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1
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.
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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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Grice, I. Darren, and 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.
Full textAbstract:
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.
Full textAbstract:
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
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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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梁韻詩 and 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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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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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.
Full textAbstract:
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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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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Corlett, Gary Keith. "Laser spectroscopy of metal-containing free radicals." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30046.
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Laser-induced fluorescence (LIF) spectroscopy has been used to probe the properties of several metal-containing free radicals, prepared in a supersonic jet expansion by either an electrical discharge or by laser ablation/photolysis. The first spectroscopic observation of the zinc monoethyl radical was carried out following an electrical discharge through a mixture of zinc diethyl and helium. The laser excitation spectra recorded contained extensive vibrational structure, and a partial assignment is presented with the aid of ab initio SCF calculations. This was the first time an electrical discharge had been used to prepare a binary organometallic intermediate in a supersonic jet. LIF excitation and dispersed fluorescence spectra of the MgCCH free radical were obtained following laser ablation of magnesium metal in the presence of methane. This was the first observation of the electronic spectrum of MgCCH, and vibrational progressions in the metal-carbon stretching mode were assigned for both the X˜2sum+ and A 2pi electronic states. Other weak vibrational structure attributable to metal-carbon bending and carbon-carbon stretching modes is also tentatively assigned. In addition, the rotational constant was found for the A 2pi state following a simulation of the observed rotational structure. Laser ablation of calcium and strontium in the presence of benzene gave intense LIF spectra of several well-known and one unknown species. Subsequent analysis of the observed vibrational structure led to the conclusion that the CaCCCH3 and SrCCCH3 free radicals were the spectral carriers, respectively. This task was aided by a series of density-functional theory calculations. This is the first spectral observation of both species. Initial attempts at characterising the alkali metal monoxides by LIF spectroscopy are also presented. These intermediates were to be prepared by laser ablation of the corresponding metal in the presence of N2O. Early experiments focused on the monoxides of Li and Na, and currently only Li + N2O has produced an LIF spectrum. The observed structure, which is quite complex and not amenable to any simple assignment, has been tentatively assigned to the C2pi -- X2pi and C2pi -- A2sum+ systems of LiO. These preliminary findings bode well for future studies of the heavier alkali monoxides.
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Bharadwaj, Lalita Anne. "Oxygen free radicals, mediators of vascular tone." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24005.pdf.
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Buckley, C. "Transient free radicals and triplets in solution." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233411.
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Meads, Roger Francis. "Kinetics and photochemistry of transient free-radicals." Thesis, University of Canterbury. Chemistry, 1992. http://hdl.handle.net/10092/7756.
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We report here several experimental and theoretical studies of free-radicals in the gas phase. Bimolecular rate constants for the reactions
BH + NO → products k = 1.26 →!± 0.07 x 10^10 cm^3 s^-1
BH + C2H4 → products k = 1.41 →!± 0.09 x 10^10 cm^3 s^-1
CN + NH3 → HCN + NH2 k = 3.0 →!± 0.4 x 10^11 cm^3 s^-1
CN + ND2 → DCN + ND2 k = 1.5 →!± 0.3 x 10^11 cm^3 s^-1
have been measured and upper limits to the rate constants for the reactions
BH + CO → products k < 1.1 x 10^11 cm^3 s^-1
BH + CH2H4 → products k < 1.6 x 10^12 cm^3 s^-1
BH + CxH6 → products k < 9.1 x 10^13 cm^3 s^-1
BH + O2 → products k < 1.3 x 10^13 cm^3 s^-1
have been set. BH (1 ) radicals were generated by excimer-laser photolysis of diborane at 193 nm and detected by time-resolved laser-induced fluorescence. The effects of varying the temperature and the nature of the buffer gas on the reactions of BH with NO and C2H4 have been investigated. CN (2 +) radicals were generated by excimer-laser photolysis of C2N2 at 193 nm and their time evolution was monitored by absorption spectroscopy.
