicals". Columbus, OH : Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1051024461.
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Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xxiv, 173 p.: ill. (some co.). Includes abstract and vita. Advisor: Terry A. Miller, Dept. of Chemistry. Includes bibliographical references (p. 171-173).
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Clauss, Rainer. "Radical cyclisation studies of chiral α-acylamino radicals : a model study towards Tacaman indole alkaloid synthesis". Master's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/16138.
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Includes bibliographical references.he radical cyclisation of chiral 4,5-substituted N-acyl-2-aza-6-heptenyl radicals, derived from D-ribose, has been undertaken as a model stuay towards Tacaman indole alkaloid synthesis. The radical cyclisations were conducted using tributyltin hydride/AIBN in refluxing benzene. The α-acylamino radicals added to double bonds which were activated by an ethoxycarbonyl substituent. No reduction of the radicals by the tributyltin hydride was observed. Those radicals incorporating an isopropylidene ketal at the 4 and 5 positions as chiral auxiliary showed excellent regio- and stereoselectivity. Out of a possible 4 diastereomers, only two were obtained in a 2:8 ratio. It was established that the isopropylidene ketal directed the cyclisation stereoselectively and that no stereoselectivity was observed in the absence of the chiral auxiliary.