@unpublished{pittir9839,
           month = {January},
           title = {Application of Ion-Molecule Reactions to Structure Characterization and Thermochemical Property Measurements},
          author = {Mingxiang Lin},
            year = {2005},
        keywords = {atomic oxygen radical anion; ion-molecule reactions; peptide sequencing; proton affinity},
             url = {http://d-scholarship-dev.library.pitt.edu/9839/},
        abstract = {This thesis explores several novel applications of gas-phase ion-molecule reactions to solve analytical problems. In all cases, the application of an ion-molecule reaction to solve a specific challenge is based on a thorough understanding of the fundamental aspects of the reaction, including kinetics, production distributions and most notably, its reaction mechanism.Ion-molecule reactions of the atomic oxygen radical anion, O *- , with selected ketones are investigated to explore a strategy to synthesize 1,3-distonic radical anions, which are precursors to 1,3-diyls. The O *- /cyclopentanone reaction is examined in detail, under the well-defined thermal conditions uniquely available in the flowing afterglow, to ascertain if cyclopentan-2-one-1,3-diyl radical anion is formed. To further the understanding of this key reaction, a series of related ketones are also examined. Rate coefficients for each ketone reaction are measured, products are identified, and the branching ratios are determined. A strategy is developed to differentiate the 1,1- and 1,3-H 2 *+ isobaric abstraction products. A total yield of 48\% [M-2H] *- is obtained for the O *- /cyclopentanone reaction, wherein {$\sim$}15\% is the absolute yield of the 1,1- and {$\sim$}33\% is the absolute yield of the 1,3-H 2 *+ abstraction product.A chemical reagent that specifically cleaves the peptide backbone will greatly simplify peptide sequencing as compared to nonselective energetic collisions with inert gases. In the search for peptide cleavage reagents, translationally-driven, endothermic ion-molecule reactions between peptide ions and potential cleavage reagents are investigated in a custom-built, electrospray ionization, triple quadrupole mass spectrometer. Strategies are adopted to minimize nonselective energetic fragmentation processes and to favor amide bond cleavage.The kinetic method is used to derive the relative and absolute proton affinities of two neuropeptides, leucine-enkephalin and methionine-enkephalin. Based on analyses of the collision induced fragmentation of the proton-bound heterodimer of leucine-enkephalin and methionine-enkephalin, leucine-enkephalin is established to be 0.1 kcal/mol lower in proton affinity than methionine-enkephalin. Based on analyses of the collision induced fragmentation of the proton-bound heterodimer of leucine-enkephalin or methionine-enkephalin and triethylamine, tripropylamine or tributylamine, the absolute proton affinities of leucine-enkephalin and methionine-enkephalin are established to be 238.5 and 238.6 ({$\pm$}5.0) kcal/mol.}
}