Dissertations / Theses on the topic 'Active oxygen'

Oxygen is one of the most important molecules in human beings. Our research is focused on how the human body can respond and adapt to the physiological challenge posed by a lack of oxygen. Ascorbic acid (Vitamin C) is one of the most important and considered the most effective water-soluble, chain-breaking antioxidant in human plasma, with the capacity to prevents damage by free radicals. This thesis presents four studies investigating the phenomenon of Reactive Oxygen Species (ROS) generation in the many different surgical conditions in the animal and in the human. Study one investigated the geometry and thermodynamic properties of vitamin C. Calculations were carried out at the restricted and unrestricted B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p) and B3LYP/EPR-II levels for two conformers (1 and 2) of L-ascorbic acid and their respective oxidation products to monodehydroascorbates of ab-initio methods by Gaussian O3W package. Conformer 1, free radical properties are compared with previously published calculations in the gaseous and aqueous solution states and with experimental EPR values. Calculated molecular structures, EPR (electron paramagnetic resonance spectroscopy), the vibration spectral and energetic properties and all are reported including some proposed changes to previous EPR assignments. Conformer 2 of L-ascorbic acid is predicted to have lower energy than Conformer 1, under the method and basis sets used, by between 11 and 26 kJ mol-1 and is stabilised by internal hydrogen bonding. Relaxed potential energy surface (PES) scans were carried out for two proton transfer processes and relative energies of stable minima and barriers between them determined. Hydrogen transfer is predicted in two systems with favourable spatial arrangements of O–H and O groups for which relaxed potential energy surface scans are reported. Calculated vibrational wavenumber values are provided for selected C=C, C=O, C–H and O–H modes assigned to particular groups and significant calculated EPR hyperfine coupling constants (HCC) values for splitting by H(1) and C(13) for radical species are also reported. These calculations contribute to a better understanding of the complex role of L-ascorbic acid and its various oxidised, neutral, ionic and radical forms in biochemistry and medicine. Study two examined if vitamin C could ameliorate the damaging effects of I-R on myocardium and we postulated that the mechanism of vitamin C protection against iii I-R-induced cell death involved quenching of ROS. In the vitamin C group after 5 min of reperfusion a significant, sudden increase of diastolic pressure in the heart was noted and reached a maximum of 77 mmHg after 12 min of reperfusion and then gradually decreased to 51 mmHg after 60 min of reperfusion period but was quicker than in Control group reaching 37 mmHg by the end of the reperfusion period. The level of A·− (ascorbate free radicals) sudden and massive increased at the time of reperfusion in the Vitamin C group. This increase was associated with poor mechanical function in hearts as indicated by the significantly depressed recovery process. After 30 min of global, now-flow ischaemia and 60min of reperfusion infarct size averaged 33% ± 1 in Control group and 30 % ± 1 in Vitamin C group, respectively, (P<0.05). There is strong evidence that oxygen centered radicals contribute to postischaemic dysfunction after global ischaemia. Our data unquestionably suggest that the large production of A·− was associated with a greater depression in myocardial contractile function, therefore could represent a marker of oxidative stress during I-R and could be related to the functional impairment during reperfusion. In summary, we have used the animal models of isolated heart perfusion to provide evidence that vitamin C did not reduce the infarct size, however “tendency” towards a decrease (↓) in infarct size with ascorbate and it protects from oxidative damage during global I-R as manifested by decreased concentrations of A·− and enhance recovery of mechanical function such as diastolic pressure and LVDP in postischaemic working rat hearts. Study three was designed to test the hypothesis that the physiological trauma associated with venous cannulation may artefactually stimulate systemic free radical formation in the acute phase that if not accounted for may under-estimate the oxidative stress response to exercise. The relationship between the time of venepuncture and the level of free radical generation during normoxic conditions was further investigated. The venous cannulation in Phase I, increased plasma A·− by 347 ± 173 AU/√G, P <0.05 after 2min of venepuncture with further increases observed after 5min and 10min of venous cannulation, respectively (403 ± 178 AU/√G; 462 ± 93 AU/√G, P < 0.05) vs baseline point time. After this time the level of A·− slightly blunted as to achieve a similar level to baseline point control after 30 minutes. In phase II the exerciseinduced increase in A·− was subsequently shown to be 48% greater (30min as opposed to the 2min post-cannulation resting baseline)(1754 ± 361 vs. 1979 ± 375 AU, P <0.05). Our findings demonstrate and confirm that venous cannulation per se stimulates iv the systemic formation of free radicals as an acute phase response which peaks at 10min and require approximately 15min to normalise. This has important interpretive implications for future studies that employ catheterisation. The final Study examined if the combination of exercise and inspiratory hypoxia would further compound regional tissue de-oxygenation that is frequently encountered during the ischaemic phase of surgery and thus, by consequence increase oxidative stress. The aim of the study was to further understand a potential relationship between oxidative stress and alterations in muscle oxygenation. Clear significant increases in the plasma concentration of A·− were detected in the peripheral blood of patients (normoxia(baseline) vs 6 data points of reperfusion after 5min of global ischaemic condition, P<0.05),(baseline vs immediate after ischaemia; 2337±525 vs 2633±508, AU, respectively). During global ischaemia the regional muscle oxygenation significantly decreased (↓∆O2Hb-oxyhaemoglobin), ↑∆HHb- deoxyhaemoglobin ), although increased regional blood volume (↑∆tHb- total haemoglobin). From the end of global ischaemia to 10 min after the regional muscle oxygenation progressively back to the start data point (↓∆HHb, ↑∆O2Hb). This study demonstrates for the first time that the I-R has got a big influence on the muscle oxygenation to increased ROS and the return of values towards baseline period in reperfusion stage appears to coincide with increased oxidative stress. Moreover, the present study has also demonstrated increased A·− level as early as the ischaemic phase of experiment independent of perioperative changes in the partial pressure of oxygen (pO2), elucidate a potentially important role for oxidative stress in provoking an appropriate vasodilation (NO-bioavailability) during the I-R period. This work demonstrates that; - Ascorbate is an antioxidant that can scavenge tissue and blood borne free radical, is essential in controlled amounts and is capable of initiating protective adaptation in the face of oxidative stress for the maintenance of physiological homeostasis. - Reperfusion is always associated with a sudden and massive release of ascorbate free radicals, with a maximal liberation within the first minutes of reperfusion. Vitamin C tended to reduce infarct size and protects from oxidative damage during global ischaemia and reperfusion. - The venous cannulation alone is enough per se stimulates the systemic formation of free radicals as a acute phase response. If this baseline artefact is not taken into account, the true magnitude of the exercise-induced oxidative stress response will be under-estimated.
The I-R has got a major influence on the muscle oxygenation to increased ROS and the return of values towards baseline period in reperfusion stage appears to coincide with increased oxidative stress. Using the state-of-the-art molecular techniques that include Electron Paramagnetic Spectroscopy (EPR) for the direct detection of free radicals and Near Infrared Spectroscopy (NIRS) for the direct detection of muscle oxygenation these studies have attempted to translate the basic mechanisms associated with free radical formation during I-R and have provided unique insight into the basic mechanisms responsible for the oxidative stress with the ultimate objective of developing novel antioxidant interventions that can provide effective prophylaxis.

