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Auswahl der wissenschaftlichen Literatur zum Thema „Photolyse UV-C“
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Zeitschriftenartikel zum Thema "Photolyse UV-C"
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Maré, George R. De, Guy J. Collin und Hélène Deslauriers. „Évaluation des ruptures de liaison α(C—H) centrale et terminale dans la photolyse du propène gazeux à 184,9 nm“. Canadian Journal of Chemistry 73, Nr. 8 (01.08.1995): 1267–73. http://dx.doi.org/10.1139/v95-155.
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The minor, α(C—H) photofragmentation processes in the far-UV photolysis of gaseous propene at λ = 184.9 nm are investigated. At this wavelength the β(C—H) and α(C—C) photofragmentation processes are of major importance, accounting for more than 95% of the primary reaction process. The total quantum yield of the three α(C—H) bond cleavage processes is close to 0.03. However [Formula: see text] and the sum of the two [Formula: see text] cleavages is 0.005 ± 0.003. Thus [Formula: see text] whereas statistically one expects 1:2. Thus the energy of the bond that is breaking is important, even though the photon energy is much higher than that required to break it. The geometrical parameters, total energies, and fundamental frequencies of the cis- and trans-propen-1-yl and propen-2-yl radicals have been determined by abinitio methods at various levels of theory (STO-3G, 3-21G, 6-31G, 6-31G*, and 6-31G** basis sets; UHF, ROHF, and GVB methods). cis-Propen-1-yl is predicted to be 0.6–1.0 kJ mol−1 lower in energy than trans-propen-1-yl, except with the minimal STO-3G basis set. The optimizations predict that propen-2-yl is more stable than the cis- and trans-propen-1-yl radicals by 14 ± 3 kJ mol−1. Keywords: propene, unimolecular reactions, photochemistry, α(C—H) cleavage, propenyl radicals.
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Guitonneau, S., S. Momege, A. Schafmeier, P. O. Viac und P. Meallier. „Étude comparative de la dégradation du bromoxynil et du bromoxynil heptanoate par photolyse UV et par oxydation chimique (H²O²/UV ; O³ ; Cl²)“. Revue des sciences de l'eau 8, Nr. 2 (12.04.2005): 201–16. http://dx.doi.org/10.7202/705219ar.
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Les dégradations du bromoxynil heptanoate et du bromoxynil ont été étudiées pour différents traitements chimiques (03, Cl2) et photochimiques (H202/W; W254) en milieu aqueux dilué. Les expériences ont été réalisées à pH 7 pour le bromoxynil (CO=5 10-5 mol 1-1) et à pH 4 pour le bromoxynil heptanoate (CO=10-6 mol 1-1) afin de limiter la réaction d'hydrolyse. Les résultats obtenus montrent une bonne dégradation de ces deux pesticides aussi bien par irradiation W que par oxydation chimique au chlore ou à l'ozone. L'ajout de peroxyde d'hydrogène dans le milieu n'augmente pas de façon significative l'efficacité du traitement par rapport à l'irradiation seule. Parmi tous les traitements étudiés, l'ozonation est le procédé le plus efficace. L'analyse par couplage GC-MS des produits de réaction au cours de l'irradiation UV a permis d'identifier quatre photoproduits correspondant à la substitution des atomes de brome soit par un atome d'hydrogène, soit par un groupement OH. Les produits identifés sont A: -3,4 dihydroxy -5 bromobenzonitrile; B: -3,4,5 trihydroxybenzonitrile; C: -3,4 dihydroxybenzonitrile; D: -4 hydroxybenzo- nitrile. Un schéma réactionnel de photodégradation du bromoxynil heptanoate a été proposé dans cette étude.
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Emmerich, Hans-Joachim, Martin Saft, Leonie Schneider, Dennis Kock, Alfred Batschauer und Lars-Oliver Essen. „A topologically distinct class of photolyases specific for UV lesions within single-stranded DNA“. Nucleic Acids Research 48, Nr. 22 (03.12.2020): 12845–57. http://dx.doi.org/10.1093/nar/gkaa1147.
