La triade non-catalytique est un motif strictement conservé des alpha-amylases chlorure-dépendentes qui est parfaitement superposable avec la triade catalytique des protéases à sérine active. Le but de ce travail était de déterminer le rôle de cette triade. Par des expériences de mutagenèse, nous avons pu montrer que ce rôle est de nature structurale. Des expériences de RMN nous ont permis de démontrer la présence d'un pont H anormalement fort dans ces enzymes, ce qui pourrait expliquer l'instabilité très marquée des mutants de la triade. Malheureusement, nous n'avons pas pu attribuer sans ambiguité ce pont H à la triade non-catalytique. La dernière partie de ce travail décrit la recherche de la triade non-catalytique dans des protéines autres que les amylases.

The Thesis describes (i) the development of add-on instrumentation extending the capabilities of conventional NMR spectrometers and (ii) the application of the designed equipments and techniques for investigating various colloidal systems. The new equipments are: Novel designs of stopped-flow and temperature–jump inserts intended for conventional Bruker wide-bore superconductive magnets. Both inserts are loaded directly from above into the probe space and can be used together with any 10 mm NMR probe with no need for any auxiliary instruments. A set of 5 mm and 10 mm 1H – 19F – 2H NMR probes designed for heteronuclear 1H – 19F cross-relaxation experiments in Bruker DMX 200, AMX 300 and DMX 500 spectrometers, respectively. A two–stage low-pass filter intended for suppressing RF noise in electrophoretic NMR experiments. The kinetics of micellar dissolution and transformation in aqueous solutions of sodium perfluorooctanoate (NaPFO) is investigated using the stopped-flow NMR instrument. The sensitivity of NMR as detection tool for kinetic processes in micellar solutions is clarified and possible artefacts are analysed. In the NaPFO system, the micellar dissolution is found to proceed faster than 100 ms while surfactant precipitation occurs on the time scale of seconds-to-minutes. The kinetics of the coil-to–globule transition and intermolecular aggregation in a poly (Nisopropylacrylamide) solution are investigated by the temperature-jump NMR instrument. As revealed by the time evolution of the 1H spectrum, the T2 relaxation time and the self-diffusion coefficient D, large (>10 nm) and compact aggregates form in less than 1 second upon fast temperature increase and dissolve in less than 3 seconds upon fast temperature decrease. The intermolecular 1H – 19F dipole-dipole cross-relaxation between the solvent and solute molecules, whose fast rotational diffusion is in the extreme narrowing limit, is investigated. The solutes are perfluorooctanoate ions either in monomeric or in micellar form and trifluoroacetic acid and the solvent is water. The obtained cross-relaxation rates are frequency-dependent which clearly proves that there is no extreme narrowing regime for intermolecular dipole-dipole relaxation. The data provide strong constraints for the dynamic retardation of solvent by the solute. / QC 20100929

The ultimate goal of organic chemistry is understanding the processes involved in carbon-carbon bond formation. Metalated nitriles are perfectly suited for the regio- and stereospecific creation of sterically congested quaternary centers. These traits are dependent on the metal and the metal's preference for coordination to either the nitrile nitrogen lone pair of electrons or the electron pair of the "anionic" carbon bearing the nitrile. This thesis outlines the structural differences in solution between lithiated, cuprated, and magnesiated nitriles, providing the first such study of magnesiated nitriles. Nuclear magnetic resonance, which has become a powerful tool for a wide variety of structural elucidation, indicates both C- and N- binding modes for magnesium with a high dependence on other functionality present within the nitrile substrate. Carbon-carbon bond formation by the attack of a magnesiated nitrile on an alkene is highly unusual. An intramolecular carbo-magnesiation was serendipitously discovered that involves attack on a terminal alkene followed by addition to the nitrile to give a cyclobutanone. Microwave heating greatly enhances the carbometalation process although the carbometalation has only been achieved in two closely related substrates. Insight into the mechanism was obtained although the reaction scope has not yet been extended to other substrates. / Bayer School of Natural and Environmental Sciences; / Chemistry and Biochemistry / MS; / Thesis;

