Bien que découverte il y a 75 ans, la fission nucléaire fait toujours l'objet de recherches. En effet, la compréhension de ce phénomène présente encore des difficultés théoriques dues à sa complexité. Cela nécessite une bonne compréhension de la structure du noyau de l'atome ainsi qu'une description détaillée du mécanisme pilotant l'évolution du système fissionnant.Un nouveau modèle statistique, appelé SPY (Scission Point Yields), a été développé pour déterminer les caractéristiques des fragments (rendements de fission, énergie cinétique, énergie d¹excitation). Ce modèle est basé sur le modèle de Wilkins développé en 1976. Il consiste en une description statistique du processus de fission au point de scission où les fragments sont complètement définis. L'une des principales avancées du modèle SPY est l'introduction de la description microscopique de la structure nucléaire dans le calcul de l'énergie du système à la scission.Il permet d'étudier la relation entre les propriétés des fragments et leur structure nucléaire. Avec le modèle SPY, il est possible de calculer les propriétés des fragments et d'identifier les tendances globales pour environ 3000 noyaux fissionnants de Z=70 à Z=109, de la drip line neutron jusqu'à la drip line proton.Après une présentation générale de la version de référence du modèle SPY, les résultats obtenus pour la fission thermique de l'uranium 235 et la fission spontanée du californium 252 sont comparés aux données expérimentales. Une étude systématique sur l'ensemble des noyaux actuellement synthétisés est également menée avant d'étendre cette étude bien au-delà de la zone des noyaux synthétisables. Deux développements seront ensuite détaillés. Le premier concerne la manière de calculer l'énergie d'interaction coulombienne entre les deux fragments. Les distributions de charges issues de calculs microscopiques seront introduites afin d'améliorer le calcul de l'énergie d'interaction coulombienne. La possibilité de redéfinir le point de scission du système grâce à ces distributions de charge sera également discuté.Le deuxième développement porte sur le lien entre la modélisation du noyau et les observables associées aux fragments de fission. D'une part, différents modèles du noyau pour le calcul de l'énergie individuelle des fragments, tel que le modèle de la goutte liquide, seront envisagés et l'impact du choix de la modélisation du noyau sera étudiée.D'autre part, l'impact de la prise en compte de la structure nucléaire des fragments dans le calcul des densités d'états sur les observables sera étudié. / Although discovered 75 years ago, nuclear fission is still under investigation. Indeed, the understanding of this phenomenon still presents theoretical difficulties due to its complexity. This requires a good understanding of the structure of atomic nucleus and at the same time a detailed description of the mechanisms driving the evolution of a fissioning system.A new statistical scission point model named SPY (Scission Point Yields) is developped to model the fission mechanism and determine nascent fragments characteristics (yields, kinetic energy, excitation energy). This model is based on the Wilkins model developed in 1976. It consists in a statistical description of the fission process at the scission point where fragments are completely defined and well separated. One of the main advance brought by SPY model is the introduction of microscopic description of the nuclear structure in the calculation of the energy of the system at scission. Therefore, this model can be regarded as a theoretical laboratory for fission modeling since it allows to study the relationship between fission fragments properties and their nuclear structure.With SPY, we were able to calculate the properties of fragments and to identify global trends for about 3000 fissioning nuclei from Z=70 to Z=109 and from proton drip line to neutron drip line.After a general presentation of SPY model, results for thermal fission of uranium 235 and spontaneous fission of 252 californium are compared with experimental data. A systematic study over all currently synthesized nuclei is also done before extending this study beyond the synthesizable nuclei area. Finally the main developments of the model performed will be detailed.The first one is related to calcultation of the Coulomb interaction energy between the two fragments. The charge distributions from microscopic calculations are introduced to improve the calculation of the energy of Coulomb interaction. The ability to redefine the scission point of the system thanks to these distributions will also be discussed. The second development concerns the relationship between nucleus modeling and observables related to fission fragments. On the one hand, different models of the nucleus to calculate the individual energy of the fragments, such as liquid drop model, will be considered and the impact of the choice of the nucleus modeling will be studied. On the other hand, the impact of the inclusion of the nuclear structure of the fragments in the calculation of states densities on observable will be studied.