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Abstract Photolyases are ubiquitously occurring flavoproteins for catalyzing photo repair of UV-induced DNA damages. All photolyases described so far have a bilobal architecture with a C-terminal domain comprising flavin adenine dinucleotide (FAD) as catalytic cofactor and an N-terminal domain capable of harboring an additional antenna chromophore. Using sequence-similarity network analysis we discovered a novel subgroup of the photolyase/cryptochrome superfamily (PCSf), the NewPHLs. NewPHL occur in bacteria and have an inverted topology with an N-terminal catalytic domain and a C-terminal domain for sealing the FAD binding site from solvent access. By characterizing two NewPHL we show a photochemistry characteristic of other PCSf members as well as light-dependent repair of CPD lesions. Given their common specificity towards single-stranded DNA many bacterial species use NewPHL as a substitute for DASH-type photolyases. Given their simplified architecture and function we suggest that NewPHL are close to the evolutionary origin of the PCSf.
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González-Burciaga, Luis A., Juan C. García-Prieto, Cynthia M. Núñez-Núñez und José B. Proal-Nájera. „Statistical Analysis of Methotrexate Degradation by UV-C Photolysis and UV-C/TiO2 Photocatalysis“. International Journal of Molecular Sciences 24, Nr. 11 (31.05.2023): 9595. http://dx.doi.org/10.3390/ijms24119595.
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Methotrexate (MTX) is a folic acid analog and has been used to treat a wide variety of malignant and non-malignant diseases. The wide use of these substances has led to the continuous discharge of the parent compound and its metabolites in wastewater. In conventional wastewater treatment plants, the removal or degradation of drugs is not complete. In order to study the MTX degradation by photolysis and photocatalysis processes, two reactors were used with TiO2 as a catalyst and UV-C lamps as a radiation source. H2O2 addition was also studied (absence and 3 mM/L), and different initial pHs (3.5, 7, and 9.5) were tested to define the best degradation parameters. Results were analyzed by means of ANOVA and the Tukey test. Results show that photolysis in acidic conditions with 3 mM of H2O2 added is the best condition for MTX degradation in these reactors, with a kinetic constant of 0.028 min−1. According to the ANOVA test, all considered factors (process, pH, H2O2 addition, and experimentation time) caused statistically significant differences in the MTX degradation results.
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Bayram, Özgür, Christoph Biesemann, Sven Krappmann, Paul Galland und Gerhard H. Braus. „More Than a Repair Enzyme:Aspergillus nidulansPhotolyase-like CryA Is a Regulator of Sexual Development“. Molecular Biology of the Cell 19, Nr. 8 (August 2008): 3254–62. http://dx.doi.org/10.1091/mbc.e08-01-0061.
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Cryptochromes are blue-light receptors that have presumably evolved from the DNA photolyase protein family, and the genomes of many organisms contain genes for both types of molecules. Both protein structures resemble each other, which suggests that light control and light protection share a common ancient origin. In the genome of the filamentous fungus Aspergillus nidulans, however, only one cryptochrome/photolyase-encoding gene, termed cryA, was identified. Deletion of the cryA gene triggers sexual differentiation under inappropriate culture conditions and results in up-regulation of transcripts encoding regulators of fruiting body formation. CryA is a protein whose N- and C-terminal synthetic green fluorescent protein fusions localize to the nucleus. CryA represses sexual development under UVA350-370 nmlight both on plates and in submerged culture. Strikingly, CryA exhibits photorepair activity as demonstrated by heterologous complementation of a DNA repair-deficient Escherichia coli strain as well as overexpression in an A. nidulans uvsBΔ genetic background. This is in contrast to the single deletion cryAΔ strain, which does not show increased sensitivity toward UV-induced damage. In A. nidulans, cryA encodes a novel type of cryptochrome/photolyase that exhibits a regulatory function during light-dependent development and DNA repair activity. This represents a paradigm for the evolutionary transition between photolyases and cryptochromes.
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González-Burciaga, L. A., J. C. García-Prieto, C. M. Núñez-Núñez, M. García-Roig und J. B. Proal-Nájera. „Methotrexate Degradation by UV-C and UV-C/TiO2 Pro-cesses with and without H2O2 Addition on Pilot Reactors“. International Journal of Environmental Science and Development 11, Nr. 10 (2020): 471–76. http://dx.doi.org/10.18178/ijesd.2020.11.10.1292.
