Dissertations / Theses: 'Free radical'

1

Barreto, Joao Pedro Cabaco Moniz. "Dioxygen free radical reactions." Thesis, Oxford Brookes University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389105.

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2

Euapermkiati, Anucha. "Free radical telomerisation reactions." Thesis, University of Bradford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278895.

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3

Shooter, Andrew James. "Living free radical polymerisation." Thesis, University of Warwick, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263817.

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4

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 Î²-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 Î²-scission reaction changes.

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5

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 Î²-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 Î²-scission reaction changes.

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6

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.

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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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7

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
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8

Johansson, Erik. "Free radical mediated cellulose degradation." Doctoral thesis, KTH, Chemistry, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3477.

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This thesis addresses the mechanisms involved in cellulosedegradation in general and Totally Chlorine Free (TCF) bleachingof pulp in particular. The thesis shows that the cellulosedegradation during high consistency ozone bleaching is explainedby free radical chain reactions.

By simulation, it has been shown that the number, weight andviscosity average of liner polymer chain length can be used tocalculate the number of random scissions in a linear polymer ofany molecular weight distribution, provided that there is acalibrated Mark-Houwink equation. A model describing partialdegradation of molecular weight distributions of linear polymersmeasured with viscometry was developed and verifiedexperimentally. The model predicts viscometric measurement ofchemical cellulose degradation by a rapidly reacting reagent tobe strongly dependent on cellulose accessibility.

The role of free radical reactions in cellulose degradationwas studied by varying the amount of ferrous ions and ozone addedto the cotton linters. The result was compared to the resultsobtained from cellulose of lower crystallinity (cellulose beads)by measuring average chain length. When a ferryl ion reacted withcotton linters in the presence of ozone, the very formation ofone glycosidic radical was more significant to degradation thanthe final step of forming one oxidised glycoside. The inefficientdegradation observed of the oxidation step is explainable by theamount of accessible glycosides being too small to influenceviscometry. The efficient degradation observed in associationwith the glycosidic radical formation is explained by initiationof free radical chain reactions that are propagated as long asthere is ozone in the system. As none of these phenomena werefound in the less crystalline cellulose, cellulose structureappears to be important for how free radical mediated cellulosedegradation develops.

The theory of free radical chain reactions coupled withdiffusion suggests a concentric expansion of the chain reactionsoutwards from the initial site of radical formation duringozonation of carbohydrates. This was confirmed by demonstratingfree radical chain reactions spreading from a spot of initiationoutwards during ozonation of a filter paper, using a pH-indicatorto monitor acid formation. Furthermore, the interior and exteriorof cellulose fibres doped with initiator were shown to bepermeated by small holes after ozonation.

Ethylene glycol was shown to improve the selectivity duringozone bleaching of oxygen bleached kraft pulp at pH 3. Optimalconditions were obtained at pH 3 for 25 wt% ethylene glycol. Theinfluence of ethylene glycol on selectivity is explained by aproportion of the free radical chain reactions being carried bythe ethylene glycol instead of the cellulose during ozonebleaching. The observations were summarised in the form of amodel where the observed degradations for pulp, bleached pulp andcotton fibres during both ozone bleaching and ethylene glycolassisted ozone bleaching were shown to agree with each other.

From g-irradiation of ozonised aqueous solutions of alcohol,the rate constant of superoxide formation from the peroxylradical of methanol was estimated to be 10 s^-1. Rate constants of the reactions between ozone andalkylperoxyl radicals were determined to be around 10⁴M^-1s^-1. The possibility of the reaction betweenalkylperoxyl radicals and ozone contributing significantly tofree radical chain reactions during ozonation of carbohydratesand alcohols could therefore be ruled out.

Cellulose, degradation, free radical, ozone, selectivity,ethylene glycol, alcohol, bleaching, kraft pulp, cotton linters,delignification, fibre, fibril, crystallinity, ferryl ion, freeradical chain reactions, TCF, viscometry, molecular weightdistributions, random scissions.

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9

Hancock-Chen, Tanya. "Biologically relevant free radical reactions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0019/NQ58282.pdf.

