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1
Škrabalová, Lada. "Hemoglobin-mediated oxidation of marine liposomes." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2012. http://www.nusl.cz/ntk/nusl-216833.
Abstract:
Cílem této práce bylo studium mechanismu oxidace lipidů katalyzované hovězím methemoglobinem a zhodnocení účinků různých experimentálních podmínek a antioxidantů (EDTA, askorbová kyselina, kávová kyselina, a-tokoferol, d-tokoferol, astaxanthin a L-askorbyl-6-palmitát) na methemoglobinem zprostředkovanou oxidaci lipidů v modelovém systému liposomů připravených z fosfolipidů. K monitorování oxidace lipidů při pH 5,5 a teplotě 30 °C bylo použito spotřeby kyslíku. Pro zhodnocení antioxidační aktivity v modelovém systému liposomů se ukázaly být důležitými faktory typ prooxidantu a koncentrace prooxidantu a antioxidantu. Dalšími důležitými faktory jsou struktura molekuly antioxidantu, jeho hydrofilita/lipofilita a umístění v systému. Všechny testované antioxidanty ve všech koncentracích (kromě koncentrace 0.1 % astaxanthinu and 0.1 % askorbyl palmitátu) inhibovaly oxidaci vyvolanou methemoglobinem. Účinnost antioxidantu stoupala s jeho zvyšující se koncentrací. Koncentrace 0.1 % astaxanthinu neměla žádný vliv na oxidaci liposomů. Koncentrace 0.1 % askorbyl palmitátu měla prooxidační efekt, který lze vysvětlit prooxidačním působením radikálu askorbylu, který může urychlit štěpení hydroperoxidů. Volné železo uvolněné z methemoglobinu se podílelo jen velmi málo na oxidaci liposomů, zatímco část prooxidační aktivity methemoglobinu byla přisouzena tvorbě singletového kyslíku (methemoglobin jako fotosenzitizátor). Antioxidační aktivita astaxanthinu, askorbyl palmitátu a tokoferolu byla z části přisouzena schopnosti zhášet singletový kyslík. Ovšem hlavním prooxidačním mechanismem methemoglobinu se ukázal být rozklad lipidových hydroperoxidů, tvorba volných radikálů a hypervalentních forem hemoglobinu. EDTA utlumila oxidaci liposomů díky chelataci přechodných kovů obsažených v liposomech a chelataci volného železa přítomného v methemoglobinovém roztoku. Velmi důležitým antioxidačním mechanismem (který vykazují askorbyl palmitát, askorbová a kávová kyselina) se ukázala být redukce hypervalentních forem hemoglobinu. Askorbová kyselina, kávová kyselina, tokoferoly a astaxanthin inhibovaly methemoglobinem zprostředkovanou oxidaci lipidů odstraňováním volných radikálů. Při použití peroxidu vodíku nebyl pozorován žádný vliv na oxidaci liposomů vyvolanou methemoglobinem. Působení vysoké teploty (tepelná denaturace) mírně utlumilo oxidaci. Významná inhibice oxidace byla pozorována u liposomů obsahujících TPP (triphenylphosphin), což značí, že je methemoglobinem vyvolaná oxidace liposomů závislá na přítomnosti již vzniklých lipidových peroxidů. Výsledky této práce přispívají k hlubšímu pochopení prooxidačních a antioxidačních mechanismů a faktorů, které ovlivňují oxidaci liposomálních roztoků, buněčných membrán a emulzí typu olej ve vodě stabilizovaných fosfolipidy.
2
Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation." Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1413.
Abstract:
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.
3
Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation." University of Sydney, 2006. http://hdl.handle.net/2123/1413.
Abstract:
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.
4
Hersey, Michelle. "Oxidation of Arsenite Via Chelator-mediated Fenton Systems." Fogler Library, University of Maine, 2006. http://www.library.umaine.edu/theses/pdf/HerseyMX2006.pdf.
5
Probert, Gareth David. "The zirconocene-mediated synthesis of amines." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242623.
6
Henderson, William Howell. "Palladium-Mediated C-H Activations." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1318003095.
7
Wright, Adam. "Investigations of singlet oxygen-mediated amino acid, peptide and protein oxidation." Thesis, The University of Sydney, 2002. https://hdl.handle.net/2123/27830.
8
Crosby, Natasha M. "The role of oxidation in hyperglycemia-mediated erythrocyte phospholipid asymmetry." [Bloomington, Ind.] : Indiana University, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3344761.
Abstract:
Thesis (Ph. D.)--Indiana University, Dept. of Biology, 2009.Title from PDF t.p. (viewed Oct. 8, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 0830. Adviser: David L. Daleke.
9
Kapinga, Sarah Kasangana. "Organic binder mediated Co3O4/TiO2 heterojunction formation for heterogeneous activation of Peroxymonosulfate." Thesis, Cape Peninsula University of Technology, 2019. http://hdl.handle.net/20.500.11838/2811.
Abstract:
Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2019.A shortage of water has resulted in the need to enhance the quality of wastewater that is released into the environment. The advanced oxidation process (AOP) using heterogeneous catalysis is a promising treatment process for the management of wastewater containing recalcitrant pollutants as compared to conventional processes. As AOP is a reliable wastewater treatment process, it is expected to be a sustainable answer to the shortage of clean water. AOP using heterogeneous catalysis based on Co3O4 particles and PMS, in particular has been found to be a powerful procedure for the degradation and mineralization of recalcitrant organic contaminants. In addition, due to the growing application of Co3O4 in lithium batteries, large quantities of these particles will be recovered as waste from spent lithium batteries, so there is a need to find a use for them. Although this method has received some promising feedback, challenges still need to be addressed, such as the toxicity of cobalt particles, the poor chemical and thermal stability and particle aggregation, and the prompting of lower catalytic efficiency in long haul application. Furthermore, the removal of the catalyst after the treatment of pollutants is also an issue. In order to be applicable, a novel catalyst must be produced requiring the combination of Co3O4 with a support material in order to inhibit cobalt leaching and generate better particle stability. From the available literature, TiO2 was found to be the best support material because it not only provides a large surface area for well dispersed Co3O4, but it also forms strong Co-O-Ti bonds which greatly reduced cobalt leaching as compared to other support materials. Moreover, it also greatly encourages the formation of surface Co–OH complexes, which is considered a crucial step for PMS activation. Therefore, the issues cited above could be avoided by producing a Co3O4/TiO2 heterojunction catalyst.
10
Han, Hyungjin Civil & Environmental Engineering Faculty of Engineering UNSW. "Mechanisms and modelling of sonochemically-mediated free radical degradation of contaminants." Awarded by:University of New South Wales. Civil & Environmental Engineering, 2009. http://handle.unsw.edu.au/1959.4/43485.
Abstract:
Hazardous and recalcitrant pollutants in the environments have led to a great many environmental issues these days. Many researchers have focused on the approaches to treatment of these pollutants which contaminate environments such as soil, surface and groundwater. As an advanced oxidation processes (AOPs), sonolysis which is the oxidation technology involving the use of ultrasonic irradiation, has proven to be successful for the treatment and remediation of contaminated environments. In this thesis, hydrogen peroxide formation and formic acid degradation by ultrasonic irradiation of well-characterised solutions are described under various conditions in order to determinate reaction mechanism by which peroxide degradation and contaminant degradation occur. The effect of gas properties and frequency on hydrogen peroxide and formic acid degradation are examined. Experimental results obtained are analyzed in light of the reactions occurring. Successful mathematical modeling of the result s obtained confirms that, for the most part, hydrogen peroxide and formic degradation occur by free radical generation within bubbles with subsequent transfer of these radicals to the bubble-water interface where the majority of the degradation occurs. The effect of Fe(II) addition which can lead to Fenton reactions in the bulk solution are also investigated. Experimental and model results show that the heterogeneous reactions can enhance the degradation of formic acid in the presence of Fe(II). Oxidation of phenol by ultrasonic irradiation under a variety of initial conditions and solution environments is also described and validated by a simple kinetic model. The model developed will be useful for improving our understanding of free radicals behaviour and the interplay between free radical generation and contaminant degradation.
11
Kristinova, Vera. "Oxidation of marine lipids in liposomes and emulsions mediated by iron and methemoglobin." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bioteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-25022.
