Les formes réactives de l’oxygène (peroxyde d’hydrogène, radicaux superoxydes et hydroxyles) sont produites lorsque la régulation du métabolisme de l’oxygène est perturbée. Ces espèces sont responsables, directement ou indirectement, de nombreux dommages oxydatifs au niveau moléculaire (acides nucléiques, protéines, lipides…) pouvant affecter les mécanismes cellulaires. Toutefois le peroxyde d’hydrogène pourrait également se comporter comme un messager secondaire dans différentes voies de signalisation et être à l’origine de processus physiologiques. Ainsi sa double fonction a suscité l’intérêt de nombreux laboratoires qui tentent à présent d’élucider son rôle et son degré d’implication dans les processus physiologiques et pathologiques. Pour la détection du peroxyde d’hydrogène, de nombreuses pro-sondes ont été élaborées sur la base d’une amorce boronate. La plupart de ces pro-sondes ont permis de détecter un stress oxydant in cellulo mais souffrent cependant d’un manque de réactivité. Le but du mon projet de thèse a alors été d’améliorer la réactivité de l’amorce en élaborant des pro-sondes à amorce borinate. Malgré des difficultés de synthèse, nous avons obtenu une telle pro-sonde à amorce borinate, dissymétrique, portant à la fois un phényle et la coumarine, choisie comme chromophore. Des études cinétiques ont montré que la réactivité de notre pro-sonde borinate est 100 fois plus élevée que celle des pro-sondes à amorce boronate actuelles, en conditions physiologiques. Un mécanisme réactionnel a été proposé. Enfin notre pro-sonde a pu être validée in cellulo sur des macrophages, activés au PMA pour la détection endogène du peroxyde d’hydrogène. Encouragés par ces résultats, nous synthetisons actuellement d’autres pro-sondes à amorce borinate présentant d’autres chromophores. / Reactive oxygen species (hydrogen peroxide, hydroxyl and superoxide radicals) are produced when the regulation of oxygen metabolism is disrupted. These species are directly or indirectly responsible for numerous oxidative damage at the molecular level (nucleic acids, proteins, lipids, etc.) which can affect cellular mechanisms. However, hydrogen peroxide could also behave as a secondary messenger in various signaling pathways and be the source of physiological processes. Thus its dual function has aroused the interest of many laboratories which are now trying to elucidate its role and its degree of involvement in physiological and pathological processes. In order to detect hydrogen peroxide, many pro-probes have been developed, based on a boronate trigger. Most of these probes proved able to detect an oxidative stress in cellulo but suffer from lack of reactivity. The goal of my thesis project was to improve the reactivity of the trigger by developing pro-probes with a borinate trigger. In spite of difficulties of synthesis, we obtained such a pro-probe with a borinate trigger, dissymmetrical, and bearing both a phenyl and a coumarin substituent, chosen as chromophore. Kinetic studies have shown that the reactivity of our borinate pro-probe is 100 times higher than that of the current boronate-based trigger pro-probe, under physiological conditions. A reaction mechanism has been proposed. Finally, our pro-probe has been validated in cellulo on macrophages, activated with PMA for the endogenous detection of hydrogen peroxide. Encouraged by these results, we are currently synthesizing other pro-probes with borinate trigger presenting other chromophores.