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10

Johansson, Erik E. "Free radical mediated cellulose degradation /." Stockholm : Department of Chemistry, Nuclear Chemistry, Royal Institute of Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3477.

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11

Singh, Rajinder. "Free radical ring expansion reactions." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293427.

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12

Yeung, May T. "Free radical studies in solution." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306870.

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13

Parkes, Caroline Margaret. "'Living'/Controlled free-radical polymerisation." Thesis, University of Manchester, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488186.

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14

Young, Adrian R. "Free radical cyclisation of imines." Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/15357.

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Introduction. The free radical cyclisation reaction onto an unsaturated bond is a well known synthetic pathway, where a wide range of cyclic compounds can be produced form acyclic starting materials. Up until recent years, free radical addition to multiple bonds other than carbon-carbon had been little studied. Nowadays there is much information available of radical addition to carbonyl, thiocarbonyl, nitrile and oxime ether (C=NOR) functional groups. However there has been surprisingly little detailed study of similar reactions involving imines (C=NR) or hydrazones (C=NNHR). Monocyclisation. In the early phase of the research, different types of imine were synthesised and subjected to the standard free radical cyclisation procedure (tributyl-tin hydride / AIBN, added by syringe pump to refluxing solvent) to determination of the regiochemistry of cyclisation onto imines and to assess the synthetic potential of the reaction. The results of this investigative study show that a variety of five and six-membered ring compounds can be synthesised in good yield. A similar study of hydrazones showed that fivemembered rings can be formed under the same reaction conditions. Tandem Reactions. In the next phase, the aim was to extend the methodology to produce more complex structures from acyclic starting materials. If a radical adds to the carbon atom of an imine, a nitrogen-centred (aminyl) radical is generated which can undergo subsequent addition to a suitably positioned double bond to yield a bicyclic amine. This type of reaction is known as tandem or cascade cyclisation. By this method, compounds could be synthesised which have similar structures to natural products. A range of suitably designed imines wct.5. prepared and underwent cyclisation, producing many different types of bicyclic amine in yields varying from moderate to good. The Synthesis of Natural Products. After the successful formation of key bicyclic structures, the third phase of the research aimed at the synthesis of one or more of target natural products. The synthetic strategy used in the tandem reactions outline above was. adapted for these purposes. However the synthesis of the desired compounds could not be achieved in the time, but progress towards their formation was achieved.

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15

Bebbington, Magnus W. P. "Nitrogen-directed free radical rearrangements." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:316d2379-4019-4361-937d-ff1e064f8bb9.

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This thesis describes efforts to develop new methods for the synthesis of bridged azacycles using nitrogen-directed free radical rearrangements. Free radical addition to 7-azanorbornadienes were carried out to give 7-substituted 2- azanorbornenes (Scheme a.l, X-Y = RS-H or PhSe-H). [illustration in text ...] Scheme a. 1 Nitrogen-directed homoallylic radical rearrangement via intermolecular radical addition. A conceptually novel and theoretically interesting nitrogen-directed neophyl rearrangement (Scheme a.2) was developed into a synthesis of 2- azabenzonorbornanes 2. [illustration in text ...] Scheme a.2 Nitrogen-directed neophyl-like rearrangement to 2-azabenzonorbornanes. In this case the radical 1 was generated by Barton deoxygenation of 7- azabenzonorbornanols. The effect on rearrangement of bicyclic core substitution and of aromatic ring electronics was probed in some detail, and the process was synthetically useful for a wide range of substrates. Variation of the protecting group on nitrogen was investigated and the product profiles from neophyl-like rearrangement were consistent with a process driven by the stability of a radical α to nitrogen as a result of SOMO-lone pair orbital interaction. The kinetics and mechanism of these processes are examined where appropriate, leading to estimates of rate constants for the rearrangements.

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16

Lampard, Christopher. "Studies in free radical chemistry." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336098.

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17

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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18

Read, Simon James. "Free radical pathophysiology in migraine." Thesis, University of Hertfordshire, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391365.

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19

Caddick, Stephen. "Aspects of free radical cyclisations." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330107.

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20

Qureshi, Tariq. "Spin chemistry." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365292.

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21

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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22

Farooq, Sabya. "Free radical induced oxidative DNA damage." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30749.

