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1
Smith, Mathew D. "Reaction of hydroxyl radical with aromatic systems". Virtual Press, 2008. http://liblink.bsu.edu/uhtbin/catkey/1399191.
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The regioselectivity of the reaction of hydroxyl radical addition to toluene and naphthalene are examined in this study over the temperature range of 25°C-45°C. Also, the relative rates of reactivity as compared to benzene are determined for toluene, naphthalene, mesitylene, and p-xylene over the same temperature range. 2-(t-Butylazo)prop-2-yl hydroperoxide was used as the hydroxyl radical source and 1,1,3,3-tetramethylisoindolin-2-yloxyl was used as radical trap. For toluene the relative rates of addition were found to be 4 times greater for the ortho position versus the meta postion and 2 times greater for the para position versus the meta position, when the number of meta and para sites are taken into account.Department of Chemistry
2
Mitroka, Susan M. "Modulation of Hydroxyl Radical Reactivity and Radical Degradation of High Density Polyethylene". Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77137.
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Oxidative processes are linked to a number of major disease states as well as the breakdown of many materials. Of particular importance are reactive oxygen species (ROS), as they are known to be endogenously produced in biological systems as well as exogenously produced through a variety of different means. In hopes of better understanding what controls the behavior of ROS, researchers have studied radical chemistry on a fundamental level. Fundamental knowledge of what contributes to oxidative processes can be extrapolated to more complex biological or macromolecular systems.
Fundamental concepts and applied data (i.e. interaction of ROS with polymers, biomolecules, etc.) are critical to understanding the reactivity of ROS. A detailed review of the literature, focusing primarily on the hydroxyl radical (HO•) and hydrogen atom (H•) abstraction reactions, is presented in Chapter 1. Also reviewed herein is the literature concerning high density polyethylene (HDPE) degradation. Exposure to treated water systems is known to greatly reduce the lifetime of HDPE pipe. While there is no consensus on what leads to HDPE breakdown, evidence suggests oxidative processes are at play.
The research which follows in Chapter 2 focuses on the reactivity of the hydroxyl radical and how it is controlled by its environment. The HO• has been thought to react instantaneously, approaching the diffusion controlled rate and showing little to no selectivity. Both experimental and calculational evidence suggest that some of the previous assumptions regarding hydroxyl radical reactivity are wrong and that it is decidedly less reactive in an aprotic polar solvent than in aqueous solution. These findings are explained on the basis of a polarized transition state that can be stabilized via the hydrogen bonding afforded by water. Experimental and calculational evidence also suggest that the degree of polarization in the transition state will determine the magnitude of this solvent effect.
Chapter 3 discusses the results of HDPE degradation studies. While HDPE is an extremely stable polymer, exposure to chlorinated aqueous conditions severely reduces the lifetime of HDPE pipes. While much research exists detailing the mechanical breakdown and failure of these pipes under said conditions, a gap still exists in defining the species responsible or mechanism for this degradation. Experimental evidence put forth in this dissertation suggests that this is due to an auto-oxidative process initiated by free radicals in the chlorinated aqueous solution and propagated through singlet oxygen from the environment. A mechanism for HDPE degradation is proposed and discussed. Additionally two small molecules, 2,3-dichloro-2-methylbutane and 3-chloro-1,1-di-methylpropanol, have been suggested as HDPE byproducts. While the mechanism of formation for these products is still elusive, evidence concerning their identification and production in HDPE and PE oligomers is discussed.
Finally, Chapter 4 deals with concluding remarks of the aforementioned work. Future work needed to enhance and further the results published herein is also addressed.Ph. D.
3
Lenton, K. J. "Hydroxyl radical scavengers and antioxidants in radiation protection". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32339.pdf.
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4
McKay, Garrett J. "Reactivity of the hydroxyl radical with organic matter". Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1527332.
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The goal of this study was to investigate some of the fundamental chemistry of the reactions between the hydroxyl radical and apply this knowledge to the treatment of chemical contaminants in real world waters. To accomplish this goal, the techniques of electron pulse radiolysis were used to quantify second-order rate constants for the reaction between the HO· radical and well characterized OM samples. Studies of HO· radical reactivity with model polyethylene glycol polymers were performed to help understand OM-HO· reactivity. Experiments using steady state radiolysis were performed in order to assess the effect of long-term, seasonal variability in OM composition on the degradation of probe compounds used as model chemical contaminants. In addition, the photochemical production of HO· from OM sensitization was also investigated.
5
Black, Helen Dinah. "Kinetics of hydroxyl radical reactions with heterocyclic compounds". Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305373.
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6
Asuru, Awuri P. "Applications of X-ray Hydroxyl Radical Protein Footprinting". Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1575877091577049.
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7
Dahlstrom, Stephen W. "Hydroxyl radical activity in bleached root-filled teeth /". Title page, contents and summary only, 1992. http://web4.library.adelaide.edu.au/theses/09DM/09dmd131.pdf.
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8
Akin, Myles. "Site specific thermodynamic study of OH radical addition to DNA bases". Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33919.
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In medical and health physics, we are interested in the effects of ionizing radiation on biological systems, in particular, human biology. The main process by which ionizing radiations causes damage to biological systems, is through the creation of radicals close to DNA strands. The radicals are very reactive and those created within close proximity to DNA will react with the DNA causing damage, in particular single strand or double strand breaks. This damage to the DNA can cause mutations that can kill the cell, either mitotically or apoptotically, or possibly lead to a cancerous formation. Therefore it is important to study how these radicals interact with DNA strands for a correlation between the resultant products of radical reactions and DNA strand breaks. For this study, we look at the most important radical, the OH radical and it's addition to DNA bases. We will study, through quantum chemistry, the thermodynamics of OH radical addition to the four bases, Adenine, Guanine, Cytosine and Thymine. The Jaguar program developed by Schrodinger was used for DFT calculations of the Gibbs free energy of the addition. In addition, calculations for the partial charge, HOMO's and Fukui indices were calculated and compared to experiment.
9
Barreto, Joao Pedro Cabaco Moniz. "Dioxygen free radical reactions". Thesis, Oxford Brookes University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389105.
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10
Houtz, Erika. "Hydroxyl radical production in Old Woman Creek National Estuarine Reserve". Connect to resource, 2007. http://hdl.handle.net/1811/28931.
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Thesis (Honors)--Ohio State University, 2007.Title from first page of PDF file. Document formatted into pages: contains iii, 24 p.; also includes graphics. Includes bibliographical references (p. 32-24). Available online via Ohio State University's Knowledge Bank.
11
Cullen, Thomas Donovan. "Hydroxyl radical reaction and lanthanide ion complexation kinetics of DTPA". Thesis, California State University, Long Beach, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1524188.
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Louie, Peter Kwok Keung. "Kinetics of some gas phase reactions of the hydroxyl radical". Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236874.
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Cryer, Danny Russell. "Measurements of hydroxyl radical reactivity and formaldehyde in the atmosphere". Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/16834/.
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Results from the laboratory characterisation of a new design of hydroxyl radical (OH) flow reactor are presented. Further to this details of its coupling with a gas chromatograph time of flight mass spectrometer (GC-TOF-MS) system, to form a new instrument for the identification of ‘missing’ OH reactivity is discussed. Preliminary measurements in ambient air demonstrated the potential value of this system which could be used to chemically identify ‘missing’ OH sinks in various environments, and also to determine bimolecular rate coefficients for their reaction with OH. Observations of OH reactivity and formaldehyde (HCHO) are presented from an urban background site in York in the summer of 2014. OH reactivity was measured using laser flash photolysis coupled with laser induced fluorescence spectroscopy (LFP-LIF). The average ‘missing’ OH reactivity was ~27 % when measurements were compared with values predicted by a calculation that utilised measured concentrations of a very detailed suite of volatile organic compounds (VOCs). It is concluded that a combination of unidentified VOCs and products of VOC photo-oxidation account for this discrepancy. HCHO was measured using a new fast response (1 s time resolution) laser induced fluorescence (LIF) spectroscopy instrument and some evidence of daytime diurnal behaviour suggested that the dominant HCHO source was photo-chemical (~1.3 ppb diurnal peak). Observations of OH reactivity and HCHO are also presented from a coastal site in Weybourne, Norfolk, using the same instrumentation during the summer of 2015. The average ‘missing’ OH reactivity was ~44 %. It is concluded that much of the ‘missing’ reactivity was likely due to unmeasured VOCs and their photo-oxidation products. Strong diurnal behaviour of HCHO was observed and is consistent with an atmosphere where the dominant source is photo-chemical (~1.1 ppb diurnal peak). Unusual behaviour was observed for HCHO during a thunderstorm where sharp fluctuations in concentration were observed. It has so far not been possible to conclude the exact cause of this, however, it is suggested that the source was marine. Finally, preliminary results from three experiments of an intercomparison of OH reactivity instrumentation are presented. The results demonstrate the reliability of the Leeds LFP-LIF instrument for the measurement of ambient OH reactivity.
14
Altizer, Chase Duncan. "Hydroxyl Radical Production via Acoustic Cavitation in Ultrasonic Humidifier Systems". Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/95935.