Este trabajo de Tesis Doctoral se ha centrado en comprender el comportamiento de electrocatalizadores basados en materiales carbonosos para la reacción de reducción de oxígeno. Con el fin de profundizar en el conocimiento de la naturaleza de los sitios activos de catalizadores basados en materiales carbonosos para esta reacción, se han seleccionado o preparado muestras con diferentes composiciones, texturas porosas y estructuras. De estos resultados se han conseguido importantes avances en el conocimiento del papel que los sitios activos de catalizadores basados en materiales carbonosos desempeñan en dicha reacción. Estos conocimientos y los materiales derivados pueden utilizarse en el desarrollo de cátodos para pilas de combustible en medio alcalino.
Heiwa Nakajima Foundation

Oxygen scavengers are used in active packages to protect the food against deteriorative oxidation processes. The aim of this work was to investigate the possibilities to produce oxygen-scavenging packaging materials based on oxygen-reducing enzymes. The enzymes were incorporated into a dispersion coating formulation applied onto a food-packaging board using conventional laboratory coating techniques. Various enzymes were used: a glucose oxidase, an oxalate oxidase and three laccases originating from different organisms. All of the enzymes were successfully incorporated into a coating layer and could be reactivated after drying. For at least two of the enzymes, re-activation was possible not only by using liquid water but also by using water vapour. Re-activation of the glucose oxidase and a laccase required relative humidities of greater than 75% and greater than 92%, respectively. Catalytic reduction of oxygen gas by glucose oxidase was promoted by creating an open structure through addition of clay to the coating at a level above the critical pigment volume concentration. Migration of the enzyme and the substrate was reduced by adding an extrusion-coated liner of polypropylene on top of the coating. For the laccase-catalysed reduction of oxygen it was possible to use lignin derivatives as substrates for the enzymatic reaction. The laccase-catalysed reaction created a polymeric network by cross-linking of lignin-based entities, which resulted in increased stiffness and increased water-resistance of biopolymer films. The laccases were also investigated with regard to their potential to function as oxygen scavengers at low temperatures. At 7°C all three laccases retained more than 20% of the activity they had at room temperature (25°C), which suggests that the system is also useful for packaging of refrigerated food.

The aim of this study was to investigate the role of ROS in the protective and pathological immune response during malarial infection. For this purpose, four isolates of Plasmodium parasites (P. berghei ANKA, P. vinckei, P. berghei K152 and P. chabaudi) and two different inbred strains of mice (CBA and DBA) were used. The patterns of mortality varied between the different mouseparasite strain combinatio ns. The mortality of CBA mice infected with P. vinckei and P. berghei K152, and DBA mice infected with P. berghei ANKA, related to the levels of parasitaemia. However early mortality of CBA mice infected with P. berghei ANKA did not relate to the parasitaem ia level but to the onset of neurologica l symptoms. Over 90% of P. chabaudi—infected CBA mice recovered from the infection. The morphologi cal examinatio n of brain tissues obtained from P. berghei ANKA-infec ted CBA mice on day 7 post-inocul ation showed haemorrag e, oedema and the infiltration of mononucle ar cells. Measurement of the permeability of the blood-brain barrier by injection of Evans blue showed the dye leaking into the brain parenchyma, suggesting a dysfunction of the barrier in this mouse model. The hypothesis that ROS play a role in the anti—malaria response was supported by previous studies demonstrati ng that malaria parasites are killed by ROS in vivo and in vitro (reviewed in Hunt & Stocker. 1990). To further test the hypothesis. the oxidative burst ability of splenic macrophage s and peripheral monocytes taken from different mouse-para site strain combinations was examined. There was a significant increase of superoxide production by splenic macrophag es at the early stage of all the infections and the spleen weight gradually increased during all the infections. Furthermore, the oxidative burst ability of monocytes was significantly increased in the late stage of all the infections, which was accompanied by increased peripheral WBC numbers, especially in the numbers of monocytes and PMNs in all the infections except the P. berghei ANKA infection in CBA mice. Of the four strains of parasites infecting CBA mice, the self-resol ving P. Chabaudi infection induced the greatest PMA-stimulable response superoxide anion production on certain days after parasite in inoculation in both splenic macrophages and monocytes . Conversely, the P. vinckei infection induced the lowest response, which may partly explain why the parasites generated faster in these mice than in the other three strains. Malaria parasites are able to induce immunosup pression at the early stage of infection as shown by the decline in the total number of WBC and the decrease of superoxide production by monocytes. This immunosuppresion may help explain why the parasites can survive even when their numbers are. small. TNF and IFN—y are known as major mediatory factors involved in the development of cerebral malaria. This was supported by the cytokine gene expression studies which showed that both TNF and IFN-y mRNAs were expressed in the brains of mice with cerebral malaria. These cytokines may stimulate mononuclear phagocytes to produce other soluble factors to cause cerebral damage. ROS release d from mononuclear phagocytes are thought to be crucial factors involved in the development of cerebral malaria (Hunt et al., 1991). However , the oxidative burst ability of splenic macrophages and monocytes in the P. berghei—ANKA infected CBA mice, which suffered cerebral malaria and died early in the infection, was lower than that in the same infection in DBA mice which recovered from the cerebral lesion but died at a later stage of infection with a high level of parasitaemia. Further more, lipid peroxidation studies showed that there was no significant difference in brain MDA formation between control mice and the mice with cerebral malaria . These results fail to provide evidence for a role of ROS in the development of cerebral malaria . Further studies to investigate lipid peroxidation and redox. status of the brain in cerebral malaria using HPLC are required.

