NEXAFS spectroscopy of homopolypeptides at all relevant absorption edges: polyisoleucine, polytyrosine, and polyhistidine.

Yan Zubavichus, Andrey Shaporenko, Michael Grunze, Michael Zharnikov

Index: J. Phys. Chem. B 111(33) , 9803-7, (2007)

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Abstract

Carefully calibrated high-resolution low-noise near-edge X-ray absorption fine structure spectra of three homopolypetides, viz., polyisoleucine, polytyrosine, and polyhistidine at the C, N, and O K-edges, are compared with the respective spectra of parent amino acids and glycine-derived cyclic dipeptide, 2,5-diketopiperazine. An assignment of the spectral features related to the nitrogen and oxygen atoms constituting the peptide bond is suggested on the basis of a comparative analysis of the experimental spectra as well as theoretical calculations for 2,5-diketopiperazine within the real-space multiple-scattering formalism. A splitting of the pi*-feature in the N K-edge spectra is identified, which is probably sensitive to the dominant conformation type of the peptide molecule (i.e., alpha-helix vs beta-sheet).