Spin selective MQ-SQ correlation has been demonstrated by either selective pulses in homo-nuclear spin systems in isotropic and weakly orienting chiral media or by nonselective pulses in hetero-nuclear spin systems in strongly aligned media. As a consequence of the spin selective correlation, the coherence transfer pathway from MQ to SQ is spin state selective. This two dimensional approach enables the utilization of the passive couplings (remote couplings) to break a complex one dimensional spectrum into many sub spectra. Each sub spectrum contains fewer transitions and hence fewer couplings (active couplings). The role of the passive couplings is to displace the sub spectra and measurement of the displacements taking into account their relative tilt provides the magnitude of the passive couplings along with relative signs. Further possibility of a spin state selective MQ-SQ resolved experiment to determine very small remote couplings otherwise buried within linewidth in one dimensional spectrum has been demonstrated. The resolution of the multiple quantum spectrum in indirect dimension has also been exploited to separate the sub spectra. The technique renders the analysis of complex spectrum in isotropic system much simpler. The potentialities of the technique have also been demonstrated for discrimination of optical enantiomers and derivation of the residual dipolar couplings from very complicated spectrum. The second order spectrum in strongly aligned media restrict selective excitation, however in hetero-nuclear spin system the nonselective pulses on protons do not interact with the hetero-nuclear spins. Thus the weakly coupled part of a strongly coupled spectrum has been exploited for simplifying the second order spectrum and thereby its analysis. Thus several methodologies derived from spin selective correlation has been demonstrated. Enantiopure spectrum has been recorded from a mixture of R and S enantiomers by a novel pulse scheme called Double Quantum Selective Refocusing Experiment. The dipolar coupled methyl protons in weakly orienting media are utilized. The selective excitation of double quantum coherence reduces the three spin system into a two spin system and remote couplings are refocused which otherwise leads to broadening. The sum of passive couplings being different for the enantiomers resolution in the DQ dimension is enhanced and thereby their discrimination. Finally several decoupling schemes has been compared in the indirect dimension of HSQC experiment to resolve 13C satellite spectra otherwise buried within line width for increased confidence in determining hetero-nuclear framework information.

Les fossiles moléculaires sont de puissants outils pour étudier l'origine, la transformation et le transfert de la matière organique dans les écosystèmes modernes et anciens. Marqueurs d'origine, ils livrent des informations sur le milieu de dépôt, en précisant notamment les sources de la matière organique et la place de leur précurseurs biologiques dans les chaînes alimentaires. De manière surprenante, la découverte de certains fossiles "orphelins" peut conduire à l'identification de nouvelles substances biologiques. L'analyse isotopique de marqueurs végétaux des sols permet d'étudier la dynamique de l'humus au niveau moléculaire. Marqueurs de processus, leur structure et leur composition isotopique révèlent la nature des réactions géochimiques opérant dans les milieux très complexes tels les sols et les sédiments. Marqueurs de maturité, les fossiles moléculaires mesurent l'intensité du stress thermique subi par la matière organique au cours de l'enfouissement dans les sédiments. À cet égard, ils s'avèrent utiles à la fois pour la recherche pétrolière et pour authentifier la présence de contamination pétrolière dans les écosystèmes modernes. Ainsi, le concept de marqueur moléculaire développé en géochimie pétrolière est à la base d'un domaine scientifique en émergence, la géochimie organique environnementale.

