Ion-molecule interactions in the gas phase.

摘要

For years Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) has been used in the study of gas phase ion-molecule reactions. In this study, a wide range of gas phase ion-molecule interactions have been examined using this "gas phase chemical laboratory." Furthermore, various mechanistic aspects have been probed in four different chemical reaction systems. First, effects of solvation have been examined for two ruthenium(II) amine complexes through microsolvation using electrospray ionization. These solvated adducts have been successfully trapped and isolated in the FTICR analyzer cell. In addition, the relative stability of these species has been studied in attempts to measure the corresponding binding energies of solvation.; In another system, FTICR has been utilized in the measurement of appearance energies for the fragmentation of a series of acylpyridinium cations. These energies were found to range from less than 23 kcal/mol to 80 kcal/mol. This fragmentation was found to occur via two alternate pathways. In one process, dissociation results in the formation of an acylium ion, while in the other, a protonated pyridinium cation is observed. Attempts to generate an S{dollar}sb{lcub}rm N{rcub}{dollar}2 reaction between these acylpyridinium cations and several neutral nucleophilic species produced several unexpected adducts but no definitive evidence for this process.; In a similar chemical system, attempts were made to generate both intermolecular and intramolecular gas phase S{dollar}sb{lcub}rm N{rcub}{dollar}2 reactions with several N-substituted pyridinium and acridinium cations. Several of these compounds were found to undergo intramolecular S{dollar}sb{lcub}rm N{rcub}{dollar}2 reactions via cyclization. Again, two different mechanistic pathways were found to occur. In the first, direct nucleophilic attack was observed resulting in the formation of a heterocyclic cation. In the second process, a protonated acridinium cation was produced via cyclization of the heteroatomic sidechain followed by fast proton transfer from an ion-induced dipole complex. Finally, several attempts to generate intermolecular S{dollar}sb{lcub}rm N{rcub}{dollar}2 reactions were unsuccessful.; In the final study, FTICR was used to measure the proton affinities of several commonly used MALDI (matrix assisted laser desorption ionization) matrices. This proton transfer process represents another gas phase process which is effectively studied using this powerful "gas phase chemical laboratory."