• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 8
  • 5
  • 3
  • 1
  • 1
  • Tagged with
  • 24
  • 5
  • 5
  • 5
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Challenges of tuberculosis prevention through early detection of latent tuberculosis infection in new immigrants to the State of Kuwait

Al-Harbi, Adel Mohanna January 2012 (has links)
Introduction: Despite management advances worldwide, tuberculosis still remains a serious uncontrolled disease. The absence of either a ‘gold’ standard diagnostic test, or a conventional rapid ‘reference’ laboratory test for asymptomatic Mycobacterium tuberculosis (MTB) carriers complicates disease control. Through mandatory screening of high-risk groups, early diagnosis of latent tuberculosis infection (LTBI) cases allows recognition and better control of the tuberculosis pandemic. Materials and Methods: The current tuberculosis screening guidelines as recommended by the World Health Organization, chest X-ray and tuberculin skin test were assessed and revealed rises in TB morbidity and fatality trends in the Kuwait population (low incidence country). In order to evaluate options for LTBI diagnosis, the current work implemented a 4-month prospective, observational, repeated-measure and randomly implemented survey on 180 new immigrants to Kuwait using a structured risk factor questionnaire whilst, simultaneously evaluating the performance of the two standard diagnostics (chest X-ray and tuberculin skin test) with the new biomarker interferon gamma release assays (T-SPOT .TB test and QuantiFERON Gold In-Tube test (QNF-GIT)); which detect the release of interferon gamma (INF-γ) released from sensitization to specific MTB antigens. Results: Associations between various epidemiological risk factors - such as socio-demographic status, smoking and environmental exposure-contact - were associated in the laboratory diagnosed LTBI participants. Positive identification of LTBI prevalence detected by two radiologists was 10.1% having ‘moderate’ inter-reader agreement (Kappa = 0.505), compared to no positives being detected by three pulmonologists. TST results were negative (less than 10-mm ‘cut-off’) even in the 86.1% Bacillus Calmette-Guérin vaccinated expatriates. Estimated LTBI using QNFGIT was 28.3% compared to 41.1% positive T-SPOT .TB test. Both interferon gamma assays revealed concordant ‘abnormal’ results in 26.1% with ‘good’ agreement (kappa = 0.627). Conclusion: Detection of latent tuberculosis infection can be facilitated by introducing evidence-based diagnostic classification depending on history taking of epidemiological-related risk factors and chest X-ray plus either interferon gamma assays.
2

A carne está servida : análise de argumentações jurisdicionais do TST sobre trabalhadores do setor frigorífico na perspectiva gramsciana

