Polyarene dendrimers with rigid aromatic regions are of interest due to their shape persistent nature. A novel series of G1 dendrimers containing a substituted 1,3-phenyl core are reported and were found to exhibit atropisomerism. This was investigated in the solid state (X ray), in solution (NMR), and via computational studies. The synthesis of fluorinated G1 dendrimers allowed for the analysis of interconversion between conformations via 19F-19F EXSY NMR (exchange spectroscopy). These were shown to exist as two distinct sets of three interconverting atropisomers. Each atropisomer was identified as well as their respective interconversion pathway. By increasing the size of the core of the G1 dendrimers resulted in physical separation of atropisomers by preparative HPLC. Results suggest certain conformers are energetically unfavourable reducing the total number of atropisomers observed.

This dissertation explores fundamental aspects of the reaction of group 4 metallocenes with methylaluminoxane (MAO) that lead to active Ziegler-Natta olefin polymerization catalysts. A novel experimental approach is described, in which a unique spectroscopic probe (a fluorinated substituent) is attached to the metallocene ancillary ligands and the metallocene/MAO mixtures are analyzed using 19F NMR spectroscopy. Group 4 metallocene dimethides bearing pentafluorophenyl (C6F5) substituents were synthesized and treated with MAO in benzene-d6. 19F NMR spectroscopic analysis demonstrated reversible methide transfer to form "cation-like" methylmetallocenium methylaluminates. A series of quantitative titration studies showed that fewer than 10% of the aluminum centers in MAO actually participate in the methide transfer process. A systematic study of metallocene substituent effects suggested that MAO contains active centers of extremely high but varying Lewis acidity. Activation of group 4 metallocene dichlorides using MAO was also analyzed using 19F NMR. Initial Cl/CH3 exchange was followed by Cl transfer to aluminum, whereas "normal" subsequent transfer of CH3 from Al to the methylmetallocenium cation was apparently inhibited by the abstracted chloride. Additional studies showed that the 19F NMR probe is sensitive to the interactions of Zr-Cl bonds with simple alkylaluminum species such as Me3Al, Me2AlCl, MeAlCl2, and Et3Al. However, the method was arguably less useful than 1H NMR spectroscopy in following the metathesis of Zr-Cl and Al-R (R = Me, Et) bonds. New methods of preparing methylhalometallocenes were investigated. The reactions of eleven metallocene dimethyls with triphenylmethyl chloride were highly selective (> 95%) with the five most electron-deficient metallocenes studied. Two other examples showed good selectivity on an NMR scale but could not be isolated from the 1,1,1-triphenylethane byproduct. Reactions of dimethylmetallocenes with benzyl bromide were also selective for formation of the corresponding methylbromo-metallocenes, however the reactions were too slow to be of practical value. The observation of long initation periods and the analysis of organic byproduct distributions suggested that these halogenation reactions may proceed by a radical chain mechanism rather than simple sigma bond metathesis. To demonstrate "proof of concept" in the use of 19F NMR to analyze the reactions of paramagnetic metallocenes, the coordination of CO and CN- to C6F5-substituted chromocenes were analyzed. Whereas CO coordinates readily to chromocene, cyanide coordinates effectively to 1,1'-bis(pentafluorophenyl)chromocene. This observation is interpreted in terms of the electron-withdrawing effect of the C6F5 substituent, which should strengthen bonding to sigma-donor ligands (CN-) and weaken bonding to pi-acceptors (CO). / Ph. D.

Design and characterization of tissue engineered substitutes rely on robust monitoring techniques that provide information regarding viability and function when exposed to various environmental conditions. In vitro studies permit the direct monitoring of cellular and construct changes because these substitutes remain accessible. However, upon in vivo implantation, changes in cell viability and function are often detected using indirect or invasive methods that make assessing temporal changes challenging. . Thus, the development of non-invasive monitoring modalities may facilitate improved tissue substitute design and, ultimately, clinical outcome. The overall objective of this thesis was to establish a method to monitor and track cells and the cellular environment within a tissue engineered substitute in vitro and in vivo. This was accomplished via 31P NMR spectroscopy and through the incorporation of perfluorocarbon (PFC) emulsions for the monitoring of DO concentration by 19F NMR spectroscopy. The first aim of this thesis was to develop a method that tracked the state of cells and of the cellular environment within alginate constructs during perfusion studies in which the perfusing medium DO concentrations were changed over time or cells were exposed to a cytotoxic antibiotic. Due to challenges in acquiring DO concentration gradient information within beads, a second aim was to develop a mathematical model that would calculate gradients from experimentally acquired volume averaged DO concentrations; thus, significantly enhancing the robustness of tracking the alginate beads. Lastly, since the PFC emulsions used in the study may affect cell viability and function, a third aim was to characterize, experimentally and via modeling, the effect of several PFC emulsion concentrations on the encapsulated and #946;TC-tet cells.