In addition to the rate constant measurements, the products of the reactions of CN with NH3and ND3 have been determined using mass spectrometry and infrared absorption spectroscopy. The methods of ab initio molecular orbital theory have been used to determine structures and relative energies of species which could conceivably be involved in these reactions. The results of all studies have been interpreted in relation to the mechanisms of the reactions concerned.
Prompt emission observed during the 193 nm excimer-laser photolyses of diborane and stannane has been characterised and the identity of the probable emitting species for each band observed has been assigned on the basis of band structure, known thermochemistry and the dependence of band intensity on photolysis laser power. The results obtained have been interpreted in terms of the nature of the photodissociation processes.
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Langford, Vaughan S. "Magnetooptical spectroscopy of matrix-isolated free radicals." Thesis, University of Canterbury. Chemistry, 1997. http://hdl.handle.net/10092/9269.
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This Ph.D. thesis presents the results of magnetooptical spectroscopic investigations of free radicals isolated in Ar matrices at cryogenic temperatures (≤20 K). The experiments required development of a high-resolution simultaneous magnetic circular dichroism (MCD) and absorption spectrometer, MOD4. Design, construction and commission of MOD4 comprised a significant portion of this project, and its description constitutes a substantial part of the 'Experimental' chapter of the thesis.
The results of matrix-isolation experiments on the first-row radical monohydrides, CH, NH (and ND) and OH (and OD), and the theoretical analyses of the data comprise the main body of this thesis, and are presented in three chapters. Temperature and magnetic-field dependencies of the MCD and absorption over the ranges T≈1.4 –17 K and B = 0 to ∼ 4.5 T, are interpreted in terms of a spin-orbit (SO) –crystal-field (CF) model. The data are analysed by the application of quantum-mechanical and group-theoretical techniques, utilising moment analysis and (in the case of NH) spectral simulation. These allow SO and CF parameters to be extracted. Assignments of structure observed in the spectra have also been attempted.
Radical monoanions and monocations of buckminsterfullerene (C₆₀) have been investigated in Ar matrices using MCD and absorption spectroscopy, over the ranges
T≈1.6 –30 K and B = 0 –4 T. Preliminary conclusions have been drawn from these data, concerning the symmetry of the molecules, but more experimental and theoretical work needs to be done.
Ferricenium, the radical cation of ferrocene, has been isolated in Ar (with a SF6 counter-ion) for the first time. Preliminary MCD and absorption data are presented, and show well-resolved vibronic structure; assignments to totally symmetric and Jahn-Teller-active vibrational overtones are made.
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MacPherson, A. P. "Gas phase heterocyclisation reactions of free radicals." Thesis, University of Edinburgh, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657154.
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A new strategy of the synthesis of benzofurans was extended to cases with substituents on the 2,3,5-and/or 6 positions. This involves pyrolysis of 2-allyloxycinnamate esters to generate oxygen centred radicals which cyclise with loss of carbon dioxide and an alkyl radical. Small amounts of substituted coumarin by-products were identified in some cases and their formation rationalised mechanistically. This work was extended in four ways. Firstly the use of 2-t-butylthiocinnamate ester, which generates a sulphur centred radical on pyrolysis, leads to benzothiophene in adequate yield. Secondly when the base benzene ring was replaced by thiophene the preparation of the unusual thieno[3,2-b]furan ring system was achieved. The attempted extension to seven membered ring formation by pyrolysis of 2-substituted-aryl pyrroleacrylates gave instead six membered ring products. Finally the attempted synthesis of pyrrolizine by cyclisation of N-pyrrolylmethyl radicals failed to give any products, although the precursors were successfully prepared. The intramolecular attack of phenoxyl, aminyl, benzyl and thiophenoxyl radicals on ortho disposed pyrrole rings was studied systematically. In the case of the unsubstituted pyrrole ring phenoxyl and aminyl radicals did not cyclise: products showed that 1,5-aryl shifts were taking place following hydrogen atom capture. Benzyl and thiophenoxyl radicals both led to good syntheses of fused tricyclic systems and an investigation of the chemistry of the little known pyrrolo[2,1-b]benzothiophene system was undertaken. 2,5-Dimethyl substituents on the pyrrole ring led to a variety of products in all cases studied (phenoxyl, benzyl and thiophenoxyl). These arose either by direct attack on the pyrrole ring or by an interesting radical transfer, cyclisation sequence from the methyl group. Finally, the radical transfer, cyclisation sequence was again observed when a phenoxyl radical reacted with 2,5-diphenyl substituents on the pyrrole ring. The corresponding thiophenoxyl radical gave a number of products which were separated and identified using a variety of NMR techniques, one of which was a dibenzopyrrolothiazepine, the first example of seven membered ring formation by this method.