Pereira, Maria Cristina Cardoso 27 June 2016 (has links)
Tese (doutorado)—Universidade de Brasília, Faculdade de Direito, Programa de Pós-Graduação em Direito, 2016. / Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-12-08T18:03:11Z No. of bitstreams: 1 2016_MariaCristinaCardosoPereira.PDF: 2842790 bytes, checksum: d1a273450b225d80c88e51fea7148a23 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2017-01-11T19:48:25Z (GMT) No. of bitstreams: 1 2016_MariaCristinaCardosoPereira.PDF: 2842790 bytes, checksum: d1a273450b225d80c88e51fea7148a23 (MD5) / Made available in DSpace on 2017-01-11T19:48:25Z (GMT). No. of bitstreams: 1 2016_MariaCristinaCardosoPereira.PDF: 2842790 bytes, checksum: d1a273450b225d80c88e51fea7148a23 (MD5) / O objetivo desta tese consiste em identificar padrões argumentativos jurisdicionais que podem ser caracterizados como "ideológicos", segundo uma leitura baseada na produção teórica gramsciana. Esses padrões argumentativos foram identificados na Jurisprudência do Tribunal Superior do Trabalho (TST) em decisões nas quais o que se discutia eram as condições de trabalho a que se encontravam submetidos trabalhadores vinculados ao setor de frigoríficos no Brasil. Tais decisões foram analisadas a partir das narrativas contidas nos discursos de justificação da Corte. Esta pesquisa apresenta uma primeira parte teórica, que consiste no resgate, a partir dos escritos marxistas e Gramscianos, da função ideológica do Judiciário e o seu papel de promotor não apenas de avaliações racionais e justificadas teoricamente acerca de conflitos sociais, mas também de Instituição que lida com formas de conflitualidades sociais que se apresentam das maneiras mais brutais e violentas. Em uma segunda parte, aborda-se a recepção pelo TST de demandas dos trabalhadores propostas privilegiadamente via Ministério Público do Trabalho, através de ações civis públicas, mas também em casos individuais paradigmáticos. O objetivo é verificar o caráter das justificativas do TST utilizadas para argumentar suas decisões e também identificar de que maneira seus discursos de justificação estão articulados com preceitos introduzidos a partir da Constituição Federal de 1988, em especial os valores humanos do trabalho e da dignidade da pessoa. _________________________________________________________________________________________________ ABSTRACT / The objective of this thesis is to establish a standard of judicial argumentative elaborations that can be characterized as "ideological," according to a reading based on Gramsci's theoretical production. These argumentative present patterns were identified in the case law of the Superior Labor Court (TST), in decisions on what was discussed were the poor working conditions that workers linked to the meatpacking industry have been submitted in Brazil. Such decisions were analyzed from the narratives contained in the Court's justification speeches. This research presents a first theoretical part, which consists of the rescue, from the writings Gramsci, the ideological of the judiciary function and its role as a promoter not only of rational and justified theoretically about social conflict assessments, but also institution that deals with forms of social conflictualities that present the most brutal and violent ways. In a second part, we discuss the issue of receipt by TST the demands of workers in cold - proposals privileged via Ministério Público do Trabalho, through class actions, but also in individual paradigmatic cases. The aim is to check to what extent the TST develops theoretical justifications not only sound to argue their decisions but also if such argumentations are centered in justifications articulated with the precepts introduced from the 1988 Constitution, which for the first time, reflected values of constitutional dignity in human values of work and dignity.
3

Étude théorique des mécanismes de combustion des alcènes à basse température / Theoretical study of the mechanisms of combustion of alkenes at low temperature

Lizardo Huerta, Juan Carlos 25 March 2015 (has links)
Ce travail de thèse a porté sur l'étude des réactions unimoléculaires de décomposition des alcènes à basse température. L'oxydation de ces molécules est primordiale dans la compréhension des mécanismes de combustion, car elles peuvent être présentes initialement dans des carburants usuels ou formées en tant qu'intermédiaires dans le processus d'oxydation. L’étude théorique menée peut se décomposer en deux parties : - L’étude des réactions de décomposition des radicaux hydroxyalkylperoxyles (HOROO•) obtenus à partir de l’addition d’un radical •OH sur l’alcène, suivi par une addition du radical •ROH sur l’oxygène moléculaire. Cette étude a été conduite de façon systématique sur un ensemble de radicaux représentatifs d'alcènes afin de mettre en évidence l'influence de l'environnement intramoléculaire sur les constantes de vitesse. Les résultats obtenus ont montré l’influence très nette de certains paramètres comme la présence d'un groupement hydroxyle en position β par rapport à l'atome de carbone réactif, la nature des atomes de carbone portant les hydrogènes transférés, la taille des cycles de transition ou encore la présence d'une liaison hydrogène intramoléculaire. - L’étude des réactions de décomposition unimoléculaires des radicaux allylperoxyles obtenus à partir de l’addition des radicaux allyliques sur l’oxygène. La grande complexité de ces systèmes a été mise en avant au cours de ce travail. Il a ainsi pu être mis en évidence que la formation d'un composé de type 1-alcenyloxirane est favorisée à basse température ce qui montre l'importance de ces réactions, souvent négligées dans les modèles / This work focused on the study of the unimolecular decomposition of the low-temperature reactions of alkenes. The oxidation of these molecules is essential in the understanding of the mechanisms of combustion, because they are initially present in conventional fuels or formed as intermediates in the oxidation process. The theoretical study can be divided in two parts: - The study of the decomposition of hydroxyalkylperoxyl radicals (HOROO•) obtained from the addition of an •OH radical on the alkene, followed by a subsequent addition of the formed radical •ROH on molecular oxygen. This study was conducted in a systematic way on a set of representative radicals of alkenes in order to highlight the influence of the intramolecular environment on the rate constants. The results clearly showed the major influence of parameters such as the presence of a hydroxyl group in β position with respect to the reactive carbon atom, the nature of the carbon atoms bearing the transferred hydrogen, the size of the transition state ring and the presence of intramolecular hydrogen bonds. - The study of the unimolecular decomposition of the allylperoxy radicals obtained from the addition of a resonance-stabilized radical on molecular oxygen. The complexity of these systems, specifically induced by the mesomeric structures of heavy allyl radicals and the role of cis and trans conformations alkenes parents, have been highlighted in this work. It has been shown that the formation of a compound 1-alkenyloxirane is favored at low-temperatures, which shows the importance of these reactions, usually neglected in the kinetic models for the combustion of alkenes
4

