The (13)C amide I band is still sensitive to conformation change when the regular amide I band cannot be distinguished at the typical position in H2O.

The attenuated total reflection technique was utilized to obtain FTIR spectra of (13)C-labeled peptides with a sequence of (AAAAK)4AAAAY in H2O. The regular amide I band was not at the typical position as reported in globular proteins, whereas the (13)C amide I band was still sensitive to conformation change.