A theoretical study of the near edge X-ray absorption fine structure of amino acids and proteins

The near edge X-ray absorption fine structure (NEXAFS) of amino acids and proteins is studied with time-dependent density functional theory in conjunction with a short-range corrected exchange–correlation functional designed for core-excited states. For glycine, alanine and glycyl-glycine, good agreement between the computed spectra and experiment is obtained at the carbon, nitrogen and oxygen K-edges. The potential of NEXAFS spectroscopy to differentiate between different elements of protein secondary structure is explored. These calculations show that the greatest sensitivity to secondary structure is found at the nitrogen K-edge.