Targeting hydrogen sulfide breakdown for regulation of myocardial injury and repair

Emerson, Barry Sean January 2015 (has links)
Hydrogen sulfide (H2S) is an endogenous gasotransmitter that regulates vascular function and blood pressure, and also protects the heart from injury associated with myocardial infarction (MI). The mitochondrial enzyme thiosulfate sulfurtransferase (TST) has a putative role in the breakdown of H2S but its role in the cardiovascular system is unknown. I hypothesised that TST reduces cardiovascular H2S availability and that inhibiting TST activity may therefore ameliorate cardiovascular pathology. In the heart, TST was expressed by cardiomyocytes and vascular smooth muscle cells. Tst-/- mice all survived to adulthood and had normal cardiac structure and function. Cardiac and hepatic H2S breakdown rates were reduced and H2S levels were higher in the blood of Tst-/- mice. However, in heart tissue, protein levels for the H2S-activated Nrf2 downstream targets, thioredoxin (Trx1) and heme oxygenase-1 (HO-1) were comparable. In contrast, protein levels for the cardiac specific H2S-synthetic enzyme, cystathionine gamma lyase (CSE) was reduced, suggesting a homeostatic negative feedback mechanism to maintain H2S at non-toxic levels. Respiration, measured using an oxygen-sensing electrode was normal in isolated mitochondria from whole Tst-/- compared to control C57BL6 hearts. Endothelial nitric oxide synthase (eNOS) protein expression was lower in Tst-/- hearts, highlighting potential cross talk between H2S and nitric oxide (NO) signalling. TST was expressed in whole aorta homogenates and in isolated endothelial cells from aorta and small intramuscular vessels of the hindlimb from C57BL/6N control mice. Myography and western blotting revealed a greater influence of NO in aorta from Tst-/- mice that was associated with increased phosphorylation of the activating serine1177 residue of eNOS (PeNOSSer1177). NO plays a lesser role in resistance arteries, but in comparison to control vessels, small mesenteric vessels from Tst-/- mice was more reliant on small and intermediate calcium activated potassium channels for relaxation. Tst-/- mice were normotensive, despite this alteration in the regulation of vascular tone. However, metabolic cage experiments identified that Tst-/- mice presented with diuresis, polydipsia, and increased urinary electrolyte excretion of sodium, potassium and chloride, possibly to compensate for increased vascular tone in order to maintain stable blood pressure. To investigate the role of TST in regulating the response to pathological challenge, MI was induced by coronary artery ligation (CAL). In control mice, gene expression of CSE was downregulated by 2 days after CAL, but TST expression was 12-fold increased, suggesting regulation of H2S bioavailability during the acute MI-healing phase. Tst-/- male mice had a 40% greater incidence of cardiac rupture during infarct healing and surviving Tst-/- mice had greater left ventricular dilatation and impaired function compared to controls. Ex vivo, isolated perfused hearts from Tst-/- mice were more susceptible to ischaemia/ reperfusion injury, suggesting an additional role of TST in determining cardiomyocyte susceptibility to injury. In conclusion, these data indicate that cardiovascular H2S bioavailability is regulated through degradation by TST. The data presented here provide evidence for significant tissue specific crosstalk between H2S synthetic and degradative mechanisms and between H2S and other local regulatory mechanisms, including ion channels and NOS. We infer TST has a physiological role in the kidney where its loss leads to changes in renal electrolyte and water handling, although other compensatory mechanisms prevent a change in blood pressure. Under conditions of pathological challenge following MI, loss of TST is detrimental, illustrating its key role in removal of H2S. The data refute the original hypothesis that TST inhibition would be protective against cardiovascular pathology. Further studies in mice with tissue specific deletion of TST are now required to more fully reveal the cardiovascular role of TST.
5

