Nitrogen 1s near-edge X-ray absorption fine structure spectroscopy of amino acids: Resolving zwitterionic effects

The nitrogen 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of several amino acids and other model compounds were acquired and their experimental measurements complemented with ab initio calculations of isolated molecules and molecular clusters to unambiguously characterize the chemical origin of the considerable variation. It is observed that the differences observed between the zwitterionic and un-ionized forms of amino acids arise directly from the structural difference, which leads to a change in the degree of Rydberg-valence mixing.