Abstract:
Long chain omega-3 polyunsaturated fatty acids (LC omega-3 PUFA) are vital for physiological functions and have therapeutic and health benefits. The consumption of LC PUFA in the Western world has been below recommended intake levels the past decades, despite promotion of seafood and omega-3 supplements. Incorporation of the LC PUFA into processed food consumed on a daily basis might therefore bridge the gap between the recommended and actual consumption of LC omega-3 PUFA. Unfortunately, the development of omega-3 enriched food is hampered by a very high susceptibility of LC PUFA to oxidative deterioration. Furthermore, oxidised lipids are believed to create health risks. It has also been suggested that gastric juice may deteriorate the healthy LC PUFA after they are ingested. Important lipid oxidation promoters in food are low molecular weight (LMW) iron (Fe) and methemoglobin (metHb). To incorporate the LC omega-3 PUFA safely into food with respect to oxidation, it is necessary to understand both Fe- and metHb-mediated oxidation of PUFA and how the oxidation is influenced by conditions and dietary antioxidants. The main objective of this thesis is therefore to study Fe- and metHb-mediated lipid oxidation in food-related lipid model systems – emulsions stabilised with phospholipids and liposomes made of phospholipids – containing LC omega-3 PUFA from fish. The focus was on clarifying the reaction mechanisms and the impact of different factors, including dietary antioxidants and gastric juice, on the prooxidant activity of Fe and metHb. Measurement of the consumption rate of the essential substrate for lipid oxidation – oxygen – by the LC PUFA was used for assessment of lipid oxidation. The continuous measurement of the dissolved oxygen concentration has been shown to be a robust method for direct and instantaneous monitoring of peroxidation in both the liposomes and emulsions. The method was especially useful for measurement of the oxygen consumption kinetics in the lipid systems. The determination of oxygen uptake rates (OUR) enabled screening and evaluation of the impact of the different factors and antioxidants on the prooxidant activity of Fe and metHb. Pre-formed lipid hydroperoxides (LOOH) were shown to be essential for the prooxidant activity of both Fe and metHb, and the prooxidant activity of metHb was not affected by the lack of light. The oxygen uptake kinetics revealed that iron behaved as a catalyst in lipid oxidation while the prooxidant activity of metHb weakened over time, presumably due to degradation of meHb molecule during lipid oxidation. MetHb was shown to be a stronger prooxidant than Fe, but the strong prooxidative activity was facilitated by a complete structure of the metHb molecule. The prooxidant mechanism of both Fe and metHb was not limited by the level of dissolved oxygen, as long as oxygen was present, or the level of pre-formed LOOH and double bonds in fatty acids, as long as they were present in higher concentrations than the prooxidant. The extent of the prooxidative activity of Fe was shown to vary in dependence on: The total surface area: Smaller liposomal vesicles with lower lipid content were more prone to oxidation than larger emulsion droplets with a higher lipid content, presumably due to more frequent interactions of Fe with pre-formed LOOH in the interphase. The amount of phospholipid emulsifier: Higher levels of phospholipids resulted in the formation of smaller droplets. The highest OUR were measured for emulsifier concentrations ranging from 5 – 10% (w/w lipid base). pH of the aqueous phase: Fe-mediated oxidation was highest at pH interval 4.5 – 5.5. Dissolved compounds: Sodium chloride (NaCl) and 0.2% of xanthan gum dissolved in the aqueous phase inhibited Fe-mediated oxidation in a concentration dependent manner. Electrostatic retention of Fe by phosphate groups within phospholipid heads has been suggested to facilitate the contact between pre-formed LOOH and Fe, and to create competitive reactions for iron precipitation at pH > 5 and iron complexation by chelating compounds. The activity of dietary antioxidants has been shown to be affected by the type of prooxidant in the lipid system. Ascorbic acid, caffeic acid, propyl gallate, astaxanthin, ascorbyl palmitate, α-tocopherol, and δ-tocopherol inhibited metHb-mediated oxidation in concentration dependent manners. EDTA had a minor effect on metHb-mediated oxidation. In Fe-mediated oxidation, caffeic acid, ascorbic acid and α-tocopherol were prooxidants. They directly interacted with Fe, reducing Fe3+ to the more catalytically active Fe2+. The magnitude of the pro-oxidative behaviour was dependent on the Fe-to-antioxidant ratio, antioxidant concentration and pH. Ascorbic acid was depleted by interactions with Fe, and decreased the pro-oxidative activity of α-tocopherol. EDTA and citric acid inhibited Fe-mediated oxidation completely at twice the ratio to Fe and pH > 3.5. Propyl gallate efficiently inhibited Fe-mediated oxidation, while astaxanthin and β-carotene had only minor effects. In addition, chemical structure and physical location of the antioxidants determined their effects. The work in this thesis shows that for correct interpretation of the effects of antioxidants it is important to assess what types of prooxidants are present in the system. Both gastric juice and hydrochloric acid solution (HCl) did not prevent oxidation of marine lipids in emulsions and liposomes (pH 4.0). Furthermore, gastric juice did not inhibit metHb-mediated oxidation, but it was capable of reducing the prooxidant activity of dietary LMW iron, compared to HCl solution. Berry juice, green tea, red wine, and caffeic acid reduced the OUR in the acidic environments while coffee, ascorbic acid and orange juice increased the OUR. Therefore, beverages accompanying foods rich in marine lipids will affect the course of post-prandial lipid oxidation.
12
Mulder, Ashley Jade. "The Surface Oxidation States of Copper Nanoparticles Generated by Ligand-Mediated Laser Ablation." Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/59636.
Abstract:
Copper nanoparticles (CuNPs) generated by Laser Ablation Synthesis in Solution (LASiS) were encapsulated and stabilised by a variety of ligands in solution. The encapsulation ligands where chosen to utilise the N-donor binding ability to the CuNPs. This facilitated the oxidative control of the CuNPs, controlling the surface plasmon resonance of the CuNPs. Exploitation of this oxidative control has implications for various nanotechnological applications.
13
MARTINOVITY, FERENC. "Coupling of soot oxidation and ammonia-mediated selective catalytic reduction of nitrogen oxides." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2907024.
14
Botfield, Andrew Civil & Environmental Engineering Faculty of Engineering UNSW. "Kinetic modelling studies of As(III) oxidation in dark pH 3 and 8 Fenton - mediated and pH 8 Cu(II) - H2O2 systems." Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2006. http://handle.unsw.edu.au/1959.4/31969.
Abstract:
In this thesis, a combination of laboratory experimentation under well defined conditions coupled with a kinetic modelling approach is used to verify the existence and respective kinetic rates of previously unconfirmed or postulated mechanisms that drive and limit dark Fenton (Fe(II)/H2O2) - mediated As(III) oxidation at pH 3 and 8 and dark Cu(II) - H2O2 - mediated As(III) oxidation at pH 8. Dark Fenton - mediated oxidation of As(III) at pH 3 is first examined and the effects of the variation in the concentration of reactants (As(III), Fe(II) and H2O2), oxygen, phosphate and organics (2 - propanol, formate, and citrate) are reported and analysed. The kinetic models developed for these systems show high applicability to full scale water treatment application and key mechanistic findings include the significance of the cycling of Fe(II) / Fe(III) via HO2 ???/O2 ??????, the effects of As(IV) termination reactions in the absence of oxygen and the retarding effects of phosphate due to the postulated formation of a Fe(III) - phosphate complex (at a derived rate constant of 2.2 x 106 M-1s-1, that also appears to have negligible kinetic activity in terms of reduction to Fe(II) by HO2 ???/O2 ??????). The work also demonstrates the significance of the free radical by products of formate and citrate oxidation by ???OH (HCOO???/CO2 ?????? and 3HGA???2???). The examination of the dark Cu(II) - H2O2 - mediated oxidation of As(III) at pH 8 with variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate and organics (2 - propanol, formate and citrate) demonstrated for the first time the high applicability of this system to the pre - oxidation of As(III) in water treatment and mechanistically that ???OH and CO3 ?????? are the dominant As(III) oxidants in this system. The As(III) oxidant CO3 ??????, is suggested to be generated by the interaction of ???OH and O2 ?????? with the carbonate matrix, at the respective rate constants of 4.9 x 107 M-1s-1 and 5.5 x 106 M-1s-1. Examination of the dark Fenton - mediated oxidation of As(III) at pH 8 and the effects of variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate, organics (2 - propanol, formate and citrate) and Cu(II) demonstrates the varied potential mechanistic pathways in relation to the generation of As(III) oxidants from the Fenton reaction, Fe(II) + H2O2 such as Fe(IV) and CO3 ?????? and the previously dismissed ???OH, due to the presence of Fe(II) - citrate complexes. This work also demonstrates and models the enhancement of As(III) oxidation in the presence of an additional transitional metal ion, Cu(II).
15
Lycksam, Jonas. "Metal Mobilization in Mine Waste as a Result of Oxidation and Bacterial Mediated Activity." Thesis, Umeå universitet, Kemiska institutionen, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-95210.
16
Tobler, Nicole Béatrice. "Iron-mediated coupling of microbial oxidation and abiotic reduction of organic contaminants in anoxic environments /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17155.
17
Vahedi, Hooshang. "Catalytic symmetric oxidation of sulfides to sulfoxides mediated by 3-substituted-1,2-benzisothiazole 1,1-dioxides." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367257.
18
Lippert, Cameron A. "Redox-active ligand-mediated radical coupling reactions at high-valent oxorhenium complexes: reactions relevant to water oxidation for artificial photosynthesis." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41199.
Abstract:
The making and breaking of O-O bonds has implications ranging from artificial photosynthesis and water oxidation to the use of O₂ as a selective, green oxidant for transformations of small molecules. Oxidative generation of O₂ from coupling of two H₂O molecules remains challenging, and well defined systems that catalytically evolve O₂ are exceedingly rare. Recent theoretical studies have invoked metal oxyl radicals (L[subscript n]M=O*) containing a singly occupied M-O π-type orbital as precursors to O-O bond forming events in both biological and synthetic water oxidation catalysts. However, the lack of stable metal oxyl complexes makes it difficult to explore and understand this hypothesis. The activation of dioxygen (breaking of O-O bonds) to produce terminal metal oxos also remains a challenge. There is an inherent kinetic barrier to the spin-forbidden reactions of triplet dioxygen, and features that engender selective O₂ reduction are not easily transferable from system to system. The primary thrust of this thesis work has been to elaborate new methods to generate well-defined metal oxyl radicals for studies of their reactions in radical bond-forming reactions similar to the radical coupling hypothesis of water oxidation.
A library of >20 5- and 6-coordinate high-valent oxorhenium complexes containing redox-inert and redox-active ligands has been prepared. The complexes containing redox-active ligands have shown the ability for ligand-mediated radical coupling reactions. Mechanistic studies of bimetallic O₂ homolysis (the microscopic reverse of water oxidation) and nitroxyl radical deoxygenation at five-coordinate oxorhenium(V) reveal that, in both net 2e⁻ reactions, coupling to a redox-active ligand lowers the kinetic barrier to the reaction by facilitating formation and stabilization of 1e⁻ oxidized intermediates.
Coordinatively unsaturated high-valent oxorhenium complexes containing redox-active ligands direct bond-forming reactions towards the metal center. This is undesirable towards the goal of forming O-O bonds. To address this problem coordinatively saturated Re(V) and Re(VII) complexes were prepared. Oxidation of these species by chemical oxidants allowed for the isolation of "masked" oxyl species. These complexes showed reactivity towards Si and trityl radicals to produce new Si-O and C-O bonds, whereas their closed-shell congeners were inert. We have successfully developed a method for the preparation and isolation of "masked" oxyl radicals and shown their utility in ligand-mediated radical coupling reactions.
19
Zhang, Lei 1970. "Sol-gel matrix-mediated synthesis of superparamagnetic iron oxide clusters and supported iron porphyrin oxidation catalysts." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9968.
20
Firth, Carole Anne. "7,8-Dihydroneopterin-mediated protection of low density lipoprotein, but not human macrophages, from oxidative stress." Thesis, University of Canterbury. Biological Sciences, 2006. http://hdl.handle.net/10092/1317.
