Spectral Marker for C<sub>α</sub> Damage in Beta Peptides

The work in this article describes a spectral signature for the detection of a C<sub>α</sub> radical damaged peptide, which should enable the use of infrared spectroscopic methods to directly monitor oxidative events. Spectra for radical damaged peptides are computed with ab initio methods. The amide bands A, I, II, and III are analyzed for trends in the damage site. The spectral signature is found in a region (i.e., 1700–1620 cm<sup>–1</sup>) normally void of vibrational absorption bands from stable undamaged beta peptides. An analysis of the vibrational motions of the spectral signature is described. The uniqueness of the spectral signature is explored by an examination and comparison with C<sub>α</sub> monoradicals and polyradicals, as well as with other bioradicals that could act as spectral interferences. The identification of unique infrared spectral features for C<sub>α</sub> damage could have important implications in diagnostics for beta conformational peptides damaged by oxidative stress processes.