Identification of polysaccharides is not a straightforward task due to the high degree of stereochemistry present in their isobaric monomers. Their isobaric nature causes traditional mass spectrometry to fall short when trying to differentiate not only the conformation of the monomers but the position of the glycosidic bonds that bind them. This structural information is important for biochemists as they study the role of different glycans in biological processes. Tandem mass spectrometry (MS/MS) allows the study of the fragment ions formed during collision induced dissociation (CID), the fragments formed depend on the structure and stability of the precursor molecule and can be used to identify the compounds. These fragmentation pathways will be as complex as the species that form them. To date, typical saccharide fragments are separated into three groups that represent the major fragments: Cross-ring cleavages (A/X), and those resulting from cleaving different sides of the glycosidic bond (B/Y) and (C/Z). Ion mobility separation (IMS) has shown to have some success at discerning polysaccharide conformers and those of other biopolymers such as proteins and polynucleotides. Ion mobility separates gas-phase ions by colliding them with non-reactive gases and relating respective increase in flight time to their collision cross-section (CCS). In this study, the relative energetics of the first steps of the cross-ring cleavage and both glycosidic bond cleavage channels for isomaltotriose [glc(α1-6)glc(α1-6)glc] as well as a minor water loss channel were explored using density functional theory (DFT) calculations at the B3LYP/6-31+g(d) level of theory. It was demonstrated that charge-remote mechanisms are a viable alternative to charge-directed mechanisms when under the high energy short time scale conditions present during an ESI-MS/MS experiment. To verify the efficiency of ion mobility for isomeric separation, the relative experimental CCS of isomaltotriose [glc(α1-6)glc(α1-6)glc], maltotriose [glc(α1-4)glc(α1-4)glc], panose [glc(α1-6)glc(α1-4)glc] and raffinose [gal(α1-6)glc(α1-2)fru] were determined by comparison with literature CCS values for dextran, a variable-length oligomer of α1-6 linked glucose was used as an external calibrant. The experimental CCS of the precursor ions were compared to literature values when available as well as the calculated effective values of the optimized DFT geometries using the trajectory method of the MOBCAL computational suite. As phosphate is often used as an adducting agent to increase the intensity of the precursor ion when running an IMS experiment, the effect of its presence on the fragmentation of isomaltotriose and large isomaltooligosaccharides was studied. It was seen that depending on the location of the phosphate ion, it will preferentially dissociate leaving behind a neutral glycan. This explains the low abundance of fragment ions observed when selecting a phosphate-adducted precursor ion during an MS/MS experiment. IMS and MS-MS are complementary methods that can be used to identify monomers within a polysaccharide and how they are bound.

Les polyoxométallates (POM) sont des composés anioniques constitués par l’assemblage de polyèdres d’oxydes métalliques {MOy}, (avec M, MoVI ou WVI) reliés entre eux par des atomes d'oxygène. Les POM forment ainsi une classe remarquable de clusters d’oxydes métalliques inorganiques nanométriques, avec une grande variété de charges et de structures. Il est possible de former des systèmes hybrides incluant la partie inorganique du POM et une partie organique greffée, permettant d’apporter de nouvelles fonctionnalités aux POM, tel que l’auto-assemblage. Nous avons consacré ces travaux de thèse à la caractérisation de systèmes classiques, hybrides et auto-assemblés de POM par spectrométrie de masse couplée à la spectrométrie à la mobilité ionique (IMS-MS). Une première approche expérimentale par spectrométrie de mobilité ionique en tube de dérive (DTIMS) nous a permis de déterminer les sections efficaces de collisions (CCS) de POM étalons dans l’hélium et dans l’azote. Les CCS des étalons POM nous ont ensuite permis d’étalonner une cellule IMS de type Travelling Wave (TWIMS). L’analyse par IMS-MS de POM hybrides organiques-inorganiques seuls ou en présence de PdCl2 a mis en évidence la présence de systèmes auto-assemblés triangulaires [POM3·cation3], carrés [POM4·cation4] ou pentagonaux [POM5·cation5] avec différents états de charges. Des valeurs de CCS de ces auto-assemblages ont également pu être estimées à partir de l’étalonnage de la cellule TWIMS. Par une approche théorique, nous avons modélisé plusieurs structures de POM standards avec et sans contre-ion tetrabutylammonium (TBA+) par la théorie de la fonctionnelle de la densité (DFT). Les structures optimisées ont été utilisées afin de déterminer des CCS théoriques grâce au logiciel MOBCAL, auquel nous avons incorporé les atomes de molybdène et de tungstène pour lesquels nous avons optimisé de nouveaux paramètres de potentiel de Lennard Jones. La correspondance des CCS expérimentales et théoriques des structures de POM standards offre de nouvelles possibilités pour une attribution structurale pour les POM hybrides auto-assemblés par coordination en présence de cations métalliques. / Polyoxometalates (POM) are anionic compounds formed by the assembly of metal oxide polyhedra {MOy}, (with M, MoVI or WVI) linked together by oxygen atoms. POM thus form a remarkable class of nanometric inorganic metal oxide clusters, with a wide variety of charges and structures. It is possible to form hybrid systems including the inorganic part of the POM and a grafted organic part, allowing new functionalities to be added to the POM, such as selfassembly. We have dedicated this thesis work to the characterization of standards, hybrid and self-assembled POM systems by mass spectrometry coupled to ion mobility spectrometry (IMS-MS). A first experimental approach using drift tube ion mobility spectrometry (DTIMS) allowed us to determine the collision cross sections (CCS) of standard POM in helium and nitrogen. The CCS of the POM standards then allowed us to calibrate an IMS cell of a Travelling Wave ion mobility instrument (TWIMS). The analysis by IMS-MS of organic-inorganic hybrid POMs alone or in the presence of transition metal cations revealed the presence of self-assembled triangular [POM3·cation3], square [POM4·cation4] or pentagonal [POM5·cation5] systems with different charge states. CCS values of these self-assemblies was estimated from the calibration of the TWIMS cell. Using a theoretical approach, we modelled several standard POM structures with and without tetrabutylammonium counterion (TBA+) using density functional theory (DFT). The optimized structures were used to determine theoretical CCS using the trajectory method of the MOBCAL software, in which we incorporated molybdenum and tungsten atoms for which we optimized new Lennard Jones potential parameters. The correspondence of experimental and theoretical CCS of standard POM structures offers new possibilities for structural attribution of self-assembled hybrid POM by coordination in the presence of metal cations.