No description available.

No description available.

archives@tulane.edu / The wavelength dependent abstraction energy profiles for CH_3 CH_2 CH_3/CH_3 CH_2 CH_2 CH_3+Br are studied using a gas expansion containing 〖Br〗_2 and either propane or butane abstraction targets. Laser-induced photolysis of cold 〖Br〗_2 in the visible region produces a narrow, tunable distribution of Br atoms whose collisional kinetic energies can be scanned up to and beyond the thermodynamic threshold of the reaction to yield HBr or DBr as photolytic reaction products. Femtosecond laser ionization allows the reactive products to be efficiently monitored over all product quantum states. Both the observed HBr and DBr reaction thresholds are consistent with thermodynamic and calculated values with no apparent barrier to reaction. Studies addressing the site-specific reaction behavior for selectively deuterated propane and butane molecules is presented and discussed. Future applications of the approach are discussed such as state-dependent detection methods, and ultra-cold nozzle expansions. / 1 / Shane J. G. McGlynn

<p> The regioselectivities of bromination and deuterium exchange of 2-butanone are shown to be the same, under identical conditions. This work firmly establishes that enolization is the rate-determining step for the former reaction, contrary to some recent reports in the literature.</p> <p> The steric effects and activation parameters in the bimolecular nucleophilic displacement reactions of a series of α-haloketones and alkyl halides are shown to be inconsistent with either a bridging or conjugation mechanism for the observed rate enhancements of haloketone over alkyl halide.</p> <p> The stereoelectronic requirements of this mechanism are tested in a system where the stereochemistry is known (cis- and trans-chlorocyclohexanones). The activation parameters suggest that only in the case where the geometry is correct for maximum conjugation (trans-chlorocyclohexanone) is there an appreciable difference in mechanism (stereoelectronically) from displacement at ordinary saturated carbon.</p> / Thesis / Doctor of Philosophy (PhD)

As células solares orgânicas, também conhecidas como (OPVs), fazem parte da terceira geração dos dispositivos fotovoltaicos. Entre outras tecnologias emergentes, a dos OPVs tem a vantagem de ser de fácil processamento e de baixo custo. Ou seja, uma tecnologia comercialmente promissora na área de conversão de energia solar em energia elétrica. No entanto, grandes desafios precisam ser superados para colocar estas células no mercado dos fotovoltaicos. Dentre esses desafios, pode estar incluído, inevitavelmente, a compreensão dos processos físicos envolvidos na fotogeração em OPVs, dentre os quais pode-se destacar o da recombinação de cargas fotogeradas. A recombinação é o principal responsável pela perda de eficiência em OPVs, uma vez que ela elimina uma fração relativamente grande de portadores de carga, diminuindo consideravelmente a potência de saída da célula. Para estudar este efeito indesejado em células orgânicas, desenvolvemos um modelo analítico para fotocorrente em OPVs do tipo bulk heterojunction (BHJ), assumindo uma recombinação bimolecular de cinética de segunda ordem. O modelo é representado por uma expressão analítica obtida a partir das equações fundamentais da eletrodinâmica clássica, onde despreza-se a contribuição da corrente de difusão e as mobilidades dos elétrons e dos buracos são consideradas iguais. Essa expressão foi de grande valia na análise dos resultados experimentais, sobretudo os de corrente-tensão (J-V) sob iluminação, e além disso, ela permitiu extrair parâmetros intrínsecos do transporte