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Ultrasonic humidifiers use sound vibrations at frequencies higher than can be heard by humans (> 20,000 Hz) to generate aerosolized water also have potential for inducing sonochemical reactions for chemicals present in water. This research focuses on examining oxidants formed within ultrasonic humidifiers, as well as the oxidants effects of contaminants in water used in the systems. Hydroxyl radicals were found using DMPO as a spin trap. Caffeine and 17β-estradiol, as pharmaceutical contaminants of drinking water, were both emitted from the humidifier when present in the water reservoir and would enter breathing air. Emitted 17β-estradiol was found at 60% of the initial concentration filled in the ultrasonic humidifier after 480 minutes. Caffeine exhibited less degradation than 17β-estradiol. Degradation of both pharmaceuticals was attributed to ultrasonic processes, most likely oxidation with hydroxyl radicals produced. Bromide as a contaminant of the fill water was found to remain constant over time.MS
15
Silvester, Stephen. "The copper-catalyzed oxidation of biologically relevant thiols". Thesis, University of York, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265370.
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Park, Ji Ho. "Experimantal and theoretical studies of isoprene oxidation initiated by hydroxyl radical". Texas A&M University, 2004. http://hdl.handle.net/1969.1/1343.
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Isoprene (2-methyl-1,3-butadiene) is the most abundant non-methane
hydrocarbon mostly emitted from the trees and its oxidation by hydroxyl radical
contributes significantly to the tropospheric ozone production. We investigate the
development of a detailed predictive mechanism for isoprene oxidation using both
theory and experiment. We have identified a novel cyclization pathway for the radicals
formed by hydroxy radical (OH) addition to the inner carbons of isoprene. The pathway
predicted that C5 carbonyl compounds are produced, and it may also provide information
on the preference of sites for OH addition. The nitrite/nitrate isomerization is directly
related to the competition between ozone production and radical termination and was
investigated using variational RRKM theory coupled with the master equation. We find
that the dominant fate of the β-hydroxy alkoxy radicals produced from the dissociation
reaction of nitrite is a prompt dissociation, whereas δ-hydroxy radicals isomerize to form
dihydroxy radicals. We have performed experiments using laser photolysis (LP)/ laserinduced
fluorescence (LIF) spectroscopy to study the initial addition reaction of the
hydroxyl radical to isoprene. The overall reaction rates were estimated from experiments
conducted at various pressures and temperatures. The determined Arrhenius rates are
k∞(T) = (3.49±0.46)x10-11exp(366±40)/T molecule-1 cm3 s-1 and k∞(T) = (3.58±0.18)x10-
11exp(356±18)/T molecule-1 cm3 s-1, for the OH and OD addition reactions, respectively.
Isoprene oxidation in the presence of O2 and NO was studied and, based on simulations
to OH cycling curves, we determined a value of (9.0±3.0)x10-12 molecule-1 cm3 s-1 for
the overall reaction rate constant of hydroxy peroxy radical with NO at 298 K. We report
a rate constant for O2 addition to the hydroxy alkyl radical of (2.3±2.0)x10-12 molecule-1
cm3 s-1 at 298 K. We find little generation of OH from the OD initiated oxidation of
isoprene, and no significant differences in OH and OD cycling, which suggests that the
H-shift isomerization is the major pathway for δ-hydroxy alkoxy radicals in agreement
with theoretical predictions.
17
Southworth, Barbara A. (Barbara Anne) 1973. "Hydroxyl radical production via the photo-Fenton reaction in natural waters". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/17548.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references.
This dissertation investigates the importance of photo-Fenton chemistry in natural waters. The Fenton reaction, H202 + Fe(ll) [right arrow] Fe(ll) + OH- + OH', can occur in sunlit waters because both H202 and Fe(ll) are photo-chemically produced. Photo-Fenton chemistry was investigated by irradiating model systems and natural water samples with simulated sunlight and measuring both H202 accumulation and OH' production in the presence and the absence of Fe reactions. Using these data, a model was developed to calculate the potential impact of the photo-Fenton reaction in sunlit natural waters. Throughout this work, a method based on the chemiluminescent reaction of an acridinium ester compound with the conjugate base of H202 was used to analyze H202. This method is sensitive, and has a greater dynamic range, greater selectivity, and fewer sources of interference than more commonly used methods. However, its behavior is not consistent with a simple reaction mechanism. The kinetics of the chemiluminescent reaction were investigated and a mechanism proposed that can explain its behavior, confirming the ability of this method to accurately measure H202, and suggesting ways to avoid potential problems with its application. The photo-Fenton reaction was studied in model systems consisting of a standard humic substance and amorphous iron oxide exposed to simulated sunlight. A probe method was adapted to allow low concentrations of OH' to be measured without otherwise influencing the chemical reactions occurring in experiments. The difference between measured H202 accumulation in the presence and absence of Fe in these systems was interpreted as the photo-loss of H202 by reaction with Fe(ll).
(cont.) Both this photo-loss, as well as measured losses of H202 by reaction with Fe(ll) in the dark, produced the expected quantities of OH'. The photo-loss of H202, as well as the production of OH' due to Fe, were eliminated by the addition of the iron ligand, desferrioxamine mesylate (DFOM). If Fe is also the major sink of H202 in natural waters, sufficient H202 is produced to be an important sink of organic compounds in relatively shallow fresh waters. The amount of H202 that will react to form OH' in natural waters is dependent on the ability of Fe(ll) to outcompete other sinks of H202. Light attenuation and mixing processes will dilute both H202 and Fe(ll) in natural waters, slowing the reaction rate with each other and decreasing the yield of OH' from H202. To investigate these effects, a model was developed using experimental data for the accumulation of H202 in model systems exposed to different intensities of light and rate constants measured in the dark. Assuming that the same processes occur in natural waters, the effects of light attenuation and mixing were calculated as a function of depth and organic matter concentration. Sufficient Fe(ll) will be produced at pH 6 to result in half-lives of organic compounds due to photo-Fenton chemistry on the order of weeks to months at depths less than 10 meters. The methods used to study photo-Fenton chemistry in model systems were applied to two natural water samples from freshwater systems in which photo-Fenton chemistry is likely to occur ...
by Barbara A. Southworth.
Ph.D.
18
Shannon, Robin Joseph. "Experimental and computational studies of hydroxyl radical kinetics at very low temperatures". Thesis, University of Leeds, 2012. http://etheses.whiterose.ac.uk/3661/.
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In this thesis low temperature rate coefficients have been measured for a number of reactions involving the OH radical using a pulsed Laval nozzle apparatus. All these reactions exhibit an energy barrier between reactants and products and in each case this barrier is preceded by either a hydrogen bonded complex ( OH + acetone, OH + DME, OH + methanol) or a weaker Van der Walls complex (OH + acetylene, OH + ammonia). The rate coefficients for these reactions are observed to increase by up to three orders of magnitude between 200 K and 63 K and complimentary Master equation calculations are able to reproduce the complicated temperature dependences that these rate coefficients exhibit. From these master equation calculations, the negative temperature dependencies of the measured rate coefficients are attributed to a mechanism involving the prereaction complex, in most cases including a contribution from quantum mechanical tunnelling. This tunnelling contribution is most especially important in the case of OH + methanol and in this case, hydrogen abstraction products through a 15 kJ mol-1 barrier are observed directly at 79 K on the same timescale as OH loss. The association between an OH radical and its co-reagent to form a weakly bound adduct, is further explored through performing the first proxy method experiments below 200 K. The proxy method is designed to give the high pressure limiting rate coefficient for two associating reactants A and B through measuring the rate coefficients for the A(v=i ) + B reaction. The reactions listed above are revisited and OH vibrational levels up to v = 3 are probed. From these measurements, lower limits for the high pressure limiting rate coefficients of these reactions are obtained at 80 K and the validity of the proxy method is explored in each case.
19
Ingle, Shakti Singh. "RNA structure investigation: a deuterium kinetic isotope effect/hydroxyl radical cleavage experiment". Thesis, Boston University, 2013. https://hdl.handle.net/2144/12787.
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Thesis (Ph.D.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.The hydroxyl radical is widely used as a high-resolution footprinting agent for DNA and RNA. The hydroxyl radical abstracts a hydrogen atom from the sugar- phosphate backbone of a nucleic acid molecule, creating a sugar-based radical that eventually results in a strand break. It was shown previously that replacement of deoxyribose hydrogen atoms with deuterium results in a kinetic isotope effect (KIE) on hydroxyl radical cleavage of DNA. The KIE correlates well with the solvent accessible surface area of a deoxyribose hydrogen atom in DNA. We chose the structurally well-defmed sarcin-ricin loop (SRL) RNA molecule as a model system to extend the deuterium KIE/hydroxyl radical cleavage experiment to RNA. We observed a substantial KIE upon deuteration of the 5'-carbon of the ribose. Values ranged from 1.20 to 1.96, and depended on the position of the residue within the SRL. We found a smaller KIE upon 4'-deuteration. Values ranged from 1.05 to 1.23. Values of 5' and 4' KIEs correlate with the extent of cleavage and with the solvent accessible surface areas of ribose hydrogen atoms ofthe SRL. Gel electrophoresis of cleavage products reveals that the strand break is terminated at the 5' end by multiple chemical species. Upon 3'-radiolabeling a specifically 5'-deuterated SRL RNA molecule, we observed a KIE on the production of a cleavage product having a gel mobility different from that of a phosphate-terminated RNA strand. Reduction with sodium borohydride gave rise to an RNA fragment terminated by a 5'-hydroxyl group. These experiments are consistent with 5' hydrogen abstraction by the hydroxyl radical producing a 5'-aldehyde-terminated RNA strand that retains the nucleotide from which the hydrogen atom was abstracted. This is the first report of such a species. This chemistry has important implications for the interpretation of structural analysis experiments on RNA that rely on primer extension to synthesize eDNA copies of hydroxyl radical cleavage products. The different 5'-terminated products resulting from hydroxyl radical cleavage at a given nucleotide would yield cDNAs of two different lengths, thereby distributing the cleavage intensity over two nucleotides instead ofone and lowering the resolution ofthe experiment.