<p>Reactive oxygen species (ROS) are critical for maintaining cellular homeostasis and function when produced in physiological ranges. Important sources of cellular ROS include NADPH oxidases (Nox), which are evolutionarily conserved multi-subunit transmembrane proteins. Nox-mediated ROS regulate a variety of biological processes including stem cell proliferation and differentiation, calcium signaling, cell migration, and immunity. ROS participate in intracellular signaling by introducing post-translational modifications to proteins and thereby altering their functions. The central nervous system (CNS) expresses different Nox isoforms during both development and adulthood. There is now emerging evidence that Nox-derived ROS also control neuronal development and pathfinding. Our lab has recently shown that retinal ganglion cells (RGCs) from <i>nox2</i> mutant zebrafish exhibit pathfinding errors. However, whether Nox could act downstream of receptors for axonal growth and guidance cues is presently unknown. To investigate this question, we conducted a detailed characterization of the zebrafish <i>nox2</i> mutants that were previously established in our group. Abnormal axon projections were found throughout the CNS of the <i>nox2 </i>mutant zebrafish. Anterior commissural axons failed proper fasciculation, and aberrant axon projections were detected in the dorsal longitudinal fascicle of the spinal cord. We showed that the major brain regions are intact and that the early development of CNS is not significantly altered in <i>nox2 </i>mutants. Hence, the axonal deficits in <i>nox2</i> mutants are not due to general developmental problems, and Nox2 plays a role in axonal pathfinding and targeting. Next, we investigated whether Nox2 could act downstream of slit2/Robo2-mediated guidance during RGC pathfinding. We found that slit2-mediated RGC growth cone collapse was abolished in <i>nox2 </i>mutants <i>in vitro</i>. Further, ROS biosensor imaging showed that slit2 treatment increased growth cone hydrogen peroxide levels via mechanisms through Nox2 activation. Finally, we investigated the possible relationship between slit2/Robo2 and Nox2 signaling <i>in vivo</i>. <i>Astray/nox2</i> double heterozygous mutant larvae exhibited decreased tectal area as opposed to individual heterozygous mutants, suggesting both Nox2 and Robo2 are required for the establishment of retinotectal connections. Our results suggest that Nox2 is part of a signal transduction pathway downstream of slit2/Robo2 interaction regulating axonal guidance cell-autonomously in developing zebrafish retinal neurons.</p>

This study is dedicated to characterisation of photosensitisation properties of polymeric nanofibres with encapsulated photosentisitiser. Main goal of thesis is demonstration and study of H2O2 photoproduction. Photosensitizer used in this study was 5,10,15,20-meso-tetrafenylporfyrin (TPP), studied were also its complexes with Cu2+ a Ni2+ . Properties of nanofibers were examined using UV-Vis molecular absorption spectroscopy, fluorescence spectroscopy and electron microscopy (SEM).

During the construction of the new urban area in the north-eastern part of Stockholm, Stockholm Royal Seaport, groundwater with extremely elevated levels of the carcinogenic aromatic hydrocarbon benzene was discovered in the area Hjorthagen. Such a contamination can be remediated in-situ by the use of chemical oxidation and biodegradation. Due to the fact that many factors such as contaminant composition, groundwater characteristics and temperature vary between sites, smaller bench scale studies are usually conducted before the full scale remediation on site. Little published research exists on the ability of these remediation techniques in areas with lower groundwater temperature such as Stockholm, why the need of a bench-scale study in this case is even larger. The objective of this master thesis is to, out of three investigated remediation agents, find the most suitable one for remediation of the benzene-contaminated groundwater in Hjorthagen. This was made in the form of a bench-scale study and the techniques studied were chemical oxidation, for which the two agents hydrogen peroxide (uncatalyzed and catalyzed in the form of Fenton’s reagent) and persulfate (activated with iron (II)) were used, and biological degradation by the use of a calcium peroxide-based compound. The study showed that the benzene-contaminated groundwater was best remediated with Fenton’s reagent, which was able to degrade the benzene with great success.