Calmodulin (CaM) is a ubiquitous calcium sensor protein which binds and activates a variety of enzymes involved in cell signaling pathways. In its calcium loaded state, CaM is extremely resistant to heat denaturation, with a melting temperature (Tm) of around 115°C. In this study, Xenopus laevis CaM was prepared such that the eight phenylalanine residues were substituted with 3-fluorophenylalanine. 19F NMR studies then focused on properties of the hydrophobic core associated with the folding process at temperatures near the regime where the protein is completely folded. Near 70°C, near-UV circular dichroism and 1H NMR-based measurements of protein diffusion rates reveal the onset of a stable, expanded near-native folding intermediate. 19F NMR solvent isotope shifts reveal a gradual loss of water from the hydrophobic core with increasing temperature, until the point at which the near-native intermediate state is attained. At this point, water is observed to enter the hydrophobic core and destabilize the protein. Paramagnetic shifts from dissolved oxygen reveal an increase in oxygen accessibility with temperature until the near-native intermediate is reached, whereupon oxygen solubility decreases. Taken together, we conclude that hydrophobicity of the protein interior increases with temperature, until a dry near-native state is established, whereupon water cooperatively enters and destabilizes the hydrophobic core. 19F CPMG experiments provide a measure of the interconversion between the folded state and the dry near-native intermediate; at higher temperatures, folding rates are on the order of 10,000 Hz. Moreover, as temperature is lowered, folding rates increase, presumably because the effect of off-pathway misfolding events on the exchange process is diminished.

Calmodulin (CaM) is a ubiquitous calcium sensor protein which binds and activates a variety of enzymes involved in cell signaling pathways. In its calcium loaded state, CaM is extremely resistant to heat denaturation, with a melting temperature (Tm) of around 115°C. In this study, Xenopus laevis CaM was prepared such that the eight phenylalanine residues were substituted with 3-fluorophenylalanine. 19F NMR studies then focused on properties of the hydrophobic core associated with the folding process at temperatures near the regime where the protein is completely folded. Near 70°C, near-UV circular dichroism and 1H NMR-based measurements of protein diffusion rates reveal the onset of a stable, expanded near-native folding intermediate. 19F NMR solvent isotope shifts reveal a gradual loss of water from the hydrophobic core with increasing temperature, until the point at which the near-native intermediate state is attained. At this point, water is observed to enter the hydrophobic core and destabilize the protein. Paramagnetic shifts from dissolved oxygen reveal an increase in oxygen accessibility with temperature until the near-native intermediate is reached, whereupon oxygen solubility decreases. Taken together, we conclude that hydrophobicity of the protein interior increases with temperature, until a dry near-native state is established, whereupon water cooperatively enters and destabilizes the hydrophobic core. 19F CPMG experiments provide a measure of the interconversion between the folded state and the dry near-native intermediate; at higher temperatures, folding rates are on the order of 10,000 Hz. Moreover, as temperature is lowered, folding rates increase, presumably because the effect of off-pathway misfolding events on the exchange process is diminished.

