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1
Whyte, Lynden J. "A kinetic and mechanistic study of tropospheric reactions". Thesis, University of East Anglia, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314391.
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2
Kalinga, Shivashankar. "Peroxynitrite-induced modifications of myoglobin : a kinetic and mechanistic study /". Zürich : ETH, 2005. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16014.
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3
Siu, Tung. "Kinetic and mechanistic study of aqueous sulfide-sulfite-thiosulfate system". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0007/MQ45585.pdf.
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4
Scott, Laura-Marie. "Kinetic and mechanistic study of Lilestralis, a synthetic muguet fragrance molecule". Thesis, University of Aberdeen, 2011. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=165414.
Testo completoAbstract (sommario):
In the multi-step synthesis of Lilestralis, a synthetic muguet fragrance, the kinetics and mechanism of the formation of 3-(3-t-butylphenyl)-2-methylpropan-1-ol (m-LOL) and 4-(3-t-butylphenyl)-2-methylpropan-1-ol (p-LOL) from 2-methyl-3-phenylpropan-1-ol (MPP) and isobutylene using concentrated liquid phosphoric acid as a catalyst was investigated. By-products that include phosphate esters of MPP, m-LOL and p-LOL and oligomers of isobutylene were produced during this reaction and their role within the kinetics and mechanism was also investigated. When crystalline phosphoric acid is dissolved in water, it can form equilibrium polyphosphate mixtures at high acid concentrations. The phosphate species have the general formula Hn+2PnO3n+1 and consist of species such as orthophosphoric acid (H3PO4), pyrophosphoric acid (H4P2O7) and triphosphoric acid (H5P3010). The presence of polyphosphate within liquid phosphoric acid solutions used in this study was investigated using 31P NMR. To investigate the influence of water on the reaction, a number of experiments were performed using 1,4-dioxane as a solvent. This was chosen as the boiling points and density are similar to water, although it is classified as an aprotic solvent. Phosphate esters of MPP, m-LOL and p-LOL are produced as by-products and can potentially undergo hydrolysis when water is present, therefore reactions using aqueous phosphoric acid solutions may not give a true reflection of the concentration of phosphate esters produced. The use of heterogeneous catalysts was also investigated in order to improve yield and selectivity for p-LOL and m-LOL. These include acid catalysts such as solid phosphoric acid supported on Kieselguhr (SPA), sulphated zirconia and ultra stable zeolite-Y (H-USY).
5
Souza, Valdir Araujo de. "Corrosion and erosion-corrosion of wc-based cermet coatings - a kinetic and mechanistic study". Thesis, Heriot-Watt University, 2004. http://hdl.handle.net/10399/318.
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6
Ahlford, Katrin. "Asymmetric transfer hydrogenation of ketones : Catalyst development and mechanistic investigation". Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-55412.
Testo completoAbstract (sommario):
The development of ligands derived from natural amino acids for asymmetric transfer hydrogenation (ATH) of prochiral ketones is described herein. In the first part, reductions performed in alcoholic media are examined, where it is found that amino acid-derived hydroxamic acids and thioamides, respectively, are simple and versatile ligands that in combination with [RhCp*Cl2]2 efficiently catalyze this particular transformation. Selectivities up to 97% ee of the corresponding secondary alcohols are obtained, and it is furthermore observed that the two different ligand classes, albeit based on the same amino acid scaffold, give rise to products of opposite configuration. The highly interesting enantioswitchable nature of the two abovementioned catalysts is studied in detail by mechanistic investigations. A structure/activity correlation analysis is performed, which reveals that the diverse behavior of the catalysts arise from different interactions between the ligands and the metal. Kinetic studies furthermore stress the catalyst divergence, since a difference in the rate determining step is established from initial rate measurements. In addition, rate constants are determined for each step of the overall reduction process. In the last part, catalyst development for ATH executed in water is discussed. The applicability of hydroxamic acid ligands is further extended, and catalysts based on these compounds are found to be efficient and compatible with aqueous conditions. The structurally even simpler amino acid amide is also evaluated as a ligand, and selectivities up to 90% ee are obtained in the reduction of a number of aryl alkyl ketones. The very challenging reduction of dialkyl ketones is moreover examined in the Rh-catalyzed aqueous ATH, where a modified surfactant-resembling sulfonylated diamine is used as ligand, and the reaction is carried out in the presence of SDS-micelles. A positive effect is to some extent found on the catalyst performance upon addition of phase-transfer components, especially regarding the catalytic activity in the reduction of more hydrophobic substrates.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: In press.
7
Gretton, Virginia Ann. "Kinetic and mechanistic study of aquated forms of platinium (II) complexes with nucleic acid derivatives". Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359254.
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8
Appleton, Amanda Jane. "A kinetic and mechanistic study of the liquid-phase reactions of ester-substituted alkylperoxyl radicals". Thesis, University of York, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265560.
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9
Trummer, Martin. "The effect of solid state inclusions on the reactivity of UO2 : A kinetic and mechanistic study". Doctoral thesis, KTH, Kärnkemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33070.
Testo completoAbstract (sommario):
The release of radionuclides is a key process in the safety assessment of a deep geological repository for spent nuclear fuel. A large fraction of the release is assumed to be a consequence of dissolution of the fuel matrix, UO2. In this doctoral thesis, the kinetics and the mechanisms behind oxidative U(IV) dissolution were studied. The eects of solid phase inclusions mimicking the presence of fission products, and solutes mimicking expected groundwater components were also evaluated. Palladium, as a model substance for noble metal particle (fission products) inclusions, was shown to catalyze surface oxidation of U(IV), as well as reduction of U(VI). The second order rate constant for the surface reduction of U(VI) by H2was found to be on the order of 10-6 m s-1 (diusion controlled). Under 40 bar H2, 1 wt.% Pd was sufficient to suppress oxidative U(IV) dissolution in 2mM H2O2 aqueous solution. During g γirradiation under 1 bar H2, 0.1 wt.% Pd were sufficient to completely suppress oxidative dissolution. Under inert conditions, where H2 is only produced radiolytically, complete inhibition is observed for 3 wt.% Pd. The presence of Y2O3 as a model substance for trivalent fission products was found to decrease U(VI) dissolution significantly under inert, as well as reducing conditions. Based on kinetic data, it was shown that pure competition kinetics cannot explain the observed decrease. From experiments using pure oxidants it was shown that Y2O3 doping of UO2 decreases the redox reactivity. In addition, from experiments where hydroxyl radical formation from the catalytic decomposition of H2O2 was monitored, it could be concluded that doping has a minor influence on this process. On the basis of numerical simulations, the H2 concentration necessary to suppressradiolytic H2O2 production was found to increase with an increase in dose rate or HCO-3 concentration. Furthermore, the steady state concentration of H2O2 was found to be inversely proportional to the H2 pressure, and proportional to the square root of the dose rate. Fe2 diers strongly from the total reaction volume, the actual dose rate should not be converted into a homogeneous dose rate in numerical simulations.QC 20110511
10
Dey, Benu Kumar. "A study on metal ion complexation with a macrocyclic ligand : a thermodynamic, kinetic, and mechanistic investigation". Title page, contents and abstract only, 1991. http://web4.library.adelaide.edu.au/theses/09SM/09smd528.pdf.
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11
Nilsson, Kristina. "Oxidative dissolution of doped UO2 and H2O2 reactivity towards oxide surfaces : A kinetic and mechanistic study". Licentiate thesis, KTH, Tillämpad fysikalisk kemi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145691.