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Yang, Guang. "Detection and assay of oxygen free radicals." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316279.
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Knight, John. "Interaction between free radicals and mucus secretions." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327216.
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Crockett, Rowena. "Generation of free radicals from heterocyclic compounds." Thesis, University of Aberdeen, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290239.
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Tetrazolinones, thiatriazole 1-oxides and meso-ionic oxatriazoles were investigated as sources of free radicals. Mono-substituted tetrazolinones decomposed at their melting points. Nitrosation and nitration of the tetrazolinone ring was unsuccessful, although alkoxyalkylation of the ring took place in ether in the presence of nitrosomium and nitronium tetrafluoroborate. The tetrazolinone ring was photolytically unstable, and both eliminated nitrogen and cycloreverted. γ-irradiation of the naphthyl deivative caused cleavage of the nitrogen-hydrogen bond to give a radical which was identified by spin trapping and esr spectroscopy. Thiatriazolyl radicals were generated from thiatriazol-1-ium salts by reduction over sodium metal. Deuterium and nitrogen-15 labelled diphenylthiatriazolium salts were prepared in the reaction between thiatriazole 1-oxides and phosphorus pentachloride or pentabromide. This allowed an unambiguous assignment of the nitrogen and hydrogen hyperfine coupling constants in the esr spectrum of the unlabelled thiatriazolyl radical. X-ray crystallographic analysis was carried out on single crystals of 2,4-diphenyl-2,5-dihydro-1,2,3,5-thiatriazol 1-oxide and 2,4-diphenyl-2H-1,2,3,5-thiatriazol-1-ium bromide. Meso-ionic oxatriazolones were relatively stable to thermolysis, whereas oxatriazolimines decomposed at their melting points. The oxatriazolones decomposed on photolysis via two mechanistic pathways, while the oxatriazol-imines were resistant to photolysis. Radicals were generated by γ-irradiation and oxidation via decomposition of the heterocyclic ring. Electrochemical reduction of nitrophenyl derivatives allowed an investigation of radicals in which the heterocyclic ring was remote from the radical centre. Photochemical reaction between the nitrophenyl derivatives of the oxatriazole and tetrahydrofuran produced oxy-nitroxide radicals which were realatively long-lived and in which the heterocyclic ring was intact. The rates of hydrolysis and crystal structures of three diacetylazolinones, including diacetyltetrazolinone were investigated with the aim of determining whether a correlation existed between bond lengths and reactivity. The relative rates of hydrolysis were found to be independent of the bond lengths. However a correlation was found between the rates of hydrolysis and the acidity of the unsubstituted azolinones.
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Stellman, Joan Lindsay. "Free radicals in the pathogenesis of delirium." Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394588.
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The aim of this thesis was to look for evidence of increased serum free radical activity in elderly hospital patients with delirium. The following parameters were measured: serum iron, copper, zinc, ascorbic acid, antioxidant activity and markers of lipid peroxidation. The results did not show evidence of increased free radical activity in patients with delirium compared to non-delirious control patients. However, the results did show that, compared to healthy community controls, inpatients with infection and delirium (Group A), or with infection only (Group C) or (unexpectedly) with delirium but without clinical or microbiological evidence of infection (Group D) showed biochemical evidence of a systemic inflammatory response. The pattern of change observed in the inpatient groups was: a reduced serum iron and transferrin saturation, reduced serum zinc, elevated serum copper and reduced plasma ascorbic acid. This pattern of change is associated with inflammation. As a result of these findings, the hypothesis is proposed that delirium represents an epiphenomenon of the systematic inflammatory response syndrome (SIRS). Reduced iron levels, reduced zinc levels and low ascorbic acid levels have all, separately, been associated with altered brain function or cognitive impairment in studies of non-inflammatory states. It is therefore argued that these biochemical changes, individually or in combination with other biochemical and immunological changes that occur during the SIRS, such as HPA axis dysfunction, may result in cognitive impairment during inflammation, and, in severe or predisposing cases, contribution to the clinical manifestation of delirium. It is suggested that the area of the brain most vulnerable to the effects of these changes and, in consequence, most likely to produce cognitive dysfunction during delirium is the limbic system and, in particular, the thalamus, hypothalamus and hippocampus.
