Studying On The Gas Phase Fragmentation Reaction Mediated By Proton-Bound Complex In Mass Spectrometry

In this thesis,a combination of high-resolution high-energy collisional dissociation mass spectrometry(ESI-HCD-MS/MS),hydrogen-deuterium exchange experiments and density functional theory(DFT)calculation was applied to investigate the gas phase fragmentation reaction for three kinds of organic compounds,including cyclic indolyl ?-amino esters,spiro[Acenaphthylene-1,2?-pyrrolidin]-2-one compounds and N-allyl-2-bromo-N-phenylcyclohex-1-enecarboxamide derivatives.Meanwhile,the possibility of the presence of‘proton-bound complex' intermediate in the formation of characterized complementary product ions from their protonated ions was discussed.Firstly,a combination of ESI-HCD-MS/MS,hydrogen-deuterium exchange experiments and DFT calculation was applied to study the fragmentation mechanisms of protonated cyclic indolyl ?-amino esters.In the collision-induced dissociation(CID)mass spectrometry,C3-C10 bond breakage was observed,which gave rise to an ion-neutral complex of [3-ethoxycarbonyl-benzo[d]isothiazole-1,1-dioxide derivatives/ protonated indoles] in a Friedel-Crafts dealkylation reaction.Direct separation of this complex formed the product ion a(protonated indole derivatives),while a stereoselectively proton transfer between the two components in the complex gave rise to the product ion b(protonated 3-ethoxycarbonylbenzo[d]isothiazole-1,1-dioxisde derivatives).Moreover,kinetic method showed that the ln([b]/[a])against the differences in proton affinities of the corresponding molecules was not a straight line,which further verified that the progress of generating product ions a and b was not mediated by a proton-bound complex.Secondly,the gas phase fragmentation mechanisms of protonated spiro[Acenaphthylene-1,2?-pyrrolidin]-2-one compounds were evaluated in ESI-MS/MS,which generated two pairs of complementary product ions: protonated2-(benzylimino)acenaphthylen-1(2H)-one(a)and protonated chalcone derivatives(b);protonated(2,3-diphenylcyclopropyl)(phenyl)-methanone derivatives(c)and protonated 2-iminoacenaphthylen-1(2H)-one(d).The formation of these product ions were investigated by kinetic method.The ln([a]/[b])and ln([d]/[c])against the differences in proton affinities of the corresponding molecules was a straight line,respectively.It implied that the progress of generating these product ions might be mediated by a proton-bound complex.However,density functional theory calculations demonstrated that product ions a and b were generated through a proton transfer in an ion-neutral complex intermediate.While the progress of generating product ions c and d was mediated by a proton-bound complex intermediate.The above results suggested that kinetic method is not the sole criterion for verifying the existence of‘proton-bound complex' intermediate.Finally,the gas phase fragmentation behavior of protonated N-allyl-2-bromo-N-phenylcyclohex-1-enecarboxamide derivatives have systematically explored.The results suggested that O1 atom of carbonyl is the most thermodynamically favored protonation site.When the additional proton was transfer to the dissociative protonation site: N2 atom of amide,the characterized complementary product ions c and d were formed by the neutral loss of N-allylaniline derivatives(f)and 6-bromocyclohexa-1,5-dienecarbaldehyde(e),respectively.In addition,the intensities of product ions were influenced by the different substituents.Electron-withdrawing groups facilitate the product ion c,whereas the electron-donating groups are strongly favored the ion d.Moreover,the kinetic method showed that the ln([c]/[d])against the differences in proton affinities of thecorresponding molecules was a straight line.Density functional theory calculations demonstrated that the formation of product ions c and d was mediated by the proton transfer reaction in an ion-neutral complex not the ‘proton-bound complex'intermediate,which further verified that kinetic method is not the sole criterion for verifying the existence of ‘proton-bound complex' intermediate.