Testo completoAbstract (sommario):
Oxidative dissolution of std. UO2 and UO2 doped with Cr2O3 and Al2O3, i.e. ADOPT, induced by H2O2 and γ radiation has been the main focus in this licentiate thesis. The catalytic decomposition of H2O2 on oxides like Gd2O3, HfO2, CeO2, Fe2O3 and CuO were also investigated. A kinetic study was performed by determining first and second order rate constants together with Arrhenius parameters for the decomposition of H2O2. The reactivity of H2O2 towards the oxides mentioned was observed to differ significantly despite their similarities. In the mechanistic study, the yields and dynamics of the formation of the intermediate hydroxyl radical from the decomposition of H2O2 was determined for the oxides and found to differ considerably. A turnover point could be found for most of oxides studied, i.e. an increase in the rate of hydroxyl radical scavenging after a specific amount of consumed H2O2. The reactivity of the std. UO2 and ADOPT towards H2O2 was similar to what was observed for other UO2-based materials in previous studies. The oxidative dissolution in radiation experiments showed a slight but significant difference. This was attributed to a difference in exposed surface area instead of an effect of doping. The difference in oxidative dissolution yield was too small to be significant which supports the previous conclusion. Leaching experiments using spent nuclear fuel were also performed on the two types of fuel showing the same behavior as the unirradiated pellets, i.e., a slightly lower 238U release from ADOPT. The difference was attributed to difference in exposed surface area. The release of fission products with low UO2 solubility displayed a higher release from ADOPT which was attributed to a difference in matrix solubility. Cs was released to a larger extent from std. UO2. This is attributed to the larger grain size of ADOPT, extending the diffusion distance. The release of lanthanides and actinides was slightly higher for the conventional UO2, nevertheless the difference was relatively small.QC 20140527
12
Yang, Chunhua. "Synthesis and Kinetic Mechanism Study of Phosphonopeptide as a Dead-End Inhibitor of cAMP-Dependent Protein Kinase". Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc500671/.
Testo completoAbstract (sommario):
DL-2-Amino-4-phosphonobutyric acid, an isostere of phosphoserine, was incorporated into the heptapeptide sequence, Leu-Arg-Arg-Ala-(DL-2-amino-4-phosphonobutyric acid)-Leu-Gly, for kinetic mechanistic studies of the cAMP-dependent protein kinase. To block the phosphono hydroxyl groups, methyl, ethyl and 4nitrobenzyl esters were studied as possible protecting groups. The phosphono diethyl ester of the N-Fmoc-protected amino acid was utilized in the synthesis of the heptapeptide. Two configurational forms of the protected peptide were obtained and were separated by C18-reverse phase HPLC. Characterization of the two isomeric forms was accomplished by 3 1P NMR, 1H NMR, 13C% NMR and amino acid analysis. The protecting groups of the isomeric phsophonopeptides were removed by HBr/AcOH and purified by cation exchange HPLC. Both phosphonopeptides were found to be inhibitors of the cAMP-dependent protein kinase, having Ki values of 0.6 mM (peptide A) and 1.9 mM (peptide B).
13
Pillay, Kriveshini. "A kinetic and mechanistic study on the oxidation of chromium oxide in pure chemicals and in ferrometallurgical slags". Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/5415.
Testo completoAbstract (sommario):
Bibliography: leaves 103-108.Chromium can exist in a number of oxidation states but the environmentally stable forms are trivalent (Cr(III)) and hexavalent (Cr(VI)) chromium. These two forms are noted for their different degrees of toxicity and mobility. Hexavalent chromium is more toxic and mobile and has been responsible for a number of illnesses in humans (Sheehan et. al., 1991). Elemental chromium and its compounds have a variety of uses in the industrial sector. The ferrometallurgical industry in particular makes use of chromium since this element imparts properties such as hardness and strenght to stainless steel. However, this industry also produces slags that contain residual amounts of chromium oxide (Cr[2]O[3]) along with other constituents such as calcium oxide (CaO). Thermodynamic data from the literature, has shown that Cr[2]O[3] can undergo oxidation at ambient temperature when in contact with CaO and atmospheric oxygen (Kilau and Shah, 1984; Hattori et al., 1978). Furthermore, the oxidation of Cr[2]O[3] in the presence of Ca(OH)[2] has also been observed at ambient temperature (Petersen, 1998).
14
劉新權 e Sing-quan Lew. "Kinetic and mechanistic study of reactions of hydroxy, methoxy, methylthio, methylseleno and amino derivatives of some heterocyclicand homocyclic polyenes". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1991. http://hub.hku.hk/bib/B31232322.
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15
Sabbagh, Ingrid Theresa. "Metathesis catalysts : an integrated computational, mechanistic and synthetic study". Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1006208.
Testo completoAbstract (sommario):
An integrated approach to the design of potential rutheniun-based metathesis catalysts is described, in which closely defined synthetic forays provide the focus and rationale for detailed computational and mechanistic studies. The ground-state geometry of a 1st-generation Grubbs catalyst has been explored at the molecular mechanics, semi-empirical and DFT levels, and the resulting structures have been shown to compare favourably with literature data and with the structure of a known crystalline analogue. The DMol³ DFT code has also been shown to represent accurately both the geometry of the corresponding co-ordinatively unsaturated monophosphine derivative, and the ligand dissociation energy associated with its formation. A DFT free-energy profile of the degenerate metathesis of ethylene has been generated, using a truncated model of the 1st-generation Grubbs catalyst, permitting location, for the first time, of the three expected transition states and providing new information regarding the rate-determining step. DFT methods have been used to facilitate the design of a tridentate camphor-derived ligand for use in the construction of a novel Grubbs-type catalyst. The phosphine ligand dissociation energy of the putative catalyst and the ethylene metathesis energy profile of a truncated model have also been studies at the DFT level. The attempted synthesis of the proposed ligand proceeded via a novel 8-bromocamphoric anhydride intermediate and afforded several unexpected and novel products, including a cisfused γ-Iactone, and a bromo camphoric acid derivative. Single crystal X-ray analysis of the latter reveals a chiral, polymeric H-bonded packing arrangement, rendering it suitable for chiral inclusion studies. Computational methods, including the GAUSSIAN-based GIAO NMR prediction technique, were used to support the structural characterisation of the novel camphor derivatives. DFT-Ievel computational analysis of the C-8- and C-9 bromination of camphor has afforded theoretical insights which permit the reconciliation of two earlier empirical explanations regarding the regioselectivity of these transformations; moreover, the theoretical results suggest that a third, previously disregarded factor, plays a significant role. A coset analysis, in conjunction with DFT-Ievel energy profiling, has also been used to resolve conflicting opinions regarding the origin of the major byproduct. Computed electronic parameters (CEP's) have been calculated for the anionic ligands involved in a series of 2nd-generation Grubbs-Hoveyda-type catalysts, and used to explain some apparently anomalous trends in catalyst activity. A linear relationship between ligand CEP's and selected ¹H NMR chemical shifts has also been demonstrated and used to identify a transient ruthenium complex in solution. The ability of the malonate di-anion to bind to ruthenium in a bidentate manner has been explored and demonstrated, under suitable conditions. DFT methods have been used to design and assess the ruthenium-chelating potential of a novel tridentate malonate derivative. A synthetic pathway to this ligand has been designed and several novel heterocyclic intermediates have been isolated and characterised. An NMR-based kinetic study of the Grubbs-catalysed self-metathesis of l-octene has been completed, and the effects of temperature, concentration and solvent variations on the kinetic parameters have been studied. Application of the Guggenheim method and a simplified mechanistic model has permitted the accurate calculation of pseudorate constants for the initiation and, for the first time, the propagation phase of the reaction. Theoretical studies of this reaction at the DFT and molecular mechanics levels have been shown to support previous assumptions regarding the selectivity and temperature-dependence of metallacycle formation.
16
Sansone, John P. "The Kinetics of Epoxidation of A,B-Unsaturated Esters by Dimethyldioxirane: A Mechanistic Study". Digital Archive @ GSU, 2009. http://digitalarchive.gsu.edu/chemistry_theses/22.
Testo completoAbstract (sommario):
The epoxidation of a series of α,β-unsaturated esters by dimethyldioxirane was studied. Second order rate constants were determined under pseudo first order conditions. The epoxide of each ester upon full conversion was found to be the only isolable product. Second order rate constants for the cis-like ethyl tiglate showed a 4 fold increase over that of trans-like angelic methyl ester. The ester substituent was found to have little effect on overall rate constants. A comparison of a relatively strained cyclopentene carboxylate to the cyclohexene carboxylate showed a 2 fold increase in selectivity for the former. Ethyl methacrylate displayed unexpected reactivity toward dioxirane; undergoing reaction faster than more substituted electron rich alkenes. Computer modeling studies using the AM-1 and density functional approaches were carried out to gain insights into the mechanistic aspects of the reaction. The esters in general favored the S-cis conformation or were evenly distributed among S-cis and S-trans except for the ethyl methacrylate case. The AM-1 approach did not predict the reactivity of open chain esters. The density functional approach predicted the relative reactivity of seven of the nine esters but could not predict the reactivity when the R1 group was substituted. One possible explanation is that the computer model predicts the methyl groups of the dioxirane to be positioned over the R1 group in the lowest energy of all other esters, but steric clash prevents this for angelic methyl ester and ethyl 3,3 dimethyl acrylate.