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Mills, Tim. "Studies in free radical chemistry." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342465.
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Zhao, Zhijun. "Laser flash photolysis studies of some gas phase reactions of atmospheric interest." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31790.
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Thesis (Ph.D)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2010.Committee Chair: Wine, Paul; Committee Member: Huey, Greg; Committee Member: Mulholland, James; Committee Member: Nenes, Athanasios; Committee Member: Weber, Rodney. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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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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Hon, Nyok-Sai. "Formation, characterization, and chemical reactions of free radicals in lignin." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54437.
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Free radicals are produced in lignin during mechanical treatment and irradiation with light of various wavelengths.
During mechanical treatment, the lignin macromolecule is degraded severely as revealed by ESR and viscosity measurements. Several types of mechano-radicals are produced in lignin during the mechanical process. Among these the phenoxy radicals are rather stable, where carbon-radicals are labile at ambient conditions. Transient mechano-radicals reacted readily with oxygen molecules to produce peroxy radicals even at 77°K, but they decayed rapidly at ambient temperature.
Photodegradation of lignin was observed when macromolecule was irradiated with light of λ<3500 Å as revealed by ESR, viscosity, and weight loss. Phenoxy radicals are the predominant intermediates in the photoirradiated lignin as shown by ESR studies. Elimination of side chains of lignin phenyl propane units took effect in α-carbonyl group bearing molecules. By contrast, β aryl ether substituents adjacent to α-carbonyl groups caused ether cleavage under identical conditions of photoirradiation. This is attributed to energy transferred from excited α-carbonyl groups to the ether bonds. The α-carbonyl groups also functioned as photosensitizers accelerating photochemical reactions of lignin.
Termination and decomposition reactions of mechano-radicals and photoinduced free radicals in lignin ultimately lead to the formation of para- and ortho-quinones, carbonyl groups, and double bonds which cause the color of lignin.
These potential choromophoric groups can be partially removed from lignin by using ultraviolet light of λ> 4000 Å; and they can be completely removed by irradiation of lignin in the presence of dioxane-water with light of λ>3500 Å. Experimental findings suggest chat chromophoric groups in lignin were being trapped or blocked by dioxanyl radicals resulting in brightening. However, the photoreduced lignin-adduct suffered color reversion. This adverse effect can be prevented by using 2-hydroxy-4-methoxy-benzophenone as a photostabilizer.
The feasibility of applying photoreduction techniques to high- yield pulps was demonstrated. However, optimal experimental conditions for photoreduction of lignin in high-yield pulps have not been established yet.Ph. D.
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Beardah, Matthew Simon. "Laser spectroscopy of small metal-containing free radicals." Thesis, University of Leicester, 1999. http://hdl.handle.net/2381/30030.
