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Etude de la dégradation photochimique de matières actives agrochimiques et de l'inhibition de ce phénomène de photodégradation / Study of the photochemical degradation of agrochemical active matters and of the inhibition of this phenomena of photodegradationFréneau, Maxime 16 December 2015 (has links)
Certains pesticides présentent une très bonne activité biologique en serre, lorsqu’ils sont protégés du rayonnement UV, mais pas en champs lorsqu’ils sont exposés à la totalité de la lumière solaire. Une dégradation photochimique par le rayonnement UV est alors suspectée. C’est le cas de la famille de fongicides contenant un groupement oxime dont nous avons étudié en détail la photodégradation d’un point de vue expérimental et théorique. La cinétique de phototransformation de ces fongicides a été mesurée en solution et en phase solide et les photoproduits de réaction ont été identifiés et quantifiés. L’ensemble des résultats nous a alors permis de proposer un mécanisme de photodégradation. Ces fongicides subissent à la fois une photoisomérisation et une photodégradation par rupture homolytique de la liaison oxime. Le rôle de certains éléments structuraux dans ces transformations a pu être établi grâce à plusieurs analogues. Une étude de modélisation moléculaire menée en parallèle a permis de déterminer la nature des voies réactionnelles mises en jeu après l’excitation de la molécule et ainsi d’expliquer les observations expérimentales. Ce travail avait pour objectif d’améliorer la photostabilité de cette famille de fongicides par des modifications structurales tout en respectant l’activité biologique par ailleurs tout à fait remarquable de ces composés. Le remplacement de l’oxime par un oxétane préparé par une réaction de Paternò-Büchi a été envisagé. / Some pesticides present a great biological activity in green house, while they are protected from UV radiations, but not in the field, while they are exposed to the whole spectrum of solar light. A photochemical degradation by UV light is then suspected. That is the case of the group of fungicides which contain an oxim moiety and that we studied the photodegradation in detail, both from experimental and theoretical points of view. The kinetics of phototransformation of these fungicides have been mesured in solution and in the solid phase and photoproducts have been identified and quantified. These results allowed us to propose a mecanism of photodegradation. These fungicides undergo simultanously a photoisomerisation and a photodegradation by a homolytic cleavage of the oxim bond. The role of some structural elements in these transformations has been set up thanks to several analogues. A parallel study of molecular modelisation allowed the determination of the nature of reactive paths followed after the excitation of the molecule and therefore the explanation of experimental observations. The objective of this work was to improve the photostability of this group of fungicides by structural modifications while keeping the remarquable biological activity of these compounds. The replacement of the oxim moiety by an oxetane prepared by a Paternò-Büchi reaction has been considered.
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Utilization of Mass Spectrometry to Characterize, Image, and Quantify Small MoleculesHilary Brown (8081510) 04 December 2019 (has links)
Ambient ionization techniques, such as nanoDESI and nanoESI, allow for the direct analysis of complex samples under atmospheric pressure with no sample pretreatment. These ionization techniques are utilized for a variety of applications, including lipidomics, online reactions and imaging of small molecules. Nanoelectrospray ionization (nanoESI) is an ionization technique that is similar to electrospray ionization (ESI) but uses smaller sample volumes. NanoESI can be used for complex biological sample analysis and when coupled with online photochemical reactions, such as the Paternò-Büchi (PB) reaction, structural information about lipids can be determined. Likewise, nanoDESI is another ambient ionization technique that employs the ESI mechanism but incorporates online liquid extraction of analytes. This technique is easily incorporated to mass spectrometry imaging (MSI) to provide spatial localization of biomolecules in tissues. Additionally, nanoDESI allows for tunable solvent extraction and online derivatization reactions. These techniques were used to determine structural information of neutral lipids, to image lipids from different developmental stages of lung tissue, and to image and quantify small molecule drugs and metabolites in tissue.
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Incorporation of the Paternò–Büchi reaction into mass spectrometry-based systems for lipid structural characterizationElissia T Franklin (8087996) 10 December 2019 (has links)
<p>Lipids are important cellular
biomolecules that perform essential functional and biological roles. For
instance, lipids in the cell are the compartmentalizer for the cytoplasm and an
energy storage unit. The knowledge surrounding lipids is abundant, yet there is
still so much to uncover. There are many categories of lipids and within each
category the structural composition is extremely diverse. In turn, the dramatic
structural complexity of lipids demands analytical methods capable of providing
in-depth structural characterization of individual molecular structures. However,
lipid structural elucidation has remained challenging, namely due to the
presence of isomeric and isobaric species with a complex mixture. In
particular, isomeric/isobaric lipid structures arise from variations in class,
headgroup, fatty acyl chain, <i>sn</i>-position,
and/or carbon-carbon double bond (C=C) position(s). Recently, recent research
suggests C=C composition impacts lipid physical properties, metabolic fate, and
intermolecular interactions. Thus, analytical strategies capable of localizing
sites of unsaturation are of interest in the lipidomics community.</p>
<p>Mass spectrometry (MS) is a
leading tool for lipid analysis. Electrospray ionization (ESI), a soft
ionization method, is the most commonly used method for lipid ionization as a
means of taking the ions from liquid-phase to gas-phase without extensive decomposition
of the species. Utilizing ESI-MS, lipids can be identified at a sum
compositional level via accurate mass measurements. . With tandem mass
spectrometers, lipid ions can be further probed, utilizing tandem-MS (MS/MS) to
generate structurally informative product ion spectra that facilitate the
assignment of lipid molecular structure. More so, gas-phase ion/ion reactions
represent a unique MS-based technique that has improved the analysis of lipids
structures. Gas-phase ion/ion reactions allow for lipid species to be charge
inverted from one polarity to the opposite polarity. This reaction enables
lipids to be ionized in a polarity that is optimal for class identification and
further investigated in the opposite polarity where more structural information
is obtained. All the information provided is captured without the requirement
of multiple solution conditions which is necessary when analyzing in both
polarities. In the case of charge inverted lipids from positive ion mode to
negative ion mode, fatty acyl composition can be obtained; however, C=C
information is lacking.</p>
<p>MS can also be paired with other
analytically technologies to assist with lipid analysis. One of those
technologies is liquid chromatography (LC), which allows for the separation of
lipids based on different characteristic depending on the column type being
used. Reverse-phase LC (RPLC) allows for the separation of lipid molecular
species based on structural composition. RPLC-MS/MS benefits from the ability
to separate lipids and determine their fatty acyl chain composition but it is
difficult to specify C=C location with the use of a synthetic standard that is
identical to each molecular species being analyzed.</p>
<p>Commonality between the
gas-phase ion/ion reactions for charge inversion of lipids and RPLC-MS/MS
approaches is the inability to provide C=C coverage. In-solution and unique ion
activation techniques have been developed for seeking such information. The
Paternò–Büchi reaction is a UV-initiated [2 + 2]-cycloaddition of an excited carbonyl
containing compound onto an olefin group. This reaction can be initiated onto
the alkene group within an unsaturated lipid aliphatic chain to form an oxetane
ring modification. There are two product ions that can be formed upon each
unsaturation site due to a lack of regioselectivity the reagent can attach at
either side of the C=C. The modified lipids can be taken into gas-phase and
collisionally activated via low-energy collision induced dissociation,
generating product ions indictive of C=C position(s). The work herein shows the
incorporation of the PB reaction into the gas-phases ion/ion reaction and
RPLC-MS/MS apparatuses for C=C localization. The methods have been applied to
the lipid extracts of bovine liver and human plasma for confident molecule
species determination.</p>
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