Les troubles du sommeil chez les adolescents libanais / Sleep disorders among Lebanese adolescents

Chahoud, Michele 29 September 2017 (has links)
Le sommeil est un état dans lequel nous passons environ le tiers de notre vie. Il fait partie des fonctions vitales de l'organisme. Une enquête a été lancée au Liban ayant pour objectifs de connaitre les habitudes du sommeil, les styles de vie des adolescents et de découvrir les troubles de sommeil les plus fréquents et leurs facteurs associés afin de combler les lacunes dans ce domaine. 41.2% des adolescents avaient un temps de sommeil total de moins de 7 heures par nuit durant la semaine, et 34.4% surfaient sur internet avant de se coucher. 13.1% semblaient souffrir d’insomnie et 26.3% semblaient être atteints de syndrome de retard de phase (SRDP). La dépression était le facteur commun associé à ces deux troubles. En conclusion, la réalisation des études longitudinales permettant de découvrir les facteurs de risque de l’insomnie et du SRDP chez les adolescents libanais ainsi que la suggestion / We spend almost the third of our lifetime sleeping. Sleep is part of the body’s vital functions. A nationwide survey was launched in Lebanon in order to examine and evaluate the Lebanese adolescents’ sleep patterns and lifestyles and to assess the most prevalent sleep disorders and their associated factors, with the purpose of filling in the gaps in this area. 41.2% of the teenagers slept less than 7 hours per night during the week, and 34.4% once in bed always surf the internet. Insomnia and delayed sleep phase disorder (DSPD) were the most common sleep disorders among Lebanese adolescents; they had a prevalence of 13.1% and 26.3% respectively. Depression was the common factor associated with these two disorders. In conclusion, conducting longitudinal studies, in order to identify the most common risk factors of insomnia and DSPD in Lebanese adolescents and suggesting solutions to facilitate the prevention of these disorders and their risk factors are currently a must.
6

Dynamics and Mechanics of Zebrafish Embryonic Tissues / Dynamik und Mechanik embryonaler Zebrafisch Gewebe

Schötz, Eva-Maria 22 April 2008 (has links) (PDF)
Developmental biologists try to elucidate how it is possible for cells, all originating from the same egg, to develop into a variety of highly specialized structures, such as muscles, skin, brain and limbs. What organizes the behavior of these cells, and how can the information encoded in the DNA account for the observed patterns and developmental processes? Cell movements and tissue flow during embryogenesis constitute a beautiful problem of bridging scales: On the microscopic scale, cells are expressing particular genes which determine their identities and also their fate during morphogenesis. These molecular determinants then lead to the macroscopic phenomena of cell movements and tissue arrangements, for which one needs a continuum description in terms of active fluids. Taking into account that the number of cells is fairly small, a complete coarse graining is not possible, and a characterization of both mesoscopic (individual cell motion) and macroscopic (flow) behavior is required for a full description. In the here presented work, a set of different experimental methods was applied to investigate the mechanical and dynamical properties of zebrafish embryonic cells and tissues. This thesis is structured as follows: In chapter 2, we introduce the fundamental concepts that are important for the study of cell motion during zebrafish embryonic development. In chapter 3, the materials and methods applied in this work are described. The experimental results of my thesis-work are presented in chapters 4-8: Chapter 4 concentrates on the physical properties of whole tissues. It is shown that tissues are viscoelastic materials. Tissue viscoelasticity is not a new concept, but this study is the first one to quantify the mechanical properties of tissues that are in actual contact in a developing embryo. In chapter 5, cell rearrangements in culture, such as cell sorting and tissue wetting are discussed. These experiments show that tissue interactions are largely determined by tissue surface and interfacial tensions. In chapter 6, an optical stretcher device is applied to measure, solely by means of laser light, the material properties of individual cells. Hereby it is shown that single cells from the two investigated tissue types differ in their mechano-physical properties. After the study of cell and tissue mechanics, the dynamics of cell migration in three dimensions in tissue aggregates and in developing zebrafish embryos is addressed: In chapter 7, 3D-cell migration in multicellular aggregates is analyzed quantitatively by studying the mean square displacement, cell velocity distribution and velocity autocorrelation. In chapter 8, we study the cell motion within the developing zebrafish embryo. By following the motion of many cells in four dimensions, we are able to generate a velocity flow profile for this cell-flow. Chapter 9 gives a brief summary of the obtained results and an outlook to future projects motivated by the presented study. The final part of this thesis are four appendices. Appendix A contains protocols and additional methods. Appendix B contains several calculations, whose results were used in the main part of this work. Appendix C contains additional data and discussions, which were excluded from the main part due to space limitations. Finally, Appendix D consists of a compact disc with 11 movies and a movie description, which serves as supplemental material to the presented data. (Die Druckexemplare enthalten jeweils eine CD-ROM als Anlagenteil: 650 MB: Movies - Nutzung: Referat Informationsservice der SLUB)
7