The structure, kinetics, and interactions of the conserved 16mer and 15mer RNA motifs of the internal ribosome entry site (IRES) of the Foot-and-Mouth Disease virus (FMDV), have been investigated by homonuclear and heteronuclear NMR techniques. The 16mer RNA is endowed with a classic GNRA tetraloop motif, which is essential for IRES activity and the 15mer RNA motif is a potential tetraloop receptor. We have determined three high resolution NMR solution structures of the 16mer apo-RNA, the 16mer Mg2+ RNA complex and the 15mer apo-RNA with RMSDs of 0.17Å, 0.16Å and 0.35Å, respectively. The high precision of these NMR structures was achieved by including a large number of NMR experimental restraints, derived from NOEs and coupling constants, and validating them using the MolProbity program. The 16mer RNA structure comprised of six base pairs with a GUAA tetraloop and the 15mer RNA structure comprised of four base pairs and a large heptaloop; this is the first heptaloop to be studied by NMR.Addition of Mg2+ to the 16mer apo-RNA caused selective chemical shift changes to the stem G177 and loop G178 imino proton resonances, suggesting Mg2+-induced conformational change to the GUAA tetraloop. This was supported by a significant chemical shift change to the selectively 19F-labelled loop U179 in the 5-FU 16mer RNA. Furthermore, variable temperature experiments revealed retarded imino proton exchange for the stem and loop imino protons, demonstrating the enhanced thermodynamic stability conferred by Mg2+. This enhancement in stability was confirmed by measuring the imino proton exchange rates for the 16mer apo-RNA and the 16mer Mg2+ RNA complex. Analysis of the 16mer apo-RNA and its Mg2+ RNA complex NMR solution structures revealed that Mg2+-induced structural changes to the GUAA tetraloop act to stabilise the loop via stronger base stacking and intramolecular interactions. Fascinatingly, we discovered that Mg2+ ions provide increased stability required for the formation of a G.A sheared base pair in the GUAA tetraloop. RNA-RNA interactions between the 16mer and 15mer RNAs and their fluorinated analogues were studied by NMR spectroscopy. Small changes to chemical shift and linewidth of proton peaks in the non-fluorinated RNA-RNA complex provided evidence for a weak interaction between the loop of the 16mer RNA and the stem of the 15mer RNA. 19F-NMR experiments revealed additional peaks for the 19F-labelled U179 of the fluorinated 16mer/15mer RNA complex providing further good evidence of RNA-RNA interaction. The NMR structures of the conserved RNA motifs and their interactions have yielded important information in understanding the properties and behaviour of RNA. This will provide the first stepping stone in understanding the IRES mechanism and its use in antiviral therapy and biotechnology.

C-H bonds are easily the most common type of ordinary chemical bond and studying carbon acidity will help us understand and predict the reactivity of organic compounds. Carbon acidities are ranked using acidity scales. One of the most prominent is the Streitwieser Lithium Indicator (SLI) scale. The term "indicator scale" implies that acids have been measured against one another in sequential fashion. The SLI scale uses lithium ion as the conjugate-base counterion and THF as the solvent. Historically, the SLI scale has emphasized the characterization of weakly-acidic hydrocarbons. Prior to the work of our group, the strongest acid on the SLI scale has a pK value of about 10. Deck and Thornberry extended the scale to ca. pK = 0 by evaluating 23 perfluoroaryl-substituted cyclopentadiene and indene derivatives, using 19F NMR spectroscopy to determine the equilibrium constants of sequential acid-base reactions. This thesis describes the further extension of the SLI scale to ca. pK = −6. To achieve this result, a set of 11 tetrasubstituted cyclopentadienes were synthesized and their acidities evaluated sequentially with the goal of reaching a low pK value while minimizing the acidity ratio at each incremental step. The four ring substituents were combinations of pentafluorophenyl, perfluoro-4-tolyl, and perfluoro-4-pyridyl, electronegative groups listed in order of increasing electron-withdrawing power. The most acidic compound in the set was 1-pentafluorophenyl-2,3,4-tetrakis(tetrafluoro-4-pyridyl)cyclopentadiene, having pK = −5.99. Trends in the acidities of tetraarylcyclopentadienes are discussed including relative electron-withdrawing power of the three selected substituents, and conformational effects among pairs of regioisomeric cyclopentadiene derivatives. / Master of Science / Carbon acidity refers to the willingness of a carbon-hydrogen bond to release a hydrogen ion. C-H bonds are easily the most common type of ordinary chemical bond, so it makes sense that studying carbon acidity will help us understand and predict the reactivity of organic compounds. For the past several decades, emphasis in this area of research has focused on weak carbon acids, especially the simplest hydrocarbons like benzene and methane. This thesis aims in the opposite direction of synthesizing and measuring stronger and stronger carbon acids until we reach the theoretical limit for a given solvent. Because our research strategy is inherently incremental, compounds were synthesized and their acidities were measured, drawing close to the theoretical limit using tetrahydrofuran as the solvent.

