Fragmentation Reactions Of N-containing Heterocyclic Compounds In ESI-MS~n

The dissociation reactions of protonated molecules are the base of structural analysis in electrospray ionization tandem mass spectrometry (ESI-MSn). However, general rules for elucidating numerous fragmentation reactions in ESI-MSn are still rather insufficient. Therefore, the mechanism investigation for fragmentation reactions in the gas phase is critical to be carried out. Thus in this thesis, the gas-phase fragmentation behaviors of N-containing heterocyclic compounds were investigated by ESI-MSn in combination with quantum calculations, including these two parts:1. Fragmentation mechanism of product ions from protonated proline-containing tripeptides in electrospray ionization mass spectrometryThe dissociation chemistry of primary fragment ions from protonated proline-containing tripeptides was discussed. Formation and fragmentation of the a2 ion were investigated. Calculations showed that the structures of the a2 ions generated from b2 were cyclic and had lower energy than those in the linear form. These results agree with results from earlier studies about this novel a2 ion structure. The prolyl residue in the structure had a significant effect on the energy hypersurface of the reaction by stabilizing the structure and lowering the energy. Fragmentations of the a2 ions from GPG and PPG produced both a1 and RCH=NH2+ ions. In contrast, only the a1 ion was produced from PGG. In GPG and PPG, the dissociation chemistry of a2 ions is the capacity of intra-molecular proton transfer from the first INC to produce another INC via a PBC. The second INC is then dissociated from the internal RCH=NH2+, which was absent in PGG.2. An experimental and theoretical study on the fragmentation of protonated N-(2-pyridinylmethyl)-indole in electrospray ionization mass spectrometryN-(2-pyridinylmethyl)-indole derivatives are very important drug molecules used as EP1 receptor antagonists, histone deacetylase inhibitors, and so on. The fragmentation reactions of protonated N-(2-pyridinylmethyl)-indoles were studied through ESI-Ion trap tandem mass spectrometry and ESI-Fourier transform ion cyclotron resonance tandem mass spectrometry in positive ion mode. In ESI-MS/MS, the ionizing proton is first bound to the most thermodynamically favorable site, the pyridine nitrogen, and then it transfers to the dissociative protonation sites and triggers the fragmentation. In the fragmentation of the target compounds, some interesting reactions, such as rearrangement, proton transfer, and electron transfer reactions, take place via INCs. The proposed mechanisms are supported by theory calculations and isotopic labeling experiments. This study aims to better understand the dissociative protonation site and enrich the knowledge about the role of INCs in ESI mass spectrometry. The study also provides useful information on the structural analysis of organic compounds, especially to drug analysis in pharmaceutical chemistry.