Gas phase studies of organic and bioorganic species by mass spectrometry
Creators: name: Xu, Jiahui
Publisher: name: No Publisher Supplied
Year: 2020

description: The research performed in this dissertation involves mass spectrometry method development in studying the kinetic and thermodynamic properties of organic and bioorganic species in the gas phase.Chapter 2 covers the background of gas phase studies of the Formamidopyrimidine Glycosylase (Fpg) excision mechanism, either by exocyclic cleaving the glycosidic C1-N bond or by endocyclic ring-opening of the ribose or deoxyribose sugar. A brief introduction of Fpg and experimental methods for measuring the gas phase acidities and proton affinities of Fpg substrates are explained. The acidity of Fpg substrates is measured and analyzed if it correlates to the Fpg excision rates. Computational data indicates the weak correlation between substrate acidity and Fpg excision rates, where the results support the endocyclic mechanism. In Chapter 3, the measurement of the deprotonation of a series of benzhydryl cations has been completed both experimentally and computationally. These studies provide the experimental basicity values of diarylcarbene for the first attempt. The deprotonation pathways, including whether the singlet or triplet carbene is formed, are examined computationally. Assessment of the protonation energy of these diarylcarbenes is of fundamental importance. In Chapter 4, a series of silane hydrides’ gas phase kinetic hydricity studies are performed. The understanding of hydricity is crucial for a series of silane hydrides in organic synthesis, hydrogen activation, and photoelectrocatalysis because hydride reactions are involved in many of these processes. We find that the gas phase hydricity trends are different from that in the solution, which reveals the solvent effect. H/D studies and calculations are performed. We find that trends of hydricity in the gas phase are different from that in solution, explaining the impact of the solvents. Computational studies and further experiments, including H/D studies, are used to explore the structure and the reactivity of studied substrates. The reported studies in this chapter also help with systematically understanding nucleophilicity and electrophilicity without the effect of the solvent.In Chapter 5, a series of positive and negative charge-tagged N-heterocyclic carbene (NHC) are synthesized to study the NHC catalyzed Umpolung reactions, such as the benzoin condensation and Stetter reaction in the gas phase. A simpler and easier synthetic route is designed to obtain the thiazolylidene catalysts with charge tags, which allows us to monitor NHC-catalyzed reactions by mass spectrometry. Computational studies are performed for choosing the appropriate substrate for NHC catalyzed Umpolung reactions.Last, in Chapter 6, fluorenylidene and diphenyl carbene’s proton basicity are computed and measured. According to the bracketing result, the experimental basicity of 2,7-dinitrofluorenylidene shows a discrepancy with DFT calculated basicity. The possible alternative deprotonation pathways of fluorenylidene are computed and analyzed by DFT calculation.