本論文主要研究銥和銠卟啉絡合物與鹵代苯 (ArX, X = Cl, Br, I)的碳-鹵鍵(Ar-X)的斷裂反應及其應用。本論文分為四個部分：（1）銠卟啉絡合物與鹵代苯(ArX, X = Cl, Br, I)之間的碳-鹵鍵(Ar-X)斷裂反應；（2）氟氯化苯的碳-氟鍵(Ar-F)與碳-氯鍵(Ar-Cl)斷裂的競爭反應；（3）氟取代基對金屬（銥和銠）-芳香碳(M-Ar)鍵強弱的影響；以及（4）銥卟啉氟硼荧絡合物的合成。 / 第一部分闡述了銠卟啉絡合物(Rh(ttp)Cl)與鹵代苯(ArX, X = Cl, Br, I) 之間的碳-鹵鍵 (Ar-X) 斷裂反應以及反應機理。在鹼性條件下，無論富電子還是缺電子的鹵代苯都能與Rh(ttp)Cl反應，生成Ar-X鍵斷裂的產物──銠卟啉芳基絡合物(Rh(ttp)Ar) 。機理研究顯示， Rh(ttp)Cl 首先與氫氧根離子反應生成Rh(ttp)OH，進而通過二聚反應生成[Rh(ttp)]₂。[Rh(ttp)]₂在加熱條件下與Rh(ttp)自由基可以互相轉化，產生的Rh(ttp)自由基與鹵代苯進行原位取代反應，生成銠卟啉芳基絡合物(Rh(ttp)Ar)和鹵素自由基。鹵素自由基可以和另一個Rh(ttp)自由基反應生成Rh(ttp)X，在氫氧根離子存在的條件下，Rh(ttp)X將再次轉化為Rh(ttp)OH繼續反應。 / 第二部分描述了氟氯化苯中碳-氟鍵(Ar-F)與碳-氯鍵(Ar-Cl)斷裂的競爭反應。機理研究顯示碳-氟鍵(Ar-F)斷裂的中間體是M(por)⁻，而碳-氯鍵(Ar-Cl)斷裂的中間體是MII(por)。因此，我們可以通過改變反應條件而控制生成物。例如，在較低溫度下和強鹼性的極性溶劑中，以M(por)⁻前體作為反應物，可以獲得較多的碳-氟鍵(Ar-F)斷裂的產物；而在較高溫度下和弱鹼性的非極性溶劑中，可以獲得較多的碳-氯鍵(Ar-Cl)斷裂的產物。 / 第三部分敘述了間位氟取代基對金屬-芳香碳(M-Ar)鍵的增強作用。有間位氟取代基的金屬（銥，銠）卟啉芳基絡合物(M(ttp)ArF)是最穩定的同分異構體。在250°C條件下，當反應30天後，Ir(ttp)C₆H₄F的三個異構體達到平衡狀態，其鄰位:間位:對位的比例大約為0:5:1。理論計算的結果也顯示Ir(ttp)(3-fluorophenyl)相對Ir(ttp)(2-fluorophenyl)和Ir(ttp)(4-fluorophenyl)有更低的能量。氟取代基在鄰位時，氟與卟啉之間空間位阻較大，減弱了金屬-芳香碳(M-Ar)鍵的鍵能。與氟取代基在對位相比，在間位時具有更好的吸電子效應，從而增加了金屬-芳香碳(M-Ar)鍵的極性，增強了金屬-芳香碳(M-Ar)鍵鍵能。 / 第四部分描述了利用碳-鹵鍵 (Ar-X) 的斷裂，合成銥卟啉氟硼荧絡合物的反應。銥卟啉氟硼荧絡合物的產率可以達到70%。銥卟啉氟硼荧絡合物在生物成像和放射療法都有潛在的應用。銥卟啉氟硼荧絡合物是用金屬自由基與氟硼荧反應合成的。 / This thesis focuses on the reaction scopes, mechanistic investigations and applications of base-promoted aryl carbon-halogen (Ar-X) bond cleavage with iridium and rhodium porphyrin complexes. This thesis is divided into four parts: (1) Ar-X (X = Cl, Br, I) bond cleavage with Rh(ttp)Cl; (2) competitive Ar-F and Ar-Cl bond cleavage with iridium and rhodium porphyrins; (3) fluorine substituent effect on the M-Ar (M = Ir, Rh) bond strength; and (4) synthesis of iridium porphyrin BODIPY complexes. / Part I describes the reaction scopes and mechanism of Ar-X (X = I, Br, Cl) bond cleavage with Rh(ttp)Cl (ttp = 5,10,15,20-tetratolylporphyrinato dianion). Under basic conditions, both electron-rich and electron-deficient ArX undergo Ar-X bond cleavage to give Rh(ttp)Ar in good yields. [with diagram] / The mechanistic investigations suggest that RhIII(ttp)Cl first undergoes ligand substitution by OH- to give RhIII(ttp)OH, which forms [RhII(ttp)]₂ through reductive dimerization. RhII(ttp) radical, which is in equilibrium with [RhII(ttp)]₂, cleaves the Ar-X (X = I, Br, Cl) bond through metalloradical ipso-substitution and gives RhIII(ttp)Ar and X radical. X radical recombines with another RhII(ttp) radical to generate RhIII(ttp)X, which gives back RhIII(ttp)OH through ligand substitution by OH-. [with diagram] / Part II describes the competitive Ar-F and Ar-X (X = Cl, Br) bond cleavage reactions of fluorochlorobenzenes with iridium and rhodium porphyrin complexes. Mechanistic studies suggest that M(por)⁻ is the intermediate for the Ar-F bond cleavage while MII(por) is the intermediate for the Ar-X bond cleavage. By taking advantage of the difference in mechanisms of the Ar-F and Ar-X bond cleavages, the selectivity of bond cleavage can be controlled by varying the reaction conditions. The Ar-F bond cleavage is favored in a polar solvent with a stronger base at lower temperatures with M(por)⁻ precursor, and the Ar-X bond cleavage is favored under non-polar conditions with a weaker base and at higher temperatures. [with diagram] / Part III describes the meta-fluorine substituent effect on strengthening the M-Ar (M = Ir, Rh) bond of M(ttp)ArF. M(ttp)ArF with meta-fluorine substituent are the most stable isomers among the isomeric Ar-H bond cleavage products. At 250 °C for 30 days, the three isomers of Ir(ttp)C₆H₄F reached an equilibrium with o : m : p = 0 : 5 : 1. The theoretical calculations also suggest that Ir(ttp)(3-fluorophenyl) is of lower