Le phénomène de résistance des bactéries à Gram négatif aux antibiotiques est aujourd’hui un problème sanitaire mondial majeur. La production de β-lactamases, et plus particulièrement de carbapénémases, enzymes capables d’hydrolyser la plupart des agents antibactériens de la classe des β-lactames, est le mécanisme de résistance le plus répandu. Dans ce mémoire, nous décrivons la conception et la synthèse de nouveaux inhibiteurs fluorés de carbapénémases. Notre objectif a été la synthèse de monobactames trifluorométhylés en position C4.Nous avons développé une nouvelle voie de synthèse diastéréosélective par expansion de cycle d’aziridines pour l’accès à des 3-bromo-4-CF3-azétidin-2-ones. Ces composés ont été fonctionnalisés par substitution nucléophile, réactions radicalaires et organométalliques en position C3. Dans une seconde partie, des essais de cyclisation de β-hydroxyaminoesters et acides ainsi que de β-hydroxy-hydroxamates ont été entrepris. Pour obtenir ces intermédiaires β-hydroxyaminoesters et acides, nous avons étudié la réactivité des hydroxylamines sur des accepteurs de Michael trifluorométhylés.Enfin, l’évaluation biologique des composés a été réalisée par des tests enzymatiques en suivi par spectroscopie UV. L’évaluation par RMN 19F a également été entreprise, et a permis le développement d’outil de diagnostique et de screening, toujours en cours d’optimisation. / Multidrug resistant gram-negative pathogens are emerging worldwide. β-lactamases production, especially carbapenemases, enzymes with broad hydrolytic capabilities towards β-lactams, is a global spread mechanism of resistance among gram-negative bacteria. We report here the design and the synthesis of new fluorinated inhibitors of carbapenemases. Our aim was to synthesize trifluoromethylated monobactams in C4 position. We have developed a new diastereoselective pathway by ring expansion of aziridines to access to 3-bromo-4-CF3-azetidin-2-ones. These compounds have been successfully functionalized in C3 position via nucleophilic substitution, radical and organometallic reactions.In a second part, cyclisation attempts of β-hydroxyaminoesters and acids, as well as β-hydroxy-hydroxamates have been conducted. A study of Michael addition of hydroxylamines on trifluoromethylated Michael acceptors have been achieved in order to obtain the β-hydroxyaminoesters and acids derivatives.Finally, biological evaluations of synthesized compounds have been realized through enzymatic tests. 19F NMR evaluation have been accomplished and led to development of diagnostic and screening tools, and it is still in under optimisation.

Ce travail porte sur la synthèse et la caractérisation de fluorures divisés obtenus par voiesolvothermale assistée par chauffage micro-ondes pour la réduction des impuretés dans lecycle du combustible nucléaire. / This work deals with the synthesis and characterization of divided fluorides obtained bysolvothermal process assisted by microwave heating to reduce impurities in the nuclear fuelcycle.

A unique characteristic of NMR is that, unlike other spectroscopic techniques, it separates the excitation of signals from their detection. By manipulating the type of signal excitation used, the chemical information content of a spectrum can be controlled. This versatility has made NMR a powerful and flexible weapon in the analytical arsenal of chemists, not only for the determination of structural, chemical, dynamic, and physical properties of molecules, but also for the analysis of mixtures, since NMR has the ability to study these intact without the need for physical separation. Chapter 1 contains an introduction to the theoretical NMR background necessary for this thesis. Chapter 2, 3 and 6 detail the development of new methods that suppress 13C satellites not only in conventional 1D 1H and 19F spectra, but also in 1H DOSY spectra, and can facilitate the analysis of minor components in high dynamic range mixtures (i.e. those with a wide range of concentrations). Chapter 4 introduces a new experiment which suppresses low-level artefacts in pure shift NMR, and gives clean pure shift spectra that can be used for the detection of minor components in the presence of strong signals. Chapter 5 and 7 illustrate how 19F NMR can be exploited for the acquisition of simplified proton spectra associated with a given 19F chemical shift, or for the virtual separation of mixture components using broadband 19F DOSY. Chapter 8 summarises the conclusions extracted from the research introduced in the main body of this thesis, and gives suggestions for future developments. Chapters 2, 3, 4, 5, and 7 contain published research articles and their Supporting Information and are presented without modification. Chapter 6 is presented as a manuscript intended for publication.