<p>Open questions remain on the influence of various conditions and ion behavior on the hydration-shell of oily molecules. My research uses Raman spectroscopy and Raman multivariate curve resolution to study the hydration-shell of oily molecules as tools to help answer some of these open questions.</p><p>More specifically, I present results on the effect of molecular crowding on the structure of water around various oily molecules, and report the effect of molecular crowding on hydrophobic crossover. These results are important, as crowding has the potential to influence several fields, such as biology and environmental sciences. This work shows that increasing molecular concentration results in oil-oil crowding, decreases the tetrahedrality of the water structure around the oily molecules, and subsequently, the crossover temperature.</p><p>In addition to studying the hydration-shell under crowded conditions, I also present work on ion affiliation for the hydration-shell of an oily molecule. Ion affiliation for oil/water interfaces has been an ongoing topic of research since the Hoffmeister experiments because of their effect on biological processes. This study focuses on hydroxide and its affiliation for tert-butyl alcohol in comparison to other electrolytes. These results show iodide is less repelled by the oil/water interface in comparison to hydroxide.</p><p>Finally, I present findings on the influence of hydrogen peroxide in comparison to other small molecules on the water structure of an oily molecule. Hydrogen peroxide has been shown to reach supercooled temperatures, which may be useful in future studies of liquid phase transitions or studies on solute behavior at supercooled conditions. It is found that hydrogen peroxide does not significantly influence the water structure around tert-butyl alcohol, while other small molecules display significant water structure changes.</p><p>All these projects aim to contribute results to heated debates, as well as share information for future experiments.</p>

Recent reports on the formation of hydrogen peroxide (H$_2$O$_2$) in water microdroplets produced via capillary condensation or pneumatic spraying have garnered significant attention. How covalent bonds in water could break under such conditions challenges our textbook understanding of physical chemistry and the water substance. While there is no definitive answer, it has been speculated that ultrahigh electric fields at the air-water interface are responsible for this chemical transformation. This thesis documents the findings of our exploration of this mystery via a comprehensive experimental investigation of H$_2$O$_2$ formation in (i) water microdroplets condensed on hydrophobic and hydrophilic substrates formed via hot water in the 50–70 ℃ range or ultrasonic humidifier under controlled air composition, and (ii) water microdroplets sprayed over a range of liquid flow-rates, the (shearing) air flow rates, and the air composition. Our glovebox experiments, with controlled gas composition, revealed that no H$_2$O$_2$(aq) was produced in water microdroplets condensed via heating water (detection limit ≥ 0.25 μM), regardless of the droplet size or the substrate wettability. In contrast, water droplets condensed via ultrasonic humidification contained significantly higher (~1 μM) H$_2$O$_2$ concentration. We pinpointed that ultrasonic humidifiers induced cavitation of tiny bubbles in water, which is known to form H$_2$O$_2$(aq) and other reactive species. Next, in the case of sprayed water microdroplets, also, we did not detect H$_2$O$_2$(aq) unless O$_3$(g) was present in the ambient atmosphere. In contrast, water microdroplets (sprayed or condensed) exposed to O$_3$(g) concentration in the range 2–5000 ppb formed 2–100 μM H$_2$O$_2$(aq); increasing the gas–liquid surface area, mixing, and contact duration enhanced the H$_2$O$_2$(aq) concentration. Therefore, we submit that the original reports suffered from experimental artifacts due to the high regional O$_3$(g) giving rise to H$_2$O$_2$(aq), and the air–water interface does not spontaneously produce H$_2$O$_2$(aq). The water surface merely facilitates the O$_3$(g) mass transfer, which then undergoes chemical transformations in the water to form H$_2$O$_2$(aq). Taken together, these findings offer an alternative explanation to the mysterious production of H$_2$O$_2$ in water microdroplets; These findings should also advance our understanding of the implications of this chemistry in natural and applied contexts.