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Methotrexate (MTX) is an anti-cancer drug that can be excreted up to 90% after administration due to its low biodegradability. Advanced Oxidation Processes (AOPs) are a feasible alternative for the elimination of MTX in the environment. In this research, AOPs were performed in specialized patented reactors (UBE Photocatalytic systems and BrightWater Titanium Advanced Oxidation Process) under experimental pilot conditions. Photolysis and heterogeneous photocatalysis (UV and UV/TiO2) experiments were performed with and without addition of H2O2 and at different initial pHs. Best degradation percentage was achieved by photolysis when initial pH was 3.5 and added H2O2 was 3 mM, reaching a MTX degradation of 82% after 120 min of reaction. HPLC-MS analysis of the resulting samples showed four possible byproducts of MTX degradation, which presented a higher ecotoxicity than the starting compound.
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González-Burciaga, Luis A., Juan C. García-Prieto, Manuel García-Roig, Ismael Lares-Asef, Cynthia M. Núñez-Núñez und José B. Proal-Nájera. „Cytostatic Drug 6-Mercaptopurine Degradation on Pilot Scale Reactors by Advanced Oxidation Processes: UV-C/H2O2 and UV-C/TiO2/H2O2 Kinetics“. Catalysts 11, Nr. 5 (29.04.2021): 567. http://dx.doi.org/10.3390/catal11050567.
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6-Mercaptopurine (6-MP) is a commonly used cytostatic agent, which represents a particular hazard for the environment because of its low biodegradability. In order to degrade 6-MP, four processes were applied: Photolysis (UV-C), photocatalysis (UV-C/TiO2), and their combination with H2O2, by adding 3 mM H2O2/L (UV-C/H2O2 and UV-C/TiO2/H2O2 processes). Each process was performed with variable initial pH (3.5, 7.0, and 9.5). Pilot scale reactors were used, using UV-C lamps as radiation source. Kinetic calculations for the first 20 min of reaction show that H2O2 addition is of great importance: in UV-C experiments, highest k was reached under pH 3.5, k = 0.0094 min−1, while under UV-C/H2O2, k = 0.1071 min−1 was reached under the same initial pH; similar behavior was observed for photocatalysis, as k values of 0.0335 and 0.1387 min−1 were calculated for UV-C/TiO2 and UV-C/TiO2/H2O2 processes, respectively, also under acidic conditions. Degradation percentages here reported for UV-C/H2O2 and UV-C/TiO2/H2O2 processes are above 90% for all tested pH values. Ecotoxicity analysis of samples taken at 60 min in the photolysis and photocatalysis processes, suggests that contaminant degradation by-products present higher toxicity than the original compound.
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Kawasaki, Koji, und Hideo Iwasaki. „Involvement of glycogen metabolism in circadian control of UV resistance in cyanobacteria“. PLOS Genetics 16, Nr. 11 (30.11.2020): e1009230. http://dx.doi.org/10.1371/journal.pgen.1009230.
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Most organisms harbor circadian clocks as endogenous timing systems in order to adapt to daily environmental changes, such as exposure to ultraviolet (UV) light. It has been hypothesized that the circadian clock evolved to prevent UV-sensitive activities, such as DNA replication and cell division, during the daytime. Indeed, circadian control of UV resistance has been reported in several eukaryotic organisms, from algae to higher organisms, although the underlying mechanisms remain unknown. Here, we demonstrate that the unicellular cyanobacterium Synechococcus elongatus PCC 7942 exhibits a circadian rhythm in resistance to UV-C and UV-B light, which is higher during subjective dawn and lower during subjective dusk. Nullification of the clock gene cluster kaiABC or the DNA-photolyase phr abolished rhythmicity with constitutively lower resistance to UV-C light, and amino acid substitutions of KaiC altered the period lengths of the UV-C resistance rhythm. In order to elucidate the molecular mechanism underlying the circadian regulation of UV-C resistance, transposon insertion mutants that alter UV-C resistance were isolated. Mutations to the master circadian output mediator genes sasA and rpaA and the glycogen degradation enzyme gene glgP abolished circadian rhythms of UV-C resistance with constitutively high UV-C resistance. Combining these results with further experiments using ATP synthesis inhibitor and strains with modified metabolic pathways, we showed that UV-C resistance is weakened by directing more metabolic flux from the glycogen degradation to catabolic pathway such as oxidative pentose phosphate pathway and glycolysis. We suggest glycogen-related metabolism in the dark affects circadian control in UV sensitivity, while the light masks this effect through the photolyase function.