energy than Ir(ttp)(2-fluorophenyl) and Ir(ttp)(4-fluorophenyl). The ortho-fluorine substituent exhibits steric effect which weakens the M-Ar bond. The meta-fluorine, which is more electron-withdrawing than para-fluorine, enhances the polarity of the M-C(ipso) bond and thus strengthens the M-Ar bond. [with diagram] / Part IV describes the application of Ar-I bond cleavage with Ir(ttp)(CO)Cl in synthesizing iridium porphyrin boron-dipyrromethene (BODIPY) complexes, which are potential photosensitizers for biological imaging and photodynamic therapy. The clinically interested iridium porphyrin BODIPY complexes have been prepared by a radical process of metalloradical with BODIPY. [with diagram] / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Qian, Yingying. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese.

Thesis (Ph. D.)--Ohio State University, 2006. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2007 Aug 15.

Thèse de doctorat : Chimie-physique : Strasbourg 1 : 2007. / Titre provenant de l'écran-titre. Bibliogr. p. 83-86.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Stephen Lombardo. Includes bibliographical references.

La raréfaction des ressources pétrolières exacerbe la demande de nouveaux produits issus de sources durables, tels que les huiles issues des plantes. Afin de pouvoir intégrer les acides gras insaturés présents dans ces produits biosourcés dans l’industrie pétrochimique, une réaction clivante revêt un grand intérêt. Cette thèse présente des voies de synthèse pour des nanocatalyseurs magnétiques, actifs pour la scission oxydante des acides gras insaturés, et notamment l’acide oléique. Les nanocatalyseurs magnétiques constituent une nouvelle catégorie de catalyseurs hétérogènes dont les propriétés catalytiques permettent d’avoisiner les performances des catalyseurs homogènes. Cependant, leur nature solide couplée à leur propriété magnétique permet facilement leur récupération, et donc leur réutilisation, au contraire des catalyseurs homogènes. Ainsi, un nano catalyseur magnétique est un type de catalyseur prometteur s’inscrivant dès lors dans une démarche de chimie verte. Cette thèse présente, en plus de deux chapitres non expérimentaux, des méthodes de synthèse pour la conception in fine de nanocatalyseurs de type cœur@coquille, permettant d’exhiber des propriétés magnétiques grâce à un cœur constitué d’oxyde de fer et d’une coquille composée en partie de la phase active qu’est le catalyseur. Ainsi, les articles présentés incluent, dans le troisième chapitre, une méthode de synthèse de nanoparticules d’oxyde de fer, la magnétite Fe3O4, ayant une très grande reproductibilité et une très faible dispersité en taille. Ces nanoparticules serviront de cœur pour la conception des nanocatalyseurs au cœur magnétique. Dans un quatrième chapitre, une nouvelle voie de synthèse de nanoparticules cœur@coquille magnétiques ayant de l’oxyde de molybdène à la surface est présentée. L’oxyde de molybdène est reconnu pour ses propriétés catalytiques pour la scission oxydante des acides gras insaturés. Finalement, dans un cinquième chapitre, une seconde voie de synthèse est présentée pour l’élaboration d’un nanocatalyseur cœur@double coquille, entièrement inorganique. Cette nanoparticule est composée d’un cœur de magnétite, le plus magnétique des oxydes de fer, d’une première coquille de silice et finalement d’une coquille d’oxyde de tungstène. En plus de présenter les étapes de synthèse détaillées et les mécanismes associés, cet article a évalué les propriétés catalytiques de cette nanoparticule de Fe3O4@SiO2@WO3.Lorsqu’employé sur l’acide oléique, et comparé à d’autres catalyseurs à base de tungstène, ce nanocatalyseur exhibe une activité catalytique