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Peptoids are versatile compounds exhibiting many applications in various fields ranging from polymeric science to drug development. Combinatorial libraries are a powerful tool for exploring various applications of peptoids. Among robust analytical tools, tandem mass spectrometry is a method of choice to decode the sequence of unknown peptoids in combinatorial libraries. In this study, we have synthesized peptoids with various side chains and found interesting fragmentation pathways. The introduction to my research and methods used for the experiments are discussed in detail in chapters one and two, respectively.In chapter three of this dissertation, a systematic study of acetylated peptoids with positioning of a basic sidechain at various locations has been conducted using a linear ion trap mass spectrometer. The fragmentation characteristics of peptoids charged with metal ions, such as Li+ and Na+, are compared with those of the protonated peptoids. The acetylated peptoids without any basic sidechain were taken as a reference. It has been found that metal ions assist in increasing the formation of N-terminal fragment ions due to chelating between the metal ions and the peptide fragments. In addition, metal ions enhances ionization efficiency of peptoids without charge trapping sites. In the fourth chapter, new fragmentation pathways of peptoids are proposed and tested. To investigate the mechanism of water loss from peptoid fragment ion, a linear ion trap mass spectrometer was used to perform tandem fragmentation experiments on selected peptoids. The absence of certain fragment ions toward the N-terminus suggests that water loss occurs through a five-membered ring intermediate instead of a six-membered ring. The fragmentation of peptoid backbone mainly yields the B- and Y-ions through an oxazolone ring intermediate. The Y-ions are formed by abstraction of a proton from the oxazolone ring, which is essentially the proton from the alpha position of the dissociating amide bond. In nonacetylated peptoids, an oxazolone ring is absent during the formation of terminal Y-ions. The mechanism behind the appearance of terminal Y-ions have been studied using deuterium labeled peptoids. Fragmentation experiments on deuterium labeled peptoids indicates that the proton is not abstracted from the alpha position. The likely proton source is the hydrogen on the amine group of the N-terminus. The comparison of fragmentation patterns between peptoids containing acidic and basic sidechains is documented in the last chapter of this dissertation. Carboxyl group on the sidechain does not appear to influence the favorable formation of C-terminal ions. Considerable abundance of low-mass B-ions is explained by a cascade secondary fragmentation of high-mass B-ions. The fragment ions formed using the linear ion trap instrument show a considerable abundance of high mass Y-ions. While fragmentation experiments using tandem quadrupole instrument show high intensity of low mass ions which are possibly formed from secondary fragmentation of high mass ions. This study will aid in understanding the nature of fragmentation behavior of peptoids and support the discovery of unknown sequences. As peptoids closely resemble peptides, the findings from this work will help to complement the fragmentation mechanism of peptides.

Les déchets plastiques s'accumulent depuis plusieurs décennies dans les océans où ils se fragmentent en particules appelés microplastiques lorsque leur taille est inférieure à 5 mm. Ces microplastiques sont retrouvés dans toutes les eaux du globe, dans les sédiments ainsi que dans de nombreux organismes marins. Le devenir physicochimique à long terme de ces particules et leur possible fragmentation en nanoplastiques sont complexes, encore peu documentés et nécessitent des études en laboratoire.Afin de comprendre les processus liés à la photodégradation et à la fragmentation des polymères dans l’environnement, mais également dans le but d’'appréhender l’évolution des fragments générés au cours de l’irradiation, un protocole de vieillissement accéléré en milieu abiotique a été mis en place sur des polymères modèles. Le suivi de l’oxydation et de la fragmentation des deux polymères étudiés,polyéthylène basse densité et polypropylène, a été mené à l’aide de techniques spectroscopiques (infrarouge, Raman), DSC, angles de contact, et microscopiques (lumière polarisée, MEB, AFM…).Ce travail a permis de mettre en évidence l’influence significative de l’environnement et de la morphologie initiale des polymères sur leurs cinétiques de vieillissement et leurs mécanismes de fissuration. Ainsi des distributions en nombres, tailles et formes de fragments très différentes ont été obtenues pour les deux polymères selon la présence d’eau. Enfin, après un long temps d’irradiation, des produits de dégradation ont pu être détectés mais la production significative de nanoplastiques n’a pas été démontrée. L'hypothèse d'une taille limite de fragmentation devrait être envisagée. / Plastic wastes have been accumulating for several decades in the oceans where they break up into particles called microplastics when their size is less than 5 mm. These microplastics are found in all earth’s waters, in sediments and in many marine organisms. Their long-term physico-chemical fate and their possible fragmentation into nanoplastics are complex, still poorly documented and require laboratory studies.In order to understand the processes related to photodegradation and fragmentation of polymers, but also in order to understand the evolution of these fragments during irradiation, an accelerated aging protocol in abiotic conditions has been set up. The oxidation and fragmentation of two model polymers, low density polyethylene and polypropylene, were monitored using spectroscopic techniques (InfraRed, Raman), DSC, contact angles and microscopic technics (light microscopy, polarized light, SEM, AFM ...).This work has demonstrated a significant influence of the environment and the initial morphology of the polymers on their kinetics of aging and cracking mechanisms. This lead to significantly different distributions in numbers, sizes and shapes of the generated fragments. Moreover, after a long time of irradiaiton, other degradation products could be detected but the significant production of nanoplastics has not been demonstrated. The possibility of a size limit below which the fragmentation rate of plastics would strongly decrease should be considered.