Abstract:
Any lipoproteins and cells present in the inflammatory environment of atherosclerotic plaques are likely to be exposed to high levels of oxidative stress. As 7,8-dihydroneopterin (7,8-NP) is synthesized by interferon-γ (IFN-γ)-activated macrophages, this pteridine is also thought to exist at sites of inflammation. 7,8-NP s in vivo role remains controversial, but numerous in vitro studies have identified a radical scavenging activity. The possibility of 7,8-NP protecting against oxidative damage in inflammatory environments like plaque was investigated in this thesis. Both human monocyte-derived macrophages (HMDMs) and low density lipoprotein (LDL) were used as substrates. The extent of protein hydroperoxide formation in each model, and 7,8-NP s effect on this process, were specifically studied since most previous research has focussed on lipid rather than protein peroxidation. For the first time, neopterin (including oxidized 7,8-NP) was also directly detected by high performance liquid chromatography in the inflammatory environments of 19 pus and two atherosclerotic plaque samples. Peak concentrations even reached the low micromolar range. The positive correlation identified in the pus between neopterin and a well known antioxidant, vitamin E, further hinted at a potential antioxidant function. However, no significant association was noted between neopterin and markers of protein or lipid oxidation. Exposure of HMDMs to the AAPH peroxyl radical generator resulted in significant quantities of lipid hydroperoxides but not protein hydroperoxides, as detected by the FOX assays. This is likely due to the large accumulation of polyunsaturated fatty acidrich lipid in the primary HMDMs during differentiation in 10% human serum and is of relevance to atherosclerotic plaque, where macrophages also become lipid-loaded. The addition of up to 200μM 7,8-NP failed to prevent AAPH-induced lipid peroxidation and was also unable to inhibit a loss of cellular thiols or viability. This lack of effect suggests the damaging peroxyl radicals are not being scavenged by 7,8-NP. The high lipid content of HMDM cells appears to cause the AAPH and/or 7,8-NP to localize to a cellular site, where they are unable to interact. Macrophage-mediated oxidation of LDL in iron(II)-supplemented Hams F10 was associated with the formation of 30-40 moles of protein hydroperoxides per mole of LDL. The close parallel between protein and lipid peroxidation supports the theory that lipid-derived radicals are involved in protein hydroperoxide formation on LDL and indicates that protein hydroperoxides are an early product of LDL oxidation. Their detection during exposure of LDL to both the THP-1 macrophage cell line and primary HMDM cells confirms that protein hydroperoxides are also a normal consequence of macrophage-mediated LDL oxidation. Incubation of LDL with micromolar 7,8-NP prevented macrophage-mediated protein hydroperoxide formation in a concentration-dependent manner. Lipid oxidation and vitamin E loss were similarly inhibited by 7,8-NP during the cell-mediated attack of LDL. Kinetic analysis revealed protection due to extension of the lag phase, with 7,8-NP depletion and initiation of the propagation phase coinciding. This supports a radical scavenging activity for 7,8-NP, resulting in protection of the entire LDL particle. By contrast, the release of nanomolar quantities of 7,8-NP by IFN-γ-stimulated THP-1 macrophages failed to prevent LDL oxidation. HMDMs activated by IFN-γ did significantly inhibit LDL oxidation, including protein hydroperoxide formation, for up to 48 hours but this antioxidant effect was not due to the de novo synthesis of 7,8-NP. These results indicate that both the prevalence of protein hydroperoxides, and the ability of 7,8-NP to act as an antioxidant, depend on the system under investigation. Neopterin exists in inflammatory environments but, considering the lack of protection against AAPH-mediated HMDM oxidation and the 7,8-NP concentration required to inhibit macrophage-mediated LDL oxidation, strong evidence for an antioxidant activity of 7,8-NP in atherosclerotic plaque is currently lacking.
21
Gladman, Calvin. "Ferricyanide Mediated Microbial Respiration - Application to the Analysis of Waters and Wastewaters." Thesis, Griffith University, 2011. http://hdl.handle.net/10072/367669.
Abstract:
A novel rapid respiration-based bioassay for the quantitative determination of microbial oxidation of organic substrate in wastewaters has been developed. By replacing oxygen as the terminal electron acceptor with the ferricyanide ion during microbial respiration, the rate and extent of the biochemical reaction (i.e. oxidation of substrate) was significantly increased. This was due to the high solubility of the ferricyanide ion in solution, thereby allowing the use of substantially larger populations of microorganisms in the assay without rapid depletion of the electron acceptor during respiration.
The ferricyanide mediated respiration (FM-Res) assay was successfully employed as a platform for the further development of both a rapid biochemical oxygen demand (FM-BOD) and rapid toxicity assay (FM-Tox). Under ferricyanide mediated conditions, both assay types exhibited biochemical behaviour analogous to where oxygen would typically act as a terminal electron acceptor, effectively establishing proof of concept.
Optimisation of the biocatalyst in the FM-Res assay showed that a broad range of phylogenetically diverse microorganisms were able to utilise the ferricyanide ion as an alternative electron acceptor in the biodegradation of a wide range of organic compounds. The most suitable type of biocatalyst for use in the FM-Res assay was shown to be a mixed microbial consortium capable of degrading large amounts and types of compounds. In the case of the FM-BOD assay, the use of a mixed microbial consortium substantially increased the dynamic linear working range when compared to more traditional methods of analysis such as BOD5.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text
22
Wang, Jin. "A mechanistic study of the preferential photo-oxidation of the 5-CH3 substituent of thymine and thymidine mediated by NH4(VO(O2)2(5-NO2phen))." HKBU Institutional Repository, 2009. http://repository.hkbu.edu.hk/etd_ra/1056.
23
Dang, Zheng. "The Investigation of Carboxyl Groups of Pulp Fibers during Kraft Pulping, Alkaline Peroxide Bleaching, and TEMPO-mediated Oxidation." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16143.
Abstract:
Over the past 10 years, growing concerns over the modification of fibers have led researchers to focus on enriching the carboxyl group content of fibers by chemical oxidation and topochemical grafting. The current series of experiments continues this line of research by investigating the carboxyl group content of fibers during kraft pulping, alkaline peroxide bleaching, and 2,2,6,6-tetrametyl-1-piperidinyloxy radical (TEMPO)-KBr-NaClO oxidation system.
The first experiment characterizes changes in the carboxyl group content of fibers for two sets of kraft pulps: 1) conventional laboratory cooked loblolly pine kraft pulps, and 2) conventional pulping (CK) versus Lo-Solids pulping (LS) pulps. The results indicate that effective alkali (EA), temperature, and H-factor are the primary factors controlling fiber charge during kraft pulping. Another set of kraft pulps distinguished by conventional pulping and Lo-Solids pulping were investigated to determine the effect of H-factor and pulping protocol on fiber charge.
The second experiment examines the influence of alkaline peroxide treatment on elementally chlorine-free (ECF) bleached softwood kraft pulp. The effect of increased fiber charge on refining, cationic starch adsorption, and hornification was examined. The final experiment investigates the effect of TEMPO-mediated oxidation of an ECF bleached softwood kraft pulp on carboxyl group content, carbonyl group contents, degree of polymerization, and water retention value of fibers. The results show that TEMPO-mediated oxidation is useful in enriching the carboxyl and carbonyl groups to fibers, as well as enhancing the property of water adsorption of fibers.
These findings suggest that: (1) kraft pulping process can be modified to obtain the target carboxyl group content, (2) terminal peroxide bleaching provides higher fiber charge which can save energy and chemical charge of subsequent refining and wet-end processes, respectively, as well as reduce hornification during drying, (3) TEMPO-mediated oxidation of fibers is capable of improving the properties of fibers, including fiber charge and water adsorption, and enhancing final paper strength.
24
Sopaci, Saziye Betul. "Microorganism Mediated Stereoselective Bio-oxidation And Bio-hydrogenation Reactions And Thiamine Pyrophosphate Dependent Enzyme Catalyzed Enantioselective Acyloin Reactions." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12610516/index.pdf.
Abstract:
In this study various microbial and enzymatic methods developed for enantioselective acyloin synthesis for preparation of some pharmaceutically important intermediates. By performing Aspergillus flavus (MAM 200120) mediated biotransformation, enantioselective bio-oxidation of meso-hydrobenzoin was achieved with a high ee value (76%). Racemic form of hydrobenzoin was also employed for the same bio-oxidation process and this bioconversion was resulted in accumulation of meso form (>90% yield) confirming the suggested mechanism of oxidation-reduction sequence of hydrobenzoin. Wieland-Miescher ketone (3,4,8,8a-tetrahydro-8a-methylnaphthalene-1,6(2H,7H)-dione) is an important starting material for bioactive compounds like steroids and terpenoids. Many synthetic approaches include enantioselective reduction of this compound. In this study Aspergillus niger (MAM 200909) mediated reduction of Wieland-Miescher ketone was achieved with a high yield (80%), de (79%) and ee (94%) value and these results were found much more superior than previously reported studies. Carboligating enzymes benzaldehyde lyase (BAL) (EC 4.1.2.38) and benzoiyl formate decarboxilase (BFD) (E.C. 4.1.1.7) are used for biocatalytic acyloin synthesis. These enzymes are immobilized to surface modified superparamagnetic silica coated nanoparticles by using metal ion affinity technique. With this system recombinant histidine tagged BAL and BFD purified and immobilized to magnetic particles by one-pot purification-immobilization procedure. SDS page analysis showed that our surface modified magnetic particles were eligible for specific binding of histidine tagged proteins. Conventional BAL and BFD catalyzed benzoin condenzation reactions and some representative acyloin reactions were performed with this system with a high enantioselectivity (99-92%) and yield. Results obtained with magnetic particle-enzyme system were also found comparable with that of free enzyme catalyzed reactions.
25
Diering, Simon [Verfasser], and Friederike [Akademischer Betreuer] Cuello. "The impact of protein oxidation on kinase-mediated phosphorylation and cardiac myocyte contractile function / Simon Diering ; Betreuer: Friederike Cuello." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1182537863/34.
26
Salem, Mohamed M. A. "H2O2-mediated oxidation and nitration enhances DNA binding capacity / DNA repair via up-regulated epidermal wild-type p53 in vitiligo." Thesis, University of Bradford, 2009. http://hdl.handle.net/10454/3348.
Abstract:
The entire epidermis of patients with vitiligo exhibits accumulation of up to 10-3M
concentrations of hydrogen peroxide (H2O2) (Schallreuter, Moore et al. 1999). Over
the last decade our group and others have focused on the effect of H2O2-mediated
oxidative stress on the function of many proteins and peptides due to oxidation of
target amino acid residues in their structure including L-methionine, L-tryptophan,
L-cysteine and seleno cysteine (Rokos, Beazley et al. 2002; Gillbro, Marles et al.
2004; Hasse, Kothari et al. 2005; Schallreuter, Chavan et al. 2005; Spencer, Chavan
et al. 2005; Chavan, Gillbro et al. 2006; Elwary, Chavan et al. 2006; Gibbons, Wood
et al. 2006; Schallreuter, Bahadoran et al. 2008; Shalbaf, Gibbons et al. 2008; Wood,
Decker et al. 2009). Moreover, it was shown that patients with vitiligo possess up
regulated wild type functioning p53 protein in their skin (Schallreuter, Behrens-
Williams et al. 2003). The reason behind this up regulation has remained unclear
(Schallreuter, Behrens-Williams et al. 2003).
Therefore the aim of this thesis was to get a better understanding of these puzzling
data. Along this project different techniques have been used including Western blot,
dot blot, immuno precipitation, immuno fluorescence, EMSA and computer
modelling.
In this thesis we confirmed the previous result on up regulation of p53 in vitiligo and
we showed that p90MDM2, the master regulator for p53 protein is not different in
patients and healthy controls. Therefore we decided to test for expression of p76MDM2
which mediates the inhibition of p90MDM2-p53 binding. Our results show for the first
time the presence and over expression of p76MDM2 protein in vitiligo compared to
3
healthy individuals. This result could provide an explanation, why up regulated p53
is not degraded in this disease.