proche du catalyseur homogène (soit l’acide pertungstique) et bien au-delà des catalyseurs hétérogènes, qu’ils soient à l’échelle macroscopique (oxyde de tungstène brut), ou à l’échelle nanoscopique avec des nanoparticules supportées. De plus, sa récupérabilité et sa réutilisabilité permettent de qualifier cette nanoparticule de nanocatalyseur. Cette méthode fiable et robuste pourrait être mise en œuvre sur d’autres oxydes métalliques pouvant être utilisés comme catalyseurs, tels que le molybdène. Elle permettrait ainsi d’ouvrir une nouvelle voie de synthèse de catalyseurs verts que sont les nanocatalyseurs magnétiques de type cœur@coquille. En effet, la silice étant facilement fonctionnalisable, cette méthode offre de multiples possibilités en termes d’applications. / The scarcity of the fossil resources exacerbates the need for new products, based on sustainable resources such as the vegetable oils. To integrate the unsaturated fatty acids of these biobased products to the petrochemical industry, a bond cleavage is required. This thesis provides new synthesis routes for magnetic nanocatalysts, effective for the oxidative cleavage of fatty acids, in particular oleic acid. The magnetic nanocatalysts are a new type of heterogenous catalysts with catalytic properties close to the performances of the homogeneous catalysts. As a solid material exhibiting magnetic properties, they are easy to recover from reaction media and thus to reuse, contrary to the homogeneous catalysts. Thus, a magnetic nanocatalyst is a promising catalyst in green chemistry. This thesis introduces, in addition two theoretical chapters on the above mentioned concepts, various methods of synthesis to in fine conceive a core@shell nanocatalyst. The latter intend to exhibit a magnetic core of iron oxide and a shell containing the active phase of the catalyst. Thus, the articles included in this thesis contribute to achieving this purpose. The first article provides a method for the synthesis of iron oxide nanoparticles, the magnetite Fe3O4, with a high reproducibility and a low dispersity in size. These nanoparticles will be further used as the core in the design of nanocatalysts with a magnetic core. The second article provides a new synthesis route for the synthesis of magnetic core@shell nanoparticles with molybdenum oxide at the external surface. Molybdenum oxide is a known catalyst for the oxidative cleavage of unsaturated fatty acids. Finally, a new method for the design of a nanocatalyst core@dual shell fully inorganic, is presented. This nanoparticle is composed of a magnetic core of magnetite, the more magnetic phase of iron oxide, a first shell of silica and then a shell of tungsten oxide. Not only the detailed step-by-step synthesis route is provided, but the catalytic activity of this Fe3O4@SiO2@WO3 nanoparticle is also assessed. When applied and compared to other tungsten-based catalysts for the oxidative cleavage of oleic acid, this nanocatalyst exhibits a catalytic activity similar to the homogeneous catalyst (i.e. pertungstic acid) and far above that of existing heterogeneous catalysts. The latter were either a macroscopic catalyst (i.e. bulk tungsten oxide) or nanoscopic catalysts with tungsten oxide nanoparticles and supported nanoparticles. In addition, the easy recovery of this material and its reusability allow qualifying this nanoparticle as a nanocatalyst. This reliable and robust method could be implemented on other catalytic active metal oxides such as molybdenum. This method is a new synthesis path for green catalysts as magnetic core@shell nanocatalysts. Indeed, as the silica is an easy functionable support, this method could be easily implemented and open new catalytic possibilities.