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The work presented in this thesis is concerned with the preparation of small supersonically-cooled alkaline-earth metal-containing polyatomic molecules by a laser ablation method, with subsequent detection using laser electronic spectroscopy. The results of spectroscopic studies involving three alkaline-earth metal-containing free radicals are presented. A new electronic transition, the D2T,+ -X2T,+ system, of the BaOH free radical is reported. The laser-induced fluorescence (LIF) spectrum is relatively straightforward, showing a simple vibrational progression in the Ba-0 stretching mode (v3). A re investigation of the C - X system of BaOH, carried out under supersonic jet conditions for the first time, is also presented. The LIF excitation spectrum is rather more complex than expected and possible explanations for these observations are considered. Five new electronic transitions of the SrOH free radical are reported for the first time. Three of these, the 52E+-r, £2S+-*2I+ and F2T1-X21,+ transitions, show simple structure in their vibrationally-resolved LIF excitation spectra. Another new transition, the C2TI- X2I,+ transition, is remarkably complex. It is proposed that a combination of Renner-Teller coupling and a 'reverse-polarised' n orbital in the C2TI electronic state is responsible for the added complexity in the LIF excitation spectrum. The 2'2S+ - X2I,+ electronic transition of SrOH shows evidence of vibronic interaction with the nearby C2Tl state. A dispersed fluorescence study of the ground state (X2I > +) of the MgCCH radical is also presented. The results of this study, in addition to a previous FTIR-matrix isolation study, have now accounted for four out of the five fundamental vibrational frequencies of ground state MgCCH. Finally, experiments involving a newly constructed REMPI-TOF mass spectrometer are discussed. Initial test experiments involving NO, CaOH, SrOH and SrCCH show that while the mass spectrometer detection aspect of the instrument is working well, supersonic cooling has proved elusive. Possible design aspects of the spectrometer which may be affecting the supersonic cooling are discussed, along with suggestions for future improvements.
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Pooley, Simon Jonathan. "Electronic spectroscopy of some metal-containing free-radicals." Thesis, University of Leicester, 1998. http://hdl.handle.net/2381/30023.
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Laser-induced fluorescence (LIF) spectroscopy has been used to probe the properties of some metal-containing free-radicals. These radicals were formed using three different techniques; fragmentation through electric discharge, laser ablation and laser photolysis and were studied in a supersonic jet expansion. A dispersed fluorescence spectroscopic study of the zinc-monoethyl free radical was performed. From this work vibrational frequencies, particularly of the Zn-C stretching and the Zn-C-C bending modes, have determined for both the X˜ and A states. In addition several peaks in the excitation spectrum reported by Povey et al. (22500--24000 cm-1) have been assigned. Recently Professor T.A. Miller and co-workers at Ohio State University recorded rotationally-resolved LIF spectra of ZnC2H5 in the 22500--23100 cm-1 region. This study complemented the dispersed fluorescence work described above, so the author was asked to generate a model and interpret this spectra. A Hamiltonian model to simulate rotational structure of asymmetric top molecules which includes spin-rotation terms has been written by the author to form part of a spectral simulation program. This program was used to simulate the rotationally resolved LIF spectra of ZnC2H5 detailed above. Unfortunately a complete analysis has not been possible but values for the A, B and C rotational constants for many of the bands are presented here along with a analysis of the observed values of spin-rotation constants. Finally, LIF spectra of a new electronic transition of BaOH, the D˜2sum+ - X 2sum+ system has been observed. Also, the C˜ - X˜ system was reinvestigated. The C˜ - X˜ system is particularly interesting because it shows much more complexity than might be expected from previous studies. Vibrationally and partially rotationally resolved spectra are reported for both systems and the C˜ - X˜ region offers some evidence that the molecule may be bent in the excited state with a large spin-rotation interaction coupling.
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Mondon, K. J. "Enzyme inactivation by pyrimidine and purine free radicals." Thesis, Brunel University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332433.
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Ma, Tongmei, and 馬彤梅. "Cavity ringdown laser absorption spectroscopy of free radicals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B30137342.
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Lush, Rachel K. "Hydrogen atom abstraction pathways to functionalised free radicals." Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:84e82ee6-f8b4-4f11-a3d2-30af12f4e0b3.