Dynamics and Mechanics of Zebrafish Embryonic Tissues

Schötz, Eva-Maria 14 September 2007 (has links)
Developmental biologists try to elucidate how it is possible for cells, all originating from the same egg, to develop into a variety of highly specialized structures, such as muscles, skin, brain and limbs. What organizes the behavior of these cells, and how can the information encoded in the DNA account for the observed patterns and developmental processes? Cell movements and tissue flow during embryogenesis constitute a beautiful problem of bridging scales: On the microscopic scale, cells are expressing particular genes which determine their identities and also their fate during morphogenesis. These molecular determinants then lead to the macroscopic phenomena of cell movements and tissue arrangements, for which one needs a continuum description in terms of active fluids. Taking into account that the number of cells is fairly small, a complete coarse graining is not possible, and a characterization of both mesoscopic (individual cell motion) and macroscopic (flow) behavior is required for a full description. In the here presented work, a set of different experimental methods was applied to investigate the mechanical and dynamical properties of zebrafish embryonic cells and tissues. This thesis is structured as follows: In chapter 2, we introduce the fundamental concepts that are important for the study of cell motion during zebrafish embryonic development. In chapter 3, the materials and methods applied in this work are described. The experimental results of my thesis-work are presented in chapters 4-8: Chapter 4 concentrates on the physical properties of whole tissues. It is shown that tissues are viscoelastic materials. Tissue viscoelasticity is not a new concept, but this study is the first one to quantify the mechanical properties of tissues that are in actual contact in a developing embryo. In chapter 5, cell rearrangements in culture, such as cell sorting and tissue wetting are discussed. These experiments show that tissue interactions are largely determined by tissue surface and interfacial tensions. In chapter 6, an optical stretcher device is applied to measure, solely by means of laser light, the material properties of individual cells. Hereby it is shown that single cells from the two investigated tissue types differ in their mechano-physical properties. After the study of cell and tissue mechanics, the dynamics of cell migration in three dimensions in tissue aggregates and in developing zebrafish embryos is addressed: In chapter 7, 3D-cell migration in multicellular aggregates is analyzed quantitatively by studying the mean square displacement, cell velocity distribution and velocity autocorrelation. In chapter 8, we study the cell motion within the developing zebrafish embryo. By following the motion of many cells in four dimensions, we are able to generate a velocity flow profile for this cell-flow. Chapter 9 gives a brief summary of the obtained results and an outlook to future projects motivated by the presented study. The final part of this thesis are four appendices. Appendix A contains protocols and additional methods. Appendix B contains several calculations, whose results were used in the main part of this work. Appendix C contains additional data and discussions, which were excluded from the main part due to space limitations. Finally, Appendix D consists of a compact disc with 11 movies and a movie description, which serves as supplemental material to the presented data. (Die Druckexemplare enthalten jeweils eine CD-ROM als Anlagenteil: 650 MB: Movies - Nutzung: Referat Informationsservice der SLUB)
8

