Figure 7.

2DIR spectra and their diagonal traces of 2DIR spectra for amide-I vibration of HIδ, HIε, and HIπ dipeptides: C-terminus (left) and N-terminus (right) amide bonds. Black, red, and blue lines represent the diagonal traces of the HIδ, HIε, and HIπ dipeptides, respectively. Green lines represent the three peaks at 1580, 1586, and 1593 cm⁻¹ for isotope-labeled bonds and 1600, 1607, and 1613 cm⁻¹ for nonlabeled amide bonds. To see this figure in color, go online.