de carga, como mobilidade e coeficiente de recombinação. Neste sentido, foram fabricados dispositivos cuja estrutura foi ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al, e com eles foram realizados inúmeros experimentos. As técnicas usadas na parte experimental foram: medidas J-V, no escuro e sob iluminação, medidas de transiente de fotovoltagem (TPV), de transiente de fotocorrente (TPC), e de Foto-CELIV (Charge Extraction Linear Increasing Voltage). Usamos como parâmetros experimentais a temperatura e intensidade de iluminação. Das medidas J-V sob iluminação, foram extraídos os parâmetros essenciais da célula: corrente de curto (Jsc), potencial de circuito aberto (Voc), fator de preenchimento (FF) e a eficiência (PCE). A partir das abordagens experimental e teórica, exploramos a influência da recombinação bimolecular no comportamento fotovoltaico dos dispositivos. O desenvolvimento do modelo teve contribuição de trabalhos que se basearam em modelagem numérica a partir de condições físicas semelhantes às usadas em nosso tratamento e que foram levadas em consideração no processo de análise dos resultados experimentais. / Organic solar cells, also known as (OPVs), are part of the third generation of photovoltaic devices. Among other emerging technologies, OPVs have the advantage of being easy to process and exhibits low cost of production. That is, it is a promising commercial technology in the area of converting solar energy into electricity. However, major challenges need to be overcome to put these cells in the photovoltaic market. Among them, it can be included, inevitably, the comprehension of the physical processes involved in photogeneration in OPVs, of which, the recombination of photogenerated carriers is included. Recombination is primarily factor responsible for the loss of efficiency in OPVs, since recombination eliminates a large fraction of the carriers, considerably reducing the output power of the cell. To study this undesirable effect in organic cells, we developed an analytical model for the photocurrent in bulk heterojunction cells (BHJ), which assumes the bimolecular recombination of second order kinetics. The model is represented by an analytical expression obtained by the equations of the classical electrodynamics, where we neglected the contribution of the diffusion current and assumed that electrons and holes have equal mobilities. The expression was of great value for the analysis of the experimental results, especially the current-voltage (J-V) measurements under illumination, and it allowed to extract intrinsic parameters of charge transport effects, such as mobility and recombination coefficient. For this, it were fabricated devices whose structure was ITO/PEDOT:PSS/P3HT:PCBM/Ca-Al, and with them were performed numerous experiments. The techniques used in the experimental part were: J-V measurements, in the dark and under illumination, transient photovoltage (TPV), transient photocurrent (TPC), and of Charge Extraction Linear Increasing Voltage (Photo-CELIV). We used as experimental parameters the temperature and the intensity of. From J-V measurements under illumination we extracted the essential cell parameters: short current (Jsc), open circuit potential (Voc), fill factor (FF) and efficiency (PCE). From the experimental and theoretical approaches, we explored the influence of bimolecular recombination on the photovoltaic behavior of the devices. The development of the model had contributions of works based on numerical modelings from physical conditions similar to those used in our treatment and that were taken into account in the process of analysis of the experimental results.