17
Lobb, Kevin Alan. "Camphor derivatives in asymmetric synthesis: a synthetic, mechanistic and theoretical study". Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1006770.
Testo completoAbstract (sommario):
A series of 3,3-ethylenedioxy-exo- and endo- bornyl esters have been prepared and subjected to α-benzylation using lithium diisopropylamide and benzyl bromide. In the exo-series of esters the diastereofacial selectivity of benzylation was found to improve (up to 34% d.e.) as the steric bulk of the O-alkyl group increased, whereas in the endo-series, a surprising decrease in stereoselectivity was observed as the steric bulk increased – an observation attributed to flexibility of the metal-coordinated endo-enolate system, compared to the relative rigidity of the exo analogues. The conformational options for each series was explored at the density functional theory level. Reductive cyclization of a range of specially prepared N-carbobenzyloxy-amino acid esters has been shown to afford the corresponding derivatives, contrary to previous reports that the cyclization is limited to the glycine derivative. The cyclization sequence has been explored in detail, and the yield has been shown to be critically dependent on the stereochemistry of the α-amino acid moiety. Moreover, it seems that reductive cyclization occurs more readily with the endo- rather than the exo-bornyl N-CBZ-amino acid esters. Molecular modelling of relevant transition states at the DFT levels indicates that L-amino acid-derived systems should cyclize preferably in the exo-series and D-amino acid-derived systems should cyclize preferably in the endo series. Studies of alkylation of an iminolactone system have reported an interesting anomaly - exo-methylation is observed while endo-alkylation predominates for larger alkyl groups. This has been studied in detail at the DFT level, and the anomaly is attributed to thermodynamic control in the methyl case, whereas kinetic control is the norm in this system. Preliminary computer modelling of the intramolecular rearrangement of a 3,3-xylylbornyl system at the HF/STO-3G level raised doubts concerning the structure assigned by Evans to one of the rearrangement products, prompting an X-ray crystallographic analysis and leading to the revision of its structure from a pinene to a camphene derivative. The previously elusive spiro[bornane-3,2’-indan]-2-exo-tosylate has been successfully isolated, and the kinetics of its ready decomposition to the two camphene products has been followed by 1H NMR spectroscopy. The endo-tosylate analogue, on the other hand, was found to be remarkably stable. Kinetic data obtained for rearrangement of this exo-bornyl tosylate have indicated the operation of tandem autocatalytic and pseudo-first-order transformations leading sequentially to the two isomeric camphene products. An extensive coset analysis of all possible rearrangement processes of the initially-formed cation formed from decomposition of the exo-tosylate has afforded a graph containing 336 classical cations (modelled at the AM1 and B3LYP levels) and 526 transition-state complexes (modelled at the AM1 level). This analysis afforded a viable 4-step classical mechanism connecting the first camphene product with the second. A more realistic study, involving non-classical carbocations, has afforded a graph of all possible (classical and non-classical) cations that could be formed by rearrangment of the initiallyformed cation. The resulting graph confirms that the only energetically feasible path corresponds to the classical mechanism, but simply involves two steps, including a novel, concerted Wagner-Meerwein – 6,2-hydride shift – Wagner-Meerwein rearrangement.
18
Buitrago, Elina. "Transition metal-catalyzed reduction of carbonyl compounds : Fe, Ru and Rh complexes as powerful hydride mediators". Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-75795.
Testo completoAbstract (sommario):
A detailed mechanistic investigation of the previously reported ruthenium pseudo-dipeptide-catalyzed asymmetric transfer hydrogenation (ATH) of aromatic ketones was performed. It was found that the addition of alkali metals has a large influence on both the reaction rate and the selectivity, and that the rate of the reaction was substantially increased when THF was used as a co-solvent. A novel bimetallic mechanism for the ruthenium pseudo-dipeptide-catalyzed asymmetric reduction of prochiral ketones was proposed. There is a demand for a larger substrate scope in the ATH reaction, and heteroaromatic ketones are traditionally more challenging substrates. Normally a catalyst is developed for one benchmark substrate, and a substrate screen is carried out with the best performing catalyst. There is a high probability that for different substrates, another catalyst could outperform the one used. To circumvent this issue, a multiple screen was executed, employing a variety of ligands from different families within our group’s ligand library, and different heteroaromatic ketones to fine-tune and to find the optimum catalyst depending on the substrate. The acquired information was used in the formal total syntheses of (R)-fluoxetine and (S)-duloxetine, where the key reduction step was performed with high enantioselectivities and high yield, in each case. Furthermore, a new iron-N-heterocyclic carbene (NHC)-catalyzed hydrosilylation (HS) protocol was developed. An active catalyst was formed in situ from readily available imidazolium salts together with an iron source, and the inexpensive and benign polymethylhydrosiloxane (PMHS) was used as hydride donor. A set of sterically less demanding, potentially bidentate NHC precursors was prepared. The effect proved to be remarkable, and an unprecedented activity was observed when combining them with iron. The same system was also explored in the reduction of amides to amines with satisfactory results.At the time of doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.
19
Mueanngern, Yutichai. "Mechanistic Study for Selective Hydrogenation of Crotonaldehyde Using Platinum/Metal-Oxide Catalysts—A Gas-Phased Kinetics Study". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462804731.
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20
Thinon, Olivier. "CO conversion over dual-site catalysts by the Water-Gas Shift Reaction for fuel cell applications : comparative mechanistic and kinetic study of gold and platinum supported catalysts". Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10187.
Testo completoAbstract (sommario):
Les piles à combustible, alimentée par de l’hydrogène, représentent une solution prometteuse pour limiter la pollution. L’une des alternatives économiques envisagées à court et moyen terme est de produire l’hydrogène à partir d’un carburant tel que le méthane ou le bio-éthanol. Cette transformation a pour objectif d’obtenir un mélange de gaz riche en hydrogène avec une très faible teneur en CO, ce dernier étant un poison pour les piles de type PEM. La réaction de Water-Gas Shift (WGS) est une étape clé du procédé ; elle convertit CO en CO2 par réaction avec l’eau et fournit une quantité d’hydrogène supplémentaire. Des catalyseurs métalliques (Pt, Pd, Ru, Rh, Au, Cu) supportés sur des oxydes (CeO2, TiO2, ZrO2, Fe2O3, CeO2/Al2O3) ont été comparés dans des conditions de WGS identiques en présence de CO2 et H2. Une étude cinétique a été réalisée sur les catalyseurs Pt/CeO2, Au/CeO2, Pt/TiO2 et Au/TiO2. Les énergies d’activation apparentes et les ordres de réaction ont été déterminés à partir d’un modèle de type loi de puissance. Un mécanisme réactionnel avec deux sites a été proposé pour décrire les différentes activités des 4 catalyseurs. Des expériences de désorption programmée en température ont été réalisées pour déterminer les paramètres cinétiques sur le supportThe Fuel Cells are promising solution to reduce the air pollution. One of the cost-efficient alternatives is to produce hydrogen from another fuel such as methane or bio-ethanol. A hydrogen fuel processor consists in generating a hydrogen-rich mixture and reducing the carbon monoxide content, as PEM fuel cells are very low CO tolerance. One of these units is the water-gas shift reactor, which converts CO into CO2 by the reaction with water and provides additional hydrogen. Catalysts based on a metal (Pt, Pd, Ru, Rh, Au, Cu) supported on an oxide (CeO2, TiO2, ZrO2, Fe2O3, CeO2/Al2O3) were compared for the WGS reaction in the same conditions and in the presence of CO2 and H2. A kinetic study was conducted on catalysts Pt/CeO2, Au/CeO2, Pt/TiO2 and Au/TiO2. A power law rate model was used to determine apparent activation energies and reaction orders. A dual-site reaction mechanism was proposed to explain the different activities between the four catalysts. The sorption parameters of H2O and CO2 on the supports was quantitatively determined from temperature-programmed desorption experiments
21
Christmann, Julien. "Photochimie moléculaire des processus de photopolymérisation : de l'étude mécanistique à la modélisation cinétique". Thesis, Mulhouse, 2017. http://www.theses.fr/2017MULH0698.
