Studying On The Gas Phase Fragmentation Of Several Kinds Of Organic Compounds In Atmospheric Pressure Ionization Mass Spectrometry

In this dissertation, atmospheric pressure ionization mass spectrometry(API-MS) and theoretical calculation were applied to investigate the fragmentation for three kinds of organic compounds.Firstly, the gas phase fragmentation mechanisms of protonated 3,3-bis(3-hydroxy-5-methyl-1H-pyrazol-4-yl)indolin-2-one analogs were studied. In the collision-induced dissociation(CID) mass spectrometry, protonated 3-(3-methyl-5-oxo-1H-pyrazol-4(5H)-ylidene)indolin-2-one derivatives(a) and protonated 5-methylpyrazolone(b) were observed. Density functional theory calculations demonstrated that the N1 atom of pyrazole ring is the most thermodynamically favored protonation site. With ionizing proton migrating to Cγ-position, the heterolytic cleavage of Cβ-Cγ bond was triggered through a retro-Michael-type fragmentation and gave rise to product ions a and b. Moreover, the kinetic method indicated that the retro-Michael-type fragmentation progress was mediated by a proton-bound complex of 3-(3-methyl-5-oxo-1H-pyrazol-4(5H)-ylidene) indolin-2-one /5-methylpyrazolone.Secondly, the fragmentation mechanisms of the protonated 3-((5-(benzylthio)-1,3,4-oxadiazol-2-yl)methyl)benzo[d]thiazol-2(3H)-one derivatives were evaluated in collision-induced dissociation(CID) mass spectrometry, which presented three different characteristic dissociation pathways: the neutral loss of 3-((5-mercapto-1,3,4-oxadiazol-2-yl) methyl)benzo[d]thiazol-2(3H)-one generates a benzyl cation, the benzyl cation transfer followed a proton shift via a ion/neutral complex gives rise to a 2-(4-benzyl-2-oxobenzo[d]thiazol-3(2H)-yl)-1-oxoethan-1-ylium and the ring-opening reaction of 1,3,4-oxadiazole results in a 1-oxo-2-(2-oxobenzo[d]thiazol-3(2H)-yl)ethan-1-ylium. Density functional theory calculations demonstrated that the progress of benzyl cation transfer was mediated by an ion/neutral complexes. The relative abundances of two corresponding product ions RC16H11NO2S+ and RC15H11NOS+ depends on the variation in the stabilization energy(-ES) of the ion/neutral complexs.Finally, the fragmentation behavior of the protonated ethyl 3-(1H-indol-3-yl)-2,3-dihydrobenzo[d]isothiazole-3-carboxylate-1,1-dioxi de derivatives have been systematically explored by kinetic methods combined with density functional theory calculations. N1 atom of the cyclic α-amino ester is the most thermodynamically favored protonation site. When the additional proton was transfer to the dissociative protonation sites: O2 atom of the cyclic α-amino ester and C3 atom of indolyl, the corresponding product ions of protonated indol(a), protonated ethyl benzo[d]isothiazole-3-carboxylate 1,1-dioxide(b) and protonated 3-(1H-indol-3-yl)benzo[d]isothiazole 1,1-dioxide(c) were formed by the charge induced heterolytic cleavages. In addition, the intensities of product ions were influenced by the substituents at phenyl ring of cyclic α-amino ester. Electron-withdrawing groups at phenyl ring facilitate the product ions a and b, whereas the electron-donating groups are strongly favored the ion c. Moreover, the kinetic method verified that the proton-competing reaction between ion a and ion b is controlled by an ion/neutral complexes.