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Xu, Bingjie, Guoyan Zhan, Bin Xu, Haijie Du, Hang Luo, Tianfeng Wang, Changchao Zhan und Yi Yang. „Degradation of acetaminophen in aqueous solution by UV and UV-activated sludge processes“. Water Science and Technology 78, Nr. 10 (23.11.2018): 2088–95. http://dx.doi.org/10.2166/wst.2018.483.
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Abstract Acetaminophen (N-acetyl-p-aminophenol, APAP) is one of the most common antipyretic analgesics used to treat common ailments throughout the world. Recently, APAP has been frequently detected in wastewater effluent and groundwater, resulting in potential risks to the environment. Current methods for eliminating APAP are complicated and cost-prohibitive. This study examined APAP degradation by ultraviolet-C (UV-C) and UV-C irradiation combined with activated sludge (UV/AS) to evaluate potential applications in wastewater treatment. The results of this study indicate that UV-C irradiation reached an APAP degradation efficiency of more than 52% and a degradation rate of 0.0012–0.0013 min−1 during 720 min of exposure, while the initial APAP concentration exhibited only a nominal effect on the degradation rate. However, the UV/AS treatment demonstrated an APAP degradation rate that was 9.6 times the rate of the UV-C-only treatment, with a degradation efficiency of 99% over the same UV irradiation period. The results further indicated that APAP photolysis efficiency was more effective when applied to sterilized AS than when applied to unsterilized AS. Finally, excessive dosage of both AS and humic acid inhibited APAP photolysis efficiency.
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Safitri, Vanny Yulia, Adlis Santoni, Diana Vanda Wellia, Khoiriah Khoiriah und Safni Safni. „Degradation of Paracetamol by Photolysis Using C-N-codoped TiO2“. Molekul 12, Nr. 2 (30.11.2017): 189. http://dx.doi.org/10.20884/1.jm.2017.12.2.378.
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Paracetamol is generally used as analgesic and antipyretic drugs. Contamination paracetamol in the environment can occur because of waste material disposal from production site and immediate disposal of household that cause water pollution. Paracetamol is degraded by photolysis method under irradiation 10 watt UV-light (λ=365 nm), visible-light (Philips LED 13 watt 1400 lux) and solar-light with and without addition C-N-codoped TiO2catalyst. The solution is analyzed by UV-Vis spectrophotometer at λ 200-400 nm. Optimum weight of C-N-codoped TiO2 catalyst obtained is 20 mg under UV-light photolysis. Paracetamol 4 mg/L is degraded 45.48% after 120 minutes under UV-light irradiation without catalyst, and increases to be 69.31% by using 20 mg catalyst. While degradation percentage of paracetamol is 16.96 % without catalyst, the percentage increases to be 34.29% after using 20 mg catalyst for 120 minutes photolysis under visible-light. Degradation of paracetamol by solar light achieves only 12.27% in absance of catalyst for 120 minutes irradiation, but it increases significantly until 70.39% in presence of 20 mg catalyst.
Dissertationen zum Thema "Photolyse UV-C"
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Nabintu, kajoka Christelle. „Utilisation de l’acide performique en traitement des eaux résiduaires urbaines : Réactivité avec les micropolluants organiques et stratégies d’intégration au sein de procédés d’oxydation avancée“. Electronic Thesis or Diss., Marne-la-vallée, ENPC, 2023. https://these.univ-paris-est.fr/intranet/2023/TH2023ENPC0048.pdf.