20
Shi, Xiaofeng. "Time-Resolved Spectroscopic Studies of the Photochemistry of riboflavin, aromatic N-Oxides and the absolute reactivity of hydroxyl radical". The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1126795561.
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Greenbaum, Jason Adam. "Experimental and computational studies of DNA structure using the hydroxyl radical as a chemical probe". Thesis, Boston University, 2006. https://hdl.handle.net/2144/30677.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
We have constructed a database of hydroxyl radical (•OH) cleavage patterns of DNA in order to investigate the relationship between the sequence of a DNA molecule and its three-dimensional structure. The hydroxyl radical cuts DNA at every nucleotide, with the amount of cutting proportional to the solvent accessible surface area (SASA) of the deoxyribose hydrogen atoms. Cleavage fragments are quantified by a fluorescence sequencer, followed by normalization and deposition into the database. Our database currently contains 151 DNA sequences with lengths ranging from 35 to 41 nucleotides. These data have enabled us to develop some general rules regarding the sequence-dependence of DNA structure as well as to predict the cleavage pattern of any given DNA sequence with remarkable precision. Using this prediction algorithm, it is possible to construct structural maps of entire genomes. As there are many examples of DNA binding proteins with highly degenerate binding sites, the use of structural information to locate these sites may be helpful. There also exists other signals, including the signal for nucleosome positioning, which have no apparent consensus, making it likely that the structure of DNA is of critical importance. We have developed algorithms to identify regions of conserved structure using •OH cleavage intensity as a proxy. Within a set of DNase I hypersensitive sites (DHS) obtained from the ENCODE Consortium, we were able to identify a stretch of 12 nucleotides for which the structural conservation is much greater than the sequence conservation. These sites have been dubbed Conserved •OH Radical Cleavage Signatures, or CORCS. Upon further analysis, these CORCS were found to be 17-fold enriched for DHS as compared to shuffled elements. Through the continued analysis of hydroxyl radical cleavage data and development of algorithms to employ the data in biologically meaningful ways, we hope to further our understanding of the relationship between DNA sequence and structure, and how the local structural heterogeneity of genomic DNA contributes to biological function.
2031-01-02
22
Semadeni, Marco. "Hydroxyl radical reactions with volatile organic compounds under simulated tropospheric conditions : tropospheric lifetimes /". [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10809.
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Jeune, Gareth Huw. "An investigation into hydroxyl radical processes for the destruction of chemical warfare agents". Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360079.
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Vimal, Deepali. "Laboratory investigations of the hydroxyl radical-initiated oxidation of atmospheric volatile organic compounds". [Bloomington, Ind.] : Indiana University, 2008. 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:3324041.
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Thesis (Ph.D.)--Indiana University, School of Public and Environmental Affairs, 2008.Title from PDF t.p. (viewed on May 13, 2009). Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4637. Adviser: Philip S. Stevens.
25
Short, Hayden B. "Chemically Accurate Calculations of Rate Constants of Spin Trap-Hydroxyl Radical Addition Reactions". Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/honors/252.
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The DMPO type spin trap 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) and the exceptionally similar spin trap 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-l-oxide (EMPO) are widely studied in computational and theoretical works. This particular study examines the addition reactions that both these molecules undergo with the carcinogenic hydroxyl radical. This work used a relatively new approximation method, called the correlation consistent composite approach or ccCA, for carrying out quantum mechanical calculations to give the free energies of the products and reactants of the reactions. The free energies are to be used to extrapolate the rate constants of the reactions from the Arrhenius equation. Though both the spin traps studied have been widely examined and assessed in both theoretical and experimental work, accurately calculated rate constants have not been previously obtained using computational methods. The results obtained here will help to assess the efficiency and the accuracy of the ccCA method, as well as lead to the design of better, more novel spin traps.
26
Ragnar, Martin. "On the importance of radical formation in ozone bleaching". Doctoral thesis, Stockholm, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3042.
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Dunford, Rosemary. "The effect of photoexcited ultrafine titanium dioxide on DNA". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389000.
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Fortier, Chanel. "Preparation, Characterization, And Application of Liposomes in the Study of Lipid Oxidation Targeting Hydroxyl Radicals". ScholarWorks@UNO, 2008. http://scholarworks.uno.edu/td/889.
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In the onset of many chronic illnesses including Parkinson’s, Alzheimer’s, and cardiovascular diseases, there is evidence to support the delicate balance between prooxidant and antioxidant species is shifted in favor of the former. Under these conditions, many reactive oxygen species (ROS) including hydroxyl radicals, are generated. Hydroxyl radicals formed in close proximity to DNA, nucleotides, proteins, and lipids rapidly oxidize these biological molecules in a nonspecific way. However, their toxicity is limited by their short lifetimes. Currently, the mechanism by which hydroxyl radicals are involved in the onset of many illnesses, particularly with regard to lipid peroxidation, has yielded some controversy in the literature. Conventional studies which generate hydroxyl radicals with Fenton chemistry through bolus additions of iron and hydrogen peroxide do not mimic conditions found physiologically because there is a steady-state concentration of hydrogen peroxide concentration found in normal cellular systems. Also, former reports that used fluorescent fatty acids or free probes intercalated within liposomal membranes did not have the probes covalently attached to the phospholipids making up the liposomes. Thus, the actual placement of the probes over the analysis time may vary with experimental conditions. The objective of this research project was to prepare, characterize, and employ liposomes as models for cell membranes during free radical oxidation. Also, compared to the popularly-used technique of electron spin resonance, (ESR), our aim was to use a fluorescence-based approach which yielded the advantages of high sensitivity, fast analysis time, and less expensive equipment requirements. Degradation of fluorescently-tagged liposomes with probes covalently bound to the phospholipids was correlated with the ability of hydroxyl radicals and other possible reactive oxygen species to penetrate into the liposomes to deeper into the lipophilic layer. However, alone this experimental setup may not fully define the mechanistic role of hydroxyl radicals in lipid oxidation. Thus, a complementary approach embracing the use of MALDI-TOF mass spectrometry, lipophilic scavenger studies, and the effects of cholesterol and temperature allow a deeper understanding of the radically-driven oxidation of lipids. It was determined that hydroxyl radicals were generated and reacted with three fluorescent probes.
29
Minakata, Daisuke. "Development of aqueous phase hydroxyl radical reaction rate constants predictors for advanced oxidation processes". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37127.
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Emerging contaminants are defined as synthetic or naturally occurring chemicals or microorganisms that are not currently regulated but have the potential to enter the environment and cause adverse ecological and/or human health effects. With recent development in analytical techniques, emerging contaminants have been detected in wastewater, source water, and finished drinking water. These environmental occurrence data have raised public concern about the fate and ecological impacts of such compounds. Concerns regarding emerging contaminants and the many chemicals that are in use or production necessitate a task to assess their potential health effects and removal efficiency during water treatment.
Advanced oxidation processes (AOPs) are attractive and promising technologies for emerging contaminant control due to its capability of mineralizing organic compound via reactions with highly active hydroxyl radicals. However, the nonselective reactivity of hydroxyl radicals and the radical chain reactions make AOPs mechanistically complex processes. In addition, the diversity and complexity of the structure of a large number of emerging contaminants make it difficult and expensive to study the degradation pathways of each contaminant and the fate of the intermediates and byproducts. The intermediates and byproducts that are produced may pose potential effects to human and aquatic ecosystems. Consequently, there is a need to develop first-principle based mechanistic models that can enumerate reaction pathway, calculate concentrations of the byproducts, and estimate their human effects for both water treatment and reuse practices.
This dissertation develops methods to predict reaction rate constants for elementary reactions that are identified by a previously developed computer-based reaction pathway generator. Many intermediates and byproducts that are experimentally identified for HO* induced reactions with emerging contaminants include common lower molecular weight organic compounds on the basis of several carbons. These lower carbon intermediates and byproducts also react with HO* at relatively smaller reaction rate constants (i.e., k < 109 M-1s-1) and may significantly affect overall performance of AOPs. In addition, the structures of emerging contaminants with various functional groups are too complicated to model. As a consequence, the rate constant predictors are established based on the conventional organic compounds as an initial approch.
