Inner Shell Excitation Spectroscopy of Amino Acids and Small Peptides

Abstract

<p> In this thesis, two inner shell excitation spectroscopy techniques, inner shell electron energy loss spectroscopy (ISEELS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy, were used to measure the C ls, N ls and 0 ls spectra of the amino acids, glycine, alanine, cysteine, phenylalanine, proline, threonine, tryptophan and the peptides, Gly-Ala, Lys-Trp-Lys (KWK), and Arg-Gly-Asp (RGD). The spectra are analysed with the aide of ab initio computations using the GSCF3 method. The characteristic spectral features of the specific side chains of amino acids are identified. Differences in the spectra of the gas and solid are related to differences between the neutral gas phase molecule and the zwitterionic solid form. A rationalization of observations of high degree of variability in theN ls spectra of amino acids is proposed. The characteristic spectral signatures of peptide bonds have been identified further by comparing the spectra of small peptides to the spectra of their subunit amino acids. A modified "building block" approach is showed to be very useful in modeling the inner shell excitation spectra of peptides through linear combinations of the spectra of the amino acids residues and peptide bonds. </p>