Since epidermal H2O2 accumulation has been extensively documented in vitiligo, we
wanted to know whether other ROS could also contribute to the overall oxidative
stress in this scenario. Therefore we turned our interest to nitric oxide (NO) and its
possible effects on p53 protein. In order to elucidate this role in more detail, the
expression levels of epidermal nitric oxide synthesase (iNOS) and the oxidation
product of NO and O2
- i.e peroxynitrite (ONOO-) were investigated. Our data
revealed over expression of iNOS and nitrated tyrosine residues, the foot print for
ONOO-. Moreover, we show for the first time the presence of abundant nitration of
p53 protein in vitiligo. In addition using purified p53 from E. coli strain (BL21/DE3)
and mutant p53 protein from HT-29 cells (colon cancer cells), we show that nitration
takes place in a dose and time dependent manner. On this basis we investigated the
effect of both H2O2 and ONOO- on p53-DNA binding capacity employing EMSA,
since this is the most acceptable technique to follow the binding between proteins
and DNA. Our results revealed that ONOO- abrogated p53-DNA binding capacity at
concentrations >300 ¿M, meanwhile oxidation of p53 protein with H2O2 at the same
concentrations does not affect binding capacity. Importantly, a much higher p53-
DNA binding capacity was observed after exposure to both ONOO- and H2O2.
Taken together, p53 is regulated by both ROS (H2O2) and RNS (ONOO-).
Next we identified the presence of phosphorylated and acetylated p53 in vitiligo.
Phosphorylation of ser 9 and ser 15 residues of the protein are associated with over
expressed ATM protein kinase, while acetylation of lys 373, 382 residues correlates
with increased PCAF expression. We show that up regulated p53 is associated with
over expressed p21 (cyclin dependent kinase inhibitor 1) and induced PCNA
4
expression. Hence, we can conclude that p53 in patients with vitiligo is up regulated,
activated and functional.
Finally we show up regulated BCL-2 supporting the long voiced absence of
increased apoptosis in vitiligo. Given that patients with vitiligo have no increased
risk for solar induced skin cancer and increased photo damage (Calanchini-Postizzi
and Frenk 1987; Westerhof and Schallreuter 1997; Schallreuter, Tobin et al. 2002),
despite the presence of increased DNA damage as evidenced by increased 8-oxoG
levels in the skin and in the plasma, our findings suggest that both p53 and PCNA
provide a powerful machinery to mediate DNA repair via hOgg1, APE1 and DNA
polymerase ß (Shalbaf 2009). On this basis it is tempting to conclude that DNArepair
is the overriding mechanism to combat oxidative stress in this disease.Egyptian government; Institute for Pigmentary Disorders in association with the EM Arndt University of Greifswald, Germany.
27
Li, Qing Qing. "Nanocellulose: Preparation, Characterization, Supramolecular Modeling, and its Life Cycle Assessment." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/49556.
Abstract:
Nanocellulose is a nascent and promising material with many exceptional properties and a broad spectrum of potential applications; hence, it has drawn increasing research interests in the past decade. A new type of nanocellulose -- with mono- or bi-layer cellulose molecular sheet thickness -- was synthesized through a combined chemical-mechanical process (TEMPO-mediated oxidation followed by intensive sonication), and this new material was named molecularly thin nanocellulose (MT nanocellulose). The overarching objective of this study was to understand the formation and supramolecular structure of MT nanocellulose and contribute to the knowledge of native cellulose structure.
The research involved four major bodies of study: preparation of MT nanocellulose, characterization of MT nanocellulose, modeling wood pulp-derived cellulose microfibril cross section structure, and a comparative life cycle assessment (LCA) of different nanocellulose fabrication approaches. The results revealed that MT nanocellulose with mono- to bi-layer sheet thickness (~0.4-0.8 nm), three to six chain width (~2-5 nm), and hundreds of nanometers to several microns length, can be prepared through TEMPO-mediated oxidation followed by 5-240 min intensive sonication. The thickness, width, and length of MT nanocellulose all decreased with extended sonication time and leveled off after 1 or 2 h sonication. Crystallinity, hydrogen bonding, and glycosidic torsion angles were evaluated by XRD, FTIR, Raman, and NMR. These experiments revealed systematic changes to structure with sonication treatments. A microfibril "cross section triangle scheme" was developed for the microfibril supramolecular modeling process and a 24-chain hexagonal/elliptical hybrid model was proposed as the most credible representation of the supramolecular arrangement for wood pulp-derived cellulose I" microfibril. Comparative LCA of the fabrication of nanocellulose indicated that nanocellulose presented a significant environmental burden markup on its precursor, kraft pulp, and the environmental hotspot was attributed to the mechanical disintegration process. Yet, overall nanocellulose still presented a prominent environmental advantage over other nanomaterials like single-walled carbon nanotubes, due to its relative low energy consumption.
Overall, this research developed a facile approach to produce a new type of nanocellulose, the MT nanocellulose, provided new insights about the supramolecular structure of cellulose microfibrils, and evaluated the environmental aspects of the fabrication process of nanocellulose.Ph. D.
28
Aybey, Ayse. "Oxidative Ring Opening Reactions Of A-hydroxy Ketones." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12609279/index.pdf.
Abstract:
Chiral polyfunctionalized 1,5-dicarbonyl compounds are important synthetic intermediates and starting materials for many biologically active compounds so their synthesis has a great importance in the literature.
In the first step, 1,3-cyclohexandione and other b-diketone derivatives are protected under acid catalyzation and their corresponding b-keto enol ether derivatives are obtained. These b-keto enol ethers are then converted to a-acetoxy enones in racemic form by Mn(OAc)3 mediated oxidation. Enzymatic kinetic resolution is applied to the racemic acetoxy enones by using different lipases and enantiomerically pure a-acetoxy and hydroxy enones are obtained. Then, dicarbonyl derivatives are obtained by hydrolizing racemic a-acetoxy enones. Oxidative cleavage of racemic a-acetoxy diketones in the presence of oxone gives corresponding racemic 1,5-dimethyl ester derivatives.
By using this reaction as a reference, same reactions are applied to the chiral a-acetoxy and hydroxy diketones in order to synthesize chiral a-acetoxy and hydroxy 1,5-diester derivatives.
29
Salem, Mohamed Metwalli AbouElloof. "H₂O₂-mediated oxidation and nitration enhances DNA binding capacity/DNA repair via up-regulated epidermal wild-type p53 in vitiligo." Thesis, University of Bradford, 2009. http://hdl.handle.net/10454/3348.
Abstract:
The entire epidermis of patients with vitiligo exhibits accumulation of up to 10-3M concentrations of hydrogen peroxide (H₂O₂) (Schallreuter, Moore et al. 1999). Over the last decade our group and others have focused on the effect of H₂O₂-mediated oxidative stress on the function of many proteins and peptides due to oxidation of target amino acid residues in their structure including L-methionine, L-tryptophan, L-cysteine and seleno cysteine (Rokos, Beazley et al. 2002; Gillbro, Marles et al. 2004; Hasse, Kothari et al. 2005; Schallreuter, Chavan et al. 2005; Spencer, Chavan et al. 2005; Chavan, Gillbro et al. 2006; Elwary, Chavan et al. 2006; Gibbons, Wood et al. 2006; Schallreuter, Bahadoran et al. 2008; Shalbaf, Gibbons et al. 2008; Wood, Decker et al. 2009). Moreover, it was shown that patients with vitiligo possess up regulated wild type functioning p53 protein in their skin (Schallreuter, Behrens- Williams et al. 2003). The reason behind this up regulation has remained unclear (Schallreuter, Behrens-Williams et al. 2003). Therefore the aim of this thesis was to get a better understanding of these puzzling data. Along this project different techniques have been used including Western blot, dot blot, immuno precipitation, immuno fluorescence, EMSA and computer modelling. In this thesis we confirmed the previous result on up regulation of p53 in vitiligo and we showed that p90MDM2, the master regulator for p53 protein is not different in patients and healthy controls. Therefore we decided to test for expression of p76MDM2 which mediates the inhibition of p90MDM2-p53 binding. Our results show for the first time the presence and over expression of p76MDM2 protein in vitiligo compared to 3 healthy individuals. This result could provide an explanation, why up regulated p53 is not degraded in this disease. Since epidermal H₂O₂ accumulation has been extensively documented in vitiligo, we wanted to know whether other ROS could also contribute to the overall oxidative stress in this scenario. Therefore we turned our interest to nitric oxide (NO) and its possible effects on p53 protein. In order to elucidate this role in more detail, the expression levels of epidermal nitric oxide synthesase (iNOS) and the oxidation product of NO and O2 - i.e peroxynitrite (ONOO-) were investigated. Our data revealed over expression of iNOS and nitrated tyrosine residues, the foot print for ONOO-. Moreover, we show for the first time the presence of abundant nitration of p53 protein in vitiligo. In addition using purified p53 from E. coli strain (BL21/DE3) and mutant p53 protein from HT-29 cells (colon cancer cells), we show that nitration takes place in a dose and time dependent manner. On this basis we investigated the effect of both H₂O₂ and ONOO- on p53-DNA binding capacity employing EMSA, since this is the most acceptable technique to follow the binding between proteins and DNA. Our results revealed that ONOO- abrogated p53-DNA binding capacity at concentrations >300 μM, meanwhile oxidation of p53 protein with H₂O₂ at the same concentrations does not affect binding capacity. Importantly, a much higher p53- DNA binding capacity was observed after exposure to both ONOO- and H₂O₂. Taken together, p53 is regulated by both ROS (H₂O₂) and RNS (ONOO-). Next we identified the presence of phosphorylated and acetylated p53 in vitiligo. Phosphorylation of ser 9 and ser 15 residues of the protein are associated with over expressed ATM protein kinase, while acetylation of lys 373, 382 residues correlates with increased PCAF expression. We show that up regulated p53 is associated with over expressed p21 (cyclin dependent kinase inhibitor 1) and induced PCNA 4 expression. Hence, we can conclude that p53 in patients with vitiligo is up regulated, activated and functional. Finally we show up regulated BCL-2 supporting the long voiced absence of increased apoptosis in vitiligo. Given that patients with vitiligo have no increased risk for solar induced skin cancer and increased photo damage (Calanchini-Postizzi and Frenk 1987; Westerhof and Schallreuter 1997; Schallreuter, Tobin et al. 2002), despite the presence of increased DNA damage as evidenced by increased 8-oxoG levels in the skin and in the plasma, our findings suggest that both p53 and PCNA provide a powerful machinery to mediate DNA repair via hOgg1, APE1 and DNA polymerase ß (Shalbaf 2009). On this basis it is tempting to conclude that DNArepair is the overriding mechanism to combat oxidative stress in this disease.