<p> Propylene oxide (PO), is a key intermediate in the production of value-added products, such as polyurethanes and propylene glycol. Current industrially practiced methods of propylene epoxidation, including hydrochlorination, epoxidation by organic peroxides, and the Hydrogen Peroxide to Propylene Oxide (HPPO) process either produce PO unselectively, necessitating energy intensive separation processes, produce environmentally damaging byproducts, or require several sequential reaction vessels. A potential solution for these issues exists in the form of a single-step, highly selective gas phase reaction to produce PO. Industrial adoption of a process utilizing this technology has not occurred due to the failure of state-of-the-art Au/TS-1 catalysts, consisting of gold supported on titanium MFI, to meet economic targets for hydrogen use efficiency, selectivity to PO, and PO rate-permass, improvement on all of which has been hindered by a lack of understanding of how Au-TS-1 catalysts fundamentally operate. Therefore, the goal of this work has been to understand the active site requirements and reaction kinetics with the aim of lowering barriers to commercialization of this more environmentally benign process. Once we had developed a general understanding of product inhibition, we applied this knowledge to the kinetics of propylene epoxidation over Au/TS-1 catalysts. We measured gas phase kinetics in a continuous stirred tank reactor (CSTR) free from temperature and concentration gradients. Apparent reaction orders measured at 473 K for H2, O2, and propylene for a series of Au-DP/TS-1 with varied Au and Ti contents were consistent with those reported previously. Co-feeding propylene oxide enabled measurement of the apparent reaction order in propylene oxide and the determination that relevant pressures of propylene oxide reversibly inhibit propylene epoxidation over Au-DP/TS-1, while co-feeding carbon dioxide and water had no effect on the propylene epoxidation rate. The measured reaction orders for propylene epoxidation, after corrected to account for propylene oxide inhibition, are consistent with a ‘simultaneous’ mechanism requiring two distinct, but adjacent, types of sites. H2 oxidation rates are not inhibited by propylene oxide, implying that the sites required for hydrogen oxidation are distinct from those required for propylene epoxidation. 26 We then shifted focus to elucidate structural details of gold active sites and their interaction with Ti active sites. To determine whether the roles of extracrystalline and intracrystalline gold nanoparticles supported on titanosilicate-1 on direct propylene epoxidation are intrinsically different, the kinetics of direct propylene epoxidation were measured in a gas-phase continuous stirred tank reactor (CSTR) over PVP-coated gold nanoparticles (Au-PVP/TS-1) deposited on TS-1 supports. The PVP-coated gold nanoparticles were too large to fit into the micropores of TS-1, even after ligands were removed in situ by a series of pretreatments, as confirmed by both TEM and TGA-DSC. The activation energy and reaction orders for H2, O2, propylene, propylene oxide, carbon dioxide, and water for propylene epoxidation measured on Au-PVP/TS-1 catalysts were consistent with those reported for Au/TS-1 prepared via deposition-precipitation (Au-DP/TS-1). However, while the reaction orders for hydrogen oxidation on Au-PVP/TS-1 were similar to those measured on AuDP/TS-1, a decrease in activation energy from approximately 30 kJ mol−1 for Au-DP/TS-1 to 4-5 kJ mol−1 for Au-PVP/TS-1 suggests there is a change in mechanism, rate-limiting step, and/or active site for hydrogen oxidation. Additionally, an active site model was developed which determines the number of Ti within an interaction range of the perimeter of extracrystalline Au nanoparticles (i.e., the number of Au-Ti active site pairs). Turnover frequencies estimated for this active site model for a dataset containing both Au-DP/TS-1 and Au-PVP/TS-1 were ∼20x higher than any previous report ( 80 s−1 vs. 1-5 s−1 at 473 K) for catalytic oxidation on noble metals, suggesting that the simultaneous mechanism occurring over proximal Au-Ti sites alone is incapable of explaining the observed rate of propylene epoxidation and that short-range migration of hydrogen peroxide is necessary to account for the catalytic rate. The agreement of reaction orders, activation energy, and active site model for propylene epoxidation on both Au-DP/TS-1 and Au-PVP/TS-1 suggests a common mechanism for propylene epoxidation on both catalysts containing small intraporous gold clusters and catalysts with exclusively larger extracrystalline nanoparticles. Rates of hydrogen oxidation were found to vary proportionally to the amount of surface gold atoms. This is also consistent with the hypothesis that the observed decrease in hydrogen efficiency and PO site-time-yield per gold mass with increasing gold loading are driven primarily by the gold dispersion in Au/TS-1 catalysts. </p>