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Oxidative DNA damage has been implicated in processes such as carcinogenesis, mutagenesis, ageing and cell death. Reactive oxygen species (ROS) such as superoxide (O2), hydrogen peroxide (H2O 2) and hydroxyl radical (OH*) are produced in mammalian cells as a result of aerobic metabolism. However excess generation of these species by endogenous or exogenous sources can result in damage to DNA, producing a large number of sugar and base lesions. In order to understand the biological consequences of such free radical induced damage it is essential to characterise and quantitate this damage. This study describes the establishment of sensitive and specific techniques to chemically characterise and quantitate three markers of oxidative DNA damage, namely: cis-thymine glycol (Tg), 5-hydroxymethyluracil (5-OHMeU) and 8-hydroxyguanine (8-OHG). Techniques using gas chromatography/mass spectrometry (GC/MS) were established for Tg and 5-OHMeU, following their derivatisation with N-methyl-N-(tert-butyldimethylsilyl) trifluoroacetamide (MTBSTFA). Standards of Tg and 5-OHMeU were synthesised, and stable isotopically labelled analogues were prepared as internal standards. Analysis of the DNA was carried out at the base level and therefore required acidic hydrolysis of the DNA in order to release the modified and intact bases. For the quantitation of 8-OHG a novel procedure using high performance liquid chromatography (HPLC) - electrochemical detection (ECD) with guanase incubation of DNA hydrolysates was established. The established assays were used to quantitate DNA lesions in vitro and in vivo. In vitro dose response curves were established for the three markers upon gamma-irradiation of DNA. In vivo results of an animal inhalation study indicated there was not a significant increase in oxidative damage upon exposure to crocidolite. An antioxidant supplementation study in humans placental DNA also did not show a significant reduction in levels of the three markers upon supplementation. Comparable background levels of Tg and 5-OHMeU were observed in human and calf thymus DNA, while 8-OHG levels were found to be significantly higher.

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23

Nzeru, Arnold. "Polymeric macroinitiators in free radical polymerisations." Thesis, Lancaster University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369585.

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24

Mann, Emma. "Novel free radical synthesis of heterocycles." Thesis, Loughborough University, 2001. https://dspace.lboro.ac.uk/2134/14589.

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The use of tri-n-butyltin hydride and an initiator to mediate free radical cyclisation as a synthetic organic process is well documented throughout the chemical literature. By using BU3SnH, and developing new 'catalytic' BU3SnH methods, many new heterocyclic compounds have been synthesised successfully. The search for new 'tin-free' radical reagents is important in order to provide a non-toxic alternative to tin. We have started initial studies on the replacement oftriorganotin hydrides with germanium analogues. An interesting number of reactions using BU3SnH do not give reduced products and have an oxidation step in the mechanism. These BU3SnH mediated cyclisations provide a useful synthetic method. Our studies were aimed at developing the synthetic protocol as well as determining the mechanism. 'Shilajit' is an ancient tribal panacea, believed to have many advantageous biological properties. The active constituents are based upon a benzochromenone skeleton. The key component of the natural product Shilajit, 3-methoxy-6H-benzo[c]chromen-6-one, as well as several analogues have been synthesised using this BU3SnH mediated 'oxidative' free radical approach. The mechanism proposed for these reactions by Bowman et ai, the pseudo SRN I mechanism, has also been studied in order to try to determine the presence of the radical anion intermediates which are essential for the pseudo SRN 1 mechanism to be correct. The BU3SnH mediated 'oxidative' cyclisation protocol was successfully applied to electron deficient pyrroles, i.e. pyrroles with electron withdrawing substituents. Radicals generated on N-substituted chains readily undergo cyclisation onto the pyrrole ring. The protocol was also applied to cyclisation reactions of analogous imidazoles. The imidazole reactions were used for an extensive examination of the mechanism of the 'oxidative' BU3SnH protocol. The studies have disproved the pseudo SRN 1 mechanism (where BU3SnH is the oxidising agent) and suggest possible alternative oxidising agents. The importance of the functionality on the heterocyclic ring is also emphasised. Free radicals have been generated using photolytic methods, and the results are contrasted with those from traditional BU3SnH reactions. The synthesis of several substituted pyrazoles and radical cyclisation reactions were attempted on various pyrazole systems with the aim of synthesising the natural product withasomnine.