Modelling nematode infections in sheep and parasite control strategies

Laurenson, Yan Christian Stephen Mountfort January 2012 (has links)
Gastrointestinal parasitism in grazing lambs adversely affects animal performance and welfare, causing significant production losses for the sheep industry. Control of gastrointestinal parasitism using chemotherapeutic treatment is under threat due to the emergence of anthelmintic resistance, thus stimulating research into alternative control strategies. Whilst investigating control strategies experimentally can be costly and time consuming, using a mathematical modelling approach can reduce such constraints. A previously developed model which describes the impact of host nutrition, genotype and gastrointestinal parasitism in a growing lamb, provided an appropriate starting point to explore control strategies and their impact on host-parasite interactions. Two contrasting mechanisms have previously been proposed to account for the occurrence of anorexia during parasitism. These were reductions in either intrinsic growth rate or relative food intake. Thus, the existing individual lamb model was modified to evaluate these mechanisms by exploring the relationship between anorexia and food composition (Chapter 2). For foods that did not constrain food intake, published data was found to be consistent with the predictions that arose from anorexia being modelled as a reduction in relative food intake. Reported genetic parameter estimates for resistance and performance traits appear to vary under differing production environments. In order to explore the impact of epidemiological effects and anthelmintic input on genetic parameter estimates the model was extended to simulate a population of lambs in a grazing scenario (Chapter 3). Whilst estimates of heritabilities and genetic correlations for drenched lambs remained constant, for lambs given no anthelmintic treatment, the heritability of empty body weight (EBW) reduced and the genetic correlation between faecal egg count (FEC) and EBW became increasingly negative with increasing exposure to infective larvae. Thus differences in anthelmintic input and pasture larval contamination (PC) may provide plausible causes for the variation in genetic parameter estimates previously reported. To investigate the interactions between host resistance and epidemiology (Chapter 4) a population of 10,000 lambs were simulated and FEC predictions used to assign the 1,000 lambs with the highest and lowest predicted FEC to ‘susceptible’ (S) and ‘resistant’ (R) groups, respectively. R and S groups were then simulated to graze separate pastures over 3 grazing seasons. The average FEC and PC predictions of these groups diverged during the first 2 grazing seasons and stabilised during the third, such that the difference in FEC predictions between R and S groups were double those predicted when grazed with the population. This was found to be consistent with experimental data. Further, anthelmintic treatment and grazing strategies were predicted to have no impact on the EBW of resistant lambs, suggesting that control strategies should be targeted towards susceptible animals. Targeted selective anthelmintic treatment (TST) has been proposed to reduce risks of anthelmintic resistance with minimal impacts on performance. To describe the short- and long-term impacts of TST and drenching frequency on sheep production and the emergence of anthelmintic resistance, the model was extended to include a description of anthelmintic resistance genotypes within the nematode population (Chapter 5). Reducing the proportion of treated animals was predicted to increase the duration of anthelmintic efficacy, whilst reducing the drenching frequency increased the long-term benefits of anthelmintic on sheep production. Various determinant criteria for use in TST regimes were compared (Chapter 5) including performance traits such as live weight and growth rate, and parasitological traits such as FEC. Using FEC as the TST criterion was predicted to allow the greatest reduction in the number of anthelmintic treatments administered whilst maintaining the highest average EBW, whilst live weight and growth rate were predicted to give little to no improvement in comparison to selecting animals at random for TST. Using estimated breeding values (EBVs) for FEC as the determinant criterion for TST regimes was compared to using measured FEC (Chapter 6). The EBV for true FEC across the entire growth period, akin to perfect genomic selection, was predicted to be a better criterion than measured time-specific FEC (including a sampling error) for a TST regime. EBVs calculated using measured time-specific FEC showed little benefit compared to measured FEC. The information gained from these simulation studies increases our understanding of control strategies and their impact on host-parasite interactions under various scenarios that may not have been possible using experimental methods. It is important to remember that the aim of alternative or complimentary control strategies is to maintain the sustainability of sheep production systems, and as such the production gain of any control strategy needs to be weighed against the financial, labour and time costs involved in implementation.
9