30
Carlsson, Daniel O. "Structural and Electrochemical Properties of Functionalized Nanocellulose Materials and Their Biocompatibility." Doctoral thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-215090.
Abstract:
Nanocellulose has received considerable interest during the last decade because it is renewable and biodegradable, and has excellent mechanical properties, nanoscale dimensions and wide functionalization possibilities. It is considered to be a unique and versatile platform on which new functional materials can be based. This thesis focuses on nanocellulose from wood (NFC) and from Cladophora algae (CNC), functionalized with surface charges or coated with the conducting polymer polypyrrole (PPy), aiming to study the influence of synthesis processes on structural and electrochemical properties of such materials and assess their biocompatibility. The most important results of the work demonstrated that 1) CNC was oxidized to the same extent using electrochemical TEMPO-mediated oxidation as with conventional TEMPO processes, which may facilitate easier reuse of the reaction medium; 2) NFC and CNC films with or without surface charges were non-cytotoxic as assessed by indirect in vitro testing. Anionic TEMPO-CNC films promoted fibroblast adhesion and proliferation in direct in vitro cytocompatibility testing, possibly due to its aligned fibril structure; 3) Rinsing of PPy-coated nanocellulose fibrils, which after drying into free-standing porous composites are applicable for energy storage and electrochemically controlled ion extraction, significantly degraded the PPy coating, unless acidic rinsing was employed. Only minor degradation was observed during long-term ambient storage; 4) Variations in the drying method as well as type and amount of nanocellulose offered ways of tailoring the porosities of nanocellulose/PPy composites between 30% and 98%, with increments of ~10%. Supercritical CO2-drying generated composites with the largest specific surface area yet reported for nanocellulose/conducting polymer composites (246 m2/g). The electrochemical oxidation rate was found to be controlled by the composite porosity; 5) In blood compatibility assessments for potential hemodialysis applications, heparinization of CNC/PPy composites was required to obtain thrombogenic properties comparable to commercial hemodialysis membranes. The pro-inflammatory characteristics of non-heparinized and heparinized composites were, to some extent, superior to commercial membranes. The heparin coating did not affect the solute extraction capacity of the composite. The presented results are deemed to be useful for tuning the properties of systems based on the studied materials in e.g. energy storage, ion exchange and biomaterial applications.
31
Salsman, Scott J. "Redox regulation of protein tyrosine phosphatases in cell membrane receptor-mediated signal transduction." Oklahoma City : [s.n.], 2005.
32
Senocak, Deniz. "Chemoenzymatic Synthesis Of Chiral Hydroxymethyl Cycloalkenols." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605056/index.pdf.
Abstract:
Chiral cyclic alkenols with hydroxymethyl functionality are important structural units in many biologically active natural compouds such as prostaglandins, sesquiterpene antiviral agents, pentenomycins, xanthocidin, sarkomycin, etc.
1,3-cycloalkanediones are converted into bicyclic polyoxo derivatives with formaldehyde and trioxane in the presence of Lewis acid. Selective oxidation of the bicyclic compounds by using manganese(III)acetate followed by enzyme-catalyzed kinetic resolution afforded chiral bicyclic hydroxy ketones. Reduction of carbonyl group and cleavage of the ether functionality furnished the desired chiral cycloalkanols with hydroxymethyl group. This study is a model for the synthesis of these type of compounds.
33
Maher, Christopher John. "Options for treatment of legacy and advanced nuclear fuels." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/options-for-treatment-of-legacy-and-advanced-nuclear-fuels(984fa9e5-3732-4f1b-b9b1-42457ef0f732).html.
Abstract:
The treatment of advanced nuclear fuels is relevant to the stabilisation of legacy spent fuels or nuclear materials and fuels from future nuclear reactors. Historically, spent fuel reprocessing has been driven to recover uranium and plutonium for reuse. Future fuel cycles may also recover the minor actinides neptunium, americium and perhaps curium. These actinides would be fabricated into new reactor fuel to produce energy and for transmutation of the minor actinides. This has the potential to reduce the long lived radioactivity of the spent fuel and reprocessing high level waste, whilst also maximising energy production. To achieve these aims there are a range of materials that could be used as advanced nuclear fuels, these include metals, oxides, carbides, nitrides and composite materials, and these fuels may also be alloyed. These advanced fuels may need to be reprocessed, and as head end is the first chemical treatment step in a reprocessing plant, the issues caused by treating these advanced fuels are faced primarily by head end. Changes to the overall reprocessing specification, such as reduction in discharge authorisations for volatile radionuclides, will have the greatest impact upon head end. All these factors may lead to the introduction of pre-treatment technologies (e.g. Voloxidation) or enhanced dissolution technologies, e.g. mediated dissolution using silver(II).Literature and experimental studies show that uranium dioxide and low plutonium content MOx dissolves in nitric acid via direct and indirect nitrate reduction. The indirect nitrous acid catalysed route is kinetically most significant. The kinetics for the dissolution of uranium dioxide and 5 % plutonium MOx have been derived experimentally. Studies of the dissolution of MOx pellets in concentrated nitric acid and near boiling conditions indicate that dissolution shows a degree of mass transfer limitation. Thermodynamic studies show that the pronounced reduction in the MOx dissolution extent at 30-40% plutonium is due to the thermodynamics of the key dissolution reactions. One technology that could be used to dissolve plutonium-rich residues that are generated from the reprocessing of MOx fuels is mediated dissolution. Inactive studies using linear staircase voltammetry (LSCV) and constant current bulk electrolysis (BE) have been used to optimise a 100 ml dissolution cell. The generation of silver(II) is dependent upon silver concentration, agitation and the size of the separator membrane. Whilst the stability of silver(II) is defined by the kinetics of water oxidation, this is dependent upon a number of factors including nitric acid concentration, silver(I):(II) ratio, temperature and the rate of migration from the catholyte into the anolyte. LSCV experiments have shown that Tafel analysis confirms there is a good relationship between potential and anode current density assuming oxygen evolution and silver(I) oxidation. Kinetic modelling of the BE experiments can be used to model the silver(II) generation, steady state and decomposition due to reaction with water. The dissolution cell has been demonstrated to be capable of dissolving plutonium dioxide to 200 g.l-1 in less than 2 hours with good faradaic efficiency.
34
Silvers, Kimberly Jane. "The role of cytochrome P450-mediated C-oxidation and cytosolic nitroreduction in the metabolism, DNA binding, and mutagenicity of 1-nitropyrene in human liver." Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1062512189.
35
Offenbacher, Adam R. "Protein structural changes and tyrosyl radical-mediated electron transfer reactions in ribonucleotide reductase and model compounds." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39473.
Abstract:
Tyrosyl radicals can facilitate proton-coupled electron transfer (PCET) reactions that are linked to catalysis in many biological systems. One such protein system is ribonucleotide reductase (RNR). This enzyme is responsible for the conversion of ribonucleotides to deoxyribonucleotides. The beta2 subunit of class Ia RNRs contains a diiron cluster and a stable tyrosyl radical (Y122*). Reduction of ribonucleotides is dependent on reversible, long-distance PCET reactions involving Y122* located 35 Å from the active site. Protein conformational dynamics are postulated to precede diiron cluster assembly and PCET reactions in RNR. Using UV resonance Raman spectroscopy, we identified structural changes to histidine, tyrosine, and tryptophan residues with metal cluster assembly in beta2. With a reaction-induced infrared spectroscopic technique, local amide bond structural changes, which are associated with the reduction of Y122*, were observed. Moreover, infrared spectroscopy of tyrosine-containing pentapeptide model compounds supported the hypothesis that local amide bonds are perturbed with tyrosyl radical formation. These findings demonstrate the importance of the amino acid primary sequence and amide bonds on tyrosyl radical redox changes. We also investigated the function of a unique tyrosine-histidine cross-link, which is found in the active site of cytochrome c oxidase (CcO). Spectrophotometric titrations of model compounds that mimic the cross-link were consistent with a proton transfer role in CcO. Infrared spectroscopic data support the formation of tyrosyl radicals in these model compounds. Collectively, the effect of the local structure and the corresponding protein dynamics involved in tyrosyl radical-mediated PCET reactions are illustrated in this work.
36
Filosa, Angelo. "Study of locally unfolded forms of cytochrome c by Fourier transform infrared and of H2O2-mediated oxidation of ferricytochrome c and metmyoglobin by mass spectrometry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63979.pdf.
37
Kose, Elif. "Chemoenzymatic Synthesis Of 4-hydroxy Enones." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/1252519/index.pdf.
Abstract:
Chiral cyclic polyoxo-ketones are important structural units in many natural products, biologically active compouds, such as prostaglandins, didemnenones, sarkomycin, punaglandin, clavulone, etc.
In this work, a chemoenzymatic synthesis of both enantiomers of the α
&rsquo
-acetoxy-&
#945
-methyl and &
#947
-hydroxy-&
#945
-methyl cyclic enones starting from &
#945
-methyl-&
#946
-methoxy cyclic enone is described. Manganese (III) acetate-mediated acetoxylation followed by the enzyme-mediated hydrolysis of &
#945
&rsquo
-acetoxy enone provides acetoxy enones. The reduction of the hydroxy enone, obtained from hydrolysis, furnished both enantiomers of 4-hydroxy enone or &
#947
-hydroxy enone by using LiAlH4. This study is a model for the synthesis of these type compounds
38
Aher, Ashish. "SYNTHESIS, CHARACTERIZATION AND APPLICATIONS OF REDUCED GRAPHENE OXIDE AND COMPOSITE MEMBRANES FOR SELECTIVE SEPARATIONS AND REMOVAL OF ORGANIC CONTAMINANTS." UKnowledge, 2019. https://uknowledge.uky.edu/cme_etds/111.
Abstract:
Among the next generation materials being investigated for membrane development, partially reduced Graphene Oxide (rGO) has received increasing attention from the membrane community. rGO-based nanofiltration membranes have shown promising results in applications such as partial desalination, organic contaminant removal, gas-phase separations, and separations from solvent media. rGO offers a unique platform compared to common polymeric membranes since it can be used for separation applications in both aqueous and organic solvent media. An rGO-based platform could also be utilized to synthesize reactive membranes, giving rGO membranes the additional capability of reactively removing organic contaminants. This research focuses on the synthesis of rGO and nanocomposite membranes for applications including the separation of high-value phenolic compounds from a solvent-water mixture, removal of organic contaminants, and treatment of refinery wastewater.
First, the behavior of a rGO membrane in water and isopropanol was investigated along with its ability to separate high-value, lignin-derived oligomeric compounds from a solvent-water mixture. This study revealed the formation of stable sorbates of water in the GO channels that resulted in declined membrane permeance and improved size-exclusion cutoff. Through controlled reduction of GO by heat treatment, it was demonstrated that physicochemical properties of the GO membrane could be modulated and separation performance tuned based on the extent of reduction. A varying degree of interlayer spacing was attained between the GO laminates by controlling the O/C ratio of GO. This allowed the rGO membrane to achieve tunable molecular separation of lignin-derived model oligomeric compounds from a solvent-water mixture.