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Cette thèse s'inscrit dans la phase 5 du programme « OPUR : Observatoire des Polluants Urbains » et a pour objectif d'améliorer la compréhension et l’élimination des micropolluants pharmaceutiques (résidus de médicaments) le long des filières de traitement des eaux résiduaires urbaines. La présence de micropolluants pharmaceutiques dans les eaux résiduaires urbaines est principalement due à la consommation répandue de médicaments dans les zones urbaines, en particulier par le biais de l'excrétion humaine. L’élimination insuffisante de ces micropolluants pharmaceutiques par les stations d'épuration est la principale raison de leur présence dans les milieux aquatiques. Afin de réduire les risques liés à la présence de ces micropolluants pour la faune et la flore aquatiques, l'ajout d'un traitement tertiaire (avancé) aux stations d'épuration conventionnelles est l'une des solutions possibles et permettrait de diminuer la concentration de ces polluants émergents dans le rejet des stations d’épuration. L'importance de cette étude réside dans l'utilisation de l'acide performique, un désinfectant employé pour améliorer la qualité des effluents rejetés par les stations d'épuration dans la Seine en préparation des Jeux olympiques et paralympiques de 2024 qui se tiendront à Paris. Ainsi, cette étude vise à optimiser les conditions d'utilisation de ce désinfectant, que ce soit en utilisation individuelle ou en couplage avec d’autres oxydants sous forme de procédé d’oxydation avancée, en vue de l'élimination des micropolluants pharmaceutiques. Les diverses expérimentations menées, d'abord en utilisant de l'eau ultrapure, ont révélé la réactivité marquée mais sélective de l'acide performique envers les composés organiques contenant du soufre réduit ou les amines tertiaires déprotonées, le mécanisme d’oxydation principal étant le transfert d'un atome d'oxygène. Dans les eaux résiduaires urbaines, l'acide performique est relativement réactif avec les micropolluants pharmaceutiques étudiés et leur élimination dépend fortement des différents constituants présents dans les effluents, certains pouvant activer l'acide performique et engendrer des espèces réactives capables de réduire un nombre plus important de micropolluants pharmaceutiques. Les résultats ont également montré que l’acide performique est efficace pour éliminer les micropolluants organiques polaires souvent moins bien éliminés par les procédés classiques. Le couplage de l'acide performique avec la photolyse UV-C ou l'ozone a significativement amélioré l'élimination des micropolluants pharmaceutiques résistants à l'acide performiqueThis thesis is part of phase 5 of the "OPUR: Urban Pollutants Observatory" program and aims to enhance the understanding and elimination of pharmaceuticals (pharmaceutical residues) in the context of urban wastewater treatment processes. The presence of pharmaceuticals in urban wastewater is primarily attributed to widespread drug use in urban areas, particularly through human excretion. The insufficient removal of these pharmaceuticals by wastewater treatment plants is the main cause of their presence in aquatic environments.To mitigate the risks associated with these micropollutants for aquatic flora and fauna, the addition of an advanced (tertiary) treatment to conventional wastewater treatment plants is one of the possible solutions. This approach would result in the reduction of the concentration of these emerging micropollutants in wastewater plant effluents.The significance of this study lies in the use of performic acid, a disinfectant employed to improve the quality of effluent discharged in the Seine River by the wastewater treatment plants in preparation for the 2024 Olympic and Paralympic Games to be held in Paris. Thus, this study aims to optimize the conditions for using this disinfectant, either individually or in conjunction with other oxidants in tertiary (advanced) oxidation processes, for the removal of pharmaceuticals.Various experiments, initially conducted using deionized water, revealed the pronounced yet selective reactivity of performic acid towards organic compounds containing reduced sulfur or deprotonated tertiary amines, with the primary oxidation mechanism involving the transfer of an oxygen atom.In urban wastewater, performic acid exhibits relatively high reactivity with the pharmaceuticals under investigation, and their removal is significantly influenced by the diverse constituents present in the effluent. Some of these constituents could activate performic acid, thereby generating reactive species that can effectively reduce a greater number of pharmaceuticals. Furthermore, the results demonstrate the efficacy of performic acid in eliminating polar organic micropollutants, a task often challenging for conventional treatment processes. The combination of performic acid with UV-C photolysis or ozone significantly improved the removal of pharmaceuticals resistant to performic acid alone
Buchteile zum Thema "Photolyse UV-C"
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Boycheva, Irina, Ralitsa Georgieva, Lubomir Stoilov und Vasilissa Manova. „Effects of light and UV-C radiation on the transcriptional activity of COP1 and HY5 gene homologues in barley.“ In Mutation breeding, genetic diversity and crop adaptation to climate change, 478–86. Wallingford: CABI, 2021. http://dx.doi.org/10.1079/9781789249095.0049.