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Les produits issus de la biomasse végétale connaissent depuis quelques années un succès grandissant dans de nombreuses industries (aromathérapie, cosmétique, parfums, etc.). L'objectif de notre étude était, d'une part de contribuer au développement des méthodes d'identification et de quantification des constituants des mélanges naturels par RMN 13C et RMN 1H (par exemple le squalène dans l'huile d'olive), et d'autre part, de contribuer à la caractérisation chimique de deux conifères introduits en Corse, le pin d'Alep (huile essentielle) et le cèdre de l'Atlas (huile essentielle, huile pyrolytique et résine). La première partie concerne la quantification du squalène présent dans l'huile d'olive. En effet, ce triterpène linéaire participe à la stabilité oxydative de l'huile d'olive et joue un rôle important dans la réduction des risques de certains cancers. Il s'agissait de mettre au point un protocole expérimental basé sur la RMN 1H ou 13C en utilisant un appareil de routine (9,4 Tesla). La quantification par RMN 13C s'est avérée fiable et elle a été appliquée à la quantification du squalène dans 25 échantillons d'huile d'olive de Corse. La seconde partie de nos travaux concerne la caractérisation chimique de l'huile essentielle de pin d'Alep introduit dans trois stations de Corse (Capo di Feno, Saleccia et Tre Padule de Suartone). L'analyse détaillée de l'huile essentielle de cônes, par combinaison des techniques chromatographiques et spectroscopiques, a permis d'identifier 48 composés. La composition chimique est largement dominée par les monoterpènes (a-pinène et myrcène) et un sesquiterpène oléfinique ((E)-a-caryophyllène). La RMN 13C a permis d'identifier divers diterpènes, dont le 8,12-époxy-14-labdèn-13-ol. Ce composé est décrit pour la première fois dans l'huile essentielle de pin d'Alep. L'analyse de 15 échantillons d'huile essentielle de cônes a mis en évidence trois types de compositions : a-pinène ; myrcène ; a-pinène/myrcène. Enfin, l'analyse de 47 échantillons d'huile essentielle d'aiguilles, associée à un traitement statistique des données (ACP, AFD), a permis de mettre en évidence une variabilité chimique intraspécifique. Ainsi, les échantillons se répartissent en trois groupes selon leur teneur en (E)-a-caryophyllène (groupe I), en E-a-caryophyllène/a-pinène/myrcène (groupe II) et en myrcène (groupe III). La dernière partie a été consacrée à l'étude de Cedrus atlantica. L'analyse détaillée d'une huile essentielle commerciale (du Maroc) a permis d'identifier 20 constituants, les composés majoritaires sont les b-, a- et g-himachalène. Par ailleurs, 7 composés absents de notre bibliothèque de données spectrales ont été identifiés par RMN 13C. Les compositions chimiques des huiles pyrolytiques artisanales du Maroc sont également dominées par les himachalènes et la (E)-a-atlantone. Enfin, nous avons réalisé l'analyse qualitative et quantitative par RMN 13C, sans séparation préalable, de 28 échantillons de résine de C. atlantica récoltés dans les 5 forêts de Corse référencées par l'ONF (Bavella, Bonifato, Ospedale, Pineta et Vizzavona). A côté des acides résiniques, nous avons également identifié 3 lignanes (pinorésinol, laricirésinol et 9-acétate de laricirésinol). Pour l'ensemble de ces composés, nous avons mis en évidence trois types chimiques. Enfin, nous avons mis au point et validé un protocole expérimental de quantification des lignanes par RMN 1H. Discipline : Chimie organique et analytique Mots clés : Analyse des mélanges complexes naturels ; Huiles essentielles ; Huiles pyrolytiques ; Huiles d'olives ; Oléorésines ; RMN 13C ; RMN 1H ; Squalène ; Lignanes ; Olea europaea ; Pinus halepensis ; Cedrus atlantica

Le travail de cette thèse a consisté à concevoir, réaliser et optimiser un montage expérimental de Polarisation Dynamique Nucléaire multi-échantillons pour des applications biomédicales en Imagerie Spectroscopique par Résonance Magnétique. Ce montage est constitué d'un aimant à fort champ magnétique (3,35T), dans lequel se place un système cryogénique à bain d'hélium (He4) liquide pompé pouvant atteindre des températures inférieures à 1,2K. Un ensemble d'inserts permet d'effectuer les différentes étapes du processus PDN dont l'irradiation des échantillons par un champ micro-onde (f=94GHz et P=50mW) et le suivi de leur polarisation par Résonance Magnétique Nucléaire. Ce système permet de polariser jusqu'à trois échantillons, de volume proche de 1mL, à des taux de polarisation de quelques pourcents. Il présente une forte autonomie supérieure à quatre heures, autorisant ainsi la polarisation de molécules à longues constantes de temps de polarisation. La possibilité de disposer quasi-simultanément, après dissolution, de plusieurs échantillons fortement polarisés ouvre la voie à de nouvelles applications dans le domaine de l'imagerie biomédicale / The aim of this thesis work was to design, build and optimize a large volume multisamples DNP (Dynamic Nuclear Polarization) polarizer dedicated to Magnetic Resonance Spectroscopic Imaging applications. The experimental system is made up of a high magnetic field magnet (3,35T) in which takes place a cryogenic system with a pumped bath of liquid helium (4He) allowing temperatures lower than 1,2K. A set of inserts is used for the different steps of DNP : irradiation of the sample by a microwave field (f=94GHz and P=50mW), polarization measurement by Nuclear Magnetic Resonance. . . With this system, up to three samples of 1mL volume can be polarized to a rate of few percents. The system has a long autonomy of four hours, so it can be used for polarizing molecules with a long time constant of polarization. Finally, the possibility to get quasisimultaneously, after dissolution, several samples with a high rate of polarization opens the way of new applications in biomedical imaging

<p>  </p> <p>Organic synthesis is the application of one or more reactions to the preparation of a particular target molecule, and can pertain to a single-step transformation or to a number of sequential chemical steps depicted by a scheme overall. The selection of a reaction or series of reactions while considering chemo-, regio-, and stereoselectivities in addition to protecting group strategies & redox manipulations highlights the complexity in designing & executing a synthetic plan while making a judgement about what is the most effective and efficient plan to synthesize any given chemical compound among numerous available options. To this end, chemical synthesis is the unifying theme of this thesis & was utilized and strategically applied to construct increasingly complex and diverse molecular architectures. </p> <p>Being the precise science that organic chemistry is, this discipline extends into many areas such as technology, biology & medicine, and even into the fine arts since it fosters unparalleled creativity and imagination in its practice. Research foci in chemical synthesis can encompass both the discovery and development of powerful reactions and the invention of strategies for the construction of defined target molecules, natural or man-made, more or less complex. Studies in the former area, synthetic methodology, fuel and enable studies in the latter area, target molecule and total synthesis campaigns, where the latter area offers a testing ground for the former. Consequently, the bulk of this research work is in organic methodology and will be covered in greater depth during chapters 2 and 3 where strategies, optimizations, & analyses are elaborated upon in light of searching & navigating the vast body of chemical literature in an effort to broaden and strengthen one's laboratory expertise as a synthetic chemist. Lastly, chapter 4 focuses not on traditional synthesis but on organic structure analysis relying on various techniques such as nuclear magnetic resonance (NMR), infrared (IR), ultraviolet-visible (UV-Vis) spectroscopy in combination with mass spectrometry (MS) and/or X-ray crystallography to hypothesize and confirm established structures, specifically phenolic oligomers. An ability to use spectroscopic data to evaluate organic structures by combining practical experience with fundamental knowledge will serve as a hallmark skill in one’s ability to problem-solve as an organic chemist.</p>