Testo completoAbstract (sommario):
Ce travail de thèse aborde l’étude mécanistique de systèmes photoamorceurs complexes et la modélisation cinétique du processus de photopolymérisation. Dans un premier temps, le mécanisme photochimique d’un système combinant le [Ru(bpy)3]2+ et des agents RAFT pour l’amorçage et le contrôle d’un processus radicalaire a été étudié. Un transfert d’énergie a été clairement démontré, contredisant le mécanisme de transfert d’électron généralement proposé. Un système photoamorceur à 3 composants bicyclique dual ITX/IOD+/RSH a ensuite été considéré pour la synthèse de matériaux hybrides organiques-inorganiques. Sous excitation lumineuse, ce système produit simultanément des radicaux et des protons, permettant d’amorcer, respectivement, des processus de polymérisation radicalaire et sol-gel. Dans un second temps, l’interdépendance entre les cinétiques de photopolymérisation et l’évolution des propriétés du milieu réactionnel a été étudiée par le biais du développement d’un modèle cinétique permettant la simulation de l’intégralité du processus de photopolymérisation. Des systèmes photoamorceurs de complexité croissante ont été inclus afin d’étudier les spécificités de leurs cinétiques. Un système de type I a permis de mettre en évidence les modes de terminaison majoritaires et leur évolution au cours de la synthèse des polymères, tandis que le rôle non négligeable du transfert d’électron inverse a été mis en exergue pour des systèmes photoamorceurs de type II. La fonction d’agent de terminaison d’un photoproduit issu d’un colorant cationique, ainsi que certaines spécificités des systèmes photocycliques à 3 composants, ont été finalement étudiés grâce à la modélisationThis thesis deals with the mechanistic study of complex photoinitiating systems and the kinetic modeling of the photopolymerization process. In a first time, the photochemical mechanism of a system combining [Ru(bpy)3]2+ and RAFT agents for the initiation and control of a radical process has been studied. An energy transfer has been clearly demonstrated, contradicting the electron transfer mechanism generally proposed. A dual bicyclic three-component photoinitiating system ITX/IOD+/RSH has been considered for the synthesis of organic-inorganic hybrid materials. Under light exposure, this system produces simultaneously radicals and protons, enabling the initiation of a radical polymerization and a sol-gel process, respectively. In a second time, interdependence between photopolymerization kinetics and evolution of the medium’s properties has been studied, through developing a kinetic model for the simulation of the whole photopolymerization process. Photoinitiating systems of growing complexity have been included in order to study specificities of their kinetics. A type-I system has shown major termination modes and their evolution during the polymer synthesis, while the non-negligible role of back electron transfer has been highlighted for type-II photoinitiating systems. Role of terminating agent of a photoproduct based on a cationic dye, as well as some specificities of photocyclic three-component systems, have been finally studied with the model
22
Montoya, Arango Juan Felipe. "Photocatalytic reactions: Mechanistic and kinetic implications". Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/131320.
Testo completoAbstract (sommario):
La Fotocatálisis Heterogénea con Dióxido de Titanio (TiO2) ha sido ampliamente estudiada en los últimos 30 años. Como resultado de este esfuerzo de investigación se han obtenido grandes avances en la comprensión de los fenómenos fundamentales involucrados en el proceso y se ha logrado la aplicación exitosa de varios dispositivos con tecnología fotocatalítica en áreas como la remediación medioambiental, la producción de energía renovable, y el diseño de materiales con propiedades de “autolimpieza”. Sin embargo, la comunidad científica en el campo de la fotocatálisis reconoce que existen diversas cuestiones de carácter fundamental sin resolver.
En las décadas de los 80 y 90 diversos mecanismos de reacción y modelos cinéticos fueron propuestos para ser empleados en la interpretación del considerable conjunto de datos experimentales reportados acerca de reacciones de fotooxidación con TiO2. A pesar del gran avance en el conocimiento de aspectos fundamentales sobre algunas de estas cuestiones, varios supuestos, tomados como verdades por la comunidad científica, fueron puestos en duda debido a los descubrimientos realizados en la primera década de este siglo en el campo de los estudios de ciencia de superficies aplicados a cristales de TiO2. En particular, se demostró que el catalizador no puede considerarse sólo como partículas desprovistas de estructura en la superficie. Al contrario, la estructura química de la superficie del catalizador y su interacción con las moléculas presentes en el medio de reacción es un factor determinante para entender los eventos que se desencadenan debido a la excitación del catalizador (TiO2).
La presente tesis doctoral se propone elucidar interpretaciones alternativas a la cinética y mecanismos de las reacciones de oxidación fotocatalítica tomando en cuenta los novedosos descubrimientos descritos anteriormente. Para desarrollar esta tarea se ha realizado un exhaustivo análisis de la literatura científica sobre la química de superficie del TiO2, y se desarrolló un estudio experimental sobre la interacción del TiO2 con diversas moléculas orgánicas, la relación de estas interacciones con la cinética de fotooxidación, y sobre algunos aspectos fundamentales del mecanismo de fotooxidación de diversos compuestos modelos.
Estos temas se discuten en detalle en cuatro publicaciones y tres manuscritos que serán enviados a publicar en un futuro cercano.
Los resultados aquí reportados confirman el rol crucial que desempeña la superficie del TiO2 en los mecanismos y la cinética de transferencia de carga interfacial de las reacciones fotocatalíticas. Específicamente, se dilucidó el rol desempeñado por los oxígenos de la superficie de la red cristalina del TiO2 en el mecanismo de reacción. Además, se demostró que el mecanismo de trasferencia de carga interfacial depende fuertemente del grado de interacción electrónica entre la superficie del semiconductor y la molécula orgánica a fotooxidar.
Los hallazgos arriba descritos aportan nuevas ideas al debate científico actual sobre aspectos fundamentales de la fotocatálisis con TiO2. De otra parte, los nuevos enfoques sobre la cinética y mecanismos de las reacciones fotocataliticas que se reportan en esta tesis puede proporcionar una base más racional para el diseño de catalizadores más eficientes que puedan ser empleados en aplicaciones prácticas.TiO2 photocatalysis has been extensively studied over the last three decades. The output of this research effort is an increasing fundamental understanding of the phenomena involved in the process and the successful application of photocatalytic technological devices in different areas such as environmental purification, renewable energy production, and design of materials with “self cleaning” properties. However, the scientific community in the field of photocatalysis recognizes that several fundamentals issues still remain unclear. In the 80 and 90’s decades several reaction mechanisms and kinetic models were proposed for the interpretation of the large body of experimental data concerning TiO2-assisted photooxidation reactions. Despite the huge advance in the fundamental knowledge of these topics that was achieved, several assumptions taken as truths by the scientific community were challenged by the findings of surface science studies on TiO2 crystals reported in the first decade of this century. These findings brought new insights into the surface chemistry of TiO2. It was demonstrated that the TiO2 catalyst can not be considered just as particles devoid of surface structure. Conversely, the chemical structure of the catalyst surface and its interaction with molecules in the reaction media is a determinant factor to understand the events triggered by TiO2 excitation. This PhD thesis is aimed at elucidating some alternative interpretations of kinetics and mechanisms of photocatalytic oxidation reactions taking into account the aforementioned novel insights. This task has been addressed by a comprehensive analysis of the scientific literature on the topic of surface chemistry of TiO2 and by an experimental study comprising TiO2-surface/substrate interactions, their relationship with kinetics of photooxidation reactions, and mechanistic issues related to photocatalytic oxidation of several model compounds. The above issues are discussed in detail in four published articles and three manuscripts that will be submitted for publication in the near future. The results reported here confirm the crucial role of the TiO2 surface in the mechanisms and the kinetics of interfacial charge transfer in photocatalytic reactions. Specifically, the role of TiO2 surface lattice oxygens in the reaction mechanism was elucidated. Moreover, it was found that the mechanism of interfacial charge transfer strongly depends on the degree of electronic interaction between the semiconductor surface and the organic substrate to be photooxidized. The above findings provide new ideas to the current scientific debate around fundamental issues of TiO2 photocatalysis. On the other hand, the new insights into the kinetics and mechanisms of photocatalytic reactions reported here can provide more rational strategies for the development of more efficient photocatalysts for practical applications.
