Methionine: Electronic structure

We review the electronic structure of methionine, determined by means of photoemission and photoabsorption spectroscopy. Valence band spectroscopy yields the energies of the molecular orbitals responsible for the chemical bonding within the molecule. The Highest Occupied Molecular Orbital of methionine has sulfur lone pair character, and we show how this helps to stabilize the molecule against photofragmentation, compared for example with amino acids having aliphatic side chains. The core level spectra give information about the local chemical properties of each heavy atom in the molecule, while x-ray absorption sheds light on the unoccupied molecular orbitals. The two lowest orbitals accessible to carbon 1s excitation both have partial sulfur character. However neither of these is the Lowest Unoccupied Molecular orbital, which is instead the antibonding ? orbital of the carboxylic acid group. © 2013 Nova Science Publishers, Inc. All rights reserved.