A group contribution method (GCM) predicts the aqueous phase hydroxyl radical reaction rate constants for compounds with a wide range of functional groups. The GCM is a first comprehensive tool to predict aqueous phase hydroxyl radical reaction rate constants for reactions that include hydrogen-atom abstraction from a C-H bond and/or a O-H bond by hydroxyl radical, hydroxyl radical addition to a C=C unsaturated bond in alkenes and aromatic compounds, and hydroxyl radical interaction with sulfur-, nitrogen-, or phosphorus-atom-containing compounds. The GCM shows predictability; factor of difference of 2 from literature-reported experimental values. The GCM successfully predicts the hydroxyl radical reaction rate constants for a limited number of emerging contaminants.
Linear free energy relationships (LFERs) bridge a kinetic property with a thermochemical property. The LFERs is a new proof-of-concept approach for Ab initio reaction rate constants predictors. The kinetic property represents literature-reported and our experimentally obtained hydroxyl radical reaction rate constants for neutral and ionized compounds. The thermochemical property represents quantum mechanically calculated aqueous phase free energy of activation. Various Ab initio quantum mechanical methods and solvation models are explored to calculate the aqueous phase free energy of activation of reactantas and transition states. The quantum mechanically calculcated aqueous phase free energies of activation are within the acceptable range when compared to those that are obtained from the experiments. These approaches may be applied to other reaction mechanisms to establish a library of rate constant predictions for the mechanistic modeling of AOPs. The predicted kinetic information enables one to identify important pathways of AOP mechanisms that are initiated by hydroxyl radical, and can be used to calculate concentration profiles of parent compounds, intermediates and byproducts. The mechanistic model guides the design of experiments that are used to examine the reaction mechanisms of important intermediates and byproducts and the application of AOPs to real fields.
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Nitisha, Hiranandani. "Impact of Reperfusion Injury on Heart". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1239720273.
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Alkhuraiji, Turki. "Ionisation par faisceau d'électrons de solutions aqueuses de benzènesulfonate et naphthalènesulfonate et sous-produits". Thesis, Poitiers, 2013. http://www.theses.fr/2013POIT2259/document.
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Ce sujet entre dans le cadre de l'étude d'un procédé d'oxydation avancé innovant dans le domaine de la dépollution des eaux, à savoir l'ionisation par faisceau d'électrons. Le radical hydroxyle (•OH) et l'électron hydraté (e−aq) sont les deux espèces majoritaires issues de l'ionisation de solutions aqueuses par un faisceau d'électrons d'intense énergie. Il a été démontré que la génération des radicaux supplémentaires tels que le radical sulfate (SO4•−) et le radical hydroxyle par les réactions radicalaires entre l'ion persulfate, le peroxyde d'hydrogène et l'électron hydraté respectivement, améliore l'efficacité de ce procédé pour la dégradation de polluants organiques en solution aqueuse. Dans le présent travail, la dégradation et la minéralisation de benzènesulfonate et naphthalènesulfonate de sodium, et d'acide gallique ont été obtenues par irradiation par faisceau d'électrons seul et couplé avec un oxydant (S2O8−−, H2O2). En absence d'oxydant une dose absorbée de 1,5 kGy a été suffisante pour l'élimination totale de ces composés. La présence d'oxydant permet généralement de réduire les doses d'irradiation nécessaires. Par ailleurs, l'augmentation de la concentration en oxydant ou de la dose appliquée a un effet bénéfique vis-à-vis de l'élimination du carbone organique. Cependant, le couplage S2O8−−/faisceau d'électrons est plus adapté que le couplage H2O2/faisceau d'électrons même en présence de constituants inorganiques. Les résultats obtenus soulignent l'importance du rôle du dioxygène dissous lors de l'étape de la minéralisation en vue de favoriser la formation des radicaux organiques (ROO•). Pour chaque une des molécules étudiées, des sous-produits d'oxydationThis research belongs to the study of the ionization of aqueous solutions by electron beam (E.B.) as an advanced oxidation process for water treatment. The hydroxyl radical (•OH) and hydrated electron(eaq¯) are the two major active species produced from the ionization of aqueous solutions by high energy electron beam. It has been shown that the generation of additional radicals such as the sulphate radical (SO4•¯) and hydroxyl radical from the reaction of persulfate ion (S2O8¯) or hydrogen peroxide (H2O2) with the hydrated electron, improved the efficiency of this process towards the degradation and mineralization of organic pollutants in aquaeous solution. In the présent work, the degradation and mineralization of naphthalenesulfonate, benzenesulfonate and gallic acid were studied by electron beam irradiation alone and coupled with oxidants (S2O8¯, H2O2).In the absence of oxidant, an absorbed dose of 1,5 kGy leads to total elimnation of these pollutants. The presence of added oxidants usually reduces the radiation dose required. In addition, increasing oxidant concentration or applied dose had a beneficial effect towards the organic carbon removal. It was found that coupling E.B./S2O8¯ has more suitable than E.B./ H2O2 even in the presence of inorganic constituents. The results also highlighted the importance of dissolved oxygen in the system when mineralization is aimed. For each of the molecules studied, oxidation by-products resulting from hydroxylation and aromatic ring opening were identified
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Li, YongChao. "DETOXIFICATION OF SELECTED CHLORO-ORGANICS BY OXIDATION TECHNIQUE USING CHELATE MODIFIED FENTON REACTION". UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/551.
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The use of hydroxyl radical based reaction (Fenton reaction) for the destruction of organic pollutants has been widely reported in the literature. However, the low pH requirement and rapid hydrogen peroxide consumption rate make the application of conventional Fenton reaction difficult for in-situ treatment. In this study, we conducted a modified Fenton reaction by introducing a chelating agent into the reaction system that could prevent Fe(OH)3 (s) precipitation even at a neutral pH condition and reduce the H2O2 consumption rate by controlling the Fe2+ concentration. A chelating agent (mono-chelate or poly-chelate) combines with Fe2+ or Fe3+ to form stable metal-chelate complexes in solution. This decreases the concentration of Fe2+ in the solution so that reactions can be carried for longer contact times. Experimental results (citrate was the chelating agent) for 2,4,6-trichlorophenol (TCP) showed that TCP degradations were greater than 95% after 2.5 h and 24 h reaction times at fixed pH 5 and 6, respectively. For the same reaction time, the normalized chloride formations were 85% at pH 5 and 88% at pH 6. Several other chlorinated organic compounds were also chosen as the model compounds for detoxification studies because of their chemical structures: trichloroethylene (unsaturated hydrocarbon), carbon tetrachloride (highly oxidized compound), 2,2-dichlorobiphenyl, and biphenyl (a dual-aromatic ring structure). Poly-chelating agents (such as polyacrylic acid-PAA) provide multiple Fe2+/Fe3+ binding sites in the modified Fenton reaction for the oxidation of contaminants (2,2-dichlorobiphenyl, and biphenyl) at a neutral pH environment. Numerical simulation based on the kinetic model developed from the well known Fenton reaction and iron-chelate chemistry fits experiment data well for both standard and chelate modified Fenton reactions. In this dissertation, it was proven that both monomeric (citrate) and polymeric (PAA) chelate modified Fenton reactions were effective for dechlorination of carbon tetrachloride from aqueous phase by the superoxide radical anion. On the other hand, PAA (a poly-chelating agent) can also be used for solid surface modification by polymerization of acrylic acid (monomer). The successful degradations of biphenyl and trichloroethylene by the PAA functionalized silica particles/membrane demonstrate the versatile applications of the chelate modified Fenton reaction.
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Chakraborty, Sourav. "Molecular Probes for Biologically Important Molecules: A Study of Thiourea, Hydroxyl radical, Peroxynitrite and Hypochlorous acid". ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/1132.
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Numerous chemical species are important to the health of biological systems. Some species can be beneficial at low doses and harmful at high doses. Other species are highly reactive and trigger serious cell damage. Improved methods to detect the presence and activity of such species are needed. In this work, several biologically important species were studied using appropriate analytical techniques. Fluoride is an important species in human physiology. It strengthens teeth and gives protection against dental caries. However, elevated concentrations of fluoride in the body can lead to health problems such as dental and skeletal fluorosis. Reported fluoride sensors used fluorescence quenching methods in determining fluoride concentration. Our study explored synthesis and characterization of 1,8-bis(phenylthioureido) naphthalene (compound 1) as a fluoride sensing molecule. Compound 1 showed a remarkable 40 fold enhancement in fluorescence with 5 eq of fluoride addition. Compound 1 also showed possibility of visual colorimetric sensing with fluoride. Free radical mediated oxidations of biomolecules are responsible for different pathological conditions in the human body. Superoxide is generated in cells and tissues during oxidative burst. Moderately reactive superoxide is converted to peroxyl, alkoxyl and hydroxyl radicals by various enzymatic, chemical, and biochemical processes. Hydroxyl radical imparts rapid, non specific oxidative damage to biomolecules such as proteins and lipids. Superoxide also reacts with nitric oxide in cells to yield peroxynitrite, which is highly reactive and damages biomolecules. Both hydroxyl radical and peroxynitrite readily react with amino acids containing aromatic side chains. Low density lipoprotein (LDL) carries cholesterol in the human body. Elevated concentration of LDL is a potential risk factor for atherosclerosis. Previous research drew a strong correlation between oxidized low density lipoprotein (ox-LDL) and plaque formation in the arterial wall. More importantly, oxidative damage causes structural changes to the LDL protein (apo B-100) which might facilitate the uptake of LDL by macrophages. In this study LDL was exposed to various concentrations of hydroxyl radical peroxynitrite and hypochlorite. Thereafter oxidized amino acid residues in apo B-100 were mapped by LC-MS/MS methods. We found widely distributed oxidative modifications in the apo B-100 amino acid sequence.