Second, the mechanism of ionic transport through the rGO membrane was studied as well as its application in partial desalination and removal of persistent organic contaminants from water. Through comprehensive experimental investigations and mathematical analysis, along with the aid of the extended Nernst Planck equation, the impacts of steric hindrance and charge interactions on the underlying ion transport mechanism were quantified. Charge interactions were observed to be the dominant exclusion mechanism for the rGO membranes. The application of rGO membranes for treatment of high TDS produced water was investigated with the goal of partial hardness and dissolved oil removal. In addition, this study demonstrated the removal of emerging organic contaminants, specifically perfluorooctanoic acid, by rGO membranes and elucidated a charge interaction-dominated exclusion mechanism for this contaminant, as well.
Finally, rGO-based and microporous polyvinylidene fluoride (PVDF)-based catalytic membrane platforms were synthesized for removal of organic contaminants via an oxidative pathway. Herein, an advanced oxidation process was integrated with membrane technology by the in-situ synthesis of Fe-based nanoparticles. The unique capability to oxidatively remove contaminants in a continuous mode of operation was explored in addition to the separation performance of the membrane. The rGO-based platform achieved high oxidative removal of trichloroethylene via a sulfate-free, radical-mediated pathway, while simultaneously removing humic acids from water and potentially eliminating undesired side reactions. A PVDF-based microporous catalytic membrane platform was shown to effectively remove organic impurities, such as Naphthenic acids, from high TDS produced water by the same pathway. The enhancement of reaction extent for elevated temperatures and longer residence times was also quantified in this study.
These studies benefit the membrane community in the following ways: 1) The work identifies the critical role of the physicochemical properties of GO, such as the O/C ratio and water sorption, for determining the permeability-selectivity of rGO membranes for solvent nanofiltration. 2) Investigations of ion transport through rGO membranes led to an understanding of a charge-dominated separation mechanism for ion retention. The Nernst-Planck equation-based approach employed in this study would enable further assessment and comparison of rGO membranes under a wide set of parameters. 3) Catalytic membrane platforms (rGO and microporous PVDF-based) were synthesized for conducting advanced oxidation reactions in the porous membrane domain, demonstrating potential applications in environmental remediation of organic contaminants.
39
Mai, Trang. "FUNCTIONALIZATION OF IRON OXIDE NANOPARTICLES AND THE IMPACT ON SURFACE REACTIVE OXYGEN SPECIES GENERATION FOR POTENTIAL BIOMEDICAL AND ENVIRONMENTAL APPLICATIONS." UKnowledge, 2019. https://uknowledge.uky.edu/cme_etds/102.
Abstract:
Iron oxide nanoparticles (IONPs) have been widely studied for a variety of applications, from biomedical applications (e.g., cell separation, drug delivery, contrast agent for magnetic resonance imaging and magnetically mediated energy delivery for cancer treatment) to environmental remediations (e.g., heavy metal removal and organic pollutants degradation). It has been demonstrated that IONPs can induce the production of reactive oxygen species (ROS) via Fenton/Haber-Weiss reactions which has been shown to be one of the key underlying mechanisms of nanoparticles toxicity. This inherent toxicity of nanoparticles has been shown to enhance the efficacy of traditional cancer therapies such as chemotherapy and radiation. In addition, the generation of ROS induced by IONPs has been also studied as advanced oxidation processes (AOP) for wastewater treatment. Recent research has also shown that exposure to an alternating magnetic field can significantly enhance the generation of ROS induced by IONPs. Moreover, the coatings of IONPs play an important role on the surface reactivity of nanoparticles since it can prevent the generation of ROS via Fenton chemistries at the surface of the nanoparticles.
In this work, co-precipitated IONPs were functionalized with small molecules including citric acid, sodium phosphate, amino silane and dopamine. The impact of coating on surface reactivity of the as-synthesized particles was studied using methylene blue dye degradation assay under AMF exposure. With the coatings of these small molecules, the IONPs induced ROS generation was significantly decreased because of the dense surface coverage. To study the effect of polymeric coatings, a degradable poly (beta amino ester) (PBAE) polymer coating was synthesized with dopamine as an anchor to bind to nanoparticles. The surface reactivity of the particles was expected to be recovered once the polymer coating was degraded. Furthermore, the impact of non-degradable PEG-based polymer coating on surface reactivity via ROS generation was also investigated using methylene blue decolorization assay with the presence of AMF. The retention of surface reactivity of PEG-based polymer coated IONPs shows promise for cancer treatment.
The application of IONPs as heterogeneous catalyst for organic contaminant degradation was investigated. Bisphenol A (BPA) was used as a model compound, and Fenton reactions were induced by IONPs with the presence of hydrogen peroxide and hydroxylamine as well as alternating magnetic field exposure. The kinetics of BPA degradation under water bath and AMF exposure at 37oC was also studied, and the results showed potential applications of IONPs for organic pollutants remediation.
40
Davidson, Stuart Cameron. "The development of organic peroxide mediated oxidations." Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=30330.
Abstract:
This thesis describes the development of two novel metal-free oxidations processes: a method to selective synthesis anti-diols directly from commercially available alkene starting materials and an organocatalytic sulfoxidation procedure using diketones as catalysts. Chapter 1 describes a novel metal-free method for the one-pot anti-dihydroxylation of alkenes to form diols using malonoyl peroxide 13. The reaction conditions were optimised and the scope of the optimal conditions were examined with a variety of stilbene, styrene and indene derivatives to give the corresponding anti-diols in good to excellent yields and selectivities. Following this, a variety of mechanistic investigations were undertaken, revealing key intermediates and allowing the proposal of a mechanism. Scheme 1-1. Optimised conditions of anti-dihydroxylation discussed in Chapter 1. [see thesis for graphic representation] Chapter 2 demonstrates the development of an organocatalytic sulfoxidation using diketone catalysts. Following a significant optimisation process, the scope of sulfoxidation, showing a wide tolerance of functional groups, was explored. Mechanistic investigation was also undertaken, exploring the intermediates isolated from the procedure and an exploration of the reactivity using tool compounds. The stoichiometric process was also investigated to generate kinetics and a postulated transition state. Scheme 1-2. Optimised conditions of organocatalytic sulfoxidation discussed in Chapter 2. [see thesis for graphic representation] Chapter 3 contains the experimental procedures and analytical data generated for all the compounds synthesised within this thesis.
41
Ohleier, Alexia. "Nickel mediated negishi and oxidative couplings." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30074/document.
Abstract:
Ce projet de recherche porte sur la formation de nouvelles liaisons C-C et la production de produits chimiques valorisables grâce à l'utilisation de complexes de nickel chélatés. La première partie de cette thèse est dédiée à des complexes bis-phosphines de nickel employés comme catalyseurs pour le couplage croisé de Negishi. Le précatalyseur [(dcpp)Ni(n2-toluene)] (dcpp = 1,3 bis(dicyclohexylphosphino)propane) permet de coupler efficacement des chloro-arènes avec des organozinciques en utilisant de faibles charges catalytiques (0,2 mol% - 0,1 mol%) et des conditions douces (THF, 60 °C). Une étude mécanistique fondée sur des réactions stœchiométriques et des calculs DFT prouve la présence d'intermédiaires Ni(0)/Ni(II) au cours de la catalyse et exclut tout passage par un mécanisme de type Ni(I)/Ni(III). La seconde partie de ce travail porte sur le couplage oxydant entre l'éthylène et le CO2 sur des complexes de nickel chélatés par des bis-phosphines ou des bis-NHC. Une étude cinétique de l'équilibre entre [(dcpp)Ni(C2H4)] et [(dcpp)nickelalactone] a été réalisée. Le complexe [(dcpp)nickelalactone] peut ensuite être réduit et fonctionnalisé en dérivé du propanol en présence de pinacolborane. Des études mécanistiques et catalytiques préliminaires ont eté menées. De plus, de nouvelles méthodologies de synthèses ont été développées afin d'obtenir les premiers complexes [(bis-NHC)Ni(C2H4)] et [(bis-NHC)nickelalactone]The aim of this research project is to promote the formation of new C-C bonds and the production of valuable chemicals by using chelated nickel complexes. The first part of this thesis is dedicated to [nickel(bis-phosphine)] complexes employed as catalysts for Negishi cross coupling reactions. Designed Ni(0) precatalyst [(dcpp)Ni(n2-toluene)] (dcpp = 1,3-bis(dicyclohexylphosphino)propane) promotes efficiently the Negishi cross coupling between aryl chlorides and phenylzinc chloride derivatives at low catalyst loadings (down to 0.2 mol% - 1 mol%) under mild conditions (THF, 60°C). Mechanistic investigations relying on stoichiometric reactions and DFT calculations prove the involvement of Ni(0)/Ni(II) intermediates rather than Ni(I)/Ni(III) species during the catalysis. The second part of this work deals with the oxidative coupling between ethylene and CO2 at bis-phosphine and bis-NHC chelated nickel complexes for the production of value-added chemicals. The equilibrium between [(dcpp)Ni(C2H4)] and [(dcpp)nickelalactone] has been investigated by kinetic studies. The subsequent cleavage of [(dcpp) nickelalactone] by pinacolborane leads to its reductive functionalization into a propanol derivative. Preliminary mechanistic and catalytic investigations have been undertaken. Moreover, new methodologies are provided for the synthesis of the first [(bis-NHC)Ni(C2H4)] and [(bis-NHC)nickelalactone] complexes
42
Grocock, Estella Louise. "Novel catalysts and mechanistic investigation in dioxirane-mediated oxidations." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/33767.
Abstract:
The work described in this thesis follows the development of a family of achiral trifluoroketones, which were studied for use as ketone catalysts for the in situ generation of dioxiranes. One of the ketones investigated was a novel solid phase polymer-bound ketone, which led to a new area for dioxirane generation that could be of particular use in industry. Oxidations were run under monophasic and biphasic solvent reaction systems, with emphasis on the former. Ranges of reactions, including epoxidation and alcohol oxidations were examined to test the efficiency of each ketone. It was found that epoxidation reactions gave the most efficient oxidations, although secondary benzylic alcohols also gave evidence of oxidation.
43
Godinho, Diana Anacleto. "Produção de nanocelulose para aplicação em papel de impressão e escrita." Master's thesis, [s.n.], 2017. http://hdl.handle.net/10316/83161.