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25

Brown, Christopher. "Applications of free-radical translocation chemistry." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359598.

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26

Brumwell, Julie E. "Heterocycle synthesis using free radical cyclisations." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357926.

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27

Bradshaw, N. "Atom and free radical reactive scattering." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375081.

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28

Harkin, C. G. "Plasma diagnostics of free radical species." Thesis, University of Sussex, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383540.

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29

Bliss, Brian Irving Alban. "Exploratory Studies in Free Radical Chemistry." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1391516343.

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30

Ashraf, Naweed. "Sequence distributions in free-radical polymers." Thesis, Aston University, 1993. http://publications.aston.ac.uk/9592/.

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The initial part of this thesis is concerned with demonstrating the use of a computer simulation technique, in illustrating the sequence distribution that would be observed upon the polymerisation of a set of monomers. The power of the computer simulation technique has been demonstrated through the simulation of the sequence distributions of some generic contact lens materials. These generic contact lens materials were chosen simply because in the field of biomaterials their compositions are amongst the most systematically regulated and they present a wide range of compositions. The validity of the computer simulation technique has been assessed through the synthesis and analysis of linear free-radical polymers at different conversions. Two main parameters were examined, that of composition and the number-average sequence lengths of individual monomer units, at various conversions. The polymers were synthesized through the solution polymerisation process. The monomer composition was determined by elemental analysis and 13C nuclear magnetic analysis (NMR). Number-average sequence lengths were determined exclusively through 13C NMR. Although the computer simulation technique provides a visual representation of the monomer sequence distribution up to 100% conversion, these assessments were made on linear polymers at a reasonably high conversion (above 50%) but below 100% conversion of ease for analysis. The analyses proved that the computer simulation technique was reasonably accurate in predicting the sequence distribution of monomer units, upon polymerisation, in the polymer. An approach has been presented which allows one to manipulate the use of monomers, with their reactivity ratios, thereby enabling us to design polymers with controlled sequence distributions. Hydrogel membranes, with relatively controlled sequence distributions and polymerised to 100% conversion, were synthesized to represent prospective biomaterials. Cell adhesion studies were used as a biological probe to investigate the susceptibility of the surface of these membranes to cell adhesion. This was necessary in order to assess the surface biocompatibility or biotolerance of these prospective biomaterials.

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31

Billuart, Guilhem. "Free radical emulsion polymerization of ethylene." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10033.

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Les travaux présentés dans cette thèse portent sur la polymérisation radicalaire de l'éthylène en émulsion, dans des conditions douces (P < 250 bar et T < 90 °C). Tout d'abord, l'homopolymérisation de l'éthylène a été étudiée. Des latex stables de polyéthylène présentant des taux de solide relativement élevés (30 %) ont été obtenus. Pour cela, deux systèmes différents d'amorçage et de stabilisation (cationique et anionique) ont été employés. Ces latex peuvent trouver des applications comme revêtements hydrophobes (par exemple du papier). L'étude des propriétés thermiques des latex a mis en évidence des phénomènes de cristallisation du polyéthylène à basse température, dû à son confinement dans les nanoparticules. Cela a une forte influence sur les morphologies finales des particules. D'autre part, la copolymérisation radicalaire de l'éthylène en émulsion a été étudiée. Les comonomères utilisés sont le styrène, l'acrylate de butyle, le méthacrylate de méthyle et l'acétate de vinyle qui différent par leur solubilité dans l'eau et leurs rapports de réactivité de copolymérisation avec l'éthylène. La composition des copolymères obtenus influence leurs propriétés thermiques (Tg, Tf). Des latex stables de copolymères de compositions variées ont pu ainsi être synthétisés. Ce travail en homo- et copolymérisation a souligné la complexité des milieux de polymérisation en émulsion impliquant un monomère gazeux supercritique comme l'éthylène
In this work, the free radical emulsion polymerization of ethylene under mild conditions (P < 250 bar and T < 90 °C) was investigated. Ethylene homopolymerization was first studied. Stable polyethylene latexes of significantly high solids content (30 %) were produced. This was achieved by the use of two different initiating and stabilizing systems (cationic and anionic). These latexes could be applied as hydrophobic coatings (e.g. on paper). Investigation of the thermal properties of the latexes evidenced crystallization phenomena at low temperatures, owing to PE confinement in the nanoparticles, which strongly impacted their final morphologies. Free radical emulsion copolymerization of ethylene was then studied. The investigated comonomers were styrene, butyl acrylate, methyl methacrylate and vinyl acetate. They differ in their reactivity ratios to ethylene and their water solubility. The composition of the obtained copolymers had a strong influence on their thermal properties (Tg, Tm). Stable latexes containing copolymers of various compositions were thus synthesized. This work on homo- and copolymerization evidenced the complexity of the polymerization media involving a gaseous supercritical monomer such as ethylene