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Radical translocation chemistry has classically been employed for the generation of carboncentred radicals as a means of remotely functionalising nominally unreactive sites. Previous work within the group had investigated vinyl radicals to effect translocation and had identified a need for a more reactive abstracting radical. In this regard, the high energy of alkoxyl radicals would facilitate rapid 1,5-hydrogen abstraction as opposed to simple reduction. This thesis describes the use of alkoxyl radicals, generated from N-alkoxyphthalimides, to abstract a hydrogen atom selectively from the α-position of a lactam ring. Alkoxyl radicals generated from precursors designed to lead to intramolecular trapping of the translocated radical were prone to β-scission in preference to 1,5-hydrogen atom abstraction. This is attributed to a combination of developing π-overlap in the transition state and stabilisation of the resulting radical both by nitrogen and the attached alkyl substituents. Incorporation of an alkenyl trap onto the lactam ring led to successful 1,5-hydrogen atom abstraction and stereoselective cyclisation, although β-scission remained the dominant pathway. Translocation initiated by nitrogen-centred radicals was investigated and it was found that 1,5-hydrogen abstraction occurred in preference to β-scission; intramolecular trapping of the translocated radical proved impossible either because the precursors were unstable to the reaction conditions or because increased steric bulk impeded hydrogen abstraction by the less reactive aminyl radical. Preparation of bicyclic pyrrolidinones via successive 5-endo-5-exo-trig cyclisations was investigated; the precursors were found to undergo direct reduction in preference to cyclisation. Alkyl or aryl groups attached to the a-acylamino carbon may lead to preferential 5-endo cyclisation by stabilisation of the developing radical in the transition state.
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Gogna, Sanjeev. "The effect of free radicals in neuronal apoptosis." Thesis, University of Warwick, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341595.
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Zaidi, Naveed Ahmed. "Ring opening/cyclisation in oxiranyl carbinyl free radicals." Thesis, Loughborough University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303179.
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Black, Michael. "Gas phase cyclisation reactions of aromatic free radicals." Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/10822.
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Robles, Eric San Jose. "Electronic spectroscopy of jet-cooled organometallic free radicals /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487776801323524.
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Nicholson, Ian. "Proton electron double resonance imaging of free radicals." Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602265.
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Puwanich, Patana. "Rapid imaging of free radicals using FC-PEDRI." Thesis, University of Aberdeen, 1999. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602006.
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In the work described in this thesis, new techniques to reduce the electron paramagnetic resonance (EPR) irradiation power required in field cycled proton electron double resonance (FC-PEDRI) and to improve the temporal resolution of FC-PEDRI have been investigated. These are the aims of this work. Details of free radicals and basic principles of EPR and EPR imaging are given and the fundamentals of NMR are also described. The principles of NMR imaging (MRI) are summarised and the essential hardware of MRI for the experiments are also described. Details of PEDRI and FC-PEDRI are also described in this thesis. It is widely realised in MRI that a surface coil, or local RF coil, generates very strong magnetic fields in the coil proximity and that the field decreases rapidly with the distance away from the coil. This should be a useful advantage to limit the EPR irradiation within the desired area of the sample. Hence, the use of a surface coil as an EPR irradiation resonator has been investigated. Not only is the EPR irradiation restricted to the area of interest close to the surface coil but a stronger RF field and high SNR are also generated in this region too. The double resonance coil assembly developed here consisted of a split-solenoid coil (for NMR) and a loop-gap resonator surface coil (for EPR). The results confirmed that the enhancement of NMR signal was higher compared to the whole-body birdcage EPR coil used previously and that the enhancement area was restricted within the proximity of the surface coil. Using the technique of rapid imaging in NMR with FC-PEDRI, fast imaging of free radicals has been investigated. A number of fast pulse sequences are presented in this thesis. A snapshot centric-reordered phase-encoding pulse sequence using the technique of population preparation has been studied and employed. With an essential ideal of EPR irradiation applied only once followed by a snapshot NMR imaging pulse sequence, the EPR power is greatly reduced and the temporal resolution is greatly improved, too. However, the experimental results showed that the image quality needed much improvement and this technique is still limited to be used with samples where the longitudinal relaxation time (Ti) is longer than 250 ms. Next, the rapid imaging of free radicals in very short Ti samples equivalent to biological tissue (typically Ti of -150 ms) was investigated. The basis of image artefacts was studied. From the experimental results, it was found that the snapshot NMR pulse sequence must be commenced very soon after the end of field cycling to avoid the signal enhancement decay. To address the problem of image artefacts, the NMR FID data have been analysed. As a result, phase shift correction and amplitude adjustment schemes have been adopted and applied to the FID data. Details of the data correction schemes are given. Experiments employing rapid imaging of free radicals in vivo using FC-PEDRI are presented. The results show that the rapid imaging in vivo using this technique are possible. However, the resulting images are still noisy. More study is required for further refinement of this technique. Experiments using EPR surface coils with rapid FC-PEDRI were also investigated. The preliminary results obtained from biological-equivalent samples show the possibility of the use of this method in in vivo experiments.