Many environmental stresses result in increased generation of active oxygen species (AOS) in plant cells, leading to the induction of protective mechanisms. In this study, signalling components linking AOS perception to downstream responses were examined, with particular emphasis on H₂O₂ signalling. All AOS investigated had an early [Ca²⁺]_cyt peak in common, but differed in other aspects of their Ca²⁺ signatures, indicating that the plant is able to discriminate between different types of AOS. An early event in AOS signal transduction may involve changes in the cellular redox balance as reduction of glutathione levels prior to stress application increased the height of the first [Ca²⁺]_cyt peak. Inhibiting or enhancing the height of the H₂O₂-triggered Ca²⁺ signature lead to inhibition or enhancement of GST1 and APX1 induction, respectively, demonstrating that the Ca²⁺ signature is required for induction of genes encoding antioxidant enzymes. OX1, encoding a putative ser/thr kinase, was shown to be involved in signal transduction in response to H₂O₂-generating stresses. Transcript levels of OX1 were increased upon treatment with H₂O₂ and a range of abiotic and biotic stresses as well as ABA, all of which have been shown to result in H₂O₂ accumulation. Inhibition of stress-induced [Ca²⁺]_cyt elevations inhibited OX1 induction, placing the OX1 kinase downstream of Ca²⁺ in the signalling chain. OX1 is required for full activation of AtMPKS and AtMPK6 in response to ozone fumigation, indicating that OX1 functions upstream of these MAP kinases. An ox1 null-mutant displayed enhanced susceptibility to infection with a virulent Peronospora parasitica isolate as well as reduced induction of several defence genes. In addition, the ox1 mutant exhibited shorter root hairs and an early flowering phenotype. AOS treatment induced several genes encoding AtERF transcription factors, but did not have an effect on other members of this family. Induction occurred in an ethylene-independent but Ca²⁺-dependent manner.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Solar-driven electrochemical splitting of water to hydrogen and oxygen is crucial for the production of inexpensive, sustainable, and carbon-neutral fuels for future global energy requirements. Of the two half-reactions for water splitting, developing catalysts for the oxygen evolution reaction (OER) is a challenge because orchestrating the coupled transfer of four protons and four electrons is kinetically demanding. Currently, inexpensive and active OER catalysts comprised of earth-abundant elements from cobalt and nickel oxides operate in neutral and alkaline pH. These same systems corrode under acidic conditions, which is a regime important for electrolyzers and photoelectrochemical devices as well as for fundamental mechanistic studies. In this thesis, we iteratively design an active, stable, and earth-abundant acidic oxygen evolution catalyst through multiple generations. The first version focused on an electrodeposited manganese oxide (MnOx) catalyst that is stable in acid but exhibits low OER activity. Kinetic and mechanistic analysis on deposition and oxygen evolution mechanisms show that its stability manifests from strong manganese-oxygen bonds and self-healing. The second generation system improved activity while retaining acid stability by activating MnOx through a voltage cycling protocol. Structural studies show that activation induces a lower bulk manganese oxidation state and turbostratic disorder. This catalyst architecture was redesigned in the third iteration as a mixed metal oxide where functionality is decoupled into separate metals: Co was employed as the catalytic element while Mn served as the structural component. These CoMnOx films demonstrate the facile OER kinetics of Co and the acid corrosion resistance of Mn. However, these films cannot operate at high potentials since Mn dissolves as permanganate. Thus in our final fourth generation catalyst, we replaced the structural component with lead (doped with iron), an optimization discovered by potential-pH analysis. These CoFePbOx films exhibit ~70 mV/decade Tafel slopes and long-term stability at 1 mA/cm² in pH 2.5, operating at only 200 mV higher overpotential than iridium oxide. Overall, we demonstrate the ability to rationally modify and design an active, stable, and earth-abundant oxygen evolution catalyst.
by Michael Huynh.
Ph. D.

Les plastiques sont devenus les matériaux les plus utilisés pour la préservation de denrées alimentaires. Malgré leurs nombreux avantages (transparence, prix, modularité, propriété barrière aux gaz), leur imperméabilité à l’oxygène doit être sans cesse améliorée afin d’éviter aux denrées de subir diverses réactions d’oxydation et ainsi prolonger leurs durées de conservation. Pour cela, une solution envisageable consiste à combiner à des polymères, des catalyseurs métalliques pour piéger l’oxygène. Cette possibilité a été étudiée dans cette thèse. Après un premier chapitre introductif, le deuxième décrit les propriétés physico-chimiques des différents catalyseurs métalliques sélectionnés (stabilité, constantes de protonation, constante de complexation envers le cobalt(II) et le manganèse (II), capacité d’oxygénation, électrochimie). Le troisième chapitre est consacré à leur utilisation en tant qu’oxydant métallique de substrats organiques. Enfin le quatrième et dernier chapitre présente une étude à l’état solide de l’oxydation de polymères en présence de catalyseurs métalliques. Une large part de ce dernier chapitre a été consacrée à la caractérisation des produits d’oxydation
Plastics are becoming the most used material for food and drinks preservation. Despite their numerous advantages (transparency, price, modularity, gas barrier property), their oxygen barrier properties have to be improved to avoid hazardous oxidation reactions to foods and drinks and so to increase their shelf-life. One alternative to solve this problem is to combine polymers and metal catalysts to scavenge oxygen. This possible strategy was investigated during this Ph.D. project. After a first introductive chapter, the second depicts the physico-chemical properties of selected metal catalysts (stability, protonation constants, complexation constants towards cobalt(II) and manganese(II), oxygenation capacity, electrochemistry). The third chapter is devoted to their use as powerful oxidant of organic substrate. Finally, the last chapter is dedicated to a solid-state study of polymer oxidation in the presence of metal catalysts. A large part of this last chapter has been devoted to the thorough elucidation of the nature/structure of the oxidized product(s)

