Theoretical study of X-ray circular dichroism of amino acids

Ordinary and rotatory X-ray absorption intensities are computed for chiral amino acids (alanine, cysteine, serine and valine) in order to explore in what way near-edge X-ray absorption and X-ray circular dichrosim (CD) can fingerprint such compounds. It is predicted that ordinary X-ray absorption spectra are quite alike for the different compounds, which is in line with that they contain similar building blocks, of which only one is changed by substitution. X-ray CD spectra are more sensitive and pose better prospects to be used as fingerprints. This seems to hold especially for spectra of unique atoms, like the nitrogen spectra of amino acids, while spectra with contributions from several chemically shifted non-unique atoms, like the carbon atoms, may appear too scrambled to be useful for experiments at moderate resolution.