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Wagner, Alec Thomas. "Fundamental Studies of Two Important Atmospheric Oxidants, Ozone and Hydroxyl Radical, Reacting with Model Organic Surfaces". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/45093.
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Heterogeneous reactions between gas-phase oxidants and particulate-phase organic compounds impact many important atmospheric chemical processes. For example, little is known about the reaction dynamics of gaseous oxidants with organic compounds found in the atmosphere. The first step of the reaction between gaseous ozone and solid pentacene was investigated using Reflection Absorption Infrared Spectroscopy (RAIRS). Ozone was found to add to pentacene non-selectively and form a range of products after heavy ozone exposure. The rate limiting step had an activation energy of 17 kJ/mol, which is consistent with the findings of previous ozone oxidation studies for the cleavage of a carbon-carbon double bond. Unfortunately the products could not be used to distinguish between probable reaction mechanisms.
Hydroxyl radicals (•OH) play a major role processing atmospheric hydrocarbons. Due to their short lifetimes, not much is known about the dynamics of the first steps of •OH reactions. To investigate these reactions, a rotational state-selector was constructed to filter a molecular beam of •OH for reaction dynamics investigations with organic surfaces. The rotational state-selector was designed to leverage the linear Stark effect to pass only suitable molecules in a particular rotational state and block the flow of any other atoms, molecules and ions in a molecular beam. The state-selector was validated and used to positively deflect molecular beams of methyl iodide and D₂O via the linear Stark effect. Future studies with the rotational state-selector will investigate the initial steps of •OH reactions with solid organic compounds.Master of Science
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Pan, Xiong. "Theoretical Studies of Atmospheric Water Complexes". PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/1163.
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Intermolecular complexes between H₂O and atmospheric species HO, HO₂, H₂O₂, O₃, NO and NO₂ have been studied by ab initio molecular orbital methods. The studies have been performed to the MP2 theory level by using 4-31G, 6-31G, D95, 6-31G**, D95**, 6-311G**, 6-311+G**, 6-311++G**, 6-311+G(2d,lp) and 6-311+G(2d,2p) basis sets. The geometries were fully optimized. The vibrational frequencies were calculated. The Basis Set Superposition Error (BSSE) were estimated. Finally, the binding energies of the complexes were predicted with other thermochemical properties. The binding energies of H₂O•HO, H₂O•HO₂, H₂O•H₂O₂, H₂O•O₃, H₂O•NO and H₂O•NO₂ are estimated to be 5.7±0.6, 8.9±1.0, 7.3±1.3, 1.8±0.2, 1.17 (no BSSE correction) and 2.98 (no BSSE correction) Kcal/Mol, respectively. The Kcq for dimerization to yield H₂O•HO, H₂O•HF, H₂O•HO₂, H₂O•H₂O and H₂O•H₂O₂ are estimated to be 0.11, 2.8, 3.3, 0.067 and 0.11 atm¯¹, respectively. The H₂O•HO, H₂O•HF, H₂O•HO₂, H₂O•H₂O and H₂O•H₂O₂ are quite strongly bonded complexes, while H₂O•O₃, H₂O•NO and H₂O•NO₂ are only weakly bonded complexes. The Kcq changes with temperature are discussed, and their importance in atmospheric chemistry are addressed.
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DeMatteo, Matthew P. "Computational investigations of hydroxyl radical addition to aromatics and alkenes in the presence of solvent, conformational preferences of dendrimers, and theoretical studies of arabinofuranosides and septanosides". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1180128001.
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Pillar-Little, Elizabeth A. "MECHANISMS OF HETEROGENEOUS OXIDATIONS AT MODEL AEROSOL INTERFACES BY OZONE AND HYDROXYL RADICALS". UKnowledge, 2017. http://uknowledge.uky.edu/chemistry_etds/80.
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Atmospheric aerosols play an important role in climate by scattering and absorbing radiation and by serving as cloud condensation nuclei. An aerosol’s optical or nucleation properties are driven by its chemical composition. Chemical aging of aerosols by atmospheric oxidants, such as ozone, alters the physiochemical properties of aerosol to become more hygroscopic, light absorbing, and viscous during transport. However the mechanism of these transformations is poorly understood. While ozone is a protective and beneficial atmospheric gas in the stratosphere, it is a potent greenhouse gas in the troposphere that traps heat near the Earth’s surface. It also impacts human heath by irritating the respiratory tract and exacerbating cardiovascular diseases. Additionally, ozone can alter the ecosystem through oxidizing plant foliage which can lead to deforestation and crop losses as well. Both gases and aerosols in the troposphere can react with ozone directly and indirectly with hydroxyl radicals. While daytime aging is thought to be primarily driven by photochemical processes and hydroxyl radicals, ozone is thought to be a key player in nighttime or dark aging processes that can alter the physicochemical properties of aerosols. Measured concentrations of trace gases and aged aerosol components in the field are higher than values predicted based on laboratory studies and computer simulations. Consequently, new experimental approaches are needed to narrow the gaps between observations and mechanistic understandings.
In this dissertation, a plume of microdroplets was generated by pneumatically assisted aerosolization and then exposed to a flow of ozone before entering a mass spectrometer. This surface-specific technique allowed for the real-time analysis of reaction products and intermediates at the air-water interface. This work explores the in situ oxidation of iodide, a component of sea spray aerosols, by 0.05 – 13.00 ppmv ozone to explore how heterogeneous oxidation could enhance the production of reactive iodide species. Methods to study the reaction channels and intermediates were also established to not only determine a mechanism of iodide oxidation by ozone, but to enable the study of more complex systems. The developed approach was then applied to examine the oxidation of catechol and its substituted cousins, a family of compounds selected to model biomass burning and combustion emissions, at the air-water interface. While literature suggested that the primary mechanism of catechol oxidation by ozone would be the cleavage of the C1-C2 bond, it was determined that this was only a minor pathway. An indirect oxidation channel dominated heterogeneous processes at the air-water interface, giving rise to hydroxyl and semiquinone radicals that recombine to produce polyhydroxylated aromatics and quinones. This new mechanism of aging represents an overlooked channel by which brown, light-absorbing carbon aerosols are produced in the atmosphere.
In addition, the work investigates how reactions on solid particulate aerosols proceed under variable relative humidity. Thin films were developed alongside a novel flow-through reactor to study of how aerosols are transformed by ozone and hydroxyl radicals when exposed to 50 ppbv - 800 ppmv of ozone. This system was employed to probe how catechol reacts with ozone under variable relative humidity. Further work was undertaken to model the adsorption process at the air-solid interface under variable humidity, permitting the estimation of the reactive uptake of ozone by the film at concentrations (50-200 ppbv) seen in rural and urban areas. Together, these results provide an increased understanding of how heterogeneous oxidation of aerosols contributes to aerosol aging processes as well as free radical production in the troposphere.
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Brosse, Fabien. "Influence de la couche limite convective sur la réactivité chimique en Afrique de l'Ouest". Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30324/document.
