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Application of Ion-Molecule Reactions to Structure Characterization and Thermochemical Property Measurements

Lin, Mingxiang (2005) Application of Ion-Molecule Reactions to Structure Characterization and Thermochemical Property Measurements. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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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 ∼15% is the absolute yield of the 1,1- and ∼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 (±5.0) kcal/mol.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Lin, Mingxiangmingxianglin@yahoo.com
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairGrabowski, Joseph Jjoeg@pitt.eduJOEG
Committee MemberMichael, Adrian Camichael@pitt.eduAMICHAEL
Committee MemberDay, Billy Dbday@pitt.eduBDAY
Committee MemberSaxena, Sunil Ksksaxena@pitt.eduSKSAXENA
Date: 31 January 2005
Date Type: Completion
Defense Date: 22 November 2004
Approval Date: 31 January 2005
Submission Date: 29 November 2004
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: atomic oxygen radical anion; ion-molecule reactions; peptide sequencing; proton affinity
Other ID: http://etd.library.pitt.edu/ETD/available/etd-11292004-110302/, etd-11292004-110302
Date Deposited: 10 Nov 2011 20:06
Last Modified: 15 Nov 2016 13:52
URI: http://d-scholarship.pitt.edu/id/eprint/9839

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