23
Jang, Mei-Huei. "Mechanistic and kinetic studies of Trimethylamine Dehydrogenase /". The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488191124572066.
Testo completo
24
Guo, Xingwei. "Kinetic and mechanistic studies on reactions of quinones". Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-177113.
Testo completo
25
Hagger, A. J. "Kinetic and mechanistic aspects of amine-epoxide reactions". Thesis, University of Surrey, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234488.
Testo completo
26
Zotova, Natalia. "Kinetic and mechanistic investigation of asymmetric organocatalytic reactions". Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/1395.
Testo completoAbstract (sommario):
The utilisation of the reaction progress kinetic methodology to advance the mechanistic understanding of the asymmetric proline catalysed aldol and α-aminoxylation reactions is demonstrated in this work. Mechanistically meaningful reaction rate laws that describe the catalytic cycles of these reactions are derived experimentally, using initially the power law driving force analysis. With the aid of the employed kinetic methodology it is shown that the processes occurring on the catalytic cycle can be deconvoluted from the influence of the reactions occurring off the cycle, and each may be studied separately. It is also shown that the synergetic efforts of experimental kinetic and spectroscopic studies are capable of suggesting and ultimately disclosing the role of additives in these reactions and understanding of catalyst deactivation pathways. In order to obtain more support towards the kinetically derived mechanistic implications, kinetic isotope studies of the aldol reaction were performed. Experimental kinetic data fit to the derived rate model helped to assess and refine the proposed mechanism of the aldol reaction in a quantitative manner and consider other factors that potentially may affect the reaction. The rationalisation of the difference in kinetic behaviour of the aldol and a- aminoxylation reactions is discussed. The proposed elucidation is also supported by reaction simulations performed using COPASI simulation software.
27
Kumar, Hans. "Mechanistic kinetic modeling of the hydrocracking of complex feedstocks". [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1063.
Testo completo
28
Silver, Sunshine Christine. "Kinetic, mechanistic and spectroscopic studies of spore photoproduct lyase". Diss., Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/silver/SilverS1210.pdf.
Testo completoAbstract (sommario):
Spore forming organisms are a health threat to humans and other animals in part due to a remarkable resistance to UV irradiation. This resistance results from two events: first, the formation of a unique thymine dimer, 5-thyminyl-5,6-dihydrothymine (spore photoproduct, or SP) upon UV irradiation; and more importantly, the rapid and specific repair of this DNA photoproduct to two thymines by spore photoproduct lyase (SP lyase). Understanding the molecular basis of this radical-mediated DNA repair will ultimately allow for a better understanding of how to address the health risks caused by spore forming bacteria. SP lyase requires S-adenosyl-L-methionine and a [4Fe-4S]¹+/²+ cluster to perform its catalysis. Presented in this work is a characterization of Clostridium acetobutylicm SP lyase and its ability to repair stereochemically defined dinucleoside and dinucleotide synthetic substrates. Careful synthesis and characterization followed by assays monitored by HPLC indicate SP lyase repairs only the 5R isomer of SP with an activity of 0.4 nmol/min/mg (dinucleoside substrate) and 7.1 nmol/min/mg (dinucleotide substrate). These results support the longstanding theory of SP formation by dimerization of adjacent thymines in double-helical DNA. Kinetic and mechanistic studies were pursued to further elucidate the mechanism of SP repair. Upon pre-reducing SP lyase, the specific activity increased nearly 4-fold to 1.29 μmol/min/mg. Mechanistic studies utilizing [C-6-³H] SP DNA as the substrate revealed a primary tritium kinetic isotope effect of 16.1, indicating a rate determining step during the repair reaction. These results suggest nonstereospecific SP formation regarding the C-6 position and subsequent stereospecific abstraction of the C-6 H atom by SP lyase. Mossbauer and Fe/S K-edge X-ray absorption studies of anaerobically prepared SP lyase aided in further characterization of the [4Fe-4S] cluster and its interaction with SAM. The Fe K-edge EXAFS provide evidence for a slight cluster distortion upon interacting with SAM as a new spectral feature indicative of longer Fe-Fe distances is observed. The Fe K-edge XANES provide further support that SAM is not undergoing reductive cleavage in the presence of reduced SP lyase. Our XAS studies may provide new insights into the mechanism by which radical SAM enzymes initiate their diverse catalysis.
'Co-authored by Tilak Chandra, Egidijus Zilinskas, Eric M. Shepard, William E. Broderick, Joan B. Broderick, Shourjo Ghose, Jeffrey M. Buis, David J. Gardenghi, BoiHanh Huynh, and Robert K. Szilagyi.'
29
Poncipe, Carlo. "Some kinetic and mechanistic studies of epoxy resin cure". Thesis, University of Surrey, 1985. http://epubs.surrey.ac.uk/842722/.
Testo completoAbstract (sommario):
Imidazoles are widely used as epoxy curing agents, producing resins with good high temperature properties. This thesis is concerned with certain aspects of the mechanism by which cure occurs and is divided into five chapters, as follows: Chapter 1 contains a general review of epoxy resin chemistry and the use of imidazoles as curing agents. Chapter 2 deals with the preparation of a number of substrates used in this study, and also with the tritiation of a range of imidazoles and epoxides. Labelling patterns are interpreted using 3Hnmr spectroscopy. In Chapter 3 details of a radio-tracer kinetic method for following epoxide cure are presented. The induction period seen in the reaction between phenylglycidyl ether and a number of imidazoles is discussed in terms of the ability of 1-unsubstituted imidazoles to form hydrogen bonds and also in terms of the formation of a cocatalyst, with the 1:1 adduct being shown to be an effective catalyst for the reaction. The observed first order rate constant for 1:1 adduct formation is shown to vary with the initial concentration of imidazole used over a range of temperatures. Rate o constants obtained at 95°C are interpreted in terms of the electron donating and withdrawing characteristics of substituents on the imidazole ring. The reaction between the 1:1 adduct of phenylglycidyl ether and 2-ethyl-4-methylimidazole is also discussed, and data obtained using an ultra violet spectrophotometric method interpreted in terms of a transition state involving attack of both the tertiary nitrogen and the hydroxyl hydrogen on the epoxide ring. The reaction at 95°C between imidazole and a number of model epoxides is discussed in Chapter 4. It is shown that, for a number of these epoxides, the observed first order rate constant for formation of the 1:1 adduct varies with the initial concentration of imidazole used. Results are interpreted in terms of the electronegativity of the groups adjacent to the epoxide ring. In Chapter 5, the use of metal-1:1 adduct complexes as curing agents is explored. Results obtained using an ultra violet spectrophotometric technique are interpreted in terms of the stability of the complexes at the reaction temperature.
30
Du, Yi. "Layered cobalt hydroxides: synthesis, characterisation, kinetic and mechanistic studies". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489431.
Testo completoAbstract (sommario):
The synthesis of layered cobalt hydroxides featuring triangular ordering, and the exploration of their phase conversion chemistry, is the main focus of this thesis. An introduction to cobalt hydroxide chemistry and to structurally similar compounds, with an emphasis on layered metal hydroxides, is given in Chapter 1. Novel synthetic methods, structural analysis and the most recent development for layered double hydroxides are sequentially introduced. The aim of the thesis is followed up as an extension of the existing work.
31
Eapen, S. S. "Kinetic and mechanistic studies of aquated cisplatin-nucleobase interactions". Thesis, University of York, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.480533.
Testo completo
32
Hlalele, Lebohang. "Kinetic and mechanistic features of nitroxide mediated (co)polymerization". Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6515.