A series of structurally related BODIPY dyes were synthesised and characterised. Their photophysical properties were studied in order to determine whether they would be suitable candidates for use as photosensitisers in the photodynamic therapy (PDT) treatment of cancer. The synthesis of two highly fluorescent BODIPY cores was achieved via the acid-catalysed condensation of a pyrrole and a functionalised aldehyde. In order to promote intersystem crossing, and hence improve the singlet oxygen generation of these dyes, bromine atoms were added at the 2,6-positions of the BODIPY core. These dibrominated analogues showed good singlet oxygen quantum yields, and excellent photostability in ethanol. In order to red-shift the main spectral bands of the BODIPY dyes towards the therapeutic window, vinyl/ styryl groups were introduced at the 3-, 5-, and 7-positions via a modified Knoevengal condensation reaction. The addition of vinyl/ styryl groups to the BODIPY core caused an increase in fluorescence quantum yield as well as a decrease in singlet oxygen quantum yield with respect to the dibrominated analogues. However, two of the red-shifted BODIPY dyes still showed moderate singlet oxygen quantum yields. The use of BODIPY dyes in nonlinear optics (NLO) was explored. The nonlinear optical characterisations and optical limiting properties of a series of 3,5-dithienylenevinylene BODIPY dyes were studied, both in dimethylformamide (DMF) solution and when embedded in poly(bisphenol A carbonate) (PBC) as thin films. The 3,5-dithienylenevinylene BODIPY dyes showed typical nonlinear absorption behaviour, with reverse saturable absorption (RSA) profiles, indicating that they have potential as optical limiters. The second-order hyperpolarizability (Y), and third-order nonlinear susceptibility (/m[/(3)]) values are also reported for these dyes. The optical limiting values of one of the BODIPY dyes in solution, and two of the BODIPY-embedded PBC films, were below the maximum threshold of 0.95 J-cm-2. The effect of addition of substituents on the electronic structure of the BODIPY dyes was investigated using TD-DFT calculations. The calculated trends closely followed those determined experimentally.

Les capteurs d’oxygène sont le plus grand apport dans la technologie des emballages actifs parce qu’ils permettent de retarder la dégradation oxydante des aliments et ainsi éviter la perte de saveurs et le développement microbien au sein des aliments. Bien que le développement des emballages actes existe depuis les années 70 dans des pays producteur agricole, la recherche sur ces emballages reste encore embryonnaire, en particulier sur les critères techniques portant sur l’absorption d’oxygène de films. Cette thèse constitue une contribution sur l’étude des cinétiques d’absorption d’oxygène de l’huile de lin comme capteur d’oxygène. L’oxydation de l’huile et d’esters insaturés (composé modèle de l’huile) est suivie sous différentes conditions d’exposition (températures comprises entre 40-110°C et pressions partielles d’oxygène entre 0 et 1 bar). Expérimentalement, on propose de caractériser l’absorption d’oxygène liée à l’oxydation de l’huile par thermogravimétrie (ATG), suivi de concentration d’oxygène et titrage de peroxide. Un modèle cinétique basé des schémas classiques avec décomposition des hydroperoxydes, est proposé pour simuler l’oxydation de l’huile de lin et des esters insaturés modèles. Ce modèle est ensuite extrapolé à des films de différentes épaisseurs de polypropylène (PP) contenant 1% d’huile de lin en considérant que cette dernière est bien dispersé dans la matrice PP et que la diffusion d’oxygène est pilotée par la matrice PP
Oxygen scavengers (OS) are one of the most important technology of active packaging, because prevents oxidative degradation related with off-flavours, off-odours and microbial growth in food. Although active packaging has been proposed since 1970s, in developing countries with a large agricultural base, active packaging still remains unexplored both in terms of application and research, there is a lack of technical criteria on O2 scavenging films, labels, sheets, and trays. This PhD thesis is a contribution in the study of linseed oil as active ingredient for OS providing a kinetic characterization of its thermo-oxidation between 40°C and 110°C in atmospheres with different oxygen concentration. In the experimental approach, innovative application of TGA was proposed to study oxygen uptake capacity complemented by headspace and peroxide value measurements. The kinetic model, derived from a classic mechanistic scheme where initiation of thermo-oxidation results from decomposition of hydroperoxides, was capable to simulated linseed oil oxidation, and also oxygen absorptions of polypropylene films, of different thickness, containing 1% of linseed oil, with hypotheses of well dispersion of linseed oil in PP matrix, and oxygen diffusion governed by the PP matrix