In this study, oligo-porphyrans, obtained by acid hydrolysis of porphyran, were investigated for their H2O2-inducing abilities in the defense responses of P. yezoensis. Oligo-porphyrans with average molecular weights (MWs) lower than 1.43 kDa had H2O2-inducing abilities. In contrast, oligo-porphyrans with average MWs of 6.12 kDa triggered no response. The active oligo-porphyrans were fractioned by anion-exchange chromatography. We found that two distinct mechanisms might be involved in the oligo-porphyran-induced H2O2 release in P. yezoensis. Mixtures of mono-sulfated oligo-galactans with degrees of polymerization (DPs) ranging from 1 to 3 might induce the response through the oxidation of cellular oligosaccharides, which enable P. yezoensis to resist rotting caused by dense incubation. Mixtures of oligo-porphyrans, consisting of 4 ~ 7 monosaccharide residues and 2 ~ 3 sulfate groups, might induce the generation of H2O2 by activation of NADPH oxidase, leading to an oxidative burst in P. yezoensis. The elicitor activity of oligo-porphyrans thus depends on their molecular size.

Screen printed electrodes (SPEs), which are prepared by patterning conductive inks or pastes onto an insulating support (e.g., plastic film), are widely employed as sensing and biosensing platforms due to their ease of fabrication and relatively low cost. This is especially applicable to electrodes of this nature prepared with carbon-based inks (SPCEs). To date, the most successful and significant commercial application of SPEs has been as test strips for glucose meters. Despite the maturity of this technology, SPE research remains very active as improvements in sensitivity and selectivity, which often involve modifying the electrode surface, hold the key to advancing their utility in routine applications and extending their benefits to other target analytes. Recent studies in the Bishop research group have demonstrated that nitrogen-doped SPCEs (N-SPCEs) exhibit enhanced electrochemical response towards hydrogen peroxide (H2O2), a product of oxidase enzyme (e.g., glucose oxidase, lactate oxidase, etc.) reactions and a common target in biosensing strategies. The presence of nitrogen heteroatoms on the carbon surface facilitates breakage of oxygen-oxygen bonds, a key step in reduction of H2O2. Since previous studies showed only modest incorporation of nitrogen species on SPCEs prepared from commercial ink, these studies aim to investigate the possibility of enhancing N-doping by performing a simple pre-treatment strategy that reportedly increases surface oxygen content of SPCEs prior to N-doping. Since surface oxygen sites have been previously reported to be preferentially modified with nitrogen during N-doping strategies, this seems like a promising technique for improving sensitivity of N-SPCEs for H2O2 reduction. To quantify the actuality of these claims, experimental groups were fabricated having undergone no enhancement, pretreatment enhancement only, nitrogen-doping enhancement only, and a combination of the pretreatment and nitrogen-doping enhancements. Here the electrochemical behaviors of pretreated SPCEs, N-SPCEs, and pretreated N-SPCEs for the detection of H2O2 by completing comparative cyclic voltammetry (CV) experiments with and with out the presence of H2O2 and with it present in varying concentrations is compared. It is projected that, if successful, the fabricated electrodes that have undergone both the pretreatment protocol and the nitrogen-doping process will have an increased sensitivity and detection limit towards H2O2.

Nitrogen-doped carbon materials have garnered much interest due to their abilities to behave as electrocatalysts for reactions important in energy production (oxygen reduction) and biosensing (hydrogen peroxide reduction). Here, we demonstrate fabrication methods and determine electrocatalytic properties of nitrogen-doped screen-printed carbon (N-SPCE) electrodes. Nitrogen doping of graphite was achieved through a simple soft-nitriding technique which was then used in lab-formulated screen-printing inks to prepare N-SPCEs. N-SPCEs displayed good electrocatalytic activity, reproducibility and long term stability towards the electrochemical reduction of hydrogen peroxide. N-SPCEs exhibited a wide linear range (20 µM to 5.3 mM), reasonable limit of detection of 2.5 µM, with an applied potential of -0.4 V (vs. Ag/AgCl). We also demonstrate that nitrided-graphite can similarly be used as a platform for the deposition of electrocatalytic platinum nanoparticles, resulting in Pt-N-SPCEs with a lower limit of detection (0.4 µM) and better sensitivity (0.52 µA cm-2 µM-1) towards H2O2 reduction.