Innershell Absorption Spectroscopy of Amino Acids
K. Kaznacheyev, A. Osanna, and C. Jacobsen Department of Physics and Astronomy, State UniVersity of New York, Stony Brook, New York 11794
O. Plashkevych, O. Vahtras, and H. Agren Theoretical Chemistry, Royal Institute of Technology, Stockholm, S-10044, Sweden
V. Carravetta ICQEM-CNR, Via Moruzzi 1, 56124 Pisa, Italy
A. P. Hitchcock Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada
Received: September 5, 2001
We present comprehensive measurements of the C (carbon) K edge near-edge X-ray absorption (NEXAFS) spectra of all 20 amino acids commonly occurring in nature. Qualitative trends among the spectra of amino acids with similar chemical character are identified and spectral features are compared with extensive ab initio calculations. The contributions of individual units and substitutional groups have been determined to explore their fingerprinting character using the building block concept. Several such units are found. Two that give particularly clear features in the C 1s NEXAFS spectra are the carboxyl group (which can be clearly identified by a pronounced structure due to the C 1s ->p*C=O transition with maximum at 288.65(5) eV) and modified phenol rings in aromatic amino acids (which give sharp C 1s ->p*C=C structures). The latter transitions are located around 285 eV, and their shape is specific for each aromatic amino acid. Other building blocks, such as the CNHn group and the CH, CC, CO, CN pair bonds, are also identified, although their characteristic features are less pronounced in the C K edge spectra than the carboxylic and aromatic structures. This study provides the basis for rigorous assignment of the NEXAFS spectra of the amino acids, and will be helpful in developing X-ray absorption spectroscopy for quantitative analysis of proteins.
10.1021/jp013385w CCC © 2002 American Chemical Society