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Abstract Photomorphogenic regulators COP1 (Constitutive Photomorphogenic 1) and HY5 (Elongated Hypocotyl 5) play a key role in plant development by guiding the transition from dark to light growth. In Arabidopsis they are also implicated in the transcriptional control of photolyase genes. Here we characterize the transcript abundance of COP1 and HY5 gene homologues in barley in relation to light-grown conditions and UV-damage response. Etiolated and green 6-day-old seedlings were UV-C irradiated and exposed to light or kept in darkness. The abundance of barley COP1 and HY5 transcripts was assessed by real-time RT-PCR. In etiolated leaves we found several-fold lower levels of COP1 transcripts which reached the levels of the green ones after 1 h of light exposure. Barley HY5 transcripts were very low in the dark-grown seedlings and after 1 h of illumination they increased drastically to levels significantly exceeding those measured in the green leaves. Both genes were upregulated by light in the irradiated plants as well, but to a lesser extent compared with their controls, probably due to the presence of non-repaired DNA damage in the etiolated leaves soon after irradiation. The enhanced transcription of barley COP1 under light is unexpected in view of the well-known function of COP1 as a negative regulator of plant photomorphogenesis but conforms to the positive role reported for AtCOP1 in UV-B signalling. HY5 is recognized as a stimulator of light-inducible genes and our data support such a role for the barley HY5 homologue as well. Our study shows that, in barley seedlings, the regulation of COP1 and HY5 gene expression is achieved through light-positive transcriptional modulation, suggesting that both genes contribute to the de-etiolation phase in barley. According to our knowledge, this is the first quantitation of the COP1 and HY5 mRNAs in barley that also regards the UV-damage response of this crop.
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Calvert, Jack G., Richard G. Derwent, John J. Orlando, Geoffrey S. Tyndall und Timothy J. Wallington. „Atmospheric Chemistry of the Haloalkanes“. In Mechanisms of Atmospheric Oxidation of the Alkanes, 379–603. Oxford University PressNew York, NY, 2008. http://dx.doi.org/10.1093/oso/9780195365818.003.0006.
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Abstract As with alkanes, reaction with OH is the dominant loss mechanism for haloalkanes. However, unlike the case for alkanes, photolysis can be an important loss mechanism for brominated and iodinated alkanes in the troposphere, chlorinated alkanes in the stratosphere, and fluorinated alkanes in the mesosphere. UV spectra and photolysis lifetimes for haloalkanes are discussed in chapter VII. In this chapter we first review the available kinetic data for reactions of OH radicals with haloalkanes (section VI-A). Reactions with Cl, O(3P), NO3, and O3 are then considered in section VI-B. Rules for the empirical estimation of rate coefficients of OH radicals with the haloalkanes are presented in section VI-C. The atmospheric chemistry of haloalkylperoxy and haloalkoxy radicals is described in sections VI-D and VI-E, respectively. Finally, the major products of the OH-initiated oxidation of haloalkanes are discussed in section VI-F.
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Calvert, Jack, Abdelwahid Mellouki, John Orlando, Michael Pilling und Timothy Wallington. „Rate Coefficients and Mechanisms for the Atmospheric Oxidation of the Organic Acids“. In Mechanisms of Atmospheric Oxidation of the Oxygenates. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199767076.003.0009.
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Organic acids, particularly formic and acetic acid, are ubiquitous components of the troposphere (Chebbi and Carlier, 1996); see table I-D-1. However, the atmospheric budget of these species is at present poorly constrained, and global models often underestimate their abundance (von Kuhlmann et al., 2003). The presence of organic acids in the atmosphere can be attributed to two distinct mechanisms: direct emission from anthropogenic and natural sources; and in situ production via gas-phase or condensed-phase chemistry. Direct emissions result from biomass burning (e.g., Christian et al., 2007), from motor vehicle use (Kawamura et al., 2000) and other anthropogenic activities (see chapter I), and from biogenic sources (e.g., Seco et al., 2007). Production in the gas phase can occur via the reactions of acylperoxy radicals with HO2: . . . CH3C(O)O2 + HO2 → CH3C(O)OOH + O2 . . . . . . CH3C(O)O2 + HO2 → CH3C(O)O + OH + O2 . . . . . . CH3C(O)O2 + HO2 → CH3C(O)OH + O3 . . . or via the ozonolysis of unsaturated species (Orzechowska and Paulson, 2005a, b). Additional in situ acid production (particularly with multi-functional species and diacids) likely occurs in the condensed phase as well, via the oxidation of carbonyl and other oxygen-containing and multi-functional organics (e.g., Ervens et al., 2004). In general, the organic acid moiety, —C(O)OH, is rather unreactive in the gas phase. This is in large part due to the strength of the O—H bond, ∼460 kJ mole−1 versus 400–420 kJ mole−1 for typical C—H bonds (Sander et al., 2006). The organic acid moiety also acts to inhibit somewhat the reactivity of neighboring sites (Kwok and Atkinson, 1995), further decreasing the reactivity of small saturated acids. UV spectra for unsubstituted acids are located at relatively short wavelengths, [e.g., λmax< 210 nm for acetic acid, Orlando and Tyndall (2003); see figure IX-A-1], so tropospheric photolysis is of negligible importance. Thus, the gas-phase lifetime for small saturated organic acids (e.g., formic and acetic acid) can be quite long, about 1 month.