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32

Lambat, Zaynab Yusuf. "Cimetidine as a free radical scavenger." Thesis, Rhodes University, 2003. http://hdl.handle.net/10962/d1003244.

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The present study was undertaken to determine the effects and possible mechanism of action of cimetidine in cancer and Alzheimer’s disease (AD). Throughout this study emphasis is placed on free radical levels since the magnitude of the relationship between diseases and the levels of free radicals vary from one disease to another. Studies were carried out to examine the effect of cimetidine on free radical levels using superoxide formation and lipid peroxidation as indicators of free radical levels. The experiments revealed that addition of cimetidine, especially in high concentrations (0.5 and 1.0 x10-6 M) significantly inhibited WHCO6 cancer cell growth rather than cancer cell growth, as no normal control was available. Free radical formation as well as hydroxyl radical formation were reduced in the deoxyribose assay. In addition, cimetidine exhibits properties of binding to metals such as copper and iron. To maintain consistency in the experiments, a WHCO6 (Wits Human Carcinoma of the Oesophagus) cell line was used to investigate the effect of cimetidine in cancer. Neurodegeneration was induced in the rat brain using neurotoxins such as cyanide to investigate the relationship between cimetidine in AD. A decrease in cancer cell growth was accompanied by a concomitant decrease in the levels of free radicals and lipid peroxidation, suggesting that the growth-inhibitory effects of cimetidine on WHCO6 cancer cells in vitro may be due to free radical scavenging properties. This proposal was further strengthened by determination of free radical levels in the rat brain. After treatment with neurotoxins to induce neurodegeneration, the levels of free radicals in the rat brain suggest that addition of cimetidine reduces free radical levels in the rat brain in a dosedependent manner. Further experiments were done in an attempt to uncover the underlying mechanism by which cimetidine exhibits free radical scavenging properties. Metal binding studies were done using electrochemical, HPLC and UV/Vis studies. The results show that cimetidine binds iron and copper. These metals have been implicated in free radical production via the Fenton reaction. By binding with cimetidine the metals become unavailable to produce free radicals and hence cimetidine indirectly reduces the formation of free radicals. The final experiment was the determination of cimetidine as a hydroxyl radical scavenger in the deoxyribose assay. Cimetidine was shown to act as a potent hydroxyl radical scavenger, thereby confirming its activity as a free radical scavenger. In addition, cimetidine protects against damage to the deoxyribose sugar, a component of DNA. Whilst there are many theories that explain the therapeutic role of cimetidine in degenerative disease, the actual mechanism of the role of cimetidine is emphasized as a free radical scavenger. Regardless of the mechanism of action, cimetidine does inhibit tumour growth according to this study and also reduce free radical levels in neurodegeneration, which suggests a role for cimetidine as a possible additive in treatment of patients with such disease states. These findings have important clinical implications, and needs to be investigated further.

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33

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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34

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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35

Thapa, Rajesh. "Regioselectivity in Free Radical Bromination of Unsymmetrical Dimethylated Pyridines." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1263340046.

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36

Grau, Etienne. "Polymerization of ethylene : from free radical homopolymerization to hybrid radical / catalytic copolymerization." Thesis, Lyon 1, 2010. http://www.theses.fr/2010LYO10242/document.

