Dissertation/Thesis Abstract

Thermochemical differences in lysine and lysine-homolog containing oligopeptides: Determination of basicity and gas-phase structure through mass spectrometry, infrared spectroscopy, and computational chemistry
by Batoon, Patrick Henry M., Ph.D., University of the Pacific, 2016, 252; 10156682
Abstract (Summary)

The data presented in this thesis is a comprehensive study on the nature of peptide structure and how subtle and systematic changes in sequence and sidechain affect the basicity, ion stability, and conformation of a peptide. The peptides characterized were acetylated polyalanine di-, tri-, and tetra- peptides containing a proton-accepting probe: lysine and or the non-proteinogenic lysine-homologs: ornithine, 2,4-diaminobutyric acid, and 2,3-diaminopropionic acid. Peptides were studied in isomeric pairs for which the basic amino acid was placed closest to the N-terminus or the C-terminus of each peptide family (AnProbe vs. ProbeAn). Using a variety of mass spectrometry based techniques and infrared multiphoton dissociation ion spectroscopy, the isomeric families of polyalanine peptides were characterized. Quantum chemical techniques were employed in parallel to provide theoretical predictions of three-dimensional structure, physical properties (dipole moment, polarizability, and accessible surface area), thermochemical values, and vibrational IR spectra, to gain further understanding of the peptides studied and to push the limits of current theoretical models. Overall it was found that the AnProbe peptide was more basic than their ProbeAn isomer. For the dipeptide systems, the greater basicity of AProbe peptides was due to efficiently charge-solvated ions which formed more compact structures compared to their ProbeA counterpart. For the tri- and tetra- peptide systems, greater basicity of the A2,3Probe peptides was likely due to formation of α or 310 helix-like structures in the protonated forms., introducing the macrodipolar effect, which cooperatively encouraged helical formation while stabilizing the charged site. On the other hand, ProbeA2,3 peptides formed charge-solvated coils which do not exhibit any kind of dipole effect, resulting in lower basicity than their A2,3Probe counterpart.

Indexing (document details)
Advisor: Ren, Jianhua
Commitee: Franz, Andreas H., Moffet, Ryan, Tsai, Jerry, Vierra, Craig A.
School: University of the Pacific
Department: Pharmaceutical and Chemical Sciences
School Location: United States -- California
Source: DAI-B 78/03(E), Dissertation Abstracts International
Subjects: Physical chemistry
Keywords: Extended cooks kinetic method, Gas-phase basicity, IRMPD, Mass spectrometry, Proton affinity, Proton-bound dimer
Publication Number: 10156682
ISBN: 978-1-369-11727-1
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