Application of Fourier transform ion cyclotron resonance mass spectrometry to reactivity studies of phospheniumions (CIP(+)CI and CH(3)OP(+)OCH(3)) and isomeric 2,3-and 2,5-dihydrofuran radical cations
Abstract
Investigations of intrinsic gas-phase reactivity of simple phosphenium ions toward various organic substrates, and the reactivity and thermochemical properties of isomeric 2,3- and 2,5-dihydrofuran radical cations, were carried out by using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. The phosphenium ion CIP+CI reacts with selected simple organic substrates via various processes, including addition/elimination, nucleophilic displacement and electron transfer. CIP+CI is extremely reactive and readily cleaves C-H, C-O, C=O, C-N, C-C and N-C(O) bonds. CH3OP +OCH3 was found to be less reactive and to follow different reaction pathways than CIP+CI. This finding is justified by the reaction exothermicity differences between the reactions involving CIP +CI and CH3OP+OCH3. CIP +CI was found to ionize and subsequently induce extensive fragmentation of neutral di- and tripeptides. This was proposed to occur for the dipeptides by elimination of H2O and Cl2P• from the CI2P+/dipeptide adduct. Exact mass measurements, bracketing and H/D exchange experiments, collision-activated dissociation, and molecular orbital calculations were used to characterize the structures of the major product ions generated in the reactions of CIP+CI with dipeptides. Upon reaction with a tripeptide, CIP+CI was found to cleave the two peptides bonds via analogous reaction mechanisms as it cleaves the dipeptides, yielding product ions that contain the intact side chains of two adjacent amino acids. Therefore, CIP+CI produces useful structural information for small peptide. In addition to the phosphenium ion studies, thermochemical properties (e.g., recombination energies) and the reactivity of 2,3- and 2,5-dihydrofuran radical cations were studied. The recombination energies of the 2,3- and 2,5-dihydrofuran radical cations were estimated by bracketing experiments to be 8.4 t 0.2 eV and 8.6 t 0.2 eV. Gas-phase ion-molecule reactions and molecular orbital calculations suggest that isomerization between the 2,3- and 2,5-dihydrofuran radical cations does not occur. However, 2,5-dihydrofuran radical cations likely isomerize to more stable species in the gas phase.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry
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