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Ce travail concerne l'étude de la polymérisation de l'éthylène allant de l'homopolymérisation purement radicalaire jusqu'à la copolymérisation utilisant un mécanisme hybride radicalaire/catalytique. Ce travail montre que le polyéthylène peut être synthétisé par voie radicalaire dans des conditions expérimentales beaucoup plus douces que celles utilisées industriellement (P>1000 bar et T>100°C). L'éthylène a été polymérisé à partir de 10°C et 5 bar de pression d'éthylène. Un important effet activateur du solvant a été mis en évidence. De plus la polymérisation en milieu dispersé aqueux de l'éthylène a aussi été étudiée. Des latex stables de PE avec des taux de solide de 40% ont pu être obtenus. Deux morphologies de nanoparticules, cylindre ou sphère, ont été observées. La copolymérisation radicalaire avec des monomères vinyliques polaires a été également étudiée en solution ou en émulsion. Des insertions d'éthylène jusqu'à 50% ont été obtenues. De plus l'influence du comonomère et du solvant organique utilisé sur la polymérisation radicalaire de l'éthylène a été quantifiée. Une nouvelle technique de polymérisation hybride radicalaire/catalytique a été développée pour pouvoir obtenir toute la gamme de compositions possibles de copolymères éthylène/monomère polaire à partir d'un complexe de nickel qui amorce la polymérisation radicalaire et catalyse également la polymérisation de l'éthylène. Ce complexe subit une rupture homolytique réversible de la liaison nickel carbone et permet la synthèse de copolymères multiblocs. Des insertions d'éthylène de 1% à 99% ont été obtenues en faisant varier la pression d'éthylène et la concentration en comonomères polaires
This work aims to study ethylene polymerization from the free radical polymerization process to the copolymerization by a hybrid radical/catalytic mechanism. PE is synthesized by free radical polymerization under milder experimental conditions than industrial ones (P>1000 bar and T>100°C). Indeed free radical polymerization of ethylene is efficient even down to pressure of 5 bar and temperature of 10°C. Several unexpected behaviors are observed such as a high solvent activation effect. Beside the slurry process in organic solvent, polymerization in aqueous dispersed media is also performed. Stable PE latexes are obtained with solid contents up to 40%. Two different PE particles morphologies are observed cylinder-like and sphere-like. Then free radical copolymerization is studied using a broad range of polar vinyl monomers in organic solvent and emulsion. Insertions up to 50% of ethylene are obtained under mild conditions. The ambivalent role of comonomer as monomer and activator of the polymerization is highlighted. In order to obtain a wide range of composition of polar/non-polar copolymers a new technique of polymerization has been developed. A nickel complex is used to initiate the free radical polymerization and to catalyse the coordination/insertion ethylene polymerization. This nickel complex is capable of a reversible homolytic cleavage of its nickel-carbon bond. Finally, this hybrid process is used to copolymerize efficiently ethylene with various polar vinyl monomers. Multiblock copolymers with ethylene content from 1% to 99% are obtained by simply varying the monomer feeds

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37

Rawlston, Jonathan A. "Multiscale modeling of free-radical polymerization kinetics." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33933.

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Polymer chain microstructure, including characteristics such as molecular weight and branch length, can impact the end-use properties of the polymer. The assumptions contained in deterministic models prevent examination of the structure of individual polymer chains, so removal of these assumptions is necessary to gain insight into molecular-level mechanisms that determine chain microstructure. The work presented here uses a combination of stochastic and deterministic models to examine two significant mechanistic issues in free radical polymerization. The zero-one assumption concerning the number of radicals is often made for miniemulsion polymerization using oil-soluble initiators because of accelerated termination due to radical confinement. Although most of the initiator is present inside the particles, opposing viewpoints exist as to whether the locus of radical generation is the particle phase or the aqueous phase. A well-mixed kinetic Monte Carlo (KMC) model is used to simulate the molecular weight distribution and the results are compared to estimated molecular weights for several chain-stopping events, with the finding that the dominant nucleation mechanism varies with reaction temperature and particle size. Intramolecular chain transfer to polymer, or backbiting, is often assumed to produce only short-chain branches. Using a lattice KMC model, a cumulative distribution function (CDF) is obtained for branch lengths produced by backbiting. Implementation of the CDF in both a rate-equation model and the well-mixed KMC model shows that, for the butyl acrylate solution polymerization system used for comparison, backbiting is responsible for most of the branches, including long-chain branches, even though overlap of the polymer coils in the solution is predicted, a condition which would normally be expected to lead to significant intermolecular chain transfer to polymer. The well-mixed KMC model provides a more thorough analysis of chain microstructure while the rate-equation model is more computationally efficient.