As células solares orgânicas, também conhecidas como (OPVs), fazem parte da terceira geração dos dispositivos fotovoltaicos. Entre outras tecnologias emergentes, a dos OPVs tem a vantagem de ser de fácil processamento e de baixo custo. Ou seja, uma tecnologia comercialmente promissora na área de conversão de energia solar em energia elétrica. No entanto, grandes desafios precisam ser superados para colocar estas células no mercado dos fotovoltaicos. Dentre esses desafios, pode estar incluído, inevitavelmente, a compreensão dos processos físicos envolvidos na fotogeração em OPVs, dentre os quais pode-se destacar o da recombinação de cargas fotogeradas. A recombinação é o principal responsável pela perda de eficiência em OPVs, uma vez que ela elimina uma fração relativamente grande de portadores de carga, diminuindo consideravelmente a potência de saída da célula. Para estudar este efeito indesejado em células orgânicas, desenvolvemos um modelo analítico para fotocorrente em OPVs do tipo bulk heterojunction (BHJ), assumindo uma recombinação bimolecular de cinética de segunda ordem. O modelo é representado por uma expressão analítica obtida a partir das equações fundamentais da eletrodinâmica clássica, onde despreza-se a contribuição da corrente de difusão e as mobilidades dos elétrons e dos buracos são consideradas iguais. Essa expressão foi de grande valia na análise dos resultados experimentais, sobretudo os de corrente-tensão (J-V) sob iluminação, e além disso, ela permitiu extrair parâmetros intrínsecos do transporte de carga, como mobilidade e coeficiente de recombinação. Neste sentido, foram fabricados dispositivos cuja estrutura foi ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al, e com eles foram realizados inúmeros experimentos. As técnicas usadas na parte experimental foram: medidas J-V, no escuro e sob iluminação, medidas de transiente de fotovoltagem (TPV), de transiente de fotocorrente (TPC), e de Foto-CELIV (Charge Extraction Linear Increasing Voltage). Usamos como parâmetros experimentais a temperatura e intensidade de iluminação. Das medidas J-V sob iluminação, foram extraídos os parâmetros essenciais da célula: corrente de curto (Jsc), potencial de circuito aberto (Voc), fator de preenchimento (FF) e a eficiência (PCE). A partir das abordagens experimental e teórica, exploramos a influência da recombinação bimolecular no comportamento fotovoltaico dos dispositivos. O desenvolvimento do modelo teve contribuição de trabalhos que se basearam em modelagem numérica a partir de condições físicas semelhantes às usadas em nosso tratamento e que foram levadas em consideração no processo de análise dos resultados experimentais. / Organic solar cells, also known as (OPVs), are part of the third generation of photovoltaic devices. Among other emerging technologies, OPVs have the advantage of being easy to process and exhibits low cost of production. That is, it is a promising commercial technology in the area of converting solar energy into electricity. However, major challenges need to be overcome to put these cells in the photovoltaic market. Among them, it can be included, inevitably, the comprehension of the physical processes involved in photogeneration in OPVs, of which, the recombination of photogenerated carriers is included. Recombination is primarily factor responsible for the loss of efficiency in OPVs, since recombination eliminates a large fraction of the carriers, considerably reducing the output power of the cell. To study this undesirable effect in organic cells, we developed an analytical model for the photocurrent in bulk heterojunction cells (BHJ), which assumes the bimolecular recombination of second order kinetics. The model is represented by an analytical expression obtained by the equations of the classical electrodynamics, where we neglected the contribution of the diffusion current and assumed that electrons and holes have equal mobilities. The expression was of great value for the analysis of the experimental results, especially the current-voltage (J-V) measurements under illumination, and it allowed to extract intrinsic parameters of charge transport effects, such as mobility and recombination coefficient. For this, it were fabricated devices whose structure was ITO/PEDOT:PSS/P3HT:PCBM/Ca-Al, and with them were performed numerous experiments. The techniques used in the experimental part were: J-V measurements, in the dark and under illumination, transient photovoltage (TPV), transient photocurrent (TPC), and of Charge Extraction Linear Increasing Voltage (Photo-CELIV). We used as experimental parameters the temperature and the intensity of. From J-V measurements under illumination we extracted the essential cell parameters: short current (Jsc), open circuit potential (Voc), fill factor (FF) and efficiency (PCE). From the experimental and theoretical approaches, we explored the influence of bimolecular recombination on the photovoltaic behavior of the devices. The development of the model had contributions of works based on numerical modelings from physical conditions similar to those used in our treatment and that were taken into account in the process of analysis of the experimental results.