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Maia, Dayanne Lara Holanda. "Malenization reaction of castor oil in the presence of free radicals initiators." Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=16561.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorThe maleate castor oil is used in drying oils, water-soluble paints, personal care products, synthetic lubricants, etc. Initially, maleate castor oil production was studied from of maleinization reaction between castor oil and maleic anhydride. Then, maleinization reactions of castor oil were carried out using benzoyl peroxide (BPO) and di-tert-butyl peroxide (DTBP) as reaction initiator to maleate castor oil production. Reactions were carried out in a batch-type reactor. The performance of the free-radical reaction was evaluated by comparing it with the reaction carried out in absence of initiator. The response surface methodology (RSM) was used to evaluate the influence of temperature and initiator concentration on castor oil conversion into maleate castor oil in the presence of BPO and DTBP. Analysis of operating conditions by RSM showed that the most significant variable the reaction was temperature, and that the initiator concentration had little significance on the conversion of castor oil. Maleate castor oil was characterized by FTIR and NMR spectroscopy. The best conversion obtained in maleinization reaction with BPO was 94.7%, at 120 ÂC and 176.6 ÂC, when initiator concentration was 0.010% in a reaction time of 180 min. The use of BPO and DTBP was most significant on increasing castor oil conversion in 30 min and 60 min reaction, respectively. After 90 min, the use of the initiator BPO and DTBP had little influence on increasing the conversion of castor oil. Besides, it was analyzed the influence of six initiators: benzoyl peroxide (BPO), di-tert-butyl peroxide (DTBP), dicumyl peroxide (DCP), tert-butyl peroxybenzoate (TBPB), sodium persulfate (PSNA) and potassium persulfate (PSK). The use of these initiators in the reaction has contributed to reduction of reaction time. The reduction was of approximately 30 min. Sodium persulfate was shown very promising in reaction at 140 ÂC to have reached 90% conversion in only 70 min, besides the initiator of lowest cost among the studied.
O maleato de Ãleo de mamona à utilizado em Ãleos secantes, tintas solÃveis em Ãgua, produtos de cuidados pessoais, lubrificantes sintÃticos, entre outros. Inicialmente, a produÃÃo do maleato do Ãleo de mamona foi estudada a partir da reaÃÃo de maleinizaÃÃo entre o Ãleo de mamona e o anidrido maleico. Em seguida, reaÃÃes de maleinizaÃÃo do Ãleo de mamona foram realizadas utilizando o perÃxido de benzoÃla (BPO) e o perÃxido di-terc-butil (DTBP) como iniciadores de reaÃÃo para a produÃÃo do maleato de Ãleo de mamona. As reaÃÃes ocorreram num reator batelada. O desempenho das reaÃÃes por radicais livres foi avaliado comparando com as reaÃÃes realizadas na ausÃncia de iniciador. A metodologia de superfÃcie de resposta (MSR) foi utilizada para avaliar a influÃncia da temperatura e da razÃo mÃssica de iniciador na conversÃo do Ãleo de mamona em maleato de Ãleo de mamona na presenÃa do BPO e do DTBP. A anÃlise das condiÃÃes operacionais pelo MSR mostrou que a variÃvel que mais influenciou a reaÃÃo foi a temperatura, e que a razÃo mÃssica de iniciador foi pouco significante na conversÃo do Ãleo de mamona. A caracterizaÃÃo do maleato de Ãleo de mamona foi analisada pelo espectrÃmetro de infravermelho por Transformada de Fourier (IV) e por RessonÃncia MagnÃtica Nuclear (RMN). A melhor conversÃo obtida na reaÃÃo de maleinizaÃÃo com o BPO foi de 94,7%, a 120 e 176,6 ÂC, quando a razÃo mÃssica deste iniciador foi de 0,010%, em um tempo reacional de 180 min. O uso do BPO e do DTBP foi mais relevante no aumento da conversÃo do Ãleo de mamona em 30 min e 60 min da reaÃÃo, respectivamente. ApÃs 90 min da reaÃÃo de maleinizaÃÃo, a presenÃa dos iniciadores BPO e DTBP pouco influenciou no aumento da conversÃo do Ãleo de mamona. TambÃm foi analisada a influÃncia de seis iniciadores de reaÃÃo na maleinizaÃÃo do Ãleo de mamona, sÃo eles: perÃxidos de benzoila (BPO), de di-terc-butil (DTBP), de dicumila (DCP) e de terc-butil-peroxibenzoato (TBPB), alÃm dos persulfatos de sÃdio (PSNa) e de potÃssio (PSK). O uso destes iniciadores na reaÃÃo contribuiu para reduÃÃo do tempo de reaÃÃo. A reduÃÃo foi de aproximadamente 30 min. O persulfato de sÃdio se mostrou bastante promissor na reaÃÃo a 140 ÂC por ter atingido 90% de conversÃo em apenas 70 min, alÃm de ser o iniciador de menor custo dentre os estudados.