L'objectif de cette thèse est d'explorer les mécanismes d'émission des neutrons émis lors du processus de la fission. En particulier, la question ouverte de l'existence d'une anisotropie dynamique dans le centre de masse des fragments de fission et/ou de la possibilité d'une émission de neutrons de scission est explorée. La thèse débute par une introduction aux concepts théoriques permettant de décrire les processus de fission et les mécanismes d'émission de neutrons. La nécessité de concevoir une méthode d'analyse appropriée pour caractériser des mécanismes très subtiles est discutée, en insistant sur l'importance de maîtriser les biais expérimentaux. Le travail effectué a exigé un effort important de simulation, à travers le développement d'une procédure Monte Carlo pour décrire la fission spontanée du 252Cf, ainsi qu'une modélisation du dispositif expérimental de l'expérience CORA3.Nous proposons pour la première fois une approche simultanée et indépendante des deux mécanismes, émission de scission et anisotropie dynamique, ainsi que des valeurs quantitatives d'anisotropie et d'émission de scission mesurées expérimentalement. / The subject of this thesis is to explore the neutron emission mechanisms in the fission process. In particular a long standing open question, the existence of a dynamical anisotropy in the centre of mass of the fission fragments and/or a possible scission neutron emission is explored. The thesis starts with an overview of the theoretical concepts on the fission process and on the neutron emission mechanisms. Also the necessity to conceive an appropriate analysis method is stressed when a very subtle mechanism is studied as various approximations and/or experimental biases not completely handled can hide the physical phenomena. In the presented work a huge effort was required to write a Monte Carlo procedure based on a coherent model for the spontaneous fission of 252Cf and to couple it with the devices exploited in the CORA3 experiment.

The topical application of sunscreens is widely practised to protect healthy and photosensitive skins from the sun. The benzophenone-derived sunscreens, e.g. 2-hydroxy-4-methoxy benzophenone-5-sulphonic acid (or benzophenone-4) and 2-hydroxy-4-methoxy benzophenone (or benzophenone-3), were ranked as the second and third most frequently used sunscreens, respectively, by the United States Food and Drug Administration (FDA) in 1996. These sunscreens are categorised as being 'safe' and 'effective'. However, it is well known that the parent compound, benzophenone, undergoes rapid hydrogen abstraction reactions on irradiation and is an extremely powerful radical generator. In addition, benzophenone has been shown to be a potent photosensitizer of thymine dimers in deoxyribose nucleic acid (DNA). More astounding to the sunscreen industry is the recent discovery that a group of non-steroidal anti- inflammatory drugs (NSAIDs) having the benzophenone backbone, e.g. ketoprofen, not only form thymine dimers when irradiated with DNA in vitro, but also photosensitize double stranded supercoiled DNA making it prone to single-strand break formation. Both these lesions, if unrepaired, may contribute to mutagenesis, carcinogenesis, inherited disease and eventually cell death. The purpose of this investigation was to determine if a group of benzophenone-derived sunscreen agents has the ability to photosensitize the cleavage of DNA, whereby supercoiled DNA is converted to the relaxed circular and linear forms. The group of UV absorbers investigated in this study included benzophenone-4, benzophenone-3 , 2,4 dihydroxybenzophenone (or benzophenone-l), 2,2'-dihydroxy-4,4'-dimethoxy benzophenone sulphonic acid (or trade name Uvinul DS49) and 2-phenylbenzimidazole-5-sulphonic acid (or trade name Eusolex 232). For comparison the parent compound benzophenone and the NSAID ketoprofen, a well-known photocleaver, were also studied. Buffered aqueous solutions of the benzophenones were irradiated in the presence of DNA at wavelengths greater than 300 nm with an Osram 500 W/2 high-pressure mercury lamp in conjunction with a 10 mm thick Pyrex filter. The irradiated samples were analysed for DNA cleavage by agarose gel electrophoresis and for DNA binding by fluorescence spectroscopy. The photostability of the UV absorbers was also investigated. In addition, computational studies were conducted to obtain the lowest energy geometrical structures of these UV absorbers and hence determine if intercalation of these UV absorbers with DNA was possible. From the photostability experiments conducted, it is apparent that the benzophenone-based UV absorbers were stable to photodecomposition when irradiated with UV light. They behaved in a manner different from their parent compound benzophenone, and from ketoprofen, where substantial photodegradation occurred upon UV irradiation. This is indicative of the rapid photoreactivity of the benzophenone backbone. The relative photostability