The product state specific stereodynamics of the photon–initiated reaction of O(¹D₂) with H₂ has been investigated by polarised Doppler–resolved laser induced fluorescence, under room temperature bulb conditions. Product state resolved differential cross sections, excitation functions and rotational angular momentum alignments are reported for the following product channels, O(¹D₂) + H₂(¹Σ⁺_g ; v = 0) -> OH(X²Pi; v' = 0;N' = 14; f) + H(²S). at a mean collision energy of 12 kJ mol^-1. The data are compared with extensive state resolved quasi–classical trajectory (QCT) calculations of the linear and angular momentum distributions and excitation functions conducted on the Schinke–Lester (SL1) and K ab initio ground state (1¹A') potential energy surfaces. Overall, good agreement is obtained between the QCT calculated and experimentally determined stereodynamical features. The results are discussed in light of other recent work on this prototypical insertion reaction, and on the related systems of O(¹D₂) + HD and CH₄.

No description available.

Ce travail est consacré à la modélisation QSPR des propriétés cinétiques et thermodynamiques des réactions chimiques à l'aide de l'approche Graphe Condensé de Réaction (CGR). Le CGR permet de coder des structures de réactifs et de produits en un seul graphe moléculaire pour lequel des descripteurs moléculaires peuvent être générés.Une base de données contenant plus de 11000 réactions collectées manuellement a été développée puis utilisée dans la modélisation. Les modèles prédictifs ont été construits pour les constantes de vitesse de réactions Diels-Alder, SN2 et E2 ainsi que pour les constantes d'équilibre des transformations tautomères. Ils sont rendus publics via un portail WEB. Une partie de la thèse concerne une étude de mécanique quantique des réactions entre des sydnones et des alcynes contraints pour lesquels la taille du jeux de données n'était pas suffisante pour produire des modèles statistiquement significatifs. / This work is devoted to QSPR modeling of kinetic and thermodynamic properties of chemical reactions using the Condensed Graph of Reaction (CGR) approach. CGR allows encoding structures of reactants and products into one sole molecular graph for which molecular descriptors can be generated. A comprehensive database containing some 11000 manually collected reactions has been developed then used in the modeling. Predictive models were built for rate constants of Diels-Alder, SN2 and E2 reaction as well as for equilibrium constants of tautomeric transformations. They are available for the users via WEB portal. A part of the thesis concerned quantum mechanics studies of reactions between sydnones and strained alkynes for which the size of the dataset was not sufficient to produce statistically meaningful models.

<p>The DNA of a cell operates as its blueprint, providing coded information for the production of the RNA and proteins that allow the cell to function. Cells can face a myriad of insults to their genomic integrity during their lifetimes, from simple errors during growth and division to reactive oxygen species to chemotherapeutic reagents. To deal with these mutagenic insults and avoid passing them on to progeny, cells are equipped with multiple defenses. Checkpoints can sense problems and halt a cell’s progression through the cell cycle in order to allow repairs. More drastically, cells can also prevent passing on mutations to progeny by triggering apoptosis, or programmed cell death. This work will present two separate discoveries regarding the regulation of DNA damage-induced apoptosis and the regulation of the spindle checkpoint.</p><p> The protease caspase-2 has previously been shown to be an important regulator of DNA damage-induced apoptosis. In unstressed cells caspase-2 is present as an inactive monomer, but upon sensing a stress caspase-2 dimerizes and becomes catalytically active. The mechanisms that regulate this dimerization are poorly understood. The first research chapter details our development of a novel method to study dimerized caspase-2, which in turn identified TRAF2 as a direct activator of caspase-2. Specifically, we utilized the Bimolecular Fluorescence Complementation technique, wherein complementary halves of the Venus fluorophore are fused to caspase-2: when caspase-2 dimerizes, the non-fluorescent halves fold into a functional Venus fluorophore. We combined this technique with a Venus-specific immunoprecipitation that allowed the purification of caspase-2 dimers. Characterization of the caspase-2 dimer interactome by MS/MS identified several members of the TNF Receptor Associated Factor (TRAF) family, specifically TRAF1, 2, and 3. Knockdown studies revealed that TRAF2 plays a primary role in promoting caspase-2 dimerization and downstream apoptosis in response to DNA damage. Identification of a TRAF Interacting Motif (TIM) on caspase-2 indicates that TRAF2 directly acts on caspase-2 to induce its activation. TRAF2 is known to act as an E3 ubiquitin ligase as well as a scaffold for other E3 ubiquitin ligases. Indeed, we identified three lysine residues in the caspase-2 prodomain (K15, K152, and K153) important for its ubiquitination and complex formation. Together these results revealed a novel role for TRAF2 as a direct activator of caspase-2 apoptosis triggered by DNA damage.</p><p> During mitosis, when the cell prepares to divide, great care is taken to ensure that the chromosomes are properly segregated between the two daughter cells by the mitotic spindle. This is primarily accomplished through the spindle checkpoint, which becomes activated when the mitotic spindle is not properly attached to each chromosome’s kinetochore. When activated, the primary effector of the spindle checkpoint, the mitotic checkpoint complex (MCC), inhibits the anaphase-promoting complex (APC/C) by binding to the APC/C co-activator, CDC20. This prevents the APC/C from targeting critical pro-mitotic proteins, like cyclin B and securin, to promote mitotic exit. Although the function of the MCC is well understood, its regulation is not, especially in regard to protein phosphatases To investigate this, we activated the spindle checkpoint with microtubule inhibitors and then treated with a variety of phosphatase inhibitors, examining the effect on the MCC and APC/C. We found that two separate inhibitors, calyculin A and okadaic acid (1uM), were able to promote the dissociation of the MCC. This led to the activation of the APC/C, but the cells remained in mitosis as evidenced by high levels of Cdk1 activity and chromosome condensation. This is the first time that phosphatases have been shown to be essential to maintaining the MCC and an active spindle checkpoint.</p> / Dissertation