Testo completo
33
Allegrezza, Michael LeGrande. "Mechanistic Insight Into Photo-Polymerization Techniques Through Kinetic Analysis". Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1605182244121264.
Testo completo
34
Kahn, Kalju. "Kinetic and mechanistic characterization of the urate oxidase reaction /". free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9924895.
Testo completo
35
Roy, Biplab. "Interfacial kinetic and mechanistic studies on Dendrimer-liposome interactions". Thesis, University of North Bengal, 2018. http://ir.nbu.ac.in/handle/123456789/2773.
Testo completo
36
Rogers, Emma Irene. "Electrode Kinetic and Mechanistic Studies in Room Temperature Ionic Liquids". Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514984.
Testo completo
37
Mohamed, M. A. "Kinetic and mechanistic studies of thermal decomposition reactions of solids". Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374228.
Testo completo
38
Li, Tie. "Kinetic and mechanistic investigation of reductive dechlorination at iron surfaces". Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/279981.
Testo completoAbstract (sommario):
The long-term performance of zero-valent iron for reductive dechlorination of trichloroethylene (TCE) and perchloroethylene (PCE) was investigated. The effects of elapsed time, mass transfer limitations, influent halocarbon concentration, and water chemistry on reductive dechlorination rates were studied in a series of column reactors. Dechlorination rates were pseudo-first order in reactant concentration for submillimolar halocarbon concentrations. With increasing elapsed time, reaction rates deviated from pseudo-first order behavior due to reactive site saturation, and increased iron surface passivation towards the influent end of each column. Corrosion current measurements indicated that halocarbon reduction on fresh iron surfaces was cathodically controlled, whereas on aged iron surfaces, iron corrosion was anodically controlled. The decrease in TCE reaction rates over time can be attributed to anodic control of iron corrosion, and not to increasing reactant mass transfer limitations associated with diffusion through porous corrosion products. The disparity between amperometrically measured reaction rates and those measured in the column reactor indicated that halocarbon reduction may occur via direct electron transfer or may occur indirectly through reaction with atomic hydrogen absorbed on the iron surface. The kinetics, reaction mechanisms, and current efficiencies for electrochemical reduction of TCE and CT were investigated using flow-through, iron electrode reactors. Typical reduction half-lives for TCE and CT in the iron reactor were 9.4 and 3.7 minutes, respectively. Comparisons of amperometrically measured current efficiencies with those measured in the flow-through reactors, and the weak effect of electrode potential on TCE reaction rates, indicated that the primary pathway for TCE reduction by iron and palladized iron electrodes was indirect, and involves atomic hydrogen as the reducing agent. For CT, similar amperometric and analytically measured current efficiencies indicated that the primary mechanism for CT reduction is direct electron transfer. Chronoamperometry (CA) and chronopotentiometry (CP) analyses were used to determine the kinetics of CT and TCE reduction by a rotating disk electrode in solutions of constant halocarbon concentration. The transfer coefficient for CT was independent of temperature, while that for TCE was temperature dependent. This indicated that CT reduction was limited by the rate of electron transfer. The temperature dependent transfer coefficient for TCE indicated that its reduction was limited by chemical dependent factors. In accord with a rate limiting mechanism involving an electron transfer reaction, the apparent activation energy (Ea) for CT reduction was found to decrease with decreasing electrode potential. Conversely, the Ea for TCE reduction showed a slight increase with decreasing electrode potential, supporting the conclusion that its reaction rate was not limited by the rate of electron transfer.
39
Wang, Zhihong. "Kinetic isotope effects, dynamic effects, and mechanistic studies of organic reactions". Texas A&M University, 2005. http://hdl.handle.net/1969.1/4886.
Testo completoAbstract (sommario):
Several organic reactions that could potentially involve coarctate transition states
were investigated by a combination of experimental and theoretical studies.
In the thermal fragmentation of âÂÂ-1,3,4-oxadiazolines, the mechanism supported by
kinetic isotope effects and theoretical calculations is a three-step process that does not
demonstrate any special stabilization in coarctate transition states. Rather than
undergoing a direct coarctate conversion to product, the mechanism avoids coarctate
steps. The last step is a concerted coarctate reaction, but being concerted may be viewed
as being enforced by the necessity to avoid high-energy intermediates.
In the deoxygenation of epoxides with dichlorocarbene, the stabilization from the
transition state aromaticity is not great enough to compete with the preference for
asynchronous bonding changes. KIEs and calculations suggested that the reaction occurs
in a concerted manner but with a highly asynchronous early transition state with much
more Cñ-O bond breaking than Cò-O bond breaking. In the Shi epoxidation, a large ò-olefinic 13C isotope effect and small ñ-carbon
isotope effect indicated an asynchronous transition state with more advanced formation
of the C-O bond to the ò-olefinic carbon. The calculated lowest-energy transition
structures are generally those in which the differential formation of the incipient C-O
bonds, the "asynchronicity," resembles that of an unhindered model, and the imposition
of greater or less asynchronicity leads to higher barriers. In reactions of cis-disubstituted
and terminal alkenes using Shi's oxazolidinone catalyst, the asynchronicity of the
epoxidation transition state leads to increased steric interaction with the oxazolidinone
when a ÃÂ-conjugating substituent is distal to the oxazolidinone but decreased steric
interaction when the ÃÂ-conjugating substituent is proximal to the oxazolidinone.
Dynamic effects were studied in Diels-Alder reaction between acrolein and methyl
vinyl ketone. This reaction yields two products in a ratio of 3.0 ñ 0.5. Theoretical studies
shows that only one transition structure is involved in the formation of both.
Quasiclassical trajectory calculations on an MP2 surface give a prediction of a product
ratio of 45:14 (3.2:1), which is in good agreement with the experimental observation.
40
Craig, Daniel Henry. "Kinetic and mechanistic studies of morphinone reductase and pentaerythritol tetranitrate reductase". Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/29647.
Testo completoAbstract (sommario):
Morphinone reductase from Pseudomonas putida strain M10 and pentaerythritol tetranitrate (PETN) reductase from Enterobacter cloacae strain PB2 are very similar Class I / barrel flavoproteins capable of catalysing biotechnologically relevant reactions. The enzymes have been characterised and conclusions have been drawn about the catalytic and chemical mechanisms of both enzymes. The kinetics of the reductive half-reaction of both enzymes have been extensively investigated under pre-steady state conditions. Morphinone reductase and PETN reductase form a charge-transfer complex with their preferred reducing substrate (-NADH and -NADPH, respectively) in a second-order rate process. Evidence for an intermediate prior to charge-transfer formation is presented for PETN reductase. Decay of the charge-transfer complex in morphinone reductase and PETN reductase is concomitant with flavin reduction. Thermodynamic analysis of charge-transfer formation and decay, and reduction of the flavin has allowed calculation of an almost complete energy level diagram of the reductive-half-reaction of morphinone reductase. Four mutant morphinone reductase enzymes were constructed. R238K, R238M and R238E were made to investigate the role of charge near the N1-C2=O2 region of the flavin. Redox potentiometry experiments and pre-steady-state kinetic analyses suggest that positive charge near this region of the flavin is not important in setting the redox potential of the cofactor. The Q104E mutant was made to investigate the role of this residue in the activity of flavin with oxygen. The mutant did not bind flavin, preventing further analysis.
41
Schweicher, Julien. "Kinetic and mechanistic studies of CO hydrogenation over cobalt-based catalysts". Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210036.
Testo completoAbstract (sommario):
During this PhD thesis, cobalt (Co) catalysts have been prepared, characterized and studied in the carbon monoxide hydrogenation (CO+H2) reaction (also known as “Fischer-Tropsch” (FT) reaction). In industry, the FT synthesis aims at producing long chain hydrocarbons such as gasoline or diesel fuels. The interest is that the reactants (CO and H2) are obtained from other carbonaceous sources than crude oil: natural gas, coal, biomass or even petroleum residues. As it is well known that the worldwide crude oil reserves will be depleted in a few decades, the FT reaction represents an attractive alternative for the production of various fuels. Moreover, this reaction can also be used to produce high value specialty chemicals (long chain alcohols, light olefins…).Two different types of catalysts have been investigated during this thesis: cobalt with magnesia used as support or dispersant (Co/MgO) and cobalt with silica used as support (Co/SiO2). Each catalyst from the first class is prepared by precipitation of a mixed Co/Mg oxalate in acetone. This coprecipitation is followed by a thermal decomposition under reductive atmosphere leading to a mixed Co/MgO catalyst. On the other hand, Co/SiO2 catalysts are prepared by impregnation of a commercial silica support with a chloroform solution containing Co nanoparticles. This impregnation is then followed by a thermal activation under reductive atmosphere.
