title: Nitrogen 1s near-edge X-ray absorption fine structure spectroscopy of amino acids: Resolving zwitterionic effects.
abstract: Considerable variation is observed in the near-edge X-ray absorption fine structure (NEXAFS) spectra of amino acids. To unambiguously characterize the chemical origin of this variation, we have acquired the nitrogen 1s NEXAFS spectra of several amino acids and other model compounds and complemented these experimental measurements with ab initio calculations of isolated molecules and molecular clusters. The systematic differences observed between the zwitterionic and un-ionized forms of amino acids arise directly from the structural difference (-NH2 vs -NH3+), which leads to a change in the degree of Rydberg-valence mixing. Further change arises from quenching of this Rydberg character in the spectra of condensed amino acids. Ab initio calculations are used to explore the degree of Rydberg-valence mixing in the solid state.
authors.affiliation: Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada.
authors.forename: Edwige
authors.initials: E
authors.lastname: Otero
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Urquhart
mesh_terms: D000465:Algorithms; D000596:Amino Acids / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013057:Spectrum Analysis; D013059:Spectrum Analysis, Raman; D014965:X-Rays
chemical_list: D000596:Amino Acids; D009584:Nitrogen