[ES] La presente tesis doctoral tuvo como objetivo desarrollar nuevos materiales biodegradables hechos a base de fibras obtenidas mediante la técnica de electroestirado, denominadas "biopapers" o biopapeles, con barrera a agua y a gases y propiedades de secuestro de oxígeno para su posible aplicación en recubrimientos de papel o como capas intermedias en envases alimentarios basados en papel y cartón. En un primer estudio, se desarrollaron biopapeles de PHB mediante electroestirado, usando dos tipos de colectores, colectores de placa plana y rotativo, para evaluar la influencia del alineamiento de las fibras. Con posterioridad se aplicó un tratamento de recocido por debajo del punto de fusión del polímero a diferentes temperaturas, tiempos y procesos de enfriamiento para obtener películas continuas por coalescencia de las fibras, lo que a su vez condujo a la adhesión entre capas, y a una mejora en las propriedades barrera y ópticas. En un segundo estudio, se depositaron biopapeles monocapa y multicapa hechos de PHB, PVOH y PLA sobre un sustrato de papel no estucado, utilizando los dos colectores citados; y el tiempo de procesamiento por electrospinning se varió para producir espesores diferentes. Para mejorar la adhesión al sustrato de papel, y las propiedades ópticas y de barrera de las multicapas, los biopapeles se sometieron a un proceso de recocido como se describe y optimiza en el primer estudio. Con respecto a la barrera al agua, el sistema de papel/ PVOH/PHB presentó las mejores propriedades. En un tercer estudio, se obtuvieron dos nanopapeles de alta barrera hechos a base de nanofibras de celulosa de dos tipos, nanofibras de celulosa (CNF) y nanofibras de lignocelulosa (LCNF) y se recubrieron con biopapeles de PHA electroestirados con barrera a agua. Como resultado, el carácter hidrófobo de los nanopapeles se mejoró significativamente. Por otra parte, estos también exhibieron un rendimiento mecánico más equilibrado. En un cuarto estudio, se desarrollaron biopapeles de PHA con capacidad activa de secuestro de oxígeno, para lo cual se usaron nanopartículas de paladio (PdNP) como catalizadores de la respuesta activa. La principal dificultad asociada con las nanopartículas es mantenerlas dispersas, por lo que en este trabajo evaluamos el uso de surfactantes CTAB y TEOS como sustancias permitidas en contacto con alimentos para ayudar a la dispersión y distribución de PdNP dentro de las fibras de PHA. Como resultado, se prepararon nanocompuestos electroestirados con capacidad de secuestro de oxígeno hechos de PHB y PdNP, seguidos de un tratamiento de recocido para obtener capas continuas y autoadhesivas. La capacidad de secuestro de oxígeno de los biopapeles, medida a un 100% de humedad relativa (HR), mostró un mejor rendimento para el material en forma de fibra que en forma de film. En cualquier caso, los resultados indicaron una cinética de absorcion relativamente baja. Con el fin de mejorar aún más la cinética de secuestro de oxígeno, incluso a una humedad intermedia y en forma de película, un quinto estudio, desarrolló biopapeles multicapa hechos de PCL y PHA aplicados sobre papel no estucado. Los nanocompuestos de PCL/PdNP mostraron uma cinética de secuestro de oxígeno mucho mayor que la del sistema PHA / PdNP anterior. Este resultado se atribuye a la mayor fración de volumen libre del PCL que permite que la humedad, el hidrógeno y la permeación de oxígeno desencadenen la reacción de eliminación catalítica de forma más eficiente. Finalmente, un sexto estudio, desarrolló un nuevo concepto de capa con capacidad de secuestro de oxígeno y con alta barrera passiva a gases y vapores orgánicos basado en PdNP, CNC y EVOH. Así, CNC y CNC oxidado com TEMPO (TEMPO oxidized CNC), se utilizaron para producir PdNP in situ sobre el nanorefuerzo, que se incorporaron en la matriz del polímero EVOH. El TEMPO oxidized CNC demostró poseer una mayor absorción de oxígeno debido a los grupos car
[CAT] La present tesi doctoral va tindre com a objectiu desenvolupar noves capes biodegradables actives obtingudes mitjançant electrospinning, denominades "biopapers" o biopapeles, amb barrera a aigua i a gasos i propietats de segrest d'oxigen per a la seua possible aplicació en recobriments de paper o com a capes intermèdies en envasos alimentaris basats en paper i cartó. En un primer estudi, es van desenvolupar bio-papers de PHB mitjançant electrospinning, utilitzant dos tipus de col·lectors, col·lectors de placa plana i rotatiu, per a avaluar la influència de l'alineament de les fibres. Amb posterioritat es va aplicar un tractament de recuita per davall del punt de fusió del polímer a diferents temperatures, temps i processos de refredament per a obtenir pel·lícules contínues per coalescència de les fibres, la qual cosa al seu torn va conduir a l'adhesió entre capes, i a una millora en les propietats barrera i òptiques. En un segon estudi, es van depositar bio-papers monocapa i multicapa fets de PHB, PVOH i PLA sobre un substrat de paper no estucat, utilitzant els dos col·lectors citats; i el temps de processament per electrospinning es va variar per a produir grossàries diferents. Per a millorar l'adhesió al substrat de paper, i les propietats òptiques i de barrera de les multicapes, els biopapers es van sotmetre a un procés de recuita com es descriu i optimitza en el primer estudi. Respecte a la barrera a l'aigua, el sistema de paper/PVOH/PHB va presentar les millors propietats. En un tercer estudi, es van obtenir dos nano-papers d'alta barrera fets a base de nanofibres de cel·lulosa de dos tipus, nanofibres de cel·lulosa (CNF) i nanofibres de lignocel·lulosa (LCNF) i es van recobrir amb bio-papers de PHA electro-estirats amb barrera a aigua. Com a resultat, el caràcter hidròfob dels nano-papers es va millorar significativament. D'altra banda, aquests també van exhibir un rendiment mecànic més equilibrat. En un quart estudi, es van desenvolupar bio-papers de PHA amb capacitat activa de segrest d'oxigen, per a això es van usar nanopartícules de pal·ladi (PdNP) com a catalitzadors de la resposta activa. La principal dificultat associada amb les nanopartícules és mantenir-les disperses, per la qual cosa en aquest treball avaluem l'ús de surfactants CTAB i TEOS com a substàncies permeses en contacte amb aliments per a ajudar la dispersió i distribució de PdNP dins de les fibres de PHA. Com a resultat, es van preparar nano-compostos electro-estirats amb capacitat de segrest d'oxigen fets de PHB i PdNP, seguits d'un tractament de recuita per a obtenir capes contínues i autoadhesives. La capacitat de segrest d'oxigen dels bio-papers, mesurada a un 100% d'humitat relativa (HR), va mostrar un millor rendiment per al material en forma de fibra que en forma de film. En qualsevol cas, els resultats van indicar una cinètica de absorció relativament baixa. Amb la finalitat de millorar encara més la cinètica de segrest d'oxigen, fins i tot a una humitat intermèdia i en forma de pel·lícula, un cinquè estudi, va desenvolupar bio-papers multicapa fets de PCL i PHA aplicats sobre paper no estucat. Els nano-compostos de PCL/PdNP van mostrar una cinètica de segrest d'oxigen molt major que la del sistema PHA/PdNP anterior. Aquest resultat s'atribueix a la major fracció de volum lliure del PCL que permet que la humitat, l'hidrogen i la permeància d'oxigen desencadenen la reacció d'eliminació catalítica de forma més eficient. Finalment, un sisè estudi, va desenvolupar un nou concepte de capa amb capacitat de segrest d'oxigen i amb alta barrera passiva a gasos i vapors orgànics basat en PdNP, CNC i EVOH. Així, CNC i CNC oxidat com TEMPO (TEMPO oxidat CNC), es van utilitzar per a produir PdNP in situ sobre el nano-reforç, que es van incorporar en la matriu del polímer EVOH. El TEMPO oxidat CNC va demostrar posseir una major absorció d'oxigen degut als grups carboxílics generats.
[EN] The present PhD thesis aimed to develop novel active fiber based biodegradable layers obtained by electrospinning, so-called biopapers, with water and gas barrier and oxygen scavenging properties for their potential use as paper coatings or packaging interlayers in fiber based packaging. In a first study, PHB biopapers were obtained by electrospinning, by means of two types of collectors namely, flat plate and rotation drum collectors, to evaluate the influence of the alignment of fibers. Annealing post-processing below the polymer melting point was carried at different temperatures, isothermal times and cooling processes to obtain transparent and pore free continuous films by fibers coalescence which in turn led to interlayer adhesion, enhanced barrier and optical properties. In a second study, mono and multilayer biopapers comprising PHB, PVOH and PLA were deposited onto a conventional uncoated paper substrate, using the cited two collectors; and the electrospinning processing time was varied to produce different thickneses. To enhance adhesion to the paper substrate, optical and barrier performance of the multilayer, the biopapers were subjected to an annealed process as described and optimized in the first study. Regarding water barrier, the system paper/PVOH/PHB presented the highest barrier performance. In a third study, environmentally friendly materials such as cellulose based nanopapers, i.e. gas barrier layers made of cellulose nanofibrils (CNFs) and lignocellulose nanofibrils (LCNFs), were obtained and coated with the water barrier electrospun PHA biopapers. As a result, the hydrophobic character of the nanopapers was significantly improved by the electrospun biopapers. Moreover, these also exhibited a more balanced mechanical performance. In a fourth study, active oxygen scavenging PHA biopapers were developed, in which palladium nanoparticles (PdNP) were used as catalysts to scavenge oxygen from the headspace. The main difficulty associated with nanoparticles is to keep them dispersed, so in this work we assessed the use of CTAB and TEOS surfactants as food contact permitted substances to help dispersion and distribution of the PdNP within the PHA fibers. As a result, oxygen scavenging nanocomposite biopapers made of electrospun PHB and PdNP were prepared, followed by annealing treatment to obtain homogeneous and continuous active layers. The oxygen scavenging capacity at 100% relative humidity (RH) of the biopapers in fiber form showed better performance than their annealed specimens as expected, but in general this was not considered optimal. In order to improve further the oxygen scavenging capacity, even at a low relative humidity and in film form, a fifth study, developed multilayered biopapers made of PCL and PHA coated on conventional cellulose paper. The PCL/PdNP nanocomposites showed much more enhanced oxygen scavenging performance in comparison with the above PHA/PdNP system. This result is attributed to the higher fractional free volume of the PCL polymer that allows moisture, hydrogen and oxygen permeation to trigger the catalytic scavenging reaction. Finally, a sixth study, developed a solvent casting high gas barrier and active oxygen scavenging layer concept based on PdNP, CNC and EVOH. Thus, CNC and TEMPO oxidized CNC, were used to produce in situ PdNP, which were incorporated into the EVOH polymer matrix. The TEMPO oxidized CNC exhibited higher oxygen absorption due to the generated carboxylic groups.
Spanish Ministry of Economy and Competitiveness (MINECO) project AGL2015-63855-C2-1-R for financial support. A. Cherpinski also would like to thank the Brazilian Council for Scientific and Technological Development (CNPq) of Brasilian Government for her predoctoral grant (205955/2014-2). A. Cherpinski also acknowledges the European Cooperation in Science and Technology (COST) Action FP1405 for funding through a Short Term Scientific Mission (STSM)
Cherpinski Correa, A. (2019). NOVEL ELECTROSPUN POLYHYDROXYALKANOATE BASED HIGH BARRIER AND ACTIVE BIOPAPERS OF INTEREST IN FOOD PACKAGING [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/123064
TESIS