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Cette thèse porte sur l'influence de la couche limite convective et nuageuse sur la réactivité chimique en Afrique de l'Ouest. Pour répondre à cette question, des simulations à haute résolution (50m) sont réalisées sur le modèle atmosphérique Méso-NH couplé à un mécanisme chimique détaillé représentant la chimie gazeuse et aqueuse. Cette échelle spatiale permet de représenter explicitement les caractéristiques spatiales et temporelles des structures turbulentes. Les thermiques en couche limite sont identifiés à l'aide d'un échantillonnage conditionnel basé sur l'utilisation d'un traceur passif à décroissance radioactive. L'impact du transport turbulent sur la redistribution d'espèces chimiques dépend du temps de vie chimique de ces espèces. La ségrégation spatiale créée au sein de la couche limite augmente ou réduit les taux de réaction moyens entre composés. La campagne de terrain AMMA, et plus récemment DACCIWA, sont utilisées pour définir des forçages dynamiques et chimiques pour des environnements simulés. Le premier est représentatif d'un environnement biogénique dominé par des émissions naturelles de COV. Le second reproduit un environnement urbain modérément pollué typique du Golfe de Guinée (Cotonou au Bénin). Pour simplifier, l'analyse des simulations est limitée aux réactions chimiques entre OH et l'isoprène dans le cas biogénique, entre les aldéhydes C>2 et OH dans le cas urbain. L'influence de la couche limite convective est étudiée à l'échelle du thermique et du domaine. Cela permet une connexion avec les modèles à résolution plus lâche qui adoptent une hypothèse de mélange parfait et immédiat, négligeant de fait les variabilités spatiales de composés chimiques au sein d'une maille. Les premiers résultats, basés sur la phase gazeuse uniquement, montrent que les nuages en couche limite convective affectent le transport vertical d'espèces chimiques. Les thermiques sont des zones de réactions privilégiées où la réactivité chimique est maximale. La plus grande intensité de ségrégation est calculée au sommet de la couche limite, toutefois de signes opposés entre les deux environnements. En environnement biogénique, le mélange non-homogène de l'isoprène et de OH dans cette zone induit une diminution maximale de 30% du taux de réaction moyen. Dans le cas urbain, la constante de réaction effective entre OH et les aldéhydes est supérieure de 16% à la constante moyenne. La réactivité de OH est supérieure de 15 à 40% dans les thermiques comparé au reste du domaine, dépendant de l'environnement chimique et de l'heure. Comme les thermiques occupent une faible portion du domaine, l'impact des structures turbulentes sur la réactivité totale de OH est une diminution de 9% pour le cas biogénique et une augmentation maximale de 5% dans le cas anthropique. Des simulations LES incluant la réactivité aqueuse révèlent une baisse importante des rapports de mélange de OH associée à la présence de nuagesThis thesis focuses on the influence of the convective and cloudy boundary layer on the chemical reactivity in West Africa. To answer this question, high resolution simulations (50m) are performed on the atmospheric model Meso-NH coupled to a detailed chemical scheme representing the gaseous and aqueous phases. This spatial scale allow to explicitly represent the spatial and temporal characteristics of turbulent structures. Thermals in the boundary layer are identified by a conditional sampling based on a radioactive-decay passive scalar. The turbulent transport influence on the redistribution of chemical species depends on the chemical lifetimes of these species. Spatial segregation is created within the convective boundary layer that increases or decreases the mean reaction rates between compounds. AMMA campaign field study, and more recently DACCIWA, are used to define dynamical and chemical forcing of two simulated environments. The first one is representative of a biogenic environment dominated by natural emissions of VOC. The second reproduces a moderately polluted typical urban area of the Guinean Gulf (Cotonou in Benin). For the sake of simplicity, simulations analysis are limited to the chemical reaction between isoprene and OH in the biogenic case, and the reaction between C>2 aldehydes and OH in the anthropogenic case. The convective boundary layer influence is studied at thermal and domain scale. This makes the connection with coarse resolution models for which a hypothesis of perfect and immediate mixing is made, neglecting the spatial variability of chemical species within a grid cell. The first results are based on the gaseous phase only. Cloudy development in the convective boundary layer only affects the vertical transport of chemical species. The simulations show that thermals are preferential reaction zones where the chemical reactivity is the highest. The top of the boundary layer is the region characterized by the highest calculated segregation intensities but of the opposite sign in both environments. In the biogenic environment, the inhomogeneous mixing of isoprene and OH in this zone leads to a maximum decrease of 30% of the mean reaction rate. In the anthropogenic case, the effective rate constant for OH reacting with aldehydes is 16% higher at maximum than the averaged value. The OH reactivity is higher by 15 to 40% inside thermals compared to the surroundings depending on the chemical environment and time of the day. Because thermals occupy a small fraction of the simulated domain, the impact of turbulent motions on the domain-averaged OH total reactivity reaches a maximum 9% decrease for the biogenic case and a maximum of 5% increase for the anthropogenic case. LES simulations including the aqueous reactivity reveal a significant decrease in OH mixing ratios associated to the presence of clouds. Consequently, isoprene and C>2 aldehydes mixing ratios increase at these altitudes
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Wu, Hong. "Sulfate radical based ceramic catalytic membranes for water treatments". Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2020. https://ro.ecu.edu.au/theses/2382.
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The discharge of antibiotics into natural aquatic environment without proper treatments results in the propagation of antibiotics-resistant strains. Effective remediation technologies are therefore urged to remove those emerging contaminants from water. However, antibiotics are difficult to be degraded through a traditional biological treatment because they would deactivate the effective bacteria used in the process. Advanced oxidation processes (AOPs) using highly reactive oxygen species (ROS) such as hydroxyl radicals ( OH) and sulfate radicals (SO4 •− • ) have been widely employed as an efficient way for antibiotics degradation owing to the high oxidation ability, non-selectivity and low cost. However, the recovery of the suspended catalysts after use is the biggest obstacle for the wide application. Meantime, membrane separation has also been extensively applied as a promising wastewater treatment technology with the advantages of long-term operation, low energy consumption and high yield of production. The membrane fouling is, however, a critical issue restricting the widespread application of membrane. For addressing above-mentioned issues, with extensive technological and scientific endeavours, this PhD study focused on the development of novel integration technology of AOPs and membrane separation for antibiotics degradation. In this research, heterogeneous AOPs processes coupled with independent membrane separation unit for suspended catalysts recovery were studied. Moreover, metal oxide based-catalytic membrane for concurrent AOPs and membrane separation were investigated. Firstly, boron, nitrogen co-doped carbon nanotubes supported FeOOH (FeOOH@BNC) was synthesized for the degradation of sulfamethoxazole (SMX) by Fenton-like reaction. The as-synthesized FeOOH@BNC showed an excellent performance in SMX removal (Chapter 3). Secondly, boron, nitrogen co-doped nanotubes (BNC) were developed. The BNC nanotubes with a high specific area, abundant active sites, and controllable N–B–C structures demonstrated prominent peroxymonosulfate (PMS) activation ability towards 4-hydroxylbenzoic acid (HBA) degradation (Chapter 4). It was also found that both FeOOH@BNC and BNC suspended catalysts in the treated solution can be well recovered via membrane filtration (Chapter 3 and 4). Finally, two metal oxide-based catalytic ceramic membranes (Co3O4@CM and MnO2@CM) were prepared via a simple one-step ball-milling method with a high temperature sintering. The as-prepared Co3O4@CM and MnO2@CM composite catalytic membranes were characterized and tested for the degradation of aqueous HBA solution by SR-AOPs procedure. It was found that the composite membranes showed excellent HBA removal efficiencies, good reusability and high anti-fouling performances (Chapter 5 and 6). Mechanistic studies, e.g. materials chemistry, generation of reactive radicals, and degradation pathways, were also carried out. The developed catalysts, catalyst membranes, and the combined processes as well as the mechanistic studies are expected to provide significant contributions in terms of both technology and scientific knowledge to remediation of emerging contaminants.
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Gallo, Inara Fernanda Lage. "Preparação e caracterização de fotocatalisadores heterogêneos de titânio e nióbio e avaliação do potencial de fotodegradação". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/59/59138/tde-05072016-152453/.
