Figure 2.

Schematic illustration of the coupling strategy used by Zanni and coworkers (39). Upon formation of repeating, ordered parallel β-sheet fibrils, the site-specifically incorporated backbone ¹³C=¹⁸O probe (represented by a star) on one peptide will be brought in close proximity to those bore on other peptides, leading to excitonic coupling among these vibrators. As a result, the IR spectrum of the peptide sample undergoes a redshift, amplification and narrowing; by changing the positions of the isotopic labels and monitoring the appearance of the spectral feature of the exciton band, it is possible to elucidate the structure of the formed fibrils.