Thesis (Ph.D.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 11, 2009) Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2001.
Title from document title page. Document formatted into pages; contains vii, 53 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 48-53).

This thesis encompasses the successful synthesis, characterization (NMR, IR, TGA) and electrochemical testing of novel, potentially redox-active organic materials. These were destined as electrodes for Li-organic cells and/or as catalysts for Li–O2 cells. The electrochemical performance of the dilithiated and tetralithiated salts of 2,5-dialkylamide hydroquinones (with ethyl, isopropyl or benzyl as the alkyl group) and of a partially lithiated polymer with a backbone of alternating 2,5-dicarbonylhydroquinone and 1,4-benzyl diaminophenylene units was evaluated. The small organicsalts exhibited redox-activity around 1.0 V vs Li/Li+ (the terephthaloyl redox system) and 2.8 V vs Li/Li+ (the quinone redox system). These values drifted depending on lithiation degree and alkyl substituent. Redox irreversibility featured these materials which decomposed and dissolved. The polymer exhibited multiple redox-activity in the region of 2.5-3.6 V vs Li/Li+, which was however also irreversible. Further on, the small organic salts were tested as to their impact on the dischargeproduct (Li2O2) yield in Li-O2 cells. Discharge profiles of cells with and without the inclusion of the salts were contrasted to each other; the former having a jagged appearance, indicative of side-reactions. The O2 electrode was studied by XRD todetect the formed products and the amount of Li2O2 present was quantified throug htitration and UV-vis spectroscopy. Organic salt inclusion was found to negatively affect the Li2O2 formation and also attack the Li-electrode.