Soil organic matter (OM) is a complex mixture of compounds, mainly derived from plants and microbes at various states of decay. It is part of the global carbon cycle and is important for maintaining soil quality. OM protection is mainly attributed to its association with minerals. However, clay minerals preferentially sorb specific OM structures, and clay sorption sites become saturated as OM concentrations increase. Therefore, it is important to examine how OM structures influence their association with soil minerals, and to characterize other protection mechanisms. Several techniques, which provide complementary information, were combined to investigate OM composition: Biomarker (lignin phenol, cutin-OH acid, and lipid) analysis, using gas chromatography/mass spectrometry; solid-state 13C nuclear magnetic resonance (NMR) spectroscopy; and an emerging method, solution-state 1H NMR spectroscopy. OM composition of sand-, silt-, clay-size, and light fractions of Canadian soils were compared. It was found that microbial-derived and aliphatic structures accumulated in clay-size fractions, and lignin phenols in silt-size fractions may be protected from further oxidation. Therefore, OM protection through association with minerals may be structure-specific. OM in soils amended with maize leaves, stems, and roots from a biodegradation study were also examined. Over time, lignin phenol composition, and oxidation; and aliphatic structure contribution changed less in soils amended with leaves compared to soils amended with stems and roots. Compared to soils amended with leaves and stems, amendment with roots may have promoted the more efficient formation of microbial-derived OM. Therefore, plant chemistry influenced soil OM turnover. Synthetic OM-clay complexes and soil mineral fractions were used to investigate lignin protection from chemical oxidation. Coating with dodecanoic acid protected lignin from chemical oxidation, and overlying vegetation determined the relative resistance of lignin phenols in clay-size fractions from chemical oxidation. Therefore, additional protection from chemical oxidation may be attributed to OM composition and interactions between OM structures sorbed to clay minerals. Overall, these studies suggest that while association with minerals is important, OM turnover is also influenced by vegetation, and protection through association with clay minerals was modified by OM structure composition. As well, OM-OM interaction is a potential mechanism that protects soil OM from degradation.

科学研究費補助金 研究種目:一般研究(B) 課題番号:06453008 研究代表者:濱 健夫 研究期間:1994-1995年度

Soil organic matter (OM) is a complex mixture of compounds, mainly derived from plants and microbes at various states of decay. It is part of the global carbon cycle and is important for maintaining soil quality. OM protection is mainly attributed to its association with minerals. However, clay minerals preferentially sorb specific OM structures, and clay sorption sites become saturated as OM concentrations increase. Therefore, it is important to examine how OM structures influence their association with soil minerals, and to characterize other protection mechanisms. Several techniques, which provide complementary information, were combined to investigate OM composition: Biomarker (lignin phenol, cutin-OH acid, and lipid) analysis, using gas chromatography/mass spectrometry; solid-state 13C nuclear magnetic resonance (NMR) spectroscopy; and an emerging method, solution-state 1H NMR spectroscopy. OM composition of sand-, silt-, clay-size, and light fractions of Canadian soils were compared. It was found that microbial-derived and aliphatic structures accumulated in clay-size fractions, and lignin phenols in silt-size fractions may be protected from further oxidation. Therefore, OM protection through association with minerals may be structure-specific. OM in soils amended with maize leaves, stems, and roots from a biodegradation study were also examined. Over time, lignin phenol composition, and oxidation; and aliphatic structure contribution changed less in soils amended with leaves compared to soils amended with stems and roots. Compared to soils amended with leaves and stems, amendment with roots may have promoted the more efficient formation of microbial-derived OM. Therefore, plant chemistry influenced soil OM turnover. Synthetic OM-clay complexes and soil mineral fractions were used to investigate lignin protection from chemical oxidation. Coating with dodecanoic acid protected lignin from chemical oxidation, and overlying vegetation determined the relative resistance of lignin phenols in clay-size fractions from chemical oxidation. Therefore, additional protection from chemical oxidation may be attributed to OM composition and interactions between OM structures sorbed to clay minerals. Overall, these studies suggest that while association with minerals is important, OM turnover is also influenced by vegetation, and protection through association with clay minerals was modified by OM structure composition. As well, OM-OM interaction is a potential mechanism that protects soil OM from degradation.