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Calvert, Jack, Abdelwahid Mellouki, John Orlando, Michael Pilling und Timothy Wallington. „Rate Coefficients and Mechanisms of Atmospheric Oxidation of the Esters“. In Mechanisms of Atmospheric Oxidation of the Oxygenates. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199767076.003.0010.
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Esters are emitted directly into the atmosphere from both natural and anthropogenic sources and are produced during the atmospheric oxidation of ethers. Methyl acetate and ethyl acetate have found widespread use as solvents. Vegetable oils and animal fats are esters. Transesterification of vegetable oils and animal fats with methanol gives fatty acid methyl esters (FAMEs) which are used in biodiesel. Many esters have pleasant odors and are present in essential oils, fruits, and pheromones, and are often added to fragrances and consumer products to provide a pleasant odor. Table VII-A-1 provides a list of common esters and their odors. It is surprising to note that despite their ubiquitous nature, volatility, and fragrance, it is only very recently that quantitative measurements of esters in ambient air have been reported (Niedojadlo et al., 2007; Legreid et al., 2007). The atmospheric oxidation of saturated esters is largely initiated by OH radical attack. Reaction with O3 and NO3 radicals contributes to the atmospheric oxidation of unsaturated esters. As discussed in chapter IX, UV absorption by esters is only important for wavelengths below approximately 240 nm and, hence, photolysis is not a significant tropospheric loss mechanism. When compared to the ethers from which they can be derived, the esters are substantially less reactive towards OH radicals. The ester functionality —C(O)O— in R1C(O)OR2 deactivates the alkyl groups to which it is attached with the deactivation being most pronounced for the R1 group attached to the carbonyl group. The atmospheric oxidation mechanisms of the esters are reviewed in the present chapter. The reaction of OH with methyl formate has been studied by Wallington et al. (1988b) and Le Calvé et al. (1997a) over the temperature range 233–372 K. Data are summarized in table VII-B-1 and are plotted in figure VII-B-1. The room temperature determination of k(OH + CH3OCHO) by Wallington et al. is in agreement with that by Le Calvé et al. (1997) within the experimental uncertainties. Significant curvature is evident in the Arrhenius plot in figure VII-B-1.
Konferenzberichte zum Thema "Photolyse UV-C"
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Mahmoud, Sawsan A., A. Abdel Aal und Ahmed K. Aboul-Gheit. „Nanocrystalline ZnO Thin Film for Photocatalytic Purification of Water“. In ASME 2008 2nd Multifunctional Nanocomposites and Nanomaterials International Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/mn2008-47034.
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A thin film ZnO nanostructured catalyst exhibited a significantly greater superiority for the photodegradation of 2, 4, 6-TCP in water over photolysis via irradiation with UV of 254 nm wavelength. This ZnO photocatalyst was prepared via Zn metal evaporation and deposition on a glass sheet followed by calcination ature from 350 to 500 °C and the calcination time from 1 to 2h shows via SEM photography a decrease of ZnO nanoparticales sizes sheet followed by calcination (oxidation). Increasing the calcination temperature from 350 to 500 °C and the calcination time from 1 to 2h shows via SEM photography a decrease of ZnO nanoparticales sizes as well as the shape of their crystals finer needles, for which the crystallinity enhances as revealed by XRD. 2, 4, 6-Trichlorophenol was used as a model pollutant in water. Its photolysis using UV only or photocatalysis using UV irradiation in presence of the ZnO thin film catalyst indicated aromatic intermediates, which suffered of Cl by OH, addition of OH in a bare carbon in the aromatic ring, whereas in Photocatalysis deeper oxidation products, e.g., quinones and hydroquinones were also formed.
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Johnson, Matthew, Yuichiro Ueno, Johan Schmidt, Alexis Gilbert, Hiroyuki Kurokawa, Tomohiro Usui und Xiaofeng Zang. „Strong 13C depletion induced by solar UV photolysis of CO2 and its implication for early Mars“. In Goldschmidt2023. France: European Association of Geochemistry, 2023. http://dx.doi.org/10.7185/gold2023.19682.
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