of the UV absorbers was not anticipated and was attributed to the substituents present on the benzophenone backbone. The agarose gel electrophoresis experiments however clearly showed that benzophenone, ketoprofen, benzophenone-l, Uvinul DS49 and Eusolex 232 cleave ?X174 DNA when irradiated with UV light at wavelengths greater than 300 nm, while benzophenone-3 and benzophenone-4 did not. For these UV absorbers with the exception of benzophenone-3 and benzophenone-4, the number of single strand breaks in the DNA increased compared to when it was irradiated in their absence. In addition, the supercoiled DNA was converted to the relaxed circular and linear forms, the latter of which was undetected in the absence of the UV absorbers. Binding of benzophenone, ketoprofen, benzophenone-l and Uvinul DS49 to calf thymus DNA was also detected by the fluorescence spectroscopy technique. However, this was not observed for Eusolex 232, benzophenone-3 and benzophenone-4, since they did not compete with ethidium bromide for DNA binding sites. Where DNA cleavage did occur, the mechanism of this interaction had to be determined hence the motivation for the computational studies. From computational studies using PM3 semi- empirical calculations, it was determined that the benzophenone-based UV absorbers investigated, apart from Eusolex 232, displayed non-planar geometrical structures. This indicated that DNA intercalation of these sunscreen agents with DNA would at best be very limited, since only one half of the molecule could possibly interact with the bases of DNA. For benzophenone, ketoprofen, benzophenone-l and Uvinul DS49, photosensitised type I and type II processes involving triplet energy transfer reactions has been identified in literature as being responsible for DNA cleavage. It was determined by ab initio calculations that Eusolex 232 exists in a planar structure unlike the other UV absorbers mentioned above that were non- planar. It was concluded that although Eusolex 232 has the ability to intercalate with the base pairs of DNA, it does not do so, as shown by its lack of binding to calf thymus DNA by the fluorescence spectroscopy study. Literature alludes to photooxidation by singlet oxygen in single stranded DNA via the type II reaction and type I electron transfer reactions in double stranded DNA as the mechanism responsible for DNA cleavage induced by Eusolex 232. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

Cheung, Chi Wai. / "December 2010." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

During mRNA synthesis, pre-mRNAs must be cleaved and polyadenylated at their 3'-end to be fully mature, before being exported from the nucleus. In yeast, there is a large protein machinery comprised of dozens of proteins that work together to perform these two reactions. Some of these proteins are capable of recognizing and binding key sequence elements in the pre-mRNA, effectively directing where in the transcript the cleavage and polyadenylation occur. In this thesis, recently reported structural findings related to the pre-mRNA 3'-end processing machinery are summarized. Within this machinery, the Cleavage Factor IA (CF-IA) complex is comprised of the Rna14, Rna15, and Pcf11 and Clp1 proteins. Results reported here include the crystal structure of the Rna14-Rna15 complex, which indicates that the Rna14 protein forms a dimer that has inherent conformational variability. The Rna15 protein binds to the C-terminal domain of Rna14, and is connected to the Rna14 HAT domain by a flexible linker, which may indicate that Rna15 functions somewhat independently of the Rna14 HAT domain. The complete CF-IA complex is explored in detail, including protein-protein interactions within the complex and the stoichiometric ratios of CF-IA components. Unlike previous reports, results indicate that CF-IA may form a dimer with a 2:2:2:2 stoichiometry of Rna14:Rna15:Clp1:Pcf11. Also reported are projects unrelated to CF-IA, including the crystal structure of the biotin-dependent alpha(6)beta(6) geranyl-CoA carboxylase (GCC) holoenzyme. Comparison of GCC to the closely related 3-methylcrotonyl CoA carboxylase (MCC) holoenzyme reveals a conserved domain swap in the carboxyltransferase (CT) domains of both enzymes. This domain swap is not present in the related biotin-dependent carboxylases propionyl-CoA carboxylase (PCC) and acetyl-CoA carboxylase (ACC), which may indicate a distinct lineage for biotin-dependent carboxylases that target the γ-carbon. In addition, comparison of the two structures also reveals a conserved Phe191 in MCC that is absent in GCC. Phe191 blocks a key substrate-binding pocket and explains the differences in substrate-specificities between MCC and GCC. The role of Phe191 is tested by site-directed mutagenesis to a Glycine to open the pocket in MCC and by mutating a structurally equivalent Glycine to Phe to close the pocket in GCC. These mutations can convert MCC to a GCC and vice versa.