Metallophthalocyanine complexes containing non-transition metals are very useful as sensitizers for photodynamic therapy, a cure for cancer that is based on visible light activation of tumour localized photo sensitizers. Excited sensitizers generate singlet oxygen as the main hyperactive species that destroy the tumour. Water soluble sensitizers are sought after for the convenience of delivery into the body. Thus, phthalocyanine (pc), tetrapyridinoporphyrazines (tppa) and tetramethyltetrapyridinoporphyrazines (tmtppa) with non-transition central metal atoms of Ge, Si, Sn and Zn were studied. First was the synthesis of these complexes, followed by their characterisation. The characterisation involved the use of ultraviolet and visible absorption spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, electrochemical properties and elemental analysis. Photochemical properties of the complexes were then investigated. Photolysis of these macrocycles showed two processes; -reduction of the dye and photobleaching, which leads to the disintegration of the conjugated chromophore structure of the dye. Photobleaching is the reductive quenching of the excited state of the sensitizers. The intensity of the quenching decreased progressively from tmtppa, tppa to pc metal complexes with photobleaching quantum yields, 6.6 x 10.5⁻¹, 1.8 x 10.5⁻¹ and 5.4 x 10⁻⁶ for Zntmtppa, Zntppa and Znpc, respectively. Efficiency of singlet oxygen sensitization is solvent dependent with very different values obtained for the same compound in different solvents, for example, 0.25 and 0.38 were observed as singlet oxygen quantum yields for Gepc complex in DMSO and DMF respectively. In DMSO the efficiency of ¹O₂ generation decrease considerably from pc to tppa and finally tmtppa. In water Getmtppa exhibits much higher singlet oxygen quantum yield, hence promising to be effective as a sensitizer for photodynamic therapy.

When proteins are unable to fold properly in the endoplasmic reticulum (ER), the resultant formation of misfolded proteins causes stress of the ER. Cells with ER stress often have a higher abundance of reactive oxygen species (ROS). Previous studies suggest that ROS could aggravate ER stress by further disrupting the ER protein folding process. More recent studies suggest that the unfolded protein response signaling pathways activated by ER stress could lead to the production of ROS. Such studies lead to the hypothesis that ER stress could be promoted by ROS, and vice versa. The aim of the present study is to test the above hypothesis by studying how ROS could be generated in ER-stressed cells. This is followed by investigating if ROS could increase or decrease the level of ER stress in cells. Finally, the extent of ER stress induced cell death in the presence and absence of ROS is assessed. The treatment of HeLa cells with tunicamycin (Tm), a common ER-stress inducing agent, resulted in the elevation of intracellular ROS that could be detected with the ROS-reactive probe dichlorodihydrofluorescein (DCF), but not dihydroethidium which is relatively specific towards superoxide anion. The Tm-induced elevation of ROS could be prevented by co-incubation of cells with thiol reductants such as dithiothreitol and N-acetylcysteine but not with the free radical scavenger ascorbate. The tunicamycin-induced elevation of ROS level could also be prevented by the over-expression of catalase in HeLa. These data is consistent with the idea that hydrogen peroxide is a major form of ROS produced in Tm-treated cells. In addition to elevation of ROS level, HeLa cells treated with tunicamycin also resulted in the phosphorylation of PERK and eIF2α, and the splicing of XBP-1. In the presence of cycloheximide to inhibit protein synthesis so as to deplete protein substrates for folding in the ER, tunicamycin-induced ER stress was greatly minimized as was evident by the absence of both the phosphorylation of PERK and splicing of XBP-1. However, the phosphorylation of eIF2α and elevation of DCF-detectable ROS remained unaffected. The cycloheximde-resistant phosphorylation of eIF2α could be prevented when cells were co-treated with thiol reductants, or upon the over-expression of catalase. These data suggest that the production of ROS in Tm-treated cells does not require the presence of ER stress as a prerequisite. Furthermore, the ROS so produced could induce phosphorylation of eIF2α without the need to cause ER stress in the first place. The quenching of ROS through the use of thiol reductants, or the over-expression of catalase, had no effect on inhibition of protein synthesis in cells treated with tunicamycin. However, the extent of cell death was significantly increased. The data obtained in this study is not consistent with the idea that ROS is a downstream product of ER stress, capable of inducing more ER-stress by a feedback mechanism. Therefore, a mutually enhancing effect between ER stress and ROS may not exist. The ROS found in stressed cells may serve to extend cellular survival under the condition of continuous stress.
published_or_final_version
Biochemistry
Doctoral
Doctor of Philosophy

Thesis (Ph. D.)--Illinois State University, 1991.
Title from title page screen, viewed December 8, 2005. Dissertation Committee: Herman E. Brockman (chair), Radheshym K. Jayaswal, Alan J. Katz, David F. Weber, Brian J. Wilkinson. Includes bibliographical references (leaves 113-125) and abstract. Also available in print.

Thesis (Ph. D.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains xi, 261 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains ix, 103 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Oregon, 2007.
Typescript. Includes vita and abstract. Includes bibliographical references (leaves 137-158). Also available for download via the World Wide Web; free to University of Oregon users.