Kinetic Studies of Hydroxyl and Hydrogen Atom Reactions

Hu, Xiaohua 05 1900 (has links)
Gas phase kinetics of the reactions involving hydroxyl radical and hydrogen atom were studied using experimental and ab initio theoretical techniques. The rate constant for the H + H2S reaction has been measured from 298 to 598 K by the laser photolysis/resonance fluorescence (LP-RF) technique. The transition state theory (TST) analysis coupled with the measurements support the suggestion that the reaction shows significant curvature in the Arrhenius plot. The LP-RF technique was also used to measure the rate constant of the H + CH3Br reaction over the temperature range 400-813 K. TST and density functional theory (DFT) calculations show that the dominant reaction channel is Br-abstraction. The reaction H + CF2=CF-CF=CF2 was first studied by flash photolysis/resonance fluorescence (FP-RF) method. The experiments of this work revealed distinctly non-Arrhenius behavior, which was interpreted in terms of a change in mechanism. DFT calculations suggest that the adduct is CF2H-CF•-CF=CF2. At lower temperatures a mixture of this molecule and CF2•-CFH-CF=CF2 is likely. The theoretical calculations show that H atom migrates in the fluoroethyl radicals through a bridging intermediate, and the barrier height for this process is lower in the less fluorinated ethyl radical. High level computations were also employed in studies of the rate constants of OH + chloroethylenes reactions. VTST calculations indicate that, except the reaction of OH + C2Cl4, these reactions present a complex behavior. For OH + C2Cl4, conventional TST calculation shows a simple positive temperature-dependence behavior.
10

Metabolic and vascular effects of thiosulfate sulfurtransferase deletion

Gibbins, Matthew Thomas George January 2018 (has links)
Hydrogen sulfide (H2S), is a gasotransmitter with several key roles in metabolism and vascular function. The effects of H2S are dependent on concentration and target organ. For example, increased H2S concentrations impair liver metabolic function but protect against vascular dysfunction and atherosclerosis. Thiosulfate sulfurtransferase (TST), a nuclear encoded mitochondrial matrix enzyme, is proposed to be a component of the sulfide oxidising unit (SOU) which metabolises H2S. Preliminary data has shown that Tst deletion in mice (Tst-/-) increases circulating H2S levels measured in whole blood. Therefore, it was hypothesised that Tst-/- mice would exhibit worsened metabolic function in the liver but also protection of vascular function under conditions of vascular stress e.g. atherosclerosis. Liver metabolism was assessed by extensive metabolic phenotyping of Tst-/-mice fed control diet and in conditions of metabolic dysfunction induced by a high fat diet (HFD). Tst deletion altered glucose metabolism in mice; gluconeogenesis was increased in liver from Tst-/-mice fed control diet. Glucose intolerance in HFD-fed Tst-/-mice was also more severe than HFDfed C57BL/6 controls. In vitro metabolic investigations in primary hepatocytes isolated from Tst-/-mice demonstrated that mitochondrial ATP-linked and leak respiration were increased compared to controls. The effect of Tst deletion on vascular function was investigated in Tst- /-mice fed control or HFD using myography. Tst deletion did not alter vessel function when mice were maintained on a normal diet. HFD feeding (20 weeks) reduced maximal vessel constriction in the presence of endothelial nitric oxide synthase and cyclooxygenase inhibitors in C57BL/6 aorta. However, in Tst-/-mice fed HFD there was no reduction in maximal constriction suggesting a protective action of Tst deletion. The effects of Tst deletion on atherosclerotic lesions was investigated by generating double knock-out (DKO) mice by deletion of the Tst gene in ApoE-/- mice and (ApoE-/-Tst-/-). Atherosclerotic lesion formation was accelerated by feeding mice a western diet. Within the brachiocephalic branch lesion volume and total vessel volume were reduced in DKO mice fed western diet for 12 weeks, indicating that Tst deletion reduced lesion formation. Plasma cholesterol was reduced in DKO mice compared to ApoE-/- controls and a trend towards reduced systolic blood pressure was also noted. Overall this work supported the hypothesis that Tst deletion engenders metabolic dysfunction but vascular protection. The findings are consistent with the reported effects of increased H2S signalling. Overall inhibition of TST represents a novel target for treatment of atherosclerosis, with the caveat that glycaemia may be worsened due to hepatic metabolic dysfunction.

Page generated in 0.0315 seconds