DETERMINATION OF THE STRUCTURE AND SEQUENCE OF GAS-PHASE PEPTIDES USING SPECTROSCOPIC AND MASS SPECTROMETRIC METHODS
thesisposted on 2021-07-22, 03:22 authored by Joshua L FischerJoshua L Fischer
The function of many biological processes depends on the structure and composition of the biomolecules involved. Both spectroscopy and mass spectrometry provide complimentary information regarding the three-dimensional conformation and the composition, respectively, as well as many other things. Here, double resonance conformer specific spectroscopy coupled with the latest ab inito computational methods is used to make structural assignments at the atomic resolution as well obtain information regarding propensities of intramolecular interactions. Additionally, rapid cooling in conjunction with IR excitation to modulate and measure the relative populations of conformers present in the expansion. Two different designer peptide systems are studied, including an achiral acylated 𝛼-aminoisobutryic acid dipeptide (Ac-AIB2-R) with various C-terminal protecting groups (R=NHBn, NHBnF, 𝛼-methylbenzylamine) and an acylated 𝛾4-phenylalanine (Ac-𝛾4Phe-NHMe) with the a methyl amine C-terminal protecting group. Mass spectrometry is used to determine the kinetics of gas-phase covalent tagging reactions used to enhance the sequence coverage. The covalent modification reactions utilize click chemistry between NHS or HOBt substituted sulfobenzoic acid tags with nucleophiles present on the residues of the amino acids composing the backbone. Effective temperatures are approximated using the Tolmachev model, which relates the statistical average internal energy of the molecule to a temperature.