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É urgente o desenvolvimento de novas tecnologias para o tratamento de água nos dias atuais. Neste contexto, os processos oxidativos avançados (POA) tem sido bem-sucedido no tratamento de contaminantes presentes em efluentes industriais e na rede de esgoto doméstico. Neste trabalho, estudamos um dos POA, a fotocatáliseheterogênea por meio da síntese de fotocatalisadores mistos de nióbio e titânio utilizando-se o método Pechini, com uma temperatura de calcinação de 470 oC. Foram sintetizados os fotocatalisadores PNB000, PNB018, PNB030, PNB070, PNB099 e PNB100, onde os números mostram aporcentagem em mols de pentóxido de nióbio presente em cada um deles. Estes fotocatalisadores foram submetidos a um segundo tratamento térmico a 800oC, durante 6 horas, e obtivemoso PNB000_01, PNB018_01, PNB030_01, PNB070_01 e PNB100_01. A caracterização dos fotocatalisadores foi feita por: análise de espectroscopia de energia dispersiva (EDS); área superficial determinadas por isotermas de adsorção e dessorção de nitrogênio, BET; imagens de microscopiaeletrônica de varredura (MEV); difração de raios-X; análises térmicas (termogravimetria e análise térmica diferencial), determinação de band gap por reflectância difusa. O potencial para serem usados como fotocatalisadores heterogêneos para degradação de compostos orgânicos foi avaliado pela eficiência fotônica de geração de radicais hidroxilas(OH)sob radiação de lâmpada UVA (15 W). A análise de EDS confirmou acomposiçãoem mol de TiO2 e Nb2O5presentes nosfotocatalisadoressintetizados. A área superficial obtida por isotermas (BET) do PNB018 (161,7 m²/g), PNB030 (130,8 m²/g), PNB070 (150,5 m²/g) mostraram-se maiores do que ado TiO2 P25 (52,68 m²/g). As imagens de MEV mostrou que estes fotocatalisadoressão constituídos de partículas manométricas. Outra característica dos óxidos com quantidade intermediária de mols de Nb2O5 (18, 30 e 70%) foi a estrutura amorfa determinada por difração de raios-X. Por sua vez, os óxidos tratados a 800oC apresentaram estruturas cristalinas edifratogramas de raios-X completamente diferentes do TiO2 e do Nb2O5, comprovando-se que são novos materiais.As medidas de energia de band gapmostrou diferenças significativas quando comparamos o TiO2 P25 (Egap 3,22eV) e o PNB000 (Egap 2,90eV). Isso leva a concluir que estes fotocatalisadores sintetizados pelo método Pechini necessitam de uma energia menor para que ocorram as transições eletrônicas. O fotocatalisador PNB070, que apresenta 70% em mols de pentóxido de nióbio, apresentouOH de 0,104 da mesma ordem de grandeza do TiO2 P25 (OH 0,134) e ligeiramente menor do que o OH do Nb2O5.nH2O (OH 0,164). Dessa maneira, supõe-se que o PNB070 tenha o mesmo potencial de eficiência que o TiO2 P25 para fotodegradações. Por sua vez, os fotocatalisadores que passaram por um segundo tratamento térmico a 800 oC mostraram valores de rendimento quântico de produção de radicais hidroxilas bem inferiores aos seus originais. Por exemplo, o PNB070_01 teve OH de 0,003. Esses resultados sugerem que o aumento da cristalinidade pode diminuir a atividade fotocatalítica, ou, que o estado amorfo dos fotocatalisadores deste trabalho favorece o aumento da velocidade de transferência de elétrons e a da fotocatálise.Nowadays, the development of new technologies for the treatment of water is urgent. In this context, the advanced oxidative processes (AOP) has been successful in the treatment of contaminants foundin industrial effluents and domestic sewage. In this work, we have studied an AOP, the heterogenousphotocatalysis, by means the synthesis of niobium and titanium mixedphotocatalysts, employing calcination temperature of 470 oC.The PNB000, PNB018, PNB030, PNB070, PNB099 and PNB100photocatalysts were synthetized, where the numbers show the percentage in mol of Nb2O5content in each of them. These photocatalytswere submitted to a second heat treatment to 800oC during 6 hours, and PNB000_01, PNB018_01, PNB030_01, PNB070_01 and PNB100_01 were obtained. The characterization of the photocatalysts was made by: analysis of the energy dispersive spectroscopy (EDS); the surface area determined by adsorption and desorption isotherms of nitrogen, BET; images of scanning electron microscopy (SEM); X-ray diffraction; thermal analysis (thermogravimetry and differential thermal analysis), determination of the band gap by diffuse reflectance.Their potential to be used as heterogeneous photocatalystsfor degradation of organic compounds was evaluated by means the determination of the photonic efficiency for hydroxyl radical production (OH)under radiation of UV-A lamp (15 W). The EDS analysis confirmed the composition in mol of TiO2 and Nb2O5 present in the synthesizedphotocatalysts. Surface area obtained by isotherms (BET) of PNB018 (161.7 m ²/g), PNB030 (130.8 m ²/g), PNB070 (150.5 m ²/g) were higher than TiO2 P25 (52.68 m ²/g). SEM images showed that these photocatalysts consist of nanoparticles. Another feature of the oxides with intermediate amount of moles of Nb2O5 (18, 30 and 70%) was the amorphous structure determined by X-ray diffraction. On the other hand, the oxides treated to 800 oC showed crystalline structures and X-ray patternscompletely different from TiO2 and Nb2O5, proving that the synthetized oxides are new materials.The band gap energy measurements showed significant differences when we compare TiO2 P25 (Egap 3.22 eV) and the PNB000 (Egap 2.90 eV). This allow us to conclude that thephotocatalysts synthesized by Pechini method require lower energy in order to have electronic transitions. The PNB070 photocatalyst, which has 70% in mols of niobium pentoxide, showed OHof 0.104 of the same order of magnitude of TiO2 P25 (OH0.134) and slightly smaller than the OH of Nb2O5.nH2O (OH 0.164). For this reason, we can assume that PNB070 has the same potential of the TiO2 P25 for organic compound photodegradation. The photocatalyststhat were submittedthrough a second heat treatment at 800 oC showed quantum efficiency of hydroxyl radical production values well below their original. For instance, PNB070_01 showed OHof 0.003. These results suggest that increased crystallinity can reduce the photocatalytic activity, or the amorphous structures of the photocatalysts of this work improve the electron transfer rates and the photocatalysis.
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Holmes, Bryan J. "Oligomerization of Levoglucosan in Proxies of Biomass Burning Aerosols". ScholarWorks @ UVM, 2008. http://scholarworks.uvm.edu/graddis/111.
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Biomass burning aerosols play an important role in the chemistry and physics of the atmosphere and therefore, affect global climate. Biomass burning aerosols are generally aqueous and have a strong saccharidic component due to the combustion and pyrolysis of cellulose, a major component of foliar fuel. This class of aerosol is known to affect both the absorption and scatter of solar radiation. Also, biomass burning aerosols contribute to cloud formation through their action as cloud-condensation nuclei. Many questions exist about the chemical speciation and chemical aging of biomass burning aerosols and how this affects their atmospheric properties and ultimately, global climate. Also, knowledge of the chemical components of these aerosols is important in the search for chemical tracers that can give information about the point or regional source, fuel type, and age of a biomass burning aerosol parcel. Levoglucosan was chosen for these studies as a model compound for biomass burning aerosols because of its high measured concentrations in aerosol samples. Levoglucosan often dominates the aerosol composition by mass. In this dissertation, laboratory proxy systems were developed to study the solution-phase chemistry of levoglucosan with common atmospheric reactants found in biomass burning aerosols (i.e. H+, •OH). To mimic these natural conditions, acid chemistry was studied using sulfuric acid in water (pH=4.5). The hydroxyl radical (•OH) was produced by the Fenton reaction which consists of iron, hydrogen peroxide and acid (H2SO4) in aqueous solvent. For studies in aqueous sulfuric acid, oligomers of levoglucosan were measured by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF-MS). A rational mechanism is proposed based on both the acid-catalyzed cationic ring-opening of levoglucosan and nucleophilic attack of ROH from levoglucosan on the hemi-acetal carbon to produce pyranose oligomers through the formation of glycosidic bonds. Oligomer formation is further supported by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Reactions of levoglucosan with •OH produced from Fenton chemistry were studied in solution. Two modes of oligomerization (2000 u) were observed for reaction times between 1 and 7 days using MALDI-TOF-MS and laser desorption ionization (LDI) TOF-MS. Single-mass unit continuum mass distributions with dominant -2 u patterns were measured and superimposed by a +176/+162 u oligomer series. This latter oligomer pattern was attributed to a Criegee rearrangement (+14 u) of levoglucosan, initiated by •OH, forming a lactone (176 u). The acid-catalyzed reaction of any ROH from levoglucosan (+162 u) forms an ester through transesterification of the lactone functionality, whereupon propagation forms polyesters. Proposed products and chemical mechanisms are suggested as sources and precursors of humic-like substances (HULIS), which are known to possess a large saccharic component and are possibly formed from biomass burning aerosols. These products could also serve as secondary tracers, giving further information on the source and age of the aerosol.
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Bones, David Lawrence. "Liquid Aerosol Photochemistry". Thesis, University of Canterbury. Chemistry, 2008. http://hdl.handle.net/10092/1500.
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Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.
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Oladiran, Oladun Solomon, e Scott J. KIrkby. "Computational Studies of the Spin Trapping Behavior of Melatonin and its Derivatives". Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/asrf/2019/schedule/186.
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The presence of excess free radicals in the body can result in severe health consequences because of oxidative damage to cells. Spin traps may be used as a probe to examine radical reactions in cells, but there is a need for less toxic and more lipid soluble examples. Melatonin is one of the numerous antioxidants used to scavenge free radicals in the body and reportedly one of the most efficient radical scavengers known. It is relatively nontoxic and easily crosses the lipid bilayer in cell membranes. Melatonin is thought to undergo a multistep oxidation process and this work investigates the potential for it to be used as a spin trap. The presence of electron withdrawing or donating groups added to melatonin may stabilize an intermediate and allow it to function as a spin trap.
The essence of this study is to conduct a computational inquiry into the relative stability of melatonin, selected derivatives, and the partial oxidation products formed from the scavenging of hydroxyl radical. To determine this, geometries were optimized for each molecule at the DFT/B3LYP/6-31G(d) and HF/6-31G(d) levels of theory.
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Lallement, Audrey. "Impact des processus photochimiques et biologiques sur la composition chimique du nuage". Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC066/document.
