Fig. 4.

Experimental and simulated 2D IR spectra of isotope diluted fibrils. (A) Experimental 2D IR spectrum and diagonal intensity slice of 10% ¹³C-labeled Q24 fibrils. Simulated 2D IR spectra and diagonal intensity slices for (B) β-arc and (C) β-turn models of ∼8% labeled Q24 fibrils. Diagonal peaks are labeled with BB for backbone modes, M for mixed backbone–side-chain modes, and TT for disordered modes from the turns and termini. Peaks arising from ¹³C-labeled peptides are highlighted with boxes. Peak frequencies are summarized in Table S2.