The mixed Co/Mg oxalates and the resulting Co/MgO catalysts have been extensively characterized in order to gain a better understanding of the composition, the structure and the morphology of these materials: thermal treatments under reductive and inert atmospheres (followed by MS, DRIFTS, TGA and DTA), BET surface area measurements, XRD and electron microscopy studies have been performed. Moreover, an original in situ technique for measuring the H2 chemisorption surface area of catalysts has been developed and used over our catalysts.
The performances of the Co/MgO and Co/SiO2 catalysts have then been evaluated in the CO+H2 reaction at atmospheric pressure. Chemical Transient Kinetics (CTK) experiments have been carried out in order to obtain information about the reaction kinetics and mechanism and the nature of the catalyst active surface under reaction conditions. The influence of several experimental parameters (temperature, H2 and CO partial pressures, total volumetric flow rate) and the effect of passivation are also discussed with regard to the catalyst behavior.
Our results indicate that the FT active surface of Co/MgO 10/1 (molar ratio) is entirely covered by carbon, oxygen and hydrogen atoms, most probably associated as surface complexes (possibly formate species). Thus, this active surface does not present the properties of a metallic Co surface (this has been proved by performing original experiments consisting in switching from the CO+H2 reaction to the propane hydrogenolysis reaction (C3H8+H2) which is sensitive to the metallic nature of the catalyst). CTK experiments have also shown that gaseous CO is the monomer responsible for chain lengthening in the FT reaction (and not any CHx surface intermediates as commonly believed). Moreover, CO chemisorption has been found to be irreversible under reaction conditions.
The CTK results obtained over Co/SiO2 are quite different and do not permit to draw sharp conclusions concerning the FT reaction mechanism. More detailed studies would have to be carried out over these samples.
Finally, Co/MgO catalysts have also been studied on a combined DRIFTS/MS experimental set-up in Belfast. CTK and Steady-State Isotopic Transient Kinetic Analysis (SSITKA) experiments have been carried out. While formate and methylene (CH2) groups have been detected by DRIFTS during the FT reaction, the results indicate that these species play no role as active intermediates. These formates are most probably located on MgO or at the Co/MgO interface, while methylene groups stand for skeleton CH2 in either hydrocarbon or carboxylate. Unfortunately, formate/methylene species have not been detected by DRIFTS over pure Co catalyst without MgO, because of the full signal absorption.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
42
Howes, Neil Uist Macdonald. "Kinetic and mechanistic studies in atmospheric chemistry using photoionization mass spectrometry". Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15766/.
Testo completoAbstract (sommario):
The aim of this thesis is to provide updated, accurate kinetic (and where possible mechanistic) information regarding the oxidation pathways of various volatile organic compounds (VOCs) and trace gas species within the troposphere. The vast majority of the experiments discussed were conducted using a pulsed laser photolysis, photoionization mass spectrometry (PLP-PIMS) set-up, which operated at low pressures (p = 2 Torr). PLP-PIMS is a time-resolved technique can be used to directly monitor multiple species simultaneously and with time; details of this method are found in Chapter II. Initially, one shortcoming of the PLP-PIMS technique was that it could not detect OH radicals (due to the ionization potential of OH). However, in Chapter III a 1 + 1’ multiphoton ionization (MPI) scheme was implemented, making OH detection possible. In Chapter IV, kinetic and mechanistic information regarding the oxidation of acetaldehyde, CH3CHO, by OH is reported. From this study a rate coefficient of kOH = (1.6 ± 0.2) × 10-11 cm3 molecule-1 s-1 was measured, this is in good agreement with other literature values. Additionally, it was observed that a small yield of methyl radicals (YCH3 ≈ 15%) was also produced. Methyl radicals were an unexpected product from this reaction and it is hypothesised that they are formed from the dissociation of nascent, chemically activated acetyl radicals. Notably, the yield of methyl radicals observed is significantly lower than would be expected from a statistical distribution of the energy between the products. Therefore, a post-reaction complex is proposed to allow for the redistribution of energy. In Chapters VI, reactions of the C1 and C2 Criegee intermediates (CH2OO and CH3CHOO, respectively) with SO2 and NO2 are reported. For the C1 Criegee intermediate (CI), rate coefficients of kC1SO2 = (3.8 ± 0.3) × 10-11 cm3 molecule-1 s-1 and kC1NO2 = (1.2 ± 0.3) × 10-12 cm3 molecule-1 s-1 are reported for the reactions with SO2 and NO2 respectively. For the C2 CI, rate coefficients of kC2SO2 = (1.8 ± 0.3) × 10-11 cm3 molecule-1 s-1 and kC2NO2 = (7.0 ± 1.6) × 10-13 cm3 molecule-1 s-1 were measured. Moreover, in the C2 CI + SO2 reaction, acetaldehyde was positively identified as a product from this reaction at low pressures. Finally, in Chapter VII the reactivity of Criegee intermediates towards different organic species was investigated. From these experiments it was observed that the C1 CI had significant rate coefficients with carboxylic acids, and rate coefficients of kC1FA = (3.7 ± 0.6) × 10-11 cm3 molecule-1 s-1 and kC1AA = (7.1±1.1) × 10-11 cm3 molecule-1 s-1 measured for the reactions with formic and acetic acid, respectively. However, the reactivity of CIs towards alkenes is thought to be considerably slower with upper limits of kC1ethene < 2 × 10-14 cm3 molecule-1 s-1 and kC1isoprene < 3 × 10-13 cm3 molecule-1 s-1 measured for the reactions of the C1 CI with ethene and isoprene.
43
Gómez, Martín Juan Carlos. "Spectroscopic, kinetic and mechanistic studies of atmospherically relevant I2-O3 photochemistry". Berlin Logos-Verl, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?id=2927252&prov=M&dok_var=1&dok_ext=htm.
Testo completo
44
Gómez, Martín Juan Carlos. "Spectroscopic, kinetic and mechanistic studies of atmospherically relevant I2/O3 photochemistry /". Berlin : Logos-Verl, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=2927252&prov=M&dok_var=1&dok_ext=htm.
Testo completo
45
Piety, Charles Andrew. "Kinetic and mechanistic studies of reactions of atomic chlorine with haloalkanes". Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/27057.
Testo completo
46
Garner, Mark. "Kinetic and mechanistic studies of Cisplatin derivatives with nucleic acid fragments". Thesis, University of York, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306475.
Testo completo
47
Ferretti, Antonio. "Kinetic and mechanistic studies of Pd-catalyzed amination of aryl halides". Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5483.
Testo completoAbstract (sommario):
The Pd-catalyzed amination of aryl halides (Buchwald-Hartwig amination) has become a versatile and widely used technology to synthesize and produce aromatic amines relevant in pharmaceutical and agrochemical industries. The aim of the work presented in this thesis is to achieve a better mechanistic understanding of this reaction. The methodologies used were not traditional and focused on kinetic studies, carried out using in-situ tools, mainly reaction calorimetry. Reactions using different amines have been considered: the kinetic behaviour of a straight-chain primary amine (n-hexylamine) was found to be very different from the kinetics of benzophenone hydrazone. This difference was rationalised by considering the mechanism and by proposing a change in the rate-limiting step. Spectroscopic studies, aimed at determining the catalyst resting state, supported our proposals. We subsequently started studies on the competitive system of two amines and one aryl halide. We found that, surprisingly, the less reactive amine, when in competition, reacted first. This intriguing behaviour was rationalised by considering the Curtin- Hammett principle and by recognizing that in this case selectivity was controlled by relative stability of intermediates, not relative reactivity. This was termed “monopolizing” regime, in contrast to the “major-minor” regime in which the minor but more reactive intermediate produces the major product. Subsequent studies revealed that the benzophenone hydrazone product also binds to the Pd/BINAP catalyst, and, during the hexylamine reaction, inhibits the rate and induces a change in the rate limiting step and catalyst resting state. Reactions using benzophenone imine were then studied. The competitive system of benzophenone imine and benzophenone hydrazone provided an example of a system showing a change from the “monopolizing regime” to the “major-minor” regime. These concepts can be generalized and applied to explain selectivity in other competitive catalytic systems.