Abstract:
Dissertação de Mestrado Integrado em Engenharia Química apresentada à Faculdade de Ciências e TecnologiaA presente tese de mestrado tem como principal objetivo a produção de nanocelulose 1 a partir de pasta kraft branqueada de eucalipto, para aplicação na matriz fibrosa do papel de impressão e escrita e posterior estudo da sua influência nas propriedades papeleiras. A “Indústria Papeleira” ao longo dos últimos anos tem vindo a otimizar o processo de produção de papel face ao aumento da competitividade, abrindo assim portas à investigação de novos materiais, com o objetivo de melhorar as propriedades finais do papel. Neste contexto, sabe-se que o carbonato de cálcio precipitado é um aditivo de extrema importância na sua produção, que para além de ser mais económico do que as fibras de celulose, a sua aplicação melhora substancialmente as propriedades óticas. Desta forma, seria importante aumentar a quantidade percentual deste aditivo na estrutura do papel sem comprometer as propriedades mecânicas. Nesta perspetiva, a área de Nanotecnologia surge como uma via promissora, através da incorporação de nanocelulose na matriz fibrosa do papel, que de certa forma poderá influenciar positivamente os custos de produção. A nanocelulose tem despertado interesse devido às suas propriedades promissoras como, biodisponibilidade da matéria-prima, biodegradabilidade, biocompatibilidade, resistência mecânica, fibrilas com razão comprimento/largura elevada e boas propriedades barreira, promovendo desta forma a sua aplicação como material de reforço em várias áreas, como por exemplo, as áreas têxtil, eletrónica ou alimentar, sendo que na área da produção de papel ainda se encontra numa fase muito preliminar. Neste trabalho produziram-se nanocelulose/microcelulose com características químicas e físicas distintas, mediante aplicação de diferentes pré-tratamentos, com posterior aplicação de tratamento mecânico num homogeneizador de alta pressão, sendo esta metodologia denominada método combinado. Diferentes intensidades foram aplicadas nos pré-tratamentos químicos (oxidação mediada por TEMPO e reação de carboximetilação), e no pré-tratamento enzimático (hidrólise enzimática), enquanto que o tratamento mecânico se manteve constante a energia aplicada. Através da variação das quantidades de hipoclorito de sódio na oxidação mediada por TEMPO, hidróxido de sódio e ácido monocloroacético na reação de carboximetilação e de enzima na reação de hidrólise enzimática, foi possível produzir diferentes amostras, que foram posteriormente caracterizadas para avaliação da influência dos diferentes pré-tratamentos. A caracterização das CNF/CMF obtidas foi fundamental para avaliar a eficiência dos prétratamentos, e a influência destes no tratamento mecânico, especialmente no rendimento global de operação. As folhas laboratoriais foram produzidas com pasta kraft branqueada de eucalipto, amido e Anidrido Alquenil Succínico como agentes de colagem, PCC como filler, poliacrilamida catiónica (CPAM) como agente de retenção e as diferentes CNF/CMF produzidas. Avaliou-se por último a influência da incorporação das CNF/CMF na matriz fibrosa das folhas através da realização de testes físico-mecânicos. Concluiu-se que as CNF produzidas por oxidação mediada por TEMPO e carboximetilação, podem ser usadas como material de reforço na matriz fibrosa do papel e como aditivo no processo de floculação do PCC, promovendo, no geral, melhores propriedades mecânicas e o aumento de cargas minerais no papel. Todavia, o pré-tratamento químico não pode ser demasiado intenso, visto que prejudica a floculação das cargas. Neste estudo, verificou-se ainda em alguns casos, que a poliacrilamida catiónica prejudica as ligações das CNF às fibras. Por esta razão, estudou-se o efeito da eliminação do agente de retenção do furnish, constatando-se que esta ação promove bons resultados nas folhas com CNF produzidas a partir da aplicação de pré-tratamentos químicos (oxidação mediada por TEMPO e carboximetilação), não acontecendo, porém, o mesmo nas folhas com as CMF obtidas através da aplicação do prétratamento enzimático.1-Entendida neste estudo como fibrilas que maioritariamente têm diâmetros até 10 nm, mas que podem apresentar diâmetros superiores, podendo neste caso ser designadas por celulose microfibrilada (CMF).
This dissertation presents a study of nanocellulose 2 production from bleached kraft pulp, obtained from the eucalyptus, and its influence in paper properties when applied on printing and writing. During the past years, the competitivity in papermaking industries has been increased. Consequently, to improve paper properties, papermaking processes used are being optimized creating new horizons to investigate new materials that will refine the paper grades. Precipitated calcium carbon is an extremely important additive in the papermaking. Its application in paper improves substantially the optical properties and it is cheaper than cellulose fibers. Thus, it is important to study how to increase the percentual amount of this additive on the paper matrix without compromise the mechanical properties. In this perspective, the nanotechnology field emerges as a promising area, since the incorporation of nanocellulose on the fibrous matrix can influence positively the production costs. Nanocelluloses has gained much interest due to their promising properties, such as high raw material biodisponibility, biodegradability, biocompatibility, mechanical strength, aspect ratio and good barrier properties, mainly as a reinforcing material in many fields, for example, textile, electronics or medicine. However, the application of CNF in the papermaking industry is in a very preliminary stage. In this work, nanocellulose/microcellulose was produced with different chemical and physical characteristics, by applying different pre-treatments with subsequent application of mechanical treatment in the high-pressure homogenizer (HPH), being this experimental methodology called, combined method. Different intensities are applied in the chemical pre-treatments (TEMPO-mediated oxidation and carboxymethylation reaction), and on enzymatic pretreatment (enzymatic hydrolysis), while the energy applied on mechanical treatment remained constant. Through the variation of the quantities of sodium hypochlorite (TEMPO-mediated oxidation), sodium hydroxide and monochloroacetic acid in the carboxymethylation reaction and also the variation of the enzyme amount in the enzymatic hydrolysis, it was possible to produce different samples that were posteriorly characterized to studied the influence of the pre-treatments. The characterization of the CNF/CMF obtained was crucial to evaluate the efficiency of the pre-treatments, and the influence of these in the mechanical treatment, especially in the overall performance of the operation. The laboratorial sheets were produced with bleached kraft pulp from eucalyptus, starch and alkenyl succinic anhydride as a binder aid, PCC (filler), cationic polyacrylamide (CPAM) as a retention aid, and the different CNF produced. Finally, the incorporation of the CNF/CMF into the fibrous matrix was studied through physical-mechanic tests. It was concluded that the CNF produced by TEMPO-mediated oxidation and carboxymethylation, could be used in the paper fibrous matrix as a reinforcing material and as an additive in the flocculation process of the PCC, promoting the improvement of the mechanical properties and the increasing of the loading material in the sheets. However, the pre-treatment may not be done with too much intensity, since it affects the fillers flocculation. In this study, it was observed in some cases, that cationic polyacrylamide damages the fibresCNF bonding. For this reason, it was also studied the effect of CPAM removal from the furnish and this action, promotes good results in the sheets produced with CNF made from chemical pre-treatments (TEMPO-mediated oxidation and carboxymethylation). Unfortunately, the same does not happened with the sheets that contains CMF produced from enzymatic pre-treatment. 2-In this study, the CNF are understood as fibrils that mostly have diameters up to 10 nm. However, these fibrils may present higher diameters, being in this case called microfibrillated celulose (CMF).
44
Mansley, Tamsin E. "Iron(III) mediated oxidative cyclisations of substituted cyclopropanes." Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389223.
45
Parry, Joel D. "Transcriptomic assessment of quinone mediated hepatic oxidative stress." Thesis, University of Leicester, 2007. http://hdl.handle.net/2381/30781.
Abstract:
Quinone based drugs are complex structures with multiple chemical properties. Therefore in this work to further understand quinone toxicity in drugs simpler structures with defined chemistry were used as tools. To discern mechanistic insight transcriptomic investigations were undertaken in rat hepatocytes and in vivo mouse liver exposed to a range of prototypical quinines. Genes important in response to quinone exposure were identified and analysed using several bioinformatic tools. Transcriptomics in hepatocytes could not differentiate quinone redox effects from other interactions, although 22 'quinone signature genes' indicated a coordinated response to redox stress. A central role for mitochondria as targets of quinone interaction was confirmed, the transcriptomic profile indicating optimisation of energy metabolism and suppression of intrinsic apoptosis. Pim1 and Pim3 kinases were central to this response, confirmed in follow up experiments. Pharmacokinetics from mice treated in vivo with 25mg/kg DMNQ or menadione interperitoneally indicated DMNQ to be more widely distributed and better suited as an in vivo redox model compound than menadione. However, in vivo redox challenge from DMNQ in the liver was transient and insufficient to cause oxidative damage. The findings indicate that DMNQ has utility for studying redox stress in vivo, although a repeat dosing approach is required in future. The findings add to the knowledge-base of quinone toxicity. Particularly the increased responsiveness and sensitivity of hepatocytes in vitro compared to in vivo which may lead to an erroneous perception of toxicity if in vitro systems are studied alone.
46
Horne, Susan C. "Free radical mediated oxidative stress in plant cancers." Thesis, Abertay University, 2006. https://rke.abertay.ac.uk/en/studentTheses/fcb5aadb-8ee1-43dd-bbd0-367b93d87d11.
Abstract:
This project provides for the first time an in depth examination of oxidative stress and antioxidant protection in plant tissue cultures undergoing various stages of ageing and neoplastic progression towards a cancerous state. Two experimental systems were investigated: (1) Beta Vulgaris cultures comprising two fully habituated (cancerous), lines, one partially abituated line and a non-habituated cell line; (2) Glycine max cultures comprised of two similar aged (15 years) cell lines, one of which has lost the ability to produce pigments. Biochemical profiles of free radical activity and the sequential stages of lipid peroxidation were constructed, together with parallel assessments of primary antioxidants (catalase, peroxidase and superoxidase dismutase and the glutathione-ascorbate couple). The main findings demonstrated that fully habituated cell lines of B. vulgaris , possessed activities and very low levels of primary antioxidants, that were on occasion at the assay limits of detection. In the partially habituated and nonhabituated cell lines antioxidant levels were low but not to the same extent. The redox status of the cultures decreased as abituation increased and the lowest GSH/GSSG redox ratio was observed in the fully habituated cell lines. Markers of lipid peroxidation increased inversely to decreased antioxidant protection; all B. vulgaris cultures had abnormal cytological manifesting morphological characteristics symptomatic of disturbed metabolism, oxidative stress and loss of totipotency. In vitro aged callus cultures of G. max maintained in tissue culture for approximately fifteen years had lost their embryogenic capacity and one of the cell lines has lost the ability to produce pigments. Activities and levels of key antioxidants in these cell lines were greatly diminished and considerable disruption of the GSH/GSSG ratio concomitant with increased markers of lipid peroxidation was observed. This study clearly demonstrates that ageing and habituation implying neoplastic progression to a cancerous state involves oxidative stress concomitant with a major and deleterious disturbance in antioxidant protection. The extent to which oxidative stress occurred increased with the age and the degree of neoplastic progression, such that the partially habituated cell line, was not demonstrably different to the normal B. vulgaris cell line. The loss of antioxidant protection associated with ageing and habituation involved the compromise of key antioxidant enzymes (catalase, peroxidase and Cu, Zn-SOD) and GSH/GSSG ratios decreased with age and the degree of habituation. This study concludes with an exploration of the role of oxidative stress in in vitro ageing and habituation and considers the importance of maintaining antioxidant status in tissue cultures used in plant biotechnology programmes, and emphasises the use of oxidative stress studies to help understand and ameliorate in vitro recalcitrance, the loss of totipotency and somaclonal variation.