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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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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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Donato, Karen Ann. "Graft polymerization of methyl methacrylate onto polytetrafluoroethylene free radicals." Ohio : Ohio University, 1985. http://www.ohiolink.edu/etd/view.cgi?ohiou1183996024.
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L-, B. Cheton Paulette 1962. "The biological role of manganese and hydroxyl free radicals /." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63965.
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Liu, Yuyan. "Far infrared laser magnetic resonance spectroscopy of free radicals." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364594.
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Feng, Ying-Hong. "Effects of oxygen free radicals upon selected biological systems." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359462.
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Gillett, David Alan. "Transient free radicals studied by laser magnetic resonance spectroscopy." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:038bdb7e-1f8c-4112-bcea-4a0ca7ab7bcf.
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A liquid nitrogen cooled, carbon monoxide laser magnetic resonance spectrometer was used to study mid-infrared vibration-rotation transitions in the gaseous free radical NCO, in its ̅X2Π state, at very high resolution. The use of an intracavity absorption cell made possible the observation of some transitions with sub-Doppler resolution. Developments to the spectrometer extended the range of operation of the CO laser. Most importantly, a CO laser operating on overtone transitions, Δν = 2, was operated in Oxford. The Δν = 2 CO laser operates over the range 2450-3800cm-1 (4.08-2.63 μm), and the Δν = 1 CO laser over the range 1200-2100 cm-1 (8.33-4.76 μm). NCO exhibits a Renner-Teller effect in its ground electronic state, an interaction between the motion of the electrons and the bending motion of the nuclei. Vibration-rotation transitions were observed in a sequence of bands involving the excitation of the out-of-phase stretching vibration, in the region of 1900cm-1. Some of the bands involved the excited bending vibration. The Zeeman effect behaviour of the molecular energy levels, particularly in the 2Σ vibronic states, clearly showed the manifestation of the Renner-Teller effect. The Zeeman effect in the 2Σ vibronic states was considered in detail. Many of the 2Σ LMR spectra were recorded at sub-Doppler resolution. NCO is complicated to model, and unassigned LMR spectra remain. A harmonic Renner-Teller model was developed for the analysis. It was implemented by constructing an explicit matrix representation of the single electronic state N2 effective Hamiltonian, which was diagonalised exactly. A new term in this Hamiltonian, describing centrifugal distortion corrections to the Renner-Teller coupling term, was developed for the 2Σ vibronic states in order to account for anharmonic vibronic interactions.
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Bruce, Ian Norman. "Phagocytes, free radicals and endothelial injury in systemic vasculitis." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295344.
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Imrie, Christopher. "The chemistry of free radicals containing a ferrocenyl moiety." Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390393.
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Wright, N. G. "Laser induced fluorescence studies of some simple free radicals." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354707.
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