Murine lymph node cells (LNC) were used as model for the assessment of a role for reactive oxygen species (ROS) in T lymphocyte activation. When 2’7’- dichlorofluorescin (DCFHz) is oxidised it becomes the fluorescent compound dichlorofluorescein. Analysis of DCFHz-loaded LNC by flow cytometry identified an increase in DCFH2 oxidation upon stimulation with a mitogenic dose of the phorbol ester, phorbol myristate acetate. This could also be seen, although to a lesser extent, with a mitogenic dose of the lectin concanavalin A. The phorbol ester-induced increase in DCFH2 oxidation was inhibited by chelerythrine and desferrioxamine (the latter at concentrations lower than that required for maximal inhibition of lymphoproliferation in vitro), indicating a role in DCFHZ oxidation for protein kinase C and iron, respectively. Analysis of LNC prelabelled with an antibody against a pan-T lymphocyte marker, Thy-1, established that phorbol ester treatment of LNC induces an increase in DCFHZ oxidation in murine T lymphocytes. The inhibition of DCFH2 oxidation in LNC by superoxide dismutase, catalase and glutathione/glutathione peroxidase suggested that the source of oxidants may have been B lymphocytes and/or phagocytic cells within the population and that the oxidation in T lymphocytes essentially represented a "bystander effect". This was supported by preliminary studies where there was little or no response to phorbol ester stimulation in DCFHz-loaded LNC from mice lacking a functional NADPH oxidase (gp91Ph0X gene knockout mice). Studies of cell-free oxidation of DCFH2 demonstrated that the fluorogen could be oxidised by peroxyl radicals from either chemical (2,2'-azobis(2-amidinopropane) dihydrochloride) or enzymatic (soybean lipoxygenase) sources. Finally, the role of iron in T lymphocyte activation was investigated using the iron chelators desferrioxamine and a set of novel pyridoxal-based compounds. The novel iron chelators were of comparable or greater potency compared to desferrioxamine with regard to inhibition of lymphoproliferation in vitro. Time course studies confirmed previous reports by showing that a major target of iron chelators in activated T lymphocytes are events late in G1 or at the G1/S transition of the cell cycle. These studies: highlight the technical difficulties of assaying oxidant production using mixed populations of cells; support the notion that DCFH2 is a general target for radical-mediated oxidation; and confirm a critical role for iron in DNA synthesis in activated T lymphocytes.

Thesis (Ph. D.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains viii, 109 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2001.
Title from document title page. Document formatted into pages; contains viii, 124 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

An online, semi-continuous instrument to measure both total and gas phase atmospheric reactive oxygen species (ROS) and determine the concentration of ROS in the particle phase (ROS(p)) was developed. This instrument was based on a fluorescent probe for quantifying ambient ROS, specifically 2'7'-dichlorodihydrofluorescin, or DCFH probe. This probe was analyzed for sensitivity to a variety of offline and online parameters for efficient use in a field instrument. The ROS(p) instrument measures the peak light intensity at 530 nm to determine ambient ROS concentrations. ROS particles and gases are collected in a mist chamber in a nebulized mist. The instrument alternates measurements of ROS(p+g), or ROS(tot) by means of an inline filter. Fine (PM₂.₅) (ROS(p) is determined by subtraction of the ROS(g) concentration from the ROS(tot), as the ROS(g) signal could not be excluded. This instrument was tested during the summer (May-July) of 2012 at urban and rural sites in the metropolitan Atlanta and surrounding region. Concentrations of ROS(p) determined from this instrument were often below limit of detection. Average concentrations of ROS(p) were found to be 0.25 nmol/m³ in urban Atlanta (Jefferson St. and Georgia Tech), and 0.15 nmol/m³ in Yorkville, a rural site. A side by side comparison of this method with a filter collection method was made in July. The average ROS(p) offline concentrations were 0.15 nmol/m³. These concentrations were comparable to the online average concentrations of 0.21 nmol/m³ for the same period of time. This average and the majority of the measurements comprising it is dominated by the high limit of detection. The ROS instrument as constructed and operated is an efficient way to conduct ROS(p) measurements at the level of a filter study while reducing the labor intensive filter collection and extraction. In order for this instrument to be successful at measuring ambient ROS in the particle phase, the removal of the gas phase from the current sampling scheme is critical as the ROS(g) concentrations are over 90% of the measured ROS. The system as currently operable is best suited for source measurements, including biomass burning plumes or fresh exhaust to capture immediate formation.

Biofilms harbor both active and inactive cells and it is a challenge to characterize the spatial and population heterogeneity of specific activities within a biofilm. Spatial patterns of DNA replication and protein synthetic activity were imaged by techniques developed using staphylococcal systems. The first technique measures DNA synthetic activity by pulse-labeling with the thymidine analog 5-bromo-2-deoxyuridine (BrdU) followed by immunofluorescent detection of brominated DNA. The second technique makes use of an inducible green fluorescent protein construct that can be used to detect the capacity for de novo protein synthesis. These techniques were applied to biofilms grown in three different reactor systems. In all cases, measurements revealed that even in simple single-species biofilms, complex spatial distributions of anabolic activity occur. In a colony biofilm system, two distinct regions of DNA synthetic activity were observed, one close to the nutrient interface and another adjacent to the air interface. A similar pattern was measured by GFP induction. The dimensions of DNA synthetic activity ranged from 25 to 31 µm and the average protein synthetic activity ranged from 36 to 38 µm at the air interface. When pure oxygen was introduced, a wider zone of active DNA replication (45 µm) and GFP synthesis (59 µm) was measured at the gas interface. Oxygen penetration calculated (26µm) corresponds with the zones of respiratory activity (19 to 38 µm), DNA synthetic activity and protein synthetic activity measured at the air interface. The dimensions of DNA synthetic activity and protein synthesis activity at the nutrient interface ranged from 13 µm to 19 µm. The addition of glucose to the media increased the zone of protein synthesis at the nutrient interface to 33 µm. Stratified patterns of activity were also observed in biofilms developed in two continuous flow reactors. While biofilms harbor regions of active anabolism, the techniques also demonstrate that these biofilms contain regions of complete inactivity. Such inactive zones may contribute to the special ecology of biofilms and tolerance to antimicrobial agents. The techniques, particularly BrdU labeling, are generic and may find application to many microbial biofilm systems.