47
Lo, Raquel. "Cystine-mediated oxidative defence in Lactobacillus reuteri BR11." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/39608/1/Raquel_Lo_Thesis.pdf.
Abstract:
Lactobacillus reuteri BR11 possesses an abundant cystine uptake (Cyu) ABC-transporter that was previously found to be involved in a novel mechanism of oxidative defence mediated by cystine. The current study aimed to elucidate this mechanism with a focus on the role of the co-transcribed cystathionine ã-lyase (Cgl). Growth studies of wild-type L. reuteri BR11 and mutants inactivated in cgl and the cystine-binding protein encoding gene cyuC showed that in contrast to the Cyu transporter, whose inactivation led to growth arrest in aerated cultures, Cgl is not crucial for oxidative defence. However, the role of Cgl in oxidative defence became apparent in the presence of severe oxidative damage and cysteine deprivation. Cysteine was found to be protective against oxidative stress, and the action of Cgl in both cysteine biosynthesis and degradation poses a seemingly futile pathway that deprives the intracellular cysteine pool. To further characterise the relationship between Cgl activity and cysteine and their roles in oxidative defence, enzymatic assays were performed on purified Cgl, and intracellular concentrations of cysteine, cystathionine and methionine were determined. Cgl was highly active towards cystine and cystathionine and less active towards cysteine in vitro, suggesting the main function of Cgl to be cysteine biosynthesis. Cysteine was found at high concentrations in the cell, but the levels were not significantly affected by inactivation of cgl or growth under aerobic conditions. It was concluded that both anabolic and catabolic activities of Cgl towards cysteine contribute to oxidative defence, the former by maintaining an intracellular reservoir of thiol analogous to glutathione, and the latter by producing H2S which is readily secreted, thus creating a reducing extracellular environment. The significance of the Cyu transporter to the physiology of L. reuteri BR11 prompted a phylogenetic study to determine its presence in bacteria. Orthologs of the Cyu transporter that are closest matches to the Cyu transporter are only limited to several species of Lactobacillus and Leuconostoc. Outside the Lactobacillales order, the closest matching orthologs belong to Proteobacteria, and there are more orthologs in Proteobacteria than non-Lactobacillales Firmicutes, suggesting that the Cyu transporter locus was present in the ancestor of the Proteobacteria and Firmicutes, and over evolutionary time has been lost or diverged in many Firmicutes. The clustering of the Cyu transporter locus with a gene encoding a Cgl family protein is even rarer. It was only found in L. reuteri, Lactobacillus vaginalis, Weissella paramesenteroides, the Lactobacillus casei group, and several Campylobacter sp. An accompanying phylogenetic study of L. reuteri BR11 using multi-locus sequence analysis showed that L. reuteri BR11 had diverged from more than 100 strains of L. reuteri isolated from various hosts and geographical locations. However, comparison with other Lactobacillus species supported the current classification of BR11 as L. reuteri. The most closely related species to L. reuteri is L. vaginalis or Lactobacillus antri, depending on the housekeeping gene used for analysis. The close evolutionary relationship of L. vaginalis to L. reuteri and the high degree of sequence identity between the cgl-cyuABC loci in both species suggest that the Cyu system is highly likely to perform similar functions in L. vaginalis. In search of other genes that function in oxidative defence, a number of mutants which were inactivated in genes that confer increased resistance to oxidative stress in other bacteria were constructed. The genes targeted were ahpC (peroxidase component of the alkyl hydroperoxide reductase system), tpx (thiol peroxidase), osmC (osmotically induced protein C), mntH (Mn2+/Fe2+ transporter), gshA (ã-glutamylcysteine synthetase) and msrA (methionine sulfoxide reductase). The ahpC and mntH mutants had slightly lower minimum inhibitory concentrations of organic peroxides, suggesting these genes might be involved in resistance to organic peroxides in L. reuteri. However, none of the mutants exhibited growth defects in aerated cultures, in stark contrast to the cyuC mutant. This may be due to compensatory functions of other genes, a hypothesis which cannot be tested until a robust protocol for constructing markerless multiple gene deletion mutants in L. reuteri is developed. These results highlight the importance of the Cyu transporter in oxidative defence and provide a foundation for extending the research of this system in other bacteria.
48
Maheshwari, Himanshu. "Functional 1D mesochannels for Electrochemical Sensors." Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0267.
Abstract:
Dans cette thèse, nous discutons de silice à mésoporosité verticale et ses méthodes de synthèses, ses propriétés caractéristiques et ses applications potentielles. Il s’agit d’un matériau particulièrement intéressant car il offre un accès direct au substrat sur lequel il est déposé au travers de mésopores et offre une grande variété d’applications telles que : la filtration à l’échelle moléculaire, la protection des surfaces d’électrodes, la détection améliorée de cations par électrochimie et électrochimiluminescence, le dépôt de nanofils isolés métalliques ou polymériques, les biocapteurs ADN, etc. Nous discutons ensuite de l’oxydation à médiation électrochimique des aminothiols naturels (cystéine, glutathion et homocystéine) par un dérivé du ferrocène selon un mécanisme EC’, et de la cinétique du transfert d’électron sur une électrode nue d’oxyde d’étain dopé à l’indium (ITO). Ensuite, des films minces de silice mésoporeuse présentant des nanocanaux verticaux ont été déposés par une méthode d’auto-assemblage assistée électrochimiquement sur une électrode d’ITO. En utilisant les électrodes déposées sur le film de silice et le ferrocenediméthanol (Fc(MeOH)2) comme médiateur en solution, il est possible d’oxyder les deux, la cystéine et le glutathion, par Fc(MeOH)2+ générés à la surface de l’électrode, par un mécanisme EC’. Les vitesses de transfert d’électrons étaient trois fois plus rapides avec la cystéine qu’avec le glutathion. Ce phénomène a été exploité pour la méthode de détection sélective et sans réactif de la cystéine par rapport au glutathion en utilisant un film de silice mésoporeuse fonctionnalisé avec du ferrocène sur une électrode d’ITO, grâce à une combinaison des limitations de la cinétique de transfert de charge et du transport de masse à l’intérieur des nanocanaux orientés. Ceci a été démontré par des méthodes de voltampérométrie cyclique et d’ampérométrie dans un mode d’analyse par injection en flux. Expérimentalement, la plus basse concentration de cystéine détectée était de 3 µM en mode d’analyse par injection en flux. De plus, des microélectrodes d’ITO et de carbone ont été fabriquées et déposées avec de la silice mésoporeuse. Les microélectrodes de carbone ont été fonctionnalisées avec du ferrocène et caractérisées électrochimiquement. Les électrodes modifiées à la silice présentent un bon potentiel dans les applications électro-analytiques pour une variété de réactifs par leur taille et leurs propriétés sélectives de chargeIn this thesis, we discuss vertically oriented mesoporous silica and their characteristic properties, synthesis procedures and applications. It is of particular interest as it provides direct access to underlying substrate through the pores and is suitable for a variety of applications such as molecular sieving, electrode protection, enhanced detection of cations through electrochemistry and electrochemiluminescence, deposition of isolated metallic and polymeric nanowires, DNA biosensor, etc. We then discuss the electrochemically mediated oxidation of natural aminothiols (cysteine, glutathione and homocysteine) by a ferrocene derivative following an EC’ mechanism and the rate kinetics at a bare indium-tin oxide (ITO) electrode. Further, mesoporous silica thin films exhibiting vertical nanochannels were grown by electrochemically assisted self-assembly method onto ITO electrode. When using the silica film deposited electrodes and ferrocenedimethanol (Fc(MeOH)2) as mediator in solution, both cysteine and glutathione can be oxidized by Fc(MeOH)2+ generated at the electrode surface, following an EC’ mechanism. Electron transfer rates were three times faster with cysteine than glutathione, suggesting that selectivity for cysteine could be achieved using mesoporous films. This was exploited for the reagent-free selective detection of cysteine over glutathione by using a ferrocene-functionalized mesoporous silica film on ITO electrode, based on a combination of charge transfer kinetic and mass transport limitations through the oriented nanochannels. This has been demonstrated by cyclic voltammetry and amperometry in a flow injection analysis mode. Experimentally, the lowest concentration of cysteine detected was 3 µM in flow injection analysis mode. Further, microelectrodes made of ITO and carbon were fabricated and modified with mesoporous silica. Carbon microelectrodes were further functionalized with ferrocene and characterized electrochemically. Overall, silica modified electrodes show a good potential in electroanalytical applications for a variety of reagents through their size and charge selective properties
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Jain, Nikita. "Chiral hypervalent iodine mediated enantioselective oxidative dearomatization of naphthols." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62521.
Abstract:
This dissertation investigates and describes the hypervalent iodine mediated dearomatization of naphthols, thereby yielding diversity of spiro-heterocyclic compounds in both racemic and chiral form.
The first part of this thesis discloses the synthesis of racemic spiropyrrolidines and spirolactams via oxidative amidation of corresponding naphtholic sulfonamides, employing DIB as the oxidant. Enantioselective variant of the same have been demonstrated by using in situ generated chiral hypervalent iodine to provide chiral spiropyrrolidines. A noteworthy side reaction discovered in the course of these studies is the asymmetric oxidative addition of meta-chlorobenzoic acid to the naphtholic sulfonamides. The resulting acyloxylated adducts were formed with a greater degree of asymmetric induction compared to spiropyrrolidines in the same reaction mixture. Based on the results obtained from optimization study and substrate scope, plausible mechanistic insights of both cyclization and acyloxylation reactions have been provided.
The second part of this thesis unravels the spiroetherification of naphtholic alcohols, thereby yielding spiroethers both in racemic and chiral form. Chiral hypervalent iodine reagents generated in situ provided a range of spiroethers with excellent ee’s and high yields. These chiral oxidants have been evaluated for kinetic resolution of naphtholic primary alcohols bearing stereogenic center at β-position in the side chain.Science, Faculty of
Chemistry, Department of
Graduate
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Hulcoop, David Geoffrey. "Manganese(III) acetate mediated domino oxidative free radical cyclisations." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613805.