Deuterium (2H) and Nitrogen 14 (14N) NMR spectroscopy were used to investigate the molecular dynamics in one thermotropic and one lyotropic liquid crystal. Quantitative analyses of deuterium spectral densities of motion for three deuteron sites (ring and C-alpha) at two different Larmor frequencies (46 and 61.4MHz) are reported in the smectic A and C* phases of (S)-[4-(2-methylbutyl)phenyl]-4’-octylbiphenyl carboxylate (8BEF5-d15), a partially deuterated smectogen. 2H spectral densities for two deuteron sites on the chain (C1 and C2/C3) at Larmor frequency 61.4MHz and 14N spectral densities for the head group (NH4+) of the molecule decylammonium chloride (DACl) at 28.9MHz are reported in the lamellar phase of a partially deuterated sample, DACl-d11/H2O binary system. The motional model is the small step rotational diffusion for reorientations plus internal rotations in the strong collision limit. In the chiral C* phase of the first molecule, 8BEF5-d15, the helical axes are aligned along the external magnetic field and the deuteron spins appear to relax in a macroscopically uniaxial environment. After including the molecular tilt, the reorientation processes in the SmC* phase are found to have higher activation energies than those in the smectic A phase. Applying the same motional models to the lyotropic molecule DACl-d11, the tumbling motion of the long axis of the molecule in the aggregates is more rigorous in comparison to the molecular spinning motion. The similarity of deuterium spectral densities from the C1 and C2/C3 sites may indicate a relatively rigid unit of C1-C2-C3-C4 in the backbone. / February 2005

Quantum information processing is a multi-disciplinary science involving physics, mathematics, computer science, and even quantum chemistry. It is centred around the idea of manipulating physical systems at the quantum level, either for simulation of physical systems, or numerical computation. Although it has been known for almost a decade that a quantum computer would enable the solution of problems deemed infeasible classically, constructing one has been beyond today's capabilities. In this work we explore one proposed implementation of a quantum computer: Nuclear Magnetic Resonance (NMR) spectroscopy. We also develop a numerical software tool, a pulse sequence compiler, for use in the implementation of quantum computer programs on an NMR quantum computer. Our pulse sequence compiler takes as input the specifications of the molecule used as a quantum register, the desired quantum gate, and experimental data on the actual effects of RF pulses on a sample of the molecule, and outputs an optimum set of pre and post 'virtual' gates that minimize the error induced.

Quantum information processing is a multi-disciplinary science involving physics, mathematics, computer science, and even quantum chemistry. It is centred around the idea of manipulating physical systems at the quantum level, either for simulation of physical systems, or numerical computation. Although it has been known for almost a decade that a quantum computer would enable the solution of problems deemed infeasible classically, constructing one has been beyond today's capabilities. In this work we explore one proposed implementation of a quantum computer: Nuclear Magnetic Resonance (NMR) spectroscopy. We also develop a numerical software tool, a pulse sequence compiler, for use in the implementation of quantum computer programs on an NMR quantum computer. Our pulse sequence compiler takes as input the specifications of the molecule used as a quantum register, the desired quantum gate, and experimental data on the actual effects of RF pulses on a sample of the molecule, and outputs an optimum set of pre and post 'virtual' gates that minimize the error induced.

Although extensive literature exists on NMR of water in MCM-41, the origin of a number of NMR spectral features in this material had not been understood. Specifically, the OH proton resonance observed in the dry material disappears completely as it is hydrated to 0.2 mono-layer hydration level. The purpose of this study was to gain insight into the physical basics for these spectral features and in the process broaden our understanding of behaviour/interactions of water molecules in porous material. First, measurements of MAS spectra as a function of temperature and hydration, at very low hydrations, made possible a definitive spectral peak assignment. Second, using 1D and 2D selective inversion recovery and magnetization exchange experiments, as well as MAS and non-MAS techniques, magnetization exchange between the water protons and surface OH group protons was quantified. The present results lead to the conclusion that chemical exchange is not responsible for producing the observed changes in proton spectra in MCM-41 as this material is hydrated up to the 0.2 mono-layer hydration level. This represents an important result as it is at odds with what is assumed in the literature in this connection and means that previous conclusions about hydration dynamics in this material need to be revisited. A dynamics model of water interaction with the surface OH hydration sites was introduced to explain the observed proton spectra. The model can successfully predict the observed chemical shifts and temperature dependent changes of proton spectra in the very low hydration MCM-41.

Quantum information processors have the ability to drastically change our world. By manipulating bits of information ruled by the laws of quantum mechanics, computational devices can perform some computations that are classically intractable. Most quantum algorithms rely on pure qubits as inputs and require entanglement throughout the computation. In this thesis, we explore a model of computation that uses mixed qubits without entanglement known as DQC1 (deterministic quantum computation with one quantum bit), using the physical system of liquid-state Nuclear Magnetic Resonance (NMR). Throughout our research, we experimentally implement an algorithm that completely encapsulates the DQC1 model, and take a close look at the quantum nature of DQC1-states as given by the quantum discord and geometric quantum discord, which are measures of non-classicality that capture correlations weaker than those measured by entanglement. We experimentally detect and quantify these correlations in an NMR DQC1 quantum information processor.

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Use of hydrogen bonding as internuclear connecting information to better determine molecular structure or dynamics.