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Dans un contexte de réchauffement climatique, une compréhension des mécanismes atmosphériques influençant le bilan radiatif terrestre est nécessaire. Les nuages peuvent participer à un refroidissement mais des incertitudes demeurent sur ces systèmes qui sont encore mal connus (notamment la composition de leur fraction organique). Depuis toujours, seules les réactions chimiques et surtout celles radicalaires sont considérées comme importantes pour jouer sur la composition des nuages. Cependant la découverte de microorganismes métaboliquement actifs pose la question de leur rôle en tant que biocatalyseurs. Ces microorganismes sont en effet à même d'utiliser des molécules carbonées comme nutriments, de dégrader des molécules précurseur des radicaux (H2O2) et de se prémunir contre le stress oxydant. L'objectif de ce travail est de mesurer l'impact des processus photochimiques et biologiques sur la composition chimique du nuage. Pour cela, la quantification de •OH, le radical responsable de la réactivité diurne, et l’évaluation de l’impact des microorganismes sur cette concentration à l’état stationnaire ont été entreprises. Après un développement en milieu modèle, la méthode a été appliquée à des eaux atmosphériques (eaux de pluies et eaux de nuages). Les concentrations obtenues sont de l'ordre de 10-17 à 10-15 M et ne sont pas modifiées en présence de microorganismes. Ces concentrations sont plus faibles que celles obtenues dans les modèles de chimie atmosphérique, ceci peut s’expliquer par un manque de connaissance sur la matière organique. Pour mieux caractériser cette dernière, des composés aromatiques simples présents dans des eaux de nuages ont été identifiés, le phénol a été retrouvé dans les 8 échantillons analysés. Une étude approfondie sur sa dégradation a donc été entreprise. Nous avons montré que des transcrits d’enzymes intervenant dans sa biotransformation sont synthétisés par les bactéries in situ dans l’eau de nuage. De plus, 93% des souches bactériennes testées, isolées de ce milieu, dégradent le phénol. Pour évaluer l'impact relatif des processus de dégradation biotique et abiotique du phénol, une expérience de photobiodégradation avec une souche modèle (Rhodococcus erythropolis PDD-23b-28) a été entreprise. Ces deux processus interviennent avec une importance de même ordre de grandeur. Ces résultats suggèrent que les microorganismes et les radicaux interviennent dans la remédiation naturelle de l'atmosphèreIn the context of global warming, more precise knowledge of atmospheric processes is needed to evaluate their impact on the Earth radiative budget. Clouds can limit the increase of temperature but this retroaction is not well understood due to a lack of knowledge of cloud media (like organic fraction composition). From the beginning of atmospheric studies, only chemical, especially radical, reactions was taken into account. However microorganisms metabolically active were found in cloud water arising questions about their role as biocatalyst. They are able to use carboxylic acids as nutriments, to degrade radical precursor (like H2O2) and to survive oxidative stress. The aim of this work is to quantify the impact of photochemical and biological processes on cloud chemistry composition. First, the concentrations of •OH, the most reactive radical, were evaluated and the influence of microorganisms on the concentrations were studied. A new method was developed in artificial medial before direct quantification of steady state •OH concentration in atmospheric waters (rain and cloud waters). Concentrations ranged from 10-17 to 10-15 M and did not change in presence of microorganisms. These measures were lower than concentrations estimated by chemical atmospheric models. A possible explanation was an underestimation of the main sink of this radical (organic matter). To better characterize this fraction, simple aromatic compounds were identified in cloud waters, phenol was found in the 8 samples analyzed. To go further, we studied phenol degradation in detail. Enzyme transcripts involved in phenol degradation were present in cloud water samples showing in situ activity of native bacteria. 93% of tested cultural strains, isolated from cloud waters, were able to degrade phenol. To quantify the relative contribution of radical versus microbial processes allowing phenol degradation, we performed photo-biodegradation experiment with a model strain (Rhodococcus erythropolis PDD-23b-28). Our results showed that these two processes participated equally to phenol degradation, suggesting that microorganisms and radicals can be involved in atmospheric natural remediation
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Kuhlmann, Rolf von. "Tropospheric photochemistry of ozone, its precursors and the hydroxyl radical a 3d-modeling study considering non-methane hydrocarbons /". [S.l.] : [s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2001/0141/diss.pdf.
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Xiao, Ai-Ying. "The central catechol-O-methyltransferase inhibitor tolcapone increases striatal hydroxyl radical production in L-Dopa, carbidopa treated rats". [S.l.] : [s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=965145298.
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Baasandorj, Munkhbayar. "Experimental and theoretical studies of the kinetics of the hydroxyl radical-initiated oxidation of oxygenated volatile organic compounds". [Bloomington, Ind.] : Indiana University, 2008. 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:3297937.
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Thesis (Ph. D.)--Indiana University, School of Public and Environmental Affairs, 2008.Title from dissertation home page (viewed Sept. 30, 2008). Source: Dissertation Abstracts International, Volume: 69-03, Section: B, page: 1537. Adviser: Philip S. Stevens.
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Liljegren, Jennifer A. "Experimental and theoretical studies of the kinetics of the hydroxyl radical (OH)-initiated oxidation of volatile organic compounds". Thesis, Indiana University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3602969.
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This research investigates the kinetics of the hydroxyl radical (OH)-initiated oxidation of several volatile organic compounds (VOCs) including ethanol, 3-methylfuran, and methyl ethyl ketone (2-butanone). Oxidation by OH is the dominant loss process for many biogenic and anthropogenic VOCs, making ambient concentrations of OH and the rate constants of OH + VOC reactions useful for determining the lifetime of various VOCs in the atmosphere. The rate constants of OH + VOC reactions are important for improving the accuracy of input parameters used in urban and regional air quality models which can be used to inform the development of air quality control strategies. The absolute rate constants for the reaction of OH with ethanol, 3- methylfuran, and methyl ethyl ketone (2-butanone) and, in some cases, their deuterated isotopomers have been measured as a function of pressure and temperature using discharge-flow techniques coupled with laser-induced fluorescence detection of OH. Theoretical studies of the potential energy surface for the various pathways in the OH + ethanol and OH + methyl ethyl ketone (2-butanone) reactions indicate a mechanism involving hydrogen-abstraction through a hydrogen-bonded pre-reactive complex. The experimental measurements of the rate constants and the kinetic isotope effect have been used in conjunction with the results of the theoretical studies to improve our understanding of the kinetics of these reactions.
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Machairas, Alexandros 1980. "The UV/H2O2 advanced oxidation process in UV disinfection units : removal of selected phosphate esters by hydroxyl radical". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/29410.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.Includes bibliographical references (leaves 96-97).
In this work, the issue of how to remove phosphate esters from drinking water is examined. From the various treatment processes available, the oxidation of phosphate esters through hydroxyl radical generated by the UV/H202 process applied at a UV disinfection unit was selected for evaluation. The second-order rate constants of the reactions of two phosphate esters, Tri(2-butoxyethyl) phosphate (TBEP) and Tri-2-chloroethyl phosphate (TCEP) , with hydroxyl radical were estimated from our experimental data to be 2.1000 M-1s-1 and 2 109 M-is-1 respectively A comprehensive kinetic model of the oxidation process was derived. Finally computer simulations were used to exhibit the potential of this treatment process and to examine the effects of pH, total carbonate species concentration, initial hydrogen peroxide dose, and light intensity on its efficiency. The results are not very encouraging when a UV unit designed for disinfection is used. For typical values of pH and total carbonate species (pH=8 and CT=5' 10-4 M) the 1 s order rate coefficients for removal of the phosphate esters are 6.3 10-4 (s-1) for TBEP and 6.3 10-5 (s-1) for TCEP. If higher light intensity is applied in the reactor (50 times higher), and initial hydrogen peroxide dose of 10-3 M and CT remains 5 10-4 M, the 1st order reaction rate coefficients become 2.9 10-2 (s-1) and 2.9-10-3 (s-1) for TBEP and TCEP respectively.
by Alexandros Machairas.
M.Eng.
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Joshi, Prasad. "Isolation and reactivity of hydroxyl radical with astrochemically and atmospherically relevant species studied by Fourier transform infrared spectroscopy". Paris 6, 2012. http://www.theses.fr/2012PA066092.
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Les radicaux OH jouent un rôle très important dans la chimie des milieux interstellaires. Dans la mesure où il s’agit d’espèces très réactives, l’isolation et la détection expérimentale de ces radicaux est délicate. Pourtant, cette étape est un prérequis nécessaire pour des études de réactivités qui pourraient s’avérer fondamentales dans de nombreux domaines, en particulier pour la chimie des milieux interstellaires et des atmosphères planétaires. Différents protocoles expérimentaux ont été utilisés pour former les radicaux OH. Dans un premier temps, de l’eau pure, à l’état gazeux, a été soumise à une décharge microonde. Les espèces formées sont condensées sur un miroir maintenu à 3 K à l’aide d’un cryostat, et analysées à l’aide d’un spectromètre IR à transformée de Fourrier (FTIR). Dans ces conditions, la formation d’eau par recombinaisons radicalaires a été observée, et la présence de radicaux OH ne pouvait pas être clairement établie dans la mesure où le signal caractéristique des glaces d’eau masquait l’éventuelle présence des radicaux. Pour minimiser les recombinaisons radicalaires, des mélanges gazeux d’eau diluée dans différents gaz rares (GR = He, Ne, Ar) ont été préparés et soumis à la décharge microonde. A l’aide de cette approche expérimentale, la signature spectroscopique des radicaux OH a pu être observée, à la fois en phase solide (GR = He) et en matrice de néon (GR = Ne). La réactivité de ces radicaux OH avec H2O, CO, NO, N2 et CH4 a ensuite été étudiée en phase solide et en matrice de néonOH radicals play a fundamental role in the chemistry of interstellar media. The isolation and the characterization of the highly reactive species is challenging and represents an important prerequisite for reactivity studies that might be crucial in different fields such as astrochemistry and atmospheric chemistry. Different experimental approaches were tested to produce OH radicals. First of all, gaseous pure water was subjected to a microwave discharge. The species thus formed were condensed onto a cryogenic mirror maintained at 3 K and further characterized with a Fourier-transform IR spectrometer (FTIR). Under these conditions, radical recombination lead to the formation of a water-ice and the presence of OH radicals cannot be clearly established. Gaseous water was diluted into different rare gases (RG = He, Ne, Ar) prior to their introduction into the microwave discharge source. This approach allows to isolate and characterize OH radicals both in solid phase (RG = He) and in neon matrix (RG = Ne). Further reactivity experiments were carried out between these radicals and small species such as H2O, CO, NO, N2, O2, and CH4 in solid phase as well as in neon matrix