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38

Dunn, Stephen Norman. "Free radical synthesis of new organofluorine systems." Thesis, Northumbria University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365437.

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39

Dunn, Stephen Norman. "Free radical syntheses of new organofluorine systems." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5194/.

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Use of the carbon hydrogen bond as a functional group in free radical addition reactions to fluoro - alkenes has been studied. Reactions involving additions of cyclic alcohols and cyclic as well as acyclic diols to hexafluoropropene, yielded selective hydroxyl group directed products in high yield. The subsequent alcohol or diol - hexafluoropropyl adducts were easily dehydrated using thionyl chloride and pyridine, forming alkenes and dienes containing a polyfluoroalkyl moety, in good yield. The resultant alkenes following bromination and epoxidation, were found to be electrophilic in nature. Furthermore, these alkenes were dehydrogenated using sulphur, yielding aromatic compounds containing the hexafluoropropyl moiety, in high yield. Additions of hydrocarbons to hexafluoropropene gave complex final mixtures, illustrating the poor selectivity of such reactions.

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40

Swales, Alan Peter. "Free-radical approaches to new fluorocarbon derivatives." Thesis, Durham University, 1989. http://etheses.dur.ac.uk/6555/.

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This thesis is concerned with the free-radical addition of nitrogen, silicon and oxygen containing compounds to fluoroalkenes and the chemistry of some of the adducts produced. Free-radical adducts of many amines cannot be produced directly since nucleophilic attack on the fluoroalkene is often the preferred reaction pathway. An alternative route to primary and secondary mono-amine adducts via N-trimethylsilylamines has been developed. An alternative synthesis of di-amine adducts via amides has met with some success. Free-radical additions of organosilicon compounds to fluoroalkenes have produced a variety of fluorosilicon adducts. The chemistry of some of these adducts has been investigated. Work with mono- and di-oxygen functional compounds has provided information on the scope and limitations of this type of free-radical addition reaction. The dehydrofluorination of ether/hexafluoropropene mono- and di-adducts has been investigated and some novel dienes have been produced. Polymers containing amide or ether groups added to hexafluoropropene under free-radical conditions. The use of a solvent dramatically increased the degree of this incorporation. The electrochemical fluorination of cyclic ether/hexafluoropropene di-adducts has been investigated. Good recoveries of highly fluorinated products were obtained, indicating that these types of adducts are good starting materials for electrochemical fluorination.

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41

Kearton, Brian L. "Controlled free radical cyclisations in imprinted polymers." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367355.

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42

Swann, Elizabeth. "An investigation of new free radical reactions." Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232882.

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43

Zhao, Zhongwei. "Free radical chemistry of iron(II) complexes." Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315384.

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44

Callaghan, Owen. "Synthetic and mechanistic studies in free radical." Thesis, University of Strathclyde, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366957.

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45

Catterall, Helen. "Mechanisms of free radical damage to DNA." Thesis, University of York, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359256.

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46

Huther, Nathalie. "Novel manganese carbonyl-mediated free radical reactions." Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403967.

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47

Upeandran, Balasubramaniam. "Novel free radical pathways to new polyhalides." Thesis, University of York, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274518.

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48

Annis, Michael Colin. "Free radical cascade reactions involving furan rings." Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394991.

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49

Sweeting, Barbara R. "The electronic spectrum of HCNN free-radical /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487676261009205.

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50

Seely, Franklin Lee. "Bis(trimethylstannyl)benzopinacolate Promoted Radical Carbon-Carbon Bond Forming Reactions and Related Studies." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1290711413.

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Dissertations / Theses on the topic 'Free radical'

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