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Islam, Zahidul. "Mechanistic and kinetic investigations of bacterial, human and cancerous thymidylate synthase". Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5779.
Testo completoAbstract (sommario):
Thymidylate synthase (TSase) is an enzyme that catalyzes the conversion of uridylate to thymidylate, one of the four DNA building blocks. Functional perturbation of this enzyme causes thymidylate deprivation in cells, thereby halting DNA production. This makes TSase crucial for cell survival and proliferation. TSase is an attractive target for chemotherapy as treatment for colorectal, ovarian, pancreatic and an array of other cancers. TSase is one of the most highly conserved enzymes across the whole spectrum of life. There is more than 45% sequence identity between E. coli and human TSases. Similarities are also observed in three-dimensional structures, functions and other kinetic and mechanistic features among most TSases from very diverse origins. Thereby, E. coli TSase is used as a model system to investigate the properties of its human counterpart.
In TSase catalysis, two H-transfers are involved: a proton abstraction and a hydride transfer. Traditional experimental biochemical kinetic studies and, more recently, computational studies (QM/MM) have been used to probe the mechanism of both H-transfers in E. coli TSase. While the traditional mechanism proposes a step-wise process for the hydride transfer, the QM/MM studies predict a concerted mechanism. The computational studies offered refined insight into the mechanism of proton abstraction by postulating the existence a novel, not covalently bound intermediate comprised of both ligands of the enzyme. Our mutational, kinetic and isotope effect work indeed supports those alternative mechanisms for the hydride transfer and the proton abstraction. The novel intermediate, which was synthesized and confirmed to be kinetically competent, opens a new avenue for finding a new class of TSase inhibitors.
Despite very high similarities in the structure and the function between E. coli and human TSase, the latter one possesses some distinctive features such as an N-terminal tail, two insertions of 8-12 residues and active-inactive conformations. Finding other functional differences between bacterial and mammalian TSase could pave the way for designing species-specific inhibitors. Our kinetic and mechanistic studies reveal some unique characteristics of human TSase, such as insensitivity of the rate to Mg2+, a more random binding sequence of ligands and a somewhat different environment of the transition state for the hydride transfer and the proton abstraction. These characteristic properties of human TSase might have implications in designing inhibitors of bacterial TSase.
5-FU is a common chemotherapeutic drug that targets TSase and has been used for the treatment of a wide variety of cancers. However, it was reported that a phenotype of colorectal cancerous cells in a certain group of patients had differential sensitivity to 5-FU drug treatment. Though the overexpression of TSase protein, its mRNA and folate receptors has previously been implicated in drug resistance, this phenotype contained a regular level of TSase. Analysis of mRNA and its cDNA revealed a single base mutation in the TSase gene, which corresponded to a point mutation of Y33 to H in the TSase polypeptide chain. The residue Y33 is remotely located and has no direct contact with either of the substrates; nevertheless, the mutation confers resistance to the drug. We aimed to obtain a comprehensive understating behind the resistance profile of Y33H. We prepared the recombinant Y33H protein and checked its inhibition profile. We found that the recombinant Y33H also confers resistance, like the one isolated from the resistant colorectal cancerous cells. There is a three-fold difference in the turnover number between the WT and the mutant, and our isotope effect experiments reveal altered transition state structures for the hydride transfer in the mutant enzyme. A crystal structure of an E. coli equivalent mutant is found perfectly superimposable on the WT human TSase structure, suggesting that no dramatic structural alteration is likely to to be present to account for the drug resistance and other changed behavior for the variant enzyme. However, analyses of isotropic B-factors of E. coli equivalent mutant and WT human TSase suggest alteration in protein dynamics across the protein chain, which imparts flexibility to the protein. Thermal melting temperature analyses of both the human WT and the mutant Y33H corroborates the notion of increased flexibility obtained from the dynamic features of crystal structures. Thereby, it seems that an alteration in protein dynamics compromises the drug sensitivity of the phenotype of cells harboring the Y33H mutant.
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Guo, Yafang <1991>. "Kinetic and mechanistic studies on unconventional antioxidant activities of natural compounds". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9950/1/Yafang_Guo.pdf.
Testo completoAbstract (sommario):
In chapter one, the autoxidation kinetics of natural oil substrates, including, triglyceric sunflower oil, olive oil, terpenic squalene, and p-cymene were calibrated through differential oximetry methods. Calibration allows their use as reference oxidizable substrates for further studies, e.g. for quantitative testing of antioxidants under biomimetic settings. Several essential oils samples, of different botanical species or different productions of same species were studied for their antioxidant activity in inhibited autoxidation kinetics. Their antioxidant activities were matched with their composition analyzed by GC-MS.
In chapter two, the molecular mechanism of the synergy between the common phenolic antioxidants such as tocopherol and catechols with widespread essential component gamma-terpinene was studied through lipid oxidation kinetics. Wherein, gamma-terpinene was able to disclose the key intermediacy HOO·, which acted as a reducing agent regenerating the phenolic antioxidant. This counterintuitive role of HOO· radicals was further investigated in detail and allowed to rationalize for the first time the purported antioxidant behavior of PDA melanin nanoparticles. It will also open to a deeper understanding of the redox biology of quinones.
Regarding melanin, its role is broadly important in living organisms and its control, including its inhibition, is of great importance with several relevant applications ranging from food preservation to control of human skin pigmentation. In chapter three, an oximetry method combined with the traditional UV-Vis spectroscopy was developed to study the tyrosinase inhibition kinetics, which allowed identifying Glabridin (from G. glabra, L.), as one of the most effective natural tyrosinase inhibitors.
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Warner, Madeleine. "Ruthenium-Catalyzed Hydrogen Transfer Reactions : Mechanistic Studies and Chemoenzymatic Dynamic Kinetic Resolutions". Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-89263.
Testo completoAbstract (sommario):
The main focus of this thesis lies on transition metal-catalyzed hydrogen transfer reactions. In the first part of the thesis, the mechanism for racemization of sec-alcohols with a ruthenium complex, Ru(CO)2Cl(η5-C5Ph5) was studied. The reaction between 5-hexen-2-ol and Ru(CO)2(Ot-Bu)(η5-C5Ph5) was studied with the aim to elucidate the origin of the slow racemization observed for this sec-alcohol. Two diastereomers of an alkoxycarbonyl complex, which has the double bond coordinated to ruthenium, were characterized by NMR and in situ FT-IR spectroscopy. The observed inhibition of the rate of racemization for substrates with double bonds provided further confirmation of the importance of a free coordination site on ruthenium for β-hydride elimination. Furthermore, we observed that CO exchange, monitored by 13C NMR using 13CO, occurs with both the precatalyst, Ru(CO)2Cl(η5-C5Ph5), and the active catalytic intermediate, Ru(CO)2(Ot-Bu)(η5-C5Ph5). It was also found that added CO has an inhibitory effect on the rate of racemization of (S)-1-phenylethanol. Both these observations provide strong support for reversible CO dissociation as a key step in the racemization mechanism. In the second part of this thesis, Ru(CO)2Cl(η5-C5Ph5) was combined with an enzymatic resolution catalyzed by a lipase, leading to several efficient dynamic kinetic resolutions (DKR). DKR of exocyclic allylic alcohols afforded the corresponding acetates in high yields and with excellent enantiomeric excess (ee). The products were utilized as synthetic precursors for α-substituted ketones and lactones. DKR of a wide range of homoallylic alcohols afforded the products in good to high yields and with high ee. The homoallylic acetates were transformed into 5,6-dihydropyran-2-ones in a short reaction sequence. Furthermore, DKR of a wide range of aromatic β-chloroalcohols afforded the products in high yields and with excellent ee. The β-chloro acetates were further transformed into chiral epoxides.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 5: Mansucript.